GEOLOGICAL SURVEY CIRCULAR 822 

Paleoclimate and Mineral Deposits 

Paleoclimate and Mineral Deposits 

Edited by Thomas M. Cronin, William F. Cannon, 

and Richard Z. Poore 

GEOLOGICAL SURVEY CIRCULAR 822 

1983 
United States Department of the Interior 

JAMES G. WATT, Secretary 

Geological Survey 

Dallas L. Peck, Director 

Library of Congress Cataloging in Publication Data 

Main entry under title 

Paleoclimate and mineral deposits 

(Geological Survey Circular; 822) 

Bibliography: p. 49 

1. Paleoclimatology-United States. 2. Mines and mineral resources-United States. I. Cronin, Thomas II{. 

II. Cannon, William F. Ill. Poore, Richard Z. IV. Series 

QE75.C5 no. 822 [QC884] 557.3s [553.1] 83--000159 

Free on application to Distribution Branch, Text Products Section, 

U. S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 
PREFACE 

Earth climate obviously plays an important role 

in our daily lives through its effects on agriculture, 

floods, droughts, energy use, and other areas. Further, 

predicting or forecasting future climatic trends has 

properly been given high priority in national research 

programs because of the expected increase of. global 

temperatures over the next 100 years owmg to 

increasing atmospheric co2. Perhaps as important, 

however, is the increasing realization by geologists 

that past climates have played a primary role in the 

genesis of economic and strategic fuel an_d n?nfuel 

minerals. Imbrie {1982) refers to the apphcahon of 

our knowledge of the geologic record of the Earth's 

climate as "hindcasting." More specifically, predicting 

the occurrence and distribution of a particular mineral on a global or local scale can be significantly enhanced 

if geologists understand the particular environmental 

conditions under which that mineral forms and is 

preserved and how the distribution of these 

environments has changed through time. In many 

marine and continental sedimentary deposits, climatic 

conditions had a major effect on the physical, 

chemical, and biological conditions during _d~position 

and diagenesis. In some cases, global conditions at a specific time in Earth history caused the widespread 

formation of a mineral; a good example is the 

formation, during middle to Late Cretaceous time, of 

major oilfields and gasfields that were caused by warm 

global climates and relatively high sea levels. 

Conversely, local conditions superimposed on broader 

climatic trends, such as the formation of major 

phosphate deposits at regions of upwelling of cool 

nutrient-rich water along continental margins, also can be important. 

Several major advances have brought 

paleoclimatology to the forefront as a major discipline 

that unites many previously disjunct areas of 

geoscience. Among these advances, the success of the 

Deep Sea Drilling Project in determining the history of 

the modern ocean basins {Society of Economic 

Paleontologists and Mineralogists Special Publication 

No. 32) has given geologists a relatively continuous 

view of the last 150 m.y. The availability of accurate 

paleogeographic maos for the Phanerozoic (Ziegler and 

others, 1979; Scotese, 1979) has provided boundary 

conditions for paleoclimate reconstructions. The 

publication of the global "sea-level" curve (Vail and 

others, 1977) has provided a model for eustatic sealevel events and a framework for examining specific 

climatic events. Research on Quaternary climates 

done primarily by the National Science Foundation's 

CLIMAP Program over the last 10 years has 

established the key role played by deterministic causes of climatic change, such as the correlation of 

Milankovitch astronomical cycles with Pleistocene 

glacial-interglacial cycles. 

These new sources of data and resulting 

concepts about Earth history have given geohgists a new perspective from which to study the ge""esis of 

economically important commodities such as oil, 

natural gas, coal, phosphate, metals, b"UXites, 

manganese, sulfides, iron, uranium, and others. 

Understanding the processes and boundary co'lditions 

of the formation and preservation of these 

commodities is a prerequisite for developing pr~~dictive 

models to guide future exploration. A recent report by 

the National Academy of Sciences (Be~er and 

Crowell, 1982) notes that our ability to locate new 

deposits of several important minerals will be 

improved by increased understanding of climates 

throughout Earth history. 

The U.S. Geological Survey (USGS) is actively 

involved with paleoclimatic research and, 

consequently, with linking patterns of past climatic 

change to mineral deposits. Because paleoclin'lltology 

involves almost the entire spectrum of the 

geosciences, a 2-day workshop (September 23-24, 1?82) was convened to bring together geochemists, 

sedimentologists, paleontologists, hydrologists, marine 

geologists, mineralogists, and other specialis~s to 

provide a forum for interchange of data and Ideas. 

This circular contains expanded abstra~ts of 

presentations made during the workshop. The wide 

variety of topics addressed demonstrates the brea~th 

of expertise, interest, and ongoing research concermng 

climates and mineralization that exists in the USGS. 

The common thread uniting all of the: papers 

presented below is that paleoclimatology is a 

multidisciplinary field that requires coordination and 

interchange of ideas and data among sc~~ntists. 

Further, it is clear that the deeper we inves":igate a sedimentary mineral, the more relevant the 

paleoenvironmental conditions during deposition and 

diagenesis become to understanding its formaH'>n. As a 

corollary, we must seek improved sedin~~ntary, 

geochemical, and paleontologic tools to identify 

paleoenvironments, and we must test these too1s in the 

field. 

Assessing the Nation's mineral and energy 

resources is a primary and congressionally mllndated 

function of the USGS. We anticipate that future 

research and advances in understanding paleoclimates 

and the effects of climate on the origin and 

distribution of resource-bearing sedimentary ro~ks will 

aid the USGS in fulfilling its mission to produce a 

better inventory of the Nation's known and p')tential 

mineral resources. 

III 

Thomas M. Cronin 

William F. Cannon 

Richard Z. Poore 

Editors 

Page 

Preface--------------------------------------------------------------------------------III 

Cbntinental aluminous weathering sequences and their climatic irrplications in the 

Uhited States, by Harry A. Tourtelot--------------------------------------------------1 

Effect of sea-level fluctuations on porosity and mineralogic changes in coastal 

aquifers, by William Back and Bruce B. Hanshaw----------------------------------------6 

Pliocene and Pleistocene calcitic veins as indicators of paleohydrologic, paleoclimatologic, and neotectonic events, southern Great Basin: An initial 

appraisal, by Isaac J. Winograd, Barney Szabo, Tyler B. Cbplen, and Gene C. 

Doty----------------------------------------------------------------------------------8 

The oxygen minimum zone of continental margins, by Thomas M. Cronin---------------------10 

r~nozoic paleoceanography, by Richard Z. Poore------------------------------------------13 

The U.S. Atlantic Cbntinental Margin: Eustasy, paleoceanography, and mineral 

deposits, by John S. Schlee----------------------------------------------------------16 

Building a biostratigraphic framework around an anoxic-kenoxic event, by 

Joseph E. Hazel----------------------------------------------------------------------18 

Inorganic geochemistry of deep-sea black shales, by Walter E. ~an----------------------19 

Same climatic and oceanographic controls on the time and place of mineralization, 

by W. F. CRnnon----------------------------------------------------------------------24 

Influences of ocean anoxic events on manganese deposition and ophiolite-hosted 

sulfide preservation, by Eric R. Force, W. F. cannon, Randolph A. Koski, 

Keith T. Passmore, and Bruce R. Doe--------------------------------------------------26 

Late Cretaceous and Paleogene nonmarine climates in North America, 

by Jack A. Wolfe---------------------------------------------------------------------30 

Volcanic manganese deposits in the Western Cbrdillera: Lithologic associations 

and paleoceanographic settings and economic deposits associated with biogenic 

siliceous rocks, by James R. Hein and Randolph A. Koski------------------------------32 

~ganic carbon, sulfur, and iron relationships as an aid to understanding 

depositional environments and syngenetic metals in recent and ancient 

sediments, by Joel S. Leventhal------------------------------------------------------34 

Paleozoic atmospheric circulation and oceanic upwelling, by Judith Totman Parrish-------37 

Paleoclimatic controls on the occurrence and quality of coal, by C. B. cecil, 

R. W. Stanton, S. G. Neuzil, F. T. Dulong, and L. F. Ruppert-------------------------40 

v 
carbon dioxide, geochemical modeling, and paleoenvironmental reconstructions, 

by Eric T. Sundquist-----------------------------------------------------------------43 

Isotopic research, climate, and the genesis of mineral deposits, by Bruce R. Doe--------44 

References------------------------------------------------------------------------------49 

I Il1JS'IRATI CNS 

Page 

FIGURE 1. Map showing selected aluminous weathering sequences in the 

Uhited States------------------------------------------------------- 2 

2. Graph showing inferred temperatures for Tertiary time------------------ 4 

3. Diagram showing interface between freshwater and seawater flow systems 

that fo~ zone of dispersion--------------------------------------- 6 

4. Graph showing upward concavity of activity coefficientYi as a function 

of ionic strength--------------------------------------------------- 6 

5-7. Diagrrnms showing: 

5. Diagenetic processes known to occur in mixing zone-------------- 7 

6. HY~othesis tha~ sane.manganese ores may be deposited 

In zone of dispersion----------------------------------------- 7 

7. Characteristics of oxygen minimum zones------------------------- 11 

8. Chart showing Tertiary sea levels and climatic trends------------------ 15 

9. Graph showing observed range and geometric mean of concentrations 

of major-element oxides and trace elements in samples of red 

and green claystone and black shale fram DSDP HOle 530A------------- 20 

10. Plots showing carbonate-free concentrations of certain elements 

versus depth in sarrples of black shale framDSDP Site 530A---------- 21 

11. Diagrams showing how certain processes may contribute to accumulation 

and redeposition of sediments containing various amounts of organic 

carbon-------------------------------------------------------------- 23 

12-13. Graphs showing: 

12. Relative rates of accumulation of marine sedimentary 

deposits of manganese, iron, and phosphate on a 

worldwide scale---------------------------------------------- 24 

13. Tons of iron in known deposits of marine sedimentary 

type as a function of time in comparison with 

accumulations of crude oil in source rocks as a 

function of time--------------------------------------------- 25 

14. Profile showing dissolved manganese and depositional model 

for anoxic event---------------------------------------------------- 26 

15. Eh-pH diagram showing oxidation path of anoxic water mass-------------- 27 

VI 
16. Stratigraphic column showing composite shallow marine manganese 

deposit------------------------------------------------------------- 27 

17. Chart showing age correspondence of ocean anoxic events, shallow 

marine manganese deposits, and ophiolitic sulfides------------------ 28 

18. Diagrmn comparing axial ridge vents during and after anoxic 

events-------------------------------------------------------------- 28 

19. Stratigraphic record of waning anoxic event at cyprus------------------ 29 

20. Graph showing relationship of carbon to sulfur in Black Sea 

marine sediments deposited below oxygenated water and H2Scontaining water---------------------------------------------------- 35 

21. Diagrmn showing geochemical relationships in oxic, anoxic, 

and euxinic sedimentary environments-------------------------------- 36 

22. Map showing atmospheric circulation in the Late cambrian 

northern winter----------------------------------------------------- 39 

23. Inferred paleoclimate changes and generalized stratigraphic 

column fram the upper Mississippian to the Lower Pennian 

central Appalachian Basin------------------------------------------- 42 

24. Chart showing distribution pattern for B 34s values of H2S and 

sulfide minerals when sulfate B 34s=+20 percent is reduced 

by various mechanisms----------------------------------------------- 45 

25. Map of North America showing contours of approximate average 

B D values of meteoric water---------------------------------------- 46 

26. Graph showing behavior of B D and B18o in meteoric water---------------- 47 

27. Plot of B D of fluid inclusions versus calculated a18o values 

of hydrothermal fluids for various epithermal ore deposits---------- 48 

VII 

PALEOCLIMATE AND MINERAL DEPOSITS 

CONTINENTAL ALUMINOUS WEATHERING SEQUENCES AND THEIR CLIMATIC IMPLICATIONS 

IN THE UNITED STATES 

By Harry A. Tourtelot 

Introduction 

Weathering sequences in the geologic record are 

characterized by accumulations of minerals that form 

chiefly by weathering processes. Weathering processes 

result in the mechanical disintegration of rocks and 

the chemical alteration of minerals at and near the 

surface of the Earth. Weathering goes on all the time, 

and the relative intensities and effectiveness of 

mechanical and chemical processes are controlled in 

large part by climate as well as other variables. Both 

mechanical and chemical weathering lead to the 

primary formation of mineral resources and soils. 

Patterson (1981) provides an excellent review of 

weathering processes and some resulting mineral 

deposits. Bauxite, coal, and evaporites are regarded in 

themselves as being indicators of warm climates 

(Frakes, 1979; Habicht, 1979). This paper is concerned 

with aluminous mineral resources, the circumstances 

of their origin in relation to climate, and their 

implications for some other mineral resources. 

Weathering sequences 

About 20 high-alumina clay deposits, which the 

present author calls weathering sequences, are 

discussed by Patterson (1967, p. 131-151) as possible 

aluminum resources. Six of these sequences as well as a residuum and two paleosols not included by Patterson 

(1967) as potential aluminum resources will be 

described briefly in order of geologic age. General 

locations are shown in figure 1. 

Cheltenham clays of Pennsylvanian age 

The refractory clays of Missouri, grouped under 

the name "Cheltenham," are interpreted by Keller 

(1968) (see also Keller and others, 1954) to represent 

the influx of kaolinite-rich weathering products into 

the early Pennsylvanian depositional system. Some of 

these products were trapped in sinkholes on the 

northern flank of the Ozark Dome, and some were concentrated in strata of Pennsylvanian age flanking 

the Ozarks on the north. The clays in the sinkholes 

1 

highest on the dome underwent further weathering in 

Pennsylvanian time to the extent that pure kaolinite, 

along with much diaspore and boehmite, was formed. 

Clays in somewhat topographically lower sinkholes 

were not as intensely altered after deposition, and 

clays in beds in equivalent sedimentary sequences still 

lower were hardly altered at all. These Missouri clays 

are contemporaneous with other refractory clays of 

Early Pennsylvanian age in Kentucky (Patt~rson and 

Hosterman, 1962), in Pennsylvania (Bolger and Weitz, 

1952; Foose, 1944), and elsewhere in the eastern 

midcontinent region (Keller, 1975). 

Sequences of Cretaceous age 

In Colorado, kaolinitic clays in the Dakota 

Formation were eroded from a weathered l'interland 

and incorporated in fluvio-deltaic sedimentr in basal 

Cretaceous strata in the Pueblo-Canyon City area 

(Waage, 1953) and in the Golden area (Waage, 1961). 

In the Golden area, volcanic ash beds in mar;ne strata 

equivalent to the fluvio-deltaic rocks C')nsist of 

smectite and can be traced into the fluvio-deltaic 

sequence where the ash beds consist of kaolinite 

(Waage, 1961, p. 25). Postdepositional processes thus 

may be responsible for the formation of some of the 

kaolinite in the thick nonvolcanic clay beds. 

At nearly the same time, a kaolinite-rich 

residuum was being formed on Precambrian and some 

Paleozoic rocks in the western part of th~ central 

craton in Minnesota (Austin, 1970; Parham, 1970), in 

North Dakota {Moore, 1979), and in South Dakota 

(Ludvigson and others, 1981). At some places, 

kaolinite was eroded from the residuum and 

concentrated in sedimentary rocks of Creta,~eous age 

where further weathering in Cretaceous tirre formed 

minor amounts of gibbsite and boehmite (Parham, 

1970, p. 56-60). 

Sequences of Cretaceous-Eocene age 

Cretaceous to middle Eocene .-A weathering 

sequence in central Georgia and weste .. n South 

Carolina is implied by derived deposits of Late 
FIGURE 1.-8elected aluminous weathering sequences in the United States. Ch, Cheltenham clays, 

contemporaneous with similar clays in Kentucky (OH, Olive Hill) and Pennsylvania (M, Mercer clays). C, 

Colorado clays. Mi, Minnesota residuum. G, Georgia-South Carolina kaolin district. SEB, Southeastern 

bauxite deposits and related occurrences of kaolin, together symbolized by dark patterns, attributed to the 

same weathering sequence. SC, Southern California paleosol. NGP, Northern Great Plains paleosol. SL, 

Spokane-Latah clays. OW, Oregon-Washington ferruginous bauxite. S, saprolite or soq that contains 

gibbsite. 

Cretaceous and middle Eocene ages. It has provided 

the largest kaolin resources in the country. These 

strata have long been regarded as being entirely of 

Cretaceous age (Lang and others, 1965, p. J4), and the 

complexity of their depositional history is shown by 

Tschudy and Patterson (1975) as well as others (Hurst, 

1979). The kaolinite was eroded from a weathered 

hinterland developed on pre-Cretaceous rdcks 

generally to the northwest of the present outcrop of 

Cretaceous and younger strata. Some of the resulting 

deposits are in nonmarine strata of Cretaceous age, 

and others are in nonmarine strata of middle Eocene 

age. A marine sequence separates the two nonmarine 

sequences and records both Paleocene and Eocene 

time, but the record is very compressed and different 

from that of other parts of the Gulf Coastal Plain. 

Local surface weathering in Cretaceous time produced 

minor amounts of gibbsite in some of the kaolin 

deposits of Cretaceous age. PostdepositiCinal 

alteration of the centers of kaolinite lenses of middle 

Eocene age has produced pisolitic clay that contains 

small amounts of gibbsite and that grades in all 

directions into the kaolin (Hurst, 1979). 

Paleocene-Eocene age.-A weathering sequence 

of Paleocene-Eocene age is related to the origin: of 

2 

bauxite deposits in the southeasterr United States 

(Bridge, 1950; Overstreet, 1964). Kaolinized bedrock_ 

in Massachusetts (Kaye, 1967) and clay deposits in 

central Pennsylvania (Hosterman, 1972) also are 

attributed to this weathering seq'.lence. These 

widespread occurrences may constitute an example of 

a widespread system by which alumin•tm and perhaps 

other mineral resources are formed. 

Residual bauxite deposits cap partly buried hills 

of syenite in Arkansas (Gordon and others, 1958, p. 

136) and were the source for transported kaolinite and 

gibbsite in the overlapping strata of late Paleocene 

and early Eocene age. Residual dep0sits formed in 

early Tertiary time may also be represented by 

kaolinitic and bauxitic weathered strata of presumed 

Cretaceous age in Alabama (Bergquist and Overstreet, 

1965) and in western Georgia (White, 1 Ptl5). 

A weathered hinterland on Paleozoic and older 

rocks in the Appalachian region i~ not directly 

rec~nizable but is implied by deposits of clay trapped 

in sinkholes formed in rocks of Paleozoic age and clay 

incorporated in strata of Eocene age. Sinkhole 

deposits in Virginia (Warren and others, 1965), 

Tennessee (Dunlap and others, 1965), Alabama (Cloud, 

1966, 1967; Denson and Waage, 196f), and Georgia 
(White and Denson, 1966) contain bauxite formed by 

postdepositional alteration of kaolinite-rich 

weathering products that accumulated in the 

sinkholes. Transported clays in strata of Eocene age 

are found in northeastern Mississippi (Tourtelot, 1964a; 

Conant, 1965), southeastern Alabama (Warren and 

Clark, 1965), and southwestern Georgia (Clark, 1965; 

Zapp and Clark, 1965; Zapp, 1965). Subaerial Eocene 

weathering of the transported clays formed minor 

amounts of bauxite in Mississippi, where there may 

have also been some Eocene weathering of Paleocene 

clays. Postdepositional alteration by ground water 

seems to have been responsible for the gibbsitic 

bauxite that makes up the centers of lenses of 

kaolinite in the Andersonville district of Georgia 

(Burst, 197 4). 

Regional paleosols of Paleocene and Eocene 

ages .-A regional kaolinitic paleosol of probable 

Paleocene-Eocene age in southern California and 

adjacent Baja California, Mexico (Peterson and 

Abbott, 1979), may represent an immature example of 

a residuum similar to that implied for the hinterland of 

the southeastern bauxite deposits. A similar paleosol 

of regional extent in the northern Great Plains 

(Dunham, 1961; Schultz, 1961; Pettyjohn, 1966) can be 

dated as Eocene and is the surface on which strata of 

Oligocene age were deposited unconformably. 

Washington and Idaho clays of Miocene age 

The clays in eastern Washington and adjacent 

Idaho include both residual (saprolite) and transported 

clays. The residual clays consist predominantly of 

halloysite formed by the weathering of basalt and 

kaolinite formed by the weathering of granodiorite in 

Miocene time. The transported clays of the Latah 

Formation consist chiefly of halloysite and kaolinite 

and were eroded from the residual clays (Hosterman 

and others, 1960; Hosterman, 1960). The fossils found 

in the Latah Formation are excellent indicators of the 

climate during Miocene time. 

Saprolite in the southeastern United States 

Saprolite is a weathered rock that contains 

secondary minerals formed by the weathering of 

susceptible minerals in the parent rock and, for the 

most part, still retains much of the original texture 

and structure of the parent rock (Patterson, 1967, p. 

148). Because it occurs at the present surface, 

saprolite is thought to have formed in the recent 

geologic past and perhaps to be forming even at 

present. Although some saprolite obviously is young 

(Clarke, 1971), at many places a wide range of ages of 

weathering is possible, perhaps even as old as 

Cretaceous (W. R. Griffitts, oral commun., 1982). 

Gibbsite is a common mineral in saprolite developed on 

crystalline rocks, in soils developed on saprolite 

(Clarke, 1972; Cate and McCracken, 1972), and in 

some soils developed on sedimentary rocks of Neogene 

age (Clarke, 1971). Enough gibbsite is present at some 

places for saprolite to have been investigated as a 

possible source of aluminum (Patterson, 1967, p. 148-

151; Beg, 1982). 

3 

The presence of gibbsite in saprolite raises 

questions concerning the relations between climate 

and mineral resources. If gibbsite and other residual 

deposits are forming today, as Knechtel (1963) and 

Hack (1965, p. 66-76) suggest, then the range of 

climate that controls their formation is broa1er than 

what is generally accepted. Conversely, the presence 

of gibbsite may indicate that some of the sarrolite is 

older than investigators had thought and form~d under 

climates much warmer than today's. Resoluticn of this 

problem could have an important bearing on the 

assessment of aluminum and perhaps other mineral 

resources in the region and depends in large part on 

concepts of climatic history. 

Climatic implications of the geologic rec'lrd 

Lateritic weathering resulting in accumulation 

of aluminous and ferruginous materials is an obvious 

feature of present tropical regions. The pre;;oence of 

these materials in the geologic record is taken to 

indicate similar climates in the past. The various 

parameters of climate, such as mean annual 

temperature, annual temperature range, and amount of 

precipitation and its seasonal distribution, can be 

quantified for the present. These numberf can be 

extrapolated into the past (Gordon and others, 1958, p. 

143-144), but the significance of such extrapolated 

numbers is uncertain because so many other factors 

are involved in the weathering process and its results 

(Patterson, 1981). 

The climate of Pennsylvanian time shows 

regional variation. The eastern coal regions are 

interpreted to have had a tropical climate ard heavy, 

seasonally uniform rainfall, whereas the Western 

Interior coal region had a similar warm clinate and 

seasonally distributed rainfall (Schopf, 1975). This 

difference is important in a climatological s~~nse, but 

its effect has not been recognized in t;e highaluminum clays of Missouri in comparison with those 

of Pennsylvania. 

The Cretaceous is generally regarded as a time 

of great warmth (Frakes, 1979, p. 178). Th~ marine 

record (Pearson, 1978, p. 147-149) suggests distinct 

warming of the seas from the earliest par~ of the 

Cretaceous to mid-Late Cretaceous time and then 

marked cooling through the rest of the Cretaceous and 

into the Paleocene. The continental record is much 

less detailed (Dorf, 1942), but regional differ~nces can be made out. Palynological floras in the Mississippi 

Embayment and the Rocky Mountain regions are 

different because they have been separate1 by the 

Cretaceous interior seaway and by latitudinal position 

(Tschudy, 1970). The climates indicated for the two 

regions are not much different and are w;thin the 

subtropical-tropical realm. On a smaller sc"'le, some 

palynological floras contain pollen derived from an 

upland source that probably was cooler and l~ss humid 

than the lowlands of the site of deposition (SJ~ivastava, 

1967; Jarzen and Norris, 1975). 

The Tertiary record is more detailed than the 

Cretaceous record and reflects considerabl ~ secular 

and geographic variation. The continental record of 

climatic variation developed by Wolfe (1978) is 

particularly useful in considering the relation~ between 
0 90 0 0 oy---- MISSISSIPPI EMBAYMENT (0) 

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w 

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80 

70 

60 

50 

40 

30 

20 

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·\ NORTH DAKOTA ( • ) 

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OLIGOCENE 

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GEOLOGIC AGE, IN MILLIONS OF YEARS 

FIGURE 2.--lnferred temperatures for Tertiary time (modified from Wolfe, 1978). Data for North Dakota 

plotted from Hickey (1977). Dotted lines indicate inferred temperatures. 

climate and mineral resources (fig. 2). Mean annual 

temperature varied from high to low at intervals of 

about 10 m.y. Expected latitudinal variation also is 

indicated, as temperatures from the Mississippi 

Embayment are higher than those from southern 

Alaska. Estimates of mean annual temperature for. a 

highly kaolinitic transported clay unit of Paleocene 

age in western North Dakota and for the directly 

overlying earliest Eocene strata also are plotted on 

figure 2 (Hickey, 1977, p. 87-88). This plot does not 

match the other curves very well. The temperatures 

seem somewhat low in comparison with those 

estimated for the middle Eocene of northern 

California and the Pacific Northwest, which are 

similar in latitude to North Dakota. The climate 

suggested by these temperatures may have been a 

relatively lo<:al feature developed because of 

orographic changes taking place in the Paleocene 

landscape. Because the kaolinite was transported from 

an unknown hinterland (Freas, 1962; Hickey, 1977), the 

climatic parameters are not necessarily applicable to 

4 

the hinterland in which the kaolinite vras formed by 

weathering. 

The highest mean annual temgeratures shown on 

figure 2 range from about 12° to 13 C for the Miocene 

to about 30°C for the Paleocene an1 Eocene, but 

bauxitic mineral resources seemingly could be formed 

throughout this range. Suitable parent material and 

other favorable characteristics of the weathering 

regime, including geologic settings conducive to the 

preservation of the weathering record, may have an 

importance equal to that of climate in influencing the 

present distribution of mineral resources. 

Given this broad range of temp~ratures, it is 

uncertain whether discrete segments of the 

temperature variation cycle are closely related to 

specific occurrences of mineral res-,urces. The 

correspondence between the times of generally high 

temperatures during Paleocene and Eocene times and 

the ages of weathering sequences and r,~lated mineral 

resources is, however, striking. 
Conclusions 

Warm, moist climates ranging from perhaps 

warm temperate to tropical are characteristic for the 

formation of aluminous and ferriferous lateritic 

accumulations of economically important mineral 

resources. The geographic distribution of such 

climates in the geologic past has been different from 

that of the present for reasons that still are not 

entirely clear (Frakes, 1979, p. 24-28). Mineral 

resources formed by weathering are part of the record 

of the past distribution of climates but do not 

necessarily indicate the complete extent of climatic 

regions. Estimates of the extent of climatic regions 

may focus attention on areas in which additional 

mineral resources may be found. 

Although climate determines the broad regions 

in which aluminous and ferriferous mineral resources 

may occur, other factors also are important in 

localizing deposits within the region. Some of these 

factors are listed below, along with examples from the 

previous discussions: 

1. A weathered hinterland in which residual 

deposits are formed on favorable rocks 

(Arkansas bauxite) or that serves as a 

source for transported clays and perhaps 

transported bauxite. 

5 

2. Accumulation of transported clays in 

favorable sites such as s·inkholes 

(Cheltenham clays; northeast Alabama 

deposits), lagoonal settings (central 

Georgia clays of Cretaceous and Eocene 

ages), or fluviatile depositional systems 

(Colorado clays, Andersonville bauxite). 

3. Further surface weathering at th~ site of 

deposition of transported clays that may 

form bauxite or bauxitic material (Georgia 

clays of Cretaceous and Eocene ages, 

Minnesota). 

4. Further subsurface alteration by ground 

water of transported clays in favorable 

hydrologic settings in fluviatile systems 

(Andersonville bauxite). 

The trapping of clay in fluviatile systems and 

subsequent postdepositional alteration seem to be 

particularly important factors. Such fluviatil~ systems 

could exist in the subsurface in areas of the Gulf and 

Atlantic Coastal Plains other than those wher~ bauxite 

and kaolin deposits now are known. Such fluviatile 

systems also could be present in strata of C"'etaceous 

age to the west of the Minnesota residuum and yet be 

unrecognized because of thick glacial cov?.r. Any 

deposits in such systems might be so deep as to be 

unminable at present, but knowledge of their 

presence-or absence-could be important in the 

future. 
PALEOCLIMATE AND MINERAL DEPOSITS 

EFFECT OF SEA-LEVEL FLUCTUATIONS ON POROSITY AND MINERALOGIC CHANGES IN 

COASTAL AQUIFERS 

By William Back and Bruce B. Hanshaw 

The ocean is the ultimate base level for groundwater regimes. Climatic changes that affect the 

relationship between freshwater head and sea level can 

have pronounced effects on ground-water flow pattern, 

rate of ground-water discharge, position of the 

freshwater-saltwater interface in coastal aquifers, and 

amount of mixing within the zone of dispersion (fig. 

3). Because part of the water discharged in coastal 

areas is brackish owing to mixing of freshwater with 

ocean water, discharged saltwater must be replenished 

from the ocean. This discharge generates a flow 

system within saltwater in the aquifer that is related 

to, but distinct from, the flow system in freshwater. 

The zone of dispersive mixing is a highly 

reactive chemical system. This reactivity results from 

differences in significant chemical parameters such as 

temperature, pH, PC02, and ionic strengths of the two 

water bodies. For example, the nonlinearity of the 

activity coefficient 'Y i as a function of ionic strength 

(fig. 4) shows that mixing two waters will yield an 

activity coefficient less than what the value would be 

if the relationship were linear. 

Because activity equals activity coefficient 

multiplied by molality, molality must increase and 

r Water Table 

.. •. 

FIGURE 3.-Diagram showing the interface between 

freshwater and seawater flow systems that forms 

the zone of dispersion. 

6 

thereby cause additional solution of the mineral of 

interest in order to maintain an activit-.• equal to that 

in either of the original solutions. Thi~ effect can be 

quite pronounced in carbonate aquifers, and it is 

possible for a water that is in equilibrium with calcite 

to be mixed with ocean water that is supersaturated 

with respect to calcite to generate a mixture that is 

undersaturated with calcite but super~aturated with 

respect to dolomite (Hanshaw and Back, 1980). 

On the basis of these relf'.tionships, we 

developed a mixing-zone model (Hanshaw and Back, 

1979) for the formation of dolomite in the zone of 

dispersion and hypothesized that the b'lulder zone of 

Florida that has conventionally been irterpreted as a 

paleokarst feature may be undergoing dissolution and 

dolomitization at the present time. Badiozamani 

(1973) named this model the Dorag mo1el and used it 

effectively to explain the origin of Ordovician 

dolomite in the midwestern part of the United States. 

Land and Epstein (1970) independently developed the 

same hypothesis to explain the do}')mitization of 

Holocene deposits in Jamaica. The petrologic work of 

Folk and Land (1975) tended to sul:>stantiate the 

mineralogic changes in the mixing zone. Knauth (1979) 

Ionic Strength 

FIGURE 4.-Graph showing the upward concavity of 

activity coefficient 'Y i as a function of ionic 

strength. 
and Land (1977) also developed a mixing-zone model to 

explain the occurrence of chert lenses and nodules 

from a biogenic opal precursor in carbonate rocks. 

Magaritz and others (1980) identified dolomite formed 

at the freshwater-saltwater interface in Israel. Sealevel fluctuations cause a zone of dispersion to 

oscillate through the carbonate rocks and thereby 

permit the rocks to be in the diagenetic environment 

repeatedly. 

We investigated this phenomena in Xel Ha 

lagoon on the east coast of the Yucatan, where we 

observed a significant amount of freshwater 

discharging and mixing with ocean water in the 

lagoon. We hypothesized that this mixing caused 

pronounced solution features such as straight-walled 

and rectilinear channels along well-developed 

fractures. However, detailed mapping of the chemical 

character of the water and mass-transfer calculations 

indicated that outgassing of carbon dioxide from the 

discharged water was a more rapid chemical reaction 

than dissolution of limestone, and water therefore 

became supersaturated at the time of discharge. We 

then were able to demonstrate that dissolution was occurring within the aquifer before the ground water 

discharged into the lagoons and submarine springs 

(Back and others, 1979). 

Our recent work in the Yucatan has 

demonstrated that lagoons such as Xel Ha and 

crescent-shaped beaches result from underground 

dissolution, which forms caves that later collapse 

(Back and others, 1981). In cores drilled for 

stratigraphic information in the Yucatan, we have seen the development of secondary porosity and the growth 

of dolomite rims on calcite cystals. Frank (1981) has 

described spectacular dolomite crystals zoned with 

calcite. He has concluded that these crystals grow in an environment where subtle changes in the chemistry 

of the water can cause pronounced differences in the 

resulting mineralogy. We believe that this type of 

dolomite would develop in a mixing-zone environment. 

At Xcaret, a major cave system on the east 

coast of the Yucatan, scuba tanks permitted us to 

observe and photograph the differential dissolution of 

the limestone in the zone of dispersion. Above the 

water level, the walls of the cave are relatively 

smooth, but, in the zone of dispersion, tremendous 

dissolution causes the rock to look like Swiss cheese. 

This appearance is reported to be very similar to that 

of reservoir rock of the Golden Lane oilfield in central 

Mexico and also typical of some reservoir rocks in 

Saudi Arabia. Not only does this dissolution cause a 

great increase in porosity, but the collapse of the cave 

roof also forms a precursor to solution breccia. Such 

solution features occur in other parts of the world but 

have no~ yet been determined to result from groundwater discharge. However, Paul van Beers (oral 

commun., 1982) of the Free University of Amsterdam 

suggested that many of the solution features in the 

Algarve of the southern coast of Portugal may be the 

result of ground-water mixing and discharge. 

Therefore, we believe it well documented that the 

zone of dispersion can increase porosity, is a suitable 

environment for dolomitization and chertification, and 

can provide conditions for formation of solution 

breccias (fig. 5). 

7 

FIGURE 5.--Diagram showing diagenetic pro~esses 

known to occur in the mixing zone. 

By applying these ideas to Cr~taceous 

sediments in Morocco, we can hypothesize that the 

manganese deposits occurring in Cretaceous dolomites 

were deposited in a mixing-zone environment (fig. 6). 

Cannon and Force (1983) show features such as zoned 

calcite and chert nodules, porosity, chert nodules 

zoned with pyrolusite, and fillings of pyrolusite in 

solution breccia. In association with the manganese ore are layers of insoluble residue that pr~sumably 

resulted from dissolution of the original c~rbonate 

material. 

The hypothesis is that ground weter was 

discharging near the shore of an anoxic sea in which 

the manganous ion was mobilized in an organic-rich 

bottom layer. Ground-water discharge would set up a 

flow system whereby the saltwater moves into the 

aquifer, carrying with it the manganous ion tl''-'lt would 

then be oxidized to pyrolusite by the oxyg~n in the 

freshwater. Along with the precipitation of the 

manganese ore would be the proce:>ses of 

chertification, dolomitization, porosity development, 

and the concomitant incipient formation of solution 

breccia. 

FIGURE 6.-Diagram demonstrating the h:rpothesis 

that some manganese ores may be dep':lsited in 

the zone of dispersion. 
PALEOCLIMATE AND MINERAL DEPOSITS 

PLIOCENE AND PLEISTOCENE CALCITIC VEINS AS INDICATORS OF PALEOHYDROLOGIC, 

PALEOCLIMATOLOGIC, AND NEOTECTONIC EVENTS, SOUTHERN GREAT BASI~T: 

AN INITIAL APPRAISAL 

By Isaac J. Winograd, Barney Szabo, Tyler B. Coplen, and Gene C. Doty 

Lakebed stratigraphic sequences currently 

provide the only major tool for deciphering pre-middle 

Wisconsin paleoclimatic conditions in the Great 

Basin. Calcitic veins, exhumed feeders of major fossil 

springs, represent a second tool potentially capable of 

providing a continuous record of paleohydrologic and 

paleoclimatologic events extending back to the middle 

Pliocene. 

The calcitic veins occur in near-vertical 

fractures in Pliocene and Pleistocene sediments within 

the Amargosa Desert of Nevada and Death Valley in 

California. The veins vary from a millimeter to a 

meter in thickness, locally occur in swarms, and are 

commonly finely laminated. They can be traced 

vertically for tens of meters and horizontally over 

hundreds of meters. 

The veins originated as low-temperature 

(<50°C) precipitates from calcite-saturated artesian 

ground water r1smg along tensional (probably 

extensional) fractures in Pliocene and Pleistocene 

alluvium, fanglomerate, and lakebeds. Evidence for 

this origin includes (1) occurrence of the veins within 

a 16-km-long structurally controlled major spring 

discharge area at Ash Meadows in the Amargosa 

Desert (Winograd and Doty, 1980) (a regional Paleozoic 

carbonate-rock aquifer feeds these modern springs via 

fractures); (2) visible transition of vein to tufa in 

Furnace Creek Wash adjacent to Death Valley; and (3) 

a variety of vein morphologies indicative of active 

flow of water through open fissures. The veins mark 

the sites of fossil ground-water flow within major 

modern (Ash Meadows) and exhumed (Furnace Creek 

Wash) discharge areas of regional flow systems 

(Winograd and Friedman, 1972; Winograd a:nd 

Thordarson, 1975; Dudley and Larson, 1976; Winograd 

and Pearson, 1976) in the southern Great Basin. 

Three veins (lOB, 13N, and AM-7) have b¢en 

dated hy the uranium-series method. This method is 

applied in \~o wNl· First, for samples in which the 

measured 2 Th/ U activity ratio !~less !~an about 

1.1, dates are calculated from the 2 TI¥:2 U value. 

Second, for samples in which the 230Th/ 34u value is 

nearly in radio~.ftive e~uilibrium, dates are calculated 

by using ¥3e 2 4M123 U activity ratio and the fact 

that the '~u123 U activity ratio of ground water 

8 

from the regional artesian carbonate aquifer varies 

narrowly from 2 to 3. Each vein was divided into 

groups of laminae representing youngest to oldest 

portions of the vein as determined from field relations, 

and each group was analyzed. The veins range in age 

from 100,000 yr to 1.7 m.y. ExtrapolE'tion of growth 

rates indicates that vein lOB may be i'~ old as 3 m.y. 

T~1 fo¥3 oldest laminae of vein lOB maintain a 4u/ 8u activity ratio of 1.0 indicating that 

closed-system conditions, necessary for reliable 

dating, prevailed throughout their geologic history. 

The veins appear to have th ... ee immediate 

uses: (1) reconstructing the paleohydrology of the Ash 

Meadows and Furnace Creek Wash area"'~ (2) building a 

3-m.y. record of deuterium (D), lBo, and 13c 

abundance fluctuations in Great Basin winter-spring1 

precipitation; and (3) providing indepe'ldent evidence 

bearing on the time and magnitude of uplift of the 

Sierra Nevada and the Transverse Ranges. 

Utilizing the geographic distribution of calcitic 

veins in the Ash Meadows area, Winc~rad and Doty 

(1980) demonstrated, before obtaining uranium-series· 

dates, that late(?) Pleistocene fossil-s":lring discharge 

occurred 14 km northeast of the present spring 

lineament and at altitudes as much as 51) m higher than 

the altitude of the highest modern spdng. Now that 

the AM-7 vein (collected within the modern spring 

lineament) is known to have been dep0sited between 

400,000 and 700,000 yr ago, we can unequivocably 

state that Ash Meadows has been a najor discharge 

area well into the Pleistocene. Mineralogic studies of 

the lakebeds of the region (Kyser ar·1 others, 1981; 

Khoury and others, 1982) provide additionaf evidence 

that such discharge has probably occurred in the same 

region since the late Pliocene. A byproduct of the 

continuing paleohydrologic studies will be an estimate 

of the time of isolation of the pupfish Cyprinodon 

diabolis in Devils Hole, a cavern near tt~ center of the 

Ash Meadows spring lineament. The time of isolation 

1studies in the principal recht:trge area-the 

Spring Mountains-indicate an absen~e of modern 

recharge from summer precipitation (I. J. Winograd, 

unpublished data). 
of this fish is of major interest to biologists studying 

rates of evolution. Our work suggests that the 

Cyprinodon may have been isolated for at least 

100,000 yr, well in excess of the late Wisconsin 

isolation time assumed by the biologists. 

The D, l8o, and 13c record in the dated veins 

is exciting and perplexing. The 4- to 11-cm-tfdck 

veins were sampled at lmm intervals for B 0, 

and B l;:sc analysis; several millimeter-thick samples 

were required for analysis of the D content of fluid 

inclusions. The B D data are as much as 50 permil 

heavier than modern (-98 permil relative to Standard 

Mean Ocean Water) or late Wisconsin (-106 to -103 

permil) recharge; most significantly, the values 

become lighter with decreasing age. We cannot 

attribute these changes to mineral-water 

fractionations because there are no major mineral 

phases in the carbonate aquifer with which hydrogen 

could have fractionated during flow from recharge 

areas to discharge areas over the past 2 m.y. At this 

reconnaissance stage of our study, we cannot 

unequivocally rule out possible enrichment of the D 

content of the fluid inclusions by the preferential 

outward diffusion of H20 over HDO after uplift of 

veins lOB and AM-7 above the water table. Nor can we 

presently evaluate the magnitude and direction of 

change in D content of several laminae that have been 

recrystallized. However, such concerns are, in 

general, not supported by the distribution of BD values 

within the veins nor by the very dense nature of the 

vein calcite. 

We believe that the 50-permil depletion of D 

with decreasing age of these veins reflects major 

uplift of the Sierra Nevada and the Transverse Ranges 

during the l~;~.st 2 m.y. Such uplift would progressively 

deplete Pacific storms entering the Great Basin from 

the west and southwest of D. The fluid inclusions in 

the veins studied preserve this progressive depletion of 

D in southern Great Basin Pliocene-Pleistocene 

recharge. Two alternate hypotheses-namely, that 

during the late Pliocene to mid-Pleistocene, winter 

precipitation was derived from more .:southerly (and 

therefore D enriched) sources than it is at present or 

that the percentage of recharge derived from sum mer precipitation (also D enriched) was considerably 

greater at that time than it is today--deserve 

consideration. The residence time of water in the 

regional carbonate aquifer--on the order of 10,000 to 

30,000 yr (Winograd and Pearson, 1976)-is a negligible 

9 

factor influencing D values in the time frame under 

consideration in all three hypotheses. 

Assuming the validity of the first 

hypothesis-namely, control of D in precipitation by 

uplift of the Sierra Nevada and Tfqnsverse 

Ranges-permits an independent estimate of the 

magnitude of uplift of these ranges sinc:e latest 

Pliocene. The major orographic effects of the Sierra 

Nevada on the D content of modern precipitation have 

been well documented by Friedman and Smith (1970) 

and by Smith and others (1979). Utilizing the Daltitude correlations that they developed. (20-50 

permil/1,000 m) and the 50-permil decrease in B D in 

the veins, one can postulate a 1,000- to 2,500-m uplift 

of the Sierra Nevada and Transverse Ranges in the 

past 2 m .y. These estimates of uplift are within the 

range postulated by structural geologists for these 

mountains. Huber (1981) believed that the Sierras have 

risen about 1,000 m since late Pliocene, whe':'eas Hay 

(1976) postulated a rise of 1,800 m in the last 4.5 m.y. 

Gable and Hatton's (1980, plate 4) synthesis of vertical 

movement data indic;rtes an uplift rate for th~ Sierras 

of about 4 to 6 m/10 yr or 800 to 1,200 m in the past 2 

m.y. Uplift rates capable of raising the Tr<tnsverse 

Ranges to their present height (up to 3,500 m) in the 

last million years have been suggested by Ye~ts (1981), 

Lajoie and others (1979), and Morton and other;;- (1982). 

In contrast to the B D data, the B 180 analyses 

of calcite comprising vein lOB display neither a long 

duration trend nor a fluctuation over the range of 

several permil needed to match the changes in the B D 

values. An attempt to understand the dis~repancy 

between the B D and s18o data in this vein C':lntinues. 

In contrast to the lack of variation of B l8o in vein 

lOB, the B 18o for vein AM-7 appears to record a 

100,000-yr Milankovitch cycle. 

In summary, the potential of the calcitic veins 

for deciphering the Pliocene and Pleistocene 

paleohydrologic history of ground-water discharge at 

Ash Meadows appears excellent. De,~iphering 

paleoclimatologic signals in the stable isotcoic data 

will be challenging, perhaps formidable, particularly if 

the postulated major neotectonic effects on B D are 

sustained by further study; yet, we have stu1ied only 

three veins to date and have B D data for only two of 

them. Future work will concentrate principally on the 

D content of fluid inclusions in dated veins from both 

the recharge areas and the discharge area.;, of the 

coincident fossil and modern regional grou"'ld-water 

flow systems of the southern Great Basin. 
PALEOCLIMATE AND MINERAL DEPOSITS 

THE OXYGEN MINIMUM ZONE OF CONTINENTAL MARGINS 

By Thomas M. Cronin 

The oxygen minimum zone is a feature of the 

ocean system produced by a combination of high 

biological productivity and oceanic advective 

circulation of oxygen-depleted water masses. The 

depth of the modern 0 2 minimum varies thuoughout 

the oceans, but it usually occurs in the bathyal zone 

and is between 200 and 500 m thick (Bubnov, 1966; 

Menzel and Ryther, 1968). It varies in intensity and is 

most strongly developed along eastern boundaries of 

oceans where equatorward winds cause upwelling of 

cool nutrient-rich subsurface waters that increase 

biological productivity in the photic zone (Margalef, 

1978). In such extreme cases, low dissolved oxygen 

(0.0-1.0 mL/L) or anoxic conditions prevent organisms 

from living on the bottom. Sediments deposited in 

regions of oxygen minimums are characterized by fine 

laminations consisting of alternating siliceous or 

calcareous and dark organic-rich layers that reflect 

anoxic conditions and the absence of bioturbation 

(Diester-Haass, 1978; Pisciotto and Garrison, 1981). 

Siliceous material consists of diatoms and 

radiolarians. Organic content of sediments averages 8 

to 17 percent in most regions of upwelling but is as 

high as 26 percent off Africa. High concentrations of 

metals such as Ni (35-455 ppm), Zn (18-337 ppm) Cu, 

P, U, and Mo also characterize these sediments. 

Phosphorite genesis, which is controlled by warm 

climates and high sea levels, occurs in regions of 

strong upwelling and extensive oxygen-depleted water 

masses. Figure 7 summarizes the biological, 

sedimentolog-ical, and chemical characteristics of the 

o2 minimum zones of a nonupwelling coast (I), a coast 

with deep anoxic silled basins (II), and an upwelling 

continental margin (III) (Demaison and Moore, 1980; 

Diester-Haass, 1978; Ingle, 1981; Pisciotto and 

Garrison, 1981; Rowe and Haedrich, 1979; Margalef, 

1978; Douglas and Heitman, 1979). 

During the Mesozoic and Cenozoic, climatic and 

paleogeographic changes have significantly altered the 

intensity and location of oxygen minimums at various 

time scales and thereby influenced the extent of ocean 

floor that was the site of mineral-rich sedimentation. 

In the Guaymas Basin in the Gulf of California, 

climatic warming during Pleistocene deglaciations 

caused a shift from homogenous, bioturbated 

sediments to finely laminated rhythmites deposited 

10 

under anoxic conditions (Schrader and others, 1980). 

Short-term climatic events such as the little ice age 

(1550-1830 A.D.) can also be recognized in varved 

sediments in the Santa Barbara Basin. In the eastern 

North Atlantic, in the Gulf of Guinea, analyses of 

benthic faunas allowed accurate d0<'1lmentation of 

fluctuations in dissolved oxygen dr .. ing sea-level 

fluctuations of the last interglacial-glacial cycle 

(Peypouquet, 1979). Relatively low d:~c;;olved-oxygen 

concentrations correspond to high eus~atic sea level, 

and high oxygen concentrations corresrond to low sea 

level. 

Over longer time scales, the Mjo~ene Monterey 

Formation of California is the prototype of oxygen 

minimum zone sedimentation in wl'ich deposition 

occurred in bathyal environments under particular 

climatic, tectonic, and oceanograpl ic conditions. 

Global cooling during the Miocene (about 15-16 m.y. 

ago) associated with the buildup of Antarctic ice 

caused the southward shift of cool waters, intensified 

upwelling, and the deposition of finely laminated 

siliceous sediments that are an important petroleum 

source and, when they are fractured, reservoir beds 

(Ingle, 1981). Fine-scale Miocene climatic changes are 

not understood well enough to predkt the detailed 

sequences of laminated and homogeneous sediments; 

however, information on the frequency and amplitude 

of climatic events has potential use in the western 

United States and throughout the Pacific, where 

similar oceanographic situations devel<'oed during the 

Miocene. For example, oil-bearing Neogene deposits 

on the pga Peninsula of Honshu, Japan, formed under 

environments similar to those of the Monterey (Ingle, 

1981). 

The formation of Cretaceous black shales has 

also been attributed to expanded 0 2 zo1es in the open 

ocean; during periods of black shale formation, high 

sea levels, warm global climates, and low latitudinal 

thermal gradients caused ocean stagnation, high 

terrigenous input, and bottom anoxia (Schlanger and 

Jenkyns, 1976; Weissert, 1981; Arthur and Schlanger, 

1979). Some authors emphasize climatically 

modulated diminishment in thermohalin?. circulation as 

a first-order cause for some black shales in the South 

Atlantic, Indian, Tethyan, and central North Atlantic 

Oceans. However, climatic control of terrigenous 
f-4 

f-4 

200 

600 

1000 

II 

500 

1000 

200 

400 

600 

800 

1000 

TOPOGRAPHY 

DISSOLVED BIOLOGICAL 

OXYGEN OCEANOGRAPHY 

SEDIMENT -WATER 

INTERFACE 

SEDIMENT MICROCHARACTERISTICS PALEONTOLOGY 

NONUPWELLING MARGIN 

(East U.S.) 

THERMOCLINE 

~~~i=i=i=i=~~~~ 

-~IBIIIIIIII 02 MIN 

~~~~~~~~~~~ 

SILLED BASIN 

OPEN BASIN (Guaymas Bason} 

Ill UPWELLING MARGIN 

(lndoan Ocean, Peru) 

~~~~~i~~~lilil O, MIN 

I 

I 

·' ( 

I 

l 

mUL 

2 4 

mUL 

2 4 

",, 

mlil 

BENTHIC 

Active burrowing, 

aerobic 

organ•sms 

(ostracodes, 

forams, etc.} 

Strong depth 

zonat1on 

Few anaeroboc 

forams, 

nematodes 

No burrowing 

0 2 4 6 

Low standong 

stock, 

no burrowong 

Anaeroboc 

bacteroa 

PLANKTIC 

Calcareous 

nannos, forams, 

etc. in euphotoc 

Sea floor 

Hogh organoc 

productivity, 

soloceous and 

calcareous 

phytoplankton 

in seasonal 

blooms 

02 

Burrows 

Homogenous, mottled, 

from booturbation: 

variable llthologoes 

Massive laminated couplets 

or laminated couplets 

consisting of doatomites 

and doatomaceous muds 

and clastoc sediment 

~ P =Phosphate 

[121 Shells 

1;3 Olove-green doatomaceous mud 

I] Shelly sand 

~ Shelly black mud 

Calcareous planktic 

microfossils dominant; 

diverse benthic fauna 

Siliceous phytoplankton 

common. Benthic foram 

Suggrunda eckisi and 

ostracode Krithe 

Fish 

FIGURE 7 .--Characteristics of oxygen minimttm ~?:on~o:;. Nrm !!)lA!~lling mqr~in from (l!it::t by C::-o:1i:1. {1933). Silled basin and upwelling margin model 

adapted from Ingle (1981) and Pisciotta and Garrison (1981); published with permission from the Society of Economic Paleontologists and 

Mineralogists. Sediment-water interface data adapted from Demaison and Moore (1980); published with permission from the American 

Association of Petroleum Geologists. Sediment characteristics data adapted from Diester-Haass (1978); published with permission from 

Springer-Verlag. 
input also controlled the deposition of northern North 

Atlantic organic shales in turbidite sequences (Dean 

and others, 1977). 

The following observations must be taken into 

account in models designed to explain and (or) predict 

the occurrence of sediments deposited in the 0 2 

minimum zone: 

1. 

2. 

3. 

The o2 minimum zone varies in intensity and 

depth throughout the world's oceans; it is not 

necessarily synonymous with anoxic conditions. 

Temporal changes in the development of oxygen 

minimum zone and anoxic conditions occur at 

time scales ranging from 101 to 106 yr in the 

geologic record. 

Different combinations of environmental 

conditions can cause anoxia; conversely, several 

sedimentary processes can produce cyclic or 

rhythmitic sediments. Anoxic conditions can 

result in the concentration of hydrocarbons and 

metals during relatively warm or cool climatic 

conditions, depending on local paleogeography 

4. 

12 

and other factors. The formathn of organic 

shales in Mesozoic and Cenozoic sedimentary 

cycles along continental margins can be most 

strongly influenced by peculiar rna rine biological 

and chemical conditions or by terrigenous input 

from the adjacent continent. 

Understanding the evolution of th~ o2 minimum 

zone and bottom anoxic condiU'>ns m general 

requires high-resolution climatic records for 

specific marine basins and more accurate 

methods of paleoenvironmental reconstruction 

that allow paleodepth estimation, 

paleogeographic reconstruction, and estimation 

of chemical and physical conc'itions at the 

sediment-water interface. Benthic organisms 

having limited tolerances for sp~~cific physical 

and chemical conditions - in particular, certain 

ostracodes (Peypouquet, 1979; Cronin, 1983) and 

foraminifera (Ingle, 1981) - hold promise for 

accurately and quickly delineating bottom 

paleoceanographic conditions alo'lg continental 

margins. 
PALEOCLIMATE AND MINERAL DEPOSITS 

CENOZOIC PALEOCEANOGRAPHY 

By Richard Z. Poore 

Marine geological and geophysical studies in 

concert with more than a decade of studying cores 

raised by the Deep Sea Drilling Project (DSDP) have 

led to increased understanding of the evolution of 

ocean basins and paleoceanography during the 

Cenozoic. At the start of the Cenozoic, a 

circumglobal ocean, which allowed latitudinal flow of 

both surface and deep water, was present at low 

latitudes. Changing ocean-basin geometry during the 

Cenozoic, however, resulted in restriction of 

equatorial circulation and concomitant development of 

circum-Antarctic circulation. In the Paleogene, 

northward movement of India and Australia greatly 

restricted circulation in the Indian Ocean and the 

western Pacific. Northward movement of Africa 

caused restriction and finally complete closing of the 

eastern Mediterranean by the early Miocene. Later, in 

the Neogene, uplift of the Isthmus of Panama first 

restricted and then terminated circulation between the 

Atlantic and the eastern Pacific. The net effect of 

these events was to greatly enhance the meridional 

aspect of low-latitude circulation. 

The separation of India and Australia from 

Antarctica, coupled with the opening of the Drake 

Passage between Antarctica and South America, led to 

development of a circum-Antarctic current. This 

current isolated Antarctica and allowed extensive 

formation of an Antarctic watermass, which provided 

a source for large quantitites of very cold bottom 

water through formation of sea ice. 

Another important development during the 

Cenozoic was the opening of the Norwegian-Greenland 

Sea, followed by the sinking of the Iceland-Faeroe 

Ridge below sea level. Major breaching of the IcelandFaeroe Ridge during the Miocene provided a route for 

cold Arctic water to enter the world's oceans and 

probably initiated formation of significant amounts of 

North Atlantic deep water. 

Knowledge of major changes in ocean-basin 

geometry has allowed construction of broad features 

of paleoceanography through the Cenozoic (Haq, 1981; 

Kennett, 1978; Berggren and Hollister, 1977). Within 

this framework, details of Cenozoic paleoceanography 

are being developed primarily from paleontologic, 

geochemical, and sedimentologic study of DSDP cores. 

13 

One of the most important recent developments 

has been the integration of biostr<~tigraphy, 

magnetostratigraphy, and isotope stratigraphy with 

radiometric dates to formulate reliable high-resolution 

time scales for correlating and dating marine 

sequences. Accurate correlations mean that timeslice maps showing the distribution of microfossil 

assemblages or lithologies for specific tim€ intervals 

can be constructed with confidence and use'i to infer 

oceanographic conditions. Under optimum conditions, 

correlations over portions of the Cenozoic are 

approaching resolution on the order of 100,000 yr. 

Similarly, time-series studies done in differe'lt regions 

can be compared with one another with a minimum of 

ad hoc "curve matching." Another important aspect of 

the development of high-resolution time scf'les is the 

ability to detect relatively brief unconformities and to 

determine sediment accumulation rates in pelagic 

sequences. For example, Keller and Barron (1982) 

identified and mapped the geographic extent of seven 

Miocene deep-sea unconformities. These 

unconformities are interpreted to be the result of 

increased bottom-current activity associated with the 

expansion of Antarctic glaciation. 

Mapping the distribution of planktonic 

microfossil assemblages can show the distrii:''.ttion and 

migration of surface-water masses and thus delineate 

the distribution and migration of climatic belts. For 

example, Haq and others (1977) demonstrated several 

poleward migrations of tropical nicrofossil 

assemblages in the Atlantic Basin during the Paleocene 

and Eocene. Moreover, individual species and 

assemblages of microfossils are indicative of upwelling 

conditions. For example, the abundance of the diatom 

genera Thalassiomena and Thalassiothrix is a reliable 

indicator of upwelling intensity in Neogene sediments 

in low and middle latitude areas of the Pacific Basin. 

It has been documented for some time that 

benthic foraminifers can be used to identify low 02 environments at the sea floor (Ingl~, 1981). 

Quantitative studies have revealed that benthic 

foraminifers can also be used to identify deep-water 

masses (Lohmann, 1978). In addition, sever,';'.l distinct 

large-scale vertical migrations of benthic 

foraminifers, which probably reflect major changes in 
deep-water circulation patterns, have been found in 

the Miocene of the Pacific (Woodruff and Douglas, 

1981). 

Oxygen and carbon stable isotope studies of 

calcareous microfossils also contribute to our 

understanding of Cenozoic paleoceanography. s18o 

were initi~ll~ interpreted as a tery~erature index. 

Ho~ever, It _Is n~w clear that the 8 0 signature of marme calcites IS a complex signal that contains 

information on a number of factors such as the 

isotopic composition of seawater and the life processes 

of _microfossils. Planktonic foraminifers show isotopic 

evidence of depth stratification in the water column as 

far back as the Mesozoic (Douglas and Savin, 1978) 

and benthic foraminifers show evidence of consistent 

offsets from presumed equilibrium values back to at 

least the Oligocene (Graham and others, 1981; Poore 

and Matthews, 1983). Interpretation of 8 13c data is 

more complex, but values obtained from some taxa 

appear to correlate with the dissolved-oxygen content 

of seawater (Belanger and others, 1981). 

The identification of sea-level cycles in seismic 

records has important implications for interpreting the 

geologic history of continental margins (Vail and 

others, 1977). The timing and magnitude of these 

cycles, however, are open to question. A number of 

studies (Keller and Barron, 1982; Poore and Wolfe, 

14 

1980) suggest significant correlat~.,n between 

paleoceanographic and sea-level events. Figure 8 

correlates terrestrial and marine paleoclimate records 

from the Atlantic Basin with glo~al sea-level 

fluctuations during the Paleocene, Eocene, and 

Oligocene. Cold intervals correlate l''ith sea-level 

minimums, whereas warm intervals correlate with sealevel maximums. These correlations suggest that 

some, if not all, of the second-or1er sea-level 

fluctuations observed in the Cenozoic may be 

glacioeustatic. Therefore, oxygen isctope records, 

which contain information on global ice. volume, may 

be used eventually to quantify the mag"'itude of sealevel changes seen in seismic records. 

In summary, the ability to unders~and Cenozoic 

paleoceanography has reached the point where these 

data can make significant contributions to 

investigations concerning sedimentary mineral 

resources. Times of intensified oceanic circulation can be identified, and regional variations in 

accumulation rates and areas of submarine erosion can be delineated. Areas of high productivity and oceanic 

climate belts can be mapped. Major oceanographic 

events can be identified, and the dis"'olved-oxygen 

content of deep water can be traced by both faunal 

and isotopic techniques. Increased unc~rstanding of 

the magnitude, frequency, and multirle causes of 

eustatic sea-level fluctuations appears neqr. 
PLANKTONIC CLIMATIC RELATIVE 

FORAMINIFER PROVINCIAL TRENDS SEA LEVEL 

EPOCH ZONE STAGE COLD WARM FALLING RISING 

2_ 

N4 

P22 

b w w z t- P21 !------- w <( 

u _J 

a 0 

(!J 

/ ::J 

0 P20 

VICKSBURGIAN v-MARINE 

>- _J P19 a: 

<( 

w P18 

P17 ///II P16 / w / 

t- JACKSONIAN / 

<( '/ _J 

f~, P15 

............. 

P14 - ............ 11 

I w P13 I 

z w I w _J 

I u Cl CLAIBORNIAN 0 Cl P12 w ~ I. 

Pll I 

PlO 

P9 

>- P8 1\ _J 

a: 

<( P7 /v w 

P6 SABINIAN NONMARINE V' 

w 

P5 >~\ I tII( w <( P4 

z _J 

w 

u P3 ' 0 

w ' ' ....J ' <! ' a.. P2 MIDWAYAN ' >- ' ' _J 

a: d <( 

w Pl -----c- I b a l II l / 

20 25 30 

INFERRED MEAN 

FIGURE 8.-Tertiary sea level and climatic trends (modified after Wolfe and Poore, 

1982). P and N refer to standard planktonic foraminiferal zones for the Paleogene and 

the Neogene, respectively. 

15 
PALEOCLIMATE AND MINERAL DEPOSITS 

THE U.S. ATLANTIC CONTINENTAL MARGIN: EUSTASY, PALEOCEANOGRAPHY 

AND MINERAL DEPOSITS 

By John S. Schlee 

The U.s. Continental Margin is a series of 

elongate sedimentary basins and shallow platforms 

that originated during the latest opening of the 

Atlantic Ocean. In the basins, as much as 16 km of 

sedimentary rock accumulated under marine shallowwater or nonmarine conditions. Although the thickness 

of Mesozoic-Cenozoic sedimentary rocks changes from 

basin to basin, the vertical succession and seaward 

changes in facies appear remarkably similiar and point 

to uniform paleoenvironmental conditions over a large 

area of the Continental Margin. 

The sedimentary sequence has been most 

closely studied in approximately 75 holes drilled 

mainly off Nova Scotia. They reveal an older rift 

sequence of Late Triassic red beds, evaporites, and 

carbonate rocks that overlies Paleozoic(?) 

metasedimentary rocks and granite. A conspicuous 

postrift unconformity, best developed toward the 

landward edge of the basins, separates the rift 

sequence from a more extensive "drift" sequence of 

carbonate and siliclastic rocks of Jurassic age and 

younger, which accumulated following the separation 

of North America and West Africa. The postrift 

section of Jurassic age is mainly limestone and 

dolomite (with some interbedded anhydrite in the 

Lower Jurassic part of the section) that interfingers 

with deltaic clastic-rock facies toward the uppermost 

part of the Jurassic. Except for the Blake Plateau, 

most of the carbonate platform buildup ceased in the 

Early Cretaceous as substantial amounts of siliclastic 

sediment overspread the margin to build a sedimentary 

blanket across the shelf and onto the Continental 

Rise. Clastic sedimentation continued at a diminished 

rate throughout the Cretaceous and Cenozoic, marked 

by short-term regressions across the shelf and 

deposition of thin, widespread transgressive 

limestones. ·Beginning in the Tertiary, the Blake 

Plateau was affected by periodic erosion and reduced 

sedimentation as flow of the ancestral Gulf Stream 

shifted into the area. Farther north, a series of 

marine regressions in the Oligocene, Miocene, and 

Quaternary resulted in a cutback of the slope to 

expose rocks as old as Early Cretaceous and build up 

the Continental Rise wedge. 

16 

Sea-level trends for five stratigraphic holes 

drilled off the eastern United States reveal a pattern 

of relative sea-level rise during the Jurassic and 

Cretaceous that reached a maximum in the Late 

Cretaceous and early Tertiary and dropped 

thereafter. Superimposed on this broad trend are 

much shorter shifts in sea level that appear to be 

nearly synchronous from basin to basin and to have 

formed interregional unconformities. Mrjor breaks are 

evident in the Cenomanian, in the late T ·ronian, in the 

Campanian-Santonian, at the Cretaceous-Tertiary 

boundary, at the Paleocene-Eocene boundary, in the 

late Eocene-early Oligocene, in the early Miocene, and 

in the Pliocene and Pleistocene. Older interregional 

unconformities also probably exist, but faunal remains 

in rocks older than Albian are scarce. 

The occurrence of petroleum sou .. ce beds along 

the Atlantic margin has been linked to paleoceanic 

circulation factors and to source factorf by Tissot and 

others (1980) and Hunt (1981). Anoxic events leading 

to the formation of organic-rich shales in the 

Cretaceous are thought to have occurred because of 

the latitudinal elongation of the North Atlantic Ocean 

basin, a warm global climate in which vrarm seawater was depleted in oxygen, and a wides')read oceanic 

transgression onto the continents that created shallow, 

warm seas having high biologic productbity. In terms 

of paleoceanography and sources of l<"erogen, these 

conditions translated into a low total hydrocarbon 

potential for rocks of Cretaceous age and a humic type 

of kerogen most likely to produce gas (if maturity, 

timing of migration, traps, and reservoirs were also 

favorable). In the Upper Jurassic rock:;-, Continental 

Offshore Stratigraphic Test (COST) we1ls drilled off 

the northeastern United States showed a similar low 

concentration of total extractable hydro~arbons of the 

humic type III (Miller and others, 1980; Miller, 1982). 

Phosphorite deposits on the Blake Plateau 

(Manheim and others, 1980) are the continuation 

offshore of Miocene sediments that probably 

originated in a cool, upwelling, shallow-water anoxic 

environment. Beneath the shelf, the phc ~ohate is a lag 

gravel that formed from the erosion of phosphatized 

carbonate-rich sediment. Further seaward where the 
unit crops out on the Blake Plateau, the boulders and 

cobbles of phosphate are impregnated by iron and 

manganese oxide crusts (todorokite and goethite). The 

iron-manganese mineralization is a later phase in two 

modes--as a replacement of preexisting phosphorite 

and carbonate and as a nodular coating over detrital 

phosphatic fragments. Its buildup occurrec' mainly in 

the area of lag carbonate and phosphate gravels and 

under conditions where the rate of oxide deposition 

exceeded the rate of sediment deposition (Manheim 

and others, 1982). 

17 
PALEOCLIMATE AND MINERAL DEPOSITS 

BUILDING A BIOSTRATIGRAPHIC FRAMEWORK AROUND AN ANOXIC-KENOXIC EVENT 

By Joseph E. Hazel 

In th:S late Cenomanian and early Turonian (at 

about 92x10 yr), sediments with high organic carbon 

and metal values were deposited at many places in the 

world. The climate was mild and equable at this 

time. Warm temperate and subtropical climatic zones 

extended into high latitudes, and the tropical zone was 

expanded. As a result, bottom-water conditions were 

sluggish, and the 0 2 minimum zone expanded 

vertically. A rapid transgression of the seas over the 

continents occurred (perhaps in response to an increase 

in volume of the midocean ridge system); the amount 

of epicontinental sea less than 300 m deep was twice 

as extensive as it is today. These drowned low-lying 

areas contributed much plant organic matter to the 

oceans (Schlanger and Jenkyns, 1976; Jenkyns, 1980; 

Ryan and Cita, 1977; Arthur and Schlanger, 1979). 

This Cenomanian-Turonian event has been 

termed an oceanic anoxic event (OAE), and it is the 

second of three such events in the Cretaceous--thus, it 

is referred to as OAE-2. The event was short lived but 

intense. It has been widely recognized. However, in 

part because of the problems inherent in dealing with 

sediments deposited under 0 2 minimum conditions, 

precise biostratigraphic correlation of many sections is 

poorly understood. Biostratigraphic frameworks that 

integrate first-appearance datums (FAD) and lastappearance datums (LAD) from microfossils, both 

calcareous and organic walled, and megafossils are 

only now beginning to be developed (for example, 

Robaszynski and others, 1982). 

The sediments of OAE's are or have the 

potential to be source rocks for much of the world's 

hydrocarbons (Arthur and Schlanger, 1979) and other 

natural resources. Exploration for such resources will 

depend in part on a cogent biostratigraphic framework, 

developed within the context of paleoclimatic 

fluctuations and tectonic-paleogeographic events. 

Without accurate correlations, determining the timing 

18 

and frequency of events associated with times of 

anoxic-kenoxic seas would be prevented. 

The integration of various types of 

biostratigraphic data into one standard model is the 

key to understanding the timing of eve'1ts associated 

with OAE-2 in North America. Such integration is 

necessary because precise correlation between the 

various areas in North America where CenomanianTuronian seas transgressed requires usin<J a variety of 

fossil groups. For example, in many parts of the 

Western Interior and the Rio Grande and East Texas 

Embayments, ammonites, inocerami, and planktic 

foraminifers occur in rocks associated with OAE-2. 

However, these are more rare in the sub.;,urface of the 

Atlantic Coastal Plain, where polle"l, calcareous 

nannofossils, and ostracodes are the most useful 

tools. Thus, for example, it is important to know how 

datums of these latter groups of organisms correlate 

with foraminiferal or molluscan datums. 

A modeling technique based or the graphic 

correlation method of Shaw (1964) (se:~ also Miller, 

1977; Murphy and Edwards, 1977) has prc~red successful 

in building robust biostratigraphic models (or 

frameworks) for several Geological Survey projects. 

Preliminary results suggest that it ce.n be used to 

produce a biostratigraphic framework fo .. OAE-2. 

Graphic correlation is a techni':lue that uses 

two-dimensional successive approximations to produce 

a scaled solution. That is, the FAD's and LAD's for 

fossils are placed in sequence, and the amount of 

spacing, expressed in either rock thickness or in a time 

sense, is apparent. If radiometric dates can be 

obtained for events in the scaled solution (usually 

termed the standard reference section), the arbitrary 

scale can be converted to time, and the position of 

biostratigraphic datums and sedimentf'.ry and other 

geologic events observed in the studied sections can be 

expressed in easily understood numbers. 
PALEOCLIMATE AND MINERAL DEPOSITS 

INORGANIC GEOCHEMISTRY OF DEEP-SEA BLACK SHALES 

By Walter E. Dean 

Cretaceous strata containing organic carbon in 

the Atlantic Ocean provide considerable insight into 

the general problem of incorporating trace metals into 

sediments rich in organic carbon. Such marine 

sediments and rocks are known to be significantly 

enriched in a variety of redox-sensitive trace elements 

(Vine and Tourtelot, 1970) relative to average marine 

sediment and shale, but the degree of enrichment 

varies greatly. Although few systematic studies have 

been made of major- and trace-element concentrations 

in Cretaceous deep-sea lithologies rich in organic 

carbon, such lithologies may be important as potential 

sinks for organic carbon, sulfur, and trace elements, 

particularly As, Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb, V, and 

Zn. During the deposition of these sediments, it is 

possible that trace elements, organic carbon, and 

sulfur are extracted from the oceans at rates greater 

than steady state and that the chemical and isotopic 

balances of the ocean are thereby perturbed. Average 

deep-sea accumulation rates of organic carbon were as 

much as 7 times greater during the peak of AptianAlbian black-shale deposition than they are today 

(Dean and others, 1983). The reasons for the enhanced 

preservation of organic carbon in the Cretaceous deepsea basins, however, are still a matter of debate. 

The enrichment of certain trace elementsespecially Cu, Zn, Mo, V, Ni, and Cr-in sediments and 

rocks enriched in organic matter has been reported by 

many investigators (Tourtelot, 1964; Calvert and 

Price, 1970; Vine and Tourtelot, 1970; Chester and 

others, 1978; Leinen and Stakes, 1979; BrongersmaSanders and others, 1980; Dean and Gardner, 1982; 

Dean and Parduhn, 1983) (fig. 9). The association of 

high trace-element concentrations with organic matter 

may be the result of concentration of these elements 

by organisms (bioconcentration) or by chemical 

sorption and precipitation under anoxic conditions 

created by a flux of excess organic carbon. Marine 

19 

plankton are known to concentrate trace elementsespecially Ba, Pb, Ni, Cu, Zn, Mn, and Fe (Boyle and 

Lynch, 1968; Knauer and Martin, 1973; Chester and 

others, 1978; Leinen and Stakes, 1979)-and the 

suggestion is that bioconcentration is a potentially 

important mechanism for incorporating certain trace 

elements into marine sediments rich h organic 

carbon. However, the great effectiveness of tracemetal adsorption by clay minerals and organic matter 

and the coprecipitation of trace metals, particularly as 

sulfide minerals, suggests that these proc~sses may 

play a more important role in the removal of trace 

metals from seawater (Tourtelot, 1964b; Holland, 

1979). Detailed trace-element profiles from thick 

sequences of organic-rich strata suggest that there is 

differential mobility of trace elements, ac~ompanied 

by diffusion of some elements over distances of at 

least tens of meters (fig. 10). The sequence of traceelement mobility, from highest to hwest, is 

approximately Ba, Mn, Pb, Ni, Co, Cr, Cu, Zn, V, Cd, 

and Mo. 

Although bottom-water anoxia may have 

occurred during periods when strata rich in organic 

carbon were accumulating, it was not ne~~essarily a 

cause of accumulation of these strata. The main 

reason for the accumulation of these strrta was an 

increase in the relative amount of organic d~bris being 

deposited. This organic debris was der'ved from 

continental margin areas where the prod·.tction and 

accumulation of organic matter from marine, 

terrestrial, or mixed sources were incr~?.ased; the 

debris was then transported to slope and basinal sites 

by turbidity currents (fig. 11). But why was the supply 

of organic debris so much greater during the middle 

Cretaceous? Local pockets of accumulated organic 

matter in continental margin areas todey are the 

result of local circulation patterns (for example, 

Walvis Bay off southwest Africa and Santa Barbara 
Mo 

PARTS PER MILLION 

10 100 1,000 

• 

MnO 

10,000 

-e- M gO o 

100,000 

I II I 

---lr---

Na20 --o1-6- --

K20 ~ I -c:,. 

Ti02~ --c:,. 

I 

Ba ---o~------------

Cu --o--

Ni --o~~==~====--­ ~ 

B 

l . • 

I ~ 

----&--

Co ---o--

EXPLANATION 

Black shale: 

--o--- Green claystone 

Red claystone 

FIGURE 9.-0bserved range (length of bar) and geometric mean (symbol) of concentrations of najor-element 

oxides and trace elements in samples of red and green claystone and black shale from Dee'"l Sea Drilling 

Project (DSDP) Hole 530A, cores 89-105 (adapted from Dean and Parduhn, 1983). 

20 
%8 lock Beds C-org MAR Fe203-cf Fe:AI-b lk. MnO-cf Be-ef Co-cf Nl-cf 

2000 .. ooo 0 100 200 0 .300 600 0 25 50 0 25 50 6 9 12 0.4 0.8 1.2 0.0 0.1 0.2 0 

940 

960 

E 980 

:5 1000 

a. 

Cl) 

0 

E 1020 

.3 

o+J 

0 1040 .D 

..0 

:l 

(/) 

1060 

1080 

1100 

0 25 50 0 25 50 6 9 12 0.4 0.8 1.2 0.0 0.1 0.2 0 2000 .. ooo 0 100 200 0 300 600 

%Black Beds C-o rg MAR Fe203-cf Fe:AI-b lk. MnO-cf Be-ef Co-cf Hl-cf 

Pb-cf Cr-cf Cu-cf Cd-cf Mo-cf V-cf Zn-cf 

0 50 100 0 .300 600 0 100 200 0 1500 .3000 0 .3000 6000 

940 

960 

E 980 

:5 1000 

a. 

Cl) 

0 

E 1020 

.3 97 0 1040 98 .D 

.D 

:l 

(/) 

1060 

1080 

1100 

0 50 100 0 300 600 0 250 500 0 50 100 0 100 200 0 1500 3000 0 3000 6000 

Pb-cf Cr-cf Cu-cf Cd-cf Mo-cf V-cf Zn-cf 

FIGURE 10.-Plots of carbonate-free (cf) concentrations versus depth for Fe2o3, MnO, Ba, Co, Ni, p·~, Cr, Cu, 

Cd, Mo, V, and Zn in samples of black shale from Deep Sea Drilling Project (DSDP) Site 530A in the southern 

Angola basin. Concentrations of Fe2o 3 and MnO are in percent; all other concentrations are in parts per 

million. The Fe:Al ratio in black-snale samples, the percentage of black-shale beds in each 9.5-m cored 

interval, and the mass accumulation rate (MAR) (in grams per square centimeter per million years) of 

organic carbon for each 9.5-m cored interval also are plotted. The vertical line through each plot is at the 

geometric mean concentration for that element or oxide. All values greater than the geometric mean are 

shaded. The numbers (89-105) within the plot for percentage of black-shale beds are the numbers of each 

core. The two horizontal lines through all plots are drawn at the top of core 97 and the bottom of core 98 

and mark the zone of maximum black-shale bed concentration (from Dean and Parduhn, 1983). 

21 
Basin off southern California). It is unlikely that such 

conditions would have existed around the entire margin 

of the middle Cretaceous Atlantic Ocean as well as on 

isolated plateaus and seamounts in the Pacific 

(Schlanger and Jenkyns, 1976; Dean and others, 1981) 

without the aid of some worldwide conditions of ocean 

circulation and productivity. Global climate during 

the middle Cretaceous was warm, eustatic sea levels 

were high, spreading rates were fast, pelagic 

sediments in the world ocean were accumulating 

rapidly, and oceanic surface- and bottom-water 

temperatures were high (Douglas and Savin, 1975; 

Fischer and Arthur, 1977; Brass and others, 1982). 

Increased surface-water temperatures would have had 

two main effects. First, thermohaline deep-water 

circulation, driven today by the sinking of cold, 

oxygen-rich surface waters in high latitudes, would 

have been more sluggish; second, the warmer water 

would have contained lower concentrations of 

dissolved oxygen. Bottom-water circulation was 

sufficient to supply some oxygen to maintain oxidizing 

conditions in the deep basins of the Pacific but slow 

enough to permit depletion of dissolved oxygen at 

midwater depths in areas of high productivity of 

organic matter. Accumulations of sediments rich in 

organic carbon at many places in the world ocean 

undoubtedly are the results of coincider~es of several 

factors acting to produce and preserve organic matter 

(fig. 11). During the middle Cretaceous, much of the 

world ocean may have been poised such that relatively 

small changes in the flux of organic rn1tter and (or) 

circulation at any one place would have caused anoxia 

or near anoxia within midwater oxygen ninimum zones 

and possibly, under extreme conditions, throughout 

much of the bottom-water mass. An expanded and 

intensified oxygen mm1mum would explain the 

excellent preservation of organic carbon and the 

increase in the accumulation rate of organic carbon 

over a much larger area in slope and de7.p-sea (largely 

by redeposition) environments during much of the 

Early and middle Cretaceous. It is not inconceivable 

that the intensified oxygen minimum zo'le extended as 

deep as 2,500 to 3,000 m; such an extent would help to 

explain the presence of Albian black shales containing 

well-preserved organic carbon on or near the crest of 

the Mid-Atlantic Ridge in the North Atl"ntic, where it 

is unlikely that turbidites derived from the continental 

margin could have been the supply of the organic 

matter. 

FIGURE 11.-Diagrams showing how the influx of terrigenous organic matter, surface-water organic 

productivity, upwelling, and turbidity currents may contribute to the accumulation and redeposition of 

sediments containing various amounts of organic carbon and, therefore, ranging in color from red to black. 

A, Period of moderate supply of organic detritus from autochthonous marine and terrigeno''S sources and 

moderate upwelling resulting in accumulation of green sediment in shelf areas, sediment witl' high organiccarbon concentrations (perhaps black in color) within the 0 2 minimum zone, and dominantly r~d clays in the 

deep basin. Such conditions might be representative of the later Cretaceous (for exam~le, SantonianConiacian) in the Atlantic Ocean. B, Per'od of rapid rate of supply of organic detritus and stronger 

upwelling resulting in an expanded and more intense o2 minimum zone that may include muc'l of the water 

mass and allow sediment rich in organic carbon to accumulate over a much greater area and provide a 

~eater source area for supply of such sediment to the deep basin by downslope transport. S'tch conditions 

might be representative of periods of accumulation of strata rich in organic carbon in the Atlantic Ocean 

(Aptian-Albian and Cenomanian-Turonian) (from Dean and others, 1983). 

22 
Green sediments 

(organic carbon t -2%) 

A 

8 

(organic 

Late Albian to Early 

Cenomanian and Coniacian 

Dark 

black sediments 

Late Cenomanian 

to Early Turonian 

23 

Terrigenous influx 

More terrigenous influx 

Higher productivity\ 

----~-- --~-~-~_{ @,~! --------

Expanded and intensified 

Green or 

black sediment 

(depending on amount 

of organic carbon) 

-4000m 
PALEOCLIMATE AND MINERAL DEPOSITS 

SOME CLIMATIC AND OCEANOGRAPHIC CONTROLS ON THE TIME AND 

PLACE OF MINERALIZATION 

By W. F. Cannon 

In the past decade, substantial advances have 

been made in understanding se~ular variations in 

climate and in the nature of the oceans and the 

interplay of the two. Examples include work by Arthur 

a_nd Schlanger (1979), Degens and Stoffers (1976), 

Demaison and Moore (1980), Jenkyns (1980), and 

Schlanger and Jenkyns (1976). In general, eustatic 

sea-level rise favors climatic warming because the sea 

surface generally has a greater capacity to retain solar 

energy than the land surface does. Warm climate and 

low pole-to-equator thermal gradients tend to diminish 

deep oceanic circulation and fa.vor the development of 

widespread stratified oceans that are anoxic below the 

zone of surface mixing. Hence, there is both a 

theoretically predictable as well as an observed 

correlation between periods of ocean stagnation and 

anoxia. The recognition in recent years of "ocean 

anoxic events," periods when oceans became largely 

anoxic on a regional or perhaps even a wor!dwide 

scale, has been a major advance both scientifically and 

practically and is now a widely applied principal in 

petroleum exploration because the products of anoxic 

oceans-black organic-rich shales-form the source 

beds for petroleum. Such considerations of 

paleoclimate and paleoceanography have not yet had 

as substantial an impact on mineral exploration, but 

TERTIARY 

CRETACEOUS 

JURASSIC 

TRIASSIC 

PERMIAN 

CARBONIFEROUS Mn 

DEVONIAN 

SILURIAN 

ORDOVICIAN 

CAMBRIAN 

their promise is great. For instance, knowing when 

oceans underwent major climatic-controlled changes in 

Eh and pH and what the effects of those changes on 

the solubility of metals were is an obyious application 

of the principals to mineral exploration. An intriguing 

possibility is that relatively discrete regionwid~ _or 

even worldwide time lines for high mineral favorab1hty 

can be defined. 

The present-day Black Sea offers a good and 

relatively well studied scale model of former anoxic 

oceans. It is anoxic below about 200 m. The oxidized 

surface layer has an Eh of about +0.4 v and a pH of 

about 8.3. The deeper anoxic water has an Eh of about 

-0.2 v and a pH of about 7.5 (Grasshoff, 1975). These 

changes place surface water and deep water on 

opposite sides of a major solubility boundary for 

manganese minerals. The dissolved manganese in deep 

water is about 500 times greater than that in surface 

water (Brewer and Spencer, 1974). Where deep anoxic 

water is welling up onto a flanking shelf, a manganese 

deposit is forming just above the anoxic-oxic 

interface. Such conditions during major ocean anoxic 

events may account for the formation of important 

marine sedimentary manganese deposits such as 

Groote Eylandt (Cenomanian) in Australia. 

100 

200 

Fe 300 

400 

500 

M.Y. 

FIGURE 12.--Relative rates of accumulation of marine sedimentary deposits of manganese, iron, and phosphate 

on a worldwide scale approximated from resource figures compiled from many sources. Horizontal (rate) 

axis is sketched on logarithmic scale. 

24 
Similar solubility controls are also possible for 

iron and phosphate, so there is a predictable direct 

relationship between the times of formation of 

important marine sedimentary deposits of iron, 

manganese, and phosphate. Figure 12 shows at least a 

crude correlation between the times of formation of 

deposits of these three commodities on a worldwide 

scale. Many deposits formed in the early Paleozoic 

(until the end of the Devonian), very few formed from 

early Carboniferous until the beginning of the Jurassic 

(with the exception of a sharp worldwide phosphate 

peak in Late Permian), and then very extensive major 

deposits throughout the world formed from Early 

Jurassic to the present. This temporal distribution is 

also remarkably similar to that for petroleum source 

beds. Figure 13 compares the temporal distribution of 

marine sedimentary iron deposits and petroleum source 

beds and also illustrates that both were favored when 

sea level was considerably higher than it is at present. 

There may also be a correlation between ocean 

anoxic events and the temporal distribution of massive 

sulfide deposits, particularly deposits formed at 

spreading centers. Such deposits forming today are 

oxidizing rapidly on the sea floor, and it appears that 

100 

>: 200 

~ 

LU 

~ 

i= 300 

400 

500 

0 5 

IRON 

(109 TONS) 

8 0 

they would be difficult to preserve in the geologic 

record. Those that formed during anoxic events, on 

the other hand, would not oxidize and would have a 

much higher probability of persisting until they could 

be buried and preserved. 

Warm, humid climate also plays an obvious role 

in forming many continental deposits, including 

bauxite, nickel laterites, residual and supergene 

deposits of iron and manganese, and heavy-mineral 

placers. Identifying periods of exceptionally warm 

climate in the relatively complete Mesozoic and 

Cenozoic marine record should allow a more efficient 

search for these deposits in the less complete 

continental record. 

The above are only a few examples of how the 

genesis of mineral deposits might be linked to 

fluctuations in climate and oceanographic conditions. 

Improving our ability to interpret paleoclimate and 

paleoceanography from the rock record and 

understanding the interplay of the two and their effect 

on the physical and chemical processes that form ore 

promise to greatly improve our ability to predict and 

discover deposits of many types of ores. 

1000 

CRUDE OIL 

(106 TONS/M.Y.) 

2000 

SEA LEVEL (METERS) 

0 

0 

"<t 

+ 

0 

0 

N 

+ 0 

0 

0 

N 

I 

FIGURE 13.--Tons of iron in known deposits of marine sedimentary type in Europe, the Soviet Union, the Middle 

East, and North Africa (total of 111 deposits) as a function of time in comparison with accumulation of 

crude oil in source rocks as a function of time (from Tissot, 1979). Age shown is age of petroleum source rock. 

25 
PALEOCLIMATE AND MINERAL DEPOSITS 

INFLUENCES OF OCEAN ANOXIC EVENTS ON MANGANESE DEPOSITION AND OPHIOLITEHOSTED SULFIDE PRESERVATION 

By Eric R. Force, William F. Cannon, Randolph A. Koski, Keith T. Passmore, 

and Bruce R. Doe 

Periods of widespread warm climate correspond 

to eustatic transgressions and to ocean anoxic events 

(Schlanger and Jenkyns, 1976; Arthur and Schlanger, 

1979; Jenkyns, 1980). The concurrence is well 

documented and has implications for sedimentary 

manganese deposits and for ophiolite-hosted sulfides. 

Shallow marine environment 

Consider first the situation in shallow seas 

during an anoxic event. A surface mixed zone of 

oxygenated water overlies anoxic water with a sharp 

interface at depths of as little as 100 m. Dissolved 

manganese concentration below the interface is as 

much as 500 times greater than that in the normal 

oxidized seawater above it (fig. 14). Mixing of the 

water masses across the interface (for example, by 

upwelling) and diffusion cause manganese 

precipitation. The precipitate is preserved in 

sheltered sites landward of the intersection with the 

shelf owing to slow manganese precipitation (fig. 14). 

Coincident transgression causes the oxic-anoxic 

I 

t 

UJ 

0 

l? 

z 

(f) 

<{ 

UJ 

a: 

u 

z 

0 

Dissolved 

Mn 

.0 

c. 

c.c 

o::::!: 

0 

L() 

interface itself to sweep up the shelf; the locus of 

manganese precipitation shifts landward, and previous 

deposits may be remobilized. The preserved 

manganese deposit thus ranges from basal to maximum 

transgressive in stratigraphic setting. In this model 

for "bathtub-ring" manganese deposits, manganese can 

be derived from a variety of sources, and anoxic 

seawater serves as ore-forming fluid. 

The process can also be represented on an EhpH diagram constructed for stratified seas like the 

present Black Sea (fig. 15). The deep anoxic water 

mass lies in the stability field of pyrite, where iron is 

removed from solution. Oxidation of this water mass 

takes it through a solution field, a manganese 

carbonate field, and finally into a manganese oxide 

field at high Eh in shallow-water environments. Note 

that both Eh and pH increase from deep anoxic water 

to shallow oxygenated water. 

Shallow marine (nonvolcanic) manganese 

deposits comprise 75 percent of the world's present 

manganese reserves and show stratigraphic features 

(fig. 16) in accordance with our model (Cannon and 

Fluvial deposits and bedrock 

FIGURE 14.--Profile of dissolved manganese (after Brewer and Spencer, 1974) and depositional model for an 

anoxic event. 

26 
Mn and Fe 

in solution 

r 

I 

\ 

\ 

Mn 

carbonate 

' ' ', 

' ' ' Fe sulfid'Ei'-, 

pH 

' ' 

FIGURE 15.-Eh-pH diagram (after Hem, 1972) 

showing oxidation path of an anoxic water mass 

(data from Grasshoff, 1975). 

Force, in press). Transgressive setting is apparent. 

The deposits are both clay and carbonate hosted and 

tend to be oxide facies above and landward of 

carbonate facies. They follow or correspond in _age to 

anoxic events where this information is available (fig. 

17). In some deposits, there are coeval black-shale 

basins nearby or a carbon isotope signature of an 

anoxic seawater reservoir. 

There is no reason why the United States should 

not have some deposits of this type. We have not 

looked for them, and manganese mineralization 

(especially MnC03) can be inconspicuous. 

Deep sea 

Now consider the situation in the deep sea at a 

spreading center. Assume continuous hydrothermal 

venting during and after an anoxic event (fig. 18). 

During the anoxic event, anoxic water reached down to 

some, if not all, oceanic rises, and sulfides were 

vented into water in which they were stable and thus 

were preserved. ' 

Anoxic events ended when renewed bottom 

currents resulted in thinner and weaker oxygen 

minimum zones (fig. 18). The base of the anoxic layer 

lifted off the bottom and the situation became 

analogous to the modern-day North Pacific, which has 

a widespread midwater oxygen m1mmum layer. 

Manganese precipitated both from hydrothermal fluids 

27 

Shallow 

marine 

sequence 

Fluvial 

Fluvial 

Mn deposit 

Old rock + + 

FIGURE 16.-Composite shallow marine manganese 

deposit (data from Cannon and Force, in press). 

and from seawater at the bottom of the oxygen 

minimum layer (explaining the gradual change in lead 

isotopes in manganese oxides away from the vent) and 

forms a manganese halo around the vent. Vented 

sulfides are unstable, develop syngenetic corrosion 

features, and eventually dissolve (unless they are 

rapidly buried by lava). Two products of corrosion are 

goethite and elemental sulfur. Oxygenated bottom 

water support the diverse "vent faunas" that function 

without light but that cannot exist in totally anoxic 

water. 

The stratigraphy resulting from this sequence of 

events is that seen in .the Troodos ophiolite of Cyprus 

(figs. 17, 19). The lower pillow lavas contain simple 

sulfides and no manganese halos. The upper pillow 

lavas contain manganiferous umbers. The onset of 

oxidizing conditions on the sea floor is recorded by 

ochers, iron-oxide deposits representing 

postdepositional corrosion of the sulfides at the top of 

the lower pillow lava. The umber deposits just 

postdate the long Aptian-Albian anoxic event (fig. 19), 

consistent with our hypothesis that sulfides were 

preserved only during anoxic events. 

The model should be subjected to faunal, 

isotopic, and petrographic tests. However, the sulfide 

potential of ophiolitic pillow lavas formed during 

anoxic events appears to be higher than that of those 

formed at other times. The parts of pillow lava 

sequences containing umbers may be systematically 

impoverished in sulfides. 
65 

!:: <x: OUJ UJ OPHIOLITIC DEPOSITS (/) SHALLOW MARINE ...J<{ 

...Jw ANOXIC a_ MANGANESE 

SERIES STAGE <I:UJ EVENTS UJ DEPOSITS TROODOS, SEMAIL, :X: UJ (/) 0 CYPRUS OMAN 

CAMPANIAN r-- Chamberlain, - South Dakota 

SANTONIAN ''''''''''''''''''' ,,,,,,,, 

(/) 

CONIACIAN "'"''."''·=· a:: 

UJ r- - 85 CD 

~ TURONIAN ~ lmini Morocco :::> UMBERS 

(/) 

JLZU ~ r- :::> CENOMANIAN 111111 111 1111 11 1 - 0 

UJ 

u Groote Eylandt, (/) (/) 

~ UJ UJ 

ALBIAN Australia 0 0 UJ r- a:: u:: u:: - u ...J ...J 

:::> :::> 

105 

c.: 

a:i 

APTIAN (/) (/) 

- -

BARREMIAN ;>.. 

E 

125 r- -

-

~ KIMMERIDGIAN ""' 'VIu'""!,Ju, Mexico (/) ,., 

r- (/) 

OXFORDIAN - <x: 145 

a:: 

:::> 

...., 

a:: CALLOVIAN 

r- UJ - a_ 

a_ 

:::> 

165 

FIGURE 17 .--Age correspondence of ocean anoxic events, shallow marine manganese deposits, and ophiolitic 

sulfides. Dashed lines indicate no data; short vertical lines indicate range ,.; uncertainty. 

'. 

ANOXIC EVENT AFTER ANOXIC EVENT 

Sea surface 

Mn in solution 

FIGURE lB.-Comparison of axial ridge vents during and after anoxic events. 

28 
tz 

W- >r--· wz 

u~ -z 

X<( 

0~ 

zo 

<(z 

o:::w 

wu 

~--~ 

u.. 

<( 

tz 

w 

> 

w 

u;:;: 

-z 

X<( o_ 

zco 

<(<t 

(!)~ 

z 

a: 

:J 

Cl 

u 

UPPER PILLOW LAVA 

LOWER PILLOW LAVA 

Ve 

FIGURE 19.-Stratigraphic record of waning anoxic event at Cyprus (relations mostly after Robertson, 1975). 

29 
PALEOCLIMATE AND MINERAL DEPOSITS 

LATE CRETACEOUS AND PALEOGENE NONMARINE CLIMATES IN NORTH AMERICA 

By Jack A. Wolfe 

Nonmarine climates have some parameters that are of major significance and that are unique, or 

nearly so, to such climates. In contrast 'to the aqueous 

and generally equable marine realm, where the major 

climatic component is mean temperature, a discussion 

of nonmarine climates must include annual 

precipitation patterns and temperature extremes. 

Indeed, the present distribution of major vegetation 

types is primarily controlled by mean annual 

temperature, mean of the cold month, mean of the 

warm month, and precipitation (Wolfe, 1979). Thus, 

the valid recognition of certain vegetation types in the 

fossil record affords a ready means of inferring the 

past distribution of climatic parameters on the 

continents. 

Most paleoclimatic inferences based on plants 

rely on the accurate identification of organisms in 

terms of extant relatives and the assumption that the 

environmental tolerances of the fossil organisms were 

fundamentally the same as those of their extant 

relatives (Wolfe, 1971). Although this floristic 

approach perhaps has some validity for Neogene and 

Quaternary organisms, it yields only gross 

paleoclimatic approximations for older assemblages, 

which display greater "paleoecologic dissonance" with 

increasing age. From evolutionary theory, the floristie 

approach cannot be rigorously applied because one of 

the major factors driving evolution is the environment; 

that is, a given lineage diversifies in response to 

changing environmental parameters, and thus 

tolerances must have changed through time. 

The most valid paleoclimatic inferences based 

on plants rely on the morphologic (physiognomic) 

convergences that result from adaptations to 

particular environments. For example, tropical rain 

forest in Indonesia is physiognomically similar to 

tropical rain forest in the Amazon, despite the 

considerable differences in floristic content. The 

broad-leaved evergreen rain forests of North Island, 

New Zealand, physiognomically resemble those of 

upland Central America, despite the almost total 

floristic differences. Emphasis on the 

physiognomy--particularly foliar-of fossil assemblages 

will yield the most valid paleoclimatic inferences. The 

physiognomic approach is also largely independent of 

identifying fossils in terms of extant relatives, an 

30 

important consideration in dealing with Cretaceous 

and Paleogene floras that contain representatives of 

many extinct genera (and of even higher level 

taxonomic groups that are now extinct). Among. the 

foliar characteristics that can be used for 

paleoclimatic inferences are leaf size, type of leaf 

margin, leaf shape, leaf texture, and certain venation 

characteristics (Wolfe, 1971, 1981). 

Application of physiognomic analyses to 

Paleogene floras of North America leads to several 

major conclusions (Wolfe, 1978): 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

The mean annual temperature fluctuated by 7° to 

8°C between the four warm and three cool 

intervals during the Paleocene and Eocene; these 

intervals apparently correlate with similar 

intervals based on Deep Sea Drilling Project work 

(Wolfe and Poore, 1982). 

A major drop of about 1 0°C occurred in mean 

annual temperature at the end of the Eocene. 

Mean annual temperatures in excess of 20°C 

occurred at paleolatitudes greater than 60°N. 

during some warm intervals (Wolfe, 1977, 1980). 

Truly tropical (mean annual temperature,~25°C) 

climates extended at times to about latitude 4 7° 

N. 

The mean annual range of temperature (that is, 

the difference between the means of warm months and those of cold months) was much less 

during the Paleocene and Eocene than it is today. 

The mean annual range of temperature increased 

drastically at the end of the Eocene and has since 

been gradually decreasing (Wolfe, 1981). 

The Mississippi Embayment assemblages indicate a pronounced drying trend from the Paleocene 

into the late Eocene. 

At the time of drying in the southeast, Pacific 

Coast assemblages indicate humid climates (the 

reverse of the present precipitation pattern). 
Late Cretaceous leaf assemblages generally 

have not been physiognomically analyzed. That the 

Paleogene fluctuations in mean annual temperature 

may have Late Cretaceous analogs is indicated by 

pollen analysis of Santonian (84 m.y.) through 

Maestrichtian samples from the Atlantic Coastal Plain 

(Wolfe, 1976); these samples show that periods during 

which conifers were abundant alternate with periods 

during which angiosperms were abundant. 

Physiognomic analyses of some described leaf 

assemblages from southeastern North America also 

indicate , some major temperature fluctuations. 

Cenomanian assemblages from the Alaskan North 

Slope (a paleolatitude almost at the pole) indicate 

polar temperatures at least 15°C higher than those at 

present. Late Cretaceous leaf assembleges are 

obviously in great need of study in order to infer 

additional information on Late Cretaceous n':lnmarine 

climates. 

31 
PALEOCLIMATE AND MINERAL DEPOSITS 

VOLCANIC MANGANESE DEPOSITS IN THE WESTERN CORDILLERA: LITHOLOGIC ASSOCIATIONS 

AND PALEOCEANOGRAPHIC SETTINGS AND ECONOMIC DEPOSITS ASSOCIATED 

WITH BIOGENIC SILICEOUS ROCKS 

By James R. Hein and Randolph A. Koski 

Preliminary investigations suggest that 3. 

numerous stratiform manganese deposits in the 

Western United States were formed by 

hydrothermal-volcanogenic processes. These deposits 

can be grouped into five categories on the basis of 

manganese mineral assemblage, lithologic association, 

and tectonic settings: 

1. Deposits in chert-graywacke sequences-for 

examole, parts of the Franciscan Complex of 

California, where lenses and beds of manganese 

carbonate and manganiferous opal are associated 

with bedded chert within thick sequences of 4. 

graywacke and conglomerate. Manganese 

minerals from the Buckeye Mine in the 

Franciscan Complex include rhodochrosite, 

braunite, bementite, birnessite, and pennantite. 

2. Deposits in chert-greenstone (ophiolite) 

sequences--for example, the late Paleozoic 

Havallah sequence in Nevada, parts of the 

Franciscan Complex of California, and the 

Nicoya Complex in Costa Rica. Manganese 

jasper, manganese oxides, and manganese 

silicates occur in lenses within bedded chert, at 5. 

the interface between basalt and chert, and 

within basalt. Manganese minerals from the 

Nicoya Complex in Costa Rica include pyrolusite, 

hollandite, romanechite, braunite, B-Mn02, and 

bixbyite. Chemically, these ores are rich in Ba 

(to 5.0 percent), Cu (to 0.2 percent), and Ni (to 

0.1 percent) but poor in Fe, Co, and Zn (Hein and 

others, 1982). The Costa Rica manganese 

deposits have not been exploited since 1920 and 

have produced about 32,000 tons of ore having an 

average grade of 50 percent manganese (Roberts, 

1944). The largest deposits in the Franciscan, 

the Ladd and the Buckeye, produced 30,000 tons 

and 26,000 tons of high-grade manganese ore, 

respectively, at grades between 35 and 55 

percent manganese (Trask, 1950). 

32 

Deposits in metachert-metavolcanic 

sequences--for example, late Paleozoic to 

Jurassic strata of the Sierra Nevf'~a and Klamath 

Mountains. These deposits are similar in 

occurrence and general lithology to those in the 

Franciscan and Havallah sequences but have 

undergone a higher grade of metamorphism, so 

that the manganese mineral assemblage includes 

rhodochrosite, rhodonite, spessartine, 

piedmontite, and manganese-ric"' pyroxene and 

amphiboles. 

Deposits in limestone-argillite-basalt 

sequences-for example, the Eocene Crescent 

Formation on the Olympic Peninsula of 

Washington, where marine carbonate and 

spilitized volcanic rocks hc~t a diverse 

manganese mineralogy dominated by silicates and 

oxides. Soren and Gunn (1967) determined the 

manganese oxides to be braunite, hausmannite, 

jacobsite, and crednerite, wherea"' the manganese 

silicates include alleghanyite, bementite, inesite, 

johannsenite, rhodonite, and tephroite. 

Deposits in Miocene and Plioce"'e sequences of 

conglomerate-sandstone-tuff-gyp"um of the 

Colorado River-Lake Mead area of Nevada and 

Arizona, where high-tonna';!e low-grade 

stratiform and largely strata-bound deposits 

consist mainly of poorly crystalline manganese 

oxide cement in clastic sedimentary rocks. 

Manganese minerals from the Lake Mead area include pyrolusite, todorokite, cr:rptomelane, and 

ramsdellite, whereas minerals from the Artillery 

Mountains in Arizona include the<'!e minerals plus 

hollandite, romanechite, and coronadite. 

Chemically, these deposits are r~ch in Pb (to 1.5 

percent), Cu (to 0.2 percent), Zn (to 0.45 

percent), and Ba (to 11.0 percent) but poor in Co, 

Ni, and Fe. The Artillery Mcuntains contain 

about 175 million tons of manr-aniferous rocks 
averaging 3.5 to 4 percent manganese and 70,000 

tons at +20 percent manganese (Lasky and 

Webber, 1949). The Three Kids district near 

Lake Mead in Nevada produced over 2,225,000 

long tons of ore averaging 18 percent manganese, 

which yielded more than 600,000 tons of 

concentrate averaging 45 percent (Crittenden, 

1964). 

Our preliminary interpretation concerning 

manganese deposits in the western Cordillera, based on 

lithologic associations, mineralogy, chemistry, and 

regional settings, is that most deposits formed in 

incipient oceanic rifts or at spreading centers close to 

a continental margin. Contemporary settings of this 

nature include the type of incipient oceanic rifts and 

back-arc basins found in the Gulf of California and the 

Red Sea. This concept can be best tested in the 

Arizona-Nevada deposits, where spreading associated 

with the proto-Gulf of California rift may be the 

source for the sandstone- and conglomerate-hosted 

manganese deposits. Deposition of manganese in 

shallow-water environments over the rift may be 

related to paleoclimatic and paleoceanographic 

factors. Sedimentological characteristics of bedded 

cherts and comparisons with open-ocean deep-sea 

chert sequences support a deep-water near-continent 

environment for most chert sequences (Hein and Karl, 

1982) and presumably for the enclosed manganese 

deposits. The bedded cherts formed in areas of 

oceanic upwelling, probably similar to the oceanic 

conditions presently found in offshore Peru, southern 

California, or the Gulf of California. In addition, the 

red limestones and argillites hosting manganese 

deposits in the Olympic Peninsula and the red-bedded 

cherts at other localities suggest an oxidizing 

paleoceanographic environment. 

In addition to manganese, biogenic siliceous 

deposits host important accumulations of iron, 

uranium, barium, phosphates, and petroleum. 

Paleozoic and Mesozoic bedded chert sequences and 

Tertiary siliceous deposits, mainly dit:ttomite, 

porcellanite, and chert, occur in several 

circum-Pacific orogenic belts. These siliceous 

deposits are derived from biogenic 

debris--radiolarians, diatoms, and sponge spicules. 

Tertiary siliceous deposits form the so·1rce and 

reservoir rocks for petroleum in many place:c;:, occur 

with important deposits of phosphate, and may be 

source rocks for uranium accumulation, whereas 

Mesozoic and older bedded chert sequences h'lst iron, 

manganese, and barium accumulations. Laminated 

diatomites were deposited in basins on continental 

shelves and slopes in areas of oceanic upwelling; 

bottom-water conditions were commonly anox:~c. 

The rhythmic bedding in Mesozoic and 

Paleozoic bedded cherts probably resulted from 

deposition by turbidity currents that carried mainly 

siliceous biogenic debris. Interbedded shales represent 

ambient hemipelagic sedimentation. Some chert 

sections in Japan, however, are thought to show an 

opposite relation; . their shale beds are identified as 

turbidites and their cherts as ambient pelagic 

deposits. As mentioned, on the basis of sed~mentary 

structures, chemical compositions, and regional 

settings, many bedded chert sequences apparently 

were deposited in deep water but near a co'ltinental 

margin. Bedded cherts show few similarities with 

open-ocean deep-sea cherts recovered from the 

Pacific. 

33 
PALEOCLIMATE AND MINERAL DEPOSITS 

ORGANIC CARBON, SULFUR, AND IRON RELATIONSHIPS AS AN AID TO UNDERS':':'ANDING 

DEPOSITIONAL ENVIRONMENTS AND SYNGENETIC METALS IN RECENT At-TD 

ANCIENT SEDIMENTS 

By Joel S. Leventhal 

Syngenetic iron sulfide phases in sediments are generally formed from aqueous sulfide resulting from 

catabolism of organic matter by anaerobic sulfatereducing bacteria. It has been shown that recent 

marine sediments below oxygenated depositional 

waters show a constant relationship of carbon to sulfur 

(Berner, 1970; Sweeney, 1972; Goldhaber and Kaplan, 

197 4). When the weight percent of organic carbon is 

plotted on the x axis and the weight percent of sulfur 

is plotted on the y axis and the data are fitted by the 

linear least-squares method to y=a+ bx,the S/C slope is 

approximately 0.3, and the line passes through the 

origin (fig. 20). New interpretation of data from 

recent sediments from euxinic marine environments 

(for example, the Black Sea) also shows a linear 

relationship between carbon and sulfur, but the slope is 

variable, and the lines for individual cores can 

intercept the y axis anywhere from 0. 7 to 2 percent 

sulfur (Leventhal, 1979). Thus, the presence of an 

anaerobic H2S-laden water column leads to an extra 

increment of sulfide without a corresponding fraction 

of residual organic carbon in the sediment. The extra 

sulfide is probably due to metal sulfide formation in 

the water column (Sweeney and Kaplan, 1980) and at 

the water-sediment interface; some is formed 

diagenetically in the sediment. Data from the two 

most recent sedimentary units of the Black Sea 

illustrate the effect of· the evolving H2s layer on 

sulfur geochemistry by producing a more positive 

sulfur intercept for the youngest unit having the 

thickest H2S layer. Between-core comparison of data 

from several sites shows variable S/C slopes, which 

can be related to location and (or) deposition rate. 

The larger S/C slope is associated with higher rates of 

deposition nearer the edge of the basin at shallower 

depths (Leventhal, 1983). 

New data from cores of Upper Devonian black 

shales from the Appalachian Basin show carbon and 

sulfur relationships similar to those found in modern 

euxinic environments. The S/C slopes for the ancient 

shales can be interpreted in relation to deposition rate, 

availability of iron, and perhaps the type of organic 

matter and the thickness of the aqueous sulfide layer. 

These carbon and sulfur data from the Devonian 

black shales of the Appalachian Basin and the 

Cambrian Alum Shale of Sweden are used as distinct 

prototypes to examine the enrichrrent controls for 

metals. These samples are cont-:-asted with the 

Permian Kupferschiefer of central Europe. Major 

controls are a relatively low sedimer1:ation rate and a 

relatively high input of organic matter and metals. 

Organic carbon and sulfide-sulfur rel?tionships can be 

used to establish the presence of an H2S-laden water 

column for these ancient shales by analogy with the 

Recent Black Sea. However, in the Alum Shale, it is 

shown that all of the iron is sulfidized; thus, the 

normal carbon-sulfur relationship is disturbed 

(Leventhal, 1981b). 

34 

Trace-element abundances (Vine and Tourtelot, 

1970) are closely related to organic C"'rbon (U, Mo) and 

(or) sulfide sulfur (As, Hg) in the Devonian shales. 

Somewhat different element-association patterns are 

present for the Alum Shale. For the Devonian shale 

(Swanson, 1961), the type of organic matter is also a 

control for the uranium. In particular, the 

terrestrially derived organic matter is specific as a 

control and residence site of the urrnium (Leventhal, 

1981a). These relationships are i'.lustrated in the 

diagram in figure 21. Trace element-organic and trace 

element-sulfide ratios vary by less than a factor of 2, 

whereas the sedimentation rate varie8 by more than an 

order of magnitude in the Appalachian Basin samples. 

Uranium and organic carbon conterts for individual 

stratigraphic units from various parts of the basin 

show an inverse relation to the thic1

<ness of the unit 

(Leventhal and Kepferle, 1982). 

The source of the uranium and certain trace 

elements is in part related to leachin~ of volcanic ash 

(near its source, on land), as demonstrated by 

increased contents of metals in samples 

stratigraphically above the ash in comparison with 

those below the ash (Leventhal and Kepferle, 1982; 

Leventhal and Hosterman, 1982). 
4 .. 

• 

• ~ 

z 

w 

3 • • 

u 

~ a: • w 

0... 

~ 

::c 

Q 

w 

3: 

z 

a:' 2 

u.. 

:::::> • ...J 

:::::> 

rJ) 

_, •• 

0~------~------~------~------~~------~------~------~------~------~ 

0 2 4 6 8 9 

ORGANIC CARBON, IN WEIGHT PERCENT 

FIGURE 20.--Relationship of carbon to sulfur in Black Sea marine sediments deposited below oxygenated water 

(normal marine) and H2S-containing water (euxinic) (Leventhal, 1983). Patterned area represents about 500 

samples from modern normal marine sediments. 

These black shales are important because they source of energy for mining and milling metels of the 

can be the host for Kupferschiefer-type ore deposits or black shale itself when higher grade metal deposits 

the source of the metals for metamorphic-type ore without such associated energy sources become 

deposits or higher grade mineralization and because uneconomic (Leventhal and others, 1981; Hatch and 

their high organic content can provide an in-place Leventhal, 1981). 

35 
WATER 

COLUMN 

FeS [As] 

HC03 ....--........ 

SULFIDE ORGANIC 

LAND 

OXIC 

ANOXIC 

OR EUXINIC? 

SEDIMENT 

EARLY 

DIAGENESIS 

AND BURIAL 

EUXINIC 

FIGURE 21.-Geochemical relationships in oxic, anoxic, and euxinic sedimentary environment~~ (modified from 

Leventhal and others, 1981). 

36 
PALEOCLIMATE AND MINERAL DEPOSITS 

PALEOZOIC ATMOSPHERIC CIRCULATION AND OCEANIC UPWELLING 

By Judith Totman Parrish 

Paleoclimatological models traditionally have 

been based on the latitudinal components of climatic 

patterns and their effects on the distribution of 

organisms and (or) climatically significant sedimentary 

rocks. The latitudinal components of climate include 

an equator-to-poles temperature gradient and a 

latitudinal distribution of atmospheric pressure, wind, 

and precipitation. The distribution of climatic 

patterns parallel to latitude results from the rotation 

of the Earth (that is, the Coriolis effect) and the 

existence of a temperature gradient. The rotation of 

the Earth prevents a direct exchange of heat between 

the equator and the poles. Three first-order vertical 

circulation cells parallel to latitude in each 

hemisphere are required to effect the heat exchange. 

The resulting surface wind pattern consists of easterly 

winds between about 20° N. and S., westerlies between 

35° and 50° N. and S., and easterlies above 65° N. and 

S. High-pr.essure {descending air) belts occur at the 

poles and at about 30° N. and S., and low pressure 

(ascending air) occurs at about 60° N. and S. and at the 

equator. Precipitation is higher in the low-pressure 

regions and lower in the high-pressure regions. 

The latitudinal model explains only the coarsest 

components of the global climatic pattern; it 

corresponds to the pattern that would be seen if the 

Earth had a homogeneous surface. The contrasting 

thermal properties (that is, specific heat capacity) of 

land and sea greatly complicate the simple latitudinal 

thermal regime imposed by the equator-to-poles 

temperature gradient. Fortunately, the role of landsea circulation in disrupting the latitudinal components 

of atmospheric circulation to create large-scale 

cellular features such as the subtropical high-pressure 

cells at low midlatitudes in the oceans is fairly well 

understood, at least for the present-day global thermal 

regime. Moreover, global paleogeographic 

reconstructions, especially for the Paleozoic, are 

becoming more reliable, as the convergence in 

reconstructions published by different research groups 

indicates. Therefore, ancient atmospheric and oceanic 

circulation patterns can be modeled with some 

confidence, and we can thereby begin to examine some 

of the elements of paleoclimatic patterns that were 

different from present ones because of different 

paleogeography. 

An example of the use of such models is the 

prediction of the locations of ancient upwelling zones 

(that is, zones of high biologic productivit:· in the 

oceans) (Parrish, 1982). Because of the large input of 

organic matter to the sediment, upwelling :mnes are 

important settings for the deposition of ver~· organic 

rich sediments and of phosphorites. T'·e most 

persistent upwelling currents are wind driven-hence, 

the necessity of first modeling the atmospheric 

circulation. Upwelling currents occur in tv1o major 

forms-as coastal upwelling zones and as oceanic 

divergences. Coastal upwelling zones occur where 

persistent winds flow parallel to a coastline sc that the 

net transport of water, which is at right angl~s to the 

wind owing to the Coriolis effect, is offsh'lre. At 

present, coastal upwelling zones occur primarily along 

the west coasts of continents (for example, C·~lifornia 

and Peru) and are driven by winds that corroose the 

eastern limbs of the subtropical high-pressure cells. 

Coastal upwelling also occurs off Somalia d1lring the 

summer monsoon in Asia and off Venezuela. The 

predominance of west coast upwelling zones is partly 

an artifact of present geography. Theoretically, zonal 

coastal upwelling currents, such as the current off 

Venezuela, are potentially more extensive. Zonal 

coasts were more prevalent in the Paleozoic; 

consequently, the potential for zonal coastal 

upwellings was higher then (fig. 22). Oceanic 

divergences have been almost completely ignored by 

geologists because, in the present world, the 

divergences tend to occur over very deep water and 

leave little mark in the sediment except a higher 

biogenic silica content. However, the V?.ry wide 

continental shelves that characterized many past 

geographies, particularly during the early Flleozoic, 

would have permitted the development of oceanic 

divergences in settings where high biologic 

productivity could have resulted in the preservation of 

organic carbon and phosphorites as well as of biogenic 

silica (fig. 22). 

37 

The following table compares the distr~bution of 

predicted Paleozoic upwelling zones v·1ith the 

distribution of phosphorites, organic-rich rocks, and 

chert. 
Comparison of distribution of predicted upwelling zones with the distribution of 

phosphorites, organic-rich rocks, and cherts 

[Number in parentheses is the total number of deposits for that time; 

first number is the number of deposits that fell into the predicted 

upwelling zones. *,statistically significant correspondences] 

Time Organic-rich rocks Phosphorites Chert 

Permian: 

Late------------- 4 ( 11) * 

Early------------ 3 ( 4)* 

Pennsylvanian: 

Late------------- 2 2) * 

Early------------ 3 3)* 

Mississippian: 

Late------------- 4 4)* 

Early------------ 3 5)* 

Devonian: 

Late------------- 13 ( 17) 

Middle----------- 5 ( 7)* 

Early------------ 3 ( 8)* 

Silurian----------- 1 ( 4) 

Ordovician-----~--- 3 ( 6) 

Cambrian----------- 2 ( 6) 

With the exception of phosphorites in the 

Ordovician, wherever sample sizes are large enough to 

give meaningful statistical results, there is a 

significant correspondence between upwelling and the 

three types of deposits commonly found in upwelling 

zones. Particularly interesting is the fact that cherts 

correspond so well, because biogenic silica in modern 

upwelling zones is almost entirely derived from 

diatoms, which did not evolve until much later. Some 

of the Paleozoic cherts are radiolarites, and 

radiolarians tend to concentrate in upwelling zones in 

8 (12)* 11 ( 12) * 

2 5) 4 ( 7) 

2 ( 4) 6 ( 2 2) 

8 ( 15) * 14(30)* 

1 ( 5) 5 ( 9) 

10 ( 2 2) 12 (20)* 

19 (40)* 10 ( 19) * 

the present world. However, other Paleozoic cherts 

either have undergone so much diagenesis that their 

orh;in cannot be determined or are derived from 

sponge spicules. The relation of siliceous sponges to 

upwelling is not well known. 

The results presented in the ta'Jle suggest that, 

despite undoubted differences in climatic parameters, 

such as the absolute value of the equator-to-poles 

temperature gradient, past atmosplleric circulation 

patterns were governed by the same factors that 

govern them today. 

38 
w 

<0 

FIGURE 22.--Atmospheric circulation in the Late Cambrian northern winter (adapted from Parrish, 1982; published with permission from the 

American Association of Petroleum Geologists). H, high pressure; L, low pressure; hatchuring, upwelling zones; dark shading, highlands; 

mediu-m shading, lowlands; light shading, continental shelf (reconstruction from Scotese and others, 1979). Dark lines are isobars; arrows 

indicate wind direction. Note the zonal coastal upwelling zones predicted for the north and south paleocoasts of North America (left center) 

and the equatorial divergence over the shelf in western Gondwana. Solid circles indicate organic-rich rocks with marine organic matter; halfsolid circles indicate organic-rich rocks of unknown origin; plus signs represent 5° longitude-latitude tick marks. 
PALEOCLIMATE AND MINERAL DEPOSITS 

PALEOCLIMATIC CONTROLS ON THE OCCURRENCE AND QUALITY OF COAL 

By C. B. Cecil, R. W. Stanton,S. G. Neuzil, F. T. Dulong, and L. F. Ruppert 

The industrial nations of the world have devoted 

many years of research to understanding coal quality; 

however, the geologic factors that contro.l the origin 

and distribution of mineral matter in coal are still 

poorly understood. In a broad sense, paleoclimate is 

recognized as one controlling factor in the worldwide 

distribution of coal. Although the quality of coal 

deposits varies worldwide, there are three general 

"families" of coal deposits (Stach and others, 1982): (1) 

banded bituminous coals of Carboniferous age of the 

Northern Hemisphere, (2) banded bituminous coals 

known as Gondwana coals of Permian, Triassic, and 

Jurassic age in India, southern Africa, eastern 

Australia, South America, Madagascar, and 

Antarctica, and (3) high-moisture lignite and 

subbituminous coals of late Mesozoic or Tertiary age 

in Europe, western North America, and southeastern 

Australia. The Carboniferous coals formed under a 

humid tropical and subtropical climate. In contrast, 

climate conditions were cold temperate during the 

formation of the Gondwana coals (Stach and others, 

1982). Climate conditions that prevailed during the 

formation of coals of Cretaceous age and younger are 

not well documented. However, paleoclimates directly 

and indirectly affect and (or) control both the 

occurrence and the quality of these three broad 

"families" of coal deposits. 

On a local or regional scale, attempts to predict 

the quality and thickness of coal beds are generally 

unsuccessful without data from closely spaced 

drilling. Models to explain variations in thickness and 

quality are limited to physical depositional 

environments such as alluvial plain, upper delta plain, 

lower delta plain, or back barrier. Coal beds whose 

origins are traced to an alluvial plain or upper delta 

plain depositional setting are generally believed to be 

low in ash and sulfur, whereas coal beds of lower delta 

plain or back barrier origin are generally believed to 

be higl) in ash and sulfur as a result of proximity to 

marine conditions. High-sulfur coal has been related 

to superjacent strata of marine origin (White and 

others, 1913; Horne and others, 1978). Williams and 

Keith (1963) and Gluskoter and Hopkins (1970) 

demonstrated that sulfur content is higher in areas 

where a coal bed is overlain by marine sediments than 

it is in areas where the same bed is overlain by 

sediments of nonmarine origin. In contrast, recent 

40 

work by Cecil and others (1982) has shown that the 

variation in sulfur is far greater among coal beds of 

strictly nonmarine origin than it is for a given coal bed 

that is overlain by both marine and nonmarine 

sediments. 

Geochemical and paleoclimatic models provide 

a more comprehensive explanation for the systematic 

variation of ash and sulfur in coal beds of the central 

Appalachian Basin. In the Upper Mississippian, coal 

beds are thin, discontinuous, and generally of poor 

quality. In the Lower and lower Middle Pennsylvanian, 

coal beds are generally low in both ash (< 10 percent) 

and sulfur (<I percent), whereas, in the upper Middle 

and Upper Pennsylvanian, coal beds contain high 

amounts of ash ( > 1 percent) and sulfur ( > 1 percent). 

Sedimentary rocks associated with the low-ash lowsulfur coal beds are noncalcareous-sandstone, 

siltstone, and shale. Coal beds that are high in ash and 

sulfur are associated with calcareous sandstone and 

shales as well as with nonmarine limestone. The 

mineralogy of the low-ash coal beds is dominantly 

kaolinite and quartz; the mineralogy of the high-ash 

high-sulfur coal beds is dominantly kaolinite, illite, 

quartz, pyrite, and calcite. In the sedimentary 

sequence of the upper Middle Pennsylvanian, flint 

clays are present that, in places, grade laterally into 

nonmarine carbonates; these sediments were 

subaerially exposed and, as a result, contain 

microkarst zones that are brecciated and have 

subaerial crusts. The Upper Pennsylvanian also 

contains nonmarine carbonates that were subaerially 

exposed; however, flint clays are not present. In 

addition, red beds as well as paleosols are present. 

The paleosols are somewhat similar to caliches 

because they contain teepee or pseudoanticlinal 

structures and are highly enriched in nodular carbonate 

at the top. 

The stratigraphic occurrence of coal, changes in 

coal quality, and changes in the lithologies of 

associated sediments in the Appalachian Basin indicate 

at least two major climatic changes during 

Pennsylvanian time. In Late Mississippian time, 

evaporation was high relative to precipitation, as the 

presence of nonmarine carbonates, red beds, and 

paleosols having the characteristics of caliches 

indicates. In the latest Mississippian or Early 

Pennsylvanian, the first climatic change occurred as 
rainfall in~reased relative to evaporation. From Early 

to late Middle Pennsylvanian time, precipitation was 

high relative to evaporation; th1_1s, highly acid 

conditions (pH>4.5) were produced in the paleo-peatforming environments. Coal derived from peat that 

formed under these acid conditions is in general low in 

both ash and sulfur (Cecil and others, 1981). 

In the upper Middle Pennsylvanian, the second 

climatic change occurred when evaporation increased 

relative to precipitation. These relatively drier 

conditions resulted in an increase of dissolved solids 

and pH in surface and near-surface waters and thereby 

changed the geochemical conditions in peat-forming 

and associated depositional environments. Coal 

derived from peat that accumulated under nearly 

neutral conditions is relatively high in both ash and 

sulfur (Cecil and others, 1981). Changing climatic 

conditions are also indicated by the presence of (1) 

nonmarine limestones that have shallow-water and 

subaerial features and (2) paleosols similar to caliche. 

The climatic changes interpreted from lithologic and 

coal-quality characteristics are summarized in figure 

23. The inferred paleoclimatic changes from the Late 

Mississippian through the Late Pennsylvanian are 

consistent with paleobotanical data (White, 1925; 

Phillips, 1978, Pfefferkorn and Thomson, 1982). 

Paleoclimate was one of the principal factors 

that controlled the geochemistry of the Pennsylvanian 

peat-forming environments. In turn, these 

geochemical conditions controlled the quality of the 

resulting coal. In the Early and lower Middle 

Pennsylvanian, water in the peat-forming 

41 

environments was dominantly derived from rainfall. 

Organic acids maintained the waters at low pH values 

because the concentration of dissolved solids was low, 

and the resulting buffering capacity was also low. In 

the upper Middle and Late Pennsylvanian, rainfall was 

reduced, and the climate became more seasonal 

(White, 1925). Water in the peat-forming environments 

was derived chiefly from surface or ground water. 

Interstitial water contained increased concentrations 

of dissolved solids; buffering capacity was increased, 

and pH values increased in interstitial water of the 

peats. These latter conditions were more conducive to 

sulfur and ash fixation in the peat. 

The climate changes and the subsequent shift in 

geochemical conditions account for the stratigraphic 

variation in the ash and sulfur contents of coal beds in 

the Appalachian Basin. This variation cannot be 

explained by physical depositional models. The marine 

influence model generally used to explain the highsulfur content of coal (Williams and Keith, 1963) is 

nothing more than a special case within a more 

encompassing geochemical model (Cecil and others, 

1982). 

The continued development and application of 

paleoclimatic-geochemical modeling will expedite 

coal-resource assessments and quantify resource 

estimates. Such modeling can also be applied to 

exploration, reserve characterization, mine planning, 

coal preparation, and the successful prediction of coal 

properties as related to coking, combustion, and 

synthetic fuels. 
FORMATION 

a:Z 

LU~ 

3::~ DUNKARD oa: ...JlU a_ 

-? 

~ MONONGAHELA 

z a:<( 

LU> (l_...J 

a..>-

-::)(/) 

z 

z 

LU CONEMAUGH a_ 

CHARLESTON 

z 

~ 

z lU<( 

...J> 

o...J 

Q>-

~(/) z 

z 

LU KANAWHA a_ 

z NEW RIVER 

~ 

z Q:<( 

LU> 

3;:...J 

o>- ...J(/) z 

z 

LU 

a_ POCAHONTAS 

z 

<( 

a:c::: 

LU~ a_(/) BLUESTONE (l_(IJ 

-:::J(f.j (/) 

~ 

LOW 

RAINFALL 

EVAPORATION 

' 

R 

R 

. 

R 

ed Bedsj 

Caliche'' l 

ed Beds 

" Caliche" 

HIGH 

EXPLANATION 

B 

Coal 

Limestone 

Sandstone 

Calcareous 

shale 

Mudstone 

§§] 

~ 

Siltstone 

Ill 

Shale 

FIGURE 23.-Inferred paleoclimate changes and generalized stratigraphic column from the Upper Mississippian 

to the Lower Permian(?) central Appalachian Basin. 

42 
PALEOCLIMATE AND MINERAL DEPOSITS 

CARBON DIOXIDE, GEOCHEMICAL MODELING, AND PALEOENVIRONMENTAL RECONSTRUCTIONS 

By Eric T. Sundquist 

Paleoclimate is sometimes linked to other 

paleoenvironmental factors by means of geochemical 

speculation on a regional or global scale. For example, 

several investigators have suggested various 

relationships among past climate, atmospheric co2, carbonate dissolution, organic carbon burial, and 

biological productivity. In order to develop 

<geochemical models of these relationships, it is useful 

to draw upon recent improvements in modeling 

atmospheric co2. 

During the past 25 years, atmospheric co2 

concentrations have increased from about 315 to about 

340 ppm. Extrapolation to future levels of fossil-fuel 

consumption suggests that atmospheric co.., will be 

twice its preindustrial level before the year 21150. The 

best climate modeling available indicates that this 

increase will enhance atmospheric absorption of 

infrared radiation enough to raise the mean global 

surface temperature by about 2° to 3°C and the polar 

surface temperature by about 5° to 8°C. Concern for 

these potential climatic effects has stimulated a broad 

international effort to understand the factors that 

control atmospheric co2 concentrations. 

The measured atmospheric increase accounts 

for only about half of the co2 produced by burning 

fossil fuels. Accounting for the other half is very 

difficult because it requires understanding the oceans 

and the biosphere, the two major reservoirs that 

exchange carbon rapidly with the atmosphere. The 

problem is further complicated because it is not clear 

whether the biosphere is a net co2 sink or an 

additional source; thus, the fossil-fuel co2 problem is 

a fundamental carbon-cycle problem. 

Because of their long-standing interest in 

geochemical cycles, geologists can offer unique and 

important perspectives on the co2 problem. One 

particularly geological concern is the long time scale 

of response to anthropogenic co2 production. 

Whereas most public attention has focused on effects 

that may occur during the next few decades or 

centuries, geochemical models suggest that some 

effects may persist for thousands or even tens of 

43 

thousands of years. Another geological conce .. n is the 

potential for significant geochemical effects, such as 

enhanced marine carbonate dissolution. These effects 

are implied by geochemical principles that will operate 

even if there are no climatic effects. Fin1Hy, the 

geological record contains abundant evidence for past 

nonanthropogenic variations in the global carbon 

cycle. Many of these variations appear to have been 

associated with changes in climate and some strongly 

influenced the deposition and preservation of fossil 

fuels. The sedimentary record of past fluctuations 

also necessitates a careful reexamination of the 

steady-state assumption that underlies all pr~dictive 

co2 and climate modeling. 

Geochemical modeling is a powerful and 

essential tool for approaching these geological aspects 

of the co2 problem. Geochemical models provide a 

way of integrating numerous kinds of geological 

evidence into paleoenvironment~! reconstructions and 

predicting how geological processes will respond to 

future co2 emissions. The models are irvariably 

rooted in the fundamental principles of chemical 

equilibrium, chemical kinetics, and mass and energy 

conservation. If they are to be applied to the 

integration of stratigraphic evidence or future effects, 

they must be time dependent. These characteristics 

are shared by many predictive carbon-cycl~ models 

developed by the C02 research community. Predictive 

co2 models provide a valuable starting p')int for 

geochemical modeling. 

However, the development of geo~hemical 

carbon-cycle models from co2 models is not 

straightforward. Three very important considerations 

are (1) the interdependence of processes and time 

scales, (2) the multiplicity and unreality of steady 

states, and (3) continuity with the present. These 

considerations imply very specific constraints on the 

form of geochemical carbon-cycle models anc the way 

that the models are applied. They also have important 

implications for predictive co2 models and for other 

geochemical models. 
PALEOCLIMATE AND MINERAL DEPOSITS 

ISOTOPIC RESEARCH, CLIMATE, AND THE GENESIS OF MINERAL DEPOSIT2 

By Bruce R. Doe 

There are several fundamental climatic factors 

that we need to study to document the history of past 

climates and to understand the relationship of 

paleoclimates to the genesis of mineral deposits. 

These climatic factors include temperature, 

temperature distribution, humidity (including 

cloudiness and windiness), oxidation state of waters, 

pH, salinity, and saline species. In addition, several 

factors that may be indirectly related to climate and 

the influence of climate on mineralization are source materials (mountains versus plains of various materials 

such as volcanic rocks or sediments) and plate tectonic 

configurations. A number of other factors that may be 

important as mechanisms for climate change include 

changes in solar luminosity, variations of the Earth's 

magnetic field, and a change in the Moon's distance 

from the Earth. Isotopes have played a large role in 

resolving many of these paleoclimatic problems. The 

following is a survey of some of these applications. 

Oceans 

Because temperature exerts a primary control on the isotopic composition of benthic and planktonic 

foraminifers, oxygen isotopes have been the workhorse 

for determining paleotemperatures in the oceans. The 

use of oxygen isotopes of benthic and planktonic 

foraminifers for paleothermometry culminated in 

delineating the temperature history of the oceans over 

the last 100 m.y. {Savin, 1977). Belemnites have also 

been important because of the ease in identifying 

recrystallization in thin section, and foraminifera have 

shown broad applicability for the Cenozoic. Several 

factors influence the application of oxygen isotopes to 

paleothermometry: diagenesis, disequilibrium, oxygen 

isotopic composition of the water in which the animals 

grow, water density in the case of planktic 

foraminifera, and salinity. Identifying the contribution 

of each parameter is essential in isotopic studies. For 

example, the extent of diagenetic recrystallization can 

often be determined through thin-section study. Also, 

some foraminifera secrete their tests out of 

equilibrium with seawater, so that some taxa are more 

44 

reliable as paleotemperature indicators. Increasing 

salinity tends to result in heavier oxygen isotopic 

compositions, so that taking the ligt'test values from 

several analyses can help compensate for this 

problem. The oxygen isotopic composition of ocean 

water is itself a problem because it is controlled by 

the growth and decay of icecaps, locF.l evaporation, or precipitation, large-scale atmospheric circulation, and 

nearby continental runoff. Berger (1979) gives a useful 

review of the use of stable isotopes in foraminifers and 

how they reflect various hydrologic and climatologic 

conditions. 

In the case of carbon isotopes in carbonate 

rocks, the thermal fractionation effect is very small 

(about 0.035 permilf>C) and, in rocks or sediments 

poor in carbon, carbon isotopes are l~ss susceptible to 

diagenetic effects than oxygen isotopes are {Scholle 

and Arthur, 1980). Carbon is concentrated into two 

main reservoirs: carbonate and organic carbon. 

Although carbon isotopes do not vary as much in the 

geologic marine record as oxyg~n isotopes do, 

Cretaceous variations have been fo·•nd to correlate 

with ocean anoxic events {Scholle ar-:1 Arthur, 1980). 

Because organic matter contains very light carbon 

{ --25 s13c), carbonates formed in the oxic layer 

during anoxic events can be expectec' to trend toward 

heavy values. Recent studies confirm this trend in the 

heavy carbon isotopic ratios found in the Albian and 

Turonian stages of the Cretaceous. Carbon isotopes 

are also governed by the following secondary 

reservoirs: carbonate from the C'Xidation of old 

organic carbonate, sedimentary and marine sulfates 

formed from oxidation of sulfide, ferric oxides formed 

from oxidation of iron, and the Earth's atmosphere. 

Sulfur is thought to be partitioned into an 

oxidized inorganic sulfate reservoir and a reduced, 

biologically mediated sulfide reservo1r containing the 

lighter values of 8 34s. Secular variations in the 8 34s 

in sulfate are well documented (Claypool and others, 

1980). The reduced sulfur in mineral deposits depends 

on several parameters, some of whi~h are shown in 

figure 24. There is a tendency for s·,lfate-sulfur and 

carbonate-carbon isotopes to be inVE"·sely correlated 
-60 -40 

8 34$, IN PERMIL 

-20 0 20 

t 

Euxinic environments sw 

Shallow marine and brackish environments 

Bacterial reduction (T <50°C) 

Decomposition of organic compounds (T>50°C) 

Organic reduction (T>80°C?) 

? 

Inorganic reduction (T>250°C) 

FIGURE 24.--Distribution pattern for S 34s values of H2s and sulfide minerals when sulfate 8 34s=+2C percent 

is reduced by various mechanisms. (From Ohmoto and Rye, 1979.) (Reproduced with permission as modified 

Geochemistry of Hydrothermal Ore Deposits, copyright 1979 by John Wiley and Sons, In~.) 

with each other (Veizer and others, 1980), and this 

tendency has led to hypotheses involving control of 

both isotopes by biologic mea~. There is also a 

correlation of sulfur with 87sr;8 Sr in marine fossils. 

For example, strontium in the oceans is radiogenic at 

the present time and was also in the Mississippian but 

was nonradiogenic in the Jurassic and Cretaceous 

(Peterman and others, 1970). Sulfate-sulfur is 

relatively heavy at the present time and was in the 

Mississippian but lighter in the Jurassic and 

Cretaceous. Nonradiogenic strontium and light sulfur 

are compatible with a young igneous component 

because of either submarine activity or erosion from 

magmatic arcs (George Claypool, oral commun., 

1981). The inverse correlation of sulfate-sulfur with 

carbonate-carbon may therefore be more complex than 

current accounts indicate. 

Lead isotopes in sedimentary manganese 

deposits might indicate the importance of volcanism in 

providing manganese to anoxic seas because, as Doe 

and Zartman (1979) pointed out, there is a large 

isotopic difference between mantle lead and the lead 

in seawater and pelagic sediments. The Cretaceous is 

a period of unusually great volcanic activity and also 

hosts some of the best-documented oceanic anoxic 

events. Radiogenic isotopes such as those of lead and 

strontium may help distinguish climatic effects from 

nonclimatic effects. 

45 

Continents 

Deuterium (fig. 25) and oxygen isotopes in 

continental surface water vary in a systematic 

fashion. There is a tendency for deuterium to 

decrease northward because precipitation is enriched 

in the light isotope, and the remaining vapor becomes 

depleted (Taylor, 1979). A decreasing temperature 

trend also tends to make the precipitation heavier. 

This trend is well illustrated in the midcontir~nt from 

the Gulf of Mexico northward. On the east coast, the 

trend is modified by the Atlantic Ocean and mountain 

ranges. The trends caused by jet-stream-related 

precipitation coming eastward across mountains in the 

western United States add additional com..,lexities. 

For example, as clouds moving up the mounteins cause 

precipitation, the vapor becomes depleted in the heavy 

isotope. Increasing elevation is accompanied by a 

temperature drop that accentuates the isotopic 

change. East of the highest elevations, th~ isotopic 

composition of surface water begins to become heavier 

because sinking clouds become warmer, anc there is 

mixing with precipitation from the Gulf of M~xico. 

Because precipitation is a process ap..,roaching 

equilibrium, oxygen varies systematically with 

deute[ium isotopes (fig. 26), deuterium be;ng about 

8 S 1 0 + 10 (in permil). This line is c1Ued the 

meteoric water line (Taylor, 1979). Most surface 
FIGURE 25.-Map of North America showing contours of the approximate average B D values of meteoric 

water. (From Taylor, 1979.) (Reproduced with permission from Geochemistry of Hydrothermal 

Ore Deposits, copyright 1979, by John Wiley and Sons, Inc.) 

46 
100 -----:VD ,, 

," 0 " Salinity 

increase 

0 

ocean water 

-100 

-20~2L5~--L_~_L--~15 __ L_~_L~ __ _L5~~--~~_L5~--L-~-L~15 __ L-J--L~--2~5~--~~~~35 

& 180, IN PERMIL 

FIGURE 26.-Behavior of () D and 8 18o in meteoric water. Crosses are values for precipitation at various 

olaces throughout the world. Values for Antarctic lakes can be more negative. Squares and t··iangles 

represent data from two lakes in the northwestern Sahara that are typical of evaporating water. Note 

reversal of data on lake represented by squares, caused by the effect of dissolved salts on the activity of 

free water. (From Pearson and Coplen, 1978.) 

water lies to the right of this line (fig. 26) because of 

surface evaporation and evaporation of the falling 

precipitation in arid areas. ;pgse relationships are expressed as a () D of about 5 8 0+10 (in permil). At 

very high salinities, the trend is reversed because of 

absorption effects on ions. In general, meteoric water 

can also be distinguished from magmatic or 

metamorphic water except in the case of highly 

evaporated systems at high latitudes. However, in the 

eastern Triassic basins, which were near the equator at 

the time they were formed, the meteoric water trends 

probably followed a heavier isotopic path than that 

shown for primary magmatic water in figure 27. These 

47 

data, coupled with data on fluid inclusions or 

alteration minerals on magmatothermal ore deposits, 

have been used to idehtify a major meteori~ water 

component in many hydrothermal mim~ralizing 

systems. The full significance of this important 

finding is not yet completely realized in ore g~nesis or 

as a guide to ore, but a number of economic gE"ologists 

are now considering topography and climatic 

conditions during igneous activities. 

Detailed analysis of the light stable isotope 

geochemistry of lakes is highly complex (Pearson and 

Coplen, 1978) but has the potential to yield significant 

paleoenvironmental information. It is pos:'l\ble to 
0 

-25 

-50 

:::::! 

~ 

a: 

w 

Tui Mine, 

New Zealand 

---------·) 

PRIMARY 

MAGMATIC 

WATER 

0 -------.. · ~__... --- «; ----- ... .......-"'--

a.. -75 

~ 

ci "' __.---! . . ·...--~COMSTOCK DISTRICT, 

IJO / l . --;.--- NEVADA y "'() Pachuca, Mexico 

-100 

-125 

0 Cortez 

-15QL------------L------------L-----------~------------~----------~----------~ 

-20 -15 -10 -5 0 5 10 

& 180, IN PERMIL 

FIGURE 27 .-Plot of 8 D of fluid inclusions versus calculated 8 18o values of hydrothermal fluids for various 

epithermal ore deposits. Offset to the left of the primary magmatic water field shows influence of 

meteoric water. SMOW, standard mean ocean water. (From Taylor, 1979.) (Reproduced with permission as 

modified from Geochemistry of Hydrothermal Ore Deposits, copyright1979,by John Wiley and 

Sons, Inc.) 

determine parameters such as temperature, pH, and 

salinity of lake waters in some cases through studies of 

fluid inclusions, fossils, travertine, chert, sanidine, and 

zeolite-type minerals formed in many lakes (Cerling 

and others, 1977). 

Preliminary investigations of cosmogenic 

radionuclides other than radiocarbon indicate that we 

may be able to date some oilfield brines and other old 

48 

fluids. Two s~c~ radionuclides currently under 

investigat\~ are Cl, which has a half-life of 0.31 

m.y., and I, which has a half-life of 15.7 m.y. 

In conclusion, the use of stable isotopes, both 

radiogenic and nonradiogenic, should play a major role 

in unraveling the importance of climate in the 

formation of many kinds of mineral de'">osits. 
REFEREl'CES 

Arthur, M. A., and Schlanger, S. 0., 1979, Cretaceous "ocean anoxic events" as causal factors in 

development of reef-reservoired giant oil fields: American Association of Petroleum Geologists 

Bulletin, v. 63, p. 870-885. 

Austin, G. S., 1970, Weathering of the Sioux Quartzite near New Ulm, Minnesota, as related to 

Cretaceous climate: Journal of Sedimentary Petrology, v. 40, no. 1, p. 184-193. 

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59