fis 

o 

Parallel Laminated Deep-Sea 

Muds and Coupled Gravity 

Flow-Hemipelagic Settling 

in the Mediterranean 

^ H 

SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES • NUMBER 19 
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SMITHSONIA N CONTRIBUTION S TO TH E MARIN E SCIENCES* NUMBER 19 

Parallel Laminated Deep-Sea Muds and 

Coupled Gravity Flow-Hemipelagic Settling 

in the Mediterranean 

Daniel Jean Stanley 

SMITHSONIAN INSTITUTION PRESS 

City of Washington 

1983 
ABSTRAC T 

Daniel Jean Stanley. Parallel Laminated Deep-Sea Muds and Coupled 

Gravity Flow-Hemipelagic Settling in the Mediterranean. Smithsonian Contributions to the Marine Sciences, number 19, 19 pages, 7 figures, 1983.—The origin 

of fine-grained deep-sea facies is often blurred because of interplay of diverse 

transport mechanisms: sediment gravity flow, traction related to fluid-driven 

circulation, and pelagic and hemipelagic "rain" mechanisms. Physical and 

chemical attributes of the Mediterranean amplify petrologic differences, thus 

facilitating distinction between mud types in this sea. Important attributes 

include small distances between sediment input and depositional site, generally low bottom current velocities in the deep basins, and shallow depths that 

permit preservation of carbonate components, an important criterion for mud 

facies definition. Particularly important in the Mediterranean are periodic 

development of intense water mass stratification and pycnoclines which act as 

sediment barriers, i.e., deviation of low concentration sediment gravity flows, 

and temporary retention of particles from turbid layer flows and hemipelagic 

settling. Release and differential settling of terrigenous silt and clay floes and 

reworked benthic and planktonic (largely coccolith and foraminifera) components from well-marked density interfaces occur in a manner such that 

particles are segregated according to size and density. The resulting varve-like 

deposits display fine parallel laminae of alternating coccolith- and terrigenousrich layers that show diverse fining-upward trends. Finely laminated sections 

of this type accumulate more rapidly than hemipelagites and are distributed 

over larger surfaces than mud turbidites. Analysis of bedform, texture-fabric, 

composition, geometry, and rates of sedimentation help distinguish (1) fine 

parallel laminated muds derived from coupled sediment gravity flow and 

hemipelagic settling from (2) laminated mud turbidites, (3) laminated hemipelagites, and (4) contourites as commonly defined. Study of mud lithofacies 

in small to moderate size seas, such as the Mediterranean, holds promise for 

better interpretation of deep-marine fine-grained deposits. 

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded 

in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: Seascape along the 

Atlantic coast of eastern North America. 

Library of Congress Cataloging in Publication Data 

Stanley, Daniel J. 

Parallel laminated deep-sea muds and coupled gravity flow-hemipelagic settling in the Mediterranean. 

(Smithsonian contributions to the marine sciences ; no. 19) 

Bibliography: p. 

Supt. of Docs. no. : SI 1.41:19 

1. Marine sediments—Mediterranean Sea. 2. Sediment transport—Mediterranean Sea. I. 

Title. II. Series. 

GC389.S8 1983 551.46'083'38 82-600337 
Contents 

Page 

Introduction 1 

Acknowledgments 2 

Climate, Hydrography, and Sedimentation 2 

Density Stratification Phases in the Mediterranean 3 

Fine-grained Facies and Isothermal Hydrographic Regimes 5 

Fine-grained Sedimentation and Density Stratification 7 

Finely Laminated Mud Variants 9 

Implications and Conclusions 14 

Literature Cited 17 
Dedicated to the memory of 

Professor Dr. Johan Ferdinand Maurits de Raaf 

1902-1982 

inspiring leader 

astute sedimentologist 

friend 
Parallel Laminated Deep-Sea Muds and 

Coupled Gravity Flow-Hemipelagic Settling 

in the Mediterranean 

Daniel Jean Stanley 

Introduction 

Deposition of silt and clay lithofacies in the 

marine environment is attributed to settling of 

particles from suspension, to transport by fluiddriven processes related to ocean circulation 

(Heezen and Hollister, 1971:335-421; Eittreim 

and Ewing, 1972), and to sediment gravity flows 

(Piper, 1978; Stanley and Maldonado, 1981). 

Theoretical and experimental studies indicate 

that suspension settling, traction, and gravitydriven high-concentration mass flow and low concentration sediment flow mechanisms each result 

in characteristic bedforms and textural-fabric and 

compositional attributes of fine-grained deposits. 

Distinct facies are thus believed to result from 

pelagic "rain," tractive mechanisms related to 

bottom current transport (Stow and Lovell, 

1979), and turbidity currents (Stow and Bowen, 

1980). Muds from the latter process have received 

by far the most attention to date. 

Conditions in marine settings tend to vary and 

be more complex than theoretical and experimental examples. For example, the transit of silt and 

clay floes to the deep marine floor usually involves 

two or more processes. Moreover, it is recognized 

that stratification features in mud deposits result 

Daniel Jean Stanley, Department of Paleobiology, National Museum 

of Natural History, Smithsonian Institution, Washington, D.C. 

20560. 

from mechanisms active just prior to, and at, the 

time of particle emplacement. It has also become 

apparent that some silty deposits, earlier interpreted as turbidites, actually have a more complex origin. 

This paper considers the interplay of transport 

mechanisms that produces a continuum of mud 

types and thus blurs the origin of deep-sea finegrained facies. Specific attention-is paid herein to 

finely laminated muds whose petrology appears 

to record the combined effects of sediment gravity 

flow, including turbidity current transport, and 

hemipelagic settling. The Mediterranean Sea is 

an appropriate area in which to conduct a study 

of lamination in that (1) there are suitable numbers of closely spaced core sites, and (2) average 

basin depths approximate 3000 m, well above the 

carbonate compensation depth (CCD), such that 

calcareous components, an important criterion of 

depositional regime, are fortuitously preserved. 

Moreover, (3) Mediterranean basins are considerably smaller than those in major world oceans, 

and present diverse temporal and spatial facies 

variations, thus allowing more precise interpretation of dispersal and transport patterns. It is 

also recalled that (4) there is strong evidence of 

large-scale Quaternary to Recent oceanographic 

changes in the Mediterranean (Stanley et al., 

1975:287-289). These conditions provide an ideal 

setting in which to assess how climatically in-
SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

duced changes in water mass stratification affect 

pelagic settling and sediment gravity flows of low 

concentration and, in turn, the formation of laminae in mud deposits. Identification of criteria for 

laminated mud types emplaced by combined sediment gravity flow-suspension settling processes, 

and distinction of such facies from laminated 

mud turbidites and hemipelagic end-members, 

are valuable outgrowths of the study. 

ACKNOWLEDGMENTS.—The author acknowledges valuable discussions during the initial phase 

of the study with P.H. Feldhausen, NUS Corporation; and A. Maldonado, University of Barcelona; and use of coarse fraction mineralogical 

counts made by R. J. Knight, Petro-Canada Ltd. 

The paper was reviewed by R. D. Flood, LamontDoherty Geological Observatory; and J.W. 

Pierce, Smithsonian Institution; useful comments 

were also made by anonymous reviewers. Funding for this investigation, part of the Mediterranean Basin (MEDIBA) Project, was provided by 

Smithsonian Scholarly Studies grant 1233S101. 

Climate, Hydrography, and Sedimentation 

It is recalled that a major control of finegrained sedimentation in the deep sea is ocean 

circulation whose driving force is the sun (Lisitzin, 1972:30-46). Climatic fluctuations, resulting 

in displacement of temperature and rainfall belts, 

modified world ocean circulation in the geologic 

past (Hay, 1974:1-5). Well documented are the 

Quarternary climatic oscillations (Climap Project 

Members, 1976) that markedly altered circulation patterns, even at great depths (Schnitker, 

1980). Such changes were of particularly large 

magnitude in the case of small- to moderate-size 

basins with silled, restricted passages that limit 

exchange with adjacent water bodies. The Mediterranean serves as an ideal example in view of 

its narrow, elongate form between Africa, Southern Europe, and the Middle East, and the restricted exchange with Atlantic and Black Sea 

waters at the shallow, narrow Gibraltar and Bosporus-Dardanelles straits. 

Moreover, Mediterranean circulation patterns 

have been affected by a complex seafloor configuration, including shallow ridges that separate 

this sea into a series of quasi-isolated depressions 

of highly variable size, shape, and depth. The 

Strait of Sicily and contiguous Siculo-Tunisian 

(or Pelagian) Platform (Carter et al., 1972; Burollet et al., 1979) is a long broad sill that effectively separates the eastern and western basins, 

and thus is particularly important in control of 

Mediterranean circulation (Allan et al., 1972:11-

25). 

Present excess evaporation relative to precipitation and runoff results in the characteristic 

Mediterranean hydrographic regime involving 

the eastward flow of a moderately thin layer of 

less saline Atlantic water above a relatively isothermal column of westwardly moving, dense 

intermediate and deep water masses (Wiist, 1961; 

Lacombe and Tchernia, 1972). Circulation patterns, however, were markedly altered in the past 

as a result of somewhat lower temperatures and 

higher rainfall and runoff than at present. Bradley (1938) postulated that basins in the eastern 

Mediterranean (Ionian, Aegean, and Levantine) 

were periodically characterized by oceanographic 

patterns involving Black Sea-type density stratification, in contrast to the present isothermal 

regime. 

What would be the sedimentary responses on 

the deep-sea floor to such Quarternary climatichydrographic oscillations? It can be predicted 

that gravity-driven, high-concentration mass displacement and dense sediment gravity flows 

transporting mixes of coarse silt, sand, and coarser 

particles downslope and onto basin plains would 

not be markedly influenced by development of 

water mass stratification. In contrast, it is envisioned that dispersal and the resulting depositional patterns of low concentration flows, carrying mostly fine-grained material in suspension, 

would have been greatly modified by the development of a distinctly stratified water column of 

the type that may periodically have prevailed in 

the Quaternary and Pliocene. This investigation 

considers the origin of laminated fine-grained 

facies, other than sapropels (Ryan, 1972), and 
NUMBER 19 

related organic-rich layers (Maldonado and Stanley, 1976b), that preferentially accumulated at 

times when conditions of water mass stratification 

were clearly different than at present. 

Density Stratification Phases in the 

Mediterranean 

In a far-sighted essay referring to modifications 

of Mediterranean hydrography induced by Quaternary oscillations, Bradley predicted (1938:377) 

that 

during the last glacial stage, the Mediterranean, because of 

the different climate, would have had a surface layer of 

essentially fresh water overlying the oceanic water that filled 

the deep basins. Furthermore, the oxygenated Atlantic water 

would have had free access to the western basin of the 

Mediterranean through the Straits of Gibraltar beneath the 

outflowing surface stream of fresh water and in consequence 

the deep water of the western basin would have continued 

to be at least partially supplied with oxygen. But with a 

blanket of essentially fresh water covering the Mediterranean 

and moving westward there appears to be no way in which 

significantly large volumes of the oxygen-bearing saline water in the western basin could move across the sill at the 

Sicily Straits so as to cause circulation and afford an oxygen 

supply in the deep saline water of the eastern basin. For this 

reason the water in the eastern deep basin probably would 

have become stagnant and depleted of oxygen soon after the 

climatic change permitted fresh water to flood the surface of 

the Mediterranean. 

Indirect, but strong, evidence for such physical 

oceanographic changes during the late Pleistocene to Holocene has been provided during the 

past two decades by studies of cores collected in 

different Mediterranean basins. Radiocarbon 

dating and facies analysis of cores establish a 

stratigraphic base for regional correlation of Late 

Quaternary sediment sections (Stanley and Maldonado, 1979). Noteworthy is the remarkable 

systematic repetition, or cyclicity, of Quaternary 

sedimentary sequences recorded by means of lithofacies (Maldonado and Stanley, 1976b), geochemical and isotopic (Vergnaud-Grazzini et al., 

1977; Dominik and Mangini, 1979; Luz, 1979), 

and faunal (Mars, 1963; Ryan, 1972; Thunell 

and Lohmann, 1979) analyses. 

Lithological cyclicity indicates that circulation 

patterns in both eastern and western basins periodically were altered markedly from those operating at present. Particularly important evidence in this respect is provided by dark, organicrich fine-grained sapropel layers broadly distributed in the eastern Mediterranean (Figure 1A). 

There is general agreement that reduced oxygen 

content favoring anaerobic conditions on the seafloor resulted from density stratification (Kullenberg, 1952; Olausson, 1961). The distribution of 

dated sapropels indicates that some stagnation 

phases resulting from temporarily altered water 

mass stratification were basin-wide and occurred 

primarily at depths in excess of 800 to 1000 m 

(Stanley, 1978). The uppermost layer, dated at 

about 9000 to 7000 year B.P., formed during a 

warming phase (Ryan, 1972). The two underlying sapropel layers are dated at about 25,000-

23,000 years B.P. (possibly during a cooling phase) 

and at >40,000 years B.P. (Stanley and Maldonado, 1979:40-42). 

Sapropels are absent in the three deep (to about 

1700 m) Strait of Sicily basins, and in the Ligurian, Tyrrhenian, Algero-Balearic, and Alboran 

seas. However, sections in many cores recovered 

in these central and western Mediterranean depressions, some dated at about 11,000 to 9,000 

years B.P., display dark gray-olive streaked mud 

layers that contain pyritized tests and burrows 

(see, for example, core logs in Huan g and Stanley, 

1972:536-538; Rupke and Stanley, 1974; 11,25; 

Maldonado and Stanley, 1976a:53-56). The radiocarbon dates of these core sections may be 

somewhat older than the age of actual sediment 

emplacement, due to the presence of reworked 

calcareous microfossil tests. It is likely that the 

streaked, gray-olive, pyrite-rich mud sections of 

western Mediterranean cores are chronologically 

equivalent to the sapropel zones of basins east of 

the Strait of Sicily. The reduced, pyrite-rich sections of the western Mediterranean, like sapropels, record phases of density stratification as 

depicted in oceanographic models presented for 

the early Holocene (Figure 1B). 

In sum, lithofacies data support the hypothesis 

that an "estuarine-type" circulation regime and 
48°-

44° 

less dense 

surface water 

stagnant (h^S-rich) 

deep water 
NUMBER 19 

current reversal dominated the Mediterranean 

for short periods of time (Bradley, 1938;377; 

Mars, 1963;67-7l). Tha t the oceanography in the 

eastern basins at times of sapropel deposition, 

when oxygen-deficient conditions prevailed, may 

be likened to that of the present Black Sea is also 

indicated by analysis of Sea of Marmar a cores 

(Stanley and Blanpied, 1980). It is postulated 

that excess glacial melt waters moved westward 

as overflow from the Black Sea across the Bosporus-Dardanelles portals, and then south across 

the Aegean Sea. After entry into the Levantine 

and Ionian seas, this less saline surface layer 

flowed westwardly to and across the strait of 

Sicily and, eventually, Gibraltar (Figure 1). Denser Atlantic water, flowing eastward below the 

surface layer, entered the Alboran Sea and western Mediterranean producing some mixing and 

precluding complete anaerobic conditions of the 

Algero-Balearic, Ligurian, and Tyrrhenian seafloor. 

Current reversal as outlined above remains 

within the realm of theory. There is little doubt, 

however, that the Quaternary sediment cover, 

showing cyclothemic development of alternately 

reduced and oxygenated facies across much of the 

Mediterranean, records the direct interaction between climatically controlled water circulation 

fluctuations and deep basin sedimentation. StraFIGURE 1.—A, Chart showing distribution of youngest organic-rich sapropel, Si (diagonal lines), deposited in the 

eastern Mediterranean at about 9000 to 7000 years B.P., a 

time when hydrographic conditions were markedly different 

from those at present. (Heavy arrows depict generalized flow 

patterns of less dense upper water mass; light arrows show 

fluvial input; Ae = Aegean Sea; B = Balearic Basin; Bo = 

Bosporus; BS = Black Sea; D = Danube; I = Ionian Sea; Le 

= Levantine Sea; Li = Ligurian Sea; N = Nile River input; 

P-A = Po-Adriatic Sea; R = Rhone River input; SS = Strait 

of Sicily; STP = Siculo-Tunisian Platform; T = Tyrrhenian 

Sea; Ly-II-3 = position of core Lynch cruise II core 3; after 

Stanley, 1978.) B, Scheme illustrating "estuarine-type" water 

mass regime in the Mediterranean at times of sapropel and 

finely laminated mud deposition. Note marked stratification 

of water masses and development of Black Sea-type anoxic 

conditions in the eastern basins unlike those presently existing. (Arrows depict possible flow patterns of water masses; 

after Stanley et al., 1975.) 

tigraphically correlated cyclothemic sequences 

from eastern and western Mediterranean basins 

highlight the nonrandom vertical and lateral distributions of different fine-grained sediment types 

(Maldonado and Stanley, 1977; Stanley and Maldonado, 1981). It is useful to compare silt and 

clay facies that accumulate in isothermal versus 

stratified water regimens. 

Fine-grained Facies and Isothermal 

Hydrographic Regimes 

M u d types, including the fine silt, clayey silt, 

and silty clay, are most reliably identified as to 

process of emplacement on the basis of structures 

visible in radiographs, size analyses, and coarsefraction composition. Silt and sand-sized terrigenous clasts and carbonate grains of biogenic 

(largely coccoliths, foraminifera, and shell fragments) and clastic (reworked limestone and dolomite) origin are valuable criteria for distinguishing mud types. 

Muddy slump, dense mud flow, and muddy 

debris flow deposits accumulated throughout the 

late Quaternary independently of hydrographic 

fluctuations (Stanley and Maldonada, 1981:278-

283). These mass flow units are concentrated in 

areas of marked seafloor relief (slopes, ridge margins, base-of-slope environments) in association 

with sand and mud turbidites and hemipelagic 

muds. In upper Holocene to recent time, mu d 

turbidite-hemipelagic mud assemblages generally prevail on basin margins in areas of low 

relief, including perched slope basins and small 

depressions in cobblestone topography. In more 

distal, low relief environments, such as basin and 

trench plains, a distinct mud turbidite-unifitehemipelagic mud assemblage is usually recovered 

(Figure 2). (Unifite is the descriptive term for 

uniform, almost structureless mud, cf. Stanley, 

1981; Blanpied and Stanley, 1981:2.) 

Temporal and spatial distribution patterns of 

this latter distal basin and trench plain lithofacies 

assemblage provides insight on the relation between oceanographic conditions and silt and clay 

transport processes in deep marine settings. Struc-
SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

3cm 
NUMBER 19 

tureless and vaguely laminated unifites (Figure 

2E,F) are distinctly restricted to flat basin and 

trench plains where they are associated with finegrained mud turbidites (Figure 2B-D): both mud 

types are laterally continuous across basins (Figure 2A). Petrologically, unifites appear similar to 

nearly structureless muds that are referred to as 

"homogenites" by some workers (cf. Kastens and 

Cita, 1981). Radiocarbon dating of unifite sections records very high rates (>200 cm/1000 

years) of accumulation. Both structureless and 

vaguely laminated unifites are somewhat finer 

grained than turbiditic muds with which they are 

associated. Unifites and turbidites fine upward 

gradually and contain comparable proportions of 

terrigenous and reworked fauna carbonate components (usually >30% of the sand-size fraction). 

Spatial distribution patterns, rapid sedimentation 

and textural and mineralogical attitudes indicate 

that both fine-grained, almost structureless turbidites and unifites are released from thick, low 

density or lower velocity sediment gravity flows 

(Stanley and Maldonado, 1981:284, 290). Unifites appear to be the dilute end-products from 

turbidity currents, turbid layer flows, and suspensate-rich clouds (Stanley, 1981; Blanpied and 

Stanley, 1981:29-35). 

Typical Mediterranean hemipelagic mud layers, in contrast to fine-grained turbidites and 

unifites, are more commonly bioturbated and 

show speckling as a result of high concentrations 

FIGURE 2.—A, Subbottom 3.5 kHz record showing part of 

the Zakinthos Trench plain in the western Hellenic Arc 

(arrow points to thick, laterally continuous, acoustically 

transparent layer, probably a fine-grained turbidite and/or 

associated unifite). B-D, Radiograph prints of selected core 

sections showing typical sharp-based, fining-upward laminated mud turbidites (t) and hemipelagic mud (He) with 

speckling. (Note cross-stratification in B and D, and distinct 

fining-up trend of entire laminated section in c.) E, Faintly 

laminated unifite. F, Structureless unifite. (B and D, respectively, Marsili cores 12 and 18 in the Kithera Trench sector; 

F, Trident core 172-34 in the Zakinthos Trench, Hellenic Arc 

(locations shown in Stanley and Maldonado, 1981); c, Lynch 

cruise II core 8A in the Algero-Balearic Basin; E, Western 

Alboran Basin core 91 (locations for c and E, respectively, in 

Rupke and Stanley, 1974, and Huang and Stanley, 1972).) 

of planktonic tests (usually >75% of sand fraction). Moreover, layer thickness and rates of accumulation (<10 cm/1000 years; Rupke and 

Stanley, 1974:33) of hemipelagites tend to be 

much lower. Structures and mineralogical composition suggest that hemipelagic muds accumulate largely from suspension "rain" mechanisms 

rather than from sediment gravity flows. 

Under conditions of poorly developed water 

column stratification, such as that displayed by 

the present Mediterranean, gravity-driven flows, 

such as turbitity currents of moderately low density that carry clay- and silt-size floes primarily 

in suspension, would likely move downslope. 

These flows would move relatively unhampered 

along the bottom, from proximal sites (outer shelf 

to upper slope, ridge, basin margin) to the baseof-slope and well onto basin plains. Th e turbulent 

head of such flows would entrain in a downslope 

direction pelagic material, settling, or recently 

deposited, from suspension "rain"; in some cases 

flows would also resuspend and transport basinward surfical biogenic and clastic material eroded 

from basin slopes. This process would result in 

heterogeneous mixtures of displaced planktonic 

tests, terrigenous grains, and older reworked 

faunas, typically recovered from associated unifites and fine-grained turbidites restricted to basin 

plains. 

There is a decreased proportion of unifites in 

the eastern Mediterranean at times of sapropel 

deposition. This suggests that the flow patterns of 

low density "clouds" were in some manner modified during downslope movement by a barrier 

effect resulting from distinct density differences 

that periodically developed within the water column. 

Fine-grained Sedimentation and Density 

Stratification 

Water masses of different temperature, salinity, 

or both, are separated by a sharp vertical gradient 

in density, or pycnocline. Theoretical calculations, supported by field observation, show that 

sharp density gradients may temporarily retain 
8 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

particles settling through the water column and 

modify the flow path of very low concentration 

plumes (Pierce, 1976). Pycnoclines would induce 

detachment of a suspensate-rich flow from the 

seafloor into the water column, rather than allowing a bottom-hugging turbid layer flow of the 

type necessary to deposit a fine-grained mud 

turbidite with typical structures and/or associated structureless unifite. Flow detachment is expected wherever suspended sediment-enriched 

water encounters a denser water layer. Off California, for example, Drake et al. (1972:328) have 

shown that minimal concentrations of 100 mg per 

liter, and generally much higher (~2500 mg/1 ; 

cf. Pierce, 1976:441), are needed to overcome 

density interfaces resulting from temperature 

changes in the water column. 

In the Mediterranean, much of the fine-grained 

sediment presently introduced by rivers (notably 

the Nile, Rhone, Po, Ebro, and Seyhan) and by 

wind tends to spread out away from the coast 

along the upper major intermediate and deep 

water (Emelyanov and Shimkus, 1972). At times 

when stratification was better developed, depositional patterns almost certainly were more complicated. Particle aggregates settling from the 

upper pycnocline would reconcentrate along one 

of several lower density interfaces before finally 

settling to the bottom. In a multiply stratified 

column, one envisions a sequence involving (1) 

detachment of a turbid layer from the bottom, 

(2) aggregation, (3) particle settling, (4) renewed 

accumulation along a lower density interface, and 

(5) subsequent settling across still deeper pycnoclines prior to (6) deposition on the seafloor (cf. 

Pierce, 1976 Fig. 2). 

Open ocean suspended sediment studies show 

that, eventually, particles either become incorporated in a near-bottom turbid (nepheloid) 

layer, or settle directly onto the bottom. Still 

limited investigations of suspended sediment concentrations in the Mediterranean show no welldeveloped nepheloid layers in the western basins 

at present (Pierce and Stanley, 1976; Pierce et al., 

1981). Nepheloid layers in this sea, however, conceivably may have been important in the past. It 

is thus possible that midwater and bottom masses 

transported silt and clay size particles over larger 

geographical areas than they do today, perhaps 

in the manner nepheloid layers in other world 

oceans presently distribute substantial volumes of 

material (Eittreim and Ewing, 1972). 

Some aspects of a generalized model for suspended sediment transport in a stratified system, 

including detachment (Figure 3), may be applied 

to the Mediterranean. For example, detailed 

lithofacies analyses of Nile cone cores indicate 

that there exists a rather direct relation between 

rates of sedimentation and the frequency of laminated layers in upper Quaternary sections (Maldonado and Stanley, 1978, 1979). It has been 

postulated that at times of sapropel formation, 

low density turbid flows emanating from the 

mouth of the Nile and moving downslope were 

retained above the cone as detached layers. Concentration of fine-grained material along pycnoclines on the Nile cone is schematically depicted 

in Figure 4. 

More specific lithologic evidence recording 

probable influence of density stratification on 

fine-grained sedimentation is provided by suites 

of cores recovered from the western Hellenic 

Trench. These show that the most recent major 

phase of finely laminated mud deposition occurred from about 17,000 to 6000 years B.P. This 

period coincides with rapid eustatic sealevel rise 

and progressive climatic warming at the end of 

the Pleistocene and early Holocene. It is recalled 

that the most recent sapropel, Si, was deposited 

between about 9000 to 7000 years B.P. (Ryan, 

1972:150). The finely laminated mud facies, as 

the Si sapropel layer, was broadly distributed 

areally over highly diverse and irregular Hellenic 

Trench slope and basin topography; however, 

unlike Si which accumulated in less than 2000 

years, finely laminated muds were deposited during a period lasting 10,000 or more years. Finely 

laminated muds during this same period also 

accumulated over large and topographically varied areas in other eastern and western Mediterranean sectors and Strait of Sicily basins. Their 

rate of accumulation is generally lower (<25 cm / 
NUMBER 19 

FIGURE 3.—Schematic of suspended sediment transport possibly applicable to the Mediterranean at times when water masses were stratified. Concentrations of suspensates (stippled areas) 

are shown as detached turbid layers along pycnoclines, and as bottom nepheloid layer, driven 

by bottom current circulation, on slope to basin plain. (Large arrows depict flow of water 

masses, a pattern similar to off U.S. East Coast, after Pierce, 1976.) 

1000 years) than that of other mud types emplaced by sediment gravity flows, but distinctly 

higher than that of hemipelagites (<10 cm/1000 

years). It is recalled that the proportion of thick 

unifites, emplaced by low concentration bottomhugging flows, is reduced during the period of 

finely laminated mud deposition. 

These considerations provide the basis for a 

generalized depositional model relating finely 

laminated facies with low concentration flows in 

a stratified water column (Figure 5). Th e scheme 

emphasizes introduction of particles from (1) 

gravity-driven flows entering along basin margins, and from (2) hemipelagic settling from surface waters. Concentrations of particles spread 

broadly on density interfaces in the water column 

as continuous or detached turbid layers. Th e 

progressive release of silt and clay size material 

over large areas of the seafloor is contrasted to 

material carried along the bottom by turbidity 

currents which, morphologically constrained, are 

more limited in seafloor surface distribution. 

Closer examination of finely laminated mu d types 

elucidates this model. 

Finely Laminated Mud Variants 

Finely laminated facies are most reliably recognized by combined radiography and petrography. Th e most diagnostic criterion is closely 
10 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

NORTH 

FIGURE 4.—Plexus of sediment processes on the Nile cone during phases of Mediterranean 

stratification (after Maldonado and Stanley, 1978). Dense turbidity currents (TC) cross 

pycnoclines as they flow downslope along the bottom, while lower concentration suspensaterich zones form detached turbid layers (DTL) on pycnoclines. (Other symbols: AC = Alexandria 

Canyon; HBP = Herodotus Basin plain; RB = Rosetta Branch; RCD = Relict coastal and 

neritic deposits; SB = stratification barrier; SL = slump; SO = shelf-edge spill-over; SP = sand 

pods on Nile cone; TD = sediment turbid discharge off the Rosetta Branch of the Nile.) 

spaced, parallel (<0.5-5.0 mm) laminae. These 

are sometimes visible in split cores (Ryan et al., 

1973; Hsu et al., 1978), but always much better 

defined by density differences observed in radiographs (Figure 6). Parallel laminae in some Mediterranean basins are often indistinct, particularly 

in shallower (<1500 m) settings (Figure 6B). In 

contrast, they are well developed in deeper basins 

and particularly those in the Hellenic Trench 

area (Got et al. 1977, fig. 4; Stanley and Maldonado, 1981, fig. 3). 

Core sections that comprise largely fine laminated facies in some of the deeper Hellenic 

Trench basins are dark olive gray. Most laminae 

are varve-like in that they consist of paired alternating layers of different mineralogy; a lamellar 

pair is termed a couplet. Some individual laminae, or couplets, do not clearly display a finingupward texture (Figure 6D). Commonly, however, 

laminae couplets show diverse fining-upward 

trends (Figure 6c, E-G) involving changes from 

clayey silt to silty clay (textural data from Smithsonian Sedimentology Laboratory data base). 

SEM analysis of the silt fraction shows that the 

layering apparent in radiographs consists of alternating coccolith- and silty clay-enriched oozes. 
NUMBER 19 11 

PROCESS 

''(HP ) 

ISLUMPING 

ii (HI 

ISUSPENSiONl 

i (HI 

MUD FLOW TURBIDITY CURRENT 

DEBRIS FLOW|-»"rTURBIDITY CURRENT 

DEPOSIT LARGELY 

FROM GRAVITATIVE 

PROCESSES: 

-F 

(CHAOTIC 

MASS) 

(DEBRIS FLOW (COMPLETE 

DEPOSIT) TURBIDITE) 

1 -\7 

j TURBID LAYER FLOW *— 

T 

ROLE OF STRATIFICATION 

• •••••••••• I 

INTERFACE AS BARRIER 

I DETACHED TURBID LAYER FLOW"! 

DEPOSIT FROM GRAVITATIVE 

& SUSPENSION-RELATED PROCESS rnTrrr" WELL-LAMINATED MUD- ! 

OCCURRENCE: PRIMARILY AREA OF RELIEF WIDESPREAD DISTRIBUTION IN STUDY AREA 

•»»- ) 

DISTAL BASIN 

PLAIN 

FIGURE 5.—Depositional model showing a basinward transformation continuum of gravitydriven processes, i.e., mechanisms of decreasing concentrations, from slumping to low density 

turbid layer flows. An important stratification interface in the water column serves as a barrier 

to particles released from low concentration turbidity currents and turbid layer flows and also 

from hemipelagic (H.P.) suspension settling. As a result of the interface, particles are distributed 

over large areas of a basin and eventually settle out as finely laminated layers, often graded. 

The nature of the stratification interface controls the degree of grain retention and ultimate 

release of terrigenous grains and pelagic components particles, which settle according to size 

and density. Periodic variations in organic productivity and fluctuations in particle density and 

settling rate give rise to varve-like alternations of coccolith- and terrigenous-rich layers, many 

of which display fining-upward trends (see Figure 6E-F). 

Radiographs reveal no two identical sequences of 

parallel laminated structures. Variations occur 

with respect to proportions and thicknesses of 

coccoliths and silty clay-rich layers (compare, for 

example, Figure 6c and D). Varved and graded 

finely laminated sections also vary with respect 

to coarseness of material. Occasionally, large 

planktonic tests such as pteropod shells are observed, and these usually are flat-lying and buried 

by fine laminae (Figure 6A). Alternations of coccoliths and clastic silt and clay aggregates may in 

some instances enclose important proportions of 

larger particles, such as disseminated organic 

matter (Figure 7A, B) and concentrations of planktonic tests (usually foraminifera, Figure 7c). 

Petrographic examination of the coarse fraction (>62 jtim), separated from finely laminated 

mud from different parts of the Mediterranean, 

reveals that in almost all instances, the bulk 

(>70%) of the coarse fraction comprises planktonic tests. Foraminifera dominate, but pteropods 

may be locally important. Benthic shell material 

usually accounts for less than 10%, while terrigenous grains generally exceed 10%. Within-core 

and core-to-core variations in the above-cited 

proportions of these mineralogical components 

are observed. 

On the basis of structure, texture, and composition the Mediterranean deep-water finely laminated facies generally can be distinguished from 

muds of purely pelagic (with little or no terrigenous components) suspension and even from 

those of essentially hemipelagic (mixed planktonic and terrigenous components) settling origin. 
12 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

B C D 

,»^M | 

H 

B9 

-

jfHHr 

//^mt^^^^^ 

• 

-'''^MH^^H 

'^iiflH 

tmm ail 

, '& 

W4 

m 

m 

0 

3cm 
NUMBER 19 13 

V 

0 cm 

FIGURE 7.—Selected radiograph prints: A,B, disseminated organic matter (some pyritized); c, 

concentrations of planktonic foraminiferal tests in finely laminated core sections. (Cores are 

from the western Hellenic Trench: A, Trident core 172-34, Zakinthos Trench; B, Marsili core 8, 

Matapan Deep; c, Marsili core 14, Gulf of Laconia, south of Peloponnesus; locations shown in 

Stanley and Maldonado, 1981.) 

The amount of sand fraction in laminated mud 

(about 2% by weight) is lower than that in typical 

Mediterranean hemipelagic muds (to >5 % by 

FIGURE 6.—Selected radiograph prints showing variations of 

finely laminated muds: A,B, examples of distinct and vague 

fine parallel laminations; C,D, two different types of varvelike stratification, both showing importance of coccolith 

(light) layers; individual pairs, or couplet, of laminae show 

fining-upward trends, but overall the entire laminated sequence is not graded (unlike turbidite section in Figure 2c); 

E-G, thicker fining-upward (arrows) type of finely laminated 

sections, comprising largely coccoliths and pelagic components rather than terrigenous silty clay in typical laminated 

mud turbidites (Figure 2B-D). (Arrow in A points to pteropod 

buried by finely laminated coccolith ooze; A,D, Trident core 

172-34 in Zakinthos Trench basin; c, E-G, Trident core 172-

36 in Strofadhes Trench basin, in western Hellenic Arc (core 

locations shown in Got et al., 1977).) 

weight); sand in the latter commonly produces 

speckling observed in radiographs (He in Figure 

2D). Moreover, hemipelagite sections, such as 

those in the Hellenic Trench, generally contain 

higher (>80%) contents of foraminifera and pteropods in the sand fraction and contain coccoliths 

in the silt fraction. 

Parallel laminated muds also can be distinguished from some laminated mu d turbidites on 

the basis of associated structures and composition. 

Unlike laminated mud turbidites (Figure 2c; also 

examples in Stow and Bowen, 1980), fine parallel 

laminated deposits (Figure 2B-D ) are not sharpbased nor are they texturally graded, i.e., showing 

a progressive decrease in mean grain size and 

lamina thickness from the base to the top of the 

laminated bed. Moreover, bedforms commonly 
14 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

attributed to traction, such as wave ripples and 

cross-laminations that commonly occur in mud 

turbidites (Figure 2B, D), are absent from finely 

laminated facies. Finely laminated muds do not 

show load structures and only rarely do they show 

bioturbation. 

Both laminated mud turbidites and finely laminated muds may contain comparable proportions of sand (to about 2% by weight), but sand 

in turbidites usually contain a higher (to >30%) 

terrigenous grain content (from mineral count 

data base, RJ . Knight, in litt.). SEM analyses 

reveal reworked biogenic components, including 

pre-Pleistocene coccoliths, in both mud turbidites 

and finely laminated facies. However, there is a 

higher proportion of coccoliths in the silt fraction 

and foraminifera in the sand fraction of some 

finely laminated mud couplets than in turbidites. 

It is noted that some fining-upward laminated 

core sections cannot strictly be attributed to fine 

parallel laminated mud, laminated mud turbidite, or hemipelagic mud facies. Apparently there 

exists a petrologic continuum among these types. 

Implications and Conclusions 

An association of different laminated endmember mud types most likely occurs in settings 

where two or more transport processes are involved. A continuum of fine-grained facies and a 

blurring of their origin should be expected where 

long distance transport increases the possibility of 

interplay among turbiditic, traction, and hemipelagic settling mechanisms. The Northwest Atlantic margin off the U.S. East Coast and Canadian Maritime Provinces, where most sedimentologic studies of fine-grained deposits have been 

made, serves as a good example. In this region 

the possible origins for lamination are reviewed 

by Stow and Bowen (1980). In the case of the 

mud turbidite end-member, these authors propose a model involving thick flows of low concentration in which laminae formation results from 

depositional sorting by increased shear near the 

base of the bottom boundary layer. 

Theoretical considerations and textural-fabric 

analysis of laminated turbidite core sections call 

attention to systematic upward and lateral-downslope decreases in modal grain size and laminae 

thickness. In contrast, lamination in typical finegrained contourites (the term is used here as 

applied by Heezen and Hollister, 1971:420) results from fluctuations in sediment flux and accumulation by both traction and suspension 

release mechanisms. Some criteria of mud contourites are sharp base and top of bedding contacts, both normal and reverse grading, common 

cross-lamination, and preferred grain orientation 

parallel to the bedding plane throughout a bed 

(Hollister and Heezen, 1972; Stow and Lovell, 

1979). However, review of published radiographs 

and descriptions of laminated mud core sections 

in large basins, such as the Atlantic, show that 

petrologic distinction between fine-grained turbidites and contourites is by no means clear-cut. 

The petrology of certain laminated mud sections 

interpreted as turbidites suggests a more complex 

origin involving release from suspension and/o r 

fluid-driven circulation; other sections interpreted as contourites appear difficult to distinguish from low concentration turbidity current or 

turbid layer deposits. 

Physical and chemical attributes of the much 

smaller and shallower Mediterranean serve to 

amplify petrologic differences that are not so 

apparent among fine-grained, deep-water deposits in large ocean basins. Important Mediterranean characteristics include periodic development of well-stratified water masses, relatively 

small distance between point of sediment input 

and final depositional site, generally low bottom 

current velocities in deep basins, and preservation 

of carbonate components. During specific periods 

in the recent past, oceanographic conditions, and 

thus sedimentation in the Mediterranean were 

somewhat more comparable to other world 

oceans. Sediment transport involved (1) periodic 

injection of sediments and their displacement 

downslope by gravity flows of low concentration, 

(2) deviation of such flows diagonally or parallel 

to the margin by current-driven circulation, (3), 

incorporation, concentration, and displacement 
NUMBER 19 15 

of particles from turbidity current-derived suspensates and hemipelagic settling on pycnoclines 

and in near-bottom nepheloid layers, and (4) 

eventual release of these particles through density 

interfaces and from nepheloid layers to the seafloor. A laminated sequence resulting from this 

plexus of mechanisms is neither a mud turbidite, 

hemipelagite, or contourite in the strict sense. 

On the basis of the petrology of Mediterranean 

laminated muds, described in the previous section, it is possible to distinguish (1) laminated 

mud turbidite and (2) hemipelagic mud endmembers from (3) a deposit originating by coupled sediment gravity flow-hemipelagic settling. 

The multiple-origin deposits, "(3)," are varve-like 

and record episodic fluxes preserved as thin, alternating sequences of clastic components that 

include reworked benthic and planktonic faunas 

mixed with clayey silt and layers comprising almost entirely tests of recent pelagic organisms. 

Two other diagnostic criteria of these finely laminated sequences are rates of deposition and areal 

distribution. Core sections show that fine parallel 

laminated facies, like those of hemipelagites, tend 

to accumulate over broad areas of a basin and its 

contiguous margins (cf. Stanley and Maldonado, 

1981, fig. 7). These muds, recording periodic 

injection by sediment gravity flows, accumulate 

at higher rates (>15 cm/1000 years) than hemipelagic deposits. In contrast to turbidites and 

unifites that are somewhat richer in terrigenous 

components and accumulate at higher rates, regional core surveys show that finely laminated 

muds display a regionally more consistent thickness and broader distribution, and are less restricted to specific depositional environments. 

The model emphasized here (Figure 5) indicates that stratification interfaces in the water 

column that affect particle retention are important for interpreting some types of fine-grained 

lamination. This scheme suggests that distinct 

pycnoclines modify particle concentration and 

particle release rates through the water column 

so as to segregate terrigenous silt and clay floes 

from planktonic tests. A well-marked density interface amplifies differences in particle release 

and settling rates through the column by density 

and size, thus resulting in (1) more effective separation of coccolith from terrigenous silty clay 

layers and (2) better development of fining-upward trends of laminae sets (Figure 6E-G). The 

varve-like configurations in Figure 6A- D record 

repetition of depositional events and modifying 

effects of pycnoclines, i.e., injection of material by 

turbidity currents and turbid layers, retention of 

periodic planktonic blooms, largely coccoliths, 

and their subsequent settling to the seafloor. 

Compositional segregation of coccoliths from terrigenous clayey silts, as distinct laminae, appears 

less well developed in laminated mu d turbidites 

than in the fine parallel mud facies. On the basis 

of an averaged depositional rate of 20 cm/1000 

years, each laminae couplet is deposited during a 

2 to 20 year period. 

On the other hand, the downslope decrease of 

grain size and laminae thickness measured in 

mud turbidites (cf. Stow and Bowen, 1980) is less 

obvious in finely laminated facies. In this respect, 

the geometry of Mediterranean upper Pleistocene 

to lower Holocene finely laminated facies (Huang 

and Stanley, 1972; Maldonado and Stanley, 

1976a; Stanley and Maldonado, 1981), recalls the 

configuration and distribution of fine parallel, 

silt-rich layers mapped over large sectors of the 

Delaware River Basin of Texas-New Mexico in 

middle Permian time. These latter laminated, not 

conspicuously graded, facies, deposited as a function of density-stratified water mass conditions, 

show no obvious proximal to distal changes 

(Harms, 1974). Hydrography and sediment gravity flows are major factors in both these modern 

and ancient deposits. Sediment gravity flows that 

displace at least 1 km' of sediment are not uncommon in Mediterranean basins (Blanpied and 

Stanley, 1981:29). Flows of this magnitude introduced into the isothermal regime, which has prevailed during the past 6000 years, are responsible 

for turbidites and unifites ranging in thickness 

from 30 cm to over 1000 cm in small basins, such 

as those of the Hellenic Trench. However, displacement of equivalent sediment volumes as low 

concentration flows, at times of a stratified water 
16 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 

regime, would result in much broader distribution of material. Varve-like sets released from 

about 1 km3 of sediment spread over large parts 

of basins, such as the Ionian or Algero-Balearic, 

would likely be less than 1 cm thick (Stanley, 

1981:83). 

Laminae preservation also sheds light on depositional origin. Some cores from the Aegean, 

Siculo-Tunisian (Pelagian) Platform (Maldonado 

and Stanley, 1976a; Blanpied, 1978), Corsican 

Trough (Stanley et al., 1980), Alboran Sea 

(Huang and Stanley, 1972), and other areas show 

indistinct (Figure 6B) or disturbed laminae recording the influence of bottom currents, or organisms, or both. In contrast, 10 to 40 cm-thick 

sections of undisturbed laminated units in the 

Hellenic Trench region indicate that deposition 

was rapid, that the influence of bottom currents 

was negligible and, more importantly, unfavorable oxygen-deficient conditions on the seafloor 

reduced benthic populations, thus minimizing 

disturbance of surficial sediments. Moreover, it is 

recalled that the well-preserved finely laminated 

mud sections have a basin-wide and temporally 

extensive distribution. It thus appears that upper 

Pleistocene to Holocene lamination in the Mediterranean was not produced by an oxygen minimum layer restricted to a specific horizon in the 

water column as recorded in the present Gulf of 

California (Calvert, 1964). Preservation of laminae is most likely related to the formation of 

thicker, more extensive columns of oxygen-deficient water and to anoxic seafloor conditions of 

the Black Sea (Arkhangel'skiy, 1927) and deep 

fjord (Strom, 1939) types; the absence of benthic 

organisms is an important factor in the preservation of well-defined parallel laminae, as illustrated by Miiller and Stoffers (1974, fig. 4). 

The varved aspect calls to mind the relation 

between sedimentary structures and organisms in 

some stratified basins off Southern California. 

There, it has been shown that small-scale and 

short-term changes in oxygen content can induce 

rather significant alterations in organic productivity, including coccolith and foraminiferal 

blooms, and modifications of benthic populations. Physico-chemical changes needed to transform hospitable to inhospitable conditions at 

depth may be small; moreover, such changes may 

occur suddenly or gradually and, as in the case of 

lakes, seasonally (cf, Hiilseman and Emery, 

1961:289). Inhospitable conditions on the seafloor, such as at times of sapropel formation, 

result in diminution or absence of benthic populations and enhanced probability of lamina preservation (Moore and Scruton, 1957). Bottom 

camera and sediment sampling surveys in various 

Mediterranean basins demonstrate that, at present, conditions above the seafloor are highly suitable for sustaining important benthic populations. High concentrations of feeding and burrowing structures indicate that fine lamination developed in recent time, at least since about 6000 

years B.P., would not likely be preserved. 

In summary, the study emphasizes the significance of climatic-oceanographic factors, the involvement of two or more processes in the development of lamination of fine facies in deep-marine environments, and that laminated muds are 

not necessarily turbidites or contourites in the 

strict sense. Observations made here commonly 

prevail and are not unique to the Mediterranean. 

In consequence, mud deposits of the type described herein—redeposition of margin sediments 

by gravity flows coupled with hemipelagic settling through a stratified water column—could 

probably be recognized in diverse marine settings. 

T he mechanism deserves to be quantified. Continuing investigation of mud lithofacies in small 

to moderate seas holds promise for better interpretation of fine-grained deposits in the larger 

world oceans and the sedimentary rock record. 
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