Calcium Carbonate, Organic 

Carbon, and Nitrogen in 

Sediments From Drill Holes 

on the Continental Margin 

Off Florida 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 581-B 

Prepared in cooperation with the Woods Hole 

Oceanographic Institution and the Joint 

Oceanographic Institutions' Deep Earth 

Sampling Program 

Calcium Carbonate, Organic 

Carbon, and Nitrogen in 

Sediments From Drill Holes 

on the Continental Margin 

Off Florida 

By JOBST HDLSEMANN 

DRILLING ON THE CONTINENTAL MARGIN OFF FLORIDA 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 581-B 

Prepared in cooperation with the Woods Hole 

Oceanographic Institution and the Joint 

Oceanographic Institutions' Deep Earth 

Sampling Program 

Analytical results and interpretations of organic 

constituents of core samples from the continental 

shelf, the Florida-Hatteras Slope, and the Blake 

Plateau 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1968 
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEW ART L. UDALL, Secretary 

GEOLOGICAL SURVEY 

William T. Pecora, Director 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 20 cents (paper cover) 
DRILLING 

ON THE CONTINENTAL MARGIN 

OFF FLORIDA 

Drilling on the continental margin off Jacksonville, 

Fla., in 1965 was the first project undertaken by the 

Joint Oceanographic Institutions' Deep Earth Sampling (JOIDES) Program, sponsored by the National Science Foundation. The U.S. Geological 

Survey cooperated with the Oceanographic Institutions in this undertaking and is publishing the results 

of these investigations in a series of professional 

papers. 

CONTENTS 

Page Page 

Abstract ____________________________________ --_____ Bl Blake Plateau______________________________________ B6 

Introduction ______________________________________ _ Results________________________________________ 6 

Geographic and geologic setting______________________ 1 

~ethods___________________________________________ 3 

Interpretation__________________________________ 7 

Summary and conclusions ___________ ----- __ -- __ -----_ 10 

Continental shelf and upper Florida-Hatteras Slope_____ 3 References_________________________________________ 10 

Results _____________________ ----- _________ ----- 3 

Interpretation__________________________________ 5 

ILLUSTRATIONS 

Page 

FIGURE 1. Index map and stratigraphic profile____________________________________________________________________ B2 

2-5. Graphs showing relation of organic constituents to2. Depth, continental shelf and upper Florida-Hatteras Slope sediments________________________________ 4 

3. Depth and geologic age, continental shelf and upper Florida-Hatteras Slope sediments_________________ 4 

4. Depth, Blake Plateau sediments_________________________________________________________________ 6 

5. Depth and geologic age, Blake Plateau sediments__________________________________________________ 7 

6. Graphs comparing average percentage of organic constituents in shelf and slope sediments with that in Blake 

Plateau sediments_______________________________________________________________________________ 8 

7. Stratigraphic profile showing percentage distribution of organic carbon in continental shelf, upper FloridaHatteras Slope, and Blake Plateau sediments_______________________________________________________ 9 

TABLE 

Page 

TABLE 1. Calcium carbonate, organic carbon, and nitrogen contents, and carbon-nitrogen ratio of samples from JOIDES 

core holes 1-6------------------------------------------------------------------------------------ B3 

v 

DRILLING ON THE CONTINENTAL MARGIN OFF FLORIDA 

CALCIUM CARBONATE, ORGANIC CARBON, AND NITROGEN IN SEDIMENTS FROM DRILL HOLES 

ON THE CONTINENTAL MARGIN OFF FLORIDA 1 

By JOBST H ULSEMANN 

ABSTRACT 

The organic constituents of sediments (calcium carbonate, 

organic carbon, and nitrogen) from six drill holes off Florida 

were analyzed in 47 samples. The drill holes penetrated the 

continental shelf, the upper Florida-Hatteras Slope, and the 

Blake Plateau. Differences in distribution and abundance of the 

organic constituents strongly suggest that two facies were 

deposited during the span of geologic time (Paleocene to Recent) 

represented by the samples. One facies (low organic carbon and 

nitrogen, uniform carbon-nitrogen ratio, and high calcium 

carbonate content) is characteristic of the Blake Plateau; the 

other facies (higher organic carbon and nitrogen, a carbonnitrogen ratio that increases with age, and relatively low calcium 

carbonate content) is typical of the shelf and of the upper FloridaHatteras Slope. 

Some significant differences in the concentrations of the 

organic constituents are correlated with changes in the rates of 

supply and accumulation of sediment. These changes appear 

to be related to tectonic movement of the sea floor or the adjacent lowland of Florida, rather than to climatic changes. 

In the sampled parts of the offshore area, the upper FloridaHatteras Slope is the most favorable site for the accumulation 

of organic matter. 

INTRODUCTION 

Organic matter is a common constituent of many 

marine sediments. It has been determined in previous 

studies for several thousand samples from the floors of 

the present oceans. Most of these samples are of surface 

sediment, and few data are available from samples 

taken deeper than several meters below the bottom of 

the ocean. 

Organic matter in marine sediments can be derived 

from land as well as from the ocean. After burial, the 

original composition of organic matter is altered by 

diagenesis. Differences in composition, such as expressed 

by the carbon-nitrogen ratio, can help to identify the 

source and subsequent fate of the organic matter, and 

thus give clues to the environmental history of the area. 

l Contribution No. 2042 of the Woods Hole Oceanographic Institution. 

In the spring of 1965, thefirstJOIDES (Joint Oceanographic Institutions' Deep Earth Sampling) Program 

succeeded in drilling six holes off northern Florida 

(Joint Oceanographic Institutions' Deep Earth Sampling Program, 1965) to depths ranging from 120 to 320 

meters below the sea floor. The following report presents 

analytical results and an interpretation of the origin 

and the diagenetic changes of organic matter based on 

4 7 samples from JOIDES drill holes. Organic constituents were determined as (1) organic carbon, (2) nitrogen 

(Kjeldahl), and (3) total carbonate as calcium carbonate. The last is included because it is of biogenic origin. 

The samples were collected by a team working on the 

drilling vessel M(V Oaldrill I with John Schlee as 

principal scientist. Mrs. M. Hamilton performed most 

of the chemical analyses. My colleagues, in particular 

John Schlee and J. C. Hathaway, U.S. Geological 

Survey, promoted the work by their comments and 

discussions. Suggestions from Henry Berryhill, Jr., of 

the Survey also improved the manuscript. The help of 

all persons is gratefully acknowledged. 

GEOGRAPHIC AND GEOLOGIC SETTING 

The holes were drilled on the continental shelf, the 

upper Florida-Hatteras Slope, and the Blake Plateau, 

off northern Florida. At the outer edge of the shelf, the 

depth of water is only 60 meters, which is considerably 

less than depths of the shelf break in other parts of the 

world. The adjoining Florida-Hatteras Slope dips about 

4°, leveling off at about 800 meters depth of water and 

connecting to the Blake Plateau. The plateau slopes 

generally seaward, at a rate comparable to the slope of 

the present shelf, to a depth of about 1,000-1,200 

meters. Holes 1 and 2 (fig. 1) are on the continental 

shelf in less than 50 meters of water, and hole 5 is on 

the upper part of the Florida-Hatteras Slope at a depth 

Bl 
B2 DRILLING ON THE CONTINENTAL MARGIN OFF FLORIDA 

of 190 meters. Holes 3, 4, and 6 are on the Blake Plateau, 

between 200 and 400 kilometers offshore. Less than 50 

kilometers seaward from the outermost hole (No. 3), 

the Blake Plateau joins the deep-sea floor by the 

Blake Escarpment, a slope that is slightly steeper than 

most other continental slopes. 

The axis of the Gulf Stream crosses the line of 

JOIDES drill holes between holes 5 and 6. Although 

measurements of the velocity of the Gulf Stream indicate a marked decrease of velocity with depth (Swallow 

and Worthington, 1961), sediment samples and bottom 

photographs strongly suggest that the bottom current 

is sufficient to transport sediment both on the shelf 

and on the Blake Plateau (Pratt, 1963), Oriented 

bottom photographs of ripple marks led Hurley and 

Fink (1963) and Heezen, Hollister, and Ruddiman 

(1966) to believe that the bottom current flows predominantly southward, or opposite to the flow of the 

Gulf Stream. 

en 

a:: 

UJ 

t 

:E 

200 

400 

~ 600 

:i 

t 

UJ 

0 

800 

1000 

1200 

VERTICAL EXAGGERATION X 222 

200 

Seismic-reflection profiles show upbuilding and prograding of the shelf and almost continuous deposition 

of sediments on the Blake Plateau since at least the 

early part of the Tertiary, although some areas have 

been eroded by currents (Emery and Zarudzki, 1967). 

The core records for holes 1 and 2 include strata of 

Eocene age, and those for holes 4 and 6 include Paleocene strata. Miocene strata are absent from holes 5 and 

6, and incomplete Miocene and Eocene sequences were 

penetrated in holes 3 and 4. (Joint Oceanographic 

Institutions' Deep Earth Sampling Program, 1965). 

With the exception of some nearshore Miocene silts 

and clays, the strata are chiefly calcarenites or lime 

stones that are medium to coarse grained under the 

shelf and fine grained and less well sorted farther off 

shore. Phosphate pebbles were found only under the 

shelf. Several volcanic-ash beds were found beneath the 

Blake Plateau (Joint Oceanographic Institutions' Deep 

Earth Sampling Program, 1965). 

DISTANCE, IN KILOMETERS 

I 

CONTINENTAL I FLORIDA-I 

LAND SHELF HATTERAS 

SLOPE 

BLAKE PLATEAU 

VERTICAL EXAGGERATION X 10 

!BLAKE 

ESCARPIMENT 

FIGURE 1.-Location of drill holes, JOIDES drill holes 1-6, 1965, and stratigraphic profile. Actual inclination of Florida-Hatteras 

Slope is about 4°. GGS 876 and FB refer to earlier drill holes in Florida. (Modified from Joint Oceanographic Institutions' 

Deep Earth Sampling Program, 1965.) 
CALCIUM CARBONATE, ORGANIC CARBON, AND NITROGEN IN DRILL-HOLE SEDIMENTS B3 

METHODS 

Most samples were collected at depth intervals of 

I0-30 meters, with closer spacing near the surface. 

An effort was made to sample the sediment types 

most typical of the entire section; however, only onethird, on the average, of the total drilled section was 

recovered in the core barrel. Details of the coring 

procedure were given by Schlee and Gerard (I965). 

Carbonate was determined by a gasometric method 

(Hiilsemann, I966). The amount of carbon dioxide 

genera ted by digestion of a sample with 2-normal hydrochloric acid was measured and computed as equivalent 

of calcium carbonate (table I). 

Organic carbon was determined by rapid dry combustion of the solid residue of the acid-treated sample 

in an induction furnace. As the sample is free of carbonate, the most common and abundant form of 

"inorganic" carbon, the carbon value obtained in this 

process is considered to be the ''organic'' carbon content 

of the sample (table I). 

Nitrogen was measured by micro-l{jeldahl analysis 

of sample fractions that were previously washed in 

distilled water. The quantities of nitrogen are reported 

as numerical values in percent dry weight of the original 

sediment in table 1. No attempt was made to convert 

the values of either nitrogen or organic carbon to total 

organic matter; however, the use of conversion factors 

for this purpose was discussed by Bader (I954). 

TABLE 1. Calcium carbonate, organic carbon, and nitrogen contents, 

and carbon-nitrogen ratio of samples from JOIDES core holes 

1-6 

[Analysts: Madalyn Hamilton and Jobst Hiilsemann] 

Depth Calcium Organic Nitrogen below carbonate carbon (Kjeldahl) Carbon- sea Geologic age (CaC03 in (percent (percent nitrogen floor percent dry dry ratio 

(meters) dry weight) weight) weight) 

Core hole 1 

TABLE 1. Calcium carbonate, organic carbon, and nitrogen contents, 

and carbon-m:trogen ratio of samples from JOIDES core holes 

1-6-Continued 

Depth 

below 

sea Geologic age floor 

(meters) 

0 ______ __I Post-Miocene_----- __ _ 

15 _______ 1 Late(?) Miocene _____ _ 

23 _______ Middle Miocene _____ _ 30 ____________ do ________________ _ 

6L ______ Early Miocene _______ _ 

92_ ___ _ __ Oligocene ____________ _ 

122 ___________ do ________________ _ 

153 ______ Middle Eocene _______ _ 

0 ________ Post-Miocene ________ _ 

2L ______ Early Miocene _______ _ 34 ____________ do ________________ _ 

7L _ _ _ __ _ Oligocene ____________ _ 

84 _______ Early Eocene ________ _ 

135_____ _ Paleocene ____________ _ 154 ___________ do ________________ _ 

168 ___________ do ________________ _ 

0 ________ Post-Miocene ________ _ 

11 ____________ do ________________ _ 

20 ____________ do ________________ _ 

30 ____________ do ________________ _ 

61 ____________ do ________________ _ 

95_ ______ Oligocene ____________ _ 

124 ___________ do ________________ _ 

154 ___________ do ________________ _ 

199 ___________ do ________________ _ 

0 ________ Post-Miocene ________ _ 

8____ ___ _ Oligocene ____________ _ 

Calcium 

carbonate 

(CaC03in 

percent 

dry weight) 

Core hole 3 

93.3 

87.6 

91.8 

89.5 

89.8 

90.6 

90.4 

90.6 

Organic 

carbon 

(percent dry weight) 

0.05 

.04 

.07 

.11 

.15 

.05 

.()4 

.07 

Core hole 4 

95.6 

86.8 

80.5 

88.7 

49.9 

58.9 

48.9 

66.1 

Core hole 5 

65.1 

71.7 

62.1 

74.6 

60.8 

63.2 

66.1 

63.0 

78.1 

Core hole 6 

94.6 

88.1 

0.11 

.11 

. 21 

.09 

.18 

.28 

.30 

.18 

0.91 

.14 

.55 

.44 

.93 

1. 22 

1.18 

1.13 1. 351 

0.08 

.13 

Nitrogen 

(Kjeldahl) Carbon-

(percent nitrogen dry ratio 

weight) 

0.010 5.3 

.012 3.2 

.009 7.8 

.011 10.1 

.013 11.5 

.006 8.3 

.007 5. 7 

.008 8. 7 

0.012 9.2 

.017 6.5 

.023 9.1 

.006 15.0 

.014 12.8 

.020 14.0 

.031 9. 7 

.021 8.6 

0.139 6.5 

.017 8.2 

.035 15.7 

.038 11.6 

.078 11.9 

.067 18.2 

.071 16.6 

.072 18.7 

.052 21.7 

0.022 3.6 

.006 21.6 o ________ Post-Miocene _________ 19.2 0.11 0.024 4. 7 15 ____________ do ________________ _ 91.3 .08 .009 8.9 

15 _______ Miocene ______________ 68.2 .71 23 _______ _____ do _________________ 46.1 1. 03 30 _______ _____ do _________________ 2.9 .90 

62 _______ _____ do _________________ 20.0 1.04 93 _______ _____ do _________________ 59.7 1.20 273 _____ - Middle Eocene ________ 99.0 .17 

Core hole 2 

o _______ - Post-Miocene __ ------_ 39.8 0.13 68 _______ Late Miocene _________ 52.1 1.13 10L _____ Early Miocene ________ 62.9 1.10 134 ______ Oligocene _____________ 81.4 . 75 

152 ______ Late Eocene __________ 83.6 1. 20 184 ______ _____ do _________________ 89.7 .23 214 ______ _____ do _________________ 84.9 .20 276 ______ Eocene ________________ 83.1 .48 

.041 

.083 

.058 

.108 

.073 

.008 

0.012 

.063 

.082 

.040 

.060 

.011 

.015 

. 014 

17.3 23 ____________ do ________________ _ 91.9 .09 .005 18.0 

12.8 

15.8 30 ____________ do ________________ _ 87.6 .05 .007 7.1 

6L ______ Late Eocene __ , ______ _ 82.4 .03 .007 4.6 

9.8 93 _______ Middle Eocene _______ _ 85.2 .07 .008 8.8 

16.4 

21.6 

11.8 

17.9 

13.4 

18.6 

20.1 

20.9 

13.3 

34.2 

CONTINENTAL SHELF AND UPPER FLORIDAHATTERAS SLOPE 

RESULTS 

The abundances of carbonate (as calcium carbonate), 

organic carbon, and nitrogen in sediments of the shelf 

and slope are plotted in figures 2 and 3 against depth 

of the samples below the sea floor for each of the drill 

holes. In figure 3 each sample value is coded to indicate 
B4 

0::.-

0 

g 

...... 

iS 

(1')150 

~ co 

:c 

~ 

~ 200 

250 

CALCIUM CARBONATE. 

IN PERCENT 20 40 60 80 100 

DRILLING ON THE CONTINENTAL MARGIN OFF FLORIDA 

0.0 

ORGANIC CARBON, 

IN PERCENT 0.4 0.8 

r 

I 

I 

_.....--_.,..-" 

\ 

\ 

NITROGEN (Kjeldahl), 

IN PERCENT 1.2 1.4 0.00 0.08 0.12 0.14 ~~~--~--.--. 

EXPLANATION 

Core hole 1 Core hole 2 Core hole 5 

CARBON- NITROGEN 

RATIO 0 10 20 30 

\ 

.\ 

u 

\ 

\ 

\ 

\ 

FIGURE 2.-Relation of organic constituents to depth in samples from JOIDES drill holes on the continental shelf and the upper 

Florida-Hatteras Slope. 

en 

0::. 

...... 

50 

~ 100 

~ 

at: 

0 

~ 

~ 150 3: 

g 

...... 

co 

:c 

~ 

~ 200 

250 

CALCIUM CARBONATE, 

IN PERCENT 20 40 60 80 100 

ORGANIC CARBON, 

IN PERCENT 

T~~ ~~'I 

6\ 

0 

J~ \ 

o1 I 

I 

... ? 0 

•''I ................... ·· I 

0.······ I 

/ /o 

<t> 

. I 

o\ o 

NITROGEN (Kjeldahl), 

IN PERCENT 0.00 0.04 0.08 

t:. I 

q6jt:. 

I 

I 

to 

o I 

I 

.. .~0 I ... ··•• I 

<:;(... I . I : I : 10 

r 

<:i.o 

EXPLANATION 

0.12 

o---- 6----- 0------ 0·· ............... .. 

Post-Miocene Miocene Olillocene Eocene 

69 \6 

6'\:, 

\ 

\ 

~ & ,: 

t 

* /6 

of 

o\. o 

FIGURE 3.-Relation of organic constituents to depth and geologic age of sediments of the continental shelf and upper FloridaHatteras Slope. 
CALCIUM CARBONATE, ORGANIC CARBON, AND NITROGEN IN DRILL-HOLE SEDIMENTS B5 

the geologic age that it represents; the curves are 

averaged for the different geologic epochs. 

Calcium carbonate is moderately abundant to abundant in the strata beneath the shelf and ranges from 

20 to 90 percent (fig. 3). The amount is most variable 

in sediments of post-Miocene age. The content is 20 

percent in uppermost Miocene sediment and increases 

rather uniformly downward to 90 percent in the oldest 

strata of Eocene age. The apparent change in calcium 

carbonate abundance from moderately high concentrations in the post-Miocene to low concentrations in the 

Miocene is caused by averaging data from nearshore 

and offshore holes 1 and 5. The carbonate is derived 

chiefly from molluscan shell fragments, foraminiferal 

tests, algae, and coral debris (Joint Oceanographic 

Institutions' Deep Earth Sampling Program, 1965). 

The concentrations of organic carbon and nitrogen vary 

by more than one order of magnitude: 0.1-1.4 percent and 

<0.01-0.14 percent, respectively (fig. 2). Carbon and 

nitrogen are least abundant in the oldest and in the 

youngest sediments of the nearshore holes (1 and 2), 

and they are generally most abundant in Oligocene 

and Miocene strata from both the nearshore and the 

offshore sholes (figs. 3, 7 A). The largest concentration of nitrogen, however, was found in the surface 

sediment of hole 5 on the upper Florida-Hatteras Slope. 

The carbon-nitrogen ratio is distinctly a function of 

age (figs. 2, 3) and reflects neither the absolute concentrations nor the pronounced changes in trend of the 

individual components. The average is less than 10 

near the surface and slightly more than 20 in the 

deepest and oldest strata (Eocene). The range and 

trend of the carbon-nitrogen ratio are much the same 

for all three drill holes on the shelf and on the upper 

Florida-Hatteras Slope. 

The curves in figure 3 were drawn for the averaged 

values of organic constituents separately by geologic 

epoch. This grouping reveals changes in the abundance 

of the components more clearly, particularly where the 

groupings are stretched out on a relative time scale as 

ordinate instead of a depth scale (fig. 6B). A fairly 

abrupt change in carbon and nitrogen contents occurs 

near the Eocene-Oligocene boundary, in contrast to 

the uniform gradient of calcium carbonate across the 

same boundary. 

INTERPRETATION 

Chang,es in the abundance of organic car bon and 

nitrogen with depth, or with time, may simply reflect 

changes in the amount of organic matter produced in 

the local waters. Several other factors, however, must 

be considered; for example, changes in the type of the 

original fauna and flora, changes in the rate of deposition, or changes in the physical and chemical conditions, such as temperature, pH, and Eh, that affect 

decomposition and diagenesis of the organic matter. 

The data suggest that the variation in abundance of 

organic carbon and nitrogen, and, hence, of organic 

matter, in the sediments is chiefly a function of (1) 

the total amount of original supply, rather than the 

type of original supply, and (2) the degree of preservation. The main evidence in favor of this hypothesis is 

the systematic decrease in both the carbon-nitrogen 

ratio and the carbonate concentration from Eocene 

to post-Miocene, in contiast to variations in the 

abundance of organic carbon and nitrogen characterized 

by a sudden increase at the end of the Eocene and a 

gradual decrease since the Miocene Epoch. 

A major climatic change at the end of the Eocene 

appears to be unlikely as a cause of the sudden increase 

in organic carbon and nitrogen because calcium carbonate 

(whose abundance in shelf sediments is largely a function of the climatic regime, particularly of the temperature of the water) changes so gradually. One factor that 

may affect only the amount of organic carbon and 

nitrogen preserved in the sediments but may not immediately change the carbon-nitrogen ratio nor the 

abundance of calcium carbonate is a change in the rate 

of sediment accumulation not related to a change in 

climate. Inasmuch as the Gulf Stream exerts a great 

influence on the rate of sediment accumulation off 

Florida, a shift of its axis or a change of its velocity 

may have changed the sedimentation rate enough to 

cause the observed variations in the abundance of 

organic carbon and nitrogen. An increased rate of sedimentation would tend to preserve a greater fraction of 

the organic carbon and nitrogen from oxidation, and 

may at the same time reduce the relative amount of 

calcium carbonate by dilution with clastic material. 

Volume, velocity, and course of the Gulf Stream are 

affected by the extent to which areas of Florida are 

emerged or submerged. Basically, emergence would 

nanow the water passage and increase the velocity, 

whereas submergence would permit the water to spread 

over a wider area and move more slowly. That the water 

circulation has changed appreciably is evident from the 

closing of the Suwannee Channel (between the Apalachee Bay and the Georgia Bight) during the late Eocene 

(Chen, 1965; Maher, 1965). The depth of water probably did not change greatly, as suggested by uniform 

shallow-water fossil assemblages and as reflected by 

the rather straight line of the carbon-nitrogen ratio 

(figs. 2, 3). Thus, the following sequence of events can 

be postulated: 

1. Crustal 1noven1ents led to a change of the position 

or velocity of the Gulf Stream. 

2. This change led to faster sediment accumulation in 

Eocene and Oligocene time in the area of the 
B6 DRILLING ON THE CONTINENTAL MARGIN OFF FLORIDA 

shelf holes, owing to the relative increase of clastic 

noncarbonate detritus. 

3. Rapid burial preserved a greater fraction of organic 

carbon and nitrogen. 

The lithology of the cores (John Schlee, R. L. 'Vait, 

G. W. Leve, and Eugene Shuter, unpub. data) and the 

mineralogic studies of JOIDES samples (John C. Hathaway, P. F. McFarlin, and D. A. Ross, unpub. data) 

corroborate the above theory for the Miocene and 

post-Miocene samples, and possibly for Oligocene 

samples, as these have more quartz and feldspar than 

samples from older beds. The grain size of the noncarbonate fraction is coarser in Oligocene and younger 

deposits, and phosphate pebbles occur in younger strata. 

The greatest abundance but also the greatest variation in the concentration of organic carbon occurs in 

hole 5, on the upper Florida-Hatteras Slope (Figs. 2, 7). 

Because the stability of sediments generally decreases 

with increasing slope and because slumps of large 

sediment masses have been found at the foot of many 

continental slopes, the high concentration of organic 

matter may be related to slumping. Incompletely decomposed organic matter suddenly buried under a slump 

mass should be cut off from the oxygen in the overlying 

water, so that the amount of further decomposition 

would be markedly reduced. 

BLAKE PLATEAU 

RESULTS 

The abundances of calcium carbonate, organic carbon, and nitrogen, an the carbon-nitrogen ratio as a 

function of depth beneath the Blake Plateau are shown 

in figures 4 and 5. Figure 5 shows the relation of the 

en 

0:: 

LU 

...... 

LU 

::E 

~50 

_j 

LU 

> LU 

...J 

< 

~100 

1.&.1 

~ a:l 

~150 LU 

Cl 

CALCIUM CARBONATE, 

IN PERCENT 20 40 60 80 100 0.0 

ORGANIC CARBON, 

IN PERCENT 

0.4 0.8 

organic constituents to geologic age and depth and 

presents curve segments that are averaged for the 

different geologic epochs. 

The calcium carbonate concentration on and under 

the Blake Plateau is high. Nearly all post-Eocene 

samples have more than 80 percent calcium carbonate. 

The only exception is in the northernmost location 

(Eocene, hole 4), where calcium carbonate diminishes 

from about 90 percent at 71 meters depth to 50 percent 

at 84 meters (fig. 4). In all cores the calcium carbonate 

is chiefly the ren1ains of pelagic plankton: foraminifers, 

pteropods, and coccolithophorids (Joint Oceanographic 

Institutions' Deep Earth Sampling Program, 1965). 

The organic carbon and nitrogen contents on and 

under the Blake Plateau are low and extraordinarily 

uniform. Carbon ranges from 0.1 to 0.3 percent (figs. 4, 

7B), and nitrogen from 0.01 to 0.03 percent (fig. 4). 

Most carbon-nitrogen ratios are about 10; only three 

samples had ratios of less than 5, and one sample had a 

ratio of slightly above 20. The highest ratios were in 

samples from the Oligocene in the inner Blake Plateau 

(hole 6); the oldest samples (Paleocene), however, had 

nearly the same carbon-nitrogen ratios as the youngest 

ones from the present sea floor. Some apparent variation in carbon-nitrogen ratios is probably a result of 

analytical inaccuracy due to the low absolute concentration of organic nitrogen. 

Lower Eocene and Paleocene rocks were reached by 

the drill only under the Blake Plateau, and the thickest 

section of these strata was penetrated in hole 4 (fig. I). 

A distinct relation of the abundance of organic constituents to age is evident if data are adjusted to geologic 

age (fig. 6B). For example, the high values for the 

0.00 

NITROGEN (Kjeldahl), 

IN PERCENT 

0.04 0.08 

CARBON- NITROGEN 

RATIO 

10 20 30 

EXPLANATION 

Core hole 3 Core hole 4 Core hole 6 

FIGURE 4.-Relation of organic constituents to depth in samples from JOIDES drill holes on the Blake Plateau. 
CALCIUM CARBONATE, ORGANIC CARBON, AND NITROGEN IN DRILL-HOLE SEDIMENTS Bi 

CALCIUM CARBONATE, 

IN PERCENT 

O Or---2r-O _4r-O _60,.----,-----fill, 

0 

ORGANIC CARBON, 

IN PERCENT 

NITROGEN (Kjeldahl), 

IN PERCENT 0.04 

EXPLANATION 

0---- t:::.--- o------ O······················· x-----·-·-

Post-Miocene Miocene Oligocene Eocene Paleocene 

FIGURE 5.-Relation of organic constituents to depth and geologic age of sediments of the Blake Plateau. 

lower Eocene sample at 84 meters depth in hole 4 that 

seem anomalous in figure 5 are not abnormal when 

adjusted for age in figure 6B. The contents of organic 

constituents are relatively uniform downward to the 

lower Eocene strata, where the amounts of all three 

change abruptly. Calcium carbonate content is reduced 

markedly in Paleocene and lower Eocene rocks to 50 

percent, whereas in younger strata it is considerably 

higher. Conversely, both organic carbon and nitrogen 

contents are lower in post-lower Eocene strata. 

INTERPRETATION 

According to its fossil content and distance from 

shore, the Blake Plateau represents deep-water marine 

conditions, as opposed to shallow-water conditions, 

typical of the shelf. The low ealcium carbonate values 

of the lower Eocene and Paleocene strata, however, 

appear to be somewhat less typical for a pelagic environment than the higher values of the younger 

strata. The increase in calcium earbonate content 

parallel with the distinct decrease in organic carbon 

and nitrogen contents in post-lower Eocene strata 

eould be a result of a shift to more typical pelagic 

conditions such as are characterized by one or more of 

the following eircumstances: 

1. A decrease in the rate of aecumulation of noncarbonate detritus. 

2. Less preservation of organic rna terial. 

3. A greater distanee from the eontinent. 

This theory of a shift to more pelagic conditions is 

supported by mineralogical results: most of the small 

amount of detrital quartz, the volcanic minerals, and 

the layers of ehert under the Blake Plateau occur in 

lower Tertiary sediments (J. C. Hathaway, P. F. 

McFarlin, and D. A. Ross, unpub. data). Perhaps, the 

Blake Plateau was closer to the Paleocene-Eocene 

shoreline, and the Florida-Hatteras Slope may not have 

existed. The development of the Florida-Hatteras 

Slope may have led in post-early Eocene time to a 

water circulation pattern that intercepted part of the 

land-derived detritus before it reached the Blake 

Plateau. The volcanic minerals in the lower Tertiary 

strata may indicate that volcanism was associated with 

the crustal movements. 

If the increase of biogenic calcium carbonate in late 

Eocene time resulted from greater surface production, 

for instance related to a climatic amelioration, then a 

similar increase in the production of organic carbon 

and nitrogen could be expected. However, the percentage of organic carbon and nitrogen did not increase 

after early Eocene time. Also, there was no increase in 

the carbon-nitrogen ratio as would be expected if the 

organic matter had been more completely decomposed. 

Conceivably, the calcium carbonate production was 

great enough to overshadow an increase in the production 

of organic carbon and nitrogen, and the calcium carbonate diluted these constituents. If so, one would 

expect a marked increase in the rate of sedimentation. 

However, on the basis of the drill-hole and seismic 

records, the sedimentation rate did not increase. 
B8 

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Q 

POST-MIOCENE 

MIOCENE 

OLIGOCENE 

EOCENE 

PALEOCENE 

DRILLING ON THE CONTINENTAL MARGIN OFF FLORIDA 

CALCIUM CARBONATE. 

IN PERCENT 

1 r ---4... 1 

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ORGANIC CARBON, 

IN PERCENT 

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EXPLANATION 

Shelf and slope 

(core holes 1, 2, 5) 

Blake Plateau 

(core holes 3, 4, 6) 

B 

NITROGEN (Kjeldahl), 

IN PERCENT 

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CARBON- NITROGEN 

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FIGURE 6.-Comparison of average percentage of organic constituents in sediments of the shelf and the slope with that in 

sediments of the Blake Plateau. A, Plotted against depth. B, Plotted against geologic age. 
If) 

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1--

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CALCIUM CARBONATE, ORGANIC CARBON, AND NITROGEN IN DRILL-HOLE SEDIMENTS 

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400 

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EXPLANATION 

<0.26 0.76-1.00 

0.26-0.50 1.01-1.25 

.. 0.51-0.75 > 1.25 

Organic carbon, in percent 

EXPLANATION 

~ <0.26 

E 

FLORIDA-HATTERAS 

SLOPE EA LEVEL----.------=-=-:..~----. 

50 100 150 

DISTANCE OFFSHORE, IN Kll .. OME.TERS 

A 

BLAKE PLATEAU 

0.26-0.50 

Organic carbon, 

in percent VERTICAL EXAGGERATION ·X250 

250 300 350 

DISTANCE OFFSHORE, IN KILOMETERS 

B 

400 450 

B9 

SE 

FIGURE 7.-Percentage distribution of organic carbon in sediments of the continental shelf, upper Florida-Hatteras Slope, and 

Blake Plateau, projected from drill holes. A, Shelf to upper Florida-Hatteras Slope. B, Blake Plateau. (Stratigraphic profile 

modified from Joint Oceanographic Institutions' Deep Earth Sampling Program, 1965.) 
BlO DRILLING ON THE CONTINENTAL MARGIN OFF FLORIDA 

SUMMARY AND CONCLUSIONS 

The distribution of organic constituents in samples 

from the JOIDES drill holes shows that two distinct 

facies are represented by the cores (figs. 6, 7): one, on 

and beneath the present shelf and the upper FloridaHatteras Slope, is typical of shallow-water conditions, 

and the other, on and beneath the Blake Plateau, is 

typical of deep-water conditions. The variations in the 

abundances of the organic constituents are systematically related to depth and age. 

The following explanation is suggested for the 

abundances of the organic constituents in the sediments 

and the changes in abundances with time. During 

Paleocene time the area of the Blake Plateau was less 

typically pelagic (pelagic in the sense used by Hedgpeth, 1957, p. 17-27) than at present and perhaps 

closer to shore, and the rate of accumulation of sediment (including volcanic material) was greater. In 

early Eocene time the Blake Plateau became more 

clearly defined as a pelagic region, characterized by 

an increase in calcium carbonate in the sediments and 

a decrease in organic carbon and nitrogen contents. 

Sediment accumulated more slowly. The abruptness 

of this change may reflect a tectonic movement along 

the present site of the Florida-Hatteras Slope, movement that lowered the Blake Plateau or raised part 

of the shelf and created the slope as a more pronounced 

boundary between the shelf and Blake Plateau. The 

seismic profiling records, as interpreted by Emery and 

Zarudzki (1967), do not reveal evidence for faulting. 

However, the records do not rule out the possibility of 

changes in the depth of the sea floor; in fact, these 

records suggest that some tectonic activity occurred 

in Paleocene and early Eocene time near the :B loridaHatteras Slope. In addition, ash layers, zeolites, and 

other indications of volcanic activity were noted by 

J. C. Hathaway, P. F. McFarlin, and D. A. Ross 

(unpub. data) to be most abundant in lower Tertiary 

samples. 

During the late Eocene and early Oligocene, conditions on the shelf became more neritic. This is shown 

by an increase of organic carbon and nitrogen, accompanied by a decrease of calcium carbonate and an 

increase in quartz and feldspar, in the shelf sediments. 

Again, the change of conditions was sudden enough to 

suggest differential crustal movement of the land or 

shallow sea floor, movement which may have caused a 

shift of the axis or velocity of the Gulf Stream. The 

Blake Plateau was apparently not affected by this 

event. 

0 

In Miocene and post-Miocene time, conditions on the 

Blake Plateau did not change significantly. Sediment 

accumulated considerably more slowly than on the shelf; 

hence, there >vas little accumulation of organic carbon 

and nitrogen. On the shelf, the more gradual changes in 

the abundances of the organic constituents in the 

Miocene and post-Miocene strata may be explained by 

changes in the axial position, velocity, and volume of 

the Gulf Stream. 

The most favorable site for the accumulation of 

organic matter, as indicated by organic carbon and 

nitrogen abundance, has been the upper FloridaHatteras Slope. Mass slumping of sediment and burial 

of younger by older sediments may have provided the 

mechanism for the preservation of a large amount of 

organic matter in an area remote from the mainland 

where the rate of deposition of terrestrially derived 

clastic material is generally low. 

REFERENCES 

Bader, R. G., 1954, Use of factors for converting carbon or 

nitrogen to total sedimentary organics: Science, v . 120, 

no. 3122, p. 709-710. 

Chen, C. S., 1965, The regional lithostratigraphic analysis of 

Paleocene and Eocene rocks of Florida: Florida Geol. 

Survey Geol. Bull. 45, 105 p. 

Emery, K. 0., and Zarudzki, E. F. K., 1967, Seismic reflection 

profiles along drill holes on the continental margin off 

Florida: U.S. Geol. Survey Prof. Paper 581- A, 8 p. 

Hedgpeth, J. W., 1957, Classification of marine environments, in 

Hedgpeth, J. W., ed., Ecology, v. 1 of Treatise on marine 

ecology and paleoecology: Geol. Soc. America Mem. 67, 

p. 17- 27. 

Heezen, B. C., Hollister, C. D., and Ruddiman, W. F., 1966, 

Shaping of the continental rise by deep geostrophic contour 

currents: Science, v. 152, no. 3721, p. 502- 508. 

Hiilsemann, Jobst, 1966, On the routine analysis of carbonates 

in unconsolidated sediments: Jour. Sed. Petrology, v. 36, 

p. 622- 625. 

Hurley, R. J., and Fink, L. K., 1963, Ripple marks show that 

countercurrent exists in Florida Straits: Science, v. 139, no. 

3555, p. 603- 605. 

Joint Oceanographic Institutions' Deep Earth Sampling Program, 

1965, Ocean drilling on the continental margin : Science, v. 

150, no. 3697, p. 709-716. 

Maher, J. C., 1965, Correlations of subsurface Mesozoic and 

Cenozoic rocks along the Atlantic Coast: Tulsa, Okla., 

Am. Assoc. Petroleum Geologists, 18 p. 

Pratt, R. M., 1963, Bottom currents on the Blake Plateau: 

Deep-Sea Research, v. 10, p. 245-249. 

Schlee, John, and Gerard, Robert, 1965, Cruise report and 

preliminary core log MV Caldrill I-17 April to 17 May 

1965: Joint Oceanog. Inst. Deep Earth Sampling Program 

Blake Panel Rept., 64 p. 

Swallow, J. C., and Worthington, L. V., 1961, An observation of 

a deep countercurrent in the Western North Atlantic: 

Deep-Sea Research, v. 8, p. 1-19.