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Pollen and associated microfossils in the marine surface sediments of the Great Bahama Bank
Review of Palaeobotany and Palynology Elsevier Publishing Company, Amsterdam - Printed in The Netherlands
POLLEN AND ASSOCIATED MICROFOSSILS IN THE MARINE SURFACE SEDIMENTS OF THE GREAT BAHAMA BANK A L F R E D TRAVERSE AND ROBERT N. G I N S B U R G
Department of Geology and Geophysics, Pennsylvania State University, University Park, Pa. (U.S.A.) Department of Geology, Johns Hopkins University, Baltimore, Md. (U.S.A.) (Received August 29, 1966)
SUMMARY
This study dearly indicates that pollen grains and certain other macerationresistant microfossils found in surface sediment of the Great Bahama Bank are sedimented primarily in response to water turbulence and other hydrological factors. Low levels of pine-pollen concentration are found in the same areas as sandy sediment--areas of relatively turbulent water. Muddy sediment and high levels of pine-pollen concentration are similarly associated in the areas of sluggish water movement. This is very significantly true of the area of quiet water west of Eleuthera Island, where pine pollen occurs abundantly in the mud, despite the absence of pine trees on the island. This shows that pine pollen is moved about widely on the Bank and sediments out inthe areasofrelativelynonturbulentwater. The discovery that large amounts of pine pollen--as much as 2,000 per 100 1. of water--are present in the water on the Bank months after the trees ceased flowering further substantiates this fact. "Microforaminifera" are more generally distributed; they occur both in muddy sediment and in sandy sediment at various locations. Apparently they are found more or less where they lived, having been moved about relatively little on the Bank. Hystrichosphaerids show a distribution intermediate between that of pine pollen and that of "microforaminifera"; they are relatively concentrated in the muddy sediment, as a response to nonturbulence of the water, but they also sediment out to some extent at other locations on the Bank. This is interpreted as showing that hystrichosphaerids are denser than pine pollen. The study shows the possible use of palynological analysis in the investigation of paleosediment types and paleohydrologic features of sedimentary basins.
INTRODUCTION
We report in this paper a study of the maceration-resistant microfossils Rev. Palaeobotan. Palynol., 3 (1967) 243-254
243
of tile calcareous surface sediment of Great Bahama Bank. The Bank is ~Lsomewhat isolated area with rather restricted water circulation. There are practically no streams and no sediments of terrigenous origin. Reworked pollen, derived from eroded sedimentary rocks--a significant constituent of pollen floras of elastic sediments--is therefore not encountered. Pollen fi'om other areas may bc brought to the Bank by currents, but it seems doubtful that significant amounts of the pollen found in Bahama sediments tire of such origin; none of the common types found is of a plant exotic to the Bahamas. The study is, therel\~re, an investigation of the sedimentation of pollen with as little complication as one could expect outside of a laboratory< We were interested in determining from the Bank--as a giant "outdoor watch-glass"--whether one could observe in nature the sort of pollen-response to differential patterns of turbulence that was observed on laboratory scale in connection with pollen preparation techniques by FUNKHOUSER and EVlrT (1959) and by TSCHUDY (1960). Although palynologists' interests naturally lean strongly toward clastic sediments, the results obtained in this study have confirmed that Great Bahama Bank was an important target, palynologically. The outlines of pollen sedimentation in clastic marine sediments have been sketched by HOFFMEISTER(1954) and MULLER (1959), both of whom emphasized that water-current patterns are the dominant factors in the deposition of pollen in marine sediments. Muller's work on the Orinoco delta, and vicinity, however, showed that the sedimentation of pollen depends on a more complex relationship of pollen size and specific gravity to current patterns than Hoffmeister believed. More recently, investigation of surface sediment of the Gulf of California by CROSS and SHAEFER ( 1 9 6 5 ) , of marine cores from the Atlantic by STANLEY (1966), and of surface sediment and cores from the Pacific by KORENEVA(1964) have made this additionally obvious. Little has been previously published on the palynology of Recent carbonate deposits. Our results could have a bearing on the application of palynological investigations to ancient carbonates. Furthermore, the studies have contributed to understanding the behavior of pollen from its original delivery to sea water to its eventual sedimentation.
GEOGRAPHY AND GEOLOGY OF THE AREA
The location and geographic layout of Great Bahama Bank are shown in Fig.1. The Bank is a somewhat irregular platform, on which the water depth is everywhere less than 15 m, and is mostly less than 10 m. The islands on the Bank have an elevation of mostly less than 30 m, with a few ridges to 60 m. The Bank is bordered by submarine slopes that plunge quite sharply to 1,500 in or more; off Eleuthera, the slopes go down to 3,660 m. It is apparent that the Bank is a 244
Rev. Palaeobotan. Palynol., 3 (1967) 243-254
./I
,,.,I
IIMINII/
~
-'~-~.~
''~
......
%
,,x
a d~,-? ~
~'000"
I0
20~
30
40
50
in feet
CHANNEL
L CAY
Depths
--600~--...---
DALE IN NAUTICAL MILES
~\~SE
'
OCATION MAP
~ig. 1. Location, geography and water depths of Great Bahama Bank. Depth contours in feet. (After TRAVERSVand GINSBURG, 1966, fig. 1).
e d ~
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submerged Pleistocene island. Sedimentation of the surface veneer of 0--8 m of unconsolidated material on the Bank is a product of only the last few thousand years, produced since the last rise of sea level. The controlling factors in sedimentation on the Bank are topography and the pattern of currents: these currents are a product of tides, oceanic swell. and winds. Tidal currents, swell and wind-driven sea prevail at the margins, and wind-driven sea alone in the interior. Most of the Bank is too broad and shallow for tidal currents to cross as more than a slow drift. In parts of the Bank, there is little or no semidiurnal tide. The stagnant circulation of these areas gives rise to higher salinities than normal and to deposition of fine grained sediment. The Gulf Stream, though it approaches near the Bank, does not cross it. The wind is the major element in control of current movement. The winds are prevailingly, almost exclusively, easterly. Fig.2 shows the kinds of sediment found on the Bank. The sediment is almost exclusively carbonate, with just traces of siliceous matter and seldom as high as 2 ~ organic matter. Skeletal sands occur on the margins of the Bank, and pelletoidal sand occur over most of the interior. O61itic sands are found near some of the margins. Local areas of skeletal sands and o61itic sands are found at places within the Bank where currents are relatively strong. Muddy pelletoidal sands and muds are found in the lee of the larger islands, where they are protected by the topographical barriers; in effect, a settling basin environment.
WIND IN RELATION TO POLLEN SEDIMENTATION
Since there are no streams on Great Bahama Bank, it seemed initially that the pollen sedimentation, especially that of pollen of wind-pollinated plants, should be a more or less direct product of the wind system. Indeed, the expectation that the Bahamas would provide a good test of wind dispersal of pollen was one of the original reasons for the study. The Bahamas were expected to show patterns of wind-distributed pollen in a region without clastic sedimentation. However, it is clear from the data produced by this study that, except insofar as wind determines the hydrographical features of the Bank, we must abandon direct aerodynamical explanations for the pollen distribution and turn to hydrodynamical explanations. Pollen is shed into the air, but once delivered to the water, either directly or by being washed from terrestrial surfaces, pollen grains behave as would any particles with the same physical properties.
PINE POLLEN DISTRIBUTION AS A FUNCTION OF SEDIMENT-TYPES AND SEDIMENTATION
By far the most abundant pollen type in surface sediment of the Bahamas 246
Rev. Palaeobotan. Palynol., 3 (1967) 243-254
t~
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co
%-
'x
%
(3
q: %
\
. . . . . . . . .
I
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IO
20
50
40
50
Depths in feet
--600'----
SCALE IN NAUTICAL MILES
0
"',1111 Ill
Exposed
Pelfefoldof Sands with Lime Mud I Motrlx, and Lime Muds Skeletal Sands and Lime Muds, chiefly of Pelagic O~igin Ridqes and islands of Pleistocene oofific ca{corenlte; see topogrophlc mop for elevations
PeHetoidal Sands
Oolitic Sands (>50% Ooliths)
Local areas of Skeletal Sands around Patch Reefs and Coral KnolJs
S~e}etal Sands(>40% Ske/eto/ Grains)
Fig.2. Distribution of major types of surface sediment, Great Bahama Bank. (After TRAVERSEand GINSBURG, 1966, fig.4).
\
/
\
LITTLE
is that of pine, prestimably Phmv caribaea MOREI,ET. Pine-pollen distribution in sediment of Great Bahama Bank is shown in Fig.3, plotted as pollen per gram ~)l" sediment. The similarity between this chart and that of sediment-type distribution (Fig.2) is very striking. The lower levels of pine-pollen concentration are found in the pelletoidal and o61itic sand provinces- those areas where current action is relatively dynamic. The pine-pollen highs are l\)und in the same areas and with practically the same borders as the lime-mud areas; that is, areas of sluggish current action. This alone suggests strongly that pine-pollen exines, large, buoyant pollen, respond to sedimentation on the Bank as would any similarly buoyant particles of the same size. The key fact in pine-pollen distribution in these sediments is the occurrence of a region of high concentration in the lee of--west of Eleuthera, which coincides with a mud area in the same location. This is important because Eleuthera has no pine trees. The pine pollen on Eleuthera must have coine iYom elsewhere on the Bank and settled out in the relatively non-turbulent water west of Eleuthera. On the other hand, New Providence Island, where Nassau is located, has pines, but little pine pollen occurs in the surface sediment on the adjacent parts of the Bank. Mere proximity to pine source is not a guarantee of pine pollen in the sediment, any more than absence of nearby pine precludes the presence of pine pollen in the sediment. The abundance of pine pollen off Eleuthera helps to eliminate both nearby source of pine trees and wind dispersal as limiting lectors in pine-pollen distribution in these sediments: there is no pine forest on Eleuthera, and the apparent sources of pine pollen are either leeward or northward from Eleuthera. in Fig.4 is shown the close agreement between deposition of pine pollen west of Eleuthera and sediment type and topography. The sensitive response of pollen to turbulence and, prestimably, to other sedimentological factors is comparable on a large scale to the differential settling effect of swirled pollen observed by FUNKHOUSERand EWTT (1959) and others on a laboratory scale. That pollen is so sensitive a hydrodynamical indicator under field conditions is a significant palynological discovery.
PINE POLLEN IN THE WATER OF GREAT BAHAMA BANK
Since study of the surface sediments indicated that pollen is moved extensively over the Bank by water currents, it seemed reasonable to examine the pollen content of the water itself. I n July, 1959, sea water was centrifuged with a continuous centrifuge at four stations on the Bank, west of Andros Island. The amount of water centrifuged per sample averaged 200 1. Fig.5 shows the distribution of pine pollen in the water. Although pine trees in the Bahamas and south Florida had completed flowering about six months before these samples were collected, the samples contained considerable amounts of pollen: as much as 2,000 pine pollen grains per 100 1 of water. Apparently pine pollen remains in the water in response 248
Rev. Palaeobotan. Palynol., 3 (1967) 243-254
D
2
D
\
BIMINt
i
"\ _-¢
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I
Li
PINE POLLEN PER GRAM
lO0-100O
I0
20 30 40
j/
Nc,.~
~Y
3CALE IN NAUTICAL MILES
50
Bohomo islonds with pine forest
>,ooo
- - 6 0 0 ' ~ Depths in feet
I
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=======I 0-20
~'ig.3. Pine pollen per gram of sediment, Great Bahama Bank. (After TRAVERSEand GINSBURG, 1966, fig.6).
19,~'\
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~"
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SEA LEVEL
’
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7136
Fig.4. Relationship fig.7).
STATIONS
of pine-pollen
-~37
SEDIMENTS
NAUTICAL
MILES-.
PINE POLLEN PER GRAM OF SEDIMENT
content of sediment near Eleuthera Island to sediment type and water depth. (After TRAVERSEand GINSBURG, 1966,
SANDY
616R
- 1000 -900 -800 -700 -600 -500 -400 -300 - 200 -100 -0 GkAlNS
PER 100 WATER
LITERS
STRAITS OF 90 58 tWohr sampled at 4.5 meters depfh water 5.4 meters deep.J
;
(Surface voter iompled; waler 3.6 meters UeepJ
9045 lSurface YOldl sampled; water 54 meters deepJ
9050
ciurface water SompM; water I.8 meters de0p.J
fsurfoce woter sampled; water 2.7 meters deco
GREAT BAHAMA 0APPRdXlMATE
4
__-
a
SCALE,
Fig.5 Pine pollen per 100 1 of water, centrifuged
12 NAUTICAL
BANK I6 MILES
July, 1959. (After TRAVERSE and GINSBURG,
1966, fig.13).
Rev. Palaeobotan.
Palynol.,
3 (1967) 243-254
251
to low turbulence and perhaps other properties ~1" water. The ,ztmple> collected nearest Andros Island, a major pine ~;ource. contained the legist pollen, while the sample collected at the edge of the Bank contained the mos! pollen. Thb, distribution is roughly a reciprocal of pollen distribution in the surface sedimenl. suggesting that the factors that: keep pollen suspended in the wate," prevent its sedimentation. Although it would be useful to centrifuge water at other seasons and from other parts of the Bank, it is already demonstrated that pollen remains in the water for long periods and moves about freely in the water on the Bank.
OTHER MICROFOSSIL TYPES AND THEIR SEDIMENTATION
A comparison of results obtained from analysis of other categories of microfossils with those for pine pollen further substantiates the sensitivity of palynology as a sedimentological tool. The other major fossil types have points of similarity in distribution to that of pine pollen, but they also present differences, and the differences are revealing in terms of sedimentation. " M icroJoraminifera "
Chitinous inner tests of certain Foraminifera--so-called "microforaminifera" - - a r e found in the sediment of regions of high pollen content, except that they are low to absent in onshore samples. But "microforaminifera" are also found in some abundance in the sediment over broad areas of pelletoidal sands on the Bank, where practically no pollen is found. Also, major concentrations of"microforaminifera" occur in sediment at various localities at the edges of the Bank, for example along the Tongue of the Ocean, west of the Exuma Islands. Very little pollen is found in sediment at such locations. Pine pollen is swept about on the Bank for extended periods and is eventually deposited as a response to such properties of the water as turbulence and salinity. "Microforaminifera" seem to be swept about on the bank relatively little; for the most part they are deposited where they lived. Hystrichosphaeri&
These are spiny marine microfossils in the same size range as pollen exines and of a similar maceration-resistant chemical nature. Their distribution in Bahama Bank sediment follows reasonably well a combination of pine-pollen and "microforaminifera" distributions: they are very high in the regions of high pollen, except for onshore samples, and are also high in the regions that are high in "microforaminifera" but low in pollen. Hystrichosphaerids, unlike "microforaminifera", are swept about in the Bank water. They were found in the centrifuged 252
Rev. Palaeobotan. Palynol., 3 (1967) 243-254
sea water described above. They are apparently denser than pine pollen and are sedimented out more rapidly. Some of them therefore sediment out even in the more turbulent areas outside of the mud areas.
DISCUSSION OF APPLICATIONS
This work is significant in relation to the theoretical basis for stratigraphical palynology. Pollen can be expected to be even more widely dispersed by marine currents than we heretofore realized, though it should be pointed out that one would not expect all pollen types to be so persistent in sea water or so sensitive to turbulence as the very buoyant pine pollen. This study also suggests that palynology might be a useful tool for investigation of the hydrography of some ancient carbonate banks, though it must be emphasized that only a small proportion of limestones contain significant amounts of fossil pollen. The senior author has never isolated fossil pollen from dolomite, though he has macerated perhaps a hundred samples. Some limestones do contain a fair abundance of macerationresistant microfossils, though relatively large samples must usually be processed, say four to ten times as large as for argillaceous rocks. Also, the microfossils analyzed may be expected to be "non-pollen" more often than pollen. Hystrichosphaerids and other chitinous micro-remains can be the raw material for very good micropaleontological work. The fact that analysis of a palynological sort could be used to investigate paleosediment types and paleohydrological features of a carbonate basin could have practical significance for work with petroliferous limestones. This study has already made a contribution to basic carbonate studies on Great Bahama Bank. On the basis of palynological information, we can venture a significant opinion on the sedimentary conditions indicated by the microfossils for given Bahama samples. For example, one of us was asked to comment on the possibility of certain samples of pelletoidal sand having originally been calcareous mud, now consolidated to pellets. The absence of pollen in the samples militates against their having originated as mud, since muddy sediments on Great Bahama Bank invariably contain abundant pine pollen.
ACKNOWLEDGEMENT
This paper is published as EPR Publication Number 443, by permission of Shell Development Company, a division of Shell Oil Company, Houston, Texas.
Rev. Palaeobotan. Palynol., 3 (1967) 243-254
253
REFERENCES CROSS, A. T. and SHAEFER,B. L., 1965. Palynology ot' modern environments, Gulf of California. Bull. Am. Assoc. Petrol Geologists, 49:337 (abstract). FUNKHOUSER,J. W. and EvrrT, W, R., 1959. Preparation techniques for acid-insoluble microfossils. Micropaleontology, 5: 369-375. HOFFMmSTER,W. S., 1954. Mierofossil Prospectingfor Petroleum. U.S. Patent 2, 686, 108, Washington, D.C., 4 pp. KORENEVA,E. V., 1964. Distribution of spores and pollen of terrestrial plants in bottom sediments of the Pacific Ocean. In: L. M. CRANWELL(Editor), Ancient Pacific Floras: The Pollen Story. Univ. of Hawaii Press, Honolulu, Hawaii, p.31. MULLER, J., 1959. Palynology of Recent Orinoco delta and shelf sediments: Reports of the Orinoco Shelf expedition, 5. Micropaleontology, 5: 1-32. STANLEY, E. A., 1966. Palynology of marine sediments off the eastern coast of the United States. Geol. Soc. Am., Program Ann. Meeting Southeastern Sect., p.41 (abstract). TRAVERSE,A. and GINSBURG,R. N., 1966. Palynology of the surface sediments of Great Bahama Bank, as related to water movement and sedimentation. Marine Geol., 4(6): 417-459. TSCHUDY, R. H., 1960. "Vibraflute". Micropaleontology, 6: 325-326.
254
Rev. Palaeobotan. Palynol., 3 (1967) 243-254
POLLEN AND ASSOCIATED MICROFOSSILS IN THE MARINE SURFACE SEDIMENTS OF THE GREAT BAHAMA BANK A L F R E D TRAVERSE AND ROBERT N. G I N S B U R G
Department of Geology and Geophysics, Pennsylvania State University, University Park, Pa. (U.S.A.) Department of Geology, Johns Hopkins University, Baltimore, Md. (U.S.A.) (Received August 29, 1966)
SUMMARY
This study dearly indicates that pollen grains and certain other macerationresistant microfossils found in surface sediment of the Great Bahama Bank are sedimented primarily in response to water turbulence and other hydrological factors. Low levels of pine-pollen concentration are found in the same areas as sandy sediment--areas of relatively turbulent water. Muddy sediment and high levels of pine-pollen concentration are similarly associated in the areas of sluggish water movement. This is very significantly true of the area of quiet water west of Eleuthera Island, where pine pollen occurs abundantly in the mud, despite the absence of pine trees on the island. This shows that pine pollen is moved about widely on the Bank and sediments out inthe areasofrelativelynonturbulentwater. The discovery that large amounts of pine pollen--as much as 2,000 per 100 1. of water--are present in the water on the Bank months after the trees ceased flowering further substantiates this fact. "Microforaminifera" are more generally distributed; they occur both in muddy sediment and in sandy sediment at various locations. Apparently they are found more or less where they lived, having been moved about relatively little on the Bank. Hystrichosphaerids show a distribution intermediate between that of pine pollen and that of "microforaminifera"; they are relatively concentrated in the muddy sediment, as a response to nonturbulence of the water, but they also sediment out to some extent at other locations on the Bank. This is interpreted as showing that hystrichosphaerids are denser than pine pollen. The study shows the possible use of palynological analysis in the investigation of paleosediment types and paleohydrologic features of sedimentary basins.
INTRODUCTION
We report in this paper a study of the maceration-resistant microfossils Rev. Palaeobotan. Palynol., 3 (1967) 243-254
243
of tile calcareous surface sediment of Great Bahama Bank. The Bank is ~Lsomewhat isolated area with rather restricted water circulation. There are practically no streams and no sediments of terrigenous origin. Reworked pollen, derived from eroded sedimentary rocks--a significant constituent of pollen floras of elastic sediments--is therefore not encountered. Pollen fi'om other areas may bc brought to the Bank by currents, but it seems doubtful that significant amounts of the pollen found in Bahama sediments tire of such origin; none of the common types found is of a plant exotic to the Bahamas. The study is, therel\~re, an investigation of the sedimentation of pollen with as little complication as one could expect outside of a laboratory< We were interested in determining from the Bank--as a giant "outdoor watch-glass"--whether one could observe in nature the sort of pollen-response to differential patterns of turbulence that was observed on laboratory scale in connection with pollen preparation techniques by FUNKHOUSER and EVlrT (1959) and by TSCHUDY (1960). Although palynologists' interests naturally lean strongly toward clastic sediments, the results obtained in this study have confirmed that Great Bahama Bank was an important target, palynologically. The outlines of pollen sedimentation in clastic marine sediments have been sketched by HOFFMEISTER(1954) and MULLER (1959), both of whom emphasized that water-current patterns are the dominant factors in the deposition of pollen in marine sediments. Muller's work on the Orinoco delta, and vicinity, however, showed that the sedimentation of pollen depends on a more complex relationship of pollen size and specific gravity to current patterns than Hoffmeister believed. More recently, investigation of surface sediment of the Gulf of California by CROSS and SHAEFER ( 1 9 6 5 ) , of marine cores from the Atlantic by STANLEY (1966), and of surface sediment and cores from the Pacific by KORENEVA(1964) have made this additionally obvious. Little has been previously published on the palynology of Recent carbonate deposits. Our results could have a bearing on the application of palynological investigations to ancient carbonates. Furthermore, the studies have contributed to understanding the behavior of pollen from its original delivery to sea water to its eventual sedimentation.
GEOGRAPHY AND GEOLOGY OF THE AREA
The location and geographic layout of Great Bahama Bank are shown in Fig.1. The Bank is a somewhat irregular platform, on which the water depth is everywhere less than 15 m, and is mostly less than 10 m. The islands on the Bank have an elevation of mostly less than 30 m, with a few ridges to 60 m. The Bank is bordered by submarine slopes that plunge quite sharply to 1,500 in or more; off Eleuthera, the slopes go down to 3,660 m. It is apparent that the Bank is a 244
Rev. Palaeobotan. Palynol., 3 (1967) 243-254
./I
,,.,I
IIMINII/
~
-'~-~.~
''~
......
%
,,x
a d~,-? ~
~'000"
I0
20~
30
40
50
in feet
CHANNEL
L CAY
Depths
--600~--...---
DALE IN NAUTICAL MILES
~\~SE
'
OCATION MAP
~ig. 1. Location, geography and water depths of Great Bahama Bank. Depth contours in feet. (After TRAVERSVand GINSBURG, 1966, fig. 1).
e d ~
\
~b
,,,j
LITTLE
submerged Pleistocene island. Sedimentation of the surface veneer of 0--8 m of unconsolidated material on the Bank is a product of only the last few thousand years, produced since the last rise of sea level. The controlling factors in sedimentation on the Bank are topography and the pattern of currents: these currents are a product of tides, oceanic swell. and winds. Tidal currents, swell and wind-driven sea prevail at the margins, and wind-driven sea alone in the interior. Most of the Bank is too broad and shallow for tidal currents to cross as more than a slow drift. In parts of the Bank, there is little or no semidiurnal tide. The stagnant circulation of these areas gives rise to higher salinities than normal and to deposition of fine grained sediment. The Gulf Stream, though it approaches near the Bank, does not cross it. The wind is the major element in control of current movement. The winds are prevailingly, almost exclusively, easterly. Fig.2 shows the kinds of sediment found on the Bank. The sediment is almost exclusively carbonate, with just traces of siliceous matter and seldom as high as 2 ~ organic matter. Skeletal sands occur on the margins of the Bank, and pelletoidal sand occur over most of the interior. O61itic sands are found near some of the margins. Local areas of skeletal sands and o61itic sands are found at places within the Bank where currents are relatively strong. Muddy pelletoidal sands and muds are found in the lee of the larger islands, where they are protected by the topographical barriers; in effect, a settling basin environment.
WIND IN RELATION TO POLLEN SEDIMENTATION
Since there are no streams on Great Bahama Bank, it seemed initially that the pollen sedimentation, especially that of pollen of wind-pollinated plants, should be a more or less direct product of the wind system. Indeed, the expectation that the Bahamas would provide a good test of wind dispersal of pollen was one of the original reasons for the study. The Bahamas were expected to show patterns of wind-distributed pollen in a region without clastic sedimentation. However, it is clear from the data produced by this study that, except insofar as wind determines the hydrographical features of the Bank, we must abandon direct aerodynamical explanations for the pollen distribution and turn to hydrodynamical explanations. Pollen is shed into the air, but once delivered to the water, either directly or by being washed from terrestrial surfaces, pollen grains behave as would any particles with the same physical properties.
PINE POLLEN DISTRIBUTION AS A FUNCTION OF SEDIMENT-TYPES AND SEDIMENTATION
By far the most abundant pollen type in surface sediment of the Bahamas 246
Rev. Palaeobotan. Palynol., 3 (1967) 243-254
t~
Ix3
co
%-
'x
%
(3
q: %
\
. . . . . . . . .
I
LEGEND
IO
20
50
40
50
Depths in feet
--600'----
SCALE IN NAUTICAL MILES
0
"',1111 Ill
Exposed
Pelfefoldof Sands with Lime Mud I Motrlx, and Lime Muds Skeletal Sands and Lime Muds, chiefly of Pelagic O~igin Ridqes and islands of Pleistocene oofific ca{corenlte; see topogrophlc mop for elevations
PeHetoidal Sands
Oolitic Sands (>50% Ooliths)
Local areas of Skeletal Sands around Patch Reefs and Coral KnolJs
S~e}etal Sands(>40% Ske/eto/ Grains)
Fig.2. Distribution of major types of surface sediment, Great Bahama Bank. (After TRAVERSEand GINSBURG, 1966, fig.4).
\
/
\
LITTLE
is that of pine, prestimably Phmv caribaea MOREI,ET. Pine-pollen distribution in sediment of Great Bahama Bank is shown in Fig.3, plotted as pollen per gram ~)l" sediment. The similarity between this chart and that of sediment-type distribution (Fig.2) is very striking. The lower levels of pine-pollen concentration are found in the pelletoidal and o61itic sand provinces- those areas where current action is relatively dynamic. The pine-pollen highs are l\)und in the same areas and with practically the same borders as the lime-mud areas; that is, areas of sluggish current action. This alone suggests strongly that pine-pollen exines, large, buoyant pollen, respond to sedimentation on the Bank as would any similarly buoyant particles of the same size. The key fact in pine-pollen distribution in these sediments is the occurrence of a region of high concentration in the lee of--west of Eleuthera, which coincides with a mud area in the same location. This is important because Eleuthera has no pine trees. The pine pollen on Eleuthera must have coine iYom elsewhere on the Bank and settled out in the relatively non-turbulent water west of Eleuthera. On the other hand, New Providence Island, where Nassau is located, has pines, but little pine pollen occurs in the surface sediment on the adjacent parts of the Bank. Mere proximity to pine source is not a guarantee of pine pollen in the sediment, any more than absence of nearby pine precludes the presence of pine pollen in the sediment. The abundance of pine pollen off Eleuthera helps to eliminate both nearby source of pine trees and wind dispersal as limiting lectors in pine-pollen distribution in these sediments: there is no pine forest on Eleuthera, and the apparent sources of pine pollen are either leeward or northward from Eleuthera. in Fig.4 is shown the close agreement between deposition of pine pollen west of Eleuthera and sediment type and topography. The sensitive response of pollen to turbulence and, prestimably, to other sedimentological factors is comparable on a large scale to the differential settling effect of swirled pollen observed by FUNKHOUSERand EWTT (1959) and others on a laboratory scale. That pollen is so sensitive a hydrodynamical indicator under field conditions is a significant palynological discovery.
PINE POLLEN IN THE WATER OF GREAT BAHAMA BANK
Since study of the surface sediments indicated that pollen is moved extensively over the Bank by water currents, it seemed reasonable to examine the pollen content of the water itself. I n July, 1959, sea water was centrifuged with a continuous centrifuge at four stations on the Bank, west of Andros Island. The amount of water centrifuged per sample averaged 200 1. Fig.5 shows the distribution of pine pollen in the water. Although pine trees in the Bahamas and south Florida had completed flowering about six months before these samples were collected, the samples contained considerable amounts of pollen: as much as 2,000 pine pollen grains per 100 1 of water. Apparently pine pollen remains in the water in response 248
Rev. Palaeobotan. Palynol., 3 (1967) 243-254
D
2
D
\
BIMINt
i
"\ _-¢
~None
I
Li
PINE POLLEN PER GRAM
lO0-100O
I0
20 30 40
j/
Nc,.~
~Y
3CALE IN NAUTICAL MILES
50
Bohomo islonds with pine forest
>,ooo
- - 6 0 0 ' ~ Depths in feet
I
2o-Joo
=======I 0-20
~'ig.3. Pine pollen per gram of sediment, Great Bahama Bank. (After TRAVERSEand GINSBURG, 1966, fig.6).
19,~'\
q:
~"
•=">~.
SEA LEVEL
’
w
7136
Fig.4. Relationship fig.7).
STATIONS
of pine-pollen
-~37
SEDIMENTS
NAUTICAL
MILES-.
PINE POLLEN PER GRAM OF SEDIMENT
content of sediment near Eleuthera Island to sediment type and water depth. (After TRAVERSEand GINSBURG, 1966,
SANDY
616R
- 1000 -900 -800 -700 -600 -500 -400 -300 - 200 -100 -0 GkAlNS
PER 100 WATER
LITERS
STRAITS OF 90 58 tWohr sampled at 4.5 meters depfh water 5.4 meters deep.J
;
(Surface voter iompled; waler 3.6 meters UeepJ
9045 lSurface YOldl sampled; water 54 meters deepJ
9050
ciurface water SompM; water I.8 meters de0p.J
fsurfoce woter sampled; water 2.7 meters deco
GREAT BAHAMA 0APPRdXlMATE
4
__-
a
SCALE,
Fig.5 Pine pollen per 100 1 of water, centrifuged
12 NAUTICAL
BANK I6 MILES
July, 1959. (After TRAVERSE and GINSBURG,
1966, fig.13).
Rev. Palaeobotan.
Palynol.,
3 (1967) 243-254
251
to low turbulence and perhaps other properties ~1" water. The ,ztmple> collected nearest Andros Island, a major pine ~;ource. contained the legist pollen, while the sample collected at the edge of the Bank contained the mos! pollen. Thb, distribution is roughly a reciprocal of pollen distribution in the surface sedimenl. suggesting that the factors that: keep pollen suspended in the wate," prevent its sedimentation. Although it would be useful to centrifuge water at other seasons and from other parts of the Bank, it is already demonstrated that pollen remains in the water for long periods and moves about freely in the water on the Bank.
OTHER MICROFOSSIL TYPES AND THEIR SEDIMENTATION
A comparison of results obtained from analysis of other categories of microfossils with those for pine pollen further substantiates the sensitivity of palynology as a sedimentological tool. The other major fossil types have points of similarity in distribution to that of pine pollen, but they also present differences, and the differences are revealing in terms of sedimentation. " M icroJoraminifera "
Chitinous inner tests of certain Foraminifera--so-called "microforaminifera" - - a r e found in the sediment of regions of high pollen content, except that they are low to absent in onshore samples. But "microforaminifera" are also found in some abundance in the sediment over broad areas of pelletoidal sands on the Bank, where practically no pollen is found. Also, major concentrations of"microforaminifera" occur in sediment at various localities at the edges of the Bank, for example along the Tongue of the Ocean, west of the Exuma Islands. Very little pollen is found in sediment at such locations. Pine pollen is swept about on the Bank for extended periods and is eventually deposited as a response to such properties of the water as turbulence and salinity. "Microforaminifera" seem to be swept about on the bank relatively little; for the most part they are deposited where they lived. Hystrichosphaeri&
These are spiny marine microfossils in the same size range as pollen exines and of a similar maceration-resistant chemical nature. Their distribution in Bahama Bank sediment follows reasonably well a combination of pine-pollen and "microforaminifera" distributions: they are very high in the regions of high pollen, except for onshore samples, and are also high in the regions that are high in "microforaminifera" but low in pollen. Hystrichosphaerids, unlike "microforaminifera", are swept about in the Bank water. They were found in the centrifuged 252
Rev. Palaeobotan. Palynol., 3 (1967) 243-254
sea water described above. They are apparently denser than pine pollen and are sedimented out more rapidly. Some of them therefore sediment out even in the more turbulent areas outside of the mud areas.
DISCUSSION OF APPLICATIONS
This work is significant in relation to the theoretical basis for stratigraphical palynology. Pollen can be expected to be even more widely dispersed by marine currents than we heretofore realized, though it should be pointed out that one would not expect all pollen types to be so persistent in sea water or so sensitive to turbulence as the very buoyant pine pollen. This study also suggests that palynology might be a useful tool for investigation of the hydrography of some ancient carbonate banks, though it must be emphasized that only a small proportion of limestones contain significant amounts of fossil pollen. The senior author has never isolated fossil pollen from dolomite, though he has macerated perhaps a hundred samples. Some limestones do contain a fair abundance of macerationresistant microfossils, though relatively large samples must usually be processed, say four to ten times as large as for argillaceous rocks. Also, the microfossils analyzed may be expected to be "non-pollen" more often than pollen. Hystrichosphaerids and other chitinous micro-remains can be the raw material for very good micropaleontological work. The fact that analysis of a palynological sort could be used to investigate paleosediment types and paleohydrological features of a carbonate basin could have practical significance for work with petroliferous limestones. This study has already made a contribution to basic carbonate studies on Great Bahama Bank. On the basis of palynological information, we can venture a significant opinion on the sedimentary conditions indicated by the microfossils for given Bahama samples. For example, one of us was asked to comment on the possibility of certain samples of pelletoidal sand having originally been calcareous mud, now consolidated to pellets. The absence of pollen in the samples militates against their having originated as mud, since muddy sediments on Great Bahama Bank invariably contain abundant pine pollen.
ACKNOWLEDGEMENT
This paper is published as EPR Publication Number 443, by permission of Shell Development Company, a division of Shell Oil Company, Houston, Texas.
Rev. Palaeobotan. Palynol., 3 (1967) 243-254
253
REFERENCES CROSS, A. T. and SHAEFER,B. L., 1965. Palynology ot' modern environments, Gulf of California. Bull. Am. Assoc. Petrol Geologists, 49:337 (abstract). FUNKHOUSER,J. W. and EvrrT, W, R., 1959. Preparation techniques for acid-insoluble microfossils. Micropaleontology, 5: 369-375. HOFFMmSTER,W. S., 1954. Mierofossil Prospectingfor Petroleum. U.S. Patent 2, 686, 108, Washington, D.C., 4 pp. KORENEVA,E. V., 1964. Distribution of spores and pollen of terrestrial plants in bottom sediments of the Pacific Ocean. In: L. M. CRANWELL(Editor), Ancient Pacific Floras: The Pollen Story. Univ. of Hawaii Press, Honolulu, Hawaii, p.31. MULLER, J., 1959. Palynology of Recent Orinoco delta and shelf sediments: Reports of the Orinoco Shelf expedition, 5. Micropaleontology, 5: 1-32. STANLEY, E. A., 1966. Palynology of marine sediments off the eastern coast of the United States. Geol. Soc. Am., Program Ann. Meeting Southeastern Sect., p.41 (abstract). TRAVERSE,A. and GINSBURG,R. N., 1966. Palynology of the surface sediments of Great Bahama Bank, as related to water movement and sedimentation. Marine Geol., 4(6): 417-459. TSCHUDY, R. H., 1960. "Vibraflute". Micropaleontology, 6: 325-326.
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Rev. Palaeobotan. Palynol., 3 (1967) 243-254