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The geology of Eleuthera Island, Bahamas: A Rosetta Stone of Quaternary stratigraphy and sea-level history

Abstract and Figures

A 5-km stretch of coastline in north Eleuthera reveals a long and detailed stratigraphy that includes all known surficial limestone units in the Bahamas, and supplements the record with several previously unrecognized ones. Eight paleosol-bounded limestone parasequences comprise at least six interglacial periods. The lithostratigraphy demonstrates cyclicity at several frequencies (105, 104 (20–40 ka), and 103 years) and displays a variety of distal to proximal shoreline facies indicative of shifting depocenters associated with changing sea-levels. Stratigraphy, petrology, pedology and whole-rock aminostratigraphy are used to correlate units and subunits among the 12 described sections. Amino acid ratios are also converted to absolute age estimates which support the lithostratigraphy. The parasequences are correlated with marine Oxygen Isotope Stages 1 to 13 or older. Evidence of middle Pleistocene highstands are abundant in the Eleutheran stratigraphy, including paleo-sea-levels of decreasing age at +2 m, +7 m, +20 m associated with Stages 11 and/or 9, and two near-present highstands during Stage 7. A complex sea-level history is associated with Substage 5e, while Substage 5a is represented by near shore aggradation of coastal dune complexes in Eleuthera and throughout the Bahamas. Concordance of sea-level deposits between Bermuda and the Bahamas reinforce their tectonic stability, while the abundance of highstand evidence during the middle Pleistocene contradicts suggestions that platform subsidence has obscured all evidence of these events below present sea-level.The high-resolution late Quaternary stratigraphy of Eleuthera is unrivaled among geologic records from stable carbonate coastlines, and thereby offers a ‘Rosetta Stone’ for interpretation of the Quaternary evolution of the Bahamas and sea-level history over the past 500 ka.
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Quaternary Science Reviews, Vol. 17, pp. 333 355, 1998
(1998 Elsevier Science Ltd.
Printed in Great Britain. All rights reserved.
02773791/98, $19.00PII: S0277-3791(98) 00046 2
THE GEOLOGY OF ELEUTHERA ISLAND, BAHAMAS: A ROSETTA
STONE OF QUATERNARY STRATIGRAPHY AND SEA-LEVEL HISTORY
PAUL J. HEARTY
Chertsey d112, P.O. Box N-337, Nassau, Bahamas
(e-mail: rockdoc@bahamas.net.bs)
Abstract—A 5-km stretch of coastline in north Eleuthera reveals a long and detailed stratigra-
phy that includes all known surficial limestone units in the Bahamas, and supplements the
record with several previously unrecognized ones. Eight paleosol-bounded limestone para-
sequences comprise at least six interglacial periods. The lithostratigraphy demonstrates cyclic-
ity at several frequencies (105,104(2040 ka), and 103years) and displays a variety of distal to
proximal shoreline facies indicative of shifting depocenters associated with changing sea-levels.
Stratigraphy, petrology, pedology and whole-rock aminostratigraphy are used to correlate
units and subunits among the 12 described sections. Amino acid ratios are also converted to
absolute age estimates which support the lithostratigraphy. The parasequences are correlated
with marine Oxygen Isotope Stages 1 to 13 or older. Evidence of middle Pleistocene highstands
are abundant in the Eleutheran stratigraphy, including paleo-sea-levels of decreasing age at
#2m,#7m,#20 m associated with Stages 11 and/or 9, and two near-present highstands
during Stage 7. A complex sea-level history is associated with Substage 5e, while Substage 5a is
represented by near shore aggradation of coastal dune complexes in Eleuthera and throughout
the Bahamas. Concordance of sea-level deposits between Bermuda and the Bahamas reinforce
their tectonic stability, while the abundance of highstand evidence during the middle Pleis-
tocene contradicts suggestions that platform subsidence has obscured all evidence of these
events below present sea-level.
The high-resolution late Quaternary stratigraphy of Eleuthera is unrivaled among geologic
records from stable carbonate coastlines, and thereby offers a ‘Rosetta Stone’ for interpretation
of the Quaternary evolution of the Bahamas and sea-level history over the past
500 ka. (1998 Elsevier Science Ltd. All rights reserved.
INTRODUCTION
The building of the Bahama Banks and the islands
upon them is in direct response to eustatic fluctuations
during the Quaternary. The geologic/oceanographic
system is particularly sensitive during highstand
phases wherein superimposed short-term oscillations
leave their mark as facies changes and/or geomorphic
features. Low-stands during full glacials and prolonged
periods of bank top emergence are recorded by terra
rossa paleosols developed on interglacial limestone de-
posits. North Eleuthera provides an ideal area for
reconstructing the Quaternary stratigraphic history of
the Bahamas because of the extent of stacked se-
quences exposed in cliff walls and roadcuts.
Of the 700 islands and cays of the Bahamas, only
a few have received any detailed scientific attention.
A basic view of the surficial geology of some Bahamian
Islands has emerged from studies in New Providence
(Garrett and Gould, 1984; Hearty and Kindler, 1997a),
San Salvador (Carew and Mylroie, 1985; Hearty and
Kindler, 1993a), Lee Stocking Island (Kindler, 1995),
and the Caicos Islands (Wanless and Dravis, 1989).
A collection of papers relevant to this study is available
in Curran and White (1995).
Many of the previously studied islands differ in
geologic architecture from the large, narrow, wind-
ward, Atlantic-bank margin buildups that characterize
the major Bahamian islands (Abaco, Eleuthera,
Cat, Long, Crooked, Acklins, Inagua, and Turks
and Caicos). The windward islands, due to vertical
stacking of deposits on the steep, exposed, high
energy coasts facing the open Atlantic Ocean, present
a longer and more detailed stratigraphic record of
the Quaternary than those from interior protected
islands (Kindler and Hearty, 1996; 1997).
An extended sea-level highstand chronology from
stable carbonate coastlines has only recently become
available (Hearty and Vacher, 1994; Hearty and
Kindler, 1995), and constitutes the depositional
framework for this investigation. In an archipelago-
wide study, Hearty and Kindler (1993b) illustrated
similar first-order lithologic sequences among several
islands, while Kindler and Hearty (1996) reinforced
this regional correlation on the basis of the similarity
of petrostratigraphic sequences from several of these
islands. In general, higher-than-present sea-levels
favor the formation of oolitic and peloidal grains,
while equal, or lower-than-present sea-level highstands
favor the production of bioclasts. Underlying this
fundamental observation of carbonate island geology
is the shift of the depocenter from the shelf margin
during lower interglacial sea-levels, to bankwide
circulation during higher-than-present sea-levels
333
FIG. 1. Regional map of the Bahamas showing the island of Eleuthera on the eastern margin of the Great Bahama Bank (modified from Kindler
and Hearty, 1997).
generating tidal channels and energetic platform envi-
ronments.
Secular changes in sea-level are predicted by Milan-
kovitchian orbital cycles with periods of approxim-
ately 100 000, 41 000, and 23 000 years — periodicities
which are confirmed in deep-sea oxygen isotope re-
cords (Imbrie et al., 1984) and U-series ages of coral
reef tracts on uplifted coastlines (Bloom et al., 1974;
Bender et al., 1979; Chappell, 1983; Radtke et al., 1988).
The platform sediments are an extremely sensitive me-
dium in their response to sea-level changes. They are
rapidly molded by wave and wind activity, lithify
quickly upon subaerial exposure, and thus uniquely
preserve a high-resolution stratigraphy. A record of
sea-level maxima from stable carbonate platforms
allows more precise calculation of ice volume changes
than afforded by stable isotopes in deep-sea cores, and
provides new data from which uplift rates on tectonic
coastlines can be evaluated. The main objective of this
study is to demonstrate the rich and unique character
of the stratigraphy of Eleuthera, and from this, extract
a better understanding of the dynamic aspects of Quat-
ernary climate and sea-level changes that shaped the
Bahamian landscape over the past half-million years.
STUDY AREA
Eleuthera lies on the northeastern margin of the
Great Bahama Bank (Fig. 1), fully exposed to the enor-
mous potential energy of the Atlantic Ocean. The
northern part of the island is rocky, narrow
(0.252 km), and high (often over 40 m). The geomor-
phology of north Eleuthera is characterized by old
limestone cliffs (Fig. 2) on both margins, washover
lobes, and younger high ridges. Foresets of older beds
generally dip toward the platform, demonstrating an
easterly source-to-sink depositional vector, which is
aligned with prevailing trade winds, energetic seas, and
hurricane tracks. Since the limestones on Eleuthera
accumulated almost exclusively from the Atlantic mar-
gin, it follows that older rocks should lie nearer the
interior lagoon side, while progressively younger ones
accreted toward the Atlantic coast. Where exposed on
the leeward margin, middle Pleistocene rocks are being
deeply notched and cliffed by biological and physical
processes. During the late Pleistocene and Holocene,
pocket beaches formed between middle Pleistocene
highs on the leeward margin. Because of the high-
energy conditions along the Atlantic coastline, coarse
334 Quaternary Science Reviews: Volume 17
FIG. 2. View north from Cotton Hole of the cliffs of north Eleuthera. Whale Point and Harbour Island are seen in the far right of the photo. The
photo shows the truncated coastal ridges of middle Pleistocene age.
FIG. 3. Study area, location of stratigraphic sections (18), and geological sketch map of North Eleuthera (modified from Kindler and Hearty,
1997). Locations of megaboulders (see text) are indicated by the triangle symbol.
P.J. Hearty.: The Geology of Eleuthera Island, Bahamas 335
TABLE 1 Stratigraphic nomenclature and correlation table of major units recognized in the Bahamas. Type sections representative of each of the
units are provided for this study in Eleuthera
San Salvador;
Carew and Mylroie
(1985)
San Salvador;
Hearty and Kindler
(1993a)
The Bahamas;
Kindler and Hearty
(1996)
Eleuthera Island;
This study (type
section d)
Inferred Isotope
Stage
Holocene Hanna Bay Mb,
Rice Bay Fm
Hanna Bay Mb,
Rice Bay Fm
Unit VIII Singing Sands (12) late 1
North Point Mb,
Rice Bay Fm
North Point Mb,
Rice Bay Fm
Unit VII Windermeer Island
(12)
mid 1
Late Pleistocene Unrecognized Almgreen Cay
Formation
Unit VI Whale Point (2);
Rainbow Cay (10)
5a
Unrecognized Fernandez Bay Mb,
Grotto Beach Fm
Unit V Whale Point (1) late 5e
Cockburn Town
Mb, Grotto
Beach Fm
Cockburn Town
Mb, Grotto
Beach Fm
Unit IV Whale Point (1) 5e
French Bay Mb,
Grotto Beach Fm
French Bay Mb,
Grotto Beach Fm
Unit IV Boiling Hole (5);
Savannah Sound (11)
5e
Middle Pleistocene Unrecognized Fortune Hill
Formation
Unit III Glass Window (4);
The Cliffs (9)
late 7
Owl’s Hole
Formation
Owl’s Hole
Formation
Unit II The Cliffs (9) early 7
Unrecognized Unrecognized Unit I Goulding Cay Q. (7, 8) 9/11
Unrecognized Unrecognized Unrecognized Goulding Cay Q. (8) 9/11
Unrecognized Unrecognized Unrecognized Goulding Cay Q. (6) 513?
sediments frequently are washed through topographic
lows between older ridges, and accumulate as wash-
over fans, lobes, and basin fills bankward of the cliffs.
This study of the Quaternary stratigraphy of the
Bahamas focuses on several informative sections
located between Whale Point and Goulding Cay
Quarry in north Eleuthera (Fig. 3). Additional sites
from central Eleuthera are used to demonstrate high-
resolution, stage and intra-substage stratigraphy. Site
names are taken from the Bahamas DOS 1:25 000
topographic sheets.
The northern study sites are situated on a very
narrow part of the island centered near Glass Window
Bridge. Large fractures along the cliffs suggest that
from time to time, perhaps mainly during glacial low-
stands as suggested by Aby (1994), the bank margin
retreats by spalling enormous blocks of limestone (Free-
man-Lynde and Ryan, 1985; Mullins and Hine, 1989).
At present, the shelf is narrow and deep, prohibiting
significant accumulation of sediment except as wash-
over deposits. Evidence from a sequence of truncated
middle and late Pleistocene coastal ridges, as depicted in
Fig. 2, suggests that significant cliff retreat occurred
after the emplacement of the last interglacial sequence.
METHODS
Recognizing that single methodological approaches
are inadequate to resolve stratigraphic problems on
Quaternary carbonate platforms, the objective of this
study was to ‘characterize’ limestone units of various
ages with several independent methods (Hearty and
Kindler, 1993a; Vacher et al., 1995). Stratigraphic
superposition and geomorphic juxtaposition (Garrett
and Gould, 1984) explain relationships among the
main units, while limestone petrology (Kindler and
Hearty, 1996), whole-rock aminostratigraphy (Hearty
et al., 1992), and development of capping soils and
calcretes were used to further characterize each unit.
Petrological results from Eleuthera are presented in
a regional perspective in (Kindler and Hearty, 1995;
Kindler and Hearty, 1996; Kindler and Hearty, 1997)
and readers should refer to those studies for methods
and thin-section summaries of major units. Soil colour
analysis (Munsell (1994) wet colours reported in dis-
cussion below) reveals a positive correlation with
stratigraphic age, while analyses of clay mineralogy,
elemental composition, and soil fabric are under way
to quantify these correlations. The underlying theory is
that with greater age, soils will become progressively
redder as ferromagnesian minerals evolve, and light-
coloured carbonate is leached from the matrix. The
soils also increase in finer textures as a function of
weathering of parent materials and dissolution of
coarser carbonate grains with time. To standardize the
soil collections, samples were generally taken from the
crests of ridges, karstic pits, or near-horizontal expo-
sures in cliffs and roadcuts.
Whole-rock aminostratigraphy on limestones has
previously shown its usefulness in establishing correla-
tion and estimating ages of units. The AAR method is
based on the racemization of amino acids preserved in
biominerals. Through time, L-amino acids racemize
(or, more specifically in the case of the amino acid
isoleucine, epimerize) to their D-isomer form. The ratio
of D/L(or isoleucine to alloisoleucine, A/I) amino
acids measures the extent of racemization. In the A/I
epimerization reaction, the ratio is initially zero and
336 Quaternary Science Reviews: Volume 17
FIG. 4. Stratigraphy and correlation of eight sections in north Eleuthera. Whole-rock A/I ratios, limestone composition (skeletal, oolitic, peloidal,
and algal), and inferred correlation with isotope stages are provided for the sections.
increases to an equilibrium ratio of about A/I"1.3
for isoleucine with time after death of an organism and
removal of biological constraints. Like other chemical
reactions, the rate of racemization/epimerization de-
pends on the ambient temperature of the reaction
medium within the rock units. In Bermuda, A/I ratios
on marine shells (Glycymeris sp.), land snails
(Poecilozonites sp.), and whole-rock bioclastic lime-
stones, effectively resolved Holocene, numerous late
and middle Pleistocene, and early Pleistocene inter-
glacial deposits in 97% of 257 stratigraphically posi-
tioned samples (Vacher et al., 1989, 1995; Hearty et al.,
1992). The integrity and concordance of whole-rock
aminostratigraphy in bioclastic and oolitic limestones
has been empirically demonstrated and discussed in
studies from Bermuda (Hearty et al., 1992), San Salva-
dor (Hearty and Kindler, 1993a, 1994), and New Provi-
dence Islands, Bahamas (Hearty and Kindler, 1997a).
Whole-rock samples were gently disaggregated with
a mortar and pestle and repeatedly sieved to exclude
finer grains and cements, and separate the 250850 km
grains for analysis. Once microscopic examination
verified that mainly carbonate grains were isolated,
samples were sent to the Amino Acid Laboratory at
Utah State University for analysis. There samples were
washed repeatedly with ultra pure H2O and leached of
the outer 30% of the grains with 2 M HCl and ana
lyzed according to the procedures outlined in Miller
and Brigham-Grette (1989). All A/I measurements used
in this study are peak height hydrolysate ratios.
To facilitate identification of units and minimize the
introduction of new terms to an already burdensome
nomenclature in the Bahamas, a correlation with iso-
tope stages and substages is inferred, and then demon-
strated through identification of stratigraphic se-
quences and aminostratigraphy. Existing nomencla-
ture in the Bahamas, and units keyed to isotopic stages
are offered in Table 1.
STRATIGRAPHIC SECTIONS
The stratigraphy of north Eleuthera is summarized
in eight sections (Fig. 4) located along a 5-km stretch of
coastline. In many cases, units are physically traceable
in outcrop from site to site, while in others, correlation
is achieved by comparison of parasequences, petrol-
ogy, pedology (Table 2) and aminostratigraphy
(Table 3). The eight stratigraphic sections, arranged in
Fig. 4 from NW to SE, concentrate on the three areas
of Whale Point, Glass Window Bridge, and Goulding
Cay. Four other sections further south are offered to
show the intra-substage stratigraphic detail. In the
interest of brevity and to minimize repetition, the fol-
lowing description of the stratigraphic sections high-
lights only the key features of each section. Soil colour
and textures are reported in Table 2.
Whale point area
Section 1 (EWP3; Figs. 4 and 5)
The Whale Point Section 1 exposes poorly-preser-
ved coral reef facies anchored on older oolitic/peloidal
eolianites, both correlated to Stages 9/11. The reef
facies is capped by an algal limestone and deep red
(2.5YR 4/8) clayey paleosols (Fig. 5). Subsequent
inundation, reef development, and marine erosion
P.J. Hearty.: The Geology of Eleuthera Island, Bahamas 337
TABLE 2 Munsell (1994) wet colour and qualitative texture of soil samples from Eleuthera. Soil data are arranged in stratigraphic order based on
lithostratigraphic position and other information
Field
Number
Collection
date
Munsell
(1994) color
(wet)
Texture Post Stage?
EHS1b 19.2.94 10YR 7/4 Sandy late 1
ETR1b 2.7.94 2.5Y 6/2 Sandy late 1
ESS1b (2) 5.6.93 2.5Y 8.3 Sandy mid 1
ESV2b 21.2.94 2.5Y 7/3 Silty mid 5e
EBH2f 12.5.93 10YR 7/3 Silty 5e/5a
EWP2d 22.5.94 10YR 7/4 Sandy 5e/5a
EBH1f 2.4.95 10YR 7/4 Sandy 5e/5a
ERC3b 7.6.93 10YR 8/4 Sandy 5e/5a
ERC2b (3) 7.6.93 7.5YR 7/8 Sandy 5e/5a
ERC2b (1) 7.6.93 10YR 7/4 Sandy 5e/5a
ERC2b (2) 11.5.93 10YR 7/4 Sandy 5e/5a
EWP1h 22.5.94 10YR 4/3 Clayey silt 5a
ESB1b 1.7.94 5YR 4/6 Clayey silt 5a
EAB3b 16.4.94 5YR 4/4 Clayey 5e
ESV2d 3.8.93 7.5YR 4/3 Mottled silt 5e
EBH1e 2.4.95 7.5YR 5/8 Stony silt 5e
ELB2b 12.5.93 5YR 3/3 Stony clay 5e
ELP2b 30.6.94 5YR 4/6 Clayey 5e
ENP2 7.6.93 7.5YR 4/4 Sandy silt 5e
EHA1b 2.7.94 5YR 4/4 Clayey 5e
ERC5b 7.6.93 2.5YR 3/4 Clayey 5e
EHA1b 20.2.94 5YR 4/6 Clayey 5e
EGC1s 2.4.95 5YR 4/6 Dense clay 5e inherited 9/11
EGW1e 25.5.94 7.5YR 8/3 Sandy mid 7
ETC1d 12.5.93 5YR 5/6 Stony sand mid 7
ETC1d/e 12.5.93 5YR 5/6 Stony sand mid 7
EGW1g 25.5.94 7.5YR 7/6 Sandy mid 7
ECH2h 2.4.95 7.5YR 5/8 Sandy silt 7
ETC1g 12.5.93 5YR 4/4 Clayey 7
ESE1d 6.6.93 10YR 8/2 Stony sand mid 9?
EAF1b 9.5.93 2.5YR 3/4 Clayey 9/11
EGC1e (1) 3.7.94 2.5YR 3/6 Clayey 9/11
EGC1e (2) 3.7.94 2.5YR 3/6 Clayey 9/11
EBH1b 2.4.95 2.5YR 4/6 Stony clay 9/11
EGC1e 24.5.94 2.5YR 2.5/4 Clayey 9/11
EWP3d 19.7.96 2.5YR 4/8 Sandy clay 9/11
ECH1d 31.3.95 5YR 3/4 Clayey 9/11
EOP1b 7.6.93 2.5YR 4/6 Stony clay 9/11
EOD1b 14.5.93 2.5YR 2.5/4 Clayey 9/11
EGT1e 4.8.93 2.5YR 3/4 Clayey 9/11
EWY2b 2.7.94 2.5YR 3/3 Silty clay *11
EWW1b (1) 31.7.93 2.5YR 3/3 Silty clay *11
ESE1b 6.6.93 5YR 4/4 Stony clay *11
EGC2b 3.7.94 5YR 5/8 Stony clay *13
associated with Substage 5e created spur and groove
topography upon the paleosol-capped, middle Pleis-
tocene reef. Sparsely distributed coral heads and re-
gressive oolitic 5e beach deposits infill the grooves.
Geochronological studies are under way to establish if
radiometric and ESR dating methods can determine
the age of the poorly-preserved middle Pleistocene
corals from Whale Point. Substage 5a skeletal
eolianites rest directly upon post-5e paleosols (10YR
7/4) and older 5e beach deposits (Fig. 6). At Whale
Point these deposits consist of lobes of low-angle bed-
ding that extend landward in topographic depressions
in the older rocks. ¹erra rossa soils and Holocene dune
and washover deposits complete the sequence.
Section 2 (EWP1, Whale Point; Fig. 4)
Section 2 is based in the same Stage 9/11 eolianite as
Section 1, but lacks the older coral reef facies. Higher in
the section, oolitic 5e beach and subtidal facies are
overlain by sandy, reddish, brecciated paleosols (10YR
7/4) and skeletal 5a eolianites (Fig. 6). A/I ratios
(5e"0.395/5a"0.309) (Table 3) confirm the passage
of several tens of thousands of years between substage
338 Quaternary Science Reviews: Volume 17
TABLE 3 Whole-rock amino acid ratios (A/I) from major units in Eleuthera. Samples were prepared by the author, and analyzed by Dr Darrell
Kaufman (Utah State University Amino Acid Laboratory)
Stage LabdFielddMean ($1p) Facies
1 1465A ESS1a 0.086$0.003 beach/eolian
1463A EWI1ab 0.100$0.001 eolian
1678A EGC3z 0.145$0.005 washover
Mean: 0.110$0.031 (n"3)
Major paleosol
5a 1464A EFI1e 0.299$0.002 eolian
1466A ESK1a 0.300$0.001 eolian
1467B ERC2c*0.248$0.003 eolian
1562A EBH1g*0.302$0.003 eolian
1573A EWP2k*0.309$0.001 eolian
Mean: 0.292$0.025 (n"5)
Minor paleosol
5e 1094D ESV1c 0.345$0.005 eolian
1094B/1104C ETP1c 0.363$0.010 eolian
1104B/1094A ETP1a 0.320$0.026 (lc)? eolian
1094C ESV1a 0.403$0.004 eolian
1275A EHA1a 0.406$0.007 beach
1275B EHA1a 0.388$0.008 beach
1564A ECH2i 0.372$0.010 beach
1467A ERC2a*0.369$0.006 eolian
1563A EBH1d*0.407$0.003 beach
1567A EWP2i*0.395$0.002 beach
1812A EMB4e 0.385$0.004 beach
1814A EMB2o 0.400$0.003 eolian
Mean: 0.379$0.027 (n"12)
Major paleosol 7
1101B ETC2c 0.352$0.004 (lc,ni) eolian
1568A ETC1e 0.382$0.013 (lc,ni) eolian
1388D EGW1h 0.569$0.022 (lc) eolian
Minor paleosol 7
1388C EGW1f 0.581$0.023 (lc) eolian
1101A ETC2a 0.576$0.008 (lc) eolian/washover
Stage 7Mean: 0.575$0.006
(n"3)
Major paleosol 9/11
1389A/1561A EGC3f 0.709$0.181 (h) beach (#1320 m)
1682A EGC6f 0.716$0.023 (h) beach (#1320 m)
Mean: 0.712$0.102 (n"2)
Unconformity 9/11
1565A ECH1c 0.542$0.009 (lc,ni) beach/washover?
1676A EGC2d 0.625$0.010 washover
1392A/1675A EGC2c 0.635$0.104 (lc) eolian
1387A EGC1d 0.632$0.013 beach (#5m)
1679A EGC5e 0.631$0.007 eolian
1388B EGW1d 0.616$0.021 eolian
Mean: 0.628$0.007 (n"5)
Numerous contacts and minor paleosols throughout 9/11
1388A EGW1c 0.434$0.013 (&, ni) eolian
1677A EGC3d 0.670$0.005 beach (#7m)
1387A EGC1c 0.678$0.024 beach
1566A ECH1a 0.651$0.019 beach (#2m)
1816A ECC1a 0.699$0.001 eolian
Mean: 0.675$0.020 (n"4)
Megaboulders
1809A EMB2g 0.734$0.019 displaced boulder
1810A EMB4g 0.737$0.025 displaced boulder
1811A EMB3 0.667$0.016 displaced boulder
1813A EMB5 0.619$0.013 displaced boulder
1815A EMB1 0.604$0.008 displaced boulder
Mean: 0.671$0.063 (n"5)
Overall 9/11 complex Mean: 0.671$0.050 (n"16)
Major paleosol *13
1392B EGC2a 0.789$0.036 (lc) eolian
1681A EGC6a Trace eolian
1680A EGC6c Trace eolian
1673A EBH3aa Trace eolian
1674A EGC2aa Trace eolian
(lc)"low concentrations of amino acids; (ni)"ratios excluded from mean. (h)"Surface heating probable based on field observations; *5e/5a
pairs (same field number prefix) in superposition, separated by a well-developed red soil. &" petrographic analysis of sample EGW1c shows two
generations of cements: the older precipitated in a freshwater vadose environment, the latter was formed in a marine phreatic environment. The
younger generation of cements may be responsible for the discordant ratio. Trace"insufficient concentation of amino acids to make accurate
measurement.
P.J. Hearty.: The Geology of Eleuthera Island, Bahamas 339
FIG. 5. Detailed stratigraphic section of the Whale Point coral reef area. (1) Stage 9/11 oolitic/peloidal eolianite; (2) deep red paleosol; (3) coral reef
of middle Pleistocene age; (4) algal limestone capping reef facies; (5) dark red paleosol (2.5YR 4/8) capping reef and algal facies; (6) Substage 5e coral
heads; (7) Substage 5e regressive beach deposits; (8) rocky, reddish brown, (10YR 7/4) 5e/5a paleosol; (9) Substage 5a skeletal eolianite; (10) post-5a
paleosol; and (11) Holocene skeletal washover deposits.
FIG. 6. Photo of paleosol at 5e/5a contact in a roadcut at Whale Point Section 2. The age difference between the two Stage 5 limestone units,
indicated by the reddish paleosol (‘p’) and karstified surface, is supported by whole-rock A/I ratios of 0.395 (5e) and 0.309 (5a). Several other sections
(1, 5, and 10) yield similar stratigraphy, petrology, and/or A/I ratios.
events, also indicated by the development of the karsti-
fied surface on 5e oolite and red paleosol separating
these two units.
Glass Window area
Section 3 (ECH2, Cotton Hole; Fig. 4)
Three or four interglacials are represented in the
area of Section 3 north of Cotton Hole. Like Whale
Point, the section is based in oolitic/peloidal beach,
washover, and eolian facies correlated to Stages 9/11.
Thin, ferruginous, skeletal deposits with Cerion land-
snails and rhizomorphs represent a distal backbeach
facies equated with Stage 7. Terrestrial bioturbation
during periods of vegetative growth has obscured all
evidence of bedding in this unit. Oolitic washover and
beach deposits of from Substage 5e rise to #10 to
#12 m a.s.l., while Holocene skeletal washover sedi-
ments fill low areas landward of the section. A/I ratios
associated with the units are Stages 9/11"0.651; 9/11
or 7?"0.542; and 5e"0.372.
Section 4 (EGW1; Glass Window; Figs. 4 and 7)
Section 4 at Glass Window contains two fairly com-
plete, stacked sequences (9/11 and 7, Fig. 7) of middle
340 Quaternary Science Reviews: Volume 17
FIG. 7. Photograph of the Glass Window Section 4 representing Stages 7 through 9/11.
Pleistocene age. The lower is oolitic/peloidal eolianite
and washover facies (A/I"0.616) capped by a thick
calcrete, while the upper sequence consists of skeletal
eolianites and protosols. Close agreement with A/I
ratios in Stage 7 sequence (0.581/0.569) suggests that
each of these deposits were probably derived from the
same offshore sediment pool. Interbedded eolianites
and reddish-yellow protosols (7.5YR 7/68/3) imply
a distal shoreline environment that was alternately
blanketed by fresh bioclastic sediments, probably de-
posited mostly during major storms, and subsequently
vegetated during periods of either ecological stability,
minor negative sea-level oscillations, or both during
Stage 7.
Section 5 (EBH1; Boiling Hole; Fig. 4)
Petrography and sedimentary facies of the Boiling
Hole Section 5 are reported in Kindler and Hearty
(1995). To add to these findings are (1) a more complex
middle Pleistocene stratigraphy; (2) confirmation by
A/I ratios of the suggested 5e and 5a ages of the upper
units; and (3) mention of the Holocene, skeletal wash-
over trough lying to the SW of the main section.
Studies subsequent to Kindler and Hearty (1995) re-
vealed that both oolitic/peloidal deposits (9/11) and
older skeletal eolianites (Stage '13?) capped by dark
red paleosols (2.5YR 4/6) are present at the base of the
section. AAR analyses of the oldest stratigraphic
(5Stage 13) unit provided unmeasurable trace levels
of amino acids, while those from ‘middle’ and ‘upper’
units produced typical 5e and 5a A/I ratios of 0.407
and 0.302, which are concordant with Section
2 (0.395/0.307). The A/I ratios and intermediate reddish
paleosol (10YR 7/4) confirm the age difference of sev-
eral tens of thousands of years between early and late
Stage 5 units. Where not overlain by skeletal eolianites,
5e oolites are capped by reddish paleosol (7.5YR 5/8)
formed during the last glacial period.
Goulding Cay Quarry area
Section 6 (EGC6; midway between Boiling Hole and
Goulding Cay; Figs. 4 and 8a,b)
The base of this section exposes a complex history of
skeletal eolianites and paleosols belonging to the oldest
surficial units recognized in the Bahamas (*Stage 13).
This lowest interglacial unit is overlain by a red
paleosol, and further by a thick oolitic/peloidal
eolianite correlated to Stages 9/11. Fenestrae-rich,
horizontally-bedded intertidal facies (Fig. 8B) lie upon
a narrow bench at #15 and #20 m, truncating an
older steeply-dipping eolianite (Fig. 8A). A slightly el-
evated A/I ratio of 0.716 from these thin and exposed
oolitic/peloidal deposits confirms a Stage 9/11 correla-
tion of these deposits.
Section 7 (EGC2; Goulding Cay Quarry, north; Figs. 4
and 9)
A shore-parallel geologic cross-section in Fig. 9
summarizes the stratigraphy in the area of the Gould-
ing Cay Quarry including both Sections 7 and 8. Sec-
tion 7 contains a thick, eolian and washover sequence
of oolitic/peloidal composition overlying Stage
'13? eolianites and a yellowish red (5YR 4/8), par-
tially-leached, stony-clay paleosol. The lower eolianite
preserves standing palmetto casts, while the upper unit
contains washover deposits and fenestrae between #8
and #20 m. These high-energy washover deposits ap-
pear to infill topographic lows among older beds, and
P.J. Hearty.: The Geology of Eleuthera Island, Bahamas 341
FIG. 8. (A) Setting of #20 m beach deposits (‘b’) at Section 6 between Boiling Hole and Goulding Cay Quarry above a Stage 9/11/13 sequence.
(B) Fenestrae-rich, horizontally-bedded beach deposits in the upper unit at Section 6, truncating older cross-bedded eolianitese of similar
composition. (C) Fenestrae-rich, horizontally-bedded beach deposits on a narrow platform from #13 to #20 m at Section 8 (‘D’ indicates
location of fenestrae in photo D). (D) Detail of beach fenestrae (‘fp’) in beach deposits at Section 8.
FIG. 9. Schematic cross-section of the Goulding Cay Quarry. With the exception of patchy deposits of Stage 1 and 5e, the entire section is of
middle Pleistocene age.
are perhaps related (although it is not stratigraphically
clear) to the sea-level regression from the #20 m sea-
level maximum.
Section 8 (EGC1/3; Figs. 4, 9 and 10; Goulding Cay
Quarry, south)
Four distinct units of middle Pleistocene age com-
prise Section 8. The lowest of these oolitic/peloidal
units exposes intertidal and subtidal facies, indicating
a sea-level at around #2 m. A subsequent highstand
eroded a greater than 50-m-wide terrace at #7 m into
the lower unit (Fig. 10A). Subtidal, beach and eolian
facies are present on the #7 m terrace (Fig. 10B),
suggesting a stable, prolonged sea-level during 9/11.
The #7 m beach is succeeded by a thin (inaccessible)
paleosol or protosol and a massive eolianite rising to
#30 m. Into this eolianite, a horizontally-bedded,
342 Quaternary Science Reviews: Volume 17
FIG. 10. Photos of the #7 m platform at Goulding Cay Section 8 showing erosional terrace (photo A) mantled with subtidal (‘s’), beach (‘b’), and
eolian (‘e’) deposits. Detail of basal contact (‘c’) and subtidal facies (‘s’) at #7 m are pointed out in Photo B by P. Kindler.
regressive beach sequence with fenestrae is deposited
on a narrow bench at #13 m (Fig. 8C,D). At Section
8, a cairn marks the highest elevation of beach fenes-
trae at #20 m. Physical characteristics, stratigraphic
position, and an A/I value of 0.712 establish a correla-
tion of the #20 m beach at Section 8 with a similar
sequence at Section 6 (0.716) (Fig. 4). A/I ratios are
statistically similar, but slightly elevated relative to
adjacent beds, probably as a result of surface heating
effects in the thin ((1.5 m) beds. Above #20 m, dark
P.J. Hearty.: The Geology of Eleuthera Island, Bahamas 343
FIG. 11. Largest of several megaboulders at the crest of a 15-m ridge in north Eleuthera near Section 5. This example measures 13]11.5]6.5 m,
and weighs over 2000 tonnes. Whole-rock A/I ratios and boulder petrology yield a middle Pleistocene age, while underlying deposits are correlated
to Substage 5e. The megaboulder setting and stratigraphy indicate that they were deposited by very large waves at the end of Substage 5e (Hearty,
1997).
red (2.5YR 3/6) clayey paleosols fill pits of deeply
(13 m) karstified Stage 9/11 limestone. Numerous
patches of younger washover deposits are distributed
throughout the trough (labeled ‘7?’ and ‘5e?’ in Fig. 9).
Westward or landward of the cliffs at Section 8, Holo-
cene skeletal washover deposits (A/I"0.145) over 8 m
thick fill at 1 km2basin.
Section 8 at Goulding Cay Quarry reveals the com-
plexity of the Stage 9/11 sequence in Eleuthera by
exposing deposits of at least three important highstand
events, with associated foreshore facies, eolianites, and
capping dark red, clayey paleosols. The lower two
units contain beach and subtidal bedding (Figs. 9 and
10), probably correlated to Stage 11. A/I ratios from
the four units (0.678; 0.670; 0.632; 0.712) confirm the
association of these deposits with a pre-Stage 7, middle
Pleistocene time interval, however unfortunately, at
this time cannot precisely establish which, if any of the
several discontinuities (contacts and soils) mark the
Stage 9/11 boundary. Independent methods will per-
haps resolve this critical point in the future.
Megaboulder deposits
In the Glass Window area, very large boulders, the
largest measuring 14 m in length and weighing over
2000 tonnes (Fig. 11), are testimony to the powerful
waves that have struck the north Eleuthera coastline in
the past. The location of these boulders are identified in
Fig. 3 by the triangle symbol. Disorientation of bed-
ding planes, sub-boulder stratigraphy, petrological
analysis, and amino acid ratios confirm that the boul-
ders are middle Pleistocene age, and that they were
deposited by waves late in Substage 5e (Hearty, 1997).
A/I ratios from five of the boulders (0.604, 0.734, 0.660,
0.737, and 0.619; mean"0.671$0.063) are consistent
with mean ratios from the in situ Stage 9/11
oolitic/peloidal unit (mean"0.660$0.040; Table 3)
situated near the base of the cliff sections. Some of the
boulders rest upon 5e marine and eolian oolites yield-
ing ratios averaging 0.393$0.011 (2), indicating strati-
graphic inversion. This mean agrees with the Eleuthera
mean (0.379$0.027 (n"12)) for Substage 5e. Hy-
potheses on the possible genesis of the large waves are
discussed elsewhere (Hearty, 1997).
Other sections
We present the following four sections in Fig. 12
from central Eleuthera (located on schematic geologic
maps in Fig. 13 and Fig. 14) to further illustrate the
detail and completeness of the Pleistocene and Holo-
cene sections. The sections in Fig. 12 show multiple
sea-level oscillations and depositional events at subst-
age and intra-substage scale. The stratigraphy, petrol-
ogy, and A/I ratios are concordant with north Eleuth-
era sections.
Section 9 (ETC1/2; The Clis; Figs. 12 and 13)
Section 9 at ‘The Cliffs’ is the most complete of the
Stage 7 sequences in Eleuthera containing four eolian
344 Quaternary Science Reviews: Volume 17
FIG. 12. Four stratigraphic sections from central Eleuthera highlighting intra-stage and substage stratigraphy. The legend is the same as Fig. 4,
and the sections are located on Fig. 13 and Fig. 14.
FIG. 13. Schematic geologic map of the area of The Cliffs (Section 9) and Rainbow Cay (Section 10).
units separated by protosols and midway by a well-
developed terra rossa (5YR 5/6) paleosol. The stratigra-
phy and petrology of this section were examined in
detail by Kindler and Hearty (1995), at which time the
skeletal eolianite sequence was correlated with Stages
7 and 9. The author’s view is that the entire span of
Stage 7 from 240 to 190 ka comprises the older portion
of Section 9. The important stony/sandy paleosol sep-
arating lower and upper eolianite pairs probably de-
veloped during a prolonged emergence (3040 ka)
within Stage 7. An A/I ratio on the lowest unit (0.576)
corresponds to Section 4 at Glass Window (0.581) and
supports the younger Stage 7 interpretation of the
sequence. Landward of, and onlapping the older Cliffs
section is an intertidal oolite correlated to 5e. These
ooid shoal deposits demonstrate active tidal circula-
tion around the middle Pleistocene islets. A landward
basin is filled with thick, skeletal, Holocene washover
deposits (Fig. 13).
Section 10 (ERC3: Rainbow Cay; Figs. 12 and 13)
The stratigraphy of Section 10 in a highway roadcut
near Rainbow Cay illustrates most clearly the age
separation between oolitic eolianites of 5e age, and
skeletal eolianites deposited late in Stage 5. A
brecciated red paleosol (7.5YR 7/810YR 8/4) and
centimeter-thick calcrete separate the two Stage 5
units (Fig. 12; Hearty and Kindler, 1993b; Kindler
and Hearty, 1996). A/I ratios from lower (0.369)
and upper eolianites (0.248) support a 3050 ka
age difference, and correlate the units with other
P.J. Hearty.: The Geology of Eleuthera Island, Bahamas 345
FIG. 14. Schematic geologic map of the area around Governor’s Harbour including sites at Savannah Sound (Section 11) and Singing Sands
(Section 12) (modified from Kindler and Hearty, 1996).
5e/5a sequences in north Eleuthera at Sections 1, 2
and 5.
Section 11 (ESV1; Savannah Sound; Figs. 12 and 14)
The stratigraphy at Section 11 from Savannah
Sound demonstrates a double-5e highstand. As with 5e
sections elsewhere in the Bahamas (Muhs et al., 1990;
Hearty and Kindler, 1997a (New Providence); Chen et
al., 1991 (Inagua); Hearty and Kindler, 1995; Neumann
and Hearty, 1996), two depositional phases are recog-
nized between 132 and 118 ka (Chen et al., 1991), with
a regression indicated at around 124 ka. Section 11
shows mainly the early and late oolitic eolian facies,
separated by a pale yellow (2.5Y 7/3) protosol with
abundant Cerion landsnails and rhizomorphs. Late in
the 5e, rapid mobilization of lagoon oolites by wind
buried living trees and palmettos. Evidence of rapid
fluctuations of sea-level late in 5e was presented by
Neumann and Hearty (1996). Among the many fea-
tures supporting this unsettled climatic interval are
chevron ridges, runup deposits, and the transport of
megaboulders (Hearty et al., in review; Hearty, 1997).
A/I ratios show some age separation between lower
(0.403) and upper (0.345) eolianites at Section 11, while
mean ratios correlate these deposits with other 5e
sections in Eleuthera and elsewhere in the Bahamas
(Kindler and Hearty, 1996; Hearty et al., in review).
Section 11 is capped by a mottled, silty, brown (7.5YR
4/3) paleosol.
Section 12 (ESS1; Singing Sands; Figs. 12 and 14)
The extent of the Holocene depositional sequence is
revealed in beach exposures and an extensive dune field
at Singing Sands near Governors Harbour. A mid
Stage 1 oolitic eolianite formed when sea-level was
lower than present, and was subsequently partially
buried by younger skeletal beach and eolian deposits.
A pale yellow (2.5Y 8/3) sandy protosol sometimes
separates the two units. A/I ratios from an equivalent
mid Holocene oolitic eolianite on Windermeer Island
yields an A/I ratio of 0.100, while that from the skeletal
unit from Singing Sands is 0.089.
COMPOSITE SECTION
Physical stratigraphy and petrology
A stratigraphic mosaic (Fig. 15) is constructed from
the most complete and exemplary of the 12 sections
illustrated and discussed above. This composite is
346 Quaternary Science Reviews: Volume 17
FIG. 15. A composite geology from Eleuthera Island showing physical stratigraphy, relative sea-level, petrographic composition of units, mean
A/I ratios (from Table 3), soil colour, and dominant sedimentary facies.
a summary of the major units identified on the basis of
stratigraphic and geomorphic position, limestone pe-
trology and diagenesis (Kindler and Hearty, 1995,
1996), sedimentary structures, pedogenesis, and amino
acid geochemistry. This composite comprises at least
six interglacial complexes. Within those, eight para-
sequences can be defined on the basis of terra rossa
paleosol-bounded limestone units. The Holocene is
counted among those, but of course, is lacking a terra
rossa paleosol at its upper contact.
Pedostratigraphy
The results of this study indicate that soil colour and
texture are good qualitative indicators of relative age
of stratigraphic units. In general, soils become redder
with greater age, a relationship graphically illustrated
in a plot of Munsell (1994) soil colour vs. stratigraphic
age (Fig. 16). In 44 sample cases, soil colour is used to
distinguish three groups of deposits. The youngest,
centered on 10YR 7/4, includes Holocene and mid-
interglacial soil samples. The next older group com-
prises both post-Stage 5 and 7 soils, but cannot distin-
guish between them. This group is centered on 5YR 4/4
with some yellower outliers of post-5e age. The oldest
group of paleosols are those capping Stage 9 and 11
limestone. With only two exceptions, the group is
centered on 2.5YR 3/4. From this preliminary and
cursory study, it is clear that soil characteristics can be
used to distinguish broad classes of ages in a majority
('80%) of cases. These findings disagree with those of
Boardman et al. (1995) who concluded on the basis of
soil type and clay mineralogy that soils were not a use-
ful stratigraphic tool in the Bahamas. Neither soil
colour nor samples representing multiple stratigraphic
horizons were examined in their study.
P.J. Hearty.: The Geology of Eleuthera Island, Bahamas 347
FIG. 16. Munsell plot of soil colour vs geologic age of 44 soil samples from Eleuthera. Three groups are defined based on colour: (1) the youngest
(Stage 1) and mid-interglacial (e.g. 5e/5a) soils; (2) a middle group including soils capping Stage 5 and Stage 7 deposits; and (3) an oldest group of
soils capping Stage 9 or older deposits.
Red paleosols are generally associated with glacial
lowstands; however, it is clear from several examples
that they may also form during periods of prolonged
emergence within interglacials (Hearty and Vacher,
1994), and thus cannot be used exclusively as a cri-
terion for defining only full glacial cycles. Major inter-
glacial terra rossa soils (formed on a 105year scale) are
generally deep red (5YR 4/4 to 2.5YR 3/6), more clayey,
and situated on a moderately to deeply karstified sur-
face ('1 m). Minor mid-interglacial soils (formed on
a10
4year scale) are generally yellowish brown or
reddish yellow (10YR 7/4 to 5YR 5/6) and contain
more silt and sand. The karstification of the underlying
limestone surface is moderate, extending downward
some decimeters. The best examples of intra-stage red-
dish paleosols (tightly centered on 10YR 7/4) are the
soils that formed between 5e and 5a (Sections 1, 2, 5,
and 10; Fig. 6), each apparently requiring around 30 to
50 ka to develop. Protosols, which are sandy and buff
colour (2.5Y 7/3), reflect brief periods (formed over
a10
3year scale) of reduced carbonate sand deposition
as a function of ecological stability, minor sea-level
regression, or both. There is no significant karstifica-
tion of the limestones underlying protosols, however,
thin (23 mm) calcrete may be present on the
limestone surface beneath the soil. With a reduced
input of sediment to land, vegetation thrives on dunes
and beach deposits, ultimately preserving root casts,
land animals, and other organic traces common in
protosols. Protosols are used to identify breaks in
sedimentation within substage events, and thus, their
formation is constrained to a few hundred to a few
thousand years.
Aminostratigraphic correlation
The whole-rock A/I ratios presented in the strati-
graphic sections are used as a geochemical signature
with which lithostratigraphic correlations can be verifi-
ed. In general, stratigraphic units keyed to isotopic
stages and substages have mean ratios of: Stage
'13?"0.79; Stage 9/11"0.67$0.05; Stage 7"
0.58$0.01; Substage 5e"0.38$0.02; Substage
5a"0.29$0.03; and Stage 1"0.09$0.01.
Stratigraphic order of the A/I ratios is maintained in
over 90% of cases. Some of those in stratigraphic order
appear to disagree with the lithostratigraphic se-
quence, indicating one or two interglacials younger
than indicated by the geology. These ‘younger’ ratios
may be either the result of slight leaching of the sam-
ples, or may indeed represent younger ages of the
deposits. The samples and sites in question will be
subject to additional tests in the future. Most samples
from the oldest unit (Stage '13) have amino acid
concentrations too low to be accurately measured.
Perhaps repeated subsequent inundation by marine
and fresh waters have leached the bulk of amino acids.
However, the near absence of amino acids is, in itself,
an indication of the great age of this stratigraphic unit.
Only those late Pleistocene samples closely associated
with soils are ever found to be significantly leached.
Thus, loss or alteration of amino acid composition
most commonly occurs in samples that are completely
recrystallized, shallowly-buried samples that have ex-
perienced significant surface leaching (generally asso-
ciated with soils), or those that have experienced re-
peated submergence.
348 Quaternary Science Reviews: Volume 17
TABLE 4 Estimated ages of stratigraphic units by apparent parabolic kinetics (Mitterer and Kriausakul, 1989) using whole-rock amino acids
ratios
Stratigraphic correlation stage A/I mean$1p(number of samples) APK age estimate (years) ($error from key#error from aminozone)
Stage 1 0.110$0.031 (n"3) 10 350$3600
Red paleosol
Stage 5a 0.292$0.025 (n"5) 73 000$6000
Reddish paleosol
Stage 5e KEY 0.379$0.029 (n"12) 123 000$7700
Red paleosol
Stage 7 0.575$0.006 (n"3) 283 000$23 000*
Red paleosol
#20 m 9/11 beach 0.712$0.102 (n"3) 434 000$95 000
Minor unconformity
Stage 9/11 0.628$0.007 (n"5) 338 000$30 600
Minor unconformity
Stage 9/11 0.675$0.020 (n"3) 390 000$38 000
Megaboulders 0.671$0.063 (n"5) 385 000$67 000
9/11 mean 0.671$0.050 (n"16) 385 000$59000
Major complex paleosol
Stage'13 0.789$0.000 (n"1) 533 000$41 000
Error of age estimates is calculated by adding the error of the key (7.7%) plus error of mean values of each aminozone.
*Stage 7 age probably an overestimate due to significant heating of samples during Substage 5e at early phase of epimerization reaction (see text).
The thin deposits associated with the #20 m beach
in Section 8 have produced samples with a whole-rock
mean A/I of 0.71, and normal levels of amino acids.
This combination of characteristics appears to be
a function of surface heating, rather than alteration of
amino acids concentrations through selective leaching
which generally lowers A/I ratios. Even with such
minor thermal effects, the A/I mean of the #20 m
beach statistically agrees with ratios from adjacent
beds, and confirms a middle Pleistocene correlation.
Younger oolites differ significantly from the #20 m
oolitic beach deposits by producing consistently lower
A/I ratios and a lower grade of diagenesis. A/I ratios
from younger oolites (Stages 5a and 1) are concordant
throughout the study area (Table 3) and the Bahamas
(Kindler and Hearty, 1996). In summary, regardless of
whether discordant A/I data are included or excluded
from the mean aminozone values, comparable and
compatible sequences are defined by both the litho-
and aminostratigraphic methods (Fig. 15).
Ages of aminozones and interglacial deposits
Age estimates for aminozones can be derived from
mean whole-rock A/I ratios for each unit (Table 3;
Fig. 15) by the apparent parabolic kinetics method (or
APK, Mitterer and Kriausakul, 1989). This dating ap-
proach uses a parabolic kinetic pathway to approxim-
ate the epimerization reaction as it proceeds from
younger to older samples. In a previous study, Hearty
and Dai Pra (1992) confirmed an imperfect parabolic
configuration of the curve with empirical data, and
identified three interim phases (I to III) of exponenti-
ally decreasing rates.
Target isotopic age ‘windows’ for the middle and late
Pleistocene interglacials are: Stage 15"617565 ka;
Stage 13"513478 ka; Stage 11"420362 ka; Stage
9"331303 ka; Stage 7"238194 ka; Substage
5e"128122 ka; Substage 5a"8771 ka; Stage
1"120 ka (Imbrie et al., 1984). The first-order age
estimates from the APK method, summarized in
Table 4, compare favorably with the target interglacial
ages identified through proxy methods.
APK age estimates are based on a Substage 5e
calibration at 123 ka, which equates with a mean A/I of
0.38$0.03 (n"12). A single A/I ratio from the oldest
Stage '13? unit predicts an age of 533$41 ka (Stage
15 or 13). Although it is well recognized that a single
ratio is inadequate to establish sound conclusions re-
garding age, this age estimate agrees with its lithos-
tratigraphic age of 5Stage 13. The Stage 9/11 mean
ratio of 0.67$0.05 (n"16) yields an APK age esti-
mate of 385$59 ka (444 to 326 ka), encompassing
depositional events during both Stages 11 and
9 — a complexity and duration that is evident in the
Goulding Cay Quarry sections. The succeeding skel-
etal eolianites yield an APK age estimate of
283$23 ka determined from an A/I mean of
0.58$0.01 (n"3). This age estimate is possibly con-
cordant with an early Stage 7 cave-flooding event in
the Bahamas TIMS dated at 233 ka by Lundberg and
Ford (1994). Stage 7 samples may be particularly sensi-
tive to accelerated rates during the warmth of Stage
5 during their earliest, fastest and most sensitive reac-
tion phase (A/I 0.10.4) during their first 100 ka dia-
genesis of the samples. Data from this interval indicate
that the epimerization reaction responds to warmer
interglacial temperatures with faster rates (Hearty and
Dai Pra, 1992), departing somewhat from the idealized
APK model of Mitterer and Kriausakul (1989).
From a mean ratio of 0.29$0.02 (n"5), an age of
73$6 ka is calculated for the post-5e Pleistocene de-
posits at several sections, and thus a correlation with
the Southampton Fm in Bermuda (Vacher et al., 1989).
P.J. Hearty.: The Geology of Eleuthera Island, Bahamas 349
TABLE 5 Correlation based on litho- and aminostratigraphy between Bermuda, New Providence, and Eleuthera Islands. Because of a cooler
temperature history, the mean aminozone A/I ratios from Bermuda are lower than those from the Bahama Islands
Isotope stage
[aminozone]
Bermuda; Hearty et al. (1992);
Hearty and Vacher (1994)
New Providence Island, Bahamas;
Hearty and Kindler (1997a)
Eleuthera Island, Bahamas (this study)
Site/Fm. W-R A/I ratio Site W-R A/I ratio Site W-R A/I ratio
1 [A] Recent 0.12$0.01 (2) Xanadu Beach 0.09$0.01 (1) Singing Sands;
Windermeer I.
0.11$0.03 (2)
5a [C] Southampton 0.23$0.03 (3)*Green Cay 0.28$0.01 (2) Whale Point;
Rainbow Cay
0.29$0.03 (5)
5e [E] Rocky Bay 0.29$0.03 (12)*Lyford Cay 0.36$0.03 (4)*Boiling Hole;
Savannah Sound
0.38$0.03 (12)
7 [F] Belmont 0.49$0.04 (11)*Skyline Estates 0.56$0.02 (3) Glass Window;
The Cliffs
0.58$0.01 (3)
9 [G] Upper Town Hill 0.56$0.02 (11) Blue Hill Ridge 0.67$0.01 (2)*Goulding Cay
Quarry; Glass
Window
11 [H] Lower Town Hill 0.69$0.01 (6) Hunt’s Cave Quarry 0.71$0.03 (2) Goulding Cay
Quarry
0.67$0.05 (16)
*13 [I] Goulding Cay
Quarry
0.78 (1)
*Correlation verified by uranium-series ages from coeval deposits.
Given a correction for cooler temperature history,
equivalent Bermuda units (both of bioclastic composi-
tion) yield parallel whole-rock ratios indicative of
a 5e/5a relationship. This relationship was confirmed
by U-series ages (Harmon et al., 1983) and epimeriz-
ation models (Hearty et al., 1992). APK predicts an
age difference between early last interglacial oolites
(Substage 5e) and late interglacial skeletal eolianites
(Substage 5a) of 40 50 ka, again supporting the infer-
red 80 ka, Substage 5a correlation of the younger de-
posits, rather than 5c. This age difference is most evi-
dent in the well developed red paleosol and karst
surface separating the two units at Sections 1,
2 (Fig. 6), 5, and 10. Ludwig et al. (1996) recently
reconfirmed the age of the Southampton Fm at 80 ka
with TIMS U-series dates on corals, and endorsed the
geological and aminostratigraphic findings of Vacher
and Hearty (1989) of an 80 ka highstand at 0 to #1m.
Parabolic kinetics characteristically yield an obvious
over estimate of 10.5 ka for Stage 1 deposits when
compared to 14C calibration of (5000 years BP
(Carew and Mylroie, 1987).
Summary of composite stratigraphy
The Quaternary geology of Eleuthera provides
a relatively complete, high-resolution stratigraphic re-
cord of at least six broad interglacial sea-level cycles
(105year cycles), comprising several intervals of pro-
longed platform emergence (104(2040 ka) year
cycles), and minor ecological or eustatic oscillations
(103year cycles) (Fig. 15) indicated by protosols. The
inferred correlation with isotopic stages is based prim-
arily on the stacked stratigraphic sequences and major
bounding deep red paleosols (Figs. 4 and 12). This
correlation requires that the age of the oldest skeletal
unit at the base of Sections 5, 6, and 7 is *Stage 13.
Both Stages 11 and 9 may be represented in the com-
plex stratigraphy (four or five units/numerous
oolitic/peloidal facies) of Sections 1, 6, 7 and 8; how-
ever, our data relevant to this point are not yet conclus-
ive. The Stage 7 skeletal eolianite complex appears to
span the full interglacial with a prolonged period of
emergence of the platform midway through the inter-
glacial.
As shown in previous studies (Garrett and Gould,
1984; Hearty and Kindler, 1995, 1997a,b; Neumann
and Hearty, 1996), Stage 5 is indeed complex. Three
major depositional phases are recognized: two oolitic
complexes associated with significant sea-level oscilla-
tions within Substage 5e (Aharon et al., 1980; Hollin
and Hearty, 1990; Hearty and Kindler, 1995), and
a final Substage 5a event, separated from 5e by a red-
dish paleosol. Extensive skeletal eolianite ridges were
deposited throughout the windward Bahama Islands
(Hearty and Kindler, 1993a; Kindler and Hearty, 1996)
and Bermuda (Vacher and Hearty, 1989; Ludwig et al.,
1996) during this interval. Remnants of a firmly-
cemented, oolitic eolianite ridge from mid Stage
1 exists only on exposed, high-energy coastlines, while
a lightly-indurated, skeletal sand late Stage 1 shoreline
complex (beach, eolian, and protosol facies) is found on
most islands of the Bahamas.
REGIONAL CORRELATION
The geology of north Eleuthera offers the most
complete and complex stratigraphic record known
from the Bahamas. Kindler and Hearty (1996) sum-
marized the petrostratigraphy of 61 sites from seven
island groups. Their study, like Hearty and Kindler
(1993b), noted the similarities of stratigraphic
columns from these and other islands, and established
350 Quaternary Science Reviews: Volume 17
the relationship between limestone composition (ooids,
peloids and bioclasts) and the magnitude of interglacial
sea-level highstands. This study expands on the find-
ings of Kindler and Hearty (1996) with the further
revelations on the complexity of the Stage 9/11 inter-
val, and recognition of an older unit exceeding Stage
13? in age (Table 1). The morpho-, litho-, pedo, and
aminostratigraphy of New Providence Island (Hearty
and Kindler, 1997a) compares favorably with Eleuth-
era back to Stage 11 (Table 5).
With the exception of early Pleistocene deposits, the
Eleuthera stratigraphy compares well with that of Be-
rmuda (Vacher et al., 1989) in duration (Hearty et al.,
1992), and rivals it in terms of detail and resolution.
Given a correction for a cooler temperature history in
Bermuda, the aminostratigraphies from Bermuda,
New Providence, and Eleuthera Islands show equiva-
lent aminozones (Table 5) between Stage 1 and 13.
Noteworthy among both island groups is the rapid and
voluminous sediment accumulations during Stages
9/11 and 5e, resulting in significant enlargement of the
islands during those times. The pre-Stage 7 record of
San Salvador Island (Hearty and Kindler, 1993a) is
more obscure due to limited exposures of the older
record.
SEA-LEVEL HISTORY
The Bahama Islands are the product of sea-level
changes in the late Quaternary. Carbonate sediment
production is greatly accelerated when sea-level rises
above the shelf margin, while carbonate grains are
either bioclastic, oolitic, or peloidal, dictated by the
degree of platform flooding (Kindler and Hearty, 1996)
and the energy setting on the platform. The overall
volume of limestone deposited on islands appears to be
a function of the duration and amplitude of the shelf-
flooding events. Regressional intervals from inter-
glacial highstands is an important period for island
growth. Sediments accumulated on the shelf during the
highstands are remobilized by water and wind, and
transported to the island margins resulting in island
growth. Furthermore, under high-energy conditions
like those in Eleuthera, sediments are transported to
higher ground during more numerous storm events,
and have a greater potential for preservation at these
elevations. Interglacial limestone deposits are bounded
by terra rossa soils reflecting glacial lowstands or pro-
tracted intra-stage regressions, while reduced carbon-
ate delivery to the shoreline during minor mid-subst-
age regressions allows for extensive vegetative growth
and ecological stability, resulting in the formation of
protosols.
Parasequences from Eleuthera yield evidence of sev-
eral important high sea-level events (Fig. 17A), and
agree well with other curves constructed from the geol-
ogy of Bermuda and the Bahamas (Hearty and Vacher,
1994; Hearty and Kindler, 1995), with some notable
differences. The oldest part of the Bermuda record
includes one or two early Pleistocene, and older middle
Pleistocene parasequences, all of which have yet to be
identified in the Bahamas. The earliest evidence (Stage
'13?) of island building in the Bahamas occurs during
the middle Pleistocene, identified by skeletal eolianites
at the base of the Goulding Cay Quarry sections
(Figs. 4 and 9). Sedimentary structures in cliff expo-
sures in Sections 6, 7 and 8 reveal important high-
stands at #2 m and #7 m, correlated to Stages 9/11,
with preference to the older interglacial (Burckle, 1993).
As part of the Stage 9/11 complex, an extensive mid
Pleistocene barrier reef (Section 1) developed under
apparently stable sea-level conditions, with head corals
rising to over #3m.
A subsequent sea-level excursion during the Stage
9/11 interval left beach deposits perched between #13
and #20 m at Sections 6 and 8 in North Eleuthera. In
Bermuda, thin, coarse beach deposits, originally de-
scribed by Land et al. (1967) at Government Quarry,
were situated on a narrow platform at #22 m, incised
into the early Pleistocene Walsingham Formation. The
site was subsequently destroyed by quarry expansion;
however, in 1997, beach sediments were again dis-
covered by the author at #22 m in a small cave not far
from the original site in the quarry (Hearty and Kind-
ler, 1997b). The #22 m beach deposits in Bermuda
show many similarities to the two sites in Eleuthera
including height above sea-level, narrowness of the
terrace, and thinness of the beach deposits. These three
localities from stable carbonate platforms support
a rise of sea-level to over #20 m and provide new
evidence of a high and rapid transgression during the
middle Pleistocene.
Assuming that northern hemisphere ice was at its
interglacial minimum at that time (no ice except
possibly in Greenland), and that Eleuthera is tectoni-
cally stable (Carew and Mylroie, 1995), melting of
Antarctic ice is necessary to account for an additional
1015 m of global sea-level. Burckle (1993) summarized
oceanographic and continental evidence indicating
that Stage 11 was the warmest interglacial in the last
500 ka. Our data from Eleuthera provide strong evid-
ence of a West Antarctic ice collapse during the Stage
9/11 interval. Interestingly, Haddad’s (Haddad, 1994)
reconstruction of a proxy glacio-eustatic sea-level
curve (Fig. 17B) from a d18O record from Site 607
(Raymo et al., 1990) suggests higher-than-present
paleo-sea-levels during Stages 11 and 9, the older rising
to near #20 m. The presence of these high deposits on
the tectonically stable coastlines of the Bahamas may
provide additional evidence that Antarctic ice may
have collapsed more than once during warm inter-
glacials of the Quaternary (Hearty and Kindler,
1997b).
Sea-level during Stage 7 rose at least twice to
near the present datum. These transgressions
were separated by a significant period during which
reddish brown, stony paleosols developed. Hearty
and Kindler (1997a) found beach fenestrae at 0 to
#2 m in coeval Stage 7 deposits (Table 5) on New
P.J. Hearty.: The Geology of Eleuthera Island, Bahamas 351
FIG. 17. (A) Sea-level highstands over the past '500 ka as interpreted from geology and dating of deposits in north Eleuthera. (B) Haddad’s
(Haddad, 1994) conversion of Raymo et al. (1990) d18O record from ODP core 607 to sea-level. Note the similarities between evidence provided by
direct (A) and interpreted (B) sea-level data.
Providence Island, indicating a rise of sea-level to near
the present datum.
Substage 5e is represented by sub-, inter-, and supra-
tidal marine deposits throughout Eleuthera and the
Bahama Islands. Because of the immediate response
time to sea-level changes in the sedimentary environ-
ment, evidence of 5e sea-level exists to over #8m,
while the slower-responding coral reefs only rise to
a maximum of #2 m. A rapid, late Substage 5e sea-
level rise and fall appears to have been responsible for
bioerosional notches at #6 m, extensive parabolic
beach/dune ridges (‘chevron ridges’; Hearty et al., in
review) across the exposed bank margins, and massive
eolian activity which built large dunes and buried
standing forests (Neumann and Hearty, 1996). As
envisioned by Hollin (1965), collapse of the West Ant-
arctic ice sheet probably underlies the rapid rise of sea-
level late in 5e. After a prolonged period of platform
emergence and the development of paleosols on 5e
oolites, large skeletal dune ridges were deposited on the
Atlantic margin during Substage 5a. Vacher and
Hearty (1989) defended a late Substage 5a sea-level rise
to 0 to #1 m at 80 ka in Bermuda. Similarly in the
Bahamas, the extensive 5a skeletal eolianite buildup
positioned on island margins supports a 5a highstand
very near the ordnance datum. The Holocene is
marked by several episodes of ridge formation, with
only the youngest periods associated with present sea-
level values.
Tectonic stability of the Bahama platform
Tectonic uplift of middle Pleistocene shoreline de-
posits in Eleuthera can be largely ruled out because of
(1) the concordance of numerous interglacial high sea-
level maxima between Bermuda and the Bahamas
(Hearty and Kindler, 1995); (2) the constant elevation
of 5e reef crests and flank marginal caves at around
#2to#3 m throughout the Bahamas (Carew and
Mylroie, 1995); and (3) the absence of historical earth-
quake activity in the Bahamas.
Tectonic stability without significant subsidence is
also supported by the extensive record of middle Pleis-
tocene highstand deposits in Eleuthera. These findings
contradict the opinion that subsidence of the platform
has obscured all evidence of pre-Substage 5e sea-level
as maintained by Carew and Mylroie (1995).
Subsidence rates of the Banks are interpolated from
deep core data over the past 100 Ma (Lynts, 1970;
Mullins and Lynts, 1977; Freeman-Lynde and Ryan,
1985), from which an average 12 m/100 ka was esti-
mated for the past 30 Ma. These rates are assumed to
continue through the Quaternary; however, there is no
dataset that can either prove or disprove the rate of
352 Quaternary Science Reviews: Volume 17
subsidence of the Banks over the past 125 ka, which
comprises only 0.1% of the subsidence record. Thus,
any conclusions based on the assumption of subsidence
are tenuous at best. It is possible, however, to infer
stability by comparison of sea-level data with other
global locations that are tectonically quiescent, as in
our comparisons with Bermuda (cf Hearty and
Kindler, 1995).
CONCLUSIONS
(1) Based on the correlation of 12 key sections in
Eleuthera, eight soil-bounded limestone parasequences
have been defined. These eight sequences represent at
least six full interglacial periods encompassing the peri-
od from the Holocene to at least Stage 13. Each of the
units have been stratigraphically ranked and charac-
terized by a unique combination of sedimentary struc-
tures, petrographic composition, soil colour, and
amino acid geochemistry (Fig. 15).
(2) Whole-rock aminostratigraphy demonstrates
its utility by supplementing lithostratigraphic
correlation, and providing a means to estimate
unit ages. Straightforward, unambiguous correlations
and concordance with the rock stratigraphy are
achieved in over 90% of cases. Radiometric dating of
corals is only rarely applicable to the largely non-
coraliferous sedimentary deposits of the Bahamas thus
making aminostratigraphy a valuable dating and cor-
relation tool.
(3) Sedimentary evidence of paleo-sea-levels support
higher-than, or near-present highstands throughout
the past 500 ka. Eleuthera’s geologically-derived sea-
level record is of much greater resolution than proxy
records, revealing multiple long-term stable sea-levels
and punctuated high-level excursions during Stages 5e,
9 and 11. In addition, minor sea-level and ecological
changes are discernible within stage and substage
levels.
(4) A half-million year history of glacial and inter-
glacial cycles is revealed in the stratigraphy of Eleuth-
era. This stratigraphy demonstrates several orders of
cyclicity governed by orbital forcing including:
a 400 ka cycle encompassing the entire Eleuthera se-
quence, 100 ka full glacialinterglacial cycles, 2040 ka
frequencies within interglacials, and numerous 14ka
cycles revealed in protosols. Shoreline facies of all types
indicate a range of depositional intervals from pro-
longed highstands forming broad terraces to individual
storm events revealed in washover deposits.
(5) The sedimentary system of the Bahama Banks is
particularly sensitive to both minor and major oscilla-
tions of sea-level. The response time of the blanket of
banktop sediments is immediate, and preservation po-
tential of the sedimentary record in this geologic envi-
ronment is high. Although coral reefs avail themselves
to radiometric dating, their response-time to sea-level
shifts is obscured, muted and delayed, recording main-
ly the prolonged highstand events. The slower response
time of reefs is best demonstrated by the inability of the
5e reef to ‘catch up’ to the brief, #6 m highstand
(Neumann and Hearty, 1996) late in the period.
(6) Assumptions of constant uplift on tectonic coast-
lines are insufficiently tested, relying mainly on the
Substage 5e ‘golden spike’ at #6 m/125 ka, which is of
dubious validity. A #2 m, 128 ka calibration point
based on maximum height of U-series dated reefs
(Chen et al., 1991) would be more appropriate. Fur-
thermore, the deep-sea oxygen isotope record is insen-
sitive to minor eustatic changes, suffering the effects of
bioturbation, diagenetic changes, biological variations
in organisms, redistribution of foraminiferal tests, and
numerous other assumptions concerning ocean salin-
ity, paleotemperatures, and calculated ice volume.
These proxy studies would benefit from the direct
sea-level data provided by the long-term, high-resolu-
tion, geological record from the Bahamas.
(7) At present, the stratigraphy of Eleuthera is
among the most complete and detailed known from the
Bahamas. It records several scales of eustatic oscilla-
tions, as well as evidence for environmental, petro-
graphic, pedogenic, and diagenetic changes over the
past 500 ka.
ACKNOWLEDGEMENTS
Pascal Kindler (University of Geneva) participated
throughout this project and contributed to the overall
understanding of the geology of Eleuthera and the
Bahamas. Many thanks to A.C. Neumann for his con-
structive review of an earlier draft and his insightful
observations in the field. Reviews by U. Radtke (Uni-
versity of Cologne) and an anonymous reviewer greatly
improved the manuscript. I am also grateful to
D. McKinny, C. Finkl, B. Jarrett, D. and S. Wehrli,
I. Cojan, S. Walker, University of South Florida field
trips, and SEPM 1995 Eleuthera Field participants for
their interesting discussions, support, and interest in
this Eleuthera Project. Cambridge Villas (Mr Harcourt
Cambridge, Gregory Town) provided comfortable and
convenient accommodations.
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P.J. Hearty.: The Geology of Eleuthera Island, Bahamas 355
... This addition to the Bahamian stratigraphic record known at that time generated much controversy in the subsequent years Hearty and Kindler, 1994;Mylroie, 1995a and mostly because, on San Salvador, stratigraphic relationships are not straightforward. Exposures showing the ACF overlying MIS 5e rocks, but separated from the latter by an intervening paleosol, were later observed at several localities in Eleuthera (Hearty and Kindler, 1995a;Hearty, 1998), but the controversy persisted as several following authors (Carew and Mylroie, 2001;Panuska et al., 2002;Mylroie, 2008) correlated these deposits with the sea-level fall at the end of the LIG. The ACF was informally renamed "Whale Point Formation" by Kindler et al. (2010), and this name was used in several subsequent papers (Godefroid, 2012;Godefroid et al., 2019;Jackson, 2017). ...
... The hill top is covered by sand and bushy vegetation, but exposures can also be found on its eastern (ocean) side due to marine erosion. First described by Hearty and Kindler (1995a), this section has subsequently been reexamined by Kindler and Hearty (1997), Hearty (1998), Tormey (1999, Panuska et al. (2002), Brentini (2008), Nawratil de Bono (2008), and Kindler et al. (2010). ...
... This name is thus commonly used in the scientific literature (see references below), although the place is now called "Queen's Bath" on Google Map. Initially described by Hearty and Kindler (1993b), this exposure has been revisited by Hearty and Kindler (1995a), Kindler andHearty (1995, 1997), Hearty (1998), Tormey (1999), Panuska et al. (2002), Kindler and Hine (2009), and Kindler et al. (2008, 2010. ...
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In this paper, we formally define a series of bioclastic eolianites and protosols exposed on high-energy bank margins throughout the Bahamas archipelago as the Whale Point Formation (WPF). The position of this new lithostratigraphic unit above and seaward of deposits dated to Marine Isotope Stage (MIS) 5e and below Holocene sediments constrains its age to the latest Pleistocene, more precisely to MIS 5a (ca. 88–74 ka BP). This age is further corroborated by amino-acid racemization data calibrated with UTh ages. Based on their sedimentological characteristics, the WPF eolianites are interpreted as landward-advancing dunes decoupled from their source beaches. Relying on the faunal content, the maximum elevation of relative sea level during MIS 5a can be roughly estimated at ca. 9 ± 2 m below the present stand. The WPF includes two phases of eolian deposition separated by an interval of negative sediment budget and pedogenesis. These different facies possibly reflect millennial-scale sea-level and climate instability during MIS 5a, the latter being likely related to shifts in the mean annual position of the intertropical convergence zone and associated rainfall belt.
... The past three decades have seen a revolution in the study of the geology and science in the Bahama Islands (e.g., Garrett and Gould 1984;Carew and Mylroie 1987;Hearty andKaufman 2000, Kerans et al. 2019;Vimpere et al. 2019). The number of scientific publications dealing with the Bahama "Banks" and islands has increased exponentially, stimulated by the potential information provided about past climate and sea-level changes, as well as the recent new applications of dating techniques. ...
... This paucity of coral reefs in time and space challenged scientists to apply new geochronological methodologies to improve dating capabilities applicable to a broader age-range of deposits. With stratigraphic and geologic mapping of many additional islands and the availability and increased application of amino acid racemization (AAR) relative dating methods, it was discovered that an extensive record of middle and late Pleistocene interglacial deposits was present among the islands (Carew and Mylroie 1995;Hearty 1998;Kindler et al. 2010;Godefroid 2012;Godefroid and Kindler 2015;Jackson 2017;Kerans et al. 2019). ...
... Identification of stratigraphic units (youngest to oldest, in stratigraphic order) is based on some or all of the following distinguishing characteristics: a) the surface morphostratigraphic position of the ridge or observed vertical stratigraphic succession in the cores; b) the geomorphology of the deposits, including anchor-catenary ridge relationships (Garrett and Gould, 1984); c) the weathering, cementation, hardness, and diagenetic state of the limestone; d) petrographic composition of the units; e) extent of karst weathering; f) the color (Munsell, 2001) and clay content of the capping soils (Hearty 1998); and g) relative aminostratigraphic age (Appendix 1). ...
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The surface and subsurface geology of the Exuma Cays in the central Bahama Islands re- cords sea-level cyclicity that extends back to the Jurasssic, however the focus of this paper is the Plio-Pleis- tocene, since approximately 1–3 million years ago. During the 1990s, the rst author surveyed a large num- ber of the islands by boat, mapped the geology on 1:25,000 topographic maps with the aid of air photos, and more recently complemented these mapping studies using Google Earth Pro. In 1994, two 33 m cores were extracted from Norman’s Pond Cay and Lee Stocking Island in the southern group of the Exuma Cays. The outcropping rocks throughout the Cays are characterized by a mix of nearly pure bioclastic and oolitic sediments and limestone units. Generally, the highstand limestone deposits are capped with lowstand terra rossa paleosols, red-stained micritic limestone, calcrete, or karst surfaces. From surface and subsurface geology, a minimum of seven stratigraphic units are recorded, yet many cycles are obvi- ously missing. Three broad eustatic intervals are evident from the δ18O record. These are associated with the Pliocene-early Pleistocene (“PP” >1.2 Ma), Mid-Pleistocene Transition (“MPT” ~1.2–0.7 Ma), and the mid-late Pleistocene (“MLP” ~0.7 Ma to present). A combination of physical stratigraphy, geomorphology, paleomagnetism, and amino acid racemization (AAR) provide a general age framework for these deposits. Pliocene beds at -25 m in only one core appear to indicate slow subsidence of the Bahama Banks. An inter- val of prolonged bank marginal or lower sea stands of the MPT are indicated by a cluster of dense, clayey red paleosols. Many MLP rocks on the islands and in the cores retain sufficient amino acids to establish a relative chronology for the MLP. The geomorphic and stratigraphic succession from the Exumas shows very rapid progradation of the over-steepened bank margin toward Exuma Sound by several km since the Plio-Pleistocene. The purpose of this paper is to: 1) characterize the geology of the existing Exuma rocks and cays; 2) demonstrate the shallow-subsurface stratigraphy in two 33-m long cores; and 3) provide some examples of how the Exuma Cays and their margins have evolved over the past 1–3 million years.
... Wanless and Dravis' (2020) emphasize in their Section 4a the importance of using observations from aerial photographic observations in the regional context of the entire leeward margin of the Caicos Platform. Our emphasis in fact is broader, linking the stratigraphy from the West Caicos MIS 5e sequence to the nearby islands such as Great Inagua, Mayaguana, and the numerous guiding studies across the Bahamas and globally (Blanchon et al., 2009;Carew and Mylroie, 1985;Chen et al., 1991;Godefroid, 2012;Hearty, 1998;Hearty andKindler, 1993, 1995;Hearty et al., 2007;Kindler et al., 2011;Skrivanek et al., 2018;Thompson et al., 2011;White et al., 1998). Although neither the AAR or U/Th methods applied here by themselves are flawless, the remarkably similar aminostratigraphic successions and ages for the lower and upper MIS 5e reefs documented here, when compared to those of Thompson et al. (2011) and Chen et al. (1991) as well as the distinctive breakout of pre-MIS 5e, MIS 5e, and Holocene units shown by the AAR, supports the framework we have presented here and in Kerans et al. (2019). ...
... Wanless and Dravis' (2020) emphasize in their Section 4a the importance of using observations from aerial photographic observations in the regional context of the entire leeward margin of the Caicos Platform. Our emphasis in fact is broader, linking the stratigraphy from the West Caicos MIS 5e sequence to the nearby islands such as Great Inagua, Mayaguana, and the numerous guiding studies across the Bahamas and globally (Blanchon et al., 2009;Carew and Mylroie, 1985;Chen et al., 1991;Godefroid, 2012;Hearty, 1998;Hearty andKindler, 1993, 1995;Hearty et al., 2007;Kindler et al., 2011;Skrivanek et al., 2018;Thompson et al., 2011;White et al., 1998). Although neither the AAR or U/Th methods applied here by themselves are flawless, the remarkably similar aminostratigraphic successions and ages for the lower and upper MIS 5e reefs documented here, when compared to those of Thompson et al. (2011) and Chen et al. (1991) as well as the distinctive breakout of pre-MIS 5e, MIS 5e, and Holocene units shown by the AAR, supports the framework we have presented here and in Kerans et al. (2019). ...
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We address concerns raised by Wanless and Dravis (2020) on our paper documenting the late Quaternary evolution of West Caicos island. We negate the claim that omitting their paper (Dravis and Wanless, 2017) had any consequences for our interpretations. We also provide reasoning and data to demonstrate that our interpretation of the Quaternary stratigraphy of the island was derived from detailed field work and high-resolution remote sensing data, which was subsequently corroborated by AAR and U-Th age-dating control, the opposite of the claim by Wanless and Dravis.
... Wanless and Dravis' (2020) emphasize in their Section 4a the importance of using observations from aerial photographic observations in the regional context of the entire leeward margin of the Caicos Platform. Our emphasis in fact is broader, linking the stratigraphy from the West Caicos MIS 5e sequence to the nearby islands such as Great Inagua, Mayaguana, and the numerous guiding studies across the Bahamas and globally (Blanchon et al., 2009;Carew and Mylroie, 1985;Chen et al., 1991;Godefroid, 2012;Hearty, 1998;Hearty andKindler, 1993, 1995;Hearty et al., 2007;Kindler et al., 2011;Skrivanek et al., 2018;Thompson et al., 2011;White et al., 1998). Although neither the AAR or U/Th methods applied here by themselves are flawless, the remarkably similar aminostratigraphic successions and ages for the lower and upper MIS 5e reefs documented here, when compared to those of Thompson et al. (2011) and Chen et al. (1991) as well as the distinctive breakout of pre-MIS 5e, MIS 5e, and Holocene units shown by the AAR, supports the framework we have presented here and in Kerans et al. (2019). ...
... Wanless and Dravis' (2020) emphasize in their Section 4a the importance of using observations from aerial photographic observations in the regional context of the entire leeward margin of the Caicos Platform. Our emphasis in fact is broader, linking the stratigraphy from the West Caicos MIS 5e sequence to the nearby islands such as Great Inagua, Mayaguana, and the numerous guiding studies across the Bahamas and globally (Blanchon et al., 2009;Carew and Mylroie, 1985;Chen et al., 1991;Godefroid, 2012;Hearty, 1998;Hearty andKindler, 1993, 1995;Hearty et al., 2007;Kindler et al., 2011;Skrivanek et al., 2018;Thompson et al., 2011;White et al., 1998). Although neither the AAR or U/Th methods applied here by themselves are flawless, the remarkably similar aminostratigraphic successions and ages for the lower and upper MIS 5e reefs documented here, when compared to those of Thompson et al. (2011) and Chen et al. (1991) as well as the distinctive breakout of pre-MIS 5e, MIS 5e, and Holocene units shown by the AAR, supports the framework we have presented here and in Kerans et al. (2019). ...
Article
Full-text available
We address concerns raised by Wanless and Dravis (2020) on our paper documenting the late Quaternary evolution of West Caicos island. We negate the claim that omitting their paper (Dravis and Wanless, 2017) had any consequences for our interpretations. We also provide reasoning and data to demonstrate that our interpretation of the Quaternary stratigraphy of the island was derived from detailed field work and high-resolution remote sensing data, which was subsequently corroborated by AAR and U-Th age-dating control, the opposite of the claim by Wanless and Dravis.
... Wanless and Dravis' (2020) emphasize in their Section 4a the importance of using observations from aerial photographic observations in the regional context of the entire leeward margin of the Caicos Platform. Our emphasis in fact is broader, linking the stratigraphy from the West Caicos MIS 5e sequence to the nearby islands such as Great Inagua, Mayaguana, and the numerous guiding studies across the Bahamas and globally (Blanchon et al., 2009;Carew and Mylroie, 1985;Chen et al., 1991;Godefroid, 2012;Hearty, 1998;Hearty andKindler, 1993, 1995;Hearty et al., 2007;Kindler et al., 2011;Skrivanek et al., 2018;Thompson et al., 2011;White et al., 1998). Although neither the AAR or U/Th methods applied here by themselves are flawless, the remarkably similar aminostratigraphic successions and ages for the lower and upper MIS 5e reefs documented here, when compared to those of Thompson et al. (2011) and Chen et al. (1991) as well as the distinctive breakout of pre-MIS 5e, MIS 5e, and Holocene units shown by the AAR, supports the framework we have presented here and in Kerans et al. (2019). ...
... Wanless and Dravis' (2020) emphasize in their Section 4a the importance of using observations from aerial photographic observations in the regional context of the entire leeward margin of the Caicos Platform. Our emphasis in fact is broader, linking the stratigraphy from the West Caicos MIS 5e sequence to the nearby islands such as Great Inagua, Mayaguana, and the numerous guiding studies across the Bahamas and globally (Blanchon et al., 2009;Carew and Mylroie, 1985;Chen et al., 1991;Godefroid, 2012;Hearty, 1998;Hearty andKindler, 1993, 1995;Hearty et al., 2007;Kindler et al., 2011;Skrivanek et al., 2018;Thompson et al., 2011;White et al., 1998). Although neither the AAR or U/Th methods applied here by themselves are flawless, the remarkably similar aminostratigraphic successions and ages for the lower and upper MIS 5e reefs documented here, when compared to those of Thompson et al. (2011) and Chen et al. (1991) as well as the distinctive breakout of pre-MIS 5e, MIS 5e, and Holocene units shown by the AAR, supports the framework we have presented here and in Kerans et al. (2019). ...
Article
We address concerns raised by Wanless and Dravis (2020) on our paper documenting the late Quaternary evolution of West Caicos island. We negate the claim that omitting their paper (Dravis and Wanless, 2017) had any consequences for our interpretations. We also provide reasoning and data to demonstrate that our interpretation of the Quaternary stratigraphy of the island was derived from detailed field work and high-resolution remote sensing data, which was subsequently corroborated by AAR and U-Th age-dating control, the opposite of the claim by Wanless and Dravis.
... Skeletal eolianite comprising Eleuthera Island are interpreted as eolian dunes and are separated from the underlying formations by paleosols (Kindler and Hearty, 1996;Hearty, 1998;Hearty and Kaufman, 2000). The authors report an inferred paleo-sea level of 0 -5 m bpsl, rather the modern elevation of the deposit (Hearty and Kaufman, 2000; Figure 2). ...
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In this review we compile and detail the elevation, indicative meaning, and chronology of Marine Isotope Stage 5a and 5c sea level indicators for 39 sites within three geographic regions: the Pacific coast of North America, the Atlantic coast of North America and the Caribbean, and the remaining globe. These relative sea level indicators, comprised of geomorphic indicators such as marine and coral reef terraces, eolianites, and sedimentary marine and terrestrial limiting facies, facilitate future investigation into Marine Isotope Stage 5a and 5c interstadial paleo-sea level reconstruction, glacial isostatic adjustment, and Quaternary tectonic deformation. The open access database, presented in the format of the World Atlas of Last Interglacial Shorelines (WALIS) database, can be found at https://doi.org/10.5281/zenodo.4426206 (Thompson and Creveling, 2021).
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This paper provides a summary of published sea-level archives representing the past position of sea level during the Last Interglacial sea-level highstand in the Bahamas, Turks and Caicos, and the eastern (Atlantic) coast of Florida, USA. These data were assembled as part of a community effort to build the World Atlas of Last Interglacial Shorelines (WALIS) database. Shallow marine deposits from this sea-level highstand are widespread across the region and are dominated by carbonate sedimentary features. In addition to depositional (constructional) sedimentary indicators of past sea-level position, there is also evidence of erosion, dissolution, and/or subaerial exposure in places that can place an upper limit on the position of sea level. The sea-level indicators that have been observed within this region and attributed to Marine Isotope Stage (MIS) 5e include corals, oolites, and other coastal sedimentary features. Here we compile a total of 50 relative sea-level indicators including 36 in the Bahamas, three in West Caicos, and a remaining 10 for the eastern seaboard of Florida. We have also compiled U-Th age data for 24 fossil corals and 56 oolite samples. While some of these archives have been dated using U-Th disequilibrium methods, amino acid racemization, or optically stimulated luminescence, other features have more uncertain ages that have been deduced in the context of regional mapping and stratigraphy. Sedimentary archives in this region that constrain the elevation of the past position of sea level are associated with uncertainties that range from a couple of decimeters to several meters. Across the Bahamas and on West Caicos, one of the observations that emerges from this compilation is that estimation of sea-level position in this region during Marine Isotope Stage 5e is complicated by widespread stratigraphic evidence for at least one sea-level oscillation. This evidence is defined by submarine features separated by erosion and subaerial exposure, meaning that there were likely multiple distinct peaks in sea level rather than just one. To this end, the timing of these individual sea-level indicators becomes important when compiling and comparing data across the region given that different archives may have formed during different sub-orbital peaks in sea level. The database can be found at https://doi.org/10.5281/zenodo.5596898 (Dutton et al., 2021).
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This paper provides a summary of published sea level archives representing the past position of sea level during the Last Interglacial sea level highstand in the Bahamas, Turks and Caicos, and the eastern (Atlantic) coast of Florida, USA. These data were assembled as part of a community effort to build the World Atlas of Last Interglacial Shorelines (WALIS) database. Shallow marine deposits from this sea level highstand are widespread across the region and are dominated by carbonate sedimentary features. In addition to depositional (constructional) sedimentary indicators of past sea level position, there is also evidence of erosion, dissolution, and/or subaerial exposure in places that can place an upper limit on the position of sea level. The sea level indicators that have been observed within this region and attributed to Marine Isotope Stage (MIS) 5e include corals, oolites, and other coastal sedimentary features. Here we compile a total of 50 relative sea level indicators including 36 in the Bahamas, three in West Caicos, and a remaining 10 for the eastern seaboard of Florida. We have also compiled U-Th age data for 24 fossil corals and 56 oolite samples. While some of these archives have been dated using U-Th disequilibrium methods, amino acid racemization, or optically stimulated luminescence, other features have more uncertain ages that have been deduced in the context of regional mapping and stratigraphy. Sedimentary archives in this region that constrain the elevation of the past position of sea level are associated with uncertainties that range from a couple decimeters to several meters. Across the Bahamas and on West Caicos, one of the observations that emerges from this compilation is that estimation of sea level position in this region during Marine Isotope Stage 5e is complicated by widespread stratigraphic evidence for at least one sea level oscillation. This evidence is defined by submarine features separated by erosion and subaerial exposure, meaning that there were likely multiple distinct peaks in sea level rather than just one. To this end, the timing of these individual sea level indicators becomes important when compiling and comparing data across the region given that different archives may have formed during different sub-orbital peaks in sea level.
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This paper presents an analysis of the transport conditions of a storm deposit (i.e. tempestite) produced by a non‐local cyclone. Observations and analysis of ‘sand to boulder’ transport and washover deposition in March 2018 at Gaulding Cay Quarry, Eleuthera, The Bahamas, confirm that swell waves can cause coastal change and affect the depositional record >1000 km from the storm centre. Drone video, news reporting, deposit stratigraphy, grain‐size measurements and wave data were all used to define three phases of washover fan construction: an aggradational phase associated with base‐level rise as the quarry filled with water; a progradational phase associated with quasi‐constant base‐level; and fan incision tied to base level fall as discharge through an outlet channel exceeded input discharge by overtopping waves. Washover fan location was controlled by antecedent topography and represented only a fraction of the swell‐impacted coastline. Sand and boulders were transported simultaneously, forming a complex poorly sorted deposit. Drone video, bedrock erosion and sediment‐transport estimates all indicated that overwash exceeded sediment availability. As a result, the measured washover fan was estimated to be an order of magnitude smaller than its potential volume if conditions had been transport‐limited. This study highlights the importance of pre‐event topography and independent measures of event duration on accurately reconstructing storm properties from the sedimentary record, as well as the challenges in reconstructing storm location, and therefore storm intensity and frequency, from sedimentary deposits alone.
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Among the specialized studies on the Quaternary of Mallorca, the knowledge of the sea paleolevels in the western Mediterranean basin has a significant body of research, developed during the second half of the last century by authors such as Karl W. Butzer and Joan Cuerda. The classic paleontological and geomorphological record, based on the study of the island's fossil beaches, was supplemented from the 70s with a new register that offered great geochronological possibilities: the study of the phreatic overgrowths on speleothems (POS) of Mallorcan coastal caves. These crystalline precipitates record the sea level with extraordinary resolution, and are also capable of being accurately dated using radiometric techniques based on the Uranium series (mainly U/Th). In the following pages, a review of the available knowledge about the sea level in Mallorca during the last interglacial stage (MIS-5) is made, starting from the classic vision based on the malacological study of the "raised beaches", to the data from numerous recently published radiometric datings of phreatic overgrowths on speleothems. This peculiar register provided by our littoral caves reliably documents that the sea level remained relatively stable, at an altitude of 2.15 ± 0.75 m, during the time span from 126.6 to 116 ka BP (MIS-5e), which would correspond to the Eemian (the very late Eutyrrhenian, according to the terminology used by Joan Cuerda); it is also documented a high sea level (+1 m approx.) between 82 and 80 ka BP (MIS-5a), which would be equivalent to the Neotyrrhenian stage of the same author.
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Bermuda, where Pleistocene eolianite was first named and analyzed in terms of glacioeustasy, can be considered the type locality of the carbonate eolianite facies. In Bermuda, this facies consists of bioclastic eolianite and associated beach deposits, weakly developed calcarenitic paleosols, and red to reddish brown paleosols termed "terra rossa" by many authors. The eolianite formed as large retention ridges, which prograded inland into a vegetated landscape; the sediment was derived from the surrounding submerged platform. Eolianite deposition in Bermuda was an interglacial phenomenon. It occurred mainly after the initial submergence, which is recorded by deposits of rocky shorelines and pocket beaches like those of the present-day erosional coastline. The terra-rossa paleosols represent relatively long hiatuses in the carbonate buildup, and therefore intervene between the limestones of successive interglacial stages; however, these paleosols do not equate exactly to glacial stages. The weakly developed calcarenite paleosols represent minor breaks within and between interglacial substages. Although sea-level history is the ultimate control of the mosaic of facies and the succession of stratigraphic units in Bermuda, attempts to define lithostratigraphic units in terms of sea-level history led to unmappable columns. Lithostratigraphic units now have been mapped successfully throughout Bermuda. These units parallel time-stratigraphic units but, in themselves, do not permit resolution of successive interglacial stages in the lower part of the column. Enhanced resolution is provided by allostratigraphic and aminostratigraphic units. The latter are zones defined by amino acid racemization (AAR) ratios that provide a measure of relative age. By use of interpretive kinetic models, the ratios have been converted to age estimates that allow direct correlation with the deep-sea oxygen isotope stages. Among the principal findings of stratigraphic mapping and analysis in Bermuda are: that shoreward superposition (lateral accretion) is the key mapping principle; and that the stratigraphic column includes a significant record of oxygen isotope stages 5, 7, 9, and 11, as well as an older history represented by the Walsingham Limestone at the base of the exposed section.
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Eight distinct rock units representing discrete high sea-level events have been identified on New Providence (NPI) and surrounding islands. Each is distinguished by a unique set of physical, biological, and geochemical characteristics. At least three of these units are new to the stratigraphic column of NPI since the landmark study of Garrett and Gould in 1984. Others previously described have been further clarified. A map of the surficial geology of NPI shows the areal distribution of the major units. Based on the number and character of paleosol-bounded limestone parasequences, it appears that at least five interglacial cycles are distinguishable. Whole-rock amino acid racemization (AAR) ratios confirm the stratigraphic sequence, and indicate that isotope Stages 1 through 11 are most likely included among eight depositional packages: (Stage 1-2 events; Stage 5-3 events; Stage 7-1 event; Stage 9-1 event; Stage 11-1 event). Six interglacial units on NPI contain intertidal sedimentary facies and shoreline indicators from which a highstand curve has been derived. Of particular significance is the recognition of higher-than-present paleosea levels associated with three middle Pleistocene units. Our findings indicate that the surficial geologic record of NPI is longer and more complex than previously thought, and that the northern Bahama Banks have experienced little if any subsidence over the past half-million years, based on the height of middle Pleistocene sea levels. The sea-level data from NPI and nearby islands have important implications for isotopic and tectonic coastline studies, and an the timing and effect of orbital parameters on sea-level and climate history during the late Quaternary.
Article
The Huon Peninsula record has been widely cited, but needs revision. This paper adds new data to the previously published information, giving a new sea-level curve for the last 340ka. Results covering the last 136ka in particular are more detailed than those available previously. -from Author
Chapter
The Holocene deposits exposed on Lee Stocking and other Bahamian islands display a record of two distinctive units that contrasts strongly with the gradual rise of sea level expressed on most regional eustatic curves. This chapter reviews the field criteria for separating the Holocene and Pleistocene units in the Bahamas, presents the results of a detailed sedimentologic and petrographic study of the Holocene succession on Lee Stocking, and proposes a five-phase model that reconciles the observed pattern of episodic sedimentation with the continuous trend of sea-level rise. The Holocene deposits of Lee Stocking include two newly named lithostratigraphic units: the Dune Pass Bay oolite, a 5,000-yr-old eolianite formed when sea level was lower than today, and the Perry Peak limestone, a younger bioclastic calcarenite deposited in beach and eolian settings when sea level was close to its present position. These units are similar to coeval deposits previously described on San Salvador and are also found on Cat and Eleuthera. On Lee Stocking, the two Holocene units appear in vertical succession and are separated by a pronounced discontinuity. However, regional sea-level curves do not show a major fall that could explain this sedimentation break. The five-phase model presented in this chapter suggests that changes in the rate of sea-level rise ultimately controlled sedimentation during the middle and late Holocene in the Bahamas. The early flooding history of the platform was characterized by shallow waters that favored production and accumulation of ooids on the bank margins. Due to the rapid rate of sea-level rise during the mid-Holocene, ooid production ceased and the newly formed coastal deposits were subjected to erosion or pedogenesis. When the transgression slowed down about 3,800 yr ago, reefs began to catch up with sea level and generate bioclasts that created new shoreline features bankward of the first deposits. Today, reefs have caught up with sea level, reducing the energy from open ocean waters. Sedimentation on most Bahamian islands has again decreased, as shown by the absence of high unvegetated dunes. This example from the Bahamas shows that discontinuities within carbonate sequences must not always be interpreted in terms of relative sea-level fall but can also result from changes in the rate of a transgression.
Chapter
The source and mode of accumulation of insoluble residue (IR) and the potential of paleosols as stratigraphic aids were investigated by megascopic, mineralogic, textural, and scanning electron microscope examination of Bahamian paleosols from San Salvador and Andros Island. Bahamian paleosols are predominantly calcium carbonate and contain minor amounts of mineral insoluble residue (quartz, plagioclase, and clay minerals). There are at least four megascopically distinct paleosol types: laminated crusts, homogeneous crusts, breccia/conglomerate, and homogeneous matrix. There is no apparent relation between megascopic type of paleosol and underlying carbonate lithology, time of formation, or mineralogic composition of the insoluble residue. The IR mineralogy and the quartz size distribution of Bahamian paleosols were compared to that of a nearby periplatform core (taken from the Northwest Providence Channel, Bahamas). This comparison suggests that there is a similar source for the insoluble residue, i.e., dust transported from the Sahara Desert. The similarity of quartz size distribution of lowstand (glacial period) sediments to the size distribution of quartz within paleosols suggests that paleosols dominantly form during lowstands of sea level. A comparison of the percentage of IR in the host limestones (<0.01%) with the percentage of IR in paleosols (ca. 6.0%) suggests that, in order for paleosols to have formed by dissolution of host limestones, unacceptably large volumes of limestone would have to have been dissolved in relatively short time periods. However, rates of dust deposition of the deep-sea core suggest that the IR of typical Bahamian paleosols could have formed by dust accretion during the several tens of thousands of years of lowstand conditions. Unfortunately, there is no mineralogic or textural "fingerprint" that can be used to assign specific lowstand (glacial) episodes to specific paleosols. Paleosols can be classified by IR mineralogy using the relative abundance of two minerals: boehmite and illite. Clay mineralogy in paleosols is primarily a function of diagenesis accompanying climatic variations through the late Quaternary. However, the difference between boehmite-rich paleosols and illite-rich paleosols appears to be due to local environmental conditions (topography) rather than regional climatic changes. Boehmite-rich paleosols result from intense leaching, whereas illite-rich paleosols represent less intense diagenetic alteration and more closely resemble the mineralogy of IR brought to the Bahamas as dust. Interpretation of paleosol IR mineralogy is complicated by erosion and redeposition of soils/paleosols. All four megascopic types of Bahamian paleosols and all mineralogic varieties of paleosols are found on stratigraphically equivalent rock units. Thus, paleosols in the Bahamas cannot be used as stratigraphic markers to correlate stratigraphic units on a single island or between islands.
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The evolution of interocean carbon isotopic gradients over the last 2.5 m.y. is examined using high-resolution delta13C records from deep sea cores in the Atlantic and Pacific Oceans. Over much of the Northern Hemisphere ice ages, relative reductions in North Atlantic Deep Water production occur during ice maxima. From 2.5 to 1.5 Ma, glacial reductions in NADW are less than those observed in the late Pleistocene. Glacial suppression of NADW intensified after 1.5 Ma, earlier than the transition to larger ice sheets around 0.7 Ma. At a number of times during the Pleistocene, delta13C values at DSDP Site 607 in the North Atlantic were indistinguishable from eastern equatorial Pacific delta13C values from approximately the same depth (ODP Site 677), indicating significant incursions of low delta13C water into the deep North Atlantic. Atlantic/Pacific delta13C values converge during glaciations between ~ 1.13-1.05 m.y., 0.83-0.70 m.y., and 0.46-0.43 m.y. This represents a pseudo-periodicity of approximately 300 kyr which cannot easily be ascribed to global ice volume or orbital forcing. This partial decoupling, at low frequencies, of the delta18O and delta13C signals at Site 607 indicates that variations in North Atlantic deep water circulation cannot be viewed simply as a linear response to ice sheet forcing. Present address: Woods Hole Oceanographic Institution, Woods Hole, MA 02543 (U.S.A.).
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Detailed studies of reef-tract stratigraphy in the southwestern part of Barbados have revealed nine, seven, and ten reef tracts in the Christ Church, Clermont Nose, and Saint George's Valley sections, respectively. The reefs have been projected onto standard traverses, and present elevations are reported for each reef crest. To date the reef crests by Th230/U and He4/U methods, the U234/U238 and Th230/U234 activity ratios and U and He4 concentrations were determined in about 35 unrecrystallized coral samples. Discordant U234/U238, Th230/U, and He4/U ages for many samples indicate that both U234 and Th230 have been diagenetically added to the samples. He4/U ages are corrected by subtracting the He4 added due to the presence of "open system" U-series nuclides; the correction ranges from 0% to 10%. The reef-tract ages and present elevations as projected on the standard traverse show that prior to 125,000 B.P., the uplift rate of the Christ Church section was much greater than the rate after 125,000 B.P. Paleo-sea levels inferred from Saint George's Valley reef tract ages and elevations cluster about the present datum, which suggests that throughout the Brunhes epoch, minimum interglacial continental ice volume was comparable to the present value. Within the uncertainty of the age and paleo-sea-level estimates, the Brunhes sea-level history inferred from Barbados reef-tract chronostratigraphy is consistent with that inferred by Shackleton and Opdyke from the oxygen isotope record of core V28-238.
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Data from carbonate bank-margin fractures in the southern Exuma Islands, Bahamas, in the vicinity of Lee Stocking Island show that these fractures have a preferred bank-margin-parallel orientation. Fractures that showed evidence of pedogenic alteration to micrite (calcretization) had an even more pronounced orientation preference. Calcretization is associated with a well-defined paleosol believed to have formed within the last glacial period and the transition to the present interglacial (˜20-13 ka). Horizontal laminations within the paleosol continue as vertical laminations within some fracture traces. Analysis of thin sections revealed root tubules and fabrics characteristic of pedogenic alteration within the calcretized parts of fracture zones. The association of bank-margin-parallel fractures with the last interglacial suggests that fracture development is related to a eustatic process. I suggest that fractures formed in response to undercutting of the bank margin during the last sea-level low. A fracture-controlled submarine cave extending to >100 m below present sea level provides additional evidence supporting a eustatic link to fracture development.