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Fig. 20.15 Character of bedrock, Cat Cay ooid shoals, Great
Bahama Bank. ( a ) Schematic fi gure of interpretations of a bed-
rock high under the shoal complex. Modifi ed from Purdy ( 1961 ) .
( b ) and ( c ) Representative shallow Chirp subbottom profi le ( b )
and interpretation ( b ) of cross section across the shoal complex.
This line, and others in the area, include no evidence for a
bedrock high underneath this shoal complex. ( d ) Detail of part
of a shallow Chirp subbottom profi le, illustrating stacked cross-
bedded units above the Pleistocene surface in some areas (Figure
modifi ed from Cruz ( 2008 ) )
(3) a maturation stage in which the production and dis-
tribution of sands led to aggradation and shoaling to
intertidal levels, along with expansion of the shoal
complex. As the shoal aggraded to shallow depths,
active bioturbation led to mixing of oolitic and peloidal
sands and muds, leading to the ooid packstone of the
sand fl at interior. In this fi nal phase, the clean oolitic
sands form a 2 km wide and 2-3 m thick accumulation
on the eastern and northern peripheries of the shoal,
where wave-driven or tidal currents agitate and actively
transport the sediments (Fig. 20.17 ).
ancient analog occurs in the Upper Pleistocene Miami
Oolite, exposed near Miami, Florida (Fig. 20.18 )
(Hoffmeister et al. 1967 ; Halley et al. 1977 ; Halley and
Evans 1983 ; Evans 1987 ) . Here, an ooid-rich late
Pleistocene shoal complex is preserved as a wedge-
shaped low ridge over 60 km long. The shoal mor-
phology is broadly similar to that of the Holocene
system of Joulter Cays (Fig. 20.14 ). The shoal com-
plex has been dated at 130 ka (marine isotope stage
5e), and was deposited when sea level was ~7 m higher
than present.
To the west, the lower-energy bryozoan-rich peloidal
sand sediments (Hoffmeister et al. 1967 ) of the plat-
form interior west of the shoal complex gently dip up
(average gradients of 0.02 m/km, up to the east) to a
broad shoal complex. The shoal system is broken into
broad fl at areas ~5 km across, separated by sinuous
depressions several 100s of meters wide and several
20.4.2 Ancient Analogs
Holocene tidal sands of the Bahamas have several well-
studied ancient analogs, preservation of which may be
favored by their early lithifi cation. One relatively young
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