A re-evaluation of facies on Great Bahama Bank I: new facies maps of western Great Bahama Bank - Perspectives in Carbonate Geology - page 41

refl ects these topographic features (Fig. 3a). The
more open character of the southern part of the
platform is also clearly shown by coarser, cleaner
sediments on these maps (Fig. 3a-d). Tidal cur-
rents entering the platform in combination with
wave action most likely caused this distribution.

of the Holocene facies in the lagoons of Belize
is strongly infl uenced by processes such as
siliciclastic input related to the uplift of the hinter-
land, and by antecedent topography of structural
origin infl uenced by karst processes during glacial
lowstands (Purdy, 1974; Purdy et al ., 2003).
The data available on the antecedent pre-
Holocene topography of GBB (Boss & Rasmussen,
1995; Boss, 1996) also suggest that the observed
facies patterns are to some extent linked to the
antecedent topography. The correlation between
the timing of the last sea-level rise fl ooding the
shallow-water areas of the platform and the onset
of sediment production, without any signifi cant
lag time, suggests that the antecedent pre-Holo-
cene topography acted as sediment production
and export site immediately after refl ooding (Roth
& Reijmer, 2004).
The facies distribution shows the interaction
of the prevailing winds and currents with the
pre-existing topography. At present considerable
accommodation space is unfi lled, which prob-
ably results from a combination of a pre-existing
topography, fl at-topped platform with no distinct
barrier, and a rate of sea-level rise that resulted in
the establishment of a current system that removes
sediment, soon after the platform was fl ooded.
This early export of platform sediments towards
the surrounding slopes and basins started at 7.2 ka,
shortly after refl ooding of the shallow-water areas,
as discussed by Wilber et al . (1990), McNeill et al .
(1998) and Roth & Reijmer (2004, 2005).

Comparisons with other platform lagoons

Other carbonate platform lagoons such as those
from Mayotte in the Indian Ocean (Zinke et al .,
2001, 2003a), show a facies distribution pat-
tern that is clearly infl uenced by the interplay
of the antecedent topography and the rate of the
Holocene sea-level rise (Zinke et al ., 2003b, 2005).
The rate with which the former topography was
fl ooded determined the development of a cur-
rent pattern within the lagoon and thus steered
the facies distribution. This current pattern also
depended on the continuity of the barrier sur-
rounding the lagoon before the platform interior
was refl ooded after the last glacial. Other present-
day facies variations were related to either the
vicinity of the barrier reef or the reefs surround-
ing the inner lagoon of the island or the input of
terrigenous material. The link between facies vari-
ations and the distance to the edge of the platform
also can be observed on the Bahamian platform.
The same holds for the infl uence of the antecedent
topography (see discussion below).
In a discussion of the sediment distribution
of three isolated carbonate platforms seaward
of the Belize barrier reef system (Glovers Reef,
Lighthouse Reef and Turneffe Islands) Gischler
(1994) and Gischler & Lomando (1999) suggested
that variations in antecedent topography and
exposure to waves and currents were the domin-
ant factors infl uencing the sediment distribution
of these three relatively small-scale carbonate
platforms. In analogy with the scenario devel-
oped for the facies distribution of the inner lagoon
of Mayotte (Zinke et al ., 2001, 2003a), Gischler
(2003) showed that the timing of refl ooding of
the Pleistocene bedrock in combination with the
rate of sea-level rise determined the sedimenta-
tion patterns in the lagoons of the Belize atolls.
The early fl ooded atolls (Glovers Reef and
Lighthouse Reef) developed an open-circulation
pattern, while the Turneffe Islands, fl ooded in a
relatively late stage, at present has restricted cir-
culation. The latter might also be related to its
present rather low-energy position in the lee of
the other platforms. Purdy & Gischler (2003) also
noted that the distribution and overall character

Mineralogy

Appreciable differences exist between the
carbonate mineralogy of the bulk sediments
(Fig. 4) and the <63 μm grain-size fraction (not
shown). The percentage of HMC and LMC
increases in the <63 μm fraction when com-
pared with the bulk sediments (Table 1). These
differences are most likely related to the export
of the fi ne aragonite mud whitings produced in
the water column (Shinn et al ., 1989; Robbins &
Blackwelder, 1992; MacIntyre & Read, 1992, 1995;
Milliman et al ., 1993; Thompson et al ., 1997;
Yates & Robbins, 1998, 1999). This production
of aragonite fi nes in the water column makes
them very sensitive to transport during tides,
storms and passing winter fronts (McCave, 1972;
Neumann & Land, 1975; Wilson & Roberts, 1992,
1995; Wilber et al ., 1993). The precise recording
of climatic variations on the slopes of GBB most
likely refl ects this process (Roth & Reijmer, 2005).