Geology Reference
In-Depth Information
79
o
W
78
o
W
77
o
W
N
26
o
N
25
o
N
Facies
5
4
3.5
24
o
N
3
2.5
Fig. 2.
Facies distribution along
Great Bahama Bank. Mud-rich wacke-
stone = 1.5; Wackestone = 2; Mud-rich
packstone = 2.5; Packstone = 3; Mud-
lean packstone or poorly washed
grainstone = 3.5; Grainstone = 4;
Rudstone = 5.
2
1.5
0
100 km
23
o
N
Grain-size variations
Mineralogy
The samples were placed in 100 mL containers and
oven dried at 40°C before sieve analysis. A small
split of the dried samples was analysed by X-ray
diffraction. The dried samples were wet sieved to
separate the coarse (>63 μm) from the fi ne fraction
(<63 μm). The fi ne fraction was left in the 5-L bottles
to settle; water was then siphoned off; and the fi ne
sediment was oven dried at 40°C. The coarse frac-
tion was dried, weighed and split into fi ve sub-
fractions (very coarse sand to gravel >1000 μm; coarse
sand, 500-1000 μm; medium sand, 250-500 μm;
fi ne sand, 125-250 μm; very fi ne sand, 63-125 μm;
after Wentworth, 1922) using a hand-held stainless-
steel sieve set. Each sub-fraction was placed in a
pre-weighed glass vial, which was weighed again,
to determine the sub-fraction weight.
Whole-rock samples were oven dried at 40°C
and hand ground in a mortar to homogenize the
sediment (Milliman, 1974). Additional samples
representative of coarse and fi ne size fractions
were similarly individually homogenized by
grinding by hand in a mortar. The areas of the
principal peaks of aragonite, HMC and LMC were
measured with Scintag and Panalytical X-ray
instruments using Cu-K
radiation at RSMAS/
University of Miami. The samples were scanned
between 20° and 40° 2
with a speed of 0.01° per
second. The proportions of aragonite, HMC and
LMC were quantifi ed using a method outlined by
Swart
et al
. (2002) assuming that the sample is
composed entirely of aragonite, HMC, and LMC,
which is generally the case for GBB samples.