Geology Reference
In-Depth Information
<63 μm) and the relative percentages of aragonite,
high-Mg calcite (HMC) and low-Mg calcite (LMC)
were determined together with their carbon and
oxygen-isotopic compositions. Each sample was
also separated into a modifi ed Dunham facies
classifi cation. At the same time water samples
were taken for salinity and stable oxygen and
hydrogen measurements. Samples for carbon
isotopic analysis of the dissolved inorganic car-
bon (DIC) were fi ltered using a 1 μm fi lter and
preserved in sealed crimped vials with excess
mercuric chloride.
deviation, based on replicate analyses of internal
standards is < 0.1‰ for
18
O and 2.0‰ for
D. The
13
C of the dissolved inorganic carbon (DIC) was
determined by acidifi cation of the sample followed
by extraction using a fl owing stream of He and
analysis in a stable isotope ratio mass spectro-
meter (Europa 20-20). Data are reported relative to
V-PDB using the conventional notation. Average
standard deviation based on replicate analyses of
internal standards is <0.1‰.
Facies classifi cation
Immediately after collection, samples were
assigned to a modifi ed Dunham scheme (Dunham,
1962). In order to supplement the classifi cation
divisions were added between wackestone and
mudstone (mud-rich wackestone), between a
packstone and wackestone (mud-rich packstone)
and fi nally between packstone and grainstone
(mud-lean packstone). For display purposes
the mudstone, wackestone, packstone, grain-
stone and rudstone classifi cation were assigned
numbers from 1 to 5, with the intermediary cat-
egories being assigned values of 1.5, 2.5 and 3.5.
Samples from all cruises were preserved in cold
storage and after the 2004 cruise all samples were
re-examined to ensure consistency between
cruises (Reijmer
et al
., 2009).
METHODS
X-ray mineralogy
The percentages of aragonite, HMC and LMC
were determined using the method of Swart &
Melim (2000). In this method the sample is
assumed to be completely composed of arago-
nite, HMC and LMC. Areas of the appropriate
peaks for each mineral are determined using a
scan between 23 and 32° 2
radiation).
These are then compared with standard relation-
ships between peak area and percentage mineral
and the percentage of the mineral in the sample
determined.
(CuK
Stable isotopes carbonates
RESULTS
18
O of the carbonate materials was
determined using dissolution in phosphoric acid
using the common acid bath method (Swart
et al.,
1991) at 90°C. The gas produced was analysed
using a Finnigan-MAT 251. Later some samples
were also analysed using a Kiel III device attached
to a Finnigan Delta plus. Data produced in both
methods were corrected for isobaric interferences
using the procedures (Craig, 1957) modifi ed for
a triple collector mass spectrometer. Data are
reported relative to Vienna Pee Dee Belemnite
(V-PDB) using the conventional notation. Average
standard deviation based on replicate analyses of
internal standards is < 0.1‰.
13
C and
The
Stable isotopes of carbonates
18
O values for the carbon-
ate sediments and the various size fractions are
shown in Tables 1 and 2 and Fig. 2. The
13
C and
The mean
18
O of
all fractions are statistically the same, but the
13
C
of the coarser material (>1000 μm) is statistically
signifi cantly more negative than the fi ner fraction
and the bulk. Relative to the modifi ed Dunham
classifi cation there is no statistically signifi cant
difference between the mean
18
O of
the coarser and fi ner sediment types (Table 3;
Figs 3 and 4). However, the range of values of
the modifi ed Dunham categories increases with
grain size (Table 3). The spatial distribution of
13
C and
Water samples
13
C and
18
O are shown in Figs 5 and 6.
The oxygen and hydrogen-isotopic composition
(
18
O and
D) were determined using the meth-
ods of Epstein & Mayeda (1953) and Coplen
et al
. (1991) respectively. All
Water samples
18
O and
18
O of the waters are shown in Fig. 7 and
range between +0.75 and +2.93‰. There is an
approximate positive correlation with salinity,
D data for
waters are reported relative to Vienna Standard
Mean Ocean Water (VSMOW). Average standard
The
