The oxygen isotopic data

The oxygen isotopic data for the 0.1–0.5 mm samples lie on
the same depth trend as that for the remaining data (Fig. 5).
Quartz overgrowths are not very abundant in Cormorant IV
(generally ,2%), due to the relatively shallow depths of
burial (2880–3060 m). Only samples from well 211/21-
14S1 yielded sufficient overgrowths for analysis, with an
average d18O ¼ 17.6 ^ 0.3‰ V-SMOW (Table 2).
Out of six samples processed for illite, only one yielded
sufficient sample for a reliable analysis. Other samples were
either too small or were heavily contaminated by detrital
K–feldspar, which makes reliable analysis impossible. The
one good sample from 2946.1 m depth in well 211/21-14S1
yielded an age of 60.3 ^ 2.0 Ma. The scarcity of recovered
illite presumably reflects the low abundance of illite, though
this is difficult to reconcile with the description of Hamilton
et al. (1992) of ‘substantial illite growth from 75 8C’ within
areas I–III of the Cormorant Field. SEM examination of
chip samples from Cormorant IV show that illite is not
particularly abundant. Why there should be less illite in
Cormorant IV compared to the adjacent Cormorant I–III is
unknown. All are at similar burial depths.

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