Page 56 - Petroleum Geology

35

result in a steepening of the flanks with depth - or, more properly, they re-
sult from a steepening of the flanks with depth, but the causes will be con-
sidered later in the book. Isopach maps over growth anticlines may be viewed
as structural contour maps on the bottom of the isopached interval below
the top of the interval as datum. More than one rock unit normally shows
crestal thinning, and the development of the growth anticline against the
time scale of accumulated sediment will be revealed both by isopach maps of
the various rock units, and cumulative isopach maps and cross-sections drawn
from them (Figs. 2-7-2-9).
Growth anticlines are commonly closed, oval or dome-like. “Drape struc-
ture” is not synonymous with “growth anticline”, but, as with growth faults,
there is an element of differential compaction in them that will contribute to

‘2

Fig. 2-7. Cumulative isopach maps reveal the history of growth of a growth anticline,
shown here in cross-section.

1 1

Fig. 2-8. Cumulative isopach intervals are taken from the deepest marker that is sufficient-
ly known.