The bulge is a 600-m-thick regional deposit of pelagic sediment
accumulated around the equator. Its stratigraphy reflects a number of
factors: how accumulation rates have varied over time, how accumulation
has been spatially focused around the equator, how much carbonate
dissolution and reworking or non-deposition by bottom currents have
occurred, and how much the deposits have been translated northwards
by motion of the Pacific tectonic plate on which they have accumulated.
In order to fully explore the effects of these processes, a spatially
continuous stratigraphic database is desirable, as existing cores provide
information at only discrete points and they tend to be sited in locally
thicker accumulations. We illustrate the utility of seismic data tied to
drill cores by comparing the carbonate dissolution effect in two north-
south lines crossing the sediment bulge. Bathymetry over our easterly
seismic line deepens relatively little going north, whereas our westerly
line deepens by 750 m from 4degN to 7degN. At a common latitude, the
primary pelagic input to both these lines will have been similar, so the
difference of their sediment mass should reflect mostly their relative
carbonate loss due to dissolution. We use this fact to calculate the slope
of the carbonate dissolution curve and find a remarkably small slope
(little relative carbonate dissolution) compared to that expected from
previous studies. The techniques here may suggest a possible way
forward for studying the equatorial carbonate stratigraphy more
generally.
NC Mitchell, MW Lyle, MB Knappenberger and LM Liberty, The Lower Miocene to Present stratigraphy of
the Equatorial Pacific sediment bulge and
carbonate dissolution anomalies, Paleoceanography, 18, 2003 (DOI: 10.1029/2002PA000828).