398
180
I
o
(0
2
3
4
3
4
140
100
60
!
20
o
PRESENT SEA LEVEL
EROSION
\
I
Ma B.P.
LONG-TERM
EUSTATIC SEA LEVEL
DRILLHOLE
._._L. _/-T·-\-.
_________ L __
BATHYMETRY (IN RELATION
TO PRESENT SEA LEVEL)
AIR-FILLED BASIN
---~A---L
------UNCORRECTED
SUBSIDENCE CURV8
CORRECTED
------FOR COMPACTION
CORRECTED
FOR BATHYMETRY
(IN RELATION TO
PRESENT SEA LEVEL)
CORRECTED FOR BOTH
COMPACTION AND BATHYMETRY
Chapter 8 Subsidence
SHALLOW
MARINE
DEEPEN- CONTIING
NENTAL
130
150
::::: : ....
180 ·O·G'·O·.~
Ma :'.;'~;,;-;;.-.!.
CORRECTIONS FOR LONG-TERM
SEA LEVEL CHANGES (FALL AND RISE)
CORRECTION FOR SEDIMENT
LOAD ABOVE SEA LEVEL
,,~.'j
'- :
"
DEPTH (km)
Fig. 8.7. Synthetic, semi-quantitative example showing drilled vertical sediment succession and derived,
uncorrected subsidence curve at a given location
within a basin. Purely thermo-tectonic subsidence in
an air-filled basin (Curve A) is magnified by a water
load (B, related to present sea level) and the load of a
permanently sediment-filled basin (C) up to the present sea leveL Curve C is modified by sediment compaction, a reduced sediment load (increasing paleowater depth or bathymetry), and eustatic sea-Ievel
changes. In addition, erosion diminishes subsidence,
or a sediment load above sea level enhances subsidence