12.2 Continental Margin and Slope Basins
a
TURBIDITES
----i
TURBIDITES
\
EROSION
PLATFORM
(BOX CANYONS)
~-')LUMPS,
DEBRIS FLOWS
~~THIN TURBIDITES ~ -=
SLOPE SEDIMENTS
3
2
BAHAMA
PLATFORM
d
565
b
WSW
PROGRADING
STRAITS
MARGIN
I BIMINI BANK i OF ANDROS
i ANDROS BANK
A
~_'t,::= _ _ _ _____ L _______ L __ ____ - - - - - -
~~~
Fig. 12.12. a Model of lateral progradation and "seIferosion" oflimestone escarpments in the Bahamas and
Marshall Islands. Note oversteepening and various
types of erosion with increasing vertical buildup (1,2,3;
angles of upper one-third of slope up to about 30°).
(Schlager and Camber 1986). b-d Location and internal
structure ofthe northwest Bahama Bank displaying two
buried banks (Bimini Bank and Andros Bank) with
completely filled former trough (Straits of Andros) in
- Early Cretaceous platfonn drowning, "Wealden"-type
fluvial clastics and marine prodelta deposits.
- Mid-Cretaceous siliciclastics and limestones and, on the
African side, black shales and cherts resulting from coastal
upwelling.
- Late Cretaceous to Paleogene hemipelagic sediments
characterized by slow sedimentation rates and high proportions ofbiogenic material.
between. Lateral pro gradation of the Birnini western
margin (by 20 km) resulted from sediment accretion on
slope. Vertical upbuilding since the rnid-Cretaceous is
about 2 km (lower correlation horizon); earlier
platform consists of carbonates and evaporites. Vertical
exaggeration about l2x. (Derived from seisrnic
profiles, ocean drilling, and dredge hauls on the
exposed flanks; Eberli and Ginsburg 1987; Schlager et
al. 1988).
During mid-Cretaceous time, the central Atlantic had already reached the size of a large ocean basin and the
depositional environments on the opposite margins of this
ocean became increasingly dissimilar. This asymmetrie
evolution is documented by the mid-Cretaceous black
shales in the Essaouira-Agadir basin, as weIl as by late
Cretaceous shelf construction in the Scotian basin, while
the marginal basin on the African side was characterized by
shallowing and the onset of emergence. In addition, the
northwest Atlantic basins drifted into a region of increas-
a
TURBIDITES
----i
TURBIDITES
\
EROSION
PLATFORM
(BOX CANYONS)
~-')LUMPS,
DEBRIS FLOWS
~~THIN TURBIDITES ~ -=
SLOPE SEDIMENTS
3
2
BAHAMA
PLATFORM
d
565
b
WSW
PROGRADING
STRAITS
MARGIN
I BIMINI BANK i OF ANDROS
i ANDROS BANK
A
~_'t,::= _ _ _ _____ L _______ L __ ____ - - - - - -
~~~
Fig. 12.12. a Model of lateral progradation and "seIferosion" oflimestone escarpments in the Bahamas and
Marshall Islands. Note oversteepening and various
types of erosion with increasing vertical buildup (1,2,3;
angles of upper one-third of slope up to about 30°).
(Schlager and Camber 1986). b-d Location and internal
structure ofthe northwest Bahama Bank displaying two
buried banks (Bimini Bank and Andros Bank) with
completely filled former trough (Straits of Andros) in
- Early Cretaceous platfonn drowning, "Wealden"-type
fluvial clastics and marine prodelta deposits.
- Mid-Cretaceous siliciclastics and limestones and, on the
African side, black shales and cherts resulting from coastal
upwelling.
- Late Cretaceous to Paleogene hemipelagic sediments
characterized by slow sedimentation rates and high proportions ofbiogenic material.
between. Lateral pro gradation of the Birnini western
margin (by 20 km) resulted from sediment accretion on
slope. Vertical upbuilding since the rnid-Cretaceous is
about 2 km (lower correlation horizon); earlier
platform consists of carbonates and evaporites. Vertical
exaggeration about l2x. (Derived from seisrnic
profiles, ocean drilling, and dredge hauls on the
exposed flanks; Eberli and Ginsburg 1987; Schlager et
al. 1988).
During mid-Cretaceous time, the central Atlantic had already reached the size of a large ocean basin and the
depositional environments on the opposite margins of this
ocean became increasingly dissimilar. This asymmetrie
evolution is documented by the mid-Cretaceous black
shales in the Essaouira-Agadir basin, as weIl as by late
Cretaceous shelf construction in the Scotian basin, while
the marginal basin on the African side was characterized by
shallowing and the onset of emergence. In addition, the
northwest Atlantic basins drifted into a region of increas-