Banks
Characteristics of Banks include:
Warm <20m
Cool 200-300m
Holocene-warm water
Modern warm water banks are typically isolated in
large shallow waters and have steep faulted margins of >40 degrees. They are
tide and wave dominated with occasional storm event having an impact on
sediment transport. Coarse sediments are present where high-energy conditions
exist while in shallow areas there are muds and pellet muds. Storm events and
nearby islands modify circulation patterns which have a significant impact on
the lithofacies of the following two examples.
Example 1: Great Bahama Bank (Background pictures).
The Great Bahama Bank encompasses an area of
approximately 96000km^2. The facies are asymmetric and have a sheet-like
geometry, precipitous sides with a sharp facies gradient but broad, flat
interiors. They include reefs on the eastern margin, a bank margin composed of
coralgal and oolite sediments, and a bank interior composed of
oolitic-grapestone, lime mud, and pelleted mud. Andros Island prevents
east-west movement of water across the bank. This area is characterized by muds
and pellet muds. Overall the sediment is largely biogenic.
Example 2: Caicos Platform
Islands are located on northern margins with
reefs in front. The banks are hit by waves causing good circulation throughout
the region. Mud is localized to tidal flats on south side of the nearby
islands. Everything else is skeletal grain and ooid sand.
Ancient-warm water
Example 1: Golden Spike reef in the Leduc
Formation
This formation has a platform rimmed by
stromatoporoid reefs, with the platform interior composed of interbedded
skeletal, sand flat grainstones and packstones and peritidal plana strombolites
(ex. Triassic strata pictured below).
These sites are typically covered in biogenic
gravels and sands from bryzoa, molluscs, echiniods, corals and gastropods.
Example 1: Three Kings Plateau
The Three Kings Plateau is located off the
northern coast of New Zealand, a site of active nutrient upwelling which is
swept by vigorous wind, storm waves, and tidal currents. Facies belts are depth
related resulting in a wide variety of biotic communities. The seafloor is
covered by bryzoa/bivalve/ahermatypic coral sands and gravels with no mud.
Active skeletal production is limited to inshore regions, areas of rough
seafloor topography, and ridge and bank crests. Sediment from this site were
most likely produced during low sea level stand.
