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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Deep Water Gulf of Mexico High Gamma-Ray Shales and Their Implications for Flooding Surfaces, Source Rocks, and Extinctions
High gamma-ray ‘hot’ Eocene shales were encountered
in southern deepwater Gulf of Mexico wells. The two
prominent shales were in the age range of 40 and 50 Ma. The
shales were originally deposited in
basin floor settings that palinspastically
restore to water depths of greater than
20,000’ sub-sea total vertical depth.
The occur rence of ‘hot ’ shales
deposited at such water depths forces
the questioning of the association of
such ‘hot’ shales and maximum
flooding surfaces. The influence from
eustatic sea level changes in very deep
water would be minimal. The deep
water ‘hot’ shales alternatively suggest
very high global temperature excursions which created extensive
algal blooms and anoxic oceanic conditions. The high temperatures
would cause the related cascade effects of hydrate melting, global
anoxic flooding events, global alginate source rock occurrences,
atmospheric compositional change, marine and terrestrial
stress/extinctions, and faunal lagerstattens. The age of these
shales correlates with lagerstatten death assemblages in the Green
River shales, the Messel fossil beds of Germany, and Whale Valley
in Egypt. The vertebrate death assemblages contain multiple
species. The articulated and unscavenged
skeletal remains indicate post-death
predation was non-existent due to
lethal atmospheric temperatures that
most likely suppressed predators and
scavengers. The large number of
specimens also suggests a rapid onset
of thermal change. The Whale Valley
lagerstatten includes a red bed
containing crabs that are found in a
hibernation position after mass
simultaneous burrowing, which suggests
a rapid transition from healthy faunal community to mass death.
Periods of high temperatures punctuated by brief episodes of
extreme heat would explain the association of marine deep water
‘hot’ organic shales and terrestrial death assemblages.
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