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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Understanding the Crust Beneath Sedimentary Basins
Understanding how sedimentary basins evolve is an exciting,
but difficult task. Seismic reflection data do a marvelous job
of imaging the internal structure of sedimentary basins. There is
no better technique. However, we often want more than just a
detailed image of the basin. Of particular
interest are the physical properties within the
basin and below it, within the crystalline
crust. For example, seismic P- and S-wave
velocities are closely tied to lithology,
and hence crustal type (oceanic versus
continental). Consequently, seismic
reflection studies are complemented by
seismic velocity
studies. Such
velocity
information is very effective in determining basin geometry, and
can be used to determine Poisson’s ratio, an important parameter
for determining the kind of source rocks, crustal type, as well
issues related to the Law of the Seas convention.
One good way to obtain reliable deep seismic velocities is to
shoot wide-offset seismic refraction profiles. Actually, this
technique is a classical one that all students encounter in their
first course about the Earth’s crust. Indeed, seismic refraction
profiles formed the basis for the early
exploration for hydrocarbon resources.
Today, high-resolution seismic refraction
profiles are recorded on land and at sea
using
a wide variety of techniques.
In this talk I will present a global synthesis of
what we have learned from deep crustal
seismic velocity
profiles, from the Gulf Coast
to the Bay of Bengal and beyond. A very extensive literature
search has been undertaken to track down as many of the seismic
refraction publications as possible. The resulting database
contains over 10,000 one-dimensional P-wave and S-wave
profiles, making it the largest such catalog in existence. These
data, especially when examined as complete crustal cross sections,
reveal a number of surprising results, such as the discovery of
highly thinned continental crust extending 100s of km offshore,
serpentinized peridotite (rather than basalt) right at the sea floor,
and evidence for deep, highly metamorphosed sediments that
mimic crystalline basement rocks, thus confounding traditional
basin interpretations. Indeed, many of these results challenge
conventional views of “how the Earth works”. That’s just what
makes this investigation so exciting!
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