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Geology
– Barnett Shale
The Barnett Shale is a blanket marine shale deposit that is
present over most of north Texas and is one of the most
stratigraphic formations in Texas.
Outcropping along the Llano Uplift in central Texas, where it
is a dark fossiliferous limestone 30-50 feet thick, the Barnett
thickens as it dips to the north, where it reaches a thickness of
1,000’ at a depth of 9,000 feet near the Texas-Oklahoma state
line. The Barnett is of
Mississippian age and in most areas is bound by the Viola/Simpson
limestone, below and the Marble Falls limestone, above.
The presence of potentially prospective Barnett Shale is
limited by the Muenster arch and associated sub-components to the
north and northwest, while the Ouchita foldbelt precludes Barnett
development to the east. The Barnett thins to the south and southwest in response to
the uplift and erosion associated with the Bend arch and Llano
Uplift. While the
Barnett unconformably overlies Early to Middle Ordovician
carbonates, it is in turn overlain conformably by shales and
limestones of the Marble Falls Formation.
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