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The AAPG/Datapages Combined Publications Database
Houston Geological Society Bulletin
Abstract
Abstract: Biostratigraphy of the Cardenas Formation (Upper Cretaceous San Luis Potosi, Mexico)
By
University of Texas, Ph.D. thesis, 72 p., 1965
The Cardenas Formation is a very fossiliferous 1050-meter thick unit of
finely clastic sedimentary rocks that crops out in an asymmetric syncline in the
folded Sierra Madre Oriental. Six versions of the stratigraphy at Cardenas
have been published, but they have included partially inverted sequences because
of failure to recognize the structure of the syncline. For this study the region
around Cardenas was mapped on topographic sheets at a scale of 1:50,000, and
the Cardenas syncline was mapped with plane table and alidade at a scale of
1:4,800. Of eleven measured sections, two were structurally uncomplicated and
complete enough to establish the sequence of stratigraphic units.
The Cardenas Formation, herein defined, is divided into three informally
designated members. The lower member is 180 meters of alternating shale,
sandstone, and biosparite (Folk, 1959); the middle member is 445 meters of
shale and siltstone; the upper member is 430 meters of siltstone, sandstone,
and biosparudite. The Cardenas Formation is uncomformably overlain by unfossiliferous
siltstone, sandstone, and conglomerate, the Tabaco Formation.
In present study 71 species of invertebrate fossils were collected from the
Cardenas Formation: 8 rudists, 36 other bivalves, 14 gastropods, 6 corals,
4 echinoids, 2 serpulids, and 1 brachiopod. These occur in three assemblage
zones at Cardenas. The middle zone and perhaps the lower zone are correlative
with the Exogyra costata Zone of the Gulf Coastal Plain. The upper zone is
probably younger than the Exogyra costata Zone, but still Maastrichtian. The
Cardenas Formation is a "regressive" type of deposit; during its formation
sedimentation changed repeatedly from deposition of fine clastics to the accumulation
of biogenic limestones.
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