Incrusting and boring bryozoans from the Dessau Chalk Formation (Cretaceous), Little Walnut Creek, Austin, Texas

Conference · Sat Sep 01 00:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:5949543

Morris, P A ^[1]

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1. Univ. of Houston, TX (USA)

Four sections were measured along a 1/4 mi length of Little Walnut Creek. The first section was 165 ft north of the US. 290 bridge while the fourth was 1/4 mi upstream. Structurally, the stream follows the fault in this section. Small faults can be found perpendicular to the primary fault and apparently account not only for minor variation in local dip (8{degrees}SE, parallel to 5{degrees}NW) but also for the placement of at least one tributary. Megainvertebrate exoskeletons were found to have been inhabited by incrusting bryozoans, boring bryozoans, and sponges. These fossils were found on both interior and exterior surfaces of Exogyra laeviuscula E tigrina, and interior surfaces of Inoceramus. A low-energy environment allowed exposure of megainvertebrate exoskeletons after death but also prevented fracturing. Low siltation rates also extended exoskeleton availability after organismic death. The nonboring bryozoans are cheilostomes and at least one species, Pyripora, has been described from the Kansas Cretaceous as well as European Cretaceous sites. The boring bryozoans are primarily represented by Terebripora sp. In conclusion, this section of Dessau Chalk Formation, Upper Austin Group, was mostly a low-energy environment, shallow, limy mud platform. This substrate was probably not stable enough for bryozoan colonization as unattached colonies have not been found in sediments. Therefore, bryozoan substrates were limited to living and dead Exogyra sp. and dead Inoceramus sp. exoskeletons.

• OSTI ID: 5949543
• Report Number(s): CONF-9010204-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 74:9; Conference: Gulf Coast Association of Geological Societies and Gulf Coast Section of SEPM (Society of Economics, Paleontologists, and Mineralogist) meeting, Lafayette, LA (USA), 17-19 Oct 1990; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CARBONATE ROCKS
DEPOSITION
TEXAS
CRETACEOUS PERIOD
FOSSILS
GEOLOGIC FAULTS
GEOLOGIC FORMATIONS
KANSAS
PALEONTOLOGY
SEDIMENTS
FEDERAL REGION VI
FEDERAL REGION VII
GEOLOGIC AGES
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
MESOZOIC ERA
NORTH AMERICA
ROCKS
SEDIMENTARY ROCKS
USA
580000* - Geosciences