Trace fossils and paleoenvironments of lower and middle Austin Chalk (upper Cretaceous), north-central Texas
- Texaco E and P Technology Div., Houston, TX (USA)
- Univ. of Texas, Arlington (USA)
Outcrops of lower and middle Austin Chalk in the vicinity of Cedar Hill and Waxahachie, Texas (designated site of the Superconducting Super Collider), are profusely bioturbated. The lower Austin (Coniacian) disconformably overlies the Eagle Ford Shale (Turonian) and consists of about 60 m of medium- to thick-bedded indurated chalk with thin intervening marls. The middle Austin (Santonian) is composed of about 65 m of thick-bedded marl containing thin beds of argillaceous chalk. Both chalk and marl units are moderately to intensely bioturbated. However, ichnofossils are more conspicuous in chalks where multiple episodes of burrowing are recognizable. Early formed burrows (indistinct mottles) represent the initial softground Austin substrate. Later generations of well-preserved burrows record a post-compaction (dewatered) firmground substrate. No hardgrounds have been recognized. The abundance and diversity of ichnofossils in Austin strata are in marked contrast to the paucity of other megafauna, except large inoceramids. Planolites, Teichichnus, Thalassinoides, and Chondrites are the predominant ichnogenera in the lower Austin; these forms are superimposed on a background of nondiagnostic, irregularly shaped mottles. Some strata contain well-preserved J-, S-, T-, U-, Y-, and X-shaped traces having menicus fillings. These subhorizontal, endogenic, full-relief burrows are typically infilled with dark gray (pyritic) chalk. Locally, pyrite or Fe-oxide-filled vertical tubes are preserved. Many traces have been deformed by compaction. The middle Austin contains Planolites, Chondrites, Thalassinoides, Pseudobilobites, and both small- and large-diameter, sinuous, horizontal burrows. These ichnofossils are infilled with chalk or comminuted shells and are more resistant to weathering than the surrounding middle Austin marl. Intensely burrowed horizons occur in association with distinctive Fe-stained chalk beds.
- OSTI ID:
- 5922379
- 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
Similar Records
Trace fossils, storm beds, and depositional sequences in a clastic shelf setting, Upper Cretaceous of Utah
Shallow and marginal marine Triassic trace fossils and ichnofabric from northwest Australia (ocean drilling program leg 122)
Related Subjects
58 GEOSCIENCES
PETROLEUM DEPOSITS
RESERVOIR ROCK
DEPOSITION
PALEONTOLOGY
TEXAS
CARBONATE ROCKS
CRETACEOUS PERIOD
FOSSILS
GEOLOGIC FORMATIONS
PYRITE
SHALES
STRATIGRAPHY
CHALCOGENIDES
FEDERAL REGION VI
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGY
IRON COMPOUNDS
IRON SULFIDES
MESOZOIC ERA
MINERAL RESOURCES
MINERALS
NORTH AMERICA
RESOURCES
ROCKS
SEDIMENTARY ROCKS
SULFIDE MINERALS
SULFIDES
SULFUR COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
USA
020200* - Petroleum- Reserves
Geology
& Exploration
580000 - Geosciences