Faunal, geochemical and paleomagnetic change across the Cretaceous-Tertiary boundary at Braggs, Alabama
Near Braggs, Alabama the Upper Cretaceous Prairie Bluff Chalk underlies the Paleocene Pine barren Member of the Clayton Formation in a well-exposed, continuous K/T boundary section composed of interbedded sands, shales, and limestones of shallow marine origin. As determined from foraminiferal and calcareous nannofossil biostratigraphies, and the Maastrichtian/Danian contact at Braggs lies below a marine hardground in a zone associated with slow sedimentation and a deepening paleoenvironment. The K/T boundary occurs within a well-defined reversed magnetozone which we correlate to the reversed interval between marine magnetic anomalies 29 and 30. This magnetozone is approx.3.2 m thick, suggesting a sedimentation rate of only 6.8 m/m.y. across the boundary. The boundary occurs in the lower part of the magnetozone, about 1 m above its base, unlike the Italian sections where the boundary occurs toward the top of the reversed magnetozone. Marine macrofossils occur abundantly throughout the sequence had have been analyzed on a bed by bed basis to document the pattern of extinction and paleoenvironmental change. To help calibrate the rate of faunal change and refine the bio- and magnetostratigraphies, the Rb-Sr systematics of glauconites from the section are being investigated and the change of /sup 87/Sr//sup 86/Sr in seawater is being investigated by analysis of CaCO/sub 3/ from molluscan shells and foraminiferal tests. Initial Rb-Sr measurements of glauconites from a bed above the contact suggest an age of 60 Ma with an initial /sup 87/Sr//sup 86/Sr compatible with /sup 87/Sr//sup 86/Sr measured in shell carbonate at this site. Values for shell carbonate range from .707713 to .707826 and appear to show a maximum near the boundary.
- Research Organization:
- Univ. of Florida, Gainesville (USA)
- OSTI ID:
- 6317541
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Vol. 17; ISSN GAAPB
- Country of Publication:
- United States
- Language:
- English
Similar Records
Stratigraphic correlation of Pleistocene California borderland marine carbonate using strontium isotopes
Sr$sup 87$/Sr$sup 86$ RATIOS IN HAWAIIAN LAVAS
Related Subjects
580300 -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
580400* -- Geochemistry-- (-1989)
ALABAMA
ALKALI METAL ISOTOPES
ALKALINE EARTH ISOTOPES
ANIMALS
AQUATIC ORGANISMS
BIOLOGICAL EXTINCTION
BRYOZOA
CENOZOIC ERA
CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
CHEMISTRY
CRETACEOUS PERIOD
DEPOSITION
FEDERAL REGION IV
FORAMINIFERA
FOSSILS
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGY
INVERTEBRATES
ISOTOPE RATIO
ISOTOPES
MAGNETISM
MESOZOIC ERA
MICA
MICROORGANISMS
MOLLUSCS
NORTH AMERICA
PALEOMAGNETISM
PALEONTOLOGY
PETROLOGY
PROTOZOA
QUANTITATIVE CHEMICAL ANALYSIS
ROCKS
RUBIDIUM ISOTOPES
SARCODINA
SEDIMENTARY ROCKS
STRATIGRAPHY
STRONTIUM ISOTOPES
TERTIARY PERIOD
USA