Paleoecology of the Devonian-Mississippian black-shale sequence in eastern Kentucky with an atlas of some common fossils
The Devonian-Mississippian black-shale sequence of eastern North America is a distinctive stratigraphic interval generally characterized by low clastic influx, high organic production in the water column, anaerobic bottom conditions, and the relative absence of fossil evidence for biologic activity. The laminated black shales which constitute most of the black-shale sequence are broken by two major sequences of interbedded greenish-gray, clayey shales which contain bioturbation and pyritized micromorph invertebrates. The black shales contain abundant evidence of life from upper parts of the water column such as fish fossils, conodonts, algae and other phytoplankton; however, there is a lack of evidence of benthic life. The rare brachiopods, crinoids, and molluscs that occur in the black shales were probably epiplanktic. A significant physical distinction between the environment in which the black sediments were deposited and that in which the greenish-gray sediments were deposited was the level of dissolved oxygen. The laminated black shales point to anaerobic conditions and the bioturbated greenish-gray shales suggest dysaerobic to marginally aerobic-dysaerobic conditions. A paleoenvironmental model in which quasi-estuarine circulation compliments and enhances the effect of a stratified water column can account for both depletion of dissolved oxygen in the bottom environments and the absence of oxygen replenishment during black-shale deposition. Periods of abundant clastic influx from fluvial environments to the east probably account for the abundance of clays in the greenish-gray shale as well as the small amounts of oxygen necessary to support the depauparate, opportunistic, benthic faunas found there. These pulses of greenish-gray clastics were short-lived and eventually were replaced by anaerobic conditions and low rates of clastic sedimentation which characterized most of black-shale deposition.
- Research Organization:
- Kentucky Univ., Lexington (USA). Dept. of Geology
- DOE Contract Number:
- AC21-76ET12040
- OSTI ID:
- 6459347
- Report Number(s):
- DOE/ET/12040-151
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
54 ENVIRONMENTAL SCIENCES
03 NATURAL GAS
04 OIL SHALES AND TAR SANDS
BLACK SHALES
GEOLOGY
PALEONTOLOGY
KENTUCKY
DEVONIAN PERIOD
FOSSILS
GEOLOGIC HISTORY
BITUMINOUS MATERIALS
CARBONACEOUS MATERIALS
CHATTANOOGA FORMATION
ENERGY SOURCES
FOSSIL FUELS
FUELS
GEOLOGIC AGES
GEOLOGIC FORMATIONS
MATERIALS
NORTH AMERICA
OIL SHALES
PALEOZOIC ERA
SOUTHEAST REGION
USA
580100* - Geology & Hydrology- (-1989)
510100 - Environment
Terrestrial- Basic Studies- (-1989)
030200 - Natural Gas- Reserves
Geology
& Exploration
040201 - Oil Shales & Tar Sands- Site Geology- (-1989)