Date of Award

Spring 1-1-1987

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geological Sciences

First Advisor

Erle A. Kaufman

Second Advisor

Don L. Eicher

Third Advisor

Dave A. Budd

Abstract

The most unusual features of the middle Late Campanian Pierre Shale in southern Colorado are conical limestone-shale mounds which rise up to 25 meters above the more easily weathering surrounding shale surface. Morphologic, lithologic, geochemical and paleontological data suggest that these mounds .represent the deposits of submarine springs.

Conical Tepee Butte limestone-shale deposits consist of vertical limestone cores, with gently dipping limestone and shale flanks that are intercalated with the surrounding shales. The submarine spring deposits are consistently characterized by several different lithofacies and by dense macrofaunal populations, especially of species that are comparably rare elsewhere on the seafloor.

Exceptionally dense macrofaunal populations and diverse microfaunal assemblages in isolated Tepee Butte deposits stand in marked contrast with the depauperate faunas of the Pierre Shale seafloor of the same stratigraphic level, and suggest that environmental conditions on the flanks of Tepee Buttes were favorable for benthic life.

Carbon isotopic data indicate that methane vented at Tepee Butte submarine springs. At modern submarine spring vents the oxidation of methane provides the energy necessary for the production of organic carbon by chemosynthetic bacteria, chemosynthetically manufactured carbon compounds provide the base of the foodchain at these vents. Nyrnphalucina, the dominant vent fossil at Tepee Butte submarine springs is typical of the Lucinidae in general, many of which are known to have bacterial symbionts. It is here suggested, that at least two species of vent animals lived in symbioses with methylotrophic bacteria, and that bacteria and organic carbon compounds provided a concentrated foodsource on the flanks of Tepee Buttes, which attracted a variety of marine organisms without bacterial symbionts. In addition, oxygen enrichment of the water in vicinity of the spring vents was a result of chemosynthesis and considerably improved the living conditions on the flanks of Tepee Butte submarine springs as opposed to those on the dysaerobic seafloor.

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