Date of this Version
Thesis (M.S.)—University of Nebraska—Lincoln, 1964. Department of Geology.
The purpose of this paper is to (1) delineate precisely the exact areal distribution and stratigraphic position within the Plattsmouth limestone member of any occurrence of Pseudozaphrentoides verticillatus (Barbour) and (2) to study the abiotic and biotic aspects of the Plattsmouth limestone in order to offer some inferences as to the paleoecological significance of these occurrences.
The Plattsmouth limestone in Nebraska is exposed in numerous quarries along the sides of the Weeping Water valley and along the Missouri River bluffs from Plattsmouth, Nebraska south to the Queen Hill quarry. Within the Plattsmouth, corals rapidly diminish in number away from the Nehawka, Nebraska area so that the area of study was primarily in Nebraska. Quarries in Iowa and in northeastern Kansas were also studied in the hope of gaining additional paleoecological evidence about the environments represented within the Plattsmouth limestone.
General conclusions in regard to the Plattsmouth member area as follows:
- Braden (1958) implied that the framework of the biosparite facies were oolitic. Svandsen (1961) proposed an algal origin. At present it seems most probably that these “grains” were rounded secondarily and redeposited.
- Most of the chart in the Plattsmouth member is probably of secondary origin.
- Plant fragments and pollen, and increased argillaceous content in the Iowa exposure, suggest a source for these materials from the east or northeast during deposition of the Plattsmouth member.
- The biogenetic bank within the Plattsmouth may have formed in water deeper than usually suggested.
- The area of bank development is centered just north of Nehawka, Nebraska, and trends in a westerly direction for about four miles. The bank is probably only a mile or two wide. Flanking the bank area on all sides is a wider periphery in which corals and the associated faunal elements are far less abundant. Few corals are found at a distance of ten miles or more to the east or west of the bank.
- The biogenetic bank environment probably offered the maximum environmental stimulus for coral growth in the area during the time of deposition.
Advisor: J. A. Fagerstrom.