Publication Date
2006
Document Type
Thesis
Committee Members
Cindy Carney (Advisor)
Degree Name
Master of Science (MS)
Abstract
A distinct sequence of orange-brown, fossiliferous grainstones with interbedded blue mudstones exists in the upper portion of the Silurian-aged (Llandoverian) Brassfield Formation exposure at Oakes Quarry Park, Fairborn, Ohio. The unit is locally referred to as the cephalopod marker bed as it can be easily identified and is continuous throughout the quarry. The unit varies considerably in thickness (0.3m-0.9m) and contains a variety of sedimentary structures and fossils indicative of a warm, shallow marine environment subject to wave action. Dominant fossils within the unit include echinoderms, cephalopods, bryozoans, abraded mollusks, gastropods, brachiopods, and trilobites. Less-common fossil organisms within the unit include ostracodes, foraminifera, algae, and stromatoporoids. Mollusk chambers are commonly filled with micrite that contain traces of microbial life, including cement in the shape of bacterial filaments and micropeloids. Samples of the cephalopod marker bed were taken in a vertical sequence at two locations and from several locations along a north-south transect. Thin-sections were created from the samples; these were then point-counted using 300 counts to attain a quantitative analysis of the rock composition. Fossil abundance and diversity increases from the bottom to the top of the sequence and lateral variations within the top two, most-fossiliferous layers were also observed. Petrographic analysis of the cephalopod marker bed revealed that on average, bioclasts represent ~75% of the rock volume, cement is the next most-abundant constituent, and dolomite composes ~9% of the the rock volume. Dolomitization is preferential: it occurs most often in micrite within mollusk shells and might be driven by microbial processes; skeletal grain replacement occurs most easily within bryozoans.
Page Count
96
Department or Program
Department of Earth and Environmental Sciences
Year Degree Awarded
2006
Copyright
Copyright 2006, all rights reserved. This open access ETD is published by Wright State University and OhioLINK.
