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Dr. Benjamin Dattilo
Department of Geosciences
Indiana University – Purdue University Fort Wayne
Despite the critical role of this dwindling resource in modern agriculture, the origin of sedimentary phosphate (the process of “phosphogenesis”) is not well understood. Based on the idea that oceanic chemistry is the primary driver of phosphogenesis, widespread phosphate deposits have been used as evidence of periods of unusual marine chemistry or circulation patterns. This study will test an alternative hypothesis, that slow sedimentation rates coupled with episodic high-energy events under otherwise normal marine conditions led to phosphogenesis in the Ordovician (450 million years old) of the Cincinnati region. These Cincinnatian limestones contain different amounts of phosphate. If the hypothesis is correct, then the amount of phosphate in the limestones should correlate to the amount of reworking that the limestone had experienced before final burial.
By microscopic study of the rocks in thin sections (thin slices of rock glued to microscope slides), the amount of phosphate can be quantified and the proxies for “sediment maturity” can be ranked or quantified. These proxies include: 1) condition of fossil seashells (breakage, abrasion, borings), 2) size distributions of shell particles, 3) the species of shell fossils present (indicating both ecology and preservation), and 4) relative abundance of shells, mud, and crystal-filled spaces (often used to classify limestones).
Sixty thin sections from a locality in Cincinnati (an old quarry face at Rice and Gage Streets, Cincinnati, Ohio) have been made and will be used for this preliminary study. For each slide, the amount of phosphate, shell breakage, abrasion, and boring will be estimated or ranked, species present will be measured, and relative abundance or mud, shells, and void space will be estimated. These measured of sediment maturity will be plotted against amount of phosphate to test for correlation.
Earth Sciences | Physical Sciences and Mathematics
Straw, Amanda, "Does Sedimentary Phosphate Reflect Sediment Maturity?" (2014). 2015 IPFW Student Research and Creative Endeavor Symposium. 66.