Date of Award

2019

Type

Thesis

Major

Earth and Space Science - Geology Track

Degree Type

Master of Science in Geology

Department

Earth & Space Science

First Advisor

Dr. Diana Oretga-Ariza

Second Advisor

Dr. Clinton I. Barineau

Third Advisor

Dr. David R. Schwimmer

Abstract

This field-based research develops a sequence stratigraphic framework and detailed facies analysis which is used as a basis for understanding depositional histories of low-latitude, shallow-water, Mississippian carbonate deposits (Fort Payne Chert and Tuscumbia Limestone) in northwestern Alabama. This in turn, is used to evaluate controls on deposition (e.g., sea level, tectonics, paleogeography, and paleoceanographic conditions). Additionally, possible sources of the silica (chert) found within these units (e.g., eolian dust, upwelling) are evaluated based upon thin section analysis. Four facies and one subfacies were identified: F1: echinoderm, bryozoan mudstone/wackestone facies and Fla: muddy echinoderm chert, F2: echinoderm, bryozoan packstone/grainstone facies, F3: echinoderm, spicule cherty mud facies, and F4: fine-grained quartz sandstone facies. Fland Fla are interpreted to be midramp deposits. F2 is interpreted to be shallow inner ramp deposits. F4 is interpreted to be a beach environment. Additionally, a spicule-rich mud facies (F3) with echinoderms (0-37%), sponge spicules (3-30%), silt grains (0- 25%), and solenoporoid algae (< 1%) between 0.25-4.75 meters in thickness was described. In outcrop, F3 exhibits mound-shaped geometry. Based on these observations, the F3 exposures of the Tuscumbia Limestone in northwest Alabama is interpreted to be a mud mound facies deposited in a deepest midramp setting, previously interpreted only in the subsurface. Based upon the regionwide distribution of these facies, three depositional sequences were interpreted (DS1-DS3). Since there is no evidence of subaerial exposure in the study area, sequence boundaries are interpreted as the regionwide deposition of shallow F2 deposits overlain by regionwide deeper F1/F1a deposits. Two such sequence boundaries were observed. The first sequence boundary (SB1) occurs between DS1 and DS2. The second sequence boundary (SB2) occurs between DS2 and DS3. Each depositional sequence contains F1 and Fla deposits at their base and F2 deposits at their tops. Basal DS1 and DS3 contain F3 deposits within F1 and Fla deposits. In addition, upper DS3 contains F4 deposits. Based on examples of Middle Mississippian carbonates across the southern United States, tectonic activity to the east of the study area, and global sea level curves, the major controls on the depositional sequences found in this study are global sea-level fluctuations and tectonic uplift and subsidence. Two sources of silica are proposed: wind-blown terrigenous silt grains from the new Appalachian highlands as a minor source based on the presence of silt grains (0-13% in F1a and 0-25% in F3) and upwelling of biogenic silica from the deeper basins of the epeiric sea covering the North American continent during the Mississippian as a major source based on dissolved sponge spicules (3-30% in F3 and 2-28% in Fla).

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