Organization and Distribution of Middle Devonian Biofacies Within a Sequence Stratigraphic Framework, Huntingdon County, Pennsylvania, USA

Open Access
Author:
Deptola, Travis Joseph
Graduate Program:
Geosciences
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
August 27, 2012
Committee Members:
  • MARK E PATZKOWSKY, Thesis Advisor
Keywords:
  • biofacies
  • gradients
  • niche
  • Devonian
  • Hamilton
  • Mahantango
  • spatial variability
Abstract:
Understanding the controls on the distribution of fossils in time and space is a fundamental aspect of paleontological research, because it underlies studies of ecosystem change through time, patterns of origination and extinction, and the geographic distribution of diversity. In the marine fossil record many studies have investigated onshore-offshore gradients and how they change through time, whereas little is known about how these ecological gradients vary spatially within and between depositional basins. For example, the temporal stability of biofacies gradients in the Middle Devonian Hamilton Group of New York state has been studied extensively using both qualitative and quantitative methodologies, yet no studies have been conducted in other regions of the Appalachian Basin to assess the spatial variability of these gradients. Field collection from an extensive outcrop of Mahantango Formation (Hamilton Group) in Huntingdon, Pennsylvania was conducted to characterize ecological gradients and to identify biofacies. Cluster analysis and detrended correspondence analysis reveal seven biofacies in the Hamilton Group of Central Pennsylvania that are distributed primarily by factors associated with water depth. Four biofacies identified in Pennsylvania (Tropidoleptus, Tropidoleptus-Devonochonetes, Devonochonetes, Ambocoelia) are qualitatively similar to biofacies identified in New York. Three novel biofacies have been identified in Pennsylvania (Pustulatia-Longispina, Rhipidomella, Rhipidomella-Devonochonetes), suggesting that additional undiscovered biofacies may exist in this basin. Quantitative comparison between Pennsylvania and New York study sites reveal that biofacies distribution throughout the Appalachian basin is governed by environmental differences associated with distance from the delta front, such as turbidity, sediment flux, or nutrient supply. For taxa shared between Pennsylvania and New York preferred environment (PE) is strongly correlated between study sites, while environmental tolerance and peak abundance are only weakly correlated.