The Appalachian Geology of John M. Dennison: Rocks, People, and a Few Good Restaurants along the Way

Dr. John M. Dennison spent his career studying the Appalachians; teaching and mentoring his students and professional colleagues; publishing papers; leading field trips; and presenting ideas at regional, national, and international conferences. This volume is a collection of papers contributed by former students and colleagues to honor his memory. Topics include stratigraphy and paleontology ranging in age from Ordovician to Mississippian in Kentucky, New York, Tennessee, Virginia, and West Virginia; Devonian airfall tephras throughout the eastern United States; a Devonian lonestone; a Middle Eocene bentonite in North Carolina and its relationship to a volcanic swarm in western Virginia; and a 3D model of a ductile duplex in northwestern Georgia. The stratigraphic and geologic diversity of the papers reflects Dennison's many interests and collaborative relationships.
Upper Ordovician Juniata Formation, Central Appalachian Basin, USA: A record of Milankovitch-forced eustatic oscillations originating from glaciations in polar Gondwana
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Published:August 12, 2020
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CiteCitation
Linda A. Hinnov, Richard J. Diecchio, 2020. "Upper Ordovician Juniata Formation, Central Appalachian Basin, USA: A record of Milankovitch-forced eustatic oscillations originating from glaciations in polar Gondwana", The Appalachian Geology of John M. Dennison: Rocks, People, and a Few Good Restaurants along the Way, Katharine Lee Avary, Kenneth O. Hasson, Richard J. Diecchio
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ABSTRACT
The Upper Ordovician Juniata Formation, Central Appalachian Basin, USA, is a thick succession of cyclically bedded arenites, wackes, and mudrocks. Sedimentary facies of the formation in West Virginia, Virginia, and Maryland indicate cyclic peritidal deposition along the northern shoreline of the basin. The subsurface Juniata Formation has been drilled throughout the basin, and long, continuous well logs are available for analysis of the cyclic deposition. A 2400-ft-long (731.52-m-long) gamma-ray (GR) log from the Preston 119 well, northern West Virginia, provides a proxy of terrigenous siliciclastic fluxes originating from the Taconic highlands, from the early Ashgillian to the Ordovician–Silurian transition. Strong cycling in the GR log shows evidence for Milankovitch-forced sea-level oscillations, hypothesized to have been produced by dynamic Late Ordovician glaciation in polar (southern) Gondwana. Juniata cycle frequencies are different from those of Quaternary Milankovitch cycles, with significantly higher obliquity and precession index frequencies, consistent with a 21.5 h Ordovician day and an Earth-Moon distance that was 95% of present day. These results support John Dennison’s long-held view that Milankovitch forcing of sedimentation took place in the early Paleozoic Appalachian Basin by action of remotely generated glacio-eustatic oscillations powered by glaciation on southern Gondwana, and that this sedimentary record has tracked “Earth’s movement through space.”
- Allegany County Maryland
- ancient ice ages
- Appalachian Basin
- climate forcing
- Cumberland Maryland
- cyclic processes
- deformation
- depositional environment
- glacial environment
- glacial geology
- glaciotectonics
- Gondwana
- Juniata Formation
- Katian
- lithofacies
- Maryland
- Milankovitch theory
- North America
- obliquity of the ecliptic
- orbital forcing
- Ordovician
- paleogeography
- Paleozoic
- sea-level changes
- unconformities
- United States
- Upper Ordovician
- Virginia
- well logs
- West Virginia