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Late Devonian climatic change and resultant glacigenic facies of western Maryland

By
David K. Brezinski
David K. Brezinski
Maryland Geological Survey, 2300 St. Paul Street, Baltimore, Maryland 21218, USA
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C. Blaine Cecil
C. Blaine Cecil
U.S. Geological Survey (Emeritus), Reston, Virginia 21092, USA
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Published:
January 01, 2015

Abstract

The latest Devonian (Famennian) is characterized by an extensive Southern Hemisphere glaciation. Deposits resulting from this glaciation are present in several formations in the mid-Atlantic region, including the Hampshire, Catskill, Rockwell, and Spechty Kopf. The Hampshire (= Catskill) Formation exhibits a noticeable stratigraphic change upsection from the middle to the top. The middle part consists of thick intervals of red, channel-phase sandstones with thin overbank siltstone and mudstone. These mudstones contain poorly developed, calcareous paleosols. The top of the Hampshire Formation consists of greenish-gray sandstones containing abundant coaly plant fragments, coalified logs, and pyrite, interbedded with thick paleo-Vertisols. The upsection increase in preserved terrestrial organic matter suggests the onset of environmental conditions that became increasingly wet. The Late Devonian escalation in climate wetness culminated in the development of a stratigraphically and spatially restricted succession of diamictite-mudstone-sandstone interpreted as having formed in glacial and proglacial environments. These glacial environments are recorded in the lower Rockwell Formation of western Maryland and contemporaneously deposited intervals of the Spechty Kopf Formation of northeastern Pennsylvania. Sheared and massive diamictite facies are interpreted as lodgement and meltout deposits, respectively; whereas, bedded diamictites are interpreted as resedimented deposits. The diamictite facies is locally overlain by a mudstone facies with variable characteristics. Both the massive and deformed mudstone lithofacies are interpreted as a clast-poor, subaqueous glaciolacustrine deposit. Laminated mudstones are interpreted as forming in quiet glaciolacustrine environments. The pebbly sandstone facies is interpreted as proglacial braided outwash deposits that both preceded glacial advance and followed glacial retreat.

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GSA Field Guide

Tripping from the Fall Line: Field Excursions for the GSA Annual Meeting, Baltimore, 2015

David K. Brezinski
David K. Brezinski
Maryland Geological Survey 2300 St. Paul Street Baltimore, Maryland 21218, USA
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Jeffrey P. Halka
Jeffrey P. Halka
Maryland Geological Survey 2300 St. Paul Street Baltimore, Maryland 21218, USA
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Richard A. Ortt, Jr.
Richard A. Ortt, Jr.
Maryland Geological Survey 2300 St. Paul Street Baltimore, Maryland 21218, USA
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Geological Society of America
Volume
40
ISBN electronic:
9780813756400
Publication date:
January 01, 2015

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