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HERO ID
6055436
Reference Type
Journal Article
Title
Organic matter accumulation, redox, and diagenetic history of the Marcellus Formation, southwestern Pennsylvania, Appalachian basin
Author(s)
Lash, GG; Blood, DR
Year
2014
Is Peer Reviewed?
1
Journal
Marine and Petroleum Geology
ISSN:
0264-8172
Publisher
Elsevier
Volume
57
Issue
Elsevier
Page Numbers
244-263
DOI
10.1016/j.marpetgeo.2014.06.001
Web of Science Id
WOS:000342530100016
URL
https://linkinghub.elsevier.com/retrieve/pii/S0264817214002086
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Abstract
Variations in the concentration of redox sensitive elements combined with pyrite framboid size data documented from a Marcellus Formation (Middle Devonian) core recovered from southwestern Pennsylvania elucidate the redox, organic matter accumulation, and diagenetic history of these deposits in this region of the basin. Uranium and Mo enrichment and Fe/Al display sharp increases coincident with diminishing Th/U upward through the initial 3rd order trangressive systems tract (lower Union Springs Member). These data as well as abundant small (<6 μm) pyrite framboids record establishment of strongly reducing benthic conditions, perhaps related to the expansion of an oxygen minimum zone induced by increased surface productivity. Strongly anoxic, even euxinic, conditions were interrupted by episodes of dysoxia, perhaps seasonal or longer term. Overlying regressive systems tract (RST) deposits record modestly improved redox conditions, likely a reflection of a receding oxygen minimum zone as base level dropped. A subsequent 3rd order base level rise and renewed expansion of the oxygen minimum zone triggered by increased surface productivity resulted in the accumulation of the organic-rich lower Oatka Creek Member. Still, the mix of abundant small and subordinate large (>10 μm) framboids preserves the record of oxygen deficient to sulfidic bottom conditions frequently interrupted by episodes of (dys)oxia. Improving redox conditions through the overlying RST were accompanied by a two-fold increase in Al and consequent dilution of the organic matter flux and authigenic trace metal uptake at the sediment–water interface. The upper half of the Oatka Creek comprises a depositional sequence not obvious from core inspection or gamma-ray signature but revealed by Mo enrichment and Al concentration profiles. Diagenetic modification of the Marcellus includes several horizons of authigenic calcium carbonate concretions and marked Ba enrichment. Both features reflect the effects of non-steady state microbial diagenesis within a methane-rich sedimentary column.
Keywords
Marcellus Formation; Trace elements; Middle Devonian; Appalachian basin; Framboids; Redox
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