Sequence stratigraphy and depositional framework of the Upper Middle Devonian Mahantango Formation in Pennsylvania and New York.
Item
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Title
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Sequence stratigraphy and depositional framework of the Upper Middle Devonian Mahantango Formation in Pennsylvania and New York.
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Identifier
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AAI9325150
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identifier
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9325150
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Creator
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Slattery, William.
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Contributor
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Adviser: Anthony Prave
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Date
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1993
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Language
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English
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Publisher
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City University of New York.
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Subject
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Geology
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Abstract
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The cyclic rocks of the Middle Devonian Mahantango Formation display rapid lateral and vertical facies changes between sandstone-dominated sections in south-central Pennsylvania and mudstone-dominated sections in north-eastern Pennsylvania and adjacent New York. This results in a confusing array of lithostratigraphic members. The sedimentology, sedimentary structures, and paleontology of the Mahantango Formation are interpreted as a succession of coarsening-upward cycles documenting repetitive shoaling episodes along a storm to tide dominated shallow shelf. Shoaling cycles are commonly capped by "lags", interpreted to be transgressively reworked deposits formed during sea-level rise. These coarsening-upward, shoaling-upward cycles are parasequences in sequence stratigraphy terminology. Parasequence sets are progradational in both mudstone-dominated and sandstone-dominated sections up to a regionally traceable "lag" deposit, and retrogradational above this datum. In the sequence stratigraphic model, this defines a Highstand system tract and a Transgressive system tract separated by a probable Type 2 sequence boundary. This exact Sequence stratigraphic succession has been independently documented in similar age strata along the north-west rim of the basin. Eustatic sea-level fall is suggested as the mechanism that produced the Type 2 boundary. Tectonic loading of the lithosphere is thought to have created the accomodation space and thus is the factor that controlled the cyclicity of the Mahantango Formation. Sedimentation rates had little effect on the overall cyclicity, other than producing more complex facies assemblages. The pattern of unconformities is consistent with the motion of a peripheral bulge, and the rheology of the lithosphere is inferred to have been elastic during this fraction of Appalachian basin history.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
