Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Shale and Mudstone Facies in the Middle to Upper Devonian Geneseo Shale to Penn Yan Shale Succession of New York: Implications for Accommodation During a Eustatic Sea Level Rise
(1) Geological Sciences, Indiana University, Bloomington, IN.
Facies analysis of the Middle to Upper Devonian Geneseo Shale to Penn Yan Shale Succession has yielded differentiation of decimeter-thick packages of shale in a seemingly monotonous succession. The Middle to Late Devonian shale succession of New York was deposited as part of the westward prograding Catskill Delta complex. Acadian uplift supplied sediments from the east to be delivered for delta growth, and coincides with a general rise of eustatic sea level. Depositional parameters and lithofacies analysis were inferred using a combination of optical petrography, scanning electron microscopy, and core description. The Geneseo Shale is a 34 m succession of black and dark gray shales. The lower Geneseo is a black shale with relict lamination and indications of surficial sediment mixing by benthos. Upsection, the Geneseo exhibits multiple black to gray shale cycles (10 to 25 cm thick) and grades into dark gray shales with scours, wave and current ripples, and macroscopically visible bioturbation. The Geneseo Shale consists of 5 facies types that by their vertical arrangement indicate simultaneous rise of sea level and sediment input, and generation of accommodation that exceeded sediment flux. Above the Geneseo follows the Lodi Limestone, a thin concretionary carbonate/calcareous siltstone unit that marks an interval of minimal clastic input. The Upper Devonian Penn Yan Shale is a 30 m succession of dark gray variably bioturbated silty shale. The lower portion of the Penn Yan is a dark gray silty shale with wave and current ripples. Silt content and current produced features increase upsection, suggestive of a general shallowing trend. The Penn Yan Shale consists of 4 distinct facies that by their vertical arrangement indicate further sea level rise, but in contrast to the Geneseo Shale, sediment flux now exceeded generation of accommodation. In the context of global eustasy in the Devonian, it appears the Geneseo Shale represents a forced transgression (growing sediment input from the east) that was overpowered by sea level rise (accommodation growth exceeds sediment flux, shoreline migrates eastward). The deposition of the Lodi Limestone marks the maximum landward (eastward) position of the shoreline. With the onset of Penn Yan deposition the balance between sediment input and newly generated accommodation is reversed and the shoreline migrated westward.