AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Sequence Stratigraphic Analysis of Middle Devonian Fluvial Deposits and Correlation with the Marine in the Appalachian Basin, New York, USA
(1) Geology, Baylor University, Waco Texas, TX.
(2) Geology and Geophysics, University of Alaska Fairbanks, Fairbanks, AK.
(3) Kansas Geological Survey, The University of Kansas, Lawrence, KS.
Middle Devonian terrestrial strata deposited in the Appalachian Basin record dynamic landscapes characterized by extreme rainfall seasonality and tectonically driven changes in sedimentation. The clastic wedge, derived from the Acadian orogen during the Devonian, was deposited as the island arc Avalon accreted onto the Laurentian continent. Stacking pattern analysis of fluvial aggradational cycles (FACs) in the Catskill Mountains State Park reveals a three-tier hierarchy of stratal cyclicity. The first frequency, characterized by the longest wavelength and highest amplitude, correlates with trends of estimated water depths of coeval marine strata. These corresponding trends may be the result of Acadian tectophases as Avalon progressively impinged on Laurentia. Thinner than average FAC successions and increased paleosol development, as highlighted by plots of cumulative deviation from mean FAC thickness and paleosol maturity, coincide with the accommodation minima in the marine realm and deposition of the Tully Limestone during this period of tectonic quiescence, low detrital influx and increased soil development. Acadian tectonism influences on sedimentation creates the opportunity for correlation of terrestrial and marine strata throughout the Appalachian Basin. To evaluate other potential influences of fluvial stacking patterns we investigated paleo-climate trends using the newly defined paleo-precipitation proxy CALMAG, a geochemical ratio from bulk soil material in fine-grained paleosols. Climate trends can effect fluvial depositional style through both changes to flood magnitude as well as fluvial response to flood events. The majority of estimated mean annual precipitation values are ~1600 mm/year from selected paleosols throughout the section. Six paleosols, however, have lower estimates (ranging from ~850—1350 mm/year), as a result of elevated weight % CaO, which occurs at or near sequence boundaries or in poorly drained paleosols in transgressive systems tract equivalents . The trends in reduced CALMAG ratios follow that of the first hierarchal frequency and may reflect changes in base-level rather than climate. Continued work towards a high resolution stratigraphic correlation of Appalachian Basin terrestrial and marine strata along with the development of respective ecological and chemical trends will aide in our understanding of connections between marine and terrestrial depositional and ecological systems.