Abstract

FLUVIAL TO MARINE TRANSITION WITHIN THE LOWER CAMBRIAN HARDYSTON FORMATION, EASTERN PENNSYLVANIA

HIGGINS, D. J., Department of Physical Sciences, Kutztown University, Kutztown, PA 19530, DILLIARD, K. A., Department of Geology, Northern Arizona University, Box, 4099, Flagstaff, AZ 86011-4099, SIMPSON, E. L., Department of Physical Sciences, Kutztown University, Kutztown, PA 19530, AND ROWELL, B. F., , Department of Physical Sciences, Kutztown University, Kutztown, PA 19530,

Identification of fluvial to marine transitions in Precambrian and Cambrian strata, is often problematic, due to lack of diagnostic, physical and biogenic sedimentary structures. Siliciclastic sediments of the Early Cambrian Hardyston Formation can be assigned to four facies associations (FA A-D), in which a fluvial to marine transition is preserved. The lowermost subdivision, FA A, consists typically of very thick-bedded, structureless arenites are replaced by trough and tabular-planar cross-bedded arenites. This facies association is best interpreted as fluvial-bar deposits. FA B consists of Skolithos burrowed, thin-bedded, normally graded arenites. FA B is analogous to nearshore deposits. Graded beds reflect storm reworking of the shoreface. Skolithos traces record opportunistic behavior of the organism. The fluvial-marine transition lies between facies association A and B and can be identified by a vertical change from 1) feldspathic (FA A) to quartz arenties (FA B), 2) bar deposits to shoreface storm deposits, 3) nonbioturbated to bioturbated strata. Sedimentary structures in facies association C and D are analogous to marine deposits. FA C is composed of trough cross-bedded conglomerates and arenites with interpreted shore-parallel and off-shore-directed currents. FA C represents a marine setting grading from facies association B to D that include Skolithos, characteristic of FA B, and tidal- and wave-generated sedimentary structures, characteristic of FA D. FA D consists of offshore-directed, tabular-planar and trough cross-bedded quartz arenite separated by siltstone-mudstone beds. Some tabular-planar cross-beds contain obliquely oriented ripples on pause planes draped with siltstone. Sinuous-crested megaripples with superimposed current ripples capp some cross-beds. Tidal currents were responsible for the formation of FA D. The variation in depositional centers, and construction/destruction of sandwave fields. Examination of the Hardyston Formation permits the precise demarcation of the fluvial-marine transition that is not often possible in similar strata.

Kutztown University of Pennsylvania

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D.J. Moore
Oct. 2002
Last modified Sept. 2004
moore@kutztown.edu