Skip to Main Content
Skip Nav Destination

Upper Devonian marginal-marine deposits exposed at Ashcraft Quarry, northern-most Pennsylvania, are unusual in that they contain limestone in addition to the sandstone and shale which is prevalent in the Catskill clastic wedge. A 3 m. thick lower unit is a lateral-accretion deposit, composed mainly of planar and cross-stratified sandstones with subordinate wavy-flaser bedding. Erosion surfaces beneath sandstones are overlain by intraformational breccias containing transported crinoid, brachiopod, bivalve and plant remains. Paleocurrents are unidirectional westward, but current ripples rarely indicate bidirectional paleoflow.

The 3.5–5.5 m. limestone unit, comprising skeletal grainstone interbedded with calcareous sandstone, fines up or coarsens up from an extensive erosional base, and shows lateral-accretion bedding. The lime-grainstone contains abraded fragments of crinoids, brachiopods, bivalves, gastropods, and fish bones; also ankerite concretions, shale chips and plant remains. The whole unit is mainly large-scale cross-stratified, with bidirectional paleocurrents; and its top surface is marked by sandwaves, interfering wave and current ripples, and abundant burrows.

The upper unit comprises interbedded sandstones, siltstones and shales. Sheet-like and channel-filling sandstones have basal skeletal lags, large- and small-scale cross-stratification, planar stratification, and hummocky cross-stratification. Finer-grained strata have wavy-lenticular bedding (with wave and current ripple marks), concretions, and abundant burrows. Throughout the exposure fauna) diversity is low relative to coeval marine-shelf facies, and trace fossils belong mainly to the Skolithos ichnofacies.

The depositional environment of the lower unit, the limestone unit, and immediately adjacent beds, is laterally migrating sand bars adjacent to curved tidal channels with strong tidal-current asymmetry, probably in an estuary with marginal intertidal flats. Overlying deposits were introduced by periodic unidirectional currents and reworked by waves, possibly in a brackish coastal bay.

You do not currently have access to this chapter.

Figures & Tables



Close Modal

or Create an Account

Close Modal
Close Modal