Upper Ordovician and Silurian Stratigraphy of the Virginia and West Virginia Valley and Ridge

Abstract

Two pronounced effects of the Taconic Orogeny were the creation of an eastern source area which influenced sedimentation through much of the Appalachian basin, and the early deformation of the eastern margin of the Appalachian basin. This field trip will investigate the stratigraphy of the Taconian (Upper Ordovician) and post-Taconian (Silurian) clastic strata in an attempt to illustrate the sedimentologic and structural effects of the Taconic Orogeny in the eastern portion of the Appalachian basin. The Taconian clastic sequence is an orogenic progradational sequence. The distal (western) facies of the clastic sequence were deposited between the carbonate shelf and the source area, in a deep basin which was created by tectonic downwarping of the eastern edge of the carbonate bank. During deposition of the Taconian clastics, there occurred a pronounced, probably glacio-eustatic lowering of sea level, which lasted until the beginning of the Silurian. The Silurian clastics are a series of post-orogenic quartz sandstones and mudrocks, the upper portion of which changes facies basinward to limestone. The sandstones comprise a number of tongues which are thickest near the basin margin, and thin to the west. The Silurian strata were deposited in relatively shallow water, implying that tectonic downwarping had ceased. The large-scale inter-tonguing of strata may have been caused by sea-level fluctuations.

Active features along a “passive” margin: The intriguing interplay between Silurian–Devonian stratigraphy, Alleghanian deformation, and Eocene magmatism of Highland and Bath Counties, Virginia

“…A second stratigraphic fi nding that has come from our mapping in this area is that we now recognize that the unnamed middle sandstone member of the McKenzie Formation (Travis, 1962;Patchen, 1974) extends ~25 km northward of the exposures along Muddy Run (Fig. 3), which is the previously identifi ed northern limit of that sandstone (Whitehurst, 1982;Diecchio, 1986;Diecchio and Dennison, 1996). It is a thick bed in the Bullpasture River Gorge (Stop 5), and it thins northward from there (Fig.…”

“…These are of interest because of several thermal springs emanating from these carbonates in the Warm Springs Figure 1. Generalized geology of the fi eld trip area showing stop locations and several major folds and faults (modifi ed from Diecchio, 1986). Inset map (upper left) shows the location of the fi eld trip area relative to Blacksburg.…”

“…In general, differential weathering in the southeastern Valley and Ridge province has resulted in northeast-trending mountain ridges that are underlain by resistant Silurian and Devonian sandstones, and valleys that are typically underlain by weak Devonian shales (e.g., Enomoto et al, 2012) or Ordovician carbonates (e.g., Diecchio, 1985Diecchio, , 1986. Smaller-scale, fault-related folds can add intriguing complexities to regional topographic patterns.…”

Hydrogeology, karst, and groundwater availability of Monroe County, West Virginia

“…At this locality, the beds are overturned and approximately 295 ft (90 m) thick. These units have been described in the study area in greater detail by Diecchio (1985).…”

Testing Tectonostratigraphic Hypotheses of the Blountian Phase of the Taconic Orogeny in the Southern Appalachians through an Integrated Geochronological and Sedimentological Study of Ordovician K-Bentonites and Quartz Arenites

“…In this scenario, tectonically driven uplift, i.e., folding and thrusting associated with deformation and shortening, was followed by a pulse (or pulses) of coarse molasse sediment moving into and then out across the nearly filled foredeep. [14,34]) with very coarse to conglomeratic Oswego Sandstone samples (from the Brocks Gap, Harshberger Gap, Shenandoah, and Duck Run sections of Diecchio [76]). The Oswego was deposited as part of the younger Queenston molasse during the main Taconian tectophase (inset, right), and it is predominantly a lithic arenite, whereas the Walker Mountain is primarily a quartz arenite to sublithic arenite.…”