MUDCRACKS AND RIPPED-UP STROMATOLITES: SUNSHINE AND STORMY WEATHER IN THE SILURIAN TONOLOWAY LIMESTONE, WEST VIRGINIA

The paleogeography of West Virginia and surrounding states during the Late Silurian was described in the 1970's as a carbonate platform with an evaporite basin to the northwest; mountains to the east; and open ocean to the southwest. A detailed carbonate ramp model was proposed in the 1990's for eastern West Virginia. The Late Silurian Tonoloway Limestone is typically a thinly-bedded gray carbonate with peri- to subtidal depositional features. During reconnaissance mapping for various STATEMAP projects, we encountered a Tonoloway outcrop along Dumpling Run Road, west of Brake in Hardy County, WV, where there are small (10 to 25 cm tall) columnar stromatolites. Additionally, these stromatolites have been ripped loose from their substrate and chaotically redeposited. The presence of columnar stromatolites requires tidal influence; the fact that they were ripped up and reworked requires the presence of strong storm activity in this region during the Silurian. Both suggest a greater depth of water than is implied by the earlier paleogeographic model. At a second outcrop near Blue Grass in Highland County, VA, approximately 75 km to the southwest, the Tonoloway contains polygonal mud cracks which are subaerial in origin. The Blue Grass locality is 75 km closer to the originally proposed, open Silurian ocean than Dumpling Run but suggests shallower water. Features observed at these two Tonoloway localities confirm the need for the more complex facies distribution of the carbonate ramp model.