Cow Branch Formation (Upper Triassic; Pit B of Solite Quarry, near Eden, North Carolina, USA) 43

            This outcrop is the wall of Solite Quarry's Pit B on the Virginia-North Carolina state line.  It's an aggregate quarry that has operated since the 1950s.  Good fossils occur at this site - the original finds were on the Virginia side of the border, while the best fossils are on the North Carolina side.  The aggregate plant's physical address is in Virginia.  The currently active pits are in North Carolina.

The rocks here are tilted, northwest-dipping sedimentary rocks of the Cow Branch Formation (Upper Triassic).  The unit is part of the Newark Supergroup, a thick, geographically-widespread stratigraphic unit in eastern America.  It is Late Triassic to Early Jurassic in age and represents sediments and some lava flows that filled up old rift valleys roughly paralleling the modern-day Eastern Seaboard of America.  The rift basins formed in the Triassic when the ancient Pangaea supercontinent attempted to break apart, but failed.  A successful breakup of Pangaea occurred during the Jurassic.  Most of the basin-filling rocks are terrestrial redbeds - hematite-rich siliciclastic sedimentary rocks, such as conglomerate, sandstone, siltstone, and shale, deposited in nonmarine environments.

Using Triassic rift basin terminology, this area is in the Danville Basin / Dan River Basin.  Cow Branch beds at the Solite Quarry are principally lacustrine in origin - Lake Danville occupied this area during the Triassic.  About 270 meters worth of mostly fine-grained siliciclastics are exposed here.  Reported lithologies include claystone, silty claystone, dolomitic claystone, carbonaceous siltstone, sandstone, and carbonaceous dolostone.

The succession has cyclicity ("Van Houten Cycles") - ten or more cycles are exposed in the wall of pit B.  Each cycle is a transgressive succession of lake sediments.  The cyclicity is interpreted as the result of Milankovitch-related climate forcing.  Changes in climate and sedimentation can be caused by slight changes in Earth's orbital parameters - e.g., eccentricity (how circular Earth's orbit is around the Sun), obliquity (the angle of Earth's axial tilt), and precession (the direction that Earth's axis points).

A lagerstätte occurs in these beds - a soft-bodied fossil deposit - a fossil occurrence with exceptional preservation.  The fossils are principally insects and vertebrates, particularly Tanytrachelos, an aquatic reptile (they're nicknamed "Tanees" in the field).  Tanytrachelos with fossil skin impressions are known from here.  The long-necked gliding reptile Mecistotrachelos aperos has also been found.  Other fossils at the site include conchostracans, a spider, fish, and plants.

Early interpretations concluded that the exceptionally preserved fossils were in a deep-water lacustrine facies.  More recent studies have shown it was likely a shallow-water, toxic lacustrine facies.

Thousands of fossil insects from the Solite Quarry have been collected by the Virginia Museum of Natural History.  Fifteen to twenty species from six insect orders are present in the lagerstätte horizon and the total insect diversity may be over twice this.  Reported insects include thrips, cockroaches, waterbugs, crane flies, etc.

Locality: southwestern wall of Pit B of the Solite Quarry, east-northeast of town of Eden, far-northern Rockingham County, northern North Carolina, USA (36° 32’ 22.87” North latitude, 79° 40’ 22.19” West longitude)
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Some info. synthesized from:

Liutkus et al. (2010) - Use of fine-scale stratigraphy and chemostratigraphy to evaluate conditions of deposition and preservation of a Triassic lagerstätte, south-central Virginia.  Journal of Paleolimnology 44: 645-666.

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Taken on: November 10, 2012

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Sets appears in: • Solite Quarry (Virginia-North Carolina border, USA) • North Carolina Rocks & Fossils more » • Newark Supergroup (Upper Triassic to Lower Jurassic; eastern USA) • Triassic Rocks & Fossils « less

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