Image: Conchostracans in nonmarine black shale (Cow Branch Formation, Upper Triassic; Route 220 roadcut north of the Dan River, Rockingham County, North Carolina, USA) 3

Description: Fossiliferous nonmarine black shale from the Triassic of North Carolina, USA. The Newark Supergroup is 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. Seen here is a nonmarine black shale sample. The original muddy sediments were deposited in a lake in the Dan River Basin (Danville Basin), a half graben rift valley. The shiny black areas on the shale (click on the photo once or twice to zoom in) are conchostracan valves. Conchostracans are basically a shrimp-in-a-clam-shell. The shell consists of two valves that mostly envelop the soft-bodied crustacean, somewhat like ostracods. Conchostracan valves are larger and have simple concentric growth lines. Classification: Animalia, Arthropoda, Crustacea, Conchostraca Stratigraphy: Cow Branch Formation, Newark Supergroup, Upper Triassic Locality: loose piece from the Dan River North Outcrop - roadcut on the eastern side of north-bound Route 220, just north of the bridge over the Dan River, east of the town of Madison, central Rockingham County, northern North Carolina, USA (36° 23’ 19.25” North latitude, 79° 56’ 27.48” West longitude) For more info., see: en.wikipedia.org/wiki/Newark_Supergroup and en.wikipedia.org/wiki/Clam_shrimp
Title: Conchostracans in nonmarine black shale (Cow Branch Formation, Upper Triassic; Route 220 roadcut north of the Dan River, Rockingham County, North Carolina, USA) 3
Credit: https://www.flickr.com/photos/47445767@N05/49985811286/
Author: James St. John
Usage Terms: Creative Commons Attribution 2.0
License: CC BY 2.0
License Link: https://creativecommons.org/licenses/by/2.0
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