File:Redbeds over black lacustrine shales (Newark Supergroup, Upper Triassic; Wadesboro Triangle Brick Company Quarry, North Carolina, USA).jpg

Redbeds & black lacustrine shales in the Triassic of North Carolina, USA. (stitched photos)

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 an active quarry that targets Newark Supergroup rocks for use in an adjacent brick factory. The sedimentary rocks are in the Wadesboro Sub-Basin of the Deep River Basin, which is the southern-most exposed Triassic rift basin in all of eastern America. The sub-basins do continue in the subsurface, heading south-southwest toward the Gulf of Mexico coast. All of the rift basins are half-grabens, with basin-fill facies becoming thicker and coarser-grained near the footwall. There are kilometers' worth of stratigraphic section in this area.

The stratigraphy used in the Wadesboro Sub-Basin was started in the 1920s: - Sanford Formation - upper redbeds unit - Cumnock Formation - swamp and lake deposits - Pekin Formation (~300 meters thick) - lower redbeds unit

This brick quarry has produced decent vertebrate fossils, including phytosaur remains. Vertebrate fossils are more common in the dark-colored, reduced rocks.

The upper part of the section at this quarry consists of reddish siltstones and sandstones - fluvial overbank and channel deposits. The base of the section is finer-grained, with black, organic-rich, lacustrine shales of the Cumnock Formation (or Cumnock equivalent).

Jurassic diabase dikes have intruded the section in places, and veins of quartz and calcite are nearby. All the rocks are quarried, delivered to the factory, and crushed into powder for making bricks. The combination of sedimentary rocks and igneous rocks seems to work well at the brick plant - they call this material "magic dirt with fossils". They don't need to use a special mix in order to produce high-quality bricks.

While visiting the site in November 2012, I observed mottled red and green micaceous mudshales, ripple marks, burrows, apparent mudcracks, blistered or puckered clayshale surfaces, and thin calcite veins that protrude from the soft shales upon weathering. Scoyenia burrows are common in places here - they are inferred arthropod burrows, possibly made by beetles or crayfish. Coarse-grained sandstones at the site have some mudclasts and some granules - they are inferred crevasse splay deposits. Coprolites were found in the lacustrine facies.

The quarry goes about 125 to 150 feet down from the surrounding land surface. The original quarry permit allowed them to go down 25 feet.

Stratigraphy: Newark Supergroup, Upper Triassic

Locality: Wadesboro Triangle Brick Quarry - active quarry adjacent to brick-making plant on the eastern side of Rt. 52, north of the town of Wadesboro, north-central Anson County, southern North Carolina, USA (35° 00’ 45.90” North latitude, 80° 05’ 13.01” West longitude)

For more info., see: