GSA Day 2

Today may have been my busiest day for attending talks, and I went through almost the entire morning without any breaks; things did ease up a bit in the afternoon.

Krishna Sinha, William Thomas, and Robert Hatcher Jr. spoke about the Ordovician/Silurian igneous rocks associated with the Taconic collision through the Appalachian Mountains.  This suite of rocks includes the Leatherwood Granite (light-colored rocks below) and the Rich Acres Gabbro (dark rocks below), which are found in the Martinsville area:

Sinha et al. suggest that this variety of igneous rocks represent different stages in a single collision event between Laurentia (proto-North America) and a volcanic island arc (comparable to modern Japan).

Ilya Buynevich showed examples of how vertebrate trackways deform sand layers. Large animals can deform sediments to a significant depth (like these mammoth tracks at Hot Springs Mammoth Site):

Specifically, he was looking at detecting the track-deformed layers of magnetite below the surface by magnetic variations, with some success.

Donald Goldstein, Michael McKinney, and Anthony Martin showed examples of traces formed when the modern predatory gastropod Agaronia propatula attacked prey animals (the gastropod Olivella and the pelecypod Donax). The talk included fabulous videos of Olivella scattering as an Agaronia chased them across the sand, and a vicious struggle as an Agaronia grabbed a Donax four times its size and pulled the Donax under the sand. There were distinctly different traces formed during each stage of the chase.

Michael Szajna and Jack Boyland reported trace fossils from the Triassic Passaic Formation in New Jersey, which like Solite is part of the Newark Supergroup. One of the tracks they interpret as a possibly from a tadpole shrimp similar to Triops. Distantly related but much smaller conchostracans (clam shrimp), are fantastically abundant at the Solite Quarry (each liight-colored disk is a conchostracan shell):

David Schwimmer and Samantha Harrell described bite marks and coprolites from the giant Cretaceous crocodylian Deinosuchus. These included healed bites on turtle bones (showing active predation), as well as apparent gnawing on dinosaur bones. They also showed possible Deinosuchus coprolites, that had apparently rolled around on the bottom and picked up various bits of detritus, and that were apparently partially eaten by coprophagous (poo-eating) fish.

Jennifer Lane presented information about the teeth and jaw musculature of the hybodont shark Tribodus, based on a remarkably well-preserved specimen from the Cretaceous of Brazil. Tribodushad a pavement dentition for crushing hard prey. It apparently had jaw modifications to allow suction feeding that are similar to what is seen in modern bat rays, but evolved convergently.

Richard Benson and Dave Powars et al. gave back-to-back talks on closely related topics. Benson spoke about Triassic rift basins (again, like Solite) buried under the Virginia and Maryland Coastal Plain sediments, while Powars et al. talked about buried basement rock faults under the Coastal Plain, and how they affect the younger Cenozoic sediments. Besides the fact that it involves Triassic rift basin deposits, why does this interest me? Because Carmel Church sits right on the edge of one of these buried basins, and may have been affected by it (geologic map modified from Google Earth/USGS):

There was also a whale talk today. Ervan Garrison, Scott Noakes, and Greg McFall reported an Atlantic gray whale (Eschrichtius robustus) that was excavated from the bottom of the Atlantic, 30 kilometers off the coast of Georgia in 70 feet of water (example at the top of the page from the USNM). Carbon 14 dating indicated that the skeleton was about 35,000 years old. Gray whales still live in the Pacific, but they were hunted to extirpation (local extinction) in the Atlantic by around 1700.

Stephen Godfrey of the Calvert Marine Museum was an author on two different posters that involved coprolites. One of these (Godfrey, Pietsch, and Carnevale) described a partial skull from a star gazer (a type of fish) that was filled with fecal pellets of some other organism. The second (Godfrey and Smith) showed large coprolites (likely from crocodylians) that had been bitten by tiger sharks. Godfrey and Smith make a pretty good case that the bites occurred while the coprolites were still inside the crocodiles. We have some somewhat similar specimens at VMNH like the one below:

More to come tomorrow.

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This entry was posted in Carmel Church Geology, Carmel Church Quarry, Chesapeake Group, Conferences, General Geology, Newark Supergroup, Solite Quarry and tagged , . Bookmark the permalink.

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