Document Type

Thesis

Abstract

This research aims to study the occurrence and characteristics of spherical carbonate nodules located in the Fossil Beach outcrop of the Eastover Formation at York River State Park near Williamsburg, Virginia. Carbonate nodules are a sedimentary mass formed by the precipitation of mineral cement within pore space of sedimentary grains in this case, carbonate cement between the sands of the Eastover. These nodules occur in a 50cm layer right above the beach surface as well as on the beach itself. Studying the structures of the nodules allowed me to investigate the origin of the nodules. To do this | studied the sediment in the outcrop, as well as the physical properties of the nodules, both macroscopic and microscopic. To examine these nodules, nodules were measured, made into slabs and thin sections, these thin sections where then examined and a point count was taken. The nodules occur in a 50 cm layer below the contact with the Yorktown Formation. The nodules can also be found weathered out on the beach surface. These nodules contain intact and crushed shells including Turitella, bivalves, and echinoderms. The long axis measured 3.1- 16.51cm and were mostly spherical. Point counting of five nodules showed that nodules averaged around 68% matrix, 26% grain, and 5% shell material. These ratios did not change within the nodules, showing that the nodules were not zoned. The lack of zonation, the uncrushed nature of the fossils in the nodules, and the large amount of carbonate material available in the outcrop suggest these nodules formed via the local-equilibrium model of growth, growth of a cement supported frame of grains, followed by radial growth.

Date Awarded

2014

Department

Geology

Advisor 1

Heather MacDonald

Advisor 2

Brent E. Owens

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