82 The Integration of Marine and Non-Marine Subsurface Sediments to the Interpretation of the Stratigraphic Record of the Atlantic Coastal Plain (Posters)

Tuesday, 16 March 2010
1:30 PM - 5:35 PM
International ABCDF

THE IMPORTANCE OF BOTH MACROMORPHIC AND MICROMORPHIC EVIDENCE IN THE DETERMINATION OF A PALEOSOL IN A CORE SAMPLE

Paper number: 82-3
Program: Theme Sessions
Time: 1:30 PM – 5:35 PM

Authors

Abstract

Initial macromorphic interpretation of the core drilled in South Dover Maryland (Talbot County)by the USGS, revealed the possibility of a paleosol profile, between 28 to 40 ft in depth from the surface. This is bound top and bottom by marine sediments that have been dated biostratigraphically to the mid-Miocene. This section is described as alternating layers of greenish grey and weak/ pale red, silt to clay sized sediment. A second core drilled by the USGS just off of Egypt Rd south of Cambridge Maryland, initially was believed to also contain a possible paleosol. The sections in question were from 14 to 38 ft and from 47 to 62 feet in depth. These sections of core were also bound on top and bottom by marine sediments. The suspected paleosol description was alternating layers of red and greenish grey very fine sand to silt sized particles.

At first glance these two cores, by there descriptions and appearance seem to be pedogenicaly modified sediment, and perhaps similar CLORPT (CLimate, Organisms, Relief, and Time) conditions. The colors, the mottled sections, and the variations could be a result of pedogensis. If this is true then that has implications of the sediment’s paleoenvironment. However only through micromorphic analysis of both core samples was the determination made that the South Dover Bridge sample was a paleosol and the sample taken from Egypt Rd was not.

Through the analysis of petrographic thin sections, the South Dover Bridge core show signs of hydromorphy and signs of weak pedogenic development. This is evidence of a sub airily exposed, at least semi stable surface, that was at or close to the water table. These indicate that it is a paleosol. Whereas the Egypt Rd core petrographic thin sections showed no signs of any pedogenic alteration. This indicates that it is not a paleosol. Also the mineralogy of the parent material was shown to be different than that of South Dover Bridge. It was never sub airily exposed, different parent material, and has a very different history than the South Dover Bridge core sediments.