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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 36 (1986), Pages 409-418

Characteristics of Organic-Rich Deposits of Coastal Hancock County, Mississippi

Gregory N. Bonn (1), Franz Froelicher (2)

ABSTRACT

The brackish marshes of coastal south Hancock County, Mississippi, consist largely of organic sediments that range in ash content from 27 to 92 percent (dry basis) and average around 55 percent. Results from 11 piston cores and 382 Macaulay cores taken along five traverses, coupled with proximate analyses, have established the most organic-rich sites in the marginal deltaic study area. These sites, which consist of very peaty sediment up to 1.5 meters thick, occur as channel-fill deposits near the Pleistocene mainland and blanket deposits between the levees of some of the larger tidal creeks meandering through the central portion of the study area.

Factors influencing the development of the organic-rich deposits are: 1) presence of channel-like depressions in the underlying topography, which initially were favorable accumulation sites; 2) location distal to estuarine-lagoonal and deltaic environments, which are sources for silts and clays deposited within the organic material; 3) protection by nearby or adjacent higher topography during periodic inundation; 4) in some cases, ability of marsh vegetation to acerete upward while keeping pace with sea level in response to locally subsiding older beach deposits; and 5) effectiveness of plant baffling relative to the previously mentioned factors.

Despite the high organic content of these deposits, good quality coals would not be expected to form upon coalification due to the high silt and clay content and absence of thick accummulations. Coals resulting from the channel-fill deposits would tend to occur as thin stringers less than 1 meter thick, while blanket deposits would produce even thinner coals interbedded with carbonaceous shales.


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