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Detailed facies analysis of Holocene marsh deposits in coastal Delaware reveals a variety of environments of varying organic composition. An understanding of the depositional environments and early diagenetic histories of these sediments is necessary to evaluate their potential as source rocks.

Distributions of marsh facies are related to sea-level changes, compaction, shoreline configuration, drainage, sediment supply, and other factors. The overall factor controlling marsh deposition in coastal Delaware is relative sea-level rise. This produces a transgressive sequence of fresh- to brackish- to salt-marsh deposits. Three typical stratigraphic sequences are developed: broad marsh-continuous barrier sequence, broad marsh-discontinuous barrier sequence, and tidal-river marsh sequence. The first two sequences contain predominantly high- and low-marsh sediments. The tidal-river sequence contains thick sections of brackish-marsh sediments. Freshwater and salt-marsh sediments may contribute significant and relatively equal amounts to that sequence.

Degradation of plant fragments can be related to surface conditions in depositional environments as well as to changes that occur with depth. Some marsh sediments are better potential source rocks than others. Carbon values are largest in detrital organic facies, large in brackish-marsh facies, variable in high-marsh facies, and small in low-marsh facies. Noncarbonate carbon values range from 2.33 to 10.9. Premaceral compositions show small amounts of preresinites, presclerotinites, and fusinites, and large amounts of premicrinites. The largest previtrinitic, preresinitic, premicrinitic, and presclerotinitic compositions occur in brackish-marsh facies. Kerogen typing suggests these sediments might produce hydrocarbons with both humic and lipid compositions.

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