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Plant Taphonomy in Tidal Swamps

Anne Raymond

Tidal swamp (mangrove) peats differ from freshwater swamp peats primarily in the ratio of shoot debris to root debris. Tidal swamp peats from southern Florida have low shoot to root ratios (average 14:86); freshwater swamp peats from the Okefenokee Swamp have high shoot to root ratios (average 67:33). Within tidal swamp peats, the relative amount of root debris belonging to each genus reflects the abundance of that genus in the swamp. However, each mangrove genus contributes different aerial organs to peat. Rhizophora wood is rare, its leaves and bark common. Avicennia wood is common, its leaves and bark rare. In addition, trunks and branches are rare. Termites attack these organs while the trees are standing, and their tissue fragments before reaching the peat surface.

Tidal transport of aerial debris out of the swamp, and the abundance of detritovores in tidal swamps account for the low shoot to root ratios of tidal peats. Mangrove peats from flooded and rarely flooded areas have uniform low percentages of aerial debris due to detritovores, which break aerial organs into small particles that can be decomposed by bacteria or flushed by tides. Tidal swamps grow on both peat and mud substrates; however, taphonomic processes appear to be similar on both.

The taphonomy of tidal swamps has implications for both coal and hydrocarbon exploration. The leaves and twigs transported from the swamp are one source of liptinite macerals in coal, and a possible source of petroleum in marine sediments. Tidal swamps should have a low percentage of liptinite macerals relative to the marine sediments that surround them, and also relative to freshwater coals.

The earliest tidal swamps are Pennsylvanian in age. None are known from the Permian and Early Triassic. However, tidal swamps may have been present from the Late Triassic to the Holocene.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.