DISPERSED ORGANIC MATTER (PALYNOFACIES) IN COASTAL ENVIRONMENTS: AN EXAMPLE FROM THE MOBILE-TENSAW RIVER DELTA AND BAY, ALABAMA

Dispersed organic matter can be a significant component in sedimentary systems, particularly where terrestrial-derived phytoclasts mix with marine-derived organic matter. These dispersed organic clasts have been used by the petroleum industry to identify source and reservoir rocks in the deep subsurface, and recently have been used in ground water applications to identify hydrological conduits in the shallow subsurface. There is significant diversity in the types of clasts that have their origin in terrestrial and marine settings. To facilitate use of these, a group of palynologists met during the 1990s to develop a standard classification system now known as the Amsterdam Classification Scheme. There are four major categories to this system - Structured OM, Palynological OM, Unstructured OM, and Indeterminate OM. Using the palynofacies character of organic debris recovered from depositional regimes, it is possible to delimit specific depositional environments. An example of how palynofacies can be utilized is presented from a study of Holocene sediments recovered from the Mobile-Tensaw River Delta and Bay in the southeastern U.S. The Amsterdam Classification scheme was used to determine proportions of organic matter types from specific depositional environments and whether those assemblages provide a unique signature for any particular depositional environment. The palynofacies analysis of bay sediments recovered from the Mobile-Tensaw River System yielded a significantly high proportion of Structured other plant parts, Unstructured Heterogeneous-granular and Heterogeneous-aggregate debris. These results indicate that a unique dispersed organic matter signature exists for sediment facies within Holocene estuarine bays.