DIFFERENTIATING MARINE AND TERRESTRIAL DEPOSITS IN TRANSITIONAL DEPOSITIONAL ENVIRONMENTS OF THE CATSKILL DELTA COMPLEX: A QUICK AND DIRTY GUIDE

While the recognition of purely marine vs. terrestrial environments of the Catskill Delta is straightforward, interpreting transitional zones of deposition between these two end-member environments is not always as clear. The term “red beds” is commonly used to describe terrestrial settings within these deposits, but color alone should not be used as the basis for interpreting depositional environments. Terrestrial settings low on a coastal plain are characterized by high water tables, resulting in dark gray/black wetland deposits and green floodplain mudrocks, where iron is reduced below a water table. Typical red beds form above water tables, not characteristic of lowermost coastal plain settings, and will have well defined soil structure, root traces, and horizonation. Where red beds closely overlie marine strata, dark/black and green mudrock rip-up clasts indicate partial erosion of lowermost terrestrial strata. Sometimes slight features distinguish terrestrial strata across the marine-terrestrial transition. Features such as desiccation cracks and red beds are useful at the gross scale. However, numerous and sometimes subtle features permit more precise delineation of terrestrial strata, including fine root traces, incipient soil development, rapidly buried in situ plant fossils, thin to lensing coals, storm surges abruptly covering soils, shelly taxa of freshwater versus normal marine versus restricted-salinity faunas (e.g., varying salinity-tolerant biomat-feeding gastropod taxa, and/or lingulid brachiopods), along with other long-established features (e.g., desiccation cracks, channel/floodplain facies) and larger scale features (e.g. including fluvial channel sandstones, and localized incised valley fills). Given the continuous fluctuation in relative and eustatic base level within these transitional settings, small scale cycles and beds with mixed marine and terrestrial indicators should be expected (e.g., shelly fossils with in situ root traces, or shelly fossils in the gaps of desiccation cracks). Although life first colonized the land to a large degree during the Devonian, features of terrestrial strata in transitional environments will be present throughout the sedimentary record, albeit they will vary as a function of the evolutionary development of life over time.