42-8 Terrestrial Carbonates in Middle Devonian Strata of Catskills, Southeastern New York State

Session: Paleozoic Events and Processes: Sedimentary Geology, Paleontology, and Geochemistry (Posters)

Presenting Author:

Authors:

Abstract:

Paleosols and lacustrine carbonates serve as valuable geological archives, preserving sedimentological and geochemical evidence of continental environments and climate, as they are highly sensitive to terrestrial climatic conditions. Limestone beds from five fluvial outcrops in the Plattekill and Manorkill Formations in the eastern Catskills of New York were examined. These outcrops are Middle Devonian in age, a period that coincided with the emergence of terrestrial ecosystems and the expansion of forest environments.

The limestone beds can be broadly divided into two types. The first type is interpreted to represent limestone deposited in a lacustrine environment. Three outcrops have 10-25 cm black micrite beds that contain fragments of fish fossils, possible ostracods, and other skeletal debris. Pyrite occurs locally as 1-2 mm crystals. Several beds contain internal surfaces characterized by downward tapering cracks that may be the result of root penetration or desiccation. In addition, several contain small, spherical calcite-filled voids that may have filled trapped gas bubbles associated with microbial mats. These beds are continuous across the outcrops in which they occur but vary in thickness. An outcrop along Catskill Creek extends over 500m, and the limestone bed changes locally into a lighter tan micrite reflecting variations in the lake environments. 

The second type of limestone bed shows post-depositional alteration (by pedogenesis or by fluvial reworking) but may have also originated in a lacustrine environment. An outcrop near East Windham contains 3 thin (<5 cm), discontinuous tan limestone beds that have a nodular weathering appearance and complex internal fabric, possibly the result of modification through soil-forming processes. The poorly exposed Rensselaerville outcrop contains a layer (up to 11cm thick) of rounded gray limestone clasts in a mudstone matrix likely originating from fluvial reworking of a lithified limestone bed. 

These limestone beds are associated with reddish and greenish mudstone containing abundant pedogenic features and cross-bedded sandstone representing fluvial channels. The black micrite beds are interpreted as having been deposited in small lakes on a fluvial floodplain. The altered limestone beds were modified by pedogenic processes and fluvial reworking. Although a minor component of the Middle Devonian strata of the Catskills, these beds are unique records that attest to an overall monsoonal climate that promoted the expansion of forest ecosystems.   

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.