Petrology, Transport, and Environment in Isochronous Upper Devonian Sandstone and Siltstone Units, New York

Abstract

ABSTRACT The Upper Devonian Sonyea Group and laterally equivalent sedimentary rocks in New York provide an ideal setting to study the effects of transport and environment on sediment composition and texture under miogeosynclinal conditions. Sandstones are lithic arenites to lithic wackes near the primary metamorphic source terrain and they grade into quartz wackes at greater distances into the basin. Near the source monocrystalline and polycrystalline quartz grains in subequal amounts (averaging 34 and 39% respectively) and fine-grain foliated metamorphic rock fragments (averaging 16%) are the chief detrital constitients. At distances of about 100 miles (160.9 km) from the source monocrystalline quartz grains and matrix (averaging 30 and 63% respectively) remained as the principal detrital com onents. Despite the limited modifying effects of diagenesis, destruction of unstable rock fragments in river channels appears to have been one of the most significant factors increasing sediment maturity near the source. Chemical weathering, dilution, and selective sorting of sand and mud during sediment transport were probably less important factors contributing to observed changes in composition and texture. Environmental processes such as winnowing and sorting were only moderately effective in altering sediment maturity in the low to moderate energy coastal environments that existed in this area in the late Devonian. Farther from the source, environmental factors were ineffective in modifying composition and texture because of the fine-grained nature (coarse silt) and mineralogical ma urity of the marine sediments which reached these deeper marine environments. A comparison of petrographic data from several Holocene and ancient basins suggests that the relative importance of any one factor (e.g. abrasion, selective sorting, etc.) is a function of the overall conditions that exist within the basin.