Geosynclinal Compositions and the New Global Tectonics

Abstract

ABSTRACT The lithological composition of several geosynclinal sequences estimated from published measured sections in the Appalachian and Cordilleran belts shows that sedimentary rock type is not a diagnostic attribute of geosynclinal assemblages. However, though no sedimentary rock types are excluded from geosynclinal assemblages, some are generally rare (evaporite), others are particularly common in either the miogeosyncline (carbonate) or eugeosyncline (graywacke), and still others are common throughout (shale). The chemical composition of individual sequences, estimated using analyses of specific stratigraphic units and average compositions for major sedimentary and volcanic rock types reveals chemical contrasts between miogeosynclinal and eugeosynclinal assemblages, and between ancient geosynclinal assemblages and the sedimentary successions which have accumulated in the deep ocean basins and along the present-day continental margins. Miogeosynclinal and eugeosynclinal assemblages differ chemically because of the respective predominance of carbonate and volcanic rocks; both contain chemically similar, highly siliceous clastics. If miogeosynclines and eugeosynclines are the respective ancient analogues of present-day continental shelf and rise areas, their contrasting compositions may reflect long-term secular changes in the mode and locus of sedimentation as a result of organic evolution and changes in the relief, volume, and location of continental blocks, ocean basins, and plate margins during and since the Paleozoic.