| dc.description.abstract | ABSTRACT Paleosols in the Lower Permian (Asselian-Sakmarian) Council Grove Group from western Kansas, USA, contain numerous pedogenic features, including carbonate nodules (caliche), redoximorphic coloration, rhizoliths, and trace fossils, which can be used to reconstruct the paleoenvironmental and paleoclimatic conditions during the interval of soil formation. Due to the paleogeographic setting of the Hugoton Basin, 5th-order cycles recorded in distant Council Grove Group outcrops are condensed in the study area into cumulic paleosols that contain pedogenic features signifying both wet and dry climates. Wet/dry cycles are interpreted to be the product of eustatically driven climate change, as well as seasonal changes related to monsoonal weather variability. Statistical analyses of the distribution of pedogenic features indicate a change from drier to wetter conditions over the upper Council Grove Group interval. Detailed study of trace fossils revealed unique morphologies that warrant the erection of a new ichnospecies, proposed here as Naktodemasis krausi. These assemblages are the oldest known occurrence of the genus Naktodemasis. Trace fossils were interpreted as the burrows of soil dwelling insects or insect larvae that colonized semiarid coastal plain environments during periods of subaerial exposure, creating topography and reducing accommodation, thereby preventing the formation of discrete 5th-order lithologic cycles. In order to provide further evidence for the origin of trace fossils, neoichnological experiments were conducted to compare ancient burrows to those of modern fossorial insects. Experimental results showed that the burrows of modern coleopterans belonging to the masked chafer beetles (Cyclocephala sp.) are convincing analogs for Permian trace fossils, and provide some general constraints on moisture tolerances for potential Permian tracemakers. The presence of these traces in Permian sediments, therefore, indicate that soil moisture levels during sea-level lowstands were high enough to support sustained populations of similar organisms. This study also conclusively demonstrates that burrows of this type could be constructed in subaerial settings, and documents the unique burrowing mechanism of the masked chafer beetle. | |
