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Controls on spatial and temporal distribution of Precambrian eolianites |
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| Authors: | Kenneth A Eriksson Edward L Simpson |
| Institution: | a Department of Geological Sciences, Virginia Polytechnical Institute and State University, Blacksburg, VA 24061, USA b Department of Physical Sciences, Kutztown University, Kutztown, PA 19530, USA |
| Abstract: | Inversely graded stratification, generated by the migration of wind ripples, and adhesion structures permit unequivocal identification of Precambrian eolianites. These criteria, in combination with scale of cross-beds, angle of inclination of foresets, geometry of depositional units, and associated non-eolian facies, are used to discriminate between Precambrian dune/draa, dune-plinth, sand-sheet, and interdune deposits that formed in inland and coastal settings. Based on an analysis of published literature, fundamental conclusions can be drawn on the spatial and temporal distribution of Precambrian eolianites. The oldest reported eolianites are from the ca. 2.1 Ga Deweras Group in Zimbabwe and Hurwitz Group in Canada and numerous examples of eolianites are reported from the 1.8 Ga and younger rock record. Lack of Archean and early Paleoproterozoic eolianites and their widespread development after 1.8 Ga are examined with respect to: absence of vegetation, crustal growth and tectonic setting, relative sea-level fluctuations, unfavorable atmospheric and/or climatic change, and non-recognition. The lack of pre-2.2 Ga eolianites may be related to reworking by braided rivers combing across non-vegetated floodplains, reworking of coastal eolianites during transgression or their non-recognition in the Early Precambrian record. The temporal concentration of eolianites at 1.8 Ga may best be related to the early stages of breakup and the assembly phases of supercontinents. |
| Keywords: | esophagus achalasia heart failure compression transthoracic echocardiography |
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