AEOLIAN SILICICLASTIC DEPOSITIONAL HYPOTHESIS FOR PRECAMBRIAN EARTH AND NOACHIAN MARS

Land areas were barren of plant material for over four billion years on Earth. During the Proterozoic, cyanobacteria, algae and fungi flourished in shallow water environments and bacterial coatings and mats certainly existed in some environments above sea level, but the continents were largely bare, rocky domains devoid of plants, humus and soil until plant colonization occurred during the Silurian and early Devonian. Plant colonization was one of the most important evolutionary/ecological triggers in Earth history, forever changing the face of continents and affecting modes of erosion and sedimentation around the globe. One of the great challenges in understanding sedimentary processes during the Precambrian is accounting for thick accumulations of widespread, planar-laminated to thinly-bedded siliciclastic units that can be traced laterally for great distances across a depositional basin. Such units exist in the Mesoproterozoic Belt Supergroup of northwest Montana and Idaho. Some beds in the Belt Supergroup (Revett Formation) have been interpreted as “sheet-flood” deposits based on bed forms coupled with flow regime models (Winston, 2016). However, not all units fit this model well, particularly those that are tabular over long distances and display even planar thin-bedding throughout. We propose that large dust/sand storms originating on Laurentia periodically (seasonally?) covered the entire Belt Basin, depositing siliciclastic sediment over shallow water environments via “shear-traction,” whereby strong storm winds sheared the water-atmosphere interface and deposited sediment in upper-regime plane-flow; sub-wave base settling would also occur in deeper water environments. Long-distance transport of suspended atmospheric sediment is well-know from modern studies of global circulation of desert-derived sediment. We believe that the role played by long-distance aeolian transport of sediment during the Precambrian is underestimated in the literature, and indeed may have been the dominant means of long-distance sediment transport until terrestrial plant colonization occurred. Seasonal dust storms on Mars during the Noachian probably had a similar role when vast areas of the northern hemisphere were covered by lakes and shallow oceans, similar to the Mesoproterozoic Belt Basin.