A Paleoproterozoic Aeolianite (the Nummana Member) from the Lower Wyloo Group, Pilbara Craton, Western Australia, and Its Implication

In the absence of vegetation, wind systems would have been very efficient in reworking terrestrial sediments. As a consequence, the Precambrian sedimentary succession should theoretically be replete with aeolian deposits; however, Precambrian aeolianites are rare. Aeolian reworking of Precambrian fluvial sediments has been described by a number of authors. Earlier researchers have reported aeolian reworking of fluvial quartz-rich sandstone unit of the Beasley River Quartzite Member of the Lower Wyloo Group (LWG). The Nummana Member is the topmost lithostratigraphic unit of the LWG. Earlier researchers interpreted the Nummana Member as a shallow marine deposit. In this note, published petrographical data from the Nummana Member are reviewed, and new field, as well as petrographical, evidence is reported. Earlier researchers did not adequately explain the origin of rounded to well-rounded grains in the Nummana sandstone. Rounded to well-rounded quartz grains, in combination with pinstripe lamination, adhesion features, and dunes with high-angle (up to 31 degrees) foresets, confirm the aeolian origin of the Nummana Member. The occurrence of subaerial basalts with continental tholeiite affinity (the Cheela Springs Basalt) on top of the Nummana Member is consistent with its nonmarine interpretation. The nearshore to terrestrial LWG succession, including the Nummana aeolianite, indicates regression and consequent emergence of the depositional surface and high continental freeboard during the early Paleoproterozoic in Western Australia.