LATE MIDDLE CAMBRIAN (STAGE 3) SHALLOW SHELF SUCCESSION IN THE PATUXENT RANGE, ANTARCTICA

The nearly 400-m-thick succession of carbonate strata exposed at Postel Nunatak in the Patuxent Range was deposited in a shallow marine setting, ranging from supratidal to lagoonal facies with rare, sparsely fossiliferous, burrowed lime mudstone intervals. Upper and lower contacts are covered by snow and ice, so the field relationships with rocks mapped as the Patuxent Formation and Dover(?) Sandstone remain uncertain. The limestone exposures can be correlated with the Nelson Limestone of the Neptune Range, 160 km to the northeast, and are not correlative with the lower Cambrian Schneider Hills Limestone of the Argentina Range. Collections of the trilobites, Suludella? davnii Palmer and Gatehouse, 1972 and Solenopleura pruina Palmer and Gatehouse, 1972 indicate a late middle Cambrian age. Solenopleura pruina is found in the Amphoton oatesi zone in the uppermost depositional sequence of the Neptune Limestone in the Neptune Range. We provisionally assign the strata in the Postel Nunatak to the Drumian and possibly lowermost Guzhangian stages of Cambrian Series 3. Isotopic analysis of rock samples collected from Postel Nunatak shows a greater than 2‰ positive excursion of δ¹³C in burrowed lime mudstone facies, but limitations in the sampling resolution does not permit confident correlation with the late middle Cambrian DICE event.