Geology of the Nelson Limestone, Postel Nunatak, Patuxent Range, Antarctica

Kevin Ray Evans,Wesley Donald Weichert,Bruce S Lieberman,Kenneth G Macleod,Lawrence W Mckenna

doi:10.1017/s0954102017000396

Kevin Ray Evans, Wesley Donald Weichert + Show 3 more

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https://doi.org/10.1017/s0954102017000396

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Abstract

AbstractPostel Nunatak in the Patuxent Range has been previously mapped as Nelson Limestone but there was no biostratigraphic support for that interpretation until now. We confirm that limestone exposures at Postel Nunatak are at least partly correlated with the Nelson Limestone of the Neptune Range, 160 km north-east, and are not correlative with the lower Cambrian Schneider Hills Limestone of the Argentina Range. Upper beds have yielded the trilobitesSuludella? davniiPalmer & Gatehouse, 1972 andSolenopleura pruinaPalmer & Gatehouse, 1972, which provide a basis for assignment to Cambrian Series 3 (late middle Cambrian), within the Drumian or lower Guzhangian stages. Limestone beds were deposited in a shallow marine setting, ranging from supratidal to lagoonal facies with rare subtidal intervals. These settings contrast with deeper water facies of the Neptune Range. Despite limitations in sampling density, isotopic analysis indicates that a greater than +2.5‰ shift in δ13C is consistent with δ13C trends documented for the Drumian Stage. Because the upper and lower contacts at Postel Nunatak are covered by snow and ice, the relationship with rocks mapped as the Patuxent Formation in the Patuxent Range remains uncertain, but part of it may belong to the Precambrian Hannah Ridge Formation.

Highlights

Exposed rock represents only 0.18% of the surface area on the continent of Antarctica (Burton-Johnson et al 2016)
This paper presents new faunal evidence that confirms the age and stratigraphic position of limestone exposures at Postel Nunatak in the Patuxent Range, which had been mapped as middle Cambrian Nelson Limestone (Schmidt & Ford 1969); it provides an interpretation of the depositional setting of the limestone, presents a reconnaissance-level survey of variations in stable isotopes of carbon and oxygen in carbonate rock samples, and discusses the broader implications of these data for regional correlation of Nelson Limestone and adjacent strata of uncertain stratigraphic affinities in the Patuxent Range
Evidence of deformation during the Ross Orogeny is expressed along the entire margin of East Antarctica from northern Victoria Land to the Pensacola Mountains, in some of the peripheral terranes and across the Australian margin of western Gondwana

Summary

Introduction

Exposed rock represents only 0.18% of the surface area on the continent of Antarctica (Burton-Johnson et al 2016). Because of the lack of exposure, exploration of remote mountain ranges and nunataks (isolated peaks surrounded by snow and ice) provide important sources of data for our understanding of continental-scale tectonic events and Antarctic geologic history. This paper presents new faunal evidence that confirms the age and stratigraphic position of limestone exposures at Postel Nunatak in the Patuxent Range, which had been mapped as middle Cambrian Nelson Limestone (Schmidt & Ford 1969); it provides an interpretation of the depositional setting of the limestone, presents a reconnaissance-level survey of variations in stable isotopes of carbon and oxygen in carbonate rock samples, and discusses the broader implications of these data for regional correlation of Nelson Limestone and adjacent strata of uncertain stratigraphic affinities in the Patuxent Range. Deformation probably resulted from accretion and partial obduction of an arc (back-arc) trench system, a collision which Federico et al (2009) argued occurred during the opening and closing of a back-arc basin, similar to the Cambrian

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