Paleoenvironmental Interpretations of the Lower Taylor Group, Olympus Range area, southern Victoria Land, Antarctica (2008)
AuthorsGilmer, Greer Jessieshow all
The Devonian Taylor Group, in the Olympus Range area, southern Victoria Land (SVL), Antarctica, is separated from the basement by a regional nonconformity (Kukri Erosion Surface). A second localized unconformity within the Taylor Group called the Heimdall Erosion Surface separates the New Mountain Sandstone and older units from the younger Altar Mountain Formation. The depositional environment of the New Mountain Sandstone has long been under contention.
The New Mountain Sandstone Formation is a predominantly quartzose cross-bedded sandstone. Its newly defined Mt Jason Member is a coarse arkosic small scale cross-bedded pebbly sandstone that grades up section into the rest of the quartzose New Mountain Sandstone with large scale cross beds. The New Mountain Sandstone has been divided into five lithofacies including the Basal Conglomerate Lithofacies, Pebbly Sandstone Lithofacies, Granule Cross-bedded Lithofacies, Pinstripe Cross-bedded Lithofacies and Cross-bedded Sandstone Lithofacies. Deposition was in a shoreface environment with minor coastal aeolian deposition. The environment changed from upper shoreface to lower shoreface up section, forming transgressive to highstand systems tracts.
The Heimdall Erosion Surface truncates the Cross-bedded Sandstone Lithofacies and the Pinstripe Cross-bedded Lithofacies and was formed due to relative sea level fall leading to exposure and erosion of underlying sedimentary and basement rocks. It forms a type 1 sequence boundary. The New Mountain Sandstone was partially or totally lithified before erosion as shown by the jagged morphology of the eroded cross beds on the surface. It is not known when cementation of the NMS took place or how much of the formation has been eroded. The Heimdall Erosion Surface and Kukri Erosion Surface converge locally due to erosion on the Heimdall Erosion Surface and relief on the Kukri Erosion Surface.
The Heimdall Erosion Surface became a shore platform and the site of deposition as relative sea level rose. The Altar Mountain Formation with its Odin Member is a cross-bedded, massive and bedded feldspathic and quartzose sandstone that fines up section and is deposited on the erosion surface. The Altar Mountain Formation is divided into four lithofacies including the Conglomerate Lithofacies, Trough Cross-bedded Lithofacies, Cross-bedded Bioturbated Lithofacies and Bedded Fine Lithofacies. Deposition was in a shoreface environment, changing up section to an inner shelf environment with minor estuarine/tidal influence near the top of the section forming transgressive to highstand to regressive system tracts.
The sedimentary rocks are derived mainly from the Granite Harbour Intrusives and Koettlitz Group, which underlie the sandstones, but were exposed elsewhere in SVL. The sandstone clasts within the Conglomerate Lithofacies could be derived from underlying older Taylor Group rocks or exotic sources from outside the field area.
Correlation with data from adjacent areas suggests deposition of the New Mountain Sandstone occurred in a shallow sea that existed from the Olympus Range, southwards into the Asgard Range and included Vashka Crag. The area around Sponsors Peak and to the north was exposed and supplying feldspathic and quartzose sediment and pebbles into the depositional basin. As relative sea level fell due to either tectonic uplift or eustatic processes a large area of southern Victoria Land was exposed including the Olympus and Asgard Ranges and Bull Pass-St Johns Range area. This lead to erosion of the New Mountain Formation and basement rocks. Deposition of the New Mountain Sandstone continued further south shown by the gradational contact between it and the overlying Altar Mountain Formation. Relative sea level rise led to deposition of the Altar Mountain Formation. Shallow seas once more dominated the southern Victoria Land with deltas in the east (in the Bull Pass-St Johns Range area) feeding feldspathic sediment into the depositional basin (Odin Member). Further sea level rise drowned the delta region and a shallow marine to inner shelf environment led to deposition of the rest of the Altar Mountain Formation.