Chapter 6: Facies of Cambrian carbonate rocks, Ellsworth Mountains, West Antarctica
Published:January 01, 1992
Werner Buggisch, Gerald F. Webers, 1992. "Chapter 6: Facies of Cambrian carbonate rocks, Ellsworth Mountains, West Antarctica", Geology and Paleontology of the Ellsworth Mountains, West Antarctica, G. F. Webers, C. Craddock, J. F. Splettstoesser
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Carbonate rocks were studied from the Middle Cambrian Drake Icefall Formation and the Middle to Upper Cambrian Minaret Formation. Additionally, carbonate clasts from the Middle Cambrian Union Glacier Formation and the Permo-Carboniferous Whiteout Conglomerate were examined. No in situ Lower Cambrian carbonate rocks are known to crop out in the Ellsworth Mountains; only reworked clasts of such rocks are found in the Heritage Group and the Whiteout Conglomerate. These clasts suggest that during Early (and Middle?) Cambrian time, a wide carbonate platform developed in or close to the Ellsworth Mountains. This was the site of skeletal algae and archaeocyathid boundstones with sparry calcite or mud as matrix—typical sediments of an open marine environment with low to medium hydrodynamic energy. Oolites are common, and a high-energy environment was required to form these oosparites. These grains, with a diameter between 4 and 7 mm, are made up of concentric ooids with simple and complex structures. Nuclei consist of abraded ooids and oolitic intraclasts. Half-moon ooids with collapsed internal structure are attributed to partial solution, and they indicate a hypersaline depositional environment (aragonite or calcium sulfate?) for some parts of the oolitic bank facies.
Laminites with fenestral structures are also present, and they represent low-energy lagoonal deposits. These occur along with dome-shaped and LLH stromatolites that indicate an intertidal environment. Some areas of the carbonate platform were elevated and partly dissolved by fresh water. During the following period of subsidence, voids were filled with fibrous carbonates by rhythmic cementation. Renewed uplift resulted in erosion and destruction of the carbonate platform.
The lowest in situ marly and oolitic carbonates are found in the Middle Cambrian strata of the Heritage Group north of Drake Icefall, but these were not extensively studied. The Upper Cambrian Minaret Formation is also autochthonous, and its thickness increases southward from 8 m in the northern Webers Peaks to several hundred meters in the Marble Hills area. Medium to high hydrodynamic energy conditions prevailed during deposition of the Springer Peak section of the Minaret Formation (biosparite, oncosparite, pelsparite). The high diversity of the fauna indicates an open marine environment. The section at Yochelson Ridge starts with a few meters of still-water carbonate rocks that are overlain by high-energy oolitic carbonate rocks and calcarenites. Farther to the south (south of Mount Dolence), facies fluctuate from medium-energy (oncolite) to high-energy (oolite) environments. Fossils (brachiopods and trilobites) are rare. Near the top of the sequence a hypersaline milieu is indicated by layers of early diagenetic dolomicrite. Similar fades are exposed in the Liberty and Marble Hills areas. Fast subsidence in this area was compensated by rapid sedimentation of shallow-water carbonates.