The geology of the Ellsworth Mountains, Antarctica, is a rock record of continuous deposition that occurred from the Cambrian to the Permian periods, with basic igneous volcanism and uplift occurring during the Middle to Late Cambrian epochs, deformation occurring in the Late Permian period or early Mesozoic era, and glacier formation occurring in the Cretaceous period and Cenozoic era. The Ellsworth Mountains are located within West Antarctica at 79°S, 85°W. In general, it is made up of mostly rugged and angular peaks such as the Vinson Massif (), the highest mountain in Antarctica.
The early Cambrian, when carbonate deposits were deposited in shallow marine conditions, is when the geologic history record across the Ellsworth Mountains began. Up to the Permian period, subsidence and deposition process persisted. Volcanism was scarce in the early history of the Ellsworth Mountains. The majority of the strata are thought to have formed in marine environments at shallow to moderate depths. After sedimentary deposition occurred during the Permian time, all strata underwent orogeny, which lead to strong folding and localised metamorphism. It is hypothesised that there are two stages of the uplift separated by a steady period of erosional gradation as the deformed rocks have raised by at least . In the Ellsworth Mountains, alpine glaciation may have first appeared during the Mesozoic era. The local glacial processes in the Ellsworth Mountains are largely responsible for the contemporary landscapes that we observe today. The mountains were covered by the continental ice sheet throughout the middle to late Cenozoic period.
Stratigraphic geological history
The Ellsworth Mountains display a thick geologic sequence of Paleozoic sedimentary and volcanic rocks. The Lower to Upper Cambrian Heritage Group is part of the lower Paleozoic series old rock strata. The uppermost Cambrian to Devonian Crashsite Group makes up the middle portion of the geologic sequence, while the Permian-Carboniferous Whiteout Conglomerate and Permian Polarstar Formation make up the remaining upper portion.
The whole stratigraphic succession has been impacted by the two post-Permian episodes of deformation, Late Permian Deformation and Permian-Triassic Deformation (which will be covered in the Structural Geology portion). During the Permian-Triassic Gondwanian deformation event, the major dextral transpressive Permian-Triassic Deformation structure locally develops and superimposes the Late Permian Deformation structures. As a result, the rocks of the Ellsworth Mountains range from the Permian Polarstar Formation to lower strata of the Cambrian Heritage Group, with a positive correlation between depth and metamorphic grade.
Heritage Group
Union Glacier Formation, Hyde Glacier Formation, Drake Ice Fall Formation at southern Soholt Peaks, Conglomerate Ridge Formation, Library Hills Formation, Springer Peak Formation, Frazier Ridge Formation, and Minaret Formation are the eight clastic sedimentary and volcanic rock formations that make up the Heritage Group. The Heritage Group as a whole is around thick. The pumpellyite-actinolite grade and the lower greenschist facies make up the majority of the bottom units of the Cambrian Heritage Group. It is discovered to be a sequence of syn-rifts. The Heritage Group's conglomerate units' clast compositions indicate that an Early Cambrian carbonate platform and widespread quartzite exposures were present in the rift succession's source region.
Union Glacier Formation The Union Glacier Formation is made up of volcaniclastic rocks that extend for around 3000 metres. Terrestrial lahar and ash-flow tuff deposits served as the raw ingredients for the formation of these rocks. In the late Early Cambrian to early Middle Cambrian era, it was developed. A continental rift, where the lithosphere was thinned, served as the tectonic backdrop for this formation during this time.
Hyde Glacier Formation The heterolithic sequence bedding of the Hyde Glacier Formation, which ranges from sand to mud, demonstrates the depositional environment from fluvial to shallow-marine delta. This formation may be the result of tectonic movement or lateral discontinuity.
Drake Icefall Formation at southern Soholt Peaks The lower Middle Cambrian black shales and interlayered limestone carbonates of the Drake Icefall Formation are found in southern Soholt Peaks. The rocks in this formation provide an evidence that sedimentation occurred in a shallow-marine and euxinic environment where with anoxic and sulfidic conditions. The quantity of free hydrogen sulphide increased since there was no oxygen present. A thin limestone that has undergone recrystallization and has a thickness of less than five metres makes up the formation's topmost depositional unit. The limestone is comparable to that which makes up the lowermost portion of the Drake Icefall Formation's immediate neighbour, the Conglomerate Ridge Formation.
Conglomerate Ridge Formation A 450-meter-long layer of polymict- and clast-supported conglomerate (also known as breccia) with beds of fine- to coarse-grained quartzite makes up the Conglomerate Ridge Formation. The conglomerate demonstrates the transition of the formation environment from river to shallow-marine. Along a reversal fault that runs parallel to the thin recrystallized limestone that makes up the top depositional unit of the Drake Icefall Formation, the Conglomerate Ridge Formation overlies the Drake Icefall Formation.
Liberty Hills Formation There have been no fossils discovered in the 1000-meter-thick Liberty Hills Formation. Based on the presence of early Cambrian (525 ± 2 Ma) granite clasts, also known as granite cobbles, the formation is determined to be of Middle Cambrian age. The Minaret Formation is atop it. Conglomerates, quartzites, and argillites make up the majority of this sequence of coarse-grained siliciclastic rocks.
Springer Peak Formation The Springer Peak Formation is around 1000 metres thick. This deposit has a trilobite fauna, which indicates that it dates from the Middle Cambrian to the basal Upper Cambrian.
Frazier Ridge Formation There have been no fossil discoveries in the Frazier Ridge Formation, which has a thickness of at least 500 metres. The dominant material in this formation is fine- to medium-grained green quartzite, which also occasionally contains layers of green argillite and black shale.
Minaret Formation In the Upper Cambrian era, the Minaret Formation was created. It is a limestone unit that is laterally interrupted. It is discovered that this formation's thickness greatly increases in the direction of the Ellsworth Mountains in the southeast. This indicates a transition from shallow-water, low-energy carbonate deposits in the south to deeper, high-energy carbonate platform deposits in the north. Along the top border of the Minaret Formation, karst features are visible that were created by the breakdown of soluble elements in the rocks.
Type of contacts - Transitional beds All places have conformable transitional beds of 20–60 metres, with the exception of Pojeta Peak, Soholt Peak, and Enterprise Hills. The transitional deposits are a narrow sequence of interbedded sandstone and siltstone from the Upper Cambrian period called argillite. It includes material from the inner to outer shelf and from shallow to deep environments. After the Minaret Formation emerged, a dramatic rise in the relative sea level caused it to develop.
Between the Springer Peak Formation and the Mount Twiss Member, which is a part of the Crashsite Group, there is an angular unconformity in the Pojeta Peak. Pojeta Peak's localised angular unconformity may have developed as a result of block tilting in regions of intrabasinal uplift. There are concordant erosional unconformities between the Minaret Formation and the base Crashsite Group at the Soholt Peaks and Mount Dolence.
Unconformities between the Heritage Group and the Crashsite Group are discovered on a local scale, but they are viewed as correlative conformity because of geographically extensive observations of this important border on a regional scale.
The Uppermost Cambrian to Devonian Crashsite Group The Crashsite Group has six distinct rock types with a combined thickness of 3000 metres. It includes the Howard Nunataks Formation, the Mount Wyatt Earp Formation, the Linder Peak Member, the Mount Twiss Member, the Landmark Peak Member, and the Mount Liptak Formation. The transitional beds are primarily covered by quartzite.
The upper part of the 13-km thick stratigraphic succession The Permian-Carboniferous Whiteout Conglomerate and the Permian Polarstar Formation make up the upper part of the 13-km thick geologic series of rock strata.
Permian-Carboniferous Whiteout Conglomerate The Permian-Carboniferous Whiteout Conglomerate is an Upper Carboniferous-Lower Permian glacial diamicite.
Polarstar Formation The deep Cambrian to Permian sequence of the Ellsworth Mountains is topped by the argillite and sandstone Polarstar Formation, which is 1 km thick. The lowest part of the Polarstar Formation is dominated by argillite, a fine-grained sedimentary rock, while the middle part of the formation is composed of cycles of argillite and sandstone that coarsen upward. Fining-upward cycles of cross-bedded, channel-form, medium-grained, and fine-grained sandstone are seen in the upper Polarstar Formation.
Paleontology history The Heritage Range in the southern Ellsworth Mountains is home to several fossil sites from various geological eras, including the Late Cambrian and Late Permian. Based on the correlation of the fossils, it appears that the Ohio Range of the Horlick Mountains is where the fossils are most constant. This is also consistent with the idea that the Pensacola Mountains of the Transantarctic Mountains previously bordered the Ellsworth Mountains.
Minaret Formation in Late Cambrian Phyla, gastropods, mollusks, and other faunal groups have been gathered and preserved as fossils in the Late Cambrian Minaret Formation.
Late Cambrian trilobite-mollusk fauna at Springer Peak The Minaret Formation's feather-edge, which is 8 metres thick and thickens to a depth of 600 metres to the south, contains the Late Cambrian trilobite-mollusk fauna at Springer Peak. The southern fossils, however, were obliterated by significant deformation. The fauna is still notable since it may be the finest preserved and most diversified Late Cambrian fauna in the whole globe. This fauna contains members of seven phyla, including the Arthropoda, Mollusca, Brachiopoda, Hyolitha, Echinodermata, Pisces, and Archaeocyatha. The feather-edge at Springer Peak was sandwiched between the feeble argillites that absorbed the deformational strain. The Minaret Formation is home to three-dimensional fossils. Shells are present, and the fauna is in superb condition. Coquina fossils make up the majority of the content.
The bulk of the fossils discovered in the Minaret Formation are trilobites, while 8% of them are mollusks. Twenty species of trilobites have been discovered, including agnostids. They have demonstrated connections with southern Russia, Australia, China, and North America. There are three species of rostroconchs, six species of gastropods, an orthothecid, and even species of monoplacophora for the mollusc.