Shackleton Formation | |
---|---|
Stratigraphic range: Cambrian Stage 3 ~ | |
Type | Geological formation |
Unit of | Byrd Group |
Underlies | Starshot Formation |
Overlies | Goldie Formation |
Lithology | |
Primary | Limestone, marble, sandstone |
Other | Quartzite, conglomerate, shale, dolomite |
Location | |
Coordinates | 82°12′S160°18′W / 82.2°S 160.3°W |
Approximate paleocoordinates | 0°42′S155°24′W / 0.7°S 155.4°W |
Region | Churchill Mountains of Antarctica |
Type section | |
Named for | Ernest Shackleton |
Named by | Laird |
Year defined | 1963 |
Paleogeography of the Cambrian with the supercontinent Pannotia and Antarctica south of the paleo-equator |
The Shackleton Limestone is a Cambrian limestone formation of the Byrd Group of Antarctica. The age of the formation is established to be Cambrian Stage 3, dated at ranging from 520 to 516 Ma. This period correlates with the End-Botomian mass extinction. Fossils of trilobites and Marocella mira and Dailyatia have been found in the formation, named after Ernest Shackleton, who led a failed expedition into Antarctica. At time of deposition, the Antarctic Plate has been established to be just south of the equator as part of the supercontinent Pannotia, contrasting with its present position at 82 degrees southern latitude. [1]
The formation, named by Laird in 1963, crops out in the Churchill Mountains, part of the Transantarctic Mountains of southwestern Antarctica. The most complete exposures are in the Holyoake Range. [2] Paleontological data and carbon isotope stratigraphy indicate that the Shackleton Limestone ranges from lower Atdabanian through upper Botomian. The formation is a thick carbonate deposit with a lower unit of unfossiliferous interbedded quartzite and limestone, overlies the Late Proterozoic argillaceous turbidite Goldie Formation and underlies the Starshot Formation. [2] [3] Other lithologies noted in the Shackleton Limestone are marble with breccia, conglomerate, sandstone and shale. [4] The abrupt transition from the Shackleton Limestone to a large-scale, upward coarsening siliciclastic succession records deepening of the outer platform and then deposition of an eastward-prograding molassic wedge. The various formations of the upper Byrd Group show general stratigraphic and age equivalence, such that coarse-grained alluvial fan deposits of the Douglas Conglomerate are proximal equivalents of the marginal-marine to shelf deposits of the Starshot Formation. [5]
The sandstone-rich lower member of the Shackleton Limestone is exposed at Cotton Plateau beneath Panorama Point, where it consists of up to 133 metres (436 ft) of interbedded white- to cream-weathering, vitreous, quartz sandstone and brown-weathering, white, fine-grained dolomitic grainstone. These beds are in fault contact with the adjacent Goldie Formation. [6] The formation postdates the Beardmore Orogeny of the Neoproterozoic, [7] and was deformed by the Ross Orogeny. [8]
The formation has provided fossils of trilobites such as Holyoakia granulosa , Pagetides (Discomesites) spinosus , Lemdadella antarcticae , Kingaspis (?) convexus , Yunnanocephalus longioccipitalis , and Onchocephalina (?) spinosa . [9] Other fossils found are Marocella mira , [1] and Dailyatia odyssei and D. braddocki. [10]
Pannotia, also known as the Vendian supercontinent, Greater Gondwana, and the Pan-African supercontinent, was a relatively short-lived Neoproterozoic supercontinent that formed at the end of the Precambrian during the Pan-African orogeny, during the Cryogenian period and broke apart 560 Ma with the opening of the Iapetus Ocean, in the late Ediacaran and early Cambrian. Pannotia formed when Laurentia was located adjacent to the two major South American cratons, Amazonia and Río de la Plata. The opening of the Iapetus Ocean separated Laurentia from Baltica, Amazonia, and Río de la Plata. A 2022 paper argues that Pannotia never fully existed, reinterpreting the geochronological evidence: "the supposed landmass had begun to break up well before it was fully assembled". However, the assembly of the next supercontinent Pangaea is well established.
Emuellidae are a small family of trilobites, a group of extinct marine arthropods, that lived during the late Lower Cambrian of the East Gondwana supercontinent, in what are today South-Australia and Antarctica.
Balcoracania dailyi is a small trilobite of the family Emuellidae. Its fossils have been found in south Australia and Antarctica.
The Adelaide Superbasin is a major Neoproterozoic to middle Cambrian geological province in central and south-east South Australia, western New South Wales, and western Victoria.
The geology of Antarctica covers the geological development of the continent through the Archean, Proterozoic and Phanerozoic eons.
Holyoakia is a genus of very small trilobites of the family Dorypygidae, from the late Lower Cambrian of South Australia and Antarctica.
Yunnanocephalus is a genus of ptychopariid trilobite. It lived during the late Atdabanian and Botomian stages, in what are currently Antarctica, Australia and China. It was a "moderately common" member of the Chengjiang Fauna. Yunnanocephalus is the only genus currently assigned to the Yunnanocephalidae family.
Lemdadella is an extinct genus of redlichiid trilobites that lived during the late Atdabanian stage, which lasted from 521 to 514 million years ago during the early part of the Cambrian Period.
The Beacon Supergroup is a geological formation exposed in Antarctica and deposited from the Devonian to the Triassic. The unit was originally described as either a formation or sandstone, and upgraded to group and supergroup as time passed. It contains a sandy member known as the Beacon Heights Orthoquartzite.
Swithinbank Range is a small range from the Churchill Mountains,
Epidote Peak is a prominent rock peak just north of the mouth of Held Glacier, lying along the west side of Shackleton Glacier in the Queen Maud Mountains of Antarctica. The Texas Tech Shackleton Glacier Expedition, 1964–65, named it for the abundance of the mineral epidote. Local concentrations of this mineral gives the peak a spotted appearance. The name was approved by US-ACAN in 1966.
Holyoake Range is a mountain range in the Ross Dependency of Antarctice. It is in the southern section of the Churchill Mountains, part of the Transantarctic Mountains System.
Marocella is a conical shelly fossil of uncertain affinity known from Cambrian strata of Europe, Morocco, Australia and Antarctica.
The Tonto Group is a name for an assemblage of related sedimentary strata, collectively known by geologists as a Group, that comprises the basal sequence Paleozoic strata exposed in the sides of the Grand Canyon. As currently defined, the Tonto groups consists of the Sixtymile Formation, Tapeats Sandstone, Bright Angel Shale, Muav Limestone, and Frenchman Mountain Dolostone. Historically, it included only the Tapeats Sandstone, Bright Angel Shale, and Muav Limestone. Because these units are defined by lithology and three of them interfinger and intergrade laterally, they lack the simple layer cake geology as they are typically portrayed as having and geological mapping of them is complicated.
The Mount Whyte Formation is a stratigraphic unit that is present on the western edge of the Western Canada Sedimentary Basin in the southern Canadian Rockies and the adjacent southwestern Alberta plains. It was deposited during Middle Cambrian time and consists of shale interbedded with other siliciclastic rock types and limestones. It was named for Mount Whyte in Banff National Park by Charles Doolittle Walcott, the discoverer of the Burgess shale fossils, and it includes several genera of fossil trilobites.
One of the major depositional strata in the Himalaya is the Lesser Himalayan Strata from the Paleozoic to Mesozoic eras. It had a quite different marine succession during the Paleozoic, as most parts of it are sparsely fossiliferous or even devoid of any well-defined fossils. Moreover, it consists of many varied lithofacies, making correlation work more difficult. This article describes the major formations of the Paleozoic – Mesozoic Lesser Himalayan Strata, including the Tal Formation, Gondwana Strata, Singtali Formation and Subathu Formation.
The Waynesboro Formation is a limestone, dolomite, and sandstone geologic formation in Virginia, Maryland, Pennsylvania and West Virginia. In some areas it is composed of limestone and dolomite. The Waynsboro Formation is one of the formations that make up the Shenandoah Valley. It dates back to the Cambrian period and is not considered fossiliferous.
The geology of Arizona began to form in the Precambrian. Igneous and metamorphic crystalline basement rock may have been much older, but was overwritten during the Yavapai and Mazatzal orogenies in the Proterozoic. The Grenville orogeny to the east caused Arizona to fill with sediments, shedding into a shallow sea. Limestone formed in the sea was metamorphosed by mafic intrusions. The Great Unconformity is a famous gap in the stratigraphic record, as Arizona experienced 900 million years of terrestrial conditions, except in isolated basins. The region oscillated between terrestrial and shallow ocean conditions during the Paleozoic as multi-cellular life became common and three major orogenies to the east shed sediments before North America became part of the supercontinent Pangaea. The breakup of Pangaea was accompanied by the subduction of the Farallon Plate, which drove volcanism during the Nevadan orogeny and the Sevier orogeny in the Mesozoic, which covered much of Arizona in volcanic debris and sediments. The Mid-Tertiary ignimbrite flare-up created smaller mountain ranges with extensive ash and lava in the Cenozoic, followed by the sinking of the Farallon slab in the mantle throughout the past 14 million years, which has created the Basin and Range Province. Arizona has extensive mineralization in veins, due to hydrothermal fluids and is notable for copper-gold porphyry, lead, zinc, rare minerals formed from copper enrichment and evaporites among other resources.
The geology of Utah, in the western United States, includes rocks formed at the edge of the proto-North American continent during the Precambrian. A shallow marine sedimentary environment covered the region for much of the Paleozoic and Mesozoic, followed by dryland conditions, volcanism, and the formation of the basin and range terrain in the Cenozoic.
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.