Huab Formation | |
---|---|
Stratigraphic range: Artinskian-Kungurian typically Artinskian ~ | |
Type | Geological formation |
Unit of | "Ecca" Group |
Underlies | Gai-As Formation |
Overlies | Basement |
Area | From Atlantic coast to Twyfelfontein |
Thickness | 75–190 m (246–623 ft) |
Lithology | |
Primary | Shale, limestone |
Other | Sandstone, conglomerate, stromatolite, coal |
Location | |
Location | Damaraland |
Coordinates | 21°12′S14°06′E / 21.2°S 14.1°E |
Approximate paleocoordinates | 51°00′S30°30′W / 51.0°S 30.5°W |
Region | Kunene & Erongo Regions |
Country | Namibia |
Extent | Huab Basin |
Type section | |
Named for | Huab River |
Geologic map of Namibia with the Huab Formation partly cropping out in the northwestern area (orange) |
The Huab Formation is an Early Permian (Artinskian to Kungurian) geologic formation correlated with the Ecca Group and designated "Ecca" Group, because it does not belong to the Karoo, in the southwestern Kunene Region and northern Erongo Region of northwestern Namibia. The Huab Formation represents the oldest sedimentary unit of the Huab Basin, overlying the basement. The oil shales within the formation were deposited in a shallow lacustrine environment, and the formation marks the transition from terrestrial deposits under glacial climatic circumstances towards a warmer fluvial and marine deltaic environment.
The Huab Formation is correlated with a series of formations in the Pelotas and Paraná Basins in southeastern Brazil, deposited in a larger basinal area, 150 million years before the break-up of Pangea. The abundance of Glossopteris and Mesosaurus fossils are characteristic of the Gondwanan correlation across present-day South America, Africa, Antarctica and Australia.
The Huab Formation is a lithological unit with an approximate maximum thickness of 190 metres (620 ft), deposited in the eponymous basin where it underlies the Gai-As Formation, separated by a significant hiatus, [1] and overlies the basement. [2] The formation crops out south of the Huab River, [3] extending from the Atlantic coast to Twyfelfontein. The thickness in the coastal area is about 75 metres (246 ft). [4]
Part of the formation in the west is composed of carbonates (domal stromatolites with an east to west orientation and thin laminae of less than 1 millimetre (0.039 in)). The stromatolites occur in a 35 kilometres (22 mi) wide zone, reaching from 3 kilometres (1.9 mi) east of the Uniab Fault to 2 kilometres (1.2 mi) east of the Bergsig Fault system. [5] The eastward sections comprise oolitic conglomeratic horizons of up to 50 centimetres (1.6 ft) thick. The carbonates (mudstones and marls) are overlain by silty, partly calcareous shales. The shales interfinger with sandstones and in certain parts coal beds are found. In the eastern domain around the Doros crater, dark iron-oxide cements occur in the upper conglomerate horizons. [5] In virtually all lithological units, bones of the amphibious reptile Mesosaurus tenuidens can be encountered in concretions. [6] The laminated mudstones and marls contain a diverse ichnofauna including Skolithos , Planolites , and large exemplars of Rhizocorallium irregulare . [7]
The depositional environment is interpreted as ranging from glacial (tillite) at the very base, [2] followed by a glacio-fluvial setting, and a warmer climate fluvial environment. [8] The sequence higher up is formed by a fan deltaic setting, [9] with a lateral shallow lake with increased salinity where stromatolite bioherms were formed. [6] [10] [11] The uppermost section of the Huab Formation, underlying the Gai-As Formation, was deposited in an estuarine environment. [12]
The depositional environments have been described in detail by Wanke in 2000 as follows: [13]
Stromatolitic bioherms acted as a barrier towards the open sea in the west. Their preferred E-W orientation coincides with tidal- and wave induced currents perpendicular to the palaeo-coastline. Lagoonal environments were established landwards of the bioherm belts, in which laminated shales developed. The lamination is due to suspension fallout in slightly agitated water. Erosive based interbeds of coarse to gritty sandstones formed during storm events and are therefore interpreted as tempestites. West of the bioherm belts, the fair weather wave basis reached the ground, expressed in oscillation-rippled surfaces.
Channels between bioherm ridges have been interpreted as tidal channels. They host flat-pebble conglomerates, which are characterized by a high ooid content. These ooid bearing flat-pebble conglomerates support the facies concept of shallow, wave dominated water in the vicinity of the bioherms: Ooids form in very shallow, fairly agitated, carbonate saturated water probably under warm climate. The flat pebbles derived from desiccated layers of unlithified cohesive fine clastics that had been reworked, preferentially under the influence of storm waves. Tidal flats or lagoons provide the conditions for the generation of both, ooids and flat-pebble conglomerates.
Shales and mudstones besides algal laminites represent deposition in a slightly agitated, shallow water body with relatively intensive carbonate production. Oscillating water-levels resulted in the formation of paleosols, which were reworked in flat pebble conglomerates after flooding. Autochthonous breccias give clear evidence for frequent sea level fluctuations, that refer to palustrine soils, which underwent periodically subaerial exposure. Coarse sandstones, partly channelized, reveal fluvial influence. The coarser material was probably sourced by a nearby delta that was temporarily flooded during storm events. The dominance of those coarse sandstones towards the top of the eastern flat-pebble facies association might indicate delta progradation. The iron-oxide cements are interpreted as ferricretes, that either formed autochthonous or derived from adjacent reworked ferricrete crusts. An early uplift of the eastern hinterland might be indicated by coarse, westwardly prograding deltaic deposits of the upper Huab Formation in the eastern Huab area. [14]
The upper part of the formation is correlated with the Irati Formation of the Paraná and Pelotas Basins in Rio Grande do Sul, Brazil, and with the Whitehill Formation in the Karoo Basin of southern Namibia and the Eastern, Northern and Western Cape, South Africa. [6] The lower section correlates with the Palermo and Rio Bonito Formations of the Paraná Basin and the Prince Albert Formation of the Karoo. [15] The Permian sequence in the Huab Basin is much thinner than those of the Paraná and Karoo Basins. [16] The fossil assemblages of Glossopteris and Mesosaurus are known from other parts of Gondwana; the Vryheid Formation of South Africa and coal deposits of the Lower Permian in Australia. [8]
Conglomerate is a sedimentary rock made up of rounded gravel-sized pieces of rock surrounded by finer-grained sediments. The larger fragments within conglomerate are called clasts, while the finer sediment surrounding the clasts is called the matrix. The clasts and matrix are typically cemented by calcium carbonate, iron oxide, silica, or hardened clay.
The Karoo Supergroup is the most widespread stratigraphic unit in Africa south of the Kalahari Desert. The supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Late Carboniferous and Early Jurassic, a period of about 120 million years.
The Ecca Group is the second of the main subdivisions of the Karoo Supergroup of geological strata in southern Africa. It mainly follows conformably after the Dwyka Group in some sections, but in some localities overlying unconformably over much older basement rocks. It underlies the Beaufort Group in all known outcrops and exposures. Based on stratigraphic position, lithostratigraphic correlation, palynological analyses, and other means of geological dating, the Ecca Group ranges between Early to earliest Middle Permian in age.
The San Juan Basin is a geologic structural basin located near the Four Corners region of the Southwestern United States. The basin covers 7,500 square miles and resides in northwestern New Mexico, southwestern Colorado, and parts of Utah and Arizona. Specifically, the basin occupies space in the San Juan, Rio Arriba, Sandoval, and McKinley counties in New Mexico, and La Plata and Archuleta counties in Colorado. The basin extends roughly 100 miles (160 km) N-S and 90 miles (140 km) E-W.
The Santos Basin is an approximately 352,000 square kilometres (136,000 sq mi) large mostly offshore sedimentary basin. It is located in the south Atlantic Ocean, some 300 kilometres (190 mi) southeast of Santos, Brazil. The basin is one of the Brazilian basins to have resulted from the break-up of Gondwana since the Early Cretaceous, where a sequence of rift basins formed on both sides of the South Atlantic; the Pelotas, Santos, Campos and Espírito Santo Basins in Brazil, and the Namibia, Kwanza and Congo Basins in southwestern Africa.
Stereosternum tumidum is an extinct genus of mesosaur marine reptile from the Early Permian of Brazil and also the Great Karoo Basin of South Africa. The taxon mesosaur is a monophyletic group containing Brazilosaurus sanpauloensis and Mesosaurus tenuidens.
The Paraná Basin is a large cratonic sedimentary basin situated in the central-eastern part of South America. About 75% of its areal distribution occurs in Brazil, from Mato Grosso to Rio Grande do Sul states. The remainder area is distributed in eastern Paraguay, northeastern Argentina and northern Uruguay. The shape of the depression is roughly elliptical and covers an area of about 1,500,000 km2 (580,000 sq mi).
The Dwyka Group is one of four geological groups that compose the Karoo Supergroup. It is the lowermost geological group and heralds the commencement of sedimentation of the Karoo Supergroup. Based on stratigraphic position, lithostratigraphic correlation and palynological analyses, these lowermost Karoo strata range between the Late Carboniferous (Pennsylvanian) to Early Permian in age.
The Mangrullo Formation is an Early Permian (Artinskian) fossiliferous geological formation in northeastern Uruguay. Some authors alternatively group it together with the Paso Aguiar Formation and the Frayle Muerto Formation as the three subdivisions of the Melo Formation, in which case it is referred to as the Mangrullo Member. Like the correlated formations of Irati and Whitehill, it is known for its abundant mesosaur fossils. It also contains the oldest known Konservat-Lagerstätte in South America, as well as the oldest known fossils of amniote embryos.
The Bass Formation, also known as the Bass Limestone, is a Mesoproterozoic rock formation that outcrops in the eastern Grand Canyon, Coconino County, Arizona. The Bass Formation erodes as either cliffs or stair-stepped cliffs. In the case of the stair-stepped topography, resistant dolomite layers form risers and argillite layers form steep treads. In general, the Bass Formation in the Grand Canyon region and associated strata of the Unkar Group-rocks dip northeast (10°–30°) toward normal faults that dip 60+° toward the southwest. This can be seen at the Palisades fault in the eastern part of the main Unkar Group outcrop area. In addition, thick, prominent, and dark-colored basaltic sills intrude across the Bass Formation.
The Laborcita Formation is a geologic formation in the Sacramento Mountains of New Mexico. It preserves fossils dating back to the late Pennsylvanian to early Permian.
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 geology of Namibia encompasses rocks of Paleoproterozoic, Mesoproterozoic and Neoproterozoic and Paleozoic to Cenozoic age. About 46% of the countryʼs surface are bedrock exposure, while the remainder is covered by the young overburden sediments of the Kalahari and Namib deserts.
The Ganigobis Formation is a Late Carboniferous (Gzhelian) to Early Permian (Artinskian) geologic formation of the Dwyka Group in the ǁKaras Region of southeastern Namibia and the Northern Cape of South Africa. The widespread formation was deposited in the Aranos and Karoo Basins of southern Africa.
The Whitehill Formation, alternatively written as White Hill Formation and formerly known as White Band or Whitehill or White Hill Member, is a regional Early Permian geologic formation belonging to the Ecca Group in the southeastern ǁKaras Region of southeastern Namibia and Eastern, Northern and Western Cape provinces of South Africa.
The Gai-As Formation is an Early to Middle Permian geologic formation correlated with the Ecca Group and designated "Ecca" Group, because it does not belong to the Karoo, in the southwestern Kunene Region and northern Erongo Region of northwestern Namibia. The Gai-As Formation represents the second-oldest sedimentary unit of the Huab Basin, overlying the Huab Formation. The formation was deposited in a fluvial to lacustrine setting.
The Omingonde Formation is an Early to Middle Triassic geologic formation, part of the Karoo Supergroup, in the western Otjozondjupa Region and northeastern Erongo Region of north-central Namibia. The formation has a maximum thickness of about 600 metres (2,000 ft) and comprises sandstones, shales, siltstones and conglomerates, was deposited in a fluvial environment, alternating between a meandering and braided river setting.
The Elbert Formation is a geologic formation that crops out in the San Juan Mountains of southwestern Colorado. The formation contains fossils indicating it is upper Devonian in age.
The Sergipe-Alagoas Basin is a continental margin basin in the Sergipe and Alagoas states of northeastern Brazil, about 20 to 50 kilometres wide onshore, but with its widest extension offshore, more precisely 13,000 km2 onshore and 40,000 km2 offshore. In general, "Sergipe-Alagoas Basin" refers to the Sergipe and Alagoas sub-basins, but it also consists of the Jacuípe and Cabo sub-basins. Studies of the basin's geology date back to the first half of the 19th century, when J. Henderson in 1821 published preliminary notes on the region's geology.
The Aksu Basin is a sedimentary basin in southwestern Turkey, around the present-day Aksu River. Located at the intersection of several major tectonic systems, in the Isparta Angle, the Aksu Basin covers an area of some 2000 square kilometers. Together with the Köprü Çay Basin and the Manavgat Basin, the Aksu Basin forms part of the broader Antalya Basin. It forms a graben relative to the surrounding Anatolian plateau.