The Andes are made up by the two Cordillera mountain chains and are separated by the Altiplano plateau. This account is a description of an area from the axis of the Western Cordillera to the foothills of the Eastern Cordillera at the latitude of Lake Titicaca. It looks at stratigraphy, structure, mineral deposits and volcanic geochemistry, putting them into the context of the evolution of the Andes.
Abstract Lithostratigraphic studies of four borehole cores drilled through the late Paleocene Lambeth Group (Upnor, Woolwich and Reading Formations) and basal London Clay Formation of central London have been supplemented with palaeomagnetic, calcareous nannoplankton and palynological data. The Woolwich and Reading Formations and the lower London Clay Formation are reversely magnetized and were deposited during the early part of Chron C24r. The first record of both NP9 and Chron C25n, hitherto missing from the Paleogene record in southern England, has been identified in the Upnor Formation (formerly the Woolwich Bottom Bed). It provides a key reference marker for linking events associated with the Paleocene-Eocene boundary (positioned within Chron C24r) to the type area of the internationally recognized Thanetian and Ypresian Stages.
This Sheet Description describes the Quaternary and bedrock geology of the Al Wathba 1:100 000 scale geological map. The district covers 2780 km2 southeast of Abu Dhabi island, and includes many of the suburbs of Abu Dhabi city, including the proposed Capital District, Madinat Khalifa A and B, Mussafah, Mohammed bin Zayed City, Mafraq, Bani Yas, Al Wathba, Al Falah, Al Shamka and Abu Dhabi International Airport. The sheet extends east as far as Al Khatim.
The pre-Quaternary bedrock comprises Miocene evaporitic mudstone and siltstone of the Gachsaran Formation (Fars Group) overlain by the dolomitic conglomerates, sandstones and siltstones of the Barzaman Formation in the north. In the south and west, the Gachsaran Formation is overlain by the dolomites and limestones of the Dam Formation which forms an escarpment around the Al Dhafra Air Base. These are overlain by the sandstones of the Shuwaihat and Baynunah Formations. Borehole evidence suggests there is a gradation from interbedded siltstones and sandstones of the Baynunah Formation in the west of the district to coarse dolomitic conglomerates of the Barzaman Formation in the north.
The Miocene rocks are locally overlain by fluvial sandstones and channel gravels of the Hili Formation which represent Quaternary outwash from the Hajar Mountains to the east. Much of the region is partially covered by pale carbonate aeolianites of the Ghayathi Formation, themselves often covered in a veneer of more recent aeolian sand. These are well exposed near the coast in spectacular zeugen and inland, they form a series of east-northeast trending linear ridges.
Modern pale carbonate-dominated low dunes occur particularly in the west of the district. The coastal zone is dominated by a range of Late Pleistocene to Holocene littoral and marine deposits, which comprise the Abu Dhabi Formation. These include coastal spits and bars, algal mats, mangrove swamps and intertidal sediments. Sabkha is developed on the surface of these deposits.
The region has seen major development over the past 30 years, which has radically changed the surface geology. Much of the coastal strip has been reclaimed or developed, with a variable amount of made ground, often composed of carbonate sand dredged from the neighbouring lagoons. Further inland, many areas have been extensively landscaped, with large areas of dunes levelled flat or quarried for fill. Much of the north-western part of the sheet is either developed or scheduled for development. Extensive areas of forestry occur along the line of the main Abu Dhabi – Al Ain highway and north of Abu Dhabi International Airport.
This Sheet Description describes the Quaternary and solid geology of the Mirfa 1:100 000 scale geological map. The Mirfa district includes a strip of the UAE mainland along the Arabian Gulf coast from Thumayriyah Island in the west and Mirfa in the east, including the islands of Marawah and Jananah. This district is particularly important for its exposures of the Miocene bedrock, notably the section at Jebal Momiya, near Mirfa, a key palaeontological site from which many vertebrate remains have been found, and Quaternary marine sediments on the island of Marawah, including type site for the Marawah Formation.
The oldest rocks in the area are the Miocene rocks of the Shuwaihat and Baynunah formations which form a series of northwest to southeast trending ridges and headlands rising up above the coastal plain, and underlie much of the southern inland part of the sheet. The Shuwaihat Formation typically comprises a number of cyclical sequences deposited in a mixed aeolian-fluvial-sabkha environment. It is overlain by the Baynunah Formation with a characteristic basal bone bed overlain by fluvial lacustrine sediments.
Quaternary sediments are present throughout much of the area. The Ghayathi Formation, moderately cemented carbonate-dominated palaeo-dune sandstones, occurs as isolated areas of outcrop resting on Miocene bedrock mostly in the southern part of the district. On the coast, deposits of the Abu Dhabi Formation are found in the subtidal, intertidal and supratidal zones, and forming extensive spits, bars and strand-plains. Inland of the coastal spit-bar complex are extensive areas of continental sabkha. Offshore, the island of Marawah is comprised of older Quaternary marine rocks of the Marawah and Fuwayrit formations.
SUMMARY Joints in coals, arranged (sub) normal to bed boundaries, are commonly termed cleats. Cleat azimuths in Carboniferous coals are reviewed, and are interpreted as reflecting Variscan stress fields across different tectonic settings. Immediately proximal to the Variscan Front (South Wales, Kent), varied cleat azimuths provide evidence of stress deflection and block rotation, whereas north of the Wales-Brabant High (central and northern England), a consistent regional north-westerly maximum horizontal stress is indicated by regionally parallel cleat orientations in most coalfield areas. In the more distal Midland Valley of Scotland, varied cleat azimuths suggest that local structural developments had a significant effect on the stress field. Throughout Britain, major fault zones separate differing cleat sets, suggesting deep crustal compartmentalization during Carboniferous times. In all areas, most main fault movements post-dated the majority of cleats.
This Sheet Description describes the Quaternary and solid geology of the Madinat Zayed 1:100 000 scale geological map. The oldest rocks in the area are the Miocene rocks of the Dam, Shuwaihat and Baynunah formations. The Dam Formation comprises pale grey, fine-grained carbonates and nodular gypsum beds which crop at low elevations above the coastal sabkha in the northern part of the district. The overlying Shuwaihat Formation is characterised by red sandstones with subordinate green mudstones and grey pedogenic beds. It typically comprises a number of cyclical sequences deposited in a mixed aeolian-fluvial-sabkha environment. It is overlain by the Baynunah Formation, of which both the Barakah and Hamra members are well-developed in this area. The lower, fluvial, Barakah Member, with its characteristic basal bone bed erosively overlies the Shuwaihat Formation. The overlying Hamra Member comprises interbedded calcareous siltstones, siltstones and fine sandstones, laid down in a low-energy fluvio-lacustrine system. This is capped by reddish-brown, playa or lacustrine sandstones of the Sahil Member. These well-cemented lithologies, particularly the calcareous siltstones and limestone of the Hamra Member commonly cap low jebals and ridges in the area north of Habshan.
Quaternary sediments are present throughout much of the area. The Madinat Zayed Formation overlies the Baynunah Formation and comprises a number of facies including reddish-brown, wavy and cross-bedded aeolian sandstones and light grey laminated lacustrine siltstones and rooted aeolian sands. The Ghayathi Formation, which is made up of moderately well-cemented, carbonate-dominated palaeodune sandstones, occurs as isolated areas of outcrop draping older Miocene or Madinat Zayed Formation bedrock mostly in the north and east of the district.
Much of the district has a cover of unconsolidated aeolian sand either as a thin veneer or as laterally extensive barchanoid dune fields, sand sheets and dune ridges. The northern part of the district includes part of the coastal sabkha, which is largely underlain by deflated unconsolidated quartzose aeolian sand.
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