SUMMARY Three new marine bands are recognized in the exceptionally thick Lower Namurian succession of the northern part of the Central Pennine Basin, namely the Blacko (late Pendleian), Cravenoceras gressinghamense (early Arnsbergian) and Saleswheel (early Arnsbergian) marine bands. The stratotype of the Blacko Marine Band (E 1c 2) is within delta-slope siltstone and sandstone of the Surgill Shale Member at the top of the turbiditic Pendle Grit Formation of the Blacko Borehole (near Colne). It comprises marginal marine siltstone and contains the bivalve Sanguinolites. The band is correlated with a bivalve-spat phase in the Widmerpool Gulf, and a Lingula band lying within the delta-top Grassington Grit Formation on the south-eastern part of the Askrigg Block. The Cravenoceras gressinghamense Marine Band (E 2a 2α) succeeds the Eumorphoceras ferrimontanum Marine Band (E 2a 2) in the Roeburndale and Sabden Shale formations. At its type locality, along Gressingham Beck, Hornby, near Lancaster, it has yielded the new name-bearing ammonoid. It also contains the lowest appearance of Selenimyalina variabilis (Hind) and is characterized by the presence of Posidonia lamellosa (de Koninck). In the Widmerpool Gulf, the band is represented by the Posidonia phase at two stratigraphical levels. The Saleswheel Marine Band (E 2a 2β) lies between the C. gressinghamense and Eumorphoceras yatesae (E2 a 3) marine bands. Its type locality is in the lower part of the Sabden Shale Formation at Ribchester, near Blackburn, where it contains Anthracoceras. The marine band thickens dramatically towards the Lancaster district into siltstone beds of the Close Hill Siltstone Member containing a Sanguinolites -dominated faunal phase. In the Widmerpool Gulf it is represented by a Lingula band. The dramatic thickness and facies changes of early Namurian marine bands across the Central Pennine Basin and on to the Askrigg Block appear to be controlled primarily by proximity to sediment supply, availability of accommodation space, and the duration, rate and amplitude of glacio-eustatic marine flooding events. A regional non-sequence is developed at the base of the Ward’s Stone Sandstone (and equivalents), associated with marked tectonic discordance. This boundary, together with the newly resolved marine band stratigraphy, necessitates lithostratigraphical revision and re-correlation of early Namurian sandstones in the northern part of the Central Pennine Basin and the Askrigg Block. One new species, Cravenoceras gressinghamense sp. nov., is described.
This Sheet Description describes the Quaternary and solid geology of the Abu Dhabi 1:100 000 scale geological map. The Abu Dhabi district covers 3620 km2 along the Arabian Gulf coast including the northern part of Saadiyat island, Abu Dhabi, part of the Mussafah district and many of the islands to the west. These include Futaisi, Bu Kesheishah, Halat al Bharaini, Al Dabiya, Bu Qumah, Bu Shara, Al Qanatir and Al Rafiq. The sheet also includes a significant part of the coastal plain southwest of Abu Dhabi between Shunayyin in the east to Borquat al Rashid in the west, and south to Maharqah, across which the main E11 coastal highway runs. In the southeast of the district, an area of higher ground is formed of Miocene rocks draped by a variable sequence of cemented and unconsolidated dune sand. The region hosts several major oilfields including the Rumaitha, Shanayel, Al Dabb’iya, Umm al Dalkh, Al Mutarib and Umm al Lulu fields.
The region is dominated by a series of offshore islands, part of a chain of barrier islands that extend from north of Abu Dhabi to Marawah Island, west of the present area. These islands, along with the sea-ward margin of the coastal plain are mostly comprised of a thin sequence of intensively studied Holocene marine carbonates termed the Abu Dhabi Formation. These sediments represent a transgressive-regressive sequence, and form the classic carbonate-evaporitic ‘sabkhas’ for which the region is justly famous. The Abu Dhabi Formation includes a range of marine and supratidal facies including coastal spits, bars and beach ridges, lagoonal muds, algal mats and ooidal tidal deltas deposited over the last 10 000 years. The southern limit of the Holocene transgression is marked by a beach ridge running parallel to the coast and clearly visible on satellite imagery.
The barrier islands commonly have a core of well-cemented Pleistocene carbonate dune sand (Ghayathi Formation) around which the carbonate spits, bars and ridges of the Abu Dhabi Formation were accreted. The islands have been largely deflated down to the local water-table leading to the development of extensive sabkhas. Consequently, the islands are generally flat but punctuated by small Ghayathi Formation mesas and zeugen, forming mushroom-shaped outcrops rising up to 6 m above sea-level, locally capped with marine limestones of the Late Pleistocene Fuwayrit Formation. Offshore to the north of the island, below low water, is the Great Pearl Bank, an area of reefs and coralgal sands named after the former pearling industry in the region.
South of the Holocene beach ridge, much of the onshore area is an extensive, very gently sloping coastal plain, dominated by a deflated planation surface developed on either unconsolidated quartzose aeolian sand or well cemented carbonate grainstones of the Ghayathi Formation. The deflation surface is commonly marked by secondary gypsum forming a sabkha. The Ghayathi Formation palaeodunes are locally well exposed, forming spectacular wind-sculpted mesas and zeugen both on the islands and within the lagoons, but also onshore draping the Miocene rocks in the southeast of the district.
This Sheet Description describes the Quaternary and solid geology of the Tarif 1:100 000 scale geological map. The Tarif district includes the northern coast of the UAE between the outskirts of Mirfa in the west and a point about 23 km west of the settlement of Tarif.
The onshore part of the sheet extends a maximum of about 11.5 km south from the coast and is traversed by the main coastal road. The entire island of Abu Al Abyadh lies within the district, separated from the mainland by up to 5 km of intertidal flats and a narrow, dredged channel about 250 m wide across which a roll-on roll-off ferry provides vehicular access.
The oldest rocks, of Miocene age, crop out in a series of mesas rising above the coastal plain in the south of the district. These consist of the Dam Formation, overlain by the Shuwaihat Formation, which is largely aeolian in origin, and the Baynunah Formation which includes aeolian and fluvial sediments.
The onshore area is a coastal plain dominated by sabkha flats less than 2 m above sea level developed on deflated cemented dune sands of Quaternary age. The northern-most 3–4 kilometres of this flat coastal plane comprise a series of sand sheets forming shallow beach ridges, ‘washover terraces’ and fans with patchy sabkha development. Southwards, the sand sheets pass into an 8–10 kilometre wide zone of low-lying, active sabkha. This zone forms part of a classic, world famous, example of a sabkha and coastal plain and has been extensively studied from both an ecological and geological perspective. In this district much of it has been disturbed by digging and reclamation.
Mesas, generally elongated north-west to south-east because of deflation by the prevailing north westerly Shamal wind, stand up to 25 m above the flats and on the rising ground at the southern limits of the sabkha flats. These are outliers of a former continuous cover of Miocene sand-dominated sequences, including the Shuwaihat and Baynunah formations.
Abu Al Abyadh Island is one of a number of barrier islands that extend from north of Abu Dhabi to Marawah Island, west of the present area. The inlet between the island and the mainland is the eastern part of an open lagoon known as the Khor Al Bazam. In common with other barrier islands, it has a core of Pleistocene aeolian dune sand around which a series of carbonate sand ridges and bars of Holocene age were accreted. These have been deflated in large areas to less than 2 m above sea-level leading to local sabkha development. The island is generally flat but punctuated by small mesas, known locally as zeugen, forming mushroom-shaped outcrops rising up to 4 m and capped with thin marine limestones attributed to the Fuwayrit Formation of late Pleistocene age. Offshore to the north of the island, below low water, is an area of reefs and coral algal sands called the Great Pearl Bank, on account of the former pearling industry in the region.
New sections and detailed mapping of the Pleistocene deposits on the west side of the Malvern Hills show that the area occupied by ice during a pre-Devensian glaciation was greater than previously envisaged. The deposits associated with the glaciation occur in a palaeovalley and comprise lacustrine silts and clays and till. They are considered to be of Anglian age as they are locally overlain non-sequentially by newly described silts of probable late Anglian to early Hoxnian age, the most westerly record of such deposits in southern Britain. Gravels underlying the glacigenic deposits are thought to have been laid down by a southward-flowing river either earlier in the Anglian or during a preceding stage. Deposits formed during two post-Hoxnian episodes of gelifluction are correlated with similar deposits on the east side of the Malvern Hills. The younger gelifluctate is probably late Devensian in age and the older, much dissected deposit is attributable to periglacial processes during an earlier Devensian or Wolstonian cold period.
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