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1.
Ken W. Glennie 《Arabian Journal of Geosciences》2010,3(4):331-349
The Emirate of Abu Dhabi is famed for its coastal carbonate, sabkhas and sand dunes; it is located in the NE part of the Arabian Plate, which formed during the Late Neoproterozoic (~820–750 Ma) by the accretion of island arcs and microcontinents to early Gondwana. Most of Arabia seems to have spent its existence within the Southern Hemisphere until it crossed the Equator during the Mesozoic; parts were involved in four glaciations, two in the Proterozoic (~750–630 Ma—Iceball or Slushball Earth?), and two more in the Palaeozoic (Late Ordovician and Permo-Carboniferous transition). In the early Palaeozoic the Arabian Plate was oriented about 90° counter clockwise relative to today’s poles. Gondwana later skirted the South Pole, migrating to the other side of the planet, eventually emerging the ‘right-way up’ with the Arabian Plate oriented to the poles more or less as seen today. Cold and temperate climate conditions ensured that for much of its early existence, Arabia was the site of mainly quartz-rich deposits. Later in the Neoproterozoic, however, extensive stromatolitic carbonate deposition took the lead, culminating around the Cambro-Precambrian boundary with deposition of the extensive Ara and Hormuz evaporites. Since south Arabia’s Permo-Carboniferous glaciation, the Arabian plate has been drifting northward, crossing temperate climatic zones conducive to fluvial and aeolian sandstone deposition and, from the later Permian, to tropical shallow-marine carbonates and evaporites In parallel with the above, the rifting of Gondwana opened an oceanic trough in the Late Permian off the NE flank of Arabia. Slope carbonates and deepwater Hawasina turbidites with a clear flow to the NE were deposited until they were obducted (together with associated ophiolites) in the Late Cretaceous on the edge of the Arabian plate in Oman and Iran. The deposition of widespread Early Silurian hydrocarbon source rocks in east-central Arabia was followed in the later Permian by extensive reservoir rocks with more during the mid-Late Mesozoic, giving rise to major oilfields both on- and off-shore, including Abu Dhabi. Arabia and Africa began to separate late in the Miocene with the opening of the Red Sea and Gulf of Aden. SSW–NNE compressive stresses caused uplift and volcanic activity in west Saudi Arabia and Yemen. Some products of erosion flowed eastward into Abu Dhabi. At the NE margin of Arabia, the Tethys Ocean narrowed, the NE flank of the newly forming Zagros Mountains of Iran is being subducted beneath southern Asia. To the SE, roughly coeval crustal compression adjacent to the Gulf of Oman led to uplift of the Oman Mountains and deposition of erosional products flanking the mountains mainly to the W and SW. The Oman Mountains are currently rising at about 2 mm/a, while northern Musandam is subsiding into the Strait of Hormuz at some 6 mm/a in association with subduction of the Arabian plate margin below the Eurasian plate. Alternations between polar glaciations and interglacials over the past few 100 ka resulted in considerable climatic changes over Arabia; slow glacial build-ups lasting some 80 to 120 ka led, somewhat erratically, to a fall in sea level of up to 130 m, to strong winds and the building of systems of extensive sand dunes such as the Rub’ al Khali. The joint Tigris–Euphrates river system flowed through a desert landscape, reaching the ocean only SE of the Strait of Hormuz. The peak of the last glaciation about 21 ka was followed by its rapid collapse and flooding of the Arabian Gulf to its present level between about 12 or 10 and 6 ka, a horizontal marine advance of some 200–300 m/a. Abu Dhabi is now the site of shallow-marine carbonates offshore and classical sabkhas and carbonate-rich sand dunes onshore. 相似文献
2.
Ellen Stolle 《Geological Journal》2016,51(2):223-235
The palynological record from the Permian part of the Çakraz Formation from the Çamdağ area of NW Turkey has been investigated in order to obtain a more precise age assessment than achieved in previous studies. The ‘Late Permian’ age and a possible age range beginning in the Roadian (mid Permian) were discussed before for sections of palynomorph‐bearing strata occurring within the formation. These deposits are now assigned to the late Cisuralian/Guadalupian and considered to be not older than early Kungurian, and not younger than Capitanian. The new age assessment was conducted via a long‐distance, intercontinental palynostratigraphic correlation from NW Turkey to South America, where results of radiometric datings were linked to some siliciclastic sections by absolute ages to the chronostratigraphy. Common conspicuous taxa in pollen‐dominated assemblages from both regions are Lueckisporites and Vittatina such as Lueckisporites virkkiae, L. latisaccus, L. stenotaeniatus, Vittatina corrugata, V. subsaccata and V. wodehousei. These species co‐occur in strata of the northern as well as southern palaeohemisphere settings (NW Turkey and S America). Thus, Lueckisporites latisaccus, L. stenotaeniatus and Vittatina corrugata are, as well as L. virkkiae or V. subsaccata, considered as being cosmopolitan. Due to the more precise palynological dating of part of the Çakraz Formation and surrounding deposits they are here broadly correlated with Permian continental successions from the Southern Alps, Italy, including the Val Daone Conglomerate and the Verrucano Lombardo/Val Gardena Sandstone (Gröden) red beds, and the Rotliegend deposits of Germany. These results support some earlier views regarding the age and stratigraphic equivalences with European deposits. The new age for the Çakraz Formation also supports recent considerations as middle Permian (part Guadalupian), and as Cisuralian for the lower parts of the formation, such as the fossil‐bearing section with plants and tetrapod traces further east in NW Turkey, where the unit also crops out. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
3.
Discovery of a middle Permian ostracod fauna in the marine Khuff Formation (Sultanate of Oman), combined with palaeobotanical data from the immediately underlying continental Gharif Formation, supports new interpretations of the palaeobiogeography of the Tethys during the late Palaeozoic. A mixed ostracod fauna existed on the Arabian platform. This new record of Permian ostracods, combined with recent data obtained in other Tethyan areas, emphasizes the close relationship between the south-western Tethys realm and South China. The macro- and microfloral assemblages of the continental Gharif Formation demonstrate that this palaeoflora represents a true mixed association in which Gondwanan, Cathaysian and Euramerian elements are intermingled. Two main models exist for the reconstruction of Pangaea during the late Palaeozoic. Both ostracods and palaeobotanical evidence favour the reduction of the oceanic area between South China and Arabian plate as in the B Pangaea model favoured by recent palaeomagnetic data. 相似文献
4.
Irfan U. JAN Shahid IQBAL Sarah J. DAVIES Jan A. ZALASIEWICZ Michael H. STEPHENSON Michael WAGREICH Muhammad HANEEF Muhammad HANIF Sajjad AHMAD 《《地质学报》英文版》2017,91(3):1063-1078
The Upper Carboniferous—Lower Permian(Upper Pennsylvanian-Asselian) Tobra Formation is exposed in the Salt and Trans Indus ranges of Pakistan.The formation exhibits an alluvial plain(alluvial fan-piedmont alluvial plain) facies association in the Salt Range and Khisor Range.In addition,a stream flow facies association is restricted to the eastern Salt Range.The alluvial plain facies association is comprised of clast-supported massive conglomerate(Gmc),diamictite(Dm)facies,and massive sandstone(Sm) Hthofacies whereas the stream flow-dominated alluvial plain facies association includes fine-grained sandstone and siltstone(Fss),fining upwards pebbly sandstone(Sf),and massive mudstone(Fm) Hthofacies.The lack of glacial signatures(particularly glacial grooves and striatums) in the deposits in the Tobra Formation,which are,in contrast,present in their timeequivalent and palaeogeographically nearby strata of the Arabian peninsula,e.g.the AI Khlata Formation of Oman and Unayzah B member of the Saudi Arabia,suggests a pro-to periglacial,i.e.glaciofluvial depositional setting for the Tobra Formation.The sedimentology of the Tobra Formation attests that the Salt Range,Pakistan,occupied a palaeogeographic position just beyond the maximum glacial extent during Upper Pennsylvanian-Asselian time. 相似文献
5.
Grant M. Cox Christopher J. Lewis Alan S. Collins Galen P. Halverson Fred Jourdan John Foden David Nettle Fayek Kattan 《Gondwana Research》2012,21(2-3):341-352
The Ad Dawadimi Terrane is an Ediacaran basin of the Arabian Nubian Shield (ANS), Saudi Arabia. This basin terrane is situated in the far eastern part of the ANS and represents the youngest accretion event of the exposed ANS. Therefore, the timing of events within the basin is key to understanding both the closure of the Mozambique Ocean and the amalgamation of Gondwana along the northern East African Orogen. Here we present U/Pb detrital zircon data for the Abt Formation, the principle basin sediments of the Ad Dawadimi Terrane, along with 40Ar/39Ar ages on muscovite and whole rock Sm/Nd data. These data indicate that deep-water deposition in the Abt Basin did not end until after ca. 620 Ma and that deformation and greenschist-facies metamorphism of the Abt Formation occurred at 620 ± 3 (2σ) Ma along an active margin. This is the youngest terrane amalgamation event reported so far in the Arabian–Nubian Shield, but we suggest even younger sutures lie further east beneath the Phanerozoic cover of eastern Saudi Arabia. Our results suggest that the Ediacaran basins of the eastern ANS were not part of the Huqf basin in Oman, which was instead part of a passive margin of Neoproterozoic India, separated from the active margin of Africa by the Mozambique Ocean that probably did not close until the late Ediacaran or early Cambrian. 相似文献
6.
Ahmad Masri 《Arabian Journal of Geosciences》2017,10(13):288
Four recently discovered glacio-fluvial paleovalleys in southeast Jordan and northwest Saudi Arabia are described for the first time. The paleovalleys formed as a result of glacial erosion by series of sub-parallel valley glaciers during the Late Ordovician (Hirnantian) southern hemisphere glaciation on the Arabian Plate. The southwest-northeast orientation of the paleovalleys, Proterozoic erratic clasts and paleocurrent vectors indicate the advance of glaciers and subsequent glacio-fluvial siliciclastics emanating from a paleo-ice sheet located to the south on the Arabian Shield. U-shaped, paleovalley cross-sectional morphologies and gently inclined longitudinal profiles indicate initial glacial erosion of the ‘finger-like’ paleovalleys, probably as wet-based valley glaciers, eroded up to 250 m depth into Late Ordovician marine bedrock formations. Paleovalley-fill sequences comprise a tripartite upwards succession: (a) basal sandstone-dominated tillite with well-rounded, grooved and striated granitoid and metamorphic basement clasts derived from the Proterozoic Arabian Shield together with locally derived, rounded and elongate boulders eroded from the local bedrock at the margins of the paleovalleys (Retrogradational Lowstand Sequence); (b) green chloritic siltstone (Zarqa Formation) deposited during a progradational sea-level rise with marine influence (Transgressive Sequence); (c) coarse-grained, trough cross-bedded sandstone (Sarah Formation) attributed to progradational fluvial sedimentation as glacial outwash. Rapid sea-level rise during latest Hirnantian to Early Llandovery time resulted in marine flooding of the glacio-fluvial alluvial plain and deposition of organic-rich mudstones representing transgressive and high-stand sequences. 相似文献
7.
《Proceedings of the Geologists' Association. Geologists' Association》2022,133(2):154-161
Crinoidal debris is common from the basal parts of the open marine Khuff Formation in Oman; yet, little is known about the diversity and affinities of this fauna. Exallocrinus khuffensis n. gen., n. sp. is described from this unit, and is the first crinoid crown from outcrops of the Wordian, Lower Khuff Member, in the northern Huqf region of Oman. This new crinoid is among the youngest Paleozoic crinoids known, yet it has a combination of more stemward and crownward characters. Because of the uncertainties concerning the latest Paleozoic and earliest Mesozoic crinoid phylogeny, Exallocrinus n. gen. is questionably assigned to the Ampelocrinidae. 相似文献
8.
L. J. Phillips J. L. Crowley D. J. Mantle J. S. Esterle R. S. Nicoll J. L. McKellar 《Australian Journal of Earth Sciences》2018,65(2):153-173
This study presents the first chemical abrasion-isotope dilution thermal ionisation mass spectrometry (CA-IDTIMS) U–Pb zircon ages from tuffs in Lopingian (upper Permian) strata of the Galilee Basin, Queensland and reassigns the B coal-seam to the ‘Burngrove Formation equivalent.’ Five Lopingian tuffs were dated: four from the CRD Montani-1 drill hole including three from the ‘Fair Hill Formation equivalent’ (255.13 ± 0.09, 254.41 ± 0.07 and 254.32 ± 0.10 Ma) and one from the ‘Burngrove Formation equivalent’ (252.81 ± 0.07 Ma, approximately the age of the Yarrabee Tuff in the adjacent Bowen Basin); and a single tuff from the Black Alley Shale in the GSQ Tambo-1-1A drill hole (254.09 ± 0.06 Ma). In the Galilee Basin, all three units are constituents of the Betts Creek Group, here formally elevated in nomenclatural status from the Betts Creek beds. On the western margin of the basin, the group thins, and the ‘J and K’ seams (formerly known as the Crossmore and Glenaras sequences, respectively) in the GSQ Muttaburra-1 drill hole have been interpreted through palynology as Cisuralian–early Guadalupian (spore-pollen assemblage APP3.2). This corroborates the exclusion of the ‘J and K’ seams from the overlying Lopingian Betts Creek Group (spore-pollen assemblage APP5), and the underlying lower to mid-Cisuralian Aramac Coal Measures (spore-pollen assemblage APP2.2), which represent the uppermost unit of the Joe Joe Group. It is proposed that the ‘J and K’ seams are restricted to a depocentre in the Hulton–Rand structure. The recognition of these strata containing APP3.2 spore-pollen assemblages suggests that the mid-Permian hiatus is locally reduced to 12–13 My from 30 Ma (where the ‘J and K’ seams are absent). The results of the radiometric dating and palynological analysis in the Galilee Basin support the proposed, albeit informal stratigraphy, that is given in terms of equivalents of formational units in the Bowen Basin and on the intervening Springsure Shelf. 相似文献
9.
The Late Permian–early Middle Triassic strata of the northern West Qinling area, northeastern Tibetan Plateau, are composed of sediment gravity flow deposits. Detailed sedimentary facies analysis indicates these strata were deposited in three successive deep-marine environments. The Late Permian–early Early Triassic strata of the Maomaolong Formation and the lowest part of the Longwuhe Formation define a NW–SE trending proximal slope environment. Facies of the Early Triassic strata composing the middle and upper Longwuhe Formation are consistent with deposition in a base-of-slope apron environment, whereas facies of the Middle Triassic Anisian age Gulangdi Formation are more closely associated with a base-of-slope fan depositional environment. The lithofacies and the spatial–temporal changes in paleocurrent data from these strata suggest the opening of a continental margin back-arc basin system during Late Permian to early Middle Triassic time in the northern West Qinling. U–Pb zircon ages for geochemically varied igneous rocks with diabasic through granitic compositions intruded into these deep-marine strata range from 250 to 234 Ma. These observations are consistent with extensional back-arc basin development and rifting between the Permian–Triassic Eastern Kunlun arc and North China block during the continent–continent collision and underthrusting of the South China block northward beneath the Qinling terrane of the North China block. Deep-marine sedimentation ended in the northern West Qinling by the Middle Triassic Ladinian age, but started in the southern West Qinling and Songpan-Ganzi to the south. We attribute these observations to southward directed rollback of Paleo-Tethys oceanic lithosphere, continued attenuation of the West Qinling on the upper plate, local post-rift isostatic compensation in the northern West Qinling area, and continued opening of a back-arc basin in the southern West Qinling and Songpan-Ganzi. Rollback and back-arc basin development during Late Permian to early Middle Triassic time in the West Qinling area explains: the truncated map pattern of the Eastern Kunlun arc, the age difference of deep-marine sediment gravity flow deposits between the Late Permian–early Middle Triassic northern West Qinling and the late Middle Triassic–Late Triassic southern West Qinling and Songpan-Ganzi, and the discontinuous trace of ophiolitic rocks associated with the Anyemaqen-Kunlun suture. 相似文献
10.
Sand and dust storms are causing hazards and problems in aviation as well as the dangers and distresses they cause on living things. The low meteorological visibility, the presence of strong winds with gust, and the transport of dust and sand particles by the wind are dangerous on landing and departure of aircrafts, and even on planes that are parked. The main aim of the study is to examine the meteorological conditions causing the dust storm that took place in the Arabian Peninsula on February 28, 2009, and to determine the source of dust caused dust storm, sand storm, blown sand, and blown dust at the airports. Within the scope of the study, aviation routine weather report (METAR) and aviation selected special weather report (SPECI) reports have been assessed at many airports over Arabian Peninsula (AP), the northern part of the AP and North Africa. As model outputs; NCEP–DOE Reanalysis 2 data, BSC–DREAM8B, and HYSPLIT model were used. In the satellite images; METEOSAT MSG dust RGB images, MODIS, and Kalpana-1 data were used. According to obtained results, dust storms were detected in Bahrain, Kuwait, Saudi Arabia, and United Arab Emirates (UAE). At Al-Ahsa Airport in Saudi Arabia, the lowest visibility measured on February 28, 2009, dropping to 200 m, which was dominated by blowing sand. The source region of the dust observed at Dubai Airport in UAE is the eastern regions of the Rub’al Khali Desert located between Saudi Arabia, Oman, and UAE. 相似文献
11.
Al-Mutairi Abdulaziz N. Galmed Mahmoud A. Aldamegh Khaled S. 《Arabian Journal of Geosciences》2015,8(4):2327-2339
Arabian Journal of Geosciences - The bauxite ore deposits are mainly found around the Az Zabirah area in the central northern part of Saudi Arabia. The age of the Az Zabirah bauxites was suggested... 相似文献
12.
《Sedimentology》2018,65(3):851-876
The Sarah Formation is a glaciogenic sedimentary unit deposited along the Gondwana margin during the latest Ordovician ice age and represents a major hydrocarbon reservoir in northern Saudi Arabia. Large‐scale glacial palaeo‐valleys cut into the Qasim Formation and were infilled by the Sarah Formation. Post‐glacial transgression in the earliest Silurian resulted in the deposition of the Qusaiba Shale Member and associated organic‐rich basal source rocks, which cap the Sarah Formation infilled palaeo‐valleys. This unique setting makes the Sarah Formation an important emerging exploration target in Saudi Arabia. This study focuses on the facies and depositional architecture in seismic‐scale outcrops of the Sarah Formation in north‐western Saudi Arabia. The Rahal Dhab palaeo‐valley provides a 100 km long dip‐oriented cross‐section which has been covered by 24 vertical sections, sedimentary architectural analyses at metre to kilometre scale and by three cored shallow boreholes. In the Rahal Dhab palaeo‐valley, the Sarah Formation was deposited in a proglacial setting that ranged from marginal marine to offshore prodelta and is made up of three units: (i) the Sarah Sandstone; (ii) the Sarah Shale; and (iii) the Uqlah Member. This study shows the relationships between these three units and architectural controls on reservoir quality in this system. This paper contributes to the regional understanding of the Sarah Formation, and the new depositional model of the Rahal Dhab palaeo‐valley provides an outcrop‐reservoir analogue for hydrocarbon exploration in adjacent areas. 相似文献
13.
14.
吉林延边地区早二叠世一个新的陆相地层单位 总被引：1，自引：0，他引：1
根据吉林省延边地区汪清县大兴沟镇和盛村附近含早二叠世华夏植物群陆相地层的发育特征,结合前人对延边地区石炭纪—二叠纪地层研究成果,提出一个新的岩石地层单位——和盛组,用来代表延边地区晚石炭世—早二叠世山秀岭组海相碳酸盐岩沉积和早—中二叠世大蒜沟组海相碳酸盐岩及碎屑岩沉积之间的一套陆相碎屑岩沉积,其时限为早二叠世晚期(亚丁斯克—空谷早期)。和盛组层型剖面为吉林省延边地区汪清县大兴沟镇和盛村剖面,厚230m,主要由灰色、灰黑色砾岩、含砾砂岩、粉砂岩及粉砂质泥岩为主的陆相沉积组成,与下伏地层山秀岭组假整合接触,与上覆大蒜沟组整合接触。和盛组与上覆大蒜沟组构成华北板块北缘早—中二叠世一个海进地层序列。和盛组的建立为探讨华北板块与佳蒙地块的分界、研究西拉木伦河—延吉缝合带在延边地区的东延提供了重要的地层证据。 相似文献
15.
Although evidence for Quaternary environmental changes in the Arabian Peninsula is now growing, research has mostly been conducted in the United Arab Emirates (UAE) and in the Sultanate of Oman. There have been virtually no recent studies in Saudi Arabia, especially in the central region such as around Al‐Quwaiayh. In this area there are a series of outwash plains developed along the eastern edge of the Arabian Shield that formed in the late Quaternary. Four sedimentary sections, which are representative of the deposits that have accumulated, have been studied and five luminescence ages obtained. These are the first luminescence ages acquired from Quaternary sediments in central Saudi Arabia. The preserved fluvial deposits in the study area have formed during humid events at ca. 54 ka, ca. 39 ka and ca. 0.8 ka. In more recent times aeolian sands have been encroaching on to the distal parts of the outwash plains. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
16.
Mohammad Eesa Al-Dabbagh 《Arabian Journal of Geosciences》2013,6(3):835-843
Paleozoic successions in Saudi Arabia are exposed around and bordering the south, north, and northeastern edge of the Arabian shield. They are represented by the Wajid group in the south and by the Taymah, Tabuk, Qalibah, Huj, and Buraydah groups in the north and northeast. The Wajid group includes Dibsiyah, Sanamah, Khusayyan, and Juwayl formations. The Taymah group includes Siq, Amai’er, Quweira, Saq, and Qasim formations. The Tabuk group includes Zarqa, Sara, and Hawban formations. The Qalibah group includes Baq’a, Qusaiba, and Sharawra formations. The Huj group includes Tawil, Jauf, and Jubah formations. The Buraydah group includes Berwath, Unayzah, and Khuff formations. The Wajid group form one block in the south and the other groups form another block in the north, and they can be correlated. There are similarities between the northern belt which consists of the Cambro-Ordovician formations of the Tayma and Tabuk groups and the southern belt which consists of the Dibsiyah and Sanama formations of the Wajid group. Similarities include sandstone composition, sedimentary environment, paleocurrent directions, unconformities, tectonic events, and influence of Gondwana glaciations. These formations and probably some or all the rest of the Paleozoic formations used to form one block but later separated after erosion caused by gradual tectonic growth, uplift, and prominence of the Arabian shield. During early Paleozoic time, the process started by poststabilization then sedimentation and at a later stage the growth and uplift of the shield occurred gradually. Growth of shields is a fact and it is the only way to explain the exposure of the Wajid sandstone on top of the highest mountain of the shield which exceeds 3,000 m in As Sawdah in Asir area in southwestern Saudi Arabia. The sandstone sediments of these outcrops were deposited on a low lying basin before been raised to this elevation. 相似文献
17.
Ercan Özcan İftikhar Ahmed Abbasi Katica Drobne Abiraman Govindan Luigi Jovane Kamel Boukhalfa 《Geodinamica Acta》2016,28(3):160-184
The upper member of the Jafnayn Formation in Wadi Rusayl and Al Khoud, Seeb Area in north Oman contains Nemkovella stockari Less & Özcan, 2007, an Early Eocene orthophragminid recorded here for the first time from the Arabian Peninsula. N. stockari, the only orthophragminid identified in Jafnayn Formation, is quite distinct from any other species from Tethys in having spiral and orbitoidiform chambers around the isolepidine embryon developed before the onset of annular chambers. The Oman specimens exhibit equal-sized principal auxiliary chambers and symmetrical spirals and are assigned to N. stockari bejaensis Özcan, Boukhalfa & Scheibner, 2014, an advanced form of the N. stockari lineage. The associated alveolinids, revised in this study, rotaliids and other age-diagnostic foraminiferal taxa in the transgressive basal part of the upper member have enabled us to revise the age as middle Ilerdian (Early Eocene), assignable to SBZ 7/8 and 8; OZ 3/4. Integrating a new record of this species from Arabian Plate margin in Belen, S Turkey, and previous records from north Africa, N. stockari appears to be a diagnostic marker for the Early Eocene along the southern peri-Tethys platforms, facilitating the Tethyan correlation by orthophragminids. The palaeobiogeographic distribution of N. stockari is discussed. 相似文献
18.
In Al Qasim Province, Saudi Arabia, calcareous pedogenic duricrust overlies the Upper Permian carbonates and clays of the Khuff Formation, and ranges in thickness from 60 cm to 2 m. It consists of white sandy duricrust capped by brown, nodular porous duricrust. Petrographic investigation led to recognition of three lithofacies that show spatial distribution: 1- structureless sandy calcareous mudstone, 2- brecciated-nodular calcareous mudstone, and 3- pisolitic calcareous mudstone. The diagenetic changes in duricrust are aggrading neomorphism and formation of calcite rims around quartz grains. Microprobe chemical analysis was performed on the diagenetically altered material. The development of the duricrust is controlled by four factors: the climate changes, the type of underlying rocks, source of carbonate and biological effects. The repeated changes from semi-arid climate with alternating wet and dry seasons are the main controlling factor, in generation of duricrust development. During humid periods, descending water carries the dissolved carbonates downward as bicarbonates, whereas dry and interpluvial period, the carbonate-rich solutions are carried upwards by capillary or evaporation. The claystone and sandstone interbeds possibly affect the development of calcareous duricrust, more than the sandstones and dolostones, because the former have the ability to attach calcium carbonate to form the duricrust. The development of calcareous duricrust is mainly attributed to the Pleistocene and Early Holocene alternating humid and arid periods that prevailed over the Arabian Peninsula during this time. 相似文献
19.
内蒙古苏尼特左旗地区二叠纪地层的划分与对比 总被引：5，自引：0，他引：5
本文讨论了内蒙古苏尼特左旗地区二叠纪地层单元的划分及其接触关系，认为本区二叠纪地层应包含大石寨组与哲斯组，缺失晚二叠世沉积；描述了代表本区地层序列演化的典型剖面，并对各单位在区域上的延伸及其对比关系进行了简述，认为本区二在纪地层的区域对比应以火山事件沉积为主线，以地层序列演化及生物化石为标志，而不应以岩性相及厚度为主要依据；根据区域地层序列演化分析，认为大石寨组与哲斯组之间的不整合是本区构造事件的代表性界面。 相似文献
20.
在雅鲁藏布江南带分区蹬岗组之上新发现硅质岩与玄武岩两套地层,分别新建为郭雅拉组和盐多组,时代为始新世;在北带分区嘎学组之下发现一套砂岩、页岩的韵律层,新建为桑果组;建立了仲巴分区泥盆纪系马攸木群,分上、中、下3个组和4个岩性;对石炭纪地层新命名为康拓组和拉沙组;将下二叠统变质玄武岩命名为才巴弄组;将原划冈仁波齐组中下部与沃马组下部地层新命名为旦增竹康组,时代为中新世,其上部地层仍为沃马组,时代为上新世,两组合称岗仁波齐群。进一步证实了雅鲁藏布江缝合带具两带夹一微陆的特点,南带在中侏罗世发生过双向俯冲事件。对蛇绿岩、混杂岩进行详细划分。 相似文献