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1.
Kapesa Lokho D. S. N. Raju R. J. Azmi 《Journal of the Geological Society of India》2011,77(3):252-260
Planktic and benthic foraminifera including uvigerinids are documented from the Upper Bhuban Formation, exposed at Thingdawl
village, Kolasib district, Mizoram. The foraminiferal assemblage is poorly preserved and consists of index fossils useful
for precise biochronology and interpretation of the depositional environment. A total of ten benthic and six planktic foraminiferal
species are described. Six species belong to the genus Uvigerina, four to Ammonia, one species each of Globorotalia, Globigerinoides, Clavatorella, Praeorbulina and two species of the genus Orbulina. Based on lithological and foraminiferal assemblage, middle neritic to upper part of outer neritic paleobathymetry is inferred
for the deposition of this part of the Upper Bhuban Formation. The foraminiferal assemblage suggests late Early Miocene to
early Middle Miocene, (∼16 Ma) equivalent to planktic foraminiferal zones N8-N9 for the Upper Bhuban Formation. 相似文献
2.
An ichnofossil assemblage is preserved in sediments of the Middle Bhuban Formation,Surma Group,of Miocene age from the Durtlang and Chanmari sections,Aizawl district,Mizoram,northeastern India.The studied sections comprise a thick,bioturbated and thinly bedded sandstone–silty shale facies.The preserved ichnofossils show high density and low diversity with the assemblage represented by feeding and resting traces,i.e.,Psilonichnus upsilon Frey et al.,1984,Ophiomorpha isp.,Teichichnus spiralis Mikulá.1990,Skolithos isp.,Palaeophycus isp.,and other horizontal burrows.Sedimentary structures associated with these traces are mainly cross bedding,flaser bedding and slump structures.Considering the distribution of the Psilonichnus ichnogenus across an integrated ichnological–sedimentological framework,the stratigraphic interval of the Middle Bhuban Formation,in which they occur,are interpreted to have been deposited under a shallow,marginal-marine channel complex dominated by tidal channels developed in quiet,brackish-water portions of a delta plain. 相似文献
3.
S.J. Gallagher C.V. MacDermot I.D. Somerville M. Pracht A.G. Sleeman 《Geological Journal》2006,41(1):61-91
The Burren region in western Ireland contains an almost continuous record of Viséan (Middle Mississippian) carbonate deposition extending from Chadian to Brigantian times, represented by three formations: the Chadian to Holkerian Tubber Formation, the Asbian Burren Formation and the Brigantian Slievenaglasha Formation. The upper Viséan (Holkerian–Brigantian) platform carbonate succession of the Burren can be subdivided into six distinct depositional units outlined below. (1) An Holkerian to lower Asbian unit of skeletal peloidal and bryozoan bedded limestone. (2) Lower Asbian unit of massive light grey Koninckopora‐rich limestone, representing a shallower marine facies. (3) Upper Asbian terraced limestone unit with minor shallowing‐upward cycles of poorly bedded Kamaenella‐rich limestone with shell bands and palaeokarst features. This unit is very similar to other cyclic sequences of late Asbian age in southern Ireland and western Europe, suggesting a glacio‐eustatic origin for this fourth‐order cyclicity. (4) Lower Brigantian unit with cyclic alternations of crinoidal/bryozoan limestone and peloidal limestone with coral thickets. These cycles lack evidence of subaerial exposure. (5) Lower Brigantian bedded cherty dark grey limestone unit, deposited during the maximum transgressive phase of the Brigantian. (6) Lower to upper Brigantian unit mostly comprising cyclic bryozoan/crinoidal cherty limestone. In most areas this youngest unit is truncated and unconformably overlain by Serpukhovian siliciclastic rocks. Deepening enhanced by platform‐wide subsidence strongly influenced later Brigantian cycle development in Ireland, but localized rapid shallowing led to emergence at the end of the Brigantian. A Cf5 Zone (Holkerian) assemblage of microfossils is recorded from the Tubber Formation at Black Head, but in the Ballard Bridge section the top of the formation has Cf6 Zone (Asbian) foraminiferans. A typical upper Asbian Rugose Coral Assemblage G near the top of the Burren Formation is replaced by a lower Brigantian Rugose Coral Assemblage H in the Slievenaglasha Formation. A similar change in the foraminiferans and calcareous algae at this Asbian–Brigantian formation boundary is recognized by the presence of upper Asbian Cf6γ Subzone taxa in the Burren Formation including Cribrostomum lecomptei, Koskinobigenerina sp., Bradyina rotula and Howchinia bradyana, and in the Slievenaglasha Formation abundant Asteroarchaediscus spp., Neoarchaediscus spp. and Fasciella crustosa of the Brigantian Cf6δ Subzone. The uppermost beds of the Slievenaglasha Formation contain a rare and unusual foraminiferal assemblage containing evolved archaediscids close to tenuis stage indicating a late Brigantian age. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
4.
5.
《Journal of African Earth Sciences》2000,30(3):535-553
Sediments of the Upper Carboniferous to Lower Jurassic Karoo Supergroup (∼ 4.5 km thick) were deposited in the mid-Zambezi Valley Basin, southern Zambia. The Upper Palæozoic Lower Karoo Group in this area ends with a Late Permian sedimentary unit called the Madumabisa Mudstone Formation. The formation is 700 m thick and comprises four lithofacies grouped into two facies assemblages, collectively interpreted as lacustrine deposits. Sediments of a massive mudrock facies assemblage were deposited from suspension, probably from sediment-laden rivers entering a lake. Concretionary calcilutite beds probably mark the positions of palæosediment-water interfaces where calcite was precipitated. A laminated mudrock facies assemblage is attributed to lacustrine deposition from inflowing rivers at the lake margins and shallow parts of the lake. Repeated thickening-upward cycles are evidence of upward shallowing, interrupted by events of more abrupt deepening. Sandstone interbeds are interpreted as fluvial deposits laid down during low lake stands, with cross-lamination and asymmetrical ripples indicating current rather than wave deposition. A fossil assemblage of ostracods, bivalves, gastropods, fish scales, the alga Botryococcus sp. and fossil burrows is consistent with a lacustrine origin for the formation. 相似文献
6.
Radiometric and palynological data of the Upper Oligocene–Lower Miocene Soma Formation from the Kalk?m-Gönen Basin yield new results related to age and palynological contents. In this study, Upper Oligocene strata from the Dani?ment and Linfa areas and Lower Miocene strata from the Bengiler area were sampled palynologically and for radiometric dating. The Dani?ment assemblage, which is older than the Linfa assemblages, mainly contains coniferous and evergreen to deciduous mixed mesophytic forest elements. Relatively high quantities of the altitudinal plants Picea and Abies, indicate a cooler palaeoclimate. The Linfa associations mainly include coniferous and riparian elements. Pollen of the riparian plant Alnus and Taxodiaceae indicative for the swamp forest community was predominant, probably as a result of a high lake level. There is a hiatus during the Oligocene–Miocene transition, probably showing a non-depositional phase and sea-level fall indicating the Mi-1 glaciation event. Higher in the sequence, the Aquitanian Bengiler sediments include high amounts of coniferous forest elements as well as components indicative for the evergreen and deciduous mesophytic forest and also riparian forest and swamp forest. Due to presence of thermophilous taxa Reveesia, Mastixiaceae and Arecaceae, a warm and humid palaeoclimate is inferred according to quantitative analyses using the Coexistence Approach. 相似文献
7.
David W. Haig Eujay W. McCartain Myra Keep Logan Barber 《Journal of Asian Earth Sciences》2008,33(5-6):366-378
The Cablac Limestone, widely recorded in Timor, has its type area on Cablac Mountain where it was regarded as a Lower Miocene shallow-marine carbonate-platform succession. The Bahaman-like facies placed in the Cablac Limestone are now known to belong to the Upper Triassic–Lower Jurassic rather than the Lower Miocene. On the northern slopes of Cablac Mountain, a crush breccia, formerly regarded as the basal conglomerate of the formation, is now considered to have developed along a high-angle fault separating Banda Terrane units of Asian affinity from an overthrust limestone stack containing units belonging to the Gondwana and Australian-Margin Megasequences. The Cablac breccia includes rock fragments that were probably derived locally from these tectonostratigraphic units after terrane emplacement and overthrusting. Clasts include peloid and oolitic limestones of the Upper Triassic–Lower Jurassic derived from the Gondwana Megasequence, deep-water carbonate pelagites of the Cretaceous and Paleogene derived from the Australian-Margin Megasequence, Upper Oligocene–Lower Miocene (Te Letter Stage) shallow-water limestone derived from the Banda Terrane, and a younger Neogene calcarenite containing clasts of mixed tectonostratigraphic affinity. There is no evidence for significant sedimentary or tectonic transport of clasts that form the breccia. The clast types and the present understanding of the geological history of Timor suggest that the crush breccia formed late in the Plio-Pleistocene uplift history of Timor. It is not the basal conglomerate of the Cablac Limestone. However, the clasts of an Upper Oligocene–Lower Miocene limestone found in the breccia suggest that a shallow-marine limestone unit of this age either outcrops in the region and has not been detected in the field, or has been eroded completely during late Neogene uplift. The clasts are similar in age and lithology to an Upper Oligocene–Lower Miocene formation that unconformably overlies a metamorphic complex in the Booi region of West Timor, similar to the Lolotoi Metamorphic Complex (Banda Terrane) that is juxtaposed against the crush breccia of Cablac Mountain. The Cablac Limestone at its type area includes a mixed assemblage of carbonate rock units ranging in age from Triassic to Plio-Pleistocene and representing diverse facies. As a formation, the name “Cablac Limestone” should be discarded for a Cenozoic unit. The Upper Oligocene–Lower Miocene shallow-water limestone unit that is typified by outcrops in the Booi region of West Timor, and that has contributed to clasts in the Cablac breccia, is informally named the Booi limestone. It is considered part of the allochthonous Banda Terrane of Asian affinity and represents the only shallow-marine Lower Miocene unit known from Timor. The only other Miocene sedimentary unit known from Timor includes carbonate pelagites – designated the Kolbano beds – probably deposited on an Australian continental terrace at water depths between 1000 and 3000 m. On the northeastern edge of Cablac Mountain, oolitic limestone and associated units of the Gondwana Megasequence, the Kolbano beds of the Australian-Margin Megasequence, and the Booi limestone and associated metasediments of the Banda Terrane were juxtaposed by a Plio-Pleistocene high-angle fault along which the Cablac crush breccia formed. 相似文献
8.
The Upper Gypsum unit of the Caltanissetta Basin (Sicily) records the last phase of the Messinian salinity crisis comprising the so‐called ‘Lago Mare’ event. A new facies analysis study recognizes nine to ten depositional cycles consisting of seven rhythmically interbedded primary gypsum bodies, and two to three sandstone bodies separated by marly terrigenous horizons showing laterally persistent vertical organization. A basal thin gypsum bed is overlain by a cluster of five thicker gypsum bodies. A marly interval containing two distinct sandstone horizons separates this cluster from the overlying uppermost (seventh) gypsum body. The terrigenous Arenazzolo Formation, in turn followed by the lower Pliocene Trubi Formation, is considered here to form the uppermost part of the Upper Gypsum unit. The rhythmic alternation in the sandy marls and gypsum/sandstone bodies records the response of sediments from shelfal to deltaic systems to precession‐driven arid‐wet climate fluctuations causing cyclical changes of both base‐level and water concentration. During wet climate phases (at insolation maxima) marl and sandstone were deposited in a hypohaline environment as suggested by: (i) the typical Lago Mare faunal assemblage and (ii) the negative δ18O values. During arid phases (at insolation minima) the reduced meteoric supply, recorded by higher δ18O values in the carbonate, caused the development of a negative hydrological budget leading to evaporite precipitation. At a basinal scale the Upper Gypsum unit unconformably overlies a mainly clastic evaporite unit containing carbonate breccia (the so‐called ‘Calcare di Base’) and/or clastic gypsum. Towards the basin centres, where the basal contact becomes conformable, a primary gypsum cumulate horizon is present. This layer is interpreted as a possible lateral equivalent of the Halite unit present only in the deepest depocentres. Based on astronomical calibration of the depositional cycles, the Upper Gypsum unit, including the Arenazzolo Formation, spans the interval between 5·33 and 5·53 Ma. This new age calibration allows the deposition of the Halite unit to be dated between 5·6 Ma (top of the Lower Evaporites) and 5·55 Ma (base of the Upper Evaporites) corresponding to isotopic stages TG12 and/or TG14. 相似文献
9.
In Jabalpur area about 18 m to 45 m thick Lameta Formation is stratigraphically divisible into five lithounits namely, Green
Sandstone, Lower Limestone, Mottled Nodular Beds, Upper Limestone and Upper Sandstone. Having differentiated lithofacies constitution
and here grouped as facies associations, these units are intensively burrowed and sparingly fossiliferous. Ichnogenera including
Arenicolites, Calycraterion, Fucusopsis, Laevicyclus, Macanopsis, Ophiomorpha, Paleomeandron, Rhizocorallium, Stipsellus,
Thalassinoides and Zoophycos are recovered from the Lower Limestone, Mottled Nodular Beds and Upper Limestone associations of the Lameta Formation of
Jabalpur area.Among these, Arenicolites, Calycraterion, Laevicyclus, Ophiomorpha, Rhizocorallium, Stipsellus and Thalassinoides belong to mixed Skolithos and Cruziana ichnofacies and indicate sandy backshore to sublittoral condition of deposition. Additionally rhyzocretes, some times chertified,
are also present in different parts of the Lameta Formation. Ichnofacies assemblage supported by sedimentological information
suggests that the Lameta Formation of Jabalpur area was deposited in coastal marine settings where sediments were subaerially
exposed intermittently. 相似文献
10.
A selachian fauna is described for the first time from the Late Cretaceous (Campanian–Maastrichtian) of Senegal. So far, the Campanian Paki Formation has only yielded a single tooth of Rhombodus sp. whereas the Cap de Naze Formation has yielded a more diverse fauna including juvenile Cretalamna cf. Cretalamna biauriculata, Serratolamna serrata, Carcharias cf. Carcharias heathi, ?Carcharias sp., Squalicorax pristodontus, Schizorhiza stromeri, Parapaleobates sp., Rhombodus binkhorsti and Rhombodus andriesi. Teeth of juvenile Cretalamna largely dominate the assemblage. Such an assemblage confirms a Late Maastrichtian age for the unit 3 in the Cap de Naze Formation. The assemblage, although composed of cosmopolitan taxa, is similar to the contemporaneous selachian assemblage from the phosphates of Morocco. 相似文献
11.
《Journal of Asian Earth Sciences》2009,34(5-6):366-378
The Cablac Limestone, widely recorded in Timor, has its type area on Cablac Mountain where it was regarded as a Lower Miocene shallow-marine carbonate-platform succession. The Bahaman-like facies placed in the Cablac Limestone are now known to belong to the Upper Triassic–Lower Jurassic rather than the Lower Miocene. On the northern slopes of Cablac Mountain, a crush breccia, formerly regarded as the basal conglomerate of the formation, is now considered to have developed along a high-angle fault separating Banda Terrane units of Asian affinity from an overthrust limestone stack containing units belonging to the Gondwana and Australian-Margin Megasequences. The Cablac breccia includes rock fragments that were probably derived locally from these tectonostratigraphic units after terrane emplacement and overthrusting. Clasts include peloid and oolitic limestones of the Upper Triassic–Lower Jurassic derived from the Gondwana Megasequence, deep-water carbonate pelagites of the Cretaceous and Paleogene derived from the Australian-Margin Megasequence, Upper Oligocene–Lower Miocene (Te Letter Stage) shallow-water limestone derived from the Banda Terrane, and a younger Neogene calcarenite containing clasts of mixed tectonostratigraphic affinity. There is no evidence for significant sedimentary or tectonic transport of clasts that form the breccia. The clast types and the present understanding of the geological history of Timor suggest that the crush breccia formed late in the Plio-Pleistocene uplift history of Timor. It is not the basal conglomerate of the Cablac Limestone. However, the clasts of an Upper Oligocene–Lower Miocene limestone found in the breccia suggest that a shallow-marine limestone unit of this age either outcrops in the region and has not been detected in the field, or has been eroded completely during late Neogene uplift. The clasts are similar in age and lithology to an Upper Oligocene–Lower Miocene formation that unconformably overlies a metamorphic complex in the Booi region of West Timor, similar to the Lolotoi Metamorphic Complex (Banda Terrane) that is juxtaposed against the crush breccia of Cablac Mountain. The Cablac Limestone at its type area includes a mixed assemblage of carbonate rock units ranging in age from Triassic to Plio-Pleistocene and representing diverse facies. As a formation, the name “Cablac Limestone” should be discarded for a Cenozoic unit. The Upper Oligocene–Lower Miocene shallow-water limestone unit that is typified by outcrops in the Booi region of West Timor, and that has contributed to clasts in the Cablac breccia, is informally named the Booi limestone. It is considered part of the allochthonous Banda Terrane of Asian affinity and represents the only shallow-marine Lower Miocene unit known from Timor. The only other Miocene sedimentary unit known from Timor includes carbonate pelagites – designated the Kolbano beds – probably deposited on an Australian continental terrace at water depths between 1000 and 3000 m. On the northeastern edge of Cablac Mountain, oolitic limestone and associated units of the Gondwana Megasequence, the Kolbano beds of the Australian-Margin Megasequence, and the Booi limestone and associated metasediments of the Banda Terrane were juxtaposed by a Plio-Pleistocene high-angle fault along which the Cablac crush breccia formed. 相似文献
12.
N. Yu. Filippova E. V. Beluzhenko L. A. Golovina 《Stratigraphy and Geological Correlation》2010,18(3):307-330
The initially obtained data characterize organic-walled phytoplankton (dinocysts), nannoplankton, spores, and pollen from
the Upper Argun, Alkun, and Lower Assa deposits of the Fiagdon and Mairamadag sections situated on the southeast of North
Ossetia (North Caucasus) in the Alkun Formation stratotype area. The lithology of the formation is described, and its position
in the Oligocene-Miocene succession is considered. According to the analyzed data on organic-walled phytoplankton from the
Fiagdon and Mairamadag sections, the transitional late Oligocene-early Miocene dinoflora from the top of the Argun Formation
and the lower part of the Alkun Formation is in general of the Miocene aspect. Based on the dinocysts, deposits from the upper
part of the Alkun Formation coupled with the Assa Formation are attributed to the lower Miocene. The entire interval of the
studied deposits corresponds to the acme subzone Def of the Ebu Zone in the Mediterranean dinocyst zonation by D. Zevenboom,
where it spans the top of the Chattian and lower part of the Aquitanian Stage. Nannoplankton assemblages from the Alkun deposits
are tentatively correlated with the nannoplankton assemblage of Zone NN1 in the standard zonation by E. Martini. It is impossible
to date precisely the Alkun Formation based on nannoplankton, as the respective deposits are lacking index species and characteristic
taxa of the standard zonation. The dominance of the cosmopolitan species Cyclicargolithus floridanus is a peculiar feature of nannoplankton assemblages from the Alkun Formation. Palynological data are used to consider the
dynamics of the evolution of the vegetation cover and climate. Four episodes of relative cooling are distinguished against
a background of warm-temperate climatic conditions in general. The most significant episodes occurred in the mid-Alkun time
and during the early phase of the Assa time. 相似文献
13.
西藏申扎和改则地区早石炭世地层及腕足类研究 总被引：1，自引：0，他引：1
西藏申扎和改则地区早石炭世地层发育,腕足类及珊瑚类化石丰富。腕足类化石计有34属45种,共建立3个组合;申扎大塘阶下部巴日阿郎寨组Ovatia-Unispirifer组合;大塘阶上部永珠组Balakhonia-Productus组合;改则大塘阶上部Latiproductus-Striatifera组合。本文系统讨论了各腕足类组合的时代及与国内外同期地层的对比,将西藏境内早石炭世的沉积物及生物群划分为3个类型。根据生物群及沉积物在空间上的分布特点,笔者认为在早石炭世时,班公湖至怒江断裂南北生物群及沉积物具有明显的差异,即南部申扎和珠峰地区生物群及沉积物特征与冈瓦纳大陆相似,而北部改则地区与扬子地台的生物群及沉积物特征相同,其间可能有宽阔的海域隔离。 相似文献
14.
The Sinuiju Formation in Paekto-dong, Sinuiju City in the Democratic People's Republic of Korea has yielded Mesozoic nonmarine bivalve fossils, which is the first occurrence of such in the DPRK. Based on these fossil specimens, a new Cretaceous bivalve assemblage, the Arguniella yanshanensis-Sphaerium anderssoni Assemblage is erected. This assemblage includes Arguniella yanshanensis, A. lingyuanensis and Sphaerium anderssoni and can be compared with the Jehol Biota. The age of the Sinuiju Formation is also clarified and on the basis of the bivalves and the presence of a Eosestheria–Ephemeropsis–Lycoptera(E–E–L) assemblage, the formation is not Upper Jurassic, but Lower Cretaceous in age. 相似文献
15.
A new species of cladid(?) crinoid, Segmentocolumnus (col.) clarksoni, based on distinctive, disarticulated stem material, is described from the Upper Llandovery Kilbride Formation. Hitherto, this unit has yielded two taxa based on single, nearly complete crinoids. In contrast, S. (col.) clarksoni is known from numerous specimens, including common long pentagonal, pentameric, heteromorphic pluricolumnals with symplectial articulations, broad pentagonal lumina and narrow claustra. A related morphospecies is known from the Ashgill (Upper Ordovician) of Ireland. The fossil echinoderms of the Llandovery (Lower Silurian) are poorly known globally. Where present in this interval, echinoderms are more commonly preserved as disarticulated ossicles and rarely as complete specimens. Complete crinoids have now been identified from nine horizons in the Llandovery of the British Isles, making this one of the better known pelmatozoan faunas from this time interval. However, only two of these occurrences have yielded as many as five or more identifiable taxa. Seven of the nine occurrences are Upper Llandovery (Telychian). Genera are typical of the Silurian or (Upper Ordovician + Silurian); the only remnant Ashgill taxon that did not survive the Llandovery was the morphogenus Segmentocolumnus (col.) Donovan, an ‘extinction’ that probably owes more to taxonomic method than any evolutionary pattern. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
16.
陕西岐山产Eumorphotis的“石千峰组”地层问题 总被引：3，自引：0，他引：3
<正> “石千峰群”的问题,是涉及华北及其相邻广大地区陆相二—三叠系划分、对比及界线的重大地层课题,自下而上分为石千峰组(孙家沟组)、刘家沟组、和尚沟组。并确认石千峰组含有晚二叠世的Lueckisporites-Protohaploxypinus 孢粉组合;Abiella sp., Microdontella sp.等瓣鳃类;Sinolimnadiopsis yaoxianensis, Huanghestheria longellipsa等叶肢介;Shihtienfenia permica, Shansisaurus xuecunensis, Tapinocephalidae等脊椎动物化石。刘家沟组含早三叠 相似文献
17.
依据丰富翔实的地层古生物资料,首次在内蒙古西部建立了比较完整的第三纪地层层序：命名或厘订了中始新统乌兰乌珠尔组、上始新统查干布拉格组、下渐新统乌兰塔塔尔组、上渐新统、下中新统乌尔图组、上中新统呼和好来组和上新统昂冈浩特组等７个地层单元;区分出了中始新世乌兰乌珠尔、晚始新世查干布拉格、早渐新世早期克克阿木、早渐新世晚期乌兰塔塔尔、晚渐新世因德里沟、早中新世乌尔图、晚中新世呼和好来和上新世昂冈浩特等８个动物群（组合）。 相似文献
18.
上扬子区下志留统四射珊瑚组合带与层序地层序列的关系 总被引：2，自引：0，他引：2
摘 要 根据动物群演替和层序地层的研究厘定上扬子区下志留统 （Llandovery） 四射珊瑚
组合带序列：（1） 香树园组 Dinophyllum-Rhabdocyclus 组合带时限为 Aeronian 期;（2） 雷家
屯组下部 Stauria-Briantelasma 组合带; （3） 雷家屯组上部 Maikottia-Kodonophyllum 组合带
它们对应于 Telychian 早期;（4） 宁强组 Gyalophylloides -Idiophyllum 组合带相当于 Telychian
晚期。上扬子区下志留统可以划分为5个三级层序四射珊瑚组合带分别位于三级层序的高
水位体系域内。 相似文献
19.
During continent–continent convergence of the Arabian and Eurasian plates, and after the late Eocene inversion of a back-arc rift, the Iranian Plateau underwent broad subsidence resulting in the formation of the Central Basin (Morley et al., 2009). New 2D seismic data acquired by National Iranian Oil Company (NIOC) in the NW–SW-trending arm of the Central Basin suggest that during the main stage of shortening (middle–late? Miocene to Pliocene), strain concentrations resulted in the development of the thin-skinned Kuh-e-Gachab, Kuh-e-Gugerd, Garmsar and Sorkh-e-Kuh structures. These structures are built of Oligocene–Miocene/Pliocene(?) rocks belonging to the Lower Red, Qom and Upper Red formations. Seismic data suggest that one of these structures comprises the south-verging Kuh-e-Gachab anticline, which is bounded by the N-dipping Kuh-e-Gachab thrust and cored by a complex array of thrust sheets forming a triangle zone. During the deformation process, two salt evaporate levels played a significant role as detachment horizons. The main detachment horizon was rooted within the Lower Red Formation, whereas the second detachment horizon was located along evaporites belonging to the Upper Red Formation. Variations in the thin-skinned style of deformation between the larger triangle zone in the western part of the Kuh-e-Gachab structure contrasts with less shortening in the smaller triangle zone to the east. This suggests that the change resulted from the increase of thickness of the mobile detachment horizon to the east. Contraction deformations are still active south of the Alborz Mountains, which is confirmed by GPS data and present-day seismicity. 相似文献