style and timing of salt movement in the persian gulf basin offshore iran insights from halokinetic sequences adjacent to the tonb e bozorg salt diapir abstract the variations in the rate of salt rise is reflected in the sedimentary sequences adjacent to salt diapirs and provides insights into the style of salt movement sedimentation interaction and the timing of halokinetic phases episodic movement of salt diapir is defined by wedge and tabular shaped salt related sedimentary strata halokinetic sequences adjacent to the diapir detailed mapping of depositional strata on 2d seismic sections adjacent to salt diapirs on the tonb e bozorg island persian gulf sw iran reveals the presence of a series of sedimentary sequences related to the halokinetic activity of two salt source layers the hormuz and fars salts respectively the hormuz salt deposited in the uppermost proterozoic mobilized in the lower paleozoic and then continued to move periodically to present and to create the deep salt structures in the tonb e bozorg region the fars salt deposited in the lower miocene and then started rising and created the central salt structure the tonb e bozorg island and several peripheral ring like salt structures around the island our results reveal that both the salt layers within the tonb e bozorg region grew by downbuilding and continued to move periodically by passive and active diapirism to the present salt movement sedimentation interaction during salt diapirism influences petroleum play and therefore is of interest in petroleum geoscience

jurassic evolution of the arabian carbonate platform edge in the central oman mountains the jurassic sahtan group exposed in northern oman was deposited in shallow marine environments at the edge of the arabian platform facing the neo tethys hamrat duru basin the upper sahtan group is made up of a mixed siliciclastic carbonate unit overlain by pure carbonate deposits assigned to a bathonian and early callovian age on the basis of brachiopods and foraminifers these carbonate depositional systems were composed of outer oolitic shoals that underwent subaerial exposure and a deeper somewhat restricted gently dipping shelf interior oolitic material was shed off the platform edge into the deep sea depositional complex of the guweyza formation the sahtan group is affected by an important thickness reduction towards northeastern jabal akhdar the angular unconformity 0 2 at the top of the sahtan group is shown to result from tilting and top truncation of genetic sequences this unconformity is overlain by the rayda formation a veneer that shows an onlap pattern including a gradual deepening upwards facies evolution the minimal time span of the stratigraphic hiatus is mid callovian kimmeridgian oxfordian and kimmeridgian sequences were probably never deposited in this area because of lack of accommodation space and or because of subaerial exposure it is proposed herein that the unconformity was shaped by subaerial carbonate dissolution during a steady tectonically driven exhumation of the platform edge during the tithonian a major eustatic sea level rise caused transgression of the rayda formation upon the platform edge and normal shelf marine conditions resumed in the eastern arabian peninsula

metamorphism and deformation along the emplacement thrust of the samail ophiolite oman abstract the base of the samail ophiolite is a metamorphic shear zone that provides key information about ophiolite emplacement the classic exposure of this metamorphic sole at wadi tayin consists of a few meters of garnet clinopyroxene mafic gneiss and 80 m of upper amphibolite facies mafic and quartzose tectonite overlying 150 m of lower amphibolite facies mafic and sedimentary schist the sole is bounded by faults but is internally coherent peak metamorphic temperatures decrease exponentially from 825 c at the top of the sole to 500 c at its base as documented by changes in grain size hornblende composition the disappearance of chlorite and epidote garnet clinopyroxene element partitioning and garnet hornblende partitioning the inverted peak temperature gradient decreases from 4000 c km in the upper 50 m to 100 c km in the lower 150 m contrary to earlier reports greenschist facies tectonites are not present at wadi tayin although the entire sole underwent greenschist facies retrogression driven by the influx of fluids from the overlying peridotite or underlying carbonate calculations based on an amphibolite constitutive relation reveal that although the section represents a lithologic continuum the lower 200 m of the sole is a relatively undeformed block whereas the uppermost 25 m represent material initially separated by tens to a couple of hundreds of kilometers and now integrated into a single column

the hawasina basin a fragment of a starved passive continental margin thrust over the arabian platform during obduction of the sumail nappe abstract a complete revision of the lithostratigraphy of the hawasina nappes in the eastern and central oman mountains as compared to that of the previous stratigraphy leads to a new palaeogeographical reconstruction of the basin five very distinct zones have been determined representing five principal structural units that succeed one another from the external to the internal zones as follows 1 1 the hamrat duru basin 2 2 the baid platform 3 3 the al avidh trough 4 4 the misfah platform and 5 5 the umar basin the history of the hawasina basin began in the late permian with the formation on the northeastern edge of gondwana of a vast intracontinental basin the hamrat duru basin however this basin became a passive continental margin only during the middle late triassic formation of the neo tethys by crustal spreading and accretion began at this time in the internal part of the basin and in continuity with the umar basin the misfah platform and the al aridh trough which formed at the same time within the hawasina basin from this period onwards the main geomorphological features of the basin and of the margin were fixed and persisted up to the late cretaceous the phase of extension by which the basin was subsequently affected during the late tithonian berriasian was mainly manifested by generalized subsidence these main stages in the formation and evolution of the hawasina basin are marked by extensive development of in general alkaline but in places transitional and locally tholeiitic morb magmatism the sediments of the hamrat duru basin are dominated by turbidites composed of material mainly derived from the arabian platform whereas the al aridh trough and umar basin are characterized by pelagic sediments however the al aridh and umar grabens also contain layers of breccia of variable extent containing clasts and blocks of late permian and late triassic shallow water carbonates derived from the adjacent baid and misfah platforms sedimentation in the hawasina basin thus began locally in the late permian and by the triassic it was taking place in the remaining parts of the basin continuing up to the late turonian early senonian when the basin closed and overthrusting during obduction of the sumail ophiolite occurred sedimentation ended the overthrusting took place in three stages 1 1 a southerly directed compressive pre early obduction phase during which the hawasina basin was detached from its substratum to form an obduction prism 2 2 an obduction phase sensu stricto which by gravitational mechanisms induced major displacement of the principal hawasina units and their piling up on the arabian platform with the outermost units at the base and the innermost at the top and 3 3 a late obduction phase which caused local north northeastward backfolding possibly associated with the development of a fracture cleavage which in the basal structural levels may pass into true schistosity

geoscience of ancient mediterranean harbours abstract although much has been written on the subject of ancient mediterranean harbours the relatively new area of harbour geoarchaeology remains dispersed in the geoscience and archaeological literature over a decade of research has amassed rich and varied datasets of anthropogenically forced coastal evolution with a remarkable number of between site analogies this new research field also shows the rich potential of geoscience to reconcile important archaeological questions no single publication however has yet drawn on these geological patterns to yield a detailed overview suitable for geoscientists and environmental archaeologists the aim of this review article is to 1 discuss how ancient harbours have come to be preserved in the geological record 2 expound the basic principles and palaeoenvironmental tools underpinning ancient harbour geoarchaeology 3 outline some of the most significant research advances made and 4 discuss a new chrono stratigraphic model applicable to harbour sequences

synchronous seafloor spreading and subduction at the paleo convergent margin of semail and arabia the semail ophiolite is the largest and best exposed ophiolite having preserved intact record of a precollision system related to neotethyan ocean closure breaking with the alternative models of ophiolite exhumation and emplacement this paper builds on integrating the joined contribution of tectonic evolution of the continental margin in the premise of the ophiolite obduction connecting the along strike segmentation of the ophiolite recorded in the lithospheric flow structure and recent high precision dating results in a 3 d model of evolution of the ophiolite and its continental margin during jurassic cretaceous time among the relevant characteristics newly accounted 1 the contamination of the ophiolite by fluids and magmas of continental origin 2 the discrimination of different types of metamorphics associated to the ophiolite and conventionally classified metamorphic soles 3 the instability of the arabian margin during the late jurassic cretaceous times 4 the new precise ages relating to overlapping of spreading and detachment and 5 the inferred vergence of neotethyan closure during late mesozoic are stressed the complex stem revealed may relate to processes associated with spreading center subduction at ridge trench transform rtt triple junction as documented along a convergent margin the semail ophiolite emplacement on the arabia continental margin would result from a temporary arabian platform directed subduction zone that consumed the southern tethyan plate during late jurassic cretaceous time

tectonic evolution of the northern oman mountains part of the strait of hormuz syntaxis new structural and paleothermal analyses and u pb dating of synkinematic calcite

permian age from radiolarites of the hawasina nappes oman mountains the hawasina napper of the oman mountains yielded permian radiolarians from cherts stratigraphically overlying a thick volcanic basement al jil formation at the base of the hamrat duru group this fauna represents the first permian radiolarians and radiolarites in the central and western tethyan realm a permain age for pelagic sequences within the hawasina complex of oman has major significance for regional paleogeographic reconstruction a clear differentiation between platform reefal sediments and basin radiolarites from the base of the late permian 255 ma is implied it suggests a flexure of the platform during permian time the present data implies that a zone of rifting was already developed adjacent to the northeast gondwana platform margin during the late permian the hamrat duru basin corresponds to an opening intracontinental rift area sphenochasm between arabia and northeast gondwana a reentrant of the paleo tethys

cretaceous sedimentary rocks on the masirah ophiolite sultanate of oman evidence for an unusual bathymetric history autochthonous sedimentary rocks on the masirah ophiolite preserve a record of vertical movements of their oceanic basement the masirah ophiolite was formed in the uppermost jurassic and subsequently underwent thermal subsidence for about 20 ma as documented by pelagic sediments submarine alkali basaltic volcanism in the lower barremian marks the onset of rapid basement uplift to or above sea level carbonate platforms grew in barremian mid aptian time on highs of oceanic basement the uplift is interpreted as the result of transpressive tectonism along a large oceanic fracture zone the platforms submerged in the mid aptian and reached the ccd in the albian ribbon cherts were deposited during the albian to santonian time the first influx of siliciclastic detritus shed from the arabian craton is recorded in coniacian sandstones ophiolitic conglomerates interfinger in the campanian to mid maastrichtian with continent derived sandstones reflecting regional compressive tectonism crystalline exotics deposited in the late maastrichtian are derived most likely from the precambrian basement of arabia whilst the origin of the sedimentary exotics dated triassic to cretaceous remains unclear the masirah ophiolite was overthrust at the cretaceous tertiary boundary by an upper ophiolite nappe and emplaced onto the margin of southeast oman

late jurassic to cretaceous evolution of the eastern tethyan hawasina basin oman mountains remnants of a mesozoic continental margin can be studied today in the nappe pile of the oman mountains successions of the arabian carbonate platform and the adjacent deep hawasina basin are preserved in the nappe pile and in the foothills of this mountain range the jurassic cretaceous sediment successions of the hawasina basin sumeini and hamrat duru group are focus of this study these basinal archives contain information on the response of an eastern tethyan equatorial ocean system to multiple perturbations of the carbon cycle and of climate during the cretaceous turbiditic continental slope and basinal successions formed near the calcite compensation depth are difficult to date with biostratigraphy and sequence stratigraphy the available stratigraphic framework for the hawasina successions was not sufficient for tracing palaeoceanography through the time window of interest in this study therefore existing sequence stratigraphy and biostratigraphy are complemented by additional biostratigraphic data and with a newly established carbon and strontium isotope chemostratigraphy the hawasina basin was affected by sea level variations by changes in oceanography and also by regional tectonics a first major modification of oceanography occurred at the end of the jurassic when pelagic maiolica type sediments were accumulated in the deep basin and on adjacent submarine highs lower member of huwar and sid r formations pelagic to hemipelagic conditions existed until the valanginian marked by a major carbon isotope excursion pelagic sediments were afterwards replaced by a succession of fine to coarse grained turbidites of hauterivian to aptian in age the transition into the mid cretaceous is marked by a sudden shift to fine grained siliceous or chert deposits at a time when sediments enriched in organic carbon were accumulated in the western tethys and atlantic oceans the continental slope as well as the hawasina basin seemed to have been well ventilated during early and mid cretaceous time siliceous limestones and chert are indicator of well mixed and nutrient rich surface water while absence of black shales suggests young and oxygenated deep water with a possible source on the vast arabian platform these peculiar oceanographic conditions were most pronounced during the onset of the extreme greenhouse episodes of the oceanic anoxic event 1a this article is protected by copyright all rights reserved

palaeoenvironmental and archaeological records for the reconstruction of the ancient landscape of the roman harbour of narbonne aude france abstract analysis of sediment records and ams radiocarbon dates are used to reconstruct quaternary landscapes and palaeoenvironments of the ancient roman harbour at narbonne capital of the roman province gallia narbonensis which extended from the pyrenees to the alps narbonne was one of the largest port cities in the northwest mediterranean during the first millennium ad yet the strategies deployed in managing the harbour particularly the management of natural processes are little understood a synthesis of archaeological geomorphological and geophysical data was made to assess the palaeoenvironmental constraints faced by residents of narbonne and what strategies they may have adopted in the management thereof harbour structures dating from the 1 st 5 th centuries ad discovered in castelou and mandirac were intended to canalize an aude river branch allowing transfer and unloading of trade goods these new insights about the harbour of narbonne provide a valuable comparison for other ancient mediterranean harbours such as ostia italy tell about hawam israel taposiris egypt

factors controlling carbonate platform asymmetry preliminary results from the great bank of guizhou an isolated permian triassic platform in the nanpanjiang basin south china abstract a well exposed isolated carbonate platform the great bank of guizhou in the nanpanjiang basin of south china developed from the latest permian to the earliest late triassic platform strata are dissected by a faulted syncline exposing a complete cross section through the interior margins and flanks enabling a detailed assessment of depositional controls previous studies portrayed the platform as having a relatively symmetrical architecture even though much of the former work was focused on the platform interior and northern margin basin transition our research reveals five aspects of the southern margin facies and stratigraphy that are significantly different from those of the northern margin 1 subaerial exposure and unconformity developed on top of the upper permian sponge boundstone and in the overlying lower triassic strata 2 permian and triassic clasts chaotically admixed within early triassic breccias 3 lower triassic strata remarkably thinner on the southern margin 4 a much narrower tubiphytes reef facies preserved along the southern margin in the middle triassic and 5 large scallop shaped reentrants at the southern margin evident in satellite images three end member models may explain the asymmetry 1 antecedent topography of the underlying upper permian reef rimmed margin coupled with eustatic sea level fluctuation 2 differential tectonic uplift and 3 large scale submarine collapse of the platform margin subaerial exposure and admixing of permian and triassic clasts observed at yungan section is best explained by the tectonic uplift model however the submarine collapse model also explains several of the observations if it is associated with uplift s or sea level fall s submarine collapse is supported by large concave erosional reentrants scallops visible in satellite images taken together our observations suggest that a combination of tectonic uplift and margin collapse contributed to platform asymmetry further work promises to further constrain the details and timing of processes that contributed to the asymmetry

thermo mechanical modeling of the obduction process based on the oman ophiolite case obduction emplaces regional scale fragments of oceanic lithosphere ophiolites over continental lithosphere margins of much lower density for this reason the mechanisms responsible for obduction remain enigmatic in the framework of plate tectonics we present two dimensional 2d thermo mechanical models of obduction and investigate possible dynamics and physical controls of this process model geometry and boundary conditions are based on available geological and geochronological data and numerical modeling results are validated against petrological and structural observations of the oman semail ophiolite our model reproduces the stages of oceanic subduction initiation away from the arabian margin the emplacement of the oman ophiolite on top of it and the domal exhumation of the metamorphosed margin through the ophiolitic nappe a systematic study indicates that 350 400 km of bulk shortening provides the best fit for both the maximum pressure temperature conditions of the metamorphosed margin 1 5 2 5 gpa 450 600 c and the dimension of the ophiolitic nappe 170 km width our results confirm that a thermal anomaly located close to the arabian margin 100 km is needed to initiate obduction we further suggest that a strong continental basement rheology is a prerequisite for ophiolite emplacement

palaeoenvironmental reconstruction of the ancient harbors of rome claudius and trajan s marine harbors on the tiber delta during the first and second centuries ad emperor claudius and then emperor trajan successively ordered the construction of two large harbors on the tyrrhenian coast research resulted in advances in understanding the palaeoenvironments of the portus from a bathymetric point of view the drillings indicate a 7 8 m depth for the main basins different sedimentary behaviors were observed claudius basin shows sand accretion whereas the access channel to trajan s basin shows mud accumulation trajan built the second hexagonal basin because claudius harbor did not protect the ships from the wind and swell and not because it was prone to rapid silting in terms of chronology the channel between both basins worked between the end of the 2nd century and the beginning of the 5th century when it became completely clogged this means that after the beginning of the 5th century only the junction channel canale traverso remained to provide an access to the tiber and to the sea

hydromagmatic eruption during the buildup of a triassic carbonate platform oman exotics eruptive style and associated deformations abstract oman exotics represent remnants of a triassic carbonate platform also named misfah formation several basaltic intrusions or lava flows were coeval with the carbonate platform buildup we present field observations related to one of these volcanic events including associated deformation of the host rocks and interaction of volcanism with the sedimentation these observations allow us to reconstruct the structure of the volcanic conduit and vent and the successive stages of the evolution of the eruption the initial ascent of magma probably occurred along on a normal fault related to gravity driven sliding towards the platform edge magma was first emplaced in a saucer shaped sill a few tens of meters below the sea floor this intrusion provided a decollement layer that may have sped up the gravity driven sliding opening fractures that brought sea water into contact with the magma hence triggering a hydromagmatic eruption eruption was followed by the collapse of the host limestones that formed a megabreccia infilling the eruptive vent and prohibiting further contact between sea water and magma most of the magma was emplaced at depth in two superposed small magmatic bodies 300 100 m and 200 50 m in sections respectively that replaced the host sediments and uplifted the overlying vent despite the shallow submarine setting this eruption produced a vent quite similar to sub aerial maars developed in soft substrate this emphasizes that the rheology of the substrate may be more important than the amount of water to control magma water interaction in hydromagmatic eruptions in an active carbonate platform like misfah formation during triassic times the early diagenesis of lime mud determined the mechanical comportment of the sediment at the time of eruption and especially the way it could be mixed with the magma and or slide into the vent

hamrat duru group revised stratigraphy of a mesozoic deep water passive margin in the oman mountains the stratigraphy of the hawasina complex is redefined and rationalized to conform with standard stratigraphical nomenclature previously proposed tectono stratigraphical units are abandoned in favour of a system that relies on the lateral correlation of lithofacies between structural units to this end the dibba dhera wahrah and al ayn formations are incorporated into an expanded hamrat duru group this group is divided into five formations the zulla guweyza sandstone guweyza limestone sid r and nayid and spans triassic to mid cretaceous cenomanian time it locally passes up into the syn orogenic sediments of the riyamah member of the muti formation the nomenclature of the deeper water chert dominated formations is left unaltered

late cretaceous early tertiary convergence between the indian and arabian plates recorded in ophiolites and related sediments abstract remnants of ocean floor forming the eastern ophiolite belt in oman and the western ophiolite belt in pakistan have a common plate tectonic history culminating in emplacement at the cretaceous tertiary boundary fragments of ocean floor in these two belts have ages between 150 and 65 ma and recorded tectonic events in the early indian ocean at 150 ma 130 120 ma 110 100 ma and 70 65 ma new radiometric and chronostratigraphic ages and paleomagnetic and sedimentary information are used to relocate these ophiolites in the frame of the evolving indian ocean which was characterised by the stepwise breakup of gondwana at 158 ma east and west gondwana 130 ma southern atlantic breakup of east gondwana 95 84 ma madagascar and india seychelles 65 ma india and seychelles and finally at 40 ma rifting between africa and arabia the 150 ma old oceanic rocks of masirah island in oman originally formed the extension of the basins now preserved along the eastern edge of the afro arabian plate masirah drifted together with india seychelles when a new ridge formed at approximately 130 ma separating microplates e g kabul block from the northern edge of greater india parts of this new ocean were later emplaced to form the western ophiolite belt in pakistan consumption of oceanic crust and emplacement of ophiolites during the closure of the neotethys occurred not only north of india seychelles but also along two or three subduction zones between the afro arabian plate and india seychelles documented by the formation of metamorphic soles beneath ophiolites relics of ocean floor formed approximately 65 70 ma ago now form the upper units in the western ophiolite belt of pakistan where they overlie an accretionary prism of pillow lavas of dominantly aptian albian age and sedimentary rocks the breakup of india and the seychelles at 65 ma was associated with the eruption of flood basalts deccan and seychelles and enhanced counter clockwise movement of india this breakup possibly caused the late jurassic early cretaceous fragments of ocean floor e g masirah to be thrust onto the eastern edge of oman the ophiolites which were emplaced onto the western edge of india drifted as part of this plate farther north where collision with eurasia and the accreted microplates occurred in the eocene 55 ma

estimating original thickness and extent of the semail ophiolite in the eastern oman mountains by paleothermal indicators abstract the oman mountains preserve permo mesozoic sedimentary rocks of the arabian passive margin that were overridden during late cretaceous time by deep water sediments of the hawasina units and by the semail ophiolite a portion of the neo tethyan oceanic crust and upper mantle passive margin sequences are exposed in the jabal akhdar culmination jac and in the jabal salakh range at the oman mountains thrust front samples of these sequences were investigated by x ray diffraction of the clay size fraction to evaluate the thermal evolution of the subophiolite rocks and estimate the thickness and extent of the obducted ophiolites the sedimentary succession from the northern flank of the jac shows a clay mineral assemblage characterized by long range ordered mixed layer i s with an illite content between 85 and 92 and the occurrence of pyrophyllite and or paragonite suggesting maximum paleotemperatures between 150 and 200 c in deep diagenetic conditions on the southern flank of the jac temperature dependent clay minerals indicate maximum paleotemperatures ranging between 120 and 150 c indicating a reduced ophiolite thickness towards the south ooid strain analyses of the subophiolite rocks from the northern flank of jac show a component of flattening and stretching in the z x plane as a result of plastic deformation and pressure solution on the southern flank such ductile deformation is absent suggesting a brittle rheology for the subophiolite carbonates and a reduced overburden 1d thermal modeling reveals that the sub ophiolite units of the jac were overthrust by 4 5 km thick semail ophiolite and hawasina units during the coniacian and exhumed since the campanian the subophiolite rocks of the jabal salakh range were buried under 1 35 km of synobduction clastics and overthrust by 2 km thick hawasina units suggesting a decrease of the thickness of allochthonous units from ne to sw consistent with strain analysis and their direction of emplacement

a tertiary asthenospheric flow beneath the southern french massif central indicated by upper mantle seismic anisotropy and related to the west mediterranean extension abstract upper mantle flow beneath the french massif central is investigated using teleseismic shear wave splitting induced by seismic anisotropy about 25 three component stations short period intermediate and broadband were installed during the period 1998 1999 in the southern massif central from the clermont ferrand volcanic area to the mediterranean sea teleseismic shear waves sks skks and pks were used to determine the splitting parameters the fast polarization direction and the delay time delay times ranging between 0 7 and 1 5 s have been observed at most of the sites the azimuths of the fast split shear waves trend homogeneously nw se in the southern massif central suggesting a homogeneous mantle flow beneath this area the observed nw se direction differs from the n100 e pyrenean anisotropy further south it does not appear to be correlated to hercynian structures nor to the present day motion of the plate but is well correlated to the tertiary extension direction we propose that the opening of the western mediterranean induced by the rotation of the corsica sardinia lithospheric block and the roll back to the se of the tethys slab may have generated a large asthenospheric mantle flow beneath the southern massif central and a deflection of the up going plume centered beneath the northern massif central toward the se

connections between the stratospheric quasi biennial oscillation and tropospheric circulation over asia in northern autumn 1 we investigate the variations in tropospheric circulation over asia associated with the stratospheric quasi biennial oscillation qbo during northern hemisphere nh autumn september november using the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis and ncep department of energy doe reanalysis ii data sets for a 25 year period 1980 2004 the anomaly fields in this study are expressed as the easterly years minus the westerly years of the qbo the zonal wind distribution at 200 hpa indicates easterly anomalies at low latitudes from india through taiwan statistically significant westerly anomalies at midlatitudes including the tibetan plateau to northern china and significant easterly anomalies in the high latitude eurasia north of 50 n a momentum balance analysis indicates that these anomalies over asia are attributable to atmospheric waves and residual mean meridional flow significant northward and descending anomalies are observed in the lower stratosphere over asia with detectable signals in the troposphere around tibet the adiabatic heating due to descending motions in the region centering on india and bangladesh is consistent with the distribution of rainfall anomalies the formation of zonal wind anomalies over south asia seems to be associated with not only wave activities but also adiabatic heating and thermal advection we suggest that the qbo may be linked to tropospheric circulation over asia through wave activities and convective activities in autumn and the wave activities in the low latitudes associated with the qbo seem to be connected with the rainfall distribution over the asian monsoon region

sumeini group oman evolution of a mesozoic carbonate slope on a south tethyan continental margin abstract deposition of the mostly mesozoic sumeini group occurred on the slope between the shallow marine arabian carbonate platform and the deep oceanic hawasina basin or south tethys sea these strata record the evolution of the northeast arabian continental margin from permian and triassic rifting to ocean basin closing with the late cretaceous obduction of the semail ophiolite platform margin type and its evolution can be inferred from exposures of these slope sediments at jebel sumeini in the western oman mountains in the lower permian base of the sequence bedded spicular limestones suggest deep marine conditions this is followed by an enigmatic thick sequence of bedded dolomite in the early to middle triassic small carbonate submarine fans formed along a distally steepened slope a subsequent interval of terrigenous clastic sedimentation was followed by development of a steep escarpment margin during ladinian to norian time with coralgal reefs at the shelf break and a debris apron at the base of the scarp the late triassic is marked by another influx of terrigenous sediment which accompanied widespread emergence of the platform in the jurassic a thick apron of thin bedded limestone formed on the slope this apron was cut by channelized gullies that now include blocks of older reefal material and oolitic sands a well documented submergence of the platform during the tithonian and early cretaceous led to the deposition of radiolarian cherts on the slope and basin upper lower cretaceous megabreccias up to 200 m thick suggest an interval of localized slope instability and or tectonism continued deposition of bedded limestone and marl with lesser calcirudite marks the top of stratigraphic sequence at jebel sumeini the early to middle triassic carbonate submarine fan deposits occur as discrete lenticular sequences of bedded calciturbidite modified grain flow and debris flow deposits which were derived from mostly slope sources the ladinian to norian base of slope debris apron deposits were derived from both slope and shallow marine sources including reefs and appear to form a laterally extensive but narrow belt of thick lenticular to sheet like beds of debris which accumulated over a long interval of time coarse limestones in the jurassic gullied slope deposits are distinct in that they occur randomly as individual channelized beds in a sequence dominated by thin bedded lime mudstones thick lower cretaceous megabreccias are distinguished by their great lateral distribution and general lack of matrix

the break up of east gondwana along the northeast coast of oman evidence from the batain basin recent detailed studies on the batain nappes northeast coast of oman which represent a special part of the so called oman exotics have led to a better understanding of the neotethyan geodynamic evolution the batain exotics bear witness to volcanic activity sea level changes tectonic instability rifting and oceanization along the eastern oman margin during late palaeozoic and mesozoic times they allow definition of the batain basin as an aborted permian branch of neotethys this marine basin was created in early permian times extending southward to the east african madagascar region and was linked to the karoo rift system the presented revised classification of the batain nappes considers the batain basin to be no longer a part of the hawasina basin and the neotethyan margin proper we attribute the batain basin to a mozambique somali masirah rift system somoma this system started in early permian times creating a marine basin between arabia and india madagascar rifting in the late triassic and oceanization during late jurassic times led to the separation of east gondwana

sequence of thrusting and origin of culminations in the northern and central oman mountains abstract detailed mapping and structural analysis of three large scale culminations sumeini and asjudi half windows and haybi hawasina window in the oman mountains shows a considerably more complex history of deformation than a simple foreland or downward sequence of thrust development early thrusting processes tended to create a regular stacking order of imbricate slices and major thrust sheets complying with the rules of thrust propagation assembled progressively downwards and forwards in the direction of translation out of sequence thrusts can also be demonstrated in places by truncation of footwall structures folds imbricate slices etc gross strain differences between thrust sheets downward facing structures in footwall units and elimination of thrust sheets beneath late stage thrusts frequently cut up section through the previously assembled stack putting previously younger lower thrust sheets over previously older higher ones many of the culminations in the northern and central oman mountains were formed by ramping associated with this late stage leap frog rethrusting event

structure and evolution of the passive margin of the eastern tethys abstract an extensive passive margin was formed in the triassic along the periphery of arabia including the tauric carbonate platform this event is related to the opening of the mesozoic tethys when a number of microcontinents split off from gondwana triassic extension and continental rifting resulted in the formation of a structural pattern which is uniform from the dinarides to oman it includes the following elements 1 1 shelf 2 2 continental slope 3 3 deep basin probably with a floor of attenuated sialic crust 4 4 inner carbonate platform in the jurassic cretaceous stable conditions prevailed influenced only by eustatic oscillations of the sea level turbidites accumulated on the continental rise while cherts and radiolarites were deposited in the deep basins hawasina pichakun antalya pindus below the ccd level sedimentation on the shelf was controlled by north northeast transverse tectonic elements which also continued across the passive margin dividing it into a number of segments collision with an island arc led to obduction of the oceanic crust deformation of the passive margin and overthrusting of its sedimentary cover onto the arabian shelf obduction and deformation lasted for about 10 m y and created a new tectonic pattern with concentric structural zones surrounding the arabian promontory these zones include 1 1 the flysch basin a remnant of the closing tethys 2 2 an uplift a site of periodical emergence and erosion corresponding to the frontal part of the ophiolitic nappes 3 3 the border furrow a depocenter of low energy calcareous marls 4 4 the arabian shield constantly emerged during the tertiary tectonic deformation of these zones caused by the collision of arabia with eurasia began prior to the early miocene and it is still going on data on afghanistan demonstrate that its central part the gelmend argandab and kabul blocks belonged during the paleozoic and early mesozoic to the continental shelf of india

oman exotics oceanic carbonate build ups associated with the early stages of continental rifting the so called oman exotic limestones form isolated masses from boulder size to 1 000 m thick of middle to upper permian and upper triassic fossiliferous limestones and crop out within imbricated thrust slices beneath the semail ophiolite in the oman mountains permian exotics are of dominantly reef and forereef facies whereas triassic exotics are more typically of back reef and lagoonal facies they are commonly associated with a substrate of alkalic and transitional tholeiitic basalts and are interpreted as a series of reef associated carbonate buildups deposited in part on oceanic islands or seamounts close to the site of initial rifting of the oman continental margin

perturbations in the carbon cycle during the carnian humid episode carbonate carbon isotope records from southwestern china and northern oman the carnian humid episode is an interval of prominent climatic changes in the late triassic we studied the carbon isotope 13c geochemistry of carbonates from sections in southwestern china and northern oman 13c records from the yongyue section western guizhou south china show a progressive positive shift from 1 4 to 2 8 in the early to middle julian 1 substage this positive trend is followed by a swift negative shift of c 4 2 from 2 8 to 1 4 in the julian 2 substage 13c from the wadi mayhah section northern oman shows a positive shift from 2 2 to 2 8 in the julian 1 substage followed by a negative shift of c 3 2 from 2 8 to 0 3 in the julian 2 substage the 13c records from the two study sections generally correlate well with each other as well as with published records pointing to a considerable input of isotopically light carbon starting in the late julian 1 substage such a large amount of light carbon probably derived from direct degassing and the sediment sill contact metamorphism of the panthalassan wrangellia large igneous province and contemporary tethyan volcanism the voluminous volcanogenic greenhouse gases probably contributed to the warming pulse in the middle carnian thus the dry wet climatic transition during the carnian humid episode is best interpreted as a warm climate driven intensification of the activities of the atmospheric circulation and hydrological cycle