triassic bedded cherts in central japan are not pelagic although the origin of bedded radiolarian cherts in orogenic belts has been widely debated1 15 their geochemistry is still poorly understood triassic bedded radiolarian cherts occur extensively in the japanese islands and are generally not associated with ophiolitic rocks but rather with clastic rocks we present here chemical data on the triassic bedded cherts of kamiaso in central japan the relationship of sio2 with al2o3 tio2 and zr shows that the bedded cherts have been formed by a simple mixing of biogenic silica derived from radiolarians and sponge spicules with lithogenic materials the ratios of several elements relative to tio2 strongly suggest that the shale partings and lithogenic portions of the cherts are consanguineous sedimentary structures as well as the geochemical evidence suggest that most kamiaso cherts are turbidity current deposits our geochemical and geological data compared with those of recent marine sediments from various environments demonstrate that the triassic cherts and associated shale partings are not deep pelagic in origin but formed in an offshore or marginal sea environment

oman exotic limestones in the uae oman border area with implications for middle upper permian neo tethyan rifting abstract the neo tethyan semail ophiolite in the uae oman region was obducted onto the arabian continental margin at the end of the cretaceous beneath the ophiolite are thrust stacked deep water mesozoic and older sediments and volcanics that include marine basalts and associated limestones of middle late permian and late triassic age these limestones are referred to as the oman exotic limestones the middle upper permian exotics are the rarer exotic type they were reef build ups on platforms that sank to ocean depths during rifting and were later engulfed by intrusive basalts an area to the east of al ain city uae exposes blocks of richly fossiliferous limestone exotic blocks within upper triassic marine basalts the studied exotics host foraminifera including dunbarula mathieui verbeekina sp tetrataxis sp geinitzina sp pachyphloia sp colaniella leei and calcareous algae mizzia velebitana rugose corals and abundant crinoids consistent with a murghabian dzulfian middle late permian age the exotics lack ooids show grainstone packstone lithofacies are only slightly affected by dolomitization these features are interpreted in a paleogeographic model involving an isolated carbonate platform comparable to the jabal qamar formation in the dibba zone that subsided during neo tethys rifting in the late permian lopingian dzulfian dorashamian

birth death and resurrection the life cycle of suprasubduction zone ophiolites 1 suprasubduction zone ssz ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites this sequence includes the following 1 birth which entails the formation of the ophiolite above a nascent or reconfigured subduction zone this stage is typically characterized by the eruption of arc tholeiite lavas and the formation of layered gabbros and sheeted dike complex 2 youth during which is continued melting of refractory asthenosphere depleted during birth occurs in response to fluid flux from the subducting slab with extensional deformation of the older plutonic suite eruption of refractory lavas and the intrusion of wehrlite pyroxenite 3 maturity with the onset of semistable arc volcanism typically calc alkaline as the subduction zone matures and stabilizes and the intrusion of quartz diorite and eruption of silicic lavas and 4 death which is the sudden demise of active spreading and ophiolite related volcanism which in many cases is linked to collision with an active spreading center and the onset of shallow underthrusting of the buoyant spreading axis expressed as dikes and lavas with oceanic basalt compositions that crosscut or overlie rocks of the older suites 5 resurrection with emplacement by obduction onto a passive margin or accretionary uplift with continued subduction the early stages 1 3 may be diachronous and each stage may overlap in both time and space the existence of this consistent progression implies that ophiolite formation is not a stochastic event but is a natural consequence of the ssz tectonic setting

upper triassic norian cephalopod limestones of the hallstatt type oman norian crinoidal brachiopod limestones and cephalopod limestones of the hallstatt type occur as blocks in a hettangian calcareous breccia of the haliw formation in the oman mountains crinoidal and brachiopod packstones up to 12 m thick prevail in the lower part of the sequence and were deposited on a substrate of norian forereef breccia the overlying cephalopod wackestones up to 4 9 m thick have a basal white bed followed by red limestones with abundant planar and scalloped corroded surfaces and local stromatolites upward red nodular wackestones and finally slumped grey wackestones follow the analysis of geopetal fabrics in orientated samples shows that bedding of these facies is in fact inclined bedding inclinations varied between 15 and 29 in addition the restored dip directions demonstrate rotation indicating deposition on a gliding block the preferred orientation of orthoconic cephalopods and imbrication of discoidal ammonoids coincide with the dip direction measured from geopetal fabrics such features generally interpreted as current induced are here interpreted as gravity induced the overall mud supported rock fabric thus indicates deposition under very low energy conditions the common mud supported texture of the rocks contrasts with evidence for current activity found in the scalloped surfaces and shell lags particularly in the crinoidal brachiopod facies and the lower stratigraphically condensed cephalopod limestones this indicates that deposition of lime mud alternated with periods of elevated current strength a comparison of the hallstatt type limestones and current influenced sediments on the northern slope of the little bahama bank suggests that condensed sequences of the hallstatt type are restricted to relatively shallow depths with strong fluctuation of contour following currents undersaturated with respect to aragonite along carbonate shelf margins facing the open ocean on steep slopes sediment bypassing may be an additional factor for stratigraphic condensation

geochemistry of the mesozoic bedded cherts of central baja california vizcaino cedros san benito implications for paleogeographic reconstruction of an old oceanic basin abstract in central baja california vizcaino peninsula and cedros and san benito islands two distinct radiolarian bedded chert sequences of late triassic and late jurassic lowermost cretaceous age can be differentiated on lithostratigraphic and geochemical criteria these bedded chert sequences are part of the conformable sedimentary cover of more or less dismembered ophiolites which are overthrusted by the san andres cedros volcanic arc system of middle late jurassic age major and trace elements permit paleogeographic zonation of the late jurassic lowermost cretaceous radiolarites lying conformably upon ophiolites considered as fragments of an oceanic basin floor which developed westward of the san andres volcanic arc progressive accretion of this oceanic basin floor along the continental margin is supported by the fact that the more distal radiolarian chert sequences belong to the lowermost structural units of this area

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

on the mesozoic ionian basin summary new seismic reflection profiles of the italian deep crust project crop provide new insights on the structure of the ionian sea in spite of the apennines and hellenides neogene subduction zones two conjugate passive continental margins are preserved at the margins of the ionian sea along the malta escarpment to the southwest and the apulian escarpment to the northeast the ionian sea is likely to be a remnant of the mesozoic tethys ocean confined by these two conjugate passive continental margins the transition from continental to oceanic crust appears sharper to the northeast than to the southwest the basin between southeast sicily and southwest puglia was about 330 km wide and suggests a low spreading rate the inferred oceanic ridge should have been flattened by thermal cooling and buried by later sediments based on stratigraphic and structural constraints to the north in the apennines belt the ocean continued to the northwest this palaeogeography is supported by the seismicity of the apennines slab underneath the southern tyrrhenian sea which implies downgoing oceanic lithosphere the adjacent absence or paucity of deep seismicity does not imply absence of subduction but rather it can be interpreted as due to the more ductile behaviour of the subducted continental lithosphere surprisingly we note that where the oceanic inherited basin is subducting underneath the apennines in the hangingwall of the subduction hinge there are outcropping slices of continental crystalline basement previously deformed by the alpine orogen

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

sedimentological and structural evolution of the arabian continental margin in the musandam mountains and dibba zone united arab emirates the northernmost extremity of the oman mountains the musandam peninsula is composed of an allochthonous sequence of permian to middle cretaceous shelf carbonates these are separated from ophiolitic rocks to the south by a northeast southwest trending belt known as the dibba zone this structurally complex belt is composed of allochthonous slope and basin facies sediments haybi volcanic rocks oman exotic limestones sub ophiolitic metamorphic rocks and ultra mafic slices lithofacies correlation confirms that fragmentation and rifting of a vast east facing carbonate platform occurred in middle to late triassic time resulting in the establishment of a shelf edge and small ocean basin this margin was typified from northwest to southeast by ooid skeletal lime sand shoals or small bioherms on the shelf edge a bypass foreslope of well laminated periplatform ooze and basin margin accumulations of carbonate turbidites or debris flows the shelf edge now coincides with the northern boundary of the dibba zone and appears to have remained stationary from middle triassic to late jurassic time periods of arrested carbonate sedimentation on the platform either because of exposure late triassic and middle cretaceous or because of drowning late jurassic are represented in the basin by starved sedimentation and deposition of radiolarian cherts a spectacular platform margin collapse occurred in the middle and late cretaceous as represented by massive conglomerates with clasts as young as albian above an unconformity that progressively removed all of the lower cretaceous the tethyan basinal and ophiolitic rocks of the dibba zone were emplaced from the east southeast during the turonian to lower maastrichtian after emplacement of these allochthonous units compressional deformation in the mid tertiary resulted in large scale open whaleback folds with wavelengths as much as 15 km generally with north south axes in places these folds which affect the complete shelf and allochthonous sequences are overturned toward the west and thrusting has caused previously lower tectonic units of the late cretaceous stacking order to be thrust over previously higher tectonic units thus reversing the late cretaceous tectonostratigraphy the maximum amount of translation on the later thrusts is in excess of 5 km on the hagab thrust where the complete shelf carbonate sequence of the musandam mountains has been thrust west northwest over the previously higher hawasina and haybi thrust sheets the tertiary folding and thrusting can be correlated in time and space with the zagros fold belt of southwestern iran

sources of elevated salinity in the mississippi river alluvial aquifer south central louisiana usa abstract salinization is a process impacting groundwater quality and availability across much of southern louisiana usa however a broad divergence of opinion exists regarding the causes of this elevated salinity updip migrating marine waters from the gulf of mexico saline fluids migrating up fault planes movement of water from salt domes and or remnant seawater from the last major marine transgression the mississippi river alluvial aquifer mraa in south central louisiana is recharged by the mississippi river and there are discharge zones to the west and east recharge waters from the mississippi river are fresh but cl levels in the western portions of the aquifer are as high as 1000 mg l the aquifer is an important source of water for several municipalities and industries but prior to this study the source s of the elevated salinity or whether the salinization can be remediated had not been determined the low br cl ratios in the groundwaters are consistent with a saline endmember produced by subsurface dissolution of salt domes not a marine source the h and o isotopic systematics of the aquifer waters indicate meteoric sources for the h2o not marine waters or diagenetically altered deep brines the westward salinization of aquifer water represents a broad regional process instead of contamination by point sources mapping of spatial variations in salinity has permitted the identification of specific salt domes whose subsurface dissolution is producing waters of elevated salinity in the aquifer these include the bayou choctaw and st gabriel domes and possibly the bayou blue dome salinization is a natural on going process and the potential for remediation or control is slight if not non existent

metallogenesis on a mesozoic passive continental margin antalya complex southwest turkey abstract a variety of fe mn and trace metal enriched mesozoic pelagic sediments are associated with the tectonically emplaced antalya complex in southwestern turkey palaeotectonic settings represented within the complex comprise a continental platform passing laterally through a mesozoic passive margin into a zone of marginal oceanic crust formed during the early stages of continental separation the origins of the metalliferous sediments are elucidated using mineralogical major trace element and ree data and comparisons with oceanic and ophiolite related sediments late triassic deposition during the initial continental separation was mostly terrigenous including detrital carbonate derived from adjacent reef complexes during the jurassic and early cretaceous the passive margin underwent accumulation of fine grained terrigenous matter and biogenic silica in deep water below the carbonate compensation depth argillaceous mudstones deposited during a regional hiatus at the end of the upper triassic show unusual fe and trace metal enrichment together with a marked positive ce anomaly indicative of slow hydrogenous accumulation the marginal oceanic crustal zone also shows dominantly terrigenous and siliceous biogenic deposition but with the addition of an important hydrothermal component represented by fe mn deposits these occur within and immediately above the upper triassic lavas of the oceanic crust and as intercalations in the overlying lower cretaceous radiolarian chert sequence most of these sediments show strong fe mn fractionation several show a negative ce anomaly implying rapid incorporation of the rees from seawater the upper triassic fe mn deposits associated with the lavas are relatively trace element depleted and record rapid localised precipitation from relatively high temperature hydrothermal solutions by contrast the more manganiferous and trace element enriched metalliferous horizons in the jurassic to lower cretaceous chert sequences represent more dilute low temperature hydrothermal discharge regional comparisons suggest that dominantly manganiferous deposits free of sulphides are characteristic of the early formed mesozoic ocean crust compared with well established spreading axes like the troodos massif cyprus

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

the jabal akhdar dome in the oman mountains evolution of a dynamic fracture system the mesozoic succession of the jabal akhdar dome in the oman mountains hosts complex networks of fractures and veins in carbonates which are a clear example of dynamic fracture opening and sealing in a highly overpressured system the area underwent several tectonic events during the late cretaceous and cenozoic including the obduction of the samail ophiolite and hawasina nappes followed by uplift and compression due to the arabia eurasia convergence this study presents the results of an extensive tectonic survey and correlates subseismic scale structures in jabal akhdar faults fractures veins and stylolites with the main tectonic events in the northeastern arabian plate as some of the studied formations host large oil reserves in neighboring areas determining the relative timing of these events in the exhumed rocks is important to understand hydrocarbon distribution and fracture patterns in these reservoirs the formation of early veins and stylolites in the oman mountains is followed by top to the south layer parallel shearing that may be associated with the obduction of the samail and hawasina nappes this compressional tectonic event is followed by normal dip slip to oblique slip faults and veins top to the northeast layer parallel shearing which corresponds to the first stage of exhumation of the autochthonous rocks offsets these structures our new data indicate that this first phase of events is overprinted by complex strike slip networks of veins and fractures as well as by the reactivation and onset of seismic scale faults strike slip structures belong to three distinct events the first one nw se oriented compression is probably associated with the oblique collision of the indian plate against the arabian platform during the late campanian to the mid eocene the second event e w oriented compression is likely to have been formed during the late oligocene middle miocene during uplift the last event ne sw oriented compression probably took place during the miocene pliocene structures of the first two strike slip events have the same orientation as seismic scale faults observed in the subsurface of oman and abu dhabi in addition increasing vein intensity towards the top of the autochthonous formations in the oman mountains as well as the small angle between conjugate vein sets indicate that high fluid pressures that are thought to be present during strike slip deformation

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

paleoseismic results from the alpine site wasatch fault zone timing and displacement data for six holocene earthquakes at the salt lake city provo segment boundary

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

geochemical evidence for the origin of late triassic melange units in the oman mountains as a small ocean basin formed by continental rifting a useful tool to elucidate past tectonic environments is the geochemistry of volcanic and sedimentary rocks when used together the regional structural setting of the oman mountains indicates that deep water sediments and volcanic rocks formed adjacent to the rifted arabian margin in the late triassic near the axis of a narrow ocean basin of red sea type tholeiitic to trachytic extrusives formed seamounts associated with late triassic reefal build ups immobile trace element compositions point to a within plate origin the interbedded and overlying late triassic deep sea sedimentary cover comprises ribbon radiolarites and both distal siliclastic and calcareous turbidites that accumulated on an abyssal plain at least ca 180 km northeast of the arabian continent associated ferromanganiferous oxide sediments are interpreted as chemical precipitates derived from high temperature vents in the spreading axis of the young ocean basin pervasive regional subsidence took place during end triassic early jurassic time later in the cretaceous oceanic crust was consumed in a northeast dipping subduction zone morb type crust was subducted while late triassic volcanic edifices and sedimentary cover were accreted during eventual trench margin collision the semail ophiolite split into blocks allowing sub ophiolite melange rocks to be expelled upwards through corridors creating the batinah melange as the ophiolite nappe ploughed inboard over already thrust assembled abyssal plain sediments hawasina complex some duplexes were uplifted oversteepened overturned and then slid backwards onto the ophiolite to form the batinah sheets

a new high resolution δ13c record for the early triassic insights from the arabian platform a new carbon isotope record with conodont biostratigraphy is presented for the entire early triassic from the musandam peninsula united arab emirates uae this is a near continuous and exclusively shallow marine carbonate succession that allows analysis of a high resolution primary carbon cycling signature in the absence of significant depth dependent or lithologic controls the musandam carbon isotope record can be broadly correlated with global isotopic events but also resolves additional features including the presence of significant negative events during the previously identified positive excursions at both the dienerian smithian and smithian spathian boundaries a further positive event is revealed during the development of the mid spathian negative excursion a feature not previously reported in any other section these new short lived events are probably related to the occurrence of the more widely recognized early triassic excursions and may represent fluctuations in the driving mechanisms superimposed on the continued instability of the global carbon cycle in the aftermath of the end permian extinction together these features highlight additional complexities to the early triassic carbon cycle perturbations than previously documented

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