impact of dynamic sedimentation on facies heterogeneities in lower cretaceous peritidal deposits of central east oman this study based in the haushi huqf area of central east oman aims to characterize the controls on facies distribution and geometries of some of the best preserved examples of lower cretaceous tidal flat facies within the tethyan epeiric platform field petrographic and geochemical data were acquired from the barremian aptian jurf and qishn formations that crop out in a 500 1000 m2 butte thus allowing for pseudo three dimensional quantitative data acquisition of the dimensions and spatial distributions of discontinuity surfaces and sedimentary bodies the interpretation presented here suggests that the main processes impacting sedimentation in the lower cretaceous peritidal environment of the haushi huqf were transport and erosion processes related to storm waves and currents the vertical evolution of the carbonate system is organized into six types of metre scale depositional sequences from subtidal dominated sequences to supratidal capped sequences which are bounded by regional discontinuity surfaces at subaerial exposure and submarine erosion surfaces associated with a base level shift sedimentary horizons along the entire depositional profile are cut by scours possibly created by storm events chemostratigraphy allows correlation between the haushi huqf and the age equivalent sections logged in the interior of the platform in oman the correlation suggests that the change from subtidal to intertidal depositional sequences during the late highstand is coeval with the development of rudist dominated shoals on the shelf this study is the first to discuss the controls on lower cretaceous peritidal carbonate cyclicity of the arabian epeiric platform the results presented here also offer a unique quantitative dataset of the distribution and dimensions of peritidal carbonate shoals and storm scours in a regional sequence stratigraphic context

eustatic controls on carbonate facies in reservoirs and seals associated with mesozoic hydrocaron fields of the arabian gulf and the gulf of mexico abstract abundant subsurface data for mesozoic and cenozoic sections of the us gulf coast and the middle east make it possible to track the relationship of shelf carbonates and evaporites associated with minor amounts of clastics to eustasy our contention is that because the sedimentary deposition for both regions was in part controlled by gentle tectonic subsidence punctuated by eustatic variations the major hydrocarbon fields which occur here can be related to sea level behaviur at the time of deposition of the reservoir sections and their early diagenesis with the exception of chalks most of these carbonate hydrocarbon fields can be related to highstand system tracts and include the following 1 1 keep up reservoirs with sheet like geometry formed when carbonate accumulation matched sea level rise aggrading to form shoaling upward cycles during sea level highstands 2 2 give up and catch up reservoirs with lense like carbonate geometry formed on drowned shelves during and following rapid sea level rises often downslope from carbonate margins give up reservoirs occur when carbonate accumulation was unable to match sea level rise and catch up reservoirs form where carbonate accumulation was initially unable to keep pace with the sea level rise but then aggraded to sea level 3 3 reservoirs with the prograded discontinuous clinoform geometry of the platform margin formed during stillstands by carbonate accumulation that not only kept up with the sea level rise but also advanced in a seaward direction source rocks for these carbonate reservoirs are often formed during rapid sea level rises while the reservoir seals are usually transgressive shales dense transgressive limestones and or highstand evaporites

elemental geochemistry and strontium isotope stratigraphy of cenomanian to santonian neritic carbonates in the zagros basin iran abstract a neo tethyan upper cenomanian santonian neritic carbonate ramp succession sarvak and ilam formations drilled in the zagros basin in southwest iran was investigated via detailed sedimentology microfacies analysis elemental geochemistry and sr isotope stratigraphy sis the succession contains two exposure surfaces which are known as the ct es and mt es cenomanian turonian and middle turonian respectively and associated prominent negative carbon isotope excursions that represent important regional stratigraphic marker horizons precise knowledge about the onset of platform exposure and the duration of the exposure related hiatus however is currently lacking due to a rather low resolved shallow water biostratigraphic framework and a bulk carbonate carbon isotope pattern that clearly differs from global late cretaceous reference curves therefore the existing bio chemostratigraphic framework was complemented by bulk carbonate strontium isotope stratigraphy sis as bulk carbonate material is in particular prone to diagenetic alteration a careful selection of least altered samples has been carried out by means of elemental geochemistry and petrography in contrast to what could be expected the meteoric alteration of limestones beneath both exposure surfaces is not clearly expressed by increasing iron and manganese and coeval decreasing strontium contents on the contrary the impact of meteoric diagenesis is well illustrated via pronounced increases in rb concentrations and concomitant prominent positive shifts to radiogenic strontium isotope values an observation that clearly reflects the decay of continentally derived 87 rb into 87 sr rubidium corrected strontium isotope values place the ct es around the cenomanian turonian boundary and point to an exposure duration of less than 0 4 myr this rather short term ct es related hiatus is supported by petrographic evidence which indicates a youth karstification stage of strata beneath the ct es following sis the ilam sarvak transition at the top of nezzazatinella dicyclina interval zone coincides with the mt es carbonates placing above this transition ilam formation are ascribed to the earliest to latest early santonian while carbonates immediately beneath the mt es sarvak formation are dated as late turonian sis thus indicates a long lasting hiatus of 4 5 myr associated with the mt es emergence represented by the ct es is here proposed as harbinger of the mt es in the zagros basin which most likely resulted from stepwise peripheral bulging due to ophiolite obduction in combination with a small scale global sea level fall around 94 ma

mg ca and sr ca as novel geochemical proxies for understanding sediment transport processes within coral reefs sediment transport is a key driver of reef zonation and biodiversity where an understanding of sediment dynamics gives insights into past reef processes and allows the prediction of geomorphic responses to changing environmental conditions however modal conditions within the back reef seldom promote sediment transport hence direct observation is inherently difficult large benthic foraminifera lbf have previously been employed as tracers to infer sediment transport pathways on coral reefs as their habitat is largely restricted to the algal flat and post mortem their calcium carbonate test is susceptible to sediment transport forces into the back reef foraminiferal test abundance and post depositional test alteration have been used as proxies for sediment transport although the resolution of these measures becomes limited by low test abundance and the lack of variation within test alteration here we propose the novel use of elemental ratios as a proxy for sediment transport two species baculogypsina sphaerulata and calcarina capricornia were analysed using a taphonomic index within one tree and lady musgrave reefs great barrier reef australia inductively coupled plasma atomic emission spectrometry icp aes was used to determine mg ca and sr ca and these ratios were compared with taphonomic data decreases in test mg ca accompany increases in sr ca in specimens from algal flat to lagoonal samples in both species mirroring trends indicated by taphonomic values therefore indicating a relationship with test alteration to delineate mechanisms driving changes in elemental ratios back scattered electron bse images elemental mapping and in situ quantitative spot analyses by electron microprobe microanalysis epma using wavelength dispersive x ray spectrometers wds were performed on un altered algal flat and heavily abraded tests for both species epma analyses reveal heterogeneity in mg ca between spines and the test wall implying the loss of appendages results in a decrease in mg ca bse imaging and wds elemental mapping provided evidence for cementation facilitated by microbial boring as the primary cause of increasing sr ca these novel proxies hold advantages over taphonomic measures and further provide a rapid method to infer sediment transport pathways within back reef environments

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

cenomanian early turonian carbonate platform of northern oman stratigraphy and palaeo environments abstract the jebel akhdar and adam foothills outcrops in northern oman arabian peninsula offer the opportunity to study in detail the lateral and vertical changes of a cenomanian early turonian carbonate platform formed by the natih formation wasia group eleven sections with less than 5 km offset were logged to express metre scale lithological and biostratigraphical vertical changes the first rudist zonation is established complementing classical benthonic foraminifer and ammonite biozones typical cenomanian rudist association caprinids and radiolitids occur in the natih e c d a lower part whereas lower turonian hippuritid rudists are represented in the upper part of the natih a a sedimentological and palaeoecological approach leads to identification and interpretation the facies and discontinuities of the natih carbonate platform and to a reconstruction of its spatial organization application of the concepts of sequence stratigraphy allows interpretation of the units of the natih in terms of systems tracts an attempt is made to correlate the sequence stratigraphical model to eustatic sea level changes and regional tectonic events three palaeoenvironmental models taking into account bio and lithofacies are proposed

stratigraphy and tectonosedimentary evolution of a late aptian albian carbonate margin the northeastern jebel akhdar sultanate of oman abstract upper aptian albian shallow water carbonates with rudists large foraminifera and calcareous algae are described from northern oman in the northeastern part of the parautochton of jebel akhdar the corresponding lithostratigraphic unit the al hassanat formation is partly a time equivalent of the nahr umr shales of albian p p age which have a wide extent on the arabian craton the al hassanat platform developed in two main phases first during the late aptian early albian the platform was fringing an emerged area central jebel akhdar with a limited extent basinward then during the middle albian the flooding of the central jebel akhdar resulted in an extensive development of the platform and a connection with the nahr umr shelf this sedimentary evolution and its palaeogeographic expressions were mainly controlled by structural patterns extensive uplift and block faulting to the edge of the antecedent early aptian platform with a significant differential subsidence then a sag of the arabian promontory this tectonosedimentary dynamics was related to the migration of the oceanic adjacent tethyan plate and took place during the global geodynamic albian revolution

extensional faults in fine grained carbonates analysis of fault core lithology and thickness displacement relationships abstract a study of 103 extensional faults hosted by fine grained carbonates in western sinai svalbard and oman reveals that faults vary geometrically between simple cores and cores comprising fault splays lenses segment linkages and overlap structures fault core rocks are typically carbonate breccias carbonate and shale gouge shale smear secondary calcite cement and veins and host rock lenses there is a significant scatter in the core thickness for any given displacement but the overall pattern is that the thickness increases with displacement this increase best fits a power law function 0 29d 0 56 that describes a gradual decrease in the thickness displacement relationship for increasing slip along faults in more detail the general function can be seen as the sum of two power law trend lines the first representing thin localized fault cores with generally simple and planar geometry the second representing thicker fault cores with complex geometry of lenses and overlap structures and with fault rock membranes the studied faults show a significant change in composition and geometry from small 0 1 m to moderate 1 10 m and to large offset faults 10 400 m the overall pattern is that fault initiates as fractures filled with calcite veins and thin shear fractures that hosts gouge membranes with increased fault offset complexity increases with breakdown of veins more extensive fault rock membranes and a trend towards development of lenses when offset exceeds 100 m cores become complex with multiple slip zones cemented breccia and shale smear membranes and various types of lenses we envision that the fault development as reflected by offset is dominated by forces extension compression acting in the fault mechanical heterogeneity of wall rocks the core lithologies and their developing rheology and especially geometric effects arising from fault irregularities

the biostratigraphy of sediments in the volcanic unit of the samail ophiolite sedimentary rocks of pelagic and ocean ridge affinity interbedded with or overlying the volcanic sequence at the top of the oman ophiolite contain datable radiolarian faunas that indicate 1 that the lavas were erupted in an oceanic environment during a narrow time interval ranging from the early cenomanian to the early turonian and 2 that the age progression within this volcanic sequence matches its development from a ridge axis to an off axis setting emplacement of the ophiolite has been dated as late campanian early maestrichtian glennie et al 1974 thus the time gap between formation and emplacement was very narrow

thrust tectonics of the dibba zone and the structural evolution of the arabian continental margin along the musandam mountains oman and united arab emirates in the northern oman mountains several major thrust sheets of tethyan oceanic rocks dibba zone and a 12km thick complete ophiolite sequence have been thrust westward onto the depressed arabian continental margin musandam zone during the turonian to campanian late cretaceous early thrusting was dominantly a downward foreland propagating sequence as the higher earlier thrust sheets are folded around structurally lower and later culminations breached roof thrusts where imbricate thrusts do not always converge with a major roof thrust but in places actually penetrate up into the overlying duplex are common at outcrop scale affecting adjacent thrust sheets late stage breakback or leap frog thrusts cut through the whole pile of duplexes on to previously higher earlier dulexes late thrusting in the musandam zone affects the deeper previously autochthonous permian cenomanian shelf carbonate sequence and probably also the pre permian basement thrusting these rocks at least 15 km over previously allochthonous hawasina rocks late stage oblique dorsal culmination collapse along the se margin of the musandam mountains has downfaulted dibba zone rocks up to 2 5 km to the se along a hinged listric normal fault strain is transferred from the ne sw trending late cretaceous dibba zone to the n s striking mid tertiary musandam culmination at a major pivot point or transfer zone sw of the shelf carbonate culmination

cretaceous sequence of deformation in the se zagros fold thrust belt several major zones across the zagros fold thrust belt have been interpreted as indicating that orogeny took place progressively from ne to sw through discrete orogenic episodes during tertiary time this paper uses field evidence of growth onlaps and angular unconformities within the cretaceous stratigraphic column as well as existing geological maps and cross sections to indicate that deformation started as early as the late aptian and folded the whole width of the zagros belt simultaneously later events are indicated by folding at the end of the cenomanian and in the late turonian and santonian following the late cretaceous deformation phases the se zagros basin was divided into several longitudinal intra shelf basins which were separated by nw se trending cretaceous anticlines however with reference to our previous work it can be suggested that each of the sub basins was folded serially from ne to sw through a series of tectonic phases during the next episode of zagros orogeny in tertiary time the change of deformation style from concomitant to serial folding during the cretaceous and tertiary respectively is attributed to the existence of the hormuz salt and shearing at the base of the former basin and its absence at the base of the tertiary intra shelf basins

cretaceous high pressure metamorphism in ne oman and its relationship to subduction and ophiolite nappe emplacement an occurrence of glaucophane bearing schists is reported from near muscat in ne oman in rocks which underlie the upper cretaceous semail ophiolite nappe these blueschists formed by the metamorphism of quartz sandstones shales and basic igneous rocks belong to a pre permian basement in the area metamorphic micas phengites from these rocks have been dated at between 101 and 80 ma k ar ages indicating a mid to late cretaceous age for the high pressure event a syn to late f 1 assemblage of almandine glaucophane phengite in the pelites shows that the peak of metamorphism reached about 400 450 c and 4 8 kbars pressure this was followed by a greenschist facies overprint with the formation of epidote and albite porphyroblasts in the meta igneous rocks and a widespread retrogression to chlorite the high pressure metamorphism is ascribed to the effects of partial subduction of the ne oman continental margin during the initial stages of ophiolite obduction and the subsequent greenschist facies event to uplift of the area during the later stages of emplacement of the nappes

subduction zone polarity in the oman mountains implications for ophiolite emplacement two end member models have been proposed to account for the structure and metamorphism of rocks beneath the semail ophiolite in the oman mountains model a involves a single continuous ne directed subduction away from the continental margin during the late cretaceous the ophiolite and underlying thrust sheets of distal to proximal oceanic sediments were emplaced a minimum of 250 km sw onto the continental margin subduction of triassic jurassic oceanic basalts to c 10 kbar c 39 km depth led to the accretion of amphibolite facies rocks to the base of the ophiolite thrusting propagated towards the continental margin and ended with subduction of the thinned continental crust to c 20 kbar c 78 km depth choking the subduction zone buoyancy forces caused the rapid exhumation of eclogites blueschists and carpholite grade hp rocks along the ne margin of the continental plate during the later phase of foreland propagating thin skinned thrusting in the sw ne facing backfolding and backthrusting occurred in the hinterland with the final exhumation of the hp rocks model b follows recent suggestions that a nascent sw dipping subduction zone dipping beneath the continental margin existed between 130 and 95 ma prior to formation and emplacement of the ophiolite a major ne facing fold nappe structure in the pre permian basement rocks of saih hatat is interpreted as reflecting subduction beneath the margin two high pressure metamorphic events have been suggested the first predating ophiolite emplacement the second caused by ophiolite loading this model is untenable being based on a misinterpretation of the ne facing structures in northern saih hatat and on some dubious older 40ar 39ar cooling ages from the eclogite facies rocks of as sifah we conclude that all structures in northern oman and all the reliable geochronology point to a single emplacement obduction event lasting from cenomanian turonian time c 95 ma when amphibolites were accreted along the metamorphic sole of the ophiolite to campanian time when the continental margin was subducted to the ne producing blueschists and eclogites to the final thin skinned emplacement of all thrust sheets which ended before the late maastrichtian at c 68 ma

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

a case study of the pore water pressure fluctuation on the slip surface using horizontal borehole works on drainage well the infiltration of rainfall reduces shear strength on the slip surface by increasing pore water pressure resulting in increased landslide movement although pore water pressure fluctuation is an important factor influencing landslide activity it is difficult to observe its mechanism at various depths of the slip surface because of the complex hydrogeological structure this study aims to examine the pore water pressure fluctuation in shallow and deep strata of the slip surface the rainfall pressure head and drainage rate were observed at the tairasawa landslide before and after the drainage well work the pressure heads were measured in the vertical observation borehole with a screened section at the depth of slip surface the horizontal drain borings of drainage well were drilled for confining groundwater in a screened section at the same depth of slip surface after drilling a horizontal drain boring the pore water pressure on the slip surface was reduced and the decreasing volume in the deep stratum was larger than that in the shallow stratum the effects of horizontal drain boring could be easily evaluated by comparing the decrease in pore water pressure before and after the works furthermore the decrease in pore water pressure on the slip surface shows two significant characteristics first the variation in pore water pressure corresponds to drilling depth and seepage water in a horizontal drain boring second the decreasing effects of pore water pressure can be clearly seen when the drilling direction of a horizontal drain boring is near the vertical observation borehole

a platform to basin transition for lower aptian carbonates shuaiba formation of the northeastern jebel akhdar sultanate of oman abstract the platform to basin transition of the lower aptian shuaiba carbonate platform throughout a large part of the arabian peninsula has hitherto mainly been documented from subsurface data and has widely been regarded as having been progradational in northeastern jebel akhdar however the shuaiba platform did not prograde and was scarp bounded early lithification accounts for the rigid nature of the scarp a biological framework being nearly absent early exposure surfaces neptunian dykes sills internal breccias and other sediment features as well as the geographic coincidence of the platform scarp with older and younger scarps suggest a tectonic control of margin morphology and dynamics a contemporaneous peak of allodapic sediments and reactivation of older basement structures in adjacent basins also tends to indicate the importance of structural influence on platform margin organization