age dates of valley network drainage basins and subbasins within sabae and arabia terrae mars the precise timing of valley network drainage basin formation is critical to understanding the history of water and climate on mars to determine whether there are any variations in ages within separate drainage basins and subbasins that may reflect local or regional variations in climate or resetting from resurfacing e g impact ejecta or lava flows we dated 27 basins and subbasins in sabaea and arabia terrae the age dating basin technique we employed allowed sufficient precision to give accurate ages and shows that fluvial activity within the basins and subbasins ceased at approximately the same time around the early hesperian late hesperian transition our results support the hypothesis that valley networks formed during a unique fluvial optimum that may have shut off gradually because of a global climate change that affected all areas simultaneously on mars

a middle miocene carbonate platform under silici volcaniclastic sedimentation stress leitha limestone styrian basin austria depositional environments sedimentary evolution and palaeoecology abstract siliciclastic influx is a major control for neritic carbonates herein we present a shallow marine mixed silici volcaniclastic carbonate system from the middle miocene coralline algal dominated leitha limestone in the styrian basin austria the analyses of facies and stratal geometries reveal a succession of four depositional units and six facies types reef facies inter reef facies coralline algal debris facies rhodolith porites facies quartz sand planostegina facies coral carpet facies depositional unit 1 comprises patch reefs reef facies and surrounding carbonate sands inter reef facies which show a characteristic lateral succession of biotic associations reef corals rhodoliths nodular celleporiform bryozoans planostegina a similar modern analogue occurs in the red sea at the transition from patch reefs to seagrass meadows in contrast the coralline algal debris facies of depositional unit 2 represents a high energetic submarine dune environment a deepening shallowing trend is suggested by the gradual shift from the muddy rhodolith porites facies to the detritic quartz sand planostegina facies in depositional unit 3 while the vertical transition of coral carpet facies to rhodolith porites facies in depositional unit 4 suggests again a deepening despite an isolated inner basin setting on the middle styrian high the coralline algal and coral dominated benthic carbonate communities in all depositional units and facies were strongly influenced by terrigenous sedimentation coarser siliciclastic sedimentation was linked to low stands of relative sea level while fine clay fraction was deposited at any time due to the submarine alteration and reworking of volcanic ashes despite a high sedimentation stress the variety of coral communities patch reefs coral carpets non framework coral communities and coral diversity is unique for the entire central paratethys leptoseris and two not identified coral species one with thin platy plocoid the other with phaceloid branching growth form are new coral records for the central paratethys this is of particular importance for paleobiogeographic reconstructions since the styrian basin was located close to the northern margin of the global coral reef belt it is assumed that the relatively high total coral diversity reflects dynamic habitat and population structures in an unstable coral ecosystem at the edge of coral reef distribution which was highly vulnerable to tectonically controlled changes affecting nature and distribution of clastic sediments in general increasing siltation stress reduced coral diversity coral cover and colony sizes and led to the replacement of massive by platy growth forms and of suprastratal by constratal growth fabrics

carbonate ramp drowning caused by flexural subsidence the south pyrenean middle eocene foreland basin abstract a detailed sedimentological and magnetostratigraphic analysis of three selected sections of the eocene carbonate platforms of the south pyrenean jaca pamplona foreland basin has been carried out in the aragonese external sierras huesca spain the stratigraphic record spans from the middle late lutetian chron 20r sbz15 to the bartonian chron 18r sbz17 the lutetian bartonian transition was characterized by a major paleogeographic change from a turbiditic foredeep with associated peripheral carbonate ramps to deltaic sedimentation in most of the outcrops of the external sierras the peripheral carbonate platforms guara formation are overlained by prodelta and outer ramp marls arguis formation the drowning unconformity between these two formations in the outcrops located in the westernmost tip of the external sierras is documented herein for the first time in this area the guara formation is overlain by glauconitic limestones deposited in a carbonate ramp setting between these units a characteristic unconformity is observed with hard ground formation and local evidence of subaerial exposure in the shallowest domains of the study area the abundant glauconite found on top of this unconformity records a starvation period in the basin followed by the development of a new carbonate ramp system during bartonian times santo domingo member of the arguis formation magnetostratigraphic and sedimentological data show that tectonic tilting occurred in latest lutetian times prior to the drowning process this suggests the influence of the flexural subsidence in the cratonic margin of the foreland as a result of the advance of a basement thrust in the hinterland nevertheless the correlation of the uppermost lutetian drowning unconformity with a basinwide regional sea level rise which may have further been global suggests an interplay between tectonic and eustatic processes in the drowning of the late lutetian south pyrenean carbonate ramps in this work we point out a narrowing of the carbonate ramp together with a relative sea level rise as the processes responsible for the drowning of the upper guara mb carbonate ramp these processes could be responsible for the development of drowning unconformities in cratonic margins of other foreland basins as carbonate ramps have a high sediment production potential the narrowing of the carbonate factory could provide the conditions for the drowning of the carbonate ramp system in a subsequent sea level rise

late stage tectonic evolution of the al hajar mountains oman new constraints from palaeogene sedimentary units and low temperature thermochronometry mountain building in the al hajar mountains ne oman occurred during two major shortening stages related to the convergence between africa arabia and eurasia separated by nearly 30 ma of tectonic quiescence most of the shortening was accommodated during the late cretaceous when northward subduction of the neo tethys ocean was followed by the ophiolites obduction on top of the former mesozoic margin this shortening event lasted until the latest santonian early campanian maastrichtian to eocene carbonates unconformably overlie the eroded nappes and seal the cretaceous foredeep these neo autochthonous post nappe sedimentary rocks were deformed along with the underlying cretaceous tectonic pile during the second shortening event itself including two main exhumation stages in this study we combine remotely sensed structural data seismic interpretation field based structural investigations and apatite u th he ahe cooling ages to obtain new insights into the cenozoic deformation stage seismic interpretation indicates the occurrence of a late eocene flexural basin later deformed by an oligocene thrusting event during which the post nappe succession and the underlying cretaceous nappes of the internal foredeep were uplifted this stage was followed by folding of the post nappe succession during the miocene ahe data from detrital siliciclastic deposits in the frontal area of the mountain chain provide cooling ages spanning from 17 3 to 42 ma consistent with available data for the structural culminations of oman our work points out how renewal of flexural subsidence in the foredeep and uplift of the mountain belt were coeval processes followed by layer parallel shortening preceding final fold amplification

nonuniform cratering of the terrestrial planets article history we estimate the impact flux and cratering rate as a function of latitude on the terrestrial planets using a model distribution of planet crossing asteroids and comets bottke w f morbidelli a jedicke r petit j m levison h f michel p metcalfe t s 2002 icarus 156 399 433 after determining the planetary impact probabilities as a function of the relative encounter velocity and encounter inclination the impact positions are calculated analytically assuming the projectiles follow hyperbolic paths during the encounter phase as the source of projectiles is not isotropic latitudinal variations of the impact flux are predicted the calculated ratio between the pole and equator is 1 05 for mercury 1 00 for venus 0 96 for the earth 0 90 for the moon and 1 14 for mars over its long term obliquity variation history by taking into account the latitudinal dependence of the impact velocity and impact angle and by using a crater scaling law that depends on the vertical component of the impact velocity the latitudinal variations of the cratering rate the number of craters with a given size formed per unit time and unit area is in general enhanced with respect to the equator the polar cratering rate is about 30 larger on mars and 10 on mercury whereas it is 10 less on the earth and 20 less on the moon the cratering rate is found to be uniform on venus the relative global impact fluxes on mercury venus the earth and mars are calculated with respect to the moon and we find values of 1 9 1 8 1 6 and 2 8 respectively our results show that the relative shape of the crater size frequency distribution does not noticeably depend upon latitude for any of the terrestrial bodies in this study nevertheless by neglecting the expected latitudinal variations of the cratering rate systematic errors of 20 30 in the age of planetary surfaces could exist between equatorial and polar regions when using the crater chronology method

unravelling the depositional origins and diagenetic alteration of carbonate breccias carbonate breccias dissociated from their platform top counterparts are little studied despite their potential to reveal the nature of past shallow water carbonate systems and the sequential alteration of such systems a petrographic and stable isotopic study allowed evaluation of the sedimentological and diagenetic variability of the cenozoic batu gading limestone breccia of borneo sixteen lithofacies representing six facies groups have been identified mainly from the breccia clast on the basis of shared textural and compositional features clasts of the breccia are representative of shallow carbonate platform top and associated flank to basinal deposits dominant inputs are from rocky karstic shorelines or localised seagrass environments coral patch reef and larger foraminiferal rich deposits early pre brecciation alteration including micritisation rare dissolution of bioclasts minor syntaxial overgrowth cementation pervasive neomorphism and calcitisation of bioclasts and matrix was mainly associated with marine fluids in a near surface to shallow burial environment the final stages of pre brecciation diagenesis include mechanical compaction and cementation of open porosity in a shallow to moderate depth burial environment post brecciation diagenesis took place at increasingly moderate to deep burial depths under the influence of dominantly marine burial fluids extensive compaction circum clast dissolution seams and stylolites have resulted in a tightly fitted breccia fabric with some development of fractures and calcite cements a degree of facies specific controls are evident for the pre brecciation diagenesis pervasive mineralogical stabilisation and cementation have however led to a broad similarity of diagenetic features in the breccia clasts thereby effectively preserving depositional features of near original platform top and margin environments there is little intra clast alteration overprint associated with subsequent clast reworking and post brecciation diagenesis the diagenetic and to an extent depositional and clast characteristics of the batu gading deposits are diagnostic of breccia origins the predominance of early and pervasive stabilisation of calcitic components pervasive compaction resulting in a fitted texture and paucity of meteoric dissolution or cementation effects are collectively all indicators of slope deposition and lithification these features are comparable with other regional and global examples of submarine slope breccias and consistent with the prior interpretation that the carbonate platform at batu gading developed in a rotating wedge top basin wannier 2009 the results of this study along with regional analogues suggest the potential for reworked carbonates debris in slope settings to be a viable way of investigating carbonate platform variability and their subsequent alteration in the absence of preserved platform top or margin deposits

paleocene lower eocene carbonate platforms of westernmost tethys abstract the paleocene lower eocene succession is well exposed in sierra espuna mula basin betic cordillera s spain and carbonate platforms are well represented as part of this succession the study of the paleoenvironmental evolution of these platforms has allowed to cover an important gap in the knowledge in the westernmost tethys thirteen microfacies mf1 to mf13 were recognized based mainly on the fossil assemblage principally larger benthic foraminifera texture and fabric of the microfacies the fossiliferous assemblage of the entire succession shows a mixture of photozoan and heterotrophic biogenic elements typical of an inner to outer ramp environment of a warm temperate biogeographic province fragments of hermatypic corals have also been detected in the lower part of the succession paleocene allowing thinking in propitious conditions in this period the succession evolves upwards lower eocene to low energy shallow marine protected environments lagoon in inner ramp settings in addition abundant porcelaneous larger benthic foraminifera such as alveolinids and soritids are indicative of euphotic shallow marine conditions in moderately oligotrophic upper subtidal environments in the upper part of the succession hermatypic corals as displaced fragments and in situ isolated coral phaceloid colonies also appear together with other biogenic components indicating warm shallow and euphotic marine conditions coral maerl environment lenticular larger benthic foraminifera characterizing marine mesophotic and oligotrophic habitats can be found in the upper part of the middle ramp and flattened larger benthic foraminifera forms indicating lowermost mesophotic conditions in a distal middle ramp the obtained results have been compared with other similar tethyan sectors obtaining a broader view the biogenic marine association is characterized by the absence of the lockhartia community of the tethyan domain together with the dominance of alveolinids nummulitids and orthophragminids during most of the paleocene northern mediterranean tethys platforms were located in the middle paleolatitudes and characterized by coral reef and coralgal biofacies the studied platforms located at a latitude close to 25 n show in a ramp like context underdeveloped in situ coral constructions probably of patch reef type in the early eocene the expansion and abundance of the larger benthic foraminifera and the practical disappearance of coral took place in the sedimentary platforms through the entire tethys however in the study area small reef coral build ups have also been observed in the lower cuisian beds indicating that in westernmost tethys coral construction continued at these latitudes

middle eocene seagrass facies from apennine carbonate platforms italy abstract two stratigraphic sections located in the latium abruzzi monte porchio central apennines central italy and in the apulian carbonate platform s cesarea torre tiggiano salento southern italy were measured and sampled to document the sedimentological characteristic and the faunistic assemblages of middle eocene seagrass deposits the faunistic assemblages are dominated by porcellaneous foraminifera orbitolites alveolina idalina spiroloculina quinqueloculina triloculina and abundant hooked shaped gypsinids associated with hooked red algae and green algae halimeda fabiania rotaliids and textulariids as well as nummulitids are subordinated the samples were assigned to lutetian sbz13 16 according to the occurrence of nummulites cf lehneri alveolina ex gr elliptica idalina berthelini orbitolites complanatus slovenites decastroi and medocia blayensis at santa cesarea reticulate nummulites occur in association with alveolina spp and halkyardia minima marking the lower bartonian sbz17 three main facies associations have been recognised i larger porcellaneous foraminiferal grainstones with orbitolitids and alveolinids deposited into high energy shallow water settings influenced by wave processes that reworked the sediments associated with a seagrass ii grainstone to packstone with small porcellaneous foraminifera and abundant permanently attached gypsinids deposited in a more protected e g small embayment in situ vegetated environment iii bioclastic packstone with parautochthonous material reworked from the seagrass by rip currents and accumulated into rip channels in a slightly deeper environment the biotic assemblages suggest that the depositional environment is consistent with tropical to subtropical vegetated environments within oligotrophic conditions

epiphyte communities on thalassia testudinum from grand cayman british west indies their composition structure and contribution to lagoonal sediments abstract thalassia testudinum the most common seagrass found in lagoons around grand cayman influences sedimentation by baffling currents binding sediment on the seafloor and providing substrates for a diverse epiphytic biota about 85 of the epiphytic biota is formed of at least 3 species of coralline algae 72 species of foraminifera and 61 species of diatoms the rest of the biota is formed of sponges gastropods ostracods coccoliths dinoflagellates brown algae and worms the epiphytes are organized in three communities that are part of an organized tripartite community succession the basal diatom community is overlain by the coralline algae community which is then overlain by a community composed of a variety of taxa the coralline algae community which is the most extensive typically covers 75 of the leaf s surface potentially the skeletons of these epiphytes can make a significant contribution to the fine grained sediment budget of these lagoons surprisingly only a few of the epiphytes were found in the lagoonal sediment it appears therefore that the epiphytes are lost through skeletal dissolution or transported out of the lagoon following storms irrespective of the cause the epiphytes do not form a significant part of the lagoon sediment in grand cayman

facies analysis and palaeoenvironmental interpretation of the late oligocene attard member lower coralline limestone formation malta the oligocene represents a key interval during which coralline algae became dominant on carbonate ramps and luxuriant coral reefs emerged on a global scale so far few studies have considered the impact that these early reefs had on ramp development consequently this study aimed at presenting a high resolution analysis of the attard member of the lower coralline limestone formation late oligocene malta in order to decipher the internal and external factors controlling the architecture of a typical late oligocene platform excellent exposures of the lower coralline limestone formation occurring along continuous outcrops adjacent to the victoria lines fault reveal in detail the three dimensional distribution of the reef associated facies a total of four sedimentary facies have been recognized and are grouped into two depositional environments that correspond to the inner and middle carbonate ramp the inner ramp was characterized by a very high energy shallow water setting influenced by tide and wave processes this setting passed downslope into an inner ramp depositional environment which was colonized by seagrass and interfingered with adjacent areas containing scattered corals the middle ramp lithofacies were deposited in the oligophotic zone the sediments being generated from combined in situ production and sediments swept from the shallower inner ramp by currents compositional characteristics and facies distributions of the attard ramp are more similar to the miocene ramps than to those of the eocene an important factor controlling this similarity may be the expansion of the seagrass colonization within the euphotic zone this expansion may have commenced in the late oligocene and was associated with a concomitant reduction in the aerial extent of the larger benthonic foraminifera facies stacking pattern analysis shows that the depositional units parasequences at the study section are arranged into transgressive regressive facies cycles this cyclicity is superimposed on the overall regressive phase recorded by the attard succession furthermore a minor highstand correlated with the ru4 ch1 sequence and subsequent minor lowstand ch2 sequence have been recognized the biota assemblages of the attard member suggest that carbonate sedimentation took place in subtropical waters and oligotrophic to slightly mesotrophic conditions the apparent low capacity of corals to form wave resistant reef structures is considered to have been a significant factor affecting substrate stability at this time the resulting lack of resistant mid ramp reef frameworks left this zone exposed to wave and storm activity thereby encouraging the widespread development of coralline algal associations dominated by rhodoliths

numerical forward modeling of carbonate platform dynamics an evaluation of complexity and completeness in carbonate strata abstract it is clear that carbonate strata are complex and incomplete but the nature and origins of the complexity and the origin and distribution of hiatuses remain poorly understood a three dimensional numerical forward model of carbonate platform systems has been used to investigate how variations in complexity and completeness arise in carbonate strata the model includes depth dependent carbonate production occurring as a stochastic mosaic of producing elements across a topographic surface it also includes depth dependent sediment erosion transport and deposition governed by a regional transport direction that can vary stochastically through time and by wave refraction that causes local variations in transport direction combined mosaic production and variable sediment transport create a complex distribution of prograding islands generating self organizing shallowing upward parasequences of variable thickness and variable lateral extent hiatuses occur throughout the parasequences not just at the base and top generated by nondeposition due to mosaic production and by erosional scour this erosion is triggered by variations in water depth and fetch distance created by complex island morphologies preserved strata represent between 15 and 60 of total elapsed time measured at a 2 ky resolution and much of the preserved thickness represents punctuated deposition with depositional events spanning only a few thousand years stratigraphic completeness depends on subsidence rate and sediment transport rate so that completeness generally increases with increasing subsidence rate and decreasing transport rate but shows a nonlinear relationship with subsidence rate this suggests that reliable estimates of completeness of ancient carbonate strata require more than knowledge of subsidence rate and sea level change particularly because the real situation is likely to be considerably more complex than represented in this model the stochastic production mosaic and stochastic variations in regional transport direction create complex strata whereas the self organizing island progradation process creates simpler ordered strata a combination of the two processes creates an intermediate level of complexity producing strata consisting of laterally impersistent parasequences with numerous erosion surfaces and complex stacking patterns and complex thickness distributions this has important implications for parasequence correlation in outcrop and the subsurface

investigation of crater saturation using spatial statistics abstract conventional techniques for investigation of crater populations make use of size frequency distributions but typically disregard the statistical properties of the spatial distribution of craters cratering of a surface is generally a spatially random process so the distributions of craters on lightly cratered surfaces can be expected to be random as crater obliteration becomes important however the situation changes every random distribution has regions of sparseness and regions of clustering craters that form in areas of sparseness obliterate few older craters so the sparseness is filled in craters that form in areas of clustering obliterate more older craters relatively reducing the clustering as sparseness is filled in and clustering is reduced the spatial distribution should progress from one that is random to one that is more uniform than random we show that the spatial distribution of craters on a lightly cratered lunar maria surface is consistent with randomness but that the distributions on heavily cratered portions of rhea and callisto are markedly more uniform than random we develop a simple model of crater formation and obliteration and use it to investigate the statistical behavior of crater spatial distributions as crater saturation is approached we find that the use of spatial distributions to investigate saturation is more robust to model uncertainties than is the use of crater density alone using a simple statistical parameter the z statistic we find that 25 of the craters formed to date on our study areas on rhea and callisto have been obliterated by subsequent cratering adjusting the z statistic for crater floor area effects we find evidence that crater saturation has been reached on rhea

the dagpazari carbonate platform mut basin southern turkey facies and environmental reconstruction of a coral reef system during the middle miocene climatic optimum abstract plate tectonics and climate change have deeply influenced the evolution of coral reef systems of the mediterranean during the miocene most of this information is based on studies of coral reefs from the western and central sectors of the mediterranean this study reports facies analyses sr isotope stratigraphy and environmental reconstructions of the dagpazari coral reef system located within the mut basin in southern turkey stratigraphic correlations and sr isotope ratios on several oyster shells date the dagpazari reef to the early langhian ten different facies have been recognized and their arrangement has led to the identification of two main depositional units interpretation of the biotic associations indicates that the dagpazari depositional system developed constantly within the euphotic zone the reef framework was mainly built by massive faviid and poritid zooxanthellate corals whereas loose grain sediments were essentially produced by halimeda coralline red algae or influenced by the presence of seagrass colonizations this study highlights for the first time the great importance of halimeda as sediment producer in the eastern mediterranean coral reef systems this role is related to the common occurrence of halimeda plates within almost all the reef facies but especially to the presence of large in situ bioherms dominated by the algal segments dagpazari langhian halimeda bioherms also represent the oldest of these structures so far recorded in the fossil record the development of the dagpazari platform was mainly controlled by eustatic fluctuations of the sea level and by the morphology of the antecedent substrate in particular the occurrence of a pre existent topographic high promoted the constant presence of shallow water environments throughout the depositional history of the reef system with the production of euphotic carbonates both landward and basinward and the consequent formation of a small elliptical platform 87sr 86sr ages place the dagpazari reef system exactly within the middle miocene climatic optimum phase the most recent warm phase of the earth this suggests that zooxanthellate corals were able to exert their reef building capacity in shallow water settings even during periods of global warming thus being not exclusively an adaptation to cooling climates as proposed in the recent debates

seagrass related carbonate ramp development at the front of a fan delta burdigalian new caledonia insights into mixed carbonate siliciclastic environments abstract past shallow water carbonate environments of the main island of new caledonia nc have been subject to high terrigenous influx derived from the erosion of ultramafic obducted nappes and are therefore a relevant case study for characterizing neritic carbonate production in mixed carbonate siliciclastic systems under a tropical climate more particularly we focused on burdigalian carbonate sedimentary records cropping out on the western coast of nc in the nepoui area based on a comprehensive sedimentological study of cores and outcrops we established a new depositional model of an alluvial fan to carbonate ramp transition shallow water euphotic carbonate production was dominated by seagrass related biota and corals derived from small sized bioconstructions extensional tectonics and associated normal faulting driven by post obduction isostatic rebound favored carbonate ramp aggradation and preservation the carbonate ramp was incised by conglomerate filled terminal distributary channels which indicate that terrigenous inputs remained significant during marine transgression and did not inhibit the development of seagrass and scleractinian carbonate factories phytal substrates induced by seagrass and or macro algae seafloor colonization strongly controlled the nature of carbonate production and promoted the accumulation of foraminiferal coralline algal sediments seagrass development at the front of the fan delta is interpreted to have controlled the preservation of a diverse and significant carbonate production by reducing water turbidity and by limiting the risk of suffocation for filter feeding biota in such a high terrigenous influx setting

heterozoan carbonates in oligotrophic tropical waters the attard member of the lower coralline limestone formation upper oligocene malta abstract photozoan and heterozoan skeletal assemblages are controlled by their trophic requirements i e light based photosynthesis versus other sources and temperature photozoan associations tend to dominate tropical and subtropical waters whereas heterozoan carbonate systems tend to occur in cooler waters and in localised areas that are affected by nutrient rich upwelling or terrestrial runoff because of the wide climatic spectrum in which heterozoan carbonates are found their interpretation is often problematic we present a high resolution analysis of the attard member of the lower coralline limestone formation upper oligocene malta the biotic associations and palaeolatitudinal reconstructions suggest that carbonate sedimentation took place in tropical waters under oligotrophic conditions an important factor controlling the spread of heterozoan assemblages in the late oligocene of malta seems to be related to the palaeoecology and evolution of zooxanthellate the limited capacity of corals to thrive in high light conditions and to form a wave resistant reef promoted the diffusion of heterozoan assemblages

architectural complexity of a carbonate transgressive systems tract induced by basement physiography three dimensional exposure of the plio pleistocene calcarenite di gravina formation around matera horst italy permits analysis of the architecture and internal complexities of carbonate sedimentary bodies around a palaeoisland spatial organization of the different lithosomes along with their skeletal composition sedimentary structures and bedding patterns helps decipher the key factors that controlled platform architecture and distribution of heterogeneities basement physiography type and loci of carbonate production bottom currents and changes in accommodation relative sea level changes resulted from high frequency glacioeustatic cycles that punctuated an overall tectonically induced transgression topographic relief fragmentation of the limestone basement and wave energy controlled lithoclastic supply basement physiography and relative sea level changes determined the area available for carbonate producing biotas and thus the amount and type of skeletal sediments on the moderately dipping south western margin waves and associated currents re distributed the lithoclasts derived from coastal abrasion bioclasts mostly derived from epiphytic seaweed production in the shoreface infralittoral prisms resulted from downdip transport progradation and longshore transport which controlled along strike continuity of the prisms where basement continuity was interrupted at the margin of the palaeoisland a lithoclastic fan was deposited from dumping sediments carried by shore parallel currents fan shaped skeletal bodies coalesced to form an apron on the steeper northern side of the palaeoisland when a structural platform was flooded and epiphytic carbonates were shed red algae contribution depended on the available oligophotic area which in turn was controlled by high frequency sea level cycles basement physiography and apron aggradation the internal architecture of this apron resembles a low stand wedge but it accumulated during transgression deeper water contour parallel currents formed a lithosome at the foot of the structural relief interpreted as drift deposits it is composed of shallow water benthonic skeletal components planktonic foraminifera and some limeclasts

k ar ages of alkaline igneous rocks in the northern oman mountains ne arabia and their relations to rifting passive margin development and destruction of the oman tethys k ar ages of biotites from a variety of alkaline volcanics and minor intrusive rocks in the nothern oman mountains allochthon give a range of ages from triassic 230 ma to mid cretaceous 92 ma and represent igneous activity on the oman continental margin throughout the mesozoic this was a passive margin destroyed by the emplacement across it of a pile of nappes in the late cretaceous including a largely intact thrust sheet of upper cretaceous oceanic lithosphere the semail ophiolite biotite ankaramite dykes cutting compositionally similar volcanics in the thrust complex immediately beneath the ophiolite give triassic ages and are related to the rifting and break up of the northeast arabian margin at the beginning of formation of the oman tethys mid cretaceous cenomanian turonian ages are mostly recorded from the northern part of the mountains where there are alkaline tuffs in a sedimentary melange they are approximately the same age as the ophiolite and may be related to tectonic instability of the oman margin immediately prior to ophiolite emplacement alkaline sills intrusive into a variety of rocks including triassic volcanics give jurassic and cretaceous ages and are interpreted as periodic alkaline activity on the oman margin throughout passive margin development

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

constraints on the source of lunar cataclysm impactors multiple impact basins formed on the moon about 3 8 gyr ago in what is known as the lunar cataclysm or late heavy bombardment many workers currently interpret the lunar cataclysm as an impact spike primarily caused by main belt asteroids destabilized by delayed planetary migration we show that morphologically fresh class 1 craters on the lunar highlands were mostly formed during the brief tail of the cataclysm as they have absolute crater number density similar to that of the orientale basin and ejecta blanket the connection between class 1 craters and the cataclysm is supported by the similarity of their size frequency distribution to that of stratigraphically identified imbrian craters majority of lunar craters younger than the imbrium basin including class 1 craters thus record the size frequency distribution of the lunar cataclysm impactors this distribution is much steeper than that of main belt asteroids we argue that the projectiles bombarding the moon at the time of the cataclysm could not have been main belt asteroids ejected by purely gravitational means

lunar impact basins stratigraphy sequence and ages from superposed impact crater populations measured from lunar orbiter laser altimeter lola data 1 impact basin formation is a fundamental process in the evolution of the moon and records the history of impactors in the early solar system in order to assess the stratigraphy sequence and ages of impact basins and the impactor population as a function of time we have used topography from the lunar orbiter laser altimeter lola on the lunar reconnaissance orbiter lro to measure the superposed impact crater size frequency distributions for 30 lunar basins d 300 km these data generally support the widely used wilhelms sequence of lunar basins although we find significantly higher densities of superposed craters on many lunar basins than derived by wilhelms 50 higher densities our data also provide new insight into the timing of the transition between distinct crater populations characteristic of ancient and young lunar terrains the transition from a lunar impact flux dominated by population 1 to population 2 occurred before the mid nectarian this is before the end of the period of rapid cratering and potentially before the end of the hypothesized late heavy bombardment lola derived crater densities also suggest that many pre nectarian basins such as south pole aitken have been cratered to saturation equilibrium finally both crater counts and stratigraphic observations based on lola data are applicable to specific basin stratigraphic problems of interest for example using these data we suggest that serenitatis is older than nectaris and humboldtianum is younger than crisium sample return missions to specific basins can anchor these measurements to a pre imbrian absolute chronology

atmospheric circulation upwelling and organic rich rocks in the mesozoic and cenozoic eras abstract by using the basic principles of atmospheric circulation and analogies from present circulation patterns it is possible to construct qualitative atmospheric circulation models on paleogeographic maps the wind patterns predicted by these models then serve as the basis for predicting the locations of ancient upwelling zones atmospheric circulation and upwelling models for seven geologic stages in the mesozoic and cenozoic were constructed and the distribution of the upwelling zones compared with the distribution of organic rich rocks for all time periods together the correlation was statistically significant when the individual time periods were analyzed separately the following pattern emerged significant correspondence between upwelling zones and organic rich rocks in the triassic middle early cretaceous to late cretaceous and middle paleogene to neogene no significant correspondence was found for the intervening times upwelling does not account for all organic rich rocks so called anoxic oceanic events and transgressions play an important role in their deposition it is suggested that upwelling contributes significantly to the pattern of organic rich rock distribution and is important in determining organic facies

warm temperate marine carbonate sedimentation in an early miocene tide influenced incised valley provence south east france the saumane venasque compound palaeovalley succession accumulated in a strongly tide influenced embayment or estuary warm temperate normal marine to brackish conditions led to deposition of extensive cross bedded biofragmental calcarenites echinoids bryozoans coralline algae barnacles and benthic foraminifera were produced in seagrass meadows on rocky substrates colonized by macroalgae and within subaqueous dune fields there are two sequences s1 and s2 the first of which contains three high frequency sequences s1a s1b and s1c sequence 1 is largely confined to the palaeovalley with its upper part covering interfluves each of these has a similar upward succession of deposits that includes i a basal erosional surface that is bored and glauconitized ii a discontinuous lagoonal lime mudstone or wackestone iii a thin conglomerate generated by tidal ravinement iv a transgressive systems tract series of cross bedded calcarenites v a maximum flooding interval of argillaceous muddy quartzose open marine limestones and vi a thin highstand systems tract of fine grained calcarenite tidal currents during stages s1a s1b and s1c were accentuated by the constricted valley topography whereas basin scale factors enhanced tidal currents during the deposition of s2 the upper part of the succession in all but s1c has been removed by later erosion there is an overall upward temporal change with quartz barnacles encrusting corallines and epifaunal echinoids decreasing but bryozoans articulated corallines and infaunal echinoids increasing this trend is interpreted to be the result of changing oceanographic conditions as the valley was filled bathymetric relief was reduced rocky substrates were replaced as carbonate factories by seagrass meadows and subaqueous dunes and the setting became progressively less confined and more open marine these limestones are characteristic of a suite of similar cool water calcareous sand bodies in environments with little siliciclastic or fresh water input during times of high amplitude sea level change wherein complex inboard antecedent topography was flooded by a rising ocean

evaluation of the simple settling theory for predicting sediment deposition by overland flow experiments were conducted in the laboratory to evaluate the influence of sediment concentration sediment grain size distribution bed slope and flow discharge on sediment deposition rates and patterns associated with a reduction in bed slope the experimental data clearly indicate that sediment deposition by overland flow is a very selective process fine particles remain almost entirely in suspension and coarse particles are deposited quickly analysis of the data shows that up to a critical unit discharge a simple settling equation without a transport term assuming continuous mixing of the sediment and water gives a good prediction of the overall sediment delivery ratio and the grain size distribution of the deposited and the exported sediment however there are some discrepancies for the clay the coarse silt and the sand fractions the assumption of continuous mixing is tested by investigating the sedimentation patterns of very narrow size classes the observed decrease of sediment concentration versus distance from the inflow point for these individual sediment size classes closely agrees with the prediction assuming continuous mixing when the critical unit discharge is exceeded hydraulic properties of the overland flow do influence the sediment delivery outcomes at discharges exceeding the threshold value the simple settling theory underpredicts the sediment delivery ratio in these hydraulic conditions a transport term needs to be incorporated into the simple settling theory it is shown that the transport capacity and the re entrainment model yield similar expressions for the description of sediment transport by overland flow over an area of net deposition the experimental data indicate that the re entrainment of previously deposited sediment is non selective copyright 1999 john wiley sons ltd

the miocene nullarbor limestone southern australia deposition on a vast subtropical epeiric platform abstract the early to middle miocene nullarbor limestone forms the vast karsted nullarbor plain in southern australia and may be the most extensive miocene carbonate deposit described to date these carbonates were deposited at southern paleolatitudes of 40 s and are interpreted to be subtropical to warm temperate in character because of the presence of certain genera of tropical coralline algae rhodoliths and articulated types large benthic foraminifera tropical molluscs zooxanthellate corals and micrite envelopes facies are dominated by skeletal grainstones and floatstones that accumulated in three interpreted paleoenvironments 1 seagrass banks upper photic zone 2 rhodolith pavements lower photic zone and 3 open seafloors lower photic to subphotic zone a decrease of tropical components from west to east across the platform implies that warm oceanic currents possibly related to a proto leeuwin current as well as a period of warm climate miocene climatic optimum resulted in subtropical deposition at southern latitudes the southern ocean extended inboard 450 km from the shelf edge during nullarbor limestone deposition but interpreted paleodepths did not extend much below the base of the photic zone a small slope angle 0 02 over a wide shelf 300 000 km2 implies deposition on an epeiric platform or epeiric ramp a miocene barrier reef was likely coeval with nullarbor limestone deposition therefore the inboard portion of the nullarbor limestone can be considered part of an extensive back reef lagoon system on a rimmed epeiric platform perhaps attaining a size similar to the modern great barrier reef system

middle cretaceous carbonate reservoirs fahud field and northwestern oman reservoir facies in fahud field and throughout northwestern oman are in shallow shelf carbonates of the middle cretaceous mishrif and mauddud formations interparticle porosity formed in the mishrif as sand aprons of lithoclast and skeletal grainstones surrounding fault block islands and less commonly in the mauddud as biostromes of rudist packstones moldic porosity after fine rudist debris is more common than interparticle porosity and occurs in thicker stratigraphic units interpreted to have formed locally in meteoric water lenses associated with islands and regionally during subaerial exposure associated with sea level lows

oligo miocene seagrass influenced carbonate sedimentation along a temperate marine palaeoarchipelago padthaway ridge south australia oligo miocene carbonates associated with the padthaway ridge form the southern margin of the murray basin south australia the carbonates are a thin somewhat condensed succession of echinoid and bryozoan rich limestones that record accumulation in the complex of islands and seaways and progressive burial of the ridge through time the rocks are grainy to muddy bioclastic packstones grainstones and floatstones composed of infaunal echinoderms bryozoans coralline algae and benthic foraminifera with lesser contributions from molluscs and serpulid worms locally as much as half of these skeletal components are fe stained relict grains that imbue the lithologies with a conspicuous yellow to orange hue this variably lithified succession is partitioned into metre scale firmground bounded and hardground bounded beds textured by extensive thalassinoides burrows dominant lithologies are interpreted as temperate seagrass facies limestones contain attributes indicative of both seagrass dominated palaeoenvironments and carbonate production and accumulation on unconsolidated barren sandflat palaeoenvironments together these two depositional systems are thought to have generated a single multigenerational amalgamated facies recording sedimentation within a complex temperate seagrass environment limestones overlying the padthaway ridge reflect a gradually warming climate increasing water temperature and decreasing nutrient content within the framework of a ridge gradually being buried in sediment this succession from cool temperate to warm temperate to subtropical through time permits recognition of the relative influence of changing oceanography on a seagrass dominated shallow inter island sea floor criteria are proposed herein to enable future recognition of similar temperate seagrass facies in cenozoic limestones elsewhere

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

planetary surface dating from crater size frequency distribution measurements spatial randomness and clustering we describe a quantitative procedure to measure the degree of clustering in an observed crater population relative to a series of randomly distributed populations we split the population by according to crater size to be able to identify clustering at different scales and find that a clustering analysis based on the mean 2nd closest neighbour distance measure more closely corresponds to visual interpretations of the spatial configuration than the mean closest neighbour distance standard deviation of adjacent area is found in certain cases to be an even more sensitive measure the technique is demonstrated for two sites on mars we were able to make use of a case where the spatial distribution was less clustered than random to reveal the transition between a crater population superimposed on a lava flow and that belonging to an underlying unit in general this type of analysis may give a better insight into the post formation modification of studied units enabling a more precise classification of which sizes of craters derive from the original accumulation population and which from areas resurfaced by later modification events consequentially improving the accuracy of dating resurfacing events clustering analysis is thus an additional tool for understanding the structure of a crater population and the effects causing an observed population to differ from an ideal one

evidence for extensive denudation of the martian highlands high resolution topographic data from the mars orbiter laser altimeter reveal evidence for widespread denudation from margaritifer sinus to northern arabia terra an area of 1 107 km2 a major resurfacing event is indicated by 1 a heavily degraded landscape hosting numerous inliers 2 truncation or absence of valley networks and 3 a break in slope at the edge of early to middle noachian plateau materials geomorphic mapping was completed on the type locale of denudation 0 30 s 0 30 w superposition relations and crater counts for geomorphic units indicate that large scale resurfacing took place in the late noachian eroding the martian highlands and resulting in transportation and deposition of 4 5 106 km3 of sediment in the northern plains this is equivalent to a 120 m thick uniform layer of sediment on the surface of mars north of 30 n geomorphic mapping and crater counts limit the timing of denudation to the late noachian an interval of 350 500 m y using this limit we estimate a minimum rate of denudation of 2 0 m yr comparable to denudation of typical slopes in a temperate maritime climate on earth the morphology rate of denudation and extensive nature of upland degradation suggest that precipitation fed surface runoff is the most likely geomorphic agent capable of such a process indicative of a warm wet mars during the late noachian epoch

halimeda dominance in the coastal wedge of pietra di finale ligurian alps italy the role of trophic conditions the middle to late miocene mixed carbonate siliciclastic coastal wedge of the pietra di finale unconformably overlying the ligurian alps succession displays a carbonate portion dominated by halimeda and porites fragments that fall in the photozoan assemblages photozoan assemblages typically develop under tropical and oligotrophic conditions while hetorozoan assemblages tend to thrive in high nutrient settings the pietra di finale formation shows however that high weathering and an increase of nutrient inputs related to alpine uplift and humid climatic conditions promoted halimeda over the seagrass carbonate factory in the photic zone the successful halimeda proliferation was due to its efficient competition for nutrients especially nitrogen thus the pietra di finale formation represents an interesting counter intuitive example in which increased nutrient concentrations promoted instead of inhibited a photozoan over a seagrass related heterozoan carbonate production

rainfall patterns and the distribution of coals and evaporites in the mesozoic and cenozoic abstract paleoclimatologists have adequately demonstrated over the last twenty years that the distribution of climatically sensitive sediments can be related to present day climatic zones that are roughly parallel to latitude for example coals were deposited at paleolatitudes that correspond to the present day rainy zones at the equator and at about 55 n and 55 s indicating that those zones were present in the past from this it can be concluded that atmospheric circulation has not been radically different from its present configuration despite some apparently great differences in some climatic parameters such as the equator to pole temperature gradient nevertheless the zonal model for predicting the distribution of climatically sensitive sediments is not wholly adequate although general atmospheric circulation may not have been radically altered from its present pattern it would have differed in some respects because the paleogeography was different from the present geography therefore we have constructed what we believe are more realistic maps of the distribution of rainfall through time these maps are based on maps of atmospheric circulation that have been successfully used to predict the distribution of some petroleum source beds and phosphorites we have compared the predicted distribution of rainfall to the distribution of coals and evaporites for each of seven geologic stages the circulation rainfall maps were more successful than the zonal model for predicting the distribution of evaporites and coals for times when the paleogeography would have maximized the development of a monsoonal circulation which most effectively disrupts the general zonal pattern for times when a monsoonal circulation would not have been important the zonal model adequately predicted the distribution of these rocks

carbonate ramp evolution during the late oligocene chattian salento peninsula southern italy abstract oligocene carbonate ramps and platforms are widespread and though they are important carbonate reservoirs detailed studies on the facies organization platform type and internal architecture are scarce within this context the chattian carbonate units cropping out in salento southern italy allow detailed study of the distribution of skeletal components and facies architecture the lower chattian castro limestone previously considered as a fringing reef is reinterpreted as a distally steepened ramp with a distal talus induced by a paleo escarpment in the substrate epiphytic biota and sediment dweller organisms thriving in seagrass meadows dominated production in the shallow water euphotic zone seawards large rotalid foraminifers dominated a detritic mesophotic zone near the edge of the escarpment also in the mesophotic zone luxurious growth of corals built discrete mounds with no evidences of wave resistant growth fabrics basinward 25 to 30 dipping clinobeds abut against the escarpment where coral rudstone floatstone textures resulted from downfall of corals and sediments the upper chattian porto badisco calcarenite represents a homoclinal ramp dominated by packstone textures in the euphotic inner ramp autochthonous biota suggests the occurrence of extensive seagrass meadows basinward large rotalid packstone and small coral mounds developed in mesophotic conditions and rhodolithic floatstone to rudstone and large lepidocyclinid packstone characterize the sediments of the deeper oligophotic zone comminuted skeletal debris depleted of light dependent organisms typifies deposition in the dysphotic aphotic zone in both examples the middle ramp meso oligophotic zones was the most prolific in terms of carbonate production whereas shallow water seagrass related production euphotic was much less important corals built mounds also in the mesophotic zone but never reached sea level hydrodynamic conditions in the meso oligophotic zone are better explained by breaking of internal waves and their induced up and down slope currents instead of the surface storm waves

a new global database of mars impact craters 1 km 1 database creation properties and parameters 1 impact craters have been used as a standard metric for a plethora of planetary applications for many decades including age dating geologic mapping and stratigraphic relationships as tracers for surface processes and as locations for sampling lower crust and upper mantle material utilizing craters for these and other investigations is significantly aided by a uniform catalog of craters across the surface of interest consequently catalogs of craters have been developed for decades for the moon and other planets we present a new global catalog of martian craters statistically complete to diameters d 1 km it contains 384 343 craters and for each crater it lists detailed positional interior morphologic ejecta morphologic and morphometric data and modification state information if it could be determined in this paper we detail how the database was created the different fields assigned and statistical uncertainties and checks in our companion paper robbins and hynek 2012 we discuss the first broad science applications and results of this work

spatio temporal evolution of a tertiary carbonate platform margin and adjacent basinal deposits abstract the variability in low to moderate energy carbonate platform margins is poorly known from the geological record here the spatial and temporal evolution of platform margin and adjacent basinal deposits is evaluated from the little known tertiary kedango limestone that developed in a semi enclosed marine embayment in se asia the hypothesis here is that platform margin development will reflect regional and perhaps global influences such as tectonics eustasy or biotic change rather than windward leeward effects and storms that typically impact strongly upon open oceanic platforms the development of the carbonate platform was determined through logging petrography facies evaluation provenance and high resolution dating studies eleven carbonate facies were identified from the 30 km long western margin of the 600 m thick platform and its adjacent slope and basinal deposits larger benthic foraminifera and coralline algal packstones and wackestones dominated in shallow waters during the oligo miocene coral patch reef related floatstones rudstones and less commonly boundstones were also present on the platform top perhaps surprisingly for a low energy platform there was considerable variation along the platform margin and much reworking of material into slope and basinal deposits during the oligo miocene reworked material includes shallow water bioclasts clasts from older siliciclastics fresh feldspars lithified slope and platform top carbonate clasts some of the latter showing evidence for karstification the western platform margin varied laterally over a few kilometres from a gently sloping unrimmed platform to a probable bank top with in places coral fringed bypass and erosional faulted escarpment margins eustasy may have influenced shallowing and deepening trends on the platform top but apparently had little impact on mass wasting instead platform margin development was strongly impacted by tectonics including active faulting terrestrial runoff together with changes in carbonate producers and local variability on the platform top

marine carbonate systems in the sarmatian middle miocene of the central paratethys the zsambek basin of hungary the study of eight stratigraphic sections at the margin of the semi enclosed zsa mbe k basin hungary allows the sedimentary anatomy of oolitic bioclastic systems in the sarmatian of the central paratethys to be reconstructed the mollusc foraminiferal and ostracod associations indicate that the carbonate systems are latest badenian to late sarmatian in age the lower upper sarmatian deposits are organized in superimposed subaqueous dunes prograding towards the basin on a low angle ramp during the late sarmatian the ramp underwent subaerial erosion linked to a moderate relative fall in sea level lagoonal deposits were later formed and microbial nubeculariid bryozoan serpulid buildups were emplaced the abnormal marine conditions of the sarmatian conducive to the development of a poorly diversified flora and fauna and dominant non skeletal grains are linked to fluctuating salinities mesotrophic to eutrophic conditions and perhaps high alkalinity

hooked and tubular coralline algae indicate seagrass beds associated to mediterranean messinian reefs poniente basin almeria se spain abstract abundant hooked and tubular crustose coralline algae cca record early messinian late miocene seagrass beds on the northern margin of the poniente basin in southeastern spain hooked and tubular shapes in cca result from their epiphytic growth over seagrass leaves and stems the lower messinian deposits consist of a thin retrograding subunit overlain by sigmoidal bed packages that prograded to the southwest at least 650 m from the basin margin seagrass deposits mainly occur as bivalve cca packstone to rudstone and cca floatstone seawards of a conglomerate facies belt in the retrograding subunit and downslope of coral reefs and serpulid packstone to rudstone in the prograding sigmoidal beds fragments of contorted foliose cca algal flakes some hooked or tubular are common components in the seagrass deposits they mainly belong to an unidentified species of mesophyllum like their present day counterparts the epiphytic cca grew attached to seagrass by the initial parts of their thalli and displayed unattached projections or open frameworks of contorted foliose plants in a few cases hooked cca occur attached to halimeda plates small benthic foraminiferal assemblages are further evidence of macrophyte vegetation hooked contorted foliose cca can be a helpful tool for the identification of ancient seagrass beds especially in mediterranean neogene and quaternary deposits in which foraminiferal taxa fully indicative of seagrass ecosystems are scarce

decline of crater obliteration rates during early martian history abstract a change in the global climate on early mars is suspected from the geologic evidence of warmer wetter conditions that prevailed during the noachian but stands in contrast to the dry and cold conditions observed currently however the timing and evolution of this climatic change represents a gap in our understanding of the history of mars here we document the time dependence of the crater obliteration rates on mars that decreased continuously between 3 8 ga and 3 ga our results indicate that the erosion responsible for crater modification and obliteration declined gradually through the noachian and into the hesperian periods these results suggest that the climatic conditions also changed gradually and the amount of water available on the surface of mars slowly decreased over time

impact of arc continent collision on the conditions of burial and exhumation of uhp lt rocks experimental and numerical modelling abstract a 2 d physical and finite element numerical modelling of arc continent collision was performed to study the deformation and failure of the overriding lithosphere the experimental technique allowed us to model the whole subduction collision process from oceanic subduction to deep subduction of the continental crust with the numerical approach we have modelled the deformation of the overriding plate only through initial stages of its failure and studied the influence of different parameters on this process the results obtained by both techniques are coherent and mutually complementary they show that the failure of the overriding plate is physically quite plausible or even inevitable during subduction the conditions for such a failure the weakening of this plate are prepared during oceanic subduction the weakening occurs due to the interaction between the subducting lithosphere and the asthenosphere in the mantle corner between the two plates and due to back arc spreading in oceanic subduction zones with a compressional regime no back arc opening thick and strong back arc lithosphere the weakest zone is volcanic arc area when weakening becomes sufficient during subduction the lithosphere fails in this area the failure occurs along a fault dipping under the arc in either of two possible directions and results either in subduction reversal or subduction of the fore arc almost half of the presently active subduction zones are characterised by a tensional subduction regime with back arc spreading in such subduction zones the weakest place is not the volcanic arc but the back arc spreading centre when a subduction regime changes from tensional to compressional failure occurs in the vicinity of the extinct spreading centre this process can occur during oceanic subduction again along either a trench vergent or trenchward dipping fault but the formation of a trench verging fault is most likely in this latter case which is a principal subject of our study the failure is followed by partial subduction of the arc plate complete subduction occurs during arc continent collision subduction of the continental margin when tectonic compression of the lithosphere increases rapidly and becomes sufficient to push the arc plate into the mantle the arc itself can be subducted completely or be partially or completely scraped off and accreted a deeply subducted material including continental margin is preserved at relatively low temperatures between the lithospheric mantle and the cold subducted arc plate to about 150 km depth subduction of the arc plate is a major phenomenon which affects all processes associated with continental subduction from deep burial and hp lt metamorphism to exhumation of subducted material does this process occur in nature future investigations will allow us to answer this question in this paper we analyse the conditions of emplacement of a very young oceanic lithosphere samail ophiolite on the continental crust in oman in the late cretaceous and argue that this lithosphere formed in a back arc basin it reached and overthrust the arabian continent after complete subduction of the arc plate

the lower rupelian cluster reefs of majella platform the shallow water record of eocene to oligocene transition abstract the eocene oligocene transition is a key interval in the evolution of the modern climate representing the last greenhouse icehouse transition faced by the earth shallow water carbonate systems hold essential information of the global changes related to the e o transition in this work we focus on the majella mountain carbonate ramp to identify the shallow water sedimentary expression of the oceanographic and sea level changes related to the e o transition and to compare it with the deep marine records and the coeval shallow water successions field observations coupled with the study of thin sections to identify textural characters and of the larger benthic foraminiferal associations for biostratigraphic purposes allowed reconstructing the depositional model and the stratigraphic distribution of the examined ramp the lower rupelian ramp outcropping in the majella mountain is characterized by seagrass meadows in the euphotic inner ramp corals developed in the middle ramp building mounded cluster reefs in the mesophotic zone below wave base in high hydrodynamic conditions produced by rip currents induced by storm events or by the breaker zone of internal waves the outer ramp consists of alternating bioturbated wackestone rich in planktonic foraminifera bioclastic packstone and skeletal rudstone to floatstone the depositional model of the oligocene ramps is the result of the major changes that occurred during the greenhouse icehouse transition in the majella platform the e o transition corresponds to an unconformity developed on the priabonian substrate where the cluster reefs grew and expanded the unconformity results from the sea level drop of tens of meters recorded also in the outer ramp related to the oi 1 event the cluster reefs started to develop when the priabonian ramp was flooded and continued to grow during the following highstands forming an extensive coral unit that prograded basinwards interfingering with the outer ramp deposits

wake capture effects observed in a comparison of methods to measure particle settling velocity beyond stokes range abstract a comparison is presented of three methods currently used to measure particle settling velocity beyond stokes range contrasting natural sediments are analyzed in a settling tube and in a modified bottom withdrawal tube and velocities which are estimated to represent single particle behavior are calculated empirically from separate measures of particle size and density and shape velocities calculated empirically for aggregated sediments are lower than measured by either sedimentation method due primarily to aggregate breakdown that occurs during measurement of size by a wet sieve method for all sediment types multi particle velocities measured in a settling tube are very close to calculated single particle velocities but multi particle velocities measured in a modified bottom withdrawal tube are higher the increased velocities measured during this progressive or batch settling are attributed primarily to hydrodynamic wake capture that occurs at reynolds numbers 0 1 when particles of different sizes and velocities settle together in a polydisperse suspension for particles that settle in a polydisperse suspension temperature correction based on single particle behavior appears to be inadequate

unravelling the influence of water depth and wave energy on the facies diversity of shelf carbonates carbonate sequence stratigraphy is founded on the principle that changes in relative sea level are recorded in the rock record by the accumulation of sediment with relative water depth dependent attributes while at the scale of a shelf to basin transect facies clearly arrange by water depth the relation blurs for depths 40 m the most vigorous zone of carbonate production the reason for this change in behaviour is two fold firstly in shallow water the intrinsic processes of storm and wave reworking influence the seabed through submarine erosion and sediment redistribution secondly facies diversity tends to be greater in shallow water than deep water because of a greater diversity in grain producers remote sensing imagery field observations and hydrodynamic models for two reef rimmed shore attached carbonate platforms in the red sea show neither water depth nor energy regime to be reliable indicators of facies type when considered in isolation considered together however the predictive power of the two variables rises significantly the results demonstrate it to be an oversimplification to assume a direct link between palaeo water depth and depositional diversity of subtidal lithofacies while highlighting the importance of hydrodynamics in directing the accumulation of carbonate sediments in the shallow photic zone while the size distributions of facies extents in the two focus areas follow power laws no direct relation between the lateral continuity of the facies belts and water depth or wave height is reported the work is relevant for the interpretation of metre scale subtidal carbonate cycles throughout the geological record by demonstrating how caution must be applied when inferring palaeowater depths from depositional facies

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

fining upwards sedimentary sequences generated in seagrass beds shallow marine clastic and carbonate environments of southeast florida contain fining upwards sedimentary sequences being generated by beds of the seagrass thalassia testudinum lateral seaward migration of flute shaped sand pockets storm blowouts in the grass platform produces a lenticular fining upwards package 10 50 m in width 20 100 m in length and 0 3 2 m in thickness migration and vegetative restabilization of recurring blowouts on a grass platform can produce a composite sequence containing numerous complete or stacked incomplete fining upwards packages a complete fining upwards sequence consists of 1 an erosional base 2 a coarse basal shell layer representing the winnowed lag of the eroded preexisting grass stabilized platform 3 a ripple laminated well sorted medium grained sand zone representing the mobile sand on the leeward slope of the blowout and 4 a shelly bioturbated sand or silty sand having a strongly bimodal texture modes at 100 and 500 mu m in which the fine mode dominates upwards this upper portion records increased trapping of storm suspensions and decreased bedload transport as seagrasses are reestablished the mollusks chione cancellata and codakia orbicularis characterize the grass stabilized zone the distinctive textural sequence and molluscan assemblage serve to differentiate these biogenically induced fining upwards sequences from others in the geological record

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

ghost of seagrasses past using sirenians as a proxy for historical distribution of seagrasses abstract seagrasses are a notable component of shallow marine habitats especially in tropical and subtropical regions their fossil record extends back to the mesozoic but it is relatively poor and fragmentary with large temporal and geographical gaps as a result very little is known about the paleobiogeography of these plants and how physical drivers such as climatic or oceanic events have affected their distribution one approach is to infer the past distribution of seagrasses using fossils of organisms dependent of seagrasses with more complete records as proxies seagrass consumers such as sirenians seacows manatees and dugongs are much better represented in the fossil record than seagrasses are the characteristically dense bones of sirenians together with the fact that they are usually found in marginal marine environments increases the potential for preservation and recognition of their fossils the long evolutionary history of sirenians extending throughout most of the last 50 ma together with their diet permits the use of their fossils as a proxy for inferring the paleobiogeography of seagrasses here i looked at the fossil record of sirenians and seagrasses from the eocene through the miocene epochs this comparison produced several inferences about seagrass paleobiogeography and how physical drivers such as climate change ocean currents and tectonic events have been influential in their distribution 1 seagrasses were well established in the western atlantic caribbean prior to the middle eocene making possible at least two instances of trans atlantic sirenian dispersal events either with the aid of tethyan currents or along the nearly continuous northern atlantic coastline that was present in the eocene 2 climatic cooling during the early oligocene seemed to have limited the extent of seagrasses and sirenians although these groups recovered and further diversified and expanded their distributions by the late oligocene in tandem with a climatic warming event 3 by the miocene seagrasses and sirenians reached the southern western atlantic and the eastern pacific aided by the presence of the central american seaway achieving a distribution similar to and sometimes surpassing that of today the fossil record of sirenians can provide a broad overview of seagrass paleobiogeography through time however several aspects such as when sirenians and seagrasses arrived to australia and the seemingly late arrival of seagrasses to south america and the eastern pacific still need further investigation

environmental evolution and geological significance of the miocene carbonates of the eratosthenes seamount odp leg 160 abstract miocene carbonates of the eratosthenes seamount located offshore from cyprus in the eastern mediterranean odp leg 160 site 966 have been re analysed the use of sedex sequential extraction to evaluate the nutrient concentrations and of ct scan for the identification of large benthic foraminifera has resulted in a more detailed palaeoenvironmental reconstruction and an improved stratigraphic framework three intervals are recognised in the succession and are attributed to the lower middle and upper miocene respectively the lower miocene interval is dominated by large benthic foraminifera and echinoids this association colonized the top of the seamount following its uplift from deep water to the photic zone the middle miocene interval is characterised by rhodoliths and corals at its base and near the top whereas seagrass seaweed assemblages with epiphytic foraminifera and hooked coralline algal crusts dominate its central part the upper miocene is represented by coral reef facies near its base and lagoonal facies toward its top the succession was deposited in an oligotrophic environment and exhibits a general shallowing upward trend that was mainly controlled by tectonic activity related to the northward subduction of the african plate the succession of the eratosthenes seamount is characterised by a diverse large benthic foraminifera assemblage in its lower part and by corals in its uppermost part whereas corallines characterise the central interval this trend is common in miocene mediterranean carbonates and its occurrence on an isolated seamount confirms its connection with the general evolution of the basin the decline of miogypsinids and lepidocyclinids after the early miocene is notable because the eratosthenes seamount was geographically close to the indo pacific ocean where both groups also thrived during the middle miocene this decline was probably caused by the early miocene closure of the deep water connection between the indo pacific and the mediterranean

seagrass meadow sedimentary facies in a mixed siliciclastic carbonate temperate system in the tyrrhenian sea pontinian islands western mediterranean abstract the paper presents the characteristics of surface sediments in a seagrass dominated environment of the inner shelf of the pontinian islands tyrrhenian shelf central mediterranean the aims of this work are to characterize the carbonate production and sedimentary processes of a representative high latitude temperate posidonia oceanica dominated area to discuss the role of seagrass in the siliciclastic carbonate mixing processes which provide analogs for interpreting the occurrence and importance of these types of deposits in the rock record the majority of sediments are poorly sorted siliciclastic skeletal sand based on grain type and abundance and carbonate content these deposits include six subfacies the different subfacies reflect environmental changes within the seagrass environment associated with variations in light penetration and hydrodynamic conditions additionally the seagrass facies range from purely carbonate to mixed carbonate siliciclastic depending on the amount of siliciclastic input and on the capacity of seagrasses to trap allochthonous sediments while hosting carbonate producing biota the type of substrate and the erosion and transport processes control the siliciclastic input in these pontinian seagrass meadows sedimentary facies contain abundant siliciclastic grains produced by erosion of the volcanic substrate and trapped by seagrass blades and rhizomes this pontinian example illustrates that in heterozoan dominated seagrass settings mud producing green algae are not present or are not calcifying and consequently seagrass deposits are much more grainy than photozoan counterparts ancient heterozoan tropical seagrass deposits likely will be discriminated from their temperate or subtropical counterparts only by careful taxonomic analysis of skeletal grains

the eocene storm dominated foralgal ramp of the western pyrenees urbasa andia formation an analogue of future shallow marine carbonate systems abstract if the ongoing phenomenon of global warming prevails three main consequences are expected in tropical seas a higher sea level a reduction in coral reefs and more intense cyclones what will shallow marine carbonate systems be like insights can be gained from the pyrenean urbasa andia formation a transgressive heterozoan like foralgal larger foraminiferal and red algal ramp that formed in middle eocene times a greenhouse interval characterized by high atmospheric co 2 content firstly the evolution of future tropical shallow marine systems subject to a sea level rise is very likely to be similar to that seen in the backstepping architecture of the urbasa andia formation secondly eocene larger foraminifers rose when the paleocene eocene hyperthermal event caused a decline in corals in tropical seas coral reefs are again among the ecosystems that are likely to be particularly affected by current global warming it is therefore probable that future shallow marine tropical ecosystems will be devoid of platform margin coral reefs heterozoan ramps being far more common thirdly strong storm influence was common on the urbasa andia carbonate ramp the most distinctive feature being a distal dune field that was formed below storm wave base by high energy return currents similar features also characterize other eocene carbonate ramps furthermore numerical simulations highlighted the effect of strong tropical cyclones during the equable climate of the eocene together this information supports the hypothesis that tropical cyclone activity may increase under future greenhouse conditions taking everything into account the transgressive storm dominated foralgal ramp represented by the urbasa andia formation can be used as a virtual analogue of future shallow marine carbonate sedimentary environments developed under greenhouse conditions

application of image analysis for delineating modern carbonate facies changes through time grand cayman western caribbean sea image analysis of air photographs showing shallow water carbonate lagoons permits easy delineation of facies and the area covered by each facies application of this technique to lagoons around grand cayman shows that the method 1 produces maps with a high degree of accuracy 90 2 allows comparison of lagoons in terms of the areas covered by the different facies and 3 permits the quantitative assessment of changes in the lagoons for the period 1971 1985 the lagoons around grand cayman can be divided into two groups by considering the area covered by the barren sand facies as opposed to the area covered by thalassia the first group of lagoons characterized by a low percentage area of thalassia and a high percentage area of sand are narrow 0 5 km shallow 2 3 m deep and periodically subjected to high energy conditions due to strong onshore winds the second group of lagoons characterized by a high percentage area of thalassia and a low percentage area of sand have some degree of protection because they are wide up to 2 km deep up to 7 m or situated in the lee of a headland collectively the protection permits the deposition of sediment which in turn allows the establishment of thalassia image analysis of air photographs for 1971 1979 and 1985 shows that there has been a substantial increase in the area of thalassia in each of the lagoons examined around grand cayman for example in south sound the area of thalassia has increased by 6 9 ha over the 15 yr period from 1971 to 1985 although this increase has been primarily at the expense of the sand facies the thalassia also replaced other facies the expansion of the thalassia facies has important implication on the dynamics of the lagoon in terms of sediment production binding and baffling collectively these processes led to the progressive shallowing of many areas of the lagoons through the period 1971 1985

recognising macrophyte vegetated environments in the rock record a new criterion using hooked forms of crustose coralline red algae abstract the role of macrophytes such as seagrasses in influencing deposition in shallow marine environments has long been understood they affect sediment textures such that they do not reflect ambient hydrodynamic conditions and so the recognition of ancient vegetated environments is important for accurate palaeoenvironmental analysis however there is little direct fossil evidence of such plants in the rock record and so the presence of former macrophyte cover generally has to be inferred from indirect evidence based on the characteristics of modern macrophyte vegetated environments we present a new criterion for the recognition of vegetated environments in the rock record based upon a distinctive hooked form of crustose coralline red algae that is definitively indicative of growth on seagrasses and also on other macrophytes with similarly flattened blades and has been recognised from both modern inhaca island mozambique and fossil the eocene of oman seagrass beds

distal enhanced sedimentation from volcanic plumes insights from the secondary mass maxima in the 1992 mount spurr fallout deposits some tephra fallout deposits show an increase of mass and thickness at distances from the source 100 km areas of secondary mass maximum asmm which demonstrates distal enhanced sedimentation from volcanic plumes we explore development of the asmms during the 1992 august and september mount spurr eruptions usa by combining eld data on the spatial distribution of mass and grain size with 1 simulations of individual particle settling through a homogeneous and horizontally strati ed atmosphere and 2 mesoscale models of the three dimensional wind eld that include the effect of the underlying topography the crosswind and downwind variations of deposit characteristics indicate that the increase of sedimentation at the asmms is not formed solely because of preferential settling of small ash particles 125 m as commonly assumed in aggregation models instead asmm grain sizes correspond to the ne modes of the bimodal total grain size distributions there also appears to be a link between the asmm and the topography the mass local minima occur across the windward ank of 2 km high mountain ranges while the asmms spread on the leeward ank mesoscale models of the three dimensional wind eld show vertical oscillations in the wind over mountainous regions which may enhance mechanisms of en masse sedimentation aggregation hydrometeor formation and particle boundary layers as well as strong spatial variations of the horizontal wind eld in the lower troposphere our study demonstrates the importance of using grain size as well as mass data to constrain the complex processes responsible for particle sedimentation from volcanic plumes

the spatial signature of a changing ancient impactor population for mars abstract ancient solar system processes are recorded by impact crater populations on mars we investigated the spatial distribution of noachian aged 3 8 4 0 ga craters in order to test hypotheses for the shortage of

epiphytic calcium carbonate production and facies development within sub tropical seagrass beds inhaca island mozambique seagrass beds have been widely recognised as playing an important role in influencing carbonate sediment facies development this reflects their role not only as facilitators of fine sediment settling and stabilisation but also as substrates for epiphytic organisms that after death contribute skeletal carbonate to the sediment substrate in low latitude reef related settings epiphytic carbonate production rates are often high and this in combination with the trapping of carbonate mud produced by a range of associated calcareous algal species typically results in the development of carbonate mud rich facies whilst such environments and their associated sediment substrates have been widely documented studies of seagrass facies in marginal sub tropical warm temperate marine settings have not been conducted from a sedimentological perspective this study determines rates of epiphytic carbonate production on two seagrass species thalassodendron ciliatum and thalassia hemprichii and examines seagrass sediment facies from a sub tropical reef related environment in southern mozambique dense seagrass beds colonise primarily siliciclastic sediment substrates and are characterised by low rates of epiphytic carbonate production mean 43 9 g caco3 m 2 year 1 for t ciliatum and 33 4 g caco3 m 2 year 1 for t hemprichii epiphytic encrusters are dominated by thin monostromatic layers of the crustose coralline red algae hydrolithon farinosum along with rotaliid smaller benthic foraminifera including asterorotalia cf gaimardi and spirillina sp and the soritid peneroplis sp as well as rare encrusting acervulinid foraminifera serpulids and bryozoans epiphytic calcium carbonate production rates are therefore low and this is reflected in the low 15 carbonate content of the seagrass sediments as well as the low 1 sediment fine 63 m size fraction content this study suggests that mud rich sediment facies do not necessarily develop in conjunction with seagrass beds and that mud poor facies may develop in some seagrass colonised environments at these sites sub tropical and siliciclastic sediment dominated this is suggested to reflect both the low levels of epiphytic and benthic algal carbonate mud production as well as a net outflux of fine grained sediment due to tidal current induced sediment resuspension in keeping with carbonate facies generally there are thus likely to be latitude and environment related shifts in the composition and character of seagrass related sediment facies

ecology of extant nummulitids and other larger benthic foraminifera applications in palaeoenvironmental analysis abstract larger benthic foraminifera lbf are important contributors to modern and ancient tropical shallow marine sediments over the past 30 years a substantial body of literature has built up on the ecology of modern lbf especially in terms of their environmentally sensitive depth distribution reproductive strategy and morphology and the symbiotic relationship between many larger foraminifera and photosynthetic algae over the same period the extinct genus nummulites which is abundant in eocene sediments of southern europe north africa and the arabian peninsula has increasingly been studied principally because significant volumes of hydrocarbons have been discovered reservoired within nummulitic limestones offshore tunisia and libya the modern ecological studies of lbf provide a powerful tool with which to develop palaeoecological models for fossil nummulites and other symbiont bearing larger foraminifera in the rock record

continental humid and arid zones during the jurassic and cretaceous abstract the global distribution of climatically significant criteria is surveyed for six successive time intervals hettangian toarcian aalenian callovian oxfordian tithonian berriasian barremian aptian cenomanian and turonian maastrichtian the criteria are primarily mineralogical evaporites coals bauxites ironstones and kaolinite but include sedimentological and palaeontological aspects of facies e g aeolian sands fossil ferns and xerophytes fresh water invertebrates in early and mid jurassic times an arid zone can be distinguished in low to mid latitudes in western pangaea with humid zones elsewhere in the late jurassic this arid zone spread northwards to embrace much of southern eurasia there followed in the early cretaceous a sharp reversal to more humid conditions over a large area extending from the eastern margin of north america to the middle east a major consequence of which was the widespread replacement of carbonates by coarse siliciclastic facies by late cretaceous times humid conditions were well established also in north america and the south atlantic margins and the tropical arid zone had contracted to a minimum the 87 sr 86 sr ratio of marine carbonates provides an independent monitor of continental runoff which is related to a area and b extent of aridity changes in the ratio confirm that taking sea level stand into account the late cretaceous was appreciably more humid than the late jurassic these climatic changes are related primarily to the progressive breakup of pangaea in the late jurassic and cretaceous which together with sea level rise in the mid to late cretaceous caused a significant increase in maritime influence this implies that monsoonal winds probably had a major role in promoting higher precipitation rates a puzzle remains as to why there was a spread of aridity in the late jurassic finally some implications for terrestrial plant evolution are noted

microbial laminite versus rooted and burrowed caps on peritidal cycles salinity control on parasequence development early cretaceous isolated carbonate platform croatia some parasequences in the interior of the early cretaceous isolated carbonate platform croatia which formed under a greenhouse climate lack the typical regressive tidal flat laminites instead these bioturbated emergent parasequences have burrowed and rooted upper parts capped with thin greenish paleo sols and are reminiscent of triassic lofer cycles we propose that the bioturbated cycle tops reflect coastal salinities that are normal marine brackish or metahaline whereas the transgressive rare and abundant regressive tidal flat laminites formed under hypersaline coastal waters thus these features may be used to track gross salinity changes of coastal waters on the platform through time in addi tion we suggest ways to evaluate whether the salinity changes relate to hypersaline embay ments on the platform or changes in the cli mate at the parasequence scale we propose that the bioturbated emer gent parasequences could have formed under semiarid conditions seaward of subtle shallow embayments on the platform con temporaneously in the bayheads micro bial laminites developed these would require time equivalent updip and downdip laminate capped and bioturbated emer gence capped parasequences however the para sequences could also have been con trolled by climate changes the laminite capped parasequences could have resulted from salinity increase with shallowing of the platform interior under semiarid condi tions stable climate in contrast the bio turbated emergence capped parasequences could have formed during times of more humid climate punctuating the overall semi arid climate the humid phase would have favored brackish to normal marine salinities in the coastal zone along with macrophytes and intense animal and plant bioturbation which would suppress development of lami nite caps thus these parasequences provide a means of tracking gross salinity of coastal waters and if climate induced then they have implications for fluctuating climates in greenhouse worlds

biofilm related calcification sediment trapping and constructive micrite envelopes a criterion for the recognition of ancient grass bed environments micrite envelopes are a common feature in carbonate sediments and are typically associated with the micrite filling of borings produced by microendolithic organisms these are referred to as destructive micrite envelopes and have long been recognized as reflecting an important early diagenetic process recent analysis of sediments collected from back reef environments at discovery bay north jamaica however has demonstrated envelope formation on the surfaces of carbonate grains clearly distinct from the micrite filling of microborings such constructive envelopes occur almost exclusively in sediments from grass bed environments and are always intimately associated with biofilms comprising abundant mucilage cyanobacteria bacteria and diatoms it is suggested that these envelopes represent a product of both biologically mediated micrite precipitation occurring within the biofilm mucilage and around the biofilm components i e cyanobacteria and diatoms and associated trapping of carbonate mud and fine grained sediment their recognition only within grass bed sediments may enable their use as a diagnostic feature of grass bed environments or vegetation stabilized substrates in the rock record

maastrichtian to early tertiary stratigraphy and palaeogeography of the central and northern oman mountains abstract maastrichtian to tertiary sedimentary rocks outcrop extensively around the periphery of the oman mountains they form part of a geologically distinct suite of strata deposited after obduction of the semail ophiolite and thrusting of the hawasina and sumeini imbricates onto the eastern edge of the arabian plate the lithostratigraphy of maastrichtian and early tertiary rocks of the central and northern oman mountains is revised and a number of new formations are erected the proto oman mountains were emergent in the early maastrichtian and were subject to subaerial erosion and weathering nw and w of the mountains gradual subsidence followed during the maastrichtian allowing for formation of a transgressive onlapping sequence represented by the qahlah fluviatile to shallow marine terrigenous clastics and simsima shallow shelf carbonate formations more rapid subsidence ne of the mountains produced fan delta and submarine debris flow turbidite apron sequences comprising the al khawd and thaqab formations respectively a low angle unconformity separates tertiary strata from older units during the palaeogene basinal and slope facies with debris flows and turbidite sequences were deposited directly upon the unconformity surface in rapidly subsiding basins nw muthaymimah formation and nne ruwaydah formation of the oman mountains elsewhere shallow carbonate shelf facies were extensively developed in less rapidly subsiding areas during the palaeogene the palaeocene and early eocene is represented by the jafnayn limestone formation this is succeeded and overlapped by a variety of later eocene units ene and e of the mountains early eocene regression is marked by restricted facies of the rusayl formation overlying the rusayl formation are shallow open shelf limestones of the seeb formation which is rich in alveolinid and nummulitic foraminifera on the arabian side of the mountains the rusayl formation is not developed and the jafnayn formation is succeeded either by the seeb formation or fine grained faunally restricted limestones and marls of the fahud beds which represent intra shelf facies

evidence for seagrass meadows and their response to paleoenvironmental changes in the early eocene jafnayn formation wadi bani khalid n oman the recognition and understanding of vegetated habitats in the fossil record are of crucial importance in order to investigate paleoecological responses and indirectly infer climate and sea level changes however the low preservation potential of plants and macroalgae hampers a direct identification of these environments in the geological past here we present sedimentological and paleontological evidences as tool to identify the presence of different seagrass vegetated environments in the shallow marine settings of the lower eocene jafnayn platform of oman and their responses to paleoenvironmental changes the studied lower eocene deposits consist of well bedded nodular packstones dominated by encrusting acervulinid and alveolinid foraminifera passing upward to an alternance of packstones with echinoids and quartz grains and grainstones rich in orbitolites smaller miliolid foraminifera and quartz grains the presence of seagrass is inferred by the occurrence of encrusting acervulinids and soritid orbitolites as well as by their test morphologies together with further sedimentological criteria the clear shift observed in the faunal assemblages and sedimentary features may be related to a major reorganization of the carbonate system passing from a carbonate platform to a ramp like platform with increased terrigenous sedimentation heterotroph tubular acervulinids and oligotroph alveolinids of the carbonate platform were replaced upward by more heterotroph organisms such as large discoidal orbitolites and smaller miliolids most likely due to enhanced nutrient levels which would have led to a change of phytal substrate from cylindrical leaf dominated grasses into flat leafed ones

the timeline of the lunar bombardment revisited abstract the timeline of the lunar bombardment in the first gy of solar system history remains unclear basin forming impacts e g imbrium orientale occurred 3 9 3 7 gy ago i e 600 800 my after the formation of the moon itself many other basins formed before imbrium but their exact ages are not precisely known there is an intense debate between two possible interpretations of the data in the cataclysm scenario there was a surge in the impact rate approximately at the time of imbrium formation while in the accretion tail scenario the lunar bombardment declined since the era of planet formation and the latest basins formed in its tail end here we revisit the work of morbidelli et al 2012 that examined which scenario could be compatible with both the lunar crater record in the 3 4 gy period and the abundance of highly siderophile elements hse in the lunar mantle we use updated numerical simulations of the fluxes of asteroids comets and planetesimals leftover from the planet formation process under the traditional assumption that the hses track the total amount of material accreted by the moon since its formation we conclude that only the cataclysm scenario can explain the data the cataclysm should have started 3 95 gy ago however we also consider the possibility that hses are sequestered from the mantle of a planet during magma ocean crystallization due to iron sulfide exsolution o neil 1991 rubie et al 2016 we show that this is likely true also for the moon if mantle overturn is taken into account based on the hypothesis that the lunar magma ocean crystallized about 100 150 my after moon formation elkins tanton et al 2011 and therefore that hses accumulated in the lunar mantle only after this timespan we show that the bombardment in the 3 4 gy period can be explained in the accretion tail scenario this hypothesis would also explain why the moon appears so depleted in hses relative to the earth we also extend our analysis of the cataclysm and accretion tail scenarios to the case of mars the accretion tail scenario requires a global resurfacing event on mars 4 4 gy ago possibly associated with the formation of the borealis basin and it is consistent with the hse budget of the planet moreover it implies that the noachian and pre noachian terrains are 200 my older than usually considered

crater size frequency distributions and a revised martian relative chronology a revised martian relative chronology is determined which dates geologic units with respect to the end of the period of heavy bombardment this analysis differs from previous studies by using viking 1 2m photomosaics to map all 25 826 craters 8km diameter which postdate the lithologic units making up the martian surface the relative plotting technique is used because it shows changes in the shape and density of the crater size frequency distribution curves more clearly than cumulative plots the changes in shapes of the distribution curves are interpreted to be due to two different impacting populations one dominating during the heavy bombardment period and the other emplaced during the post heavy bombardment period the 8 km diameter limit was chosen to exclude the majority of secondary craters and to minimize obliteration effects acting over the age of the planet the results obtained are average ages valid for units with typical thicknesses between about 1 and 3 km and extending over an area of about 105 km2 the shapes and densities of the crater distribution curves indicate that approximately 60 of the martian lithologic units in which these craters occur formed during the period of heavy bombardment many of the small volcanoes those generally less than 200 km diameter including most in the tharsis and elysium regions date from this period the hellas and argyre impacts bracket the average age of the intercrater plains in the highlands the ridged plains distribution curves indicate formation during the period of heavy bombardment but their lower crater density indicates that they are the last geologic unit to retain the scars from this population of impactors they therefore likely formed near the end of heavy bombardment the remaining 40 of martian terrain units show distribution curves indicative of emplacement since the end of heavy bombardment the wide range in crater densities among different regions of plains indicate a range in formation ages although the general view of martian geologic evolution does not differ significantly from previous studies the present analysis explicitly states the relationship of numerous geologic units to the period of heavy bombardment and has revised the relative ages of localized regions across mars

grain susceptibility to the effects of microboring implications for the preservation of skeletal carbonates the boring activity of microendolithic organisms such as cyanobacteria chlorophytes rhodophytes and fungi represents a major destructive process affecting sediment preservation within reef environments this study demonstrates the presence of two distinct assemblages of microborers within sediments collected from the fringing reefs of north jamaica correlating to the upper 18 m depth photic zones the upper photic zone assemblage is dominated by cyanobacteria and chlorophytes whilst rhodophytes and fungi become more abundant with increasing water depth most significant from a grain preservation perspective is the variable nature of grain infestation observed between different reef sites and different carbonate grain types the highest degree of grain infestation occurs within shallow low energy back reef environments and the most susceptible grains at all sites are corals molluscs and foraminifera coralline algae halimeda and echinoid fragments are rarely heavily infested high rates of infestation at back reef sites result in rapid diminution of the most susceptible grains especially coral which are either underrepresented or contribute only to the finer sediment fractions in the subsurface fore reef grain assemblages undergo relatively little alteration microboring therefore has potential to bias the fossil record by removing the most susceptible skeletal grains the impact of microboring upon back reef grain assemblages must be considered when attempting to model depositional processes within both modern and ancient reef environments

deepening upward subtidal cycles murray basin south australia abstract decimeter scale deepening upward cycles are the basic depositional motif of oligocene miocene murray supergroup limestones in the murray basin southeastern australia cycles formed in this large intracratonic basin on a centripetal temperate water epeiric ramp they reflect generation by trophic resource influenced carbonate production under mostly transgressive conditions listed from the base up each cycle is ideally composed of five parts part a biotically depauperate carbonates reflecting relatively shallow water restricted variably stressed highly mesotrophic environments part b increasingly biotically diverse limestones recording progressively more physical energy and less mesotrophic conditions upward om1 a conspicuous hardground to firmground surface formed during late transgression to stillstand during which wave sweeping and reworking contributed to omission and lithification part c relatively biotically diverse epifauna dominant sediments that were highly abraded during periods of condensed sedimentation under marginally oligotrophic conditions and om2 cycle boundary a rarely conspicuous surface representing arrested sedimentation and variable cementation as trophic resources increased and conditions for carbonate production deteriorated ten cycle types are grouped into four major styles clay cycles mollusc cycles echinoid cycles and bryozoan cycles these are interpreted to form a lithological continuum from inner restricted terrigenous locales to outer open marine bryozoan colonized environments deepening upward cycles were profoundly sensitive to autogenic factors such as nutrient influx terrigenous content and turbidity hydrodynamic energy water temperature salinity and water depth manifested in this intracratonic setting although these cycles share a similar sedimentological motif and hydrodynamic energy based cycle capping process with open shelf epicratonic shallowing upward subtidal cycles of tertiary age they formed in a very different way reflecting the distinctive intracratonic environment in which they formed murray basin cycles preserve a record of relative sea level rise whereas open shelf cycles accumulated mostly during relative sea level fall

meco and alpine orogenesis constraints for facies evolution of the bartonian nummulitic and solenomeris limestone in the argentina valley ligurian alps

evidence for the southward migration of mud banks in florida bay article i nfo article history the latticework of shallow polygonal mud banks encircling deeper ponds is a key morphological characteristic of florida bay composed of lime mud produced largely by calcareous algae and epibionts these banks limit water exchange between the interior bay and ocean waters from both the gulf of mexico and the atlantic they also influence salinity and benthic habitat distribution it has been proposed that the position of mud banks may be dynamic migrating southwards with time but no long term study has examined the spatial arrangement of banks within florida bay over sufficiently long timescales to ascertain movement using time separated bathymetry surveys and aerial photography datasets spanning a period of many decades this study establishes that indeed the bank positions are temporally dynamic the work was conducted using geographic information systems gis with all data referenced to the position of relatively stable islands the analysis reveals a southward migration trend headings ranging from 280 to 240 with rates averaging 1 27 m year for the first time in florida bay the migration and vector of movement for mud banks have been documented despite the southward movement mud bank morphology remained consistent it is speculated that strong winter winds out of the north northeast provide the mechanism for such migration the southward migration of fine grained biogenic mud banks in florida bay demonstrates how change detection remote sensing can be used to audit a geological process operating at time scales of centuries though the available data may be unusually rich for florida bay the study shows how the dynamics of other coastal systems may be accessed using a comparable work flow similarly the results here have implications for the geologic record and reevaluating paleo landscapes where mudrock shoals have been identified

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

genesis of the batinah melange above the semail ophiolite oman abstract the batinah melange which overlies the late cretaceous semail ophiolite in the northern oman mountains comprises mostly sedimentary rocks of deep water facies alkalic lavas and intrusives all of continental margin affinities together with smaller volumes of semail ophiolitic and metamorphic rocks four intergradational textural types of melange can be recognized sheet melange has large 1 km intact sheets either with little intervening matrix or set in other melange types and with an organised sheet orientation fabric slab melange is finer textured 100 m and more disrupted block melange has smaller m blocks with some matrix and a weak to random block fabric clast melange is matrix supported rudite with a weak depositional clast fabric structural relationships particularly the absence of tectonic fabrics the decreasing strength of fragment fabrics with increasing fragmentation and the abundance of brittle fragmentation suggest that these melange types formed by either gravity driven sedimentary processes or superficial sliding or thrusting of individual rock slabs in the slab melange long sequences can be pieced together passing up from upper triassic mafic sub marine extrusives and sediments into radiolarian cherts hemipelagic and redeposited limestones and terminating in non calcareous radiolarities with mn deposits of early cretaceous age mafic sills are numerous these sequences can be matched with sub ophiolite rocks now exposed in fault corridors through the semail these sequences become progressively disrupted upwards in the corridors and can be traced continuously into overlying melange which then thins away from the corridors we argue that during late cretaceous emplacement over the arabian margin active fault corridors split the semail slab and acted as conduits up which sub ophiolite rocks were supplied to the ophiolite surface there the rocks were redisributed by superficial processes

the influence of waves and seagrass communities on suspended particulates in an estuarine embayment resuspension of bottom sediments by waves corresponding changes in suspended particulate material spm concentrations in the overlying water column and transport pathways of spm were investigated in a shallow estuarine embayment colonized by seagrass communities in chesapeake bay in shallow 2 m unvegetated regions significant resuspension of bottom sediments was evident when northerly winds exceeded 25 km h 1 increasing spm concentrations up to 10 fold high concentrations of spm generated by resuspension dissipated rapidly within 24 h after winds became calm patterns of spm along the embayment s depth gradient suggest that part of this resuspended material was transported offshore into deeper reaches of the estuary in areas of the embayment colonized by seagrasses wave energy was attenuated by the vegetation suppressing resuspension and enhancing deposition as a result spm concentrations were significantly lower inside seagrass beds than in adjacent unvegetated areas during periods of high winds when wave induced resuspension occurred in unvegetated areas spm concentrations remained unchanged inside the bed at normal water levels however when water levels were elevated by spring tides or storm surges plants were less effective at attenuating wave energy and spm concentrations increased inside the seagrass bed due to resuspension and advective processes calculations based on the results of this study indicate that sedimentation rates are substantially higher in seagrass communities than in unvegetated areas

stratigraphy of the mesozoic rocks above the semail ophiolite oman a revised stratigraphy is presented for the rocks which lie between the upper cretaceous semail ophiolite and its post emplacement sediment cover of uppermost cretaceous to tertiary age above the pelagic sediments of the ophiolite suhaylah formation cenomanian turonian occur ophiolite derived clastic sediments zabyat formation turonian campanian related to early stages of ophiolite emplacement these formations are structurally overlain by the batinah complex comprising triassic to cretaceous lithologies all previously equated with the hawasina rocks that now lie tectonically beneath the ophiolite we recognize a lower melange unit to the complex which demonstrably includes hawasina lithologies the melange formed by superficial rather than deep processes but the mechanism by which hawasina material was supplied to the ophiolite surface is unproven the upper unit of the batinah complex shows a coherent stratigraphy which contrasts with that of the hawasina it comprises three main allochthonous tectonic sheets within which we recognize three formations and one other informal unit the upper batinah complex may have been tectonically derived not from the now subjacent arabian margin but from another margin with a passive mesozoic history

resurfacing of the martian highlands in the amenthes and tyrrhena region the southern cratered highlands of mars contain a large population of flat floored rimless craters which have previously been interpreted to have formed by aeolian mantling or flood volcanism neither of these geologic processes accurately explains the observed morphology or the crater statistics geologic mapping in the amenthes and tyrrhena region indicates that craters with this morphology occur on undulating intercrater materials near the dichotomy boundary and on more rugged materials farther into the highlands containing numerous ancient valley networks cumulative size frequency distribution curves indicate ages of n 5 790 early to middle noachian and n 5 540 middle noachian for the cratered plateau and cratered highland materials respectively opposite the observed stratigraphic relations for crater diameters 16 km the population of impact craters is consistent with stratigraphy but the population of smaller craters in the region indicates the importance of resultacing superposed fresh craters indicate a resultacing event that ceased at n 5 200 250 late noachian to early hesperian crater counts divided into 5 o latitudinal bins show an increase in the number of craters between the 8 and 50 km diameter range with increasing northerly latitudes suggesting that the resurfacing was not a single event statistical modelling of an erosive event capable of removing the continuous ejecta deposits from the craters eroding them to reduce the apparent diameter and simultaneously burying smaller eroded craters explains both the morphology of the flat floored rimless craters and their population distribution matching the slope of the modelled curves with that of the cratered highland materials suggests that up to 1400 m of erosion may have taken place in the highlands some of this eroded material probably remained locally burying the smaller craters later stripping of this material indicated by exposed layering and inverted topography has exhumed the smaller craters in the cratered plateau material resulting in the apparent age discrepancy determined from crater counts up to 1 0 km of material may have been removed by this later erosive event to explain the low density of ancient valley networks in the cratered plateau materials

rhizolith evidence in support of a late holocene sea level highstand at least 0 5 m higher than present at key biscayne florida r fairbridge and f shepard proposed different sea level curves for the late holocene south florida as a tectonically stable platform provides a key locale from which late quaternary sea level measurements have been attempted previous studies supporting holocene sea level curves have focused on mangrove peat deposits barrier ridges and archaeological sites however in situ biological indicators provide the best evidence in support of varying sea level positions during the late holocene the northeastern side of key biscayne florida has two areas of rock reef where rhizoliths i e fossilized root casts are exposed within the intertidal zone they have previously been interpreted as the fossilized roots of a former black mangrove avicennia germinans forest however the morphology size orientation and areal extent of the rhizoliths is best understood if they are interpreted as the former root casts of turtle grass thalassia testudinum this interpretation would constitute in situ biological evidence of a late holocene sea level position at least 0 5 m higher than at present previously published 14c dating of the calcareous paste inside the rhizoliths suggests that they formed 1 2 k y before present this corresponds to a higher than present sea level highstand supported by independent evidence from other areas in south florida

the upper batinah complex oman allochthonous sediment sheets above the semail ophiolite the upper batinah complex consists of allochthonous sedimentary sheets that structurally overlie both the semail ophiolite and its cover of melange lower batinah complex sequences represent a former sedimentary transition across the outer part of a passive mesozoic continental margin from proximal to distal units include redeposited quartzitic sandstones and shallow water limestones large carbonate buildups floored by triassic mafic lavas and pelagic radiolarites or hemi pelagic calcilutites also underlain by triassic mafic lavas sheets of these upper batinah complex sequences were emplaced onto the upper surface of the semail ophiolite in late cretaceous time during or soon after the advance of the semail nappe onto the arabian margin emplacement was along subhorizontal fault zones with sheets of distal facies followed by successively more proximal sheets structural style suggests a low overburden during deformation with ductile flow of argillaceous material but more brittle behavior of othe