the closing of tethys and the tectonics of the himalaya recent geological and geophysical data from southern tibet allow refinement of models for the closing of southern neo tethys and formation of the himalaya shelf sediments of the indian passive continental margin which pass northward into deep sea tethyan sediments of the indus tsangpo suture zone were deposited in the late cretaceous an andean type margin with a 2 500 km long trans himalayan kohistan ladakh gangdese granitoid batholith formed parallel to the southern margin of the lhasa block together with extensive andesites rhyolites and ignimbrites lingzizong formation the southern part of the lhasa block was uplifted deformed and eroded between the cenomanian and the eocene in the western himalaya the kohistan island arc became accreted to the northern plate at this time the northern part of the lhasa block was affected by jurassic metamorphism and plutonism associated with the mid jurassic closure of the bangong nujiang suture zone to the north the timing of collision between the two continental plates ca 50 40 ma marking the closing of tethys is shown by 1 the change from marine flysch like to continental molasse like sedimentation in the indus tsangpo suture zone 2 the end of gangdese i type granitoid injection 3 eocene s type anatectic granites and migmatites in the lhasa block and 4 the start of compressional tectonics in the tibetan tethys and indus tsangpo suture zone south facing folds south directed thrusts after the eocene closure of tethys deformation spread southward across the tibetan tethys zone to the high himalaya deep crustal thrusting barrovian metamorphism migmatization and generation of oligocene miocene leucogranites were accompanied by south verging recumbent nappes inverting metamorphic isograds and by south directed intracontinental shear zones associated with the main central thrust continued convergence in the late tertiary resulted in large scale north directed backthrusting along the indus tsangpo suture zone more than 500 km shortening is recorded in the foreland thrust zones of the indian plate south of the suture and 150 km shortening is recorded across the indian shelf zanskar range and the indus suture in ladakh there was also large scale shortening of the karakoram and tibetan microplates north of the suture as much as 1 000 km shortening occurred in tibet the more recent deformation however involved the spreading of this thickened crust and the lateral motion of the tibetan block along major approximately east west trending strike slip fault zones

the impact of depositional events and burial rate on carbonate silica diagenesis in a middle jurassic stromatactis carbonate mud mound sainte baume massif se france abstract understanding the processes and conditions of chertification in carbonates is a challenging problem to assess the marine silica cycle this contribution highlights parameters of internal silica recycling processes from their biogenic source to quartz cementation by describing a unique case of carbonate silica diagenesis in a mesozoic mud mound stromatactis carbonate mud mounds exposed in the sainte baume massif basse provence france developed in an outer shelf environment during the late aalenian concavum ammonite zone middle jurassic they form part of a cherty succession punctuated by hardgrounds and stratigraphically condensed intervals interpreted to record deepening episodes these mud mounds rich in siliceous sponge spicules and stromatactis are similar to their widespread paleozoic counterparts but are particular in being extensively silicified carbonate silica paragenesis forms a polymud fabric including four microcrystalline carbonates m1 to m4 all low mg calcite lmc five spar cements c1 to c5 c1 with high mg calcite hmc precursor mineralogy and four silica phases s1 to s4 s1 to s3 replacive chalcedony after opal ct s4 euhedral quartz cement m1 assumedly related to the degradative calcification of siliceous sponges forms a labyrinthine network into which m2 to m4 were infiltrated spar cements c1 to c3 include a successive decrease of 18 o at fairly invariable 13 c interpreted to represent marine to shallow burial conditions suggesting burial and successive transformation of marine bottom waters temperature estimation based on the average 18o value of c4 18o 7 9 indicates a temperature of around 50 c at a maximum burial depth of about 1000 meters replacive chalcedony s1 to s3 occurs between calcite cementation c3 and c4 in combination with traces of corrosion on c3 mg calcite was preferably replaced particularly the precursor of cement c1 that surrounds peloids of m2 and preserved some ghost structures corrosion and substrate selectivity suggest that acidification mg hydroxyl complexes and surface area are the triggers for flocculation of a silica gel because dissolution of opaline sponge spicules started almost contemporaneously with c1 the dissolved silica was retained in a connate fluid as phases c1 to c3 were precipitated and stagnant conditions prevailed for around 1 ma bulk 18o d values s1 s3 below the marine chert line together with the range of s1 s3 18o 18o smow 28 3 1 0 suggest silica flocculation in a shallow burial environment at temperatures of 25 30 c the establishment of acidic conditions might have been favored by sulfide oxidizing micro organisms numerical simulation of early diagenetic silica flux in such marine sediments is consistent with the interpretation that small grain size changes and fluid barriers that create diffusion controlled conditions such as those induced by stratigraphic condensation are key parameters to retain pore water dissolved silica over geologic time inversely paleozoic stromatactis carbonate mud mounds typically form part of large scale coarsening and shallowing upward successions that correspond to rapid burial these conditions support convergent pore water flux and drainage of pore water dissolved silica in the shallow burial realm hence spicule rich mounds should tend to silicify if they form part of a condensed section

high resolution surface and subsurface sequence stratigraphy of late middle to late ordovician late mohawkian cincinnatian foreland basin rocks kentucky and virginia the late middle to late ordovician late mohawkian to cincinnatian supersequence in kentucky and virginia was deposited in a tectonically active foreland basin during a transition from the ice free early ordovician to the glacial late ordovician this sequence was deposited in less than 12 m y is 250 500 m thick and is composed of four large third order sequences each 40 150 m thick that are regionally correlative in outcrops cores and gamma ray logs smaller scale third order parasequence sets up to 20 m thick and component parasequences 1 8 m thick make up the larger sequences and are only locally correlative subtidal dominated parasequences comprise the basal part of each sequence whereas shallower subtidal or peritidal dominated parasequences compose upper parts of sequences each large third order sequence is asymmetric and marked by lowstand transgressive and highstand systems tracts with unique lithologic and gamma ray log response characteristics ramp margin wedges rmw are poorly developed and consist of marine siltstone or grainstone packstone sheets extending into deep ramp settings these sheets have high gamma ray values in their base and lower blockier gamma ray responses in their tops transgressive systems tracts tst are thin composed of high energy locally phosphatic grainstone copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received february 7 1996 revised manuscript received may 27 1997 final acceptance june 16 1997 2department of geology virginia tech blacksburg virginia 24061 0420 present address department of earth atmospheric and planetary sciences massachusetts institute of technology cambridge massachusetts 02139 3department of geology virginia tech blacksburg virginia 24061 0420 this study was supported by nsf grant ear 9316057 to j f read a grant from mobil oil company and grants in aid of research from the geological society of america and appalachian basin industrial associates to mike pope we thank john haynes brian keith and rick major for thorough and insightful reviews of an earlier version of this manuscript

a mid ordovician temperate carbonate shelf the black river and trenton limestone groups of southern ontario canada abstract mid ordovician limestones of southern ontario are usually considered to be tropical shelf limestones and interpreted using facies models derived from recent tropical carbonate environments nevertheless depositional rates grain types faunas erosion surfaces mineralogy and geochemistry are more compatible with a temperate or even cold shelf environment in view of the low latitudes 20 s indicated by paleomagnetism this suggests deposition in relatively cold seas deposition below a tropical thermocline or that the paleomagnetic data are wrong similar features in other caradocian limestones of eastern north america show that these inferred cooler conditions were widespread if deposition occurred below a tropical thermocline most shallow water caradocian limestones must be re interpreted as deeper water deposits more likely in view of the evidence for temperate conditions in shallow water is that the whole eastern seaboard of north america was affected by cold currents arising from southern polar ice caps and thus was a temperate shelf environment

a physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins rift flank uplifts and the breakup or postrift unconformity are characteristic features of many rifted passive or atlantic type continental margins but are not predicted as primary features of simple lithospheric stretching models the explanations that have been proposed for their origin remain controversial either because they call upon special circumstances or because they are difficult to test plane strain finite element models are used in this paper to explore the dynamics of lithospheric necking during rifting and rupture the results agree with the conceptual interpretation that uplift of the rift boundaries to form flank mountains and uplift of the basin responsible for the breakup unconformity are related consequences of regional isostatic compensation of mass that is redistributed during the necking and rupture phases although the amplitudes of these uplifts depend on the model parameter values the relations between and relative signs of these two effects appear to be fundamental the explanation we propose may have been missed in recent studies because there has been a tendency to concentrate on kinematic stretching models which assume local isostatic equilibrium through out the rifting process such an approach is predicated on the assumption that the lithosphere has an insignificant strength or flexural rigidity during extension which is not true if our explanation is correct

provenance of lower cretaceous wolong volcaniclastics in the tibetan tethyan himalaya implications for the final breakup of eastern gondwana abstract lower cretaceous volcanic lithic arenites widely distributed in the tethyan himalaya provide insights into the continental breakup of eastern gondwana in southern tibet they are represented by the wolong volcaniclastics the volcanic rocks that contributed clastic material to the lower parts of this unit were predominantly alkali basalts whereas rhyolitic dacitic volcanism becomes the predominant source of the upper strata geochemical analyses of basaltic grains and of detrital cr spinels from the wolong volcaniclastics demonstrate the alkaline character of the volcanism and suggest within plate tectonic setting for the volcanism zircon u pb ages confirm that this volcanism continued from 140 ma to 119 ma hf isotope data on these early cretaceous zircons indicate that their parental magmas were mantle derived but in the later stage of magmatic activity mantle derived magmas were mixed with partial melts derived from the continental crust the lower cretaceous volcaniclastics occur along a broad belt paralleling the northern margin of greater india the onset of volcaniclastic deposition in the himalayas appears to become progressively younger toward the west but it ended synchronously during the late albian 102 ma the low volume of volcanic rocks and their intra plate tectonic setting suggest that they are the result of decompressional melting along extensional deep seated fractures cross cutting the continental crust and reflect changes in regional intra plate tectonic stresses when greater india began to separate from the australia antarctica supercontinent

early palaeozoic cooling events peri gondwana and beyond the short lived end ordovician hirnantian glaciation allied to marine mass extinction is variously considered as a short lived event or as the peak of long drawn out climatic cooling through at least late ordovician early silurian times evidence from early palaeozoic facies faunas and stable isotope excursions used to interpret climatic cooling events ranges farther from late mid cambrian to late silurian times glacigenic sediments structures and geomorphology provide direct evidence of glacial episodes cool water carbonate deposition which is particularly widespread during the late ordovician boda event in high latitude peri gondwana gondwana and beyond into mid low palaeolatitudes is interpreted as indicating global cooling not warming as has been proposed such carbonates also characterize mid latitude continents widely at horizons earlier in the ordovician and more locally in the mid silurian in high latitude gondwana cool water carbonate mounds have distinctive facies controlled mound faunas across palaeocontinents other facies evidence for palaeoclimates includes black shale deposition including deglacial organic rich hot shales which indicate transgression in epeiric seas and sea level curves interpreted from facies and faunal successions correlation is shown between facies evidence and positive c isotope excursions from which cyclicities are apparent the possible interface of orbitally controlled rhythms is considered against evolving palaeobiogeography and changes in global sea level and in pco2 facies and faunal evidence from peri gondwanan terranes armorica central europe alborz is assessed with that from gondwana mostly north africa south america and correlatives in avalonia baltica and laurentia to establish a wider picture of early palaeozoic cooling events

an investigation into possible facies changes across the triassic jurassic boundary in southern tibet abstract a complete marine succession across the triassic jurassic boundary is reported from southern tibet on the northern flanks of the himalayas both youngest triassic and oldest jurassic ammonites together with palynological data allow a combined facies and gamma ray study indicating no significant change across the system boundary unlike elsewhere in the world

the earliest evolutionary link of metazoan bioconstruction laminar stromatoporoid bryozoan reefs from the middle ordovician of korea abstract sub metre scale patch reefs composed primarily of stromatoporoids and bryozoans are reported from the duwibong formation upper middle ordovician taebaeksan basin korea in the eastern margin of the sino korean block the reef framework is constructed of alternating thin laminae of the primitive labechiid stromatoporoid cystostroma the bryozoan nicholsonella subordinate solenopora and minor siliceous sponges alternating laminae of stromatoporoids and bryozoans are largely responsible for the formation of a globular framework composed of columnar branching bulbous to irregular masses solenopora sporadically occurring as tiny patches or thin laminae attached to the stromatoporoid bryozoan framework is considered to be subordinate encrusters siliceous sponges occur within the stromatoporoid bryozoan framework and within the growth framework and bored cavities interpreted as subordinate encrusters and cryptic dwellers the compact globular framework of the duwibong stromatoporoid bryozoan consortium represents a new type of ordovician skeletal bioconstruction but with a certain structural similarity to lower ordovician bryozoan reefs in the south china block together with coeval labechiid reefs occurring near the current study area the duwibong reefs suggest that incursion of the primitive stromatoporoids into the earliest bryozoan reefs resulted in the dominance of reef building stromatoporoids in peri gondwana in contrast to coeval reefs in laurentia which commonly contain tabulate corals

role of gravity waves in triggering deep convection during toga coare the role of gravity waves in the initiation of convection over oceanic regions during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare experiment is investigated first an autocorrelation method is applied to infrared temperature observations of convective events from satellite images it reveals that new deep convective cells often occur a few hours after a previous intense event at a typical distance of a few hundred kilometers such fast moving modes faster than 15 m s 21 are interpreted as the trace of gravity waves excited by previous convection and contributing to trigger further convection second the specific case of 11 12 december 1992 during which an active squall line is generated after the collapse of a previous mesoscale convective system mcs nearby is analyzed with a nonhydrostatic model the triggering of the second mcs is well reproduced explicitly owing to the use of the two way interactive grid nesting the convective source appears to emit pulses of gravity waves on a wide range of small scales on the contrary the troposphere response to the convective source exhibits a spectral simplicity a slowly evolving mode characterized by an ascent in the pbl and a compensating subsidence in the free troposphere favors shallow convection and inhibits deep convection respectively traveling modes propagating away from the convective source are characterized by a fast mode 50 m s21 and a slower mode 25 ms 21 associated with the convective and stratiform development of the source respectively in agreement with previous studies a budget analysis reveals the different factors leading to the deep convection triggering first an active pbl characterized by strong surface fluxes and mean ascent initiates shallow convection lasting about 2 h inhibited above by the subsiding motions maintaining a dry layer second horizontal advection of moist and cooler air at midlevels and detrainment from cumuli contribute to destroy the dry air layer capping the shallow convective layer finally vertical advection induced by the gravity waves passage modulates the vapor and temperature evolution ascending phases favor moistening and cooling whereas subsiding phases stop these effects delaying the deep convection onset the triggering occurs after a strong subsidence when the ascent phases of deep and shallow modes are combined

digital reconstruction and stratigraphic evolution of a microbial dominated isolated carbonate platform terminal proterozoic nama group namibia abstract a terminal proterozoic ca 550 ma isolated carbonate platform developed downdip on a carbonate ramp of the nama group of southern namibia the stratigraphic evolution of the platform was reconstructed from an extensive dataset that was compiled by using digital surveying technologies and traditional outcrop observations digital field geology techniques enabled rapid and accurate mapping over the 10 km outcrop belt with spatial and geological information captured at scales ranging from centimeters to kilometers furthermore these digital geology techniques made the reconstruction and interpretation of the development of the carbonate platform considerably more efficient and quantitative the carbonate platform deposits encompass three accommodation cycles in which each subsequent cycle experienced progressively greater influence of a long term accommodation increase aggradation and progradation during the first cycle produced a flat topped sheet like platform deposits of the first cycle show a coarsening upward motif grading from dominantly columnar stromatolitic thrombolites and interbedded mudstone grainstone at the base to dominantly massive and cross bedded dolostones toward the top the second cycle features aggradation and is typified by the formation of a distinct margin and development of a bucket shaped geometry the margin contained thrombolite mounds and domes whereas columnar stromatolitic thrombolites dominated the platform interior the third and last cycle records a gradual deepening trend with initial aggradation and formation of well bedded thin deposits in the interior and microbial mounds at the margins while the interior drowned the platform margins kept up with rising sea level and complex pinnacle reefs formed which contained fused and coalesced thrombolite mounds flanked by bioclastic grainstones and collapse breccias the top of the unit consists of a set of isolated large thrombolite mounds flanked by shale and is interpreted to indicate the final stage of the carbonate platform before drowning the overall geometric evolution and spatial scale of this platform from flat topped to bucket shaped with elevated margins is recorded in many proterozoic and phanerozoic isolated carbonate platforms this study clearly illustrates that accommodation changes are a fundamental control on the development of carbonate platforms regardless of whether they are formed from microbial or metazoan components or are of precambrian or phanerozoic age significantly the architectural elements and spatial dimensions are comparable throughout earth history

evolution of the eastern indian ocean since the late cretaceous constraints from geosat altimetry we propose a new model for the tectonic evolution of the eastern indian ocean from the late cretaceous to the present two types of data are used to improve previously published reconstructions first recent reinterpretations of seafloor magnetic anomalies between australia and antarctica and in the wharton basin provide new constraints on spreading rates and the timing of major reorganizations second vertical deflection profiles i e horizontal gravity anomaly derived from 22 repeat cycles of geosat altimeter data reveal the tectonic fabric associated with fracture zones these new geosat data provide tight constraints on paleospreading directions for example three prominent fracture zones can be traced from south of tasmania to the george v basin antarctica providing an important constraint on the relative motions of australia and antarctica through the late eocene in addition the geosat profiles are used to locate the conjugate continental margins and continent ocean boundaries of australia and antarctica as well as the conjugate rifted margins of kerguelen plateau and broken ridge based on a compilation of magnetic anomaly data from the crozet basin the central indian basin the wharton basin and the australian antarctic basin ten plate tectonic reconstructions are proposed reconstructions at chrons 5 11 ma 6 21 ma 13 36 ma and 18 43 ma confirm that the southeast indian ridge behaved as a single plate boundary since chron 18 the constraints from the geosat data provide an improvement in the fit of the kerguelen plateau and broken ridge at chron 20 46 ma to avoid overlaps between broken ridge and the kerguelen plateau prior to their breakup our model includes relative motions between the northern and southern provinces of the kerguelen plateau finally we examine the implications of our model for the relative motions of india australia and antarctica on the tectonic evolution of the kerguelen plateau and broken ridge and the adjacent labuan basin and diamantina zone as well as the emplacement of the ninetyeast ridge and the kerguelen plateau over a fixed hot spot

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

provenance of jurassic cretaceous tethyan himalayan sequences in the thakkhola section nepal inferring pre collisional tectonics of the central himalaya abstract the jurassic cretaceous upper tethyan flysch well exposed in the thakkhola section nepal was deposited prior to the continent continent collision between the indian and eurasian plates this tethyan himalayan sequence ths has preserved the extreme northern passive margin of the indian plate with its direct deposition onto the eroded precambrian rocks in the lowest part of this relatively continuous section the clastic rocks of the ths as they are useful to constrain the paleogeography and paleotectonics of the himalayan orogen in this study we report the petrography detrital zircon u pb isotopic ages and zircon trace element data for sandstone samples from the upper part of a triassic stratigraphic section the mineral modal composition data indicates that these quartz rich units were derived from recycled orogen this is supported that the youngest zircons analyzed can be dated to 400 ma that predates the depositional age by hundreds of millions of years a total of 85 of the zircon ages are

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

a case study of the interaction of a mesoscale gravity wave with a mesoscale convective system abstractthis study documents the high amplitude mesoscale gravity wave mgw event of 7 march 2008 in which two mgws strongly impacted the sensible weather over a large portion of the southeast united states these mgws exhibited starkly contrasting character despite propagating within similar environments the primary i e long lived mgw was manifest by a solitary wave of depression associated with rapid sinking motion and adiabatic warming while the secondary short lived mgw was manifest by a solitary wave of elevation mgwel dominated by rising motion and moist adiabatic cooling genesis of the primary mgw occurred as a strong cold front arrived at the foot of mexico s high terrain and perturbed the appreciable overriding flow the resulting gravity wave became ducted in the presence of a low level frontal stable layer and caused surface pressure falls up to 4 hpa the mgw later amplified as it became coupled with a stratiform precipitation system which led to its evolution into an intense

geometry facies and development of middle ordovician carbonate buildups virginia appalachians large carbonate buildups from 1 to 60 km wide and 20 to 250 m thick in the lower part of the middle ordovician foreland basin sequence in virginia include shallow ramp and downslope types the buildups overlie peritidal and lagoonal carbonates shallow ramp buildups are overlain by deep ramp nodular limestone downslope buildups are overlain by slope and basin limestone and or shale lime wackestone and or mudstone commonly with stromatactoid structures occurs in cores of buildups and as abundant small pods enclosed in skeletal sand bindstone is rare but bryozoan bafflestone locally marine cemented is common in downslope cores and pods pelmatozoan ramose bryozoan sands and rudstone locally with abundant mud pods may form sheets beneath flanking and above core facies they are planar bedded or less commonly have large scale foresets black shaly skeletal limestone containing siliceous sponges brachiopods bryozoans and pelmatozoans forms deep flank beds surrounding downslope buildups and grades outward into basinal limestone and or shale the buildups are carbonate banks that developed in a transgressive setting involving sea level rise and subsidence of the foreland basin they formed as a result of high rates of skeletal production by bank biotas and by baffling action of stalked and branching organisms widespread marine cementation converted the loose bank sediments into rigid structures some downslope buildups were initiated on unconformity highs but most buildups overlie thick sequences of shallow water facies some shallow ramp buildups may be localized above a linear high tazewell arch shallow ramp buildups were killed by influxing mud following incipient drowning of the shallow ramp downslope buildups were killed following basin subsidence when they were covered by anoxic basin waters exploration models involving buildups on carbonate ramps should recognize the potential for both shallow ramp and downslope buildup trends such downslope buildups are particularly important because buildup facies are closely associated with potential reservoir rocks of the slope and basin

convectively generated gravity waves and their effect on the cloud environment this study uses a two dimensional cloud resolving model to examine how convectively generated gravity waves modify the environment of an isolated convective cloud the model is initialized with an idealized sounding and the cloud is initiated by adding a locally buoyant perturbation the modeled convection generates a spectrum of gravity waves with vertical wavelengths that are harmonics of the depth of the troposphere it is shown that the first three wave modes significantly modify the cloud environment the modification of the cloud environment is quantified in terms of the convective available potential energy cape and convective inhibition cin the first two wave modes travel fastest away from the cloud and are responsible for the changes in cape whereas the third wave mode causes low level lifting and hence a reduction in cin the maximum far field perturbations in cape and cin are approximately 15 and 33 of the initial background values respectively these results agree with previous studies of more organized convection predicting the existence of a region surrounding the convective system that favors the development of new convection

paleocene eocene foreland basin evolution in the himalaya of southern tibet and nepal implications for the age of initial india asia collision siliciclastic sedimentary rocks derived from the southern lhasa terrane sitting depositionally upon rocks of the northern indian passive continental margin provide an estimate of the age of initial contact between the continental parts of the indian and asian plates we report sedimentological sedimentary petrological and geochronological data from upper cretaceous paleocene strata in the sangdanlin section located along the southern flank of the indus yarlung suture zone in southern tibet this is probably the most proximal and therefore the oldest record of the india asia collision these strata were deposited by high density turbidity currents or concentrated density flows and suspension settling of pelagic biogenic debris in a deep marine setting an abrupt change from quartz arenitic to feldspatholithic sandstone compositions marks the transition from indian to asian sediment provenance the abrupt compositional change is accompanied by changes in u pb ages of detrital zircons diagnostic of a sediment provenance reversal from indian to asian sources the timing of the transition is bracketed between 60 ma and 58 5 0 6 ma by detrital zircon u pb ages and zircon u pb ages from a tuffaceous bed in the upper part of the section in the context of a palinspastically restored regional paleogeographic framework data from the sangdanlin section combined with previously published data from the northern tethyan himalaya and the frontal nepalese lesser himalaya and subhimalaya suggest that a flexural wave migrated 1300 km southward across what is now the himalayan thrust belt from paleocene time to the present

deep water stratigraphic cyclicity and carbonate mud mound development in the middle cambrian marjum formation house range utah usa in mid middle cambrian time shallow water sedimentation along the cordilleran passive margin was abruptly interrupted by the development of the deep water house range embayment across nevada and utah the marjum formation 330 m in the central house range represents deposition in the deepest part of the embayment and is composed of five deep water facies limestone argillaceous limestone rhythmites shale thin carbonate mud mounds bioturbated limestone and cross bedded limestone these facies are cyclically arranged into 1 5 to 30 m thick parasequences that include rhythmite mound rhythmite shale rhythmite bioturbated limestone and rhythmite cross bedded limestone parasequences using biostratigraphically constrained sediment accumulation rates the parasequences range in duration from 14 to 270 kyr the mud mounds are thin 2 m closely spaced laterally linked symmetrical domes composed of massive fenestral peloidal to clotted microspar with sparse unoriented poorly sorted skeletal material calcitized bacterial filaments tubes and abundant fenestrae and stroma tactoid structures these petrographic and sedimentological features suggest that the microspar peloids clots and syndepositional micritic cement were precipitated in situ from the activity of benthic microbial communities concentrated growth of the microbial communities occurred during periods of decreased input of fine detrital carbonate transported offshore from the adjacent shallow water carbonate platform in the neighbouring wah wah range and throughout the southern great basin coeval mid middle cambrian shallow water carbonates are composed of abundant metre scale upward shallowing parasequences that record high frequency 104 105 years eustatic sea level changes given this regional stratigraphic relationship the marjum formation parasequences probably formed in response to high frequency sea level fluctuations that controlled the amount of detrital carbonate input into the deeper water embayment during high frequency sea level rise and early highstand detrital carbonate input into the embayment decreased as a result of carbonate factory retrogradation resulting in the deposition of shale base of rhythmite shale parasequences or thin nodular rhythmites followed by in situ precipitated mud mounds lower portion of rhythmite mound parasequences during the ensuing high frequency sea level fall lowstand detrital carbonate influx into the embayment increased on account of carbonate factory pro gradation towards the embayment resulting in deposition of rhythmites upper part of rhythmite mound parasequences reworking of rhythmites by a lowered storm wave base cross bedded limestone deposition or bioturbation of rhythmites by a weakened lowered o2 minimum zone bioturbated lime stone deposition this interpreted sea level control on offshore carbonate sedimentation patterns is unique to palaeozoic and earliest mesozoic deep water sediments after the evolution of calcareous plankton in the jurassic the presence or absence of deeper water carbonates was influenced by a variety of chemical and physical oceanographic factors rather than just physical transport of carbonate muds

triassic to cenozoic evolution of the nw australian continental margin and the birth of the indian ocean preliminary results of odp legs 122 and 123 the northwest australian continental margin is a very old sediment starved ne gondwanan margin with the opportunity to study the early structural and depositional evolution during the triassic to jurassic rifting stages neo tethys the earliest cretaceous transition from rifting to drifting and the early tectonic volcanic and paleoceanographic history of the indian ocean ocean drilling program odp legs 122 and 123 drilled eight sites in the area of the exmouth plateau and the adjacent abyssal plains sites 759 761 and 764 studied the triassic to cenozoic evolution of wombat plateau a small sub plateau of the northern exmouth plateau sites 765 penetrated almost 1 km of cretaceous to cenozoic sediments of the nearby argo abyssal plain and 270 m of the oldest indian ocean crust sites 762 and 763 studied the southern central exmouth plateau whereas site 766 was drilled into intrusive volcanics with morb affinity under the adjacent gascoyne abyssal plain at the foot of the western escarpment of the plateau the major discoveries during the drilling of the two continental margin deep ocean basin transects led to a better understanding of the early rift history of this margin during late permian to late triassic times stretching block tectonic movements fluviodeltaic shallow water carbonate environments major rhaetian carbonate buildup early rift volcanism of the rift drift transition processes major blockfaulting during jurassic times with local uplift rift flank tilting and subaerial erosion forming a post rift unconformity of the age and paleoenvironment of the oldest part of the indian ocean possibly not earlier than late berriasian to early valanginian breakup 20 ma younger than expected of the juvenile ocean stage transgressive condensed early neocomian belemnite sands calcisphere chalks and bentonites on wombat plateau of the mature ocean stage post mid cretaceous eupelagic chalks of the geochemical nature and origin of old oceanic crust and the overlying sediments in a geochemical reference hole and of the mesosoic chrono bio magneto stratigraphy and the age and causes of major relative sea level fluctuations especially during late triassic and early cretaceous times

pre breakup continental extension in east gondwanaland and the early opening of the eastern indian ocean abstract extension of continental crust by up to 360 km on a north northeast azimuth in the great australian bight occurred prior to the middle cretaceous 96 ma onset of seafloor spreading between australia and antarctica this large amount of continental extension is constrained to the late jurassic 160 ma middle cretaceous interval about a pole estimated to lie about 40 southeastward of southeastern australia using bathymetric data combined with seismic and magnetic determinations of the continent ocean boundaries off australia india and antarctica we determine a revised fit of east gondwanaland prior to continental extension and at various stages thereafter in the first stage from 160 to 132 5 ma m11 india australia rotated from antarctica with continental crustal extension between australia and antarctica and largely transform motion between the coromandel coast margin of india and the kron prins olav kyst margin of antarctica in the second stage from 132 5 to 96 ma india rotated northwestward away from australia antarctica producing m10 and younger magnetic anomalies along the western margin of australia continental extension was greatest between australia and antarctica during this stage the newly determined 132 5 96 ma rotation between india and australia provides an improved fit between the orientation of observed m10 m0 magnetic anomalies and the southward decrease in spreading rate off the western australian margin together with bathymetry the new rotation parameters lead to identification of the abandoned 96 ma spreading ridge along the lost dutchmen and dirck hartog ridges the naturaliste fracture zone is found to lie nearly parallel to the early cretaceous transform direction between india and antarctica suggesting that slow seafloor spreading required between australia and antarctica to accommodate the continental extension further east occurred between naturaliste fracture zone and the m4 m0 anomalies adjacent to the naturaliste plateau the revised fit of india in east gondwanaland reduces the eastward extent of greater india to 95 e but does not change its extent as far north as the cape range fracture zone the new pole determined for the early cretaceous rotation between india and australia antarctica lies within 15 of the southern tip of india significantly closer than in previous determinations thereby reducing the amount of seafloor spreading generated between africa and antarctica by the india antarctica rotation and thus offering a possible solution to the perceived spreading rate problems between m11 and m0 in the somali mozambique and antarctic basins

response of convection to relative sea surface temperature cloud resolving simulations in two and three dimensions 1 the properties of equilibrated tropical convection are studied using a cloud resolving model with large scale dynamics parameterized by the weak temperature gradient wtg approximation model integrations are performed in both 2 d and 3 d geometries the target profile toward which horizontal mean free tropospheric temperature is relaxed is held fixed while sea surface temperature sst is varied consistent with previous studies large scale ascent and precipitation increase under wtg as the sst is increased but more rapidly in two dimensions than in three dimensions this is related to greater extremes of near surface buoyancy in two dimensions as well as a lower gross moist stability and perhaps also to weaker entrainment in both two and three dimensions the vertical profiles of large scale vertical velocity are top heavy and remarkably self similar in shape as sst is increased when all integrations are analyzed together precipitation increases with column integrated relative humidity once the latter reaches a threshold as in observations and other models however within each integration the two quantities are correlated negatively albeit over a very narrow range

a forced gravity wave model of serf organizing convection abstract a two dimensional hydrostatic nonrotating numerical model with a cumulus paramelerizafion is developed to study the early stages of mesozcale convective systems amplifying forced gravity waves occur when peneirative downdrafts are present updraft heating by itself is unable to cause convective sysiems to intensify propagation speeds are in rough agreement with those observed in midlatitude mesoscale convective systems the conditionalityof the convection and the horizontal advection of precipitation by the relative wind produce las between lifting and convection that are not found in conventional wave cisk models these lags slow the growth and reduce the propasation speeds of forced gravity waves

discrete propagation in numerically simulated nocturnal squall lines abstract simulations of a typical midlatitude squall line were used to investigate a mechanism for discrete propagation defined as convective initiation ahead of an existing squall line leading to a faster propagation speed for the storm complex radar imagery often shows new cells appearing in advance of squall lines suggesting a causal relationship and prompting the search for an action at a distance mechanism to explain the phenomenon in the simulations presented the identified mechanism involves gravity waves of both low and high frequency generated in response to the latent heating which subsequently propagate out ahead of the storm the net result of the low frequency response combined with surface fluxes and radiative processes was a cooler and more moist lower troposphere establishing a shallow cloud deck extending ahead of the storm high frequency gravity waves excited in response to fluctuations in convective activity in the main storm were subsequently ducted by the storm s own upp

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

detailed record of the mid oxfordian late jurassic positive carbon isotope excursion in two hemipelagic sections france and switzerland a plate tectonic trigger the oxfordian late jurassic was a time of widespread change in jurassic marine carbonate sedimentation patterns a marked positive excursion in 13 c is dated as middle oxfordian in age in this study we investigate if changes in carbonate sedimentation coincided with altered carbon cycling and climate we use c isotope records as a proxy for the evolution of the carbon cycle and compare 13 c trends with the evolution of sedimentation in a segment of the opening tethys seaway one of the studied sections is located in the subalpine basin of france trescleoux and oze the other in the swiss jura mountains liesberg carbon isotope stratigraphy of carbonate carbon locates the peak values of the middle oxfordian positive excursion to theantecedens andparandieri subzonesoftheplicatilisandtransversariumammonitezones respectively causesofthe excursionremain enigmatic theexcursion seems not to coincide with a global oceanic anoxic event but regionally enhanced organic carbon accumulation during the early and early middle oxfordian may be the cause of the increase in 13 c the excursion occurs during a time of progressive climate warming anditspeakvaluescoincidewiththefirstcalcareoussedimentsrecurringafteraperiodofreducedcarbonateaccumulationintheearly and early middle oxfordian the excursion is also time equivalent to a major reorganisation of global ocean currents the opening atlantic and tethys oceans combined with rising sea level led to the formation of an efficient circumglobal seaway we conclude that this favoured the widespread recurrence of carbonate producers by providing new habitats as a result ccarb burial increased leading to a lower corg ccarb burial rate and therefore to stabilisation and decrease in 13 c in the middle oxfordian thus the mid oxfordian positive excursion in carbonate c isotopes may reflect changes in the carbon cycle that were triggered by a copious reorganisation of the ocean current system caused by major plate tectonic movements 2007 elsevier b v all rights reserved

examination of gravity waves associated with the 13 march 2003 bow echo abstractnumerical simulations of the 13 march 2003 bow echo over oklahoma are used to evaluate bow echo development and its relationship with gravity wave generation multiple fast moving with speeds of 30 35 m s 1 gravity waves are generated in association with fluctuations in the first vertical mode of heating in the convective line the surface impacts of four such waves are observed in oklahoma mesonet data during this case observations of surface pressure surges ahead of convective lines prior to the bowing process are reproduced a slower gravity wave produced in the simulation is responsible for a prebowing pressure surge this slower gravity wave moving at approximately 11 m s 1 is generated by an increase in low level microphysical cooling associated with an increase in rear to front flow and low level downdrafts shortly before bowing the wave moves ahead of the convective line and is manifested at the surface by a positive pressure surge the pattern of low level vertical motion associated

early cretaceous radiolarians of the northeast indian ocean leg 123 sites 765 766 and dsdp site 261 the antarctic tethys connection abstract during odp leg 123 abundant and well preserved neocomian radiolarians were recovered at site 765 argo abyssal plain and site 766 lower exmouth plateau assemblages are characterized by the numerical dominance of a small number of non tethyan forms and by the scarcity of tethyan taxa remarkable contrasts exist between radiolarian assemblages extracted from claystones of site 765 and reexamined dsdp site 261 and faunas recovered from radiolarian sand layers only found at site 765 clay faunas are unusual in their low diversity of apparently ecologically tolerant or solution resistant ubiquist species whereas sand faunas are dominated by non tethyan taxa comparisons with sites 766 and 261 as well as sedimentological observations lead to the conclusion that this faunal contrast resulted from a difference in provenance rather than from hydraulic sorting or selective dissolution the ranges of 27 tethyan taxa from site 765 were compared to the tethyan radiolarian zonation by jud 1992 by means of the unitary associations method this calculation allows to directly date the site 765 assemblages and to estimate the amount of truncation of ranges for tethyan taxa over 70 of the already few tethyan species of site 765 have truncated ranges during the valanginian hauterivian radiolarian assemblages recovered from claystones at sites 765 and 261 in the argo basin apparently reflect restricted oceanic conditions during the latest jurassic barremian neither sedimentary facies nor faunal associations bear any resemblance to what we know from typical tethyan sequences we conclude that the argo basin was paleoceanographically separated from the tethys during the late jurassic and part of the early cretaceous by its position at higher paleolatitudes and or by enclosing land masses assemblages recovered from radiolarian sand layers are dominated by non tethyan species that are interpreted as circumantarctic their first appearance in the late berriasian early valanginian predates the oceanization of the indo australian breakup m11 late valanginian but coincides with a sharp increase in margin derived pelagic turbidites the indo australian rift zone and the adjacent margins must have been submerged deeply enough to allow an intermittent influx of circumantarctic cold water into the argo basin creating increased bottom current activity cold water radiolarians carried into the argo basin upwelled along the margin died and accumulated in radiolarite layers due to winnowing by bottom currents high rates of faunal change and the sharp increase of bottom current activity are thought to be synchronous with possible pronounced late berriasian early valanginian lowstands in sea level hypothetically both phenomena might have been caused by a tendency to glaciation on the antarctic australian continent which was for the first time isolated from the rest of gondwana by oceanic seaways as a result of jurassic early cretaceous sea floor spreading the absence of most typical tethyan radiolarian species during the valanginian hauterivian is interpreted as reflecting a time of strong influx of circumantarctic cold water following oceanization m11 and rapid spreading between southeast india and west australia the reappearance and gradual abundance diversity increase of tethyan taxa along with the still dominant circumantarctic species are thought to result from overall more equitable climatic conditions during the barremian early aptian and from the establishment of an oceanic connection with the tethys ocean during the early aptian

palaeogeography of radiolarite and organic rich deposits in mesozoic tethys siliceous and marine organic rich deposits are sometimes associated sometimes separate in space and time however both are generally accepted to be the result of high planktonic productivity among the siliceous marine deposits the phtanite family facies is distinguished from the radiolarite family facies by several characteristics they contain organic material and as a result are blackish vs red green for radiolarite facies their time of deposition corresponds with strong faunal modifications and they are deposited generally in shallower environments a palaeogeographic analysis of locations of tethyan biosiliceous and marine organic rich rocks both resulting from a high planktonic palaeoproductivity for three mesozoic high sea level intervals toarcian kimmeridgian and cenomanian show a during jurassic times these tethyan deposits were dissociated the siliceous deposits being closer to open ocean waters than the organic rich ones this is a common disposition in modern upwelling systems and suggests a common process b during cretaceous times these tethyan deposits were often associated i e both occur at the same site and are probably the result of a different process from that in the jurassic

multiscale convective wave disturbances in the tropics insights from a two dimensional cloud resolving model abstract multiscale convective wave disturbances with structures broadly resembling observed tropical waves are found to emerge spontaneously in a nonrotating two dimensional cloud model forced by uniform cooling to articulate the dynamics of these waves model outputs are objectively analyzed in a discrete truncated space consisting of three cloud types shallow convective deep convective and stratiform and three dynamical vertical wavelength bands model experiments confirm that diabatic processes in deep convective and stratiform regions are essential to the formation of multiscale convective wave patterns specifically upper level heating together with low level cooling serves to preferentially excite discrete horizontally propagating wave packets with roughly a full wavelength structure in troposphere and dry phase speeds cn in the range 16 18 m s 1 these wave packets enhance the triggering of new deep convective cloud systems via low level destabilization the new convection in turn caus

early cretaceous strata of the nepal himalayas conjugate margins and rift volcanism during gondwanan breakup early cretaceous sandstones shales and marlstones chukh tangbe and muding formations at least 625 m thick crop out north of the main central thrust in central nepal they were strongly deformed during himalayan collision with telescoping of facies transitions as a result of crustal shortening the sediments show northerly palaeoflow and were deposited on the steadily subsiding northern tethyan margin of gondwana berriasian deltaic deposits pass upward into valanginian albian storm dominated shelf deposits and into latest albian pelagic slope carbonates an unconformity probably of valanginian age separates the chukh and tangbe formations locally and is overlain by volcanic conglomerates the gondwanan margin succession matches well with that observed on the formerly conjugate margin of nw australia which separated from greater india during the valanginian to hauterivian volcanic detritus where suitable for analysis shows within plate geochemical affinity and reflects gondwanan fragmentation abundant volcanic detritus in aptian strata may have been derived from extensions of the rajmahal traps of northeast india however volcanism was active near central nepal in the valanginian and volcanic detritus possibly far travelled reached the area during the berriasian early cretaceous strata1 successions and relative sea level changes show a first order relationship to tectonism associated with gondwanan break up

numerical simulations of a gravity wave event over ccope part iii the role of a mountain plains solenoid in the generation of the second wave episode abstract mesoscale model simulations have been performed of the second episode of gravity waves observed in great detail in previous studies on 11 12 july 1981 during the cooperative convective precipitation experiment the dominant wave simulated by the model was mechanically forced by the strong updraft associated with a mountain plains solenoid mps as this updraft impinged upon a stratified shear layer above the deep well mixed boundary layer that developed due to strong sensible heating over the absaroka mountains the gravity wave was created this wave rapidly weakened as it propagated eastward however explosive convection developed directly over the remnant gravity wave as an eastward propagating density current produced by a rainband generated within the mps leeside convergence zone merged with a westward propagating density current in eastern montana the greatly strengthened cool pool resulting from this new convection then generated a bore wave that appeared to be continuous with the move

sedimentologic and stratigraphic constraints on the orientation of the late triassic northern indian passive continental margin abstract the orientation and distribution of the northern indian passive continental margin basin during different epochs constrained the geometric characteristics of the hyperextended northern indian edge greater india traditional paleogeographic reconstructions envisage the late triassic northern indian passive continental margin as e w trending whereas paleomagnetic data support an 55 counterclockwise rotation during northward drifting this case study of upper triassic units from the northern indian margin based on facies analysis sandstone petrography heavy mineral assemblages u pb detrital zircon geochronology and stratigraphic correlation from the zanskar range to southern tibet provides new constraints and suggests that the northern indian passive continental margin might have been n s trending in the late triassic given the dominance of quartz sandstones with zircon tourmaline and rutile indicating a provenance from continental blocks and the recycling of older quartz rich sandstones and detrital zircon age spectra characterized by a neoproterozoic detrital zircon u pb age peak 921 13 ma the upper triassic sandstones widespread along the tethyan himalayas may have been partly derived from the eastern ghats mobile belt in eastern india and the rayner orogen in eastern antarctica the upper triassic quartzite series comprises feldspatho quartzose to pure quartzose sandstones with intercalated bioclastic oosparites deposited in backshore foreshore and shoreface coastal environments without considering the subsequent counterclockwise rotation of india the consistent pattern of the upper triassic bidirectional e w paleocurrent observed throughout the himalaya suggests that the paleoshoreline was striking near n s approximately perpendicular to the regional orientation of the northern indian margin progressive eastward thickening of the sandstone layers and eastward younging of the quartzite series suggest diachronous sedimentation such stratal patterns and the strike of the late triassic paleoshoreline were attributed to the neo tethys transgression from the zanskar range to southern tibet

cloud resolving simulation of toga coare using parameterized large scale dynamics 1 variations in deep convective activity during the 4 month tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare field campaign are simulated using a cloud resolving model crm convection in the model is coupled to large scale vertical velocities that are parameterized using one of two different methods the damped gravity wave damped wave method and the weak temperature gradient wtg method the reference temperature profiles against which temperature anomalies are computed are taken either from observations or from a model integration with no large scale vertical motion but other forcings taken from observations the parameterized large scale vertical velocities are coupled to those temperature or virtual temperature anomalies sea surface temperature radiative fluxes and relaxation of the horizontal mean horizontal wind field are also imposed simulations with large scale vertical velocity imposed from the observations are performed for reference the primary finding is that the crm with parameterized large scale vertical motion can capture the intraseasonal variations in rainfall to some degree experiments in which one of several observation derived forcings is set to its time mean value suggest that those which influence direct forcings on the moist static energy budget surface wind speed and sea surface temperature which together influence surface evaporation and radiative cooling play the most important roles in controlling convection particularly when the damped wave method is used the parameterized large scale vertical velocity has a vertical profile that is too bottom heavy compared to observations when the damped wave method is used with vertically uniform rayleigh damping on horizontal wind but is too top heavy when the wtg method is used

mesoscale predictability of moist baroclinic waves convection permitting experiments and multistage error growth dynamics a recent study examined the predictability of an idealized baroclinic wave amplifying in a conditionally unstable atmosphere through numerical simulations with parameterized moist convection it was demonstrated that with the effect of moisture included the error starting from small random noise is characterized by upscale growth in the short term 0 36 h forecast of a growing synoptic scale disturbance the current study seeks to explore further the mesoscale error growth dynamics in idealized moist baroclinic waves through convection permitting experiments with model grid increments down to 3 3 km these experiments suggest the following three stage error growth model in the initial stage the errors grow from small scale convective instability and then quickly o 1 h saturate at the convective scales in the second stage the character of the errors changes from that of convective scale unbalanced motions to one more closely related to large scale balanced motions that is some of the error from convective scales is retained in the balanced motions while the rest is radiated away in the form of gravity waves in the final stage the large scale balanced components of the errors grow with the background baroclinic instability through examination of the error energy budget it is found that buoyancy production due mostly to moist convection is comparable to shear production nonlinear velocity advection it is found that turning off latent heating not only dramatically decreases buoyancy production but also reduces shear production to less than 20 of its original amplitude

jurassic sedimentary cycles and eustatic sea level changes in southern tibet abstract the marine jurassic sequence in southern tibet is well exposed has an abundant fossil record and provides a good basis for the study of paleoeustasy from measured sections nine lhtho facies representing four broad sedimentary environments inner and outer shelves slope and bathyal can be recognised their vertical ranges show that shelf deposits are mainly present in the lower and middle jurassic whilst outer shelf slope and bathyal environments dominate in the middle and upper jurassic on the basis of these after comparison of the two main approaches used in analysing sea level movements i e the exxon eustatic curve and eustatic cycles jurassic eustatic sea level changes in southern tibet are described the resulting curve is seen to correspond closely with earlier published global curves the cause of these sea level changes is thought to lie in the breakup of gondawanaland and the northwards drift of the indian subcontinent and associated microplates

numerical simulations of a gravity wave event over ccope part ii waves generated by an orographic density current a mesoscale numerical model and detailed observations are used to investigate the generation and maintenance of a mesoscale gravity wave event observed in eastern montana on 11 july 1981 during the cooperative convective precipitation experiment ccope it is shown that the interaction between an orographic density current and a mountain barrier leads to the generation of the gravity waves the simulation results suggest the following four stage conceptual model during stage i shortly after sunset the remnant up branch of a thermally driven upslope flow east of the rockies was driven back toward the mountain by the pressure gradient force associated with a cool pool over north dakota the nocturnal stable layer over eastern montana was strengthened during passage of this density current during the 1 2 h transition period of stage ii the advancing density current became blocked as it encountered the higher terrain an isentropic ridge developed above the original warm lee trough due to strong adiabatic cooling caused by the sustained upward motion in the presence of orographic blocking during stage iii an even stronger upward motion center formed to the east of the density current head updraft in response to an eastward horizontal pressure gradient force produced by the isentropic ridge in stage iv as the density current head collapsed and downward motion developed to the west of the original updraft in quadrature phase with the isentropic perturbation a gravity wave was generated this wave propagated eastward with the mean wind opposite to the motion of the earlier density current and was maintained by the strong wave duct established earlier by the density current thus the mountain plains circulation may at times generate mesoscale gravity waves and deep convection hours after diurnal heating has ended

did early land plants produce a stepwise change in atmospheric oxygen during the late ordovician sandbian 458 ma abstract a stepwise change in atmospheric oxygen o2 levels during the ordovician has been attributed to the emergence of land plants this phenomenon is tied to a major baseline shift in the stable carbon isotope 13c curve and inferred increase in nutrient delivery and enhanced primary productivity in nearshore settings which led to high organic carbon burial the timing and magnitude of this baseline shift however is still elusive in part because of the lack of high resolution 13c data that span this period much of the existing ordovician 13c literature is focused on isotopic excursions with less emphasis on identifying long term shifts in baseline pre and post excursion values this study presents new high resolution 13c data from stratigraphic sections at germany valley west virginia and union furnace pennsylvania in the central appalachian basin these sections span the entire sandbian stage and continue into the lower katian stage the 13c data from both sections are characterized by relative stability carbon isotope values mean 0 61 in the lower sandbian followed by a 1 2 shift in the upper sandbian mean 0 62 herein we propose that the positive shift represents a long term global shift in baseline 13c values of dissolved inorganic carbon the timing of this positive shift coinciding with the diversification of early land plants i e bryophytes supports earlier models that suggested enhanced organic carbon burial rates served as a mechanism for the stepwise oxygenation of the atmosphere during the late ordovician

numerical simulation of the large amplitude mesoscale gravity wave event of 15 december 1987 in the central united states abstract an observational study employing spectral methods is first made to establish a background for a modeling effort of the mesoscale gravity wave event of 15 december 1987 the waves are found to have wavelengths of 100 160 km phase speeds of approximately 30 m s 1 and lifetimes of over 6 h conditions for their maintenance are evaluated indicating the presence of a wave duct and a supportive role for wave cisk convection shearing instability and geostrophic adjustment are all implicated as possible source mechanisms for the observed waves the case is then simulated with the pennsylvania state university national center for atmospheric research mm4 mesoscale forecast model with the following primary objectives i to test the model s ability to simulate a mesoscale gravity wave event ii to examine in detail the environments of mesoscale gravity wave development and iii to investigate the mechanisms of mesoscale gravity wave generation and maintenance the full physics control experim

a study of a mesoscale solitary wave in the atmosphere originating near a region of deep convection abstract an analysis of a mesoscale wave which occurred over the eastern united states on 6 march 1969 is presented its origin is attributed to the perturbation of a midtropospheric inversion by a squall line after the wave formed it propagated in the direction of the mid and upper level tropospheric flow and expanded as an arc with the center located near the region of convective activity the wave travelled from western tennessee and kentucky over a distance of more than 1000 kilometers to nova scotia with a mean speed of 55 m s 1 the event was quite obvious on surface barographs throughout this region pressure traces showed an obvious v shaped pressure drop of 3 to 6 mb over much of the wave path the wave persisted for about 9 hours with little change in character the synoptic situation is analysed and compared with similar atmospheric conditions in other studies the generation mechanism of an internal gravity wave of depression is investigated by a simple model it is found that wave of depre

characteristic trace fossil associations in oxygen poor sedimentary environments the sedimentologic record of oxygen poor depositional environments typically includes trace fossils produced by deposit feeding organisms we propose an oxygen controlled trace fossil model in which increasing oxygen concentration of interstitial water in sediment parallels a transition from fodinichnia dominated through pascichnia dominated to domichnia dominated trace fossil associations in certain places such as parts of the late paleozoic oquirrh basin in utah this model provides a reasonable alternative to the more traditional depth controlled model of trace fossil distribution

sedimentology of a mid late ordovician carbonate mud mound complex from the kathmandu nappe in central nepal abstract this sedimentological study of the godavari quarry is the first relating to the palaeozoic tethyan sedimentary rocks of the kathmandu nappe central nepal sedimentological analyses led to the identification of six microfacies belonging to a large carbonate mud mound complex which can be divided into mound flank and off mound main depositional settings identification of two dasycladaceans dasyporella cf silurica stolley 1893 and vermiporella sp in the mound facies gives a mid late ordovician age to this newly discovered godavari carbonate mud mound which makes this mound one of the oldest ever described in the asian continent the mound microfacies are characterized by a high micritic content the presence of stromatactis and the prevalence of red coloured sediments the red pigmentation probably being related to organic precipitation of iron the flank microfacies are characterized by a higher crinoid and argillaceous content and the presence of bio and lithoclasts concentrated in argillaceous lenses finally the off mound microfacies show very few bioclasts and a high argillaceous content palaeoenvionmental interpretation of microfacies in terms of bathymetry leads us to infer that the godavari mud mound started to grow in a deep environment setting below the photic and wave action zones and that it evolved to occupy a location below the fair weather wave base cementation of cavities within the mound facies underlines a typical transition from a marine to a burial diagenetic environment characterized by 1 a radiaxial non luminescent feroan calcite cement marine showing a bright orange luminescent band in its middle part 2 a bright zoned orange fringe of automorphic feroan calcite meteoric phreatic 3 a dull orange xenomorphic feroan calcite cement in the centre of cavities burial and 4 a saddle dolomite within the centre of larger cavities the faunal assemblage diversity and relative proportion of the godavari mound facies is dominated by crinoids and ostracods which makes this carbonate mud mound comparable to the meiklejohn peak mounds nevada

a case study on the far field properties of propagating tropospheric gravity waves abstractmesoscale gravity waves were observed by barometers deployed as part of the usarray transportable array on 29 june 2011 near two mesoscale convective systems in the great plains region of the united states simultaneously airs satellite data indicated stratospheric gravity waves propagating away from the location of active convection peak perturbation pressure values associated with waves propagating outside of regions where there was precipitation reached amplitudes close to 400 pa at the surface here the origins of the waves and their relationship to observed precipitation are investigated with a specialized model study simulations with a 4 km resolution dry numerical model reproduce the propagation characteristics and amplitudes of the observed waves with a high degree of quantitative similarity despite the absence of any boundary layer processes surface topography or moist physics in the model the model is forced with a three dimensional time dependent latent heating cooling field that

sequence development of a mixed carbonate siliciclastic high relief ramp mississippian kentucky u s a abstract the discovery of the supergiant oil fields of the caspian region has focused attention on eustatic tectonic and climatic controls on lower carboniferous facies this paper documents the development of a highly complex mixed carbonate siliciclastic ramp succession of the lower mississippian upper osagean lower meramecian fort payne salem interval kentucky that formed peripheral to an abandoned delta system borden formation following drowning of the paleoshelf during a time of arid climate and tectonic quiescence the antecedent borden deltaic marine paleoshelf stood 100 m above the starved basin plain to the southwest and had marginal slopes of less than 0 5 the succession is a supersequence 0 to 150 m thick approximately 5 to 10 my duration composed of two upper osagean fort payne and two lower meramecian warsaw salem depositional sequences which correlate with the global sea level cycles of ross and ross 1988 the supersequence lowstand systems tract on the basin floor consists of the lower part of a unit of green shale and mounds mound growth appears to have continued during supersequence transgression culminating in some mounds up to 60 m thick on the borden paleoshelf the supersequence transgressive systems tract is a condensed glauconite horizon s the supersequence highstand tract consists of marine quartz sandstone and shale peritidal carbonates high energy crinoidal bryozoan grainstone banks and deep ramp and slope siliceous calcisiltite third order sequences have local lowstand transgressive sand bodies those in sequence 2 are clinoformed strike sand lobes up to 50 m thick while those in the younger sequences are discontinuous sheets dip oriented lobes the siliciclastic units appear to be associated with a paleodrainage system off the borden paleoshelf in upper osagean sequences 1 and 2 third order highstand systems tracts are aggradational on the paleoshelf and prograded to the southwest as a series of clinoforms into the starved basin lower meramecian sequences 3 and 4 highstand systems tracts are relatively layer cake reflecting loss of accommodation during late osagean basin filling and they prograded more to the west into the subsiding reelfoot graben illinois basin the extremely complex facies relations reflect the interaction of the antecedent shelf slope basin topography the mixed carbonate and siliciclastic systems mounded basin floor topography the highly channeled margin morphology eustasy and relatively stable tectonics

strontium isotope variations in middle jurassic late bajocian callovian seawater implications for earth s tectonic activity and marine environments abstract strontium isotope ratios of well preserved belemnite rostra and ammonite shells are presented from stratigraphically well dated upper bajocian callovian sediments of the polish jura chain in central poland nekto benthic belemnites show a narrow trend of changes of 87 sr 86 sr ratio that are interpreted to record secular variations in the strontium isotope composition of seawater a new fit of the seawater strontium isotope curve for the late bajocian callovian is presented based on current and literature data the data show a gradual decrease of seawater 87 sr 86 sr ratio throughout the late bajocian earliest middle callovian lowest 87 sr 86 sr ratios 0 706850 and the flat minimum of the curve were reached in the latest middle and the late callovian the middle jurassic decrease in seawater 87 sr 86 sr ratio is interpreted to have been a result of the increased volcanic activity of the seafloor studied nektonic ammonites are considered to have lived in surface or shallow near coastal waters of the polish jura chain basin and been affected by the freshwater influx a slight enrichment of ammonite shells in 87 sr isotope is linked to a change in strontium isotope composition of the surface or near coastal waters due to the riverine strontium input

mesozoic tethyan strata of thakkhola nepal evidence for the drift and breakup of gondwana the thakkhola region of central nepal contains at least 1 5 km of coastal to neritic and upper slope deposits of late triassic to mid cretaceous latest albian age new paleomagnetic paleobiogeographic and paleoflow data confirm that the strata were deposited on the northern gondwana margin bordering tethys while thakkhola lay at mid latitudes 28 41 s late triassic coastal deposits are overlain by early mid jurassic shelf units thick early jurassic carbonates correspond with the most northerly paleolatitude recorded probably reflecting thakkhola s rapid drift into the subtropics the late jurassic to early cretaceous drift again in higher latitudes resulted in deposition of terrigenous clastics a hiatus spanning late early callovian through early oxfordian time corresponds to a global transgression that may reflect accelerated sea floor spreading in both the atlantic and pacific oceans late jurassic dark shales correlative with the regionally extensive spiti shale are deep shelf to slope deposits septal strength indices for cephalopods suggest depths 250 m the shales contain an indo sw pacific ammonite assemblage but also a diversified agglutinated foraminiferal assemblage of boreal affinity such deep water foraminiferal assemblages probably had a large cosmopolitan component the shale is intensely deformed and its overmature condition probably reflects in part cenozoic orogenic events lower cretaceous berrisian through aptian deltaic deposits overlying the shales contain volcanoclastic material that probably was derived from coeval volcanics of the lesser himalayas to the south based on compositional paleoflow and facies analysis volcanism reflects the onset of sea floor spreading between greater india and northwestern australia in late valanginian time at the top of the thakkhola mesozoic sequence are hemipelagic slope carbonates of latest albian age the thakkhola succession generally correlates well with that observed on a formerly contiguous continental margin offshore northwestern australia

revised middle upper jurassic strontium isotope stratigraphy abstract a study is conducted to supplement the uppermost lower jurassic lowermost cretaceous marine strontium isotope dataset and to present new statistical fits of the middle late jurassic seawater strontium isotope curve based on a numerical time scale and a detailed biostratigraphical zonal scheme the use of the stratigraphical scheme allows reduction of dating errors related to uncertainty of numerical age determinations the presented correlation charts enable direct calibration between strontium isotope stratigraphy and regional biostratigraphical frameworks new strontium isotope data have been obtained from well preserved lower bajocian uppermost callovian oxfordian kimmeridgian and upper volgian belemnite rostra the presented seawater 87 sr 86 sr curve is characterized by reliable 95 confidence limits mean width of 0 000007 which take into account precision of dating of particular data points a decrease of seawater 87 sr 86 sr ratio from ca 0 70730 to ca 0 70683 is observed throughout the middle aalenian early oxfordian 172 1 160 8 ma ago the steepest phanerozoic fall of the ratio with a rate of change of up to 0 00015 per 1 ma is recorded in the bajocian segment of the strontium isotope curve the phanerozoic minimum of the marine 87 sr 86 sr ratio occurred at the early middle oxfordian transition the 87 sr 86 sr ratio increased starting from the middle oxfordian till the end of the jurassic 160 8 145 7 ma reaching a value of ca 0 70720 at the jurassic cretaceous transition the middle earliest late jurassic decrease in seawater 87 sr 86 sr ratio is interpreted as a result of the increased hydrothermal activity of the seafloor during the breakup of gondwana and the formation of new atlantic tethyan oceanic basins the successive rise of the ratio is probably related to the decelerated hydrothermal venting of the oceanic crust although a partial increase in radiogenic strontium input from continental weathering cannot be excluded

the gravity wave response above deep convection in a squall line simulation abstract high frequency gravity waves generated by convective storms likely play an important role in the general circulation of the middle atmosphere yet little is known about waves from this source this work utilizes a fully compressible nonlinear numerical two dimensional simulation of a midlatitude squall line to study vertically propagating waves generated by deep convection the model includes a deep stratosphere layer with high enough resolution to characterize the wave motions at these altitudes a spectral analysis of the stratospheric waves provides an understanding of the necessary characteristics of the spectrum for future studies of their effects on the middle atmosphere in realistic mean wind scenarios the wave spectrum also displays specific characteristics that point to low physical mechanisms within the storm responsible for their forcing understanding these forcing mechanisms and the properties of the storm and atmosphere that control them are crucial first steps toward developing

stratigraphy and sedimentary history of the nepal tethys himalaya passive margin abstract the sedimentary history of the nepal tethys himalaya began with deposition of thick carbonates in the cambro ordovician followed by a mixed siliciclastic carbonate epicontinental succession recording two major deepening events in the early silurian and late devonian fossiliferous carbonate ramp deposits in the tournaisian were disconformably followed by white quartzose sandstones and black mudrocks with locally intercalated diamictites derived from sedimentary rocks and deposited in asymmetric tectonic basins rift stage break up in the mid early permian locally associated with effusion of tholeiitic lava flows was followed by a transgressive sandy to shaly locally coal bearing or bioclastic unit capped by condensed pelagic carbonates in the middle to late permian juvenile ocean stage subsidence of the cooling stretched crust led close to bathyal water depths in the olenekian but then slowed down in the middle triassic to increase again sharply in the late triassic owing to renewed extensional tectonic activity and sediment loading during up and out building of the indian continental terrace deposition of tropical platform carbonates finally became widespread in the middle liassic mature passive margin stage the initial fragmentation of gondwana in the middle jurassic led to rejuvenation of the indian craton and deposition of quartzo feldspathic hybrid arenites capped by condensed oolitic ironstones deposited at warm subtropical latitudes in the late bathonian middle callovian next a discontinuous pelagic grey marly limestone unit was followed by the ammonoid rich offshore spiti shale in the late jurassic the final disintegration of gondwana began in the berriasian when quartzose siliciclastics derived again from the rejuvenated indian craton and partly from recycling of older clastic successions were followed by thick deltaic to shelf volcaniclastics documenting eruption of alkali basalts in the valanginian followed in the hauterivian to albian by more felsic differentiates such as the trachyandesites exposed in the lesser himalaya 120 km to the south a widespread drowning episode fostered by waning volcaniclastic supply during a global eustatic rise is documented by a major glauconitic horizon deposited at middle southern latitudes in the late albian overlain by scaglia like pelagic limestones in the latest albian the final part of sedimentary history during the rapid northward flight of india and its collision with eurasia is not documented anywhere in nepal due to later erosion of upper cretaceous to lower tertiary strata

a review of the broad pattern of jurassic sea level changes and their possible causes in the light of current knowledge abstract an assessment is made of the current state of research into jurassic sea level changes based on new insights into depositional patterns in relation to these changes and new stratigraphic information from several widely separated regions across the world the bearing of this information on alternative models respectively involving sea level rise interrupted by stillstands or falls is then evaluated the gross pattern appears to be one of more or less gradual rise of sea level through the period interrupted by episodes of comparative stillstand rather than eustatic fall and several episodes of significant regression are shown to be the result of regional tectonics major episodes of eustatic rise took place in the early hettangian early sinemurian early pliensbachian early toarcian early and late bajocian middle callovian and late oxfordian to kimmeridgian a significant episode of rapid and very extensive regression possibly global took place at the end of the triassic but other regressive episodes in the late aalenian bathonian late oxfordian kimmeridgian and tithonian are clearly only regional in extent there is no evidence for glacioeustasy and most if not all of the regional or global changes recognised can readily be related to plate tectonics the events at the triassic jurassic boundary seem to be the result of mantle plume activity centred on the central atlantic region

a mesoscale gravity wave event observed during ccope part ii interactions between mesoscale convective systems and the antecedent waves abstract this paper presents the results of a very detailed investigation into the effects of preexisting gravity waves upon convective systems as well as the feedback effects of convection of varying intensity upon the waves the analysis is based on the synthesis of synoptic surface and barograph data with high resolution surface mesonetwork radar and satellite data collected during a gravity wave event described by koch and golus in part i of this series of papers use is also made of the synoptic barograph data and satellite imagery to trace the waves beyond the mesonetwork and thus determine their apparent source region just upstream of the mesonetwork it is shown that two of the gravity waves modulated convection within a weak squall line as they propagated across the line the other six waves remained closely linked with convective systems that they appeared to trigger however it is shown that the waves were not excited by convection furthermore the waves retained their signatures in the su

anatomy of the middle ordovician sevier shale basin eastern tennessee abstract the sevier shale basin in eastern tennessee comprises one of the thickest clastic sequences nearly 2500 m of middle ordovician age in north america the lower one half of the sequence is composed of lenoir whitesburg blockhouse and sevier formations in ascending order the sequence ranges in age from whiterockian to lower wilderness in north american stages the middle ordovician sequence exhibits tidal flat mosheim member of lenoir fm subtidal main body of lenoir fm slope whitesburg fm anoxic basin blockhouse fm turbidite and contourite sevier fm facies the sevier basin evolved in five stages first a widespread marine transgression initiated carbonate shelf deposition in the study area second a major tectonic downwarping event caused the stable shelf to break and subside rapidly at a rate of 60 65 cm 1000 yrs 1 and areas of shelf facies became areas of slope and basin facies third global transgressions maintained the deep anoxic conditions for nearly 10 ma fourth turbidites began to fill the basin from a westward prograding submarine fan system fifth contour currents reworked the turbidites and progressively ventilated the sevier basin the basin filling process terminated with shallow water subaerial clastics at the end of middle ordovician

paleomagnetic results from the early cretaceous lakang formation lavas constraints on the paleolatitude of the tethyan himalaya and the india asia collision abstract to better constrain the early cretaceous paleogeographic position of the tethyan himalaya and the india asia collision process a paleomagnetic study was performed on the lakang formation lava flows in the cuona area in the southeastern tethyan himalaya stepwise thermal and alternating field demagnetizations successfully isolated reliable characteristic remanent magnetization chrm directions that include antipodal dual polarities and pass positive fold tests at the 99 confidence level and reversal tests at 95 confidence level indicating prefolding primary magnetizations the distribution patterns of chrm directions from the lakang formation lava flows are consistent with young lava flows at similar latitudes suggesting that secular variation has likely been averaged out the tilt corrected site mean direction for 31 sites is d 261 6 i 68 5 with 95 3 6 which provides a paleopole at 26 8 s 315 2 e a 95 5 7 corresponding to a paleolatitude of 52 2 5 7 s for the study area comparison of the paleolatitude observed from the lakang formation lava flows with that expected from the apparent polar wander paths of india at 130 ma show a paleolatitude difference of 2 1 230 km indicating that neither a great north south continental crustal shortening occurred between the indian craton and the tethyan himalaya after 130 ma nor that a wide ocean separated them at that time comparison with reliable cretaceous paleocene paleomagnetic results observed from the tethyan himalaya and the lhasa terrane indicates that the latitudinal width of the neo tethyan ocean could have been up to 7000 km at 134 130 ma and an extension should have existed between the indian craton and the tethyan himalaya during the late cretaceous and paleocene furthermore reliable paleomagnetic results suggest that the india asia collision was a dual collision process consisting of a first collision of the tethyan himalaya with the lhasa terrane asia at 54 9 2 3 ma and a final continent continent collision of the indian craton with the tethyan himalaya at 40 0 3 3 ma

ordovician metre scale cycles implications for climate and eustatic fluctuations in the central appalachians during a global greenhouse non glacial to glacial transition abstract metre scale shallowing upward cycles in ordovician carbonates of the central appalachian basin record climate and eustatic fluctuations during a transition from early ordovician global greenhouse to late ordovician icehouse conditions peritidal facies and shale abundance suggest a long term trend in this area from semi arid early ordovician to more humid middle to early late ordovician conditions with a return to semi arid conditions during the late ordovician the climatic fluctuations were most likely produced by tectonics uplift and erosion related to taconic orogenesis plate motion of north america and the areal extent of water covering the shelf peritidal cyclic facies indicate that high frequency relative sea level fluctuations were of small amplitude 20 m relative sea level fluctuations that decreased into the later ordovician if these sea level changes are eustatic then the increased amplitude may mark the early initiation of continental glaciation on gondwana in the late middle ordovician followed by waning of ice sheets prior to the latest ordovician glaciation

marine faunal realms of the mesozoic review and revision under the new guidelines for biogeographic classification and nomenclature consensus among the friends of paleobiogeography produced tentative guidelines to the classification and nomenclature of marine biogeographic units i e biochores based on these loose rules the present paper is a critical review of all published mesozoic marine realms subrealms and superrealms formerly called climatic belts biochores are defined by the overall endemism within geographic and time envelopes that include choro and chrono types without consideration of facies or climate the hierarchy of ranks or tiers is superrealm realm subrealm province subprovince only ranks in italics are obligatory region is informal these ranks scale with endemism geographic range and persistence in time biochores are named geographically following nomenclatural guidelines not strict rules of synonymy and homonymy with priority beginning with uhlig s paper of 1911 uhlig s two climatic belts are tentatively accepted as optional top ranking superrealms for times of exceptional global endemism available names for them are euroboreal or panboreal new and tethys panthalassa the validity of the 29 existing names for realm group biochores realms subrealms and superrealms in the marine mesozoic is discussed 19 names are rejected for a variety of reasons including synonymy homonymy and usefulness the most important realm group biochores are arctic and boreal atlantic in the boreal euroboreal realm or superrealm and tethyan mediterran caucasian indo pacific jurassic early cretaceous and austral middle late cretaceous in the tethys panthalassa superrealm

generation of mesoscale gravity waves in upper tropospheric jet front systems abstract multiply nested mesoscale numerical simulations with horizontal resolution up to 3 3 km are performed to study the generation of mesoscale gravity waves during the life cycle of idealized baroclinic jet front systems long lived vertically propagating mesoscale gravity waves with horizontal wavelengths 100 200 km are simulated originating from the exit region of the upper tropospheric jet streak in a manner consistent with past observational studies the residual of the nonlinear balance equation is found to be a useful index in diagnosing flow imbalance and predicting wave generation the imbalance diagnosis and model simulations suggest that balance adjustment as a generalization of geostrophic adjustment is likely responsible for generating these mesoscale gravity waves it is hypothesized that through balance adjustment the continuous generation of flow imbalance from the developing baroclinic wave will lead to the continuous radiation of gravity waves

sensitivity of mesoscale gravity waves to the baroclinicity of jet front systems abstract this study investigates the sensitivity of mesoscale gravity waves to the baroclinicity of the background jet front systems by simulating different life cycles of baroclinic waves with a high resolution mesoscale model four simulations are made starting from two dimensional baroclinic jets having different static stability and wind shear in order to obtain baroclinic waves with significantly different growth rates in all experiments vertically propagating mesoscale gravity waves are simulated in the exit region of upper tropospheric jet streaks a two dimensional spectral analysis demonstrates that these gravity waves have multiple components with different wave characteristics the short scale wave components that are preserved by a high pass filter with a cutoff wavelength of 200 km have horizontal wavelengths of 85 161 km and intrinsic frequencies of 3 11 times the coriolis parameter the medium scale waves that are preserved by a bandpass filter with 200 and 600 km cutoff wavelengths ha

a study of cyclone mesoscale structure with emphasis on a large amplitude inertia gravity wave abstract an analysis is presented of prominent mesoscale structure in a moderately intense cyclone with emphasis on a long lived large amplitude inertia gravity wave igw that moved through the northeastern united states on 4 january 1994 available national weather service wsr 88d doppler radar and wind profiler observations are employed to illustrate the rich time dependent three dimensional structure of the igw as the igw amplified peak crest to trough pressure falls exceeded 13 hpa 30 min 1 it also accelerated away from the cyclone reaching a peak forward speed of 35 40 m s 1 across eastern new england the igw was one of three prominent mesoscale features associated with the cyclone the others being a weak offshore precursor warm frontal wave and an onshore band of heavy snow snow bomb in which peak hourly snowfalls of 10 15 cm were observed none of these three prominent mesoscale features were well forecast by existing operational prediction models particularly with regard to preci

wavelet analysis and the governing dynamics of a large amplitude mesoscale gravity wave event along the east coast of the united states detailed diagnostic analyses are performed upon a mesoscale numerical simulation of a well observed gravity wave event that occurred on 4 january 1994 along the east coast of the united states the value of using wavelet analysis to investigate the evolving gravity wave structure and of using potential vorticity pv inversion to study the nature of the flow imbalance in the wave generation region is demonstrated the cross stream lagrangian rossby number the residual in the nonlinear balance equation and the unbalanced geopotential height field obtained from pv inversion are each evaluated for their usefulness in diagnosing the flow imbalance all of these fields showed clear evidence of strong imbalance associated with a middle to upper tropospheric jet streak and tropopause fold upstream of the large amplitude gravity wave several hours before the wave became apparent at the surface analysis indicates that a train of gravity waves was continuously generated by geostrophic adjustment in the exit region of the unbalanced upper level jet streak as it approached the inflection axis in the height field immediately downstream of the maximum imbalance associated with the tropopause fold a split front in the middle troposphere characterized by the advance of the dry conveyor belt above the warm front was overtaken by one of these propagating waves during this merger process a resonant interaction resulted which promoted the rapid amplification and scale contraction of both the incipient wave nonlinear wave development and the split front frontogenesis the gravity wave and front aloft became inseparable following this merger the situation became even more complex within a few hours as the vertical motion enhanced by this front wave interaction acted upon a saturated potentially unstable layer to produce elevated moist convection an analysis of the temporal changes in the vertical profile of wave energy flux suggests that moist convective downdraughts efficiently transported the wave energy from the midlevels downward beneath the warm front surface where the wave became ducted however pure ducting was not sufficient for maintaining and amplifying the waves rather wave cisk conditional instability of the second kind was crucial this complex sequence of nonlinear interactions produced a long lived large amplitude gravity wave that created hazardous winter weather and disrupted society over a broad and highly populated area although gravity waves with similar appearance to this large amplitude wave of depression occasionally have been seen in other strong cyclogenesis cases involving a jet streak ahead of the upper level trough axis it is unknown whether other such events share this same sequence of interactions

a case study of gravity waves convective storms interaction 9 may 1979 abstract an analysis is presented of a series of severe storms which occurred in the north central united states on 9 may 1979 and whose spatial distribution and movement correlate well with observed gravity waves two gravity wave trains of 2 1 3 mb amplitude 2 5 3 3 h period and 240 265 km horizontal wavelength were isolated through power spectra analysis and cross correlation techniques applied to national weather service barograph traces the wave trains propagated in the 200 direction which coincided with the jet axis with a phase velocity of 20 30 m s 1c and within a 300 km wide band the storms were identified on enhanced infrared goes satellite pictures with the help of radar summaries these convective systems initially developed in nebraska and propagated north northeast at 25 m s 1 revealing wave like characteristics with a separation of 300 400 km the convective systems were closely linked to the observed wave trains with cell intensity height and associated rainfall maximized at the wa

numerical simulation and analysis of a prefrontal squall line part ii propagation of the squall line as an internal gravity wave abstract a numerical study of the squall line that occurred on 17 18 june 1978 was described in part i of this paper the squall line was collocated with a surface front during its initial development at 0000 utc 18 june 1978 but then propagated faster than the front resulting in a separation of approximately 200 km by 0300 utc and 300 400 km by 0600 utc in this paper part ii the movement of the squall line in the model is shown to be due to the propagation of a deep tropospheric internal gravity wave in a wave cisk like conditional instability of the second kind process the thermal and dynamic perturbations associated with the hypothesized wave are shown to be consistent with internal gravity wave theory and the characteristics of the wave are compared to similar results from other wave cisk studies the current literature favors the mechanism of gust front convergence to explain squall line propagation although there are other modeling studies that show specific instances of squall line pro

testing the validity of nd isotopes as a provenance tool in southern tibet for constraining the initial india asia collision abstract sm nd isotopic systematics has been proven to be a powerful tool for investigating the source provenance and tectonic significance of sedimentary rocks here i report the nd isotopic compositions of mesozoic to paleogene siliciclastic sediments from southern tibet in an attempt to determine the temporal variations in their provenance the data reveal a shift in end 0 values of mesozoic strata in the tethyan himalaya varying from 16 3 to 12 7 in the jurassic to 8 1 to 3 7 in the cretaceous the less negative end 0 values of the cretaceous siliciclastic rocks indicate increasing input of a juvenile mantle component from the source region such a shift can be attributed to the early cretaceous mantle derived magmatism that was predominant in northern greater india this study indicates that there is a significant overlap in the end 0 values of rocks from the tethyan himalaya and lhasa block implying that nd isotopes may not be a good provenance proxy to constrain the initiation of the india asia collision such an inference is also evidenced by similar nd isotopic compositions between rocks from the bhainskati formation in the nepalese foreland basin sourced from the tethyan himalaya and the enba and zhaguo formations in southern tibet sourced from the lhasa block

interactions between upper and lower tropospheric gravity waves on squall line structure and maintenance abstract using a simplified thermodynamic sounding and variable vertical wind shear we investigate the role of gravity waves on the structure and propagation of a simulated two dimensional squall line based on an observed squall line environment the modeled troposphere has been divided into three distinct thermodynamic layers these consist of an absolutely stable atmospheric boundary layer abl an elevated well mixed layer and an upper tropospheric layer of intermediate stability we find the mixed layer to have a dual role it has a reduced stability and thus provides abundant buoyancy for the convective scale updrafts and it provides an ideal layer to trap meso scale 20 200 km wave energy generated in the stable layers the generated waves thus have a significant and lasting impact on the simulation we also find this thermodynamic structure to be conducive to both strong surface wind perturbations and long lived squall lines experiments that vary the vertical wind shear profile demonstrate

influence of differential diagenesis on primary depositional signals in limestone marl alternations an example from middle permian marine successions south china abstract the diagenetic alteration of rhythmic successions remains one of the main challenges in paleoclimatology and cyclostratigraphy to address this very important problem thin sections and geochemical data of the limestone marl alternations from middle permian carbonate successions in south china are examined to identify differential diagenetic effects in the petrography organic and inorganic compositions strontium concentrations and stable isotopic compositions of limestone beds and marl interlayers in the lengshuixi outcrop and the jy66 1 drill core the most conspicuous features are that the limestone beds exhibit dense cementation high strontium concentrations negative oxygen isotopic values and positive carbon isotopic values in contrast the marl interlayers contain talc and exhibit strongly deformed and oriented bioclasts low strontium concentrations positive oxygen isotopic values and negative carbon isotopic values although differential diagenesis has occurred some paleoclimate proxies e g computed gamma ray values still preserve their primary signals and thus are suitable for cyclostratigraphic research eccentricity rhythm and millennial scale rhythm are obviously recorded in middle permian limestone marl alternations in south china the variations in the oxygen and carbon isotopic values of limestone marl alternations from different basins represent responses to different processes of differential diagenesis this knowledge assumes that differential diagenesis occurs in diagenetically closed systems under the deep sea floor however this assumption may not be valid in diagenetically open systems where exotic fluids may add unexpected disturbances hence it is crucial to understand diagenetic systems by determining the variations in strontium concentrations which are as important as variations in carbon and oxygen isotopic values

observations of a mesoscale ducted gravity wave abstract this paper reports coordinated observations of a mesoscale gravity wave made during the fronts 84 field experiment conducted in southwestern france in the summer of 1984 the observations were unique in the sense that all relevant wave characteristics including its detailed vertical structure could be directly ascertained and shown to be mutually consistent the wave was observed to be ducted the static stability structure of the atmosphere was favorable for the existence of such a duct a critical level where the phase velocity of the wave matches the wave parallel background wind speed was present in or just above a layer of low static stability that capped a stabler layer at a still lower level the observed vertical structure was that of a standing wave with the top of the stable lower layer corresponding roughly to an antinode and one half the vertical wavelength below the critical level the wave was observed when there was extensive activity associated with two line of deep convection

random sampling of carbonate mounds an example from the upper ordovician of alabama abstract paleontological and lithological studies of a carbonate mound provide the necessary data from which characterizations for that mound or locality can be constructed these data based characterizations are a convenient mechanism for making qualitative comparisons with other mounds as has been done in some previous studies that discussed middle ordovician now considered upper ordovician mounds of the appalachian basin each of these studies had a different focus including the paleoecology of individual mound localities issues of ecological zonation and regional stratigraphical investigation quantitative comparisons are precluded among these studies because each mound was sampled using different procedures resulting in paleontological data sets of dissimilar density and depth two mound localities from carbonates of the upper ordovician chickamauga group stones river equivalent of jefferson and blount counties al were chosen for study to investigate the application of random sampling techniques to mound populations in outcrop one mound from each locality was completely censused to generate population compositional and structural data the location and higher level identification of each macrofossil on the surface of these mounds were recorded these bryozoan dominated data sets represent the best estimates available concerning the underlying population of mound constructors dwellers and occasional visitors rarefaction analysis was used to predict the number of randomly chosen fossils needed to detect the major taxonomic groups from each of these populations a computer program target was written to validate rarefaction predictions by conducting random sampling experiments using the census data sets the program prompts for input of three user defined variables that set the parameters of a sampling experiment and then throws randomly located sampling boxes at the mound data set recording the results statistical analysis of results from these sampling experiments validated the predictions of rarefaction analysis and led us to employ a conservative approach for sampling additional mounds at these localities

effects of convectively generated gravity waves and rotation on the organization of convection abstract the effects of latent heating gravity waves and planetary rotation on numerically simulated convective cloud systems are investigated first the nonlinear response of an initially motionless uniformly stratified dry atmosphere to steady heating that interacts with the environment through inertial gravity waves is examined planetary rotation confines the subsidence induced adiabatic warming to the neighborhood of the heated region on a time scale comparable to the lifetime of mesoscale convective systems in a moist atmosphere rotation induced localized descent stabilizes and dries the near environment and decreases the convective available potential energy the tropics is therefore a preferred region for convective clustering this hypothesis is tested in two sets of multiday convection resolving simulations on f planes representative of the tropics subtropics and midlatitudes convection is maintained by radiative cooling and surface fluxes of heat and moisture in a motionless mean sta

ammonite faunas and palaeobiogeography of the himalayan belt during the jurassic initiation of a late jurassic austral ammonite fauna abstract new data obtained in nepal and spiti india on stratigraphy and jurassic ammonite faunas form the basis for a new biogeographical interpretation of the peri gondwanan faunas faunas of the same ages from new guinea new zealand antarctica and south america are also considered from the upper bathonian up to the tithonian berriasian six main successive assemblages are distinguished in nepal and are compared to the faunas described in the above mentioned areas the latter often without accurate stratigraphic support the faunas of nepal show 1 low taxonomic and generic diversity of the ammonites and 2 dominance of one genus or a small number of genera in the same family and the subordinate place of the associated taxa with a few exceptions the classical biogeographical schemes do not recognize the existence of an austral ammonite fauna and or austral province bipolar distributions of several benthic or nekto benthic invertebrates as well as intertropical distribution of calpionellids express a latitudinal pattern of marine faunal distribution austral and tethyan ammonite faunas show less marked contrast than the tethyan and boreal realms and transitional or mixed faunas of subaustral type of relatively high diversity are developed in the indo malagasian trough or seaway and the andean region the austral fauna of low diversity was spread around east and south gondwanaland from the himalaya to patagonia the lack of a geographical trap such as the arctic basin almost completely enclosed by land explains why the austral faunas were never as distinct as the tethyan faunas from the boreal in addition to the role in the differentiation of the boreal faunas the land locked geography of the arctic basin magnified the role of the other environmental factors especially those linked with a high latitude situation seasonal fluctuations of illumination in high latitude resulted in environmental instability which promoted eurytopic taxa with high density and low diversity populations

paleogeographic and paleo oceanographic influences on carbon isotope signatures implications for global and regional correlation middle upper jurassic of saudi arabia abstract carbon isotope data 13c can provide an essential means for refining paleogeographic and paleo oceanographic reconstructions and interpreting stratigraphic architecture within complex carbonate strata although the primary controls on global 13c signatures of marine carbonates are well understood understanding their latitudinal and regional variability is poor to better constrain the nature and applications of 13c stratigraphy this study 1 presents a new high resolution 13c stratigraphic curve from middle to upper jurassic carbonates in the upper tuwaiq mountain hanifa and lower jubaila formations in central saudi arabia 2 explores their latitudinal and regional variability and 3 discusses their implications for stratigraphic correlations analysis of 13c data identified six mappable units with distinct 13c signatures units 1 6 between up dip and down dip sections and one unit unit 7 that occurs only in the down dip section of the study succession 13c data from the upper tuwaiq mountain formation and the lower hanifa formation units 1 2 which represent upper callovian to middle oxfordian strata and record two broad positive 13c excursions in the upper part of the hanifa formation units 3 6 early oxfordian late kimmeridgian 13c values decreased upward to unit 7 which showed a broad positive 13c excursion isotopic data suggest similar 13c trends between the southern margin of the tethys ocean arabian plate low latitude represented by the study succession and northern tethys oceans high latitude despite variations in paleoclimatic paleogeographic and paleoceanographic conditions variations in the 13c signal in this succession can be attributed to the burial of organic matter and marine circulation at the time of deposition our study uses 13c signatures to provide independent data for chronostratigraphic constraints which help in stratigraphic correlations within heterogeneous carbonate successions

relative sea level change and carbon isotopes data from the upper jurassic oxfordian of central and southern europe studies on cretaceous pelagic limestones have shown a close correspondence between putative sea level curves and the carbon isotope profile suggesting a possible relationship between the two phenomena such a relationship could relate to shelf sea area governing the global burial rate of organic carbon which in turn controls the 13c 12c ratio of dissolved inorganic carbon in the oceanic reservoir in order to see whether or not this relationship might be of more general applicability the major mid oxfordian jurassic transgression is documented to zonal level and appropriate carbon isotope data are presented although the applicability of ammonite zonation to the mid oxfordian is problematic on a regional scale a clear 13c excursion is present in the trunsversariurn zone which is coincident with regional overstep and or evidence of shoreline retreat and or evidence of bathymetric deepening in europe and elsewhere the use of the carbon isotope curve as a proxy for shelf sea area or relative sea level is worthy of further exploration

the synoptic setting and possible energy sources for mesoscale wave disturbances abstract thirteen case studies of mesoscale wave disturbances characterized by either a singular wave of depression or wave packets with periods of 1 4 h horizontal wavelengths of 50 500 km and surface pressure perturbation amplitudes of 0 2 7 0 mb are reviewed to isolate common synoptic features for these cases and to shed light on possible energy sources for the waves a strong thermal inversion in the lower troposphere north of a frontal boundary and a jet streak propagating toward a ridge axis in the upper troposphere are commonly observed in all the cases in general the area of wave activity is bounded by the jet axis to the west or northwest a surface front to the southeast an inflection axis between the trough and ridge axes to the southwest and the ridge axis to the northeast the conditions specified by lindzen and tung as being necessary to form a wave duct which include the existence of the lower tropospheric inversion seem to be met in many of these cases this suggests that a du

implications of ordovician 460 myr marine cement for constraining seawater temperature and atmospheric pco2 abstract the marine diagenetic history of the effna buildups virginia lower caradocian 460 myr is atypical of phanerozoic carbonates and reflects variable redox conditions in the semi restricted appalachian foreland basin fibrous marine cements are the focus of this study least altered fibrous calcite from the effna formation has a translucent appearance in transmitted light and a 2 3 mol mgco3 composition the latter is similar to values 2 5 mol from translucent fibrous calcite in other caradocian units holston tennessee and kullsberg sweden formations some fibrous calcite is overlain by hardgrounds that in places have an irregular micro topography with sharp overhangs indicative of syn depositional dissolution geochemical evidence supporting the marine dissolution includes 18o values from altered fibrous calcite that are more positive up to 3 9 pdb than coeval least altered fibrous calcite from holston buildups in tennessee up to 4 8 to 5 8 pdb syn depositional dissolution was likely associated with sulfide oxidation along an oxic anoxic interface and not due to upwelling of cold bottom water in the appalachian foredeep faunal and lithologic evidence suggests that oxic surface waters had a normal salinity and a water temperature conducive for metazoan growth 14 present atmospheric level during the early caradocian

jurassic ammonite faunas from nepal and their bearing on the palaeobiogeography of the himalayan belt abstract from the upper bathonian up to the tithonian berriasian six main faunas and twelve basic faunal assemblages within them are distinguished in nepal the successive faunas show 1 low taxonomic diversity and 2 the dominance of a small number of genera and the subordinate place of the associated taxa the assemblages include 1 strictly tethyan e g mediterranean or european tethyan species and or genera very few in number and occurring as isolated individuals or discontinuous faunal horizons 2 indo malagasian components some scattered others with a wide occurrence in the sw pacific some as far as antarctica and or patagonia 3 indigenous genera endemic for the himalayas and the sw pacific region faunas of the same age for the sula islands papua new guinea australia new zealand antarctica and south america are also considered in spite of common components the himalayan faunas contrast with the relatively higher diversity of the indo malagasian faunas low diversity and dominance of indigenous genera mean that the faunas extending from the himalayas to antarctica and patagonia represent an actual biogeographical unit the indo pacific faunas and realm indo pacific and tethyan faunas show a less marked contrast than the tethyan and boreal transitional or mixed faunas of subaustral type developed in the indo malagasian and andean regions this is explained by the absence of a geographical trap comparable to the land locked palaeogeography of the arctic basin the palaeogeography of the arctic amplified the role of the other environmental factors among these the high latitude seasonal effects are likely to have resulted in environmental instability controlling trophic resources and therefore the structure of the ecosystems for instance low diversity and high density of the high latitude ammonite faunas