mesozoic collision extrusion tectonics in eastern asia abstract the eastern part of the asian continent was intensively deformed in early cretaceous time deformation has been interpreted to be related to subduction tectonics along the eastern continental margin we propose an alternative tectonic framework of collision extrusion tectonics resulting from collision of the indochina block with the eurasian continent this event controlled the jurassic to cretaceous tectonic history in eastern asia and the evolution of the subduction zone along the eastern margin of the continent

paleoenvironmental evolution of the late pliocene early pleistocene fluvio deltaic sequence of the denizli basin sw turkey abstract the late pliocene early pleistocene tosunlar succession denizli basin southwestern turkey represents fluvial dominated delta environments at the margins of a brackish long lived lake two main facies associations are documented i a delta front facies association with a distal df1 and proximal df2 deposits and ii a delta plain facies association that contains distributary channel dp1 and interdistributary swamp dp2 deposits the stable isotopic analysis of the mollusc faunas exhibit a narrow range of values 4 68 18 o 13 c 18 o 13 c correlation r 0 16 may indicate hydrologically open lake and significant diagenetic alteration the mollusc faunas and their stable isotope ratios show a biogeographically isolated brackish lake system under semiarid climatic conditions under special environmental conditions the endemic faunal composition remained constant which is very unusual for a semi isolated long lived lake setting

on the initiation of subduction estimates of shear resistance associated with lithospheric thrusting and convergence represent lower bounds on the force necessary to promote trench formation three environments proposed as preferential sites of incipient subduction are investigated passive continental margins transform faults fracture zones and extinct ridges none of these are predicted to convert into subduction zones simply by the accumulation of local gravitational stresses subduction cannot initiate through the foundering of dense oceanic lithosphere immediately adjacent to passive continental margins the attempted subduction of buoyant material at a mature trench can result in large compressional forces in both subducting and overriding plates this is the only tectonic force sufficient to trigger the nucleation of a new subduction zone the ubiquitous distribution of transform faults and fracture zones combined with the common proximity of these features to mature subduction complexes suggests that they may represent the most likely sites of trench formation if they are even marginally weaker than normal oceanic lithosphere

ecospace utilization paleoenvironmental trends and the evolution of early nonmarine biotas paleozoic nonmarine trace fossils evidence paleoenvironmental trends that are linked directly to progressive ecospace utilization spatial and functional these trends resulted in a considerable increase of ichnodiversity throughout the paleozoic colonization of nonmarine settings began as early as the late ordovician as recorded by the presence of terrestrial burrow systems associated with ancient soils in the other cases the presence of nonmarine trace fossils in cambrian and ordovician sedimentary rocks was the result of temporary colonization by marginal marine organisms and does not reflect establishment of true fresh water faunas devonian trace fossils have been reported from alluvial and alluvial lacustrine transitional environments surface arthropod trackways are dominant in marginal lake settings representing the development of true nonmarine biotas the presence of vertical burrows in fluvial deposits records the establishment of deep suspension feeding infaunal organisms trace fossils from the carboniferous reflect migration farther into the lakes ichnofossils have been reported from shallow and deep lake deposits and from alluvial and alluvial lacustrine transitional environments lake assemblages are dominated by surface grazing trails the permian was characterized by the establishment of a deep deposit feeding infauna commonly recorded by the scovenia ichnofacies represented by backfilled meniscate burrows

87sr 86sr test of the degree of impact induced slope failure in the maastrichtian of the western north atlantic analyses of 8 7 sr 8 6 sr in foraminifera and sedimentological observations suggest that the chicxulub impact was not the trigger for slumps or a hiatus within the maastrichtian section recovered at ocean drilling programsites 1049 1050 and 1052 subtropical western north atlantic the slumps and hiatus occur within a sequence dominated by pelagic chalk the 8 7 sr 8 6 sr measurements show a general increase through the maastrichtian at each site but suggest chronostratigraphic gaps on the order of 10 6 yr across the slumps some of the slumps have burrowed upper surfaces and are composed of material that is older and coarser grained than the bounding chalks pelagic deposition punctuated by gravity flows easily explains the maastrichtian record on blake nose whereas an impact based explanation for slumping is difficult to reconcile with sedimentological and geochemical observations

40ar 39ar geochronology of the eocene green river formation wyoming the deposits of eocene lake gosiute that constitute the green river formation of wyoming contain numerous tuff beds that represent isochronous correlatable stratigraphic markers tuff beds selected for 40ar 39ar analysis occur within laminated mudstone are matrix supported and lack evidence of reworking these tuffs contain 2 15 euhedral phenocrysts of quartz plagioclase sanidine biotite and minor amphibole pyroxene and zircon encased in a matrix of altered glassy ash air abrasion and handpicking under refractive index oils were required to obtain clean unaltered phenocrysts of sanidine 40ar 39ar age determinations from single crystal and 1 mg multigrain aliquots of sanidine and biotite allowed the identification and exclusion of xenocrystic contamination laser fusion experiments on phenocrysts from the rife firehole c bed grey main sixth and analcite tuff beds from the tipton wilkins peak and laney members yielded weighted mean ages 2 analytical uncertainties of 51 25 0 31 ma 50 70 0 14 ma 50 56 0 26 ma 50 39 0 13 ma 49 96 0 08 ma 49 70 0 10 ma and 48 94 0 12 ma respectively ages for sanidine and biotite from the main tuff are indistinguishable when presumably xenocrystic contaminants are excluded from the age calculation moreover the 40ar 39ar ages are consistent with the stratigraphic order of the tuff beds and with provenance in the absaroka and challis volcanic fields our 40ar 39ar based age model indicates that sediment accumulated three times more rapidly 327 86 m yr during the evaporative wilkins peak phase than the freshwater to saline tipton 88 34 m yr and laney 104 18 m yr phases the much lower accumulation rates for the tipton and laney members are permissive of an annual origin for 1 mm thick laminae and precessional forcing of 1 3 m thick depositional cycles in these units however previously described cycles in the wilkins peak member have average durations that are significantly shorter than the 19 23 k y precessional modes the green river formation encompasses an 5 m y period between ca 53 5 and 48 5 ma spanning magnetic chrons 24n through 21r the green river formation was therefore deposited during the warmest period of the cenozoic corresponding to the early eocene climatic optimum as defined by the global marine o isotope record deposition of bedded evaporites trona of the wilkins peak member began at ca 51 ma or 2 m y after the onset of the highest inferred temperatures of the climatic optimum the bridgerian wasatchian faunal turnover occurred subsequently during wilkins peak time at ca 50 6 ma thus our 40ar 39ar ages strongly suggest that wilkins peak evaporite deposition and the turnover from wasatchian to bridgerian fauna were not directly caused by the initiation of maximum greenhouse conditions

assessing the extent of carbonate deposition in early rift settings select lacustrine and marine depositional settings show a spectrum of styles of carbonate deposition and illustrate the types of carbonates with an emphasis on microbialites and tufa to be expected in early rift settings early rift lake examples examined in this review article are all from east africa lakes turkana bogoria natron and magadi manyara and tanganyika other lake examples include four from the western united states great salt lake and high lake level lake bonneville mono lake and high lake level russell lake pyramid lake and high lake level lake lahontan and searles lake and two from australia lakes clifton and thetis marine basin examples are the hamelin pool part of shark bay from australia marginal marine and the red sea marine rift landsat images and digital elevation models for each example are used to delineate present and past lake basin margins based on published lake level elevations and for some examples the shorelines representing different lake levels can be compared to evaluate how changes in size shape and lake configuration might have impacted carbonate development the early rift lakes show a range of characteristics to be expected in lacustrine settings during the earliest stages of continental extension and rifting whereas the red sea shows well advanced rifting with marine incursion and reef skeletal sand development collectively the lacustrine examples show a wide range of sizes with several of them being large enough that they could produce carbonate deposits of potential economic interest three of the areas great salt lake and high lake level lake bonneville pyramid lake and high lake level lake lahontan and the red sea are exceedingly complex in that they illustrate a large degree of potential depositional facies heterogeneity because of their size irregular pattern and connectivity of subbasins within the overall basin outline

petrology and origin of primitive lavas from the troodos ophiolite cyprus parental magmas to the troodos ophiolite are characterised by low tio2 and al2o3 and high sio2 extremely fresh and chemically primitive high mgo rocks are found within the upper pillow lavas and along the arakapas fault belt of cyprus and contain forsteritic olivine enstatite and groundmass clinopyroxene set in glass or plagioclase with accessory magnesiochromite and sometimes hornblende they are quartz normative and may have originally contained up to 3 wt h2o geochemically there are three distinct groups of primitive lavas based on tio2 and zr contents but also reflected by cao na2o and ree abundances these groups cannot be related by crystal fractionation and are considered to have been generated by incremental melting of a variably depleted source region the parental magma to the least depleted group group i was that of the major portion of the troodos plutonic complex and is similar to those postulated for other low ti ophiolites chemically it has close affinities with komatiitic basalts the most depleted lavas group iii all have u shaped ree profiles and variable 143nd 144nd ratios interpreted in terms of metasomatism of the source region by an incompatible element enriched component which was probably derived from a subducted slab these lavas represent an intermediate step in the development of boninite series rocks

tectono magmatic evolution of the west philippine mariana region and the origin of boninites re examination of published data on the tectomagmatic evolution of the west philippine mariana region indicate that arc magmatism and back arc extensional pulses are not synchronous but are largely asynchronous arc volcanism ceases within a few million years of the development of a back arc basin and recommences oceanward on a new arc during the final stages in the development of the back arc basin following karig s model we believe that ascent beneath the arc axial chain of a line of diapirs of morb source mantle interferes with processes of arc magma generation and arc magmatism wanes partial melting of the diapirs produces voluminous morb type tholeiites which split the arc and form the crust of a widening back arc basin we show for both the west philippine mariana region and occurrences of boninite like lavas in ophiolites that boninites appear to be erupted after arc magmatism and immediately before eruption of morb type lavas passage of a diapir of hot morb source mantle through refractory sub arc peridotite which has been enriched in lile and h2o will result in limited partial melting of the hydrous peridotite and the restricted production of boninitic magmas these are more likely to erupt modified or only slightly modified by crystal fractionation through the thin forearc crust continued ascent of the morb source mantle diapir will result in it partially melting to yield morb tholeiites which erupt shortly after and in considerably more voluminous amounts than the boninites finally we suggest that forearcs regions are likely to be incorporated into foldbelts and that boninite or low ti lava bearing ophiolites may characterize such regions

strontium isotope record of paleohydrology and continental weathering eocene green river formation wyoming sr isotope ratios in carbonate rich lacustrine strata provide highly resolved and geo graphically specific records of past changes in weathering and regional drainage patterns the eocene green river formation is perhaps the best documented pre quaternary la custrine unit in the world therefore these strata are ideally suited for studying the be havior of sr the 87 sr 86 sr ratios measured for primary carbonate in lake expansion contraction cycles of the laney member are directly linked to changing lake facies four distinct cycles are preserved in a 6 4 m interval of the arco washakie basin no 1 core each represented by a vertical succession of transgressive stromatolite facies containing dolomicritic intraclasts laminated micrite facies deposited during lake highstands and lake marginal dolomicrite facies which represent subsequent lowstands initial 87 sr 86 sr ratios range from 0 711 99 to 0 713 31 the least radiogenic isotope compositions are as sociated with laminated micrite that records increased regional runoff from phanerozoic marine carbonate and tertiary volcanic rocks during lacustrine highstands the most radiogenic isotope compositions are associated with dolomicrite recording a higher pro portion of runoff from basin bounding precambrian uplifts and the exposed lake plain during lacustrine lowstand the observed 87 sr 86 sr variations may also be due in part to changes in differential weathering of the surrounding landscape where drier climates are associated with decreased differential weathering and therefore higher 87 sr 86 sr in runoff

plate tectonics and orogenic research after 25 years a tethyan perspective abstract orogeny the process by which the earth s prominent mountain ranges are constructed has been a central topic of interest in the earth sciences since at least the end of the 18th century the recognition that strains and displacements of very considerable magnitude occur along all of the three dimensions within an orogenic belt during its evolution has grown gradually during the last two centuries emphasis on primary vertical movements dominated the ideas on the nature of orogeny during the first half of the 19th century whereas compression and consequent uplift across mountain belts were believed to be the main cause for their origin during the subsequent one hundred years or so that were spent under the dominance of the fixist contraction theory mobilist tectonicians realised that continental drift in places also required motion along the trend of orogenic belts but this view did not gain general acceptance recognition of significant strike slip motion parallel or subparallel with mountain ranges evolved independently and mostly within the fixist camp by the 1960 s presence of important motions both along and across mountain belts had become common knowledge but no theoretical basis existed to account for them all

vertical and lateral distribution of lacustrine carbonate lithofacies at the parasequence scale in the miocene hot spring limestone idaho an analog addressing reservoir presence and quality lacustrine carbonate lithofacies in the hot spring limestone vary systematically at meter to decameter scales and record paleobathymetry limnologic conditions and paleogeographic influences this unit accumulated during the late miocene in a lake system in an extensional basin complex closely associated with lava flows and volcaniclastics sedimentology and sequence stratigraphy enable understanding and prediction of the occurrence distribution and character of lacustrine carbonates occurrence of lacustrine carbonates is a function of lake basin type in this case a volcanically mediated balanced filled lake basin that contains various lithofacies microbialite grainstone packstone wackestone and carbonate mudstone distribution of lithofacies is strongly controlled by depositional subenvironment and gradient through water depth bottom energy circulation and accommodation internal character of microbialites i e type size porosity vertical and horizontal permeability associated lithotypes diagenesis is influenced by stratal position at the parasequence scale and location along the depositional profile depositional reservoir quality characteristics such as microbialite porosity and thickness grainstone size and sorting and overall carbonate continuity and connectivity peak in the medial sublittoral zone conversely secondary diagenetic effects such as dissolution carbonate and quartz cement and possible authigenic clays are highest in the updip lake plain littoral zones and are less common lakeward thus the medial sublittoral zone has the optimum potential where primary depositional characteristics are best developed and negative secondary diagenetic effects are minimal these strata share many attributes with the cretaceous presalt systems of the south atlantic and can provide insights about controls on potential reservoir character distribution and connectivity for exploration and development

triple junction migration during paleozoic plate convergence the aracena metamorphic belt hercynian massif spain new data on the petrology and structure of the aracena metamorphic belt shows that this is a subduction related low pressure high temperature complex developed by plate convergence at the north margin of gondwana during the paleozoic the low pressure inverted metamorphic gradient in morb derived amphibolites resulted from heating from the continental hanging wall during subduction this implies that the previous heating of the continental rocks was related to subduction of an oceanic ridge and the creation of a slab window beneath the continental margin this slab window brought the asthenosphere in contact with the continental margin inducing a shallow thermal anomaly and partial melting of the lithospheric mantle resulting in boninite magmatism

collision of the izu arc with honshu and the effects of oblique subduction in the miura boso peninsulas abstract collision of the izu arc in central japan is discussed with a focus on its tectonic effects to the east of the arc in the miura boso peninsulas of honshu the tectonics are the combination of the following events philippine sea plate spreading in the late oligocene to early miocene opening of the sea of japan in the middle miocene obduction of ophiolitic rocks in the northeasternmost corner of the philippine sea plate and forearc sedimentation between the honshu and izu arcs oblique subduction has shifted the plate boundary from northeast to southwest from the present mineoka tectonic belt through the miura fold belt to the sagami trough since the miocene remarkable right lateral transpressional deformation occurred throughout this period of the oblique collision and subduction

applications of ichnology in lacustrine sequence stratigraphy potential and limitations abstract in comparison with their marine counterparts lacustrine ichnofaunas have not been extensively used in sequence stratigraphy application of trace fossils in continental sequence stratigraphy cannot be based simply on the extrapolation of marine sequence stratigraphy marine substrate controlled ichnofacies in particular the firmground glossifungites ichnofacies develop in stable and cohesive substrates reflecting erosive exhumation of the sediment in contrast in lacustrine sequences substrate controlled ichnofossils only rarely indicate erosional exhumation because they are commonly related to desiccation of water bodies the tripartite division of overfilled balanced fill and underfilled lakes provides a comprehensive framework to evaluate the potential and limitations of lacustrine ichnofaunas in sequence stratigraphy based on a number of case studies spanning the three lake basin types a model of trace fossil distribution in overfilled balanced fill and underfilled basins is proposed overfilled lake basins contain well developed softground trace fossils mermia and skolithos ichnofacies and the softground suite of the scoyenia ichnofacies that are useful to delineate parasequences and parasequence sets fluvial discharge into overfilled lakes usually generates density currents that oxygenate lake bottoms allowing the establishment of epifaunal and infaunal communities additionally these are freshwater lakes where no stress due to hypersalinity occurs leading to the development of a relatively diverse benthos land plant derived organic matter is the prime source of nutrients favoring the development of a deposit feeding benthic fauna in permanently subaqueous low energy zones firmground suites are rare because such large lakes usually do not experience desiccation abundant firmground trace fossil suites of the scoyenia ichnofacies occur in balanced fill lakes but softground assemblages are usually depauperate lowstand deposits contain abundant and widespread ichnofaunas commonly meniscate trace fossils and arthropod trackways of the scoyenia ichnofacies lake hydrology is closed during lowstands and salinity usually increases imposing a stress factor on the lake biota and therefore softground ichnofaunas are depauperate ichnofaunas from turbidite systems in balanced fill lakes are less abundant and diverse than those from overfilled lacustrine turbidites freshwater conditions are common during transgression but dysaerobic conditions may prevail imparting a stress factor on the benthic biota in hydrologically closed lakes the scoyenia ichnofacies is widespread but the mermia ichnofacies is commonly absent or impoverished the scoyenia ichnofacies is associated with lowstand desiccated substrates in underfilled lakes the density of arthropod trackways may be high forming tracked omission surfaces some of these omission surfaces may represent sequence boundaries expressed by co planar surfaces of lowstand and subsequent flooding rapid changes in depositional conditions reflecting desiccation during vertical aggradation can lead to the formation of composite ichnofabrics that reflect successive bioturbation events

comments on the paper very coarse grained beaches as a response to generalized sea level drops in a complex active tectonic setting pleistocene marine terraces at the cadiz coast sw spain abstract gonzalez acebron et al 2016 attributed the coastal deposits of torre bermeja la barrosa area cadiz sw spain to the early pleistocene 1 3 ma they also considered that an extremely high energy event such as a tsunami affected the basal deposits of the sequence in this paper both the chronological attribution and the stratigraphic sedimentary model are discussed previous information shows that sequence 1 is late pliocene lowermost early pleistocene based on biostratigraphic magnetostratigraphic and regional scale stratigraphic correlation in addition stratigraphic facies and sedimentary analyses indicate that sediments attributed to sequence 1 were formed due to south easternward longshore currents reworking wave and tidal dominated coarse grained delta sediments deposited further to the north

the first evidence for morb like lavas from the outer mariana forearc geochemistry petrography and tectonic implications abstract the mariana forearc the region between the active mariana volcanic arc and the trench axis is considered to be composed of rocks entirely of arc origin this conclusion was based upon the lack of an accretionary wedge and recovery of arc volcanics from sites throughout the forearc including the inner trench wall new chemical data from dredged samples demonstrate that exposures of altered basalts similar to mid ocean ridge basalt morb and of ocean island basalt oib exist in the mariana forearc several forearc sites including a 2000 m scarp bounding a large graben at 19 30 n two small scarps in the inner trench wall and a seamount were dredged morb like and oib lavas in addition to island arc tholeiite iat and boninite were recovered all samples exhibit low temperature seafloor alteration and some are metamorphosed to lower greenschist facies iat samples have low tio 2 2 of 1 2 and zr of 60 93 ppm oib samples typically have high tio 2 3 and zr 180 ppm several oib samples contain modal nepheline and all have high alkali contents the presence of oib and morb like lavas in the outer forearc may suggest either that entrapment of philippine sea or kula plate or that obduction of pacific plate has occurred in the evolution of the mariana forearc however the intimate association of morb like lavas with arc lavas in the fault scarp requires that either iat magma was injected into entrapped or obducted oceanic crust or that morb like magma was injected into an arc crust during forearc rifting or deformation

evolution of the freshwater ecosystem the fossil record abstract the freshwater ecosystem may be as old as most life although freshwater life is taxonomically impoverished in comparison with marine and terrestrial biotas and ultimately derived from them it cannot be assumed that freshwater communities have necessarily been less complex in the geologic past than they are today although it is clear they have undergone a number of major changes freshwaters contain not only their own ancient and peculiar groups some with ancestries as far back as the middle paleozoic but they have been a theater for adaptive radiation of more recent immigrants from the land or sea and a way station for still other groups that passed through both from sea to land and the reverse this review summarizes first fossil records in freshwaters for many of these organisms and examines the question of the changing complexity of the freshwater ecosystem through time by looking at the fossil record of continental aquatic habitats

the lyngen gabbro the lower crust of an ordovician incipient arc we present evidence for the origin of the lyngen gabbro of the ordovician lyngen magmatic complex in troms northern norway the two magmatic suites of the lyngen gabbro strike parallel nne ssw and have distinct magmatic signatures we define these signatures by using major and trace element analyses together with selected major and trace element mineral analyses and 143nd 144nd isotope whole rock analyses of gabbroic to tonalitic plutonic rocks from seven detailed cross sections from this large gabbro complex the western suite of the lyngen gabbro precipitated from magma that may have been derived from the same system as the associated volcanic rocks the gabbros have high an content an 90 of their plagioclases relative to co existing mafic minerals together with somewhat high nd t values 6 this implies that the parental magmas were hydrous tholeiites similar to those found in back arc basins today the eastern suite on the other hand consist of cumulates that were precipitated from melts resembling those of ultra depleted high ca boninitic magmas found in fore arcs extremely high an plagioclases an 95 co exist with evolved mafic minerals and oxides and the nd t values are lower 4 than in the western suite the eastern suite has no volcanic counterpart but dikes intersecting the suites have compositions that possibly represent its parental magma the oceanic rypdalen shear zone generally separates the two suites in the north but several non tectonic transitions from boninitic to tholeiitic signatures southwards advocate that the magmatism happened concurrently the magmatic proximity between the suites the hydrous magmatism and the absence of a silicic or calc alkaline mature arc section suggests that the lyngen gabbro formed in the iapetus ocean under conditions presently found in incipient arcs later emplaced as outer arc highs

the potential of paleozoic nonmarine trace fossils for paleoecological interpretations abstract many late paleozoic environments have been interpreted as marine because of the co occurrence of supposedly exclusively marine trace fossils beginning in the late ordovician however nonmarine trace fossil diversity increased throughout the paleozoic this diversification of nonmarine organisms and nonmarine trace fossils was especially prevalent in devonian and later times diversification of freshwater organisms is indicated by the large number of freshwater fish arthropods annelids and molluscs that had developed by the carboniferous in addition to diverse freshwater assemblages entirely terrestrial vertebrate and invertebrate ecosystems had developed by the devonian this rapid diversification of freshwater and terrestrial organisms is inherently linked to development and diversification of land plants and subsequent shedding of large quantities of organic detritus in nonmarine and marginal marine areas nearshore marine organisms and their larvae that are able to tolerate relatively short periods of lowered salinities will follow salt water wedges inland during times of reduced freshwater discharge similarly amphidromous marine organisms will migrate periodically inland into nonmarine environments undoubtedly both of these processes were active in the paleozoic however both processes are restricted to stream distributary channels interdistributary bays or estuaries therefore the presence of diverse trace fossil assemblages in association with floodplain deposits is interpreted to reflect true nonmarine adaptation and diversity conversely diverse trace fossil assemblages in association with stream distributary channel deposits interdistributary bay deposits or estuarine deposits may reflect migration of salt water wedges inland or migration of marine organisms into freshwater environments amphidromy or both

comparing species diversity in the modern and fossil record of lakes abstract lake faunal diversity has been the focus of many modern studies however there have been few studies comparing the lacustrine diversity in the modern and fossil record whether or not this comparison is possible is dependent on preservation by comparing the exceptional preservation of the konservat lagerstatten of the eocene green river formation with its various modern analogs in east africa unique factors controlling diversity within a lake system can be determined such factors would include lake surface area lake longevity productivity and lake type in order to effectively compare lake diversity in the modern and fossil record we first estimated the potential preservational bias of the fauna from modern lake tanganyika and determined that at maximum approximately 43 8 of species 59 3 of genera and 65 8 of families would be identifiable with this taphonomic filter in place we compared fish species diversity versus lake area no strong relationship was found faunal species div

carbonate deposition in an ephemeral siliciclastic alluvial system jurassic shuttle meadow formation newark supergroup hartford basin usa abstract nonmarine carbonate accumulation from a sedimentologic perspective has multiple possible origins clastic load springs groundwater discharge soil development biochemical seasonal changes cave speleothems and eolian influx many of these carbonates contain diagnostic textures from which origin is easy to ascertain however differentiating between clastic and spring groundwater carbonates especially in depositional systems dominated by siliciclastics is not always simple here criteria for recognition are developed subsurface hydrology and tectonic origin of the depositional basin source rocks surrounding the basin sedimentologic packaging and extent of the carbonates in question as well as their sedimentary structures and fossil content and stable isotopic analyses of the carbonates can all aid in determining carbonate origin and correctly assessing sedimentary and basin evolution the present study focuses on a nonmarine carbonate deposit found within the jurassic shuttle meadow formation of the hartford basin one of many rift basins which formed as a result of the opening of the north atlantic ocean during the late triassic to early jurassic the upper 50 m of the formation at plainville connecticut is interpreted as continental in origin and is composed of five facies red ripple cross laminated muddy siltstones to sandstones fr sr massive red siliciclastic mudstones fm buff fine to medium grained horizontally laminated sandstones sh red to white disrupted calcareous shales fl3 and rare micritic carbonates pm facies fr sr sh and fm are interpreted as an alluvial plain system in an ephemeral setting with bedload sheetflooding as the dominant depositional mechanism similar to the channel country drainage system of central australia in addition preservation of lateral accretion sandstone sheets accretionary benches indicate that the shuttle meadow alluvial system was rapidly accreting the anomalous existence of carbonate beds in facies fl3 and pm in the smf bedload dominated siliciclastic sequence is attributed mainly to the unique nature of the clastic sediment load in the basin no direct evidence for a spring groundwater input is apparent the shallow carbonate lake margin or a pond with vegetation and periodic exposure is envisioned as the depositional environment the intraclastic texture of the micrites with rare primary relict lamination indicates early diagenetic alteration from root penetration desiccation cracks and burrowing

fan deltas and braid deltas varieties of coarse grained deltas two types of coarse grained deltas are recognized fan deltas and braid deltas fan deltas are gravel rich deltas formed where an alluvial fan is deposited directly into a standing body of water from an adjacent highland they occupy a space between the highland usually a fault bounded margin and the standing body of water in contrast braid deltas here introduced are gravel rich deltas that form where a braided fluvial system progrades into a standing body of water braid deltas have no necessary relationship with alluvial fans as exemplified by fluvioglacial braid deltas braid deltas have previously been classified as fan deltas even though the geomorphic and sedimentologic settings of the two systems can be vastly different braid deltas are a common present day geomorphic feature and are abundant in the geological record fan deltas and braid deltas can be distinguished in the rock record by distinctive subaerial components of these depositional systems the shoreline and subaqueous components of both are similar fan delta sequences have a subaerial component that is an alluvial fan facies comprising interbedded sheetflood debris flow and braided channel deposits fan deltas produce small a few tens of square kilometres wedge shaped bodies of sediment commonly displaying high variability in paleocurrent patterns and abrupt changes in facies the deposits are generally very coarse grained with large out sized clasts very poorly sorted matrix rich polymictic heterolithic partially cemented by penecontemporaneous carbonate and have low porosity and permeability braid deltas in contrast have a subaerial component consisting entirely of braided river or braidplain facies their deposits display better sorting roundness and clast orientation than do fan delta sediments they lack a muddy matrix they display size grading and bar migration they commonly have a sheet geometry with high lateral continuity tens to hundreds of square kilometres and they exhibit moderate to high porosity and permeability valuable paleogeographic and tectonic information concerning the proximity of highlands and major fault zones may be misinterpreted or lost if these two coarse grained deltaic systems are not differentiated

estimating the age of formation of lakes an example from lake tanganyika east african rift system age estimates for ancient lakes are important for determining their histories and their rates of biotic and tectonic evolution in the absence of dated core material from the lake s sedimentary basement several techniques have been used to generate such age estimates the most common of these herein called the reflection seismic radiocarbon method rsrm combines estimates of short term sediment accumulation rates derived from radiocarbon dated cores and depth to basement estimates derived from reflection seismic data at or near the same locality to estimate an age to basement age estimates form the rsrm suggest that the structural basins of central lake tanganyika began to form between 9 and 12 ma estimates for the northern and southern basins are younger 7 to 8 ma and 2 to 4 ma respectively the diachroneity of estimates for different segments of the lake is equivocal and may be due to erosional loss of record in the northern and southern structural basins or to progressive opening of the rift the rsrm age estimates for lake tanganyika are considerably younger than most prior estimates and clarify the extensional history of the western branch of the east african rift system 31 refs 3 figs 1 tab

detailed record of the neogene sr isotopic evolution of seawater from dsdp site 590b a detailed study of strontium isotope variations in neogene marine carbonate sediments from deep sea drilling project site 590b using techniques that allow the 87sr 86sr ratio to be determined to better than 0 00001 gives a high resolution record of the sr isotopic evolution of seawater the data show that the rate of change of the marine 87sr 86sr ratio has varied significantly even on time scales as short as 1 m y periods of particularly rapid growth appear to follow major marine regressions and probably reflect an increase in the delivery of radiogenic sr from the continents coupled with a decreased submarine carbonate dissolution rate greater carbonate compensation depth periods of relatively slowly changing 87sr 86sr follow major marine transgressions on the basis of correlations with the marine oxygen isotope record and the times of major continental glacier growth it is inferred that the effects of sea level variations are modified by climatic factors that affect the intensity of continental weathering and runoff the effects of sea floor generation rate variations are not discernible for the neogene the maximum attainable stratigraphic resolution using sr isotopes is between 0 1 and 2 m y for this time period

variety of subduction and accretion processes in cretaceous to recent plate boundaries around southwest and central japan abstract the shimanto and miura boso terranes in southwest and central japan are analyzed for the understanding of variation of the subduction accretion process in convergent plate boundaries the shimanto is a cretaceous to recent honshu accretionary prism of 200 km width in the honshu arc side and is made up of melange flysch and olistostrome units these are repeated by many thrust faults and local broad and tight folds to make schuppen structures shallow marine and olistostromal bodies overlie part of the schuppen structures unconformably or are included within the structures normal subduction tectonics prevail for the formation of the accretionary prism but the effects of probable transform tectonics during late oligocene to early miocene are considerable the miura boso region is a terrane newly accreted from the izu arc to the honshu arc this terrane is made up of miocene and younger volcaniclastic sedimentary rocks dismembered ophiolitic materials and some of the rocks from the shimanto supergroup the miura boso terrane is characterized by transpressional tectonics associated with eduction during the sedimentation on the highly oblique subduction zone between the eurasia later north america and philippine sea plates several cases for the emplacement of the basaltic and other oceanic rocks to the landward side of the accretionary prism are discussed to account for the basic problem of the subduction accretion tectonics

mid carboniferous diversification of continental ecosystems inferred from trace fossil suites in the tynemouth creek formation of new brunswick canada we report skolithos scoyenia and mermia ichnofacies from sub humid tropical fluvial megafan deposits in the lower pennsylvanian tynemouth creek formation of new brunswick canada and discuss their evolutionary and palaeoecological implications especially regarding the colonization of continental freshwater terrestrial environments the skolithos ichnofacies comprises annelid arthropod spreite in the upper storey of a fluvial channel the scoyenia ichnofacies comprises tetrapod tracks arthropleurid trackways and shallow annelid arthropod burrows in active abandoned fluvial channels and rapidly aggrading levees splays in proximal interfluve areas the mermia ichnofacies comprises abundant xiphosuran trackways along with diverse traces of other arthropods annelids mollusks and fish in shallow freshwater lakes ponds and coastal bays in slowly aggrading distal interfluve areas transitional mermia scoyenia ichnofacies comprise tetrapod mollusk and annelid arthropod traces in coastal bay deposits on the distal edge of the megafan these trace fossil suites 1 provide the clearest documentation yet of the mid carboniferous diversification event when tropical continental environments became more densely populated 2 suggest that euryhaline visitors xiphosurans microconchids and other taxa from open marine settings played a key role in this episode of freshwater colonization and 3 provide empirical support for the deja vu effect the evolutionary concept that new or empty ecospace recurrent in spatially and temporally variable environments is colonized by simple ichnocoenoses

tectonic record of convergence changes in a collision area the boso and miura peninsulas central japan abstract late cenozoic formations in boso and miura have been affected by several tectonic events tectonic analysis enables us to reconstruct six different paleostress types 1 early extension affecting the oligocene early miocene mineoka group 2 and 3 relatively minor compressional and extensional events probably early pliocene in age 4 major nne ssw compression dominating prior to 2 or 3 ma ago and 5 and 6 more recent major nnw sse compression to the west and wnw ese extension to the east both types affecting the pleistocene and prevailing since 1 2 ma ago the counterclockwise change from nne ssw to nnw sse compression is not accurately dated but very likely occurred between 2 and 3 ma ago it is compared to similar evolutions in other areas of the izu collision zone we conclude that it corresponds to a major counterclockwise change in the direction of plate convergence from sse nnw to se nw the relationships between the directions of convergence and the distributions of plio quaternary compressional paleostresses in and around the collision zone are described through a simple analogy for the two stages of plio quaternary collision this counterclockwise change in stress fields and relative motions also described in the taiwan collision zone along the same philippine sea plate eurasia boundary is interpreted as a major event at the scale of the plate the possible significances of the other paleostress types identified in boso are discussed we conclude that tectonic analysis in and along collision boundaries provides a key for understanding kinematic evolution

wave influence in the construction shaping and destruction of river deltas a review abstract waves are an important agent in the construction shaping and destruction of river deltas notwithstanding the commonality of waves in oceans and seas wave influence on deltas varies considerably depending on the coastal morphology and nearshore bathymetry although there have been advances in understanding the way waves approaching a delta shape its shoreline much still remains to be known of the interactions between waves and river deltas deltas are built essentially from sediments supplied by rivers sand sized and coarser sediments may also be derived from nearby abandoned delta lobes or from older relict nearshore deposits transported by wave reworking and longshore currents alternatively delta erosion by waves can also release sediment that is redistributed alongshore or that accumulates offshore the extent to which bedload is supplied to and sequestered in or lost by deltas through waves and longshore transport strongly depends on interactions between waves and fluvial discharge at the river mouth these interactions and the mutual adjustments they engender are not only important in the overall balance between delta retreat progradation or aggradation but also in processes such as avulsion and channel switching as well as in the eventual survival of a delta in the face of sea level rise where waves are important fluvial liquid discharge is high and sediment supply is rich in bedload two important aspects are the blocking of waves and longshore currents by strong river discharge and the formation of bars at the river mouth field studies of the complex interactive processes prevailing where river flows encounter waves are however non existent and numerical modelling though promising hampered by scale constraints and the difficulty of replicating them and generating mouth bars in the presence of longshore currents this interaction influences the seaward extent of the delta mouth protuberance and its stability this protuberance then forming the regional shoreline template to which waves and longshore currents adjust longshore currents can redistribute wave reworked mouth bar deposits emplaced during strong river flow transport may be either divergent from the mouth or may be regionally unidirectional but wherein the symmetry of some deltas probably rare may be maintained by a strong river blocking effect on transport from the updrift flank the mouth protuberance may be such as to foster transport reversal counter drift at the delta margins that contributes to sediment sequestering within the delta these interactions largely contribute in shaping delta shorelines and together with the abundance of sediment supply and grain size determine the resultant wave formed shoreline barrier types which include spits more or less closely spaced beach ridges and barrier islands and cheniers in situations of punctuated progradation or retreat where several distributary mouths occur pronounced longshore variability in wave processes and wave induced sediment transport may ensue resulting in multiple drift cells that assure the retention of sand and coarse grained sediments within the delta waves can also be an important agent in the reworking and retreat of mud rich deltas that generally conform in morphology to the river dominated such as the mississippi or tide dominated such as the ganges brahmaputra or chao phraya types resulting in the episodic formation of sandy cheniers and beach ridges although sea level rise is likely to lead to enhanced wave reworking of deltas the possible prevalence of aggradation in lieu of progradation channel switching and avulsion and washover processes may contribute to the disorganization of waves and longshore transport fostering deltaic sequestering of sand and coarser sized sediment and delta survival the weakening of river discharges resulting from human activities will invariably lead however to enhanced wave reworking of deltas and to deltaic sediment redistribution by longshore currents the massive swing towards significant reductions in fluvial sediment supply today may signify the ultimate demise of many deltas in the coming decades through a process of delta shoreline straightening by waves in addition to accelerated sinking these various foregoing aspects of the relationship between waves and river deltas are reviewed here across a range of timescales and new interaction concepts proposed using numerous examples of deltas in the world and on the basis of case studies conceptual studies and numerical modelling studies in the literature spanning more than forty years

lake type controls on petroleum source rock potential in nonmarine basins based on numerous empirical observations of lacustrine basin strata we propose a three fold classification of lacustrine facies associations that accounts for the most important features of lacustrine petroleum source rocks and provides a predictive framework for exploration in nonmarine basins where lacustrine facies are incompletely delineated 1 the fluvial lacustrine facies association is characterized by freshwater lacustrine mudstones interbedded with fluvial deltaic deposits commonly including coal shoreline progradation dominates basin fill resulting in the stacking of indistinctly expressed cycles up to 10 m thick in map view the deposits may be regionally widespread but laterally discontinuous and contain strong facies contrasts transported terrestrial organic matter contributes to mixed type i iii kerogens that generate waxy oil type i kerogen is hydrogen rich and oil prone type iii kerogen is hydrogen poor and mainly gas prone the luman tongue of the green river formation wyoming and the honyanchi formation junggar basin china provide examples of this facies association which is also present in the songliao basin of northeastern china the central sumatra basin and the cretaceous doba doseo basins in west central africa 2 the fluctuating profundal facies association represents a combination of progradational and aggradational basin fill and includes some of the world s richest source rocks deposits are regionally extensive in map view having relatively homogenous source facies containing oil prone type i kerogen examples include the laney member of the green river formation wyoming the lucaogou formation junggar basin china the bucomazi formation offshore west africa and the lagoa feia formation campos basin brazil 3 the evaporative facies association represents dominantly aggradational fill related to desiccation cycles in saline to hypersaline lakes and may include evaporite and eolianite deposits sublittoral organic rich mudstone facies are relatively thin but may be begin page 1034 quite rich and widespread the highest organic enrichment coincides with the deepest lake stages low input of land plant organic matter results in minimal lateral contrasts in organic content in some cases a distinctive type i s sulfur rich kerogen may generate oil at thermal maturities as low as 0 45 vitrinite reflectance equivalent examples include the wilkins peak member of the green river formation wyoming the jingjingzigou formation junggar basin china the jianghan and qaidam basins china and the blanca lila formation argentina

very coarse grained beaches as a response to generalized sea level drops in a complex active tectonic setting pleistocene marine terraces at the cadiz coast sw spain abstract the studied pleistocene deposits at the cadiz coast are located on the current intertidal zone or at cliffs parallel to the actual coast 6 50 m a s l from the localities of el puerto de santa maria to chiclana five sequences of very coarse grained beaches have been recognized and dated they unconformably overlie pliocene units and are formed by clast supported conglomerate and coarse grained sandstone chronological ages 87 sr 86 sr and ams 14 c analysis and stratigraphic correlation stand that the oldest marine terrace is the one placed topographically higher and towards the se of cadiz city dated as early pleistocene 1 3 ma after it the sea retreatment produces subaerial exposure of sequence 1 and the development of several calcrete profiles and a paleokarst subsequent sea level rises allow the sedimentation of sequences 2 3 and 4 during early middle pleistocene 1 to 0 8 ma in areas close to cadiz city with subaerial exposure recorded at the top of sequences 3 and 4 during the very upper pleistocene sedimentation of sequence 5 occurs towards the se of cadiz city based on the spatial position of sequence 5 we can conclude that this area constituted a downthrown block during the latest pleistocene in relation to neotectonic processes and diapirism sandstone framework hybrid arenites reveals that main source areas for these marine terraces include units from the betic orogene betic external zones triassic and jurassic rocks and the gibraltar arc the guadalquivir basin passive margin iberian massif the guadalquivir foreland basin marine miocene and pliocene record and local inputs of pleistocene units the siliciclastic supplies from sources were mainly constant during the sedimentation of all set of sequences suggesting maturation processes as reworking and recycling of homogenized sediments during transport early diagenetic processes have been identified as carbonate cementation neomorphism and dissolution outlining the deduced sea level fluctuations during deposition of pleistocene sequences the marine terraces arrangement and its comparison with regionally adjacent areas allows to deduce that the southern and central portuguese coast iberian massif and of the southern and southeastern spanish coast betic orogene were predominantly tectonically raising during pleistocene however the cadiz gulf coast formerly guadalquivir foreland basin was mainly sinking during the same time interval

hardly used habitats dearth and distribution of burrowing in paleozoic and mesozoic stream and lake deposits limited use of substrate ecospace by a meager infauna in streams and lakes is indicated by analysis of more than 10 000 observations of bioturbation in permian through jurassic freshwater deposits in contrast marine substrates have been inhabited and bioturbated since the cambrian colonization of freshwater substrates differed fundamentally from that of marine substrates bioturbation enhanced flux of dissolved materials across the sediment water interface was not operating until after the paleozoic in freshwater ecosystems

geochemical evidence for formation of the bay of islands ophiolite above a subduction zone the bay of islands boi complex in western newfoundland is one of the world s best known ophiolites and has generally been interpreted as a fragment of ocean floor emplaced on the eastern margin of north america1 2 the similarities of the boi to litho sphere formed at mid ocean ridges has led many investigators to use the boi as an onland laboratory in which to study the geochemical tectonic and geophysical properties of the oceanic lithosphere1 9 there have been nonetheless a few suggestions that the boi ophiolite formed above a subduction zone10 12 as have most other ophiolites13 15 here i report the existence of a substantial tantalum depletion in boi magmas jenner et al 16 demonstrate that boi magmas have a niobium depletion as well these depletions are characteristic of magmas erupted above subduction zones but not at mid ocean ridges indicating that the boi is not after all a good analogue for lithosphere formed at mid ocean ridges

upper cretaceous muti formation transition of a mesozoic nate platform to a foreland basin in the oman mountains the upper cretaceous turonian campanian muti formation sayja member documents the transition from a passive continental margin to a foreland basin related to overthrusting of continental margin and ophiolitic nappes derived from the tethys ocean upper cretaceous northeastward subduction culminated in collision of a trench with the arabian margin as the trench docked with the margin the lithosphere was flexed forming a peripheral bulge that migrated cratonward with time the platform edge was initially uplifted turonian and deeply eroded creating the wasia aruma break after passage of the peripheral bulge subsidence began with accumulation first of ferruginous crusts on hardgrounds lime muds were then deposited on a deepening unstable sea floor along with phosphatic nodules and crusts turonian coniacian passage of the overthrust load over the arabian continental margin edge downflexed the lithosphere santonian campanian resulting in drastic foundering of the old shelf edge to form a foredeep upper platform horizons collapsed as slump sheets and debris flows limestone blocks and lithoclastic debris flows were shed by mass wasting of the already deeply eroded old platform edge mud and silt were derived from the uplifted arabian continent and deposited by mainly gravitational processes in a foredeep below the c c d subsidence of the arabian platform edge allowed the semail ophiolite nappe finally to override the muti basin late campanian with little internal deformation submarine emplacement is suggested by the absence of ophiolitic detritus in the muti formation the stratigraphic evolution of the muti formation is in good general agreement with a model of the transition of an old thermally mature passive continental margin to a foreland basin where the emplaced load is submerged

tectonics and geology of spreading ridge subduction at the chile triple junction a synthesis of results from leg 141 of the ocean drilling program an active oceanic spreading ridge is being subducted beneath the south american continent at the chile triple junction this process has played a major part in the evolution of most of the continental margins that border the pacific ocean basin a combination of high resolution swath bathymetric maps seismic reflection profiles and drillhole and core data from five sites drilled during ocean drilling program odp leg 141 provide important data that define the tectonic structural and stratigraphic effects of this modern example of spreading ridge subduction a change from subduction accretion to subduction erosion occurs along strike of the south american forearc this change is prominently expressed by normal faulting forearc subsidence oversteepening of topographic slopes and intensive sedimentary mass wasting overprinted on older signatures of sediment accretion overthrusting and uplift processes in the forearc data from drill sites north of the triple junction sites 859 861 show that after an important phase of forearc building in the early to late pliocene subduction accretion had ceased in the late pliocene since that time sediment on the downgoing oceanic nazca plate has been subducted site 863 was drilled into the forearc in the immediate vicinity of the triple junction above the subducted spreading ridge axis here thick and intensely folded and faulted trench slope sediments of pleistocene age are currently involved in the frontal deformation of the forearc early faults with thrust and reverse kinematics are overprinted by later normal faults the chile triple junction is also the site of apparent ophiolite emplacement into the south american forearc drilling at site 862 on the taitao ridge revealed an offshore volcanic sequence of plio pleistocene age associated with the taitao fracture zone adjacent to exposures of the pliocene aged taitao ophiolite onshore despite the large scale loss of material from the forearc at the triple junction ophiolite emplacement produces a large topographic promontory in the forearc immediately after ridge subduction and represents the first stage of forearc rebuilding

stratigraphic classification of ancient lakes balancing tectonic and climatic controls lakes and lake deposits present two fundamental paradoxes 1 modern lakes are vastly complicated but the rock records of lakes are relatively simple extensive observations reveal three distinct facies associations of common and widespread occurrence these are referred to here as fluvial lacustrine fluctuating profundal and evaporative facies associations 2 most explanations of modern and ancient lakes attribute their nature to climate but neither modern lake parameters lake size depth and salinity nor the character of ancient lake strata thickness extent lithology correlate with measured or inferred climatic humidity we propose that it is the relative balance of rates of potential accommodation mostly tectonic with sediment water fill mostly a function of climate that controls lake occurrence distribution and character lake basins may be termed overfilled balanced fill or underfilled depending on the balance between these rates we conclude that climate and tectonics exert coequal influence on lake deposits at both mesoscales 1 m to hundreds of meters and macroscales hundreds to thousands of meters

provenance and tectonic setting of the neoproterozoic yanbian group western yangtze block sw china abstract tectonic evolution of the yangtze block of south china during neoproterozoic time has been a major focus of debate and is important in the reconstruction of the rodinian supercontinent the yanbian group in the western margin of the yangtze block is a well preserved neoproterozoic volcanic sedimentary sequence and provides a rare opportunity to examine the provenance and tectonic setting it consists of a lower part composed of 1500 m thick basaltic lavas and an upper part of 3500 m thick flysch deposits the flysch sequence contains typical deep marine turbidites consisting mainly of fine grained volcaniclastic sandstones and mudstones indicating a submarine fan depositional system detrital zircon dating yields ages ranging from ca 865 ma to 1000 ma with two peaks at ca 900 ma and 920 ma respectively the yanbian group is intruded by the 860 ma guandaoshan dioritic pluton constraining its depositional age at ca 870 ma the sandstones contain abundant feldspar and lithic fragments with minor amounts of quartz and have an average composition of q16f35l49 suggesting a proximal source and an undissected to transitional arc setting the lithic fragments in the sandstones point to andesitic and felsic volcanic rock sources the sandstones and mudstones have intermediate sio2 al2o3 typically 3 6 high fe2o3 mgo contents 5 12 wt and moderate to high k2o na2o ratios generally 0 1 1 and 1 10 for sandstones and mudstones respectively in comparison with average upper continental crust they show strong negative nb ta anomalies slight depletion of zr hf la and th but moderate enrichment of v cr ni and sc these rocks show lree enrichment la ybn 5 3 7 4 with flat hree and pronounced negative eu anomalies eu eu 0 6 0 74 in chondrite normalized ree patterns similar to post archean shales geochemical data for these rocks suggest an arc setting and intermediate felsic volcanic source consistent with a back arc basin scenario for the basaltic lavas in the lower yanbian group together with regional geological evidence the turbidites of the yanbian group strongly support a model in which the western margin of the yangtze block was a major magmatic arc active probably from 920 ma to 740 ma a period of more than 180 million years

marine continental magnetobiostratigraphic correlation of the dolomys subzone middle of late ruscinian implications for the late ruscinian age abstract lacustrine deposits which form part of a continental unit cropping out in many localities of the jerez basin sw spain have for the first time been dated these deposits are attributed to the lower part of the dolomys subzone the upper part of the mn 15 neogene mammal unit late ruscinian this continental unit unconformably overlies a marine unit since the isochrony of the unconformity is not precisely established the biostratigraphic results and palaeomagnetic data give two possibilities in correlating the dolomys subzone with the marine magnetobiostratigraphy 1 it can be correlated with the c2ar reversed polarity chron or 2 with the c2an 2r reversed polarity subchron or c2an 1r therefore the lower boundary of the mn 15 would be at the base of the c2ar or at the very top of the early pliocene respectively in any case considering the magnetobiostratigraphy correlation carried out in other pliocene continental basins of the southeastern spain the top of mn 15 seems to be within the late pliocene

paleozoic lake faunas establishing aquatic life on land abstract lakes are important archives for continental records of paleoenvironmental as well as paleoclimatic change they also record a unique macroevolutionary pattern that occurred when faunas invaded the continental realm in order to document that pattern we compiled a database of over one hundred and six lake basins from the neoproterozoic to permian looking at this critical time in lacustrine evolution several patterns emerge for the neoproterozoic through silurian time there is a paucity of documented lake deposits and lake faunal records however the records that are available indicate that lakes were oligotrophic and their nutrient cycling regimes primitive it is not until the establishment of land plants in the silurian that lakes began to respond with higher diversities and more complex physical and chemical conditions during the devonian carboniferous periods diversity was on the rise as trophic structure became more complex most lakes of the devonian and carboniferous formed along continental margins or in tectonic basins with occasional connection to the marine realm the faunas from these types of lakes were commonly comprised of mixed marine and freshwater elements and were far more diverse than other more inland lakes this estuary effect created a gateway or filter through which faunas invaded the continental realm the early history of lake faunas is one of opportunity and amelioration the feedback loops created by the establishment of vascular plants altered the nutrient cycle on land and in lakes all trophic levels were established early but became increasingly complex throughout the paleozoic as roles changed and faunal elements became established groups invading the continents via the estuary effect did so numerous times before establishing themselves permanently this was linked with the episodic re establishment in marine freshwater connections along these continental margins

reply to comment on gonzalez acebron l mas r arribas j gutierrez mas j m perez garrido c very coarse grained beaches as a response to generalized sea level drops in a complex active tectonic setting pleistocene marine terraces at the cadiz coast sw spain abstract a series of pleistocene marine terraces comprised of conglomerate and coarse grained sandstone aligned nnw sse along the cadiz coast have been recognized and interpreted as formed in very coarse grained beaches in our work gonzalez acebron et al 2016 they unconformable overlie either pliocene units or older pleistocene deposits in these terraces five sedimentary sequences were described and dated by sr isotopic analysis of well preserved oysters this dating provided an early pleistocene age 1 3 ma for the oldest marine terrace which corresponds to sequence 1 aguirre 2018 does not agree with the dating of the first sequence instead in aguirre 1995 and aguirre et al 1995 these deposits are considered as laterally equivalent to lacustrine deposits located more than 50 km far away mesas de asta jerez basin and their age late pliocene lowermost early pleistocene extrapolated to sequence 1 this is an impossible correlation given the fact that the studied deposits sequences 1 to 5 are marine terraces without lateral continuity inland finally aguirre s 2018 sedimentological interpretation of the deposits of sequence 1 as part of a wave and tide dominated delta breaks down when one considers that this delta would be a mixture of non coeval deposits the continental deposits of mesas de asta together with sequence 1 deposits