puzzling distribution of the fossil and living genus hiatella bivalvia abstract the bivalve hiatella has been present for the last 150 ma and is consistently linked to cool temperate and polar regions its origin can be traced back to at least the jurassic with earliest known records being temperate forms that occurred on the northern side of the tethys the subsequent fossil record suggests two possible alternative migration routes the more plausible one is that hiatella invaded the southern seas from the atlantic by the eocene from there it migrated northward to eastern asia with first valid north pacific records in the far east region of russia japan and alaska from the oligocene to miocene a second explanation is that during the mesozoic hiatella penetrated into the circumpolar zone and reached the boreal pacific province before the arctic became isolated in the late cretaceous 60 ma due to the formation of beringia as its subsequent oldest records in the north pacific are from the oligocene to miocene hiatella probably evolved during the paleogene in the north pacific and migrated to southern latitudes antarctica southern south america new zealand and australia as connecting seaways formed in the trans pacific route in any case the north pacific lineage has been separated from the circum atlantic lineage of hiatella since at least the opening of the bering strait 3 0 3 5 ma during the late pliocene when it probably participated in the trans arctic migration during the late pliocene pleistocene hiatella evolved adopting its present widespread cold temperate distribution in both hemispheres although best developed in the polar regions of the northern hemisphere hiatella probably achieved extinction resistance by virtue of broad geographic distributions associated with dispersal facilities and great plasticity in its habitat and mode of life

marine biodiversity through the late cenomanian early turonian palaeoceanographic controls and sequence stratigraphic biases changes in the marine macro and microfauna sedimentary geochemistry and surface water palaeoproductivity through the last 500 000 years of the cenomanian and first 300 000 years of the turonian are documented these are based on the succession at eastbourne the thickest and most complete section through the late cenomanian and early turonian in the anglo paris basin two levels of rapid faunal and geochemical change are identified one coincident with a significant increase in siliciclastic input at the base of the plenus marls member and the other with a marked drop in surface water productivity near the top of the same unit faunal change is demonstrated to be largely a pattern of immigration emigration rather than true extinction and our sequence stratigraphical analysis shows that it was coincident with major sea level changes no evidence is found to support the hypothesis that reduced bottom water oxygenation developed and was responsible for extinctions amongst the benthos in mid shelf environments the onset of pure chalk facies is interpreted to mark the breakdown of shelf break fronts and the spread of oligotrophic oceanic waters over much of the continental shelf initiated by rising sea level the cenomanian turonian event far from recording a mass extinction of shelf fauna is most probably an artifact caused by a significant switch in the nature of the surviving sedimentary record as a result of a major but perfectly ordinary oceanographic change

strontium isotope evidence for the age of eocene fossil whales of kutch western india the indian subcontinent is widely considered to be the birthplace of whales cetacea and the middle eocene harudi formation of kutch has long been known to be a major source of early whales the kutch cetaceans are of critical importance in understanding the evolutionary transition of whales from land to sea strontium isotope analysis of marine biogenic carbonates from the harudi formation was conducted to obtain a numerical age of the whale bearing strata although the measured 87 sr 86 sr ratios 0 707742 to 0 707764 correspond to two distinct age clusters of 46 47 5 ma or 41 42 5 ma we prefer the latter late lutetian age cluster

palaeobiogeography and the ordovician and mesozoic cenozoic biotic radiations curves of taxonomic diversity through geological time consistently show major evolutionary radiations during the ordovician period and from the mid mesozoic to the present day both intervals were characterized by marked biotic provincialism reflecting episodes of major continental break up and global tectonism and their later histories featured steep global climatic gradients the ordovician radiation can be recognized at a wide spectrum of taxonomic levels from species to class and the biogeographical patterns associated with the radiation of individual clades reflect a complex combination of plate distribution tectonic activity sedimentary environment sea level rise and ultimately glaciation the true scale of the mid mesozoic cenozoic biotic radiation is currently a topic of intense debate but there is no doubt that it affected plants and animals in both the marine and terrestrial realms the role of land bridges and ocean gateways in controlling the for mation of biodiversity patterns has been a persistent theme in mesozoic cenozoic bio geography and a complex set of neogene tectonic events probably aided the development of both latitudinal and longitudinal provinces during the cenozoic the present volume highlights some of the successes across a spectrum of approaches to unravelling the ordovician and mesozoic cenozoic radiations within the context of palaeobiogeography

the permo triassic extinction the end permian mass extinction brought the palaeozoic great experiment in marine life to a close during an interval of intense climatic tectonic and geochemical change improved knowledge of latest permian faunas coupled with recent advances in isotopic studies and biostratigraphy have greatly enhanced our understanding of the events of 250 million years ago and have begun to provide answers to many questions about the causes of extinction

strontium isotope stratigraphy potential resolution and event correlation abstract a new generation 87sr 86sr isotope curve for the phanerozoic seawater based on a compilation of 3635 stratigraphically well defined and well preserved skeletal components results in a substantially narrower band with some discrepancies if compared to the curve of burke et al 1982 which is based mostly on whole rock samples the results obtained from low mg calcite shells foraminifers belemnites brachiopods and oysters are mostly superior to those from phosphatic skeletal components such as conodonts even if the latter are exceptionally well preserved cai 1 5 at this stage the phanerozoic data set based on fossils is patchy for the cambrian upper ordovician lower devonian and upper carboniferous triassic intervals the major practical constraint that precludes delineation of an unequivocal sr isotope curve for the phanerozoic seawater is the uncertainty in the assignment of absolute ages to the samples as a result the curve is in reality a band this is a reflection of the limitations of biostratigraphy and geochronology that are inherited by any derivative correlation and dating technique including isotope stratigraphy it is therefore unlikely that in the near future the sr isotope stratigraphy will surpass the resolution capability of biostratigraphy as a global correlation tool on the other hand if complemented by lithostratigraphy it is potentially a valuable tool for correlation of sequences on intrabasinal and regional scales taking into account the above limitations careful consideration must be given to assignment of higher order isotope peaks to specific events within a biozone and to the use of such events as a global correlation tool

lignite deposits of the kutch basin western india carbon isotopic and palynological signatures of the early eocene hyperthermal event etm2 abstract this study presents new results of combined palynological and stable carbon isotope 13 c investigations carried out in the well known lignite sequence at panandhro district kutch in the gujarat state of western india dinoflagellate cysts and associated spore pollen assemblage assign an early eocene ypresian age to the lignitic succession at panandhro furthermore a pronounced negative carbon isotope excursion cie of about 2 7 correlated to the second eocene thermal maximum 53 7 ma a globally recognized hyperthermal event was discovered in the middle part of the succession consistent with the palynological constraints this is the first record of an eocene hyperthermal event etm2 from the kutch basin our data has regional implications for the age of the lignitic sequences across western india as it demonstrates that there is no significant age difference between the lignite deposits of the kutch and cambay basins our results also support a lutetian age for the previously described vertebrate fossils including whales from the panandhro mine section

trilobite diversity patterns in the middle cambrian of southwestern europe a comparative study abstract this paper describes the pattern of trilobite diversity throughout the middle cambrian in two fossiliferous basins of the western gondwana margin the iberian chains northeastern spain and the montagne noire southern france the documented fluctuations of species diversity allow us to recognize 1 a substantial extinction event recorded in latest early cambrian times named valdemiedes event which separates the culmination of a widespread decline of trilobites and the stepwise immigration of cosmopolitan invaders 2 a major trilobite radiation occurring in the earliest leonian and culminating across the caesaraugustian languedocian transition in which a peak in diversity of trilobites and carpoids was close to a major flooding surface 3 a major reduction of trilobite taxa across the early middle languedocian transition related to a well documented regressional trend and 4 a second immigration of trilobite fauna in the late languedocian which coincided with trangressional pulses and the establishment of suitable shaly substrates in addition we summarize the known trilobite occurrences from the middle cambrian of southwestern europe maps of the distribution of some relevant taxa genera and species over the western gondwana margin are documented

radiogenic isotopes systematics and applications to earth surface processes and chemical stratigraphy radiogenic isotopes have wide application to chemical stratigraphy geochronology provenance studies and studies of temporal changes in earth surface processes this paper briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number of elements of interest in the environment and then uses this information to explore the range of applications to chemical stratigraphy and other fundamental subjects of sedimentary geology many of these applications center on the reconstruction of secular variations in paleoseawater isotope signals these seawater isotope curves can be used for stratigraphic correlation and to assess changes through earth history in processes such as tectonic uplift climate change biogeochemical cycling ocean circulation crustal growth and surface water evolution understanding the modern biogeochemical cycle of the element isotope system of interest is essential for gaining the maximum information regarding the operation of ancient cycles the main sources of uncertainty for reconstructing seawater isotope curves involve diagenetic alteration sample impurities and errors in age assignments rigorous sample selection criteria and pretreatment methods are keys to reconstructing the most accurate seawater isotope curves applications are discussed for the rb sr sm nd la ce lu hf re os u th pb k ar and cosmogenic isotope systems d 2003 elsevier b v all rights reserved

a unique assemblage of epibenthic sessile suspension feeders with archaic features in the high antarctic we suggest that the epibenthic communities of passive suspension feeders that dominate some high antarctic seafloors present unique archaic features that are the result of long isolation together with the effects of environmental features including reduced terrestrial runoff and favourable feeding conditions these features probably originated during the late cretaceous when the high antarctic environment started to become different from the surrounding oceans modern antarctic communities are thus composed of a mixture of palaeozoic elements taxa that migrated from the deep ocean during interglacial periods and a component of fauna that evolved from common gondwana cretaceous ancestors we explore this hypothesis by revisiting the palaeoecological history of antarctic marine benthic communities and exploring the abiotic and biotic factors involved in their evolution including changes in oceanic circulation and production plankton communities the development of glaciation restricted sedimentation isolation life histories and the lack of large predators the conditions favouring the retention of apparently archaic features in the antarctic marine fauna remain to be fully elucidated but high antarctic communities are clearly unique and deserve special conservation

palaeoenvironmental trends in the history of trace fossils tracks trails and burrows made by organisms are commonly preserved in phanerozoic sedimentary rocks these biogenic sedimentary structures or trace fossils have been most intensively studied from rocks deposited in marine environments and have proven to be extremely useful in palaeoenvironmental reconstruc tions our systematic analysis of occurrences in the stratigraphic record of two of the most common trace fossils zoophycos and ophiomorpha indicates that occurrences for each show an environmentally linked directional pattern through time zoophycos is commonly reported from palaeozoic strata deposited from nearshore to deep sea environments whereas in post palaeozoic stratait is generally reported only from rocks deposited in deeper water environments ophiomorpha first appeared in permian shallowwater environments and was common in deep sea fan environments by the cretaceous and has been distributed from nearshore to deep sea environments since then these onshore offshore trends which are similar to those previously reported for phanerozoic benthic macroinvertebrate assemblages and individual higher taxa require integration into future palaeoenvironmental reconstructions that use trace fossils

permian marine paleoecology and its implications for large scale decoupling of brachiopod and bivalve abundance and diversity during the lopingian late permian abstract the transition during the permian triassic interval from brachiopod rich benthic marine assemblages to communities with diverse molluscs has been well constrained by measures of global taxonomic richness but its ecological context has not been studied using quantitative relative abundance data new relative abundance data from early middle and late permian silicified fossil assemblages from offshore shelf carbonate environments indicate that molluscs increased significantly in relative abundance from 0 8 in the middle permian guadalupian to 65 4 in the late permian lopingian these numerical changes are accompanied by increases in the abundance of infaunal bivalves and motile gastropods in the late permian although this ecological change was coincident with the end guadalupian extinction a new global diversity compilation indicates that the overall genus level severity of that biotic crisis was substantially lower than previous estimates the pronounced ecological shift was instead concurrent with the onset of deep marine anoxic or euxinic conditions around the guadalupian lopingian boundary suggesting that increased environmental variability in proximity to the deep water mass may have given eurytopic molluscs a competitive advantage over more stenotopic brachiopods however the lack of global changes in relative genus richness implies dramatic decoupling of global taxonomic and local ecological processes the pronounced increase in molluscan abundance and alpha diversity in the silicified assemblages contrasts with their unchanged global taxonomic richness and may also have resulted from increased environmental stress in offshore shelf environments these results demonstrate that the ecological transition from the brachiopods to molluscs was more complex than inferred from global measures of taxonomic richness and imply that initial stages of permo triassic environmental deterioration may have been responsible for the decoupling of local ecological from global taxonomic processes during the dramatic late permian rise of the modern fauna

the space time relationship of taxonomic diversity and morphological disparity in the middle jurassic ammonite radiation the middle jurassic ammonite radiation from the late aalenian to the end of the mid bathonian is traced using combined analyses of morphological disparity and taxonomic diversity the global signals of disparity and diversity are compared these signals are then broken down by paleogeographical provinces to detect any heterogeneity in the radiation an examination of the global signals reveals three biodiversity crises discordances between signals where morphological disparity grows while taxonomic diversity declines the subdivision of the signals indicates the radiation was heterogeneous between provinces the global signal is an aggregate of signals from each province the three biological crises have different paleogeographical signatures the first is visible in a few provinces only while the other two are visible in most provinces first order crises can be distinguished from second order ones by studying the number of paleogeographical provinces affected

assessing the record and causes of late triassic extinctions accelerated biotic turnover during the late triassic has led to the perception of an end triassic mass extinction event now regarded as one of the big five extinctions close examination of the fossil record reveals that many groups thought to be affected severely by this event such as ammonoids bivalves and conodonts instead were in decline throughout the late triassic and that other groups were relatively unaffected or subject to only regional effects explanations for the biotic turnover have included both gradualistic and catastrophic mechanisms regression during the rhaetian with consequent habitat loss is compatible with the disappearance of some marine faunal groups but may be regional not global in scale and cannot explain apparent synchronous decline in the terrestrial realm gradual widespread aridification of the pangaean supercontinent could explain a decline in terrestrial diversity during the late triassic although evidence for an impact precisely at the boundary is lacking the presence of impact structures with late triassic ages suggests the possibility of bolide impact induced environmental degradation prior to the end triassic widespread eruptions of flood basalts of the central atlantic magmatic province camp were synchronous with or slightly postdate the system boundary emissions of co2 and so2 during these eruptions were substantial but the contradictory evidence for the environmental effects of outgassing of these lavas remains to be resolved a substantial excursion in the marine carbon isotope record of both carbonate and organic matter suggests a significant disturbance of the global carbon cycle at the system boundary release of methane hydrates from seafloor sediments is a possible cause for this isotope excursion although the triggering mechanism and climatic effects of such a release remain uncertain d 2003 elsevier b v all rights reserved

palaeoatmospheres in the phanerozoic except in the recent geological past palaeoatmospheric composition cannot be measured but only inferred from palaeontological or geochemical observations the likely controls on atmospheric composition are reviewed and the role of organisms stressed as monitors recorders motors and moderators of palaeoatmospheric changes whereas there is a good general case for changes in po 2 and pco 2 during phanerozoic time proposals for timing and mechanism in the earlier phanerozoic are speculative at present it seems probable that the late palaeozoic spread of land plants raised o 2 and reduced co 2 levels in the atmosphere the end cretaceous crisis had a transient impact on the atmosphere whose general constancy through geological time is one of the most remarkable features of earth history

island arc carbonates characterization and recognition in the ancient geologic record abstract carbonates of island arc origin that are preserved in paleozoic mesozoic terranes of the north american cordillera exhibit a distinctive suite of paleontologic and lithologic features and share a fundamental similarity with limestones forming in modern volcanic arcs this study provides the first detailed synthesis of carbonate depositional systems in island arcs and documents primary sedimentary constituents based on facies relationships and faunal communities models are developed that show patterns in the long term evolution of shallow marine organisms and the construction evolution and demise of carbonate platforms in island arcs a suite of criteria is identified that may be used to differentiate island arc carbonates from limestones that accumulated in other platform settings biogeographic isolation prolonged subsidence steep submarine slopes and tectonic instability of volcanic edifices contribute to the development of relatively high levels of species endemism impoverished normal marine faunas complex provincial affinities and relict biotas in limestones that are characterized by exceptionally thick platform and periplatform sequences fringing and barrier reefs at the shelf margin extensive lagoonal deposits and rapid lateral and vertical facies changes although destructive tectonic and geologic processes in island arcs may hinder determining the original size and extent of the carbonate platform and particular facies types may not be represented e g fringing and barrier reefs may be replaced by sand shoals at the platform margin many characteristics have potential value for identifying carbonates of island arc origin in the ancient rock record apart from being associated with calc alkaline volcanic and volcaniclastic assemblages the most valuable suite of features for recognizing island arc carbonates is marine biotas that exhibit elevated levels of endemism and mixed paleobiogeographic affinities extraordinary thicknesses of platform shallow marine and periplatform carbonates and rapid facies changes between volcanic and carbonate rocks and between shallow and deep water limestones recognizing that an ensemble of features is distinctive within island arc carbonates considerably enhances identification of volcanic arcs in the ancient geologic record and thus improves the likelihood of successfully unraveling the complex geologic history of ocean basins

late cretaceous and paroxysmal cretaceous tertiary extinctions the various geological signatures at cretaceous tertiary time including iridium and other associated elements microspherules and shock deformation features are compatible with the suggestion that the transition is marked by a period of intense volcanism the volatile emissions from this volcanism would lead to acid rain reduction in the alkalinity and ph of the surface ocean global atmospheric temperature changes and ozone layer depletion these environmental effects coupled with those related to the major sea level regression of the late cretaceous provide the framework for an explanation of the selective nature of the observed extinction record

geomagnetic excursion captured by multiple volcanoes in a monogenetic field 1 five monogenetic volcanoes within the quaternary auckland volcanic field are shown to have recorded a virtually identical but anomalous paleomagnetic direction mean inclination and declination of 61 7 and 351 0 respectively consistent with the capture of a geomagnetic excursion based on documented rates of change of paleomagnetic field direction during excursions this implies that the volcanoes may have all formed within a period of only 50 100 years or less these temporally linked volcanoes are widespread throughout the field and appear not to be structurally related however the general paradigm for the reawakening of monogenetic fields is that only a single new volcano or group of closely spaced vents is created typically at intervals of several hundred years or more therefore the results presented show that for any monogenetic field the impact of renewed eruptive activity may be significantly under estimated especially for potentially affected population centres and the siting of sensitive facilities