antarctic climate at the eocene oligocene boundary climate model sensitivity to high latitude vegetation type and comparisons with the palaeobotanical record abstract simulated climate for the antarctic continent using the genesis version 2 1 global climate model with 34 ma boundary conditions is shown to be highly sensitive to polar vegetation type six experiments were run using different levels of atmospheric co2 orbital configurations ice sheet geometries and vegetation types to assess model sensitivity to antarctica being covered with either a needle leaf evergreen forest or tundra simulations using 2 pre industrial levels of co2 combined mean annual temperature mat 19 c are about 7 c cooler than minimum estimates from the antarctic cenozoic plant record mat 12 to 15 c however simulations using 3 co2 mat 7 c are in good agreement with our empirical estimates of mean annual temperature with ice sheets and orbits set up to represent early oligocene interglacial conditions the tundra climate is significantly cooler than the evergreen forest climate with local austral summer averages up to 6 c cooler in non glaciated areas and continental averages 2 5 c cooler in the model this is mainly due to higher albedo and decreases in net radiation and sensible and latent heat flux especially during spring and summer feedbacks between coastal and continental cooling marginal sea surface temperatures and sea ice also appear to be significant a review of the late palaeocene to earliest miocene plant fossil record in the antarctic peninsula and ross sea regions shows that the vegetation was in transition 34 ma from a relatively diverse mainly evergreen forest to a tundra vegetation the modelled sensitivity of continental temperatures to a change from forest to tundra suggests vegetation climate feedbacks during the eocene oligocene transition played a significant role in the initial rapid glaciation of the continent

a paleogene flora from the upper bonnet plume formation of northeast yukon territory canada palaeontological exploration of the bonnet plume basin in northwestern yukon territory canada has revealed a late paleocene to early eocene macrofloral assemblage from a channel fill deposit the flora is typified by cosmopolitan taxa and dominated by deciduous angiosperms with the notable presence of zizyphoides ettingshausenia and corylites floras with a similar composition are known from late cretaceous through early eocene deposits in alaska and the canadian arctic archipelago where they have been interpreted as evidence for warm equable temperatures this collection represents the most diverse known paleogene plant macrofossil assemblage from the yukon territory and helps to expand our knowledge of ancient high latitude floras

model for the origin of the yakutat block an accreting terrane in the northern gulf of alaska a composite oceanic and continental terrane the yakutat block is currently colliding with and accreting to north america in the northern gulf of alaska marine geophysical data indicate that the block has moved with the pacific plate during pliocene and quaternary time but are indeterminant about its previous movement history a model that explains some observed geologic and structural features of the block is that it originated as a result of subduction of the kula farallon spreading center beneath north america in this model the spreading center that formed the basaltic basement of the yakutat block was offset from a spreading center to the south by a left lateral transform fault 400 500 km long subduction of the northern spreading center about 45 m y ago sliced off part of the north america continental margin attached it to the kula plate and initiated northward movement of the composite terrane as the yakutat block during eocene and oligocene time migration of the southern spreading center toward north america truncated the yakutat block on the south and left a fossil fracture zone that is now seen as the transition fault the southern spreading center subducted about 25 m y ago and the yakutat block has since traveled with the pacific plate to southern alaska

accretionary tectonics of the north american cordillera continental geology stands on the threshold of a change that is likely to be as fundamental as plate tectonic theory was for marine geology ongoing seismic reflection investigations into the deep crustal structure of north america are verifying that orogenic zones are underlain by low angle faults of regional extent brown et al 1981 the growing body of regional field relations is likewise delineating numerous orogenic sutures that bound discrete crustal fragments paleomagnetic and paleobiogeographic studies are revealing major latitudinal shifts and rotations within and between suture bounded fragments particularly within the north american cordillera such interdisciplinary studies are leading to a consensus that the cordillera has been built by progressive tectonic addition of crustal fragments along the continent edge in mesozoic and early cenozoic time such crustal growth is referred to as accretionary tectonics in this paper we review some of the important concepts in accretionary tectonics discuss the nature of the materials accreted between central alaska and southern california in jurassic and cretaceous time and consider the general relations between cordilleran accretion and the movement of lithospheric plates the concept of continents growing by peripheral accretion through geologic time has long been a topic of great interest with the advent of plate tectonics a number of different mechanisms for crustal accretion have arisen along with mechanisms for crustal attrition accretion mechanisms include the growth of imbricated sedimentary prisms along inner trench walls slicing off of submarine topographic irregularities within subducting plates and collision of continents and volcanic arcs by ocean basin closure tectonic attrition mechanisms include rifting transform faulting and strike slip or underthrust removal of inner trench wall materials coincident with or in place of accretionary prism growth growth of intraorogenic ocean basins by seafloor spreading is an additional important mechanism for creating accretionary materials as well as displacing crustal fragments an important implication of plate kinematic theory is the likelihood for accretionary and attritionary mechanics to operate in series both in time and space along continental margins since attrition by nature leaves little material evidence of having operated one of the major problems confronting cordilleran geologists lies in the recognition of such attrition within the ancient record particularly when interspersed with accretionary events the spectrum of accretion and attrition mechanisms viewed at cm yr 1 plate transport rates over time scales of 100 m y leads one to suspect a highly mobile history for continental margin orogens the serial arrangement of subducting transform and rifting links along the modern cordillera plate juncture system and both serial and parallel arrangements in the western pacific systems show the complex interplay of such mechanisms through space similar arrangements overprinted through time are suggested by the rock assemblages and structural patterns within the cordillera which presently resemble a collage of crustal fragments davis et al 1978 recognition of the structural state of this collage geologic field mapping and geophysical investigations will bring about a new level of understanding in the growth of continental crust and the reading of stratigraphic records within the fragments and future palinspastic restorations will lead to a new level of understanding in paleogeography and earth history the first problem to be considered is the recognition of native north american crust from exotic fragments that have been accreted to its edge

palaeoecology of late cretaceous polar vegetation preserved in the hansen point volcanics nw ellesmere island canada abstract mesozoic polar forests represent an extinct biome subject to a polar light regime and elevated atmospheric co2 levels in this paper new cretaceous fossil plant assemblages are reported from nw ellesmere island canada at a paleolatitude of 75 n these occur in a campanian maastrichtian aged interval of the hansen point volcanics a unit interpreted as a coastal plain peat mire complex within an active volcanic setting studies of palynomorphs sterile and fertile foliage and wood indicate that mire environments were dominated by amber producing taxodiaceous conifers with other conifers ginkgos cycads angiosperms ferns lycopsids and bryophytes occurring in subordinate numbers leaf physiognomic studies imply that most vegetation was deciduous occurrence of traumatic rings in the woods together with a high year to year variability in ring width indicates disturbed growing conditions possibly linked to a combination of frosts volcanic eruptions and flooding abundant charcoal remains indicate that an additional important disturbance process was wildfire results of this study compare closely with those from coeval circum arctic fossil sites and augment our knowledge of the community scale ecology of the cretaceous polar biome

effect of precessional insolation changes on cretaceous climate and cyclic sedimentation the often striking presence of cyclical beddings has frequently been noted in cretaceous marine sediment deposits in many instances these beddings appear to have periodicities similar to those of the earth s orbit i e its precession obliquity and eccentricity variations in the primary deposition of ocean sediments are strongly linked to atmosphere land ocean interactions we report a set of numerical experiments using an atmospheric general circulation model that are designed to examine the sensitivity of mid cretaceous climate to insolation changes due to the precessional cycle we restrict attention to a single orbital parameter because most limestone black shale bedded sequences were deposited at low latitudes where precessional insolation variations predominate we varied systematically the precessional index between the maximum positive and negative values calculated over the last 2 m y and used mid cretaceous paleogeographic and paleotopographic reconstructions and zonally symmetric sea surface temperatures based on earlier work by barron and washington surface wetness and albedo values appropriate for grassland were prescribed uniformly over all land regions to capture the seasonality of precession we employed both perpetual january and perpetual july simulations changes in surface heating due to the imposed insolation anomalies resulted in a strong basically linear response of monsoonal circulations dominated by changes over the northern hemisphere the hydrologic cycle shows a significant response over many regions the low latitude proto south atlantic region varies from a strong net sink for water vapor excess precipitation to a strong source excess evaporation over the precession cycle this variation is consistent with an alternation between a stagnant stratified ocean basin with anoxic bottom water and an evaporative basin that produces bottom water that is warm saline and oxygenated the portion of the tethys ocean that overlays the limestone black shale sequences now found in present day italy does not exhibit comparable behavior but the reconstruction of orography and basin boundaries in this region is less known the simulations show however that as the monsoonal flow over south proto asia intensifies water vapor evaporated in this part of tethys is prevented from crossing the proto alps into the interior of the continent thereby remaining in the tethian drainage basin as a result central proto asia shifts between arid and moist conditions with precessional variations the water vapor budget over northeast africa varies systematically from zero seasonality to a marked wet dry seasonal cycle the deposition of eolian material can be inferred from a combination of continental aridity favorable mean wind directions and significant wind variances in our experiments the mean surface and upper winds often show a systematic response to precession but surface wind variances show a systematic response only in isolated regions our simulations do not provide a simple mechanism to explain the cyclicity in eolian deposition that has been reported for north central tethys

conflicting isotopic and biotic evidence for tropical sea surface temperatures during the tertiary abstract the biotic evidence from a varied group of shallow water organisms including mangroves zooxanthellate corals mainly reefal and larger foraminifera suggests that sea surface temperatures at low latitudes during the tertiary from at least the early eocene to the middle miocene were subtropical to tropical in nature and similar to temperatures prevailing at low latitudes at the present day 20 28 c in a recent paper shackleton 1984 the suggestion is made on the basis of oxygen isotope studies of foraminiferal shells that low latitude sea surface temperatures during the palaeogene and much of the neogene were invariably lower than those in similar regions today with a stable temperature of around 18 c this paper discusses the conflicting evidence for sea surface temperatures obtained from palaeontological and isotopic sources and suggests that palaeotemperatures derived from some isotopic studies are too low to account for the distribution and diversity of many tertiary tropical and subtropical biotas

magnetic overprinting in southeastern australia and the thermal history of its rifted margin the magnetizations of many rock units in southeastern australia have been severely overprinted interpretation of early work was hindered by this and one of the aims of the current research is to ascertain the nature of the overprint mechanism its geological significance and its regional extent results from three igneous bodies from the sydney basin which have been studied previously in a reconnaissance fashion have provided a new insight into the reason for such widespread magnetic overprinting the hornsby breccia hb and milton monzonite mm yield similar magnetic signatures both containing discrete high and low temperature magnetizations with directions of dec 72 inc 83 95 4 and dec 13 inc 76 95 2 respectively for hb and dec 60 inc 78 95 4 and dec 348 inc 79 95 6 respectively for mm the corresponding pole positions are 29 s 166 e a95 7 and 59 s 139 e a95 4 for hb and 22 s 171 e a95 7 and 55 s 158 e a95 11 for mm the paleomagnetic direction and pole from the third body studied the mogo hill basalt mh are dec 241 inc 81 95 5 and 41 s 130 e a95 9 this pole position and the two low temperature overprint pole positions from hb and mm are consistent with ages ranging from 100 m y to approximately 70 m y when compared to the late mesozoic apparent polar wander path we relate the overprinting to uplift erosion and rapid supracrustal cooling of the southeastern margin of australia associated with initial phases of marginal rift development prior to seafloor spreading in the tasman sea the temperatures of rocks now exposed may have reached 200 c or higher before the rapid cooling blocked and stabilized the overprint magnetizations

spore pollen evidence for early oligocene high latitude cool climatic episode in northern canada climatic cooling in the eocene leading to markedly lower temperatures in the oligocene has been documented in oxygen isotope studies in the north pacific1 2 new zealand3 south pacific4 and north sea5 these lower temperatures in the oligocene correspond to palaeoclimatic interpretations of north american leaf floras6 7 which suggest a profound cooling occurring towards the end of the eocene indicated also in the southeastern united states from studies on mid tertiary spores and pollen8 recently collinson et al 9 have shown palaeobotanically that in southern england cooling occurred gradually starting in the latest early eocene leading to two major periods of floristic change before the end of the eocene thick tertiary sections in the subsurface mackenzie delta region northwest territories10 11 provide well preserved palaeogene palynofloras12 discussed here which indicate a cooler climate in the oligocene following warm temperate conditions in the eocene this widespread early middle oligocene cool episode is thus represented in both high latitude and lower latitude floras and seems to have been of global extent persisting until towards the end of the oligocene but its precise dating remains a problem in northern canada it is followed by an amelioration of the climate in the late oligocene which persisted probably until the middle miocene the rate of cooling during the eocene and oligocene may have varied depending on locality but once established the cooler oligocene climate exerted a profound influence on biotic development

dinosaurs on the north slope alaska high latitude latest cretaceous environments abundant skeletal remains demonstrate that lambeosaurine hadrosaurid tyrannosaurid and troodontid dinosaurs lived on the alaskan north slope during late campanian early maestrichtian time about 66 to 76 million years ago in a deltaic environment dominated by herbaceous vegetation the high ground terrestrial plant community was a mild to cold temperate forest composed of coniferous and broad leaf trees the high paleolatitude about 70 to 85 north implies extreme seasonal variation in solar insolation temperature and herbivore food supply great distances of migration to contemporaneous evergreen floras and the presence of both juvenile and adult hadrosaurs suggest that they remained at high latitudes year round this challenges the hypothesis that short term periods of darkness and temperature decrease resulting from a bolide impact caused dinosaurian extinction

paleogene biomarker records from the central arctic ocean integrated ocean drilling program expedition 302 organic carbon sources anoxia and sea surface temperature 1 during integrated ocean drilling program expedition 302 arctic coring expedition acex a more than 200 m thick sequence of paleogene organic carbon oc rich black shale type sediments was drilled here we present new biomarker data determined in acex sediment samples to decipher processes controlling oc accumulation and their paleoenvironmental significance during periods of paleogene global warmth and proposed increased freshwater discharge in the early cenozoic specific source related biomarkers including n alkanes fatty acids isoprenoids carotenoids hopanes hopenes hopanoic acids aromatic terpenoids and long chain alkenones show a high variability of components derived from marine and terrestrial origin the distribution of hopanoic acid isomers is dominated by compounds with the biological 17 h 21 h configuration indicating a low level of maturity on the basis of the biomarker data the terrestrial oc supply was significantly enriched during the late paleocene and part of the earliest eocene whereas increased aquatic contributions and euxinic conditions of variable intensity were determined for the paleocene eocene thermal maximum and eocene thermal maximum 2 events as well as the middle eocene time interval furthermore samples from the middle eocene are characterized by the occurrence of long chain alkenones high proportions of lycopane and high ratios 0 6 of n c35 lycopane n c31 the occurrence of c37 alkenenones which were first determined toward the end of the azolla freshwater event indicates that the oc becomes more marine in origin during the middle eocene preliminary u37k based sea surface temperature sst values display a long term temperature decrease of about 15 c during the time interval 49 44 5 ma 25 to 10 c coinciding with the global benthic 18o cooling trend after the early eocene climatic optimum at about 46 ma parallel with onset of ice rafted debris sst interpreted as summer temperatures decreased to values 15 c for the late early miocene a sst of 11 15 c was determined most of the middle eocene acex sediments are characterized by a smooth short chain n alkane distribution which may point to natural oil type hydrocarbons from leakage of petroleum reservoirs or erosion of related source rocks and redeposition

the paleocene eocene transition in the antarctic indian ocean inference from planktic foraminifera isotopic depth stratification and relative abundance studies of planktic foraminifera at odp site 738 reveal three major faunal turnovers during the latest paleocene and early eocene reflecting the climatic and structural changes in the antarctic surface ocean faunal event 1 occurred near the paleocene eocene boundary and is characterized by a faunal turnover in deep dwellers decreased relative abundance in intermediate dwellers and increased relative abundance in surface dwellers this event marks a temporary elimination of the vertical structure in the surface ocean over a period of more than 63 000 years that is apparently associated with the sudden shutdown of the antarctic intermediate water production the appearance of morozovellids before this event suggests that polar warming is the cause for the shutdown in the production of this water mass at this time warm saline deep water may have formed at low latitudes faunal event 2 occurred near the ap5a ap5b subzonal boundary and is characterized by a faunal turnover in deep dwellers with no apparent change in surface and intermediate dwellers increased individual size wall thickness and relative abundance in deep dwelling chiloguembelinids suggests the formation of a deep oxygen minima in the antarctic oceans during the maximum polar warming possibly as a result of upwelling of nutrient rich deep water faunal event 3 occurred in subzone ap6 and is characterized by a faunal turnover in surface dwellers and a delayed diversification in deep dwellers this event marks the onset of antarctic cooling a drastic decrease in the 13c 18o values of the deep assemblage in zone ap7 suggests an intensified thermocline and reduced upwelling following the polar cooling

an interpretation of cretaceous and tertiary biota in polar regions abstract rich fossil floras and vertebrate faunas lived within the arctic and atarctic circles during the cretaceous and paleogene these occurrences seem explicable by the nature of the thermal environments in polar regions and by the physiological responses of plants and animals allied to those that lived there there seems no need to invoke a lower tilt to the earth s axis to provide greater warmth and light in polar regions to account for these fossil records

endemism and heterochroneity in the late cretaceous campanian to paleocene palynofloras of seymour island antarctica implications for origins dispersal and palaeoclimates of southern floras

a terrestrial scenario for the cretaceous tertiary boundary collapse of the marine pelagic ecosystem in this paper we present an expansion of the model for marine ecosystem collapse at the cretaceous tertiary boundary presented by brinkhuis and zachariasse 1988 a long term sea level drop at the end of the cretaceous culminated in a short term regressive pulse at k t time deep water production was curtailed minimizing the vertical advection of nutrients and oxygen in the oceans consequently a productivity crisis developed which could only be survived by cosmopolitan shallow dwellers and the oxygen minimum zone omz expanded no sustained oceanic anoxic event followed the k t boundary event since productivity had dropped to extremely low values at k t time however the short term expansion of the omz invoked by the combination of minimized oxygen advection and abrupt mass mortality caused dysoxic conditions even to reach up to the shelves as can be deduced from sedimentological chemical and faunistic observations

the 17 august 1991 honeydew earthquake north coast california a case for revising the modified mercalli scale in sparsely populated areas we present an isoseismal map of the 17 august 1991 ms 6 2 honeydew earthquake and proposed modifications of the 1931 modified mercalli scale of wood and neumann to accurately estimate peak intensities for this earthquake and others in similar rural settings modifications introduced de emphasize reliance on damage to masonry construction in assigning intensities and attempt to bring physical phenomena such as rockfall landsliding tree and limb fall and water changes in line with the damage indicators

climatic evolution on the southeastern margin of the tethys negev israel from the palaeocene to the early eocene focus on the late palaeocene thermal maximum during the early palaeocene zones p1 to p2 the southeastern tethyan margin experienced a warm and humid climate with high rainfall as indicated by the abundance of kaolinite within marine sedimentary rocks subsequently in zone p2 arid climatic conditions evolved in the coastal basins of the southern tethys margin as indicated by the gradual disappearance of kaolinite and the increased abundance of palygorskite and sepiolite arid climatic conditions persisted during the selandian and thanetian late palaeocene and reached a maximum in the ypresian early eocene during the late palaeocene thermal maximum warm climatic conditions were associated with increased aridity and led to sea surface warming though not bottom water warming as suggested by the planktic 18 o excursion observed at the zomet telalim basin negev israel strongly reduced surface productivity accompanied by unusually light 13 c are associated with the late palaeocene thermal maximum in the negev as well as globally

two long geological records of continental ecosystems abstract the early paleogene continental sequence of northwestern wyoming and south central montana usa and the neogene siwalik sequence of northern pakistan are exceptionally long fossiliferous and well studied in terms of geology paleontology mammalian evolution paleoecology and paleoclimatology each record spans about 15 myr of alluvial deposition in a foreland basin the fluvial systems differed in size drainage of floodplains and change in alluvial architecture through time both sequences preserved abundant paleosols which are a source of paleoclimatic signals in stable isotopes from soil carbonates fossil collections from both records are dominated by vertebrate remains and especially by mammals the paleogene sequence also preserved abundant floral remains patterns of vertebrate preservation differed markedly between the two sequences placing inherent limitations on paleoecological reconstruction and on the scope of evolutionary studies of mammalian lincages in this introductory paper we summarize the major similarities and differences in geologic setting chronology and time resolution and mammalian faunal composition of these two long sequences finally we present a brief overview of the organization of papers in this special issue

palaeomagnetism of volcanic rocks of the kodiak islands indicates northward latitudinal displacement in the past decade it has become widely accepted that southern alaska is composed of allochthonous terranes1 4 but the times of amalgamation and their accretion to north america remain controversial palaeomagnetists and geologists generally agree that the talkeetna superterrane consisting of the wrangellia and peninsular terranes fig 1 was far to the south of its present position with respect to north america in triassic and jurassic time1 4 this consensus is lost when it comes to the question of the relative position of these terranes in the tertiary previously limited palaeomagnetic evidence suggested that the peninsular terrane may have lain substantially south of its present position4 but the timing of deformational and thermal events and the apparent absence of a tertiary suture zone argue for a cretaceous docking of wrangellia and the peninsular terrane5 6 here we present new palaeomagnetic results demonstrating that the kodiak islands were indeed at a more southerly latitude 62 myr ago around 43 n and discuss the implications of this conclusion

abrupt climate change and transient climates during the paleogene a marine perspective detailed investigations of high latitude sequences recently collected by the ocean drilling program odp indicate that periods of rapid climate change often culminated in brief transient climates with more extreme conditions than subsequent long term climates two examples of such events have been identified in the paleogene the first in latest paleocene time in the middle of a warming trend that began several million years earlier the second in earliest oligocene time near the end of a middle eocene to late oligocene global cooling trend superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice sheet on antarctica in both cases the climate extremes were not stable lasting for less than a few hundred thousand years indicating a temporary or transient climate state geochemical and sedimentolog

palaeomagnetism of lower cretaceous tuffs from yukon kuskokwim delta region western alaska during the past decade the prescient arguments1 3 for the allochthoneity of large portions of southern alaska have been corroborated by detailed geological and palaeomagnetic studies in south central alaska4 9 the alaska peninsula10 kodiak island11 12 and the prince william sound area13 fig 1 these investigations have demonstrated sizeable northward displacements for rocks of late palaeozoic mesozoic and early tertiary age in those regions with northward motion at times culminating in collision of the allochthonous terranes against the backstop of nuclear alaska14 15 a fundamental question is which parts of alaska underwent significantly less latitudinal translation relative to the stable north american continent thereby serving as the accretionary nucleus into which the displaced microplates 16 were eventually incorporated17 18 here we present new palaeomagnetic results from tuffs and associated volcaniclastic rocks of early cretaceous age from the yukon kuskokwin delta region in western alaska these rocks were probably overprinted during the cretaceous long normal polarity interval although a remagnetization event as recent as palaeocene cannot be ruled out this overprint direction is not appreciably discordant from the expected late cretaceous direction for cratonal north america the implied absence of appreciable northward displacement for this region is consistent with the general late mesozoic early tertiary tectonic pattern for alaska based on more definitive studies little to no poleward displacement for central alaska though substantially more northward drift for the southern alaska terranes comprising alaska peninsula kodiak island prince william sound area and matunuska valley since late cretaceous to palaeocene time

the evidence and implications of polar ice during the mesozoic abstract the mesozoic perhaps representing the longest period of warmth during phanerozoic earth history contains in general sparse and frequently equivocal evidence for polar ice although this time is undoubtedly punctuated by oscillations in climate whether sufficient to lead to polar cooling and the formation of polar ice an inviting mechanism to account for faunal and floral distribution patterns and large scale sea level change has been widely debated mesozoic evidence for glacial conditions includes abraded rock surfaces generally unsorted stone rich beds and the presence of dropstones rafted by ice within a finer grained host sediment faunal and floral evidence has also been utilised to determine the presence or absence of cold or sub freezing polar conditions together with more indirect evidence for glacial conditions derived from general circulation model gcm simulations of climate the analysis of clay mineral distributions glendonite abundance and palaeontological and sedimentological evidence for globally synchronous sea level change the extent of possible glacial environments during the mesozoic has been established by plotting published reports of glacial sediments on palaeogeographic reconstructions the general clustering of evidence at high palaeolatitudes suggests that the extent of polar ice during the mesozoic is likely to have been approximately one third the size of the present day based on such evidence a number of episodes of cold or sub freezing polar climates during the bajocian bathonian tithonian volgian valanginian and aptian are recognised evidence exists possibly also for a cold episode during the early jurassic pliensbachian although poorly constrained owing to limited biostratigraphical control the longevity of these events may be represented by a cold snap within a stage although undoubtedly the possible smearing of ages may have had the effect of lengthening and hence promoting the importance of these proposed events the climate regime of the earth during these times may be hypothesised to be characterised by a relatively steep pole to equator temperature gradient where low latitude regions are as warm or warmer than today the evidence to support such reasoning includes sharp increases in the areal distribution of both glendonites and deposits with affinities to glacial tillites and dropstones for these times coincidental falls of sea level arid events and an increased bipolarity of faunas at these times imparts further confidence that these events were of a magnitude to effect the earth as a whole

calcareous nannofossils from the paleocene eocene thermal maximum of the equatorial atlantic odp site 1260b evidence for tropical warming abstract independent geological and micropaleontological lines of evidence suggest a 200 kyr period of intense warming covering the paleocene eocene boundary interval petm it has been suggested that this warming was initiated by a massive release of methane from the continental slopes among other groups of organisms calcareous nannofossils are characterized by a remarkable increase of warm water taxa during this interval here we report the tropical response of calcareous nannofossils to the paleocene eocene interval in odp site 1260b 283 15 276 35 mbsf the petm is about 1 38 m thick 279 88 278 5 mbsf as defined by the onset and termination of the 13c excursion and is marked by a 12 cm thick laminated clay layer at the start of the excursion a 30 cm thick interval 279 75 279 45 mbsf directly above the clay layer is characterized by common discoaster spp and coccolithus subpertusus syn ericsonia subpertusus and the first occurrences of discoaster araneus rhomboaster cuspis and tribrachiatus bramlettei all five taxa are interpreted as proxies for warm surface waters the increase of discoaster spp during the petm is solely caused by the onset of the new species d araneus which is here seen as a malformed discoaster related to specific petm conditions these possibly include an acidification of the surface waters and or higher salinity the rhomboaster tribrachiatus group which first occurs in the petm is also thought to be a proxy for increased salinity the abundance of the genus toweius indicative for mesotrophic conditions declines simultaneously discoaster abundance decreases in the later stages of the petm being substituted by chiasmolithus and campylosphaera indicating a change to more eutrophic conditions the genus fasciculithus very common in the tropical paleocene suffered a dramatic decline in the clay layer basal petm without recovering later in the eocene this decline and the subsequent extinction of fasciculithus a solid robust nannolith are here thought to be related to a calcification crises perhaps caused by a high co2 concentration and an acidification of the oceans the observed changes in the composition of the calcareous nannofossils were relatively short lived following the course of the petm which was characterized by warm surface waters with possibly low ph conditions

paleoclimate and polar wander abstract fossil faunas floras and 18 o temperatures indicate that weak or no meridional temperature gradients existed over the continents from triassic to eocene for much of this time tropical pacific 18 o temperatures were some ten degrees colder than at present while arctic and antarctic regions apparently enjoyed warm temperate to semitropical climates polar wander involving displacement of the poles to what are now tropical marine latitudes is offered to explain this uniformly warm paleoclimate this hypothesis is supported by a theoretical model which is discussed

paleolatitudes versus time for southern alaska paleomagnetic determinations of the inclination of the ancient geomagnetic field for localities in the alaska peninsula wrangellia chugach and kuskokwim tectonostratigraphic terranes of alaska show systematic northward motion from late cretaceous time until the present prior to this the ambiguity of polarity of the ancient geomagnetic field allow several interpretations however the preferred interpretation involves southerly motion of the terranes from triassic to early jurrassic time and steady northward motion from then up to the present the latitudinal rate is about 6 cm yr

geological evidence for post 40 m y b p large scale northwestward displacement of part of southeastern alaska the leech river complex on southern vancouver island and schistose rocks on southern baranof island have very similar geologic histories both were derived from probable upper jurassic cretaceous terrigenous clastic rocks and minor associated volcanogenic rocks and chert each underwent 1 at least two penetrative deformations locally involving folding disruption and transposition of thinly layered sequences and 2 synkinematic low pressure buchan type metamorphism progressive metamorphic zones ranging from greenschist to amphibolite facies are related to granitic intrusive bodies deformation metamorphism and intrusion culminated about 40 to 42 m y ago apparently these units now separated by more than 1 100 km were once contiguous and lay at least as far south as the latitude of southern vancouver island shortly after 40 m y b p the allochthonous leech river complex was emplaced at the southern edge of vancouver island and the schists of baranof island and perhaps the entire chugach terrane began their long northwestward journey along a system of dextral transcurrent faults

southern polar forests the early cretaceous floras of victoria and their palaeoclimatic significance abstract a diverse fossil flora including cryptogams pteridosperms cycadales bennettitales ginkgoales coniferales and angiosperms occurs in early cretaceous fluvial and lacustrine strata in the otway and gippsland basins in southern victoria both evergreens e g araucarians cycads ferns and deciduous or semi deciduous forms e g certain pteridosperms and ginkgoales seem to have been represented certain ferns ginkgos and conifers grew to a large size overall the assemblages are typical of early cretaceous floras the associated fauna includes dinosaurs hypsilophodontids allosaurs lepidosaurs chelonians birds fish including the lungfish ceratodus and insects the evidence of the biota as a whole suggests a warm to cool temperate relatively equable climate of moderate seasonality with no widespread winter freezing the complex mesozoic apparent polar wander path apw indicated for australia places victoria in high to polar palaeolatitudes ca 70 85 s during the early cretaceous this apw path is supported by paths for other gondwana continents the existence of the victorian early cretaceous forest and biotic communities through polar nights of about two to five months duration is difficult to accept evergreen species would have required relative equability of light whatever the temperature the dinosaurs foliage throughout the year and the lungfish warm to temperate conditions without freezing in view of the consistency of mesozoic palaeomagnetic results for gondwanaland and the enigmatic presence of mesozoic and early cenozoic fossil floras and faunas in very high northern palaeolatitudes the possibility of a reduced obliquity of the ecliptic in mesozoic early cenozoic time should be considered

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

the tethys sea and the alpine himalayan orogenic belt mega elements in a new global tectonic system abstract analysis of meso cainozoic palaeomagnetic data for africa india and eurasia has led to the development of a new mobilistic alpine plate tectonic model characterized by a hierarchical system of plates in relative rotation the new model which discounts seafloor spreading implies that there have been no significant palaeogeographic changes in the overall distribution of continental and oceanic regions the mid oceanic ridges are interpreted as transpressive tectonic features caused by rotation of megaplates containing both continental and oceanic crust the isostatic uplift due to crustal lithospheric thickening giving rise to the general ridge topography as well as to the ridge parallel structural grain the new plate tectonic theory gains strong support from a variety of geophysical geological and palaeoclimatological evidence and several observations that have remained enigmatic or awkward within the context of the orthodox model can be readily accounted for in the new tectonic framework the model maintains the tethys as a relatively narrow epicontinental sea which during its maximum extent stretched latitudinally from the caribbean across the central atlantic to se asia the alpine himalayan orogenic belt developed along the boundary of two megaplates in relative rotation which provided a transpressive tectonic regime the location of the plate boundary to the north of the mediterranean has important implications for discussion of mediterranean microplates for example it now seems that italy has been subjected to 10 15 of clockwise microplate rotation previous conclusions in favour of 30 40 of anticlockwise rotation are regarded as artefacts which arise from incorrectly linking the mediterranean region to the european palaeomagnetic frame instead of to the african one the model suggests further that the indo pakistani plate was closely tied to eurasia this challenges the conventional view that the peninsula was part of an alleged gondwanaland the new pre drift configuration implies that the indo pakistani plate rotated 135 clockwise at around the cretaceous tertiary boundary before redocking with asia in approximately its present relative orientation

late paleocene arctic ocean shallow marine temperatures from mollusc stable isotopes late paleocene high latitude 80 n arctic ocean shallow marine temperatures are estimated from molluscan 18o time series sampling of individual growth increments of two specimens of the bivalve camptochlamys alaskensis provides a high resolution record of shell stable isotope composition the heavy carbon isotopic values of the specimens support a late paleocene age for the youngest marine beds of the prince creek formation exposed near ocean point alaska the oxygen isotopic composition of regional freshwater runoff is estimated from the mean 18o value of two freshwater bivalves collected from approximately coeval fluviatile beds over a 30 34 range of salinity values assumed to represent the tolerance of c alaskensis the mean annual shallow marine temperature recorded by these individuals is between 11 and 22 c these values could represent maximum estimates of the mean annual temperature because of a possible warm month bias imposed on the average 18o value by slowing or cessation of growth in winter months the amplitude of the molluscan 18o time series probably records most of the seasonality in shallow marine temperature the annual temperature range indicated is approximately 6 c suggesting very moderate high latitude marine temperature seasonality during the late paleocene on the basis of analogy with modern chlamys species c alaskensis probably inhabited water depths of 30 50 m the seasonal temperature range derived from 18o is therefore likely to be damped relative to the full range of annual sea surface temperatures high resolution sampling of molluscan shell material across inferred growth bands represents an important proxy record of seasonality of marine and freshwater conditions applicable at any latitude if applied to other regions and time periods the approach used here would contribute substantially to the paleoclimate record of seasonality

character distribution and tectonic significance of accretionary terranes in the central alaska range the central part of the alaska range near mount mckinley is composed of nine separate tectonostratigraphic terranes that were accreted in southern alaska during late mesozoic time these terranes now form long linear fault bounded belts that are subparallel to the denali fault on the north but oblique to the fault on the south the postaccretion right lateral offset along the denali fault system is about 200 km from north to south the major terranes are 1 yukon tanana terrane metasedimentary and metavolcanic rocks mostly undated but including rocks of known late paleozoic age polymetamorphosed with terminal events in late mesozoic 2 pingston terrane isoclinally folded upper triassic deep water silty limestone quartzite and carbonaceous slate folded with upper paleozoic phyllite chert tuff and minor limestone 3 mckinley terrane upper paleozoic flysch chert and minor limestone intruded by large gabbro sills and dikes and overlain by thick piles of triassic porphyritic pillow lava the top of the section is thick sequence of upper mesozoic conglomerate flysch chert and phyllite 4 dillinger terrane very thick sequence of strongly folded lower paleozoic micaceous sandstone turbidites graptolitic shale and deep water limestone locally overlain unconformably by jurassic fossiliferous sandstone or triassic pillow basalt 5 windy terrane heterogeneous assemblage of serpentinite basalt tuff and chert ophiolite with paleozoic and mesozoic flysch and blocks of mid paleozoic fossiliferous limestone 6 mystic terrane predominantly upper paleozoic flysch and conglomerate but also includes lower paleozoic graptolitic shale pillow basalt and shallow water limestone and upper paleozoic fossiliferous limestone sandstone chert and undated pillow basalt 7 chulitna terrane upper devonian ophiolite overlain by upper paleozoic chert volcanic conglomerate limestone and flysch capped by lower triassic limestone and upper triassic red beds basalt and interbedded basalt and limestone later mesozoic rocks are sandstone chert and argillite 8 westfork terrane jurassic chert sandstone conglomerate and triassic and jurassic crystal tuff 9 broad pass terrane upper paleozoic chert tuff and argillite with blocks of devonian and older limestone locally associated with serpentinite these diverse terranes of mixed oceanic and continental affinities are now juxtaposed to form a complex sequence of folded and faulted rootless nappes major suture zones between them are occupied by intensely deformed upper mesozoic flysch all of the terranes differ markedly from wrangellia the southermost coherent accreted terrane in alaska paleomagnetic measurements from triassic rocks prove that wrangellia originated near the equator probably in the southern heimsphere paleolatitudes for terranes in the central alaska range are not yet determined but other lines of evidence biogeographic and lithologic suggest large scale northern transport for some terranes

some limitations in using leaf physiognomic data as a precise method for determining paleoclimates with an example from the late cretaceous pautut flora of west greenland abstract plant parts of the late cretaceous west greenland pautut flora are derived from vegetation growing in lower delta plain delta upland and levee habitats a large river system drained the uplands and deposited leaves from species there and levee areas into a shallow bay setting the large drainage area of the rivers caused a great diversity of species to be preserved in the bay when these upland and levee species are combined with those that grew and were deposited in the lower delta plain areas 12 fern six cycad cycadeoid 1 ginkgoalean 35 conifer and over 85 angiosperm species represent the pautut flora when the paleotemperature derived from the angiosperm leaf margin ratio of the complete pautut flora 8 c is compared to other paleobotanical data and oxygen isotope values warm temperate to subtropical there is a serious discrepancy that puts the leaf physiognomic approach for precisely determining paleoclimate in the cretaceous in serious doubt also paleoclimatic interpretations based on the angiosperm leaf margin data of leaves from the lower delta plain species would indicate slightly cooler conditions than that suggested by the upper delta plain species leaf size would indicate wetter conditions in the lower delta plain even though other leaf features e g drip tips suggest moist conditions did occur in the upper delta plain these preservation enough that regional paleoclimate scenarios drawn from only one depositional setting or loclity can be erroneous a sampling size of less than 30 angiosperm species for a fossil flora also is suspect for reliably indicating climatic conditions unless the flora was originally impoverished of angiosperm species taphonomic factors play a significant role in fossil leaf preservation so collected fossil assemblages must closely represent the original vegetation before paleoclimatic interpretations based on leaf physiognomy can have a degree of credibility a limit to plausibility is especially significant in cretaceous floras because they have a limited diversity due to evolutionary constraints and appear to have consisted of more successional species than younger floras thus displaying intermediate climatic conditions moisture and arctic light levels further restrict determination of paleoclimatic conditions derived from leaf margin ratios and leaf size

a comparison of eocene climate model results to quantified paleoclimatic interpretations abstract the integration of climate model results and geologic information offers considerable potential for deriving greater insight into the geologic record in this study climate model results and quantified climatic interpretations derived from proxy data are compared to assess model capabilities and to examine proxy data interpretations atmospheric general circulation model experiments were used to produce a range of possible representative eocene climate states based on current knowledge of the eocene record the climate model experiments incorporate two idealized endmembers of eocene ocean surface temperature distributions characterized by very different latitudinal gradients model results are compared to quantified interpretations of the climate of early eocene north america in an attempt to identify one of the sea surface temperature distributions as more likely to have existed during the eocene the comparisons do not produce a conclusive match between inferred paleoclimatic information and any single case of model results but some interesting insights become apparent model predictions of mean annual temperature and mean annual precipitation compare favorably to interpretations from geologic evidence but there are large differences between model results and interpreted paleoclimatic parameters of minimum surface temperature and mean annual temperature range several possible causes for these differences are discussed

three growth in the mesozoic and early tertiary and the reconstruction of palaeoclimates abstract evidence from the distribution and characteristics of fossil wood in the mesozoic and early tertiary indicates that a much warmer global climate prevailed in those times there appears to have been a broad zone of largely non seasonal climate stretching from about 32 n to 32 s palaeolatitudes in addition to this low latitude zone forest growth extended into very high palaeolatitudes where trees cannot grow at the present day a number of theories have been proposed to account for the palaeoclimate responsible for this distribution of forests most notable have been those involving changes in the amount of carbon dioxide in the atmosphere in the positions of the continents or in the obliquity of the earth s axis of rotation evidence from fossil forests indicates that a combination of the effects of an increased quantity of carbon dioxide in the atmosphere and the palaeopositions of the continents in the mesozoic and early tertiary appears at the moment to be the simplest explanation for the climate of those geological times without the need to invoke axial movement

biodiversity and terrestrial ecology of a mid cretaceous high latitude floodplain alexander island antarctica the biodiversity and terrestrial ecology of the late albian triton point formation fossil bluff group alexander island antarctica is analysed to improve our understanding of polar biomes during the mid cretaceous thermal optimum this formation was deposited on a high latitude 75 s floodplain and consists of two facies associations a lower braided alluvial plain unit and an upper coastal meander belt unit analysis of fossil plants in well exposed palaeosols reveals the existence of spatially complex plant communities braidplains supported patchy low density 91 trees ha stands of podocarp and taxodioid conifers on floodbasin substrates and conifer cycadophyte fern angiosperm thickets in riparian settings coastal meander belts supported medium density 568 trees ha podocarp araucarian conifer forests on mature floodbasin soils and fern angiosperm ginkgo thickets in riparian settings growth ring analysis indicates plants experienced stressful growing conditions on the braidplain characterized by high frequency flood events but more favourable growing conditions on the coastal plain additional vegetation disturbances were caused by arthropod fungal attack frost and wildfire in terms of structure composition ecology and productivity these predominantly evergreen broad leafed conifer forests bear similarities to the extant temperate rainforests of new zealand

a review of mesozoic climates there is overwhelming evidence based on the distribution of distinctive sediments and fossils and oxygen isotope data that the climate of the mesozoic world was appreciably more equable than that of today with no polar ice caps but precise quantitative data are not available except for an episode of late cretaceous cooling there is no good documentation of any significant change in global temperature distributions through the era the distribution of coals and evaporites together with other criteria indicates a pattern of humid arid and zones appreciably different in important respects from that of today during the triassic and jurassic western pangaea in low to middle latitudes was largely arid but in the early cretaceous the lands on the margin of the newly opening central atlantic and western tethys experienced a humid climate by late cretaceous times arid zones had become very restricted in extent because of insufficient suitable data attempts at climatic modelling have had only modest success and only to a limited extent can the major long term changes in climate between the permian and the present be explained in terms of changing geography the most probable explanation of mesozoic equability is an increased atmospheric co 2 content a number of enigmas remain such as the existence of flourishing forests in polar palaeolatitudes whereas for the late cenozoic short term climatic changes can be related successfully to variations in the geometry and mechanics of the earth sun system there is a long way to go before comparable success can be claimed for the mesozoic

a note on the main forcing of the northeastward flowing current off the southeast china coast abstract the effects of sea surface slope wind stress barometric pressure and water density on the formation of the northeastward flowing current off the southeast china coast are examined the long term mean sea surface slope is estimated to be 2 62 10 7 based on tidal station records and land leveling its effect is about three times the sum of the other three effects and is thus regarded as the main forcing the seasonal variations of these forcing terms are also evaluated a set of simple solutions of the current components induced by these four terms and the resultant current are given to illustrate the vertical structure of the current the sea surface inclination along the southeast coast of china is assumed to be related to the high sea surface elevation in the western tropic pacific and relatively low elevation in the northwest pacific it is also proposed that the difference between sea surface elevations in the western tropic pacific and the northwestern pacific may generate a current starting from the northeast part of the south china sea passing through the taiwan strait east china sea korea strait japan sea and tsugaru soya straits and finally joining the oyashio