north pacific halocline and cold climate induced by panamanian gateway closure in a coupled ocean atmosphere gcm 1 the influence of the closure of the panamanian gateway during the late cenozoic on climate in and around the north pacific is investigated by using a coupled ocean atmosphere general circulation model with an open and closed gateway in the case of an open closed gateway deep convection is present absent in the north pacific the deep convection is associated with surface saline water transported from the subtropical atlantic through the open gateway to the north pacific on the other hand with the closed gateway the lack of saline water transport from the atlantic induces halocline formation over the subarctic pacific with cold climate the deep convection in the north pacific leads to a vigorous thermohaline circulation with larger meridional heat transport and causes warmer climate in and around the north pacific these results are generally consistent with paleoceanographic and paleoclimatic estimates related to the closure of the panamanian gateway

lethal sandslides from eolian dunes fossil vertebrates entombed within the upper cretaceous djadokhta formation of southern mongolia bear testimony to a heretofore unknown geologic phenomenon mass wasting of eolian dunes during heavy rainstorms evaporation of shallow penetrating rainwater led to progressive calcite accumulation in a thin layer of sand about 0 5 m below the surface of dune lee slopes during rare heavy rainstorms a perched water table developed at the top of calcitic zones positive pore water pressure led to translational slides and fast moving sediment gravity flows that overwhelmed animals on the lee slopes of large dunes and in interdune areas

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

early mid pleistocene environments in the valsequillo basin central mexico a reassessment the valsequillo basin in central mexico has been of interest due to the presence of megafauna and evidence for early human occupation but research has been controversial it has been suggested that extensive and deep lakes characterised the early pleistocene environment but sediment exposure is highly fragmentary and reliable dating has been difficult here we report for the first time early pleistocene palaeoenvironmental reconstructions using stable isotopes diatoms tephra and pollen we studied several stratigraphic sections of mainly non volcanic rocks containing the 1 3 ma xalnene ash as a stratigraphic marker the isotope and other proxy data show that topographically low points in the basin were occupied by spring fed shallow water lakes during the early mid pleistocene with a trend to drier conditions the basin was a dynamic volcaniclastic environment during this period with the production of the toluquilla volcano sequence and other rhyolitic dacitic volcanic ashes interbedded with the lake sediments at the sections studied there is no evidence from the sections for extensive and deep lakes before or after the xalnene ash deposition the presence of lakes in the basin during the early pleistocene would have made it attractive for megafauna

the real southern basin and range mid to late cenozoic extension in mexico much of northern and central mexico underwent east northeast extension in the mid to late cenozoic this area constitutes a major but little recognized part of the basin and range province the extended region is bounded on the east by the laramide thrust front of the sierra madre oriental on the west the relatively unfaulted sierra madre occidental separates the extended area in central mexico from that around the gulf of california extension occurred as far south as what is now the trans mexican volcanic belt and in oaxaca south of the belt the basin and range province in mexico constitutes approximately half of the 19 x 10 5 km 2 of western north america that underwent mid to late cenozoic extension north northwest orientations of numerous epithermal vein systems indicate that east northeast extension began as early as 30 ma in areas north of the volcanic belt major episodes of faulting began at about 23 to 24 ma and 12 to 13 ma both in mexico and in the southwestern united states faulting was commonly accompanied by eruption of alkali basalts typical of intraplate rifting widespread quaternary fault scarps and alkali basalts indicate that extension continues to the present in the region north of the trans mexican volcanic belt in contrast the tectonics in and south of the belt are now probably related to subduction of the rivera plate contemporaneity of the 12 ma episode with early extension around the gulf of california attributed to pacific north american plate boundary reorganization suggests that extension is related predominantly to plate boundary effects the beginning of extension at 30 ma may be related to initial encroachment of the east pacific rise upon the trench that lay off western north america

an integrated micropalaeontological approach applied to late pleistocene holocene palaeoclimatic and palaeoenvironmental changes gaeta bay tyrrhenian sea

vegetation in western central mexico during the last 50 000 years modern analogs and climate in the zacapu basin the late glacial and the transition towards the holocene marked a period of significant environmental change at a global scale in western central mexico few records span beyond the holocene and little is known about pleistocene climatic and environmental variability here we report on the pollen record of a composite sequence made of three cores that cover the last 50 ka thousands of calibrated radiocarbon years before present in the zacapu basin western central mexico 1970 m asl the conjunction of modern pollen rain from the area with the composite fossil pollen sequence from cores cantabria cantabria 1 and cemca point 1 provided a detailed history of the vegetation of the area recognition of modern environmental patterns through individual modern pollen taxa proved difficult but multivariate analysis separated different vegetation types no modern analog communities relative to the modern vegetation cover of the area were evident especially during periods of drought apparently summer precipitation was significant before 40 ka and after the deglaciation however this moisture source declined from 40 to 10 ka because tradewinds from the gulf of mexico were blocked by the eastern mountains of central mexico as a result of lower temperatures by contrast westerly and northerly winds were enhanced by maximum ice cover from 19 to 17 ka providing abundant winter precipitation and therefore preventing extreme drought in the area copyright 2012 john wiley sons ltd

depth profiles of δ13c in bottom water and core top c wuellerstorfi on the ontong java plateau and emperor seamounts we have measured the carbon isotopic composition of dissolved inorganic carbon in bottom waters of the ontong java plateau western equatorial pacific and on the northern emperor seamounts northwest pacific each of these locations is several hundred miles from the nearest geochemical ocean sections study geosecs stations and the observed 13c values at each site differ substantially from regionally averaged geosecs 13c profiles we discuss the possible causes of these differences including horizontal variability near bottom effects and problems with the pacific geosecs 13c data we also measured the isotopic composition c and o of core top c wuellerstorfi from a depth transect of cores at each location the 18o data are used to verify that our samples are holocene comparison of foraminiferal and bottom water 13c values shows that this species faithfully records bottom water 13c at both sites and demonstrates that there is no depth related artifact in the dissolved inorganic carbon c wuellerstorfi 13c relationship at these sites

closure of the isthmus of panama the near shore marine record of costa rica and western panama the final closure of the isthmus of panama at 3 5 ma divided the american tropical ocean into two separate and different oceanographic regions consequences for the marine biota were profound but hitherto correlation of the pacific and caribbean coastal sections has not been precise enough to track biologic patterns we present here a correlation of 31 sections from the pacific and caribbean coasts of costa rica and western panama using calcareous nannofossils and planktonic foraminifera at both the tops and bottoms of each formation we estimate that the caribbean section ranges from 8 2 ma to 1 7 ma and the pacific sequence from 3 6 ma to 1 7 ma these intervals bracket postulated dates for final closure of the isthmus and provide the first well dated record of middle and late pliocene faunas from the region the caribbean and pacific sections include very different environments of deposition yet there is sufficient overlap and diversity of habitats to permit meaningful biological comparisons on the caribbean side formations tied together by the overlap of the upper pliocene markers sphenolithus abies and pseudoemiliana lacunosa 3 5 ma to 3 6 ma range from very shallow to shallow inner shelf 200 m and upper slope 200 800 m the pacific coast sections were mostly deposited in a trench slope environment which is absent on the caribbean side these sections fortuitously include abundant thick intra formational slumps containing shallow water fauna more appropriate for biological comparison with the caribbean biota similarly the 1 9 ma to 1 5 ma interval well constrained by various taxa includes middle to outer shelf and inner shelf to upper slope deposits on the caribbean side and marginal marine to inner shelf deposits on the pacific coast using our new biostratigraphic framework to correlate previously poorly constrained mollusc collections we show that evolutionary divergence of the pacific and caribbean near shore marine faunas had occurred by 3 5 ma this strongly suggests that the isthmus was effectively closed by this time

simulating late pliocene northern hemisphere climate with the lln 2 d model deep sea sediment records suggest northern hemisphere glaciation intensified at approximately 2 75 ma in this paper we simulate the fluctuations of the late pliocene northern hemisphere ice sheets volume using the lln 2 d model forced by the astronomically derived insolation and by scenarios of co2 concentrations the model simulates the waxing and waning of the northern hemisphere ice volume in an acceptable agreement with geological reconstructions and in particular supports the geological evidence that the development of significant northern hemisphere ice sheets started between 2 75 and 2 55 ma a time interval accompanied by quite high and stable eccentricity values and increased obliquity amplitude when the co2 concentration is lower than a threshold value the milankovitch forcing explains the suddenness and specific timing of this entrance into the ice age during the late pliocene

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

tethyan cenomanian pelagic rhythmic sedimentation and pleistocene mediterranean sapropels is the biotic signal comparable a comparison between the biotic signal recorded in the tethyan cenomanian black shales and in the mediterranean pleistocene sapropels is proposed here to this end the antruiles section northeastern dolomites italy has been investigated as a reference section for the cenomanian black shales the data obtained based on calcareous nannofossils and foraminifera have been compared to those from a core in the mediterranean sea containing a complete succession of late pleistocene holocene sapropels our study suggests that deposition of black shales like sapropels occurred when the water column was stratified as implied by increased abundance of the cenomanian deeper dwellers rotalipora cushmani and r greenhornensis the superficial subsuperficial opportunist form heterohelix reussi which strongly increases in numbers within the black shales could be analogous to the modern surface dweller globigerinoides ruber which is abundant in late pleistocene holocene mediterranean sapropels the peaks of g ruber can be related to decreased salinity in surface water thus the increase of h reussi could also be related to a freshwater superficial layer we hypothesise also that an increase in abundance of watznaueria barnesae reflects conditions of superficial low salinity in black shales increases in abundance of dicarinella algeriana and praeglobotruncana gibba by analogy to modern neogloboquadrina dutertrei could reflect availability of food restricted to subsuperficial waters however a cretaceus equivalent of the pleistocene nannoplankton form florisphaera profunda which proliferates within the deep chlorophyll maximum is not observed in addition the abundance of h reussi indicates a well expanded oxygen minimum zone although less in extent than in pleistocene sapropels as shown by the occurrence within the cenomanian black shales of a benthic fauna even though reduced in size and impoverished spectral analysis applied to calcareous nannofossils identifies close relations with the milankovitch precession and eccentricity cycles in both the black shales and the sapropels

quaternary intra arc extension in the central trans mexican volcanic belt the trans mexican volcanic belt is an active volcanic arc related to subduction along the middle america trench and characterized by shallow seismicity and synvolcanic to postvolcanic extensional arc parallel faulting major intra arc basins within the central part of the belt between long 998w and 1028w are from west to east the cuitzeo and acambay grabens the aljibes half graben and the mezquital graben in this region 100 eastwest2striking 2 km long steeply dipping normal faults expressed by pronounced multi event fault scarps have been mapped of the 100 faults 65 displace rocks of known quaternary age younger than 1 6 ma and 22 cut rocks with a documented age younger than 750 ka known historical surface ruptures are limited to faults of the acambay graben overall the faults cause north south to north northwest2south southeast2oriented extension of 1 km which is distributed over a 30250 km wide zone that has 5210 faults in cross section and a relative extension of 3 quaternary vertical slip rates estimated for 13 of the faults have a mean of 0 07 mm yr they are highest at the southern margin of the cuitzeo graben the northern margin of the acambay graben and in the aljibes half graben where they measure between 0 16 and 0 18 mm yr the north south to north northwest2south southeast2oriented quaternary bulk extension rate of the system is likely to be 0 2 6 0 05 mm yr this fault system is in an initial stage of coalescence its western and eastern parts consist mostly of isolated fault segments whereas in the central part deformation is localized onto a few through going faults the longest of these are the venta de bravo fault 45 km and the acambay tixmadeje fault 34 km the short fault traces have a simple structure whereas the longer ones are commonly composed of two or more segments there is no obvious migratory pattern of quaternary fault activity which suggests that the entire region is tectonically active

limnologic history of lago de patzcuaro michoacan mexico for the past 48 000 years impacts of climate and man abstract lago de patzcuaro lies at an elevation of 2035 m 19 36 n 101 39 w on the west part of the volcanic meseta central of mexico about 50 km east southeast of morelia pollen diatom and geochemical records from a 15 m core taken in 6 m of water continuously track vegetation and limnological changes in the patzcuaro basin for the past 48 ky calendar years pine oak and alder pollen dominate both the wisconsin and holocene vegetation record and indicate that this region did not witness strongly arid climates during that time before the holocene juniperus type and artemisia pollen document cooler climates of more effective moisture at least seasonally isoetes characterizes the full and late glacial interval 25 13 ka and implies along with the diatoms aulacoseira and stephanodiscus cool deep freshwater conditions at lago de patzcuaro the freshest and deepest lacustrine phase in the lake occurred 38 to 25 ka during this time lago de patzcuaro may have drained into the lerma river system between 30 and 10 ka diatom species that bloom in the winter and early spring imply moisture during those seasons evaluation of contemporaneous marine and terrestrial records west and east of lago de patzcuaro suggests that this moisture probably originated from westerly storm tracks shifted south by the laurentide ice sheet after 10 ka lago de patzcuaro became shallower and more eutrophic rooted aquatic plants prospered under a climate regime of negative hydrologic budgets increased seasonality and moisture arriving during the summer as it does today the lake became alkaline enough by the mid holocene to deposit ostracode rich marls at the core site for the first time in the past 48 ky indigenous agriculture in the patzcuaro drainage and around the lake appears about 4 ka with the appearance of zea and chenopodiineae pollen iron and potassium track increased soil erosion and planktic diatoms cyclostephanos record nutrients flushed into the lake from the drainage basin

a δ13c record of upper north atlantic deep water during the past 2 6 million years benthic foraminiferal 813c data from site 502 in the caribbean sea sill depth 1800 m indicate that throughout the past 2 6 m y glacial 8 3c values in the middepth atlantic were higher during glaciations than interglaciations this is interpreted as indicating a greater proportion of upper north atlantic deep water unadw relative to southern source waters during glaciations the contribution of unadw during interglaciations to the middepth atlantic remained approximately constant and the contribution during glaciations may have been as much as 10 higher in the late pleistocene than in the late pliocene this small increase is in striking contrast to the much larger decrease in glacial lower north atlantic deep water lnadw contribution relative to southern sources from about 80 to about 20 that occurred over the past 2 6 m y glacial intensification over the past 2 6 m y was probably coupled with a decrease in northward heat transport by the upper limb of the north atlantic circulation cell as was previously suggested on the basis of a lnadw record alone late pleistocene 1 ma present 813c values in the caribbean sea were approximately 0 2 0 higher than they were from 2 6 to 2 0 ma the 813c rise is not due to an increase in the mean ocean 8 3c value nor can it be entirely attributed to an increase in the proportion of high 8 3c source waters an increase in the 813c value of the surface source waters must have contributed to the 8 3c rise

a bloat and float taphonomic model best explains the upside down preservation of ankylosaurs abstract it is widely held that within the cretaceous fluvial and marine deposits of north america ankylosaur remains are typically preserved upside down however this anecdotal observation has yet to be substantiated likewise none of the various hypotheses that purport to explain the frequent occurrence of overturned ankylosaurs has been tested either this study is the first to apply quantitative and modeling approaches to address these shortcomings we find strong statistical support for the dominance of upside down occurrences and favour a bloat and float model to account for them according to this model ankylosaur carcasses become reworked into fluvial or marine settings where they bloat and overturn prior to their final deposition differential floating behaviour between ankylosaurids and nodosaurids may have implications regarding the occurrence of the latter in marine depositional environments this consideration of ankylosaur taphonomy might similarly help to explain the purported frequency of overturned glyptodonts which share a similar bauplan with ankylosaurs

neogene diatoms of cuitzeo lake central sector of the trans mexican volcanic belt and their relationship with the volcano tectonic evolution lake cuitzeo within the central sector of the trans mexican volcanic belt forms part of a series of palaeolakes of tectonic origin limited by e w or ne sw trending major faults the lake basin itself is subdivided into half grabens where the blocks are tilted southward this tectonic disposition results in a series of sedimentary environments such as terrigenous facies near step faults that have an influence on the lake hydrology and therefore on sedimentary and biogenic facies associations in outcrops of palaeolake cuitzeo the deposits are formed by three members that correspond to three well marked cycles of sedimentation the basal predominantly formed by clays a diatom rich intermediate one and an upper one formed by silts and pyroclastic deposits that close the limnic cycle two interruptions are observed within the lacustrine development the first associated with an oxidized horizon and the second with an erosional conglomerate of tectonic origin a marker diatom species for the miocene pliocene boundary thalassiosira cuitzeonensis nov sp was found that enables differentiation of the most ancient sequences from the most recent ones

long lived magmatic phases at los azufres volcanic center mexico abstract the los azufres volcanic complex has had a long eruptive history of 1 5 myr or more less than 3 myr subsequent to the building of a large miocene and pliocene andesitic complex since about 1 5 ma its development consists of two main periods of volcanic activity the first period from 1 5 to 0 8 ma has two magmatic cycles about 200 000 years in duration characterized by acidic followed basaltic volcanism such a magmatic evolution suggests successive emptyings of a shallow reservoir in which differentiation previously occurred about 0 6 ma major deep magma supplies were probably responsible for the resurgent doming which led to uplift of the southern part of the caldera from 0 6 ma to present the second period exposes volcanic products grading from basalts to rhyolites considering the recent age of the last ignimbrites 26 000 to 29 000 years one can assume that the volcanic activity related to a voluminous differentiated magma body at shallow depth has not yet ended especially in the southern area in and around the resurgent zone occupied by the geothermal field

geochronology of hemphillian blancan aged strata guanajuato mexico and implications for timing of the great american biotic interchange abstract we present new geochronologic magnetostratigraphy fission track and 40ar 39ar radioisotopic dates biostratigraphy data constraining the age of three separate sequences and a composite section from guanajuato mexico those data make this one of the most complete and precisely age calibrated sequences in north america spanning the hemphillian blancan north american land mammal age nalma boundary interval and the data further constrain the timing and pattern of the great american biotic interchange gabi in total 196 samples 77 sites were used to construct the magnetic polarity stratigraphies with eight fission track analyses and four new 40ar 39ar radioisotopic dates the sections sampled are possibly latest miocene to late pliocene in age spanning about 2 7 m yr 5 5 2 7 ma from chrons c3n 4n or c3r to c2an 1n the radioisotopic dates and magnetostratigraphic correlations indicate the hemphillian blancan nalma boundary at guanajuato in central mexico is 4 7 4 8 ma and it pro

astronomic timescale for the pliocene atlantic δ18o and dust flux records of ocean drilling program site 659 high resolution benthic oxygen isotope and dust flux records from ocean drilling program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the atlantic from 2 85 ma back to 5 ma spectral analysis of the 18o record indicates that the 41 kyr period of earth s orbital obliquity dominates the pliocene record this is shown to be true regardless of fundamental changes in the earth s climate during the pliocene however the cycles of sahelian aridity fluctuations indicate a shift in spectral character near 3 ma from the early pliocene to 3 ma the periodicities were dominantly precessional 19 and 23 kyr and remained strong until 1 5 ma subsequent to 3 ma the variance at the obliquity period 41 kyr increased the timescale tuned to precession suggests that the pliocene was longer than previously estimated by more than 0 5 m y

missing history 16 71 ma of the galapagos hotspot implications for the tectonic and biological evolution of the americas we present the results of volcanological geochemical and geochronological studies of volcanic rocks from malpelo island on the nazca plate 15 8 17 3 ma belonging to the gala pagos hotspot tracks and igneous complexes 20 8 71 3 ma along the pacific margin of costa rica and panama the igneous complexes consist of accreted portions of ocean island and seamount volcanoes and aseismic ridges representing the missing primarily subducted history of the gala pagos hotspot the age and geochemical data directly link the gala pagos hotspot tracks on the pacific ocean floor to the caribbean large igneous province ca 72 95 ma confirming a pacific origin for the caribbean oceanic plateau from the gala pagos hotspot we propose that emplacement of this oceanic plateau between the americas and interaction of the gala pagos hotspot tracks with the central american arc played a fundamental role in the formation of land bridges between the americas in late cretaceous paleocene and pliocene holocene time the land bridges allowed the exchange of terrestrial faunas e g dinosaurs mastodons saber tooth cats and ground sloths between the americas and served as barriers for the exchange of marine organisms between the central pacific ocean and the caribbean sea and the central atlantic ocean

calcareous nannofossils planktonic foraminifera and oxygen isotopes in the late quaternary sapropels of the ionian sea core m 25 4 12 a long piston core 12 20 m recovered in the ionian sea during cruise m25 4 of the r v meteor summer 1993 at a water depth of 2467 m shows an almost complete sequence of sapropels s 1 s 3 to s 10 over the last 330 ka this paper presents the results of an integrated study based on quantitative biostratigraphic analyses performed on both calcareous nannofossils and planktonic foraminifera coupled with the 18o record a decrease in syracosphaera sp 1 and an increase in the abundance of the genus rhabdosphaera and of helicosphaera carteri florisphaera profunda and of the reworked specimens has been found in the calcareous nannofossil assemblage within the sapropels the planktonic foraminiferal assemblage of the sapropels is characterized by a peak in the frequency of globigerinoides ruber var alba and rosea and neogloboquadrina dutertrei the 18o record of globigerinoides ruber and globigerina bulloides allows recognition of isotope stages 1 to 9 and shows a negative fluctuation that corresponds to the sapropel layers these features support the idea of increased productivity coupled to the presence of reduced salinity surface waters that caused the deposition of the sapropels however the need for a good understanding of the ecological requirements of modern assemblages is stressed this is necessary to correctly interpret fossil assemblages this in turn will allow a better understanding of the palaeoceanographic conditions leading to sapropel deposition

the last 100 000 years in the western mediterranean sea surface water and frontal dynamics as revealed by coccolithophores a quantitative analysis was carried out on coccolith assemblages from two pleistocene cores k1 and k10 from the western mediterranean the distribution of selected coccolithophore species provides new paleoclimatic and paleoceano graphic data a continuous sequence from the top of isotope stage 5 to the holocene was recorded the reversal in dominance between gephyrocapsa muellerae and emiliania huxleyi was dated in both cores at ca 73 ka at about 47 ka e huxleyi shows a regular increase whereas g muellerae progressively decreases in abundance during interglacial periods high concentrations of coccoliths are observed whereas in glacial times coccoliths are more diluted and the percentage of reworked forms increases as a consequence of the higher terrigenous input after taking careful account of the dilution factor we conclude that the production of coccolithophores was higher during warm periods maxima in coccolith concentrations coincide with highstand episodes probably as a result of the intensification of the atlantic flux into the mediterranean across the gibraltar strait this intensification could have produced an increase in nutrient content in the surface mediterranean waters during cold periods the western mediterranean front underwent a reduction in activity probably due to an increase in the saline and or thermal gradients between the superficial waters and intermediate waters in the liguro provencal basin

are productivity and stratification important to sapropel deposition microfossil evidence from late pliocene insolation cycle 180 at vrica calabria we present the results of a micropaleontological study performed on the sapropel sequence associated with insolation cycle 180 from the plio pleistocene vrica sequence calabria italy we performed a high resolution study on the 3 38 m thick layer c from a core drilled close to the classical outcrop section in which we analyze fluctuations in the abundance and composition of calcareous nannofossils and planktic and benthic foraminifera changes in the fossil assemblages reveal at least three major paleoenvironmental phases in layer c the base of the sapropel contains an abrupt decrease in benthic fauna that continues through all of layer c it also has an increase of the coccolithophorids species coccolithus pelagicus planktic foraminifera show at the same depth a peak of the cold species globorotalia scitula these changes are followed by decreases in the carbonate preservation index and in abundances of globigerinita glutinata globigerinita uvula and neogloboquadrina pachyderma sinistral which suggest cold and highly productive upwelling waters a short interval in the middle of the sapropel is characterized by low values of c pelagicus a fluctuating increase of pseudoemiliania lacunosa and among the foraminifera an increase of globigerinoides ruber together with the presence although decreased of g glutinata g uvula and n pachyderma sinistral we interpret these features as suggesting high seasonality with warm stratified and probably oligotrophic waters during summer and relatively cold conditions during winter finally the topmost interval of the vrica layer c exhibits the re appearance of p lacunosa together with abundant siliceous phytoplankton planktic microfauna show the disappearance of the cold species g glutinata g uvula and n pachyderma sinistral thus this interval appears to be characterized by warmer temperature the transition from the laminated to the massive sediment displays a sequence of events including a decrease of the carbonate preservation index and peaks of globorotalia inflata and g scitula suggesting again upwelling and mixing of the whole water column and thus transition to the oxygenated conditions characterizing the massive layer neither increased productivity nor stratification appear to characterize the whole sapropel interval which is however always dysoxic

coccolithus pelagicus a productivity proxy related to moderate fronts off western iberia abstract the traditional interpretation of coccolithus pelagicus as a cold water proxy is examined based on its distribution patterns in the water column off the portuguese coast using data from eleven cruises and in holocene surface sediment samples and quaternary cores from the same region coccolithus pelagicus is common in the portuguese upwelling system an area where surface waters are predominantly of subtropical origin although revealing an affinity for low temperature upwelled waters the species was found in waters up to 18 c associated with riverine plume and shelf break fronts c pelagicus seemed to consistently occupy a particular ecological niche between other phytoplankton groups related to moderate turbulence conditions combined with nutrient availability from this behaviour it is proposed that c pelagicus can be used as a tracer of the periphery of areas of enhanced productivity coccolithus pelagicus preferences for fronts of moderate temperature and salinity gradients are tentatively used to explain particular features of its sedimentary record the repeated increase of c pelagicus in thanatocoenoses surface sediment assemblages close to three river mouths on the portuguese shelf are interpreted as a positive response to the development of riverine plumes on the other hand inconsistencies in the correlation between sea surface cooler glacial and warmer interglacial isotope stages and the relative abundance pattern of c pelagicus during the late quaternary as registered in two galicia bank piston cores 42 n are tentatively explained in terms of shifts in the extent of the outer limit of the local palaeoproductivity belt off the iberian peninsula

djadokhta formation correlative strata in chinese inner mongolia an overview of the stratigraphy sedimentary geology and paleontology and comparisons with the type locality in the pre altai gobi because the bayan mandahu redbeds of inner mongolia share similar sedimentary facies and fossil assemblages with the djadokhta formation of pre altai gobi the two units are interpreted as stratigr

extraordinary preservation in a new vertebrate assemblage from the late cretaceous of mongolia we report here a new locality ukhaa tolgod brown hills from the upper cretaceous of the gobi desert of mongolia which shows an unmatched abundance of well preserved vertebrate fossils including the highest concentration of mammalian skulls and skeletons from any mesozoic site in the main collecting area about 4 km2 recovered and uncollected articulated skeletons of thero pod ankylosaurian and protoceratopsian dinosaurs represent over 100 individuals specimens collected also include skulls many with associated skeletons of over 400 mammals and lizards skeletons including the first known skull of the bird mononykus and nest sites that preserve the first known theropod dinosaur embryos1 in contrast to other mesozoic localities the diversity and abundance of theropods mammals and lizards are unusually high the exceptional preservation of vertebrates from the red bed facies of the gobi upper cretaceous has been attributed to arid conditions2 4 possibly involving catastrophic death and burial during major sandstorms5 although fossils are found in fluvial facies at ukhaa tolgod high concentrations of excellent specimens in aeolian facies support the argument for rapid entombment in sand this contrasts with conditions for the terrestrial upper cretaceous in north and south america where accretionary preservation of fossils in fluvial deposits predominates

distribution des kystes de dinoflagelles dans les sediments pleistocenes de la marge guineenne de l afrique equamarge i 1983 abstract in sediments from core ks 03 from the guinean margin west coast of africa it is possible to distinguish two groups of dinoflagellate cysts serving as indicators of change of temperature a group of warm to temperate species including impagidinium paradoxum impagidinium strialatum impagidinium aculeatum and impagidinium patulum and a group of cold to temperate species including operculodinium centrocarpum nematosphaeropsis labyrinthae and spiniferites mirabilis the ratio of the relative abundances of the two groups indicates the ecological nature of the water masses which have migrated in the north atlantic during the pleistocene the curve of the ratio of warm temperate species to cold temperate species shows a high similarity to the 18o curve from the tests of benthic foraminifers a high percentage of operculodinium centracarpum among the cold temperate species reveals not only the presence of subpolar water masses but also the importance of the north atlantic current along the west coast of africa the reworked and transported species from the coastal zone give evidence of the characters of the guinean littoral environment this being determined by the moisture and the aridity of the climate lingulodinium machaerophorum grows in waters rich in nutrients with normal salinity polysphaeridium zoharyi prefers highly saline waters and indicate the beginning of aridity operculodinium israelianum is abundant in restricted environments containing high percentages of organic matter core ks 03 corresponds to the interval of time between 800 000 and 122 000 yr b p during the glacial stages stages 20 and 18 the water masses with planktonic assemblages of transitional subtropical character associated with spiniferites mirabilis come close to the guinean coast as during the last glacial stage and produce an intense aridity on the continent at that period the influence of subpolar water masses and of the north atlantic current characterised by operculodinium centrocarpum can be perceived on the west african margin aridity tends to regress at the end of stage 16 the tropical water masses remained preponderant even during glacial stages restricted humid environments with operculodinium israelianum extended along the coast after stage 11 transitional to subtropical waters extended down again along the african coast but the glacial stages were less cold and less arid

palaeoenvironmental significance of diatom and vertebrate fossils from late cenozoic tectonic basins in west central mexico a review abstract pronounced lacustrine sedimentation developed in west central mexico during the late miocene between approximately 11 and 7 ma this was in response to tectonic extension associated with the initial emplacement of the late miocene substrata of the trans mexican volcanic belt climatic conditions in west central mexico during this interval were relatively warm and humid based on the widespread distribution of interpreted lacustrine beds following a latest miocene 8 0 5 4 ma stage of arid conditions and greatly reduced deposition of fine grained lacustrine sediments extensive east west oriented relatively deep perennial lakes ensued they mark the early pliocene 5 3 4 0 ma lower pliocene diatomites contain the same diatom species e g stephanodiscus carconensis and tertiarius aff baikalensis found in rocks of this age in the western united states the relatively warm and humid conditions that characterized this interval in central mexico coincide with a period of high latitude warming higher global sea level and a reduction in size of the antarctic ice sheets because the central american seaway persisted until at least the latest miocene it might have acted to increase precipitation in central mexico this could have continued into the earliest pliocene mexican pliocene mammalian faunas also support a savanna setting with moist and warm conditions prevailing at the time shallow lakes and fluvial conditions dominate after 4 0 ma until the end of pleistocene a combination of reduced precipitation due to general global cooling and drying as well as volcanic and tectonic processes are presumed to have been the cause for this mid pliocene reduction in lake size and extent in central mexico

lacustrine record in a volcanic intra arc setting the evolution of the late neogene cuitzeo basin system central western mexico michoacan abstract late miocene to quaternary lacustrine and alluvial lacustrine sequences were deposited in the charo morelia sub basin to the south of the recent cuitzeo lacustrine depocentre central western mexico where deposition was largely controlled by widespread faulting and block tilting moreover pyroclastic and epiclastic deposits occur throughout the terrigenous and biogenic sequence which indicates intense synchronous volcanic activity directly linked to the faulting the charo alluvial lacustrine sequences crop out extensively to the south of the present cuitzeo lake and their exposures record the development and spreading of late miocene and pliocene alluvial lacustrine zones the resulting sequences are up to 40 m thick and record four major evolutionary stages related with specific tectonic and volcanic events which caused changes in the basin morphometry and the palaeodrainage conditions the first of these stages late miocene caused the generation of small ne sw oriented shallow lacustrine and swampy zones which resulted from the activity of strike slip faults with the same orientation alluvial deposits and shallow lacustrine diatomaceous horizons were deposited during this stage the second stage early pliocene gave rise to the formation of ne sw trending basins related to the extensional reactivation of the earlier ne sw strike slip faults within this second stage the charo morelia lacustrine depocentre became a larger deeper tropical lake the planktonic and planktonic facultative lacustrine diatom floral assemblages record the development during this stage of a major lake transgression which could be caused both by wetter climate and tectonic watershed and drainage rearrangement the third and fourth stages quaternary were related to widespread block tilting processes which were linked to the generation of e w oriented extensional faults and which resulted in the shifting and restriction of the larger perennial steadier lacustrine zones to the present cuitzeo lake to the south of this lake the sedimentary record of this stage started with widespread fluvial sequences which erosively overlaid the diatomitic deposits the lacustrine zones developed during this alluvial dominated stage were restricted to small depressions and consisted of small lakes and pond related environments which were fed by ephemeral fluvial currents these minor water bodies were infilled and overlain by acidic pyroclastic fall deposits developed during a major volcanic episode which affected the charo morelia sub basin fourth stage the cuitzeo and other ancient to recent lacustrine systems i e chapala lake evolved in the trans mexican volcanic belt as a result of its tectono volcanic evolution which largely influenced the highly sensitive lacustrine systems therefore the analysis of the development sedimentary evolution and shifting of the lacustrine zones may help us to understand the structural evolution of the central mexican igneous arc complex and the ongoing processes developed along the related major subduction zone which is oblique to the middle american trench in the pacific margin

freshwater diatom influx in intertropical atlantic relationships with continental records from africa diatom assemblages from modern west african rivers and from lacustrine sediments subjected to deflation represent the present day sources of continental diatoms to the sea diatom productivity in large rivers is high especially for the genus melosira windblown diatoms derive mainly from the central and northern sahara summer dust plume where saline chloride water assemblages are widespread or from the southern edge of the sahara winter dust plume where melosira rich assemblages of dilute water predominate freshwater diatom peaks in atlantic cores may reflect 1 phases of increased river influx correlated with humid episodes on the continent or 2 phases of enhanced deflation and wind transport during arid episodes the single hypothesis for fine sediments from mid ocean sites genus melosira dominates the freshwater assemblages of many modern and fossil marine samples whatever the transport agent is therefore it is not an accurate paleoclimate indicator by itself but associated taxa may provide information on the environmental and geographical origin of the displaced diatoms this tentative approach shows that freshwater diatoms in atlantic cores may be a good tool for reconstructing paleoclimates and for establishing continent ocean correlations if species analyses are made and if the continental distribution of the taxa encountered is considered

neogene stratigraphy paleoceanography and paleobiogeography in northwest south america and the evolution of the panama seaway abstract the atrato basin in the pacific coastal region of nw south america colombia exhibits stratigraphic and biostratigraphic characteristics similar to other neogene pacific coastal basins of southern central america and northern south america an evaluation of the neogene stratigraphy and foraminiferal biostratigraphy with emphasis on paleoceanographic and paleobiogeographic phenomena indicate the following 1 previous to the middle miocene well aerated deep and open oceanic conditions and free and active water circulation prevailed along the steep continental margins of nw south america 2 during the early middle miocene right after the neogene hiatus nh 2 15 2 ma tectonic disturbances triggered the initial uplift of the panama sill bottom water circulation foraminiferal and sedimentation changes are observed in both the pacific and caribbean coastal areas of nw south america 3 during the middle miocene coinciding with the neogene hiatus nh 3 12 9 11 8 ma an abrupt paleobathymetric change from lower to middle bathyal depths indicates a major uplift of the panama sill to about 1000 m reflecting the middle miocene tectonic disturbances in nw south america 4 during the late middle miocene immediately following this uplift a distinctive pacific benthic foraminiferal fauna abruptly appeared and extended from ecuador to california because these assemblages do not occur in the adjacent caribbean region a circulation barrier between the atlantic and pacific oceans as a result of intensification of the cool marginal california current is proposed anoxic middle to upper bathyal environments prevailed under well aerated cool surface waters in the pacific coastal areas of nw south america 5 during the latest miocene immediately following the neogene hiatus nh 6 7 0 6 3 ma surface water circulation between the caribbean and the pacific was re established and the previous influence of the california current disappeared a rapid filling and shallowing of the basin to mostly neritic depths is indicated along the pacific and caribbean coastal basins of colombia as well as a progressive increase in similarity between the coastal pacific and caribbean benthic biotas this shallowing in the early late miocene also appears to have been associated with the earliest terrestrial interchange of ground sloths to north america and raccoons and their allies to south america 6 immediately following early pliocene time the panamanian isthmus became completely emergent providing a terrestrial environment favourable for intermingling of terrestrial faunas and floras between north and south america i correlate this pliocene uplift with the neogene hiatus nh 8 3 7 3 1 ma four regional unconformities associated with tectonic disturbances in the nw corner of south america have also been recognized and correlated with neogene hiatuses recorded from the oceans early middle miocene middle miocene late miocene and early pliocene

paleoseismology of the 1912 acambay earthquake and the acambay tixmadeje fault trans mexican volcanic belt the acambay graben is a major intra arc basin of the trans mexican volcanic belt trenching studies at four sites along the acambay tixmadeje fault reveal evidence for the 1912 acambay earthquake and at least four late pleistocene and holocene ground rupturing earthquakes with similar displacements to the 1912 event evidence for multiple events was recognized by a combination of upward terminating faults fissure fills erosionally truncated fissures colluvial wedge fills and downward increasing separation of stratigraphic units sites along the central part of the ese wnw trending rangefront fault indicates large dip slip separations across a multi event scarp in holocene colluvium with a penultimate event that occurred since 5230 calibrated years before present cal yr b p on the huapango plain near the eastern end of the 1912 rupture where slip was oblique the penultimate earthquake occurred after 4700 cal yr b p and there is evidence for at least four more earthquakes in the last 34 000 cal yr b p three dimensional excavation of lacustrine and channel deposits at las lomas yields a left normal slip vector of s40 5 e with 105 10 cm of slip for the last three events there this slip vector is consistent with nne oriented extension across the graben the amount and style of slip documented for prehistoric ruptures are also consistent with the 1912 rupture with a mean of 60 cm event of dip slip on the rangefront and a mean of 35 cm event of oblique slip on the n48 w trending huapango plain assuming these values represent a characteristic behavior yields an average recurrence interval of 3600 years for the last four large earthquakes since 11 570 cal yr b p and a slip rate of 0 17 mm yr across the rangefront empirical earthquake parameters calculated from our paleoseismic data support instrumental measures indicating that the 1912 acambay earthquake was of m 6 8 7 0 the 1912 event is representative of ground rupturing earthquakes on the acambay tixmadeje fault and demonstrates that large seismic events m 7 can be generated by faults in the trans mexican volcanic belt and in other intra arc settings

skeletal reconstruction and life restoration of sauropelta ankylosauria nodosauridae from the cretaceous of north america a skeletal reconstruction and life restoration are presented for the early cretaceous nodosaurid ankylosaur sauropelta edwardsi this composite is based on several partial skeletons having armor preserved in situ from the lower cretaceous cloverly formation of wyoming and montana comparison of foot morphology with that of the ichnofossil tetrapodosaurus borealis from the lower cretaceous gething formation of british columbia suggests that the footprint is that of sauropelta a hypothesis is presented suggesting that most ankylosaurs are found on their backs because of bloating

pronounced mid pleistocene southward shift of the polar front in the atlantic sector of the southern ocean abstract ocean drilling program odp site 1094 situated in the atlantic sector of the antarctic region below the polar front pf is dominated by silica rich sediments during the pleistocene but does contain occasional calcium carbonate rich intervals the analysis of the coccolithophore assemblages of one of these intervals in the mid pleistocene allows us to interpret a prominent southward displacement of the pf an age model constructed using paleomagnetic and biostratigraphic information places this event around 1 ma close to the jaramillo subchron in an interval of strong eccentricity and high amplitude in the insolation record we distinguish five intervals based on coccolithophore assemblage and abundances according to the age model used this calcium carbonate rich period should include marine isotope stage 31 the most significant interglacial period recorded at this time however this model cannot decipher if adjacent isotope stages are partially represented interval v the oldest is interpreted as an episode with progressive abundance of coccolithophores with a characteristic assemblage from the polar front zone pfz but with dominance of siliceous micro organisms interval iv contains the maximum abundance of coccolithophores with an assemblage characteristic of the subantarctic zone saz with peaks in abundance of calcidiscus leptoporus coccolithus pelagicus helicosphaera carteri and syracosphaera spp related with the proximity of the subantarctic front saf the southward displacement of the frontal system linked to an increase in sea surface temperature produced increases in diversity and in productivity conversely we consider that the presence of some coccolithophore taxa linked in other environments with anomalies in salinity could reflect a pulse in the melting of west antarctic ice sheet as suggested previously for this interval interval iii is characterized by a pfz assemblage reflecting again a northward shift of the pf interval ii is considered in this context as another southward pulse but less important than interval iv and with the absence of saf and or melting related taxa interval i is considered a transition from a situation similar to the present day pfz to the antarctic zone conditions as consequence of a northward displacement of pf and weddell gyre antarctic circumpolar current boundary

ankylosaurian tail clubs of middle campanian to early maastrichtian age from western north america with description of a tiny club from alberta and discussion of tail orientation and tail club function there are numerous undescribed tail clubs of diverse morphologies that may be assigned to euoplocephalus ornithischia thyreophora ankylosauridae of middle campanian to early maastrichtian age among these is an exceptionally small club the smallest so far described from north america most but not all clubs can be placed into one of three shape categories round bluntly pointed or elongate much of this diversity is ontogenetic or individual but some of it may be taxonomic caudal structure restricts lateral and especially vertical tail flexibility analysis of hindlimb length tail length and downward angle of the tail from the hips suggests that the tail was normally carried and swung just above the ground and was used primarily defensively for striking at the metatarsals of an attacking theropod intraspecific agonistic functions are possible but improbable

the late miocene panama isthmian strait miocene sediments of the caribbean gatun and chagres formations panama canal basin were deposited within an archipelagic strait that connected caribbean and pacific waters shallow water 25 m benthic foraminifera of the gatun formation have a strong caribbean affinity indicating that a significant interoceanic biogeographic barrier had formed at 8 ma however benthic foraminifera of the overlying chagres formation are bathyal and markedly pacific in affinity indicating that at 6 ma waters of the panama isthmian strait deepened to 200 500 m and pacific bathyal waters flowed into the caribbean the chagres formation crops out at the caribbean entrance to the panama canal in a large wedge of cross laminated sandstone and coquina the cross laminations and coarse grain size indicate high energy currents atypical of bathyal settings we infer that a jet of the pacific north equatorial countercurrent equatorial undercurrent passed through the panama isthmian strait to deposit these sediments on the caribbean side this later entry of pacific taxa into the caribbean had no apparent effect on the subsequent composition of caribbean faunas

molecular stratigraphy of cores off northwest africa sea surface temperature history over the last 80 ka the molecular stratigraphy of biogeochemical oceanic flux study core 31k 19 n 20 10 w and ocean drilling program hole 658c 20 45 n 18 35 w has been studied for c37 alkenone abundances over the past 80 ka at high resolution circa 200 500 years the derived uk37 sea surface temperature record for both cores shows a range of temperatures from about 18 c during the last glacial to 21 5 c during the early holocene both records also reveal changes in sea surface temperature as much as 2 4 c over a few hundred years which correlate well with similar abrupt climatic changes observed in cores from elsewhere in the ne atlantic associated with heinrich events our results indicate that meltwater produced by these ice rafting events was transmitted southward by the canary current where it had considerable impact on sea surface temperatures in the subtropical eastern atlantic

millennial surface water dynamics in the ria de vigo during the last 3000 years as revealed by coccoliths and molecular biomarkers a combined study of coccolith assemblages and biomarkers in a gravity core collected from the ria de vigo nw spain allowed us to reconstruct the paleoenvironmental conditions for the last 3000 years the quantitative distribution of coccolithophore species points to three different intervals within the core dated by ams radiocarbon measurements the first interval ca 975 bc 252 ad characterized by high abundances of calcidiscus leptoporus and gephyrocapsa muellerae i s thought to represent moderate water temperatures suggesting a transition from a warmer to a cooler period the second interval ca 252 1368 ad characterized by the dominance of coccolithus pelagicus helicosphaera carteri and syracosphaera spp and a high concentration of hexacosanol linked to terrestrial input is interpreted as having been a humid period with fluvial input the third interval ca 1368 ad 1950 is characterized by a high abundance of gephyrocapsa oceanica high alkenone values and low values of hexacosanol and is thought to represent a period dominated by oceanic conditions within the ria taking into account the ocean atmospheric system affecting the region studied here we propose an alternation in the mean state of north atlantic oscillation nao at millennial time scales awell developed upwelling system and an active ria ocean connection during the warmer interval i suggest a nao phase influenced by a hypsithermal period the occurrence of the humid and relatively warm interval ii is consistent with a negative phase in the nao as well as a relative restriction in ocean ria exchange interval iii which was drier and more productive again suggests the dominance of a positive phase in the nao with a more intense oceanic connection and more energized upwelling d 2004 elsevier b v all rights reserved

control of north atlantic deep water circulation by the greenland scotland ridge coherent bathymetric features along the reykjanes ridge indicate that there were significant changes in the flux of buoyant material within the icelandic hot spot during the neogene the radial extent of the topographic swell associated with this hot spot is of the order of 1000 to 2000 km and therefore these changes affected the greenland scotland ridge gsr at present sill depths along the gsr are generally less than 500 m with the deepest passage being less than 1000 m making the overflow water sensitive to even small changes in the ridge depths reconstructions of neogene mantle plume activity correlate with the deepwater circulation patterns in the north atlantic times of high mantle plume activity caused northern component water ncw production to cease ncw fluxes resumed once this phase of high mantle plume activity slowed the long term climate change during the neogene must be controlled by factors other than ncw production however climatic optima during the late early miocene and early pliocene appear to have been augmented by high ncw fluxes while subsequent middle miocene and middle pliocene coolings correlate with uplifts on the gsr and reduced ncw flux we suggest that reductions in ncw may have contributed to both of these cooling events

geological and environmental controls on the change of eruptive style phreatomagmatic to strombolian effusive of late pleistocene el caracol tuff cone and its comparison with adjacent volcanoes around the zacapu basin michoacan mexico abstract the 28 300 year bp cal 32 300 bp el caracol tuff cone complex is one of the few phreatomagmatic volcanoes in the scoria cone dominated plio quaternary michoacan guanajuato volcanic field mgvf it displays a shallow circular crater of 1 km in diameter that is filled with several meter thick lava flows and is located between two ne sw trending normal faults dipping nw it lies directly on top of pliocene lavas of the san lorenzo shield volcano that forms part of a tectonic horst topographic high separating the zacapu lake basin 1980 m in the south from the rio angulo river valley 1760 m to the north detailed study of the tephra sequence indicates that the eruption occurred in two stages 1 weak phreatomagmatic in which about 0 1 0 5 km 3 dense rock equivalent dre of magma was issued within 1 to 3 months at the rate of 4 40 m 3 s and 2 purely magmatic strombolian effusive during which the vent shifted slightly its position toward the nw forming a small scoria cone 100 m high on the crater rim of the tuff cone from this scoria cone lava flows were issued first into the tuff cone crater occupying its bottom and subsequently toward the nw down the outer flank of the tuff cone and into the plain where they reached a distance of 3 5 km during this stage 0 6 km 3 dre of magma was produced at the rate of 4 m 3 s in a period of 5 months although el caracol displays many features that are characteristic for a phreatomagmatic vent its morphology types of deposits and its complex process of formation makes it strikingly different from the more typical case of the 21 000 year bp cal 25 300 bp alberca de guadalupe maar volcano situated not far at the se margin of the zacapu basin the latter was solely phreatomagmatic during the course of its eruption and is formed in its entirety by surge and fallout breccias consisting largely of xenolithic material in contrast at el caracol the hydrogeological environment namely the low groundwater flow gradient did not allow for sustained water magma interactions at ideal conditions ratio of 0 2 hence the system soon dried out due to insufficient groundwater flow toward the eruption site and the eruption turned purely magmatic this study shows that despite of its proximity to a large water reservoir zacapu lake basin and similarities with alberca de guadalupe maar in regard to age climate magma composition and tectonic environment several other specific parameters play a crucial role in shaping a monogenetic phreatomagmatic volcano the case of el caracol phreatomagmatic style followed by magmatic during the course of a monogenetic eruption has been reported from other volcanic fields around the globe where it might have similar causes furthermore the general scarcity of this type of volcanoes in the michoacan guanajuato volcanic field implies that the conditions required for their formation are rarely met in this region

transfer functions between diatom assemblages and surface hydrology in the southern ocean interpretation of the distribution of 31 marine diatom species and two silicoflagellate genera in 28 core tops from the atlantic and west indian sectors of the southern ocean by q mode factor analysis allows definition of three significantly different floral assemblages one associated with subantarctic and two with antarctic waters these three areas are clearly delineated by prominent oceanographic limits the antarctic convergence and the maximum retreat of sea ice during the summer season a set of palaeoecological transfer functions is derived by comparison between the distribution of these associations and surface water hydrological parameters using these equations estimated summer temperatures from core top floral assemblages range from 12 c in the north of the study area to 2 0 c near the southernmost cores the standard errors of estimate are 1 1 c for summer temperatures 1 5 months year for sea ice cover 0 2 mg atp l for sea surface phosphate concentrations numerical tests of these paleoecological equations demonstrate their usefulness to reconstruct the evolution of the surface oceanography of the austral ocean at different periods of the last climatic cycle

primary signal ecological and environmental factors report from working group 2 alkenone based proxies are routinely used for paleoceanographic and climatologic reconstructions despite the fact that their calibration to environmental parameters is still a matter of debate significant differences are observed among culture calibrations using different strains of alkenone producers between regional field calibrations within the euphotic zone and between water column and core top based calibrations the reasons for these discrepancies are not well understood and call for further evaluation the possibility is raised that several aspects of genetics physiology and ecology of alkenone producing haptophytes may be responsible and suggestions of future research are proposed

isotopic paleoceanography of the caribbean and east pacific role of panama uplift in late neogene time comparisons of carbon isotopic data on benthic foraminifera from deep sea drilling project sites 502 western caribbean and 503 eastern pacific indicate that the difference between the atlantic and the pacific in the per mil enrichment in carbon 13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago when the difference reached the modern level 1 per mil comparisons of planktonic foraminiferal oxygen isotopic data for the caribbean and the pacific suggest that the salinity of caribbean surface waters began increasing 4 million years ago possibly in response to shoaling of the panama isthmus these results suggest that modern circulation patterns in the caribbean and eastern pacific developed by 3 million years ago in concert with changing tectonic climatic and biogeographic patterns

ankylosaurian dinosaur palaeoenvironmental associations were influenced by extirpation sea level fluctuation and geodispersal abstract more species of nodosaurid ankylosaurians than ankylosaurid ankylosaurians have been found in marine sediments and some previous quantitative studies of global dinosaur occurrences provide support for an association between nodosaurids and marine depositional environments we compiled a dataset of global ankylosaurian occurrences and found that the geographic distribution of marine ankylosaurian occurrences is regionally biased with 54 of records stemming from western north america in the cretaceous a time of regional highstands in sea level and epicontinental flooding coupled with differential extirpation of ankylosaurian subclades inhabiting the western interior basin wib within the western interior basin we found little statistical support for an association between ankylosaurian subclades and palaeoenvironment in a chronological context only the albian cenomanian transgressive regressive cycle had statistical support for an overabundance of nodosaurids in marine environments compared to ankylosaurids the apparent overabundance of nodosaurids relative to ankylosaurids in marine sediments in the western interior basin overall cannot be decoupled from the extirpation of north american ankylosaurids during the cenomanian and the subsequent absence of ankylosaurids in north america during the turonian to early campanian prior to the immigration of asian ankylosaurine ankylosaurids the north american ankylosaurian record highlights the difficulty in interpreting habitat preferences in the context of a shifting seaway regional extinctions and intercontinental dispersals

skeletal and dermal armor reconstruction of euoplocephalus tutus ornithischia ankylosauridae from the late cretaceous oldman formation of alberta previously life reconstructions of ankylosaurid dinosaurs are incorrect in that they show uniformly shaped keeled plates arranged in neat longitudinal and transverse rows and large spines projecting laterally from the flanks of the body articulated armor of euoplocephalus tutus previously described as the types scolosaurus cutleri nopsca and dyoplosaurus acutosquameus parks from the late cretaceous oldman formation shows that armor shape and size varied considerably along neck back and tail an attempt is made to reconstruct the skeleton and arrangement of the dermal armor of euoplocephalus

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

history of the last deglaciation in the alboran sea western mediterranean and adjacent north atlantic as revealed by coccolith floras abstract a series of cores recovered from the alboran sea western mediterranean and the adjacent part of the north atlantic has revealed very high rates of accumulation which have enabled us to identify the stages of the last deglaciation in great detail isotopic analyses of the cores show the two steps of the deglaciation terminations 1a and 1b separated by the bolling allerod warm phase 14 c dating of the cores has allowed the dating og the climatic succession we have identified each event of the deglaciation on the basis of changes in the coccolith flora especially in species of the genus gephyrocapsa such changes reflect surface water changes since coccolith live only in the photic zone the abundance of g muellerae in the cold intervals prior to each termination is greater than that in the bolling allerod and holocene warm intervals which follow the terminations coversely g oceanica is virtually absent during cold intervals but becoms more common during the warmer periods during the first deglacial warming there is a large influx of fine grained detrital material presumably derived from increased run off from the nearby mountains of southern spain and north west africa in the alboran sea cores with the most expanded sections there is a marked increase in the percentage of syracosphaera histrica at the beginning of this increase of detritus no increase was found in the atlantic core at this time

estimation of the paleoepicentral area from the spatial gradient of deformation in lacustrine seismites tierras blancas basin mexico abstract a new methodology is introduced to estimate the most probable epicentral area for a paleoearthquake interpreted from seismites within a quaternary basin seismites were described from various detailed stratigraphic logs within the tierras blancas basin tbb a pleistocene lacustrine area located in the central part of the trans mexican volcanic belt tmvb the lacustrine landscape evolution of tbb has been determined by the recent fault activity of the morelia acambay fault system mafs the tbb is bounded by active normal faults striking e w this fault activity has generated soft sediment deformation structures sand silt and gravel dikes pillows diapirs and decametric slumps disturbing the sedimentary infilling from these seismites and their stratigraphic spatial correlation five strong moderate paleoearthquakes e1 e5 have been established in the basin the spatial distribution of these seismites exhibits a gradient of perturbation defined by the intensity of deformation three different degrees of intensity deformation ddi are associated with the liquefacted grain size sediments i silt liquefaction ii silt and sand liquefaction and iii silt sand and gravel liquefaction this spatial gradient indicates an increase of the energy involved from the seismic activity related with the proximity of the source mapping the boundaries among these zones of deformation and interpolation of each ddi limit for paleoearthquake e4 was used to construct paleoseismic isolines of deformation as a potential indicator of the most probable paleoepicentral zone a 1 5 km 2 elongate zone oriented nnw sse is the potential paleoepicentral area associated with paleoearthquake e4 within the tbb

floral and solution patterns of coccoliths in surface sediments of the north pacific coccolith assemblages from core top samples of the north pacific seafloor follow the distribution of surface water masses gephyrocapsa caribbeanica umbellosphaera tenuis and coccolithus pelagicus are the most important identifiers of surface water mass different multivariate statistical techniques group shallow samples in somewhat different spatial patterns factor analysis condenses the information contained in sixteen ies percentages to four new variables that can be interpreted as species assemblages by canonical correlation analysis these assemblages can in turn be related to the environment the first canonical correlation indicates that factor 2 the g caribbeanica assemblage is represented in samples underlying cooler surface water a second possible correlation describes a direct relationship between factor 3 the umbilicosphaera sibogae assemblage and the remaining environmental variable surface water salinity factor 1 the g oceanica assemblage and factor 4 the emiliania huxleyi assemblage are not as closely related to the selected environmental measures of temperature salinity dissolved oxygen and inorganic phosphate phosphorus as are factor 2 and factor 3 because samples were coded according to their overlying water mass group separations produced by discriminant analysis are easily interpreted in terms of the environment overlap of group assignments occurs for samples from the south china sea and extreme western pacific even partially dissolved samples retain the signature of surface water mass group assignment for those samples is generally reliable with the exception of samples from the central water mass where almost half of the shallow and half of the deep samples show strongest affinities with one of the other three water masses selective solution therefore only partially obscures the record of floral provinciality partial dissolution of coccolith assemblages does not proceed according to one systematic rank order the sequence of species removal is variable from region to region the more abundant species tend to consistently appear at an extreme of the ranking for example umbilicosphaera sibogae is among the least resistant and c leptoporus and g oceanica are among the most resistant species maximum depths of coccolith lysocline and compensation depth occur generally in the central part of the basin and shoal towards its margins as previously observed for planktonic foraminifera

surface water conditions in the mediterranean basin during earliest pliocene as revealed by calcareous nannofossil assemblages comparison between western and eastern sectors abstract the abundant and diverse calcareous nannofossil assemblages found in the sediments of two odp cores from the western site 975b south balearic basin and eastern site 969b mediterranean ridge mediterranean sea have been taken into account for the paleoenvironmental reconstruction of the surface water conditions during the first 490 kyrs immediately following the end of the messinian salinity crisis chronostratigraphically settled at 5 332 ma the areal distribution of the calcareous nannofossils is closely linked to their ecological and environmental affinities mostly driven by temperature salinity nutrients or other chemical parameters of the water masses hence taxa or groups of taxa showing well known ecological behaviors were considered and different environmental evolutions were recognized for the two sectors of the mediterranean basin during the early zanclean early pliocene specifically in the western mediterranean a switching from a warm and oligotrophic water environment showing normal open marine conditions to a colder and eutrophic one characterized by a decrease in salinity rates and the development of a more restricted environment can be recorded conversely in the eastern mediterranean the environmental setting immediately following the msc is indicative of temperate waters and normal open marine conditions which evolves in the younger layers to a warmer environment characterized by high salinity rates and typical of a restricted marine context the timing of the environmental transitions recognized at the two sites has been set through the principal component analysis taxa and groups of taxa reflecting precise ecological affinities have been handled together and a transition interval have been defined between 5 20 5 15 ma and 5 06 4 98 ma and between 5 10 ma and 4 92 ma in the western and eastern mediterranean respectively

response of the pelagic environment to palaeoclimatic changes in the central mediterranean sea during the late quaternary abstract three central mediterranean deep sea cores have been studied to reconstruct the palaeoclimatic history of the basin over the time interval 34 0 kyr bp the intensity and duration of the climatic events that occurred in the mediterranean sea during the last glacial postglacial transition were estimated by observing compositional changes in the planktonic foraminifera and calcareous nannoplankton coccolithophores assemblages together with a reconstruction of sea surface temperatures using the modern analogue technique and u 37 k index the 18 o signal and pteropod fluxes the application of two independent and well established techniques for the determination of the past sst led to a number of considerations about the accuracy and efficacy of the use of such methodologies in the mediterranean sea notoriously dominated by local factors and characterised by a number of independent environments the recognition of millennial to centennial climatic instabilities in both the sst and microfossil records was possible because of the high resolution of the study a succession of nine main biozones and six sub zones based on the major changes in the planktonic foraminifera records has been recognised and compared with grip and gisp2 ice cores 18 o values and with records from four other studies from the central mediterranean sea during the early phase of the holocene a period characterised by relatively higher temperatures and lighter 18 o values has been recognised as being coeval with the climatic optimum between 10 5 and 6 1 kyr bp calendar age this interval was characterised by an abrupt drop in the pteropods relative abundances and fluxes the pteropodal fossil assemblage may have been affected by a possible event of selective dissolution of the aragonite driven by the shoaling of the acd a coeval change in the position of the pycnocline may have been responsible for a strong relative increase in abundance of neogloboquadrina pachyderma r c and a decrease in the abundance of globorotalia inflata in the western sector of the mediterranean sea

active fault systems and tectono topographic configuration of the central trans mexican volcanic belt abstract the central trans mexican volcanic belt tmvb reflects the interplay between three regional fault systems the nnw sse to nw se striking taxco queretaro fault system the ne sw striking system and the e w striking morelia acambay fault system the latter is the youngest and consists of fault scarps up to 500 m high whose formation caused structural and morphological reorganization of the region in this paper we investigate possible activity of the three systems within the central tmvb and assess the role that they play in controlling the tectono topographic configuration of the area our study is based on dem derived morphometric maps longitudinal river profiles geomorphologic mapping and structural field data concerning recent faulting we find that all three regional fault systems are active within the central tmvb possibly with different displacement rates and or type of motion and that nnw sse and ne sw striking faults control the major tectono topographic elements that build up the region which are being re shaped by e w striking faults we also find that tectonic information can be deciphered from the topography of the youthful volcanic arc in question regardless its complexity

effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation the late cenozoic closure of the seaway between the north andsouth american continents is thought to have caused extensive changes in ocean circulation and northern hemisphere climate1 2 but the timing and consequences of the emergence of the isthmus of panama which closed the seaway remain controversial1 2 3 4 5 here we present stable isotope and carbonate sand fraction records from caribbean sediments which when compared to atlantic and pacific palaeoceanographic records indicate that the closure caused a marked reorganization of ocean circulation starting 4 6 million years ago shallowing of the seaway intensified the gulf stream and introduced warm and saline water masses to high northern latitudes these changes strengthened deep water formation in the labrador sea over the next million years as indicated by an increased deep water ventilation and carbonate preservation in the caribbean sea and favoured early pliocene warming of the northern hemisphere the evaporative cooling of surface waters during north atlantic deep water formation would have introduced moisture to the northern hemisphere although the pronounced intensification of northern hemisphere glaciation between 3 1 and 2 5 million years ago substantially lagged the full development of north atlantic deep water formation we propose that the increased atmospheric moisture content was a necessary precondition for ice sheet growth which was then triggered by the incremental changes in the earth s orbital obliquity

deciphering latitudinal shifts in coccolith accumulation in the eastern tropical pacific ocean through the pleistocene abstract middle and late pleistocene coccolithophore assemblages from ocean drilling program odp sites 1241 and 1242 in the northeastern tropical pacific north etp were analyzed to reconstruct coccolithophore productivity and surface water conditions over the last 925 kyr stratigraphic control was provided by 18o data and geomagnetic time scales and the identification of synchronous calcareous nannofossil events formerly described in mid and low latitudes changes in sea surface coccolithophore productivity were inferred by estimates of the so called n ratio an independent proxy on conversion to accumulation rates and the total coccolith derived carbonate accumulation rate car car variations follow those of the n ratio but show larger amplitude changes fluctuations in the n ratio and total car values imply coccolithophore productivity maxima during glacial times most likely as a result of a shallower nutri thermocline defined as the boundary beneath the sea surface at which nutrient rich cool and nutrient poor warm waters are separated low interglacial values of the n ratio and car suggest lower coccolithophore productivity and a deeper nutri thermocline deep stratification of the mixed layer this result implies that coccolithophore productivity controlled cars and dissolution were driven by the ratio between caco3 production and organic matter oxidation and that effects of dissolution were enhanced when coccolith production fell the data suggest high coccolithophore productivity and a shallow nutri thermocline during mis 22 through mis 6 likely due to the reinforcement of northeastern wind driven advection of nutrient rich waters which is compatible with a la nina like state the dominance of gephyrocapsa caribbeanica during the mid brunhes event mbe is consistent with this eutrophic environment conversely data from mis 5 suggests a weakening of trade winds in the etp which would have reduced the normal upwelling of cool water and warmed sst and which is compatible with the oligotrophic setting of an el nino like state during mis 4 through mis 1 coccolithophore productivity was not significantly different from mis 5 and therefore not indicative of a prominent la nina like state as previously reported for the equatorial cold tongue ect comparison with coccolithophore data from site 1240 supports a reduction of coccolithophore productivity and nutri thermocline deepening from the ect to the costa rica margin and suggests that nutrient availability was the primary control on the distribution of the whole assemblage during the past 925 kyr