tectonic interactions between india and arabia since the jurassic reconstructed from marine geophysics ophiolite geology and seismic tomography gondwana breakup since the jurassic and the northward motion of india toward eurasia were associated with formation of ocean basins and ophiolite obduction between and onto the indian and arabian margins here we reconcile marine geophysical data from preserved oceanic basins with the age and location of ophiolites in nw india and se arabia and seismic tomography of the mantle below the nw indian ocean the north somali and proto owen basins formed due to 160 133 ma n s extension between india and somalia subsequent convergence destroyed part of this crust simultaneous with the uplift of the masirah ophiolites most of the preserved crust in the owen basin may have formed between 84 and 74 ma whereas the mascarene and the amirante basins accommodated motion between india and madagascar east africa between 85 and circa 60 ma and 75 and circa 66 ma respectively between circa 84 and 45 ma oblique arabia india convergence culminated in ophiolite obduction onto se arabia and nw india and formed the carlsberg slab in the lower mantle below the nw indian ocean the nne ssw oriented slab may explain the anomalous bathymetry in the nw indian ocean and may be considered a paleolongitudinal constraint for absolute plate motion nw india asia collision occurred at circa 20 ma deforming the sulaiman ranges or at 30 ma if the hindu kush slab north of the afghan block reflects intra asian subduction our study highlights that the nw india ophiolites have no relationship with india asia motion or collision but result from relative india africa arabia motions instead key points we present a new tectonic model for the evolution of nw indian ocean subducted slab under the carlsberg ridge resulted from arabia india convergence

himalayan forelands palaeontological evidence for oligocene detrital deposits in the bugti hills balochistan pakistan in the southwestern sulaiman geological province balochistan pakistan terrestrial detri tal facies from the bugti hills region have yielded the richest tertiary vertebrate faunas to be found in asia thus far new fossils from five successive and distinct bone beds bridge the supposed oligocene sedimentary hiatus within the sulaiman geological province the lowermost continental levels of the previously described miocene chitarwata formation known as the bugti member are oligocene in age in the bugti area neither a mixture of heterochronic faunal elements nor endemism of any fauna is evident in this area additional microfaunal material from the bugti member constrains an oligocene age for the lower chitarwata formation in zinda pir northeast of the bugti hills this oligocene transition between the marine kirthar eocene and continental siwalik miocene deposits consists of a regressive fluvio deltaic system occupying a vast floodplain it represents an early stage molasse in the palaeo indus basin which drained western orogenic highlands resulting from the colli sion between the indian and eurasian plates

late eocene to early miocene ice sheet dynamics and the global carbon cycle paired benthic foraminiferal trace metal and stable isotope records have been constructed from equatorial pacific ocean drilling program site 1218 the records include the two largest abrupt 1 myr increases in the cenozoic benthic oxygen isotope record oi 1 in the earliest oligocene 34 ma and mi 1 in the earliest miocene 23 ma the paired mg ca and oxygen isotope records are used to calculate seawater 18o w calculated w suggests that a large antarctic ice sheet formed during oi 1 and subsequently fluctuated throughout the oligocene on both short 0 5 myr and long 2 3 myr timescales between about 50 and 100 of its maximum earliest oligocene size the magnitudes of these fluctuations are consistent with estimates of sea level derived from sequence stratigraphy the transient expansion of the antarctic ice sheet at mi 1 is marked in the benthic 18o record by two positive excursions between 23 7 and 22 9 ma each with a duration of 200 300 kyr bottom water temperatures decreased by 2 c over the 150 kyr immediately prior to both rapid 18o excursions however the onset of each of these phases of ice growth is synchronous within the resolution of the records with the onset of a 2 c warming over 150 kyr we suggest that the warming during these glacial expansions reflect increased greenhouse forcing prompted by a sudden decrease in global chemical weathering rates as antarctic basement silicate rocks became blanketed by an ice sheet this represents a negative feedback process that might have operated during major abrupt growth phases of the antarctic ice sheet

the role of carbon dioxide during the onset of antarctic glaciation earth s modern climate characterized by polar ice sheets and large equator to pole temperature gradients is rooted in environmental changes that promoted antarctic glaciation 33 7 million years ago onset of antarctic glaciation reflects a critical tipping point for earth s climate and provides a framework for investigating the role of atmospheric carbon dioxide co2 during major climatic change previously published records of alkenone based co2 from high and low latitude ocean localities suggested that co2 increased during glaciation in contradiction to theory here we further investigate alkenone records and demonstrate that antarctic and subantarctic data overestimate atmospheric co2 levels biasing long term trends our results show that co2 declined before and during antarctic glaciation and support a substantial co2 decrease as the primary agent forcing antarctic glaciation consistent with model derived co2 thresholds

discovery of the palaeo indus delta fan complex the indus river carries sediments from the western himalaya and deposits some of these as channel and floodplain sediments or molasse the rest of its load forms the indus delta at the margin of the indian ocean the indus delta passes some of its sediments to be deposited as indus submarine fan turbidites thus as elsewhere himalayan molasse delta and fan deposition are related hi tune and space however when we examine fluvial and marine age range data of the older indus deposits in terms of this sedimentary assemblage a major portion of its marine record is missing the oldest known molasse along the indus suture zone and hi the foredeep are middle eocene and late palaeocene hi age respectively a recent synthesis of sedimentation in the northern indian ocean however shows that turbidite sedimentation started around early miocene in the modern indus fan and even later in the bengal fan where are the palaeogene indus delta and fan sediments we suggest herein that these are preserved as the palaeogene siliciclastic khojak formation hi the katawaz basin and eastern makran the modern indus river is 2900 km long coumes kolla 1984 and has 30 000 m 3 s 1 discharge milliman et al 1984 in summer fig 1 twice that of the mississippi river the annual suspended sediment load wells coleman 1984 varies between 395 and 435 x 10 3 t almost equal to that of the mississippi the existence of the middle eocene to middle miocene indus molasse along the

provenance of cenozoic sedimentary rocks from the sulaiman fold and thrust belt pakistan implications for the palaeogeography of the indus drainage system abstract the provenance of middle eocene to early miocene sedimentary rocks cropping out in the sulaiman fold and thrust belt has been determined examining the mineralogy bulk rock major and trace elements and nd sr isotopes the older 50 30 ma deposits are characterized by a mixed orogenic provenance with a major contribution from the karakorum and the tethyan belt c 80 as the 50 30 ma deposits have a provenance distinct from that of coeval subathu khojak and ghazij shallow marine formations of india and pakistan we propose that they were deposited as a distinct delta system that once fed the palaeo indus fan we document a major change in provenance that occurred before the early late oligocene transition at c 30 ma this change in provenance is marked by the appearance of chlorite and monazite and a shift toward more radiogenic nd sr isotopic compositions we interpret this change as the result of the exhumation and erosion of the proto higher himalaya the 30 15 ma sampled rocks are characterized by a major contribution from the tethyan belt and the higher himalayan crystallines 70 90 and a subordinate contribution 10 30 from the karakorum ophiolitic suture and trans himalaya as the end 0 values of our 30 15 ma samples are similar to those of the palaeo indus fan deposits we suggest that the 30 15 ma sedimentary rocks of the sulaiman fold and thrust belt were the fluvial onshore record of the indus fan other coeval deposits of india and pakistan recorded similar increasing exhumation of the higher himalaya range so that we postulate that these sedimentary rocks all derived from the palaeo indus drainage basin this would suggest that the modern indus drainage basin is no younger than 30 ma

substrate control on distribution of subglacial and glaciomarine seismic facies based on stochastic models of glacial seismic facies deposition on the ross sea continental margin antarctica abstract a quantitative approach was utilized to establish the nature of spatial and temporal variations of glaciomarine and subglacial seismic facies deposition in the ross sea the ross sea is an excellent area to study antarctic ice sheet volume variations because it receives ice sheet drainage from approximately 25 of the continent and it contains subsiding basins to preserve the stratigraphic record of the ice sheet volume fluctuations this region receives most of the influence on deposition from the marine based west antarctic ice sheet which is believed to have been subject to catastrophic surges hollin j t 1962 on the glacial history of antarctica journal of glaciology 4 173 195 the eastern basin in particular has been subsiding creating accommodation space in which to preserve the plio pleistocene record of ice sheet fluctuations evidence from high resolution seismic data in conjunction with dsdp leg 28 drilling results are used to test hypotheses of paleo ice sheet behavior here we present quantitative evidence for a dynamic polar style of glaciation meaning that the ice sheets have had dynamic or large ice volume change not merely in the plio pleistocene but back to the late oligocene high resolution seismic data correlated to dsdp sites 270 273 shows evidence of multiple ice sheet grounding events in central and eastern ross sea strata a recipient of both west and east antarctic ice sheets from the late oligocene until the present we suggest that the west and east antarctic ice sheets are dynamic and have gone through a full spectrum of thermal states temperate through polar since the late oligocene and not necessarily in any particular preferred temporal order statistical analysis of the spatial distribution of seismic facies within seismic cores indicates that tectonic influence on distribution of basal substrate is a significant contributor to spatial variability of subglacial depositional processes and therefore distribution of subglacial facies

marked decline in atmospheric carbon dioxide concentrations during the paleogene the relation between the partial pressure of atmospheric carbon dioxide pco2 and paleogene climate is poorly resolved we used stable carbon isotopic values of di unsaturated alkenones extracted from deep sea cores to reconstruct pco2 from the middle eocene to the late oligocene approximately 45 to 25 million years ago our results demonstrate that pco2 ranged between 1000 to 1500 parts per million by volume in the middle to late eocene then decreased in several steps during the oligocene and reached modern levels by the latest oligocene the fall in pco2 likely allowed for a critical expansion of ice sheets on antarctica and promoted conditions that forced the onset of terrestrial c4 photosynthesis

impact of antarctic circumpolar current development on late paleogene ocean structure global cooling and the development of continental scale antarctic glaciation occurred in the late middle eocene to early oligocene 38 to 28 million years ago accompanied by deep ocean reorganization attributed to gradual antarctic circumpolar current acc development our benthic foraminiferal stable isotope comparisons show that a large 13c offset developed between mid depth 600 meters and deep 1000 meters western north atlantic waters in the early oligocene indicating the development of intermediate depth 13c and o2 minima closely linked in the modern ocean to northward incursion of antarctic intermediate water at the same time the ocean s coldest waters became restricted to south of the acc probably forming a bottom ocean layer as in the modern ocean we show that the modern four layer ocean structure surface intermediate deep and bottom waters developed during the early oligocene as a consequence of the acc

global chemical erosion during the last glacial maximum and the present sensitivity to changes in lithology and hydrology geographically based calculations for 18 000 years ago 18 ka and today were made to examine the potential effects on terrestrial chemical erosion of changes in lithology and hydrology on glacial interglacial timescales runoff fields were derived from general circulation model predictions of precipitation minus evaporation then global lithologic maps were prepared so that empirical relationships for runoff versus bicarbonate flux for different rock types could be used to calculate global chemical erosion rates assuming that significant chemical erosion does not occur beneath ice sheets we find that chemical erosion in ice free areas at 18 ka was only slightly greater than today this result arises because the amount of land covered by ice sheets is roughly compensated for by exposed shelf areas and because there is little difference in global runoff the small 20 increase in the global chemical erosion rate during glacial conditions is due to exposure on the shelves of a relatively high proportion of carbonates which weather faster than average data on glacial interglacial movements of the calcite compensation depth ccd are inconclusive but seem to indicate little change whereas even a 20 increase in the riverine bicarbonate flux should cause an observable deepening if the ccd did not indeed change then our predicted increase in the bicarbonate flux from land during glaciations would have to be accommodated by other means such as increased carbonate productivity about half of the observed decrease in atmospheric pco2 at 18 ka could be explained if increased silicate chemical erosion accompanied increased total chemical erosion in ice free areas consideration of the maximum possible effect of meltwater at ice margins leads to an 80 increase in the global chemical erosion rate at 18 ka such an increase would lead to a larger and faster drop in atmospheric pco2 but also to an excessive deepening of the global ccd this scenario seems unrealistic our results are contrary to interpretations of a much higher silicate chemical erosion rate during glaciations based on recently published records of quaternary marine sr isotopic ratios therefore if these records are indeed globally representative and entirely due to increased silicate chemical erosion as opposed to changes in source areas or hydrothermal inputs then other factors such as a shift in the global weathering regime which we do not explicitly consider here may be involved sensitivity tests show that considering spatial heterogeneities in lithology and runoff leads to lower predictions of global chemical erosion rates than what one would obtain by considering only global averages in a non spatially resolved calculation

reconstructing greater india paleogeographic kinematic and geodynamic perspectives abstract key in understanding the geodynamics governing subduction and orogeny is reconstructing the paleogeography of greater india the indian plate lithosphere that subducted since tethyan himalayan continental collision with asia here we discuss this reconstruction from paleogeographic kinematic and geodynamic perspectives and isolate the evolution scenario that is consistent with all three we follow recent constraints advocating a 58 ma initial collision and update a previous kinematic restoration of intra asian shortening with a recently proposed model that reconciles long debated large and small estimates of indochina extrusion our new reconstruction is tested against paleomagnetic data and against seismic tomographic constraints on paleo subduction zone locations the resulting restoration shows 1000 1200 km of post collisional intra asian shortening leaving a 2600 3400 km wide greater india from a paleogeographic sediment provenance perspective eocene sediments in the lesser himalaya and on undeformed india may be derived from tibet suggesting that all greater indian lithosphere was continental but may alternatively be sourced from the contemporaneous western indian orogen unrelated to india asia collision a quantitative kinematic paleomagnetic perspective prefers major cretaceous extension and a greater india basin opening within greater india but data uncertainty may speculatively allow for minimal extension finally from a geodynamic perspective assuming a fully continental greater india would require that subduction rates close to 20 cm yr was driven by a down going lithosphere crust assemblage more buoyant than the mantle which seems physically improbable we conclude that the greater india basin scenario is the only sustainable one from all three perspectives we infer that old pre collisional lithosphere rapidly entered the lower mantle sustaining high subduction rates whilst post collisional continental and young greater india basin lithosphere did not inciting the rapid india asia convergence deceleration 8 myr after collision subsequent absolute northward slab migration and overturning caused flat slab subduction tibetan shortening arc migration and arc volume decrease

oligocene paleoceanographic changes based on an interbasinal comparison of cibicidoides spp δ18o records and a new compilation of data abstract oligocene paleoceanographic changes are useful for assessing future changes in the warming world because the levels of atmospheric pco2 in the oligocene were similar to those expected within the next century however the overall oligocene history is still unclear even though our understanding has been improved by previous studies in this paper we review the preexisting hypotheses for the eocene oligocene and oligocene miocene changes as well as the long term global changes based on newly compiled cibicidoides spp 18o 18ocib records we divide the oligocene paleoceanographic changes into five phases an abrupt increase in 18ocib values during the eocene oligocene transition eot phase 1 a gradual decrease in the early oligocene phase 2 a long term slow increase in the early to middle oligocene phase 3 a gradual decrease in the late oligocene phase 4 and an abrupt increase near the oligocene miocene transition omt phase 5 these recurring sequential changes in the global scale 18ocib profile following the eot are likely not directly connected to the strengthening and stratification of ocean currents during the oligocene as a result of the unidirectional strengthening of the antarctic circumpolar current acc and the northern component water ncw instead we suggest that the strengthened ocean currents contributed significantly to interbasinal differences in 18ocib values for a more robust explanation of oligocene long term 18ocib changes following the eot future studies will require high resolution and more reproducible records of changes in the volume of antarctic ice and atmospheric pco2 as well as information about the tectonic history

miocene stratigraphy and mammal fauna from the sulaiman range southwestern himalayas pakistan abstract the thick 4000 m coarsening upward terrestrial neogene sequence of the sulaiman range middle indus basin central pakistan is the western extension of the siwalik outcrop belt of the sub himalayas the near shore to terrestrial sedimentation in the sulaiman range represented by the chitarwata formation began by the late oligocene to basal miocene when the main himalayan foreland was primarily a non depositional region the fluvial system of channel floodplain deposits was fully established in the late early miocene marking the beginning of the vihowa formation there is a sudden increase in the proportion of sandstones to mudstones and change in the geometry of the sandbodies at the conformable contact of the vihowa with the overlying litra formation the trend of coarsening and increased complexity of sandbodies with more conglomerate interbeds continued upward from the litra to the chaudhwan formation which in the upper reaches becomes a conglomerate dominant sequence our mammalian faunal collections from the vihowa and litra formations though small are definitive providing a temporal framework for interpreting the sulaiman depositional regimes in the context of himalayan orogeny the vihowa and litra mammalian faunas are strikingly similar to the middle to late miocene siwalik faunas from the potwar plateau fauna from the lower vihowa records diversification in the small boselaphine bovid eotragus around 17 ma the three toed hipparionine horses appear in the lower litra formation giving a late miocene age to those strata the middle litra formation has entirely different species of bovids suids and giraffids suggesting a more open country habitat similar community restructuring with substantial faunal turnover occurred about 7 5 7 0 ma on the potwar plateau the chaudhwan formation is probably of pliocene age paleocurrent data suggest a southerly flowing river system which perhaps was part of a much larger river system analogous to the modern indus river draining southwestern himalayas since miocene the chitarwata through chaudhwan sequence in the sulaiman range contains an almost continuous terrestrial record of the neogene perhaps more complete than anywhere else in the himalayan foreland

late oligocene climatic changes evidence from calcareous nannofossils at kerguelen plateau site 748 southern ocean abstract palaeoecological changes in nannofossil assemblages in the southern ocean during oligocene times are examined through high resolution quantitative analyses of samples from ocean drilling program odp site 748 kerguelen plateau we quantitatively characterized the palaeoecological preference of groups of species and compared their general trends with those determined at maud rise odp sites 690 and 689 persico d villa g 2004 eocene oligocene calcareous nannofossils from maud rise and kerguelen plateau antarctica palaeoecological and palaeoceanographic implications marine micropaleontology 52 153 179 we then attempt a correlation between the main assemblage variation and sea surface temperature sst changes in the southern ocean at this time relatively stable cool conditions are interpreted to have persisted from earliest to late oligocene times when an increase in abundance of temperate water taxa is recorded both at maud rise and kerguelen plateau before the mi 1 event this reveals a climatic event that probably involved both sites and which is comparable to that indicated by the global oxygen isotope curve miller k g wright j d fairbanks r g 1991 unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion journal of geophysical research 96 6829 6848 zachos j pagani m sloan l thomas e billups k 2001 trends rhythms and aberrations in global climate 65 ma to present science 292 686 693 in the uppermost oligocene at site 689 the temperate water taxa index temperate temperate cool 100 increases from 25 2 ma similarly at site 748 the temperate water taxa index indicates an increase in sst in the late oligocene from about 26 5 ma at the base of chron c8n 2n which is offset by about 1 m y between the two areas the reason for this time difference can probably be found in the location of site 748 with respect to site 689 and in the palaeoceanographic setting taking into account that site 748 lies north of a deep water passage that separates kerguelen plateau from antarctica and north of the present day front of the antarctic circumpolar current the presence of warm water taxa exclusively at site 748 corroborates this hypothesis

application of benthic foraminiferal mg ca ratios to questions of cenozoic climate change abstract we investigate the evolution of cenozoic climate and ice volume as evidenced by the oxygen isotopic composition of seawater 18osw derived from benthic foraminiferal mg ca ratios to constrain the temperature effect contained in foraminiferal 18o values we have constructed two benthic foraminiferal mg ca records from intermediate water depth sites ocean drilling program sites 757 and 689 from the subtropical indian ocean and the weddell sea respectively together with the previously published composite record of lear et al science 287 2002 269 272 and the neogene record from the southern ocean of billups and schrag paleoceanography 17 2002 10 1029 2000pa000567 we obtain three almost complete representations of the 18osw for the past 52 myr we discuss the sensitivity of early cenozoic mg ca derived paleotemperatures and hence the 18osw to assumptions about seawater mg ca ratios we find that during the middle eocene 49 40 ma modern seawater ratios yield mg ca derived temperatures that are in good agreement with the oxygen isotope paleothermometer assuming ice free conditions intermediate waters cooled during the middle eocene reaching minimum temperatures by 40 ma the corresponding 18osw reconstructions support ice growth on antarctica beginning by at least 40 ma at the eocene oligocene boundary mg ca ratios and hence temperatures from weddell sea site 689 display a well defined maximum we caution against a paleoclimatic significance of this result and put forth that the partitioning coefficient of mg in benthic foraminifera may be sensitive to factors other than temperature throughout the remainder of the cenozoic the temporal variability among 18osw records is similar and similar to longer term trends in the benthic foraminiferal 18o record an exception occurs during the pliocene when 18osw minima in two of the three records suggest reductions in global ice volume that are not apparent in foraminiferal 18o records which provides a new perspective to the ongoing debate about the stability of the antarctic ice sheet maximum 18osw values recorded during the pleistocene at southern ocean site 747 agree well with values derived from the geochemistry of pore waters schrag et al science 272 1996 1930 1932 further highlighting the value of the new mg ca calibrations of martin et al earth planet sci lett 198 2002 193 209 and lear et al geochim cosmochim acta 66 2002 3375 3387 applied in this study we conclude that the application of foraminiferal mg ca ratios allows a refined view of cenozoic ice volume history despite uncertainties related to the geochemical cycling of mg and ca on long time scales

early middle miocene paleodrainage and tectonics in the pakistan himalaya the 18 14 ma kamlial formation himalayan foreland basin sedimentary rocks in the chinji village region potwar plateau pakistan are characterized by 1 lithofacies indicative of deposition by a large river 2 a dominant magmatic arc provenance completely unlike the recycled orogen foreland basin deposits stratigraphically below above or coeval with these rocks and 3 subordinate contribution from a rapidly exhuming source interpreted as either the nanga parbat haramosh massif or the southern margin of the asian crust the start of kamlial formation deposition at this locality at 18 ma marks a major break with the older murree formation rocks which were deposited by rivers draining predominantly the himalayan thrust stack south of the arc we interpret this change as the result of diversion of the paleo indus river to its present position which crosses the kohistan arc and himalayas and debouches into the foreland if the rapidly exhuming subordinate source region were the nanga parbat haramosh massif then initiation of its uplift would have resulted in significant arc detritus to the basin as the overlying arc carapace was exhumed as the carapace was progressively breached arc material would have become a less substantial component of detritus to the basin consistent with the reported petrography of the overlying siwalik deposits

lithofacies depositional environments regional biostratigraphy and age of the chitarwata formation in the bugti hills balochistan pakistan abstract the oligocene early miocene chitarwata formation records a critical interval of terrestrial sedimentation that predates the siwalik deposits on the potwar plateau of north central pakistan this oligocene early miocene time interval has long been considered as lacking in the entire indo pakistan region the chitarwata formation is widely exposed in the sulaiman range but has never been described in detail in the sulaiman lobe where the famous fossiliferous strata called bugti bone beds have been known for over a century and half the chitarwata formation represents coastal delta at the base and plain and fluvial environments at the top lithofacies and sedimentary structures of the chitarwata formation in the bugti area are described in detail and show a clearly distinct lithologic pattern different from that reported from the zinda pir area the chitarwata formation also records an important transition in the evolution of the drainage systems in the area during the late paleogene and early neogene this transition from the west flowing paleo indus fluvial system to the development of the ancestral indus drainage system may explain the numerous hiatuses that characterize the chitarwata formation the abundance of fossil mammals from the chitarwata and overlying vihowa formation in the bugti hills provides critical biochronologic information that sheds new light on biostratigraphic correlation with the zinda pir area and for the entire sulaiman range

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

thresholds for cenozoic bipolar glaciation the long standing view of earth s cenozoic glacial history calls for the first continental scale glaciation of antarctica in the earliest oligocene epoch 33 6 million years ago1 followed by the onset of northern hemispheric glacial cycles in the late pliocene epoch about 31 million years later2 the pivotal early oligocene event is characterized by a rapid shift of 1 5 parts per thousand in deep sea benthic oxygen isotope values3 oi 1 within a few hundred thousand years4 reflecting a combination of terrestrial ice growth and deep sea cooling the apparent absence of contemporaneous cooling in deep sea mg ca records4 5 6 however has been argued to reflect the growth of more ice than can be accommodated on antarctica this combined with new evidence of continental cooling7 and ice rafted debris8 9 in the northern hemisphere during this period raises the possibility that oi 1 represents a precursory bipolar glaciation here we test this hypothesis using an isotope capable global climate ice sheet model that accommodates both the long term decline of cenozoic atmospheric co2 levels10 11 and the effects of orbital forcing12 we show that the co2 threshold below which glaciation occurs in the northern hemisphere 280 p p m v is much lower than that for antarctica 750 p p m v therefore the growth of ice sheets in the northern hemisphere immediately following antarctic glaciation would have required rapid co2 drawdown within the oi 1 timeframe to levels lower than those estimated by geochemical proxies10 11 and carbon cycle models13 14 instead of bipolar glaciation we find that oi 1 is best explained by antarctic glaciation alone combined with deep sea cooling of up to 4 c and antarctic ice that is less isotopically depleted 30 to 35 than previously suggested15 16 proxy co2 estimates remain above our model s northern hemispheric glaciation threshold of 280 p p m v until 25 myr ago but have been near or below that level ever since10 11 this implies that episodic northern hemispheric ice sheets have been possible some 20 million years earlier than currently assumed although still much later than oi 1 and could explain some of the variability in miocene sea level records

drake passage and cenozoic climate an open and shut case drake passage opening has often been viewed as a single discrete event possibly associated with abrupt changes in global circulation and climate at or near the eocene oligocene boundary a new plate tectonic model based on recent reinterpretations of the opening history of basins in the scotia sea suggests that an effective ocean gateway may have developed even earlier during the middle eocene this is consistent with a growing body of evidence from sediment core proxy data for eocene changes in southern ocean circulation and biological productivity the period between earliest opening after 50 ma and the latest eocene was characterized by the evolution of various current pathways across the subsiding continental shelves and intervening deep basins this shallow opening may have caused important changes in southern ocean circulation contributing to eocene cooling and the growth of antarctic ice sheets

early oligocene paleosols of the dagshai formation india a record of the oldest tropical weathering in the himalayan foreland abstract this study reports paleopedological features of the fossil soils that formed during the earliest phase of continental sedimentation in the himalayan foreland the fluvial sequence of the dagshai formation 31 6 3 9 ma to 30 3 3 9 ma exposed along the koshaliya river nw himalaya contains four pedofacies named pedofacies a d of ferruginous paleosol sequences contained within overbank sediments the dagshai formation unconformably overlies the marine subathu formation pedofacies a consists of 3 4 well developed ferruginous paleosols overlain by gray sandstone beds pedofacies b d are marked by a progressive decrease in pedogenesis these paleosols occur as 0 5 m to 1 5 m thick bw bt btk bk bss horizons that are marked by extensive development of rhizoliths pedogenic carbonate and iron rich clay pedofeatures that correspond to modern entisols inceptisols alfisols and vertisols based on early oligocene paleogeographic position of the northward drifting indian plate it is inferred that these paleosols were formed at 18 n paleolatitude in the dagshai sub basin in the himalayan foreland micromorphology geochemical analyses weathering indices and stable isotope composition of paleosols indicate tropical climate paleoprecipitation of 947 1256 mm and paleotemperature of 25 c with an initial phase of monsoonal conditions during pedogenesis these paleoclimatic conditions favored c3 paleovegetation immediately after the transition from greenhouse to icehouse conditions

paleobiogeography of africa how distinct from gondwana and laurasia abstract although africa was south of the tethys sea and originally belonged to the gondwana its paleobiogeographical history appears to have been distinct from those of both gondwana and laurasia as early as the earliest cretaceous perhaps the late jurassic this history has been more complex than the classical one reconstructed in the context of a dual world gondwana vs laurasia geological and paleobiogeographical data show that africa was isolated from the mid cretaceous albian aptian to early miocene i e for ca 75 million years the isolation of africa was broken intermittently by discontinuous filter routes that linked it to some other gondwanan continents madagascar south america and perhaps india but mainly to laurasia interchanges with gondwana were rare and mainly out of africa dispersals whereas interchanges with laurasia were numerous and bidirectional although mainly from laurasia to africa despite these intermittent connections isolation resulted in remarkable absences poor diversity and emergence of endemic taxa in africa mammals suggest that an african faunal province might have appeared by late jurassic or earliest cretaceous times i e before the opening of the south atlantic during isolation africa was inhabited by vicariant west gondwanan taxa i e taxa inherited from the former south american african block that represent the african autochthonous forms and by immigrants that entered africa owing to filter routes nearly all or all immigrants were of laurasian origin trans tethyan dispersals between africa and laurasia were relatively frequent during the cretaceous and paleogene and are documented as early as the earliest cretaceous or perhaps late jurassic i e perhaps by the time of completion of the tethys between gondwana and laurasia they were permitted by the mediterranean tethyan sill a discontinuous route that connected africa to laurasia and was controlled by sea level changes interchanges first took place between southwestern europe and africa but by the middle eocene a second eastern route the iranian route involved southeastern europe and southwestern asia the iranian route was apparently the filtering precursor of the definitive connection between africa and eurasia the relationships and successive immigrations of mammal mostly placental clades in africa allow the recognition of five to seven phases of trans tethyan dispersals between africa and laurasia that range from the late cretaceous to the eocene oligocene transition these dispersal phases involve dispersals toward laurasia and or toward africa immigrations the immigrations in africa gave rise to faunal assemblages the african faunal strata afss all successful and typical african radiations have arisen from these afss we recognize four to six afss each characterized by a faunal association even major old african clades such as paenungulata or the still controversial afrotheria which belong to the oldest known afs involving placentals ultimately originated from a laurasian stem group africa was an important center of origin of various placental clades their success in africa is probably related to peculiar african conditions endemicity weak competition although strongly marked by endemicity the african placental fauna did not suffer extinctions of major clades when africa contacted eurasia the present geographic configuration began to take shape as early as the mid cretaceous at that time the last connections between africa and other gondwanan continents began to disappear whereas africa was already connected to eurasia by a comparatively effective route of interchange

high resolution 104 years deep sea foraminiferal stable isotope records of the eocene oligocene climate transition we have constructed high resolution 104 105 years benthic foraminiferal 13c and 18o records for the upper eocene through lower oligocene of two pelagic sequences deep sea drilling project dsdp site 522 in the angola basin south atlantic ocean and ocean drilling program odp site 744 in the southern indian ocean these records provide improved constraints on both the timing and magnitude of marine oxygen and carbon isotope events from 30 to 35 ma the oxygen isotope records indicate that the ubiquitous 18o increase oi 1 which marks the rapid expansion of continental ice sheets and a minimum of 3 to 4 c of cooling of bottom waters in the earliest oligocene 33 6 ma occurred in 350 kyr more than half the transition occurred over the final 40 50 kyr this period of lower temperatures and widespread continental glaciation persisted for roughly 400 kyr i e the duration of magnetochron c13n these records also indicate that this interval was characterized by at least two 100 kyr waxing and waning cycles oi 1a and oi 1b and possibly several higher frequency events the benthic foraminiferal 13c records show a positive 0 8 excursion that is nearly isochronous with the oi 1 oxygen isotope increase similar magnitude 13c increases at other sites indicate this was a global phenomenon suggestive of an unusually large perturbation to the carbon cycle this excursion was followed by smaller amplitude 13c oscillations with periods of roughly 400 kyr we suspect that the ubiquitous oi 1 13c excursion resulted from a brief but substantial increase in export production and carbon burial

cooler winters as a possible cause of mass extinctions at the eocene oligocene boundary the eocene oligocene boundary at about 33 7 myr ago marks one of the largest extinctions of marine invertebrates in the cenozoic period1 for example turnover of mollusc species in the us gulf coastal plain was over 90 at this time2 3 a temperature change across this boundary from warm eocene climates to cooler conditions in the oligocene has been suggested as a cause of this extinction event4 but climate reconstructions have not provided support for this hypothesis here we report stable oxygen isotope measurements of aragonite in fish otoliths ear stones collected across the eocene oligocene boundary palaeotemperatures reconstructed from mean otolith oxygen isotope values show little change through this interval in agreement with previous studies5 6 from incremental microsampling of otoliths however we can resolve the seasonal variation in temperature recorded as the otoliths continue to accrete new material over the life of the fish these seasonal data suggest that winters became about 4 c colder across the eocene oligocene boundary we suggest that temperature variability rather than change in mean annual temperature helped to cause faunal turnover during this transition

the detrital record of orogenesis a review of approaches and techniques used in the himalayan sedimentary basins the sediment archive of material eroded from an active tectonic region and stored in adjacent basins can provide a valuable record of hinterland tectonism especially when information in the source region itself is obscured by later metamorphism or removed by tectonism or erosion using the sediment record to document tectonism is a well established approach but more recently there has been a burgeoning of the number of isotopic techniques which can be applied to detrital material in particular single grain analyses thus the scope for application of detrital studies to a number of different tectonic problems has widened considerably in this review the example of sediments eroded from the himalayan orogen and preserved in the suture zone basin foreland basin remnant ocean basins and deep sea fans is used to illustrate the approach techniques as diverse as petrography heavy mineral xrf and sr nd studies single grain dating by ar ar u pb and fission track methodologies and single grain sm nd and pb isotopic analyses are described the paper documents how the sediment record can be used to determine the thermal and tectonic evolution of the orogen constrain mechanisms of continental deformation exhumation rates and palaeodrainage

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

a new assemblage of stem pecoran ruminants from the oligocene chitarwata formation bugti hills baluchistan pakistan paleoenvironmental and paleobiogeographic implications abstract a new assemblage of stem pecoran ruminants from the oligocene chitarwata formation lower bugti member bugti hills pakistan consists of three identified genera and another indeterminate ruminant although limited the dental and postcranial material is sufficient to identify the genera amphitragulus and mosaicomeryx two common forms known from middle to late oligocene deposits of europe thus reinforcing the middle oligocene age of the lowermost chitarwata formation mosaicomeryx is reported for the first time from the indian subcontinent and this occurrence considerably expands its geographical distribution a new genus and species paalitherium gurki is erected on the basis of an unusual and unique association of characters on its lower molars the unclear definition and occurrences of gelocus gajensis pilgrim 1912 are re examined in the light of new data from the bugti and zinda pir areas pakistan the new ruminant fauna from paali is clearly distinctive from the early miocene assemblage known from bugti in accordance with other fossil evidence the ruminant fauna described here suggests the existence of a tropical forested environment under monsoonal regime with soft food supplies during the time of deposition of the lowermost chitarwata formation

antarctic glaciation caused ocean circulation changes at the eocene oligocene transition a climate model is used to show that the growth of the antarctic ice sheet at about 34 myr ago drove changes in ocean circulation but the opening of ocean gateways had relatively little impact antarctica developed an ice sheet about 34 million years ago following a period of ice free conditions known as the super greenhouse climate previous research has suggested that ice sheet growth was driven by either the thermal isolation of antarctica arising from the opening of ocean gateways or by progressively lower atmospheric co2 content matt huber and colleagues now use a climate model to show that the growth of the ice sheet forced by changes in co2 drove the changes in ocean circulation in contrast the opening of the gateways had relatively little impact on ocean circulation two main hypotheses compete to explain global cooling and the abrupt growth of the antarctic ice sheet across the eocene oligocene transition about 34 million years ago thermal isolation of antarctica due to southern ocean gateway opening1 2 3 4 and declining atmospheric co2 refs 5 6 increases in ocean thermal stratification and circulation in proxies across the eocene oligocene transition have been interpreted as a unique signature of gateway opening2 4 but at present both mechanisms remain possible here using a coupled ocean atmosphere model we show that the rise of antarctic glaciation rather than altered palaeogeography is best able to explain the observed oceanographic changes we find that growth of the antarctic ice sheet caused enhanced northward transport of antarctic intermediate water and invigorated the formation of antarctic bottom water fundamentally reorganizing ocean circulation conversely gateway openings had much less impact on ocean thermal stratification and circulation our results support available evidence that co2 drawdown not gateway opening caused antarctic ice sheet growth and further show that these feedbacks in turn altered ocean circulation the precise timing and rate of glaciation and thus its impacts on ocean circulation reflect the balance between potentially positive feedbacks increases in sea ice extent and enhanced primary productivity and negative feedbacks stronger southward heat transport and localized high latitude warming the antarctic ice sheet had a complex dynamic role in ocean circulation and heat fluxes during its initiation and these processes are likely to operate in the future

stratigraphic evidence for an early collision between northwest india and asia the collision of india with asia1 had a profound influence on late cretaceous and cenozoic oceanography2 climate3 fauna extinctions4 and the motion of at least some of the earth s litho spheric plates5 as the collision ended a period of rapid indo asian convergence6 a precise knowledge of its timing when the crust of the neo tethys ocean was completely subducted7 at some point along the plate boundary is important for understanding its wider consequences but current estimates of the collision age range from 65 to 38 myr before present6 8 11 here we report the results of extensive biostratigraphic analyses from waziristan and kurram in northwest pakistan which show that accretionary prism and trench strata were first thrust onto the northwest indian passive margin after 66 myr but before 55 5 myr after this time volcanic arc fragments the accretionary prism trench material and imbricates of the north indian slope were raised to shallow water depths and overlapped by upper palaeocene shallow water carbonates and shales12 14 indicative of post collision thrusting in this region finally both the suture and the indian craton were overlapped by continuous unconformable upper lower eocene shallow marine strata demonstrating that suturing was complete by 49 myr

cenozoic prograding sequences of the antarctic continental margin a record of glacio eustatic and tectonic events abstract sedimentary sections up to 6 14 km thick lie beneath many areas of the antarctic continental margin the upper parts of the sections contain up to 6 km of cenozoic glacial and possibly non glacial sequences that have prograded the continental shelf up to 85 km we describe the cenozoic sequences using two general categories based on their acoustic geometries type ia sequences which account for most prograding of the antarctic continental shelf have complex sigmoidal geometries and some acoustic characteristics atypical of low latitude margins such as troughs and mounds lying parallel and normal to the shelf edge and high velocities 2 0 2 6 km s for flat layers within 150 m of the seafloor type iia sequences which principally aggrade the paleoshelf lie beneath type ia sequences and have mostly simple geometries and gently dipping reflections the prograding sequences are commonly located near the seaward edges of major mesozoic and older margin structures relatively rapid cenozoic subsidence has occured due to the probable rifting in the ross sea thermal subsidence in the antarctic peninsula and isostatic crustal flexure in wilkes land in prydz bay and the weddell sea prograding sequences cover mesozoic basins that have undergone little apparent cenozoic tectonism grounded ice sheets are viewed by us and others as the principal mechanism for depositing the antarctic prograding sequences during the initial advance of grounded ice the continental shelf is flexurally overdeepened the inner shelf is heavily eroded and gently dipping glacial strata are deposited on the shelf i e type iia sequences the overdeepened shelf profile is preserved a during glacial times by grounded ice sheets episodically crossing the shelf eroding sediments from onshore and inner shelf areas and depositing sediments at the front of the ice sheet as outer shelf topset banks and continental slope foreset aprons i e type ia sequences and b during interglacial times like today by little or no clastic sedimentation on the continental shelf other than beneath retreated ice shelves lying far from the continental sheld edge ice streams carve broad depressions across the shelf and carry abundant basal sediments directly to the continental shelf edge thereby creating troughmouth fans and sheet like prograding sequences i e type ia sequences numerous acoustic unconformities and multiple overcompacted layers within the prograding sequences suggest major fluctuations of the antarctic ice sheet the available drilling and seismic interpretations provide the following history 1 cenozoic ice sheets have existed in places near the continental shelf since middle to late eocene time 2 a grounded antarctic ice sheet first expanded to the continental shelf edge with probable overdeepening of the outer shelf in late eucene to early oligocene time in prydz bay possibly in early miocene time in the ross sea and at least by middle miocene time in the weddell sea 3 the relative amounts of shelf prograding and inferred ice volume variations and related sea level changes have increased since middle to late miocene time in the eastern ross sea prydz bay and possibly weddell sea our analysis is preliminary further acoustic surveys and scientific drilling are needed to resolve the proximal antarctic record of glacio eustatic climatic and tectonic events recorded by the prograding sequences

two stepping into the icehouse east antarctic weathering during progressive ice sheet expansion at the eocene oligocene transition in conjunction with increasing benthic foraminiferal 18 o values at the eocene oligocene transition eot ca 34 ma coarse grained ice rafted debris ird 425 m appears abruptly alongside fossil fish teeth with continentally derived neodymium nd isotope ratios e nd in kerguelen plateau southern ocean sediments increased antarctic weathering flux as inferred from two steps to less radiogenic e nd values coincides with two steps in benthic foraminiferal 18 o values these results indicate that two distinct surges of weathering were generated by east antarctic ice growth during the eot weathering by ice sheets during a precursor glaciation at 33 9 ma did not produce significant ird accumulation during the first e nd shift glacial weathering was sustained during a terrace interval between the two steps probably by small high elevation ice sheets a large increase in weathering signals the rapid coalescence of small ice sheets into an ice sheet of continental proportions ca 33 7 ma rapid ice sheet expansion resulted in a suppression of weathering due to less exposed area and colder conditions parallel changes in antarctic weathering flux and deep sea carbonate accumulation suggest that ice sheet expansion during the eot had a direct impact on the global carbon cycle possible mechanisms include associated changes in silicate weathering on the east antarctic craton and enhanced fertilization of southern ocean waters both of which warrant further investigation

late oligocene to early miocene geochronology and paleoceanography from the subantarctic south atlantic mi2 as well as several other distinctive isotope events our data suggest that the d 18 o maximum commonly associated with the oligocene miocene o m boundary falls within c6cn 2r 23 86 ma the d 13 c maximum coincides within the temporal resolution of our record with c6cn 2n r boundary and hence to the o m boundary comparison of the stable isotope record from site 1090 to the orbitally tuned stable isotope record from odp site 929 across the o m boundary shows that variability in the two records is very similar and can be correlated at and below the o m boundary site 1090 stable isotope records also provide the first deep southern ocean end member for reconstructions of circulation patterns and late oligocene to early miocene climate change comparison to previously published records suggests that basin to basin carbon isotope gradients were small or nonexistent and are inconclusive with respect to the direction of deep water flow oxygen isotope gradients between sites suggest that the deep southern ocean was cold in comparison to the north atlantic indian and the pacific oceans dominance of cold southern component deep water at site 1090 at least until 17 ma suggests that relatively cold circumpolar climatic conditions prevailed during the late oligocene and early miocene we believe that a relatively cold southern ocean reflects unrestricted circumpolar flow through the drake passage in agreement with bathymetric reconstructions index terms 4267 oceanography general paleoceanography 1035 geochemistry geochronology 4870 oceanography biological and chemical stable isotopes keywords paleoceanography 1035 geochronology stable isotopes

glaciation across the oligocene miocene boundary in southern mcmurdo sound antarctica new chronology from the ciros 1 drill hole few palaeogene and neogene sediment cores from the antarctic continental margin have been dated with sufficient precision to enable establishment of direct linkages between glacial events on the antarctic continent and marked events in deep sea delta 18o records as a result much of our knowledge of the gradual but stepwise shift from greenhouse climates of the cretaceous to the ice house climates of the quaternary is inferred from well dated and more continuously deposited deep sea sediments in this study we present new magnetostratigraphic results from the ciros 1 drill core from mcmurdo sound antarctica along with a reinterpretation of a published diatom biostratigraphic zonation that is constrained by correlation to a high precision age model from the nearby crp 2 2a drill core our results suggest that most of the upper 350 m of the ciros 1 drill core represents rapid sediment accumulation during a short time interval spanning the oligocene miocene boundary chronostratigraphic control is precise enough to enable correlation of this interval of glacimarine sedimentation with the mi 1 deep sea delta 18o event which confirms that the mi 1 event was related to a major expansion of antarctic ice a major unconformity at 366 m in the ciros 1 drill core which is widely observed in regional seismic reflection studies represents 9 myr of missing time this unconformity can be traced offshore into the ross sea using seismic stratigraphy and is interpreted to indicate significant east antarctic ice sheet development during the mi 1 glaciation the stratigraphic expression of this 400 kyr glacial event is evidently multiphase and complex in the victoria land basin probably because it was punctuated by higher frequency orbitally induced glacial oscillations the presence of nothofagidites pollen throughout the ciros 1 drill core and the presence of a nothofagus southern beech leaf within the early miocene portion of the core indicate that antarctic mean summer temperatures did not decrease below 5 deg c throughout the mi 1 glaciation these temperatures are significantly warmer than present day mean summer temperatures at sea level in mcmurdo sound the persistence of a nothofagus forest in coastal southern victoria land throughout this time interval suggests that the present state of deep refrigeration was not reached until some time after the mi 1 glaciation

a review of fossil rhinoceroses from the neogene of myanmar with description of new specimens from the irrawaddy sediments abstract four genera and one indeterminate genus total eight species of fossil rhinoceroses mammalia perissodactyla rhinocerotidae are recognized from the neogene of central myanmar in the early miocene most area of central myanmar were under the shallow marine condition and no rhinocerotid remain has been documented yet during the middle to late miocene the rhinocerotid remains are commonly found and are represented by diceratherium naricum brachypotherium perimense brachypotherium fatehjangense and an indeterminate rhinocerotid in the latest miocene these archaic rhinoceroses became extinct in the late neogene the extant genera rhinoceros late miocene to pleistocene and dicerorhinus plio pleistocene first appeared in myanmar they appear to have dispersed to the island southeast asia from the continental asia during the early pleistocene to middle pleistocene when the eustatic sea level became low remarkably

lithostratigraphy and vertebrate biostratigraphy of the early miocene himalayan foreland zinda pir dome pakistan abstract deposits in the sulaiman foothills and zinda pir dome in west central pakistan provide new insight into the critical early miocene record of himalayan foreland sedimentation and paleobiology the chitarwata formation which underlies the vihowa formation in the sulaiman foothills predates the siwalik deposits on the potwar plateau of north central pakistan and provides a record of mammals spanning the interval between the early miocene bugti fauna and middle miocene to pleistocene siwalik faunas siwalik deposits on the potwar plateau are no older than middle miocene they represent fluvial environments in contrast the chitarwata and lower vihowa formations in the zinda pir dome represent coastal delta plain and fluvial environments respectively biostratigraphic information from the chitarwata formation coupled with paleomagnetic data reported by friedman et al 1992 from coincident strata suggest that coastal environments persisted in the area of the sulaiman foothills until about 18 6 ma when they were replaced by fluvial environments probably representing the ancestral indus river system apparently during the early miocene when sediments of the chitarwata formation were accumulating on the western portion of the himalayan foreland basin much of the area of the potwar plateau to the north was being eroded the overlying vihowa formation along with the relatively contemporaneous kamlial formation on the potwar plateau represent the appearance of widespread terrestrial sedimentation in the himalayan foreland basin

siwalik age faunas from the himalayan foreland basin of south asia abstract the himalayan foreland basin is characterised by three principal sedimentary successions these are the subathu group palaeocene eocene the murree or dharamsala group oligocene miocene and the siwalik group miocene pleistocene the basin was linked in the east to the bay of bengal through the bengal basin and its western part was connected to the arabian sea through rajasthan and kachchh gujarat the himalayan foothills have long been known for yielding rich mammalian fossil occurrences and significant localities in the indian siwaliks include kalagarh ramnagar haritalyangar chandigarh and jammu regions the bugti basin and zinda pir area of sulaiman range of pakistan were also part of the foreland basin as lower and middle siwalik fossils are known from the vihowa and litra formations respectively the marwat formation of bhittani and marwat ranges pakistan have also yielded pinjor age vertebrate fossils the middle and upper siwalik age fossils are also known from the irrawaddy formation of myanmar where older pegu beds have also yielded scanty lower siwalik age fossils this faunal succession in the irrawaddy valley may have geologically and biogeographically belonged to the himalayan foreland basin in the past additional mammalian fossils having an affinity with the lower and middle siwaliks are known from the khari nadi formation of kachchh the bokabil formation of tripura also yielded scanty lower to middle siwalik fossils a younger siwalik late miocene assemblage is known from piram island of gujarat these areas are also part of the foreland basin most recently a late miocene suid species was discovered and reported from near baripada odisha the paper discusses the respective faunal lists of the various successions mentioned above finally the paper discusses the implications of the foreland faunas the faunas of lower and middle siwaliks of foreland basin have links with europe turkey africa and central asia and throw light on the uplift of the himalaya the post siwalik faunas of central and peninsular india and indo gangetic plains have also yielded remnant siwalik taxa including stegodon insignis elephas hysudricus and potamochoerus theobaldi the kurnool cave fauna and recent fauna of india have also generic resemblance with the foreland faunas

orbitally paced climate oscillations across the oligocene miocene boundary the late oligocene and early miocene periods some 21 to 27 million years ago have generally been viewed as times of moderate global warmth and ice free conditions yet several lines of evidence suggest that this interval was punctuated by at least one and possibly several episodes of high latitude cooling and continental glaciation1 2 3 here we present stable isotope and per cent coarse fraction data from an equatorial western atlantic deep sea sediment core that provide high resolution records of the climate variability across the oligocene miocene transition 22 5 25 7 million years ago a strong 40 kyr periodicity in the oxygen isotope record is consistent with a high latitude orbital obliquity control on ice volume and temperature orbital influences are also apparent at precession and eccentricity frequencies including a series of 400 kyr oscillations that culminate in distinct maxima at the oligocene miocene boundary about 23 7 million years ago covariance between the carbon and oxygen isotope records suggests that the oceanic carbon cycle may have contributed to global cooling during the 400 kyr cycles particularly at the oligocene miocene boundary

evolution of atlantic thermohaline circulation early oligocene onset of deep water production in the north atlantic the flow of deep water masses is a key component of heat transport in the modern climate system yet the role of deep ocean heat transport during periods of extreme warmth is poorly understood the present mode of meridional overturning circulation is characterized by deep water formation in both the north atlantic and the southern ocean however a different mode of meridional overturning circulation operated during the extreme greenhouse warmth of the early cenozoic during which time the southern ocean was the dominant region of deep water formation the combination of general global cooling and tectonic evolution of the atlantic basins over the past 55 m y ultimately led to the development of a mode of overturning circulation characterized by both southern ocean and north atlantic deep water sources the change in deep water circulation mode may in turn have affected global climate however unraveling the causes and consequences of this transition requires a better understanding of the timing of the transition new nd isotope data from the southeastern atlantic ocean indicate that the initial transition to a bipolar mode of deep water circulation occurred in the early oligocene ca 33 ma the likely cause of significant deep water production in the north atlantic was tectonic deepening of the sill separating the greenland norwegian sea from the north atlantic

cenozoic global sea level sequences and the new jersey transect results from coastal plain and continental slope drilling the new jersey sea level transect was designed to evaluate the relationships among global sea level eustatic change unconformity bounded sequences and variations in subsidence sediment supply and climate on a passive continental margin by sampling and dating cenozoic strata from coastal plain and continental slope locations we show that sequence boundaries correlate within 0 5 myr regionally onshore offshore and interregionally new jersey alabama bahamas implicating a global cause sequence boundaries correlate with 18o increases for at least the past 42 myr consistent with an ice volume glacioeustatic control although a causal relationship is not required because of uncertainties in ages and correlations evidence for a causal connection is provided by preliminary miocene data from slope site 904 that directly link 18o increases with sequence boundaries we conclude that variation in the size of ice sheets has been a primary control on the formation of sequence boundaries since 42 ma we speculate that prior to this the growth and decay of small ice sheets caused small amplitude sea level changes 20 m in this supposedly ice free world because eocene sequence boundaries also appear to correlate with minor 18o increases subsidence estimates backstripping indicate amplitudes of short term million year scale lowerings that are consistent with estimates derived from 18o studies 25 50 m in the oligocene middle miocene and 10 20 m in the eocene and a long term lowering of 150 200 m over the past 65 myr consistent with estimates derived from volume changes on mid ocean ridges although our results are consistent with the general number and timing of paleocene to middle miocene sequences published by workers at exxon production research company our estimates of sea level amplitudes are substantially lower than theirs lithofacies patterns within sequences follow repetitive predictable patterns 1 coastal plain sequences consist of basal transgressive sands overlain by regressive highstand silts and quartz sands and 2 although slope lithofacies variations are subdued reworked sediments constitute lowstand deposits causing the strongest most extensive seismic reflections despite a primary eustatic control on sequence boundaries new jersey sequences were also influenced by changes in tectonics sediment supply and climate during the early to middle eocene low siliciclastic and high pelagic input associated with warm climates resulted in widespread carbonate deposition and thin sequences late middle eocene and earliest oligocene cooling events curtailed carbonate deposition in the coastal plain and slope respectively resulting in a switch to siliciclastic sedimentation in onshore areas oligocene sequences are thin owing to low siliciclastic and pelagic input and their distribution is patchy reflecting migration or progradation of depocenters in contrast miocene onshore sequences are thicker reflecting increased sediment supply and they are more complete downdip owing to simple tectonics we conclude that the new jersey margin provides a natural laboratory for unraveling complex interactions of eustasy tectonics changes in sediment supply and climate change

changes in paleocurrents during the development of an obliquely convergent plate boundary sulaiman fold belt southwestern himalayas west central pakistan abstract pre orogenic cretaceous shelf sandstones at the northern and southern ends of the sulaiman range in west central pakistan show basically westward dispersal which is off the craton however paleocene marine sandstones in the south spread east southeast and early eocene deltaic sandstones in the north spread southeast and north these are mostly onto the craton and indicate slope reversal of the cretaceous shelf post oligocene fluvial molasse shows mostly southward drainage a 3852 m section of molasse in the northern sulaiman range comprises a lower 2378 m of claystones and upwardly fining sandstones that represent meandering rivers and an upper 1474 m that are dominated by conglomerates that represent gravelly braided rivers paleocurrents in the lower meandering part of the section were generally southward but very variable whereas those in the upper braided part were more uniform and show eastward flow a 3146 m section of molasse in the southern sulaiman range comprises 1 a basal 1160 m sequence of claystones and sandstones meandering streams with very diverse flow directions overall to the southwest 2 a middle 1603 m sequence dominated by pebbly sandstone with large bedforms big sandy braided rivers with less diverse flow to the southwest and 3 an upper 383 m conglomeratic sequence gravelly braided streams that still flow uniformly southwest rivers in the early molasse paralleled the modern sulaiman range in the north and flowed obliquely into it in the south which suggests no uplift of the modern front of the range until the onset of modern transverse eastward drainage and the associated influx of conglomerates in present and admittedly uncertain lithostratigraphic terms uplift of the modern front of the range apparently began about 700 m lower in the north than in the south the northern and southern molasse sections otherwise show broadly similar histories of river development

eocene oligocene ocean de acidification linked to antarctic glaciation by sea level fall one of the most dramatic perturbations to the earth system during the past 100 million years was the rapid onset of antarctic glaciation near the eocene oligocene boundary some 34 million years ago this climate transition was accompanied by a deepening of the calcite compensation depth the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear merico et al use a global biogeochemical box model to test competing hypotheses put forward to explain the eocene oligocene transition they find that only shelf to deep sea carbonate partitioning can explain the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor this work sheds new light on the mechanisms linking glaciation and ocean acidity change during this important climate transition a global biogeochemical box model is used to test competing hypotheses put forward to explain the eocene oligocene transition it is found that only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor this work sheds new light on the mechanisms linking glaciation and ocean acidity change across the climate transition of the cenozoic one of the most dramatic perturbations to the earth system during the past 100 million years was the rapid onset of antarctic glaciation near the eocene oligocene epoch boundary1 2 3 34 million years ago this climate transition was accompanied3 by a deepening of the calcite compensation depth the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution changes in the global carbon cycle4 rather than changes in continental configuration5 have recently been proposed as the most likely root cause of antarctic glaciation but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear here we use a global biogeochemical box model to test competing hypotheses put forward to explain the eocene oligocene transition we find that of the candidate hypotheses only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor in our simulations glacioeustatic sea level fall associated with the growth of antarctic ice sheets permanently reduces global calcium carbonate accumulation on the continental shelves leading to an increase in pelagic burial via permanent deepening of the calcite compensation depth at the same time fresh limestones are exposed to erosion thus temporarily increasing global river inputs of dissolved carbonate and increasing seawater 13c our work sheds new light on the mechanisms linking glaciation and ocean acidity change across arguably the most important climate transition of the cenozoic era

late paleogene terrestrial fauna and paleoenvironments in eastern anatolia new insights from the kagizman tuzluca basin abstract in eastern turkey relatively little work has been undertaken to characterize the sedimentologic and stratigraphical context of the kagizman tuzluca basin until now extending across the turkey armenian border this basin documents the syn and post collisional evolution of eastern anatolia resulting from the closure of the neotethyan seaways and the final collision of the afro arabian and eurasian plates from detailed sedimentological and paleontological studies we propose an interpretation of the lithology and depositional environment of the late paleogene alhan formation located on the western bank of the aras river this sequence of terrestrial clastics rests directly and unconformably onto the ophiolitic melange and it documents several depositional sequences deposited in alluvial plain and lacustrine environments at this stage the age of the alhan formation can only be calibrated by fossil evidence several stratigraphic levels yielding fossil data along the section have been identified but these poor assemblages of fauna and flora hamper extensive comparisons with roughly contemporaneous localities of central and southern asia carnivorous and ruminant mammal remains are reported for the first time from the supposed late oligocene gungormez formation the identified fossil mammal taxa reveal biogeographic affinities between central anatolia and southern asia thus suggesting dispersal between these areas during the oligocene or earlier further studies of the fossil assemblages from the kagizman tuzluca basin and other basins of eastern anatolia and lesser caucasus regions are needed to better constrain the paleobiogeographic models

an osmium isotope excursion associated with the late paleocene thermal maximum evidence of intensified chemical weathering in the latest paleocene an abrupt shift to more negative 13c values has been documented at numerous marine and terrestrial sites bralower et al 1997 cramer et al 1999 kaiho et al 1996 kennett and stott 1991 koch et al 1992 stott et al 1996 thomas and shackleton 1996 zachos et al 1993 this carbon isotope event cie is coincident with oxygen isotope data that indicate warming of surface waters at high latitudes of nearly 4 6 c kennett and stott 1991 and more moderate warming in the subtropics thomas et al 1999 here we report 187os 188os isotope records from the north atlantic and indian oceans which demonstrate a 10 increase in the 187os 188os ratio of seawater coincident with the late paleocene cie this excursion to higher 187os 188os ratios is consistent with a global increase in weathering rates the inference of increased chemical weathering during this interval of unusual warmth is significant because it provides empirical evidence supporting the operation of a feedback between chemical weathering rates and warm global climate which acts to stabilize earth s climate walker et al 1981 estimates of the duration of late paleocene cie bains et al 1999 bralower et al 1997 norris and rohl 1999 rohl et al 2000 in conjunction with the os isotope data imply that intensified chemical weathering in response to warm humid climates can occur on timescales of 104 105 years this interpretation requires that the late paleocene thermal maximum os isotope excursion be produced mainly by increased os flux to the ocean rather than a transient excursion to higher 187os 188os ratios in river runoff although we argue that the former is more likely than the latter we cannot rule out significant changes in the 187os 188os ratio of rivers

evidence for late oligocene establishment of the antarctic circumpolar current removal of the last impediment to circum antarctic flow opening of the drake passage between antarctica and south america is essential to establishment of the acc and has been placed in both the earliest oligocene and earliest miocene on the basis of paleomagnetic reconstructions the tasman gateway between antarctica and tasmania notably deepened following 33 5 ma completion of the acc circuit has been seen as the key to major growth of the east antarctic ice sheet by thermal isolation of the continent an alternative argument attributes ice sheet growth to changes in atmospheric pco2 we present evidence on current strength and water mass properties suggesting a clear increase in flow speed and homogeneity of southern ocean water masses in the latest oligocene after about 23 95 ma marking establishment of the acc attributable to deep opening of drake passage the mi 1 glaciation may be a consequence establishment of a permanent low altitude ice sheet does not appear to take place prior to mid miocene cooling

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

late oligocene initiation of the antarctic circumpolar current evidence from the south pacific the antarctic circumpolar current acc is a key feature of the southern ocean its development may have helped cool antarctica and initiate southern hemisphere glaciation the deep circulation of the acc must have been established after both the tasman gateway between antarctica and australia and the drake passage between south america and antarctica opened however estimates for acc initiation range over 20 m y from the middle eocene to early miocene a new piston core of upper oligocene to holocene sediments from the south pacific has allowed us to delimit the formation of the acc to the late oligocene ca 25 23 ma upper oligocene current worked sediments and a hiatus to the upper miocene result from the beginning of the modern acc flow i e when strong currents and mixing throughout the water column were established previously published nd isotope data date the first intrusion of pacific water into the atlantic much earlier the discrepancy with our results can be reconciled by the different methods measuring different flow regimes tracer methods such as nd are sensitive to relatively small and shallow incursions of water whereas pelagic erosional regimes require vigorous deep flow

deep water temperature carbonate ion and ice volume changes across the eocene oligocene climate transition 1 paired benthic foraminiferal stable isotope and mg ca data are used to estimate bottom water temperature bwt and ice volume changes associated with the eocene oligocene transition eot the largest global climate event of the past 50 myr we utilized odp sites 1090 and 1265 in the south atlantic to assess seawater 18o w antarctic ice volume and sea level changes across the eot 33 8 33 54 ma we also use benthic 13c data to reconstruct the sources of the deep water masses in this region during the eot our data together with previously published records indicate that a pulse of northern component water influenced the south atlantic immediately prior to and following the eot benthic 18o records show a 0 5 increase at 33 8 ma eot 1 that represents a 2 c cooling and a small 10 m eustatic fall that is followed by a 1 0 increase associated with oi 1 the expected cooling of deep waters at oi 1 33 54 ma is not apparent in our mg ca records we suggest the cooling is masked by coeval changes in the carbonate saturation state co32 which affect the mg ca data to account for this the bwt ice volume and w estimates are corrected for a change in the co32 of deep waters on the basis of recently published work corrected bwt at sites 1090 and 1265 show a 1 5 c cooling coincident with oi 1 and an average w increase of 0 75 the increase in ice volume during oi 1 resulted in a 70 m drop in global sea level and the development of an antarctic ice sheet that was near modern size or slightly larger

newly discovered paleogene deltaic sequence in katawaz basin pakistan and its tectonic implications in the katawaz basin pakistan the deltaic and turbidite facies of the khojak formation are the paleogene analogue of the modern indus river emptying into the arabian sea to form the indus delta fan system facies identified include upper continental slope to prodelta distal to proximal distributary mouth bar distributary channel interdistributary bay estuary fluvial channel natural levee and flood plains of lower and upper delta plains the proposed model is a fluvial dominated wave modified delta that axially fed khojak submarine fan turbidites exposed in the southwestern part of the basin these sediments were eroded from the early himalayan orogenic highlands and transported southwestward down the axis of the katawaz remnant ocean basin

paleogeographic and paleotectonic evolution of the himalayan range as reflected by detrital modes of tertiary sandstones and modern sands indus transect india and pakistan detrital modes of sandstones derived from the himalayan suture belt record the history of the mountain range since initial collision between india and asia which began in latest paleocene time tertiary clastic wedges deposited in fore arc foreland and remnant ocean basins and exposed along the indus transect from northernmost india to the arabian sea represent the best opportunity to study sedimentary responses to successive tectonic events during continental collision quartzose continental block and feldspatholithic magmatic arc sandstones were deposited respectively on the passive indian tethys himalayan succession and active asian indus group continental margins during late cretaceous paleocene time closure of the neotethys was marked by sudden arrival of volcanic and ophiolitic detritus on the passive continental margin of the indian plate during deposition of sediments dated at foraminiferal zones p6 pakistan to p8 india starting in early eocene time deposition of chulung la formation and murree supergroup volcanic and ophiolitic to metasedimentary detritus was accumulated in rapidly subsiding piggy back and foreland basins homogeneous petrographic composition within the eocene lower miocene murree supergroup with only slight progressive increase of detrital feldspars suggests erosion of largely supracrustal rocks involved in thrusting in the north in middle miocene time marked enrichment in medium to high grade metamorphic detritus in foreland sandstones siwalik group reflects rapid uplift of a warm wedge of indian crust which was carried southward along the main central thrust this major paleogeographic change was recorded also by quartzolithic remnant ocean turbidites which were fed great distances along transverse fracture zones and later accreted in the coastal makran subduction complex panjgur association and makran group recycled orogen detritus derived from the elevated himalayan chain is still accumulating today in the indus fan enrichment in feldspars with respect to ancient sandstones reflects deep erosion levels into mid crustal rocks along the core of the growing orogen

stratigraphic response and mammalian dispersal during initial india asia collision evidence from the ghazij formation balochistan pakistan initial continental collision between india and asia is thought to have caused significant changes to global climate and biota yet its timing and biogeographic consequences are uncertain structural and geophysical evidence indicates initial collision during the early paleogene but sedimentary evidence of this has been controversial owing to the intense deformation and metamorphism along the suture zone modern orders of mammals that appeared abruptly on northern continents coincident with the global warming event marking the paleocene eocene boundary are hypothesized to have originated on the indian subcontinent but no relevant paleontological information has been available to test this idea here we present new paleomagnetic sedimentologic and paleontologic evidence to show that the lower eocene ghazij formation of western pakistan records continental sedimentation and mammalian dispersal associated with initial india asia collision our results are consistent with the initial collision occurring near the paleocene eocene boundary but modern orders of mammals appeared later in indo pakistan and thus did not likely originate on the indian subcontinent

timing and nature of the deepening of the tasmanian gateway 1 tectonic changes that produced a deep tasmanian gateway between australia and antarctica are widely invoked as the major mechanism for antarctic cryosphere growth and antarctic circumpolar current acc development during the eocene oligocene e o transition 34 33 ma ocean drilling program odp leg 189 recovered near continuous marine sedimentary records across the e o transition interval at four sites around tasmania these records are largely barren of calcareous microfossils but contain a rich record of siliceous and organic walled marine microfossils in this study we integrate micropaleontological sedimentological geochemical and paleomagnetic data from site 1172 east tasman plateau to identify four distinct phases a d in the e o tasmanian gateway deepening that are correlative among odp leg 189 sites phase a prior to 35 5 ma minor initial deepening characterized by a shallow marine prodeltaic setting with initial condensation episodes phase b 35 5 33 5 ma increased deepening marked by the onset of major glauconitic deposition and inception of energetic bottom water currents phase c 33 5 30 2 ma further deepening to bathyal depths with episodic erosion by increasingly energetic bottom water currents phase d 30 2 ma establishment of stable open ocean warm temperate oligotrophic settings characterized by siliceous carbonate ooze deposition our combined evidence indicates that this early oligocene tasmanian gateway deepening initially produced an eastward flow of relatively warm surface waters from the australo antarctic gulf into the southwestern pacific ocean this proto leeuwin current fundamentally differs from previous regional reconstructions of eastward flowing cool water e g a proto acc during the early oligocene and thereby represents an important new constraint for reconstructing regional to global scale dynamics for this major global change event

sea ice feedback and cenozoic evolution of antarctic climate and ice sheets 1 the extent and thickness of antarctic sea ice have important climatic effects on radiation balance energy transfer between the atmosphere and ocean and moisture availability this paper explores the role of sea ice and related feedbacks in the cenozoic evolution of antarctic climate and ice sheets using a numerical climate model with explicit dynamical representations of sea ice and continental ice sheets in a scenario of decreasing cenozoic greenhouse gas concentrations our model initiates continental glaciation before any significant sea ice forms around the continent once variable ice sheets are established seasonal sea ice distribution is highly sensitive to orbital forcing and ice sheet geometry via the ice sheet s control on regional temperature and low level winds although the expansion of sea ice has significant climatic effects near the coast it has only minimal effects in the continental interior and on the size of the ice sheet therefore the cenozoic appearance of antarctic sea ice was primarily a response to the growth of grounded ice sheets and was not a critical factor in episodes of paleogene and neogene glaciation the influence of the east antarctic ice sheet on sea ice southern ocean surface temperatures and winds has important implications for ocean circulation the marine carbon cycle and the development of the west antarctic ice sheet the sensitivity of sea ice to grounded ice sheets implies reconstructions of sea ice based on marine diatoms are good indicators of glacial conditions in the continental interior and may provide insight into the long term stability of antarctic ice sheets

new tropical carcharhinids chondrichthyes carcharhiniformes from the late eocene early oligocene of balochistan pakistan paleoenvironmental and paleogeographic implications new selachians sharks and rays have been collected from several late eocene and early oligocene marine localities in the bugti hills balochistan pakistan two new species of requiem sharks close to the recent bull shark are described carcharhinus balochensis and carcharhinus perseus the rest of the fauna is notable for the strong representation of carcharhiniformes these selachian faunas represent a unique tropical association for the oligocene period and one of the first modern tropical selachian faunas with modern taxa such as the two new species of bull sharks negaprion sp and one of the first occurrences of sphyrna sp moreover these faunas permit paleoenvironmental interpretation of adjacent land masses the relatively modern aspect of these faunas compared with other contemporaneous and younger selachian associations from atlantic and mediterranean seas suggests biogeographic isolation of selachian communities living in eastern and western parts of the tethys before its final closure during the early middle miocene

mapping of sea ice production for antarctic coastal polynyas 1 active sea ice production in antarctic coastal polynyas causes dense water formation finally leading to antarctic bottom water aabw formation this study gives the first mapping of sea ice production in the antarctic ocean based on heat flux calculation with ice thickness data derived from satellite data the highest ice production occurs in the ross ice shelf polynya region the ice production there decreased by 30 from the 1990s to the 2000s which can be one candidate for causing the recent freshening of aabw the cape darnley polynya in east antarctica is found to be the second highest production area suggesting a possible aabw formation area according to our estimation around 10 of southern ocean sea ice is produced in the major antarctic coastal polynyas the mapping provides surface heat and salt flux conditions in the ice covered region which have not been well understood

new remains of the baluchithere paraceratherium bugtiense pilgrim 1910 from the late latest oligocene of the bugti hills balochistan pakistan new dental and postcranial remains referred to the giant rhinocerotoid paraceratherium bugtiense are described originating from its type locality lundo chur in eastern balochistan pakistan probable sexual dimorphism is revealed on the lower incisors the manus was tridactyl with a reduced fifth metacarpal the stratigraphic range of both p bugtiense and the amynodontid cadurcotherium indicum extends from the early early oligocene to the late latest oligocene in the bugti hills q 2004 published by elsevier ltd

detrital modes and provenance of the paleogene khojak formation in pakistan implications for early himalayan orogeny and unroofing different tectonic settings have characteristic detrital modes and sediment dispersal patterns detrital modes and sediment dispersal patterns of the siliciclastic khojak formation in the katawaz basin pakistan suggest that its sand was derived from the early himalayan orogen and longitudinally transported to the katawaz remnant ocean where it was deposited as a delta submarine fan complex modal analysis of the khojak formation suggests composition that is dominated by subangular quartz with abundant lithic fragments and minor feldspar i e qt 60 f 9 l 31 qt total quartz f feldspar l lithic fragments the predominance of quartz sedimentary and low grade metamorphic lithic fragments suggests early derivation from a collision orogen scarcity of detrital feldspar and volcanic lithic fragments precludes a magmatic arc as the main source the decrease in monocrystalline quartz concomitant increase in total lithic percentages and relative abundance of low grade metamorphic lithic fragments from the bottom to the top of the khojak formation reflect progressive erosional history of the early himalaya this history is part of a previously known major unroofing trend collectively depicted by the detrital modes of the murree formation siwalik group and the modern indus fan in the indian ocean these detrital modes are also related in time and space

effect of the deepening of the tasman gateway on the global ocean 1 we examine the effect of the deepening of the tasman seaway at the end of the eocene in a climate model with realistic late eocene bathymetry and winds for this we have constructed an eocene numerical model based on the university of victoria climate model with wind forcing derived from a fully coupled eocene simulation the model climate state is characterized by an oceanic meridional overturning circulation moc involving southern hemisphere sinking and a northward atmospheric moisture transport across the equator the deepening of the tasman seaway in the presence of an open drake passage and the associated establishment of the antarctic circumpolar current acc have a limited climatic impact on antarctica nonetheless the antarctic deep sinking regions cool sufficiently to lead to a global deep ocean cooling of 3 c no initiation of northern component water is found indicating that this may require the development of a more mature acc previous studies suggest that the ross sea gyre cools the east coast of australia and expected the deepening of the tasman seaway to lead to a warming east of australia due to the introduction of warmer water from the australo antarctic gulf we here find that this warming is limited to close to the australian coast and that widespread cooling prevails further off shore

resolving apparent conflicts between oceanographic and antarctic climate records and evidence for a decrease in pco2 during the oligocene through early miocene 34 16 ma abstract an apparent mismatch between published oxygen isotopic data and other paleoclimate proxies for the span from 26 16 ma is resolved by calibration against global sea level estimates obtained from backstripping continental margin stratigraphy ice volume estimates from calibrated oxygen isotope data compare favorably with stratigraphic and palynological data from antarctica and with estimates of atmospheric pco2 throughout the oligocene to early miocene 34 16 ma isotopic evidence for an east antarctic ice sheet eais as much as 30 larger than its present day volume at glacial maxima during that span is consistent with seismic reflection and stratigraphic evidence for an ice sheet covering much of the antarctic continental shelf at the same glacial maxima palynological data suggest long term cooling during the oligocene with cold near tundra environments developing along the coast at glacial minima no later than the late oligocene a possible mechanism for this long term cooling is a decrease in atmospheric pco2 from the middle eocene to oligocene reaching near pre industrial levels by the latest oligocene and remaining at those depressed levels throughout the miocene

a time slice approach to the history of cenozoic sedimentation in the indian ocean abstract results from drilling at over 100 sites have been combined with a new plate tectonic model to produce a series of palinspastic maps which represent snap shots of the changing patterns of sediment accumulation in the indian ocean through the cenozoic the maps clearly delineate the main sedimentary depocenters and show how the sedimentary record has responded on an oceanwide scale to major changes in paleogeography tectonics paleocirculation and or climate paleogene sediment accumulation rates were generally low with significant accumulation in only limited areas suggesting weak ocean circulation and stable well stratified conditions by contrast the vigorous thermohaline circulation of the neogene resulted in substantial widespread sedimentation accumulation rates were generally high and displayed a wide range of values following rapid growth of the east antarctic ice sheet in the mid miocene carbonate sedimentation has been progressively restricted to the shallow ridges and plateaus of the western indian ocean but accumulates there with locally high rates the link between tectonics and terrigenous sedimentation is exemplified by the major deep sea fans off east africa zambezi fan and india indus and bengal fans which developed in response to uplift and erosion beginning in late oligocene time in the east african rift system and the himalayas respectively although maps from only five widely spaced times are shown the methodology is such that a continuous series of maps at intervals as close as 1 m y can readily be generated ultimately the combination of such time slice maps with the results of detailed time series studies will provide a powerful tool for understanding past oceanic environments

early rhinocerotids mammalia perissodactyla from south asia and a review of the holarctic paleogene rhinocerotid record the earliest rhinocerotids from south asia are identified on the basis of few dental remains originating from the late eocene of thailand wai lek mine krabi basin and the early oligocene of pakistan paali nala c2 bugti hills once synthesized the holarctic paleogene rhinocerotid record points out a westward diachronism of rhinocerotid first appearance data from north america to europe via asia throughout mid cenozoic times the faunal similarity among mammal localities from the late eocene and early oligocene of peninsular thailand southern china and pakistan suggests the existence of a single south asian paleoprovince during this interval and the persistence of a tropical subtropical climate substantial faunal changes recorded in eastern balochistan reveal a significant climatic deterioration from the middle part of the oligocene neither provinciality nor endemism is noticeable for rhinocerotoid taxa recognized in the oligocene of the indian subcontinent neither the himalayas nor the tibet plateau was a paleogeographic barrier for large mammals during this interval resume les plus anciens rhinocerotides d asie du sud sont identifies gr ce a quelques restes dentaires provenant de l eocene superieur de thailande mine de wai lek bassin de krabi et de l oligocene inferieur du pakistan paali nala c2 collines bugti la synthese du registre fossile paleogene holarctique des rhinocerotides revele un net diachronisme des premieres apparitions de rhinocerotides depuis l est amerique du nord vers l ouest asie puis europe au cours du cenozoique moyen la similarite des communautes de mammiferes entre les localites de l eocene superieur et de l oligocene inferieur de thailande peninsulaire de chine du sud et du pakistan suggere l existence d une seule paleoprovince sud asiatique pendant la periode consideree sous un climat tropical a subtropical les changements fauniques enregistres au balouchistan oriental revelent une deterioration climatique significative a partir du milieu de l oligocene aucun indice de provincialisme ou d endemisme n est releve pour les rhinocerotoides oligocenes du sous continent indien ni les himalayas ni le plateau du tibet ne constituaient a l epoque une barriere paleogeographique pour les grands mammiferes

timing and climatic consequences of the opening of drake passage age estimates for the opening of drake passage range from 49 to 17 million years ago ma complicating interpretations of the relationship between ocean circulation and global cooling secular variations of neodymium isotope ratios at agulhas ridge southern ocean atlantic sector suggest an influx of shallow pacific seawater approximately 41 ma the timing of this connection and the subsequent deepening of the passage coincide with increased biological productivity and abrupt climate reversals circulation productivity linkages are proposed as a mechanism for declining atmospheric carbon dioxide these results also indicate that drake passage opened before the tasmanian gateway implying the late eocene establishment of a complete circum antarctic pathway

ocean overturning since the late cretaceous inferences from a new benthic foraminiferal isotope compilation 1 benthic foraminiferal oxygen isotopic d 18 o and carbon isotopic d 13 c trends constructed from compilations of data series from multiple ocean sites provide one of the primary means of reconstructing changes in the ocean interior these records are also widely used as a general climate indicator for comparison with local and more specific marine and terrestrial climate proxy records we present new benthic foraminiferal d 18 o and d 13 c compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to 80ma andtentatively to 110ma first order variations ininterbasinal isotopicgradients delineate transitions from interior ocean heterogeneity during the late cretaceous 65 ma to early paleogene 35 65 ma homogeneity and a return to heterogeneity in the late paleogene early neogene 35 0 ma we propose that these transitions reflect alterations in a first order characteristic of ocean circulation the ability of winds to make water in the deep ocean circulate we document the initiation of large interbasinal d 18 o gradients in the early oligocene and link the variations in interbasinal d 18 o gradients from the middle eocene to oligocene with the increasing influence of wind driven mixing due to the gradual tectonic opening of southern ocean passages and initiation and strengthening of the antarctic circumpolar current the role of wind driven upwelling possibly associated with a tethyan circumequatorial current in controlling late cretaceous interior ocean heterogeneity should be the subject of further research

the magnetostratigraphy of the chitarwata and lower vihowa formations of the dera ghazi khan area pakistan abstract three sections of the chitarwata and lower vihowa formations were sampled along the dalana river on the southeastern flank of the zinda pir dome in the southern sulaiman range near dera ghazi khan pakistan together they provide nearly 800 m of a continuous sedimentary record of the miocene derived from the uplifted himalayan highlands previous studies have examined the middle and upper miocene sediments the siwalik group of the potwar plateau to the north however detailed investigations of earlier periods are impossible in that area due to the absence of oligocene and lower miocene sediments caused by continued overthrusting associated with the himalayan orogeny fortunately the sulaiman basin to the south which was further removed from the tectonic activity provides a record of the early miocene in the form of the chitarwata formation the dalana a b and c sections dga dgb and dgc were examined and sampled for this study a magnetostratigraphic analysis was carried out to correlate and date the chitarwata and vihowa formations exposed in this area the samples were subjected to step wise demagnetization to resolve the primary and secondary remanent magnetization components thermal demagnetization trajectories indicate that the majority of samples have sufficient internal consistency that their calculated polarities are reliable likewise the majority of the 126 measured sites showed statistically significant agreement between the three measured samples per site however the bimodal data set does not pass the reversal test and so is deemed unsuitable for tectonic interpretations the individual sections were initially correlated using lithologic and stratigraphic methods and the relationship was reinforced by the magnetostratigraphy the composite dg section was tentatively correlated with the standard magnetic polarity time scale placing the disconformable base of the chitarwata in the dga section at just older than 22 ma the chitarwata vihowa contact at 18 6 ma and the top of the vihowa in the dgc section at about 16 ma the assignment of these dates to the chitarwata will aid in future biostratigraphic and lithostratigraphic correlation of early miocene sediments effectively extending the well established siwalik faunal sequence back by four million years

pakistan mammal tooth stable isotopes show paleoclimatic and paleoenvironmental changes since the early oligocene abstract this research presents an isotopic study of three large mammal groups elephantoid proboscideans hyracodontid and rhinocerotid rhinocerotoids equids of the hipparion group from the bugti hills sequence eastern balochistan pakistan combined with published data from the miocene siwalik group northern central pakistan these two exceptional fossil records from pakistan provide an unambiguous source of biotic information from the early oligocene up to the late miocene the 13 c c and 18 o c results from the same herbivore groups show several significant variations in environmental and climatic conditions throughout the 30 to 7 5 myr period in this region first from 30 to 22 myr the environment is characterized by a relatively dry but dense forest existing under a temperate to subtropical climate with a more closed tropical environment at 23 myr oligocene 18 o of the terrestrial herbivore teeth agrees with the marine foraminifera 18 o and mg ca trends suggesting that the pakistan region was affected by global climate rather than regional conditions after 22 myr the 18 o c mammal enamel results show a long term decreasing trend until 15 myr toward a wetter environment with the appearance of tropical forests in response to the probable onset of the asian monsoon this is a period of high tectonic activity with the india asia collision leading to uplift of the tibetan plateau and shrinkage of the epicontinental paratethys sea this activity modified the land sea distribution and the thermal contrast between ocean and continent the driving force of the monsoon climate the middle miocene environment in pakistan experienced moist conditions under an intense monsoon system with relatively closed rainforest after 12 myr the 18 o c enamel values record a positive shift until 9 3 myr toward a drier environment with an increase of seasonality as suggested by higher 18 o c variability after 9 3 myr these late miocene drier climatic conditions and the asian monsoon intensification could potentially favour the c 4 photosynthetic pathway and hence the development of grassland to the detriment of subtropical forests resulting in the higher enamel 13 c values recorded after 9 3 myr