impact of india asia collision on se asia the record in borneo abstract borneo occupies a central position in the sundaland promontory of se asia it has a complex cenozoic geological history of sedimentation and deformation which began at about the same time that india is commonly suggested to have started to collide with asia some tectonic reconstructions of east and se asia interpret a large se asian block with borneo at its centre which has been rotated clockwise and displaced southwards along major strike slip faults during the cenozoic due to the indentation of asia by india however the geological history of borneo is not consistent with the island simply forming part of a large block extruded from asia the large clockwise rotations and displacements predicted by the indentor model for borneo are incompatible with palaeomagnetic evidence and there is no evidence that the major strike slip faults of the asian mainland reach borneo seismic tomography shows there is a deep high velocity anomaly in the lower mantle beneath se asia interpreted as subducted lithosphere but it can be explained just as well by alternative tectonic models as by the indentor model very great thicknesses of cenozoic sediments are present in borneo and circum borneo basins and large amounts of sediment were transported to the crocker turbidite fan of north borneo from the eocene to the early miocene but all evidence indicates that these sediments were derived from local sources and not from distant sources in asia elevated by india asia collision the cenozoic geological history of borneo records subduction of the proto south china sea and miocene collision after this ocean lithosphere was eliminated and a variety of effects resulting from long term subduction beneath se asia there is little to indicate that india asia collision has influenced the cenozoic geological record in borneo

the composition and evolution of the continental crust rare earth element evidence from sedimentary rocks the composition of the present day upper crust inferred from the uniformity of sedimentary rock r e e rare earth element patterns is close to that of granodiorite a revised andesite model is used to obtain total crustal composition the lower crust is the composition remaining assuming that the upper crust one third of the total is derived from intracrustal partial melting the upper crustal r e e pattern has pronounced eu depletion eu eu 0 64 the lower crustal pattern has eu enrichment eu eu 1 17 and the total crust has no eu anomaly relative to chondritic abundances the eu depletion in the upper crust is attributed to retention of eu in plagioclase in the lower crust because plagioclase is not stable below 40 km 10 kbar the anomaly is intracrustal in origin the archaean upper crust has a different r e e pattern to that of the present day upper crust being lower in total r e e and la yb ratios and lacking an eu anomaly these data are used to infer the archaean upper crustal composition which resembles that of the present day total crust except that ni and cr contents are higher the archaean crustal composition can be modelled by a mixture of tholeiites and tonalite trondhjemites the latter have steep light r e e enriched heavy r e e depleted patterns consistent with equilibration with garnet and hence probable mantle derivation there is little reason to suppose that the archaean lower crust was different in composition from the upper crust except locally where partial melting episodes occurred the r e e evidence is consistent with isotopic and geological evidence for a low continental growth rate in the early archaean a massive increase to about 70 of the total crust between about 3000 and 2500 ma b p and a slow increase until the present day the change from archaean to post archaean r e e patterns in the upper crust is not isochronous but is reflected in the sedimentary rock r e e patterns at differing times in different continents on the basis of a model composition for the mantle 36 of the potassium 30 of uranium 15 of lanthanum and 3 of ytterbium are concentrated in the present continental crust this enrichment is related to ionic size and valency differences from common mantle cations e g mg fe pre 3 9 ga b p crusts were obliterated by meteorite bombardment no geochemical evidence exists for primordial anorthositic sialic or mafic crusts

rocks of ages propagation of hot rock cookery in western north america cook stone technology s old world roots were established by 30 000 b p and reappeared in the new world by 10 000 b p after millennia of direct fire cooking hot rock cookery which is necessary for foods that require prolonged cooking facilitated land use intensification by affording greater utilization of nutrients in available foods on a given landscape this technology gradually diversified during the early holocene in western north america by 4000 b p its initial intensification was underway final intensification began by 2000 b p and typically peaked during the last 1500 years propagation of hot rock cookery exemplifies pre columbian food crises and signals carbohydrate revolutions wherein more high cost foods feed growing populations as modeled cook stone griddles earth ovens and steaming pits with rock heating elements are more costly facilities insofar as fuel is used to heat rocks that in turn extend cooking time and temperature more expensive still is stone boiling given that fuel heats rocks that in turn heat water that cooks the food even more expensive in terms of energy expended is the manufacture of heating elements in the form of stone ceramic and metal cooking containers all of which afford further evidence of land use intensification

stratigraphy sedimentology and environmental significance of late mid holocene dunes lauder sand hills glacial lake hind basin southwestern manitoba mid holocene eolian dune and sand sheet deposits rare in the northern great plains are buried under a meter or more of younger sediment in the glacial lake hind basin southwestern manitoba six facies observed in three cut bank exposures allow reconstruction of sedimentary processes and resulting landscape at the study site in the basin center around 6100 cal calibrated bp a mosaic of parabolic dunes with interdune and dune marginal lightly vegetated sand sheets developed in the souris river flood plain that was least partly covered with woodlands and wetlands during floods nearby interdune areas were inundated dune foreset orientation and stratification indicate a more easterly sand transport direction lending support to the hypothesis that more pervasive westerly zonal flow contributed to mid holocene aridity evident elsewhere in the northern great plains more arid conditions during the mid holocene may have helped trigger eolian activity however with the exception of a more active eolian

a new approach to identifying bone marrow and grease exploitation why the indeterminate fragments should not be ignored abstract the economic importance of bone fat to past peoples is discussed and the ethnography of bone marrow and grease extraction is briefly outlined models for expected patterns of bone fracture and fragmentation relating to the exploitation of bone marrow and grease are described current methods for assessing bone fracture and fragmentation in archaeological assemblages are discussed and a new methodology is suggested the importance of retaining and studying the indeterminate class of fragments is stressed the new methodology employs a fracture freshness index ffi to study fracture type and fragmentation is assessed through the separation of fragments into size classes and different bone types an example application is given

backstacking apatite fission track stratigraphy a method for resolving the erosional and isostatic rebound components of tectonic uplift histories measuring tectonic uplift of the mean surface of earth using thermochronological data to document uplift histories is often plagued by confusion arising from the independent nature of the thermal and sea level frames of reference the technique of backstacking apatite fission track stratigraphy differentiates between vertical movement of rocks toward earth9s surface due to erosional or tectonic denudation and tectonic uplift of earth9s surface apatite fission track analysis can also be used to identify episodes of erosion where no other evidence for the erosional event exists in addition to providing information about the timing magnitude and geographic distribution of erosion

mount mazama eruption calendrical age verified and atmospheric impact assessed geochemical identification of mount mazama ash in the greenland ice sheet project 2 gisp2 ice core gives a calendrical age of 7627 150 cal yr b p 5677 150 b c for the eruption thus providing a more accurate early holocene stratigraphic time line than previously available the gisp2 record of volcanically derived sulfate suggests a total stratospheric aerosol loading between 88 and 224 mt spread over an 6 yr period following the eruption of mount mazama taking into account the likelihood of some tropospheric aerosol transport to greenland realistic estimates of the resulting atmospheric optical depth range from 0 6 to 1 5 these values may have produced a temperature depression of 0 6 to 0 7 c at mid to high northern latitudes for 1 3 yr after the eruption these results indicate that the 5677 b c eruption of mount mazama was one of the most climatically significant volcanic events of the holocene in the northern hemisphere we also calculate a maximum stratospheric cl release of 8 1 mt by the eruption which may have led to substantial stratospheric ozone depletion

late quaternary vegetation and climate changes in central texas based on the isotopic composition of organic carbon stable carbon isotope analysis of organic carbon in alluvial deposits and soils of three streams in central texas reveals significant shifts in the ratio of c3 to c4 plant biomass production during the past 15 000 yr these temporal changes in vegetation appear to be in response to changes in climate during the late pleistocene c4 plants comprised only about 45 to 50 of the vegetative biomass in this area suggesting that conditions were cooler and wetter than at any time during the past 15 000 yr the time between 11 000 and 8000 yr b p is interpreted as transitional between late pleistocene conditions and warmer and drier holocene conditions based on a slight increase in the abundance of c4 plant biomass during the middle holocene between approximately 6000 and 5000 yr b p mixed c3 c4 plant communities were replaced almost completely by c4 dominated communities indicating prairie expansion and warmer and drier climatic conditions by 4000 yr b p the abundance of c4 plant biomass decreased to levels similar to the early holocene transitional period suggesting a return to cooler and wetter climatic conditions no significant shift in the ratio of c3 to c4 productivity has occurred during the last 4000 yr except for a slight increase in the abundance of c4 plant biomass around 2000 yr b p the results of this investigation correlate well with other regional late quaternary climatic interpretations for central and north texas the southern plains region and with other portions of the great plains

landscape evolution and human occupation during the archaic period on the northern plains recent archaeological excavations at a deeply stratified site in northwest calgary alberta have uncovered four occupation layers spanning the interval from 8000 to 2000 bp depending on the dating one accepts for the holocene thermal maximum two or more of these occupations occurred during this interval of aridity this site thus provides a record of human occupation during the archaic middle prehistoric i period in the calgary area more importantly the site occurs in an upland setting apparently far removed from reliable sources of water and normal environments of deposition yet the cultural deposits occur in sediments which extend 2 m below surface and include five sedimentary units as well as a minimum of three pedogenic units this paper presents the results of geoarchaeological research on the changing landscape for the site and notes the implications of these changes for the study of archaic manifestations on the northern plains

a reconstruction of holocene geomorphology and climate western cypress hills alberta and saskatchewan received january 28 1990 revision accepted july 18 1990 the cypress hills of southwestern saskatchewan and southeastern alberta are a key area for quaternary research because the permanent lakes and coniferous forest are sources of proxy paleoenvironmental data generally not available on the surrounding northern great plains in this paper the holocene paleoclimate of the western cypress hills is reconstructed from the pollen and organic matter contents of a 9 6 m sediment core from harris lake saskatchewan this climatic history is considerably longer than others from the semiarid interior plains of canada chronological control consists of a basal conventional radiocarbon date of 9120

cenozoic palaeogeographic evolution of sulawesi and borneo abstract sulawesi and borneo are located in the middle of the indonesian archipelago an area which has been extremely tectonically active throughout the cenozoic this paper compiles current knowledge on the geology and palaeogeography of this complex region and includes the first attempt to synthesise palaeogeographic data onto plate tectonic reconstructions construction of palaeogeographic maps helped to identify some of the strengths and weaknesses of current plate tectonic models for the region thereby highlighting areas where further geological research is required palaeogeographic maps presented using plate tectonic reconstructions as a base illustrate the evolution of borneo and sulawesi and highlight important changes in the environment during the cenozoic the tertiary geological history of eastern borneo and sulawesi is inextricably linked to the progressive accretion of continental and oceanic material from the east onto the eastern margin of sundaland and to the resultant development of volcanic arcs large tracts of western sulawesi eastern borneo the east java sea and the makassar straits formed an extensive basinal area throughout much of the tertiary implications for plate tectonics exploration for natural resources and biogeography are discussed from the palaeogeographic reconstructions of sulawesi and borneo

evidence of cultural responses to the impact of the mazama ash fall from deeply stratified archaeological sites in southern alberta canada abstract in a series of papers we adopted a regional perspective to explore the short and long term impacts of the mount mazama eruption on the plant and animal communities of the northwestern plains and later developed a model to explain human responses to this natural disaster the model assumed the convergence of natural disasters which forced the local bison hunters to abandon the impacted zone and to seek refuge among their distant relatives living beyond the eastern limits of their homeland together the refugees and their hosts intensified their subsistence strategies and adapted or developed new methods of food preparation to accommodate the increased pressure on the local resource base throughout their stay the groups continued to monitor the rebirth of their traditional homeland and eventually returned to the places occupied by their ancestors upon their return the groups continued to hunt bison but adapted the stone boiling technology to produce bone grease and pemmican this nutritious storable and transportable food source alleviated the concerns about long term shortages and became an important product in the regional exchange networks the primary objective of this paper is to test this model using sedimentary pedological and archaeological data recovered from two deeply stratified sites with evidence of human occupations before and after the eruption of mount mazama

a triassic to cretaceous sundaland pacific subduction margin in west sarawak borneo metamorphic rocks in west sarawak are poorly exposed and studied they were previously assumed to be pre carboniferous basement but had never been dated new 40ar 39ar ages from white mica in quartz mica schists reveal metamorphism between c 216 to 220 ma the metamorphic rocks are associated with triassic acid and basic igneous rocks which indicate widespread magmatism new u pb dating of zircons from the jagoi granodiorite indicates triassic magmatism at c 208 ma and c 240 ma u pb dating of zircons from volcaniclastic sediments of the sadong and kuching formations confirms contemporaneous volcanism the magmatic activity is interpreted to represent a triassic subduction margin in westernmost west sarawak with sediments deposited in a forearc basin derived from the magmatic arc at the sundaland pacific margin west sarawak and nw kalimantan are underlain by continental crust that was already part of sundaland or accreted to sundaland in the triassic one metabasite sample also previously assumed to be pre carboniferous basement yielded early cretaceous 40ar 39ar ages they are interpreted to indicate resumption of subduction which led to deposition of volcaniclastic sediments and widespread magmatism u pb ages from detrital zircons in the cretaceous pedawan formation are similar to those from the schwaner granites of nw kalimantan and the pedawan formation is interpreted as part of a cretaceous forearc basin containing material eroded from a magmatic arc that extended from vietnam to west borneo the youngest u pb ages from zircons in a tuff layer from the uppermost part of the pedawan formation indicate that volcanic activity continued until c 86 to 88 ma when subduction terminated

postglacial palaeoecology of the subalpine forest grassland ecotone of southwestern alberta new insights on vegetation and climate change in the canadian rocky mountains and adjacent foothills postglacial vegetation change at the subalpine forest grassland ecotone in the foothills of southwestern alberta is reconstructed from fossil pollen plant macrofossils and fossil charcoal the fossils were obtained from the sediments of a small lake chronological control for the record is provided by tephra analysis and the 14c dating of terrestrial plant macrofossils the fossil record is compared with the results from similar studies at sites in the rocky mountains and foothills of alberta and british columbia the comparison of vegetation change at the upper and lower elevational limits of the subalpine forest provides a record of changes in temperature and aridity over the holocene at 10 000 yr b p the study site supported a shrub and herb dominated vegetation picea pinus abies forests were present at mid to high elevations in the mountains and in the northern foothills by this time the climate in the southern foothills was likely arid but not severely cold a relatively open picea and pinus forest was established in the study area between 9400 yr b p and 8000 yr b p fire activity in the region was at a postglacial maximum during this period the transition to forest suggests moister conditions by 8000 yr b p the importance of members of the chenopodiaceae amaranthaceae and typha latifolia increased suggesting an onset of arid conditions characterised by low and fluctuating water levels in lakes between 8000 yr b p and 5000 yr b p the picea and pinus contorta forest at the study site was largely replaced by grassland and pinus flexilis at high elevation sites treeline was located above its modern position during this period little vegetation change is recorded at sites in the northern foothills and at mid elevations at this time the vegetation change in the southern foothills and at high elevations suggests both an elevational and latitudinal displacement of vegetation zones during the mid holocene warm and arid conditions were prevalent in southwestern alberta picea glauca pinus contorta populus tremuloides forest has occupied the site since 5000 yr b p when cooler and moister conditions were established

new insights on the late pleistocene holocene lithic industry in east kalimantan borneo the contribution of three rock shelter sites in the karstic area of the mangkalihat peninsula this paper aims to present some aspects of the late pleistocene holocene lithic industry in the inland east kalimantan region by studying the assemblages found in three rock shelter sites in the karstic area of the mangkalihat peninsula this study analyzes these assemblages in their regional techno complex taking into consideration the environmental components it focuses on certain aspects of stone flaking technology and the trends in the reduction sequences of the assemblages our results shows that the reduction sequences flaking technology and the typology of the blanks and tools persisted across the pleistocene holocene boundary as revealed in liang abu where the lithic artifacts were found throughout the stratigraphic sequence over at least 20 000 years other excavations in liang jon and liang pemalawan have confirmed this continuity until the historical eras in addition this research emphasizes the potential influence of the environmental and climatic stability persistence of the rain forest during at least the last 40 000 years in this region as well as the inland geographical location on the continuity of the local stone flaking technology

the timing and nature of late quaternary vegetation changes in the northern great plains usa and canada a re assessment of the spruce phase abstract this paper revises the chronology for the northward migration of picea glauca white spruce across the northern great plains following the recession of the laurentide ice sheet and reinterprets the species composition and structure of the late glacial vegetation on the basis of pollen and plant macrofossil analysis the timing of spruce migration is based on 26 14 c ages obtained from picea macrofossils the date for the appearance of white spruce in southern south dakota usa remains unchanged 12 600 14 c yr bp ca 15 000 cal yr bp but its arrival in southern saskatchewan canada by 10 300 14 c yr bp ca 12 100 cal yr bp is about 1500 years later than previously estimated based on an organic sediment date picea glauca thus migrated northwards at an average rate of 0 38 km 14 c year 0 30 km calendar year significantly slower than the previously published rate of 2 km 14 c year white spruce trees probably inhabited lake shorelines whereas prairie parkland and boreal plants occupied both lowlands and uplands forming an open white spruce parkland this interpretation differs from a previous reconstruction of a boreal type spruce forest and thus offers another paleoclimatic interpretation precipitation was probably low and summer temperatures relatively mild averaging about 19 c

denudation vertical crustal movements and sedimentary basin infill denudation and vertical crustal movements are linked through the isostatic equation for conservation of lithospheric mass recent empirical results from a wide range of sources are presented on the rates of these processes denudation alone can cause non tectonic isostatic surface uplift of the right magnitude predicted by theory a case is made following ahnert for a single linear relationship although with much scatter between denudation rate and mean drainage basin relief for large basins some recent determinations of denudational time constants have neglected to include tectonic and isostatic terms which oppose the reduction of relief by denudation application of diffusional transport models to determine the rate of sediment deposition are severely limited by inherent one dimensionality and neglect of suspended and washload contributions basin infill sequences may be used to determine past sediment transfer coefficients from a hinterland but problems arise in the apportionment of the various hinterland fluxes that occur in real world three dimensional basins sediment yields in smaller half graben and growth fold basins must reflect the magnitude of drainage basins and the complex local controls upon sediment yields examples are given from extensional basins in the western usa and greece the length of tectonic relief produced in tilt blocks and growth folds will control the area of drainage basin developed through the fractal form of hack s law and hence the magnitude of deposition in sedimentary basins adjoining tectonic uplands

the application of fission track analysis to the dating of barren sequences examples from red beds in scotland and thailand in continental red beds facies which often contain little or no organic material for biostratigraphic dating fission track ft analysis of detrital zircon crystals represents one method by which a maximum stratigraphic age may be determined in addition ft analysis of detrital apatite provides a means of palaeotemperature estimation especially in areas where there is insufficient or unsuitable organic matter for vitrinite reflectance two examples of the application of ft analysis to the solution of stratigraphic problems in red bed sequences are described from scotland and thailand from authors

a late oligocene tectono volcanic event in east kalimantan and the implications for tectonics and sedimentation in borneo new apatite fission track data k ar radiometric ages and major and trace element geochem istry from the northern part of the kutai basin borneo document a major regional tectono volcanic episode apatite fission track data from late cretaceous sandstones indicate a period of rapid cooling in the late oligocene cooling initiated by a rapid temperature drop of over 40 c within c 2 ma might have been caused by increased denudation associated with tectonic movements rapid cooling is also concomitant with a phase of igneous activity new k ar radiometric ages of andesitic dacitic high level intrusive rocks and associated volcanic rocks give ages of 23 18 ma which correlate with the regionally extensive late oligocene miocene sintang intrusives suite these andesitic dacitic high level intrusive rocks also have geochemical characteristics of arc related rocks the sedimentary response to this tectono volcanic event is the eastwards shift of the western basin margin and the inception of deltaic deposition around the newly re defined basin margins up to 9 km of sediment was deposited in the basin during miocene delta progradation covering thick sequences of palaeogene bathyal shales providing an excellent decollement surface for later inversion elsewhere in borneo and adjacent areas of se asia major events recorded in the late oligocene to early miocene include major thrust imbrication and volcanic arc activity the cause of which is unclear possibilities include the collision of australia with the philippine sea plate the counter clockwise rotation of borneo in the neogene and the initial impingement of blocks of south china origin with northern borneo south palawan

estimating hinterland exhumation from late orogenic basin volume nw borneo a new approach for restoring sediment volumes onto the sediment source area to estimate uplift timing and magnitude is discussed and used in the context of late tertiary basin and topographic development in nw borneo sediment volumes for the baram deltaic province were estimated for four time periods latest early middle and late miocene and pliocene recent using 2d and 3d seismic horizons wells and outcrops volume restoration onto the palaeo sediment source area determined exhumation amount at the drainage divide c 5 km from 17 ma to recent and provided a reasonable match with other denudation estimation methods cooling ages and an older regional sediment restoration study using 1979 vintage sediment isopach maps restoration took into account 1 changing sediment densities during the erosion deposition cycle 2 changing area of the sediment source province with time e g changing shoreline location as a result of eustacy uplift and delta progradation tectonic shortening 3 uplift and partial erosion of baram deltaic province sediment denudation at the drainage divide for the middle miocene late miocene and pliocene recent has proceeded at a similar rate for each period initial uplift of central borneo has been attributed to buoyancy of thinned continental crust that jammed the subduction zone under nw borneo in the early miocene however the absence of decay in the erosion rates with time from the middle miocene to recent suggests operation of an additional uplift mechanism that may be related to delamination of mantle lithosphere slab detachment is the favoured explanation

spatio temporal evolution of a tertiary carbonate platform margin and adjacent basinal deposits abstract the variability in low to moderate energy carbonate platform margins is poorly known from the geological record here the spatial and temporal evolution of platform margin and adjacent basinal deposits is evaluated from the little known tertiary kedango limestone that developed in a semi enclosed marine embayment in se asia the hypothesis here is that platform margin development will reflect regional and perhaps global influences such as tectonics eustasy or biotic change rather than windward leeward effects and storms that typically impact strongly upon open oceanic platforms the development of the carbonate platform was determined through logging petrography facies evaluation provenance and high resolution dating studies eleven carbonate facies were identified from the 30 km long western margin of the 600 m thick platform and its adjacent slope and basinal deposits larger benthic foraminifera and coralline algal packstones and wackestones dominated in shallow waters during the oligo miocene coral patch reef related floatstones rudstones and less commonly boundstones were also present on the platform top perhaps surprisingly for a low energy platform there was considerable variation along the platform margin and much reworking of material into slope and basinal deposits during the oligo miocene reworked material includes shallow water bioclasts clasts from older siliciclastics fresh feldspars lithified slope and platform top carbonate clasts some of the latter showing evidence for karstification the western platform margin varied laterally over a few kilometres from a gently sloping unrimmed platform to a probable bank top with in places coral fringed bypass and erosional faulted escarpment margins eustasy may have influenced shallowing and deepening trends on the platform top but apparently had little impact on mass wasting instead platform margin development was strongly impacted by tectonics including active faulting terrestrial runoff together with changes in carbonate producers and local variability on the platform top

paleomagnetism of borneo abstract the paleomagnetism of borneo remains controversial although the preponderance of results both from the island itself and from the surrounding regions suggest that counterclockwise ccw rotation has taken place ccw rotations are seen in minor intrusions in sarawak sabah and kalimantan which increase systematically with the age of the intrusion to a maximum value of 51 8 3 7 the rotation can be no older than 25 ma which is the age of the intrusion showing the maximum rotation the rotation appears to have neared completion by 10 ma similar ccw rotations are seen in sites from peninsular malaysia through borneo to sulawesi the celebes sea and palawan in the philippines but the ages of these rotations are for the most part unknown in mesozoic rocks in kalimantan and sarawak a stronger declination rotation of nearly 90 ccw is recorded at seven sites including sites which pass fold and reversal tests this strong rotation is no older than youngest cretaceous and although seen over a wide region in borneo it is not seen in peninsular malaysia nor in the celebes sea or palawan where only the weaker ccw rotation is seen the widespread occurrence of this strong rotation in western borneo suggests that it is essentially a rigid plate or microplate rotation and not a series of local rotations caused by distributed shear in limited deformation zones the rotation of borneo appears to be a consequence of convergence between the australian and eurasian plates which is accommodated by subduction along the northwest margin of borneo

holocene geomorphology and stratigraphy of the lower falcon valley dinosaur provincial park alberta canada a tributary of the red deer river in dinosaur provincial park southern alberta contains evidence of a sequence of valley cutting and the deposition of three alluvial fills and one eolian deposit with the exception of the eolian deposit and minor amounts of shield and cordilleran rocks the sediments are derived from local bedrock incision of the bedrock valley occurred in the early postglacial period about 14 000 12 000 bp by rapid drainage of proglacial lakes and meltwaters the valley was subsequently partly infilled as locally fed stream discharges declined during the early to middle holocene by 6000 5000 bp alluvial fans had formed along the base of the valley walls fan development was followed by two phases of stream entrenchment and alluvial deposition including the most recent phase of cutting and filling that began approximately 800 bp the erosional and depositional events may reflect climatic changes as inferred in lacustrine deposits in southern alberta and in valleys elsewhere in the

paraglacial origin for terraced river sediments in bow valley alberta fluvial terraces flank the course of the bow river for 100 km from the eastern margin of the rocky mountain front ranges to calgary and beyond the terraces are cut predominantly in gravel fill which ranges in thickness from approximately 10 m in the calgary area to 30 m near the mountain front sedimentary structures in the gravels indicate a braided stream sedimentary environment in contrast to the present quasi stable sinuous single channel form of the bow river radiocarbon dates on ungulate remains from the gravels indicate the main period of fill occurred ca 11 500 10 000 rcybp radiocarbon years before present previous workers have postulated that the gravels originated directly as outwash from a glacial advance to or beyond the mountain front this explanation has been refuted by recent stratigraphic and palynological investigations a complex nonglaciofluvial origin is proposed for these terraces and the sediments that form them the last glacial advance to reach the mountain front was well

geological implications of new biostratigraphic data from east and west kalimantan indonesia abstract this paper presents palaeontological ages based on new nannofossil and foraminiferal studies from a range of sedimentary rocks from the provinces of west and east kalimantan indonesia the age of sedimentary rocks in kalimantan away from the main hydrocarbon exploration areas of the coastal regions represents a major gap in our basic knowledge of the island of borneo the implications of these new results and existing and new correlations are reviewed and suggested in particular the base of the tertiary section in the kutai basin is shown to be upper middle eocene in age rather than late eocene as originally thought the limestones of the batu belah member of the ujoh bilang formation are dated as np24 25 late oligocene rather than early oligocene as earlier work had suggested in the western part of the mangkalihat peninsula area the base of the tertiary section is determined to be late oligocene various basement units from both east and west kalimantan contained late jurassic to late cretaceous microfossils

tertiary tectonic and magmatic evolution of western sulawesi and the makassar strait indonesia evidence for a miocene continent continent collision

new accelerator mass spectrometry radiocarbon ages for the mazama tephra layer from kootenay national park british columbia canada charcoal fragments recovered from the mazama air fall tephra layer in cores from dog and cobb lakes kootenay national park british columbia yielded accelerator mass spectrometry ages of 6720 70 and 6760 70 14c years bp respectively these two new ages together with other previously published radiocarbon ages on charcoal and twig fragments from mazama air fall deposits indicate that the climactic eruption of mount mazama occurred 6730 40 14c years bp

a neogene history of mantle convective support beneath borneo abstract most but not all geodynamic models predict 1 2 km of mantle convective draw down of the earth s surface in a region centered on borneo within southeast asia nevertheless there is geomorphic geologic and geophysical evidence which suggests that convective uplift might have played some role in sculpting bornean physiography for example a long wavelength free air gravity anomaly of 60 mgal centered on borneo coincides with the distribution of neogene basaltic magmatism and with the locus of sub plate slow shear wave velocity anomalies global positioning system measurements an estimate of elastic thickness and crustal isostatic considerations suggest that regional shortening does not entirely account for kilometer scale regional elevation here we explore the possible evolution of the bornean landscape by extracting and modeling an inventory of 90 longitudinal river profiles misfit between observed and calculated river profiles is minimized by smoothly varying uplift rate as a function of space and time erosional parameters are chosen by assuming that regional uplift post dates eocene deposition of marine carbonate rocks the robustness of this calibration is tested against independent geologic observations such as thermochronometric measurements offshore sedimentary flux calculations and the history of volcanism a calculated cumulative uplift history suggests that kilometer scale bornean topography grew rapidly during neogene times this suggestion is corroborated by an offshore miocene transition from carbonate to clastic deposition co location of regional uplift and slow shear wave velocity anomalies immediately beneath the lithospheric plate implies that regional uplift could have been at least partly generated and maintained by temperature anomalies within an asthenospheric channel

adakites without a slab remelting of hydrous basalt in the crust and shallow mantle of borneo to produce the miocene sintang suite and bau suite magmatism of west sarawak abstract we present new geochronological and geochemical data for neogene magmatism from west sarawak zircon u pb geochronology divides neogene magmatic rocks of west sarawak into a lower miocene west sarawak sintang suite with ages of c 19 to 21 ma and a middle miocene bau suite with ages of c 12 to 14 ma magmatism occurred in multiple short lived pulses from approximately 24 ma and was coeval with magmatic activity in nw kalimantan and east kalimantan the majority of but not all bau suite samples display adakitic chemistry while the west sarawak sintang suite is predominantly non adakitic there was no active subduction zone or subducted slab associated with this adakitic magmatism instead the geochemical diversity is consistent with the bau and west sarawak sintang suites representing mixtures of mafic mantle derived magma with felsic magma derived from remelting of hydrous mafic rock that had been emplaced into the lithosphere of borneo as arc basalt tens or hundreds of millions of years previously this origin is most evident in the main sintang suite of central borneo kalimantan which has preserved less contaminated examples of the mafic endmember this endmember resembles basaltic rocks from several locations across borneo suggesting that intraplate mantle derived magmatism was responsible for remelting older hydrated basaltic rocks in the crust

embaluh group turbidites in kalimantan evolution of a remnant oceanic basin in borneo during the late cretaceous to palaeogene turbidites crop out in large parts of nw borneo including kalimantan and sarawak the strata predominantly comprise the embaluh group in kalimantan and lateral equivalents the rajang group in sarawak collectively known as the rajang embaluh group previous interpretation of these rocks as the product of deep marine deposition and deformation as part of an accretionary prism during late cretaceous to palaeogene subduction implies south dipping thrusts northward stratigraphic younging the existence of a complete arc to trench system and significant deformation and metamorphism of the turbidites however new fieldwork described here established consistent southward stratigraphic younging in kalimantan no evidence for southward dipping thrusts and a lack of metamorphism and associated accretionary complex related deformation features furthermore all available palaeontological and radiometric age data indicate that deposition of the bulk of the rajang embaluh group postdates in board subduction related magmatism and thus a complete arc trench system cannot be demonstrated consequently the rajang embaluh group turbidites are re interpreted as having formed in either a post collisional foreland basin or a remnant ocean basin the lack of a identifiable mountain belt and linked thrust system and probable oceanic aynity of crust beneath the rajang embaluh group basin favour the latter interpretation borneo occupies a pivotal position within southeast asia this new model of a remnant oceanic basin setting for extensive turbidite units of borneo therefore has far reaching implications for the tectonic evolution of borneo the south china sea and se asia the new model is compared with older palaeozoic orogenic belts which also contain thick turbidites sequences

a miocene collisional belt in north borneo uplift mechanism and isostatic adjustment quantified by thermochronology subduction followed by underthrusting of continental lithosphere driven by oligocene early miocene spreading in the south china sea marginal basin account for the tectonic features of sabah isostatic rebound then caused late miocene uplift of the western cordillera the strata were buried under 4 8 km of overburden then rapidly exhumed and cooled at 10 c ma 1 a rate of exhumation of 0 5 0 7 mm a 1 is deduced from thermochronology the same order of uplift in the labuk highlands has exposed metamorphic rocks of the epidote glaucophane facies rapid erosion of the western cordillera supplied abundant clastic sediments to the miocene pliocene baram delta oil bearing basin and to the eastern lowlands and sulu sea the eastern lowlands were affected by miocene rifting of the sulu sea marginal basin in contrast to the western cordillera the strata contain apatite crystals whose fission track ages pre date the containing rocks indicating burial by only about 2 3 km of overburden the terrain has been isostatically stable some apatite and all zircon crystals extracted from tertiary strata yield cretaceous fission track provenance ages

the influence of basement reactivation on the extensional and inversional history of the kutai basin east kalimantan se asia the kutai basin east kalimantan is one of several large extensional basins formed in the middle to late eocene formed above an orogenic complex of late cretaceous early tertiary age basement fabrics oriented nw se and ne sw strongly influenced basin extension and inversion remote sensing data and fieldwork show basement fabric on the margins and tertiary cover are dominated by ne sw nw se and nne ssw trending structures similarly on a larger scale nw se narrow linear gravity lows cut nne ssw highs on the gravity data within the basin reconstruction of the basin architecture shows nne ssw basin bounding faults overlapping in a right stepping en echelon manner these overlaps relay ramps were breached by faults oriented ne sw through reactivation of the basement fabric opposing antithetic and synthetic half grabens were linked by highly oblique nw se transfer faults inversion utilized extensional faults as reverse faults however nw se oriented structures were reactivated as zones of lateral offset along the fold thrust belt whilst fault kinks oriented ne sw were reactivated as oblique slip reverse faults the kutai basin provides an example of the controls that basement heterogeneities play on both extension and inversion

sedimentology stratigraphy and geomorphology of glacial lake calgary at cochrane alberta canada stratigraphic and sedimentologic field data in the cochrane alberta area demonstrate that glaciolacustrine sediment comprising the calgary formation underlies glaciofluvial and fluvial sediment o

neogene arc continent collision in sabah northern borneo malaysia abstract the neogene evolution of sabah can be interpreted in terms of an arc continent collision initiated during early middle miocene time and followed by intraplate shortening the latter being active in this area at the present day the volcanic arc of late oligocene middle miocene age is imbricated with melanges and thrust northwestward on a polyphase deformed turbiditic sequence of late cretaceous middle miocene age crocker range intraplate shortening is seen in the thrusting and folding offshore sabah along the palawan north borneo trench and also by broad open folds and strike slip faulting in the previously sutured terranes this collision can either be interpreted as the final stage of southward subduction of the hypothetical proto south china sea or the result of back thrusting of the sulu volcanic arc resulting from the subduction of the celebes sea toward the north

fission track evidence for the thermotectonic evolution of a mesozoic cenozoic fore arc antarctica zircon and apatite fission track data from the lemay group accretionary complex and fossil bluff group fore arc basin sequence on alexander island antarctica record a common regional cretaceous and cenozoic thermal and denudational history with the exception of zircon data from samples closest to the trench the apatite and zircon central ages are substantially less than known and inferred stratigraphic ages thermal modelling of the data indicate cooling from maximum palaeotemperatures in the range 180 350 c at c 100 ma a younger period of accelerated cooling occurred between 40 and 35 ma with final cooling to surface temperatures taking place at reduced rates through the tertiary the start of cooling was close in time to the end of deposition within the fore arc basin and is consistent with structural evidence for cretaceous deformation in a strike slip setting the accelerated early tertiary cooling episode was broadly coeval with and may have been caused by ridge trench collisions and cessation of subduction off shore alexander island zircon and apatite age data from magmatic rocks emplaced in the fore arc region in late cretaceous and tertiary times are close to their age of crystallization this indicates rapid cooling of both fission track systems from temperatures 350 c to c 60 c at high crustal levels of emplacement the formation of these magmatic rocks together with the cooling history of the accretionary prism are related to changes in subduction zone parameters during cretaceous and cenozoic times slowing of subduction rates and role back of the slab prior to cessation of subduction by ridge trench collision may have been responsible for migration of the magmatic focus into the fore arc region uplift of the prism and formation of the high mountain ranges and the extensional graben that separates alexander island from the antarctic peninsula

cenozoic carbonates in southeast asia implications for equatorial carbonate development cenozoic equatorial carbonate production was at its most extensive and diverse in the seas of southeast asia yet the carbonates of this region remain poorly documented this paper presents the first published review of carbonate deposition during the cenozoic collating sedimentological data for carbonate successions throughout the region current models of warm water carbonate platform evolution sedimentation and facies distribution inspired by studies of the classic sub tropical areas provide inadequate analogues for the evaluation of modern or cenozoic equatorial carbonates in southeast asia the equatorial carbonates differ in being dominated by bioclasts coated grains and associations with evaporites or dolomites are rare the carbonate systems occur in a range of depositional settings which were often affected by coeval tectonism siliciclastic input or volcanism an understanding of the carbonate depositional environments spatial facies distributions and controls on deposition and diagenesis is essential in order to characterize equatorial carbonate development and to evaluate their considerable economic potential

paleoenvironmental interpretation of the paleosols and sediments at the stampede site djon 26 cypress hills alberta a 3 65 m thick sequence of paleosols and sediments exposed at the stampede archaeological site provides an opportunity for studying climate change and its impact on ancient site utilization over a 7200 year period three radiocarbon dates establish temporal boundaries for the lower sequence of paleosols and sediments at 7200 and 6100 bp this lower sequence is characterized by lack of cultural material in most paleosols high accumulation rates and evidence for fluvial deposition the upper sequence dates from 6100 bp and is characterized by low accumulation rates increased pedogenesis and increased evidence for human occupation particularily between 4660 and 5230 bp phytoliths provide a strong signal for grassland vegetation beginning at 6100 years bp coincident with the most intensive occupation of the site stable carbon isotopes and carbon nitrogen c n ratios support the presence of grass the differences evident between the lower and upper sequences can be attributed to the change from warm dr

an integrated study of geochemistry and mineralogy of the upper tukau formation borneo island east malaysia sediment provenance depositional setting and tectonic implications abstract an integrated study using bulk chemical composition mineralogy and mineral chemistry of sedimentary rocks from the tukau formation of borneo island sarawak malaysia is presented in order to understand the depositional and tectonic settings during the neogene sedimentary rocks are chemically classified as shale wacke arkose litharenite and quartz arenite and consist of quartz illite feldspar rutile and anatase zircon tourmaline chromite and monazite all of them are highly matured and were derived from a moderate to intensively weathered source bulk and mineral chemistries suggest that these rocks were recycled from sedimentary to metasedimentary source regions with some input from granitoids and mafic ultramafic rocks the chondrite normalized ree signature indicates the presence of felsic rocks in the source region zircon geochronology shows that the samples were of cretaceous and triassic age comparable ages of zircon from the tukau formation sedimentary rocks granitoids of the schwaner mountains southern borneo and tin belt of the malaysia peninsular suggest that the principal provenance for the rajang group were further uplifted and eroded during the neogene additionally presence of chromian spinels and their chemistry indicate a minor influence of mafic and ultramafic rocks present in the rajang group from a tectonic standpoint the tukau formation sedimentary rocks were deposited in a passive margin with passive collisional and rift settings our key geochemical observation on tectonic setting is comparable to the regional geological setting of northwestern borneo as described in the literature

the geology of northern sabah malaysia its relationship to the opening of the south china sea basin abstract the northern part of sabah consisting of sedimentary and igneous rocks of early cretaceous to pliocene age has experienced three major episodes of deformation associated with nw se and n s oriented compressions the earliest episode deformed and uplifted an oceanic basement chert spilite formation to form an elongate basin trending approximately ne sw during the late cretaceous to early eocene this elongate basin became the site for the deposition of middle eocene to early miocene quartzose sediments of the crocker and kudat formations sourced from continental basement towards the southwest and north respectively these sediments were subsequently deformed by a second episode of deformation associated with nw se and n s oriented compressions during the latter part of the late oligocene and the early middle miocene to form a series of imbricate thrust slices the n s trending compressive direction controlled the development of approximately e w trending basins during the deposition of the upper miocene sediments of the south banggi and bongaya formations the continuation of n s compression which represents the third episode of deformation gently deformed these sediments the three episodes of deformation were related to the differential southward movements of continental blocks separated from the southern margin of china during the intermittent opening of the south china sea subbasins the first episode was related to the opening of the southwest subbasin while the second episode was related to both the opening of the southwest and east subbasins the third episode was related to continued opening in the east subbasins

a continuous record of holocene pollen from harris lake southwestern saskatchewan canada abstract holocene vegetation change in the west block of the cypress hills on the northern great plains is interpreted from a continuous 9120 year pollen record this is one of the few continuous pollen records available from the northern great plains which extends to the early holocene the west block rises to a maximum elevation of 1465 m and is a mosaic of grassland populus forest coniferous forests and wetland vegetation because of the ecotones present climatic changes produced vegetation changes discernible from the pollen record the record indicates that a populus forest grassland complex was established by 9000 yr bp very little coniferous forest was present at that time the predominance of grassland and saline tolerant vegetation between 7700 and 5000 yr b p defines the altithermal for this region climatic deterioration followed as indicated by increases in relative amounts of conifer and aquatic taxa pollen the pinus contorta and picea glauca forests characteristics of the cypress hills today only have been prevalent since about 4600 yr b p both species were present in very low numbers throughout the altithermal by 3230 yr b p the modern vegetation was established with little change since then

the cypress hills formation upper eocene to miocene a semi arid braidplain deposit resulting from intrusive uplift the upper eocene miocene cypress hills formation of the cypress hills plateau in southwestern saskatchewan and southeastern alberta is interpreted as a braidplain deposit the regional paleoslope dipped to the northeast and the east west distribution of outcrop exposes facies representing lateral variation across the slope of the braidplain overall the average clast size of the deposits decreases from west to east with western area sediments dominated by boulder sized gravels deposited on longitudinal bars the eastern outcrop area contains deposits of braided channels cut into and interbedded with finer interchannel material including lacustrine marlstones silcretes and debris flow deposits the latter commonly containing abundant fossils the gravels of the cypress hills formation are multicyclic they were originally derived from the western ranges of the rocky mountains during laramide orogenesis and later shed farther into the basin during rebound due to unloading of the laramide thrusts by

the geomorphic influences of beaver dams and failures of beaver dams abstract uncounted millions of beaver ponds and dams existed in north america prior to european contact and colonization these ponds acted as sediment traps that contained tens to hundreds of billions of cubic meters of sediment that would otherwise have passed through the fluvial system removal of beavers by overtrapping in the 16th 19th centuries severely reduced their number and the number of ponds and dams dam removal altered the fluvial landscape of north america inducing sediment evacuation and entrenchment in concert with widespread reduction in the wetlands environments partial recovery of beaver populations in the 20th century has allowed reoccupation of the entirety of the pre contact range but at densities of only one tenth the numbers nevertheless modern beaver ponds also trap large volumes of sediment in the high hundred millions to low billions of cubic meters range failure of beaver dams is a more common phenomenon than often assumed in the literature during the past 20 years numerous cases of dam failure have been documented that resulted in outburst floods these floods have been responsible for 13 deaths and numerous injuries including significant impacts on railway lines

human responses to middle holocene altithermal climates on the north american great plains abstract the climate of the great plains during the middle holocene varied considerably but overall it was marked by a north south gradient of increasingly warmer and drier conditions with a reduction in effective moisture surface water and resource abundance and an increase in resource patchiness sediment weathering erosion and aeolian activity pronounced drought conditions were most evident on the southern high plains understanding the human responses to middle holocene climates is complicated by a lack of archaeological data which is partly a result of geomorphic processes that removed or deeply buried sites of this age and by the varying adaptive responses of hunter gatherers during this period on the southern high plains where drought was most severe surface and groundwater sources dried and bison populations were diminished prompting substantial adaptive changes including local abandonment well digging to tap underground water and a widening of the diet breadth to incorporate higher cost lower return seed and plant resources sites of this age on the central and northern plains also show a possible increase in diet breadth with the incorporation of plant foods in the diet and perhaps changes in settlement mobility including possible shift into higher elevation areas or mapping on to extant rivers and springs but linking those changes to middle holocene drought is less straightforward