applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

magnetic links among lava flows tuffs and the underground plumbing system in a monogenetic volcano derived from magnetics and paleomagnetic studies abstract a combined study using magnetics and paleomagnetism of the toluquilla monogenetic volcano and associated lavas and tuffs from valsequillo basin in central mexico provides evidence on a magnetic link between the lavas ash tuffs and the underground volcanic conduit system paleomagnetic analyses show that the lava and ash tuff carry reverse polarity magnetizations which correlate with the inversely polarized dipolar magnetic anomaly over the volcano the magnetizations in the lava and tuff show similar southward declinations and upward inclinations supporting petrological inferences that the tuff was emplaced while still hot and indicating a temporal correlation for lava and tuff emplacement modeling of the dipolar anomaly gives a reverse polarity source magnetization associated with a vertical prismatic body with southward declination and upward inclination which correlates with the reverse polarity magnetizations in the lava and tuff the study documents a direct correlation of the paleomagnetic records with the underground magmatic conduit system of the monogenetic volcano time scale for cooling of the volcanic plumbing system involves a longer period than the one for the tuff and lava suggesting that magnetization for the source of dipolar anomaly may represent a long time average as compared to the spot readings in the lava and tuff the reverse polarity magnetizations in lava and tuff and in the underground source body for the magnetic anomaly are interpreted in terms of eruptive activity of toluquilla volcano at about 1 3 ma during the matuyama reverse polarity c1r 2r chron

source rocks and hydrocarbon generation in slovenia mura depression pannonian basin abstract source rock analysis organic carbon rock eval gas chromatography vitrinite reflectance and numeric modelling techniques have been applied to evaluate the hydrocarbon potential and the timing of hydrocarbon generation in northeastern slovenia mura depression pannonian basin source rocks of mesozoic age were not detected most tertiary samples are gas prone oil prone sediments occur mainly in egerian eggenburgian karpatian and sarmatian levels the maturity pattern reflects complex neogene subsidence and thermal histories so the thickness of the oil window varies from about 300 m maribor somat area to 1500 m ljutomer depression the top of the oil window lies below a depth of 2500 m in the ljutomer depression whereas it reaches the surface in the maribor area three main hydrocarbon generation phases are distinguished in different parts of the mura depression a a karpatian badenian stage due to extremely elevated heat flow maribor somat radkersburg area boc anticline probably ormoz selnica anticline b a middle late miocene to early pliocene stage due to miocene deep burial ormoz selnica anticline c a late miocene to present generation stage ljutomer depression eastern margin of the murska sobota high

geology and quaternary environments of the first preglacial palaeolithic sites found in alberta canada abstract a pebble tool industry including two chronologically different stone artifact assemblages reminiscent of the eurasian palaeolithic has been recorded in late pleistocene sections at two locations in the bow river valley southwestern alberta authenticity and provenance of the deeply buried archaeological record is evidenced by culture diagnostic percussion flaked artifacts incorporated in preglacial fluvial gravels and overlying glacial diamictons and by identical textural patterns on stone tools found in and eroded from the exposures geological context suggests a fluctuating braided river setting during the earlier occupation discarded lower series quartzite and hard carbonate rock artifacts subglacially entrained into the cordilleran bow valley till document distortion of the earlier site silver springs by a valley glacier emerging from the rocky mountain ice lobe following the valley deglaciation a later occupation episode is manifested by a formally analogous flaked lithic assemblage excavated in situ on top of the till at a nearby site varsity estates this more recent occupation surface was subsequently buried under 24 m of glaciolacustrine sediments after submergence of the river valley by a proglacial lake glacial lake calgary dammed by the laurentide ice advance into the eastern calgary area implying a minimum early late wisconsinan age ca 21 000 bp for the lithic industry the presence of the later upper series artifact assemblage and the associated palynological data do not support the view that envisages an extremely cold inhospitable glacial environment on the eastern slopes of the canadian rocky mountains throughout the late wisconsinan their stratigraphic position also indicates temporal asynchroneity between cordilleran and laurentide ice during the last glacial maximum in the bow river valley the area of presumed coalescence of the two ice masses although a more rapid response of the western mountain glacier to climatic change is evident the apparent absence of pedogenic alteration of the till surface and the fresh appearance of the excavated stone artifacts suggest that a short time span separated the two glacial events the archaeological record provides evidence of an earlier palaeo american peopling of western interior canada long before the emergence of the final pleistocene palaeoindian cultures characterized by elaborate bifacial stone projectile point flaking technologies traditionally regarded as the earliest cultural manifestations in north america silver springs is the first early site on the continent found below glacial deposits realization that other american palaeolithic sites potentially of considerable antiquity should be recognized in similar geological settings and introduction of adequate geoarchaeological site survey techniques have crucial relevance for elucidation of the earliest new world prehistory

miocene thermal history of the southwestern margin of the styrian basin vitrinite reflectance and fission track data from the pohorje kozjak area slovenia the kozjak possruck and pohorje mountains form the southwestern basement rim of the neogene styrian basin this region was affected by two tertiary magmatic events the emplacement of the oligocene pohorje tonalite and of early middle miocene dacites in the western pohorje vitrinite reflectance and fission track data are used to reconstruct the thermal history and to constrain the exhumation of the pohorje kozjak area early miocene sediments lacking a thermal overprint contain apatite grains of eggenburgian 19 ma cooling age only 1 2 ma older than the time of deposition the cooling rate of the mainly austroalpine source units was very fast denoting tectonic denudation it means that in the eastern alps during early middle miocene time the pohorje kozjak region in addition to the tauern and rechnitz windows was supplying sediment into the surrounding basins with nearly syn sedimentary apatite cooling ages vitrinite reflectance anomalies in early miocene sediments in the ribnica selnica trough located between the kozjak and pohorje mountains and at the eastern margin of the kozjak mountains give evidence for a strong post depositional thermal overprint thermal models based on nearby wells suggest that miocene temperatures were as high as 220oc apatite fission track ages indicate that the thermal overprint had terminated by middle badenian 14 4 2 3 ma time vitrinite reflectance anomalies in the ribnica selnica trough are a result of early middle miocene volcanic activity another vitrinite reflectance anomaly situated at the eastern margin of the kozjak mountains extends eastward into the somat radkersburg area the heat source in this region is not obvious possible heat sources are 1 a shallow pluton beneath this area which easily can explain the reconstructed early middle miocene heat flow of more than 250 mw m 2 and 2 advective heat transport due to rapid exhumation of hot metamorphic rocks in the pohorje kozjak region rapid exhumation is proven by fission track dating it would explain the appearance of the nearly syn sedimentary detrital apatite ft ages in the sediments and the post depositional heating 1998 elsevier science b v all rights reserved

the relationship between quaternary volcanism in central mexico and the seismicity and structure of subducted ocean lithosphere late quaternary volcanism in central mexico is related to the subduction of young ocean lithosphere at the middle america trench along arc variations in seismicity volcano structure and composition of volcanic products bear a remarkable correlation with the age and structural framework of the downgoing slab morphological and petrographic characteristics of major volcanoes within the trans mexican volcanic belt tmvb serve to distinguish two calc alkaline subprovinces 1 a western arc averaging 60 km in width associated with aseismic subduction of the rivera plate the main cones of this region are dominated by two pyroxene andesites comprise volumes 70 km 3 and stand less than 3 000 m above sea level 2 a broad central and eastern arc related to subduction of a gently inclined segment of the cocos plate bounded by the rivera transform and the tehuantepec ridge major volcanic edifices possess summit elevations in the range 4 000 to 6 000 m have appropriately larger volumes typically 200 km 3 and are constructed with a high proportion of amphibole bearing lavas the boundary between these subprovinces is marked by a north south oriented structural depression the colima graben and it coincides with a 100 km offset in the volcanic front extensional tectonism in the colima graben accompanied by mixed calc alkaline and alkaline volcanism of potassic affinity is likely related to a hinge type transform fault which marks the cocos rivera plate juncture in the downgoing slab a third segment of ocean floor is presently interacting with continental lithosphere south of the gulf of tehuantepec where quaternary volcanism is weakly developed within a tectonically complex region that marks the diffuse cocos noam caribbean triple junction the northern limit of this triple junction is defined by the seismically active isthmus fault which may be related to alkaline volcanic activity at san andres tuxtla a tectonic reconstruction based on the evolution of oceanic crust reveals that the distribution of intermediate depth earthquakes along the arc is directly dependent upon the age of the subducted slab ocean lithosphere younger than approximately 20 m y is subducted aseismically at convergence rates approaching 9 cm yr the length of the inclined seismic zone indicates that the time constant for thermal relaxation in the slab is approximately 4 m y the tmvb overlies the aseismic extension of this young ocean lithosphere several aspects of this study have a bearing on the segmented nature of converging margins in general 1 the tectonic evolution of the ocean floor may determine the nature of segmentation at the site of subduction 2 the complete record of volcanism in the tmvb over the past million years can be related to the present plate configuration 3 alkaline and calc alkaline volcanism have developed contemporaneously at a converging plate margin 4 lineaments in volcanic arcs may reflect the structural complexity of the crust rather than segment boundaries in the subducted slab

subsidence analysis and quantitative basin modelling in the styrian basin pannonian basin system austria abstract we present the results of subsidence analysis and of quantitative basin modelling using isostatical and flexural models for basin evolution along four cross sections in the styrian basin the westernmost subbasin of the pannonian basin system subsidence analysis reveals a first ottnangian karpatian synrift phase our local isostatic models predict crustal stretching values up to 1 3 and subcrustal stretching values of 1 6 for this event stretching factors of a minor sarmatian extension phase are below 1 04 the termination of subsidence during the pannonian and a rapid quaternary uplift phase can be explained by major changes in the regional stress field a w e cross section through the northern furstenfeld subbasin provides a key for the understanding of the dynamics of basin formation it crosses a narrow karpatian rift basin the metamorphic core complex of the penninic eisenberg window and shows an eastward tilting of the easternmost part of the basin during pannonian times uplift of the penninic window can only be modelled with an extremely weak lithosphere equivalent elastic thickness eet 2 km whereas a best fit between observed and modelled tilting is obtained with an eet value of 5 km these results suggest that the lithosphere was extremely weak during the onset of basin evolution in ottnangian karpatian times probably caused by high extension rates and high heat flows associated with karpatian to early badenian magmatic activity subsequent cooling led to a pronounced increase in flexural rigidity an eet of 5 km fits well with estimations in other parts of the pannonian realm depth dependent rheology models based on palaeo heat flow estimates indicate a similar increase in lithospheric strength with time the impact of plio pleistocene volcanism on rheology appears to be relatively modest which can be explained by a deep position of the magma chamber for this event

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

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

organic geochemistry and petrography of lower cretaceous wealden black shales of the lower saxony basin the transition from lacustrine oil shales to gas shales abstract ninety seven wealden black shale samples from three wells in the lower saxony basin have been studied by organic geochemical and organic petrographical methods to determine their maturity organic facies and depositional environment the maturities of the three wells range from early mature ex a late to postmature ex c to overmature ex b as determined by vitrinite reflectance measurements diamondoid ratios and other geochemical maturity parameters ex c and ex b show distinct petrographic features related to oil generation and migration in particular the occurrence of dispersed solid bitumen replacing initial type i kerogen suggests a formerly active petroleum system structural and textural differences between early mature alginites and solid bitumen in postmature to overmature samples show an alteration of the pore system with increasing maturity a freshwater depositional environment is indicated by widespread occurrence of botryococcus algae and other small alginite particles predominating in the immature well these alginites are absent in the more mature gas shales of wells ex c and ex b geochemical evidence of algae and phytoplankton in general is provided by numerous biomarker parameters while the occurrence of carotane in some samples indicates events of increased salinity although no hypersaline conditions are inferred due to very low gammacerane indices increased amounts of vitrinite and inertinite in samples of ex b suggest locally significant terrigenous input of organic matter for some periods during wealden shale deposition high sulfur organic carbon ratios provide evidence for sulfate rich waters and partly anoxic bottom water conditions while the lower mature lacustrine source rocks generate paraffinic waxy oils gas and condensates are produced at post mature stages furthermore maturity distribution maps from 3d numerical petroleum systems modeling reveal substantial differences in respect to petroleum generation

the 23 500 y 14 c bp white pumice plinian eruption and associated debris avalanche and tochimilco lava flow of popocatepetl volcano mexico abstract the white pumice wp is one of the thickest and most voluminous plinian fallouts produced by popocatepetl volcano in central mexico during the late pleistocene holocene its eruption 23 500 14 c y bp 27 800 cal bp was triggered by the catastrophic failure of the sw flank of the volcano the resulting debris avalanche was highly mobile reaching 72 km from the cone with an apparent coefficient of friction l h of 0 06 the deposit covers an area of 1200 km 2 and has a volume of 10 4 km 3 this gigantic landslide characterized by exceptionally large proximal hummocks 400 m provoked the sudden decompression of the hydrothermal and magmatic systems which produced an initial blast followed by the rise of a plinian column that reached an altitude of 33 km the isopach map allows the recognition of a dispersal axis pointing toward the south where an area of 2490 km 2 was covered by 10 cm of pumice and ash the total volume of the pumice fallout was estimated at 1 9 km 3 dre dense rock equivalent pumice clasts are dacitic 62 66 wt sio 2 anhydrous basis highly vesicular 55 88 vol and display a seriate texture with phenocrysts of plagioclase hornblende augite hypersthene oxides ti magnetite and ilmenite apatite as the eruption advanced discharge rates became more intermittent and the height of the column fluctuated and finally collapsed generating pumice and ash flows that were emplaced around the volcano this short but intense activity was followed during subsequent years by rain induced lahars that reached great distances from the volcano at the same time more degassed andesitic dacitic 61 65 wt sio 2 magma was erupted effusively 4 4 km 3 dre in the new horseshoe shaped 5 km wide crater from which the tochimilco lava flow descended toward the sse where it inundated an area of 68 km 2 and reached as far as 22 km from its source since then multiple eruptions have reconstructed the summit cone almost completely obliterating the horseshoe shaped crater during the course of this catastrophic eruption vei 5 a total volume of 6 3 km 3 dre of juvenile magma pumice and lava were emitted and at least an additional 10 km 3 of pre existing rocks debris avalanche mobilized it surpasses in magnitude most other known plinian eruptions from popocatepetl and can be envisaged as an example of a worst case scenario for hazard evaluation purposes it dramatically changed the morphology of the volcano and had profound and far reaching effects beyond its immediate vicinity along rivers draining surrounding plains as well as on the lacustrine basins e g chalco to the ne a repeat of such an eruption in this densely populated area would certainly cause a major calamity of unprecedented dimensions

genesis and diagnostic value of soft sediment deformation structures a review abstract soft sediment deformation structures are recognized as important diagnostic features in the rock record for determination of depositional environments and slope processes the diagnostic value of these structures is reevaluated by analysis of the parameters controlling sediment deformation soft sediment deformation is contemporaneous with deposition and occurs dominantly in course silt to fine sand the high depositional rate low permeability and low shear strength of grains within this sediment range maximize the occurrence of deformation the dominant mechanisms responsible for sediment deformation include 1 liquefaction or fluidization 2 reverse density gradation 3 slumping or slope failure and 4 shear stress in most cases a combination of these mechanisms occurs the processes function in a continuum producing features that are microscopic to megascopic in scale it is shown that the processes and thus the structures are not environment specific the true diagnostic value of the structures may be in defining hydrodynamic conditions and in interpreting paleocurrents and paleoclimatic and paleoseismic events ultimately for the best diagnostic results soft sediment deformation structures should be studied in association with all other available lithologic structural and paleontological information

mixed fluvial systems of the messak sandstone a deposit of the nubian lithofacies southwestern libya abstract the messak sandstone is a coarse grained to pebbly tabular crossbedded deposit of the widespread nubian lithofacies it was deposited during late jurassic and or early cretaceous time at the northern edge of the murzuq basin in southwestern libya although the sedimentary record is predominantly one of braided fluvial systems a common subfacies within the formation is interpreted to record the passage of straight crested sand waves across laterally migrating point bars in sinuous rivers similar to parts of the modern ganga and yamuna rivers because the sand waves were larger on the lower parts of the point bar lateral migration created diagnostic thinning upward cosets of tabular crossbeds as well as fining upward grain size trends common thick interbedded claystones deposited in associated paludal and lacustrine environments and high variance in crossbed dispersion patterns also suggest the local presence of sinuous fluvial systems within the overall braided regime the messak sandstone contains some of the features that led to the proposal of an unconventional low sinuosity fluvial environment for the nubian lithofacies in egypt and the continuously high water levels of this model may explain channel scale clay drapes and overturned crossbeds in the messak however most of the messak characteristics are incompatible with a low sinuosity model suggesting instead that the fluvial channels in the murzuq basin alternated between braided and high sinuosity channel patterns

early proterozoic stream deposits braided or meandering evidence from central australia abstract it has been suggested that meandering stream deposits should be rare in proterozoic rocks this question was addressed during study of the early proterozoic hatches creek group in central australia as the lower part of the group includes up to 4000 m of fluvial sediments most of the 3000 m thick kurinelli sandstone appears to result from braided streams but there is evidence for the existence of meandering stream deposits in the overlying taragan sandstone and in sediments within the treasure volcanics the basal taragan sandstone consists of a fining up cycle in part of which lateral accretion surfaces are present a 28 m thick sedimentary member in the treasure volcanics contains preserved bedforms form sets which provide indirect evidence for the existence of meandering streams the bedforms including dunes 0 1 1 m high are preserved beneath a mudstone layer as a result of a very sudden drop in current velocity during deposition the observed structures can be explained by neck cut off in a meandering stream although the damming or diversion of a stream by lava flows cannot be discounted the hatches creek group thus contains evidence consistent with the existence of meandering stream deposits at two stratigraphic levels meandering streams should form when suitable combinations of bed and suspended load material are available for transport and discharge and slope parameters are within certain limits evidently the lack of land vegetation has not totally precluded the development of meandering streams in the proterozoic

cross strata and bedforms of probable transitional dune to upper stage plane bed origin from a late precambrian fluvial sandstone northern norway a late precambrian fluvial sandstone sequence in northern norway is dominated by large scale cross sets that show either lenticular or tabular geometries in the streamwise sections the lenticular sets interdigitate and in places show nearly symmetrical formsets the tabular sets are in places solitary but are mainly grouped in cosets in both cross set types the cross strata range from concave up to sigmoidal in shape with the latter variety comprising subhorizontal to gently inclined topset strata with parting lineation that merge uninterruptedly downflow into the steeper 10 2 foresets within the cross sets the geometry and dip azimuths of the foresets are conspicuously consistent although the concave up and sigmoidal strata commonly alternate downcurrent the cross strata characteristics suggest flood stage deposition from relatively high velocity steady currents heavily laden with suspended sand both cross set types are interpreted as representing bedforms generated by flow in the dune to upper stage plane bed transition the lenticular cross sets probably represent periodic dunes but it is far less clear whether the long bedforms represented by the tabular sets should be classified as dunes or rather as solitary to quasi periodic bars

geometry and origin of large scale deformation structures in some ancient wind blown sand deposits large scale deformational features that disrupt the cross bedded strata of some ancient wind blown dune sand deposits jurassic aztec and navajo sandstones u s a can betraced laterally for at least tens of metres information from four exposures leads to an idealized deformation style characterized by 1 a head portion marked by collapse features 2 a middle portion marked by a thrust ramp or a large recumbent fold and 3 a toe portion marked by a planar shear zone with small recumbent folds drag folds and possibly small horizontal shear faults an hypothesis involving earthquake induced liquefaction and collapse of the dunes is proposed sands liquefied during earthquakes cannot support an unequal surface load resulting in the collapse of surface dunes above the liquefied substrate compensatory lateral squeezing of liquefied sand and buried strata produces the shear zone in the toe portion engineering studies suggest that buried strata underlying interdunal lows where over burden stress is least will be most susceptible to liquefaction other considerations suggest that it will be the steeper lee sides of advancing surface dunes that collapse squeezing liquefied sand forward or downwind i e away from the lee slope of surface dunes if the liquefied condition persists load structures can be formed when unliquefied layers founder into the liquefied substrate

late wisconsinan proglacial sedimentation along the west chicago moraine in northeastern illinois abstract a large outwash complex occupies a northwest southeast trending intermorainic low land in northeastern illinois the complex can be divided into four assemblages arranged in zones paralleling the margin of the west chicago moraine on the east 1 the marginal assemblage occurs along the margin of the moraine and consists of gravelly mud flows fluvial sand and gravel in large deep channels and lacustrine muds deposited in shallow basins developed on mudflow surfaces 2 the proximal assemblage occurs in a 1 km wide band lying west of the moraine it consists of cobble gravels in crude horizontal strata deposited on longitudinal bars and cross bedded sand and fine gravel deposited in interbar channels as migrating dunes or accretionary wedges during low flow conditions 3 the media assemblage occurs in a 1 km wide band in the center of the intermorainic lowland and consists of cross bedded sands and fine gravel deposited on transverse bars or interbar channels coarser gravels deposited on longitudinal bars and ripple bedded sands and silts deposited in inactive channels or pools of active channels during low flow conditions 4 the distal facies underlies the other assemblages of the complex and consists of laminated lacustrine muds that accumulated in one or more large proglacial lakes and fine grained cross bedded sands deposited in a braided stream system developed on the eroded lake plain after it was drained sediments were derived from the west chicago moraine and were carried perpendicularly away from it until they reached the center of the lowland where they were transported southeasterly down the axis of the intermorainic trough

interplay of thrust back thrust strike slip and salt tectonics in a fold and thrust belt system an example from zakynthos island greece the southwestern flank of the hellenic fold and thrust belt situated along the southern edge of the dinarides albanides hellenides continental convergent zone was examined for reconstructing the tectonic deformation this investigation presents an integrated study of onshore sedimentological and structural analyses as well as offshore seismic lines across the pliocene pleistocene sedimentary succession in zakynthos island back thrust faults using the triassic evaporites as decollement surface during the pliocene and coeval diapiric intrusions formed three sub basins on the hangingwall of the kalamaki back thrust fault this interaction is responsible for the growth of the skopos mountain and the soft sediment deformation that formed synclines and slumps respectively back thrust and strike slip faults were active during the early pleistocene and diapiric intrusions modified the bathymetry on the sea floor giving rise to slumps and recumbent folds at least five events of synsedimentary diapiric intrusions have been recognized and are marked by five slump horizons during the holocene the diapiric intrusions between the kalamaki back thrust and the vrachionas anticline could be either related to normal faults or gravitationally driven

deformed cross stratified deposits in the early pleistocene tidally dominated catanzaro strait fill succession calabrian arc southern italy triggering mechanisms and environmental significance abstract the early pleistocene catanzaro strait fill succession consists of large scale tidal sets accumulated in a tectonically confined basin during a phase of rapid relative sea level rise it crops out mainly in the present day catanzaro trough where numerous field sections supported the characterization of the vertical and lateral facies variations and the documentation of a variety of soft sediment deformation structures exposed throughout their vertical and lateral extents the soft sediment deformation structures ssds are the result of liquefaction and fluidization processes that deformed cross laminations and other primary structures into folds fluid escape structures and structureless expanses three different groups of ssds have been documented in the cross stratified deposits of the catanzaro strait the detailed description of these soft sediment deformation structures in a depositional context established by facies analysis enables interpretation in terms of possible trigger mechanisms consistent relationships between the occurrence of distinctive ssds and specific tidally dominated facies have been established indicating a probable autogenic origin for the soft sediment deformations liquefaction and fluidization features are interpreted as the result of increases in water pore pressure induced by overloading in particular two types of overloading agents are hypothesized which affect the lee and stoss sides of the migrating dunes in distinct events and inducing the deformation of foreset laminae or sets of cross strata respectively

thermal history of tertiary basins in slovenia alpine dinaride pannonian junction abstract the transition zone between the alps the dinarides and the pannonian basin was affected by syn collisional magmatism in oligocene time and post collisional lateral escape followed by extreme extension in early and middle miocene times numeric heat flow models for sixteen sites and 650 vitrinite reflectance data from paleogene and neogene sediments were used to evaluate temporal and lateral heat flow variations related to these events oligocene oligocene smrekovec volcanism is the main heat source for paleogene sediments south of the periadriatic lineament vitrinite reflectance patterns suggest dextral displacement along the donat fault of the order of 50 km coalification of paleogene coal bearing sequences south of the pohorje is a result of the emplacement of the oligocene pohorje tonalite early middle miocene extremely elevated early middle miocene heat flow 200 mw m2 occurred in the styrian basin the pohorje area the maribor radgona area and along the boc anticline it is partly a consequence of magmatic activity however no igneous rocks are known from the maribor radgona area a large shallow early miocene pluton could explain the observed miocene heat flow rapid uplift of hot basement rocks in the pohorje kozjak region may have increased surface heat flow neither volcanic rocks nor metamorphic core complexes are known from the boc area the ormo selnica anticline was probably influenced by a middle miocene heating event 150 mw m2 coeval volcanism south of the anticline represents a potential heat source post middle miocene the wsw ene trending ljutomer and radgona depressions are characterized by moderate neogene heat flow 60 75 mw m2 whereas late miocene to present day heat flow in the ormo selnica anticline is 80 90 mw m2 a recent heat flow anomaly occurs in the somat benedikt area

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

terrestrial ocean environmental change in the northwestern pacific from the glacial times to holocene abstract the mixed water region mwr between the oyashio current and the kuroshio extension and surrounding terrestrial region have been affected by the global climatic change the sedimentary core kr02 15 pc6 collected at 40 23 8871 n 143 29 8663 e in the mwr provides detailed records of pollen and spores and alkenone sea surface temperature sst during the last 15 kyr showing that both ocean and terrestrial environments have been appreciably linked abundance of picea a proxy for terrestrial cool climate fluctuated coinciding with the alkenone sst change during the interstadial period 15 0 7 7 cal kyr b p alkenone sst increased to the modern level at 8 0 cal kyr b p and remained almost constant until 2 0 kyr b p while the terrestrial warming still continued until 4 0 cal kyr b p the rainfall under terrestrial warm condition increased gradually from 7 9 cal kyr b p and rapidly from 2 0 cal kyr b p both terrestrial and marine environments cooled down during the last 2 kyr possibly due to the intensified cold oyashio current

changing seas in the early middle miocene of central europe a mediterranean approach to paratethyan stratigraphy the miocene palaeogeographic evolution of the paratethys sea is still poorly constrained here we use modern mediterranean biochronology to provide an up to date overview of changing seas in central europe instead of a paratethys sea that waxed and waned with fluctuating global sea level we show that the evolution of different seas was mainly controlled by tectonic phases the early miocene ottnangian sea 18 ma was connected to the mediterranean via the rhone valley while the karpatian sea 16 5 ma was initiated by a tectonically induced marine transgression through the trans tethyan gateway in most central european basins the establishment of the badenian sea 15 2 ma triggered by subduction related processes in the pannonian and carpathian domain is significantly younger by 1 myr than usually estimated the updated palaeogeographic reconstructions provide a better understanding of the concepts of basin dynamics land sea distribution and palaeoenvironmental change in the miocene of central europe this article is protected by copyright all rights reserved

a preliminary view of the coexistence of mammoth and early peoples in mexico abstract a progress report about human mammoth interactions in mexico is provided based primarily on a literature search more than 270 mammoth localities are known in mexico but only 17 of them have shown some evidence of an association between early peoples and mammoth however that number is even less when each locality is assessed in detail due to the lack of a supportable association or the loss of the actual specimens that precludes their analysis using current techniques only six localities have modified mammoth bone among them the greatest potential for demonstrating such a relationship is at santa isabel iztapa valsequillo villa de guadalupe and tocuila establishing an analysis methodology for the materials from those as well as new localities is warranted to provide the basis for interpreting the human mammoth relationship in mexico future research calls for detailed stratigraphic and radiometric control and an analytical protocol for bone analysis focused on taphonomy and biotechnology

palaeogeography subsidence and thermal history of the neogene styrian basin pannonian basin system austria abstract the neogene styrian basin represents an extensional structure on top of a crustal wedge which was moving eastward during the final stages of the alpine orogeny eastward extrusion was a consequence of continental escape and extensional collapse within the eastern alps in a simple model the evolution of the styrian basin can be subdivided into an early miocene ottnangian to karpatian synrift and a subsequent postrift phase basement subsidence rates during the synrift phase reached 30 cm 100 yr and more than 2000 m of limnic to marine sediments were deposited the coincidence of the synrift phase and the formation of pull apart structures along strike slip zones bordering the eastward moving wedge is evidence for the close genetic relation between extrusion tectonics and basin formation a miocene magmatic phase is related to subduction along the carpathian front magmatic activity started during the synrift stage and continued into the postrift stage heat flow in the vicinity of the miocene volcanoes increased dramatically 300 mw m2 a second volcanic phase producing basalts in plio pleistocene times had only little influence on the heat flow pattern limnic to marine sediments of the synrift stage are separated by a major unconformity from middle to late miocene badenian to pontian marine to limnic fluvial postrift sediments sedimentation during the postrift phase was controlled by marine ingressions during middle miocene early badenian and sarmatian times from the south and a subsequent regression with a decline in salinity subsidence rates during the postrift stage were mostly below 2 5 cm 100 yr in pliocene times subsidence was replaced by uplift which resulted in erosion of a few hundred metres of sediment present day high heat flows are a consequence of thinned crust beneath the styrian basin

reappraisal of the 1982 eruptions of el chichon volcano chiapas mexico new data from proximal deposits additional data from proximal areas enable a reconstruction of the stratigraphy and the eruptive chronology of phases iii and iv of the 1982 eruption of el chichon volcano phase iii began on 4 april at 0135 gmt with a powerful hydromagmatic explosion that generated radially fast moving 100 ms 1 pyroclastic clouds that produced a surge deposit s1 due to the sudden reduction in the confining pressure the process continued by tapping of magma from a deeper source causing a new explosion the ejected juvenile material mixed with large amounts of fragmented dome and wall rock which were dispersed laterally in several pulses as lithic rich block and ash flow f1 partial evacuation of juvenile material from the magmatic system prompted the entrance of external water to generate a series of hydromagmatic explosions that dispersed moisture rich surge clouds and small volume block and ash flows iu up to distances of 3 km from the crater the eruption continued by further decompression of the magmatic system with the ensuing emission of smaller amounts of gas rich magma which with the strong erosion of the volcanic conduit formed a lithic rich plinian column that deposited fallout layer b associated with the widening of the vent an increase in the effective density of the uprising column took place causing its collapse block and ash flows arising from the column collapse traveled along valleys as a dense laminar flow f2 in some places flow regime changes due to topographic obstacles promoted transformation into a turbulent surge s2 which attained minimum velocities of approximately 77 ms 1 near the volcano the process continued with the formation of a new column on 4 april at 1135 gmt phase iv that emplaced fall deposit c and was followed by hydromagmatic explosions which produced pyroclastic surges s3

petroleum generation and migration in the styrian basin pannonian basin system austria an integrated geochemical and numerical modelling study abstract source rock analysis and numerical modelling techniques have been applied to evaluate the hydrocarbon potential of the styrian basin oil and gas prone sediments occur in the lower miocene section ottnangian and karpatian levels kinetic parameters indicate that hydrocarbons are generated at higher temperatures and within a narrower temperature interval from ottnangian sediments than from karpatian sediments the thermal history of the basin is governed by miocene magmatic activity due to subduction along the carpathian front heat flow during magmatic activity in close vicinity to the volcanic centres was about 300 mw m2 decreasing to about 120 mw m2 at a distance of a few kilometres after the magmatic activity the heat flow decreased and has remained at 60 85 mw m2 since the end of the middle miocene the increased heat flow resulted in an early miocene karpatian to early badenian petroleum generation phase near the volcanoes because no traps were formed at that time the generated hydrocarbons may have been lost thus the early magmatic episode had a negative impact on the hydrocarbon potential from a timing aspect at some distance from the volcanoes generation continued up to the end of the middle miocene early sarmatian hydrocarbons generated during and since the middle badenian have had a good chance of becoming trapped and forming accumulations only small amounts of oil formed after the middle miocene the numerical modelling of petroleum migration provides important information on its timing and pathways and predicts correctly the only drilled hydrocarbon occurrence in the styrian basin the calculated gas to oil ratio is 0 5 the integration of all these data helps to define areas with high petroleum potential

syntectonic sedimentation in the proterozoic upper belt supergroup northwestern montana deepening environments in the proterozoic libby formation record a tectonically induced style of sedimentation distinctly different from that of older belt rocks facies associations and sedimentary structures indicate that deposition in the lower libby formation occurred above fair weather wave base thick widespread hummocky cross stratified quartzite in the upper libby formation lacks the association of shallow water features present in the lower libby formation suggesting that upper libby deposition occurred below fair weather wave base and above storm wave base independent evidence for tectonism during deposition of the belt supergroup exists but is plagued by poor age control the angular unconformity that occurs between libby equivalent rocks and the overlying windermere supergroup indicates tectonic activity between deposition of the belt purcell and windermere supergroups the interpreted subsidence or rise in basin water level combined with newly uplifted source areas as recorded in the upper libby formation and garnet range formation could have been an early manifestation of movements that produced this unconformity

incremental subglacial meltwater sediment deposition and deformation associated with repeated ice bed decoupling a case study from the island of funen denmark abstract on the island of funen denmark sediments that are 4 7 m below the land surface consist of a 2 4 m thick sequence of stacked and folded glaciofluvial sediments overlain by a 2 3 m thick basal till the glaciofluvial sediments consist of tabular beds of planar stratified massive and cross stratified sand and gravel with localized channel fills of open framework gravel sand and gravel beds exhibit curvilinear sheath folding often leading to eye folds this folding is attributed to repeated glacier bed decoupling and recoupling with subglacial deposition of sand and gravel by meltwater occurring during the decoupling phase and deformation occurring during recoupling sand and gravel beds are typically separated by silty clay beds and laminations recording slackwater deposition within subglacial cavities folds frequently display attenuated upper limbs reflecting shearing associated with overlying ice movement on lower fold limbs only localized thrusting is observed suggesting water saturation of sands and gravels during deformation and relatively low strain rates folds are frequently truncated by overlying sand and gravel beds no evidence of shearing is found along these contacts which are interpreted as erosional surfaces thus we propose that the glaciofluvial sediment sequence records incremental step wise subglacial deposition and deformation rather than wholesale deformation following emplacement of the entire glaciofluvial sequence specifically we envisage that individual beds were deposited and folded subglacially with ice bed decoupling occurring during sediment deposition followed by recoupling and shearing of the upper bed surface by the ice base to produce folds with attenuated upper limbs incremental deformation and folding were facilitated by elevated porewater pressure within the sediments silty clay beds helped to maintain elevated porewater pressure by acting as local aquitards a general absence of till from the glaciofluvial sequence save for localized cm scale blocks suggests either non deposition or reworking into the glaciofluvial sediments deposition of tabular sand and gravel beds and open framework gravel filling scours within single beds suggest broad sheet like subglacial flows 10 100 m wide that become increasingly channelized we propose that the sedimentary sequence records a highly dynamic glaciohydraulic system characterized by repeated localized subglacial cavity development and storage and release of meltwater leading to glacier decoupling that may have facilitated fast flow of the baltic ice stream

massive sandstone facies in the hawkesbury sandstone a triassic fluvial deposit near sydney australia abstract massive sandstone is a common facies in the hawkesbury sandstone a triassic formation attributed to deposition by a large braided river the massive sandstone occurs as sheets and in elongate depressions trending perpendicular to the paleoslope as indicated by the unidirectional mean orientation of abundant cross strata some of the depressions filled with massive sandstone also contain angular mudstone intraclasts up to several meters in length massive sandstone is also associated with deformed cross strata formed by progressive loss of lamination during mass movement down foreset slopes foreset failure is attributed to liquefaction due to falling water level or to collapse of adjacent mud banks the latter mechanism resulted in rapid loading of bedform foresets and introduce large mudclasts into the massive sand sand and mudclasts accumulated in transverse scours at the foot of the foreset slopes but also travelled along the scours or spilled out to form massive sheet sands the abundance of massive sandstone in the hawkesbury sandstone is attributed to deposition in a large river in which flood stage bedforms were probably up to 15 m high because of the size of the bedforms large volumes of liquefied sand were generated when foreset slopes failed

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

thermal history of sedimentary basins maturation indices and kinetics of oil and gas generation temperature is the most sensitive parameter in hydrocarbon generation thus reconstruction of temperature history is essential when evaluating petroleum prospects no measurable parameter can be directly converted to paleotemperature maturation indices such as vitrinite reflectance tmax from rock eval pyrolysis spore coloration thermal alteration index tai or concentration of biological markers offer an indirect approach all these indices are a function of the thermal history through rather complex kinetics frequently influenced by the type of organic matter their significance and validity are reviewed besides the problems of identification e g vitrinite and interlaboratory calibration it is important to simultaneously interpret kerogen type and maturation and to avoid difficult conversions from one index to another geodynamic models where structural and thermal histories are connected are another approach to temper ture reconstruction which could be calibrated against the present distribution of temperature and the present value of maturation indices kinetics of kerogen decomposition controls the amount and composition of hydrocarbons generated an empirical time temperature index tti originally introduced by lopatin does not allow such a quantitative evaluation due to several limitations no provision for different types of kerogen and different rates of reactions poor calibration on vitrinite reflectance it is of limited interest unless one has no access to a desk top computer kinetic models based on a specific calibration made on actual source rock samples can simulate the evolution of all types of organic matter and can provide a quantitative evaluation of oil and gas generated examples from the jurassic source rocks of the paris basin monterey formation of california green river shales of utah paleozoic source eds of the algerian sahara and miocene rocks of the mahakam delta indonesia illustrate various aspects of the discussion geological geochemical models are the most efficient way to integrate geological seismic and geochemical data and they should greatly help to reduce the risk in exploration

thermal effects of exhumation of a metamorphic core complex on hanging wall syn rift sediments an example from the rechnitz window eastern alps the removal of overburden by tectonic processes displaces the rock masses and their temperature with respect to the surface consequently high cooling rates and increased heat flow have been reported from rapidly exhuming terrains previous studies were mainly focused on the greenschist and amphibolite facies tectono thermal evolution of the footwall a two dimensional numerical thermal model presented in this study concentrates on the thermal history of the hanging wall and the footwall blocks and evaluates the variation of the near surface heat flow above an evolving metamorphic core complex based on structural thermobarometric and geochronological constraints from the rechnitz core complex of the eastern alps the modelling suggests that rapid movement along the extensional fault took place between 22 and 17 ma during this period the heat flow reached values of 140 150 mw m 2 in the hanging wall in a 10 15 km wide zone parallel to the fault trace the increased heat flow caused the high coal rank in the miocene syn rift sediments deposited on the hanging wall apatite fission track geochronology of the thermally overprinted sedimentary deposits gives the time at which the bottom of the syn rift sediment pile passed through 110oc 13 6 0 9 ma the vitrinite reflectance data rr 0 67 1 04 suggest significant burial of the margin of the hanging wall at the time of core complex formation considering the coal rank data and the thermal conductivity of the sedimentary deposits by modelling of the organic maturation we calculate syn rift early middle miocene burial of the hanging wall margin of the rechnitz core complex to be 1100 1600 m this value shows the importance of the post middle miocene erosion of the region which was related to the inversion of the pannonian basin 1998 elsevier science b v all rights reserved

seismites as a tool in the palaeoenvironmental reconstruction of fluvial deposits the cambrian guarda velha formation southern brazil abstract soft sediment deformation ssd is widely described in the literature but there is no clear consensus regarding its origin and significance existing models for ssd in fluvial sediments do not clearly demonstrate a relationship between the structures preserved facies expression and larger scale depositional architecture in this study several types of ssd structures are recorded in cambrian fluvial deposits and these occur interbedded with undeformed strata throughout the entire stratigraphic interval the random distribution of these features in relation to primary facies types and fluvial forms indicates that they have neither a direct nor indirect relationship with any depositional processes or bedform type we propose that the relationship of ssd at the bed set scale to larger scale depositional architecture combined with tectono stratigraphic analysis allows the determination of both short term fluvial hydraulic conditions in ancient stream systems such as the nature of the flow regime responsible for depositing ancient fluvial stream successions and the long term subsidence rates in the form of mean recurrence interval of the seismic events responsible for triggering the generation of ssd in tectonically active basins

deformed cross bedding patterns in the upper triassic molteno formation in the main karoo basin south africa a model for their genesis the upper triassic fluviatile molteno formation in the main karoo basin south africa forms a northerly thinning intracratonic clastic wedge comprising conglomerate coarse pebbly sandstone fine sandstone thin lenticular shale and rare coal arranged in large scale fining upward sequences deposition was controlled by tectonism basin margin faulting associated with the early phase of rifting between east and west gondwanaland

basin modelling a new comprehensive method in petroleum geology abstract integrated basin modelling is used to understand and reconstruct the geological and thermal evolution of a sedimentary basin to quantify this information and hence to derive among other results the history of generation migration and accumulation of petroleum this new methodical approach is rapidly gaining world wide recognition throughout the geo scientific community because it offers two distinct advantages when addressing geological problems firstly it enables a logical quantitative treatment of very complex interrelated geological processes and secondly it permits these processes to be examined on the basis of an absolute geological time scale the prerequisites for basin modelling are 1 the translation of logical and consistent geological concepts into numerical form and then into suitable computer programs and 2 the application of these programs using high speed computers with large memories using such an approach is an important part of modern petroleum exploration because 1 1 provision is made for total coverage of the basin by allowing extrapolation to non drilled often deeper parts of the basin accessible only by using seismic data 2 2 a three dimensional view of the basin can be constructed and followed through geological time 3 3 an internal logic is utilised which is consistent with physical and chemical laws 4 4 geological geophysical and geochemical data are integrated and modelled iteratively and therefore control each other this paper shows the rapidly widening scope of basin modelling and points out some of the present day limitations and necessary research directions for the future it describes concepts for modelling of tectonic processes and for simulating expulsion of liquid petroleum

sedimentology and tectonic significance of wolfcampian lower permian conglomerates in the pedregosa basin southeastern arizona southwestern new mexico and northern mexico a single interval of red chert clast conglomerate and associated strata rcc crcc interval occurs within the earp formation pennsylvanian lower permian at many localities in southeastern arizona southwestern new mexico and northern mexico this interval records a middle wolfcampian erosional event in the northern pedregosa basin and adjacent shelf the rcc and crcc intervals are probably proximal and distal braided stream deposits respectively consisting of conglomeratic longitudinal and transverse bar deposits fluvial channel sandstone and interfluvial fine grained sandstone siltstone and shale and they are interstratified within a much thicker sequence of shallow marine deposits the rcc crcc interval is uniformly thin average 5 m thick yet it is characterized by sheet like lateral continuity indicating that deposition occurred on an extensive low lying surface on which fluvial channel migration and channel switching were important processes paleoflow directions were generally southeastward biostratigraphic evidence suggests that middle and lower wolfcampian strata below the rcc crcc interval were beveled northward much clastic material of the rcc crcc interval may be composed of reworked residuum of the beveled strata with additional contributions possibly from regions north and northwest of the pedregosa shelf middle wolfcampian emergence of the northern pedregosa basin and shelf and accompanying deposition of the rcc crcc interval were probably caused by tectonics other less important factors such as eustatic sea level fluctuations may have amplified the regression evidence favoring a tectonic cause of regression are synchronous timing of tectonism and synorogenic sedimentation throughout a wide area in the ouachita foreland the rcc crcc interval was probably deposited on a forebulge peripheral to the pedregosa foreland basin stratigraphic evidence indicates that the southern pedregosa basin evolved rapidly from a slowly subsiding platform to a deep foreland basin during early or middle wolfcampian time subsidence of the pedregosa foreland basin was presumably caused by downflexure under northward verging thrust sheets in the chihuahua region during the ouachita orogeny downflexure of the pedregosa foreland basin evidently caused flexural forebulging and subaerial exposure of large areas cratonward flexural models predicting deflection of lithosphere under isostatic thrust and sediment loads agree satisfactorily with the forebulge concept for the origin of the rcc crcc interval

convolute laminations a theoretical analysis example of a pennsylvanian sandstone abstract data from an outcropping laminated interval were collected and analyzed to test the applicability of a theoretical model describing instability of layered systems rayleigh taylor wave perturbations result at the interface between fluids of contrasting density viscosity and thickness in the special case where reverse density and viscosity interlaminations are developed the deformation response produces a single wave with predictable amplitudes wavelengths and amplification rates physical measurements from both the outcropping section and modern sediments suggest the usefulness of the model for the interpretation of convolute laminations internal characteristics of the stratigraphic interval and the developmental sequence of convoluted beds are used to document the developmental history of these structures

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

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

reconstruction of late pleistocene climate in the valsequillo basin central mexico through isotopic analysis of terrestrial and freshwater snails we aim to reconstruct the climatic and environmental conditions in the valsequillo basin during the deposition of the valsequillo gravels between c 40 000 and 8000 years ago when large mega fauna and potentially humans occupied the basin fossil freshwater fossaria sp and sphaeriidae family and terrestrial polygyra couloni holospira sp and cerionidae family snail shells from sections within the barranca caulapan were collected for oxygen and carbon stable isotope analysis oxygen and carbon isotopes in terrestrial and freshwater snail shells relate to local climatic parameters and environmental conditions prevailing during the lifetime of the snail whole shell isotope analysis showed that c 35 000 years ago climate in the valsequillo basin was similar to the present day between c 35 000 and 20 000 bp conditions became increasingly dry after which conditions became wetter again although this record is truncated intra shell isotopic analyses show that the amount of precipitation varied seasonally during the late pleistocene if people did reach this part of the americas in the late pleistocene they would have experienced changing long term and seasonal climatic conditions and would have had to adapt their life strategies accordingly

eo alpine metamorphism and the mid miocene thermal event in the western carpathians slovakia new evidence from multiple thermochronology a combination of zircon u th he zhe apatite fission track aft and apatite u th he ahe dating methods is applied to constrain the metamorphic and exhumation history of the tatric part of the branisko mountains in the western carpathians zhe ages from the basement samples prove the basement experienced a very low grade to low grade eo alpine metamorphic overprint in mid cretaceous times miocene aft and ahe ages found in the basement and in the palaeogene sediments conclusively demonstrate that the branisko mts experienced a mid miocene thermal event this thermal event had a regional character and was related to magmatic and or burial heating that exposed the sediment and basement samples to 120 130 c and 100 190 c respectively

petroleum generation and accumulation in the berkine basin eastern algeria the berkine ghadames basin is regarded as an important hydrocarbon play in eastern algeria an evaluation of organic source facies the application of petroleum geochemistry and an extensive basin modeling study were carried out to improve the understanding of the petroleum charge of the basin geochemical data indicate that the llandoverian wenlockian and the frasnian hot shales are the most important oil prone source rocks for the known hydrocarbon accumulations in the basin maturity data reflect the late cretaceous tertiary burial and are consistent with a 60 63 mw m2 heat flow in the vicinity of the anticlines and 50 mw m2 heat flow farther away from the folded area a two dimensional basin modeling study revealed the importance of poorly constrained parameters such as the amount and rate of hercynian erosion on hydrocarbon generation and trapping efficiencies the model shows that a cretaceous tertiary petroleum generation and emplacement for both source rocks can better explain the different gas and oil fields than can an earlier hercynian event the faults related to the triassic jurassic rifting are most certainly permeable and can be considered as major migration pathways for petroleum in contrast the overpressure that developed along the el biod hassi messaoud axis in the ordovician reservoirs was probably caused by the low permeability of the faults bounding the anticlines that therefore prohibited any lateral or vertical fluid movements the model also indicates two petroleum systems that have triassic reservoirs 1 a frasnian sourced system that is confined to the central part of the basin and 2 a llandoverian wenlockian sourced system in the western part of the basin migration into paleozoic reservoirs was followed by dismigration into overlying triassic traps after the cretaceous compressive movements

fluvial processes and recumbently folded crossbeds in the pennsylvanian sharon conglomerate in summit county ohio u s a abstract the sharon conglomerate in northern ohio represents braided streams in incised paleovalleys it is distinguished by big compound bars huge scours apparently at braid channel confluences in front of the bars and abundant world class recumbently overturned crossbeds tangential and tabular foresets deformed into horizontally oriented v s and parabolic u s elsewhere these have usually been attributed to liquefaction by earthquakes followed by deformation under normal stream currents but earthquakes seem insufficiently frequent incapable of causing distinctive bar head upthrusting and unlikely to result in deformation that was not exactly parallel to paleoflow we suggest that sudden onslaught floods may provide a more attractive explanation in many cases

human footprints in central mexico older than 40 000 years abstract the timing route and origin of the first colonization to the americas remains one of the most contentious topics in human evolution a number of migration routes have been suggested and there are different views as to the antiquity of the earliest human occupation some believe that settlement happened as early as 30 ka bp but most of the currently accepted early sites in north america date to the latest pleistocene related to the expansion of the clovis culture while the oldest directly radiocarbon dated human remains are 11 5 ka bp in this context new evidence is presented in this paper in the form of human footprints preserved in indurated volcanic ash to suggest that central mexico was inhabited as early as over 40 ka bp human and animal footprints have been found within the upper bedding surfaces of the xalnene volcanic ash layer that outcrops in the valsequillo basin south of puebla mexico this ash layer was produced by a subaqueous monogenetic volcano erupting within a palaeo lake dammed by lava within the valsequillo basin during the pleistocene the footprints were formed during low stands in lake level along the former shorelines and indicate the presence of humans deer canids big felids and probably camels and bovids the footprints were buried by ash and lake sediments as lake levels rose and transgressed across the site the ash has been dated to at least 40 ka bp by osl dating of incorporated baked lake sediments

holocene eruptive activity of el chichon volcano chiapas mexico geologic and radiometric age data indicate that el chichon was frequently and violently active during the holocene including eruptive episodes about 600 1250 and 1700 years ago and several undated older eruptions these episodes involving explosive eruptions of sulfur rich magma and associated dome growth processes were apparently separated by intervals of approximately 350 to 650 years some of el chichon s eruptions may correlate with unusual atmospheric phenomena around a d 1300 and possibly a d 623

new aspects of deformed cross strata in fluvial sandstones examples from neoproterozoic formations in northern norway abstract extensive 20 200 m long exposures of tabular cross sets in neoproterozoic fluvial sandstone in northern norway demonstrate that deformed cross strata in the form of recumbently folded cross strata with associated massive sand are localized features passing in both up and down current direction into undeformed concave upward or sigmoidal cross strata the deformation occurs in down current inclined tangential wedge shaped zones beneath reactivation surfaces and less commonly as flat topped lenticular zones the localized nature of the sediment deformation is attributed to local liquefaction below the top of the bed in the case of the flat topped lenses and at the dune front in the case of the more common tangential wedges the position of the flat topped lenses suggests deformation by the shear stress of high velocity suspension laden currents although liquefaction of the dune front implies the action of gravity forces it is argued that the fluvial currents were the main driving force at the instant of bed liquefaction post folding gravitational shearing probably enhanced the deformation within the upper part of the wedges with their long flat lying toeset resulting from redeposition of downslope moving liquefied sand the down current alternation of deformed tangential wedges and undeformed cross strata suggests that the mechanism that triggered the liquefaction of the dune lee side was related to the fluvial system itself and hence was of autokinetic origin the tabular cross sets have previously been interpreted as a product of the dune upper stage plane bed flow regime in this flow context it can be speculated that the liquefaction and deformation occurred when the flow conditions approached the plane bed phase probably inducing a highly differential turbulent pattern and pressure fluctuations sufficient to liquefy the fine medium sand the small flat topped deformation lenses also suggest liquefaction by cyclic loading whereas the solitary nature of the large lenses may alternatively be the result of impulsive loading from bank collapse in less well exposed fluvial successions the auto or allokinetic origin of recumbently folded cross strata may be difficult to determine however the common occurrence of recumbent folds in cross stratified fluvial sandstones and their virtual absence in marine cross stratified deposits suggests strongly that in the majority of cases the deformation was autokinetic resulting from flow phenomena typical of river channels this kind of deformation structure should thus not be attributed to an allokinetic seismic triggering mechanism unless independent evidence of fault activity can be documented

late pleistocene holocene stratigraphy and radiocarbon dating of la malinche volcano central mexico abstract previous studies of la malinche identified and radiocarbon dated several volcanic layers the youngest of which yielded an age of ca 7 5 ka an additional ash fallout layer that crops out at high altitudes was considered the most recent deposit with an estimated age of 6 ka in the present work 38 new radiocarbon ages are presented from these several date the young ash fallout layer and lie around 3 1 ka with the aid of these dates a new and comprehensive stratigraphy documenting the late pleistocene holocene eruptive history of la malinche is presented the stratigraphy indicates two main stages of volcanic activity pre malinche and malinche the first undoubtedly comprises the major part of the eruptive history but its deposits are largely covered by the products of the latter stage on which this study is focused the malinche stage was subdivided into three eruptive periods period 1 started with the emplacement of the huamantla pumice more than 45 ka ago this deposit consists of a thick pumice fallout overlain by pyroclastic flow deposits subsequently several episodes of construction and collapse of summit domes occurred the oldest dome was dated at ca 45 ka period 2 started 21 5 ka ago with the malinche pumice i a widespread pumice fallout covering the entire slopes of the volcano pyroclastic flows and lahars related to this eruption were channeled along deep barrancas and reached considerable distances deposits produced by partial sector collapse and dated at ca 20 9 ka and a pumice and ash flow deposit dated at 15 9 ka were also generated during this period the last period started with the eruption of the malinche pumice ii a distinctive fallout deposit overlain by ash flow deposits on the ne slope of the volcano the age of this pumice layer is estimated between 12 and 9 ka formation of block and ash flows lahars and pumice and ash flows followed during this period and peaked in a most intensive episode that was dated at 7 5 ka after this a long interval of quiescence was interrupted 3 1 ka ago with the eruption of an ash fallout accompanied by small pyroclastic flows whose deposits are the youngest volcanic products recognized at la malinche the new stratigraphic findings identify la malinche as a potentially active and dangerous volcano that could severely affect densely populated areas at its lower slopes in addition the results of this work can shed some light on archaeological research that is being carried out in the puebla tlaxcala region

the klagenfurt basin in the eastern alps an intra orogenic decoupled flexural basin abstract the klagenfurt basin is an e w trending narrow sarmation to quaternary flexural basin formed by flexure of the austro alpine lithosphere by loading through the southerly adjacent karawanken mountains in the eastern alps austria the tectonic evolution of the basin is kinematically connected to miocene brittle transpressive dextral strike slip deformation along the periadriatic fault which separates the south alpine unit from the austro alpine unit in the eastern alps the final nw directed overthrust of the karawanken mountains onto the foreland is characterised by a positive flower structure which is kinematically linked to dextral transpressive shearing along the periadriatic fault only a small part of the lithosphere appears to support the regional isostatic response to the load by the karawanken mountains the area is characterised by a crustal thickness between 40 and 45 km elevated heat flow and a strength distribution which suggests that only the upper crust elastically supports the topographic load ductile flow of the lower crust is also supported by the absence of a crustal root beneath the karawanken chain rheologic models for this lithospheric configuration indicate a mechanical decoupling of upper crust lower crust and mantle and generally low strengths for the lower crust and mantle

the october 1902 plinian eruption of santa maria volcano guatemala abstract the october 1902 eruption of santa maria volcano guatemala was one of the largest this century it was preceded by a great earthquake on april 19 centered at the volcano as well as numerous other major earthquakes the 18 20 hour long plinian eruption on october 25 produced a column at least 28 km high reaching well into the stratosphere the airfall pumice deposit covered more than 1 2 million km2 with a trace of ash and was only two meters thick at the vent white dacitic pumice dark gray scoriaceous basalt with physically and chemically mixed intermediate pumice and loose crystals of plagioclase hornblende hypersthene biotite and magnetite make up the juvenile components of the deposit lithic fragments are of volcanic plutonic and metamorphic origin the plinian deposit is a fine grained crystal rich single pumice fall unit and shows inverse grading mapping of the deposit gives a volume of 8 3 km3 within the one mm isopach crystal concentration studies show that the true volume erupted was at least 20 km3 equivalent to 8 5 km3 of dense dacite and that 90 of the ejecta was less than 2 mm in diameter the plinian volume eruption rate averaged 1 2 105 m3s 1 and the average gas muzzle velocity of the column exceeded 270 ms 1 a total of 8 3 1018 j of energy were released by the eruption a knowledge of both theoretically derived eruption parameters and contemporary information allows a detailed analysis of eruption mechanisms this eruption was the major stratospheric aerosol injection in the 1902 1903 period however mid to low latitude northern hemisphere temperature deviation data for the years following the eruption show no significant temperature decrease this may be explained by the sulfur poor nature of dacite magmas suggesting that volatile composition rather than mass of volatiles is the controlling parameter in climatic response to explosive eruptions

an isotopic biogeochemical assessment of shifts in organic matter input to holocene sediments from mud lake florida abstract a molecular and isotopic study of sediment cores from a sinkhole lake mud lake florida usa was performed in order to relate documented changes in the regional terrestrial vegetation and water table over the last 5500 years to molecular and isotopic proxies for biological sources of organic matter to the lake sediments temporal shifts in the source of organic matter to the sediment as determined by the stable carbon isotope composition of bulk organic matter and biomarkers correspond with previously defined regional scale transitions in forest ecosystems quercus to pinus at 5500 14 c yr bp and taxodium expansion at 2500 14 c yr bp and coincident increases in the floridan water table the 13 c values for total sedimentary organic carbon showed a shift from terrestrial and aquatic macrophyte sources 27 8 in sediments dated at 5400 14 c yr bp within the basal peat to a cyanobacterial dominated sapropel 18 1 at the surface a comparison of the 13 c values of bulk sediment and biomarkers representative of cyanobacterial and algal input e g 7 and 8 methylheptadecane and the n alkane c 17 indicates that the present shallow lake was fully developed by 2400 14 c yr bp differences among the 13 c values of specific biomarkers derived from vascular plants c 29 and c 31 n alkanes and cuo lignin oxidation products and from cyanobacteria and algae are nearly equivalent in magnitude to the shift recorded in 13 c of toc indicating their effective use as source proxies in this system

coalification and thermal histories of tertiary basins in relation to late alpidic evolution of the eastern alps the thermal histories of tertiary basins situated around and within the eastern alps are examined using coalification data waples method is used to estimate paleogeothermal conditions the data suggest that the basins thermal histories are intimately related to late alpidic geodynamics of the eastern alps

geologic evidence for age of deposits at hueyatlaco archeological site vasequillo mexico direct tracing of beds during excavation in may 1973 confirmed that the artifact bearing layers at hueyatlaco underlie 10 m of fine grained water laid deposits that constitute part of the wide spread valsequillo gravels dissection of these deposits by the adjacent rio atoyac has reached a depth of 50 m the stratigraphic section at hueyatlaco includes four distinctive tephra units the oldest one occupies a small channel in a series of cut and fill stream deposits that have yielded bifacial tools it lies more than a meter above flat lying fine grained beds from which edge retouched tools have been recovered the three other tephra units occur higher in the section fission track ages on zircon phenocrysts from two of the younger tephra layers 370 000 200 000 and 600 000 340 000 yr 2 agree with concordant uranium series dates for a camel pelvis that was found associated with bifacial tools at hueyatlaco 245 000 40 000 yr by 230th and 180 000 yr by 231pa these dates are compatible with the depth of burial and subsequent dissection of the hueyatlaco deposits as well as with the degree of hydration of volcanic glass shards and with the extent of etching of heavy mineral phenocrysts from within the tephra layers these findings suggest to us that further search for archaeological remains in deposits as old as those at hueyatlaco would be warranted

the 1985 nevado del ruiz volcano catastrophe anatomy and retrospection abstract this paper seeks to analyze in an objective way the circumstances and events that contributed to the 1985 nevado del ruiz catastrophe in order to provide useful guidelines for future emergencies the paper is organized into two principal parts in the first part an anatomy of the catastrophe is developed as a step by step chronicle of events and actions taken by individuals and organizations during the period november 1984 through november 1985 this chronicle provides the essential background for the crucial events of november 13 this year long period is broken down further to emphasize important chapters the gradual awareness of the awakening of the volcano a long period of institutional skepticism reflecting an absence of credibility the closure of the credibility gap with the september 11 phreatic eruption followed by an intensive effort to gird for the worst and a detailed account of the day of reckoning the second part of the paper retrospection examines the numerous complicated factors that influenced the catastrophic outcome and attempts to cull a few lessons from armero in order to avoid similar occurrences in the future in a nutshell the government on the whole acted responsibly but was not willing to bear the economic or political costs of early evacuation or a false alarm science accurately foresaw the hazards but was insufficiently precise to render reliable warning of the crucial event at the last possible minute catastrophe was therefore a calculated risk and this combination the limitations of prediction detection the refusal to bear a false alarm and the lack of will to act on the uncertain information available provided its immediate and most obvious causes but because the crucial event occurred just two days before the armero emergency management plan was to be critically examined and improved the numerous circumstances which delayed progress of emergency management over the previous year also may be said to have contributed to the outcome thus the catastrophe was not caused by technological ineffectiveness or defectiveness nor by an overwhelming eruption or by an improbable run of bad luck but rather by cumulative human error by misjudgment indecision and bureaucratic shortsightedness armero could have produced no victims and therein dwells its immense tragedy

determination of gross kinetic parameters for petroleum formation from jurassic source rocks of different maturity levels by means of laboratory experiments abstract solvent extracted core samples of lower toarcian carbonate rich shales posidonia shale lias of the hils syncline area lower saxony basin northern germany covering a wide maturity range vitrinite reflectance rr 0 48 0 88 and 1 45 and a kimmeridge mudstone rr 0 45 are pyrolyzed at three different heating rates 0 1 0 7 and 5 0 k min by application of non isothermal first order reaction kinetics to the resulting hydrocarbon evolution curves activation energy distributions between 46 and 70 kcal mol and pre exponential arrhenius factors are obtained by an iteration method hypothetical hydrocarbon generation curves are calculated for the lias assuming three geological heating rates 0 5 5 and 50 k 106a peak hydrocarbon generation temperatures range from 135 to 165 c

paleoecological studies at lake patzcuaro on the west central mexican plateau and at chalco in the basin of mexico abstract a 1520 cm sediment core from lake patzcuaro michoacan mexico is 44 000 yr old at the base all parts of the core have abundant pollen of pinus pine alnus alder and quercus oak with frequent abies fir the interval dated from 44 000 to 11 000 yr ago has a homogeneous flora characterized by abundant juniperus juniper pollen and frequent artemisia sagebrush it is believed to represent an appreciably drier and colder climate than at present the holocene at lake patzcuaro is characterized by a moderate increase in pinus pollen and the loss of juniperus pollen as the modern type of climate succeeded alnus was abundant until about 5000 yr ago its abrupt decrease with the first appearance of herbaceous weed pollen may reflect the cutting of lake shore and stream course alder communities for agricultural purposes or it may simply reflect a drying tendency in the climate pollen of zea corn appears at lake patzcuaro along with low peaks of chenopod and grass pollen at 3500 yr b p apparently recording a human population large enough to modify the natural environment as well as the beginning of agriculture a rich aquatic flora in this phase suggests eutrophication of the lake by slope erosion in the most recent period corn is absent from the sediments perhaps reflecting a change in agricultural practices the environment changes at lake patzcuaro are similar to and correlate with those in the cuenca de mexico where diatom stratigraphy from the chalco basin indicates fluctuations in lake levels and lake chemistry in response to variations in available moisture before 10 000 yr ago climates there were cool and dry and the chalco basin was occupied by a shallow freshwater marsh that drained north to lake texcoco where saline water accumulated by evaporation increases in effective moisture and possible melting of glaciers during the holocene caused lake levels to rise throughout the cuenca de mexico and lake texcoco flooded the chalco basin with brackish water after 5000 yr ago such flooding decreased and shallow freshwater ponds and marshes were restored in the chalco basin this environmental change coincides with the appearance of zea pollen and suggests cultural control of lake levels and salinity

principles of geochemical prospect appraisal our current understanding of the geochemical processes responsible for the creation of commercial accumulations of oil and gas can be reduced to simple rules and equations to allow the petroleum geologist to use geochemistry to estimate before drilling the likely volumes and compositions of oil and gas delivered to the trap in most sedimentary basins oil is expelled from source rocks between 120 and 150 c whereas most gas and gas condensate are released between 150 and 230 c when the initial potential of source rocks exceeds 10kg mt oil expulsion efficiencies are between 60 and 90 expelled oil and gas migrate as petroleum rich phases driven by fluid potential gradients most flow is laterally updip in beds with effective horizontal permeabilities greater than 1 md in lower permeability rocks the petroleum fluids move vertically up or down along the path of least resistance i e the most permeable or thinnest beds separating them from a high permeability lateral carrier bed the residual saturations of petroleum left behind along the migration pathway are of the order of a few percent of the porosity geochemical analysis of source rocks helps determine the yields and compositions of petroleum fluids expelled in the catchment area of a prospect these fluid masses are converted to volumes from knowledge of the phase relations and densities of petroleum fluids evaluation of the total volume of rock through which the petroleum potentially can migrate and the mean porosity of the rocks that constitute the migration pathway allow migration losses to be assessed these losses constrain both the range of migration of petroleum fluids away from the mature source rock and the volumes of petroleum remaining for entrapment in the prospect

interpreting rock eval pyrolysis data using graphs of pyrolizable hydrocarbons vs total organic carbon kerogen the major organic component of sedimentary rocks is commonly analyzed by rock eval pyrolysis plotting the data on a graph of s 2 vs total organic carbon toc and determining the regression equation is the best method for determining the true average hydrogen index and measuring the adsorption of hydrocarbon by the rock matrix such a plot also indicates the type of kerogen present and avoids the problem of increasing hydrogen index with total organic carbon content with the s 2 vs toc diagram the organic component of different suites of samples may be compared and their petroleum generation potentials established as an example the diagrams are used to evaluate the sedimentary environments and petroleum potential of the paleogene evaporitic sediments of the mulhouse basin alsace france

sandstones glaciers burrows and transgressions the lower palaeozoic of jabel az zalmah al kufrah basin libya abstract field studies in the jabel az zalmah region at the northern flank of al kufrah basin provide new insights into the stratigraphy and evolving depositional environments of cambro ordovician through devonian sediments at the base of the succession the hawaz formation is about 300 m thick and is characterised by frequently skolithos burrowed fine to medium grained sandstones with occasional silty intervals and rare conglomerates deposited in a generally high energy tidal shelf setting bioturbation is pervasive and includes spectacular cruziana traces produced by early to mid ordovician trilobites at the bottom and the top of the hawaz formation respectively these strata were incised during the late ordovician hirnantian glaciation ice sheets flowing over jabel az zalmah cut a palaeo topography of up to 100 m relief this relief is overlain by a coarsening upward succession of clastic sedimentary rocks recording re advance of an ice sheet which overrode the uppermost sandstones ice sheet retreat was accompanied by marine transgression and erosion which left a thin transgressive lag conglomerate capped sharply by siltstones of the tannezuft formation progradation resumed after post glacial maximum flooding depositing tide storm and river influenced parasequences of a major delta complex 200 m thick acacus formation fluvial incision and the development of a disconformity preceded the deposition of the tadrart formation 50 m thick a succession of trough cross bedded braided river deposits transgression and the re establishment of shallow or marginal marine systems is represented by the extensively bioturbated binem formation in which zoophycos burrows offer a tentative middle devonian stratigraphic fix an understanding of the lithological character of the lower palaeozoic strata in jabel az zalmah together with the character of unconformities that punctuate the succession will be vital for successful hydrocarbon exploration in this frontier basin which has until now been unsuccessful

the sedimentary record of carboniferous rivers continuing influence of land plant evolution on alluvial processes and palaeozoic ecosystems abstract evidence from modern rivers and the deep time geological record attests to the fundamental importance of plant life for the construction of physical habitats within fluvial environments data from an extensive literature review and original fieldwork demonstrates that many landforms and geomorphic features of modern river systems appear in the palaeozoic stratigraphic record once terrestrial vegetation had adopted certain evolutionary advances for example stable point bars are associated with the onset of rooted plants in the siluro devonian and avulsive and anabranching fluvial systems become common at the same time as extensive arborescent vegetation in the carboniferous in this paper we demonstrate a correlation between the diversification of physical fluvial environments and the expansion of terrestrial fauna and flora with an emphasis on the culmination of these trends within carboniferous alluvial systems many extrinsic factors have been considered as possible controls on the evolutionary timelines of terrestrialization for organisms however a fundamental prerequisite for achieving terrestrial biodiversity was the variety of physical habitats especially riparian systems available for newly evolved organisms in association with abundant lowland meandering systems the widespread appearance across carboniferous alluvial plains of fixed channel and anabranching reaches created further physical landforms for colonization and would have promoted increasingly complex hyporheic flow regimes furthermore the associated increase in arborescent vegetation and supply of large woody debris to inland and coastal rivers would have created a wealth of microhabitats for continental organisms we argue that the expanding extent and diversity of physical alluvial niches during the palaeozoic is an underappreciated driver of the terrestrialization of early continental life the study of the deep time fossil and stratigraphic record also illustrates that vegetation is a fundamental prerequisite for the creation of biogeomorphic alluvial landforms and physical habitats and microhabitats

the art of maturity modeling part 1 finding a satisfactory geologic model an example of one dimensional maturity modeling of the miti rumoi well a stratigraphic test drilled in a frontier area of japan is worked out in detail to illustrate how maturity modeling should be carried out prior to and during modeling an effort was made to integrate all available geological geochemical and geophysical concepts and data to create a single geologic model called here the good model that was as plausible and internally consistent as possible where data sets were internally inconsistent or in conflict with other data decisions had to be made about data reliability some vitrinite reflectance data subsurface temperatures and thermal conductivity measurements were rejected for a variety of reasons the justifications for these decisions which influenced the results of the modeling are discussed in detail using the good model we evaluated the timing and amount of oil and gas generation from coals in the haboro formation the only proposed source rocks in northwest hokkaido japan generation has occurred continually since the middle miocene but the fractional conversion of kerogen to hydrocarbons to date has been small as a result the total volume of hydrocarbons available for expulsion and migration from the haboro source rock probably is small unless very large volumes of coal are present the good model does not represent a unique solution however it thus should be regarded as one of a number of viable models rather than as the only correct one alternative models are considered in a companion paper the modeling process itself by which and during which we learn much about the geologic system is at least as important as the final numerical answer highly interactive modeling programs greatly aid in proper modeling

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

chronology of the principal scientific and governmental actions leading up to the november 13 1985 eruption of nevado del ruiz colombia abstract the virtue of studying the chronology of an event is the insight it affords as to how man views and responds to the forces of nature this chronology reflects the fumbling nature of mankind as only appreciated in hindsight when faced by an impending event of uncertain nature in this case in a developing nation but it might have happened anywhere it is hoped that we as volcanologists might improve our response to such crises knowing how they have evolved previously

some problems in the late quaternary pollen records of central mexico basins of mexico and zacapu most pollen analyses of late quaternary sediments have been carried out in closed basins of the trans mexican neovolcanic belt in central mexico climatic changes have been inferred from these pollen data however some problems arise from reinvestigations the dominance of a few pollen types in general pinus quercus and alnus is almost constant among these records in spite of the importance of vulcanism and tectonism in the evolution of this region no effects of these factors are evident from the pollen records some of the problems are illustrated in the pollen records from lake texcoco and lake chalco in the basin of mexico and lake zacapu in michoacan

the art of maturity modeling part 2 alternative models and sensitivity analysis the sensitivity of exploration decisions to variations in several input parameters for maturity modeling was examined for the miti rumoi well hokkaido japan decisions were almost completely insensitive to uncertainties about formation age and erosional removal across some unconformities but were more sensitive to changes in removal during unconformities which occurred near maximum paleotemperatures exploration decisions were not very sensitive to the choice of a particular kinetic model for hydrocarbon generation uncertainties in kerogen type and the kinetics of different kerogen types are more serious than differences among the various kinetic models results of modeling using the tti method were unsatisfactory thermal history and timing and amount of hydrocarbon generation estimated or calculated using the tti method were greatly different from those obtained using a purely kinetic model we strongly recommend use of the kinetic r o method instead of the tti method if we had lacked measured r o data subsurface temperature data or both our confidence in the modeling results would have been sharply reduced conceptual models for predicting heat flow and thermal conductivity are simply too weak at present to allow us to carry out highly meaningful modeling unless our input is constrained by measured data maturity modeling therefore requires the use of more not fewer measured temperature and maturity data the use of sensitivity analysis in maturity modeling is very important for understanding the geologic system for knowing what level of confidence to place on the results and for determining what new types of data would be most necessary to improve our confidence sensitivity analysis can be carried out easily using a rapid interactive maturity modeling program

a high elevation holocene pollen record from iztaccihuatl volcano central mexico pollen data from 3860 m in the agua el marrano valley on the northwest side of iztaccihuatl volcano southeastern part of the basin of mexico 198n combined with data on the glacial chronology and tephrochronology document holocene climatic and vegetation changes near the present timberline glacial advances occurred between 12 000 and 10 500 cal yr bp milpulco 1 and between 8300 and 7300 cal yr bp milpulco 2 a 450 cm core was drilled in sediments accumulated in a milpulco 1 moraine depression the sequence covers the last 11 000 cal yr bp according to three 14 c dates and the presence of a distinctive pumice deposit dated elsewhere at 5700 cal yr bp the pollen record of agua el marrano shows barren conditions after glacier retreat followed by a gradual colonization by elements of the alpine grasslands around 10 900 cal yr bp this plant community remained until c 7200 cal yr bp between c 7200 cal yr bp and 6500 cal yr bp coniferous forest grew close to or at the site but alpine grasslands were re established between 6500 cal yr bp and c 5000 cal yr bp apparently in connection with mid holocene dry conditions recorded in central mexico the upper timberline attained its modern altitude 4000 m in the last 3000 years during this period no significant changes are observed in the pollen spectra comparison with other palaeoecological records from central mexico suggests that the timberline fluctuated in response to both temperature and precipitation changes during the holocene