predicting gas oil and water intervals in niger delta reservoirs using gas chromatography formation evaluation experts usually have little difficulty in interpreting wireline logs to assess the type of reservoir fluid oil gas water in sand shale sequences this assessment is usually accomplished by a combination neutron density tool that detects low hydrogen and low electron densities typical of gas zones and the repeat formation tester rft which uses both the pressure gradient and sample acquisition techniques to evaluate reservoir fluid in the niger delta however many of the sands exhibit a poor neutron density response to gas and rft testing has been largely eliminated because poor hole conditions commonly result in stuck tools oil fingerprinting of residual hydrocarbons from sidewall core extracts can provide an independent means of identifying eservoir fluid type in conjunction with the nigerian national petroleum company we completed numerous chromatographic analyses on solvent extracts of sidewall core samples from various wells in the mefa field offshore west niger delta oil fingerprints of sidewall core extracts clearly reflect the type of hydrocarbons in the reservoir fingerprints of oil saturated sands are typical of topped c15 whole oils whereas fingerprints of hydrocarbons extracted from the gas dominated sands show an abbreviated hydrocarbon distribution more typical of gas condensates fingerprints of extracts from water productive intervals show a further abbreviated signature suggesting that higher molecular weight hydrocarbons did not migrate into these intervals these signatures are distinct and intact despit poor sample preservation due to prolonged storage of up to 3 yr additional applications of this technique include the reevaluation of older wells that lack modern wireline measurements but have sidewall or conventional core material available and in thin or low permeability sands that may not yield definitive rft or wireline log responses application potential for this technology is worldwide and includes the gulf coast of the united states canada indonesia and papua new guinea

comparative methods for distinguishing flakes from geofacts a case study from the wenas creek mammoth site archaeologists have long struggled with distinguishing lithic materials modified by humans artifacts from natural objects e g geofacts or zoofacts this problem is especially difficult for finds of small numbers of flake like lithic specimens and particularly for very old finds we attempt to address the artifact versus geofact problem at a paleontology site by employing three systematic and objective tests on the two recovered possible artifacts first they are compared with debitage attributes typically expected of artifacts and geofacts based on published experimental and actualistic data second they are compared in terms of nine of these attributes with a toolstone sample from the site excavation matrix third the two possible artifacts are scored for these nine attributes and graphed against the toolstone matrix sample and two samples of flintknapped debitage assemblages in all three comparisons the two specimens are more like artifacts than geofacts while this does not prove the specimens are artifacts it at least shows they cannot be easily dismissed as the sort of geofacts typically expected in the site matrix we argue that this distinction is an important first step in the evaluation of possible lithic artifacts

eruptive style and location of volcanic centers in the miocene washington cascade range reconstruction from the sedimentary record primary and reworked pyroclastic material in the ellensburg formation of central washington records middle and late miocene volcanism in the cascade range despite the absence of correlative volcanics within the volcanic chain volcanics marking sources for ellensburg detritus were eroded during late neogene uplift facies patterns and paleocurrent data suggest that the bulk of the volcaniclastics were derived from a source near bumping lake a k ar date for an intrusion in this area supports this conclusion depositional patterns and characteristics of the detritus allow hypothetical reconstruction of the style of volcanism during this period eruptive episodes began with modest sized plinian eruptions followed by extended periods of dome growth aggradation in adjacent sedimentary basins occurred principally in response to introduction of large volumes of lithic pyroclastic material during eruptive episodes

charm ii a deep reflection profile within the central england microcraton the results of a deep reflection profile crossing the precambrian rocks of charnwood forest and the postulated buried caledonian mountsorrel granodiorite in central england are reported a prominent subhorizontal reflector to the ne of charnwood forest is suggested as marking the base of the pre carboniferous widmerpool gulf and possibly arises from the top surface of the granodiorite intrusion a lack of returned energy from the upper crust beneath charnwood forest contrasts with a mass of reflectors beneath the intrusion which itself appears relatively transparent to seismic energy two subparallel bands of reflectors within the lower crust continuous across the whole profile and previously observed on another section about 20 km to the east suggest that the emplacement of the granite has caused little disturbance within the lower crust in the plane of the section the origin of the twin reflections is unexplained similar twin reflections occur in the lower crust in northern germany immediately to the se of the london brabant massif over whose nw region the charm profile was sited

seismic refraction evidence for a basement ridge between the derbyshire dome and the w of charnwood forest results from a 40 km seismic refraction profile crossing a series of positive gravity anomalies extending across the postulated mouth of the widmerpool gulf are reported a refractor with a similar velocity to the precambrian rocks of charnwood forest dips away from charnwood to the southern flank of the derbyshire dome to a depth of 2 km this refractor is faulted into horst and graben structures the horst blocks correlate with the positive gravity anomalies a northern boundary fault to the precambrian outcrops of charnwood is defined

case for periodic colossal jokulhlaups from pleistocene glacial lake missoula two classes of field evidence firmly establish that late wisconsin glacial lake missoula drained periodically as scores of colossal jokulhlaups glacier outburst floods 1 more than 40 successive flood laid sand to silt graded rhythmites accumulated in back flooded valleys in southern washington hiatuses are indicated between flood laid rhythmites by loess and volcanic ash beds disconformities and nonflood sediment between rhythmites are generally scant because precipitation was modest slopes gentle and time between floods short 2 in several newly analyzed deposits of pleistocene glacial lakes in northern idaho and washington lake beds comprising 20 to 55 varves average 30 40 overlie each successive bed of missoula flood sediment these and many other lines of evidence are hostile to the notion that any two successive major rhythmites were deposited by one flood they dispel the notion that the prodigious floods numbered only a few the only outlet of the 2 500 km 3 glacial lake missoula was through its great ice dam and so the dam became incipiently buoyant before the lake could rise enough to spill over or around it like grimsvotn iceland lake missoula remained sealed as long as any segment of the glacial dam remained grounded when the lake rose to a critical level 600 m in depth the glacier bed at the seal became buoyant initiating underflow from the lake subglacial tunnels then grew exponentially leading to catastrophic discharge calculations of the water budget for the lake basin including input from the cordilleran ice sheet suggest that the lakes filled every three to seven decades the hydrostatic prerequisites for a jokulhlaup were thus re established scores of times during the 2 000 to 2 500 yr episode of last glacial damming j harlen bretz9s spokane flood outraged geologists six decades ago partly because it seemed to flaunt catastrophism the concept that lake missoula discharged regularly as jokulhlaups now accords bretz9s catastrophe with uniformitarian principles

dissected paleotopography and base level changes in a triassic fluvial sequence at one stratigraphic level in petrified forest national park in arizona fluvial mudrocks of the chinle formation are truncated by areally extensive deep scours that are filled dominantly by pedogenically modified mudrocks color differences between paleosols developed on scoured and scour fill deposits facilitate recognition of the dissected interval the mudstone filled scour system records a period of channel incision and widespread gullying caused by lowered base level although it is difficult to document subsidence rates in the chinle basin the tectonic setting suggests that the enormous scour system could be the result of fluctuations in regional thermal activity during late triassic time similar scour and fill should occur in other fluvial sequences however because they both truncate and are filled by mudrocks identification can be difficult recognition of them is important because they are indicators of base level fluctuations and thus are useful in unraveling the depositional history of a basin

downstream dilution of a lahar transition from debris flow to hyperconcentrated streamflow nearly instantaneous melting of snow and ice by the march 19 1982 eruption of mount st helens released a 4 106 m3 flood of water from the crater that was converted to a lahar volcanic debris flow through erosion and incorporation of sediment by the time it reached the base of the volcano over the next 81 km that it traveled down the toutle river the flood wave was progressively diluted through several mechanisms a transformation from debris flow to hyperconcentrated streamflow began to occur about 27 km downstream from the crater when the total sediment concentration had decreased to about 78 by weight 57 by volume the hyperconcentrated lahar runout flood wave transporting immense quantities of sand in suspension continued to experience progressive downstream dilution although turbulence was significantly dampened by the extremely high suspended load very large standing waves and antidune waves were observed the hyperconcentrated lahar runout flow deposited an unusual faintly stratified coarse sand which locally contained small isolated gravel lenses very similar deposits in the quaternary stratigraphy of mount st helens and other cascades volcanoes suggest that lahars may be more frequent than previously recognized

vein quartz in lithic traditions an analysis based on experimental archaeology abstract worldwide vein quartz was a commonly used raw material for stone tools but this material has proved difficult for archaeologists to analyse because many quartz assemblages appear to be comprised of amorphous pieces not easily recognised as humanly modified or forming tools this paper discusses the analysis of the debitage focusing on the debitage fragmentation rate the debitage break and fragment types and the quantitative analysis of the complete flakes resulting from experimental knapping of quartz which formed part of a project which investigated the use of quartz in irish prehistoric lithic traditions the results have highlighted the complexity involved in analysing quartz assemblages and the significant differences between the debitage products of quartz and chert knapping assemblages while bipolar knapping is generally easy to differentiate from direct percussion it is harder to differentiate between soft and hard hammer percussion

neogene synvolcanic and syntectonic sedimentation in central washington neogene drainage evolution and sedimentation in central washington were controlled by extrusion of flood basalts aggradation of volcanism induced sedimentary sequences and fold belt deformation most columbia river basalt group lavas accumulated between 17 0 and 13 5 ma and repositioned streams to the margin of the columbia plateau lava dammed lakes were not major contributors to the stratigraphic record fluvial sedimentation in response to lowered gradients produced broad flood plain dominated alluvial sequences distribution of basalts and the thickness and facies trends in intercalated sediments record growth of the yakima fold belt throughout the middle miocene to pliocene adequate topographic relief to generate widespread basaltic gravel however lagged behind initial deformation by at least 10 m y because of burial of the slowly developing folds by high frequency eruptions of large volume basalt flows neogene uplift and incision of the cascade range are recorded by derivation of successively younger epiclastics from lower levels of the cascade stratigraphic sequence episodes of dacitic volcanism in the cascades produced widespread monomictic sediments with abundant pyroclastic material in proximal to medial positions this detritus was deposited primarily by floods and debris flows

a relative p wave delay study between eskdalemuir and charnwood forest summary the relative p wave delay between cwf a permanent seismic station on the precambrian rocks of charnwood forest in the english midlands and eka the eskdalemuir seismological array shows a large azimuthal variation of 1 3 s this is examined and is consistent with a thinning of the crust from eka to cwf together with a considerable thickness of high velocity most probably greater than 7 0 km s 1 lower crust beneath cwf the southern uplands fault approximately 42 km to the north west at its closest approach to eka seems to be associated with a large anomaly in the relative p wave delay raypaths from events originating between azimuths 260 to 350 from eka apparently pass through anomalously high velocity material entering the crust just to the south of the fault

geochemical evaluation of niger delta sedimentary organic rocks a new insight a geochemical evaluation of niger delta organic matter was carried out using supercritical fluid extraction sfe sample preparation procedure comparison of geochemical significance of gas chromatographic data of rock extracts of sfe with those of soxhlet extraction method from previous studies was made in order to establish the usefulness of sfe in geochemical exploration the assessment of geochemical character of the rock samples from the comparison and interpretation of other geochemical parameters were used to give more insights into understanding the source rocks characteristics of onshore and shelf portions of the niger delta basin the results of the gas chromatographic gc analysis of the rock extracts across the lithostratigraphic units show that pr ph pr nc17 pr nc18 cpi and odd even preference ranged from 0 07 to 12 39 0 04 to 6 66 0 05 to 13 80 0 12 to 8 4 and 0 06 to 8 12 respectively the rock eval pyrolysis data and geochemical ratios and parameters calculated from the gc data showed that most of the samples are mature and have strong terrestrial provenance while a few samples have strong marine provenance the few marine source rocks are located in the deeper depth horizon pr ph and standard geochemical plots indicate that most of samples were derived from organic matter deposited in less reducing conditions i e more of oxidizing conditions while a few samples have predominantly influence of reducing conditions the results of trace metal analysis of older samples from agbada formation also indicate marine and mixed organic matter input deposited in less reducing conditions the results obtained in this study are comparable with those obtained from previous studies when soxhlet extraction method was used and also indicated the presence of more than one petroleum systems in the niger delta

quantitative diamondoid analysis indicates oil cosourcing from a deep petroleum system onshore niger delta basin the niger delta basin is one of the most prolific hydrocarbon provinces in the world yet the origin of the vast amounts of oil and gas found in the numerous sub basins across the delta remains contested a total of 180 oil samples from more than 40 oil fields in the niger delta were analyzed by gas chromatography gc gc mass spectrometry gc ms and selected samples by gc tandem mass spectrometry gc msms the interpreted thermal maturity and source depositional environments of these hydrocarbons show significant variation depending on the components analyzed and allow no clear correlation to a single source rock but rather imply extensive mixed contributions diamondoid hydrocarbon parameters were used for the first time on these paleogene neogene reservoired oils to investigate source thermal maturity and mixing effects and to perform cross correlations of these oils the diamondoid abundances and distributions support the hypothesis of co sourcing of oil from a thermally cracked sub delta type ii marine source which was then mixed with oils of relatively lower maturities in the paleogene neogene reservoirs future geochemical interpretations should treat the niger delta oils as potential mixtures of oils of variable maturities from different sources often with the most important source biomarkers depleted because of the extent of thermal cracking

migration effects on the composition of hydrocarbon accumulations in the oml 67 70 areas of the niger delta systematic changes in gas oil ratios in the oml 67 70 area joint venture acreage of the niger delta nigeria illustrate the effects of hydrocarbon migration on the compositional changes observed in the accumulations over large depth intervals one interpretation is that the reservoirs are currently both filling and leaking hydrocarbons indicating that trap styles affect the migration pathways in this region of the niger delta the accumulations are more liquid prone with depth based on the bubble point of the fluids in the reservoir applying these results to regional exploration opportunities indicates that fluid contacts in the normally pressured section are controlled by leaking seals class iii traps the potential exists for pressure controlled filled to spill traps class ii traps in the overpressured section where a high quality seal impedes the vertical flux of hydrocarbon fluids although these conclusions apply to a specific portion of the niger delta combining the concept of trap style with compositional changes resulting from migration processes is useful in identifying new play concepts and opportunities in other regions of the world

sedimentology and characteristics of dispersed organic matter in tertiary niger delta origin of source rocks in a deltaic environment organic matter in tertiary strata of the niger delta is mainly a mixture of types ii and iii kerogen as defined by pyrolysis has a high pristane phytane ratio 1 and is composed of the macerals vitrinite and minor liptinite the main palynofacies are structured woody material opaque organic matter cuticles pollen and spores and minor amorphous organic matter the geochemistry petrology palynofacies and distribution data indicate a predominantly terrestrial and detrital source of the organic matter irrespective of facies formation or age the distribution and abundance of the organic matter are related to both the age of the strata and depositional environment the most significant variation is the decline in mean total organic carbon toc content from late eocene 2 2 toc to pliocene strata 90 toc and an associated general decline in pyrolysis defined hydrogen index hi and pristane phytane ratio the decrease in toc and hi in younger strata reflects increased dilution of a nearly constant supply of terrestrial organic matter with the generally higher sedimentation rates of younger strata a simple linear dilution model accounts for about 50 of the variance in measured toc the low pristane phytane ratio of younger strata may reflect less oxidizing depositional conditions the variation in organic matter with depositional environments and environmental depth zones defined by foraminiferal assemblages is significant although less important than variation due to age the highest toc and hi values occur in nonmarine swamp marsh and floodplain deposits reflecting proximity to the organic source beach barrier and offshore bar facies have lower toc and hi values due to selective winnowing of organic matter and greater oxidation from continental to transition marine depth zones a marked decline in toc and hi occurs as a result of dilution selective transport and oxidation of the organic matter from transitional to bathyal depth zones little variation is found in toc but a general increase is found in hi which reflects a relative increase in more hydrogen rich autochthonous organic matter in all facies autochthonous organic matter comprises less than 20 of the toc no interpretable variation appears in maceral or palynofacies abundance with sediment type which probably reflects the homogeneity of the organic matter paradoxically no rich source rocks occur in the tertiary succession in the niger delta and as conventionally measured the strata have little or no oil generating potential the poor quality of the source rocks has been more than compensated for by their great volume by the excellent migration routes provided by interbedded permeable sands and possibly by the relatively rapid rate of maturation niger delta type of source rock although an end member in terms of general source rock composition appears to be relatively typical of tertiary deltas

determination of the three dimensional seismic structure of the crust and upper mantle in the central midlands of england summary teleseismic p wave residuals relative to cwf a permanent shortperiod seismic station on charnwood forest in the central midlands of england have been determined for two small aperture arrays deployed over the precambrian block of charnwood and its surrounding phanerozoic sediments the data have been inverted to produce a block model of the p wave velocity variations in the crust and upper mantle beneath the study region the results are consistent with significant variations penetrating to a depth of at least 50 km low velocities are associated with two upper crustal intrusive bodies the caledonian mountsorrel granodiorite and the south leicestershire diorites a longer wavelength variation at lower crustal upper mantle depths could arise from the moho dipping to the south west beneath the study region and whose strike sub parallels the dominant charnian trend of the major basement structures in this part of central england

explosive activity associated with the growth of volcanic domes abstract domes offer unique opportunities to measure or infer the characteristics of magmas that at domes and elsewhere control explosive activity a review of explosive activity associated with historical dome growth shows that 1 1 explosive activity has occurred in close association with nearly all historical dome growth 2 2 whole rock sio 2 content a crude but widely reported indicator of magma viscosity shows no systematic relationship to the timing and character of explosions 3 3 the average rate of dome growth a crude indicator of the rate of supply of magma and volatiles to the near surface enviornment shows no systematic relationship to the timing or character of explosions and 4 4 new studies at arenal and mount st helens suggest that water content is the dominant control on explosions from water rich magmas whereas the crystal content and composition of the interstitial melt and hence magma viscosity are equally or more important controls on explosions from water poor magmas new efforts should be made to improve current rather limited techniques for monitoring pre eruption volatile content and magma viscosity and thus the explosive potential of magmas

organic matter of agbada formation niger delta nigeria the status of the agbada formation as a major source rock for oil and gas in the niger delta is debatable an organic matter survey of the formation in three exploratory wells makaraba 26 abiteye 13 and okan 25 shows that on the average amorphous organic matter constitutes 63 of the kerogens whereas terrestrial organic matter woody remains spores and pollen and recycled coaly organic matter make up 30 and 7 respectively pyrolysis data indicate essentially type iii kerogen for the agbada shales thermal alteration index tai and pyrolysis data show that the kerogens are mature in the three wells we estimate that about 2 000 4 000 ft 600 1 200 m of mature agbada shales are present in the western part of the niger delta results of organic carbon determinations show that the agbada shales contain moderate to high amounts of organic matter which could have sourced some of the oils found in the makaraba abiteye and okan fields although this view is valid for the western part of the niger delta the situation in the other parts of the delta might be different

three dimensional seismic raytracing for the forward modelling and direct inversion of teleseismic delay times summary this paper describes a simple robust technique of 3 d seismic raytracing through anomalous receiver structure the technique uses a shooting approach and a vectorial description of both the ray and the anomalous structure through which it passes by representing the receiver structure as a network of blocks each with a constant velocity anomaly the technique may be applied to the newly developed least squares inversion method aki christoffersson husebye to define the required travel times of each ray through each block the technique enables subvertical and non parallel block boundaries to be handled and positioned to mimic known tectonic contacts such as the boundaries of descending plates or craton margins an inversion using such a network will better define the velocity contrasts than one using a regular grid of arbitrarily positioned block boundaries alternatively delay times slowness and azimuth anomalies may be modelled by raytracing through assumed anomalous receiver structures as the anomalies will deflect a ray away from its mean earth path an iterative procedure is necessary to achieve the required end point a novel efficient procedure is presented which involves making a search for the point through which the ray passes at the base of the receiver structure the slowness azimuth anomaly of each trial ray is determined as a mislocation vector trial rays with significantly different mislocation vectors can initially be regarded as possible different phases convergence of more than one phase to the required end point indicates the presence of multipathing lack of convergence of all these phases indicates the presence of a shadow zone

effective petroleum source rocks of the world stratigraphic distribution and controlling depositional factors six stratigraphic intervals representing one third of phanerozoic time contain petroleum source rocks that have provided more than 90 of the world s discovered original reserves of oil and gas in barrels of oil equivalent the six intervals are 1 silurian generated 9 of the world s reserves 2 upper devonian tournaisian 8 of reserves 3 pennsylvanian lower permian 8 of reserves 4 upper jurassic 25 of reserves 5 middle cretaceous 29 of reserves and 6 oligocene miocene 12 5 of reserves this uneven distribution of source rocks in time displays no obvious cyclicity and the factors that controlled the formation of source rocks vary from interval to interval maps that show facies structural forms and petroleum source rocks were prepared for this study analysis of the maps indicates that several primary factors controlled the areal distribution of source rocks their geochemical type and their effectiveness i e the amounts of discovered original conventionally recoverable reserves of oil and gas generated by these rocks these factors are geologic age paleolatitude of the depositional areas structural forms in which the deposition of source rocks occurred and the evolution of biota the maturation time of these source rocks demonstrates that the majority of discovered oil and gas is very young almost 70 of the world s original reserves of oil and gas has been generated since the coniacian and nearly 50 of the world s petrole m has been generated and trapped since the oligocene the term petroleum as used in this study includes oil gas condensate and gas but does not include bitumen and other solid and semisolid oil derivatives

geophysical and petrological modelling of the structure and composition of the crust and upper mantle in complex geodynamic settings the tyrrhenian sea and surroundings abstract information on the physical and chemical properties of the lithosphere asthenosphere system las can be obtained by geophysical investigation and by studies of petrology geochemistry of magmatic rocks and entrained xenoliths integration of petrological and geophysical studies is particularly useful in geodynamically complex areas characterised by abundant and compositionally variable young magmatism such as in the tyrrhenian sea and surroundings a thin crust less than 10 km overlying a soft mantle where partial melting can reach about 10 is observed for magnaghi vavilov and marsili which belong to the central tyrrhenian sea backarc volcanism where subalkaline rocks dominate similar characteristics are seen for the uppermost crust of ischia a crust about 20 km thick is observed for the majority of the continental volcanoes including amiata vulsini roccamonfina phlegraean fields vesuvius vulture stromboli vulcano lipari etna and ustica a thicker crust is present at albani about 25 km and at cimino vico sabatini about 30 km the structure of the upper mantle in contrast shows striking differences among various volcanic provinces volcanoes of the roman region vulsini sabatini alban hills sit over an upper mantle characterised by vs mostly ranging from about 4 2 to 4 4 km s at the alban hills however slightly lower vs values of about 4 1 km s are detected between 60 and 120 km of depth this parallels the similar and rather homogeneous compositional features of the roman volcanoes whereas the lower vs values detected at the alban hills may reflect the occurrence of small amounts of melts within the mantle in agreement with the younger age of this volcano the axial zone of the apennines where ultrapotassic kamafugitic volcanoes are present has a mantle structure with high velocity lid vs 4 5 km s occurring at the base of a 40 km thick crust beneath the campanian volcanoes of vesuvius and phlegraean fields the mantle structure shows a rigid body dipping westward a feature that continues southward up to the eastern aeolian arc in contrast at ischia the upper mantle contains a shallow low velocity layer vs 3 5 4 0 km s just beneath a thin but complex crust the western aeolian arc and ustica sit over an upper mantle with vs 4 2 4 4 km s although a rigid layer vs 4 55 km s from about 80 to 150 km occurs beneath the western aeolian arc in sardinia no significant differences in the las structure are detected from north to south the petrological geochemical signatures of italian volcanoes show strong variations that allow us to distinguish several magmatic provinces these often coincide with mantle sectors identified by vs tomography for instance the roman volcanoes show remarkable similar petrological and geochemical characteristics mirroring similar structure of the las the structure and geochemical isotopic composition of the upper mantle change significantly when we move to the stromboli campanian volcanoes the geochemical signatures of ischia and procida volcanoes are similar to other campanian centres but sr pb isotopic ratios are lower marking a transition to the backarc mantle of the central tyrrhenian sea the structural variations from stromboli to the central vulcano and lipari and western aeolian arc are accompanied by strong variations of geochemical signatures such as a decrease of sr isotope ratios and an increase of nd pb isotope and lile hfse ratios the dominance of mafic subalkaline magmatism in the tyrrhenian sea basin denotes large degrees of partial melting well in agreement with the soft characteristics of the uppermost mantle in this area in contrast striking isotopic differences of plio quaternary volcanic rocks from southern to northern sardinia does not find a match in the las geophysical characteristics the combination of petrological and geophysical constraints allows us to propose a 3d schematic geodynamic model of the tyrrhenian basin and bordering volcanic areas including the subduction of the ionian adria lithosphere in the southern tyrrhenian sea and to place constraints on the geodynamic evolution of the whole region

alluvial river response to neotectonic deformation in louisiana and mississippi repeat geodetic surveys show uplift of the monroe and wiggins anticlines in louisiana and mississippi there are deformed quaternary terraces which indicate long term deformation in the valleys of the alluvial rivers that cross these structures and there are floodplain and channel convexities that provide evidence of modern deformation in addition the channels show significant variations of morphology sinuosity gradient and depth and behavior appropriate to reaches of increased and decreased valley slope these alluvial rivers are adjusting to modern deformation and their adjustment confirms two geodetic leveling anomalies

lithic taphonomy in desert environments contributions from fuego patagonia southern south america abstract this paper focuses on the contributions of taphonomic approaches to the study of lithic assemblages based on actualistic and archaeological case studies from fuego patagonia south america here i summarize some of the main taphonomic issues identified for the regional lithic record which are of relevance for the archaeological research in other desert environments specifically distributional patterns in lithic assemblages produced by wind are highlighted and main guidelines for pseudoartifact study are presented and discussed actualistic data show lithic artifacts up to 50 mm in size or weighting 13 g can be moved by winds blowing at 90 km h finally a methodological exercise banyai s zoom is proposed for lithic mimic recognition

atmospheric methane from organic carbon mobilization in sedimentary basins the sleeping giant abstract the mass of organic carbon in sedimentary basins amounts to a staggering 1016 t dwarfing the mass contained in coal oil gas and all living systems by ten thousand fold the evolution of this giant mass during subsidence and uplift via chemical physical and biological processes not only controls fossil energy resource occurrence worldwide but also has the capacity for driving global climate only a tiny change in the degree of leakage particularly if focused through the hydrate cycle can result in globally significant greenhouse gas emissions to date neither climate models nor atmospheric co2 budget estimates have quantitatively included methane from thermal or microbial cracking of sedimentary organic matter deep in sedimentary basins recent estimates of average low latitude eocene surface temperatures beyond 30 c require extreme levels of atmospheric co2 methane degassing from sedimentary basins may be a mechanism to explain increases of atmospheric co2 to values as much as 20 times higher than pre industrial values increased natural gas emission could have been set in motion either by global tectonic processes such as pulses of activity in the global alpine fold belt leading to increased basin subsidence and maturation rates in the prolific jurassic and cretaceous organic rich sediments or by increased magmatic activity such as observed in the northern atlantic around the paleocene eocene boundary increased natural gas emission would have led to global warming that was accentuated by long lasting positive feedback effects through temperature transfer from the surface into sedimentary basins massive gas hydrate dissociation may have been an additional positive feedback factor during hyperthermals superimposed on long term warming such as the paleocene eocene thermal maximum petm as geologic sources may have contributed over one third of global atmospheric methane in pre industrial time variability in methane flux from sedimentary basins may have driven global climate not only at time scales of millions of years but also over geologically short periods of time earth system models linking atmospheric ocean and earth surface processes at different timescales with the sedimentary organic carbon cycle are the tools that need to be developed in order to investigate the role of methane from sedimentary basins in earth s climate

coarse grained nonmarine volcaniclastic sediment terminology and depositional process modern and ancient volcaniclastic sedimentary sequences contain depositional units whose features cannot be attributed to fully turbulent dilute stream flow or viscous debris flow the characteristics of these poorly sorted sediments suggest rapid deposition from high concentration dispersions but not en masse sedimentation thus appears related to high discharge flows intermediate in sediment water ratio between stream flow and debris flow the term hyperconcentrated flood flow is proposed for describing this intermediate condition hyperconcentrated flood flow deposits are distinguished from debris flow deposits by lack of matrix support or reverse grading and instead exhibit distribution normal grading and horizontal stratification these deposits are distinguished from normal dilute stream flow deposits by lack of cross stratification in sand facies and by very poor sorting poor imbrication and numerous clasts with long axes oriented parallel to flow direction in gravel facies the horizontal bedding that dominates sandy hyperconcentrated flood flow deposits consists of sediment too coarse grained and strata too thick to have been produced in the boundary layer of the upper flow regime and should not be confused with the more familiar thin graded laminae of fine to medium grained sand often associated with parting lineation hyperconcentrated flood flow deposits are not unique to volcanic settings they also occur in arid alluvial fan sequences debris flow and hyperconcentrated flood flow deposits however are much thicker and more extensive in volcanic regions than on alluvial fans because explosive volcanism leads to rapid mobilization of large volumes of sediment and water on a scale unparalleled in nonvolcanic settings in volcanic regions therefore these deposits have greater preservation potential show greater lateral variability and are more voluminous transformation of channelized debris flow to hyperconcentrated flood flow by dilution with stream water recently observed at mount st helens is recorded in ancient volcaniclastic sequences and may serve as the primary mechanism for generating hyperconcentrated flood flow

sedimentology of proximal to distal volcaniclastics dispersed across an active foldbelt ellensburg formation late miocene central washington late miocene volcaniclastics of the ellensburg formation washington northwestern usa are exposed in basins within an integrated palaeodrainage over the depositional reach from 15 to 120 km eastward from a cascade range source area two facies associations are recognized the first is composed of laterally restricted well sorted polymictic conglomerates representing a gravel bedload regime during inter eruption periods the second comprises laterally extensive sheets bounded by deeply developed paleosols composed of monomictic pebbly pumiceous dacitic sandstones with intercalated debris flow and hyperconcentrated flood flow deposits these sheets aggraded in response to eruptive events that are sometimes recorded by air fall tephras at the bases of sequences debris flow and hyperconcentrated flood flow deposits occur as far as 120 km from source but are uncommon beyond 50 km hyperconcentrated flood flow deposits initially increase in abundance away from source as debris flow deposits diminish suggesting formation of hyperconcentrated flood flows by dilution of debris flows sandy facies form broad sheets dominated by scour fill bedding in proximal and medial settings and grade to narrower trough cross bedded sheets in distal settings suggesting moderation of flood discharges with distance base level changes associated with episodic sediment influx caused incision aggradation cycles in mainstream settings and episodic impoundment of tributaries to form lakes or rapidly aggrading poorly drained floodplains although volcanism was the primary control on depositional style concurrent development of the yakima fold belt produced a structure consequent drainage pattern that determined sediment dispersal and basin subsidence permitted preservation of both syn eruption and inter eruption facies detritus from rising anticlines was generally diluted by the volumetrically superior extrabasinal volcaniclastics but dominates deposits of small tributary streams flowing toward rather than from the cascades

improved understanding of the petroleum systems of the niger delta basin nigeria biomarker and n alkane compound specific stable carbon isotope analyses csia were carried out on 58 crude oil samples from shallow water and deepwater fields of the niger delta in order to predict the depositional environment and organic matter characteristics of their potential source rocks using a source organofacies prediction approach from oil geochemistry the presence in the western deepwater oils relatively abundant c27 steranes c30 24 n propyl cholestane low oleanane index relatively low pr ph ratios gammacerane and positive to nearly flat c12 c30 n alkane compound specific stable carbon isotope profiles suggests that the source facies that expelled these oils contain significant marine derived organic matter deposited under sub oxic and stratified water column conditions this contrasts with the terrigenous organic matter dominated source rocks accepted for shallow water niger delta oils oils in the shallow water accumulations can be separated into terrigenous and mixed marine terrigenous families the terrigenous family indicates expulsion from source rock s containing overwhelmingly higher plant source organic matter average oleanane index 0 48 high c29 steranes as well as having negative sloping n alkane isotope profiles oxic source depositional conditions pr ph 2 5 and non stratified conditions absence to low gammacerane content are inferred for the terrigenous family the mixed marine terrigenous family has biomarker properties that are a combination of the deepwater and terrigenous shallow water oils bitumen extracts of the sub delta late cretaceous araromi formation shale in the dahomey basin are comparable both molecularly and isotopically to the studied western deepwater oil set but with an over all poor geochemical correlation this poor geochemical match between araromi shale and the western deepwater oils does not downgrade the potential of sub delta cretaceous source rock contribution to the regional oil charge in the deepwater niger delta

the saddle mountains the evolution of an anticline in the yakima fold belt the saddle mountains uplift is an asymmetrical north vergent anticline with a length of about 110 km it varies from an open to tight fold and is divided into six segments based upon differences in geometry flows of the columbia river basalt group intercalated sedimentary deposits of the ellensburg formation and suprabasalt sediments thin over the uplift and thicken into the synclines variations in thickness are used to determine the timing of deformation and age of major and minor structures the close correlation of growth rate of the folds with rate of magma supply of the columbia river basalt group suggests that the yakima fold belt resulted from the same tectonic processes that produced eruption of the columbia river basalt modified journal abstract

reservoir characterization and paleo stratigraphic imaging over okari field niger delta using neural networks reservoir geometry and internal architecture in the niger delta can vary over short distances with rapid lateral and vertical changes in lithology and porosity understanding such variations is critical to designing an optimum development strategy for prospects in this basin it was in order to fully understand the variations in reservoir facies and internal architecture over okari oil field in the niger delta that this study was undertaken conventional seismic interpretation attribute analyses and subsequent drilling had located a stack of reservoirs in a rollover anticline to unravel the paleo stratigraphy of the field and fully populate the field with log properties we used a multilayered feed forward neural network mlfn to predict shale volume and porosity from seismic and well log data sets earlier rock physics analyses had been undertaken to understand litho fluid facies associations in the field and assist in further quantitative interpretation and calibration of neural network predictions

recent archaeo palaeontological findings from barranca del muerto site santiago chazumba oaxaca mexico abstract this article presents the first results of an archaeo palaeontological study which began in 2007 at the sites of chazumba i and ii in the barranca del muerto located in the sierra madre del sur santiago chazumba oaxaca mexico the excavation work is part of a larger international cooperation project titled biodiversity and quaternary hunter gatherer societies from mexico led by the institut de paleoecologia humana i evolucio social iphes tarragona spain and the instituto nacional de antropologia e historia of mexico the main objective of the project is to study hunter gatherer groups and their relationships with pleistocene fauna and rock art to date five excavation campaigns have been carried out 2007 2008 2010 2013 2014 which have primarily yielded faunal remains from the late pleistocene and from within a still undetermined period during the rancholabrean age nalma the fauna is represented by megaherbivores giant sloth glyptodont and gomphothere among others and mesoherbivores deer prong horns horses and even small mammals reptiles and amphibians some lithic materials have been recovered in association with these remains and several fossils have been examined to determine the presence of cut marks there is an ams 14c date of 27 720 27 500 cal bp obtained from a charcoal sample from sediments on top of the bone layers further sample assays are warranted in order to confirm the antiquity of the archaeological assemblage

velocity structure of the pamir hindu kush region possible evidence of subducted crust the arrival times of compressional p and shear s waves from approximately 580 microearthquakes recorded by a temporary array in the pamir hindu kush region in central asia are used to deduce one and three dimensional velocity structures of this region the results for one dimensional structures imply that the moho is at 70 5 depth also there is a velocity reversal near 160 km depth which is inferred to be the beginning of the low velocity zone this reversal continues to depths of approximately 230 km below 230 km velocities are somewhat higher than those of normal mantle at similar depths 9 3 km s versus 8 4 km s for p waves the outstanding feature of the results for three dimensional velocity structures is a broad 40 km centrally located region with 8 to 10 lower velocities than those in the surrounding regions this low velocity region envelopes the seismic zone at depths between 70 and 150 km the region may actually extend beyond these depths but the results for shallower and deeper structure lack sufficient resolution to decide several tests using both hypothetical and real data were performed to estimate the reliability of the three dimensional solutions the results of these tests suggest that the inferred velocities are reasonably accurate representations of the average velocities in the blocks although one must be cautious of the effects of averaging in interpreting the solution the low velocity region is inferred to be a manifestation of substantial quantities of subducted continental crust therefore while subduction has occurred in the pamir hindu kush the results of the three dimensional inversions suggest that continental rather than only oceanic lithosphere has been subducted to depths of at least 150 km appendices are available with the entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j81 013 1 00 payment must accompany order

source characteristics of marine oils as indicated by carbon isotopic ratios of volatile hydrocarbons carbon isotopic ratios of volatile hydrocarbon fractions of marine oils are diagnostic of organic facies and depositional environments of source rocks for carbonate oils low molecular weight volatile hydrocarbons c9 are isotopically lighter than high molecular weight volatile hydrocarbons c9 c17 in contrast for deltaic oils low molecular weight volatile hydrocarbons are isotopically heavier than high molecular weight volatile hydrocarbons marine shale oils show patterns intermediate between carbonate and deltaic oils this relative variation of carbon isotopic ratios among volatile hydrocarbons of oils is explained by earlier expulsion of marine oils derived from isotopically homogeneous algal bacterial kerogens in rich so rce rocks and secondary cracking of petroleum prior to expulsion for marine oils derived from isotopically heterogeneous terrestrial kerogens in lean source rocks in basins with multiple source rocks carbon isotopic ratios of volatile hydrocarbons are useful for determining oil oil correlation and for inferring oil source rock relationship

a seismic refraction investigation of the charnian basement and granitic intrusions flanking charnwood forest results from two seismic refraction profiles radiating ne and sw from the precambrian charnian block of charnwood forest in the central midlands of england are described and interpreted using surface geology borehole aeromagnetic and gravity data and previous seismic research charnian rocks probably extend beneath palaeozoic and mesozoic cover along the length of the profiles however to the ne of charnwood the charnian basement is intruded by a ne extension of the mountsorrel granodiorite complex while to the w it is intruded by a possible nw extension of the s leicestershire and or s charnwood diorites