microseismic event location for monitoring co2 injection using double difference tomography increases in pore pressure and volume caused by co2 injection will perturb the ambient stress field and possibly trigger brittle failure on small fractures or faults resulting in microearthquakes monitoring this induced seismicity can help understand the migration of the co2 front and the stress and strain changes in the reservoir miyazawa et al 2008 as part of research efforts of the southwest regional partnership on carbon sequestration supported by the u s department of energy and managed by the national energy technology laboratory a large number of microseismic events have been recorded since early 2008 using a geophone string cemented into a well for monitoring co2 injection at the aneth oil field in utah we use double difference tomography to obtain high precision locations of microseismic events and improve the spatial resolution of the velocity structure simultaneously the double difference seismic tomography method was developed for improving earthquake source locations and tomograph

carbonate shale cycles in the middle devonian of new york an evaluation of models for the origin of limestones in terrigenous shelf sequences thin widespread carbonate beds in the predominantly siliciclastic hamilton group middle devonian of new york appear to represent biogenic accumulations of winnowed shallow normal to storm wave base shelf areas rather than products of transgression induced sediment starvation as frequently assumed in western new york these fossiliferous limestones form the centers of subsymmetrical marine cyclothems carbonates are overlain and underlain by calcareous gray to black laminated shales and they grade laterally into siltstones or sandstones that cap upward coarsening sequences in central new york thus the limestones appear to represent shallow water facies of regressive hemicycles instead of transgressive maxima as argued by earlier workers

symmetrical and upward shallowing cycles in the middle devonian of new york state and their implications for the punctuated aggradational cycle hypothesis the middle devonian eifelian and givetian hamilton group in western and central new york composed largely of fossil rich marine shelf and slope facies is subdivisible into repetitive facies sequences of varying thicknesses minor cycles include 1 to 3 m thick upward coarsening shale to siltstone hemicycles resembling sixth order punctuated aggradational cycles pacs in central new york probably correlative 0 5 1 0 m shale to argillaceous nodular limestone couplets occur in western areas major cycles in western new york include subsymmetrical 3 to 5 m thick packages with medial limestone beds analogous to upper limestones of pennsylvanian cyclothems the center of each cycle marks a regressive maximum and grades vertically above and below into black shale or dark gray mudstone corresponding in a facies sense to cyclothemic core shales in the midcontinent pennsylvanian these widespread units appear to be allocyclic in nature and approximate fifth order transgressive regressive cycles based upon average unit thickness relative to the encompassing well zoned hamilton sequence correlations show that most key regressive events marked by limestones in western new york are expressed by equivalent siltstone or fine sandstone units in central new york most cycles which are nearly symmetrical in western new york grade eastward into 5 to 20 m upward coarsening pac motif hemicycles these asymmetric cycles apparently reflect rapid sediment aggradation to limits imposed by wave energy in a region of abundant sediment supply further minor shallowing was accompanied by winnowing and bypass of fine grained sediments generating condensed capping deposits of coarser silt and sand reworked shells and commonly phosphatic nodules ensuing sea level rises were accompanied by initial sediment starvation followed by sedimentation in deeper water hence asymmetrical upward shallowing hemicycles pacs appear to grade offshore into thin but symmetrical cycles both pac and symmetrical motifs are local responses to the same probably allocyclic sea level fluctuations we suggest that the pac motif is partially facies controlled being largely restricted to shallow shelf settings with relatively high rates of sediment accumulation

faunal response to transgressive regressive cycles example from the jurassic of western india abstract upper callovian to oxfordian shelf sediments at ler in the kachchh basin western india are interpreted in terms of transgressive regressive cycles the transgressive phases are represented by thin layers of reworked and bored concretions sometimes in association with skeletal concentrations the regressive phases are documented by much thicker units of largely fine grained sediments the benthic fauna of transgressive and regressive phases differes markedly and thus mirrors the sedimentary cycles during transgressive phases non sedimentation produced hard substrates colonized mainly by byssate cemented or pedicle attached suspension feeding epifaunal species whilst sediment input during regressive phases lead to soft substrate conditions characterized by infaunal deposit and suspension feeders as well as by epifaunal opportunists whereas the composition of the regressive fauna remains fairly constant through time that of successive transgressive faunas often differs drastically this is possibly due to a greater environmental sensitivity of epifaunal taxa as compared to infaunal taxa

using ambient noise seismic interferometry and local and teleseismic earthquakes to determine crustal thickness and moho structure of the northwestern gulf of mexico margin

geometry of submarine slides in the bowland basin dinantian and their relation to debris flows sedimentary slide deformation structures in the lower carboniferous dinantian sediments of the bowland basin show a spoon shaped morphology with extension in the head region and compression in the toe the particular structures developed depend on the rheological properties of the sediment involved slides in soft sediment have deformation distributed throughout the slide mass with folding being the dominant deformation style slides within more lithified sediment have deformation concentrated along slip planes both types of deformation may be present within a particular slide depending on diagenetic factors and the depth to which slide planes cut down disaggregation of slides to yield material for sediment gravity flows is explained by processes operating within the slide unit

high rate injection is associated with the increase in u s mid continent seismicity an unprecedented increase in earthquakes in the u s mid continent began in 2009 many of these earthquakes have been documented as induced by wastewater injection we examine the relationship between wastewater injection and u s mid continent seismicity using a newly assembled injection well database for the central and eastern united states we find that the entire increase in earthquake rate is associated with fluid injection wells high rate injection wells 300 000 barrels per month are much more likely to be associated with earthquakes than lower rate wells at the scale of our study a well s cumulative injected volume monthly wellhead pressure depth and proximity to crystalline basement do not strongly correlate with earthquake association managing injection rates may be a useful tool to minimize the likelihood of induced earthquakes

devonian lake margin environments and processes se shetland scotland the devonian lake or lakes of se shetland were characterized by 4 environments 1 a marginal environment dominated by the high energies of the surf zone and just lakeward of the breaker zone 2 an additional marginal environment consisting of small shallow oxidizing lakes on a low gradient coastal flood plain over which waters from the main body of the lake fluctuated 3 an intermediate environment characterized by continuous to intermittent wave agitation in water depths of probably 5 10m the marginal environment was influenced by both wave and current processes a friction dominated outflow produced sedimentary structures that indicate a south easterly flow and depositional slope outflow competed with shoaling waves which advanced from e to w onto the lake shoreline where outflow was weakest wave processes dominated longshore drift was an additional component in the movement of the nearshore waters the devonian lake or lakes of se shetland possessed rather shallow shoaling margins

increasing seismicity in the u s midcontinent implications for earthquake hazard abstract earthquake activity in parts of the central united states has increased dramatically in recent years the space time distribution of the increased seismicity as well as numerous published case studies indicates that the increase is of anthropogenic origin principally driven by injection of wastewater coproduced with oil and gas from tight formations enhanced oil recovery and long term production also contribute to seismicity at a few locations preliminary hazard models indicate that areas experiencing the highest rate of earthquakes in 2014 have a short term one year hazard comparable to or higher than the hazard in the source region of tectonic earthquakes in the new madrid and charleston seismic zones

gps observed horizontal ground extension at the hutubi china underground gas storage facility and its application to geomechanical modeling for induced seismicity abstract induced earthquakes and ground displacements were seldom reported in relation to gas injection or extraction the hutubi underground gas storage hugs facility is the largest one in china and is also a unique case with both earthquakes and ground displacements detected during multiple cycles of injection and extraction since 9 june 2013 unlike previous studies with a primarily seismological focus here we conducted quantitative analysis on the geomechanics of seismicity induced by the hugs through developing a hydrogeologic framework which systematically integrated geodetic geophysical and geological data first we measured horizontal ground extension and shortening on the order of cm in response to gas injection and extraction of the hugs at depth using a local gps network which was not reported in other regions with induced seismicity second we synthesized a variety of data including seismic reflection profiles a newly acquired local velocity model rock physics measurements well drilling and logging data to build up a 2d geomechanical model for the hugs third based on fully coupled poroelasticity we proposed two methods to optimize the permeability of the upper aquifers as well as the reservoir porosity and permeability with constraints from well level gps and well pressure data numerical simulations using the calibrated 2d model revealed that the horizontal extension due to the reservoir dilation is larger than ground uplift the observed seismicity on faults without hydraulic connections to the gas repository was probably induced by the poroelastic effect of reservoir dilation our study provided a prototype scheme for detecting and characterizing the geomechanical behavior of cyclic fluid injection and extraction in a deep reservoir which would be applicable to other ugs facilities

gradient analysis of faunal distributions associated with rapid transgression and low accommodation space in a late pennsylvanian marine embayment biofacies of the ames member glenshaw formation conemaugh group in the northern appalachian basin usa abstract the ames sea situated in a shallow marine embayment in the appalachian basin was the result of the most extensive marine transgression of the pennsylvanian in this region gradient analysis of the proportional abundance of taxa reveals an environmental continuum across the ames embayment along which four biofacies were distributed biofacies distribution is interpreted to be controlled by salinity turbidity and oxygen gradients associated with the geometry of the ames depositional basin and relative sea level change the eastern portion of the ames sea resembled a foredeep trough located on the detrital slope of the recently uplifted appalachian highlands biofacies 1 and 2 occur exclusively in the eastern part of the ames depositional basin and are dominated by eurytopic molluscs tolerant of terrigenous influx biofacies 3 occurs in both the eastern and western portions of the ames depositional basin this biofacies is dominated by the opportunistic brachiopod neochonetes which would quickly colonize the seafloor in the wake of transgression d biofacies 4 occurs exclusively in the western part of the ames depositional basin and is composed primarily of stenotopic crinoids bryozoans brachiopods and epifaunal bivalves that inhabited a clear water cratonic ramp on the eastern flank of the cincinnati arch vertical variations of faunal assemblages in the ames member were the result of variations in relative sea level associated with glacio eustatic cycles biofacies 3 dominated by neochonetes was deposited at the base of the ames member during the initial rapid transgression in a mostly dysoxic environment with low turbidity and marine salinity during the first regression low density surface water from eastern sources restricted vertical circulation established a stratified water column and promoted estuarine conditions in the ames embayment well oxygenated surface waters were unable to circulate to the benthic habitat which led to periodically dysoxic conditions and the establishment of biofacies 1 and 2 composed of diminutive eurytopic molluscs a second stratigraphically higher occurrence of biofacies 3 is interpreted to represent a second transgression however unlike the first transgression lithologic and faunal data suggest that the benthic habitat was well oxygenated above the mid ames marine zone occurrence of biofacies 3 biofacies 1 and 2 were deposited in the final regressive phase as local terrigenous source areas brought increasing turbidity and fluctuating salinity to the ames embayment previous paleoecological research on the ames member cited freshwater and or clastic influx as the major controls on biotic distribution but the results of the present study suggest that oxygen availability was also a major control stratification of the water column during the ames sea level cycle promoted estuarine circulation that prevented well oxygenated surface waters from reaching the benthic habitat this led to the deposition of dark gray to black fissile shales that contain fossil assemblages dominated by diminutive molluscs and brachiopods that were tolerant of low oxygen conditions

a marine fauna from the dartmouth beds lower devonian of cornwall a brachiopod fauna is described from a marine horizon within the dartmouth beds at bull cove cornwall the fauna indicates a middle or late siegenian age and aspects of the palaeoecology are discussed the lower devonian succession of south devon and north cornwall is discussed and the terms meadfoot facies and standon facies are proposed to replace the meadfoot beds and staddon grits of the old terminology

sea level curve for pennsylvanian eustatic marine transgressive regressive depositional cycles along midcontinent outcrop belt north america at least 55 cycles of marine inundation and withdrawal are recognized in the mid desmoinesian to mid virgilian midcontinent outcrop sequence in north america they range from widespread major cycles classic cyclothems with deep water facies extending across the northern shelf through intermediate cycles persisting as marine horizons across the shelf to minor cycles developed on the lower shelf or as parts of major cycles biostratigraphic differentiation of the cycles should establish interbasinal correlation on a scale fine enough to allow evaluation of differential tectonics and sedimentation sequential groupings of cycles are more irregular than proposed megacyclothems or mesothems but they may be obscured by the distinctness of the major cyclothems estimates of cycle periods range from about 40 to 120 x 10 sup 3 yr for the minor cycles up to about 235 to 400 x 10 sup 3 yr for the major cyclothems the range for all cycles corresponds well to the range of periods of earth s orbital parameters that constitute the milankovitch insolation theory for the pleistocene ice ages and it further supports gondwanan glacial control for the pennsylvanian cycles even though the dominant period of the major pennsylvanian cyclothems is up to four times longer than the dominant 100 000 yr period inmore the pleistocene the shapes of both curves display rapid marine transgression rapid melting of ice caps and slow interrupted regression slow buildup of ice caps which suggest similar linkages between the climatic effects of the orbital parameters and ice cap formation and melting at the two different scales widely separated in time 28 references 3 figures less

testing patterns and causes of faunal stability in the fossil record with an example from the pliocene lusso beds of zaire abstract two central issues emerge from recent discussions of coordinated stasis in the fossil record testing pattern and testing causality testing the generality of brett and baird s observations of faunal stability in the paleozoic appalachian foreland basin is important to determine whether such clustering of evolutionary and ecological change into relatively brief intervals of time is a general phenomenon in the fossil record or a quirk of that particular time and place methods for assessing the linkage between paleoecological and evolutionary change are discussed using examples drawn from the molluscan faunas of the pliocene edward mobutu basin of zaire and uganda in the late pliocene lusso beds of eastern zaire an interval of paleoecological and morphological stability appears to be terminated by an episode of coordinated change this paper illustrates a quantitative approach to simultaneously testing for the presence of coordinated change in paleoecological composition and species morphology with due attention to taphonomic and stratigraphic controls testing for the generality of faunal stability in the fossil record is a relatively straightforward exercise causality however is a thornier issue three broad classes of explanation for the presence of coordinated faunal change in the fossil record can be identified in the literature these span a continuum from the purely evolutionary through combined evolutionary ecological to purely ecological explanations i argue here that the critical test to distinguish between different causal hypotheses for coordinated faunal stability and turnover is an examination of correlation between environmental change and biotic change in the fossil record

sedimentology and depositional setting of the dartmouth group bigbury bay south devon the lower devonian dartmouth group records some of the earliest stages in the evolution of the variscan basins of southwest england this thick mudstone dominated group has previously been interpreted as distal fluvial sediments deposited on a coastal mudplain the sequence at bigbury bay is made up of two large scale sedimentary cycles the base of each cycle consists of pebbly mudstones graded siltstones and sandstones massive mudstones and heterolithic sediments with sporadic phosphatic nodules these facies were deposited in substantial lakes they were modified by phases of syn sedimentary deformation which generated subaqueous debris flows and turbidites the overlying parts of the cycle making up the bulk of the succession consist of mudstone and thin sheet like sandstones these are fluvial and were probably deposited in mud dominated terminal fans each cycle represents a phase of rapid probably fault controlled subsidence followed by relative tectonic quiescence this behaviour may reflect pulses of rifting or extension in strike slip basins followed by thermal relaxation

anatomy of collapsed and re established delta front in lower cretaceous of eastern spitsbergen gravitational sliding and sedimentation processes spectacular coastal cliff exposures in an early cretaceous deltaic succession near kvalvagen in eastern spitsbergen norwegian arctic show a variety of styles of gravity driven deformation and resedimentation associated with delta front progradation and instability the large scale collapse involved a distributary channel sand unit some 20 m thick and the underlying delta slope prodelta shaly heterolithics the deformation was essentially brittle whereby large blocks of the delta front succession slid and rotated its gross style involved two large cuspate tear away scars at least 1 1 5 km wide and 50 60 m deep separated by narrow remnant buttresses of in situ strata the basement in the region was tectonically active and the delta front failure was most likely sei mically triggered initial infill of the collapse scars involved slumps and debris flows derived from scar walls and locally from the sliding blocks themselves these deposits partly smoothed the local topography created by the slide blocks this early infill was followed by deposition of thin mainly muddy turbidites probably shed from the scar walls by small localized failure renewal of fluvial supply of sand led to the main infill of the scar depressions this stage involved effluent generated turbidites heterolithic and increasingly sandier turbidites and liquefied sandflows derived from unstable oversteepened distributary mouthbars the mouth bar systems eventually achieved stability and prograded across the infilled scars they were affected by periodic storm wave attack and sudden increa es of water depth the scar infill at that stage was subject to minor growth faulting possibly related to new seismic tremors

desert sand plain and sabkha deposits from the bunter sandstone formation l triassic at the northern margin of the german basin facies studies of well cores from the bunter sandstone formation in the tonder area denmark indicate that the formation is composed of two desert sand plain sequences associated with sabkha and inland basin lake mudstones the lower desert sand plain sequence consists of subaerial sand flat deposits overlain by aeolian sand sheet and dune facies topped by interbedded aeolian and ephemeral river deposits the upper desert sand plain sequence consists of ephemeral river deposits partly interbedded with and overlain by sabkha and inland basin mudstones two shoreline sandstones occur in the uppermost part both sequences are interpreted mainly in terms of tectonic subsidence of the basin and related upheavals of the source regions the lower sequence represents a rather continuous progradation of the desert sand plain followed by a rapid transgression of the waters from the inland basin the upper sequence represents brief periods of fluvial progradation followed by a gradual retreat of the river plain the most distal part of the sand plain was finally reworked by weak wave action

a late atokan regional encrinite early late moscovian middle pennsylvanian in the sierra agua verde sonora state nw mexico

sandy high energy flood sedimentation some criteria for recognition with an example from the devonian of s w england abstract many modern sand deposits resulting from episodic floods in semi arid zones are dominated by parallel laminations but parallel laminated sands are not a major feature in perennial streams single flood events may deposit over 1 5 m of parallel laminated sand hence ancient parallel laminated sand dominated alluvial deposits may be the product of ephemeral flows the trentishoe formation hangman sandstone group middle devonian of north devon consists in part of laterally extensive beds of parallel laminated fine grained red sandstones that build multistorey sand bodies individual beds are little more than 1 m thick but may extend laterally for hundreds of metres a vertical sequence of erosion surface sparse silt clasts parallel laminations silt drape is often found suggesting high flow stage deposition of plane bedded sand followed by a very rapid waning of flow with silt fallout in the final stages of the flood this sequence bears marked similarity to certain modern ephemeral flow sands

glacial eustatic sea level curve for early late pennsylvanian sequence in north central texas and biostratigraphic correlation with curve for midcontinent north america at least 30 transgressive regressive cycles of deposition are recognized from the upper desmoinesian east mountain shale to the mid virgilian wayland shale in north central texas maximum regressive deposits are typically paleosol mudstones and fluvial sand stones maximum transgressive deposits are typically widespread ammonoid bearing conodont rich dark phosphatic shales in more major cycles and persistent fossiliferous shales or limestones overlying terrestrial deposits in more minor cycles delta complexes dominate the regressive sequences of many cycles using biostratigraphic criteria of first last sole or acme occurrence of ammonoid conodont and fusulinid taxa we correlate 17 cycles in the texas sequence directly with 17 glacial eustatic cycles of similar magnitude in the northern midcontinent this correlation suggests that glacial eustacy was the basic control over the cyclic sequence in texas that tectonic masking of the eustatic signal by nearby orogenic movement in texas was negligible and that delta shifting though conspicuous was only a secondary control over the cyclicity there minor cycles recognized between the correlated cycles also match well enough between texas and the midcontinent to further discount potential tectonic or deltaic masking of glacial eustatic cyclicity this strengthens the likelihood of correlating glacial eustatic events across larger parts of north america and perhaps with other parts of the world

long term ecosystem stability in an early miocene estuary the question of ecosystem stability is central to ecology and paleoecology and is of particular importance for estuaries which are environmentally highly variable considered as geologically short lived and among the most degraded modern ecosystems of our planet understanding their ecological dynamics over geological time scales requires paleontological data in a sequence stratigraphic framework which allows evaluation of paleocommunity dynamics in an environmental context a 445 m thick estuarine succession in a satellite basin of the vienna basin austria shows continuous sedimentation over 700 k y and can be divided into two transgressive systems tracts and a highstand systems tract in contrast to expectations no major physical disturbances of the ecosystem involving abrupt changes in diversity and biofacies composition occurred at fl surfaces and at the sequence boundary accommodation space remained remarkably constant over the depositional history of the basin and all changes between depositional environments were therefore more or less gradational biotic change along the studied succession can be described as a gradual faunal replacement in response to habitat tracking a process also reported for some normal marine shelf environments benthic assemblages in the estuarine succession were strongly dominated by a few taxa and developed along two indirect gradients water depth and hydrodynamic energy these gradients show subtle long term trends corresponding to the sequence stratigraphic architecture tectonics affected the sequence architecture in this particular marginal marine setting it controlled accommodation space and sedimentary input and provided stable boundary conditions over hundreds of thousands of years our study demonstrates for the fi rst time that estuaries which are under great environmental pressure today are resilient to natural environmental perturbations and can persist over geological time scales

gas injection may have triggered earthquakes in the cogdell oil field texas between 1957 and 1982 water flooding was conducted to improve petroleum production in the cogdell oil field north of snyder tx and a contemporary analysis concluded this induced earthquakes that occurred between 1975 and 1982 the national earthquake information center detected no further activity between 1983 and 2005 but between 2006 and 2011 reported 18 earthquakes having magnitudes 3 and greater to investigate these earthquakes we analyzed data recorded by six temporary seismograph stations deployed by the usarray program and identified 93 well recorded earthquakes occurring between march 2009 and december 2010 relocation with a double difference method shows that most earthquakes occurred within several northeast southwest trending linear clusters with trends corresponding to nodal planes of regional focal mechanisms possibly indicating the presence of previously unidentified faults we have evaluated data concerning injection and extraction of oil water and gas in the cogdell field water injection cannot explain the 2006 2011 earthquakes especially as net volumes injection minus extraction are significantly less than in the 1957 1982 period however since 2004 significant volumes of gases including supercritical co2 have been injected into the cogdell field the timing of gas injection suggests it may have contributed to triggering the recent seismic activity if so this represents an instance where gas injection has triggered earthquakes having magnitudes 3 and larger further modeling studies may help evaluate recent assertions suggesting significant risks accompany large scale carbon capture and storage as a strategy for managing climate change

global review of human induced earthquakes the human induced earthquake database hiquake is a comprehensive record of earthquake sequences postulated to be induced by anthropogenic activity it contains over 700 cases spanning the period 1868 2016 activities that have been proposed to induce earthquakes include the impoundment of water reservoirs erecting tall buildings coastal engineering quarrying extraction of groundwater coal minerals gas oil and geothermal fluids excavation of tunnels and adding material to the subsurface by allowing abandoned mines to flood and injecting fluid for waste disposal enhanced oil recovery hydrofracturing gas storage and carbon sequestration nuclear explosions induce earthquakes but evidence for chemical explosions doing so is weak because it is currently impossible to determine with 100 certainty which earthquakes are induced and which not hiquake includes all earthquake sequences proposed on scientific grounds to have been human induced regardless of credibility challenges to constructing hiquake include under reporting which is 30 of m 4 events 60 of m 3 events and 90 of m 2 events the amount of stress released in an induced earthquake is not necessarily the same as the anthropogenic stress added because pre existing tectonic stress may also be released thus earthquakes disproportionately large compared with the associated industrial activity may be induced knowledge of the magnitude of the largest earthquake that might be induced by a project mmax is important for hazard reduction observed mmax correlates positively with the scale of associated industrial projects fluid injection pressure and rate and the yield of nuclear devices it correlates negatively with calculated inducing stress change likely because the latter correlates inversely with project scale the largest earthquake reported to date to be induced by fluid injection is the 2016 m 5 8 pawnee oklahoma earthquake by water reservoir impoundment the 2008 m 8 wenchuan people s republic of china earthquake and by mass removal the 1976 m 7 3 gazli uzbekistan earthquake the minimum amount of anthropogenic stress needed to induce an earthquake is an unsound concept since earthquakes occur in the absence of industrial activity the minimum amount of stress observed to modulate earthquake activity is a few hundredths of a megapascal and possibly as little as a few thousandths equivalent to a few tens of centimeters of water table depth faults near to failure are pervasive in the continental crust and induced earthquakes may thus occur essentially anywhere in intraplate regions neither infrastructure nor populations may be prepared for earthquakes human induced earthquakes that cause nuisance are rare but in some cases may be a significant problem e g in the hydrocarbon producing areas of oklahoma usa as the size of projects and density of populations increase the potential nuisance of induced earthquakes is also increasing and effective management strategies are needed

desert stream sequences in the sinai peninsula abstract desert sedimentary sequences of late quaternary age mainly subrecent were studied in several stream segments of wadi el arish northern sinai egypt morphologically these stream systems can be divided into three types confined open and terminal floodplains the confined and open floodplain sequences consist of repeated flood originated sedimentation units each around 50 cm thick an idealized sequence begins with mud clasts or either sand or pebble bearing plane beds reflecting the upper flow regime during peak flow stage of the flood these are overlain by cross bedded sands and climbing ripples lower intensities of the flow result in sequences beginning with cross stratified sands cracked mud layers represent the final desiccation stage of the flood in comparison with th confined floodplain units the open up to thousands of meters wide floodplain units are thinner 20 50 cm the horizontal strata are less developed and the mud layers are thicker the terminal floodplain which in the modern examples is a flat a few kilometers wide is the area where the remaining flood energy dissipates and therefore the resultant sedimentation units axe very thin usually less than 20 cm and consist of either finely laminated massive mud or cross laminated fine sand the wadi systems studied are in close geographic relationship with eolian dune fields nevertheless the wadi sequences consist of waterlaid units only

deep injection and closely monitored induced seismicity at paradox valley colorado the u s bureau of reclamation s paradox valley unit pvu extracts aquifer brine from nine shallow wells along the dolores river paradox valley in southwestern colorado and after treating high pressure injects the brine 4 3 4 8 km below the surface pvu injects at rates between 800 and 1300 l min since 1991 pvu has emplaced over 4 106 m3 of fluid and induced more than 4000 surface recorded seismic events the events are recorded on the local 15 station paradox valley seismic network the induced seismicity at paradox separates into two distinct source zones a principle zone 95 of the events asymmetrically surrounding the injection well to a maximum radial distance of 3 km and a secondary ellipsoidal zone 2 5 km long and centered 8 km northwest of the injection well the expansion of these zones has stabilized since mid 1999 about three years after the onset of continuous injection within the principal zone hypocenters align in distinct linear patterns showing at depth stratigraphy and the local wray mesa fracture and fault system the primary faults of the wray mesa system are aseismic striking subparallel to the inferred maximum principal stress direction with one or more faults probably acting as fluid conduits to the secondary seismic zone individual seismic events in both zones do not discernibly correlate with short term injection parameters however a 0 5 km2 region immediately northwest of the injection well responds to long term large scale changes in injection rate and the surpassing of a threshold injection pressure focal mechanisms of the induced events are consistent with simple double couple strike slip moments and subhorizontal extension to the northeast in addition the fault planes are consistent with principal stress directions determined from borehole breakouts more than 99 9 of the pvu seismicity is below human detection m 2 5 however approximately 15 events have been felt locally with the largest being a magnitude m 4 3 because of the m 4 3 and two earlier felt m 3 5 events and injection economics pvu changed injection strategies three times since 1996 these changes reduced seismicity from 1100 events year to as low as 60 events year

revisiting the timpson induced earthquake sequence a system of two parallel faults the 17 may 2012 m4 8 timpson earthquake is the largest known earthquake in eastern texas it is suspected to have been induced by wastewater injection from two nearby high volume wells its catalo

submarine fan and slope facies of tonkawa missourian virgilian sandstone in deep anadarko basin the tonkawa sandstone missourian virgilian in the anadarko basin consists of upper middle and lower sandstone units separated by intervening shales the lower tonkawa sandstone consists of coarse to pebbly sandstones deposited in thick coarsening upward sequences the unit is up to 400 ft 120 m thick and the sandstones grade to shale from the southeast to the northwest gross sand isopachs outline northwest southeast oriented linear thicks that extend for tens of miles the middle tonkawa sandstone consists of thin and thick bedded fine grained sandstones displaying wavy and flaser bedding a convolute laminae and some small scale cross laminae these sandstones range in thickness from 100 ft 30 m to 400 ft 120 m the thicks in the middle tonkawa extend nly for a few miles and do not show a preferred directional orientation the upper tonkawa sandstone caps the entire sequence and is overlain by oolitic limestones we interpret the lower tonkawa sandstone to represent a submarine fan complex for the following reasons the regional setting indicates that the sandstones were deposited tens of miles from the shelf edge graded beds convolute laminae and load casts indicate transportation by sediment gravity flows the areal geometry of sandstones indicates channelized flows that coalesced to form an overall fanlike geometry the middle tonkawa sandstones are interpreted as a sequence deposited on the basin slope regional setting indicates that the unit is located immediately basinward of the shelf edge and that it progrades over the lower tonkawa sandstone deposition as sheets or aprons is suggested by lateral continuity at least for several miles of individual beds small scale cross laminae wavy and flaser bedding and sharp bed contacts suggest bottom current activity presence of short numerous channels is suggested by the thick beds of middle tonkawa sandstones that extend for only a few miles although the sedimentology and areal geometry of the upper tonkawa are not discussed in this paper the regional setting and lithologic character suggest shallow water nearshore deposition the entire tonkawa clastic sequence is capped by shallow water marine limestone the lower and middle tonkawa sandstones represent offshelf deposition in an interior basin setting the present study shows that the understanding of the geologic setting and the integration of all available data rather than sedimentologic data alone are required for proper identification the following formations in the anadarko basin also appear to contain fan and or slope facies springer morrow springerian morrowan red fork desmoinesian and cleveland marchand and cottage grove all missourian if the deep water sandstones in interior basins are indeed as common as they appear to be in the anadarko basin then it is crucial for stratigraphic exploration that we recognize and document such deposits in other interior basins as well

geographical heterochrony comtemporaneous coexistence of neogene and recent molluscan faunas in the americas abstract geographical heterochrony is a biogeographical pattern that within a single faunal province represents the contemporaneous coexistence of newly evolved faunas and those which have persisted unchanged from earlier geological ages this array of discrete adjacent and asynchronous faunules produces a mosaic pattern in both time and space based on the faunas of three anachronistic subregions within the recent caribbean molluscan province one off the yucatan peninsula one off roatan island and one near the gulf of venezuela this geographically heterochronous province is shown to contain two types of relict pockets the term primary relict pocket is proposed for a faunule that contains the same genera and species as the older more extensive parent fauna and differs only in being reduced spatially the term secondary relict pocket is proposed for a faunule that contains relict genera that were once widespread but have persisted and speciated within the boundaries of the pocket based on the faunas of the caribbean relict pockets on patterns seen in the fossil record and on the unusual ecological conditions of the gulf of venezuela area a new reconstruction of neogene caribbean molluscan provinciality is proposed and two new neogene molluscan provinces the caloosahatchian and the gatunian are described to explain the existence of the caribbean relict pockets and their affinities to the recent panamic and neogene floridian faunas a new interpretation of upper pliocene biological catastrophism and extinction is proposed incorporating aspects of the effects of the closing of the isthmus of panama and glacially induced sea level fluctuations and temperature changes a new scheme of recent tropical american marine molluscan provinciality is presented taking into account the two paleoprovinces and the distribution of the post pleistocene caribbean fauna

monitoring the earthquake source process in north america with the implementation of the usgs national earthquake information center prompt assessment of global earthquakes for response system pager rapid determination of earthquake moment magnitude is essential especially for earthquakes that are felt within the contiguous united states we report an implementation of moment tensor processing for application to broad seismically active areas of north america this effort focuses on the selection of regional crustal velocity models codification of data quality tests and the development of procedures for rapid computation of the seismic moment tensor we systematically apply these techniques to earthquakes with reported magnitude greater than 3 5 in continental north america that are not associated with a tectonic plate boundary using the 0 02 0 10 hz passband we can usually determine with few exceptions moment tensor solutions for earthquakes with m w as small as 3 7 the threshold is significantly influenced by the density of stations the location of the earthquake relative to the seismic stations and of course the signal to noise ratio with the existing permanent broadband stations in north america operated for rapid earthquake response the seismic moment tensor of most earthquakes that are m w 4 or larger can be routinely computed as expected the nonuniform spatial pattern of these solutions reflects the seismicity pattern however the orientation of the direction of maximum compressive stress and the predominant style of faulting is spatially coherent across large regions of the continent

filtration models guilds and biofacies crinoid paleoecology of the stanton formation upper pennsylvanian midcontinent north america abstract filtration models make several predictions concerning the distribution of crinoids among benthic habitats 1 generally higher energy shoreward settings should contain crinoid assemblages dominated by taxa with dense mesh filtration fans 2 generally lower energy offshore settings should be dominated by crinoids with open mesh filtration fans 3 diversity should be highest in nearshore settings which generally contain low energy microhabitats within high energy settings where both dense fan and open fan forms can co occur whereas offshore assemblages should be dominated by open fan taxa thus open fan forms should be more eurytopic than dense fan forms also previous empirical models for crinoid distribution patterns note that nearshore assemblages are dominated by large forms whereas offshore assemblages are dominated by small forms filtration fan morphology and body size interact significantly to determine how and where crinoids feed and thus are used here as criteria for distinguishing late paleozoic crinoid guilds the distribution patterns of crinoid taxa and guilds among the benthic paleoenvironments of the upper pennsylvanian missourian stanton formation were used to test the predictions of the filtration models the results of quantitative analyses show that large dense fan crinoids are significantly more abundant in shoreward assemblages than smaller open fan crinoids which are more abundant in offshore assemblages these results are consistent with the aforementioned models however diversity patterns are not consistent with the filtration models indicating that mid depth and aerobic offshore assemblages are more taxonomically and trophically diverse than nearshore and dysaerobic offshore assemblages ostensibly due to the overlapping ranges of characteristically nearshore and offshore taxa analysis of guild distribution patterns also indicates some contradictions to predicted patterns of stenotopy and eurytopy indicating additional complexities to late paleozoic crinoid paleoecology five recurrent crinoid assemblages or biofacies have been identified from the stanton formation of midcontinent north america the guild structure and diversity of these biofacies are characterized here as 1 a moderate diversity nearshore biofacies dominated by large calyx dense fan guilds 2 a high diversity midshelf biofacies characterized by equitable contributions of many taxa and guilds 3 a moderate diversity offshore biofacies dominated by non pinnulate and small calyx open fan pinnulate guilds 4 a low diversity offshore dysaerobic biofacies dominated by small calyx pinnulate guilds 5 a depauperate offshore biofacies dominated by a unique stalkless species paragassizocrinus tarri except for biofacies 5 the number of guilds appears to increase offshore however the equitability of taxa among and within the guilds generally decreases offshore this pattern indicates that the heterogeneity of resources or the recognition by taxa of different classes of resources as reflected by the variety of functional types increased from nearshore to offshore but that the abundance or accessibility of these resources and or the relaxation of competition within guilds increased from offshore to nearshore

the dallas fort worth earthquake sequence october 2008 through may 2009 this paper describes a sequence of small earthquakes m b 3 3 that occurred at the dallas fort worth airport texas between 30 october 2008 and 31 may 2009 analysis of records at regional station wmok identified more than 180 earthquakes in the sequence about 90 percent occurred in four clusters on 30 october 1 november 20 november 26 december and 15 17 may after the sequence began a six station temporary local network obtained high quality three component records for 11 earthquakes occurring between 20 november and 1 december analysis of these data demonstrated that all 11 earthquakes originated from a focus near 32 855 n 97 051 w with an estimated depth 4 4 km this location is less than 0 5 km from a well completed in august 2008 that extends to a depth of 4 2 km drilled to dispose of brines collected during flowback of hydraulic fracturing fluids associated with the production of natural gas brine disposal commenced at the well on 12 september 2008 seismograms and s p intervals for the earthquakes are similar though not identical and relative locations indicate they occurred along a north northeast south southwest trend with horizontal and vertical dimensions of 1 1 km and 0 2 km respectively this trend is approximately coincident with that of a mapped normal fault in the subsurface and consistent with the maximum horizontal in situ stress direction because of the absence of previous historical earthquakes the proximity of the brine disposal well and the similarity with other documented cases of induced seismicity it seems likely that fluid injection induced the 2008 2009 sequence

human induced seismicity and large scale hydrocarbon production in the usa and canada we compare current and historic seismicity rates in six states in the usa and three provinces in canada to past and present hydrocarbon production all states provinces are major hydrocarbon producers our analyses span three to five decades depending on data availability total hydrocarbon production has significantly increased in the past few years in these regions increased production in most areas is due to large scale hydraulic fracturing and thus underground fluid injection furthermore increased hydrocarbon production generally leads to increased water production which must be treated recycled or disposed of underground increased fluid injection enhances the likelihood of fault reactivation which may affect current seismicity rates we find that increased seismicity in oklahoma likely due to salt water disposal has an 85 correlation with oil production yet the other areas do not display state province wide correlations between increased seismicity and production despite 8 16 fold increases in production in some states however in various cases seismicity has locally increased multiple factors play an important role in determining the likelihood of anthropogenic activities influencing earthquake rates including i the near surface tectonic background rate ii the existence of critically stressed and favorably oriented faults which must be hydraulically connected to injection wells iii the orientation and magnitudes of the in situ stress field combined with iv the injection volumes and implemented depletion strategies a comparison with the seismic hazard maps for the usa and canada shows that induced seismicity is less likely in areas with a lower hazard the opposite however is not necessarily true

identifying potentially induced seismicity and assessing statistical significance in oklahoma and california we develop a statistical method for identifying induced seismicity from large datasets and apply the method to decades of wastewater disposal and seismicity data in california and oklahoma the study regions are divided into gridblocks we use a longitudinal study design seeking associations between seismicity and wastewater injection volume along time series within each gridblock in each gridblock we find the maximum likelihood estimate for a model parameter that relates induced seismicity hazard to total volume of wastewater injected each year to assess significance we compute likelihood ratio test statistics in each gridblock and each state california and oklahoma resampling with permutation and random temporal offset of injection data is used to estimate p values from the likelihood ratio statistics we focus on assessing whether observed associations between injection and seismicity occur more often than would be expected by chance we do not attempt to quantify the overall incidence of induced seismicity the study is designed so that under reasonable assumptions the associations can be formally interpreted as demonstrating causality wastewater disposal is associated with other activities that can induce seismicity such as reservoir depletion therefore our results should be interpreted as finding seismicity induced by wastewater disposal and all other associated activities in oklahoma the analysis finds with extremely high confidence that seismicity associated with wastewater disposal has occurred in california the analysis finds moderate evidence that seismicity associated with wastewater disposal has occurred but the result is not strong enough to be conclusive

statistical testing for paleocommunity recurrence are similar fossil assemblages ever the same abstract observations of the recurrence of similar fossil assemblages through long intervals of geologic time punctuated by rapid changes in both the composition and structure of fossil assemblages has recently resulted in the concept of coordinated stasis to describe this pattern in the behavior of paleocommunities through time coordinated stasis may imply the existence of ecological mechanisms that actively maintain particular community structures and thus have a significant impact on the process of macroevolution however before such mechanisms can be invoked it must be shown that ecological stasis as observed in the fossil record is more significant than the persistence of similar community types due to the repeated reinvasion of recurring habitats from a persistent species pool the null hypothesis for paleocommunity recurrence analysis of the relationship between communities and paleocommunities and an expansion of the ecological hierarchy at the community paleocommunity level allows the creation of a rigorous definition of the entities composing the local paleocommunity the samples collected within a stratigraphic horizon at a single locality paleocommunity groups of samples shown to be statistically identical and paleocommunity type groups of samples that are similar but can be shown to be statistically different these definitions permit the development of the null model for paleocommunity recurrence and establish a base level of variability within a local paleocommunity that permits rigorous statistical comparisons to be made between paleoecological samples at larger temporal and geographic scales paleoecological samples from four marine tongues in the middle pennsylvanian breathitt formation are used to analyze species abundance variability at several spatial and temporal scales and to test for paleocommunity recurrence although recurrence of statistically identical local paleocommunities occurs at single localities and between localities within individual marine units it is usually not detectable between marine tongues suggesting that paleocommunity recurrence in the marine strata of the breathitt formation is the recurrence of paleocommunity types and does not falsify the null hypothesis

shaking from injection induced earthquakes in the central and eastern united states abstract in this study i consider the ground motions generated by 11 moderate m w 4 0 5 6 earthquakes in the central and eastern united states that are thought or suspected to be induced by fluid injection using spatially rich intensity data from the u s geological survey did you feel it system i show the distance decay of intensities for all events is consistent with that observed for tectonic earthquakes in the region but for all of the events intensities are lower than the values predicted from an intensity prediction equation that successfully characterizes intensities for regional tectonic events i introduce an effective intensity magnitude m ie defined as the magnitude that on average would generate a given intensity distribution for all 11 events m ie is lower than the event magnitude by 0 4 1 3 magnitude units with an average difference of 0 82 units this suggests stress drops of injection induced earthquakes are systematically lower than tectonic earthquakes by an estimated factor of 2 10 however relatively limited data suggest intensities for epicentral distances less than 10 km are more commensurate with expectations for the event magnitude which can be reasonably explained by the shallow focal depth of the events the results suggest damage from injection induced earthquakes will be especially concentrated in the immediate epicentral region

the effects of neogene thrusting on deposition in the bermejo basin argentina abstract in the bermejo basin of western argentina semi arid sandy low gradient sedimentation has accompanied deformation of the frontal cordillera and precordillera since the mid miocene utilizing the precise geochronology established for strata at sierra de huaco we document an immediate basinward migration of facies coincident with thrusting in the central precordillera 8 7 ma an earlier shift in environment 10 3 ma is related to a change in drainage patterns produced by more distant deformation in the western precordillera evidence from sierra de huaco suggests that depositional environments are largely independent of the net subsidence rate sedimentologic features observed at sierra de huaco bear directly on the nature and scale of the processes that operate in sandy ephemeral settings 1 lateral accretion was the dominant process within an ephemeral braidplain the jarillal formation 2 fining upward cycles in sandflat deposits were a consequence of the dynamics of unconfined flows coupled with lobe switching on alluvial fans the huachipampa and quebrada del cura formations and 3 unconfined flow deposition in the bermejo basin occurred and still occurs over distances on the order of 50 km from point sources at alluvial fan heads

the upper jurassic boulder beds and related deposits a fault controlled submarine slope ne scotland during the late jurassic kimmeridgian rifting in the north sea large scale normal faults developed to form relatively deep marine basins the north western margin of one of these basins defined by the helmsdale fault is described to show the nature of sedimentation associated with a submarine fault scarp subsidence to the se of the helmsdale fault led to a fault scarp down which various sediment mass flows moved including debris flow rockfall high and low concentration turbidity currents and possible storm surge wash over deposits redeposition by soft sediment sliding was important as a slope accretion process deep channels were incised into the slope and infilled by coarse grained elastics contemporaneous small scale submarine fans located farther off in the present north sea may have developed as a result of slope bypassing sediment flows down such channels the succession is characterized by extreme sediment heterogeneity compared to many deep water environments and it may be part of an ancient fan delta the main influences upon slope accretion were the synsedimentary movements on the helmsdale fault and the nature of the available sediment input such that the succession represents structurally controlled and sedimentologically modified slope development

crinoid biofacies in upper carboniferous cyclothems midcontinent north america faunal tracking and the role of regional processes in biofacies recurrence abstract coordinated stasis is a pattern of long term multispecies evolutionary and ecological stability bounded by rapid turnover events one class of models proposed to explain the paleoecological pattern of biofacies stability typified by ecological locking states that biotas within habitats become integrated into ecological units that through population and community level processes rebound and persist through short term disturbances this high frequency community resilience allows the units to persist through geologic time tracking their preferred habitats during transgressions and regressions because species are tightly woven into the fabric of the ecosystem there is little opportunity for speciation this also buffers them against extinction this ecological locking by ecosystem homeostatic processes produces long intervals of regionally stable biofacies in the fossil record in these models the primary structuring mechanisms are at the local community level controlled by species autecology species interactions and local disturbance regime an opposing class of models states that species are fundamentally independent and that species interactions are not strong nor spatio temporally persistent enough to forge communities into integrated units with long term persistence community recurrence would be expected as long as the various habitat types recur in time and space species autecologies remain stable the pool of available species remains intact and the recruitment of species into local habitats is not interrupted the focus of these models is dominantly at the regional level controlled by biogeographic history and dispersal among as well as within communities the results of this study of crinoids from the upper carboniferous lansing group of midcontinent north america show that they are distributed among five recurrent paleocommunity types or biofacies which are generally arrayed along an onshore offshore gradient two of these biofacies are restricted to the offshore dysaerobic horizons of the most extensive cyclothem in the group the other three biofacies recur consistently among the cycles however this repeated pattern includes a regionally distributed offshore biofacies unique to late transgressive deposits that is not found in analogous regressive deposits while the distribution of the two shoreward biofacies is consistent with faunal tracking the recurrence of a biofacies unique to late transgressive horizons is not consistent with an integrated paleocommunity that tracks shifting habitats through transgression and regression these results favor the alternative models namely that biofacies develop in place via dispersal from a persistent species pool in response to prevailing environmental conditions the recurrence of apparently ephemeral biofacies through time underscores the importance of regional processes in controlling local paleocommunity composition the establishment of refuges or source populations during environmental bottlenecks i e lowstands is critical to maintaining the regional species pool through time for continued recruitment into local sink paleocommunities during more amenable times i e highstands metapopulation dynamics among habitats are equally important in maintaining species within a region through time conflicting observations of stochastic individualistic and deterministic integrated behaviors of the same ecological systems probably result from differences in the scales of analyses and therefore the processes being studied

the confrontation of structural styles and the evolution of a foreland basin in central sw england detailed mapping of the rocks to the north and south of plymouth reveals a sedimentary sequence deformed by a series of folds and thrusts two structural zones exist each with a different style of deformation in the lower to upper devonian rocks of the southern zone slip vectors vergence and facing of d1 folds indicate that the transport direction is to the north west an associated first phase cleavage dips to the south east the northern zone of upper devonian and lower carboniferous strata extends into central devon and east cornwall and the geometry and facing of the early folds in these rocks indicate a transport direction to the south or south east d1 folds generally verge north but are downward facing towards the south a flat lying penetrative slaty cleavage occurs in the mudrocks and also indicates southward facing generally the carboniferous rocks in this area are inverted the two structural zones confront each other at an e w trending line which passes through cargreen 8 km north of plymouth here the deformation is more intense as the cleavage common to the southern zone overprints that of the northern zone resulting in the formation of d2 folds the confrontation is interpreted as a northerly dipping backthrust produced by large scale underthrusting it is proposed that the northward advancing variscan thrust belt progressively underthrust the carboniferous foreland basin flysch deposits which became inverted and backthrust towards the south

coordinated stasis biofacies revisited and the conceptual modeling of whole fauna dynamics abstract the observation of stratigraphic intervals characterized by faunas displaying coordinated stasis in the appalachian basin of new york state brett and baird 1995 is based on the existence of biofacies thus any claims as to the significance or unusual nature of patterns of coordinated stasis are really statements about these underlying biofacies common features of the fossil record that have long been recognized evaluation of the bimodal distribution of evolutionary and ecological change through time apparent in biofacies and ecological evolutionary subunits must be done in relation to the clearly stated expectations of null models the evolutionary and ecological bases for such models are explored here using a conceptual approach founded on two ecological and two evolutionary neutral rules 1 communities are capable of considerable compositional flux 2 multiple stable states are available to communities 3 allopatry is the main mode of speciation and 4 stabilizing selection is effective the aspects of biofacies that appear counter intuitive when compared to the predictions of this conceptual framework are discussed documentation of environmental dynamics alongside faunal dynamics seems to be the key to understanding whether biofacies and coordinated stasis fall outside our expectations

facies sequences and trace fossils in lacustrine fan delta deposits hornelen basin m devonian western norway abstract study of a lacustrine fan delta succession in a marginal tract of hornelen basin shows that occasional lakes were infilled by marginal accretion and progradation of the adjacent fluvial system the lake deposits are dominantly thin graded rhythmites and thicker massive fine sandstones both of great lateral extent and formed by fine sediment gravity flows wave generated ripple lamination is also very common whereas current especially climbing ripple lamination occurs increasingly towards the southern edge of the lake much of the lacustrine sequence is contorted convoluted or deformed to a lesser degree trough cross stratified sandstones and pebbly sandstones characterised the lowsinuosity stream systems which fed the lakes from the south in a narrow transitional zone interpreted in terms of high sinuosity distributary channels and shoreline there are significant amounts of planar cross strata as well as ripple and plane parallel lamination eight distinct types of trace fossils chiefly arthropod tracks trails and burrows scoyenia ichnofacies are present in the fine sediments mudflats pools and low bars of this latter zone behaviour patterns are dominantly locomotion and resting traces possibly with some surface feeding but an absence of infaunal feeding or dwelling structures the repeated progradation and retreat of the sandy fan delta system into the lakes generated mudstone bounded sedimentary bodies these are mainly alluvial coarsegrained upward coarsening and 5 25 m thick in the proximal areas they are mainly lacustrine fine grained symmetrical coarsest in the middle or uniform and generally less than 5 m thick distally in origin these bodies probably represent northward crevassing out of the main westward flowing axial fluvial system and were possibly triggered by repeated base level changes caused by lowering of the basin floor against the northern fault margin the trace fossils described here for the first time in norway are also known from several other devonian alluvial sequences although the closest comparable ichnofauna occurs in ephemeral lacustrine deposits in south scotland the type of arthropod that made the trace fossils cannot be identified at present

early jurassic sedimentation of a rift valley lake culpeper basin northern virginia gray calcareous lacustrine strata of early jurassic age crop out adjacent to the faulted western margin of the culpeper basin a mesozoic graben dominated by fluviogenic red beds sedimentological mineralogical and paleontological aspects reveal a distinct zonation of littoral sublittoral and profundal deposits in the lacustrine sequence reconstructed physiographic profiles of the lake exhibit shore terrace slope and basin plain subenvironments dominant sedimentary processes in these domains were respectively sediment agitation by waves deposition from suspension slumping and proximal sediment gravity flows and suspension and distal turbidity current deposition deposition of the lacustrine sediments occurred in a eutrophic calcite precipitating permanently or normally stratified lake the lake occupied an elongate actively subsiding sub basin adjacent to or possibly straddling the western border fault the sedimentary fill of the sub basin is characterized by several cyclic fluvio lacustrine sequences which average 150 m in thickness and closely resemble sedimentary cycles of other newark rift basins the maximum areal extent of the lake may have exceeded 3 000 km2 with an average maximum depth of 35 m proterozoic and lower paleozoic strata of the blue ridge anticlinorium to the west constituted the major source of clastic sediments in the lacustrine sequence but uptilted basalt flows and interbedded sedimentary units of the culpeper group simultaneously shed detritus from the east

sensitivity of induced seismic sequences to rate and state frictional processes it is well established that subsurface injection of fluids increases pore fluid pressures that may lead to shear failure along a pre existing fault surface concern amongst oil and gas geothermal and carbon storage operators has risen dramatically over the past decade due to the increase in the number and magnitude of induced earthquakes efforts to mitigate the risk associated with injection induced earthquakes include modeling of the interaction between fluids and earthquake faults here we investigate this relationship with simulations that couple a geomechanical reservoir model and rsqsim a physics based earthquake simulator rsqsim employs rate and state dependent friction rsf which enables the investigation of the time dependent nature of earthquake sequences we explore the effect of two rsf parameters and normal stress on the spatiotemporal characteristics of injection induced seismicity we perform 200 simulations to systematically investigate the effect of these model components on the evolution of induced seismic sequences and compare spatiotemporal characteristics of our synthetic catalogs to observations of induced earthquakes we find that the rsf parameters control the ability of seismicity to migrate away from the injection well the total number and maximum magnitude of induced events additionally the rsf parameters control the occurrence absence of premonitory events lastly we find that earthquake stress drops can be modulated by the normal stress and or the rsf parameters insight gained from this study can aid in further development of models that address best practice protocols for injection operations site specific models of injection induced earthquakes and probabilistic hazard and risk assessments of induced earthquakes

geomorphology of a pennsylvanian land surface pedogenesis in the rock lake shale member southeastern nebraska abstract extensive fresh exposures of reddish brown mudstones in the rock lake shale member in a quarry in southeastern nebraska show pedogenic features calcite glaebules blocky spar crystallaria peds silt and clay or micrite filled pedotubules slickensides mottling and overall horizonation which indicate protracted subaerial exposure under increasingly arid conditions the rock lake paleosol is bounded above and below by marine cyclothem deposits probable events represented by the paleosol are 1 clay and silt illuviation under humid conditions 2 subsequent carbonate precipitation under progressively drier conditions and 3 gleying of the a horizon during a marine transgression the rock lake paleosol developed on a flat and laterally extensive semiarid to arid plain during a low stand of sea level examination of the rock lake at other localities well cores and exposures in nearby counties shows a distinct eastward facies change toward lower topography earlier marine transgression and arrested pedogenesis which is consistent with transect direction from the nemaha uplift to the forest city basin

coping with earthquakes induced by fluid injection large areas of the united states long considered geologically stable with little or no detected seismicity have recently become seismically active the increase in earthquake activity began in the mid continent starting in 2001 1 and has continued to rise in 2014 the rate of occurrence of earthquakes with magnitudes m of 3 and greater in oklahoma exceeded that in california see the figure this elevated activity includes larger earthquakes several with m 5 that have caused significant damage 2 3 to a large extent the increasing rate of earthquakes in the mid continent is due to fluid injection activities used in modern energy production 1 4 5 we explore potential avenues for mitigating effects of induced seismicity although the united states is our focus here canada china the uk and others confront similar problems associated with oil and gas production whereas quakes induced by geothermal activities affect switzerland germany and others

upper carboniferous fine grained turbiditic sandstones from southwest england a model for growth in an ancient delta fed subsea fan abstract the upper carboniferous crackington and bude formations of southwest england comprise laminated black mudstones gray siltstones thin medium and thick bedded sandstones and contorted silty sandstones the thick bedded sandstones only occur in the bude formation which overlies the crackington the sandstones were deposited predominantly by turbidity currents in a relatively shallow basin they are unusual for two reasons 1 sediment coarser than fine sand is entirely absent 2 unlike many previously described ancient subsea fan deposits organized bundles of sandstones displaying asymmetric upward thickening or upward thinning sequences are no more common than symmetric sequences and both types of organized bundles are much less common than disorganized nonsequential bundle particularly in the bude formation sediment was supplied directly from a delta to the north by resedimentation of delta front sands and slumping of upper pro delta muds and silts to form a lower pro delta turbidite fan fan growth is not readily explained by current models for single sourced tripartite subsea fans displaying radial growth it developed instead a bipartite growth pattern which was strongly influenced in its upper part by external variables including grain size distributary channel switching and other deltaic processes active tectonism within the basin and possibly sea level fluctuations the fan grew by down slope construction of independent levee channel complexes each of which headed in the upper pro delta and even possibly the delta front slumping and mobilization of argillaceous facies resulted in the random occurrence of contorted beds in all parts of the fan regionally extensive mudstones known as key shales within the fan deposits probably reflect large scal upslope delta lobe abandonment the crati and ebro fans of the mediterranean sea would appear to be good modern analogs for the crackington bude fan system

depositional subenvironments in an arid closed basin the wilkins peak member of the green river formation eocene wyoming u s a the wilkins peak member of the green river formation is a non marine dolomitic deposit that formed in an arid hydrologically closed basin a transect from the margin to the centre of the wilkins peak basin was examined in outcrop exposures in the south eastern corner of the basin and was supplemented with published core descriptions the rocks were divided into seven facies based upon lithology layering style and sedimentary fabrics 1 af facies quartzose conglomerates and sandstones representing sandy alluvial fans coming from the uinta mountains 2 sf facies quartzose peloidal dolomitic sandstones which represent sheet flood deposits extending basinward from the alluvial fans 3 dm facies irregularly laminated dolomitic mudstones with abundant mudcracks which represent sheet flood deposits on a subaerially exposed mudflat 4 el facies dolomitic mudstones with regular lamination and fewer but larger mudcracks representing sporadically exposed lake margins or shallow ponds 5 pl facies finely laminated oil shales and dolomitic mudstones with rare mudcracks which represent shallow perennial lakes 6 sm facies trona or halite deposits with dolomitic mudstone partings or dolomitic mudstones and sandstones disrupted by evaporites of varied morphology these represent a central salt pan and the surrounding saline mudflat 7 as facies arkosic sandstones siltstones and mudstones which represent braided river and more basinal deltaic plain deposits the five dolomitic facies form poorly defined cycles representing the intersection of sheet floods with a lake which transgressed and regressed in response to climatic variations there are at least forty 3 4 m thick cycles in the wilkins peak and one large scale cycle comprising the whole member which mimics the facies changes of the smaller cycles this is compatible with the transitions of the wilkins peak member to the tipton and laney members as climatic responses and not shifts in drainage the sheet flood sandstones actively aggrading subaerial mudflats and bedded evaporites of the wilkins peak are apparently unique within the green river formation they reflect the unusual provenance and hydrology of the wilkins peak and suggest chemical and sedimentary models established for the other green river members will not be applicable

temporal variation in the magnitude frequency distribution during the guy greenbrier earthquake sequence the recent increase in earthquake activity in the central u s has led to concerns about the hazard posed by induced earthquakes understanding earthquake phenomena and monitoring in all settings can be improved by the detection of small events however the catalog of induced earthquakes is incomplete for small events due to the sparse instrumentation this is particularly true in settings of low background seismicity like the central u s we apply single station template matching to detect small earthquakes during the guy greenbrier sequence in central arkansas and find over 100 times more earthquakes than are registered in the advanced national seismic system catalog between july 2010 and october 2011 a complete catalog over nearly 4 units of magnitude enables us to analyze the magnitude frequency distribution of induced earthquakes we find that earthquakes deviated from the gutenberg richter statistics during the operation of nearby injection wells but returned to gutenberg richter statistics after the wells were shut in

development of tectonic cyclothems in rift pull apart and foreland basins sedimentary response to episodic tectonism the thickest part of asymmetric rift pull apart and foreland basin fills commonly consists of large scale hundreds to thousands of metres thick tectonically generated cyclothems of fine grained marine lacustrine or longitudinal fluvial deposits and coarse grained transverse braid plain or alluvial fan deposits the appearance of coarse clastics in these basin fills is typically noted as the time of tectonically rejuvenated source area uplift based on the conceptual tie between relief and coarse grain size and on the application of the davis theory of landform development we propose the opposite interpretation that the commencement of fine grained sedimentation above coarse grained deposits in a tectonic cyclothem is the best indicator of renewed tectonic activity this reinterpretation is more consistent with 1 modern examples 2 the consideration of source area and sedimentary basin geomorphology 3 the disparity between the reaction rates of the various environments to subsidence 4 the disparity between the rates of tectonic uplift and erosion and 5 the controls on elastic wedge progradation in our model extensive coarse grained clastic wedge progradation is an indicator of tectonically quiescent phases

aftermath of the permian triassic mass extinction event paleoecology of lower triassic carbonates in the western usa paleoecologic study of invertebrate faunas from three successive early triassic seaways reveals that biotic recovery from the end permian mass extinction event was slow and that full recovery did not occur until after the early triassic simple cosmopolitan opportunistic generalists and low diversity low complexity paleocommunities were characteristic of the entire early triassic in the western usa an increase in guild and taxonomic diversity was observed with the addition of several new higher taxa in the late early triassic spathian to the almost exclusively molluscan faunas of the earlier early triassic nammalian potential disaster forms the inarticulate brachiopod lingula and the paper pecten claraia dominated the earliest early triassic faunas griesbachian and even occurred in the late early triassic normal marine stromatolites comparison with data on faunas from the permian and triassic suggests that even the most diverse early triassic faunas in the spathian were rather low in guild diversity and species richness these characteristics of genera and paleocommunities in the early triassic may be typical of mass extinction aftermaths

induced seismic deformation in the cogdell oil field of west texas a sequence of induced earthquakes occurred at the cogdell oil field in west texas from about 1974 to 1982 the earthquakes occurred within an array of injecting wells which surrounded the perimeter of the field and which decreased in radius during the life of the injection project we examine this sequence of earthquakes in terms of two failure models in the first model seismic failure occurs when and where fluid pressures exceed some critical value in the second model earthquakes occur at the edges of low fluid pressure areas where stresses have been transferred as a result of aseismic deformation in adjacent high fluid pressure regions we calculate the history of fluid pressures in the cogdell field using the theis equation for fluid flow in an areally infinite aquifer the calculations show that the earthquakes occur in a region of relatively low pressure surrounded by regions of higher fluid pressure the cogdell earthquakes may occur on pre existing faults however fluid pressures are sufficiently high in surrounding portions of the field to also produce failure a long time delay between the start of injection and the onset of seismicity may correspond to the time required for fluid pressures on a pre existing fault to reach critical values or may be the result of an evolving injection pattern whereby the inward migration of injecting wells produces aseismic failure which loads stress onto stronger regions within the center of the field injection of fluids for secondary recovery occurs at over three thousand sites in the state of texas many of these sites are geographically near cogdell and many have higher injection pressures and volumes of injected fluid than cogdell however they do not exhibit any seismicity a failure model which incorporates stress loading suggests that the perimeter injection pattern is responsible for the onset of seismicity a consequence of this interpretation is that many other injection fields may be undergoing large amounts of aseismic deformation

sheet flow deposits of graded beds and mudstones on an alluvial sandflat playa system upper triassic blomidon redbeds st mary s bay nova scotia the 400 m of blomidon redbeds accumulated in a semi arid rift valley in the subtropics at st mary s bay these redbeds are 64 sandy mudstone playa mudflats 25 graded beds sandflats at the toes of alluvial fans 10 fissile claystone playa lakes and 1 channel sandstone stream channels flash floods in mountains south of the valley flowed down alluvial fans to spread out to the north east as sheet flows on sandflats and playa mudflats deceleration of the sheet flows deposited graded beds 2 83 cm in thickness on the sandflats and thin layers of mud on the playas nine sequences consisting of arrangements of six lithologies compose 90 of the graded beds in order of decreasing abundance these are ripple cross laminated siltstone horizontally laminated mudstone fining upward ripple cross laminated siltstone ripple cross laminated sandstone horizontally laminated mudstone cross bedded sandstone horizontally laminated mudstone ripple cross laminated sandstone ripple cross laminated siltstone rippledrift cross laminated siltstone horizontally laminated mudstone fining upward ripple drift cross laminated siltstone cross bedded sandstone ripple cross laminated siltstone and cross bedded sandstone ripple cross laminated siltstone horizontally laminated mudstone the sheet flows perhaps up to 1 m in depth had a high concentration of suspended load deposition was dominantly during lower flow regime conditions and moderate to rapid flow deceleration there are 32 thinning and fining up cycles where a sandflat package of graded beds is transitionally followed by a playa package of sandy mudstone the cycles range in thickness from 1 3 to 13 3 m averaging 4 6 m each cycle is initiated by avulsion to a new active channel network on a fan gradual abandonment of the channel network produces the thinning and fining up cycle the cycles are grouped in three 60 70 m fining up megacycles upwards within each megacycle the packages of sandy mudstone compose a progressively larger proportion of the cycles each megacycle evidently was initiated by a brief period of tectonic movement on the border faults that produced greater relief of the highlands relative to the valley floor subsequent erosion gradually lowered the relief to yield a fining up megacycle