numerical modelling of lithosphere shortening application to the laramide erogenic province western usa abstract a two dimensional model of lithosphere shortening is presented which quantifies crustal thickening temperature perturbations and flexural isostatic components the model assumes that the upper brittle layer of the crust deforms by thrusting while the lower ductile lithosphere accommodates compressional deformation by a pure shear or squashing mechanism model results suggest that basement uplift foreland basin development and underlying crustal structure are controlled by the amount and configuration of the compressional deformation in the upper and lower lithosphere the perturbation of the temperature field erosion and the flexural rigidity of the lithosphere the model is applicable to regions of thick skinned thrust tectonics and is applied to the laramide orogenic province in the western usa model simulations of structural cross sections across the laramide province show basement uplifts and adjacent foreland basins that are comparable in magnitude with those suggested by geological data the model has also been used to provide insights into the tectonic evolution of the laramide province and an attempt has been made to determine the flexural rigidity of the lithosphere at the time of laramide deformation as well as quantify both the effects of the post shortening re equilibration of the temperature field and thrust uplift erosion the amount of crustal thickening and post shortening cooling of the geotherm predicted by the two dimensional model of lithosphere shortening are used in strength calculations to determine the relative strength or weakness of the lithosphere the results suggest that the lithosphere is relatively strong immediately following shortening due to the cooling of the geotherm following shortening however gradual weakening occurs as the temperature field returns back to its unperturbed state in the presence of an enhanced crustal thickness the results are compatible with the evolution of the laramide province which has experienced a change in tectonic regime to one of extension over the last 20 30 ma

flexural modelling of continental lithosphere deformation a comparison of 2d and 3d techniques abstract the flexural isostatic response of the lithosphere in response to loading caused by continental tectonics has been modelled in 3d the modelling approach used has been to determine hanging wall deformation following movement over a pre defined fault surface in addition the lower crust is assumed to deform by a pure shear mechanism the changes in crustal thickness resulting from these structural processes impose loads upon the lithosphere which responds by isostatic adjustment algorithms have been developed to quantify the flexural isostatic response to these loads in 3d these deflections are then superimposed upon the results from the structural modelling to generate isostatically compensated hanging wall footwall and fault surfaces schematic models are presented for extensional compressional and strike slip deformation model results are dependent upon the interaction between fault geometry displacement along the fault which can be varied along strike and the methodology used to quantify the flexural response of the lithosphere to loading emphasis has been placed upon contrasting models which include a structural component only with those that incorporate both structural and flexural isostatic processes following extension structural processes generate a relatively deep half graben with no deformation at the basin edges isostatic compensation modifies this structure to produce a relatively shallow but variable basin depth with uplift typically between 1 and 2 km experienced at the basin edges compressional models have been generated which show the formation of large uplift structures which are modified by isostatic compensation so that they are considerably reduced in magnitude a regional depression i e foreland basin is also generated adjacent to the remaining uplift both 2d and 3d implementations of flexural isostasy have been investigated to provide insights into the validity of results provided by commonly applied 2d methods a major advantage arising from 3d tectonic modelling is the ability to investigate the effects of oblique or entirely strike slip components of fault movement strike slip deformation has been modelled in the context of a single fault surface which varies along strike to show the development of pressure ridge and pull apart basin structures the isostatic compensation of these structures shows complex patterns of uplift and subsidence due to the interference of negative and positive loading and associated flexural deflections

was the black sea catastrophically flooded in the early holocene abstract a catastrophic flooding of the black sea basin was proposed to have occurred during its reconnection to the ocean in the early holocene possible cultural consequences of the flood include the migration of neolithic farmers from around the black sea towards central europe as well as the creation of flood myths stratigraphic and paleo geomorphologic information from danube delta aided by radiocarbon ages on articulated mollusks constrain the level in the black sea before the marine reconnection to ca 30 m below the present sea level rather than 80 m or lower if the flood occurred at all the sea level increase and the flooded area during the reconnection were significantly smaller than previously proposed

khvalynian transgression of the caspian sea was not a result of water overflow from the siberian proglacial lakes nor a prototype of the noachian flood abstract the paper presents a critical review of the hypothesis that the khvalynian transgression resulted from abundant inflow of meltwater from siberian proglacial lakes through the aral sea and along the uzboi channel into the caspian sea had a catastrophic character and could be considered as a prototype of the biblical noachian flood a thorough analysis of evidence cited by the proponent of the hypothesis revealed the lack of factual substantiation 1 there are no data indicative of aral drainage 2 there is no evidence that siberian proglacial water was inflowing into the caspian sea 3 taxonomic and spatial distribution of molluscs in khvalynian sediments do not indicate that transgression was essentially influenced by thawing of ice sheets on the russian plain 4 there is no evidence that the khvalynian transgression was catastrophic sea level rose by few centimeters per year over several thousands of years 5 there are no data indicating that khvalynian water overflowing through the manych spillway into the neoeuxinian lake was significant inflow could increase the level and salinity of the lake by 30 m and 5 respectively thus there is no evidence that the khvalynain transgression could serve as a reliable source for the biblical noachian flood

flexure of the continental lithosphere beneath apennine and carpathian foredeep basins the formation and development of foredeep basins adjacent to marginal fold and thrust belts are thought to be the result of flexural loading of the foreland lithosphere by migrating thrust sheets1 and this concept has formed the basis for many recent studies of the deformation of the continental lithosphere and consequent evolution of foreland basins2 7 the preservation of foredeep basins after the associated mountain belt has been greatly reduced by erosion suggests that an additional load independent of the topography must act on the lithosphere of the subducted slab6 to determine whether such an additional load might be present in some very young orogenic belts we constructed transects through the apennine and outer flysch carpathian thrust belts of the mediterranean region fig 1 using a simple elastic model which assumes a semi infinite broken elastic plate of constant flexural rigidity overlying a weak fluid we show that the topographic loads present along these transects are insufficient to cause the observed plate deflection this suggests that there is an additional load or downward force acting on the plate to produce the observed plate deflection beneath the foredeep troughs we suggest that this extra load resulted from either the negative bouyancy contrast between the subducted slab and the surrounding asthenosphere or modification of the crustal structure within the overriding plate due to the initiation of backarc rifting in the hinterland

modelling natural stresses in the arc syncline and comparison with in situ measurements abstract in the provence coal basin the hbcm company mines lignite at great depths several measurements of the natural stresses were carried out using flat jack and hydraulic fracturing a strong stress anisotropy and high stresses were observed to interpret these measurements large scale numerical modelling is used this study presents a comparison between the predicted natural stresses and those measured during field investigations three models are successively developed and loaded on the basis of assumptions about current tectonics and historical tectonics calculations lead to a better explanation of the orientations and magnitudes of the principal stresses which are not in contradiction with the observation of a ne sw stress deviation in the vicinity of the area where the measurements were carried out it appears that the natural stresses in the arc depend mostly on the major geological structures in comparison to the loading type the results indicate that there is a relatively good match between predicted and measured stress magnitudes and orientations finally on the basis of a good estimation of the tectonic loading stages it is possible to explain the distribution of the natural stresses in the arc syncline even though the magnitudes of the tectonic stresses were unknown

the co evolution of black sea level and composition through the last deglaciation and its paleoclimatic significance abstract the black sea was an inland lake during the last ice age and its sediments are an excellent potential source of information on eurasian climate change showing linkages between regionally and globally recognized millennial scale climate events of the last deglaciation here we detail changes from the last glacial maximum lgm through the transition to an anoxic marginal sea using isotopic strontium and oxygen and trace element sr ca ratios in carbonate shells which record changing input sources and hydrologic conditions in the basin and surrounding region sr isotope records show two prominent peaks between 18 and 16 ka bp cal reflecting anomalous sedimentation associated with meltwater from disintegrating eurasian ice sheets that brought black sea level to its spill point following a sharp drop in sr isotope ratios back toward glacial values two stages of inorganic calcite precipitation accompanied increasing oxygen isotope ratios and steady sr isotope ratios these calcite peaks are separated by an interval in which the geochemical proxies trend back toward glacial values the observed changes reflect negative water balance and lake level decline during relatively warm periods bolling allerod and preboreal and increasing river input less evaporation resulting in higher lake levels during the intervening cold period the younger dryas a final shift to marine values in sr and oxygen isotope ratios at 9 4 ka bp cal corresponds to connection with the global ocean and marks the onset of sedimentation on the black sea continental shelf this date for the marine incursion is earlier than previously suggested based on the appearance of euryhaline fauna and the onset of sapropel formation in the deep basin

fault chronology and uplift history of the southern wind river range wyoming implications for laramide and post laramide deformation in the rocky mountain foreland the stratigraphy provenance and structural involvement of tectogenic sedimentary rocks along the southern and western margins of the wind river range in western wyoming record a complex laramide and later uplift history and identify the timing and position of individual faulting events the chronology of these events is 1 main uplift of the range by displacement on the wind river fault between 90 and 49 to 50 ma 2 the formation of reverse faults in the hanging wall of the wind river fault ca 50 to 51 ma 3 sagging of the toe of the wind river fault into sedimentary fill of the green river basin between 46 and 23 ma 4 uplift of the core of the range along reactivated precambrian shear zones between 30 and 23 ma and 5 collapse of the southern part of the range along normal faults beginning at 13 ma the sedimentary record of uplift and erosion indicates that erosion and basin fill kept pace or caught up with uplift so that by the end of the laramide there was little topographic relief between the crest of the range and the adjacent green river basin the present topography of the range characterized by a high level erosion surface and distinct crestal ridge derives from uplift of the erosion surface by the late laramide reverse faulting post laramide uplift of the crest of the range and neogene exhumation initial uplift of the range as early as 110 ma and prior to displacement on the wind river fault suggests either a pre laramide event of unknown origin or that laramide crustal shortening began nearly 35 m y earlier than commonly assumed

permian to late triassic evolution of the longmen shan foreland basin western sichuan model results from both the lithospheric extension and flexure abstract the lithosphere was extended during the permian middle triassic in the yangtze craton where the sichuan basin located and then bent due to thrusting of the longmen shan orogen leading to formation of the longmen shan foreland basin western sichuan during the late triassic indosinian orogeny the lateral variation of the lithospheric strength resulted by former differential extension would inevitably influence the subsequent evolution of the foreland basin in order to investigate this both extensional and flexural models were applied in modeling permian late triassic basin evolution a 2d kinematic extensional model was initially developed along a profile crossing the yangtze craton to simulate the lithospheric thermal evolution during the permian middle triassic based on the thermal results the thermal rheological structure as well as the effective elastic thickness of the lithosphere te was then determined extension model show that the stretching factors decrease gradually from songpan ganzi to the sichuan basin leading to variable thermal rheological structure and increased te from west to east taking into account of the te variation a flexural model was finally constructed to investigate the evolution of the longmen shan foreland basin during the late triassic spanning the time period c 227 206 ma three episodes were divided according to the corresponding tectonostratigraphic units by matching the stratigraphic observations three phase advance distances eastward of the longmen shan along the qingchuan maowen fault turned out to be 18 22 and 18 km it implied a slow and similar thrust advance rate of 3 6 c 227 222 ma 2 2 c 222 212 ma and 3 mm yr c 212 206 ma respectively

lithospheric flexure and the evolution of sedimentary basins the sediments that have accumulated in sedimentary basins during geological time represent a load on the lithosphere that should respond by flexure simple elastic and viscoelastic maxwell plate models have been used to examine quantitatively the contribution of flexure to basin formation the models have been used to predict the stratigraphy and gravity anomalies associated with basins for different thermal and loading histories the predictions of the models have been compared with observed stratigraphy and free air gravity anomalies from interior and cratonic basins the best overall fit to the observations is for an elastic plate model in which the flexural strength of the lithosphere increases with age a similar model has recently been used successfully to explain observations from continental margin basins oceanic islands and seamounts and deep sea trench outer rise systems this model explains the increase in the overall width of basins during their evolution as well as the stratigraphy of the basin edges the apparent decrease in the widths of some basins through time can be explained by the model if sediment deposition is followed by erosion of the basin and its edges the models results suggest that the flexural properties of continental and oceanic lithosphere are generally similar and that flexure is an important factor to consider in backstripping studies in which the tectonic subsidence of a basin is isolated and stratigraphic studies in which relative changes of sea level are estimated

the relationship between the geometry of normal faults and that of the sedimentary layers in their hanging walls abstract we derive an analytical expression that relates the shape of a fault in cross section to the shape of the bedding horizons in its hanging wall block the expression assumes that the hanging wall deforms by simple shear and that the footwall remains undeformed throughout although this paper concentrates on normal faults the expression is equally valid and applicable to thrust faults the direction of simple shear in the hanging wall block is arbitrary and has a dramatic effect on the predicted fault or bedding geometry there is no reason to believe that the simple shear occurs on vertical planes as is commonly assumed in graphical approaches to this problem and ignoring the presence of inclined simple shear is likely to lead to considerable underestimates of the amount of extension across normal faults and in the amount of shortening across thrusts similar though more complicated expressions can be obtained when compaction within the hanging wall block is taken into account for a planar normal fault such compaction may result in the development of a hanging wall syncline

evolution of lithospheric strength after thrusting modeling of an eroding thrust belt indicates that immediately after thrusting the lithosphere is about twice as strong as unthickened cratonic lithosphere but after 10 to 20 m y it becomes weaker than cratonic lithosphere reaching a minimum of 40 to 70 of cratonic strength 30 to 100 m y after thrusting this may explain why rifting of thrust belts commonly occurs several tens of million years after thrusting ceases relative weakening results from 1 elevation of the geotherm caused by burial of radioisotope enriched surface rocks and 2 replacement of strong mantle rocks by weak crustal rocks in the lithospheric column low denudation rates enhance weakening by allowing radioisotope enriched rocks to remain buried longer our modeling indicates that 1 magmatism after thrusting is favored by high concentrations of heat producing elements in the lower plate and by slow denudation rates and 2 factors that affect denudation rate such as climate and the development of external drainage can significantly influence evolution of a thrust belt

unlocking the spatial dimension digital technologies and the future of geoscience fieldwork the development of affordable digital technologies that allow the collection and analysis of georeferenced field data represents one of the most significant changes in field based geoscientific study since the invention of the geological map digital methods make it easier to re use pre existing data e g previous field data geophysical survey satellite images during renewed phases of fieldwork increased spatial accuracy from satellite and laser positioning systems provides access to geostatistical and geospatial analyses that can inform hypothesis testing during fieldwork high resolution geomatic surveys including laser scanning methods allow 3d photorealistic outcrop images to be captured and interpreted using novel visualization and analysis methods in addition better data management on projects is possible using geospatially referenced databases that match agreed international data standards collectively the new techniques allow 3d models of geological architectures to be constructed directly from field data in ways that are more robust compared with the abstract models constructed traditionally by geoscientists this development will permit explicit information on uncertainty to be carried forward from field data to the final product current work is focused upon the development and implementation of a more streamlined digital workflow from the initial data acquisition stage to the final project output

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

late glacial to holocene climate and sedimentation history in the nw black sea abstract gravity cores from the continental slope in the northwestern black sea were studied using high resolution stable isotope grain size and xrf scanning data the measurements provide a 30 000 years ams 14c dated record of variations in the hydrological regime of the black sea and give insight into changing paleoenvironments in the surrounding areas stable climatic conditions during the last glacial maximum were followed by a series of meltwater pulses most likely originating from the scandinavian ice sheet between 18 000 and 15 500 yr bp 1 this meltwater input rose the level of the caspian sea to a point that caspian water could spill into the black sea via the manych depression north of the caucasian mountains high frequency oscillations in the xrf data during this period suggest a probable link to the arctic climate regime later during the bolling allerod and the early holocene prevailing high temperatures led to authigenic calcite precipitation through increased phytoplankton activity interrupted by the younger dryas and the 8200 yr bp cold event with dominant clastic sedimentation

an abrupt drowning of the black sea shelf abstract during latest quaternary glaciation the black sea became a giant freshwater lake the surface of this lake drew down to levels more than 100 m below its outlet when the mediterranean rose to the bosporus sill at 7 150 yr bp 1 saltwater poured through this spillway to refill the lake and submerge catastrophically more than 100 000 km2 of its exposed continental shelf the permanent drowning of a vast terrestrial landscape may possibly have accelerated the dispersal of early neolithic foragers and farmers into the interior of europe at that time

displacement transfer from borders to interior of a plate a crustal transect of iberia abstract a n s crustal transect of the whole iberian plate is presented the displacement transfer during the alpine deformation from the border ranges cantabrian and betic chains toward the interior ones was analyzed by means of balanced crustal sections inconsistencies in shortening values between upper and middle lower crust in the cantabrian mountains basque cantabrian zone imply a mid crustal detachment transferring orogenic shortening southward toward the spanish central system depending on the shortening value attributed to the central system this mid crustal detachment could involve the entire iberian plate connecting the cantabrian mountains and the betic chain the very small crustal root in the central system can be explained as a result of the tectonic load caused by the upper crustal shortening that was transferred from the border ranges we conclude that a simple shear model rather than a pure shear with lithospheric folding better explains the whole iberia deformation finally the total alpine shortening of the iberian plate is estimated between 267 and 292 km

the east carpathians indications of phase transitions lithospheric failure and decoupled evolution of thrust belt and its foreland abstract an analysis is presented of the tectonic development of the east carpathians since the late oligocene the geological and geomorphological data show that five epochs of convergence and nappe emplacement took place with the last one occurring 11 12 m y b p after these compressional events the nappe surface remained near sea level the crustal uplift which formed the present mountains began 3 m y b p and after 99 of the shortening of the carpathians had been completed the pre carpathian foreland basin up to 3 5 km deep formed on the margin of the east european platform in the middle miocene analysis of the evolution of the basin shows that it deepened away from the nappe stack and most of the subsidence occurred when there was no convergence this precludes lithospheric flexure due to convergence as a mechanism for basin formation at 11 12 m y b p the inner part of the basin 50 km wide was overridden by the carpathian nappe up to 12 14 km thick at that time a slight crustal uplift took place rather than subsidence in the shallow remnant outer basin part the present foredeep which emerged above sea level an additional 7 8 km of subsidence then occurred in the foredeep of the southeastern carpathians in the late miocene early pleistocene when very little convergence took place the evolution of the carpathian foredeep shows that lithospheric flexure of 2 5 km occurred in regions 20 40 km wide similar amounts of flexure and large basement faults exist under the nappe this style of deformation indicates flexural rigidity of the lithosphere that is several orders of magnitude smaller than in stable cratonic regions under a low flexural rigidity the crust should be close to local isostasy then the isostatic response to superposition of a 10 13 km thick nappe on the platform margin which was near sea level would form high mountains the crustal surface however remained at a low altitude we interpret this to be the result of contraction of gabbro in the lower crust with the formation of dense garnet granulites during nappe emplacement a layer of these dense rocks 20 km thick with p wave velocities 7 5 7 6 km s exists in the lower crust of the east carpathians according to the geophysical data there is no cool high velocity slab now subducting towards the intra carpathian area an increase in the mean height of the carpathians by only 1 km since the termination of convergence precludes a recent slab detachment rapid metamorphism of mafic rocks in the lower crust requires the infiltration of volatiles from the asthenosphere infiltration of volatiles into mantle lithosphere and the upper crust could strongly reduce their viscosity these phenomena might be the cause of an abrupt loss of lithospheric rigidity on the margin of the east european platform in the neogene lithospheric failure allowed the incorporation of this region into the carpathian fold belt after a long period of cratonic development

paleo evolution of the black sea watershed sea level and water transport through the bosporus straits as an indicator of the lateglacial holocene transition the paleo evolution of the black sea level during the lateglacial holocene transition is still unclear which motivates us to provide new estimates for that period based on the analysis of water budget hydrological conditions in the black sea catchment area are reconstructed here using water balance equation available data and constraints based on simple theory relating the runoff ratio with climatic characteristics in order to estimate the impact of the aridity of climate we consider two alternative scenarios 1 climate change under constant in time gradient in precipitation and evaporation over land and sea and 2 climate change accounting for changes in the horizontal distribution of precipitation and evaporation hydrological data are compiled from available present day data and paleo observations a number of sensitivity experiments is carried out revealing that the hydrological conditions in the black sea watershed should have evolved towards a very arid climate similar to the present day climate in the caspian sea area in order to initiate a drop of sea level of 100 m below the sill depth of the bosporus straits as speculated in some recent research estimates of sea level changes reveal a qualitative agreement with the coast line evolution inferred from paleo observations the younger dryas draw down of the black sea starts at about 13 3 to 13 kyr bp with a maximum low stand of 104 m at 11 5 kyr bp in an arid climate scenario the sea level reaches the outlet at about 8 8 to 7 4 kyr bp approximately at that time mediterranean sea level was about 10 m higher making flooding events of the black sea possible however the nature and exact timing of the holocene reconnection depends also on other not well known factors one of them is the bosporus sill depth motivating further research in this field estimates of the water transport through the bosporus straits are also provided for the time of lateglacial holocene transition

organic matter production and preservation and evolution of anoxia in the holocene black sea dating of sediments collected in gravity cores during leg 1 of the 1988 r v knorr expedition to the black sea suggests that the onset of water column anoxia at 7 5 ka was virtually synchronous across the basin over a depth range of 200 2250 m a finely laminated organic carbon oc rich sapropel unit ii was produced as a result of this anoxia the trigger for increased oc production and development of anoxia was the spillover of saline waters through the bosporus that probably began at 9 0 ka and peaked between 7 0 and 5 5 ka this spillover enhanced vertical mixing and nutrient cycling and caused a short term 2 3 kyr burst in surface water productivity during the early part of unit ii deposition continued incursion of saline waters enhanced vertical stability and inhibited mixing of nutrients into surface waters thus limiting primary production and decreasing the oc flux to sediments beginning 5 5 ka concentration accumulation rate and degree of preservation of organic matter all decreased in the upper part of unit ii as a result of decreasing productivity but anoxia persisted throughout most of the water column the end of unit ii sapropel deposition was synchronous across the black sea as the result of the first blooms of the coccolith emiliania huxleyi which presumably marked an increase in surface water salinity above 11 and the beginning of unit i deposition the high coccolith carbonate fluxes that occurred during deposition of unit i diluted the oc concentration in the sediments but oc accumulation rates are about the same as those in upper part of unit ii

the flexural isostatic response of the lithosphere to extensional tectonics abstract the tectonic loading resulting from the extension of the lithosphere is examined loads resulting from crustal thinning thermal perturbations and basin infill are recognised and the resulting flexural isostatic deflection of the lithosphere is modelled in response to each of them in the presence of a listric fault during rifting regional uplift or rebound occurs as a result of both crustal thinning due to normal faulting simple shear and the elevation of the geothermal gradient while subsidence is generated by the downward acting loads created by both basin infill and thinning of the lower crust by stretching pure shear following rifting further flexural subsidence occurs in response to the cooling of the temperature field and associated sedimentary infill one of the major tectonic effects resulting dominantly from crustal thinning by normal faulting is the generation of footwall uplift the magnitude of this uplift along with basin depth and underlying crustal structure are strongly determined by the flexural rigidity of the lithosphere the amount of extension and the dip of the major basement fault along which extension is taking place depending upon the values of these parameters model calculations predict between a few tens of metres and 1 5 km of footwall uplift these values correlate closely with the magnitude of footwall uplift estimated from examples within the geological record the erosion of this rift induced topography is also proposed as a possible driving mechanism for the generation of major basin unconformities

postglacial connection of the black sea to the mediterranean and its relation to the timing of sapropel formation the opening of the connection between the mediterranean and black seas as sea level rose above the bosporus sill has long been associated with the formation of the most recent holocene sapropel deposit s1 in the eastern mediterranean but the mechanism has remained elusive we present a model for the opening of the black sea based on hydraulics arguments which demonstrates that increased freshwater flux out of the black sea began 500 1000 years after sea level reached sill depth and that the timescale for the increased freshwater flux that drained the freshwater reservoir of the black sea is about 2500 3500 years we argue that the increased freshwater discharge out of the black sea would lead to decreased deep water formation and higher productivity in the surface waters in the eastern mediterranean two conditions generally associated with sapropel formation the delay in increased freshwater flux after the opening of the black sea and the period of increased freshwater discharge appear to match the onset and duration of sapropel deposits in the eastern mediterranean

structure of the bighorn mountain region wyoming from teleseismic receiver function analysis implications for the kinematics of laramide shortening basement cored uplifts are observed globally and remain an enigmatic feature of plate tectonics due to the fact that in many cases they occur distant from a plate boundary the laramide bighorn arch in wyoming is an archetypal basement involved foreland arch and provides an excellent setting for the investigation of such structures previous studies proposed diverse arch formation models each of which predicts a unique crustal geometry we use high resolution crustal imaging from teleseismic p wave receiver functions to test these models we obtained our data from 239 three component seismometers deployed as part of the bighorns arch seismic experiment as well as coeval regional transportable array stations a sequential two layer thickness vp vs h stacking algorithm constrains sediment and crustal structure receiver function common conversion point stacking results in 2 d transect images across the arch our results define an upwarp of the crust beneath the central and northern arch that extends into the powder river basin north northeast of the arch the lack of moho cutting faults or a moho geometry mirroring the arch rules out most shortening models except a crustal detachment model where shortening was accomplished by fault propagation folding on a thrust splay ramping off a midcrustal detachment fault the mismatch between gentle symmetric moho and asymmetric laramide arch geometries and their trends suggests a pre laramide origin for at least a part of the moho high this high perhaps in combination with a lesser degree of laramide lithospheric buckling may have caused emergent laramide thrusting and thus nucleated the bighorn arch our results suggest that midcrustal detachment can form basement involved foreland arches and suggest the hypothesis that preexisting undulations in the moho may have nucleated individual arches

hydraulic calculations of postglacial connections between the mediterranean and the black sea a series of simple hydraulic calculations has been performed to examine some of the questions associated with the reconnection of the black sea to the mediterranean through the turkish strait system during the holocene ryan et al s catastrophic flood scenario whereby the erosive power of the marine in fluxes initiated after eustatic sea level reached the sill depth opened up the bosphorus allowing saline water to pour into the black sea and filling it on a short time scale is examined the calculations show that although it might be possible to fill the palaeo black sea within the order of a decade a 1 2 year filling time scale is not physically possible a hydraulic model is also used to examine the more traditional connection hypothesis of near continuous freshwater outflow from the black sea with a slowly increasing saline inflow from the mediterranean beginning around 8 9 kyr bp the model considers two forms for the structure of the bosphorus a shallow sill as seen today and a deep sill associated with no sediments filling the 100 m gorge above the bedrock in the strait sensitivity experiments with the hydraulic model show what possible strait geometric configurations may lead to the black sea reaching its present day salinity of 18 psu salinity transients within the black sea are shown as a function of time providing for values that can be validated against estimates from cores to consider a deep non sediment filled bosphorus 100 m deep the entry of mediterranean water into the sea of marmara after 12 0 kyr bp is examined a rapid entry of marine water into the sea of marmara is only consistent with small freshwater fluxes flowing through the turkish strait system smaller than those of the present day by a factor of at least 4 such a small freshwater flux would lead to the salinification of the black sea being complete by an early date of 10 2 9 6 kyr bp thus the possibility of a deep bosphorus sill should be discounted

the late pleistocene holocene history of the caspian sea abstract repeated fluctuations of the caspian sea are correlated with climate fluctuations with transgressions associated with climatic warming and regressions characteristic of cooler periods during the late pleistocene and holocene transgressions are associated with the early khvalynian 32 24 ka and late khvalynian 16 8 ka corresponding to the bryansk interstaidal and final deglaciation respectively regressions occured during the yenotavian event 24 17 ka corresponding to the last glacial maximum valdai and from 8 ka until the present corresponding to the waning of the holocene climatic optimum in the region variations in meltwater supply appear to be the primary factor controlling the caspian sea levels throughout the late quaternary

intraplate lithosphere deformation and the strength of the lithosphere summary the intraplate deformation of continental lithosphere in response to applied stress has been investigated using a mathematical model which incorporates the elastic ductile and brittle response of lithosphere material ductile deformation is assumed to be controlled in the crust by dislocation creep in quartz and in the mantle by dislocation creep and plasticity in olivine brittle failure is predicted using modified griffith theory a fundamental feature of the model is the redistribution of stress within the lithosphere following stress release by both ductile and brittle deformation this redistribution produces high levels of stress in the middle or lower crust immediately above the elastic ductile or brittle ductile transition lithosphere deformation is shown to be critically dependent on the temperature structure of which surface heat flow is a convenient indicator for higher geothermal gradients the release of stress in the lower lithosphere by ductile deformation is more rapid and complete and results in large stress levels in the upper lithosphere for sufficiently large applied stresses or steep geothermal gradients the stress levels in the upper and middle crust will cause complete fracture of the upper lithosphere whole lithosphere failure wlf then results by continued brittle and ductile deformation causing geologically significant strains the critical value of applied stress required to give wlf has been calculated for both tensional and compressional deformation as a function of surface heat flow the predicted lithosphere bulk strength is then compared with expected levels of intraplate stress arising from plate boundary forces and isostatically compensated loads which are thought to give net stress levels in the continental lithosphere in the range 0 25 to 0 25 kb using these expected maximum stress levels the model predicts significant extensional deformation in regions of moderate heat flow with q c 60mwm e g central europe as well as for areas of high heat flow like the basinand range province significant compressional deformation is predicted for areas of high heat flow with q c 75 mwm 2 but only for restricted conditions of stress combination these results are in good agreement with

a simple evolutionary model for water and salt in the black sea this paper presents a time dependent variable size box model for the total fluid and salinity balances of the black sea in addition to the advective flows due to riverine and mediterranean inputs of water the model accounts for entrainment flows which are parameterized using the theory of ellison and turner 1959 and employs a modified version of the gargett 1984 formulation for eddy diffusivity in describing cross pycnocline mixing flows the variable volume of the boxes permits explicit simulation of the replacement of the preexisting late pleistocene lake water by the inflow of denser mediterranean water our results indicate that the time needed to displace the old deep water with new saltier water is 2000 years or less because of the effects of mixing the salinity of both the surface and deep waters requires a greater time interval to obtain present day values i e 4000 years if the inflow of mediterranean water is constant in time at its present value and 6000 years if this input changes with time in approximation to the rate of sea level rise the occurrence of the marine coccolithophorid emiliania huxleyi in the holocene sapropel layer requires a minimum surface salinity of 11 which takes some 1600 to 3100 years to develop this range is a result of the uncertainty in the history of the mediterranean water input the model is also employed to investigate the freshening of the black sea after cutoff of mediterranean input the salinity of both surface and deep waters is found to fall below 11 in less than 3000 years and the freshening process is complete in 9000 years

end carboniferous fold thrust structures oxfordshire uk implications for the structural evolution of the late variscan foreland of south central england interpretation of commercial seismic reflection data from the west of banbury south central england has provided information on the late carboniferous structural evolution of the oxfordshire syncline end carboniferous structures are preserved in the footwall of the main basin bounding faults of the permo triassic worcester graben restoration of major pre triassic normal faults has allowed reconstruction of earlier compressional structures in contrast to the wnw ese trend of structures to the south in the variscan foreland fold thrust belt major faults and folds in oxfordshire are approximately n s trending the structures seen to deform westphalian d stephanian aged sequences on the seismic profiles are a combination of steep 30 40 dip fault bounded uplifts and less dominant thin skinned tectonics apparently showing transport to the east in the south some thin skinned structures are present and in the north cover sequences are uplifted in a narrow zone of deformation on reactivated basement faults the amount of shortening also changes along strike from c 1600 m in the south to c 950 m in the north reactivation of major basement faults with differential basement shortening accounts for the main structures localized detachment in the young and weak sediments close to the palaeo land surface explains the thin skinned structures seen on some of the seismic lines these end carboniferous structures in oxfordshire and structures in the malvern abberley hills represent the structural limits of a large n s striking intra stephanian uplift in the late variscan foreland it is suggested that the structures formed during a discrete phase of intra stephanian e w directed regional shortening prior to the final phase of movement in the variscan belt

developing digital fieldwork technologies at the british geological survey geological surveys are faced with budget constraints and calls for efficiency gains the effective application of digital techniques is often seen as a route to meeting these demands while increasing the value of outcrop studies and reducing the inherent subsurface uncertainty the british geological survey may be the oldest national survey in the world established in 1835 however developing and implementing new innovative and efficient technologies for fieldwork is a high priority efficient tools for capturing integrating manipulating and disseminating outcrop data and information are imperative to enable geoscientists to increase their understanding of geological processes and therefore to reduce subsurface uncertainty and risk systems for capturing structured digital field data and for visualizing and interacting with large datasets are increasingly being utilized by geoscientists in the uk and internationally augmented reality and unmanned aerial vehicles are amongst the developing technologies being explored for future operational implementation this paper describes the digital field mapping bgs sigmamobile and visualization geovisionary systems and refers to a case study outlining their contribution to reducing uncertainty and risk in hydrocarbon exploration

lithosphere rheology a note of caution abstract it has become common practice to use laboratory determined low temperature frictional sliding data together with power law equations for steady state creep of rocks at high temperatures to construct inferred profiles of rock strength and mode of failure with depth in the lithosphere in some cases this may involve unwarranted extrapolation of rock mechanics behaviour beyond the region of its validity the form of transition from frictional behaviour to intracrystalline plastic flow in the earth is much more complex than is suggested by the above model within the regime of plastic flow substantial changes in flow strength and mode of failure whether flow becomes localized into shear zones may accompany microstructural changes developed over large strains when deformation is accompanied by metamorphic changes existing flow laws for rocks are likely to be wholly inapplicable until a clearer understanding has emerged of the full range of expression of the rheological behaviour of rocks existing models of lithosphere rheology should be treated with caution

drones in carbonate geology opportunities and challenges and application in diagenetic dolomite geobody mapping unmanned aerial vehicles uavs or drones have become widely available for use in a broad range of disciplines despite the decreased cost and technological developments of platforms sensors and software the use of drones in carbonate geology has yet to be exploited nevertheless drones offer multiple advantages over traditional field work or high altitude remote sensing techniques in that they enable the reconstruction of three dimensional models of inaccessible or unsafe outcrops and can bridge the spatial scale gap in mapping between manual field techniques and airborne high altitude remote sensing methods in this contribution we present our methodology of structure from motion photogrammetry on drone captured images and highlight opportunities and challenges of using drones in carbonate geological studies moreover we apply this method to document the spatial distribution and dimensions of diagenetic dolomite geobodies in carboniferous limestone host rock of the picos de europa northern spain the results of our study indicate that dolomite geobodies occur preferentially near to strike slip faults rather than thrust faults or specific types of limestone host rock lithology in the study area the geobody dimensions appear to be related to the strain magnitude of the strike slip faults we propose that these identified links and controls are applicable to structurally controlled dolomitization on a more general basis our study has demonstrated the potential for using drones in carbonate geological studies

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

testing the physical oceanographic implications of the suggested sudden black sea infill 8400 years ago 1 we apply a shock capturing numerical model based on the single layer shallow water equations to an idealized geometry of the black sea and the sea of marmara in order to test the implications of a suggested sudden black sea infill 8400 years ago the model resolves the two dimensional flow upstream and downstream of the hydraulic jump provoked by the cascade of water from the sea of marmara into the black sea which would occur during a sudden black sea infill the modeled flow downstream of the hydraulic jump in the black sea would consist of a jet that is in part constrained by bathymetric contours guided by the bosporus canyon the modeled jet reaches depths of up to 2000 m and could explain the origin of the sediment waves observed at this depth at a late stage of the infill the modeled jet is attached to the coast and might account for the course of a submerged channel at the mouth of the bosporus the preservation of continuous barrier washover lagoonal fill systems occurring on the black sea shelf is however not easily reconcilable with the large flows over the southwest black sea shelf predicted by the model intensified flow in the upstream basin sea of marmara is restricted to the immediate vicinity of the bosporus suggesting that a sudden reconnection need not have disturbed sediments in the wider sea of marmara

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

black sea marmara sea quaternary connections new data from the bosphorus istanbul turkey abstract previous studies concluded that the bosphorus strait was formed during the quaternary by fluvial incision of a valley between the black sea to the north and the marmara sea in the south hitherto however few details of the evolution of this connection have been elucidated from the sediments deposited within the bosphorus itself we report here details of sedimentological and palaeontological evidence relating to this history obtained from five boreholes drilled into the unconsolidated sediment fill in the north central sector of the bosphorus together with nearby geophysical profiles the quaternary fill of this part of the bosphorus comprises two major facies associations yellow arkosic sands dominate the lower facies association a these are assigned a middle to late pleistocene age and the contained faunas have a lagoonal to lacustrine character and a black sea provenance paratethyan affinities the abruptly succeeding units of facies association b comprise fining and coarsening upwards units of coarse to fine shelly and clayey sands that alternate with shell bearing green clays these sediments were formed in a range of marine and coastal settings and biostratigraphic evidence and absolute dating demonstrate the mid late holocene age of this upper unit initially brackish faunal assemblages in this upper unit show an upward increase in marine and mediterranean affinities integrating these new data with previously published observations from coeval deposits in the southern bosphorus and izmit bay ne marmara sea we conclude that during the late pleistocene and early holocene a topographic barrier existed in the south central sector of the bosphorus on both sides of which estuarine and lagoonal sediments accumulated with distinctive black sea and mediterranean faunas during a significant rise in sea level between 7000 and 5300 years ago this barrier was finally submerged permitting interchange of marine waters between the mediterranean and the black sea and creating the present oceanographic situation this evolution conflicts with the cataclysmic role of the bosphorus in the early holocene as postulated in the catastrophic flood hypothesis of ryan et al mar geol 138 1997 119 126 annu rev earth planet sci 31 2003 525 554 it also contrasts with the history recorded from the gulf of izmit where intermittent connection between these two bodies of water throughout much of the quaternary is evident

thick skinned tectonics and basement involved fold thrust belts insights from selected cenozoic orogens defining the structural style of fold thrust belts and understanding the controlling factors are necessary steps towards prediction of their long term and short term dynamics including seismic hazard and to assess their potential in terms of hydrocarbon exploration while the thin skinned structural style has long been a fashionable view for outer parts of orogens worldwide a wealth of new geological and geophysical studies has pointed out that a description in terms of thick skinned deformation is in many cases more appropriate this paper aims at providing a review of what we know about basement involved shortening in foreland fold thrust belts on the basis of the examination of selected cenozoic orogens after describing how structural interpretations of fold thrust belts have evolved through time this paper addresses how and the extent to which basement tectonics influence their geometry and their kinematics and emphasizes the key control exerted by lithosphere rheology including structural and thermal inheritance and local regional boundary conditions on the occurrence of thick skinned tectonics in the outer parts of orogens

on the origin of the bosphorus abstract the palaeozoic upper cretaceous basement palaeomorphology of the bosphorus the strait of istanbul bears the evidence of a valley of a palaeostream running to the black sea in the north a palaeobasin deeper than 160 m opening to the sea of marmara in the south and a barrier between these two features this suggest that the northern part of the bosphorus was formed mainly by fluvial activity whereas the southern part developed as a basin by faulting the recent sediment thickness exceeds 130 m in the basin indicating that the southern part of the bosphorus was once essentially depositional rather than an erosional the present form of the bosphorus was established in holocene time by the connection of the basin in the south with the stream in the north the barrier and the stream valley in the north have been deepened by erosion and faulting to form a strait connecting the black sea and the mediterranean

preferential rifting of continents a source of displaced terranes lithospheric rifting while prevalent in the continents rarely occurs in oceanic regions to explain this preferential rifting of continents we compare the total strength of different lithospheres by integrating the limits of lithospheric stress with depth comparisons of total strength indicate that continental lithosphere is weaker than oceanic lithosphere by about a factor of 3 also a thickened crust can halve the total strength of normal continental lithosphere because the weakest area acts as a stress guide any rifting close to an ocean continent boundary would prefer a continental pathway this results in the formation of small continental fragments or microplates that once accreted back to a continent during subduction are seen as displaced terranes in addition the large crustal thicknesses associated with suture zones would ironically make such areas likely locations for future rifting episodes this results in the tendency described as the wilson cycle of new oceans to open along the suture where a former ocean had closed

a hydrological model of the black and caspian seas in the late pleistocene and early middle holocene abstract this topic area has been a controversial one since the concept of a catastrophic black sea flood was first proposed and there is still considerable disagreement between experts as to the exact sequence of events this paper describes a numerical model of the caspian and black sea basins together with flows through the manych spillway and the bosphorus strait the model has been calibrated against the deductions made by various researchers concerning past water levels and parameters such as river flow volumes and evaporation rates have been assigned to give reasonable agreement with these deductions the model successfully predicts flow through the manych spillway during the early khvalynian transgression of the caspian sea between 15 2 and 12 3 ky bp and not thereafter the black sea is predicted to reach a lowstand of 163 m in about 11 ky bp and then to fill relatively rapidly due to increased river inflow combined with a breakthrough of mediterranean water across the bosphorus sill in about 10 5 ky bp this is followed by a period of high outflow through the bosphorus and between 9 3 and 8 ky bp by rapidly rising salinity due to marine inflow at depth the model also highlights two significant points of conflict with the physical evidence these concern the lack of apparent reason for the sudden onset of sapropel formation in the black sea in 7 6 ky bp and the significant erosion that has apparently occurred across the manych sill

the last sea level changes in the black sea evidence from the seismic data abstract high resolution shallow seismic data collected from the southwestern shelf of the black sea indicate five different seismic stratigraphical units the lower three of them belong to the upper cretaceous eocene oligocene miocene and early quaternary prior to holocene sediments respectively these units are considered as a basement for the recent sediments deposited related to the latest connection of the black sea and the mediterranean the surface of these units are truncated to form an etchplain developed before the flandrian transgression the fourth unit covers the older units by an onlap its contact with the older units seen at 105 m is the shoreline of the black sea prior to the last major sea level change the fifth unit has been deposited since drowning of the black sea shelf the principal cause of drowning of the black sea shelf is not only the last sea level rise as it is at the shelves of the sea of marmara but also the opening of the strait of istanbul it is also realised by the comparison of the shelf area and the catalca kocaeli etchplain that the present continental part of this etchplain has been considerably uplifted with respect to the shelf area along the present shoreline this uplifting must have also reactivated the faults around the strait of istanbul foundering the strait valley and thus permitting the mediterranean waters to pass into the black sea and initiating the sudden drowning of the black sea shelf