estimation of kerogen porosity in source rocks as a function of thermal transformation example from the mowry shale in the powder river basin of wyoming evaluations of porosity relevant to hydrocarbon storage capacity in kerogen rich mudrocks i e source rocks have thus far been plagued with ambiguity in large part because conventional core and petrophysical techniques were not designed for this rock type the growing recognition of an intraparticle organic nanopore system that is related to thermal maturity is beginning to clarify this ambiguity this mode of porosity likely evolved with the thermal transformation of labile kerogen and probably neither depends nor interacts except perhaps chemically with previously assumed matrix or mineral porosity that is dominated by bound water and that may be largely irrelevant to hydrocarbon storage capacity in these rocks to address this newly recognized and important nonmatrix kerogen pore system that is arguably the dominant hydrocarbon storage and mobility network in these rocks we introduce a relatively simple kinetic model that describes porosity development within kerogen as a function of thermal maturation kerogen porosity development is estimated within the upper albian mowry shale in the powder river basin of wyoming to illustrate the approach relevant storage capacity is considered to have evolved with thermal decomposition of organic matter during catagenesis where we estimate that kerogen porosity does not typically exceed 3 of bulk rock volume modeled oil in place estimates are comparable to residual oil estimates from pyrolysis data s1 at lower maturities but exceed pyrolytic s1 yields at higher maturities we hypothesize therefore that a subsurface kinetic porosity model might represent a means to account for s1 losses at surface conditions and to circumvent difficulties surrounding estimations of expulsion efficiencies that are inherent to more traditional mass balance calculations

microscale evidence of liquefaction and its potential triggers during soft bed deformation within subglacial traction tills published conceptual models argue that much of the forward motion of modern and ancient glaciers is accommodated by deformation of soft sediments within the underlying bed at a microscale this deformation results in the development of a range of ductile and brittle structures in water saturated sediments as they accommodate the stresses being applied by the overriding glacier detailed micromorphological studies of subglacial traction tills reveal that these polydeformed sediments may also contain evidence of having undergone repeated phases of liquefaction followed by solid state shear deformation this spatially and temporally restricted liquefaction of subglacial traction tills lowers the shear strength of the sediment and promotes the formation of transient mobile zones within the bed which accommodate the shear imposed by the overriding ice this process of soft bed sliding alternating with bed deformation facilitates glacier movement by way of stick slip events the various controls on the slip events have previously been identified as i the introduction of pressurised meltwater into the bed a process limited by the porosity and permeability of the till and ii pressurisation of porewater as a result of subglacial deformation to which we include iii episodic liquefaction of water saturated subglacial traction tills in response to glacier seismic activity icequakes which are increasingly being recognized as significant processes in modern glaciers and ice sheets as liquefaction operates only in materials already at very low values of effective stress its process form signatures are likely indicative of glacier sub marginal tills

the origin of a giant downward directed clastic dyke in a kame belchatow mine central poland a kame near czubata gora in the pleistocene overburden of the belchatow open cast browncoal mine in central poland shows several types of deformations a number of diapirs occur but also a structure that shows all characteristics of a diapir but consists of sediments that apparently intruded the underlying rather than the overlying sediments analysis of this structure shows that it consists of material that was originally deposited as a fine grained mainly silty glacilacustrine sediment seismic activity triggered the material to fluidise resulting in a structureless mass part of the fluidised material flowed down into a fissure that had formed in the underlying sediments probably due to tectonics in the active graben thus forming a clastic dyke more of the overlying silty material was later pressed down into a dyke with the shape of a downward directed diapir

problems and progress in the research on soft sediment deformations abstract the study of soft sediment deformations has gradually evolved from describing them as remarkable features into a structural analysis that should contribute to the reconstruction of the sediments early diagenetic history it appears that most attention has been devoted to this field during a few phases of the development of sedimentology a third phase when interest was renewed started in the eighties but progress is still hampered by inefficient scientific communication due to the absence of an unambiguous terminology specific topics deserving of much more attention in the near future are the interrelationships between the various forces that may effect a sediment simultaneously the development of deformational structures during a number of subsequent stages the preservational potential of the structures and systematic experiments that deal with the influence of the physico chemical and physico mechanical properties of the sediment

cenozoic erosion and sedimentation in the western barents sea abstract seismic reflection data and well logs are used to interpret cenozoic sedimentary environments in the south western barents sea using volumetric calculations and compaction trend analysis the cenozoic erosion and sedimentation rates have been quantified marine environments ranging from neritic to bathyal water depths dominated the southern barents sea during the late palaeocene at the palaeocene eocene boundary a southwards progradation commenced along the uplifted and eroded loppa and stappen highs during the early eocene to mid miocene sedimentation continued in the intracratonic basins as well as along the newly established continent ocean boundary in the embryonic northern norwegian greenland sea substantial erosion occurred on the westernmost margin particularly on the stappen high during this time interval in the mid miocene during a period of relative lowstand of sea level a system of lowstand fans was deposited west of the stappen high later a pronounced progradation of the shelf edge commenced during the mid miocene to late pliocene the shelf edge prograded between 20 and 40 km during the mid pliocene to early pleistocene the barents sea and adjacent land areas were uplifted a fluvial glaciofluvial drainage system developed on the continental shelf resulting in pronounced erosion there and very high sedimentation rates on the continental margin during the last 0 8 ma several large glaciations on the barents sea shelf proper have resulted in overdeepened troughs and high sedimentation rates at the continental shelfbreak and on the continental slope the overall cenozoic erosion varies spatially as well as temporally in the svalbard area close to 3 km of rocks have been eroded since the oligocene the same amount or more was eroded from the stappen high during the palaeocene and early neogene in the south western areas during the eocene mid miocene erosion occurred along the margin in addition the loppa high and adjacent areas served as sediment source areas during the late pliocene and pleistoncene the average erosion in the south western barents sea amounted to about 600 m erosion was greater in the south east than to the west and north and was more extensive where the former glacial ice streams had flowed

cenozoic margin development and erosion of the barents sea core evidence from southwest of bjornoya abstract five stratigraphic boreholes at the western barents sea margin reveal an evolution from a palaeocene normal shelf setting to a complex late cenozoic offshore marginal marine system influenced by mass flows and finally a glacially influenced shelf environment palaeocene epeiric sea sedimentation was sourced by erosion at the stappen high earliest eocene extension associated with volcanism was followed by rapid subsidence of the vestbakken volcanic province which became filled by sediments from an uplifted stappen high by the middle eocene siliciclastic shelf sediments were deposited and the infill had reached a balance with subsidence tectonic movements at this time may have caused local uplift which restricted the ventilation of local basins west of the stappen high but marine conditions existed in the area until early oligocene times when subaerial exposure was caused by tectonic uplift and probably also a fall in eustatic sea level pronounced oligocene and pliocene unconformities reflect major events of uplift and erosion at the margin and abundant fossil reworking indicates erosion of the uplifted cretaceous and tertiary strata the oligocene erosion had its associated depocentre to the south and west of the study area and was less important regionally than the pliocene pleistocene phase the pliocene uplift first led to local erosion along the margin subsequent subsidence may initially have had a thermal component this was followed by extensive downwarping under the load of largescale deposition sourced by regional erosion in the barents shelf region an eocene volcanic phase was probably related to the initiation of seafloor spreading isotopically dated volcaniclastic intervals in one of the cores give evidence of a late pliocene volcanic phase this event was associated with local tectonic movements which may be part of a regional uplift in the western northwestern part of the barents sea glaciations caused by the neogene climatic deterioration became enhanced by uplift and this led to extensive regional glacial erosion the main depocentre was offset to the south by ice flow curving around the uplifted area

chronology of tertiary fan deposits off the western barents sea implications for the uplift and erosion history of the barents shelf abstract a combined biostratigraphic and seismic study was performed on three holes drilled in the western barents sea two holes penetrate the thick sedimentary wedge which forms a large fan located off a trough on the barents sea shelf the bjornoyrenna fan the study shows that the fan was built over a short time span in the late pliocene pleistocene mainly due to glacial erosion of the barents shelf region this contrasts earlier age assignments which concluded that fan deposition started in the oligocene the results have a major impact on the understanding of trough mouth fan formation and has important bearing on the history of the sedimentary basins of the barents shelf

the vistulian aeolian succession in central poland abstract central poland is situated in the centre of the late pleistocene and holocene european aeolian sand belt this area has the highest frequency of round mat grains of all europe due to intense aeolian abrasion aeolian processes were very active during several glaciations but the changes in aeolian activity in the course of an entire glaciation can be studied only for the vistulian weichselian wisconsinan the reason is that a continuous blanket of glacial sediments either covered or partly eroded older aeolian sediments in central poland during the wartanian saalian ii aeolian processes began just after deglaciation and became intense under the periglacial conditions of the late wartanian and the whole vistulian the evolution of these processes is reconstructed especially for the interval of the highest and most effective aeolian activity i e the late plenivistulian oxygen isotope stage 2 the coldest stage of the last glaciation a model of the sequence of periglacial aeolian events during an entire glaciation is presented this model may be used for the reconstruction of older pleistocene cycles of high periglacial aeolian activity

the jameson land basin east greenland a fission track study of the tectonic and thermal evolution in the cenozoic north atlantic spreading regime abstract the late mesozoic and cenozoic thermal history of the jameson land basin is constrained by new apatite and zircon fission track ft data of surface permian to jurassic sedimentary rocks the results show a general regional thermal evolution related to burial to temperatures close to and in excess of the maximum temperatures of the apatite annealing interval 125 c followed by cooling mainly due to cenozoic uplift and erosion faulting and differential movements in the basin generally occurred after cooling below the apatite partial annealing zone paz 75 125 c however in the northern part of the basin the data suggest a thicker sediment cover or localized heating related to an earlier fracture zone both apatite ft analysis and vitrinite reflectance values reveal a postmature signature for the studied rocks in the northeastern jameson land and premature to mature for the western central and southern jameson land rocks with respect to generation of hydrocarbons the chemical variations of apatite enhance the possibility of recognizing sample positions near maximum temperatures in the paz furthermore the pb zn mineralization pattern closely follows the tertiary maturity trend given by the ft data the type and distribution of mineralization suggest that it was influenced by the regional thermal evolution of the basin in the northeast domain circulating fluids may have overprinted the regional thermal record before ca 20 ma basaltic dyke and sill intrusions 55 45 ma locally caused resetting of apatite ft ages but generally the direct influence from upper crustal magmatic activity played only a minor role the thermal evolution in northeast jameson land is related to the late tectonic evolution of the northeast atlantic involving a change in ridge position at ca 25 ma which followed the passage of the proto icelandic mantle plume at 63 40 ma

primary migration by oil generation microfracturing in low permeability source rocks application to the austin chalk texas fracturing of low permeability source rocks is induced by pore pressure changes caused by the conversion of organic matter to less dense fluids oil and gas these fractures increase the permeability and provide pathways for hydrocarbon migration an equation for the pressure change is derived using four major assumptions 1 the permeability of the source rock is negligibly small 0 01 d 10 20 m2 so that the pore pressure buildup by the conversion is much faster than its dissipation by pore fluid flow 2 the stress state is isotropic so that horizontal and vertical stresses are equal the source rock fails when the pore pressure equals the overburden pressure 3 the properties of the rock organic matter and fluids remain constant during oil generation this assumption is valid when the change in depth i e pressure and temperature is small 4 only two reaction rates are required for the conversions a low temperature reaction rate for the kerogen oil conversion e approx 24 kcal mol a approx 1014 m y and a high temperature reaction rate for oil gas conversion e approx 52 kcal mol a approx 5 5 1026 m y the equations for generation rate and pressure change are applied to the austin source rock by adjusting the several variables to fit geochemical data core saturations and observed levels of oil and gas production this application demonstrates that the equations are easily applied in calculating depths of primary migration for low permeability source rocks

an outline of the pleistocene stratigraphy of the kleszczow graben bechatow outcrop central poland abstract the pleistocene sequence of the kleszczow graben central poland is located in a brown coal quarry 8 km long and 4 km wide it contains ten separate organic horizons in part stacked one above another and in part correlated by reference to associated inorganic units using heavy minerals and gravel petrography three of the organic horizons represent interglacials ferdynandovian mazovian holsteinian and eemian others represent interstadial or periglacial deposits the tertiary quaternary boundary is recorded at the site by reuverian c and prae tiglian biostratigraphy occurring in a single section a major hiatus exists above the prae tiglian and lower pleistocene and cromerian deposits are absent glacial deposits are represented by three elsterian tills five saalian tills and glaciofluvial and glaciolacustrine deposits the czyzow formation lies between the elsterian and saalian deposits and contains at least two interglacials the ferdynandovian and mazovian and several interstadial units without glacial intervening deposits the lower saalian odranian drenthe deposits are separated from the middle saalian wartanian 1 by fluvial sands and organic deposits of the pilica interstadial the middle wartanian 1 and upper saalian wartanian 2 also may be separated by an interstadial palaeosol the evidence from the kleszczow graben supported by other central european quaternary sequences suggest that only four glaciations occurred within the region during the middle pleistocene and that these glaciations were separated by long periods with a complex climate ranging from temperate to periglacial

late cenozoic erosion of the high latitude southwestern barents sea shelf revisited the southwestern barents sea has experienced profound erosion during the last 2 7 m y that has resulted in the development of a characteristic glacial morphology of the continental shelf and deposition of a several kilometer thick sediment fan along the western margin prograding into the deep sea in the period from ca 2 7 to 1 5 ma proglacial processes including fluvial and glaciofluvial erosion dominated for this period the total average erosion of the shelf was 170 230 m the average erosion rate was 0 15 0 2 mm yr and the average sedimentation rates on the fan were 16 22 cm k y subglacial erosion affected an area of 575 000 km 2 during the period from ca 1 5 to 0 7 ma total average erosion is estimated at 330 420 m for this interval and the average erosion rate was 0 4 0 5 mm yr average sedimentation rates were 50 64 cm k y during the last 0 7 m y glacial erosion mainly has occurred beneath fast flowing paleo ice streams topographically confined to troughs 200 000 km 2 the total average erosion is estimated at 440 530 m average erosion rate is 0 6 0 8 mm yr and average sedimentation rate on the continental slope is 18 22 cm k y the amount of erosion was mainly determined by the duration of the glaciations and the location velocity and basal properties of the ice streams in total glacial erosion of the troughs has been relatively high throughout the last 2 7 m y at 1000 1100 m for the banks erosion is inferred to have increased from ca 2 7 ma to a peak between 1 5 and 0 7 ma subsequently little erosion occurred in these areas which implies a total of 500 650 m of erosion compared with other high latitude areas our rates are among the highest so far reported this comparison also demonstrates that there have been large variations in the rate of sediment delivery to the glaciated continental margins

under pressure clastic dykes in glacial settings abstract clastic dykes are widespread in glacial settings and we provide examples from switzerland patagonia iceland and the antarctic ranging in age from tertiary to recent on the basis of these examples we establish the general characteristics of clastic dykes and proceed to establish the direction of propagation on sedimentological grounds micromorphological analysis reveals that sedimentation in the dykes is ruled by pressure gradients and that ordinary sedimentological rules do not apply clastic dykes act like safety valves in the subglacial hydraulic system their development depends on specific subglacial conditions like water volume and pressure the nature of the bed sediments or bedrock and the hydraulic properties of the bed a number of scenarios for clastic dyke development are presented as there is not just one set of conditions under which they form development of clastic dykes affects glaciodynamics like velocity and surging and landform formation like till thickness and bedrock disruption

estimating organic maturity from well logs upper cretaceous austin chalk texas gulf coast abstract the austin chalk is both a source rock for oil and a fractured reservoir and the evaluation of its organic maturity from well logs could be an aid to exploration and production geochemical and core measurements have shown three zones of organic maturity for source materials 1 an immature zone above 6000 ft 2 a peak generation and accumulation zone from 6000 to 7000 ft and 3 a mature expulsion and migration zone below 7000 ft the response of common well logs identifies these zones true resistivity rt is low in the immature zone increases to a maximum in the accumulation zone and decreases to intermediate values in the migration zone density and neutron porosities are different in the immature zone but are nearly equal in the accumulation and migration zones correlations with conventional core analyses indicate that rt values between 9 and 40 ohm m in the migration zone reflect a moveable oil saturation of 10 to 20 in the rock matrix the moveable saturation provides oil from the matrix to fractures and is essential for sustained oil production therefore the log evaluation of moveable oil could be important in exploration

the development of cavities and clastic infills along fault related fractures in tertiary basalts on the ne atlantic margin field based geological observations have revealed the hitherto unrecognised development of post magmatic brittle deformation structures cutting tertiary volcanic rocks in the faroe islands these faults and fractures are characteristically associated with different styles of clastic sedimentary infill including 1 0 3 1 0 m thick clastic units infilling open fractures formed along pre existing steeply dipping to sub vertical faults 2 0 1 0 6 m thick sub horizontal clastic units displaying internal features consistent with deposition from flowing water passing through complex open subterranean cavity systems within fractured basalts 3 anastomosing mm scale and planar dm scale clastic intrusion features mobilised and emplaced during transient fault related overpressuring events along pre existing fractures cutting the surrounding volcanic units the infill features provide evidence for the existence of sustained open cavities in the sub surface the clastic materials are commonly internally affected by later fault related deformation and lack mineralisation unlike all preceding faulting episodes in the faroes region perhaps reflecting their near surface development we believe structures equivalent to these features may occur widely in other parts of the ne atlantic margin particularly along the outer arcs of gentle regional scale fold hinges the uncemented fracture hosted clastic infills potentially represent important fluid migration pathways within the otherwise low permeability cenozoic volcanic sequences of the ne atlantic region

examination of avo responses in the eastern deepwater gulf of mexico exploration programs in deepwater tertiary basins e g the gulf of mexico typically rely on bright spot and amplitude variation with offset avo technology to help identify oil and gas charged sands the reliance on these attributes along with the high cost of exploration programs in deepwater environments has driven the need to examine the limitations of these technologies and to build robust models for the conditions under which avo is useful as a fluid and or lithology indicator we build subregional avo background trends for both brine and gas saturated sands from several wells from the eastern deepwater gulf of mexico these trends are built from the depth dependencies of velocities and densities for both shale and sands brine saturated simple models of avo gradient and intercept are constructed as a function of depth below the mud line sand and shale properties show little velocity contrast justifying the interpretation of these data in the context of linearized avo models in addition

quantification of the magnitude of net erosion in the southwest barents sea using sonic velocities and compaction trends in shales and sandstones abstract during specific intervals within mesozoic and cenozoic times several areas of the southwestern barents sea were subjected to uplift and erosion areas with missing shallow stratigraphic interval sections and major erosion can be seen at several places along interpreted regional profiles in the southwestern barents sea a new normal compaction trend nct for two selected shale and sandstone dominated lithologies has been constructed based on sonic logs in the southwestern barents sea the shale dominated nct is calibrated to the cretaceous shales in the northern north sea and norwegian sea and applied to the cretaceous shales of the barents sea the sandstone dominated nct is calibrated to the lower jurassic are formation of the norwegian sea and applied to the lower jurassic upper triassic coastal plain section in the barents sea by utilising the nct model the study estimates net apparent erosion in 28 selected barents sea wells based on comparison of sonic log velocities a net apparent erosion map of the study area was constructed by gridding of the well values the accuracy of the map is limited in areas with little well control such as in the northwest where the east west transition into the southwestern barents sea region is poorly constrained with that in mind the map clearly shows two regional trends which dominate the erosion pattern in the study area an increasing amount of erosion towards the north and a sharp decrease of erosion westwards of the hinge zone into the southwestern barents sea the highest erosion estimates are observed towards svalbard with values up to 2500 m the results of this study can be further utilized in petroleum system studies in the eroded areas

tectonostratigraphic modelling of cenozoic uplift and erosion in the south western barents sea abstract cenozoic subsidence patterns in the south western barents sea punctuated by periods of uplift and erosion deviate from thermal subsidence patterns predicted by stretching models of basin formation three regional seismic lines crossing the south western barents sea show that a substantial amount of erosion occurred at the shelf whereas at the margin a thick wedge of cenozoic sediments has been observed quantitative basin modelling of the profiles allows different mechanisms for erosion and uplift to be tested the modelling shows that the palaeocene early eocene flank uplift during rifting and late neogene intraplate stresses superimposed on a middle miocene sea level change and pliocene quaternary de glaciation play a major role in the development of the late cenozoic stratigraphy stress induced uplift of flank areas could augment the regional uplift of scandinavia possibly leading to climatic changes such as the onset of cooling and glaciation intraplate stresses related to plate boundary processes in the north atlantic realm also have important implications for the depth of the hydrocarbon window in the south western barents sea

dike filled extensional structures in cenozoic deposits of the kleszczow graben central poland abstract the origin and development of the cenozoic kleszczow graben were strongly influenced by a pre existing fault pattern within the permian mesozoic bedrock dike filled fractures penetrating neogene quaternary deposits analysed in the opencast belchatow browncoal mine follow extensional structural patterns parallel to the axes of the local anticlinal forms established or rejuvenated in the quaternary these structures are particularly well developed along the fold crests the spacing and structural features of the fractures and normal faults are explained in terms of the tensile stress operating in beds subjected to folding the main localities of the quaternary folds precisely align with segments of two deep seated reverse faults the kleszczow kodr b fault and the gomunice piaski fault both are nw se orientated dislocations along a hinge zone of the laramide ekinsko anticline subcropping the cenozoic graben infill in the open mine the origin of the quaternary folds as fault overlying folds is attributed to a young block uplift on the ekinsko anticline area which is well recorded by a strong reduction in thickness of the cenozoic sediments the quaternary succession is reduced in thickness twice as much as the neogene the successive stages of quaternary reactivation of the ekinsko anticline during the cromerian through the late saalian with diminishing intensity are believed to be correlatable with the sequence of glacial rebound events coupled with mobility of the deep rooted fault zone

time depth relationships for multilayer depth conversion the conversion of seismic time to depth through the use of analytical functions has been a common procedure in seismic work for many decades with the exception of recent examples dealing with the linear function none of the published time depth relationships corresponding to these functions is applicable to multilayer depth conversion the present work redresses this situation it presents formulae applicable to multilayer depth conversion for a large number of analytical functions the derivation is based on a procedure generally similar to that presented by japsen 1993 most of the functions considered date back to a publication by kaufman in 1953 and earlier publications a number of other functions hitherto not known in the industry are also presented

palaeoenvironmental interpretation of an ice contact glacial lake succession an example from the late devensian of southwest wales uk abstract during the late devensian late weichselian glaciation a number of large proglacial lakes developed in dammed river valleys along the southwest coast of wales u k this paper presents sedimentological data together with a digital terrain model to establish the sedimentation history dynamics and evolution of the largest lake glacial llyn lake teifi buried valley fill sequences within the margins of the former lake basin reveal a thick succession of glaciolacustrine muds which coarsen upward into or are locally abruptly overlain by proximal deltaic subglacial and glaciofluvial deposits sediment delivery pathways represented in the lacustrine succession include gravity flows suspension settling deltaic aggradation and iceberg rafting the latter indicating ice contact conditions the lacustrine muds are variably deformed with a range of syn and post depositional structures some of which indicate subglacial deformation associated with overriding of the lacustrine succession syn depositional structures indicate high sedimentation rates which may explain an absence of bioturbation structures the overall coarsening upward succession and cap of subglacial and or glaciofluvial deposits support recent theories suggesting that glacial llyn teifi formed during glacial advance there is no evidence to support glaciomarine conditions of sedimentation in this area of the irish sea basin

evolution of the cenozoic sedimentary wedge during rifting and seafloor spreading west of the stappen high western barents sea abstract the cenozoic sedimentary wedge west of the stappen high is divided into five main stratigraphic units from oldest to youngest these are unit r unit b unit tec unit ted and unit tee unit r was deposited in a faulted relatively deep marine basin prior to the onset of seafloor spreading in the northernmost part of the norwegian greenland sea the unit was probably deposited from early eocene to early oligocene time with the stappen high as a major source area the base of unit b represents the onset of a second episode of faulting erosion and subsidence west of the stappen high the unconformity is probably related to the early oligocene anomaly 13 change in relative plate movements to a more west northwest trend causing rifting and later seafloor spreading in the northern norwegian greenland sea a period of heavy erosion on the paleocontinental slope and shelf break occurred in mid miocene time 15 5 ma the base of unit tec the relatively deep erosion west of the stappen high was probably related to compression and uplift along northeast southwest oriented faults combined with a period of low eustatic sea level the mid miocene to intra pleistocene parts of the cenozoic sedimentary wedge units tec and ted are dominated by complex lowstand fan deposits and prograding sequences deposited during gradual thermal subsidence of the margin several unconformities related to relative sea level changes are identified within this part of the wedge the most important sequence boundaries are the 5 5 ma base of unit ted boundary and the intra pleistocene 0 8 ma base of unit tee boundary which probably represent the onset of extensive ice sheet formation on the barents shelf

soft sediment deformations in the kleszczow graben central poland abstract a wide variety of soft sediment deformation structures is found in the quaternary overburden of a giant open cast browncoal mine near belchatow sw of od central poland situated within a graben the deformation structures range in size from tens of meters to only millimeters it is remarkable that their size is often related to a specific type of genesis most large scale deformations appear to result from tectonic activity other structures commonly of intermediate size result from exogenic processes such as glaciotectonism and overburden induced diapirism penecontemporaneous and other early diagenetic deformational processes among which bioturbation and cryoturbation are commonly of small size only they are nevertheless important because their analysis allows a reconstruction of not only the depositional environment but also the deformational history of the sedimentary succession in spite of the different types of genesis many of the soft sediment deformation structures are in one way or another related to the graben activity since the tectonic conditions in the quaternary deposits within the graben are in many respects comparable to those in rift valleys the deformation structures in the graben might be considered as representative for rift valleys as well the analysis of the structures resulting in an improved insight into their genesis may thus contribute to a better understanding of the conditions to which sediments in rift valleys can be exposed