stratigraphic responses to a major tectonic event in a foreland basin the ecuadorian oriente basin from eocene to oligocene times the eocene to oligocene sediments of the ecuadorian oriente basin record two kinds of second order stratigraphic response to the tectonic evolution lower eocene shows evidences of local scale syntectonic deposits this tectonic activity can be related to right lateral convergent movements inverting pre cretaceous extensional structures upper eocene and oligocene sediments are integrated as the expression of an isostatic rebound characterizing a basin scale syntectonic deposition this response is evidenced by a reciprocal architecture of the depositional sequences identified in the sedimentary formations these data have allowed us to propose a new geodynamic model for the paleogene evolution of the oriente basin

closing of the central american seaway and neogene coastal upwelling along the pacific coast of south america abstract the final closing of the central american seaway is estimated to have occurred at ca 3 7 3 ma separating the equatorial pacific and atlantic oceans and the caribbean sea this event greatly influenced not only areas near the seaway but also the larger pacific ocean two paleoceanographic events recorded by planktonic foraminifera on the pacific coast of south america in pliocene times are considered to be responses to the closing of this ocean gateway event 1 involves an expansion of coastal upwelling in the southeast pacific event 2 involves the abrupt cooling of surface water temperatures along the coast of ecuador both events occurred around 3 5 ma coincident with the closing of the central american seaway

emplacement of the cuera and picos de europa imbricate system at the core of the iberian armorican arc cantabrian zone north spain new precisions concerning the timing of arc closure the final stages of the variscan orogeny mostly carboniferous in the western european variscan belt involved the development of the iberian armorican arc which is cored by the cantabrian zone nw iberia the cantabrian zone is the foreland of the western european variscan belt and it is interpreted to record the waning stages of the closure of the rheic ocean the distalmost tectonic units within the cantabrian zone the cuera unit and the picos de europa province were the last tectonic units emplaced at the core of the western european variscan belt orocline together they form an imbricate system and associated wedge top basins that are key to understanding the development of the orocline the emplacement of the cuera unit and the picos de europa province occurred in the latest pennsylvanian between moscovian and gzhelian times new detailed mapping together with stratigraphic sedimentologic and biostratigraphic data analysis of syntectonic successions and structural information constrain the timing and evolution of this imbricate system our analysis indicates that the thrust sheets were emplaced roughly perpendicular to previous tectonic units of the cantabrian variscan foreland fold and thrust belt most probably during the oroclinal bending of the sw european variscan belt that formed the iberian armorican arc the n s directed imbricate system was characterized by a shallow dip of the topographic surface 150 15 km and complex structure of the orogenic wedge are thought to result from the progressive increase in the dip of the basal decollement during bending of the underlying gondwana lithosphere and may reflect the closure of the iberian armorican arc

fluvial gravel facies architecture of late pleistocene age at po chue tam lantau island hong kong tectonic versus climatic control abstract a cross section of fluvial gravel deposits of late pleistocene age exposed at po chue tam lantau island hong kong contains two facies a lower facies of planar cross bedded gravel gp and an overlying facies of clast supported massive gravels gcm the gp gravels include five gravel couplets each couplet consists of a clast supported coarse gravel dominated bed and an overlying clast supported fine gravel dominated bed with a discrete bounding surface tectonic uplift predating the last interglacial transgression produced a large amount of detritus in the source area excessive peak rainfall intensity resulting from enhanced seasonality of monsoonal precipitation in the following glacial period triggered catastrophic floods which transported mature detritus in large quantities into a fault controlled piedmont basin the gp gravels were deposited by pulsating flood flows in relation to kinematic waves of particles bedload sediment was longitudinally sorted and segregated into a train of gravel sheets they draped over each other and accreted laterally due to expansion of flow producing planar cross stratifications that are characteristic of recurrent couplet style coarse fine cross beds in contrast gcm gravels were laid down as a single nearly horizontal bed by a catastrophic flood that was not subject to flow pulsation

migration of the carbonate ramp and sponge buildup driven by the orogenic wedge advance in the early stage carnian of the longmen shan foreland basin china abstract the marine carnian the maantang fm overlies a flexural forebulge unconformity and records the initial establishment drowning and migration of a carbonate ramp and sponge buildup along the forebulge margin of the longmen shan foreland basin the maantang fm is of wedge shaped geometry and is composed of oolitic and bioclastic limestones siliceous sponge reef and shale in an upward fining succession the formation shows the establishment and drowning of a distal margin carbonate ramp and sponge buildup deepening into offshore marine muds followed by progradation of marginal marine siliciclastics the formation also shows the transition from shale cratonward into carbonate rock southeastward the sponge reefs and shoal were deposited on a carbonate ramp on the distal margin of the early foreland basin the growth rate of sponge reefs is 0 04 mm yr equivalent to the rate of relative sea level rise of 0 01 0 05 mm yr the sponge buildup and oolitic shoal are divided into seven zones southeastward on the carbonate ramp along the basal unconformity their migration rate of 18 mm yr from nw to se coincides with the estimated orogenic wedge advance rate 5 15 mm yr li et al 2003 a clear indication that the advancing wedge controlled the migration rate of foreland oolitic shoal siliceous sponge reef we have inferred that the tectonic load of the longmen shan orogenic wedge led to flexural subsidence and rising relative sea level in the foreland basin located at the western margin of the yangtze craton driving the growth and subsequent drowning of the oolitic shoal sponge buildup in the early stage of the foreland basin we propose that the drowning and migration processes were the sedimentary response to the orogenic wedge advance toward the yangtze craton and to the rapid closure of the carnian songpan ganzi remnant ocean basin

truncated higher order sequences as responses to compressive intraplate tectonic events superimposed on eustatic sea level rise abstract high resolution sequence stratigraphic analysis of the lignite bearing miocene siliciclastic sequence of the salotarjan lignite formation slf has been performed by lithostratigraphic dissection of more than 1350 boreholes and by detailed analysis of well logs from more than 150 boreholes biostratigraphic data indicate that the slf represents a single 3rd order eustatic sequence namely the bur 4 of vakarcs et al vakarcs g hardenbol j abreu v s vail p r varnai p tari g 1998 oligocene middle miocene depositional sequences of the central paratethys and their correlation with regional stages sepm special publication vol 60 209 231 as for facies conditions facies models for sandy shorefaces and or wave dominated deltas can be applied twenty six parasequences have been identified and mapped in the adjacent sub basins from well log correlations the sharp based sand bodies of ps 10 and 17 were interpreted as the falling stage systems tract fsst of higher order sequences the subsequent transgressive systems tracts tst are represented by retrograding sets of 2 3 parasequences ps 11 13 18 19 based on the regional unconformity at the base and the regionally extended sharp based sand bodies three sequence boundaries sb were determined that dissect the 3rd order sequence into three higher order sequences one of the special features of the sequence is that the fssts interrupt the rapid relative sea level rises ps 9 and 16 and lie directly on the silty material of nearshore environments leading to the lack of the higher order highstand system tracts hst truncated transgressive semi cycles another characteristic is the striking basinward fore stepping of the sedimentary depocentres and that of the facies belts of the lignite seams the rapid relative sea level falls implied by the two fssts are unexpected in the context of an overall eustatic rise thus the possibility of tectonic origin of shallowing was investigated this verification was based primarily on the observations that 1 the basin was united when parasequences 1 to 13 were developed whereas 2 by the end of the sequence development the palaeozoic basement protruded to the surface dividing the basin reflecting intense tectonic events simultaneous with sequence development the fssts with the sbs above and the formation of higher order sequences can thus be regarded as sedimentary responses to syn sedimentary tectonic elevation and tilting of the basement this elevation was induced by tectonic compression and associated imbrication along a regional reverse fault that was known as the darno line the imbrication could have controlled not only the repeated relative sea level falls but also the striking fore stepping of the sedimentary depocentres and facies belts of the associated lignite seams tectonic tilting influenced not only the fssts but the subsequent early tsts as well thus lignite seams associated with the tectonically counteracted tsts are characterized by multiple seams with several accessory seams va iiia b and ia while those associated with tectonically quiescent periods are aerially extensive and solitary comparison with other coal bearing formations enhanced the importance of the fsst in the interpretation of stratigraphic truncations coal seam geometry conditions facies shiftings and stratal geometry enabling a more accurate description of syn sedimentary tectonic events

late cenozoic tectonic evolution of the southern chinese tian shan structural sedimentological magnetostratigraphic and 40ar 39ar thermochronological investigations were conducted in the southern chinese tian shan on the basis of our own mapping and earlier investigations in the area the late cenozoic southern tian shan thrust belt may be divided into four segments based on their style of deformation from west to east they are 1 kashi aksu imbricate thrust system 2 the baicheng kuche fold and thrust system 3 the korla right slip transfer system and 4 the lop nor thrust system the westernmost kashi aksu system is characterized by the occurrence of evenly spaced 12 15 km imbricate thrusts the baicheng kuche and korla systems are expressed by a major north dipping thrust the kuche thrust that changes its strike eastward to become a nw striking oblique thrust ramp the korla transfer zone the lop nor system in the eastern most part of the southern chinese tian shan consists of widely spaced thrusts all involved with basement rocks geologic mapping and cross section construction suggest that at least 20 40 km of crustal shortening with a horizontal shortening strain of 20 30 has occurred in the southern chinese tian shan during the late cenozoic these estimates are minimum because of both conservative extrapolation of the thrust geometries and partial coverage of the thrust belt by the cross sections the timing of initial thrusting is best constrained in the kuche basin where crustal shortening may have occurred at 21 24 ma the time of a major facies transition between lacustrine and braided fluvial sequences constrained in general by biostratigraphy and in detail by magnetostratigraphy this estimate represents only a minimum age as development of thrusts in the southern chinese tian shan may have propagated southward toward the foreland thus the sedimentary record only represents the southernmost and therefore youngest phase of thrusting if our estimate of timing for the thrust initiation 21 24 ma is correct using the estimated magnitude of shortening 20 40 km and shortening strain 20 30 the averaged rates of late cenozoic horizontal slip and shortening strain are 1 1 9 mm yr 1 and 2 9 4 5 10 16 s 1 respectively our reconnaissance 40ar 39ar thermochronological analysis in conjunction with earlier published results of apatite fission track analysis by other workers in the chinese tian shan suggests that the magnitude of cenozoic denudation is no more than 10 km most likely less than 5 km we demonstrate via a simple airy isostasy model that when the thermal effect on changes in surface elevation is negligible determination of the spatial distribution and temporal variation of both horizontal shortening strain and denudation becomes a key to reconstructing the elevation history of the tian shan using this simple model the loosely constrained magnitude of crustal shortening strain and denudation in the southern chinese tian shan implies that it may have been elevated 1 0 2 0 km since the onset of cenozoic thrusting

numerical modelling of drainage basin evolution and three dimensional alluvial fan stratigraphy abstract a forward numerical model is presented to study the effects of bedrock erodability thrust displacement rate pulsating tectonic activity and sea level fluctuations on drainage basin morphology and stratigraphy of large alluvial fan systems a low value of the bedrock erodability coefficient k b 0 5 10 4 year 2 3 vs thrust rate 2 0 m ky is associated with a time lag between cessation of tectonic activity and maximum sedimentation rates observed on the alluvial fans applying higher k b values ranging between 1 0 and 8 0 10 4 year 2 3 results in higher sediment yields due to more rapid headward catchment erosion and elaborate sideways branching of drainage networks pulsating tectonic activity is reflected in a stratigraphic alternation of prograding and retrograding alluvial fan gravels during tectonic activity fan gravel fronts and coastlines retreat because catchment yields are insufficient to fill the accommodation space created by the flexural response due to thrust loading phases of tectonic quiescence and cessation of flexural subsidence are indicated by progradation of the gravel front depending on the position in the basin the lag time for arrival of the gravel associated with tectonic cessation is several tens to hundred thousands of years a combination of pulsed tectonic activity with sinuous sea level fluctuation leads to a more complex stratigraphic pattern in that case stratigraphic response to tectonic pulses is masked by a similar but higher order frequency stacking pattern especially in the more distal parts

episodic uplift of the tianshan mountains since the late oligocene constrained by magnetostratigraphy of the jingou river section in the southern margin of the junggar basin china 1 thick cenozoic sediments in the southern margin of the junggar basin accumulated in response to the uplift and deformation of the tianshan mountains to better constrain this mountains tectonic history we report a detailed magnetostratigraphic study of the jingou river section located in the northern piedmont of the tianshan mts a total of 1133 samples were used to establish the magnetostratigraphy of a more than 3000 m thick section from the exposed base of the anjihaihe formation to the middle of the xiyu formation two vertebrate fossil sites and a good correlation with the ck95 geomagnetic polarity timescale suggest that the section was deposited from 30 5 to 4 6 ma and the age of the top of the xiyu formation is 2 6 ma based on an extrapolation of the sedimentation rates our results show that significant increases in sedimentation rates as well as notable changes in depositional environments occurred at 26 22 5 ma 13 11 ma and 7 ma which represent the initial uplift of the tianshan mts and two subsequent rapid uplift events in addition changes in sedimentation rates imply that the uplift of the tianshan mts was episodic and relatively short with intervals of intensified deformation with long periods of tectonic weakness or quiescence

sedimentological constraints on the evolution of the cordilleran arc new insights from the sonsela member upper triassic chinle formation petrified forest national park arizona usa the sonsela member of the upper triassic chinle formation in petrified forest national park arizona forms a distinctive part of an extensive fluviolacustrine complex that blanketed the colorado plateau region and surrounding areas upper triassic sediments were deposited within a continental backarc setting synchronous with the development of the cordilleran magmatic arc although the chinle formation was derived from a broad variety of source terranes petrographic and geochemical data clearly fingerprint the cordilleran arc as a region important to provenance the sonsela member exhibits a stratigraphically abrupt change in depositional style and sedimentary architecture that likely reflects the dynamics of the evolving backarc fluvial system and syndepositional arc magmatism the stratigraphic boundary between the two disparate depositional styles is marked by a laterally persistent red silcrete horizon that is also associated with a biostratigraphically significant faunal turnover the lower sonsela member a coarse grained assemblage dominated by persistent sheet sandstone and conglomerate bodies reflects a coarse grained progradation of sediment that suggests low rates of dynamic subsidence and high rates of sediment input the upper sonsela member characterized by an overall finer grained assemblage and ribbon sand bodies with an increased proportion of encasing mudstone reflects an increasing rate of basin subsidence that likely persisted throughout the deposition of the overlying petrified forest member these packages reflect a sharp change from lower to higher sinuosity river systems that closely coincides with the increased rate of subsidence across the regional stratigraphic marker previous studies have suggested the importance of the silcrete horizon as a key biostratigraphic marker associated with a significant faunal turnover this study supports the hypothesis that this horizon may represent a regional unconformity as opposed to local channeling perhaps the product of an abrupt change in basin geometry followed by an increase in basin subsidence because the sonsela member is the stratigraphically lowest unit of the chinle formation dominated by volcanic clastic detritus on the colorado plateau architectural analysis of the sonsela member serves as the most reliable indicator of short term fluctuations in arc dynamics of the poorly preserved and disjointed mesozoic portion of the cordilleran magmatic arc

basin scale stratigraphic architecture and potential paleocene distributive fluvial systems of the cordilleran foreland basin alberta canada abstract the paleocene paskapoo formation in western canada is composed of several hundred meters of fluvial strata that were deposited in an actively subsiding retro arc foreland basin adjacent to the southern canadian cordillera here we utilize newly available subsurface data from down hole gamma ray well logs to reconstruct the large scale fluvial stratigraphy and depositional history of the paskapoo formation in the central portion of the cordilleran foreland basin in alberta paleocene fluvial strata in this region contain several notable characteristics including variable degrees of channel sandstone amalgamation regionally variable stratigraphic architecture and a large fan shaped sandstone unit that emanated from the adjacent fold thrust belt fluvial channel sandstone bodies are abundant and amalgamated near the base of the formation in the southern portion of the basin but become less apparent in the northernmost 100 km of the basin the middle interval of the paskapoo formation characterized by abundant mudstone with isolated channel sandstone bodies is prevalent across the entire study area the upper portion of paskapoo formation is dominated by a large 5000 km2 north northwest trending laterally continuous sandstone in the northern portion of the basin that abuts against the fold thrust belt and fans outward into the basin this feature is interpreted as either a distributive fluvial system or a fixed outlet river system that experienced repeated avulsions this area of the fold thrust belt may be the site of a long lived fluvial outlet the variable degree of sandstone amalgamation in the paskapoo formation suggests two different modes in the relative ratio of accommodation to sediment supply periods of rapid subsidence likely associated with thrust emplacement in the adjacent fold thrust belt resulted in mudstone dominated successions with isolated sandstone bodies whereas tectonically inactive periods associated with less subsidence resulted in amalgamated sandstone units the principal stratigraphic features reconstructed from the data in this area can be used to better understand and predict fluvial stratigraphy within other foreland basins

paradox of downstream fining and weathering rind formation in the lower hoh river olympic peninsula washington although downstream fining of clasts is typical in modern and ancient river systems the hoh river a cobble and boulder bed river in washington state contains surprisingly little downstream fining of the coarsest tail of the grain size distribution along its lower 63 km mean rate of fining of the coarsest size fraction is only 0 24 mm km barely significant given uncertainties in measurement in addition these same clasts have weathering rind thicknesses that change very little along the length of the river they decrease by 0 01 mm km because weathering rinds are well developed in this setting and both tumbler studies and field observations show that abrasion of weathering rinds greatly accelerates clast diminution there seems to be a paradox between predicted and observed downstream fining rates field study shows that detritus is constantly being resupplied to the river by erosion of late glacial materials along the river9s cutbanks and tributaries the clasts supplied range in size but include abundant coarse grains with very thick weathering rinds the continuous resupply of grains strongly attenuates the rate of downstream fining despite the fact that these weathered grains abrade relatively rapidly thus the dominance of reworked glacial debris overwhelms any processes by which grains are reduced in size in the modern river these results suggest that relatively infrequent glaciation can have a long lived effect on river sedimentation

thrusting and gravel progradation in foreland basins a test of post thrusting gravel dispersal the use of gravels as syntectonic indicators of thrusting has recently been questioned by foreland basin models that assign gravels to a post thrusting interval of progradation except in very proximal areas on the basis of precise temporal control provided by magnetostratigraphically dated sections the history of gravel progradation after a major thrusting and uplift event in the northwestern himalaya is shown to be a virtually syntectonic phenomenon despite considerable crustal subsidence driven by a thick skinned thrust gravels prograded approximately 70 km during a 1 5 m y long thrusting event by 3 m y after the start of thrusting gravels extended more than 110 km into the basin although delayed gravel progradation appears appropriate for many rocky mountain foreland basins it is clearly not valid for the himalaya the authors attribute the difference in depositional response between these basins to difference in the quantity of sediment supplied to them sediment starved vs overfilled the availability of resistates in the source area and the size of the antecedent drainage

far traveled latest cretaceous paleocene conglomerates of the southern rocky mountains usa record of transient laramide tectonism a solitary thin widespread conglomerate is found in latest cretaceous paleocene sections in each of these laramide basins of the southern rockies the table cliff northwestern kaiparowits plateau and uinta basin utah the piceance creek and denver basins colorado and the san juan basin new mexico these units are unusual compared to typical syntectonic conglomerates in that they occur as a thin interval underlain by a disconformity are far traveled across most of the length of their basins generally reflect a change in dispersal direction relative to underlying deposits and were deposited during a period of reduced subsidence all units were deposited well after local initiation of the laramide orogeny but within 8 m y of each other however each conglomerate unit was separately derived from individual source areas and is not part of a once continuous gravel sheet similar widespread conglomerate units of this age are apparently absent in other rocky mountain laramide basins previous studies postulate the shallow subduction of an oceanic plateau the conjugate shatsky rise beneath the u s cordillera during the time interval of conglomerate deposition the distribution timing and dispersion directions of the far traveled conglomerates are grossly consistent with vertical motions and surface tilting along the transport path of the oceanic plateau an exact match of conglomerate timing differs from previously proposed models but uncertainties in timing of deposits and the lack of constraints on the shape and structure of the subducted plateau preclude our ability to further refine the comparison elsewise local tectonic activity climate change and sea level fluctuations fail to explain the observed spatiotemporal pattern hence we suggest that these deposits record a transient mantle derived tectonic effect traversing the rocky mountain region and demonstrate the utility of stratigraphy as a record of subtle tectonic events

foreland basin sequence response to collisional tectonism as structural salients and recesses evolved from reentrants and promontories along the collisional continental margin associated with the taconic orogeny cross strike structural features provided a mechanism for transferring zones of relative subsidence and uplift across the appalachian foreland basin the regional distribution of lower silurian clastic sequences reflects this tectonic influence thick aggradational sequences formed in areas corresponding to salients in response to high rates of sediment supply and creation of sediment accommodation as the rate of sediment supply exceeded the rate of accommodation added shoreline progradation onto the distal foreland ramp produced upward coarsening sequences in areas of structural recesses accommodation was created by erosion during sea level fall and lowstand upward fining sequences formed as the topographic lows were filled during subsequent sea level rise results from this investigation indicate that predictable variations in foreland basin deposition and in the resulting stratigraphic pattern occur along regional tectonic strike as well as in the dip direction the thickness of foreland ramp sequences is greater in areas of salients than in recesses whereas the ratio of sandstone to total thickness is greater in the recesses aggradational sequences grading laterally into upward coarsening progradational sequences of the distal ramp characterize areas of relative subsidence which provides a mechanism for creating sediment accommodation in contrast deep erosion common unconformities and incised valley fills are present in areas corresponding to recesses where the rate of eustatic fall commonly exceeds the subsidence rate these along strike stratigraphic variations in response to collisional tectonism should be considered in the interpretation of other foreland basin successions

evolution of miocene fluvial environments eastern potwar plateau northern pakistan the miocene pliocene siwalik group records changing fluvial environments in the himalayan foreland basin the nagri and dhok pathan formations of this group in the eastern potwar plateau northern pakistan comprise relatively thick tens of metres sandstone bodies and mudstones that contain thinner sandstone bodies metres thick and palaeosols thick sandstone bodies extend for kilometres normal to palaeoflow and are composed of large scale stratasets storeys stacked laterally and vertically adjacent to each other sandstone bodies represent single or superimposed braided channel belts and large scale stratasets represent channel bars and fills channel belts had widths of km bankfull discharges on the order of 103 cumecs and braiding parameter up to about 3 individual channel segments had bankfull widths maximum depths and slopes on the order of 102 m 101 m and 10 4 respectively and sinuosities around 1 1 these rivers are comparable to many of those flowing over the megafans of the modern indo gangetic basin and a similar depositional setting is likely thin sandstone bodies within mudstone sequences extend laterally for on the order of 102 m and have lobe wedge sheet and channel form geometries they represent crevasse splays levees and floodplain channels mudstones are relatively bioturbated disrupted and represent mainly floodbasin and lacustrine deposition mudstones and sandstones are extremely disrupted in places showing evidence of prolonged pedogenesis these mature palaeosols are m thick and extend laterally for km lateral and vertical variations in the nature of their horizons apparently depend mainly on deposition rate the 500 m thick nagri formation has a greater proportion and thicker sandstone bodies than the overlying 700 m thick dhok pathan formation the thick sandstone bodies and their large scale stratasets thicken and coarsen through the nagri formation then thin and fine at the base of the dhok pathan formation compacted deposition rates increase with sandstone proportion 0 53 mm year for nagri 0 24 mm year for dhok pathan and palaeosols are not as well developed where deposition rates are high within both formations there are 100 m scale variations representing on the order of 105 years in the proportion and thickness of thick sandstone bodies and tens of m scale alternations of thick sandstone bodies and mudstone sandstone strata that represent on the order of 104 years formation scale stratal variations extend across the potwar plateau for at least 100 km although they may be diachronous however 100 m and smaller scale variations can only be traced laterally for up to tens of km alluvial architecture models indicate that increases in the proportion and thickness of thick sandstone bodies can be explained by increasing channel belt sizes mainly average deposition rate and avulsion frequency on a megafan comparable in size to modern examples 100 m scale variations in thick sandstone body proportion and thickness could result from regional shifts in the position of major channels possibly associated with fan lobes on a single megafan or with separate megafans however such variations could also be related to local changes in subsidence rate or changes in sediment supply to the megafan system formation scale and 100 m scale stratal variations are probably associated with interelated changes in tectonic uplift sediment supply and basin subsidence increased rates of hinterland uplift sediment supply and basin subsidence recorded by the nagri formation may have resulted in diversion of a relatively large river to the area alternatively changing river sizes and sediment supply rates may be related to climate changes affecting the hinterland possibly linked to tectonic uplift climate during deposition of the siwalik group was monsoonal although the deposits contain no direct evidence for climate change independent evidence indicates global cooling throughout the miocene and the possibility of glacial periods e g around 10 8 ma corresponding to base of nagri formation if the higher himalayas were periodically glaciated a mechanism would exist for varying sediment supply to megafans on time scales of 104 105 years although eustatic sea level changes are related to global climatic change they are not directly related to siwalik stratigraphic changes because the shoreline was many 100 km away during the miocene

tectonic history of the altyn tagh fault system in northern tibet inferred from cenozoic sedimentation the active left slip altyn tagh fault defines the northern edge of the tibetan plateau to determine its deformation history we conducted integrated research on cenozoic stratigraphic sections in the southern part of the tarim basin fission track ages of detrital apatites existing biostratigraphic data and magnetostratigraphic analysis were used to establish chronostratigraphy whereas composition of sandstone and coarse clastic sedimentary rocks was used to determine the unroofing history of the source region much of the detrital grains in our measured sections can be correlated with uplifted sides of major thrusts or transpressional faults implying a temporal link between sedimentation and deformation the results of our studies together with existing stratigraphic data from the qaidam basin and the hexi corridor suggest that crustal thickening in northern tibet began prior to 46 ma for the western kunlun shan thrust belt at ca 49 ma for the qimen tagh and north qaidam thrust systems bounding the north and south margins of the qaidam basin and prior to ca 33 ma for the nan shan thrust belt these ages suggest that deformation front reached northern tibet only 10 5 m y after the initial collision of india with asia at 65 55 ma because the aforementioned thrust systems are either termination structures or branching faults of the altyn tagh left slip system the altyn tagh fault must have been active since ca 49 ma the altyn tagh range between the tarim basin and the altyn tagh fault has been a long lived topographic high since at least the early oligocene or possibly late eocene this range has shed sediments into both the tarim and qaidam basins while being offset by the altyn tagh fault its continuous motion has made the range act as a sliding door which eventually closed the outlets of westward flowing drainages in the qaidam basin this process has caused large amounts of oligocene miocene sediments to be trapped in the qaidam basin the estimated total slip of 470 70 km and the initiation age of 49 ma yield an average slip rate along the altyn tagh fault of 9 2 mm yr remarkably similar to the rates determined by gps global positioning system surveys this result implies that geologic deformation rates are steady state over millions of years during continental collision

anatomy and evolution of a lower cretaceous alluvial plain sedimentology and palaeosols in the upper blairmore group south western alberta canada the lower cretaceous albian upper blairmore group is part of a thick clastic wedge that formed adjacent to the rising cordillera in south western alberta regional transgressive intervals are superimposed on the overall regressive succession alluvial conglomerates sandstones and mudstones were deposited in east north eastward draining fluvial systems orientated transverse to the basin axis five facies associations have been identified igneous pebble conglomerate thick sandstone interbedded lenticular sandstone and mudstone thick mudstone with thin sandstone interlayers and fossiliferous sandstone and mudstone the facies associations are interpreted as gravelly fluvial channels sandy fluvial channels sand dominated floodplains mud dominated floodplains and marine shoreline deposits respectively five types of palaeosols are recognized in the upper blairmore group based on lithology the presence of pedogenic features clay coatings root traces ferruginous nodules slickensides carbonate nodules and degree of horizonization the regional distribution of the various types of palaeosols enables a refinement of the palaeoenvironmental reconstruction permitting an assessment of the controls on floodplain evolution in source proximal areas palaeosol development was inhibited by high rates of sedimentation in source distal locations poor drainage resulting from high watertables low topography and lower rates of sedimentation also inhibited palaeosol development the best developed palaeosols containing bt horizons occur in intermediate alluvial plain positions tectonic hinge zone where the floodplains were most stable due to a balance between sedimentation erosion and subsidence rates extrapolating from the upper blairmore group suggests that the tectonic hinge zone of continental foreland basins can be established by palaeosol analysis at the hinge zone soil development is controlled primarily by climate and tectonics and their effect on sediment supply whereas closer to the palaeoshoreline relative sea level fluctuations resulting in poor drainage may have a more significant influence

foreland basin subsidence driven by topographic growth versus plate subduction the subsidence of foreland basins is classically thought to accelerate with time however a synthesis of data from numerous foreland basins recognizes a wide range of signals and rates our analysis investigates the influence of two broadly ubiquitous controlling factors 1 the upward and outward growth of mountain topography and 2 the subduction velocity of the underthrust lithosphere these two factors have contrasting subsidence signals the former tends to be slow and decelerates while the latter is more rapid and accelerates the geodynamic setting of a foreland basin determines the degrees to which these components dominate the final signal of tectonically induced subsidence in small collisional mountain ranges the common asymmetry of subduction defines a pro and a retro foreland basin based on model experiments and the synthesized data we demonstrate that pro foreland basins exhibit short lived usually 0 05 km m y 1 accelerating subsidence histories recording only a portion of the orogenic history of the mountain range type examples are the carpathian foredeep and the north alpine foreland basin in contrast retro foreland basins are characterized by relatively slow 0 05 km m y 1 protracted usually 40 m y subsidence that records the majority of the orogenic history a good example is the aquitaine foreland basin retro arc foreland basins such as the alberta basin appear comparable to collisional retro foreland basins examples where there is more protracted subsidence appear to record greater evidence of episodic loading and unloading as the topography of the range grows or shrinks in response to the balance between crustal thickening and erosion rates

the transition from passive to active margin sedimentation in the cantabrian mountains northern spain devonian or carboniferous abstract in the cantabrian mountains of northern spain a cambrian through pennsylvanian sedimentary succession is preserved that was deformed during the hercynian orogenic cycle within this succession silurian and devonian strata indicate sedimentation on a passive margin pennsylvanian deposits are the product of syndeformational uplift and erosion of the newly forming orogen and were deposited in a rapidly filling foreland basin in front of the orogenic belt the intervening mississippian succession is strongly condensed and consists of coarse grained sandstones mantling a regional angular unconformity crinoidal limestones followed by phosphatic black shales nodular limestones and siliceous shales this succession shows abundant erosional surfaces and mass flow deposits and it is here interpreted as the initial starved foreland basin fill if this interpretation is correct the foreland basin system had already developed during the late devonian much earlier than hitherto assumed its initiation can be correlated to processes in the internal zones of the iberian hercynian orogen where during the late devonian there is the change from subduction of oceanic lithosphere to intended continental subduction its blocking and the subsequent collisional type deformation as a direct long distance effect of these changes in the plate tectonic regime the cantabrian hercynian foreland basin was created

three dimensional structural reconstruction of a thrust system overprinted by postorogenic extension wah wah thrust zone southwestern utah extensional collapse after crustal shortening is a common process in mountain belts the resulting overprinting of structures can make structural reconstruction quite challenging especially where both extensional and shortening structures are geometrically complex we address this challenge in a segment of the sevier thrust belt located in the basin and range province of southwestern utah the wah wah mountains are unusual because all known thrusts in this part of the sevier belt are exposed in a single range and therefore it is unnecessary to correlate thrusts between ranges in order to assemble a complete cross section across the thrust belt however the thrusts are overprinted by a three dimensional array of extensional faults that make conventional two dimensional cross section restoration methods inadequate on the basis of new mapping in the blawn mountain rose spring canyon area and published maps of adjacent areas we re construct the geometry and kinematics for part of the sevier thrust stack which we here refer to as the wah wah thrust system by iterative restoration and balancing of a grid of three dimensional cross sections we removed the effects of tertiary extensional faulting and then restored the thrust geometry the results of the final restoration indicate that the structure of the wah wah thrust system is more complex than previously recognized and comprises a roof thrust above a stack of two major and four minor footwall imbricates minimum total shortening across the thrust system is 38 km the internal evolution of the thrust system appears to have been mainly backward breaking in contrast to the overall regional forward breaking sequence of the sevier thrust belt along strike cross section restorations indicate that the roof thrust accumulated at least 15 km of slip after emplacement of all footwall imbricates we speculate that bleeding off of pore pressure from the decollement by fluid discharge along ramp thrusts caused incremental strengthening and abandonment of the frontal area of the decollement and therefore led to development of the backward breaking thrust sequence

early miocene basin evolution in northern hungary tectonics and eustasy abstract it is presumed that the oligocene early miocene basin evolution in northern hungary was primarily driven by compressional tectonics producing a major second order transgressive regressive facies cycle the early miocene basin evolution is best understood in terms of molasse sedimentation in an overfilled flexural basin during this time the gradual cessation of thrusting in the adjacent west carpathian thrust fold belt resulted in its uplift and subaerial exposure significant amounts of sediment were delivered to the flexural basin filling it up to sea level during the late stage uplift of the flexural basin a shallow marine depositional environment developed as a result of isostatic rebound and signals of third order eustatic sea level changes can be revealed sedimentological studies of outcrops of the lower miocene succession proved marked changes in facies along the gently dipping distal southeastern flank of the basin a sudden inception of shallow marine coarse elastics on top of siltstones deposited in significantly deeper water may have been the result of a third order eustatic sea level fall shortly before the burdigalian at the boundary of the nn1 nn2 nannofossil zones during the resulting lowstand various tide dominated facies aggraded which were subsequently flooded by the burdigalian sea level rise the highstand is represented by upwards shallowing progradational units due to accelerating sedimentation and or tectonic uplift the typically elongated and narrow flexural basin characterized by small water depth had dimensions which were particularly suitable for the amplification of tidal motions this resulted in the deposition of tide influenced sandy sediments in contrast to examples where the evolution of a strong tidal influence is related to transgressions here such conditions developed following a drop of sea level

assessing tectonic and climatic causal mechanisms in foreland basin stratal architecture insights from the alborz mountains northern iran the southern foreland basin of the alborz mountains of northern iran is characterized by an approximately 7 3 km thick sequence of miocene sedimentary rocks constituting three basin wde coarsening upward units spanning a period of 106 years we assess available magnetostratigraphy paleoclimatic reconstructions stratal architecture records of depositional environments and sediment provenance data to characterize the relationships between tectonically generated accommodation space a and sediment supply s our analysis allows an inversion of the stratigraphy for particular forcing mechanisms documenting causal relationships and providing a basis to decipher the relative contributions of tectonics and climate inferred changes in precipitation in controlling sediment supply to the foreland basin specifically a s 1 typical of each basal unit 17 5 16 0 13 8 13 1 and 10 3 9 6 ma is associated with sharp facies retrogradation and reflects substantial tectonic subsidence within these time intervals arid climatic conditions changes in sediment provenance and accelerated exhumation in the orogen suggest that sediment supply was most likely driven by high uplift rates conversely a s 1 13 8 and 13 8 11 ma units 1 and 2 reflects facies progradation during a sharp decline in tectonic subsidence caused by localized intra basinal uplift during these time intervals climate continued to be arid and exhumation active suggesting that sediment supply was again controlled by tectonics a s 1 at 11 10 3 ma and 9 6 7 6 ma and possibly 6 2 top of units 2 and 3 is also associated with two episodes of extensive progradation but during wetter phases the first episode appears to have been linked to a pulse in sediment supply driven by an increase in precipitation the second episode reflects a balance between a climatically induced increase in sediment supply and a reduction of subsidence through the incorporation of the proximal foreland into the orogenic wedge this in turn caused an expansion of the catchment and a consequent further increase in sediment supply copyright 2013 john wiley sons ltd

crustal thickening or isostatic rebound of orogenic wedge deduced from tectonostratigraphic units in indosinian foreland basin longmen shan china abstract longmen shan is located at the boundary between the sichuan basin and tibetan plateau representing the steepest gradient of any edges of the plateau three endmember models of uplift process and mechanism have been proposed including crustal thickening crustal flow and crustal isostatic rebound here we use tectonostratigraphic units in the late triassic foreland basin to restraint uplift process and mechanism in the longmen shan during indosinian orogeny the late triassic foreland basin developed as a flexural foredeep on the yangtze passive continental margin during the indosinian orogeny the basin fill includes the maantang formation the xiaotangzi formation and the xujiahe formation and it is divided into four tectonostratigraphic units with wedge shaped or tabular cross sectional geometry by unconformities and flooding surfaces in this paper the first and third ones are wedge shaped tectonostratigraphic units and correspond to underfilled condition with basal unconformities or major flooding surfaces the high rate of subsidence and sediment accumulation coarsening upward succession and a dual sediment supply and them may link to strong active thrust loading events or the rapidly advance rate of the orogenic wedge the second and fourth ones are tabular tectonostratigraphic units and correspond to overfilled condition with the unconformity the low rate of subsidence and sediment accumulation fining upward succession a single sediment supply the mass emergence of conglomerate layers and they may be related to isostatic rebound and erosion unloading two endmember models of uplift process and mechanism in the longmen shan during indosinian cycle have been proposed by coeval late triassic sedimentary sequences in the foreland basin here 1 crustal thickening during the wedge shaped tectonostratigraphic units 2 crustal isostatic rebound during the tabular tectonostratigraphic units this two endmember models proposed in this paper may be helpful to understand the mechanism of the wenchuan earthquake

cyclic facies architecture as a key to depositional controls in a distal foredeep campanian mesaverde group wyoming usa the mesaverde group consists of a thick wedge of fluvial littoral deltaic and shallow marine clastics shed into the cretaceous western interior seaway of north america the western parts of the seaway lay within the strongly subsiding foredeep of the active sevier fold and thrust belt further to the west the study area is located east of the axis of maximum subsidence and is thus in a favourable position to record competing effects of eustasy sediment supply and thrust load induced subsidence facies and sequence analysis carried out on high quality outcrop and well log data led to the recognition of a complex depositional cycle hierarchy within the typical storm and wave dominated inner shelf shoreface strand plain and delta systems of the mesaverde

braided stream and flood plain architecture the rio vero formation spanish pyrenees early to middle miocene fluvial sandstones of the rio vero formation were studied in an area around the town of barbastro south central pyrenees spain the outstanding quality of outcrops in this area allows a three dimensional study of architectural elements six architectural elements are recognised described in detail and interpreted from three key localities seven main lithofacies were identified and sub divided into gravelly sandy and fine grained lithofacies the architectural elements and lithofacies have been combined with a hierarchy of depositional bounding surfaces to fully interpret the evolution of the depositional system at the meso and macro scale not only the different architectural elements and lithofacies of the complete braided fluvial system but also the lateral variation of the architectural elements were emphasised in this study differential tectonic movements seasonal climate change and their effect on vertical and lateral evolution of the area were the main control on basin sedimentation channel interconnection palaeocurrent patterns and consequently the fluvial architecture the presence of lateral ramp anticlines caused the fluvial system to be laterally restricted with the main channel belts being located in the areas of highest subsidence and lowest topography intervening topographic highs acted as both flood plains and lateral barriers between the main channel systems the proposed depositional model comprises broad low sinuosity perennial but seasonal moderate energy streams the sandstone architecture is dominated by channel fill and sheet sands and associated simple and more complex bars adjacent to the main channel belts fine grained sandstones siltstones and immature paleosols occur the along strike relationship between major fluvial systems and their outlets into a foreland basin has important implications for the infill of the basin and the modelling of fluvial systems along mountain belt fronts

geochemical characteristics and organic matter enrichment mechanism of black shale in the upper triassic xujiahe formation in the sichuan basin implications for paleoweathering provenance and tectonic setting abstract the first third and fifth members henceforth referred to as t 3 x 1 t 3 x 3 and t 3 x 5 respectively of the upper triassic coal bearing xujiahe formation black shale are among the most significant hydrocarbon source rocks in the sichuan basin here we present geochemical data for the upper triassic black shales from core from well ld 1 to determine their paleoenvironmental conditions paleoweathering provenance transitions and tectonic setting the v v ni vs u th v cr vs u th and ni co vs u th bivariate plots and the tfe toc ts total fe total organic carbon total sulphur ternary diagram indicate that the synsedimentary redox regime of almost all the shale samples was oxidizing ba al sr al and p ti data combined with quantitative biogenic ba data indicate that moderate high primary paleoproductivity levels prevailed during deposition the sr cu ratio and c value combined with the sedimentary features are indicative of warm humid climate conditions the ti al deposition rate proxy and decompacted sedimentation rate are positively correlated with the total organic carbon toc content according to our multiproxy approach black shale development in the xujiahe formation was mainly controlled by the primary productivity level foreland basin setting high tectonic subsidence and sedimentation rate and exhibited a limited correlation with water column redox conditions through the compilation and calculation of various weathering indices for the xujiahe black shale we suggest that caution must be taken when inferring paleoclimate characteristics based on the chemical index of alteration cia because of the influence of multiple nonweathering factors provenance sensitive elemental ratios th sc vs zr sc and co th vs la sc indicate that the clastic contribution to xujiahe black shales was of a predominantly felsic character the black shales exhibit a transition from t 3 x 1 to t 3 x 3 to t 3 x 5 whereby t 3 x 1 was primarily sourced from the proterozoic to early paleozoic strata of the qinling orogeny t 3 x 3 was primarily sourced from the neoproterozoic complex in the longmen shan and t 3 x 5 was primarily sourced from the songpan ganzi flysch strata which contributed recycled material because of folding and strong southeastward thrusting

a late archean foreland fold and thrust belt in the north china craton implications for early collisional tectonics abstract the archean north china craton is divided into the western and eastern blocks along the central orogenic belt a 1600 km long archean foreland basin and thrust belt fringes the eastern side of the central orogenic belt rocks in the orogen form tectonically stacked east vergent fold and thrust sheets including foreland basin sediments 2 50 ga ophiolitic melange and an island arc complex foreland basin sediments overlie a passive margin sequence and include a 2 50 ga deep water turbidite sequence that grades upward and westward into shallow water molasse now disposed in structurally imbricated east verging thrusts and asymmetric folds that gradually migrated craton ward with deformation uplift and erosion of the orogen there is a strong linked relationship of the formation of the foreland basin to collision of the east and west blocks of the north china craton along the central orogenic belt at 2 50 ga the qinglong foreland basin and central orogenic belt of the north china craton represents one of the best preserved archean orogen to craton transitions in the world its classic internal to external zonation and flexural response to loading demonstrate that convergent tectonics in the archean were broadly similar to phanerozoic convergent margin processes

post messinian drainage changes triggered by tectonic and climatic events eastern southern alps italy abstract the messinian quaternary history of tectonic and climatic control on sedimentation in the eastern southern alps northern italy was reconstructed using an integrated petrographic and sedimentological analysis of five sedimentary successions these units mainly consist of fluvial conglomerates of the tagliamento sequence deposited within the eastern southern alps since the upper miocene messinian salinity crisis at that time the closure of marine gateways between the atlantic ocean and the mediterranean sea caused a drop in sea level causing exchanged fluvial erosion and widening of the alpine catchments sediment composition in the upper miocene to lower pliocene units shows an abrupt change in the source areas from sediments characterized by carbonate rock fragments to detritus rich in low grade metamorphic grains in spite of tectonic activity within the eastern southern alps no major modifications in sediment supply took place during the pliocene early pleistocene time span in the middle pleistocene the first major expansion of the alpine glaciers triggered a change in drainage patterns and a marked increase in erosion rates predominantly climatic control on sedimentation in the tagliamento basin and the erosion of the carnic alps produced sediments rich in quartz siltstone and metamorphic rock fragments deposited in the upper pleistocene unit and in modern river sediments

two phase stratigraphic model of foreland basin sequences application of flexural models to nonmarine foreland basin evolution indicates that two different stratigraphic styles of basin fill may develop over time basin subsidence is most rapid during times of thrust load emplacement associated sedimentation is coarse grained immediately adjacent to the thrust front and grades rapidly into fine grained deposits that cover most of the basin the distal part of the basin may also contain deposits derived from streams that flow from beyond the basin toward the thrust belt subsequent removal of the thrust load by erosion and other processes results in flexural rebound of the thrust belt and adjacent foreland basin during this postorogenic phase of adjustment a regional unconformity develops in the proximal part of the foreland basin proximal deposits along with thrust derived sediment are redeposited in the distal foreland basin and beyond this two phase model of foreland sedimentation predicts that coarsening upward sequences in the proximal and distal parts of the basin have reciprocal significance the proximal sequence represents thrust belt advance whereas the distal sequence represents thrust belt cessation

tectonic control on sedimentary facies pattern and sediment accumulation rates in the miocene foreland basin of the southern alborz mountains northern iran 1 the southern alborz mountains of northern iran are an integral part of the arabia eurasia collision zone a magnetostratigraphic and rock magnetic investigation of the eyvanekey stratigraphic section in the southern alborz mountains reveals the spatiotemporal character of sedimentary facies migration in the alborz foreland basin the section constitutes three coarsening upward units units 1 2 and 3 comprising the upper red and hezardarreh formations our data reveal that the upper red formation was deposited between 17 5 and 7 5 ma while the depositional age of the top of the hezardarreh formation can be extrapolated to 6 2 ma slow sediment accumulation rates correlate with sedimentary facies comprising prograding coarsening upward units this is likely the result of intraforeland uplift units 1 and 2 and basin inversion probably associated with a growth syncline located in the proximal foreland unit 3 in contrast fine grained strata at the bottom of each cycle are associated with faster sediment accumulation rates testifying to enhanced flexural basin subsidence in the course of thrust loading progradation of coarse grained facies also occurred during relatively fast sediment accumulation top of unit 2 suggesting that the influx of coarse grained sediment outpaced the storage capacity of the proximal foreland thus despite an overall southward propagation of deformation into the southern alborz foreland the locus of active deformation must have migrated back and forth on a time scale of circa 0 7 to 2 ma

paleo environmental cyclicity in the early silurian yangtze sea south china tectonic or glacio eustatic control abstract the yangtze sea of the south china craton experienced strong environmental perturbations during the first 5 6 myr of the silurian the lower silurian lungmachi formation in the jiaoye 1 drillcore chongqing china records three sea level cycles stratigraphic sequences characterized by rapid deepening at the base of each cycle followed by slow shallowing each deepening event was associated with shifts toward higher marine productivity more intensely reducing bottomwater conditions reduced watermass restriction lower detrital input and enhanced siliciclastic weathering intensity we infer control by glacio eustasy in which deglacial sea level rises and concurrent climatic warming triggered the observed environmental changes shallowing was associated with renewed glaciation and characterized by the opposite set of conditions the results of this study thus provide evidence in support of continued continental glaciation during the early silurian i e following the termination of the major end ordovician hirnantian glaciation the study core also exhibits a long term shallowing trend through the entire lower silurian the origin of which may have been tectono epeirogenic uplift of the south china craton during the kwangsian orogeny

differentiating the effect of episodic tectonism and eustatic sea level fluctuations in foreland basins filled by alluvial fans and axial deltaic systems insights from a three dimensional stratigraphic forward model many studies of foreland basins have recognized a hierarchical organization in the stacking of sequences deposited by axial deltaic and alluvial fan systems the hierarchy is often explained in terms of the competing control of eustasy and pulsed tectonic subsidence and the different frequencies at which these processes operate unravelling the relative contributions of tectonic and eustatic controls on the sequence stacking pattern is a fundamental question in foreland basin analysis yet this is difficult because of the lack of independent stratigraphic evidence in this study a three dimensional numerical model is presented which aids in the interpretation of alluvial successions in foreland basins filled by transverse and axial depositional systems under conditions of variable tectonism and eustatic sea level change the tectono sedimentary model is capable of simulating the hierarchical stratigraphic response to both eustatic and tectonic forcing and is of higher resolution than previous models of foreland basin filling numerical results indicate that the onset of tectonic activity is reflected by rapid retrogradation of both depositional systems and by widespread flooding and onlap of carbonate sediments syntectonic fluvial patterns on the axial deltaic plain are dominated by bifurcating channels swiftly relocating in response to the general rise in relative sea level induced by flexural subsidence the resulting surface morphology of the axial delta is convex upwards syntectonic eustatic sea level fluctuations result in parasequence scale packages of retrograding and prograding fan and delta sediments bounded by minor flooding surfaces and type 2 sequence boundaries incised channels are rare within the syntectonic parasequences and are formed only during phases of tectonic quiescence when eustatic falls are no longer compensated by the subsidence component in the rise in relative sea level suites of amalgamating axial channels corresponding to multiple eustatic falls delineate the resulting type 1 unconformities coarse grained incised channel fills are found in the zone between the alluvial fan fringes and the convex upward body of the axial delta as the axial streams tend to migrate towards this zone of maximum accommodation

obsidian hydration dating and temperature controls in the punta negra region of northern chile abstract effective hydration temperature eht is essential for the computation of obsidian hydration dates in the atacama desert the scarcity of air temperature records combines with extremes of elevation and local temperature to encourage or even require the use of buried thermal cells to record on site mean annual temperatures compositional analysis sourcing and hydration rate development in the laboratory are also necessary especially where other dating methods are unavailable to confirm the hydration rate paleoindian or early archaic through modern obsidian dates support a human settlement pattern history derived from archaeological geomorphological studies of climatological and hydrological change

basin orogen patterns and the late triassic foreland basin conversion process in the western yangtze block china abstract due to the formation of the qinling and sanjiang orogenic belts along the northern and southwestern margins the western yangtze block experienced a complex basin orogen tectonic transformation forming a unique pattern for a basin orogen system in the late triassic that should be recorded by sediments in the sichuan basin this paper combines with regional tectonics field observations and borehole and seismic exploration data to establish the prototypes of the basins and tectonic frameworks of basin orogen from member 1 m1 to 6 m6 of the xujiahe formation during the late triassic in the western yangtze block from stage m1 to m2 a set of deltaic deposits formed and extended parallel to the qinling orogenic belt indicating that the start of the scissor type collision in the northern margin of the western yangtze block led to the development of the northern sichuan basin and songpan ganzi peripheral foreland basin meanwhile a set of deltaic deposits which occur in the southeastern sichuan basin were controlled by the uplift of the jiangnan xuefeng tectonic belt transforming into a denuded zone at that time a set of deltaic deposits developed in the southwestern part of the western yangtze block indicating the beginning of the initial stage of the related foreland basin in this area at stage m2 from stage m3 the intensive activity of orogenic belts surrounding the western yangtze block shaped the tectono sedimentary features along the margin of the western yangtze block the successive development of delta plain and alluvial fan deposits and their westward and eastward expansions respectively in the north and southwest margins of the western yangtze block reflect the uplift of the qinling and sanjiang orogenic belts while the formation of a set of deltaic deposits in the southeastern part of the western yangtze block results from the persistent uplift of the jiangnan xuefeng tectonic belt during stages m5 to m6 the lacustrine swamp deposits began expansion and became the main sedimentary facies in the western yangtze block southward and northward migrations of the aforementioned two separated foreland basins respectively controlled by qinling and sanjiang orogenic belts caused these two separated foreland basins to connect with each other and to form a single unified complex foreland basin that was controlled by these two orogenic belts these results suggest a two stage foreland basin evolution mode for the western yangtze block during the late triassic at stage i m1 to m4 two separated foreland basins developed in the northern and southwestern margins of the western yangtze block controlled respectively by the qinling and sanjiang orogenic belts during stage ii m5 to m6 these two separated foreland basins connected with each other to form a single composite foreland basin related to those two orogenic belts

geomorphic appraisals of active tectonics associated with uplift of the gohpur ganga section in itanagar arunachal pradesh india abstract the gohpur ganga section is located southwest of itanagar india the study area and its adjacent regions lie between the main boundary thrust mbt and the himalayan front fault hff within the sub himalaya of the eastern himalaya the senkhi stream draining from the north passes through the mbt and exhibits local meandering as it approaches the study area here five levels of terraces are observed on the eastern part whereas only four levels of terraces are observed on the western part the senkhi and dokhoso streams show unpaired terraces consisting of very poorly sorted riverbed materials lacking stratification indicating tectonic activity during deposition crude imbrications are also observed on the terrace deposits a wind gap from an earlier active channel is observed at latitude 27 04 42 4 n and longitude 93 35 22 4 e at the height of about 35 m from the present active channel of senkhi stream linear arrangements of ponds trending northeast southwest on the western side of the study section may represent the paleochannel of dokhoso stream meeting the senkhi stream abruptly through this gap earlier major lineament trends are observed along nne ssw ne sw and ene wsw direction the gohpur ganga section is on quaternary deposits resting over the siwaliks with angular contact climatic changes of pleistocene holocene times seem to have affected the sedimentation pattern of this part of the sub himalaya in association with proximal tectonism associated with active tectonic activities which uplifted the quaternary deposits older and younger terrace deposits seem to mark the pleistocene holocene boundary in the study area with the older terraces showing a well oxidized and semi consolidated nature compared to the unoxidized nature of the younger terraces

influence of attenuated lithosphere and sediment loading on flexure of the deep water magallanes retroarc foreland basin southern andes flexural subsidence in foreland basins is controlled by applied loads such as topography water sediment and subcrustal forces and the mechanical properties of the lithosphere we investigate the controls on subsidence observed within the upper cretaceous magallanes retroarc foreland basin of southern south america to evaluate the impact of lateral variations in flexural rigidity due to late jurassic extension conventional elastic models cannot explain the observed basin deflection and thick accumulation of deep water cenomanian turonian basin strata however models in which the lithosphere has been previously thinned and deflects under topographic and sedimentary loads successfully reproduce regional subsidence patterns results satisfy paleobathymetric observations in the magallanes basin and suggest that lithospheric thinning is necessary to produce both long wavelength and deep subsidence during late cretaceous basin evolution results indicate that elastic thickness decreases westward from 45 25 km in the distal foreland to 37 15 km beneath the foredeep these findings are consistent with a westward reduction in crustal thickness associated with the jurassic extensional history of the patagonian lithosphere our results also show that sediment loading exerts an important control on regional deflection patterns and promotes a wider region of subsidence and reduced forebulge uplift we propose that lateral variations in mechanical properties and large sediment loads restrict depocenter migration and may cause the foredeep to remain fixed for prolonged periods of time these findings confirm that loading of thinned lithosphere imposes different mechanical controls on the flexural profile and have potential implications for other retroarc foreland basins characterized by earlier extensional histories

a magnetostratigraphic age constraint for the proximal synorogenic conglomerates of the late cretaceous cordilleran foreland basin northeast utah usa

pulsed miocene range growth in northeastern tibet insights from xunhua basin magnetostratigraphy and provenance author s lease ro burbank dw hough b wang z yuan d abstract sedimentary rocks in tibetan plateau basins archive the spatiotemporal patterns of deformation erosion and associated climate change that resulted from cenozoic continental collision despite growing understanding of basin development in northeastern tibet during initial india asia collision as well as in the late miocene holocene surprisingly little is known about the intervening period a time when the plateau may have undergone fundamental tectonic changes to fill this gap we present new magnetostratigraphy from a g2300 m thick fluviolacustrine succession that spans ca 30 9 3 ma an integrated analysis of sedimentology subsidence and provenance from this section reveals the sequential pulsed erosion of multiple ranges bordering the xunhua basin emergence of the wnw trending laji shan is highlighted by a doubling of sediment accumulation rates between 24 and 21 ma and a transition to coarse allu vial facies at 20 3 ma detrital zircon u pb age spectra show that these coarse sediments came from basement terranes within the laji shan together these observations suggest accelerated growth of the laji shan and its coupled foreland basin at ca 22 ma the most rapid accumulation rates in xunhua basin occur within the finest grained strata and suggest an underfilled basin during the fastest interval of laji shan deformation growth of the laji shan occurred northward of the contemporaneous plateau margin which had been defined since ca 45 50 ma by the west qinling lying 60 km farther south hence following 20 25 m y of apparent stability the deformation front in this region jumped 60 km to the north at ca 22 ma subsequently growth of the north trending jishi shan occurred at ca 13 ma and is highlighted by an acceleration in xunhua basin accumulation rates between 12 and 9 ma as well as by a significant change in detrital zircon provenance of nearby linxia basin deposits by 11 5 ma initial growth of the wnw trending laji shan in the early miocene and subsequent growth of the north trending jishi shan 10 m y later support interpretations of a middle mio cene kinematic reorganization in northeastern tibet 2012 geological society of america

depositional models for fluvial sediments in an intra arc basin an example from the upper cenozoic tokai group in japan abstract the upper cenozoic tokai group is an example of fluvial sedimentation in the japanese intra arc region the sedimentary basin in which the group was deposited consiss of several small basement blocks the depositional models and their controlling factors of the tokai group around the east coast of ise bay are clarified on the basis of facies analysis five sedimentary facies associations are recognized in the group they represent deposits from gravelly low sinuosity trunk streams gravelly to sandy low sinuosity streams sandy low to middle sinuosity streams sandy high sinuosity streams with a muddy flood plain and sandy tributary high sinuosity streams with an extensive flood plain spatial and termporal facies distributions within the stratigraphic framework of the group show depositioal processes with a resolution of 0 5 to 1 m y synthesizing tectonic movements and volcanism depositional models were mainly controlled by syndepositional movement of small basement blocks involving collapse subsidence and tilting in particular the change in tilt direction of a block resulted in high sinuosity streams instead of low to middle sinuosity streams fluvial sedimentation controlled by volcanism is also recognized in the group thus fluvial depositional models in this intra arc basin are controlled by the interaction of tectonism and volcanism

responses of two lithosomes of lower cretaceous coarse clastic rocks to tectonism in kuqa foreland sub basin northern tarim basin northwest china abstract coarse clastic rocks developed widely at foredeep adjacent to orogene were usually regarded as the mark of renewed thrusting action however a good example from the lower cretaceous in kuqa foreland sub basin illustrated that the coarse clastic rocks developed not only in initial thrusting stage but in early quiescence stage the kuqa foreland sub basin adjacent to the south tianshan orogene lies to the north of tarim basin northwest china the lower cretaceous outcrop in the front of south tianshan orogene was identified as a filling sequence of foredeep which includes two depositional cycles of kapushaliang group and bashijiqike formation each of them presents fining upwards and then coarsening upwards sequences two lithosomes of coarse clastic rocks developed in the lower of yageliemu formation of kapushaliang group and bashijiqike formation respectively both of them are mainly composed of thick bedded massive and chaotic conglomerate with debris flow microfacies of fan delta plain the analyses on stratigraphic and depositional records for tectonism revealed abrupt sedimentary change from delta facies to fan delta facies stratal geometry transformation and reflection termination migration of truncation and top lap between the kapushaliang group and the bashijiqike formation these records indicated that foredeep subsided rapidly while forebulge uplifted in the development of kapushaliang group which coincided perfectly with lithosphere deformation during thrusting stage foredeep uplifted rapidly while forebulge subsided in the later development of bashijiqike formation which coincided with lithosphere deformation during quiescence stage of foreland basin development therefore the lower cretaceous recorded a whole episode of foreland basin evolution from earlier thrusting to later quiescence the underfilled cycle of kapushaliang group corresponding to the thrusting stage is much thick with mainly muddy and silty sediments the overfilled cycle of bashijiqike formation corresponding to the quiescence stage is thin with mainly sandy sediments the two lithosomes of coarse clastic rocks were very similar with each other in the lithology and sedimentology however the one from lower yageliemu formation is responded to the renewed thrusting but the other from the lower bashijiqike formation is responded to the lithosphere rebounding during primary quiescence stage therefore cannot only coarse clastic rocks indicated a renewed thrusting

evolution of devonian alluvial systems in an oblique slip mobile zone an example from the broken river province northeastern australia abstract the lower 1500 m of the late devonian bulgeri formation was deposited in a tectonically active foreland basin in response to a major late devonian orogeny in the broken river province northeastern australia the basin was bounded to the east by an uplifted belt of palaeozoic sedimentary and volcanic rocks that was deformed east of an active thrust zone gray creek fault to the south the basin was bounded by igneous and metamorphic basement rocks uplifted along a major oblique slip fault zone clarke river fault facies analysis and mapping of alluvial stratigraphy has resulted in the recognition of compositionally distinct coalescing axial and transverse alluvial drainage systems the axial drainage system flowed to the northeast approximately parallel to the gray creek fault and away from the clarke river fault the system drained the cratonic basement to the south and west and accumulated mainly feldspathic and quartzose sediments a lower fine grained succession and an upper coarse grained succession are recognised the lower succession rockfields alluvial system was deposited in broad sandy low sinuosity channels and semi permanent floodplain lakes these rivers drained ultimately northward into a retreating coastal plain and shallow sea that lay over the georgetown province the upper succession bulgeri alluvial system was deposited in gravelly and sandy braided rivers emanating from south of the clarke river fault the transverse distributary system stopem blockem alluvial system accumulated mainly lithic coarse grained sediments deposited in gravelly braided rivers sourced from the uplifted orogenic belt to the east these rivers flowed towards the northwest before coalescing with the axial drainage system where they changed to a northerly orientation uplifted fault blocks of devonian limestone within the basin locally contributed limestone gravel to these rivers between the coalescing axial and transverse river systems lay extensive floodplains which received a slow but compositionally mixed supply of mainly fine grained sediments long periods of weathering resulted in the development of reddened palaeosols with well developed calcrete horizons the palaeogeography and fluvial style of the lower bulgeri formation is compared to the gulf of carpentaria in northeastern australia analysis of the architecture of these alluvial systems has led to recognition of at least three subsidence driven tectonic cyclothems and this is supported by simple quantitative modelling the lower part of each cycle begins with a thin conglomeratic succession above an unconformity and is overlain by thick relatively fine grained syn tectonic alluvial facies deposited during maximum subsidence the upper part of each cycle is marked by increasingly coarse grained post tectonic alluvial facies these were deposited by gravel progradation following cessation of uplift or thrusting in the source areas and concomitant slowing of subsidence rates

tectonic sedimentology sediment systems deciphering global to local tectonics tectonic sedimentology has broad appeal because it can be applied at many time and length scales such as sedimentary consequences of changing rates of plate creation at mid ocean ridges continent continent collisions plateaux uplift active plate margins extensional rift tectonics and the birth growth and death of individual folds and faults tectonic sedimentology deals with the direct influence of neotectonics on sedimentation and basin development and with the inverse problem of reconstructing the order and development of palaeotectonic structures this review attempts to show how the scope and importance of the subject has developed over the last decade and is divided into five themes i at the largest tectonic scale constraints on mid ocean ridge activity and continent continent collisions come from a precise chemical analyses of fluid inclusions in marine halite deposits dating back to ca 550 ma b sr isotopic ratios of marine phanerozoic calcitic fossils and c chemical composition of archaean and proterozoic banded iron formations ii at regional scales constraints on the timing and extent of continental plateau uplift incision and cratonic tilting are given by a palaeoaltimetry estimates from oxygen isotope depletion in carbonate palaeosols b radiometric dating of palaeowater table speleothems and c preferential river migration iii at basin scales catchment processes are emphasized as key controls on sediment flux from tectonic uplands to sedimentary basins the inadequacy of sediment transport algorithms based on tractive stress and flow power to describe erosion incision and sediment transport during the most formative catchment hydrological events is emphasized iv rates of basin scale fault and fold growth displacement death and basement uplift are provided by application of facies analysis and sequence stratigraphy to accurately dated sediments in sedimentary basins v the effects of changing climate and varying basin base level in modifying tectonic influences on erosion and sedimentation are examined in such cases experimental and numerical modelling using multi variate parameters of subsidence rate sediment supply and sea level change can shed light on the problem future developments will undoubtedly improve such models hopefully establishing full linkage and feedback between sediment water supply and changing climate within an overall tectonic framework that may itself be changing

sedimentology of the whiteclay gravel beds ogallala group in northwestern nebraska usa structurally controlled drainage promoted by early miocene uplift of the black hills dome abstract the newly recognized whiteclay gravel beds wgb of the miocene ogallala group crop out as a narrow discontinuous ribbon of sands and gravels in dawes and sheridan counties northwestern nebraska usa the wgb are exposed in a series of municipal gravel quarries and natural exposures that define a linear trench in underlying strata at least 20 m deep and up to 300 m wide with short southeast trending reaches separating generally longer east trending sections this gravel filled trench can be recognized from the nebraska south dakota border near whiteclay nebraska southeastward to east of gordon nebraska a distance of 30 km the outcrop belt of the wgb is coincident in location and trend with the whiteclay fault zone where exposed in quarries the walls of the trench are steep sided vertical or locally overhanging polished surfaces slickensides and parallel joint sets are common in the walls of the trench near whiteclay but uncommon in those to the east the narrow belt defined by this trench is filled by stratified gravel the wgb are interpreted to have formed in response to tectonic upheaval associated with uplift of the black hills of south dakota in early miocene times fault rupture topography facilitated formation of a steep sided canyon or valley up to 20 m deep being virtually straight with sharp bends at intervals of several km an alluvial channel belt developed in the floor of the valley filling the available accommodation space with coarse sand and gravel via aggradational stacking of the deposits of successive channels and channel belts channel belts were probably braided with individual channels up to 4 m deep and a few tens of metres wide the multi storey character of the deposit indicates multiple episodes of cutting and filling the coarse grain size of the fill suggests energetic discharge with frequent bankfull flows even though the system had a relatively low gradient 0 004 an abundance of reworked fossil debris is derived from several stratigraphic units clasts of which have been identified in the fill the presence of a contemporary merychippine horse and a primitive species of the oreodont brachycrus constrain formation of the wgb to a short interval within the early miocene c 17 5 ma the mammal fauna suggests that this stream was a valuable source of water while fragments of aquatic organisms such as turtles and fish indicate perennial discharge the wgb provides a crucial window into a pluvial period in the miocene that is largely unpreserved elsewhere in the basin facilitated in part by fault rupture topography