sedimentology sequence stratigraphy and geochemical variations in the mesoproterozoic nonesuch formation northern wisconsin usa abstract we use core descriptions and portable x ray fluorescence analyses to identify lithofacies and stratigraphic surfaces for the mesoproterozoic nonesuch formation within the ashland syncline wisconsin we group lithofacies into facies associations and construct a sequence stratigraphic framework based on lithofacies stacking and stratigraphic surfaces the fluvial alluvial facies association upper copper harbor conglomerate is overlain across a transgressive surface by the fluctuating profundal facies association lower nonesuch formation the fluctuating profundal facies association comprises a retrogradational sequence set overlain across a maximum flooding surface by an aggradational progradational sequence set comprising fluctuating profundal fluvial lacustrine and fluvial alluvial facies associations middle nonesuch through lower freda formations lithogeochemistry supports sedimentologic and stratigraphic interpretations fe s molar ratios reflect the oxidation state of the lithofacies values are most depleted above the maximum flooding surface where lithofacies are chemically reduced and are greatest in the chemically oxidized lithofacies si al and zr al molar ratios reflect the relative abundance of detrital heavy minerals vs clay minerals greater values correlate with larger grain size vertical facies association stacking records depositional environments that evolved from fluvial and alluvial to balanced fill lake to overfilled lake and returning to fluvial and alluvial elsewhere in the basin where accommodation was greatest some volume of fluvial lacustrine facies is likely present below the transgressive stratigraphic surface this succession of continental and lake basin types indicates a predominant tectonic driver of basin evolution lithofacies distribution and geochemistry indicate deposition within an asymmetric half graben bounded on the east by a west dipping growth fault while facies assemblages are lacustrine and continental periodic marine incursions are probable especially across maximum transgressive surfaces we demonstrate a sequence stratigraphic approach may be applied to fine grained precambrian sediments using traditional rock description and supporting lithogeochemistry identification of a characteristic lithofacies succession in mesoproterozoic sediments demonstrates fundamental controls commonly interpreted for phanerozoic lake systems may be extended into the precambrian these controls result in a predictable association of lithofacies with distinct physical biological and geochemical properties this has regional significance for carbon sequestration and the distribution of mineral and hydrocarbon resources and broader significance for addressing mesoproterozoic paleogeographic reconstructions and questions related to the evolution of terrestrial life

evolution characteristics of transtensional faults and their impacts on hydrocarbon migration and accumulation a case study from the huimin depression bohai bay basin eastern china abstract the study of transtensional faults is significantly important for analysing migration and accumulation of hydrocarbons in petroliferous basins the purpose of this study is to present disparities in the temporal and spatial evolution of two boundary transtensional faults northern linshang fault and southern xiakou fault in the huimin depression by 2d structural restoration and quantitative calculations of fault activity this paper also reveals the controls of transtensional faults on the migration and accumulation of hydrocarbons by considering the stress normal to the fault plane p the shale gouge ratio sgr of the fault zone and models of migration pathways the results show that the transtensional systems within the huimin depression were generated from the reactivation of basement faults under an oblique extensional stress field the linshang fault linked two initially separated segments and then behaved as a single fault since the ek period whereas the xiakou fault retained significant three segment growth properties during the paleogene during the hydrocarbon charging period the weak activity and strong vertical sealing restricted the occurrence of vertical migration around the xiakou fault while the relatively strong movement and weak vertical sealing resulted in multilayer hydrocarbon accumulations around the linshang fault meanwhile the vertically closed fault with high sgr 0 6 acted as barriers and trapped hydrocarbons on the lateral migration pathways whereas the vertically closed fault with low sgr

the 1971 may 12 burdur earthquake sequence sw turkey a synthesis of seismological and geological observations summary it is now widely accepted that the rapid extension observed in western turkey is mainly accommodated by large active normal faults which control the geomorphology the ne sw trending burdur acigol and baklan basins bounded by large faults form a system of half graben whose orientation is evident in both the topography and the tilting of neogene sediments adjacent to them we used long period p and sh waveforms to determine the source parameters of the two largest earthquakes of the 1971 may 12 sequence that occurred in the burdur region the main shock was followed by many aftershocks which were distributed in a broad zone elongated ne sw parallel to the long axes of the basins in the region documented surface breaks of the 1971 event suggest that the northwest dipping faults along the southern margin of the burdur basin are those which moved well exposed fault planes are found dominantly to the south of burdur lake the surface dips of these faults are greater than that of the nw dipping nodal plane obtained for the main shock combined seismological and geological observations suggest that these faults have listric geometries

climatic and tectonic signature in the fluvial infill of a late pliocene valley siena basin northern apennines italy abstract incised valleys entirely filled with fluvial deposits are rarely described in the literature and even rarer are accounts of incised valleys whose filling is not driven by relative sea level changes valleys of this type have not been widely recognized in the stratigraphic record because they are likely to occur in areas undergoing intense erosion or to be encased within alluvial deposits with no strong lithologic contrast in this paper an upper pliocene fluvial valley fill encased within shallow marine middle pliocene deposits and pre neogene bedrock eastern siena basin northern apennines italy and accumulated in response to tectonics and climate changes is described the recognition of this fluvial body up to 40 m thick in an incised valley setting is based on its overall geometry lithofacies characteristics gravel composition and fossil content upvalley fill is represented by amalgamated gravels emplaced by heavily sediment laden flows whereas downvalley fill shows a more organized depositional style and consists of two fining upward successions notable is the presence at the top of the lower succession of decameter thick floodplain fines which extend from one valley wall to another and have no fine grained correlatives in the upvalley fill valley incision resulted from a drop in relative sea level arising from late middle pliocene regional uplift stratigraphic and paleontological data constrain valley filling to the late pliocene early pleistocene time span such a filling stemmed from an increase in sediment supply which resulted from the interplay between uplift of the chianti ridge and a climatic change toward humid conditions as recorded in the coeval strata of the adjacent valdarno basin beyond the regional significance an important implication of the case study is that the incision and filling factors need not be genetically related moreover the stratigraphic architecture of the studied fluvial fill is discussed in terms of the relations between sediment supply and sediment storage en route from the source area to the depositional site and their association with tectonic movements specifically the valley wide floodplain fines are thought to record the response of the fluvial system to a tectonic rejuvenation of catchments which modified the valley gradient and promoted upstream gravel storage whereas the overlying gravels manifest the reestablishment of a new equilibrium river profile

large scale alluvial architecture and correlation in a triassic pebbly braided river system lower wolfville formation fundy basin nova scotia canada abstract determining what the controls are on the large scale 10 km horizontal architecture of coarse grained fluvial deposits is important for understanding subsurface fluid distribution and extraction from these important aquifers and hydrocarbon reservoirs this contribution describes the architecture of coarse grained fluvial sediments from an almost continuous lateral profile 27 km long by 115 m high in the upper triassic wolfville formation fundy basin nova scotia the lateral extent and quality of exposure allows development of a high resolution correlation scheme and definition of architectural elements the lower wolfville formation lithofacies composed of breccias conglomerates sandstones mudstones and paleosols comprises alluvial fan fluvial and ephemeral lake margin facies associations alluvial fan deposits form 15 of the studied section and are developed locally between the overlying fluvial facies and the unconformity with carboniferous strata where they infill remnant topography the succession is dominated 80 by pebbly sandstones deposited as part of a gravelly braided fluvial system and ends abruptly with a thin ephemeral lake margin facies association 5 the large scale architecture and sedimentology of the pebbly sandstone succession is documented with particular attention focussed on bounding surfaces and stacking patterns in the fluvial facies association two scales of development of erosion surface and cycles can be recognized the s surfaces can be correlated across the profile 27 km and show evidence of up to 10 m of erosion a significant facies or grain size change onlap and association with mature calcic paleosols the e surfaces can be correlated between 5 and 17 km display erosion of the regional extent of the e and s surfaces indicate that the gravelly fluvial system has a large scale sheet like geometry which comprises a series of stacked erosion dominated multi story bodies high resolution architectural elements are poorly defined in this coarse fluvial system and make it difficult to constrain the scale of the depositional system an individual high resolution cycle records braid plain development and is interpreted as a multi story channel belt the braid plain width is estimated at 19 km but the width of individual active channels is unknown the sediments were deposited in a proximal fluvial setting disconnected from marine influences we interpret the high resolution cycles and bounding e surfaces to record a progressive decrease in runoff and fluvial transport capacity indicative of a drying upward climatically driven signal the origin of the s surface bounded packages is more difficult to determine a variety of mechanisms are considered including changes in discharge driven by climatic fluctuations changes in stream power related to drainage capture within the source area and tectonic tilting an important aspect of the study is that the s surfaces can be identified and correlated for 27 km and provide an example of a robust high resolution correlation framework in coarse grained braided fluvial deposits that could be applied elsewhere in contrast the e surfaces do not display any significant changes in facies or grain size across them such that many of the smaller scale cycles could potentially be miscorrelated

tectonic controls on spatio temporal development of depositional systems and generation of fining upward basin fills in a strike slip setting kyokpori formation cretaceous south west korea the kyokpori formation cretaceous south west korea represents a small scale lacustrine strike slip basin and consists of an 290 m thick siliciclastic succession with abundant volcaniclasts the succession can be organized into eight facies associations representing distinctive depositional environments i subaqueous talus ii delta plain iii steep gradient large scale delta slope iv base of delta slope to prodelta v small scale nested gilbert type delta vi small scale delta lobe system vii subaqueous fan and viii basin plain facies associations i iii and iv together constitute a large scale steep sloped delta system correlation of the sedimentary succession indicates that the formation comprises two depositional sequences the lower coarsening to fining upward succession up to 215 m thick and the upper fining upward succession up to 75 m thick based on facies distribution architecture and correlation of depositional sequences three stages of basin evolution are reconstructed stage 1 is represented by thick coarse grained deposits in the lower succession that form subaqueous breccia talus and steep sloped gravelly delta systems along the northern and southern basin margins respectively and a sandy subaqueous fan system inside the basin abutting against a basement high this asymmetric facies distribution suggests a half graben structure for the basin and the thick accumulation of coarse grained deposits most likely reflects rapid subsidence of the basin floor during the transtensional opening of the basin stage 2 is marked by sandy black shale deposits in the upper part of the lower succession the black shale is readily correlated across the basin margins indicating a basinwide transgression probably resulting from large scale dip slip suppressing the lateral slip component on basin bounding faults stage 3 is characterized by gravelly delta lobe deposits in the upper succession that are smaller in dimension and located more basinward than the deposits of marginal systems of the lower succession this lakeward shift of depocentre suggests a loss of accommodation in the basin margins and quiescence of fault movements this basin evolution model suggests that the rate of dip slip displacement on basin margin faults can be regarded as the prime control for determining stacking patterns of such basin fills the resultant basinwide fining upward sequences deviate from the coarsening upward cycles of other transtensional basins and reveal the variety of stratigraphic architecture in strike slip basins controlled by the changes in relative sense and magnitude of fault movements at the basin margins

post collisional rapid exhumation and erosion during continental sedimentation the example of the late variscan salvan dorenaz basin western alps the salvan dorenaz intramontane basin formed between ca 308 293 ma as an asymmetric graben along crustal scale transtensional fracture zones within the aiguilles rouges crystalline massif western alps and represents a feature of the post collisional evolution of the variscan orogens it contains 1 5 1 7 km of continental clastic deposits which were eroded from granitic volcanic and metamorphic rocks textural and compositional immaturity of the sandstones and the numerous lithic fragments with low chemical and physical stability suggest only short range transport 40ar 39ar analyses of detrital muscovite are interpreted to represent cooling of the crystalline basement below the respective closure temperatures ages from detrital muscovite range between ca 280 330 ma 40ar 39ar white mica plateau ages from granitic boulders range between 301 312 ma and suggest rapid cooling the very short time interval recorded between the 40ar 39ar cooling ages and the stratigraphic age of the host sediment suggests that considerable portions of the upper crust were removed prior to the formation of the basin late variscan granitic boulders document surface exposure and erosion of late carboniferous granites during early stages of the infilling of the basin therefore unroofing of basement units magmatic activity and formation of the fault bounded salvan dorenaz basin were acting concomitantly and are highly suggestive of extensional tectonics when compared with other orogens this situation seems specific to the variscan especially the exclusively young ages of detrital material however modern analogous may exist

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

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

emergence of the canadian rockies and adjacent plains a comparison of physiography between end of laramide time and the present day abstract the landscape of the canadian rockies in southern alberta is not a direct result of constructional processes that is the ridges and peaks have not been pushed into the positions in which we see them today tectonic activity provided original elevation but not mountains at the end of laramide time what are now the front ranges and foothills of the rockies comprised a high elevation upland of relatively low relief the present mountain physiography is the result of 55 60 million years of post orogenic differential erosion in which more resistant rocks have been left at higher elevations than less resistant rocks the canadian rockies and the foothills are developed in a thin skinned thrust and fold belt created during the laramide orogeny the adjacent interior plains cut across foreland basin sediments derived from the mountains the mountains currently consist of large parts of ridges of well indurated paleozoic and locally proterozoic rock alternating with valleys developed in soft mesozoic clastic rock in the foothills where the soft mesozoic rock is at the surface relief is subdued but ridges of more resistant sandstone rise above shaley lowlands the plains are relatively flat but also contain erosional outliers of higher paleo plains surfaces numerous lines of evidence suggest that the mountains and foothills have lost several kilometers of overburden since the end of the laramide orogeny while the western plains have lost at least 2 km requiring that the local relief of the mountains and foothills that we see is erosional in origin local physiography is adjusted to lithology the mountains have high relief because the exposed sub mesozoic rocks can hold up high steep slopes whereas the foothills have low relief because the underlying cretaceous rocks cannot hold up high steep slopes the east facing escarpment at the mountain front is a fault line scarp along a low angle thrust mesozoic rocks involved in the deformation originally extended all the way across the thrust and fold belt and physiography of the belt at the end of laramide time 60 55 ma depended mainly on whether mesozoic or paleozoic proterozoic rocks were exposed at the surface at that time a reconstruction using critical taper theory generally agrees with reconstructions from earlier stratigraphic and paleothermometry studies what are now the front ranges at the eastern edge of the rocky mountains were mostly or perhaps entirely covered with mesozoic rocks and despite that high elevation had a hilly not mountainous character the main ranges in the central rocky mountains were in part stripped of mesozoic cover by then and more mountainous treeline was higher then and the thrust belt may have been largely or entirely vegetated generation of modern relief in the front ranges including the escarpment at the mountain front had to await stripping of mesozoic rocks and incision of rivers into harder substrates in post laramide time the interior plains are an erosional surface that was cut 1 to 3 km below the aggradational top of the foreland basin sediments although some of the present low local relief of the plains results from weakness of underlying cretaceous tertiary rocks the low relief is probably largely related to the process of denudation

sediment provenance and dispersal in a deep marine foreland basin the lower carboniferous culm basin czech republic the lower carboniferous culm basin of the czech republic represents the most easterly and southerly part of the european variscan foreland basin system the nne ssw trending basin is exposed along the eastern flank of the bohemian massif it contains up to 7 5 km of deep marine sediment deposited as an axial turbidite system sourced from south southwest of the basin heavy mineral data and clast types indicate that for much of the visean sediment was sourced from a predominantly low grade metamorphic terrane and visean limestones in the latest visean a progressive change in source material is recorded by an increase in high grade metamorphic detritus studies of variscan nappe pile emplacement along the eastern flank of the bohemian massif allow an assessment of the relationship between basin development and nappe emplacement basin initiation coincided with underthrusting of high grade metamorphic moldanubian nappes at 340 ma sedimentation was synchronous with nappe emplacement throughout the visean which resulted in uplift and erosion of a low grade metamorphic terrane moldanubian nappes were exhumed at approximately 330 ma when high grade metamorphic detritus entered the basin two phases of northward directed sediment progradation are recognized sediment progradation is considered to be related to changes in drainage basin size and or climatic fluctuations within the variscan orogen since sediment is inferred to have been supplied to the basin axially rather than laterally and subsidence curves show no significant change in subsidence rates in contrast to many models of foreland basin sediment distribution filling of the culm basin was largely independent of tectonic activity adjacent to the basin margin and or of subsidence rate changes sedimentation in the culm basin commenced 10 15 ma earlier than the rest of the variscan foreland and records the first impact of the northwardly propagating variscan orogen in northern europe

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

linking lacustrine cycles with syn sedimentary tectonic episodes an example from the codo formation late aptian northeastern brazil the codo formation exposed in the eastern grajau basin northeastern brazil consists mostly of black shales limestones and evaporites arranged into several shallowing upward cycles formed by progradation of lake deposits three ranks of cycles are distinguished the lower rank cycles correspond to millimetric interbeddings of bituminous black shales with evaporites calcimud stones or peloidal wackestone packstone grey green shale with calcimudstone peloidal wackestone packstone or ostracodal wackestone grainstone and ostracodal wackestone grainstone and or calcimudstones with cryptomicrobial mats and ooidal pisoidal packstones the intermediate rank cycles average 1 7 m in thickness and are formed by complete and incomplete cycles complete cycles show a transition from central to intermediate and then to marginal facies associations and include two types c1 cycle with central lake deposits consisting of evaporites and black shales and c2 cycle with central lake deposits formed by grey green shale complete cycles were produced by the upward gradation from central to marginal environments of the lake or saline pan sabkha system incomplete cycles are those where at least one facies association is lacking having been formed by successions either with central and intermediate facies associations i1 or intermediate and marginal facies associations i2 the higher rank cycles are on average 5 2 m thick and consist of four depositional units that display shallowing upward successions formed by complete and incomplete intermediate rank cycles that vary their distribution upward in the section and are bounded by sharp surfaces while the lower rank cycles display characteristics that reveal their seasonal signature detailed sedimentological characterization and understanding of stratal stacking patterns related to the intermediate and higher rank cycles support a genesis linked to syn sedimentary tectonic activity this is particularly suggested by the high facies variability limited lateral extension and frequent and random thickness changes of the intermediate rank cycles additionally the four higher rank cycles recognized in the codo formation match with stratigraphic zones having different styles of soft sediment deformation structures attributed to seismic activities therefore the several episodes of lake shallowing recorded in the codo formation are linked to seismic pulses that alternated with sediment deposition this process would have created significant changes in the lake water level and resulted in sharply bounded successions with upward gradation from deeper to relatively shallower facies associations

climate and landscape reconstruction of the arroyo chijuillita member of the nacimiento formation san juan basin new mexico providing environmental context to early paleocene mammal evolution abstract the sedimentologic stratigraphic and paleopedologic attributes of a laterally continuous outcrop exposure of the basal portion of the lower paleocene arroyo chijuillita member of the nacimiento formation located in the bisti de na zin wilderness area was examined to provide paleoenvironmental context for the puercan north american land mammal age nalma terrestrial ecosystems of the san juan basin new mexico the studied outcrop spans the middle and late puercan pu2 pu3 nalma and thus is an ideal location to assess the potential causes of faunal turnover between pu2 and pu3 the stratal succession consists of fluvial channel and laterally continuous sandstone and associated fine grained floodplain deposits including paleosols that document variability in drainage and maturity quantitative and qualitative reconstructions of paleoclimate from paleosols supplemented by analyses of fossil floras indicate no change in climate through the studied interval further there is no evidence that regional tectonics relate to changes in depositional environments given the lack of evidence for climate change or regional tectonics and the characteristics of the fluvial facies and the paleosols across the study locality we interpret the spatial and temporal variability in paleopedologic and sedimentologic characteristics to be the result of autocyclic channel avulsion and migration additionally the stable climatic conditions and lack of tectonic influence between the pu2 and pu3 biozones suggest that mammalian turnover is unlikely to have been caused by extrinsic environmental changes i e climate or tectonics and is instead probably the result of rapid evolution following the k pg boundary and or competition from the migration of new mammalian species into the basin

growth destruction and facies architecture of effusive and explosive volcanics in the miocene shama basin southwest of saudi arabia subaqueous subaerial volcanism in a lacustrine setting abstract this paper presents for the first time detailed stratigraphical and petrographical analyses of the harrat shama volcanic basin hsvb of miocene age in sw saudi arabia this basin is filled by abundant volcanics intercalated with fluvio lacustrine sedimentary successions these successions are characterized by a syneruptive intereruptive cycle which results from the intercalation periods of volcanics and volcaniclastic sedimentation along with periods of fluvial incision two depositional sequences showing an overall fining upward trend are preserved within the hsvb the first comprises hyaloclastites zeolite bearing bedded tuffs and bedded accretionary lapilli tuffs interpreted as deep lake whereas the second is made up of extensive pumiceous pyroclastic flows peperitic breccias and basaltic lava flows which are in turn capped by siliciclastic deposits of lacustrine deposits the passage between two sequences is defined by lateral variations of the lithofacies and textural features reflecting a change in paleogeography the fining upward volcaniclastic deposits of the hsvb sequence are interpreted to represent the sedimentation pattern induced by tectonic subsidence with the influence of volcaniclastic sediment input indicating well established proximal distal relationship hsvb was evolved through three stages including pre syn and post caldera stages the first two stages correspond to proximal aggradational syn eruptive event whereas the latter stage refers to distal degradational inter eruptive event these stages overlap in time as shown by the alternation of explosive effusive and their resedimented deposits reflecting diverse eruptive sequences formed by different fragmentation processes the difference in the latter coupled with the variability in the magma water interaction and the nature of substrate are responsible for such diversity resulting in progressive environmental changes from subaqueous to subaerial regime from bottom to top the development of such contrast in the depositional sequences reflects variation in the sediment flux and subsidence rate during the evolution of the hsvb

pliocene burdur basin sw turkey tectonics seismicity and sedimentation the pliocene burdur formation of sw turkey was deposited in a ne sw trending half graben with a major basement fault along its se margin hangingwall sourced fans were confined proximally by basement topography distally they developed 9ideal9 fan geometries these fans became submerged by the lake that occupied the centre of the basin this transgression was caused by the migration with time of the hangingwall pivot away from the basin controlling fault footwall sourced fans exhibit three distinctly different geometries at the northern end of the basin a wide braidplain developed due to the rapid erosion of both penecontemporaneous volcaniclastic deposits to the east and the footwall crest of a newly formed fault within the basin along the footwall scarp in the central part of the basin a narrow bajada formed in the south a large alluvial fan had its source in the relay structure between two left stepping en echelon fault segments the small size of footwall sourced fans compared with those sourced on the hangingwall slope was due to rapid subsidence of the basin floor adjacent to the footwall scarp although this suggests high levels of seismicity the general paucity of wet sediment deformation within the burdur formation indicates that seismicity in the burdur region during the pliocene was more subdued than at present

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

isotopic constraints on fluid evolution and precipitation mechanisms for the boleo cu co zn district mexico stable and radiogenic isotope composition of stratiform cu co zn mineralization and associated sedimentary rocks within the boleo district of the miocene santa rosalia basin baja california sur constrains the evolution of seawater and hydrothermal fluids and the mechanisms responsible for sulfide and oxide deposition stable isotope geochemistry of limestone and evaporite units indicates a strong paleogeographic influence on the chemistry of the water column near shore limestone at the base of the boleo formation is characterized by modified marine carbon 13cpdb 6 0 to 4 4 and oxygen 18osmow 19 5 to 26 2 isotope composition due to the influx of 13c and 18o depleted fluvial water sulfate sulfur isotope composition 34scdt 17 21 to 22 3 and 18osmow 10 7 to 13 1 for basal evaporite and claystone facies are similar to miocene seawater strontium isotopes are less radiogenic than expected for miocene seawater due to interaction with volcanic rocks low s c ratios high mn contents and sedimentological evidence indicate the basin water column was oxidizing the oxygenated basin restricted sulfide precipitation to within the sedimentary pile by replacement of early diagenetic framboidal pyrite and pore space filling by cu co zn sulfides to produce disseminated sulfides quartz mn oxide oxygen isotope geothermometry constrains mineralization temperature between 18 and 118 c sulfur isotopes indicate the following sources of sulfide 1 bacterial sulfate reduction within the sedimentary pile produced negative 34s values 20 in framboidal pyrite and 2 bacterial sulfate reduction at high temperature 80 118 c within the sedimentary pile during the infiltration of the metal bearing brines produced cu co zn sulfides with negative but close to 0 34s values isotope modeling of fluid rock reaction and fluid mixing indicates 1 sedimentary and marine carbonates 13c 11 6 to 3 2 and 18o 19 0 to 21 8 precipitated from basin seawater pore water that variably mixed with isotopically depleted meteoric waters and 2 hydrothermal calcite 13c 7 9 to 4 3 and 18o 22 1 to 25 8 formed by dissolution and replacement of authigenic marine calcite by downward infiltrating metalliferous brine and brine sediment exchange that prior to reaction with calcite had mixed with isotopically depleted pore water the downward infiltration of metalliferous brine is inferred from lateral and stratigraphic metal distributions and from the concentration of cu sulfides along the upper contact of pyrite bearing laminae the co existence and textural relationships among framboidal pyrite base metal sulfides carbonate and mn fe oxides including magnetite within mineralized units are consistent with carbonate replacement and high temperature bacterial reduction within the sedimentary pile occurring simultaneously below a seawater column under predominantly oxygenated conditions

tectono sedimentary evolution of sedimentary basins from late paleoproterozoic to late neoproterozoic in the sao francisco craton and aracuai fold belt eastern brazil abstract two first order regional unconformities separate proterozoic supracrustal rocks of the sao francisco craton and the aracuai fold belt eastern brazil into three genetic units these constitute three superimposed first order basin fill cycles the espinhaco macaubas salinas and bambui megasequences the paleo mesoproterozoic espinhaco megasequence ca 1730 1500 ma was deposited in an intracratonic rift sag basin in four stages pre rift rift transitional and flexural each of these stages is bounded by regional second order unconformities basin evolution was controlled primarily by tectonics although sea level variations were also important in the transitional and flexural stages after a hiatus of several hundred million years subsidence renewed during extension related to the early neoproterozoic breakup of the supercontinent rodinia with rift to passive margin sedimentation in the macaubas salinas basin ca 950 700 ma initial glaciogenic sedimentation possibly induced by uplift related to a mantle plume occurred in a rift setting subsequent a shelf slope deep sea passive margin deposits represent opening of a northern branch of the adamastor ocean tectonic magmatic climatic and eustatic processes all combined to control basin evolution the bambui megasequence ca 800 650 ma was deposited in a foreland basin during convergent and collisional tectonics related to closure of the brazilide ocean and generation of the brasilia fold belt west of the sao francisco paleocontinental region the evolution of the bambui basin whose fill is characterized by three transgressive progradational shallowing upward sequences was mainly controlled by tectonic processes

tracing tectonic deformation using the sedimentary record an overview tectonic activity on a range of scales is a fundamental control on sedimentary activity the range of structural deformation within a region extends from the plate tectonic scale governing for example rift initiation to the basin scale with the formation of basin bounding faults internal basin configuration is also strongly influenced by tectonic activity however the relationship between tectonic activity and sedimentation is a complex one given the many additional factors which can also influence sedimentary activity including erosion sediment transport source area lithology groundwater chemistry range of depositional environments climate eustasy and the relative location of an area and its distality to marine influences in this paper we provide a selective overview of the issues associated with the interlinked themes of tectonics and sedimentation examining the main basin types forming in both extensional and compressional plate settings we then review the various models of sedimentation in the selected basins both on a local and a basinal scale finally we look to the future providing a series of possible research areas almost exclusively multidisciplinary which would help to improve existing models of interlinked sediment tectonics systems

nanpanjiang basin a window on the tectonic development of south china during triassic assembly of the southeastern and eastern asia abstract as the largest siliciclastic sink in the south china block the triassic nanpanjiang basin is generally thought of as a foreland basin related to indosinian collision between the south china and indochina blocks our basin analysis spanning an eight years period provides details of lopingian to middle triassic stratigraphic fill and tectonic subsidence of the basin field observation and sedimentological analyses reveal that the basin was not filled by a monotonous turbidite system and suggest instead the development of five primary depositional units constituted by deep water turbidite systems mass transport deposits condensed drapes shallow water isolated carbonate platforms and volcano volcaniclastic rocks the stratigraphic completeness of the basin the coexistence of widespread but localized carbonate platforms within axially filled deep water basin tectonically generated cyclothems of transverse mass transport deposits along intrabasinal faults and basin fill of extrusive rocks of bimodal composition together apparently call in question the claim that crustal shortening prevailed during the late permian to pre norian triassic patterns of basin fill differential tectonic subsidence and very high subsidence rate of the region adjacent to master fault are more closely match the pattern expected for extensional to transtensional basin in a back arc setting the crustal extension in the southwestern south china was not consistent with hypothesized indosinian collision between south china and indochina blocks but more likely developed in response to northwestward subduction of the paleo pacific plate our results combined with regional considerations lead to a new model for the triassic tectonic evolution of south china during triassic assembly of the southeastern and eastern asia

lithofacies and depositional environments of miocene deposits from tectonically controlled basins red river fault zone northern vietnam abstract the lao cai yen bai and bao yen basins connected with the red river fault zone rrfz are filled with over 1000 m thick neogene miocene clastic deposits of different type and origin coarse grained alluvial deposits predominate along the south western margin of the lao cai and yen bai basins while different types of conglomerates and sandstones even siltstones occur in their central and along their north eastern parts such asymmetry in the cross section basin fill points to the south western active margin of these basins three main facies associations composed of 12 lithofacies have been recognized in the miocene succession filling the studied basins 1 debris flow dominated alluvial fan association 2 sheetflood dominated alluvial fan association and 3 lacustrine association both alluvial fan facies associations are broadly spread in the studied basins especially along their south western margins the debris flow dominated deposits are represented by decimetre to several meters thick sand and mud supported disorganized pebble to cobble size occasionally boulder breccia and conglomerate beds the sheetflood dominated deposits are represented by alternating planar bedded pebble and cobble gravel couplets the occurrence of conglomerate bodies within and overlapping fine deposits of the lacustrine facies association may suggest deposition in a debris flow and sheetflood dominated alluvial fan setting associated with narrow elongated basins that could be occupied by lakes and bordered by active fault scarps the facies pattern of the particular basins is connected with the evolution of the rrfz the origin of these basins may be correlated with a sinistral transtensional regime which occurred in the early to middle miocene moreover the high grade metamorphic core of the day nui con voi massif presently the main structural element of the rrfz was probably not exposed during sedimentation of most of the strata in the studied basins

miocene synextension sedimentation patterns whipple mountains southeastern california implications for the geometry of the whipple detachment system a sedimentary basin formed in the southern and eastern whipple mountains during early to middle miocene detachment faulting stratigraphic relations and facies patterns indicate that the shape and size of the sedimentary basin was controlled both by fault activity and by sedimentary processes high angle normal faults formed the southwestern and perhaps also the northeastern boundary of the half graben whereas a transfer fault probably formed the southeastern boundary the transfer fault influenced the earliest synextension sedimentation in the basin the location of this fault and similar faults in the mohave mountains and aubrey hills of arizona is inferred to have been controlled by the position of primary irregularities or corrugations of the detachment fault shifts in facies patterns particularly a shift in the position of the basin depocenter reflect changes in basin geometry comparison with adjacent areas is necessary to distinguish between tectonic and nontectonic causes a shift in depocentral position parallel to regional transport direction in the whipple mountains basin is interpreted as resulting from a change in the location of the high angle normal fault forming the southwestern margin of the basin whereas a shift perpendicular to transport direction probably resulted from overtopping of topographic barriers within a fault block the most active phase of faulting occurred prior to deposition of stratigraphic units younger than the 18 5 ma peach springs tuff relative uplift of the core of the whipple mountains probably as a result of isostatic rebound following tectonic denudation influenced sedimentation patterns after deposition of the peach springs tuff

interaction of an antecedent fluvial system with early normal fault growth implications for syn rift stratigraphy western corinth rift greece continental overfilled conditions during rift initiation are conventionally explained as due to low creation of accommodation compared with sediment supply alternatively sediment supply can be relatively high from the onset of rifting due to an antecedent drainage system the alluvial lower group of the western plio pleistocene corinth rift is used to investigate the interac tion of fluvial sedimentation with early rifting this rift was obliquely super imposed on the hellenide mountain belt from which it inherited a significant palaeorelief detailed sedimentary logging and mapping of the well exposed syn rift succession document the facies distributions palaeocurrents and stratigraphic architecture magnetostratigraphy and bios tratigraphy are used to date and correlate the alluvial succession across and between fault blocks from 3 2 to 1 8 ma a transverse low sinuosity braided river system flowed north north east to east across east west striking active fault blocks 4 to 7 km in width deposits evolved downstream from coarse alluvial conglomerates to fine grained lacustrine deposits over 15 to 30 km the length scale of facies belts is much greater than and thus not directly controlled by the width of the fault blocks at its termination the distribu tive river system built small stacked deltas into a shallow lake margin the presence of a major antecedent drainage system is supported by i a single major sediment entry point ii persistence of a main channel belt axis iii downstream fining at the scale of the rift basin the zones of maximum sub sidence on individual faults are aligned with the persistent fluvial axis sug gesting that sediment supply influenced normal fault growth instead of low accommodation rate during the early rift phase this study proposes that facies progradation can be controlled by continuous and high sediment sup ply from antecedent rivers

the recognition of reactivation during continental deformation reactivation involves the accommodation of geologically separable displacement events intervals 1 ma along pre existing structures the definition of a significant period of quiescence is central to this phenomenological definition and the duration of the interval chosen represents the resolution limit of reactivation criteria found in most ancient settings in neotectonic environments reactivation can be further defined as the accommodation of displacements along structures that formed prior to the onset of the current tectonic regime this mechanistic definition cannot always be applied to ancient settings due to the uncertainties in constraining relative plate motion vectors four sets of criteria may be used to recognize reactivation in the geological record stratigraphic structural geochronological and neotectonic some structural criteria may not be reliable if used in isolation to identify reactivated structures much of the previously published evidence cited to invoke structural inheritance is equivocal as it uses similarities in trend dip or three dimensional shape of structures numerous fault and shear zone processes can cause significant weakening both synchronously with deformation and in the long term and may be invoked to explain reactivation the collage of fault bounded blocks forming most continents therefore carries a long term architecture of inheritance which can explain much of the observed complexity of continental deformation zones

fluvial processes and cyclicity in terminal fan deposits an example from the late devonian of southwest ireland abstract the gun point formation is a sandstone dominated sequence approximately 1 5 2 5 km thick which forms part of a major 6 km late devonian alluvial basin fill succession in southwest ireland it is interpreted as the deposits of a southerly flowing terminal fan system which operated under a semi arid climate the proximal zone was characterized by low sinuosity gravelly feeder channels which passed downstream into a medial zone dominated by a sandy braidplain further south in the distal zone phases of high energy flood activity were centred on transient low sinuosity ephemeral channels and were separated by more quiescent periods of shallow sheetflooding subaerial exposure and non deposition sedimentary parameters such as set thickness coset thickness channel sand body density and maximum sand body thickness all exhibit regular cyclic fluctuations with a periodicity of 160 180 m the cycles are interpreted as evidence of regular discharge variations which may have been a response to the 412 ka orbital eccentricity cycle a second periodicity of approximately 700 m has also been detected and is thought to reflect long term variations in basin subsidence

upper plate deformation as marker for the northern step fault of the ionian slab tyrrhenian sea central mediterranean abstract the eastern tyrrhenian margin etm the active boundary of the tyrrhenian sea backarc basin is the key for understanding the geodynamics of the central mediterranean numerous seismic tomography studies have been carried out in this region proposing different reconstructions of the lower subducting plate and cause of the slab break off existing beneath the southern apennines however the area and mode of the recent deformation of the tyrrhenian sea are still not fully defined and understood in this study we combine the analysis of a recent seismic tomography model and geological data in order to understand the relationship between the subducting lower plate and the tectonic evolution of the sedimentary basins formed on the upper plate with this aim we interpreted a large data set of seismic reflection profiles and several well logs the results consist in 2d and 3d geological models of the basins sedimentary infill and fault networks taking into account the geological data of the etm and those of the adjacent inner flank of the apennines we observe i a system of linked sedimentary basins developed on a narrow deformation belt bounded by transform fault zones ii a polyphase rifting within the upper plate iii an abrupt change of the direction of extension 90 from ne oriented in the lower pleistocene to se oriented in the middle pleistocene since these etm features are not the typical expressions of the current backarc extensional models we propose a link between the evolution of upper plate and the onset and development of a step subduction transform edge propagator fault along the northern margin of the ionian slab

quaternary structural partitioning within the rigid tarim plate inferred from magnetostratigraphy and sedimentation rate in the eastern tarim basin in china abstract it has been proposed that within the tarim basin tectonic activity has been limited since triassic time however on the basis of magnetostratigraphy from the eastern tarim basin which defines the chronology of sedimentation and structural evolution of the basin we show that the basin interior has been uplifted and partitioned during quaternary the magnetostratigraphy was constructed from 2228 samples that yielded acceptable inclination values characteristic remnant magnetization chrm with both normal n1 n11 and reversed r1 r11 polarity was isolated by thermal demagnetization the data correlate best with polarity chrons c3r to c1n which range from 5 39 ma to recent on the geological time scale 2004 gts2004 an abrupt decrease in the sedimentation rate is observed at 1 77 ma in the ls1 core this change does not overlap with known pleistocene climate change events we attribute this sedimentation rate decrease to a structurally controlled local decrease in accommodation space where basin basement uplifts occur this period of sedimentary environmental change reveals that structural partitioning in the basement of the tarim basin occurred since 1 77 ma and we speculate that tilting of the southeast uplift a sub basin unit within the tarim basin began in early pleistocene time

lacustrine fan delta deposition alongside intrabasinal structural highs in rift basins an example from the early cretaceous jiuquan basin northwestern china development of fan deltas alongside intrabasinal structural highs has been overlooked compared to those forming on basin margins however these fan deltas may provide important clues regarding the tectonic and climatic controls on deposition during rift development this paper documents fan delta deposition alongside an intrabasinal structural high within the early cretaceous xiagou formation of the jiuquan basin china using subsurface geological and geophysical data deposits observed in drill core support fan delta deposition occurring almost exclusively through subaerial and subaqueous gravity flows subsurface mapping reveals a consistent decrease in the areal extent of fan deltas from lowstand to highstand system tracts suggesting that deposition alongside the structural high is sensitive to lake level changes the temporal and spatial distribution of the fan deltas display retrogradational stacking patterns where fan deltas exhibit a decreasing lateral extent up sequence until fan delta deposition terminated and was replaced by deposition of fine grained lacustrine deposits the retrogradational stacking patterns observed alongside the intrabasinal structural high are not observed in fan deltas along the basin margin in the lower parts of the xiagou formation subsidence profiles also show differential subsidence across the basin during the earliest stages of this formation likely resulting from border fault movements these data suggest that non uniform stacking patterns in the lower parts of the xiagou formation reflect basin scale tectonic movements as the dominant control on synrift deposition patterns however later stages of xiagou formation deposition were characterized by uniform subsidence across the basin and uniform retrogradational stacking patterns for fan deltas alongside the intrabasinal structural high and border fault these observations suggest that basin scale tectonic movements played a relatively limited role in controlling sediment deposition and imply a potential change to regional scale processes affecting fan delta deposition during later synrift stages climate change is favored here as the region scale control on the uniform retrogradational fan delta stacking patterns this assertion is supported by pollen assemblages isotope signatures and organic geochemical analyses which collectively suggest a change from a humid to semi arid environment during later synrift stages we suggest that variations in stacking patterns between different fan delta systems can provide insights into the basin and regional scale processes that control rift basin deposition

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

development of tectonostratigraphy in distal part of foreland basin in southwestern taiwan abstract in the young and active tectonic belt of southwestern taiwan reconstructed stratigraphy in the distal part of the foreland basin reveals at least two regional unconformities with the younger ones covering the areas farther from the mountain belt in contrast with the previously proposed monotonous basin development the temporal spatial distribution of the unconformities indicates the back and forth migration of the foreland basin margin three distinct episodes of rapid subsidence during the foreland basin development have also been identified the onset of the basin development can be well constrained by the initial rapid subsidence at 4 4 4 2 ma which happened only in the proximal part of the basin this was followed by two younger episodes of rapid subsidence events at 2 1 8 ma and 0 45 ma which were encountered initially in the areas progressively farther from the orogenic belt we propose a model of episodic tectonic evolution in the distal part of the foreland basin in southwestern taiwan during each episode of rapid subsidence uplifting that corresponds to the forebulge began with a concurrent rapid subsidence in the areas closer to the basin center and was followed by rapid subsidence and deposition of widespread strata onlapping toward the basin margin part of the widespread strata and its overlying deposits would be eroded in the beginning of the next episode when the forebulge shifted toward the orogenic belt in general rate of forebulge migrating away from the orogenic belt during the early stage was slower than that derived from a previously proposed kinematic model of a steady migration of the orogenic belt this might be due to a rifted and weaker lithosphere beneath the foreland basin once the foreland basin migrated onto the less stretched lithosphere the basin would expand rapidly into the craton

late quaternary geomorphic evolution of the lower narmada valley western india implications for neotectonic activity along the narmada son fault geomorphic data combined with stratigraphic studies provide significant information to constrain timing and amount of fault movement the lower narmada valley lies astride the narmada son fault nsf an important ene wsw trending tectonic element responsible for the current intraplate seismicity being experienced in the central part of the indian plate varying nature and degree of tectonic movements along the nsf during late pleistocene and holocene have produced four geomorphic surfaces in the lower narmada valley the alluvial plain s1 ravine surface s2 a gravelly fan surface s3 and the valley fill terrace surface s4 two major phases of tectonic movements in a compressive stress regime are recorded along the nsf slow synsedimentary subsidence of the basin during late pleistocene due to differential movement followed by inversion of the basin during the holocene marked by differential uplift along the nsf the study suggests that the inversion of the basin is in response to the significant increase in the intensity of compressive stresses in the indian plate mainly during the early holocene the present incisive drainage and recent seismic activity indicate that the compressive stresses continue to accumulate along the nsf due to continued northward movement of the indian plate

sea level rise depth dependent carbonate sedimentation and the paradox of drowned platforms a mathematical model of carbonate platform evolution is presented in which depth dependent carbonate growth rates determine platform top accumulation patterns in response to rising relative sea level this model predicts that carbonate platform evolution is controlled primarily by the water depth and sediment accumulation rate conditions at the onset of relative sea level rise the long standing paradox of a drowned platform arose from the observation that maximum growth rate potentials of healthy platforms are faster than those of relative sea level rise the model presented here demonstrates that a carbonate platform could be drowned during a constant relative sea level rise whose rate remains less than the maximum carbonate production potential this scenario does not require environmental changes such as increases in nutrient supply or siliciclastic sedimentation to have taken place a rate of relative sea level rise that is higher than the carbonate accumulation rate at the initial water depth is the only necessary condition to cause continuous negative feedbacks to the sediment accumulation rates under these conditions the top of the carbonate platform gradually deepens until it is below the active photic zone and drowns despite the strong maximum growth potential of the carbonate production factory this result effectively resolves the paradox of a drowned carbonate platform test modelling runs conducted with 2 5 m and 15 m initial sea water depths at bracketed rates of relative sea level rise have determined how fast the system catches up and maintains the keep up phase this is the measure of time necessary for the basin to respond fully to external forcing mechanisms the duration of the catch up phase of platform response termed carbonate response time scales with the initial sea water depth and the platform top aggradation rate the catch up duration can be significantly elongated with an increase in the rate of relative sea level rise the transition from the catch up to the keep up phases can also be delayed by a time interval associated with ecological re establishment after platform flooding the carbonate model here employs a logistical equation to model the colonization of carbonate producing marine organisms and captures the initial time interval for full ecological re establishment this mechanism prevents the full extent of carbonate production to be achieved at the incipient stage of relative sea level rise the increase in delay time due to the carbonate response time and self organized processes associated with biological colonization increase the chances for platform drowning due to deepening of water depth ca 10 m furthermore this implies a greater likelihood for an autogenic origin for high frequency cyclic strata than has been estimated previously

the impact of climate change tectonism and hydrology on the formation of carboniferous tropical intermontane mires the springhill coalfield cumberland basin nova scotia abstract both climate and tectonism are influential in determining basin and mire hydrology in the rapidly subsiding intermontane basins of euramerica which formed in response to the variscan hercynian alleghenian orogeny however the record of climate change has been muted and may therefore go unrecognized the complex interplay of climate and tectonism in a tropical continental setting is recorded in the 4 km thick westphalian a b fill of the cumberland basin thick peat accumulation was favoured at the southern basin margin where rheotrophic forested mires 4 9 km wide flourished between basin axis rivers and coalesced alluvial fans derived from the cobequid highlands as a result of their geomorphic setting the thicker coals 4 3 m exhibit distinct areal zones piedmont inner mire and riverine evidence that the forest swamps were nourished both by rainfall and by groundwater discharge from alluvial fans includes the stratigraphic affinity of thick coals and basin margin conglomerates interfingering of distal fan sheetflood and mire deposits petrographic evidence of elevated ph partial gelification of tissues and predominance of the arboreous lycopsids lepidodendron and paralycopodites whereas such groundwater supply is crucial to maintenance of modern wetlands in drier periods a subhumid climate is implied coals at joggins further removed from groundwater discharge at the basin margin are less well developed a 600 m thick coal window within the fining and reddening upward basin fill sequence at springhill is inferred to represent a coincidence of optimal groundwater supply and net subsidence the ultimate decline of peat accumulation in the basin may reflect decrease in catchment area and fan size and loss of rainshadow as the cobequid massif was denuded and the basin filled the coal window ca 6 9 10 5 yr is punctuated by non marine cyclothems of coal grey sideritic mudrock and multistorey sandstone that share similar time frames with astronomic cycles of axial precession ca 1 4 10 4 yr the stress of related climate change is inferred to have caused peat accumulation to fall into disequilibrium with sediment flux and basin subsidence the late quaternary history of certain african mires illustrates the dramatic impact of climate change especially temperature and seasonality and orographic effects on tropical continental peat accumulation aspects of the groundwater recharge model may be applicable to the westphalian stephanian intermontane mires of spain and mesozoic coal basins of northern china

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

lacustrine system evolution during early rifting el castellar formation galve sub basin central iberian chain abstract a detailed sedimentological study of the first synrift deposits recorded in the galve sub basin of ne spain during the early cretaceous aided in the reconstruction of climatic and tectonic influences the el castellar formation is composed of siliciclastics and carbonates unit 1 claystones gypsum and carbonates unit 2 and marls and limestones unit 3 unit 1 facies formed in alluvial and palustrine plains a local alluvial fan and low energy shallow lake subenvironments low energy lacustrine facies characterised unit 2 in contrast palustrine low and high energy lake facies were identified for unit 3 the spatial and temporal distribution of lithofacies representing the several environments were used to propose a general lacustrine system evolution from isolated ponds and marshes to low energy shallow lakes and finally to an extensive high energy lake lake evolution is related to changes in the subsidence pattern from local to basin scale subsidence which was ultimately related to the transition from the initial rift to rift climax stage shallowing upwards lacustrine successions have been interpreted as climatically forced and linked to sediment and water supply both tectonics and climate determined the change from an overfilled to a balanced fill lake basin through time

historical adjustments by walker river to lake level fall over a tectonically tilted half graben floor walker lake basin nevada abstract historical records of lake and river adjustments in the tectonically active north south elongated walker lake extensional basin of west central nevada provide important insight to the style and rate that rivers react to tectonic tilt in half grabens the northern part of this basin historically containing walker lake is now occupied by the south flowing walker river walker lake presently restricted to the central basin sector is a perennial water body 30 m deep sustained by and forming the terminus of walker river both the river and lake have a strongly asymmetric distribution located preferentially near the active walker lake fault bounding the western basin margin walker lake has withdrawn from the northern basin sector since 1882 due to a 45 m drop in lake level caused by human diversion of the river upstream this withdrawal has forced walker river to incrementally lengthen and to sequentially reposition its delta along the retreating northern lake margin twelve deltas have been deposited since 1882 in response to these changes the initiation of eight of the twelve post 1882 deltas was associated with channel avulsion and four with channel lengthening ten of the twelve channel and delta relocation events entailed significant westward lateral movements toward the walker lake fault illustrating the dominating influence of the basin floor tectonic tilt on river adjustments the two eastward shifts were triggered intrinsically by avulsions resulting from erosion of the outer bank of channel meanders the three phases of progressive westward shifting of the river towards the walker lake fault occurred over periods of 18 6 and 16 years respectively documenting the rapid response time of walker river to basin floor tectonic tilt despite the countering effects of the intrinsic avulsions and hindrances to lateral migration caused by the muddy substrate of the former lake bottom deposits within which the river is incised

early cretaceous gangdese retroarc foreland basin evolution in the selin co basin central tibet evidence from sedimentology and detrital zircon geochronology the selin co basin in the northern lhasa terrane includes more than 3000 m of upward coarsening lower cretaceous strata and the sedimentary sequence from the flysch to the molasse indicates the evolution of a foreland basin petrographic analysis shows that sandstones are rich in volcanic and sedimentary lithics and most of them fall into recycled orogen and magmatic arc uranium lead u pb ages were determined for 435 detrital zircons from the lower cretaceous strata in the selin co basin relative probability of detrital zircon ages shows the eshaerbu formation was rich in zircon grains with the age of 125 140 and 160 180 ma and the duoni formation was dominated by one main age cluster of 125 150 ma analysis of the potential provenances suggests the early cretaceous zircon grains were primarily derived from the gangdese magmatic arc to the south the youngest zircon ages in the lowermost exposure of the eshaerbru formation are c 130 ma providing a maximum depositional age of sediments in the selin

tectono sedimentary evolution and hydrocarbon reservoirs in the early cretaceous tanan depression tamtsag basin mongolia abstract the responses of depositional patterns to extensional faulting during the rift cycle are discussed in this article based on an integrated analysis of 3d seismic reflections wire logs and cores from the early cretaceous tanan depression in the tamtsag basin mongolia the synrift succession comprises four third order sequences sq1 4 a four stage fault evolution is defined including early synrift sq1 initial isolate faults early synrift sq2 rapid fault propagation climax synrift sq3 maximum fault relief and late synrift sq4 minor fault activity stages the initial isolated fault stage is defined by separated and small sized half grabens associated with short dispersal alluvium in contrast the rapid fault propagation stage is characterised by much longer dispersal systems of fan delta deposits as rifting progressed a considerable increase in the basin subsidence occurred and the maximum fault displacement led to a dustpan basin geometry the coalescence of depocentres and extensive deep water deposits the observed both sediment starvation and balanced filled patterns in sq3 indicate that caution must be exercised when attempting to correlate reservoirs and source rocks since variations in basin filled patterns would be enhanced by the displacement localisation on several major faults during the significant basin formation during the early period of the climax synrift stage footwall sourced systems were prominent but drainages in prior relay zone sites were mostly decayed or submerged in response to the subsequent degradation of the footwall sources axial sourced braided deltaic systems became more important during the later period an abrupt decrease of faulting at the end of the rift cycle gave a rise to an increased sediment supply and long dispersal axially sourced systems in the tanan depression petroleum exploration shows that fan delta front sandstones in sq2 are the most prospective hydrocarbon reservoirs whereas the nearshore and offshore sub lacustrine fan deposits in sq3 have proved to be secondary potential oil bearing reservoirs this study indicates that sediment dispersal patterns would be significantly re organised by the differential faulting displacement patterns and varied sediment potentials during the different synrift stages the rapid fault propagation allowed the fault arrays to reach their nearly maximum length during the early period of the basin evolution while the displacement remained almost constant this fault growth pattern tends to establish large scale topographic lows including overlapped transfer zones and hanging dip slope hence major drainage catchments and long dispersal depositional systems of sand rich deposits are facilitated during this early fault propagation stage which may be a key aspect for the tectono sedimentary evolution in rift basins in addition the fault and sedimentary relationships defined here may be used as a model when studying less data rich rift basins elsewhere

basinal setting and origin of thick 1 8 km mass flow dominated grand conglomerat diamictites kamoa democratic republic of congo resolving climate and tectonic controls during neoproterozoic glaciations

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

tectonic systems tract and depositional architecture of the western border of the triassic iberian trough central spain abstract during the permian and triassic a sedimentary wedge developed overlying a listric normal fault on the western border of the iberian trough central spain an area was selected for study that provides optimal conditions for a detailed analysis to be made of relationships between geometric strata arrangements tectonic control and sedimentary responses the excellent quality of the outcrops allows the observed patterns of strata to be related to fault growth and developmental of the basin the recognition and mapping of local discontinuities throughout the study area were possible packages of similar strata with different angularity can be discerned between the two main discontinuities geometrical relationships can be established for depositional unit boundaries the architectural style and sediment dispersal patterns interpreted as the results of interactions between sedimentation and tectonics are integrated into a three dimensional tectono sedimentary facies model to explain the basin s infilling is interpreted to be tectonic the rift related three dimensionally linked depositional systems recognized might be defined as tectonic systems tract prosser s 1993 rift related linked depositional systems and their seismic expression in williams g d dobb a eds tectonics and seismic sequence stratigraphy geol soc london spec publ 71 35 66 five such tracts are recognized and related to specific phases of tectonic development

alluvial fans and fluvial fans at the margins of continental sedimentary basins geomorphic and sedimentological distinction for geo energy exploration and development alluvial fans and fluvial fans are the most common depositional landforms along the margins of continental sedimentary basins their occurrence is determined by the area relief and hydrology of the catchment which ultimately control the relative ratios of sediment v flow discharge and runoff regimes fundamental morphological and process distinctions exist between these two kinds of deposystem which are seen as essentially different facies associations and internal architectures for the corresponding deposits alluvial fans commonly develop over short radial distances hundreds of metres to a few kilometres and are constructed by ephemeral flash flow events that lead to poor organization of the sedimentary facies and overall architecture of the corresponding deposits by contrast fluvial mega fans are fed by proper river systems which aggrade much larger volumes of clastic sediment over distances of up to a few hundred kilometres distinct channel belt and overbank domains are developed with a marked heterogeneity in the distribution of sedimentary facies represented by hierarchically well organized fluvial deposits the general properties of alluvial and fluvial fans reflect the different potentials for the corresponding successions to host economically attractive oil and gas resources and the different approaches required in exploration and prediction

stratigraphic architecture of the proterozoic succession in the eastern chattisgarth basin india tectonic implications abstract the basin fill succession of the proterozoic eastern chattisgarth basin comprises a sandstone shale conglomerate dominated shallow marine assemblage and an assemblage of limestone shale pyroclastics deposited in off shelf slope base of slope environments the proximal and distal lithologic assemblages developed as lateral equivalents and show signatures of sea level fluctuations amenable to chronostratigraphic correlation the stratigraphic architecture of the proximal assemblage is characterized by cyclic deposition on different scales the largest order cyclicity is represented by alternating sandstone sequences and mudstone dominated sequences of the order of several tens of metres the smallest order cyclicity is represented by metre scale units punctuated aggradation cycles pac bounded by isochronous surfaces the lowermost large scale sandstone sequence the lohardih sandstone unconformably overlies the highly deformed rocks of the gneissic basement complex the sequence was deposited as alluvial fan fan delta complexes controlled by basin margin faulting the upper two sandstones the daihan sandstone and the kansapathar sandstone represent two different phases of major sand accumulation in fan or river deltas their rapid emplacement over muddy shelf deposits along erosional surfaces signaled abrupt sea level fall and basinward migration of facies belts generation and accumulation of very large volumes of sand and their rapid influx into the basin accompanied by major changes in depositional motif and in the circulation system in the basin collectively indicate that larger order sand depositing cycles were caused by tectonic uplift of the cratonic basement the smallest order cycles the pacs on the other hand may be attributed to glacioeustacy though tectonic control cannot be ruled out the sand deficient mud dominated large scale sequences are attributed to major transgression during periods of relative tectonic quiescence and subsidence of the cratonic hinterland episodic tectonic uplift and derivation of sands from similar quartzo feldspathic sources suggest repeated rifting of the cratonic basement and expansion of the rift into a major marine basin

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

distinctive characteristics of a streamflow dominated alluvial fan deposit sanghori area kyongsang basin early cretaceous southeastern korea abstract in the northwestern part of the non marine kyongsang basin early cretaceous conglomeratic deposits occur at intervals along the northern basin margin and grade basinward into interbedded sandstone and mudstone one of these conglomeratic deposits referred to as the sanghori deposit is 150 m thick and characterized by amalgamated sheets of conglomerate and sandstone facies assemblages 1 and 2 alternating with interbedded sandstone and purple siltstone facies assemblage 3 facies assemblage 1 comprises clast supported disorganized and organized sheet conglomerates interbedded with massive to stratified sandstones this assemblage is interpreted as the product of proximal gravel bed stream deposition facies assemblage 2 consists of trough and planar cross stratified and horizontally stratified sandstones it represents sandy braided stream deposits in which sand bars and dunes were common sedimentary facies and architecture of the coarse grained facies assemblages suggest that the gravel bed and sandy braided streams were wide and shallow and rapidly aggraded during flash floods facies assemblage 3 consists of interbedded purple siltstone and tabular sandstone which show evidence of weak pedogenic modification and bioturbation these characteristics are interpreted as the result of floodplain processes sediments were supplied from the north and dispersed radially forming a streamflow dominated alluvial fan system the sanghori alluvial system was most probably fed from a large drainage basin resulting in the predominance of streamflow deposits and rounded clasts the alternation of the gravel bed stream and floodplain deposits was due to autocyclic switching of active fan sectors under the conditions of relatively slow and steady basin subsidence

geodynamic evolution of the outer arc forearc belt in the andaman islands the central part of the burma java subduction complex the andaman islands the central part of burma java subduction complex expose tectonostratigraphic units of an accretionary prism in an outer arc setting and turbidites of a forearc setting a number of n s trending dismembered ophiolite slices of cretaceous age occurring at different structural levels with eocene trench slope sediments were uplifted and emplaced by a series of e dipping thrusts subsequently n s normal and e w strike slip faults resulted in the development of a forearc basin with deposition of oligocene and mio pliocene sediments metapelites and metabasics of greenschist to amphibolite grade occur in a melange zone of ophiolites the eocene mithakhari group represents pelagic trench sediments and coarser clastics derived from ophiolites evidence of frequent facies changes predominance of mass flow deposits syn sedimentary basinal disturbance and wide palaeogeographic variation indicate deposition of eocene sediments in isolated basins of an immature trench slope setting deposition of the oligocene andaman flysch group in a forearc setting is indicated by the large scale persistence of beds lack of small scale lithological variation bimodal provenance less deformation a well defined submarine fan sequence and development predominantly on the eastern part of the outer arc the mio pliocene archipelago group includes alternations of siliciclastic turbidites and subaqueous pyroclastic flow deposits in the lower part and carbonate turbidites in the upper part suggesting its deposition in the shallower forearc compared to the siliciclastic oligocene sediments

rift related sedimentary evolution and its response to tectonics and climate changes a case study of the guaizihu sag yingen ejinaqi basin china abstract distinguished from most existing rift basin evolutionary models the succession of deep water deposits in the guaizihu sag were mainly developed during rift initiation instead of the greatest tectonic subsidence phase this paper focuses on the detailed analysis of rift related sequence stratigraphy and sedimentary evolution in this continental rift sag and discusses tectonic and climatic controls on filling patterns the deposits of the guaizihu sag can be ascribed to four major depositional systems alluvial fan and fan delta braided delta sublacustrine fan and shallow to deep lacustrine deposits they are in part contemporaneous and some succeeding each other forming five sequence units and corresponding substages of basin evolution i rift initiation ii early rift climax iii middle rift climax iv late rift climax and v late syn rift substages with the onset of fault movement and hot humid climate conditions the first substage is characterized by a number of poorly linked depocenters which consist of alluvial fan fan delta and deep lacustrine deposits with organic rich mudstones the second substage is associated with an enhanced activity of border faults and block rotation this unit is dominated by lacustrine deposits but fan or braided delta and sublacustrine fans also can be observed the third substage is marked by the maximum subsidence rate and shallow lakes fringed by fan and braided deltas the arid environment is likely to be the main factor controlling the lithofacies and filling characteristics of this unit during the fourth substage two early sub sags gradually converged to form a uniform one the relative tectonic quiescence and climate fluctuations sub humid to sub arid favored carbonate deposition the late syn rift unit which is dominated by fine grained deposits is a consequence of degradation of source area mostly tectonic this study shows that the effects of tectonics and climate on lacustrine sedimentation are intimately interwoven tectonism determines the sag structure stratigraphic architecture and spatial distribution pattern of depositional systems climatic conditions superimposed on tectonics tends to be the major control on sediment supply lithofacies types and sedimentary features

the pulse of calm fan deltas abstract at the heart of interpreting the history of earth surface evolution preserved in the rock record is distinguishing environmental allogenic forcing from internally generated autogenic noise allogenic deposits classically have been recognized by their cyclic nature which apparently results from periodic changes in base level sediment supply or tectonics autogenic deposits which are quite variable in their origin and scale are caused by the nonlinearity of sediment transport and might be expected to have a random or scale free fractal signature here we describe a robust mechanism that generates cyclic deposits by an autogenic process in experimental fan deltas sheet flow over the fan surface induces deposition and an increase in fluvial slope and curvature to a point where the surface geometry is susceptible to a channelization instability similar to channel initiation on hillslopes channelized flow results in incision and degrading of the fan surface to a lower slope releasing a

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

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

reconstructing the deadly eruptive events of 1790 ce at kīlauea volcano hawai i a large number of people died during an explosive eruption of k lauea volcano in 1790 ce detailed study of the upper part of the keanak ko i tephra has identified the deposits that may have been responsible for the deaths three successive units record shifts in eruption style that agree well with accounts of the eruption based on survivor interviews 46 yr later first a wet fall of very fine accretionary lapilli bearing ash created a cloud of darkness people walked across the soft deposit leaving footprints as evidence while the ash was still unconsolidated lithic lapilli fell into it from a high eruption column that was seen from 90 km away either just after this tephra fall or during its latest stage pulsing dilute pyroclastic density currents probably products of a phreatic eruption swept across the western flank of k lauea embedding lapilli in the muddy ash and crossing the trail along which the footprints occur the pyroclastic density currents were most likely responsible for the fatalities as judged from the reported condition and probable location of the bodies this reconstruction is relevant today as similar eruptions will probably occur in the future at k lauea and represent its most dangerous and least predictable hazard

facies and basin architecture of the late carboniferous salvan dorenaz continental basin western alps switzerland france the salvan dorenaz basin formed during the late palaeozoic within the aiguilles rouges crystalline basement western alps as an asymmetric intramontane graben elongated in a ne sw direction and bounded by active faults at least 1700 m of fluvial alluvial fan and volcanic deposits provide evidence for a strong tectonic influence on deposition with long term average subsidence rates of 0ae 2m m yr 1 the early basin fill was associated with coarse grained alluvial fans that were dominated by braided channels unit i these issued from the south western margin of the basin the fans then retreated to a marginal position and were overlain by muddy floodplain deposits of an anastomosed fluvial system unit ii that drained towards the ne deposition of thick muds resulted from a reduction in the axial fluvial gradient caused by accelerated tectonic subsidence overlying sand rich meandering river deposits unit iii document a reversal in the drainage direction from the ne to the sw caused by synsedimentary tectonism reflecting large scale topographic reorganization in this part of the variscides with subsidence now preferentially in the w and sw and uplift in the e and ne coarse grained alluvial fan deposits unit iv repeatedly prograded into and retreated from the basin as documented by coarsening upward cycles tens of metres thick reflecting smaller scale tectonic cycles volcanism was active throughout the evolution of the basin and u pb isotopic dating of the volcanic deposits restricts the time of basin development to the late carboniferous 308 295 ma 40 ar 39 ar ages of detrital white mica indicate rapid tectonic movements and exhumation of the nearby basement in unit i youngest ages are close to that of the host sediment but the age spectrum is wide in unit ii high subsidence and or sedimentation rates coincide with very narrow age spectra indicating small homogeneous catchment areas in unit iii age spectra became wider again and indicate growing catchment areas

progressive changes in sedimentary facies and stratal patterns along the strike slip margin northeastern jinan basin cretaceous southwest korea implications for differential subsidence abstract in strike slip basins proximal stratal patterns are a function of displacement on basin bounding faults in order to better understand factors that control changes in sedimentary facies and stratal patterns of the northeastern part of the jinan basin cretaceous a strike slip basin we made a detailed analysis of sedimentary facies depositional architecture and paleoflows the sedimentary successions can be grouped into five facies associations representing five depositional environments 1 facies association fa i alluvial fan 2 fa ii small scale gilbert type delta 3 fa iii large scale steep delta slope 4 fa iv base of large scale steep delta slope and prodelta and 5 fa v lacustrine plain the successions are divided into two distinct sedimentary fills on the basis of facies associations depositional architecture and paleocurrents 1 marginal fill and 2 longitudinal fill the marginal fill ca 3 2 km thick is present along the strike slip basin bounding fault the lower part of the marginal fill ca 1 3 km thick consists of alluvial fan deposits fa i along the bounding fault which are transitional northward to small scale gilbert type delta fa ii and lacustrine plain fa v deposits the upper part of the marginal fill ca 1 9 km thick contains large scale steep delta slope fa iii and base of delta slope prodelta fa iv deposits accompanied with a northward change in facies associations in the marginal fill the successive alluvial fan small scale gilbert type delta and large scale steep delta prodelta deposits are overlapped shingled northeastward the longitudinal fill ca 2 km thick is characterized by eastward overlapped stacks of large scale steep delta slope fa iii and base of delta slope prodelta fa iv deposits with a westward progradation the longitudinal fill was overstepped by the marginal fill the northeastward shingled geometry of the marginal fill was most likely caused by sinistral strike slip displacements on the basin bounding fault the slightly oblique northward progradation of the marginal fill was due to the northward basin floor tilting in the marginal fill the progressive changes in facies and depositional architecture from the lower alluvial fan small scale gilbert type delta to the upper large scale steep delta prodelta are suggestive of increase in basin subsidence along the strike slip basin margin that was closely related to the variation in displacement on the basin bounding fault the sinistral strike slip movements on the bounding fault also caused the eastward overlapping of the longitudinal fill

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

record of palaeoenvironmental changes in a lower permian organic rich lacustrine succession integrated sedimentological and geochemical study of the rudnik member krkonose piedmont basin czech republic abstract this study presents an integrated sedimentological and geochemical analysis of the lower permian rudnik member the most extensive lacustrine deposits in the krkonose piedmont basin grey to black and variegated lacustrine mudstones laminites and carbonates of the rudnik member have a lateral extent of more than 400 km 2 in the studied sections four facies associations were recognised a anoxic offshore b suboxic to oxic offshore c nearshore and mudflat and d slope deposits in the northern part of the e w elongated basin anoxic to suboxic organic rich offshore lacustrine facies dominate and form a succession up to 130 m thick fan delta and turbidite facies occur locally along the faulted northern basin margin the central part of the basin is occupied by anoxic to oxic offshore facies interfingering with nearshore carbonate and mudflat facies of the low gradient lacustrine margin in the central part of the basin the thickness of the lacustrine deposits of the rudnik member reaches up to 60 70 m in the southern part of the basin fluvial and alluvial plain facies dominate and alternate with minor lacustrine nearshore facies the lateral facies distribution indicates that subsidence along the northern basin fault was the main mechanism generating the asymmetric infill geometry in the basin s half graben setting the 1 8 o values of primary and early diagenetic calcite range between 11 0 and 1 3 v pdb and 1 3 c values between 5 1 and 3 7 most of the data fall within the range of freshwater limestones coarser grained pure microspar laminae show more positive 1 3 c values in comparison to clayey organic rich micrite laminae and are interpreted as a record of bioinduced precipitation during seasonal eutrophication the obtained 1 3 c toc values range from 29 0 to 24 0 the total organic carbon toc content from 0 26 to 23 maceral analysis and rock eval pyrolysis indicate that most of the samples contain a mixture of aquatic and terrestrial organic matter but two minor distinctive groups of samples with algally dominated and terrestrially dominated organic matter composition respectively were also found the study of vertical changes in boron content in the clay fraction of the lacustrine mudstones shows that high lake level stages were periods of lower salinity with the lowest boron contents from 73 to 268 ppm and periods of falling lake level were followed by significant increases in salinity with much higher boron values 293 603 ppm lake level fluctuations of the rudnik lacustrine system which are recorded by shallowing up units of sedimentary facies within most of the sections throughout the basin can also be traced within the monotonous black shale dominated sections where no sedimentological evidence of these lake level changes exists good indicators for such changes seem to be the 1 8 o and 1 3 c values of primary calcite 1 3 c toc and hi these lake level fluctuations are interpreted as driven by climatic oscillations in the order of tens of thousands years which could reflect climatic changes connected with the last glaciation event of gondwana

metalliferous manganese oxide mineralization associated with the boleo cu co zn district mexico apart from its large reserves of cu co zn mineralization contained within stratiform ore beds or mantos the boleo district of central baja mexico also contains significant concentrations of mn oxides typically 2 3 wt mn interspersed with hydrothermal sulfides and both hydrothermal and weathering related metal oxide minerals within the mantos mn oxides occur as concentric nodules disk shaped concretions laminae granules or aggregates veins dendrites and various replacements the oxides are composed of varying amounts of hollandite cryptomelane todorkite romanechite pyrolusite and x ray amorphous mn oxide chemically the manto oxides are unique owing to their extraordinarily high abundances of co cu pb and zn typically 2 5 wt but up to 23 wt existing mineralogical and geochemical classifications are ambiguous regarding the genetic classification of mn oxides within the mantos a new mno 2 fe 2 o 3 t mgo diagram is proposed in order to discriminate among highly metalliferous mn oxides based on the new classification scheme manto mn oxides record a complex interaction between hydrothermal and diagenetic processes to better understand the mechanism of oxide deposition radiogenic isotopes sr and pb and ree geochemistry were used to delineate fluid and metal sources isotopic and ree constraints indicate that the boleo mn oxides are largely hydrothermal in origin however they show varying degrees of modification resulting from diagenetic processes hydrothermal mn oxides are syngenetic synsedimentary to syndiagenetic in origin and were precipitated in association with sulfides reflecting localized variations in redox conditions within the manto sequence due to the downward infiltration of metal bearing brines apart from morphological and stratigraphic evidence e g occurrence of nodular crusts along the upper contact of the manto a syngenetic origin is supported by a single k ar date of 7 0 0 2 ma which is within the estimated age range for deposition of boleo formation clastic sediments interaction between brine and seawater or brine and pore fluid as it infiltrates the sedimentary pile produced hydrothermal precipitates with certain hydrogenetic attributes i e positive ce anomaly lree enrichment on the other hand oxides with hydrogenetic and with mixed hydrothermal hydrogenetic affinities represent diagenetic alteration and remobilization of earlier formed hydrothermal oxides by meteoric fluids by far the greatest degree of remobilization occurred in response to compactional dewatering of the manto where the dewatering pore waters enriched the uppermost manto strata in mn fe zn co and to lesser degrees cu later diagenetic modifications coincided with the development of a supergene overprint which typifies boleo formation strata at elevations above the present day water table

thrust ridge paleodepositional model for the upper freeport coal bed and associated clastic facies upper potomac coal field appalachian basin u s a abstract a blind thrust ridge model is proposed to explain the lack of coarse clastic material in the vast minable upper freeport coal bed uf this coal bed contains only fine elastic partings and is overlain by regionally extensive closely spaced channel belt deposits in the upper potomac coal field of the appalachian basin a blind thrust ridge may have formed a sediment trap and prevented c coarse fluvial sediments from entering the swamp during a period westphalian d when the thick upper freeport peat accumulated anticlinal thrust ridges and associated depressions may have existed uninterrupted for about 40 km parallel to the appalachian orogen sediment shed from the breached anticlinal ridges accumulated in the sediment trap and was carried out of the ends of the trap by streams that occupied the shear zone at the ends of the blind thrust ridge the extent parallel to the orogen of thick areally extensive uf is related to the length of the blind thrust ridge that in turn controlled the spacing of the river derived coarse clastic sediments that entered the main basin from the east the thrust plane eventually emerged to the surface of the blind thrust ridge and peat accumulation was terminated when the ridge became eroded and the sediment trapped behind it was released the peat was buried by abundant coarse clastic sediment which formed closely spaced channel belts and intervening flood basins this model has implications for widespread peat deposits now coal that developed in tropical regions a few hundred kilometers from the sea in a tectonically active foreland basin