the composition of the subsurface neogene shales of the surma group from the sylhet trough bengal basin bangladesh abstract nineteen shale samples from six wells penetrating the neogene surma group in the sylhet trough in northeastern bangladesh were analyzed by x ray diffraction x ray fluorescence spectrometry and direct current plasma optical emission spectrometry mineralogically the subsurface neogene shales of the surma group comprise predominantly quartz plagioclase illite chlorite kaolinite with lower amounts of k feldspar dolomite and smectite and minor to trace amounts of calcite and siderite significant variation in the content of k feldspar smectite and illite smectite mixed layer clays with depth has been observed k feldspar has not been noted below the depth of about 3200 m and smectite has not been observed deeper than 3000 m it is inferred that illite chlorite quartz and feldspar are predominantly detrital in origin reflecting a fast rising source terrain with no intense weathering activity geochemically the mean major element composition of the shales is similar to that of the average shale with the exception of the cao content which is lower here the low cao content could be due to lower carbonate and total organic content the samples are enriched in sc and cu and are depleted in be sr and la other trace elements have values close to the average shale the geochemical characteristics suggest that the neogene shales of the surma group were derived from an active margin setting related to a recycled source

geochemistry and provenance of the middle ordovician austin glen member normanskill formation and the taconian orogeny in new england the austin glen member of the upper middle ordovician normanskill formation is a sandstone shale ysch succession deposited in the foreland of the taconian orogen petrographic major and trace element and nd pb isotopic data provide substantial constraints on its provenance lack of k feldspar and paucity of plagioclase in addition to the dominance of sedimentary rock fragments indicate that the source was dominated by recycled sedimentary components major and trace element data support this conclusion and indicate that the provenance of both shales and sandstones was the same no evidence of an ophiolitic or volcanic component was observed interpretation of nd isotopic characteristics are complicated by a partial resetting of the nd isotope system at about the time of sedimentation but indicate that the provenance of the austin glen member had a long term history of light rare earth element lree enrichment average tdm 1a8 ga furthermore nd isotopic compositions are extremely homogeneous end 8a1 0a6 1 s d n 23 at 450 ma the approximate depositional age indicating either a single source or very well mixed sources 207pb 204pb ratios are variable but within the range of pb isotopic compositions typically described as grenvillian the range of 207pb 204pb is greater than expected for the range of 206pb 204pb and suggests an additional component of pb possibly introduced during diagenesis the immediate source of the austin glen member may have been the accretionary prism that developed as older sediments of the laurentian margin were scraped off the basin oor incorporated within the accretionary prism and shed into the basin no evidence indicating the arrival of an undifferentiated island arc or continental fragment during the taconian orogeny has been found the data acquired during this study can be explained almost exclusively by grenville province source components but with possible additional contributions from older laurentian terranes and late proterozoic rift volcanics that are not readily quanti ed but likely to have been minor accordingly we conclude that the taconian orogeny in new england involved either 1 a continental arc that involved exclusively laurentia 2 collision of a continental block with identical geochemical characteristics as laurentia or 3 essentially no detritus from any exotic colliding block island arc or continental fragment reached the foreland basin at the time of austin glen deposition

provenance of xigaze fore arc basin clastic rocks cretaceous south tibet the xigaze group of south tibet was deposited in a fore arc basin produced by northward subduction of the neotethys under eurasia during middle cretaceous time clasts of andesite from the gangdese magmatic belt to the north and limestone clasts from a shelf rimming the basin to the north are the near exclusive detrital components in the xigaze group in the eastern part of the studied region and in older albian deposits in the west younger cenomanian coniacian deposits from western and central parts of the xigaze group show increasing amounts of tonalite pebbles in conglomerates and quartz sand these trends reflect differential arc uplift and erosional dissection with higher rates in the west some arenites show evidence for sediment contribution from an additional source probably from an orogen to the north of the lhasa block the presence of this orogen indicates that crustal thickening of tibet is not restricted to cenozoic times the middle cretaceous gangdese belt apparently lacked acid volcanic rocks this suggests a low degree of crustal contamination and or differentiation of primitive magma probably because the crust beneath the arc area was thin a thin crust is in accordance with a low elevation of the arc deduced from continuous carbonate production on and marine excursions beyond the arc magma eruption rates of the arc estimated from the xigaze basin sediment volume were probably low 7 5 km 3 km arc segment per million years but within the range of modern arcs the varying sediment compositions of the xigaze group may be typical of fore arc basin deposits in front of continental magmatic arcs the lack of a correlation of trends in sediment composition with fining upward sedimentary supercycles in the xigaze group is taken as evidence in favor of a eustatic cycle control

minimum age of initiation of collision between india and asia north of everest based on the subsidence history of the zhepure mountain section the collision of india with asia one of the most profound tectonic events to have occurred in past 100 m y is thought to have had geological geochemical and climatological consequences of global extent surprisingly the age of initiation of this collision remains poorly constrained estimates range from the late cretaceous 65 ma to latest eocene 40 ma with little consensus in between this paper reviews the stratigraphic section preserved on zhepure mountain on the north flank of everest mount qomolongma and its implied subsidence history zhepure mountain lies about 65 km south of the indus yarlung zangbo suture and contains the most complete and youngest passive margin shelf sediments in the tethyan himalayas on the basis of the subsidence history of the preserved section there is no evidence of acceleration of the subsidence up to the youngest rocks therefore collision related loading and accelerated subsidence must post date the youngest sediments preserved which date from the earl

flexural eustatic numerical model for drowning of the eocene perialpine carbonate ramp and implications for alpine geodynamics the paleocene2eocene nummulitic limestone formation of the alpine periphery occupies the lowermost part of a stratigraphic trinity above a major basal unconformity it is thought to have accumulated as a foraminiferal carbonate ramp at the distal featheredge of the underfilled north alpine and southwest alpine foreland basin we present the results of a numerical model that links carbonate sedimentation at the distal featheredge of a peripheral foreland basin to the flexural subsidence of an elastic plate subjected to a distributed load with a superimposed eustatic sea level history carbonate accumulation is treated as depth dependent model parameters are constrained by geological and geophysical observations of the alpine orogen and its peripheral foreland basin and from literature on the ecology of benthic foraminifers the generic alpine model shows that the carbonate ramp accumulates as a number of sedimentary cycles before rapid drowning giving rise to a retrogradational stratigraphic package terminated by a surface of accelerated transgression and backstepping running the model with sets of parameter values appropriate to the paleocene to middle eocene nummulitic limestone in central eastern switzerland and the late eocene nummulitic limestone

age of initiation of the india asia collision in the east central himalaya abstract we document the stratigraphy and provenance of the lower tertiary terrigenous sections in the zhepure shan region of the tethyan himalaya southern tibet using petrographic and geochemical whole rock and single grain techniques the cretaceous early tertiary shelf deposits of shallow marine carbonates and siliciclastics of the former indian passive margin near the western end of the zhepure shan are conformably overlain by lower tertiary clastic rocks sandstones in the jidula formation paleocene mostly contain monocrystalline quartz grains of cratonic origin in contrast significant amounts of immature framework grains with a distinct ophiolitic and volcanic arc influence are present in the youxia early eocene and shenkeza post early eocene formations major trace and rare earth element concentrations in both sandstones and shales complement the petrographic data and indicate that the source of the jidula formation consisted primarily of quartzose basement rocks probably of indian con

the xigaze forearc basin evolution and facies architecture cretaceous tibet abstract the mid cretaceous to eocene flysch deposits of the xigaze forearc basin in southern tibet were investigated in a 120 km segment along the indus yarlung suture zone the basin evolved south of the magmatic arc gangdise belt of the lhasa block on top of trapped oceanic or transitional crust remnants of shelf carbonates are preserved along the northern edge of the basin the mapped segment was shortened by about 65 metamorphism reached low grade conditions along the northern margin of the basin the flysch sequence reaches a thickness of at least 5 km and consists to a large degree of volcaniclastic andesitic to dacitic material shed from the magmatic arc gangdise belt particularly in the western part of the study area plutonic and sedimentary rocks from deep erosion levels and or more distal sources contributed to the basin fill rivers from the lhasa block acted as point sources and fed five major deep sea channel systems turbidity currents in the channels were directed towards the growing accretionary wedge of the subduction zone thus indicating that the basin was continuously filled up to outer ridge level and gradually shallowing the forearc flysch is subdivided into at least three megasequences which begin with wide up to several km incised 10 to 50 m coarse grained channel fills and their associated fan deposits the upper parts of the megasequences contain hemipelagic dark shales and marls deposited above the calcite compensation depth lateral channel migration channel lobe switching but also volcanic pulses generated a predominantly fining upward high frequency cyclicity after continental collision the marine sedimentation in the forearc basin was replaced by fluvial deposits of the eocene oligocene qiuwu formation which is time equivalent to the kailas and indus molasses farther west and rich in coarse gravel derived from the gangdise belt both forearc flysch and qiuwu formation were deformed simultaneously during the miocene we assume that the molasse type qiuwu formation represents the final continental facies of the forearc basin filling

the yarlung zangbo paleo ophiolite southern tibet implications for the dynamic evolution of the yarlung zangbo suture zone the yarlung zangbo suture zone a major geological structure in tibet is well known as the locus of tectonic emplacement of the tethyan ophiolites current models propose that most of the east tethyan oceanic lithosphere was subducted within a single subduction zone active during the middle or late cretaceous which was completed during the paleogene collision between india and asia the early cretaceous sedimentary giabulin formation in southern tibet includes conglomeratic members that contain ultramafic and mafic plutonic pebbles as well as radiolarian chert clasts that record the erosion of oceanic lithosphere involved in a subduction event which occurred earlier than previously believed geochemical analyses mineral chemistry stratigraphic chronology and sedimentary analysis including source provenance suggest that the pebbly conglomerate was formed through erosion of an unknown ophiolitic source that was geochemically distinguishable from the xigaze ophiolites within the yarlung zangbo suture zone southern tibet we infer the existence of an older ophiolitic source termed the yarlung zangbo paleo ophiolite that was dismembered and eroded during an earlier subduction stage not taken into account in current models q 2000 elsevier science ltd all rights reserved

sr isotope evolution of seawater the role of tectonics we use a high resolution seawater sr isotopic evolution curve for the last 100 m y in conjunction with modern riverine sr flux measurements and also geologic tectonic and geochronological data to make the case for a close relationship between seawater sr isotopic composition and the india asia continental collision using a simple seawater sr budget model we begin by showing that the sr flux associated with alteration of seafloor basalts is too small and does not have the right time evolution to account for much of the seawater sr isotopic curve of the last 100 m y the flux of dissolved sr carried by rivers originating in the himalaya tibet region on the other hand is presently a significant fraction of the global sr budget we calculate how this riverine flux would have had to change with time in order to match the observed seawater sr isotopic curve and find that the riverine flux remains relatively constant prior to the collision of india with asia but then increases very significantly after collision we note that the period of most rapid change in seawater sr isotopic ratio from 20 ma to 15 ma is also a period of exceptionally high erosion in parts of the himalayas and the tibetan plateau as further evidence that sr derived from the collision of india with asia plays a major role in the sr isotopic evolution of seawater we show that the total amount erosion of the himalaya tibetan plateau since collision which we calculate separately represents a total amount of sr that is very nearly the same as the cumulative amount required by the sr isotopic change of seawater since collision the relationship between erosion and riverine sr flux allows us to use the sr isotopic evolution of seawater to reconstruct a history of erosion since collision and we find that the erosion rate accelerates with time since collision with the present having the largest rate when we apply the sr budget model to the entire phanerozoic using a new compilation of deformed continental area versus time we find that we can account for the large scale structure of the seawater sr isotopic curve but fail to reproduce several local maxima and minima especially in the period 100 300 ma the present high s7sr s6sr of seawater and similar highs in the devonian and cambrian do correlate with extensive deformation on the continents

latest marine horizon north of qomolangma mt everest implications for closure of tethys seaway and collision tectonics the newly discovered marine horizon at zhepure syncline north of qomolangma revises timing of the closure of the eastern neo tethys seaway in the central himalayas the marine pengqu formation conformably overlies a lutetian shallow water carbonate platform and comprises shales interbedded with sandstones deposited in a neritic shelf environment the strata are dated by nannofossils and foraminifera as late early lutetian to late priabonian age np15 np20 deposited 47 34 ma indicating that the final closure of the tethys seaway in this region occurred at 34 ma the newly discovered strata provide evidence about emplacement of a major thrust sheet south of southern tibet prior to 37 ma which affected the regional climate

age of initiation of the india asia collision in the east central himalaya a discussion in their recent article zhu et al 2005 provide new data on the stratigraphy and provenance of the paleogene terrigenous strata in the zhepure shan range of the tethyan himalayas southern tibet using petrographic and geochemical whole rock and single grain techniques observed changes in the sandstone composition according to the authors indicate the onset of the india asia collision and the first development of the foreland basin immediately south of the india asia suture zone which occurred at ma the authors pre50 6 0 2 sent valuable new geochemical data for the paleogene clastic rocks in southern tibet including their source areas and tectonic affinity which they use to interpret the geotectonic history of the tethyan himalaya the aim of the present discussion is to point out several erroneous claims and conclusions made by the authors that have a considerable effect on the interpretation of regional stratigraphy lithofacies the closing of the tethys seaway and the initiation of the india asia collision the authors reject most of the conclusions reached by wang et al 2002 which were derived from a study of the same stratigraphic sequence at the same location qumiba section for details see fig 1 the location of the section as given in wang et al 2002 was based on a chinese military map and the location given by zhu et al 2005 using a gps locator was not correct but their section is the same one studied by wang et al 2002 see fig 1 the main objective of the wang et al 2002

detrital chromian spinels in rhenohercynian greywackes and sandstones givetian visean variscides germany as indicators of ultramafic source rocks more than 75 of heavy mineral spectra of rhenohercynian greywackes from the harz mountains famennian visean the werra greywacke frasnian famennian and the rhenish slate mountains frasnian visean contain small amounts of detrital chromian spinels similar grains have also been proven in sandstones of the givetian stiege beds east harz nappe these sandstones are derived from the area of the mid german crystalline rise which is commonly interpreted as the source area of the rhenohercynian greywackes microprobe analyses have revealed mainly a picotite composition presumable source rocks were chiefly alpine type peridotites due to the onset of spinel sedimentation in givetian times these peridotites must be at least partly of pre givetian age and are assumed to be linked to cadomian subduction potential source rocks are not exposed in the present outcrops of the mid german crystalline rise nor in the rhenohercynian zone or the northern phyllite zone which implies that the presumed mafic to ultramafic lithologies were completely eroded and or downfaulted during later stages of the variscan orogeny

kinematics topography shortening and extrusion in the india eurasia collision we examine the problem of partitioning between shortening and extrusion in the india asia collision since 45 ma we compute the amount of shortening expected from the kinematics of india s motion with respect to eurasia using the reconstruction at collision time to put bounds on the possible amounts of surface loss within greater india and within eurasia we then compute the amounts of surface loss corresponding to the thickened crust of tibet and of the himalayas assuming conservation of continental crust the spatial distribution of the topography reveals a large systematic deficit of crustal thickening distributed rather uniformly west of the eastern syntaxis but an excess of shortening east of it this distribution indicates an important eastward crustal mass transfer however the excess mass east of the eastern syntaxis does not account for more than one third to one half of the deficit west of the eastern syntaxis the deficit may be accounted either by loss of lower crust into the mantle for example through massive eclogitization or by lateral extrusion of nonthickened crust a mass budget of the crust of the himalayas indicates that lower crust has not been conserved there but the deficit is so large that local loss in the mantle is unlikely to be the unique cause of the deficit alternatively following zhao and morgan 1985 lower crust may have been transferred below the tibetan crust we conclude that a combination of possible transfer of lower crust to the mantle by eclogitization and lateral extrusion has to account for a minimum of one third and a maximum of one half of the total amount of shortening between india and asia since 45 ma this conclusion leaves open the possibility that the partitioning between extrusion and loss of lower crust into the mantle on the one hand and shortening on the other hand has significantly changed during the 45 m y history of the collision

provenance of the lower tertiary murree redbeds hazara kashmir syntaxis pakistan and initial rising of the himalayas abstract the murree supergroup of northern pakistan is represented by an over 6 km thick succession of deltaic redbeds and intercalated impure foraminiferal limestones of latest palcocene to middle eocene ilerdian to lutetian age cropping out in the northern part of the hazara syntaxis and by redbeds of younger age early middle eocene to early miocene cropping out in the southern part of the syntaxis rawalpindi area the quartzolithic composition of the murree redbeds testifies to a collision orogen provenance detritus was derived from a suture belt including thrust sheets of metasedimentary and subordinately sedimentary rocks volcanic or volcaniclastic rocks and ophiolites phyllite rock fragments are most common in the ilerdian sandstones whereas volcanic and carbonate rock fragments are more abundant in the lutetian sandstones minor quantities of chert and serpentineschist indicating contribution from uplifted subduction complex sources as well as siltstone shale and limestone grains are invariably present detrital modes of sandstones and southwestward progradation of tertiary clastic wedges both testify to provenance from the proto himalayan chain located to the north and uplifted since the very first stages of the india asia continental collision at the end of the paleocene the coeval chulung la redbeds of the tethys himalaya instead consisting of volcanic and subordinate ophiolitic detritus testify to exclusive provenance from the obducting trans himalayan are trench system this major petrographic difference may be accounted for by the different structural setting of the chulung la piggy back and murree foreland basins these two distinct collisional basins have been separated probably since the onset of collision by a fold thrust belt beginning to rise in the position occupied today by the high and lesser himalayan structural domains throughout the murree supergroup main petrographic parameters do not vary greatly and volcanic sedimentary low grade metasedimentary and ophiolitic detritus persisted until the early miocene indicating slow progressive growth of the chain only during the middle miocene when the highly metamorphosed rocks of the high himalaya were carried southward along the main central thrust mct the mountain range began to rise to dramatic heights and huge amounts of detritus started to feed the siwalik foreland basin sandstones and the remnant ocean turbidites of the indus and bengal fans

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

stratigraphic relationships and detrital composition of the medial ordovician flysch of western new england implications for the tectonic evolution of the taconic orogeny a reply to rodgers we present new stratigraphic and petrographic data on the easterly derived medial ordovician flysch sequence of western new england and eastern new york state a conformable relationship exists between the flysch and underlying early paleozoic continental rise sediments within the western taconic allochthon farther east in the allochthon we observe a possibly disconformable relationship contrary to previous interpretations these facts suggest that at any place within this paleogeographic realm the sediments were undeformed and untransported at the initiation of flysch deposition at least three sources contributed detritus to the flysch 1 taconic sequence sediments 2 deformed and metamorphosed pelitic psammitic and volcanic lithologies and 3 igneous rocks of dominantly mafic ultramafic affinities these three sources are respectively interpretable as continental rise accretionary prism and ophiolitic volcanic arc assemblages which are recognized in the regional geology of western new eng

melt inclusions in detrital spinel from the se alps italy slovenia a new approach to provenance studies of sedimentary basins detrital spinel is a widespread heavy mineral in sandstones from the maastrichtian middle eocene sedimentary basins in the se alps chemistry of detrital spinels from the claut clauzetto and julian basins n italy and nw slovenia is used to constrain petrological and geochemical affinities and tectonic provenance of the source rocks in addition we have analysed melt inclusion compositions in the detrital volcanic spinels to better constrain the nature of their parental magmas this is the first study of melt inclusions in detrital spinels two principal compositional groups of detrital spinels are recognised based on their tio2 and fe2 fe3 one derived from peridotites the other from basaltic volcanics peridotitic spinels are more abundant and have tio2 0 2 better distinguish the differences between the compositions of their host spinels and help to further clarify the geodynamic provenance of extrusive source rocks several compositional groups of melt inclusions have been recognised and represent diverse magmatism of marginal basins including morb and subduction related geochemical types as well as magmas characteristic of early continental rifting these results combined with the data on regional ophiolitic complexes and tectonic reconstructions favour the internal dinarides of yugoslavia as a possible source area for the se alps sediments

the ophiolites of the tibetan geotraverses lhasa to golmud 1985 and lhasa to kathmandu 1986 ophiolite belts are found in tibet along the zangbo banggong and jinsha river sutures and in the anyemaqen mountains the eastern extension of the kunlun mountains where studied the zangbo suture ophiolites are characterized by apparently thin crustal sequences 3 3 5 km an abundance of sills and dykes throughout the crustal and uppermost mantle sequences common intraoceanic melanges and unconformities and an n morb petrological and geochemical composition the ophiolites probably formed within the main neo tethyan ocean and the unusual features may be due to proximity to ridge transform intersections rather than to genesis at very slow spreading ridges as the current consensus suggests the banggong suture ophiolites have a supra subduction zone petrological and geochemical composition although at least one locality in the ado massif shows morb characteristics however it is also apparent that the dykes and lavas show a regional chemical zonation from boninites and primitive island arc tholeiites in the south of the ophiolite belt through normal island arc tholeiites in the central belt to island arc tholeiites transitional to n morb in the north the ophiolites could represent fragments of a fore arc island arc back arc complex developed above a jurassic northward dipping subduction zone and emplaced in several stages during convergence of the lhasa and qiangtang terranes the ophiolites of the jinsha river suture have a n morb composition where analysed but more information is needed for a proper characterization the anyemaqen ophiolites where studied have a within plate tholeiite composition and may have originated at a passive margin it is not however certain whether true oceanic lithosphere as opposed to strongly attenuated continental lithosphere existed in this region

eocene early miocene foreland basin development and the history of himalayan thrusting western and central nepal sedimentologic petrographic and u pb detrital zircon ages from middle eocene through early miocene sedimentary rocks in the lesser himalayan zone of western and central nepal indicate that a peripheral foreland basin system had developed in the eastern himalayan collision zone by middle eocene time the shallow marine eocene bhainskati formation accumulated in a back bulge depozone between a southward migrating forebulge and the indian craton migration of the forebulge through this region during eocene oligocene time produced a regional unconformity that spans 15 20 myr by early miocene time the forebulge unconformity was onlapped by the distal fringes of the southward migrating foredeep depozone represented by fluvial deposits of the dumri formation continued southward migration of the foredeep during the neogene accommodated the fluvial siwalik group light mineral provenance data and u pb detrital zircon ages suggest that the bhainskati was derived partly from tethyan sedimentary rocks of the tibetan himalayan zone during initial growth of the himalayan fold thrust belt the dumri was derived from metasedimentary and crystalline rocks of the greater himalayan zone during emplacement of the main central thrust and contemporaneous tectonic unroofing by normal faulting along the south tibetan detachment system the lesser himalayan crystalline thrust sheets were emplaced soon after deposition of the dumri formation 15 10 ma paleocurrent and lithofacies data from the dumri formation indicate deposition by west southwestward flowing rivers that drained into the indus portion of the himalayan foreland basin system during the early miocene thick channel sandstones in the lower dumri may represent the early miocene counterpart of the modern ganges river eastward diversion of the ganges drainage system to near its present location had occurred by 15 ma as the high standing aravalli range on the northern indian shield approached the front of the fold thrust belt assuming reasonable values for the flexural rigidity of indian lithosphere the time span of the forebulge unconformity yields a velocity of 14 33 mm yr for the southward migration of the fold thrust belt relative to india this range of values is consistent with neogene and present day estimates and suggests that only one third to one half of india eurasia convergence has been accommodated by shortening in the himalayan fold thrust belt since the onset of collision

classification of paleosols despite increased interest in paleosols during the past decade no satisfactory classification is in current use presented here is a largely descriptive classification system that utilizes those pedogenic features that have the highest preservation potential in the rock record emphasized in the classification are morphological and mineralogical features that are easily recognizable in the field and through the petrographic microscope the classification is based on evaluation of the relative prominence in a paleosol of six pedogenic features or processes organic matter content horizonation redox conditions in situ mineral alteration illuviation of insoluble minerals compounds and accumulation of soluble minerals the most prominent of these six features processes provides the key to classifying a paleosol into one of nine orders four of the order names are borrowed from soil taxonomy histosol spodosol oxisol vertisol whereas the other five order names are presented here for the first time calcisol gypsisol gleysol argillisol protosol the orders may be preceded by one or more subordinate modifiers that describe other important features of the paleosol the classification is relatively easy to apply to the rock record and should enhance communication and aid in the standardization of terminology

a reinterpretation of the balakot formation implications for the tectonics of the nw himalaya pakistan 1 the balakot formation of the himalayan foreland basin in pakistan was originally described as a 8 km thick clastic red bed succession within which are stratigraphically intercalated four gray marl bands containing fossils dated at 55 50 ma on this basis and the reported conformable contact with the underlying paleocene patala formation the balakot formation red beds were interpreted as tidal facies dated at 55 50 ma by 20 myr the oldest foreland basin sediments eroded from the metamorphic orogen however our new detailed structural mapping shows the balakot formation to be in tectonic contact with the underlying patala formation and the marl bands to be structurally intercalated with the red beds hence neither the nature of the balakot formation lower contact nor the intercalated marl bands can be used to date the red beds our ar ar dating of 257 individual detrital white micas from the balakot formation red bed sandstones shows that the red bed succession must be younger than 37 ma and we thus conclude that the first exposed foreland basin continental sediments eroded from the metamorphic mountain belt were deposited after 37 ma at least 15 myr later than previously believed these new structural stratigraphic and isotopic data from the balakot formation provide new constraints to the early tectonic evolution of the mountain belt result in reassessment of the facies and provenance of the balakot formation and force reconsideration of models of orogenesis basin evolution and the timing and diachroneity of india asia collision that are based on the original documentation of the balakot formation index terms 1040 geochemistry isotopic composition chemistry 8099 structural geology general or miscellaneous 8102 tectonophysics continental contractional orogenic belts 9320

stratigraphy of the upper cretaceous and lower tertiary strata in the tethyan himalayas of tibet tingri area china the 1500 m thick marine strata of the tethys himalaya of the zhepure mountain tingri tibet comprise the upper albian to eocene and represent the sedimentary development of the passive northern continental margin of the indian plate investigations of foraminifera have led to a detailed biozonation which is compared with the west tethyan record five stratigraphic units can be distinguished the gamba group upper albian lower santonian represents the development from a basin and slope to an outer shelf environment in the following zhepure shanbei formation lower santonian middle maastrichtian outer shelf deposits continue pebbles in the top layers point to beginning redeposition on a continental slope intensified redeposition continues within the zhepure shanpo formation middle maastrichtian lower paleocene the series is capped by sandstones of the jidula formation danian deposited from a seaward prograding delta plain the overall succession of these units represents a sea level high at the cenomanian turonian boundary followed from the turonian to danian by an overall shallowing upward megasequence this is followed by a final transgression regression cycle during the paleocene and eocene documented in the zhepure shan formation upper danian lutetian and by upper eocene continental deposits the section represents the narrowing and closure of the tethys as a result of the convergence between northward drifting india and eurasia the plate collision started in the lower maastrichtian and caused rapid changes in sedimentation patterns affected by tectonic subsidence and uplift stronger subsidence and deposition took place from the middle maastrichtian to the lower paleocene the final closure of remnant tethys in the tingri area took place in the lutetian

the provenance of sediments in the barreme thrust top basin haute provence france abstract this paper records the results of an integrated analysis of heavy minerals sedimentary facies palaeocurrents and structural data the objective of the study was to evaluate the provenance of the sediments of the barreme thrust top basin this basin contains a late eocene to late oligocene succession of shallow marine alluvial and lacustrine sediments late eocene marine transgression resulted in starvation of clastic supply to the basin hence the calcaires nummulitiques received only a limited influx of heavy minerals derived from local sedimentary sources augmented by the first appearance of assemblages with andesitic affinities at c 42 41 ma clastic members associated with the overlying marnes bleues record a significant diversification of provenance and sediment transport paths clastic detritus supplied to the shallow marine gres de ville were derived from permo triassic sediments to the south conglomeratic submarine channels of the la poste member mark the introduction of alpine ophiolite blueschist derived minerals at c 37 35 ma eroded from the embrun ubaya thrust complex to the ne the deltaic st lions member is dominated by volcaniclastic assemblages completing the marine fill the shoreface gres de senez received detritus from the southerly maures esterel crystalline massif the succeeding oligocene continental sediments record an increasing supply of minerals from alpine lithologies the alluvial molasse rouge contains reworked sedimentary detritus including material cannibalized from the underlying marine tertiary and first cycle alpine minerals the succeeding lacustrine serie saumon serie grise show the increasing diversity of alpine suites the youngest sediments the fluvial gres verts signal a major influx of alpine derived assemblages related to reactivation of the embrun ubaye thrusts between c 28 27 and 25 24 ma

ophiolitic source rocks for taconic age flysch trace element evidence flysch generated along the appalachian orogen during the ordovician taconic orogeny ranges in age from late arenig to early caradoc allochthonous flysch and from late llanvirn to ashgill autochthonous flysch sandstones in these units are dominantly lithic arenites with a heavy mineral suite containing common to abundant mg rich chromite north of the canada united states border the only reasonable sources for the chromite were the lower ultramafic units of obducted ophiolites trace element analyses cr ni v cu ti zr y of flysch sandstones indicate a striking increase in cr and ni concentrations from the united states appalachians to the canadian appalachians in the united states units cr is in the range of 10 to 50 ppm canadian flysch units average an order of magnitude more cr these results suggest that ophiolite obduction either did not occur or was of minor importance during the taconic orogeny in the united states appalachians the difference in ophiolite abundance between the canadian and united states appalachians suggests a fundamental difference in tectonic style along the orogen a feature that must be accommodated by plate tectonic models new models will probably need to consider both obliquity of subduction and geological complexity of the ordovician collision zone in order to explain the spatial distribution of obducted ophiolite sheets

the transition from tethys to the himalaya as recorded in northwest pakistan early cenozoic sedimentary rocks exposed in the kohat plateau of northwestern pakistan record tectonic closure of the tethys sea and development of a restricted marine basin that formed during himalayan collision between india asia and a series of microplates in the paleocene initial subsidence of the basin was caused by the downward deflection of the indian plate in response to loading of the asian plate the western margin of the early eocene basin was dominated by deposition of shale sandstone and conglomerate derived from microplates located to the north and west of the indian continental margin the eastern margin of the basin was a carbonate shelf and sabkha flat salt deposition occurred subaqueously in the central parts of the basin in the late early eocene redbeds derived from the northwest were deposited by a fluvial and or deltaic system this influx of clastic sediments marks the earliest record of terrestrial foreland basin deposition in northwest pakistan during the middle eocene the basin was reflooded and a carbonate shelf developed relative sea level rise may reflect subsidence of the indian plate in response to continued crustal loading in the himalayan suture zone uplift and erosion occurred between the late eocene and miocene possibly related to a peripheral bulge south of the himalayan suture zone the main phase of himalayan foreland basin fluvial deposition began in the miocene renewed uplift related to final collision of india and afghanistan during the pliocene is recorded by a thick sequence of conglomerate in the western kohat plateau correlation with eocene sedimentary rocks from southern pakistan to northern india delineates the depositional systems that developed as the tethys sea closed during himalayan convergence

reconstruction of environmental and climate changes at braamhoek wetland eastern escarpment south africa during the last 16 000 years with emphasis on the pleistocene holocene transition abstract a paleo environmental record covering the last 16 ka 16 000 cal yrs bp from the eastern areas of the summer rainfall region in south africa is presented this area is until now sparsely investigated due to the lack of well preserved natural archives for this study we used a peat section from a wetland situated close to the drakensberg escarpment where the high annual rainfall amounts supported a continuous peat accumulation since c 16 ka one peat core was analysed in terms of fossil pollen composition carbon and nitrogen content isotope composition 13c 15n and microscopic charcoal concentration the greatest degree of temporal resolution was achieved from the late pleistocene and early holocene section where proxy records indicate relatively dry conditions between ca 16 13 7 ka 12 8 10 5 ka 9 5 8 2 ka and wet conditions between c 13 7 12 8 ka and 10 5 9 5 ka a weak moisture signal is also evident at c 8 2 7 5 ka the late pleistocene to early holocene period was relatively cool while conditions became generally warmer after 11 8 ka the interpretation of the mid and late holocene sequence is limited due to a slow accumulation and low sample resolution but the available data suggest relatively dry conditions until c 1 5 ka followed by more humid conditions until c 0 5 ka we suggest that the millennial scale variability within the record can be attributed to shifts in the circulation systems dominating the region i e the latitudinal movements of the inter tropical convergence zone itcz and the dynamics of the mid latitude low pressure belts

paleogeographic and paleotectonic evolution of the himalayan range as reflected by detrital modes of tertiary sandstones and modern sands indus transect india and pakistan detrital modes of sandstones derived from the himalayan suture belt record the history of the mountain range since initial collision between india and asia which began in latest paleocene time tertiary clastic wedges deposited in fore arc foreland and remnant ocean basins and exposed along the indus transect from northernmost india to the arabian sea represent the best opportunity to study sedimentary responses to successive tectonic events during continental collision quartzose continental block and feldspatholithic magmatic arc sandstones were deposited respectively on the passive indian tethys himalayan succession and active asian indus group continental margins during late cretaceous paleocene time closure of the neotethys was marked by sudden arrival of volcanic and ophiolitic detritus on the passive continental margin of the indian plate during deposition of sediments dated at foraminiferal zones p6 pakistan to p8 india starting in early eocene time deposition of chulung la formation and murree supergroup volcanic and ophiolitic to metasedimentary detritus was accumulated in rapidly subsiding piggy back and foreland basins homogeneous petrographic composition within the eocene lower miocene murree supergroup with only slight progressive increase of detrital feldspars suggests erosion of largely supracrustal rocks involved in thrusting in the north in middle miocene time marked enrichment in medium to high grade metamorphic detritus in foreland sandstones siwalik group reflects rapid uplift of a warm wedge of indian crust which was carried southward along the main central thrust this major paleogeographic change was recorded also by quartzolithic remnant ocean turbidites which were fed great distances along transverse fracture zones and later accreted in the coastal makran subduction complex panjgur association and makran group recycled orogen detritus derived from the elevated himalayan chain is still accumulating today in the indus fan enrichment in feldspars with respect to ancient sandstones reflects deep erosion levels into mid crustal rocks along the core of the growing orogen

geochemical signature of provenance in sand size material in soils and stream sediments near the tobacco root batholith montana u s a abstract trace element geochemistry of sandstones are being used to determine provenance we have conducted preliminary and limited experiments to determine to what extent daughter sands retain the geochemical signature of parent rocks six sets of first order stream sediments soils from adjacent slopes and a variety of parent rocks were collected from southwestern montana u s a sampling in a low relief area ensured that climate and residence time of soils on slopes could be eliminated as variables sand size fractions of stream sediments and soils and the corresponding parent rocks granodiorite quartz monzonite granite gneiss biotite tonalite gneiss and amphibolite were analyzed for most major elements and selected trace elements petrologic modal analysis of the parent rocks and the 0 25 0 50 mm fraction of each sand was done to monitor major mineralogic control if any on chemical compositions of the samples our data show that the abundances of the si and al in sediments do not discriminate provenance abundances of ca mg fe and ti may broadly distinguish between sands derived from metamorphic and igneous source rocks at least in the area studied differences in abundances of the ba and th and the ratio of la lu between granitic tonalitic and amphibolitic parent rocks are preserved in the daughter sediments that we studied however the size of the eu anomaly in the ree patterns of different daughter sediments is not diagnostic of parent rocks abundances of co and sc distinguish between sediments derived from felsic and mafic rocks a better provenance discrimination is obtained if the ratios la sc th sc la co ba sc and ba co are used petrologic modal data show that mineral contents and chemical compositions of parent rocks are compatible with each other the chemical composition of the sands may be roughly correlated to the petrological modal data but the abundances of some minor and trace elements of sediments cannot be inferred from modal mineralogy this is expected because these elements may concentrate in accessory minerals and or may weather out into aqueous or clay mineral fractions it is also compatible with conclusions of previous studies that some of these elements do not reside in sand size fractions of siliciclastic sediments

chemical compositions and tectonic significance of chrome rich spinels in the tianba flysch southern tibet abstract turbiditic sandstones from the mid late cretaceous tianba flysch sequence are well exposed near tianba in the north nieru valley southern tibet and contain significant amounts of chrome rich spinels microprobe results show that the spinels have a well developed fe ti trend and have cr documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape mathrm cr mathrm al end document 0 4 0 65 mg documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs

dating the indian continental subduction and collisional thickening in the northwest himalaya multichronology of the tso morari eclogites comment and reply de sigoyer et al 2000 1 studying tso morari eclogites in northern ladakh northwest himalaya claim to have dated eclogite formation and therefore the timing of the onset of india asian contact in the northwest himalaya at 55 6 ma their ages lu hf 55 12 ma sm nd 55 7 ma

detrital modes and provenance of the paleogene khojak formation in pakistan implications for early himalayan orogeny and unroofing different tectonic settings have characteristic detrital modes and sediment dispersal patterns detrital modes and sediment dispersal patterns of the siliciclastic khojak formation in the katawaz basin pakistan suggest that its sand was derived from the early himalayan orogen and longitudinally transported to the katawaz remnant ocean where it was deposited as a delta submarine fan complex modal analysis of the khojak formation suggests composition that is dominated by subangular quartz with abundant lithic fragments and minor feldspar i e qt 60 f 9 l 31 qt total quartz f feldspar l lithic fragments the predominance of quartz sedimentary and low grade metamorphic lithic fragments suggests early derivation from a collision orogen scarcity of detrital feldspar and volcanic lithic fragments precludes a magmatic arc as the main source the decrease in monocrystalline quartz concomitant increase in total lithic percentages and relative abundance of low grade metamorphic lithic fragments from the bottom to the top of the khojak formation reflect progressive erosional history of the early himalaya this history is part of a previously known major unroofing trend collectively depicted by the detrital modes of the murree formation siwalik group and the modern indus fan in the indian ocean these detrital modes are also related in time and space

the chemistry of detrital chromian spinels and its implications for the geodynamic evolution of the eastern alps detrital chromian spinel is a key mineral in paleogeographic reconstructions the chemical compositions of the spinels provide even more specific information about their host ophiolites because their chemistry is related to the degree of melting of the mantle peridotite and thus to the geotectonic environment of ocean crust formation

required but disguised environmental signals in limestone marl alternations the nature of rhythmic carbonate rich successions such as limestone marl alternations has been and still is subject to controversy the possibility of an entirely diagenetic origin for the rhythmic calcareous alternations is discarded by most authors one problem with an entirely diagenetic self organized development of limestone marl alternations is the fact that limestone and marl beds in many examples are laterally continuous over hundreds of meters or even kilometers in an entirely self organized system lateral coupling would be very limited thus one would expect that rather than laterally continuous beds randomly distributed elongate nodules would form we address the origin of limestone marl alternations using a computer model that simulates differential diagenesis of rhythmic calcareous successions the setup uses a cellular automaton model to test whether laterally extensive rhythmic calcareous alternations could develop from homogeneous sediments in a process of self organization our model is a strong simplification of early diagenesis in fine grained partly calcareous sediments it includes the relevant key mechanisms to the question whether an external trigger is required in order to obtain laterally extensive limestone marl alternations our model shows that diagenetic self organization alone is not sufficient to produce laterally extensive correlatable beds although an external control on bedding formation could be considered to have solved the problem as commonly assumed we here suggest an interesting third possibility the rhythmic alternations were formed through the interaction of both an external trigger and diagenetic self organization in particular we observe that a very limited external trigger either in time or amplitude readily forms correlatable beds in our otherwise diagenetic model remarkably the resulting rhythmites often do not mirror the external trigger in a one to one fashion and may differ in phase frequency and number of couplets therefore the interpretation of calcareous rhythmites as a one to one archive of climate fluctuations may be misleading parameters independent of diagenetic alteration should be considered for unequivocal interpretation

earth s oldest reported glaciation physical and chemical evidence from the archean mozaan group 2 9 ga of south africa the pongola supergroup is a thick succession of archean 2 9 ga supracrustal rocks in the eastern part of the kaapvaal craton of southern africa its upper part the mozaan group 5000 m thick includes diamictites with a highly varied suite of clasts some of which are striated and faceted clasts in associated stratified siltstones are interpreted as ice rafted debris a glacial origin is also supported by geochemical investigation of diamictite matrix materials and associated mudstones plots of sio2 al2o3 and tio2 al2o3 suggest that these rocks underwent little chemical weathering an interpretation confirmed by calculation of a chemical index of alteration with low values typical of other glacial deposits the analyzed rocks are rich in fe average fe2o3 t is 24 wt like rocks of many other glaciomarine successions the diamictites and associated mudstones of the mozaan group have low th sc ratios suggesting preferential incorporation of mafic materials into the diamictite matrix material

composition and classification of paleozoic flysch mudrocks of eastern australia implications in provenance and tectonic setting interpretation abstract the mudrock suites of paleozoic flysch sequences of eastern australia can be characterised on the basis of the relative abundances of phyllosilicates and tectosilicates mainly feldspar and quartz a mudrock maturity index is defined as the ratio of total phyllosilicates to phyllosilicates feldspar quartz mudrocks are classified into tectic phyllo tectic and phyllic types on the basis of increasing maturity based on studied examples of eastern australia preliminary characteristics of mudrocks of various tectonic settings are identified oceanic island arc mudrocks are of the tectic type characterised by high feldspar and low phyllosilicate content they are derived from calc alkaline andesitic rocks of the magmatic arc mudrocks of the continental island arc and active continental margins andean type and strike slip basins are characterised by a higher phyllosilicate content and are mainly phyllo tectic in type passive margin mudrocks are of the phyllic type characterised by extremely high phyllosilicate and low feldspar contents suggesting their recycled nature mudrock maturity is accompanied by an increase in the k2o na2o ratio from oceanic island arc to continental island arc and active continental margin to passive margin type mudrocks

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

laser 40ar 39ar dating of single detrital muscovite grains from early foreland basin sedimentary deposits in india implications for early himalayan evolution in india the dagshai and overlying kasauli formations represent the oldest exposed continental foredeep sediments eroded from the himalayan orogen 40ar 39ar dating of individual detrital white micas from these sedimentary units has provided maximum depositional ages of 28 ma for the dagshai formation at one locality and 25 ma at a second locality whereas deposition of the kasauli formation occurred after 28 ma at two localities and after 22 ma at a third locality this timing suggests that in india the start of substantial exhumation and erosion from the rising himalayan orogen was delayed until 28 ma

geochemical investigation of a neoproterozoic glacial unit the mineral fork formation in the wasatch range utah the mineral fork formation is an isolated unit of neoproterozoic glaciogenic rocks in the wasatch range in northwestern utah geochemical analyses of diamictite and mudstone samples were carried out to document its major and trace element geochemistry comparison of the lower and upper parts of the formation which have been ascribed to different tectonic and sedimentological settings revealed no striking differences but the analyzed samples show a gradual upward increase in cao mgo fe 2 o 3 mno and p 2 o 5 and a decrease in sio 2 tio 2 al 2 o 3 ratios that suggest a provenance throughout the formation with an average composition slightly more mafic than average upper crust the mudstones are more k rich than the diamictites calculation of a chemical index of alteration cia is complicated by the presence of carbonate minerals after making corrections for carbonate content cia values range from 65 to 70 these values are higher than those from paleoproterozoic glaciogenic deposits some mudstones in the upper part of the formation are fe rich 15 fe 2 o 3 approaching the composition of iron formations the ferruginous nature supports previous correlation with fe rich glaciogenic rocks of the rapitan group in the northern canadian cordillera trace elements including rare earth elements suggest that the materials in the mineral fork formation were largely derived from a post archean source most of the widespread glaciogenic rocks of the neoproterozoic were derived from older sedimentary materials whereas the deposits of the earlier great glacial episode in the paleoproterozoic contain a much higher proportion of crystalline materials

dating the indian continental subduction and collisional thickening in the northwest himalaya multichronology of the tso morari eclogites multichronometric studies of the low temperature eclogitic tso morari unit ladakh india place timing constraints on the early evolution of the northwest himalayan belt several isotopic systems have been used to date the eclogitization and the exhumation of the tso morari unit lu hf sm nd rb sr and ar ar a ca 55 ma age for the eclogitization has been obtained by lu hf on garnet omphacite and whole rock from mafic eclogite and by sm nd on garnet glaucophane and whole rock from high pressure metapelites these results agree with a previously reported u pb age on allanite and together these ages constrain the subduction of the indian continental margin at the paleocene eocene boundary during exhumation the tso morari rocks underwent thermal relaxation at about 9 3 kbar characterized by partial recrystallization under amphibolite facies conditions ca 47 ma as dated by sm nd on garnet calcic amphibole and whole rock from metabasalt rb sr on phengite apatite and whole rock and ar ar on medium si phengite from metapelites ar ar analyses of biotite and low si muscovite from metapelites which recrystallized at 5 kbar toward the end of the exhumation show that the tso morari unit was at upper crustal levels ca 30 ma these results indicate variable exhumation rates for the tso morari unit beginning with rapid exhumation while the indian margin subduction was still active and later proceeding at a slower pace during the crustal thickening associated with the himalayan collision