testing the sensitivity of geomorphic indices in areas of low rate active folding eastern betic cordillera spain abstract active deformation structures have an incidence in topography that can be quantified by using geomorphic indices most of these indices have been checked in faulted regions with high deformation rates the application of several geomorphic indices hypsometric curve analysis normalized stream length gradient and valley width to valley height ratio to the drainage network of the southern limb of the sierra de las estancias antiform internal zones eastern betic cordillera where low rate active folding has been recognized allows us to investigate the suitability of these indices to identify active structures in such a scenario hypsometric curves clearly identify regions with recent uplift and young topography but they do not provide any constraint on the location of active folds local valley width to valley height index variations have been detected just coinciding whit the position of ene wsw active folds normalized stream length gradient index serves to locate active folds in areas of hard rock substratum but not in those areas with soft sediments neogene quaternary sedimentary basins this is most likely due to the fact that in the basins erosion is much more intense than in the hard rock sectors in view of these results we consider that geomorphic indices constitute a valuable tool for identifying sectors affected by low rate uplift related to active folding with the best results obtained in hard rock areas

the flank margin model for dissolution cave development in carbonate platforms the bahama islands contain many abandoned dissolution caves at elevations between two and seven metres above current sea level the development of dissolution caves in tropical carbonate islands is dependent on the position and nature of the freshwater lens lens position is controlled by sea level which in stable carbonate platforms like the bahamas is a function of glacioeustatic sea level still stands caves in the bahamas that are currently subaerial must have developed during past higher sea levels during the late quaternary sea levels higher than present have been relatively short lived and that limits the amount of time that a freshwater lens could be situated at the elevation required for the cave formation the bahama islands are low lying landforms where only aeolian ridges extend to elevations higher than six metres above current sea level past high sea level events greatly reduced the exposed land area of the bahama islands thus also limiting both the catchment for and size of freshwater lenses caves must be younger than the rock in which they are developed most subaerial bahamian caves are found in limestones that are less than 150000 years old development of large dissolution caves under these limitations of time and lens size requires a powerful dissolutional mechanism the mixing of discharging freshwater with tide pulsed incoming marine water under the flanks of emergent dune ridges may have produced the conditions necessary bahamian caves formed by this process are phreatic chambers with complex interconnections and blind tubes their presence demonstrates that significant dissolution can occur rapidly as a result of the mixing of fresh and marine waters beneath small carbonate islands

geochemical and petrographical characterization of fine grained carbonate particles along proximal to distal transects the origin of carbonate ooze particles is often poorly understood this is due to their polygenic origin and potential post depositional alteration here the outcome of a physical separation study with regard to different component classes of micritic carbonates is shown the focus is on grain size and morphology mineralogy and isotope signatures two contrasting proximal to distal transects were investigated 1 the miocene leeward margin of great bahama bank odp leg 166 and 2 the transition between the maiella platform and the umbria marche basin in central italy near the cenomanian turonian boundary in both case settings carbonate particles of biogenic origin include at least three groups of organisms i planktonic foraminifera ii calcareous nannofossils and iii fragments of unspecified neritic skeletal material two further particle types lack diagnostic structures and based on particle size and mineralogy are here referred to as iv macroparticles 5 20 m mainly xenomorphic and v microparticles 12 m mainly automorphic to sub automorphic macro and microparticles represent 50 to 80 of the carbonate phase in slope and toe of slope domains and share characteristic carbon and oxygen isotope signatures macro and microparticles are considered shallow water precipitation products subsequently exported into the slope and toe of slope domains macroparticles are probably related to the fragmentation of neritic skeletal components while microparticles point to inorganic and or bioinduced precipitation in the water column in some cases macro and microparticles may have an early diagenetic origin the identification of the origin of fine grained particles allows for a quantitative assessment of exported in situ and diagenetic carbonate materials in periplatform environments the data shown here represent an important step towards a more complete characterization of carbonate ooze and micrite

palaeo mixing zone karst features from palaeocene carbonates of north spain criteria for recognizing a potentially widespread but rarely documented diagenetic system abstract marine meteoric mixing zone dissolution effects are a major feature of present day karst systems in carbonate platforms yet are rarely reported in the geological record an example is described from the upper danian platform limestones of the alava province in the western pyrenees north spain this consists of several narrow zones with sponge like porosity analogous to the swiss cheese features found in present day mixing zones these zones are stained by fe oxides and overlie limestones which are irregularly dolomitized and contain disseminated pyrite these high porosity zones are interpreted as having developed in marine mixing zones where mixing corrosion and microbially mediated processes increased dissolution if collapsed ancient mixing zones could be misinterpreted as terra rossa palaeosols the main criteria to identify them as mixing zone products are their occurrence below a palaeo meteoric phreatic zone their association with stratified oxic and anoxic redox zones and petrographic evidence for highly variable calcite saturation states

climatic and tectonic controls on sedimentation and erosion during the pliocene quaternary in the qaidam basin china the qaidam basin is an internally drained basin located in the northeastern tibetan plateau presently over 50 of the basin floor exposes thick 1 km sections of pliocene quaternary strata that are deformed by folding and faulting we investigated this nearly continuous pliocene quaternary sedimentary record for the effects of global climate change and deformation on basin sedimentation new detailed stratigraphic magnetostratigraphic and stable isotope 18 o 13 c data from the pliocene shizigou and pleistocene qigequan formations along the southwestern flank of an intrabasin fold within the north central qaidam basin are presented here strata reveal climatically controlled meter scale parasequences within shallow lacustrine marginal lacustrine and deltaic lithofacies paleocurrents shift from eastward at the base to southwestward for the majority of the section but they abruptly shift toward the south southeast in the upper 400 m twenty two magnetozones constrain deposition between 5 2 ma and ca 0 8 ma and reveal that sedimentation rates were fairly constant 474 34 m m y from 5 2 to 3 0 ma after which time rates abruptly decreased to 154 40 mm yr before increasing again to 750 m m y since 1 2 ma the 18 o values shift from relatively constant values avg 6 8 range 9 6 to 4 5 relative to vienna peedee belemnite vpdb to less negative values avg 1 2 range 1 2 to 2 7 vpdb between 3 1 and 2 6 ma and to extremely variable values avg 2 9 range 8 3 to 4 0 after ca 2 6 ma the post 2 6 ma extreme variability in stable isotopes reflects the same timeframe of enhanced climatic cyclicity associated with northern hemisphere glaciation the 13 c values remain relatively constant average 4 0 range 5 7 to 1 0 until ca 0 9 ma when the values increase to 0 3 range 1 0 to 1 5 vpdb the appearance of growth strata at 3 0 ma shallow water evaporite deposition after 2 6 ma and the observation of paleoyardangs buried wind sculpted landforms within lake marginal strata at 2 4 ma imply that emergence of the adjacent anticline was followed by the shallowing and partitioning of the lake basin and subaerial exposure and erosion of marginal lake sediments these data reflect a significant change to a more arid climate in the qaidam basin between ca 3 1 ma and 2 6 ma overlapping with the onset of significant northern hemisphere glaciations and basin floor deformation lake level cycles were on 230 000 yr frequency from 2 6 ma to 1 2 ma before increasing to 12 000 yr frequency suggesting increased aridity and broad subaerial exposure of lake sediments after the pliocene quaternary transition deformation of intrabasin sediments by at least 3 0 ma caused uplift of the basin floor which provided an environment rich in friable material for wind deflation of the qaidam basin a likely source for sediments on the chinese loess plateau and nutrients for the pacific ocean carried by westerly winds by 2 6 ma deformation of the qaidam basin created closed depressions that facilitated evaporite sedimentation that continues today coeval intrabasin deformation combined with increasing aridity after 3 1 ma thus controlled both deposition and erosion within the region

three dimensional seismic geomorphology and analysis of the ordovician paleokarst drainage system in the central tabei uplift northern tarim basin western china high quality three dimensional seismic data acquired in the central tabei uplift tarim basin western china provide a rare opportunity to characterize in exceptional detail the three dimensional geomorphology of a deeply buried 5500 6500 m 18 045 21 325 ft ordovician unconformity and the related paleokarst drainage system an integrated approach was applied that emphasized integration of seismic data with available conventional core wireline logs and age equivalent outcrops the exceptional quality of the seismic data allowed a seismic detection limit of karstified features of less than 75 75 m 246 246 ft horizontally and 6 m 20 ft vertically interpreted geomorphologic and depositional elements include fluvial channels and canyons fluvial valleys sinkholes and tower karsts and hills the modern tower karst drainage system in guilin china is very similar to the mapped ordovician karst drainage system and is used as a modern analog the interaction between the surface karst drainage system and the shallow subsurface cave passage system is evidenced by the observation that surface canyons appear to initiate in areas associated with intense sinkhole development also surface river valleys tend to correspond to dip oriented surface depressions partly related to near surface cave collapse during burial into the deeper subsurface the combination of intrastratal collapse karstified strata and suprastratal collapse postkarst deposited strata created large damage zones hundreds of meters thick and kilometers wide coalesced collapsed paleocave systems can be interpreted from the unique circular pattern of faults observed in map view that are associated with seismic bright spots

yardang geometries in the qaidam basin and their controlling factors abstract the hyperarid qaidam basin features extensive fields of yardangs covering an area of 40 000km2 sculpted in tectonically folded sedimentary rocks we extracted the geometries of 16 749 yardangs such as length to width ratio l w spatial density and spacing from multi source remote sensing data provided by google earth we classified the yardangs into four types based on their l w short axis 1 2 whale back 2 6 hogsback 6 10 and long ridge 10 210 we interpreted the yardang geometries in the context of their geologic setting bedding orientation location along anticline crests or syncline troughs and lithologic heterogeneity our results show that the yardang geometries in the qaidam basin are mainly controlled by the structural geology and rheology of the sedimentary rocks e g strike and dip of bedding the presence or absence of interbedded soft and hard beds and structural position with folds the angle between geomorphically effective wind directions and the strike of bedding and the relative cumulative wind shear force where two geomorphically effective wind directions are present our analysis revealed the following 1 nearly 69 of the yardangs with long ridge and hogsback geometries are distributed in syncline areas whereas 73 of the yardangs with short axis geometries are distributed in anticline areas 2 the l w ratio of yardangs exposed along the windward limbs of anticlines is lower than that of yardangs exposed along the leeward limbs and 3 in the westernmost parts of the basin yardangs are locally sculpted into mounds by two geomorphically effective wind directions

response of late ordovician paleoceanography to changes in sea level continental drift and atmospheric pco2 potential causes for long term cooling and glaciation abstract we performed sensitivity experiments using an ocean general circulation model at two stages of the late ordovician caradoc 454 ma ashgill 446 ma under a range of atmospheric pco2 values 8 18 pal pre industrial atmospheric level at high and low sea level the model results indicate that the long term cooling trend during the late ordovician can be explained by progressive cooling of the global ocean in response to falling levels of atmospheric pco2 sea level change and paleogeographic change these results also explain the occurrence of low latitude cool water carbonates in north america in all simulations a drop in sea level led to a reduction in poleward ocean heat transport this indicates a possible positive feedback that could have enhanced global cooling in response to sea level drop during the late ordovician alterations in poleward ocean heat transport linked to changes of atmospheric pco2 also indicate that there is a threshold of 10 pal above which ocean current change cannot be responsible for glaciation in the late ordovician continental drift could explain the observed global cooling trend in the late ordovician through a combined poleward ocean heat transport feedback and increased ice albedo effect if atmospheric pco2 was low during the entire late ordovician the model results further indicate that the response of meridional overturning to changes in paleogeography atmospheric pco2 and sea level is stronger than the response of surface circulation to these perturbations because the overturning circulation is so strong meridional overturning was the dominant mechanism for described changes in heat transport in the late ordovician

landscape form and millennial erosion rates in the san gabriel mountains ca abstract it has been long hypothesized that topography as well as climate and rock strength exert first order controls on erosion rates here we use detrital cosmogenic 10 be from 50 basins ranging in size from 1 to 150 km 2 to measure millennial erosion rates across the san gabriel mountains in southern california where a strong e w gradient in relief compared to weak variation in precipitation and lithology allow us to isolate the relationship between topographic form and erosion rate our erosion rates range from 35 to 1100 m ma and generally agree with both decadal sediment fluxes and long term exhumation rates inferred from low temperature thermochronometry catchment mean hillslope angle increases with erosion rate until 300 m ma at which point slopes become invariant with erosion rate although this sort of relation has been offered as support for non linear models of soil transport we use 1 d analytical hillslope profiles derived from existing soil transport laws to show that a model with soil flux linear in slope but including a slope stability threshold is indistinguishable from a non linear law within the scatter of our data catchment mean normalized channel steepness index increases monotonically though non linearly with erosion rate throughout the san gabriel mountains even where catchment mean hillslope angles have reached a threshold this non linearity can be mostly accounted for by a stochastic threshold incision model though additional factors likely contribute to the observed relationship between channel steepness and erosion rate these findings substantiate the claim that the normalized channel steepness index is an important topographic metric in active ranges

wind as the primary driver of erosion in the qaidam basin china deserts are a major source of loess and may undergo substantial wind erosion as evidenced by yardang fields deflation pans and wind scoured bedrock landscapes however there are few quantitative estimates of bedrock removal by wind abrasion and deflation here we report wind erosion rates in the western qaidam basin in central china based on measurements of cosmogenic 10 be in exhumed miocene sedimentary bedrock sedimentary bedrock erosion rates range from 0 05 to 0 4 mm yr although the majority of measurements cluster at 0 12570 05 mm yr these results combined with previous work indicate that strong winds hyper aridity exposure of friable neogene strata and ongoing rock deformation and uplift in the western qaidam basin have created an environment where wind instead of water is the dominant agent of erosion and sediment transport its geographic location upwind combined with volumetric estimates suggest that the qaidam basin is a major source up to 50 of dust to the chinese loess plateau to the east the cosmogenically derived wind erosion rates are within the range of erosion rates determined from glacial and fluvial dominated landscapes worldwide exemplifying the effectiveness of wind to erode and transport significant quantities of bedrock

sea level curve for the middle to early late ordovician in the armorican massif western france icehouse third order glacio eustatic cycles abstract this contribution deals with the middle to early late ordovician of the armorican massif western france the aim is to reconstruct a multi order eustatic curve from the stratigraphic record the studied section crozon peninsula area shows sediments deposited in tidal to storm dominated shelf environments a sequence analysis facies and stacking pattern analyses combined with a gamma ray record and a backstripping procedure was carried out chitinozoan assemblages provide the biostratigraphic framework including time calibration the stratigraphic succession is dominated by the stacking of sequences representing different orders of sea level change i e very high formosa and pissotensis biozones of the darriwilian the reconstructed sea level curve reveals that most of the third order cycles comprise three fourth order cycles of assumed 400 kyr duration this 1 2 myr duration of the ordovician third ordersequences suggests that they may be related to long period obliquity cycles an orbital forcing characteristic of icehousesequences in the late cenozoic and the quaternary these results imply that the major part of the middle and early late ordovician was characterized by icehouse conditions and third orderglacio eustatic cycles a time calibration of the chitinozoan biozones was developed from the sequential analysis it suggests that the early darriwilian biozones from henryi to calix biozones have short durations of several 10 to several 100 kyr whereas the pissotensis biozone has a temporal extent of several myr extending into the early sandbian

log derived thickness and porosity of the barnett shale fort worth basin texas implications for assessment of gas shale resources this study estimates reservoir quality and free gas storage capacity of the barnett shale in the main natural gas producing area of the fort worth basin by mapping log derived thickness porosity and porosity feet in the barnett shale the density porosity dphi log curve is a very useful tool to quantitatively assess shale gas resources and gamma ray gr and neutron porosity log curves are important factors in identifying the shale gas reservoir the key data were digital logs from 146 wells selected based on the availability of gr and density log curves log quality and good spatial distribution the barnett shale pay zone was determined on the basis of 1 dphi 5 2 high gr values commonly 90 api units 3 no significant intercalated carbonate rich beds and 4 individual pay zones being thick enough to be commercially successful for the current design of horizontal wells in the study area the barnett shale pay zone varies from about 165 ft 50 m to 420 ft 128 m in thickness h average dphi values of individual wells for the pay zone vary from 8 5 to 14 0 porosity feet maps of the pay zone show that areas of high dphi h values coincide with areas of high natural gas production indicating that log derived porosity feet maps are a good method for evaluating reservoir quality and assessing natural gas resource in the barnett shale play a limitation to this method is shown in the northwestern corner of the study area which is located in the liquids rich window with lower thermal maturity

sandstone provenance of north western sectors of the intracontinental cenozoic qaidam basin western china tectonic vs climatic control abstract sandstone samples from all cenozoic formations of the nonmarine internally drained qaidam basin have been collected for provenance analysis to monitor possible changes in sandstone composition driven either by tectonics or climate provided an appropriate hinterland biotite contents may be a reasonable indicator for aridity moderately sorted sandstones with subangular to subrounded grains from the northwestern part of the qaidam basin are immature indicated by a high proportion of feldspars and lithic fragments nevertheless they have relatively high quartz contents of 29 65 averaging between 40 and 45 the average framework compositions of the formations show only a slight variation over time limited to the oldest and youngest cenozoic formations contents of white mica and biotite are significantly higher in upper portions of the section white mica contents increases from 1 0 to 3 7 and biotite from 0 1 to 1 6 respectively this change can be explained by increasing aridity during neogene and surface uplift of altyn mountains and qimantagh which led to higher relief when plotted on basic variation diagrams total quartz feldspar lithic fragments there is a slight shift from continental block field to orogenic field which might reflect the motion of the altyn tagh fault since oligocene times although climate changed during the cenozoic from arid over semiarid back to arid we could not find any distinct changes in the framework mineral compositions over time that could be related to climatic events few selected mudstones from eocene to lower miocene formations have been geochemically analysed by icp ms all samples display uniform high enrichment in light rees in chondrite normalized diagrams with one exception the ree concentrations are decreasing in a stepwise manner although insignificantly from formation to formation with time due to a diluting effect by carbonate

the structural evolution of active fault and fold systems in central otago new zealand evidence revealed by drainage patterns abstract central otago in new zealand is an area of active continental shortening in which a peneplain surface cut into schist has been deformed by folds which are developed above buried reverse faults we use the drainage patterns in this region to demonstrate various processes in fold and fault growth and interaction that would be difficult to identify by other means in particular we show 1 how simple asymmetric folds can develop into box folds 2 how apparently continuous ridges were formed by the coalescing of quite separate propagating fold and fault segments 3 evidence for the relative ages or relative uplift rates of adjacent structures and 4 evidence for the propagation direction of folds or faults as they grow the few quantitative estimates we obtain for fault propagation rates suggest an increase in length of 10 50 m per earthquake on faults about 20 km long these estimates are very uncertain but are similar in magnitude to an estimate made in nevada for a normal fault of similar size and are also similar to predicted estimates from theoretical growth models they raise the question of whether fault growth earthquake recurrence rates and climate change can interact to produce semi regular discrete features in an active landscape

matrix micrite δ13c and δ18o reveals synsedimentary marine lithification in upper jurassic ammonitico rosso limestones betic cordillera se spain abstract matrix micrites are a commonly used carbonate archive for the reconstruction of past environmental parameters but one that is submitted to known limitations main reasons for the often ambiguous value of many micrite based isotope data sets are the unknown origin of the micrite components and their poorly resolved diagenetic history here we present carbon and oxygen isotope data retrieved from oxfordian to tithonian ammonitico rosso nodular micrites sampled from three sections in the betic cordillera southern spain all three sections were correlated and sampled using a rigorous biostratigraphic framework a noteworthy feature is that analyzed matrix micrites are more conservative in terms of their isotopic composition than other carbonate materials commonly considered to resist diagenetic alteration under favourable circumstances remarkably this refers not only to 13 c ratios which reflect the typical late jurassic global trend but also to 18 o ratios that range around 0 3 the 18 o enriched oxygen isotope ratios are considered to represent diagenetic stabilization of carbonate ooze under the influence of marine porewaters within the sediment water interphase i e the immature sedimentary section usually submitted to biogenic activity this interpretation agrees with the very early lithification of micrite nodules with cements precipitated from marine porewaters enriched by the dissolution of aragonite skeletals i e ammonite shells according to the model proposed low sedimentation rates as well as rapid early marine differential cementation under the influence of currents and seawater pumping affected the sediment water interphase of epioceanic swells where deposition resulted in early lithified ammonitico rosso facies the data obtained show that special care must be taken to prevent oversimplified interpretations of carbonate archives particularly in the context of epioceanic settings

soft sediment deformation structures in cambrian siliciclastic and carbonate storm deposits shandong province china differential liquefaction and fluidization triggered by storm wave loading abstract this paper focuses on soft sediment deformation structures ssds in both siliciclastic and carbonate storm deposits of the cambrian mantou and chaomidian formations shandong province china in order to understand their deformation mechanisms and possible triggers siliciclastic ssds e g sand volcanoes and pillows and carbonate ssds e g sedimentary dykes grainstone matrix breccias deformed cross beddings and marlstone matrix breccias occur exclusively in hummocky cross stratified fine sandstone and peloidal grainstone respectively the siliciclastic ssds formed in porous and permeable surface sediment whereas the carbonate ssds formed under shallow burial conditions when early marine cementation prevailed the various deformation structures resulted mainly from differences between siliciclastic and carbonate sediment conditions and resulting deformation mechanisms sand volcanoes formed by upward extrusion of over pressured fluidized sandy sediment whereas sand pillows resulted from upward injection of lower density muddy sediment into overlying liquefied sandy sediment sedimentary dykes and grainstone matrix limestone breccias formed as a result of differential liquefaction and fluidization of heterogeneously cemented carbonate sediment whereas deformed cross beddings and marlstone matrix limestone breccias developed by the thixotropic liquidization and injection of clayey sediment and further disruption of thin peloidal layers sedimentary facies analysis and analysis of the physical processes indicate that the ssds were most likely caused by cyclic loading of storm waves

loss of primary texture and geochemical signatures in speleothems due to diagenesis evidences from castanar cave spain geochemical signals from speleothems are commonly used in the investigation of palaeoenvironments in most cases however little attention is paid to whether or not these signals are primary or altered by diagenesis the speleothems of the castanar cave caceres spain which are initially formed of calcite or aragonite have undergone a variety of meteoric diagenetic processes such as micritization and neomorphism inversion that collectively modify their primary features textures mineralogy geochemical signals the mean 13c and 18o values of the aragonites in the cave are 8 66 and 4 64 respectively whereas the primary calcites have mean 13c and 18o values of 9 99 and 5 77 respectively following the diagenetic process of micritization the aragonite isotopic signals averaged 7 63 13c and 4 74 18o and the calcite micrite signals 9 53 13c and 5 21 18o where inversion took place some secondary calcites after the aragonite show preserved aragonite whereas others do not the secondary calcites without aragonite relics show isotopic values slightly higher than those of the primary calcite due to the inheritance of the aragonite signal where aragonite relics are preserved the isotopic signatures are very similar to those of the aragonite micrite in addition the stable isotopic values and sr and mg contents of the speleothems became also modified by micritization and or inversion these diagenetic processes were driven by the changes in composition of the cave waters over time and space but also in the case of aragonite by its initial unstable mineralogy the present results highlight how important diagenesis is in caves and how the initial features of cave minerals may be lost these changes alter the geochemical signals shown by speleothems which may have an impact on the interpretation of the results obtained in palaeoenvironmental studies

river profiles along the himalayan arc as indicators of active tectonics abstract longitudinal profiles along sixteen major transverse himalayan rivers add important constraints to models of active continental subduction and its evolution these profiles are characterized by a zone of relatively high gradient that cannot be associated with differential resistence to erosion in all cases the base of the zone of increased gradients correlates with 1 the topographic front between the lesser and high himalayas 2 the narrow belt of intermediate magnitude thrust earthquakes 3 the main central thrust zone mct these features define a small circle in the central portion of the himalayan arc these correlations suggest that the discontinuity in the river profiles and the other features are controlled by a major tectonic boundary between the rising high himalayas and the lesser himalayas no sharp increases in gradient are observed near the main boundary thrust mbt except on a few rivers such as the jhelum or kundar where the mbt lies close to both the mct and the seismic belt thus it is unlikely that the mbt is a major tectonic boundary the diversion of river courses along the mbt and around anticlines in the sub himalayas has probably been caused by aggradation near the rosion deposition boundary upstream of uplifts in the mahabharat range and sub himalayas a parallel is drawn between the himalayas and new guinea based on the hypothesis that continent arc collision of the type occurring in northern australia preceded continent continent collision in the himalayas the present sedimentary tectonic phase in new guinea resembles the subathu paleocene eocene phase in the himalayas incipient counterparts of the major himalayan structures including the mct and the mbt are recognized in new guinea the drainage patterns in the himalayas and in new guinea bear a similar relation to major structures this suggests that 1 the tectonic evolution of the himalayas has been rather uniform since early stages of collision and 2 the himalayan drainage was also formed at these early stages and is therefore antecedent to the rise of the high himalayas

fault related folding drainage network evolution and valley incision during the neogene in the andean precordillera of northern chile abstract we describe neogene drainage network development before during and after regional folding in the precordillera of the andes of northern chile 18 19 s the drainage network developed on an extensive regular erosional surface formed on oligocene miocene ignimbrites oxaya formation the folding affecting the rocks of the precordillera is represented by the oxaya anticline oa which trends n to nw is 50 km long and 30 km wide the fold is gentle west vergent and has resulted in an uplift of the hinge zone by up to 850 m it formed by the propagation on its western border of a subvertical east dipping blind reverse fault ausipar fault af the folding occurred in the middle late miocene essentially between 11 7 0 7 and 10 7 0 3 ma its maximum duration was 2 my two phases of drainage development are recognised in the precordillera an initial lower middle miocene 19 12 ma parallel drainage network is well preserved and synchronous with fluvial and lacustrine sedimentation in the central depression the network was poorly structured and attained maximum incision of to 250 50 m the minimum long term rate of incision was 36 7 m my folding generated the progressive abandonment and fossilisation of the initial parallel drainage network which became trellissed and concentrated in a few deeply incised valleys in the anticline hinge the lluta and azapa main valleys present a total incision of 1650 50 and 1605 50 m respectively whereas the cardones valley presents 595 50 m during folding river incision at the fold hinge was equal to or greater than the amplitude of the folding which is 790 50 m in the lluta valley and 715 50 m in the azapa valley consequently the long term rate of synfolding incision was much greater than 395 25 lluta valley and 358 25 m my azapa valley the cardones valley was fossilised approximately in the middle of the folding after folding 11 to 0 ma the incision in the lluta and azapa rivers was 610 100 and 640 100 m and with a rate of 56 9 and 58 9 m my respectively the postfolding incision rate is approximately twice than of the prefolding incision rate this implies an acceleration of valley incision since the late miocene which is considered as consequence of regional uplift of the andean forearc

features and effects of basement faults on deposition in the tarim basin the tarim basin as the largest inland oil producing basin in china is a large scale composite basin which formed from a palaeozoic craton basin that was overprinted by a mesozoic cenozoic foreland basin based on comprehensive analyses of gravitational data aeromagnetic data and seismic data from the basin 38 basement faults can be identified demonstrating that the tarim basin has undergone several tectonic cycles according to their distributional locations in the basin basement faults can be divided into marginal and internal basin basement faults moreover on the basis of the distribution characteristics in the plane and controlling effects on the basin the basement faults can be divided into 20 primary basement faults and 18 secondary basement faults combined with the interpretations of seismic profiles we can determine the relationship between the basement faults and sedimentary cover faults considering the section balance of seismic profiles we find that some basement faults are syn depositional with continuous long term activity during the basin s evolution and control the deposition in the basin by counting fault growth indexes of the main sections it is obvious that different parts of the same fault have different growth indexes but show similar activity within the same geological period the faults stress states remain consistent with their geological history although the growth indexes of different faults are inconsistent

the early diagenetic origin of lower carboniferous mottled limestones pseudobreccias dark mottles are a prominent and widespread feature of the regressive cyclic shallow marine limestones which form the late asbian succession in many parts of britain the colour difference which defines mottles in outcrop is caused by distinct but often subtle petrographic differences in the limestone fabric specifically mottles contain a light brown coloured opaque inclusion rich calcite spar with characteristic dull brown luminescence mottle spar outside mottle margins this calcite spar is absent with clear inequant blocky cements forming the pore filling phase mottle spar comprises a fabric of irregular crystals predominantly 5 40 m in diameter with more regular crystals up to 100 m diameter often occurring in intraparticle and large interparticle pores under cathodoluminescence mottle spar displays crystal morphologies and growth patterns which indicate that both localized neomorphism and patchy cementation contributed to mottle formation cathodoluminescence cement stratigraphy shows that mottle spar pre dates all other major pore filling cements in the local asbian succession but post dates marine micritization mottle spar sharply defines the moulds of former aragonitic allochems which are now filled by the later clear inequant spar cements this shows that aragonite dissolution occurred after the formation of mottle spar mottles in calcretes contain unaltered allochems which have been protected from the effects of subaerial micritization by mottle spar although mottles are often affected by subaerial brecciation this evidence shows that mottles formed during early diagenesis after marine micritization but before dissolution of aragonite subaerial exposure and meteoritic phreatic cementation mottles represented lithified patches of very low porosity which are interpreted to have formed in the marine freshwater mixing zone during the repeated phases of regression and emergence in the late asbian

active tectonics in the sierra nevada betic cordillera se spain insights from geomorphic indexes and drainage pattern analysis article i nfo the sierra nevada of the central betic cordillera is a 3000 m high mountain range surrounded by neogene quaternary sedimentary basins having been uplifted since late miocene times the southern and western mountain fronts of the sierra nevada are fault bounded while the northern one is an unconformity between the neogene quaternary sediments of the guadix baza basin and the metamorphic rocks of the nevado filabride complex we have carried out a geomorphic study by examining drainage patterns and characteristics of mountain fronts in order to reveal areal variations and styles of rock uplift mountain front sinuosity smf area altitude relations hypsometric curves and valley floor entrenchment differ significantly between the northern western and southern mountain fronts the lack of important faults along the northern sierra nevada mountain front together with the elevated topographic position of the guadix baza basin average altitude is around 1100 m points to similar uplift of both geomorphic units sierra and basin in a single large scale crustal block the asymmetry factors show systematic asymmetries at both sides of the lanjaron river probably due to the presence of an active nne ssw oriented antiform in the western sierra nevada finally river profiles indicate maximal river entrenchment in the western part of the sierra nevada probably related to the uplift of the footwall of the padul niguelas fault system therefore our geomorphic analysis suggests that the western part of the sierra nevada is tectonically active by means of a combination of normal faults along the mountain front and nne ssw oriented active folds which in turn likely have a gravitational origin related to the exhumation of the footwall of the normal fault system

tectonic geomorphology of active folding over buried reverse faults san emigdio mountain front southern san joaquin valley california investigation of the tectonic geomorphology of active folding over buried reverse faults at the san emigdio mountain front southern san joaquin valley california provides insight concerning the tectonic and geomorphic development of mountain fronts produced by active folding and faulting monoclinally flexed gravels with dips as great as 50 and a minimum age of about 65 ka provide evidence of late pleistocene deformation at the active range front studies of the surface folding of alluvial fans and fluvial terraces indicate a holocene vertical deformation rate of 1 9 3 0 m k y at the active range front and 0 8 1 3 m k y 2 km basinward geomorphic evidence also indicates that the locus of active folding and vertical deformation along the northern flank of the san emigdio mountains has migrated and continues to migrate basinward this evidence includes a relict mountain front now within the uplifted block 5 km from the present active mountain front and the existence of recently initiated folds in the active alluvial fan 2 km basinward from the mountain front northward migration of tectonic activity results in the progressive widening of the uplifted block as the location of active folding moves basinward this migration of tectonic activity appears to occur through the onset and subsequent increase of vertical deformation along more northerly folds and faults accompanied by reduction and eventual cessation of activity along the older more southerly structures

bathymetric and isotopic evidence for a short lived late ordovician glaciation in a greenhouse period the end ordovician glaciation is distinct among phanerozoic glaciations in that co 2 levels were generally high yet major continental ice sheets accumulated on the gondwana supercontinent new oxygen isotopic data indicate substantial changes in sea water temperatures and ice volume coinciding with glacio eustatic changes in sea level reflecting the growth and decay of the gondwana ice cap major glaciation was apparently confined to the hirnantian and was 0 5 1 m y long rather than the 35 m y of earlier estimates carbon isotope values indicate significant changes in carbon cycling as the oceans changed from a state with warm saline bottom waters to a state with cold deep water circulation and then back again we believe that the changes in the carbon cycle effected a reduction in p co 2 levels in the oceans and atmosphere and thus promoted glaciation but were unable to sustain icehouse conditions in a greenhouse world

river system reformed by the eastern kunlun fault implications from geomorphological features in the eastern kunlun mountains northern tibetan plateau abstract the eastern kunlun fault is a famous sinistral strike slip fault and the eastern kunlun mountains is one of the most outstanding landmarks on the tibetan plateau comprehensive geomorphic analyses in this study constrain the activation of the eastern kunlun fault and the uplift process of the eastern kunlun mountains the three largest rivers flowing into the qaidam basin the nalenggele river the golmud river and the xiangride river all run across the mechanically strong granitoid belt and precambrian basement in the eastern kunlun mountains and reach the soft mesozoic and cenozoic hoh xil basin meanwhile the drainage patterns and longitudinal profiles of these three rivers are significantly reformed by the eastern kunlun fault the horizontal throws caused by the eastern kunlun fault inferred from drainage pattern 110 km for the golmud river and 90 km for the xiangride river are consistent with the previous estimated strike slip displacement of the eastern kunlun fault horizontal segments occur on river longitudinal profiles induced by the rapid strike slip movement of the eastern kunlun fault all the above evidences imply that the river system of the eastern kunlun mountains was built before the initiation of the eastern kunlun fault meanwhile the distribution of normalized steepness indices ksn shows that rapid rock uplift occurred between the eastern kunlun fault and the northern front of the eastern kunlun mountains

cenozoic tectonic evolution of the qaidam basin and its surrounding regions part 3 structural geology sedimentation and regional tectonic reconstruction the qaidam basin is the largest topographic depression inside the tibetan plateau because of its central position understanding the tectonic origin of the qaidam basin has important implications for unraveling the formation mechanism and growth history of the tibetan plateau in order to achieve this goal we analyzed regional seismic reflection profiles across the basin and a series of thickness distribution patterns of cenozoic strata at different time slices the first order structure of the basin is a broad cenozoic synclinorium which has an amplitude ranging from 16 km in the west to 48 in the west to 15 s 1 to 1 3 10 17 s 1 the eastward decrease in upper crustal shortening requires a progressive shift in crustal thickening mechanisms across qaidam basin from dominantly upper crustal shortening in the west to dominantly lower crustal shortening in the east although sedimentation began synchronously at 65 50 ma across the entire basin the initiation ages of the southern and northern basin bounding structures are significantly different deformation started at 65 50 ma in the north and at 29 24 ma in the south this information and the existing inference that the uplift of the eastern kunlun range south of qaidam basin began after 30 20 ma imply that the paleogene 65 24 ma qaidam and hoh xil basins on both sides of the eastern kunlun range may have been parts of a single topographic depression 500 km wide in the north south direction between the qilian shan and fenghuo shan thrust belts in the north and south the development of this large paleogene basin in central tibet and its subsequent destruction and partitioning by the neogene uplift of the eastern kunlun range requires a highly irregular sequence of deformation possibly controlled by preexist ing weakness in the tibetan lithosphere

along strike variations of morphotectonic features in the western foothills of taiwan tectonic implications based on stream gradient and hypsometric analysis abstract the taiwan mountain belt provides a key example for analyzing the relation between morphology and tectonics in an active compressional environment there is a striking geometrical relationship between the location of salients and reentrants of the mountain belt and the presence of major crustal inhomogeneities such as structural highs in the foreland basin major along strike variations of structural styles occur in range front rock units of the fold thrust belt stream gradient and hypsometric analysis has been carried out to highlight the along strike variations of morphotectonic features and to illustrate the relative activities in different tectonic regimes of the western foothills the normalized stream length gradient index sl index and the hack profile are two of the stream gradient indices that effectively reflect the tectonic uplift in a region de trending and residual analysis of the hypsometric integral hi eliminates the spatial dependency of small drainage basins and the residual hypsometric integral corresponds to differential uplift activity integration of stream gradient indices and hypsometry provides more robust tectonic interpretation five morphotectonic provinces have been identified in the western foothills based on stream gradient indices and hypsometry each province is bounded by a series of n140 e trending transfer fault zones either inherited from the eurasian passive margin and or newly formed in the sedimentary cover in response to the presence of basement highs within the foreland basin the peikang and kuanyin highs the morphotectonic features as well as deformation styles vary within each province a high uplift but low shortening rate typifies the crustal deformation style in the transpressional regime north of the peikang basement high on the contrary a low uplift but high shortening rate characterizes the crustal deformation style in the transtensional regime south of the peikang basement high the higher geomorphic indices suggest that greater tectonic activity occurs in central than in southwestern taiwan this inference is also supported by the coseismic deformation of the 1999 chi chi earthquake

mesogenetic dissolution of the middle ordovician limestone in the tahe oilfield of tarim basin nw china abstract the mesogenetic dissolution is well developed in the middle ordovician yijianfang formation o2yj limestone and the dissolution pores are very important for petroleum accumulation in the south slope area of the tahe oilfield which lies in the north of the tarim basin northwestern china mottled dotted or laminar dissolution can be observed in the o2yj limestone under microscope the grains lime matrix and all stages of calcite cements including oil inclusion bearing blocky calcite cements can all be found dissolved ubiquitously the stylolites in the limestone were enlarged and rounded because of dissolution some dolomite rhombs precipitated along stylolites in burial environment were found dissolved as well the dissolution of the blocky calcite cements and dolomite rhombs and the enlarging of stylolites demonstrate that the dissolution took place in the mesogenetic environment concentration of trace elements including rees of the eroded part of the o2yj limestone is intermediate between that of the uneroded part and that of the underlying lower ordovician limestone hydrocarbon source rocks both 13cpdb and 18opdb values of the eroded part are less than those of the uneroded part respectively the geochemical characteristics indicate that the eroding fluids are hydrocarbon bearing fluids coming from the underlying hydrocarbon source rocks

palaeohydrogeological control of palaeokarst macro porosity genesis during a major sea level lowstand danian of the urbasa andia plateau navarra north spain abstract an extensive palaeokarst porosity system developed during a pronounced mid paleocene third order lowstand of sea level is hosted in danian limestones of the urbasa andia plateau in north spain these limestones were deposited on a 40 50 km wide rimmed shelf with a margin characterised by coralgal buildups and coarse grained bioclastic accumulations the sea level fall that caused karstification was of approximately 80 90 m magnitude and 2 5 ma in duration during the exposure a 450 m wide belt of sub vertical margin parallel fractures developed a few hundred metres inboard of the shelf edge most fractures are 90 100 m deep average 1 m in width and are associated with large erosional features created by collapse of the reefal margin inland from the fracture belt three superimposed laterally extensive cave systems were formed over a distance of 3 5 km perpendicular to shelf edge at depths ranging from 8 31 m below the exposure surface the palaeocaves range from 0 3 to 2 m in height average 1 5 m high they show no evidence of meteoric processes and are filled with thanetian grainstones rich in reworked microcodium a lithology that also occurs infilling the fractures the caves are interpreted as due to active corrosion at the saline water fresh water mixing zone caves are missing from the shelf edge zone probably because the fractures beheaded the meteoroic lens preventing mixing zone cave development beyond the fracture zone towards the platform interior each cave system passes into a prominent horizon averaging 1 m in thickness of spongy porosity with crystal silt infills and red fe oxide coatings the spongy horizons can be traced for 5 5 km inboard from the cave zone and occur at 10 5 m 25 m and 32 m below the exposure surface in the inland zone two additional horizons with the same spongy dissolution have been recognised at depths of 50 m and 95 m all are analogous to swiss cheese mixing zone corrosion in modern carbonate aquifers and probably owe their origins to microbially mediated dissolution effects associated with a zone of reduced circulation in marine phreatic water in the most landward sections a number of collapse breccia zones are identified but their origin is unclear the palaeokarst system as a whole formed during the pulsed rise that followed the initial sea level drop with the three main cave spongy zones representing three successive sea level stillstands recorded by stacked parasequences infilling large erosional scallops along the shelf margin the geometry of the palaeo mixing zones indicates a low discharge system and together with the lack of meteoric karstic features favours a semi arid to arid climatic regime which is further supported by extensive calcrete bearing palaeosols occurring in coeval continental deposits

cenozoic fault systems in southwest qaidam basin northeastern tibetan plateau geometry temporal development and significance for hydrocarbon accumulation we present a detailed structural analysis of geometry and temporal development of the cenozoic faults in the southwestern part of the qaidam basin the largest petroliferous sedimentary basin and the only one producing oil and gas within the tibetan plateau northwest china based on three dimensional 3d seismic and well log data the cenozoic faults are mostly steep 50 70 basement involved reverse faults trending primarily west northwest and secondarily north south the two fault sets are commonly linked to each other by west northwest oriented faults bending either southward at their eastern tips or northward at the western tips and originated possibly from inversion of pre existing extensional faults in response to the far field effect of the cenozoic india eurasia collision faults or fault segments active during different time periods were identified from isopach maps and verified via seismic reflection profiles showing that the faults became active as early as the paleocene in the southern part of the southwest qaidam basin and propagated dominantly northward and subordinately eastward over time measurement of throws on major faults indicates that fault activity intensified over time and culminated since the mid miocene these faults have been an important factor in forming the oil fields in the southwest qaidam basin by improving permeability forming anticlinal traps and acting as conduits for oil migrating from source rocks to the reservoirs

characterization and discrimination of paleokarst breccias and pseudobreccias in carbonate rocks insight from ordovician strata in the northern tarim basin china abstract ordovician carbonates in the central and southern halahatang area of the tarim basin host highly productive hydrocarbon reservoirs previous studies suggest that the yingshan and yijianfang formations the primary producing intervals have been extensively karstified however the current author has not observed significant karst features in the formations based on the detailed study of 380 m long cores from 16 wells in the current study true breccias are only identified in two wells in the lianglitage formation including crackle and mosaic breccias as well as chaotic clast supported breccias the breccias are interpreted as karst related breccias that formed in near surface environments during pre silurian subaerial exposure and timing of karstification probably coincided with eustatic sea level fall caused by the middle katian glaciation widespread karst features of the yijianfang and yingshan formations identified as breccias or sediment filled cavities in many previous studies are actually only a mottled fabric pseudobreccia caused by selective diagenetic alteration and infiltration of bitumen in the deeper subsurface the color difference between pseudoclasts and pseudomatrix does not reflect a mixture of clasts and cave sediments but instead is characterized by distinct nevertheless commonly subtle variations in the limestone texture and whether bitumen is present one the basis of core and thin section observations sem scanning electron microscope and xrd x ray diffraction analyses the author presents criteria to distinguish karst breccias and pseudobreccias that can be applied to other similar carbonate deposits discrimination between karst breccias and nodular limestones is also presented differentiation of karst and pseudokarst features serves not only an academic interest but also has important applications for the exploration and development of carbonate reservoirs

tectonic uplift of the northern qinling mountains central china during the late cenozoic evidence from dem based geomorphological analysis abstract the qinling mountains which stretch from east to west in central china represent an important geological and geographical boundary between north china and south china because of the northeastward growth of the tibetan plateau since the late cenozoic the northern qinling mountains have been strongly reactivated and uplifted to investigate the landscape response to the tectonic uplift the geomorphic indices of the northern qinling mountains including the hypsometry mathematical function of the longitudinal profile channel longitudinal profile and steepness index were analyzed the topographic analysis reveals that the landscape evolution of the heihe river basin is in a transient state the upstream of the heihe river basin has undergone a long period of erosion and represents relict landscape in contrast the downstream represents adjusting landscape which formed by river incision in response to the rapid uplift of the northern qinling mountains this is a result of the extension of the weihe graben which has formed due to the northeastward growth of the tibetan plateau during the late cenozoic the spatial distribution of the geomorphic indices reveals that the ne striking taibai fault has experienced strong tectonic activity since the late cenozoic and is a secondary fault that accelerated the uplift rate of the northern qinling mountains the tectonic stress due to the northeastward growth of the tibetan plateau has been transmitted to the northern qinling mountains along the taibai fault therefore we proposed that the uplift of the northern qinling mountains is due to the combined effects of the weihe graben extension and taibai fault activity forming the highest peak taibai mountain of the northern qinling mountains near the intersection of the qinling piedmont fault and taibai fault

the use of the stream length gradient index in morphotectonic analysis of small catchments a case study from central italy abstract the aim of this work is to test an integrated quantitative geomorphic approach based on stream length gradient index sl index analysis within the small catchment of the tarugo river in the northern marchean apennines central italy the tarugo river basin 92 km 2 wide strikes sw ne across the marchean ridge and the western sector of marchean piedmont the area is characterized by a series of nw se trending ne verging thrust folds affecting the meso cenozoic bedrock that pass upward from dominantly carbonate to dominantly terrigenous rocks the area investigated has been affected since the pliocene by extensional tectonics accompanying a regional uplift decreasing in rate north eastwards in this work the sl index analysis has been integrated with the spatial analysis of the amplitude of relief a r and compared to geological and geomorphological field data results of this work indicate that the sl index is a valid tool to detect the long wavelength structural effect on topography as well as the incipient local response to regional processes i e regional uplift that is often undetectable by other morphotectonic parameters in contrast the sl index analysis seems not be a valid tool for discriminating the local lithological influence from the tectonic one

chemical mass transfer during hydrothermal alteration of carbonates controls of seafloor subsidence sedimentation and zn pb mineralization in the irish carboniferous abstract petrographic and geochemical data were acquired to evaluate models for the formation of hydrothermal dolomite breccias that host zinc lead orebodies in the rathdowney trend of the irish orefield and assess element mobility during hydrothermal alteration of carbonates macroscopic and microscopic textures indicate that the breccias largely formed by a pseudobrecciation process involving dissolution and replacement of precursor waulsortian dolomite of diagenetic origin during subseafloor hydrothermal fluid flow geochemical analyses show that compared with the waulsortian dolomite precursor breccia clasts and matrix contain respectively higher concentrations of al ti and light rare earth elements which are linearly correlated indicative of mass loss during hydrothermal interaction bulk rock mass loss estimates average 33 indicating extensive dissolution of carbonate although petrographic evidence and limited clast rotation or translation rule out the development of significant open space this supports a mechanism of alteration whereby hydrothermal fluids migrating along grain boundaries microcracks and solution seams drove dissolution and replacement of the surrounding host rock with partial collapse of the transient microporosity produced progressive interaction led to the gradual isolation of domains clasts surrounded by replacement dolomite matrix massive sulfide mineralization formed subsequently by stratabound replacement of the dolomite pseudobreccia by hydrothermal fluids preferentially focused within the more permeable and possibly more reactive lithology this process involved further volume loss 30 of the replaced rock quantitative mass transfer analysis indicates that during hydrothermal interaction net loss of na p mn sr and sometimes cu and net gain in li k fe as well as the ore associated elements typically occurred marked fractionation of the ree is observed eu was added implicating elevated temperature acidic and reduced hydrothermal fluids ce was also added possibly derived from remobilization of pre sulfide oxide mineralization the lree were typically immobile or partially removed and the hree were preferentially mobilized and transported beyond the scale of sampling thus the hree together with na p mn sr and possibly cu may form a distal chemical anomaly at the base of the waulsortian limestone formation the net addition of li k and be in dolomite breccia matrix samples combined with their increase in concentration due to dolomite dissolution produced a broad anomaly of these elements extending for at least 1 5 km from the center of the lisheen deposit these various geochemical anomalies have potential utility in mineral exploration a total volume loss of up to 68 at lisheen is consistent with a marked thinning of the waulsortian biomicrite facies above massive sulfide the observed thickening of upper and supra waulsortian facies in the trough developed above this zone is interpreted to reflect infill of a seafloor depression up to 90 m deep developed in response to underlying hydrothermal dissolution this model implies mineralization initiated during the latter stages of waulsortian deposition in the late courceyan early chadian at a depth of approximately 150 m below the seafloor

spatial analysis of stream power using gis slk anomaly maps the stream length gradient index sl shows the variation in stream power along river reaches this index is very sensitive to changes in channel slope thus allowing the evaluation of recent tectonic activity and or rock resistance nevertheless the comparison of sl values from rivers of different length is biased due to the manner in which the index is formulated thus making correlations of sl anomalies along different rivers difficult therefore when undertaking a comparison of sl values of rivers of different lengths a normalization factor must be used the graded river gradient k has already been used in some studies to normalize the sl index in this work we explore the relationships between the graded river gradient k the sl index and the stream power proposing the use of a re named slk index which enables the comparison of variable length rivers as well as the drawing of slk anomaly maps we present here a gis based procedure to generate slk maps and to identify slk anomalies in order to verify the advantages of this methodology we compared an slk map of the ne border of the granada basin with both simple river profile knickpoint identification and with an sl map the results show that the slk map supplies good results with defined anomalies and suitably reflects the main tectonic and lithological features of the study area copyright 2008 john wiley sons ltd

component specific petrographic and geochemical characterization of fine grained carbonates along carboniferous and jurassic platform to basin transects abstract fine grained carbonates are present throughout much of the geological record and are widely used as geochemical archives even though their origin and diagenetic pathways remain poorly understood here petrographical and geochemical properties of granulometrically separated component spectra of marine mudstones sampled along two proximal to distal transects carboniferous of spain and jurassic of morocco are documented these settings represent end members in terms of platform geometry steep flanked versus gentle ramp and the aragonite versus calcite sea mode the data from spain reveal a bimodal organization of microcrystalline carbonate isotope values from platform top and slope and toe of slope settings the data from morocco lack a clear spatial and bathymetrical pattern the significance of the complex site specific biological and physico chemical parameters is emphasized mudstones have been separated in granulometric fractions of 8 5 5 3 and

active tectonics in southern xinjiang china analysis of terrace riser and normal fault scarp degradation along the hotan qira fault system the northern piedmont of the western kunlun mountains xinjiang china is marked at its easternmost extremity south of the hotan qira oases by a set of normal faults trending n50e for nearly 70 km conspicuous on landsat and spot images these faults follow the southeastern border of a deep flexural basin and may be related to the subsidence of the tarim platform loaded by the western kunlun northward overthrust the hotan qira normal fault system vertically offsets the piedmont slope by 70 m highest fault scarps reach 20 m and often display evidence for recent reactivations about 2 m high successive stream entrenchments in uplifted footwalls have formed inset terraces we have leveled topographic profiles across fault scarps and transverse abandoned terrace risers the state of degradation of each terrace edge has been characterized by a degradation coefficient derived by comparison with analytical erosion models edges of highest abandoned terraces yield a degradation coefficient of 33 4 m 2 profiles of cumulative fault scarps have been analyzed in a similar way using synthetic profiles generated with a simple incremental fault scarp model the analysis shows that 1 rate of fault slip remained essentially constant since the aggradation of the piedmont surface and 2 the occurrence of inset terraces was synchronous at all studied sites suggesting a climate driven terrace formation observation of glacial and periglacial geomorphic features along the northern front of the western kunlun range indicates that the qira glaciofluvial fan emplaced after the last glacial maximum during the retreat of the kunlun glaciers 12 22 ka the age of the most developed inset terrace in uplifted valleys is inferred to be 10 3 ka coeval with humid climate pulses of the last deglaciation the mass diffusivity constant k t being time b p in the hotan region is determined to be 3 3 1 4 m 2 10 3 years consistent with other estimates in similar climatic and geologic environments of western china these results imply a minimum rate for the tarim subsidence of 3 5 2 mm yr if western kunlun overthrusts the tarim platform on a crustal ramp dipping 40 45 to the south it would absorb at least 4 5 3 mm yr of convergence between western tibet and tarim

interplay of cementation mechanical compaction and chemical compaction in nodular limestones of the rosso ammonitico veronese middle upper jurassic northeastern italy abstract the rosso ammonitico veronese middle upper jurassic is a thin 25 30 m lithostratigraphic unit consisting of red mostly nodular pelagic limestones deposited on a current swept structural high in the southern alps sedimentation rates were very low and omission surfaces and mineralized hardgrounds were widespread facies are varied and commonly show evidence of early lithification near the sediment water interface petrographic observations of both mud and grain supported facies rich in thin shelled bivalves enabled reconstruction of the diagenetic evolution some layers or nodules within layers underwent a phase of early lithification acquiring a rigid framework that prevented deformation and rearrangement of grains during later burial in the uncemented beds and in the matrix of nodular beds the effects of subsequent mechanical and chemical compaction are clearly recognizable the response to chemical compaction varied with texture grain supported sediments developed fitted fabrics whereas in mud supported sediments dissolution seams were generated after these diagenetic processes when all the layers had acquired the same degree of coherence laterally extensive stylolites developed cutting across older depositional and or diagenetic fabrics total compaction was evaluated quantitatively by different methods diverse compaction values related to the changing interplay of early cementation and burial diagenetic processes were obtained but an average of about 60 volume reduction for the whole formation is estimated

structural coupling between the qiman tagh and the qaidam basin northern tibetan plateau a perspective from the yingxiong range by integrating field mapping seismic imaging and analogue modeling

characterizing seismic bright spots in deeply buried ordovician paleokarst strata central tabei uplift tarim basin western china anomalous seismic amplitude bright spots are a common feature in deeply buried 5500 to 6500 m ordovician limestone strata in the central tabei uplift area of the tarim basin in northwest china those anomalies have proven to be useful indicators of reservoir quality the bright spots as seen on seismic data are tied to high gamma ray low velocity zones in wireline logs and correspond to clastic cave sediment fills in the host limestone in core synthetic seismic models confirm this relationship between seismic bright spots and cave sediment fills a seismic traveltime map of the top ordovician unconformity illustrates erosional topography and seismic geomorphologic patterns associated with the unconformity with numerous sinuous fluvial channels and canyons fluvial valleys sinkholes and tower karsts and hills a mature surface drainage system interacted with a near surface karst system and allowed terrigenous sediments to enter an underground cave system karst related bright spots probably correspo

impact of wind erosion on detecting active tectonics from geomorphic indexes in extremely arid areas a case study from the hero range qaidam basin nw china abstract geomorphologic analysis has been used widely to detect active tectonics in regions where fluvial incision is the major erosional process in this paper however we assess the feasibility of utilizing these frequently used geomorphic indexes e g hypsometric curves longitudinal channel profiles normalized stream length gradient slk index to determine active tectonics in extremely arid areas where wind erosion also plays an important role the case study is developed on the hero range in the western qaidam basin one of the driest regions on earth with severe wind erosion since late pliocene the result shows that in the west and south sectors as well as the western part of the east sector of the hero range where fluvial incision prevails these geomorphic indexes are good indicators of active faulting and consistent with the geological result based on study of fault traces scarps faulted holocene fans and historical seismicity within the past four decades in contrast along the northeastern margin the ne and the se parts of the east sector of the range where wind erosion is also important the results from the geomorphic indexes show quite active tectonics contrary with the geological evidence favoring weakly active tectonics moreover the positive slk anomaly lies oblique to the fault trace and the anticline axis but parallel to the wind direction to reconcile the contradiction we propose that wind erosion caused by northwestern winds has a tendency to make geomorphic indexes exhibit anomalous values that indicate higher activities by way of 1 lowering the base level to generate knickpoints on the longitudinal channel profiles and therefore positive slk anomalies and 2 lateral erosion of the mountain front making the hypsometric curves and even the longitudinal channel profiles more convex and producing obvious slope breaks

fluvial dissection isostatic uplift and geomorphological evolution of volcanic islands gran canaria canary islands spain abstract digital analysis of torrential gullies barrancos deeply incised into the volcanic island of gran canaria canary islands allows us to extract the longitudinal profiles and pre incision surfaces for individual basins from which morphometric parameters length elevation area slope have been calculated other derived parameters such as ridgeline profiles maximum incision values volume removed by fluvial erosion geophysical relief and isostatic uplift have also been computed based on k ar ages for the island well constrained incision uplift rates have been calculated by means of the combination of different methodological approaches commonly used in orogens and large mountain ranges the geomorphological and morphometric analyses reveal that the island is clearly divided into four environmental quadrants determined by the combination of a couple of key factors the age of the volcanic surfaces and the climatic conditions these factors determine a young sector covered with plio quaternary platform forming lavas finished at 1 9 1 5 ma evolving under contrasting wet ne to dry se climates and an older sector conserving the residual surfaces of the miocene shield building 14 5 8 7 ma at the ridgelines also subjected to wet nw and dry sw climates incision is related to the age zonation of the island maximum incisions

active tectonic influence on the evolution of drainage and landscape geomorphic signatures from frontal and hinterland areas along the northwestern himalaya india abstract the kangra re entrant in the nw himalaya is one of the most seismically active regions falling into seismic zone v along the himalaya in 1905 the area experienced one of the great himalayan earthquakes with magnitude 7 8 the frontal fault system the himalayan frontal thrust hft associated with the foreland fold janauri anticline along with other major as well as secondary hinterland thrust faults provides an ideal site to study the ongoing tectonic activity which has influenced the evolution of drainage and landscape in the region the present study suggests that the flat uplifted surface in the central portion of the janauri anticline represents the paleo exit of the sutlej river it is suggested that initially when the tectonic activity propagated southward along the hft the janauri anticline grew along two separate fault segments north and south faults the gap between these two fault and the related folds allowed the sutlej river to flow across this area later the radial propagation of the faults towards each other resulted in an interaction of the fault tips which caused the rapid uplift of the area rapid uplift resulted in the disruption and longitudinal deflection of the sutlej river channel fluvial deposits on the flat surface suggest that an earlier fluvial system flowed across this area in the recent past geomorphic signatures like the sharp mountain fronts along the hft in some places as well as along various hinterland subordinate faults like the nalagarh thrust nat the barsar thrust bat and the jawalamukhi thrust jmt the change in the channel pattern marked by a tight incised meander of the beas channel upstream of the jmt indicate active tectonic movements in the area the prominent v shaped valleys of the beas and sutlej rivers flowing across the thrust fronts with vf values ranging from

the recognition and interpretation of paleokarsts two examples from the lower carboniferous of south wales abstract criteria for the identification and interpretation of paleokarstic surfaces in ancient carbonate sequences are discussed and two examples of such surfaces are described from the lower carboniferous of south wales one type is compared to kavornossen karren a type of tropical karst well developed today on puerto rico the second example a mammillated paleokarstic surface of a type common in the lower carboniferous is interpreted as a deckenkarren formed beneath a vegetation cover and similar to the makondo karsts of south africa paleokarsts can provide information on the paleoclimates paleohydrology and vegetation cover existing at the time of their formation

scale dependence of hypsometric integrals an analysis of southeast african basins abstract previous studies have shown that the hypsometry of individual drainage basins is sensitive to both tectonic uplift rates and variations in erosional resistance of different lithological units however basin hypsometry has also been found to be related to the size the shape and relief of the sampled area as well as factors such as the type of dominant erosional process this study extends the evaluation of the controls on a basin s hypsometry by assessing factors that might influence the spatial distribution of hypsometric integrals at different scales the method is applied to catchments draining the southeast margin of southern africa kwazulu natal region because of the region s rather uniform runoff a rather well constrained denudational history and a relatively simple coastward sequence of bedrock geology several sets of basins were extracted from an srtm derived 90 m resolution dem one set of main basins those that have outlets at sea level and six sets of sub basins of different size based on strahler order the mean area of the sub basins sampled ranged from 9 km2 for strahler order 2 through to 3215 km2 for strahler order 6 in contrast to previous studies data from this study fail to show a correspondence between hypsometric integral and indices of basin dimension such as basin area and basin relief rather basin hypsometry in se africa varies spatially and with scale in particular a mountain range scale positive hypsometric integral anomaly situated between 10 and 100 km of the coast line was observed but only in basins of strahler order 5 and less this anomaly is compatible with moderate crustal displacement focussed midway between the coast and the drakensburg escarpment some intermediate scale positive hypsometric integral anomalies in basins of strahler order 4 and less was also observed in some cases these anomalies correspond to differences in erosional resistance among major lithological groups finally numerous local basin scale positive hypsometric integral anomalies in basins of strahler order 3 and less were also observed in many cases these latter anomalies are related to local differences in lithological resistance e g the presence of dolerite sills and dikes the analysis of the spatial variation of hypsometric integrals in basins of different size ranges is therefore a useful first step in assessing factors that control landscape development

karst controlled reservoir heterogeneity in ellenburger group carbonates of west texas petroleum production from restricted shelf carbonates of the lower ordovician ellenburger group is commonly considered to have been a result of a pervasive relatively homogeneous tectonic fracture system within the reservoir rock however regional facies and diagenetic paleokarst studies of ellenburger strata based on cores and wireline logs have demonstrated that significant reservoir compartmentalization was caused by karst modification in the upper part of the unit ellenburger group carbonates which attain a thickness of over 1 700 ft 520 m record sedimentation on a shallow water restricted shelf occupying most of west texas logging of over 10 000 ft 3 050 m of core from 63 wells has allowed recognition of six facies assemblages 1 lithic arenite 2 mixed siliciclastic carbonate packstone grainstone 3 ooid peloid grainstone 4 mottled mudstone 5 laminated mudstone and 6 gastropod intraclast packstone grainstone these facies assemblages record initial transgression and subsequent progradation and aggradation paleoslope was generally south and east from the texas arch toward the ouachita and marathon orogenic belts all facies assemblages with the local exception of the ooid peloid grainstone assemblage are characterized y very low intergranular and intercrystalline porosity porosity development in ellenburger group carbonates is directly related to a prolonged period of subaerial exposure that coincided with a middle ordovician eustatic lowstand prior to transgression of simpson group siliciclastics during this episode a widespread system of caves sinkholes joint controlled solution features and collapse breccias developed of particular importance to reservoir development was the formation of a regionally extensive cave system between 100 and 300 ft 30 and 90 m beneath the exposed ellenburger surface infill of this cave system by simpson group sand and clay segmented the upper ellenburger into three karst facies which are in descending order 1 cave roof dolomites fracture and mosaic breccias 2 laterally persistent cave fill facies siliciclastic matrix supported and carbonate matrix supported breccias and 3 lower collapse facies chaotic clast supported breccias of the cave floor pronounced vertical segregation of permeable zones defined by the three karst facies is evident in the emma andector martin block 13 and several other major ellenburger reservoirs lateral reservoir heterogeneities formed by localized laterally extensive collapse structures such as in the shafter lake reservoir also contribute to compartmentalization of producing zones within the upper ellenburger group secondary and tertiary recovery programs in these ellenburger reservoirs can be optimized by integrating concepts of lateral and vertical heterogeneity predicted by the karst model

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

palaeokarst evidence for widespread regression and subaerial exposure in the middle katian upper ordovician of baltoscandia significance for global climate we report on widespread and contemporary palaeokarst in the middle katian upper ordovician of sweden estonia and latvia the first major palaeokarst horizon to be reported from the ordovician of baltoscandia the solution features occurwithin a fewmetres of thick zone of limestone immediately belowthe widespread fjacka shale and are related to an unconformity with preserved palaeorelief in the slandrom limestone in sweden and the time equivalent saunja formation in estonia and latvia facies evidence for a karst origin comes fromseveral outcrops and core sections and includes 1 frequent karren likemorphologies interpreted as swiss cheese karst sensu baceta et al 2001 2 local occurrences of solution collapse breccia 3 presence of bladed pseudospar crystals in solution cavities and 4 carbon isotope values indicating meteoric influence to the succession these findings are herein put in context with previously reported large scale erosional channels that may cut down several tens of metres below the fjacka shale in the subsurface baltic sea area and with regional anomalous thickness variations in the slandrom limestone and saunja formation all together forming strong support for regional exposure of the baltoscandian continent in the middle katian high resolution stable isotopic data show that the regression and lowstand of sea level overlap with thewaynesville carbon isotope excursion it resulted in basin wide cessation of carbonate production near the amorphognathus superbus and a ordovicicus conodont zonal boundary the contemporary development of palaeokarst in different confacies belts of the basin suggests that this was an extraordinary sea level lowstand herein interpreted as reflecting a middle katian glaciation less

high frequency eustatic sea level changes during the middle to early late ordovician of southern jordan indirect evidence for a darriwilian ice age in gondwana abstract the middle to early late ordovician hiswah and dubaydib formations in southern jordan provide a well constrained sedimentary record of 4th and 3rd order relative sea level change along the northern tectonically quiescent subpolar gondwana continental margin cyclic deposition occurred on a wave and storm dominated microtidal shelf dominated by shoreface and offshore transition zone facies cycles are commonly bounded by amalgamated bounding surfaces sb ts or sb mfs and are characterised by stacked transgressive systems tracts tsts the small facies dislocation across key sequence bounding surfaces indicates a 15 50 m change in relative sea level fourth order sequences are hypothesized to be paced by the long eccentricity 405 kyr cycle and consequently 3rd order sequences are calculated to be 1 2 m y and 2 4 m y long these correlate with the global eustatic sea level curve in comparison with mesozoic and cenozoic sequence stratigraphical data we conclude that the 1 2 m y cycles correspond with long obliquity cycles predominant in icehouse conditions and the 2 4 m y cycles with the long eccentricity cycle predominant during greenhouse conditions we propose a darriwilian ice age during which orbitally induced cold snaps caused the expansion and amalgamation of small medium scale ice sheets the reduced size of the correlative positive carbon isotope excursion compared to that in the hirnantian may indicate that the darriwilian ice sheets only reached the sea in a few places the absence of glacio terrestrial deposits of middle ordovician age is most likely due to subsequent glacial erosion during repeated ice advances up to and including those in the hirnantian the existence of darriwilian ice sheets is consistent with zooplankton province distributions that indicate a polar front at 40 s during the ice age it is likely that polar ice existed throughout the ordovician

ordovician metre scale cycles implications for climate and eustatic fluctuations in the central appalachians during a global greenhouse non glacial to glacial transition abstract metre scale shallowing upward cycles in ordovician carbonates of the central appalachian basin record climate and eustatic fluctuations during a transition from early ordovician global greenhouse to late ordovician icehouse conditions peritidal facies and shale abundance suggest a long term trend in this area from semi arid early ordovician to more humid middle to early late ordovician conditions with a return to semi arid conditions during the late ordovician the climatic fluctuations were most likely produced by tectonics uplift and erosion related to taconic orogenesis plate motion of north america and the areal extent of water covering the shelf peritidal cyclic facies indicate that high frequency relative sea level fluctuations were of small amplitude 20 m relative sea level fluctuations that decreased into the later ordovician if these sea level changes are eustatic then the increased amplitude may mark the early initiation of continental glaciation on gondwana in the late middle ordovician followed by waning of ice sheets prior to the latest ordovician glaciation

effects of active folding and reverse faulting on stream channel evolution santa barbara fold belt california abstract the santa barbara fold belt sbfb is an area of active crustal shortening comprising younger east west and older southeast northwest oriented reverse faults and folds changes in channel position and stream incision are the result of active fold growth and uplift rates of incision range from 0 4 0 1 m ka to 1 2 0 04 m ka lateral stream diversion from fold and fault growth varies from 6 7 to 0 4 km minimum uplift of western mission ridge anticline is 0 8 0 1 m ka and minimum uplift on the mesa fault is 0 3 0 4 m ka the hypothesis that east to west folds are younger is suggested by a cross cutting relationship and is tested using geomorphic indices of active tectonics including valley width to height ratios vf mountain front sinuosity smf and drainage densities dd east to west trending structures have mean values of vf smf and dd of 2 7 1 2 and 2 2 km km2 respectively while southeast to northwest trending structures have mean values of 5 0 1 5 and 3 7 km km2 respectively we present a new geomorphic tool the stream diversion index which uses diversion timing and distance to assess relative tectonic activity these values range from 6 to 260 m ka all of these values support the hypothesis that the east to west folds are younger and more active clockwise rotation of the western transverse ranges is probably the process that produced the two sets of structures with rotation the older set that started out east to west eventually became northwest to southeast and more difficult to maintain with the north to south contractional shortening associated with the big bend of the san andreas fault 80 km to the north the second set of younger structures formed with a more favorable east to west orientation to the shortening

the history and nature of wind erosion in deserts recently the importance of wind erosion has been reevaluated many low angle surfaces developed on susceptible materials possess closed depressions pans and these often have a distinctive morphology and lunette dunes on their lee sides it has also become apparent that in drylands there are extensive areas of stone pavements some of which have been molded by deflation however it is now recognized that other horizontal sorting processes have played a role especially movement of fines by overland flow vertical sorting associated with wetting and drying salt heave bioturbation frost action and dust accretion have also played a role in hyperarid areas especially with unidirectional winds bedrock outcrops and old lake beds have been molded to give aerodynamic forms called yardangs the study of dust storms by analysis of climatological data and remote sensing has revealed the importance of deflation especially in hyperarid areas with centripetal drainage deflation hot spots such as the bo

pseudobreccias revealed as calcrete mottling and bioturbation in the late dinantian of the southern lake district uk two types of pseudobreccia one with grey and the other with brown mottle fabrics occur in shoaling upward cycles of the urswick limestone formation of asbian late dinantian carboniferous age in the southern lake district uk the grey mottle pseudobreccia occurs in cycle base packstones and developed after backfilling and abandonment of thalassinoides burrow systems burrow infills consist of a fine to coarse crystalline microspar that has dull brown to moderate orange colours under cathodoluminescence mottling formed when an early diagenetic aerobic decay clock operating on buried organic material was stopped and sediment entered the sulphate reduction zone this probably occurred during progradation of grainstone shoal facies after which there was initial exposure to meteoric water microspar calcites then formed rapidly as a result of aragonite stabilization the precipitation of the main meteoric cements and aragonite bioclast dissolution post date this stabilisation event the brown mottle pseudobreccia fabrics are intimately associated with rhizocretions and calcrete which developed beneath palaeokarstic surfaces capping cycle top grainstones and post date all depositional fabrics although they may also follow primary depositional heterogeneities such as burrows they consist of coarse inclusion rich microspar calcites that are always very dull to non luminescent under cathodoluminescence sometimes with some thin bright zones these are interpreted as capillary rise and pedogenic calcrete precipitates the d 18 o values 5 to 8 pdb and the d 13 c values 2 to 3 pdb of the pseudobreccias are lower than the estimated d 18 o values 3 to 1 pdb and d 13 c values of 2 to 4 pdb of normal marine calcite precipitated from late dinantian sea water reflecting the influence of meteoric waters and the input of organic carbon

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

two stage evolution of the altyn tagh fault during the cenozoic new insight from provenance analysis of a geological section in nw qaidam basin nw china introductionthe 1600 km long active altyn taghfault atf de nes the northern edgeof the tibetan plateau links thewestern kunlun eastern kunlun andqilian orogenic belts fig 1a and gures prominently in constrainingthe timing mechanism and stress dis sipation of the tibetan uplift e g yinand harrison 2000 tapponnier etal 2001 cowgill et al 2003 aspectof its cenozoic evolution has beenattracting hot debate zhou and gra ham 1996 yue and liou 1999 yinet al 2002 liu et al 2007 and akey issue is the initiation of left slipmovement on the fault which wasconsidered to occur i during lateeocene early oligocene evidenced bythermochronology in the altynmountain chen et al 2001 andsedimentology adjacent to the fault meng et al 2001 yue et al 2001 ritts et al 2004 or ii since middlemiocene through structural analysisin the qaidam basin yuan et al 2008 wang et al 2010 apatite s sion track result along the atf wanet al 2001 chen et al 2002 andcomprehensive analysis of the north ern tibetan plateau burch el et al 1989 wang 1997 meyer et al 1998 yin et al 2002 argued a much earlierinitiation age 49 ma of the westernand central segments of the atf butwith questionable proofs ritts et al 2004 two factors probably lead tothis uncertainty i the atf is toolarge to allow us to nd an appropri ate proxy deciphering accurately itsevolution and ii most extant studiesshare a bias that the atf has beenalways a left slip fault during thecenozoic which we regard as a mis understanding in this paper provenance analysis has beenproved e ective on revealing theuplifting history of mountains andevolution of major faults e g lindseyet al 2007 miao et al 2008 linet al 2009 marsaglia et al 2010 the qaidam basin is the largest sed imentary basin inside the tibetan pla teau and accumulated thick terrestrialsediments during the cenozoic rieseret al 2006 making itself an idealplace for deciphering the uplift andpropagation of the plateau yin et al 2007 2008 as it is bounded by theatf to the northwest fig 1b itssedimentation has possibly been tiedto the development of this large scaleintracontinentalfault fewworkshavebeen done on this subject due to thetough geographic conditions in thispaper we investigated a geologicalsection spanning eocene pliocene inthe nw qaidam basin and analysedin detail provenance of the sediments we link the result to cenozoic evolu tion of the atf and try to illustrate together with some other evidences that the atf was used to be a basalshear zone before its initiation of left slip since middle miocene which rec onciles the two contrasting viewpointson the cenozoic initiation of the atfabovementioned geological settingthe study section is seated at thesouthern side of the atf and incisesthe western limb of the nw trendingganchaigou anticline bounded to thenorth by a north directed reversefault a branch fault of the atf fig 1c the cenozoic strata are wellexposed in the section including thexiaganchaigou xg shangganchai gou sg xiayoushashan xy shangyoushashan sy and shizigou szg formations in an ascendingorder the xg formation consists of redmudstone siltstone and sandstoneattaining bed thickness of 0 2 1 m interbedded with conglomerate andpebble sandstone layers 10 20 cmthick figs 2 and 3a the stratumeven comprises more than 100 mthick calcareous mudstones in theupper part in the drillhole chaishen 3 about 6 km east of the sectionabstract

carbonate dissolution in a modern mixing zone the potential for dissolution of calcite and aragonite and precipitation of dolomite by the mixing of fresh and saline ground waters has been demonstrated theoretically1 3 although geologists have used these processes in the explanation of the diagenesis of recent4 7 and ancient8 12 carbonates there has been only limited investigation of the geochemical processes of modern mixing zones13 14 here we report the results of chemical and rock profiling through a modern mixing zone on andros island in the bahamas our results demonstrate undersaturation of the waters in the mixing zone with respect to aragonite and calcite and corresponding pervasive dissolution of the carbonate rocks at this level undersaturation is significantly enhanced by bacterial processes which are also responsible for precipitation of an iron rich crust despite chemical supersaturation precipitation of dolomite was not observed thereby casting some doubt on the mixing zone model of dolomitization

geomorphological and structural characterization of the southern weihe graben central china implications for fault segmentation abstract the cenozoic graben systems around the tectonically stable ordos block central china have been considered as ideal places for investigating active deformation within continental rifts such as the weihe graben at the southern margin with high historical seismicity e g 1556 m 8 5 huaxian great earthquake however previous investigations have mostly focused on the active structures in the eastern and northern parts of this graben by contrast in the southwest tectonic activity along the northern margin of the qinling mountains has not been systematically investigated yet in this study based on digital elevation models dems we carried out geomorphological analysis to evaluate the relative tectonic activity along the whole south border fault sbf on the basis of field observations high resolution dems acquired by small unmanned aerial vehicles suva using structure for motion techniques radiocarbon 14c age dating we demonstrate that 1 tectonic activity along the sbf changes along strike being higher in the eastern sector 2 seven major segment boundaries have been assigned where the fault changes its strike and has lower tectonic activity 3 the fault segment between the cities of huaxian and huayin characterized by almost pure normal slip has been active during the holocene we suggest that these findings would provide a basis for further investigating on the seismic risk in densely populated weihe graben

geomorphic response to uplift along the dragon s back pressure ridge carrizo plain california we used high resolution topography geomorphic mapping of active surface processes and geologic mapping to study the topographic and erosional response of small drainage basins to rock uplift along the dragon s back pressure ridge along the san andreas fault in the carrizo plain california we infer the history of deformation experienced by 40 small drainage basins formed in poorly consolidated sedimentary rocks a space for time substitution directly images the erosional and topographic responses to deformation progressive deformation and rock uplift are accompanied by increases in channel steepness and basin relief as uplift ceases channel concavity rapidly increases causing channels to undercut hillslopes this undercutting promotes the consumption of hillslopes by landsliding this undercutting also causes basin relief to be greatest after uplift has stopped this analysis indicates that channels of the dragon s back pressure ridge respond to changes in rock uplift rates over thousands of years whereas hillslope processes may take more than an order of magnitude longer to adjust to changes in rock uplift rates our study directly measures changes in erosional processes due to the initiation and cessation of rock uplift which can typically only be inferred using numerical models by direct field observations

origin and architecture of fractured cavernous carbonate reservoirs and their influences on seismic amplitudes ordovician carbonate is important for petroleum exploration and production in the tarim basin the matrix porosity of the carbonate reservoirs is usually less than 2 because of their age old sedimentary history and depth deeper than 5500 m the storage spaces are secondary dissolution pores and fractures which are dominated by visible dissolution caves holes and fractures zhou et al 2006 the reservoirs are therefore called fractured cavernous reservoirs good quality reservoir usually appears as a strong reflection called bead like reflection or br on poststack seismic sections and the corresponding reservoir is called a fracture cave body fcb which is the main drilling target of current e p in tarim basin the fcbs are unevenly distributed in carbonate strata and the storage spaces inside an fcb are also unevenly distributed therefore the reservoirs have both macroscopic and microscopic heterogeneities which bring great challenges to petroleum exploration

channel planform geometry and slopes from freely available high spatial resolution imagery and dem fusion implications for channel width scalings erosion proxies and fluvial signatures in tectonically active landscapes article i nfo the rapid expansion of high spatial resolution optical sensors and imagery over the last decade presents ex ceptional opportunities for quantifying visible attributes of geomorphic systems in this study we detail a simple robust methodology changeom to extract continuous channel width and centerline datasets for single thread channels using freely available high spatial resolution imagery currently available in google earth and bing maps comparisons with a global dataset of field and lidar derived channel widths indicate minimal errors associated with the imagery and changeom methodology b1 overall while examples from the goriganga river indian himalaya and the yakima river wa usa emphasize the benefit of em pirical width values over established channel width scalings in deciphering fluvial responses to complex landscape forcings in tectonically active regions additionally accurate centerline delineation from the changeom methodology provides improved sinuosity measurements and when fused with coarse resolution digital elevation models dems removes along profile shortening and coincident increases in reach scale channel slope lastly comparisons of aster gdem v2 srtm v4 1 and lidar channel profiles extracted in moderate to high relief regions demonstrate the inferiority of the aster gdem for channel slope calcula tions despite the apparent spatial resolution advantages 9 the methodology presented here will facili tate new discoveries in the fluvial environment that have historically been difficult due to access and imagery resolution issues and provide greater perspective on channel signatures and responses to a host of landscape forcings especially in tectonically active bedrock and lower order drainage systems

ordovician stable carbon isotope stratigraphy in the tarim basin nw china abstract the tarim basin located in nw china represents one of china s major palaeoplates its palaeogeographic position in the ordovician however is debated in this study we present biostratigraphically controlled stable carbon isotope data from some 600 samples spanning almost the entire ordovician in order to provide a tool that can be used for future chemostratigraphic correlations the data correlate well with results from south china and several major global 13c excursions such as the mdice dw2 3 saice sa2 gice ka1 and whitewater excursion ka4 are documented for the first time from the tarim basin major sedimentary gaps are detected in the lower floian between the penglaiba and yinshan formations in the upper darriwilian to lower sandbian between the dawangou and saergan or kanling formations and in the latest sandbian between the kanling and qilang formations as well as between the tumuxiuke and lianglitag formations three scenarios for the depositional history of the late darriwilian to early sandbian saergan formation which represents an important hydrocarbon source rock in the tarim basin are discussed with respect to their bio and chemostratigraphic implications the mid upper ordovician rocks recording high 13c values have been deposited during transgressive or highstand intervals whereas the regressive intervals are mostly missing this results in a stacking of several positive excursions and thus chemostratigraphic correlation without biostratigraphic control might produce misleading results especially for shallow water carbonates

dem and gis analysis of geomorphic indices for evaluating recent uplift of the northeastern margin of the tibetan plateau china the northeastern margin of the tibetan plateau is a tectonically active region consisting of a series of faults with bounded intermountain basins and is located in the transition zone between the tibetan plateau and the loess plateau active deformation that may affect the topography in this region can be quantified using geomorphic indices therefore we applied geomorphic indices such as the hypsometric integral and the stream length gradient index to infer neo tectonics in the northeastern margin of the tibetan plateau different time scaled geodetic leveling data and river incision rates were also integrated into the investigation the results show that the hypsometric integrals are not significantly affected by lithology but spatially correspond to the hanging walls of thrust faults the hypsometric integrals are also positively correlated with the leveling data although the stream length gradient index is influenced by lithology its most pronounced anomalies of the stream length gradient are associated with the thrust faults consequently the uplift in the northeast margin of the tibetan plateau appeared to be concentrated along the hanging walls of the thrust faults

long lived glaciation in the late ordovician isotopic and sequence stratigraphic evidence from western laurentia the timing and causes of the transition to an icehouse climate in the late ordovician are controversial results of an integrated 13c and sequence stratigraphic analysis in nevada show that in the late ordovician chatfieldian stage mid caradoc a positive 13c excursion in the upper part of the copenhagen formation was closely followed by a regressive event evidenced within the prominent eureka quartzite the chatfieldian 13c excursion is known globally and interpreted to record enhanced organic carbon burial which lowered atmospheric p co2 to levels near the threshold for ice buildup in the ordovician greenhouse climate the subsequent regressive event in central nevada previously interpreted as part of a regional tectonic adjustment is here attributed in part to sea level drawdown from the initiation of continental glaciation on gondwana this drop in sea level which may have contributed to further cooling through a reduction in poleward heat transport and a lowering of p co2 by suppressing shelf carbonate production signals the transition to a late ordovician icehouse climate 10 m y before the widespread hirnantian glacial maximum at the end of the ordovician

wavy and lenticular bedded carbonate ribbon rocks of the upper cambrian conococheague limestone central appalachians abstract thinly interbedded limestones and dolostones are common in paleozoic and proterozoic carbonate sequences such rocks called ribbon rocks are characteristic of the 750 m thick upper cambrian conococheague limestone a platform deposit exposed in western maryland limestones of conococheague ribbon rocks occur as continuous wavy thin beds to isolated centimeter scale pods commonly have flat bottoms and ripple form tops typically are internally current or wave ripple cross laminated and are composed of peloidal grainstones dolostones interbedded with these limestones are typically continuous on the outcrop scale drape underlying limestone ripple forms are commonly mudcracked and are composed of 10 40 b dolomite rhombohedrons in a carbonate clay matrix some ribbon rocks are di rupted by filled tubes soft sediment deformation features and abrupt lateral changes in rock type ribbon rocks within meter scale cycles of the conococheague have gradational contacts with cross stratified grainstones below and grade into mud cracked laminites above these observations suggest that the limestone dolostone alternations of ribbon rocks reflect original carbonate sand mud alternations this interpretation is strongly amplified by comparing conococheague ribbon rocks to examples of lenticular and wavy bedding from mixed siliciclastic sand and mud flats from the modern north sea conococheague ribbon rocks are interpreted as ancient carbonate examples of lenticular and wavy bedding deposited on mixed carbonate sand and mudflats in a shallow subtidal to intertidal setting this is consistent with an overall interpretation of conococheague cycles as the regressive deposits of carbonate tidal flats

late neogene magnetostratigraphy in the western qaidam basin ne tibetan plateau and its constraints on active tectonic uplift and progressive evolution of growth strata abstract the qaidam basin as the largest intermontane basin of the ne tibetan plateau is the ideal place to provide constraints on depositional and tectonic patters to determine its tectonic deformation history and progressive evolution of growth strata we conducted paleomagnetic study on the late neogene stratigraphic section in the western qaidam basin a magnetostratigraphic study of the well exposed 805 m qigequan section at the qigequan anticline in the western qaidam basin reveals twelve pairs of normal and reversed polarity zones which can be readily correlated with chrons c1n 3ar of the geomagnetic polarity time scale gpts from this correlation we can conclude that the shizigou and the qigequan formations were formed at 6 9 ma 2 5 ma and 2 5 0 4 ma respectively accumulation rates determined from our chronology together with the occurrence of unconformities suggest four phases of tectonic uplift which began at about 3 6 ma 2 5 ma 1 1 ma and 0 8 ma the results also suggest that offlap growth strata according to the limb rotation model on the anticlinorium started to occur at 8 2 ma they progressively become younger from the frontal region of the altyn tagh mts 8 2 ma to the southwestern basin 2 5 ma and to further east of the qaidam basin

distribution of active rock uplift along the eastern margin of the tibetan plateau inferences from bedrock channel longitudinal profiles 1 current models of long term river incision into bedrock suggest that the local rate of differential rock uplift should exert a primary control on the gradient of channel longitudinal profiles however discrimination of this effect from the influence of variations in substrate erodibility sediment flux precipitation and transient changes in profile shape has proved difficult in practice here we investigate the controls on the spatial distribution of bedrock channel gradients adjacent to the sichuan basin in an effort to assess the degree and nature of active deformation along this margin of the tibetan plateau analysis of river longitudinal profiles utilizing a channel steepness index a measure of profile gradient normalized for drainage area reveals a zone of anomalously steep channels adjacent to the topographic front of the plateau margin channel profiles are systematically less steep in their headwater reaches on the plateau and in their lower reaches east of the plateau margin comparison of steepness indices to mapped lithologic variations reveals that lithology has only a limited influence on channel gradient in this field area we observe no systematic relationship between steepness indices and upstream drainage area channels of all size are steeper near the plateau margin we argue that these systematic changes are not readily explained as a consequence of increased sediment flux or of orographic precipitation we are led to conclude that steep channel profiles along the topographic front of the plateau reflect active differential rock uplift between this region and the foreland

causes of concavity in longitudinal profiles of rivers a smooth concave configuration represents the most common quasi equilibrium profile of alluvial rivers in the present paper a generalized unified set of models for the longitudinal profile of rivers is presented various independent effects that drive concavity in longitudinal rivers are considered and classified the driving mechanisms considered here are 1 horizontal wavelike progradation of the river profile 2 abrasion of bed particles 3 aggradation of the river profile balancing subsidence at a constant speed and 4 the effect of tributaries adding sediment and water to the main stem of the river for simplicity it is assumed that the long term supply of water and sediment is constant hence a single discharge that is bank full discharge is used as an approximate characterization of the hydrologic regime for each point along the river sediment sorting has been studied elsewhere and is excluded from this analysis the river is assumed to have uniform bed material although the mean size may vary downstream it is concluded that the quasi equilibrium longitudinal profile created by each of the first three driving mechanisms mentioned above is concave the degree of concavity varies however depending on a set of physical conditions that can be identified by a set of dimensionless numbers a comparison of these numbers reveals the relative importance of the driving mechanisms for concavity a condition for concavity driven by the fourth mechanism that is tributary input is delineated