seismic and geologic characteristics of drowning events on carbonate platforms carbonate platform drowning events are recorded in upper jurassic lower cretaceous carbonates of the baltimore canyon area offshore united states east coast and lower miocene carbonates of the pearl river mouth basin offshore people s republic of china cursory examination of seismic data from both areas would indicate that the platforms fit the classic definition of a drowning unconformity however detailed lithologic and paleontologic data indicate that the depositional erosional hiatuses vary widely in each area from 0 25 m y in the baltimore canyon area to a condensed section with no hiatus in the pearl river mouth basin the sedimentary sequence produced during drowning the drowning sequence in both areas is gradational with underlying shallow platform carbo ates and in some places overlying deeper marine limestones and shales the generalized facies models proposed for drowning events suggest that they may appear as instantaneous or gradual changes in geologic and seismic data however high resolution seismic data across the baltimore canyon and pearl river mouth basins show that some drowning sequences may be masked on conventionally processed seismic sections because of this resolution problem a distinction should be made between seismically and geologically defined unconformity surfaces the geologic characteristics of drowning events on carbonate platforms include a gradational lower and sometimes upper contact chemical sedimentation glauconite phosphate open marine shelf sediments and a variable hiatus at the upper boundary late growth shelf margin reefs also can be a diagnostic feature of drowned platforms seismic characteristics include horizontal to sub horizontal basinal marine onlap basin parallel reflector continuity above the carbonate sequence boundary and downlap of later highstand units evidence from platforms adjacent to continental margins baltimore canyon indicates that drowning occurs in a step wise fashion advancing more or less symmetrically across the platform from shelf to nearshore environments data from isolated open ocean atolls pearl river mouth basin indicate that they respond differently to drowning showing an asymmetric decrease in shallow platform environments as drowning occurs proper recognition by a geoscientist of the seismic and geologic characteristics of drowning events can lead to better reservoir and seal estimates and the correct reconstruction of the depositional tectonic and eustatic histories of an area

erosional and climatic effects on long term chemical weathering rates in granitic landscapes spanning diverse climate regimes abstract we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes our 42 study sites encompass widely varying climatic and erosional regimes with mean annual temperatures ranging from 2 to 25 c average precipitation ranging from 22 to 420 cm year 1 and denudation rates ranging from 23 to 755 t km 2 year 1 long term chemical weathering rates range from 0 to 173 t km 2 year 1 in several cases exceeding the highest granitic weathering rates on record from previous work chemical weathering rates are highest at the sites with rapid denudation rates consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock a simple empirical relationship based on temperature precipitation and long term denudation rates explains 89 95 of the variation in long term weathering rates across our network of sites our analysis shows that for a given precipitation and temperature chemical weathering rates increase proportionally with fresh material supply rates we refer to this as supply limited weathering in which fresh material is chemically depleted to roughly the same degree regardless of its rate of supply from breakdown of rock the temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter comparisons of catchment mass balance data from the field our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought at least in actively eroding unglaciated terrain similar to our study sites to the extent that chemical weathering rates are supply limited in mountainous landscapes factors that regulate rates of mineral supply from erosion such as tectonic uplift may lead to significant fluctuations in global climate over the long term

palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record interest in palustrine carbonates and calcretes has increased over the last 20 years since they contain significant environmental information much of the work performed in this area has focused on either of two types of terrestrial carbonate palustrine carbonates or calcretes pedogenic and groundwater yet their simultaneous study shows there may be a gradual transition from one form to the other revealing the interplay between pedogenic sedimentary and diagenetic processes three main factors control the formation of these carbonates the position of the water table the host rock and the period of sub aerial exposure in pedogenic calcretes precipitation of carbonate takes places mostly in the vadose zone above the water table and within a previous host rock or sediment in groundwater calcretes the precipitation of carbonate also occurs within a previous host rock and around the groundwater table in palustrine carbonates however the precipitation of lime mud occurs in a lacustrine water body palustrine carbonates necessarily form on previous lacustrine mud whereas both types of calcretes may form on any type of sediment or soil the sub aerial exposure time needed to form palustrine carbonates may by relatively short even a season whereas pedogenic calcretes need more time several years to millions of years groundwater calcretes do not form on the topographic surfaces so there is no need of sub aerial exposure however stable surfaces favour the development of thick groundwater calcretes small fluctuations in the water table cause gradual transitions of these three types of terrestrial carbonates and the subsequent mixture of their characteristic features causing difficulties in the interpretation of these carbonates the formation of these carbonates is controlled by palaeoenvironmental factors both commonly form in semi arid climates arid climates are also suitable for calcretes but sub humid conditions are more suitable for palustrine carbonates more indications of climatic conditions may be obtained through the analysis of the d18o content of both calcretes and palustrine carbonates and from the depth of the horizon containing carbonate nodules in pedogenic calcretes vegetation is also important in the formation of these types of carbonates data on the prevailing vegetation can be obtained from the analysis of the micro and macrofabric as well as from the d13c signal of the primary carbonates which in pedogenic carbonates has also been used to estimate atmospheric pco2 during the phanerozoic these terrestrial carbonates are widely distributed on floodplains and distal areas of alluvial basins their presence and characteristics can be used as indicators of aggradation subsidence or accommodation rates and therefore as indicators of different tectonic regimes even though the study of these carbonates has notably increased in recent years much less is known about them than about marine carbonates presently there is much emphasis on obtaining a general model for sequence stratigraphy in terrestrial basins with a need to include the carbonates analysed in this paper

manganese in pelagic carbonates indication of major tectonic events during the geodynamic evolution of a passive continental margin the jurassic european margin of the tethys ligurian sea abstract mid oceanic hydrothermal activity is the main source of manganese in the pelagic realm consequently long term fluctuations of manganese in bulk carbonates could represent the variations in the hydrothermal flow intensity through time depending on global tectonic activity within this scope we analysed three jurassic sedimentary series in the southeastern basin france thus providing valuable information for further palaeogeographic and geodynamic reconstructions of the european tethyan passive margin the long term variations of the manganese curve can be correlated with second order sea level changes the main transgressive phases early toarcian late aalenian to bajocian and late bathonian to callovian are marked by a manganese content increase whereas the regressive phases late pliensbachian late toarcian to middle aalenian early bathonian to middle bathonian oxfordian are characterized by decreasing trends furthermore some manganese positive anomalies can be superimposed on the global geochemical record of sea level changes these coincide with periods of increasing subsidence rate early toarcian late bajocian middle and late oxfordian and also with phases of extension early aalenian of the european margin of the ligurian ocean the major event is the very sharp increase of manganese content localised in the athleta zone late callovian and corresponds to the first occurrence of oceanic crust moreover the manganese enrichments recorded in carbonates deposited before callovian times may have resulted from hydrothermal emanations during the first stages of rifting

paleoclimate and extensional tectonics of short lived lacustrine environments lower cretaceous of the panormide southern tethyan carbonate platform nw sicily abstract subaerial erosion and continental sedimentation interbedded with shallow water carbonates are unequivocal stratigraphic records to evaluate paleoenvironmental and paleoclimate evolution of emerged landmass stratigraphic analysis of the cretaceous monte gallo section of the mesozoic panormide carbonate platform in the northern side of the palermo mountains nw sicily records a peculiar continental derived clays that interrupted the shallow water carbonate sedimentation these clays rest with lenticular geometries above the tectonically enhanced subaerial erosional unconformity of the barremian lower aptian requienid limestones and are covered by the upper cretaceous rudistid limestone sedimentological investigation combined with mineralogical and petrographic results reveal the occurrence of alkaline to saline lake clays deposition in pond filling depositional environment recording stressed conditions evaporation especially in its final living phase they were formed when a half graben tilted block tectonics produced footwall uplift of the gallo faulted blocks carbonate platform paleoclimate evaluations of the continental derived clays highlighted that a period of warm humid conditions which favoured their formation interrupted the uniform warm climate conditions highlighting a greenhouse climate phase

tectonics and magmatism in turkey and the surrounding area this volume contains 23 papers from a range of international contributors describing recent research into the tectonics and magmatism of turkey and its surroundings this region is sited at the collision zone between eurasia and afro arabia and as such provides an extraordinarily complete and well exposed record of the staged tectonic evolution of this sector of the alpine himalayan orogen the geological history of this area involves separation of continental fragments from the margin of gondwana their migration across the tethyan oceans the subsequent closure of these oceans and finally the development of the neotectonic regime which continues to evolve to the present day such a comprehensive record is relevant to the understanding of collisional zones worldwide the volume is divided into five sections tethyan evolution neotethyan ophiolites post tethyan basin evolution neotectonics and igneous activity the first two sections deal with tethyan oceans whose growth and subsequent closure dominated the geodynamic framework in the mesozoic and cenozoic the subsequent sections deal with more recent geological developments from the balkan peninsula in the west to the transcaucasus in the east that followed consumption of the tethyan oceans there is a broad mix of papers throughout the volume wide ranging review papers on ocean development and extensional tectonics are followed by detailed descriptions of petrology and geochemistry and geographically focused studies on basin evolution specific aspects of extensional and strike slip tectonics and discussions of the relationship of magmatic activity to the tectonic development of the area tectonics and magmatism in turkey and the surrounding area presents up to date results and ideas from a large number of international contributors on a wide range of current research activity in this region it is essential reading for all geoscientists with an interest in both academic and applied aspects of eastern mediterranean geology

chemical processes affecting the mobility of major minor and trace elements during weathering of granitic rocks abstract the behaviour of 38 major and trace elements as well as changes in the mineralogy have been examined in 10 weathering profiles developing on some portuguese granitic rocks element mobilities are calculated from geochemical data normalized with respect to ti in the fresh parent rock chemical elements are divided into two groups immobile and mobile on the basis of their geochemical distribution during weathering elements that are immobile during weathering are zr hf fe al th nb sc and the ree very mobile are ca na p k sr ba rb mg and si mobile elements are derived mainly from leachable minerals such as feldspars micas and apatites whereas immobile elements are either concentrated in resistate phases or strongly adsorbed by secondary minerals the geochemical behaviour of mn cr v fe and ce is very dependent on redox conditions redox transformations of these elements can be used to set limits on the oxidation state of a weathering suite the ree are mobilized or fractionated during late stages of weathering but not during moderate stages of weathering this fractionation is caused by selective leaching of rocks composed of both stable and unstable minerals containing ree

chemical weathering of granite under acid rainfall environment korea chemical weathering was investigated by collecting samples from five selected weathering profiles in a high elevation granitic environment located in seoul korea the overall changes of chemistry and mineralogical textures were examined reflecting weathering degrees of the samples using polarization microscopy x ray diffraction xrd electron probe micro analysis epma x ray fluorescence spectroscopy xrf and inductively coupled plasma mass spectroscopy icp ms the chemical distribution in the weathering profiles shows that few trace elements are slightly immobile whereas most major particularly ca and na and trace elements are mobile from the beginning of the granite weathering on the other hand there were mineralogical changes initiated from a plagioclase breakdown which shows a characteristic circular dissolved pattern caused by a preferential leaching of ca cation along grain boundaries and zoning the biotite in that region is also supposed to be sensitive to exterior environmental condition and may be easily dissolved by acidic percolated water as a result it seems that some rock forming minerals in the granitic rock located in seoul are significantly unstable due to the environmental condition of acidic rainfall and steep slopes where they are susceptible to be dissolved incongruently leading some elements to be highly depleted

late quaternary glaciation history of monsoon dominated dingad basin central himalaya india abstract the study presents the late quaternary glaciation history of monsoon dominated dokriani glacier valley dingad basin central himalaya india the basin is tested for the mechanism of landforms preservation in high relief and abundant precipitation regimes of the higher himalaya field geomorphology and remote sensing data supported by optical stimulated luminescence osl dating enabled identification of five major glacial events of decreasing magnitude the oldest glacial stage dokriani glacial stage i dgs i extended down to 8 km 2883 m asl from present day snout 3965 m asl followed by other four glaciations events viz dgs ii dgs iii dgs iv and dgs v terminating at 3211 3445 3648 and 3733 m asl respectively the dgs i glaciation 25 22 ka bp occurred during early marine isotope stage mis 2 characterized as last glacial maximum lgm extension of the valley similarly dgs ii stage 14 11 ka bp represents the global cool and dry older dryas and younger dryas event glaciation the dgs iii glaciation 8 ka bp coincides with early holocene 8 2 ka cooling event the dgs iv glaciations 4 3 7 ka bp corresponds to 4 2 ka cool and drier event dgs v 2 7 1 ka bp represents the cool and moist late holocene glacial advancement of the valley this study suggests that the dokriani glacier valley responded to the global lowering of temperature and variable precipitation conditions this study also highlights the close correlation between the monsoon dominated valley glaciations and northern hemisphere cooling events influenced by north atlantic climate

carbonate and silicate weathering in glacial environments and its relation to atmospheric co2 cycling in the himalaya this paper presents new insights into the global carbon cycle related to co2 consumption from chemical denudation in heavily glacierised himalayan catchments data from previous studies of solute concentrations from glacierised catchments were reprocessed to determine the regional scale of co2 consumption and solute hydrolysis the results show that 90 of the so42 is derived from crustal sulphide oxidation and 10 from aerosols and sea salts however hco3 flux calculation estimates contribution from sulphide oxidation to carbonate dissolution so cd 21 similar to the contributions from silicate dissolution and simple hydrolysis 21 and 20 respectively furthermore the atmospheric co2 consumption estimations suggests 10 6 104 mole km 2 a 1 19 through silicate weathering 15 7 104 mole km 2 a 1 28 through simple hydrolysis 9 6 104 mole km 2 a 1 17 through so cd reaction and 5 9 104 mole km 2 a 1 11 through carbonate carbonation reaction our solute provenance calculations clearly indicate that hco3 production and co2 consumption via silicate weathering reactions is balanced by the simple hydrolysis and coupled so cd process this shows a counter mechanism operating in subglacial environments of the himalaya as a source of co2 to runoff rather than a sink

the fate of foramol temperate type carbonate platforms abstract on rimmed shelves of bahamian type characterized by chlorozoan associations and typical of tropical seas carbonate production keeps pace with normal sea level rise except when rapid rise or drastic environmental changes occurs on the other hand open temperate carbonate shelves are characterized by low carbonate production of the foramol association molluscs benthic foraminifera bryozoans coralline algae etc and generally show seaward relict sediments because carbonate production cannot keep pace with normal rate of sea level change several examples of recent drowning foramol carbonate platforms e g large areas of the mediterranean sea eastern northeastern yucatan shelf as well as analogous ancient drowned foramol type carbonate platforms e g early to middle miocene of the southern apennines miami terrace may support the idea that the drowning of many ancient carbonate platforms has been favoured by their biogenic foramol sensu lato constitution because of their typically low rate of growth foramol carbonate platforms are fated to be drowned even if the sea level rise is one with which the normal growth of chlorozoan platforms can keep pace similar conditions may also occur in tropical areas where variations in environmental conditions such as the presence of cold waters changes in salinity and increased nutrients preclude the development of chlorozoan associations

hydroclimatic influence on particle size distribution of suspended sediments evacuated from debris covered chorabari glacier upper mandakini catchment central himalaya abstract sediments released from high altitude glaciers exhibit varying evacuation patterns and transport characteristics owing to the presence of thick debris cover over the glacier despite the recent needs for integrated hydrometeorological studies in the himalaya little is known about the impacts of suspended sediment on hydropower generation reservoir sedimentation and abrasion of turbine components present study involves analysis of particle size distribution of suspended sediments to understand sediment evacuation patterns and transport characteristics in variable energy conditions during the ablation season peak suspended sediments were evacuated during extreme rainfall events the estimated seasonal modern sediment erosion rate varies from 0 6 to 2 3 mm y 1 for the study period 2009 2012 the analysis shows dominance of medium silt sized to fine sand sized particles having sediment size of 0 0156 0 25 mm corresponding to 70 80 without any significant seasonal variation these transported sediments show that they are poorly sorted coarser in nature with a nearly symmetrical to coarse skewed texture and kurtosis analysis suggesting mesokurtic distribution of sediments the particle size fraction ranges between 4 65 and 5 23 which is dominantly medium to coarse silty in texture results indicate that suspended sediments are evacuated in highly variable energy conditions through subglacial transport pathways because of increase in availability of meltwater with the progressive ablation season bulk geochemical characterization has been carried out to differentiate the source of suspended sediments and intensity of weathering chemical index of alterations cia values of sediment flux range from 54 68 to 55 18 compared to the upper continental crust ucc 50 indicating moderate intensity of weathering mean seasonal 2009 2012 elemental fluxes and their contribution to the suspended sediment flux reflect that si and al are responsible for about 85 of the total detrital elemental flux trace elements show high concentrations of radioactive elements like u th pb and rb that suggest their high anomalous presence in the catchment lithology an overall study indicates that the hydroclimatic conditions over the debris covered glacier play a dominant controlling factor in erosion transportation and evacuation of suspended sediments during the ablation season

backthrusts and passive roof duplexes in fold and thrust belts the case of central western sicily based on seismic reflection data abstract seismic reflection profiles crossing the area bounded by the m kumeta ridge and the m maranfusa m galiello rocca busambra morphostructural feature central western sicily were used to constrain the deep structural setting of the sicilian maghrebian fold and thrust belt ftb by integrating seismic field and well data we attempted to correlate outcropping and deep seated contractional structures shedding light on the internal geometries of the thrust system results of the new seismostratigraphic analysis presented in this paper reveal structural variations along the tectonic edifice this suggests dividing the study area into two sectors the western sector is characterized by foreland verging thrusts comparable to the already known structural model of the chain conversely in the easternmost sector duplexes and hinterland verging structures here highlighted for the first time prevail in fact the main carbonate relief of this area rocca busambra ridge appears as the outcropping part of a thick tectonic pile bounded on its northern side by a high angle backthrust while at depth a blind southern verging i e forelandward thrust can been recognized this structural setting suggests that underthrusting of the buried s verging carbonate body induced the n verging i e hinterlandward dislocation of the overlying units on the whole this structure can be interpreted as a triangle zone where the outcropping relief represents a passive roof duplex bounded on its northern side by the high angle backthrust deeply connected with a low angle decollement layer the recognized backthrust appears as the product of a deep seated tectonic activity that played a key role for the upper thrust sheet emplacement

particle size characteristics of suspended sediment transported in meltwater from the gangotri glacier central himalaya an indicator of subglacial sediment evacuation abstract proglacial meltwater streams draining out of the himalayan glaciers carry considerable amounts of suspended sediment with a variety of particle sizes because of the supraglacial englacial and subglacial debris as well as formation of sediments from erosion by the movement of the ice this paper examines particle size transported in the proglacial meltwater stream of gangotri glacier for seven consecutive melt seasons may october 2000 2006 in order to provide information on i temporal variations in the particle size distribution ii texture and mineralogy of the sediments and iii origin and evacuation pattern of the sediments our results indicate dominance of silt size 0 002 0 06 mm particles 71 followed by sand size 0 06 0 6 mm particles 24 and clay size

optically stimulated luminescence dating of sediments over the past 200 000 years optical dating of sediment using optically stimulated luminescence has become important for studying earth surface processes and this technique continues to develop rapidly a group of closely linked luminescence methods can be used to estimate the time since grains of quartz and feldspar were last exposed to daylight by detecting their subsequent response to environmental ionizing radiation exposure the technique is well suited to the dating of deposits as young as one year to several hundred thousand years recent technical developments have established a dating protocol with improved precision a high degree of reliability and an in built means to detect incomplete signal removal during deposition this approach has been extended to age estimation for single grains opening up a wider range of potential environments and new possibilities for understanding postdepositional grain movement ongoing research offers the possibility of significant age range extension and novel applications including low t

association of tepees and palaeokarst in the ladinian calcare rosso southern alps italy the ladinian calcare rosso of the southern alps provides a rare opportunity to examine the temporal relationships between tepees and palaeokarst this unit comprises peritidal strata pervasively deformed into tepees repeatedly capped by palaeokarst surfaces mantled by terra rossa palaeokarsts characterized by a regional distribution across the southern alps occur at the base and at the top of the unit local palaeokarsts confined to this part of the platform occur within the calcare rosso and strongly affected depositional facies tepee deformation ranges from simple antiformal structures peritidal tepees to composite breccias floating in synsedimentary cements and internal sediments senile tepees peritidal tepees commonly occur at the top of one peritidal cycle in association with subaerial exposure at the cycle top while senile tepees affect several peritidal cycles and are always capped by a palaeokarst surface cements and internal sediments form up to 80 of the total rock volume of senile tepees the paragenesis of senile tepees is extremely complex and records several superimposed episodes of dissolution cement precipitation fibrous cements laminated crusts mega rays and deposition of internal sediments marine sediment and terra rossa petrographical observations and stable isotope geochemistry indicate that cements associated with senile tepees precipitated in a coastal karstic environment under frequently changing conditions ranging from marine to meteoric and were altered soon after precipitation in the presence of either meteoric or mixed marine meteoric waters stable isotope data for the cements and the host rock show the influence of meteoric water average 18o 5 8 while strontium isotopes average 87sr 86sr 0 707891 indicate that cements were precipitated and altered in the presence of marine triassic waters field relationships sedimentological associations and paragenetic sequences document that formation of senile tepees was coeval with karsting senile tepees formed in a karst dominated environment in the presence of extensive meteoric water circulation in contrast to previous interpretations that tepees formed in arid environments under the influence of vadose diagenesis tepees initiated in a peritidal setting when subaerial exposure led to the formation of sheet cracks and up buckling of strata this porosity acted as a later conduit for either meteoric or mixed marine meteoric fluids when a karst system developed in association with prolonged subaerial exposure relative sea level variations inducing changes in the water table played a key role in exposing the peritidal cycles to marine mixed marine meteoric and meteoric diagenetic environments leading to the formation of senile tepees the formation and preservation in the stratigraphic record of vertically stacked senile tepees implies that they formed during an overall period of transgression punctuated by different orders of sea level variations which allowed formation and later freezing of the cave infills

misinterpreting proxy data for paleoclimate signals a reply to srivastava and jovane 2020 srivastava and jovane 2020 have made several comments on our assessment of proxy data and challenged the outcome of shukla et al 2020 based mainly on interpretation of environmental magnetic p

middle ordovician multi stage penecontemporaneous karstification in north china implications for reservoir genesis and sea level fluctuations abstract palaeokarsts contain important information about subaerial exposures due to sea level regression which has been considered as a dominant genesis of reservoirs herein we describe a typical sedimentary core section of the middle ordovician majiagou formation that records multi stage penecontemporaneous karstification in north china petrographic observations and stable isotopic data reveal high frequency penecontemporaneous subaerial exposure and resulting karstification evidence for this includes erosional surfaces gypsum breccias facies controlled dissolution vugs and vadose infillings fabric selective dissolution and negative carbon and oxygen isotopic excursions karstification generally occurred in the middle and upper parts of an upward shallowing sequence within a single depositional cycle leading to meteoric water dissolution of shoals and mounds this significantly enlarged the primary pores and generated new reservoir space as such high quality hydrocarbon reservoirs became well developed which are regularly and cyclically stacked at locations a few meters below the multiple exposure surfaces reservoir porosity also varies systematically with the high frequency sedimentary cycles and is generally at a maximum in the middle and upper parts of a cycle the multi stage penecontemporaneous subaerial exposure and resulting karstification reflect high frequency changes in relative sea level in north china at this time thereby providing a framework for identifying thin carbonate reservoirs in and around the ordos basin

structural and tectono stratigraphic review of the sicilian orogen and new insights from analogue modeling abstract the apennines sicilian maghrebian fold and thrust belt originated from the subduction of the alpine tethys and the later collision of drifted continental blocks against the african and apulian paleomargins from north to south the sicilian fold and thrust belt sftb is divided in four main tectono stratigraphic domains 1 the calabro peloritani terrane drifted from the european margin 2 the remnants of the alpine tethys accretionary wedge atw related to the subduction of the tethys 3 the folded and thrusted platform panormide and deep water imerese sicanian series of the offscrapped african margin and 4 the african foreland hyblean unfortunately scarce quality seismic lines and outcrops of key tectono stratigraphic units make the structure and dynamic evolution of the central eastern part of the sftb controversial first this study outlines through a review of the tectono stratigraphic evolution of the central eastern sector of the sicilian orogen the major remaining issues concerning 1 the occurrence of inferred alpine tethys units far from the region where the remnants of the atw outcrop nebrodi mountains both in a forearc position above the peloritani block to the north and in an active foreland context along the present day southern front of the belt and 2 the diverging tectonic styles from stacked large scale tectonic nappes to foreland imbricated thrust systems rooted into a main basal decollement secondly new constraints are given using analogue modeling to test mechanically the hypothesized structural and tectono stratigraphic evolution of the sftb the experiment simulates the orogenic evolution of the sftb at crustal scale from the oligocene tethys subduction to the middle miocene late pliocene continental collision between the european and african paleomargins the tectono stratigraphic synthesis is used to model the first order mechanical stratigraphy of the sedimentary units involved in the sicilian belt as well as the imprint of the african margin structural inheritance the experiments succeed in reproducing the general structure and tectono stratigraphic evolution of the sftb in particular the models support field observations hypothesing a gravity driven origin of the inferred alpine tethys units intercalated within the forearc and foreland syntectonic sedimentation moreover the model testifies of the main tectonic steps that led to the sftb building first a low tapered accretionary wedge was accreted above the alpine tethys oceanic crust from the oligocene to the early miocene the following underthrusting of the stretched african continental margin and its frontal panormide platform shortened and thickened the accretionary wedge this phase provided favorable conditions for significant pulses of reworked alpine tethys units that intercalated within the forearc and foredeep successions during the middle miocene the decollement of the african meso cenozoic cover panormide platform and imerese sicanian deep water basin enhanced a deep seated deformation phase along with duplexing of the panormide platform beneath the alpine tethys wedge leading to its emersion since the late messinian activation of basement faults led to a generalized emersion of the orogenic units through large wavelength fold culminations accompanied by syn tectonic deposition at their southern limbs concurrently the prism front was partly indented to the southeast by the thick and locally already emerged hyblean platform

neptunian dykes and associated features in southern spain mechanics of formation and tectonic implications neptunian dykes and sills in jurassic carbonate platform strata of the betic region of spain occupy spaces created by wholly mechanical fracturing and displacement of the host strata and later filled by pelagic sediments from above or by precipitation of calcite from circulating solutions in some places joint bounded blocks of platform carbonates have been wholly removed possibly by sliding down submarine slopes leaving a staircase topography commonly fe encrusted that was subsequently filled by pelagic sediments other cavities that formed during cretaceous times were developed by dissolution and current erosion in moderately deep submarine environments and then filled by pelagic sediments from above none of the cavities hosted by either platform or pelagic strata contain evidence for their formation by dissolution in a subaerial environment the jurassic and cretaceous history of subsidence of the betic margins is thus simpler than in versions requiring repeated emergence to form subaerial karstic cavities

on the mesozoic ionian basin summary new seismic reflection profiles of the italian deep crust project crop provide new insights on the structure of the ionian sea in spite of the apennines and hellenides neogene subduction zones two conjugate passive continental margins are preserved at the margins of the ionian sea along the malta escarpment to the southwest and the apulian escarpment to the northeast the ionian sea is likely to be a remnant of the mesozoic tethys ocean confined by these two conjugate passive continental margins the transition from continental to oceanic crust appears sharper to the northeast than to the southwest the basin between southeast sicily and southwest puglia was about 330 km wide and suggests a low spreading rate the inferred oceanic ridge should have been flattened by thermal cooling and buried by later sediments based on stratigraphic and structural constraints to the north in the apennines belt the ocean continued to the northwest this palaeogeography is supported by the seismicity of the apennines slab underneath the southern tyrrhenian sea which implies downgoing oceanic lithosphere the adjacent absence or paucity of deep seismicity does not imply absence of subduction but rather it can be interpreted as due to the more ductile behaviour of the subducted continental lithosphere surprisingly we note that where the oceanic inherited basin is subducting underneath the apennines in the hangingwall of the subduction hinge there are outcropping slices of continental crystalline basement previously deformed by the alpine orogen

till as a glacial tectomict its internal architecture and the development of a typing method for till differentiation abstract till has been studied for over a century yet still a clear understanding of the mechanics of deposition and or emplacement of till eludes us tills in the past have been generally subdivided into sediments formed in various sub environments of the glacial system as such it has been generally agreed that tills can be separated in terms of these types based on various attributes such as clast fabric increasingly such separation into various sub types of till has become however highly debatable and tenuous based upon the use of micromorphology and a greater in depth appreciation of the internal architecture of till it has become apparent that previously established classifications of till are erroneous micromorphology reveals that deposition and or emplacement of tills is a complex tectonic process such that lodgement melt out and flow tills as previously defined do not appear to exist rather a new term better describes tills as glacial tectomicts by using micromorphology in establishing the presence of sets of microstructures a statistical method is introduced that permits differentiation of tills from other diamictons the implications for this new understanding of tills allied to statistical typing is considerable in terms of till formation glacial stratigraphy and understanding glacial environments in terms of stress histories porewater transmission subglacial deformation mechanics till rheological phase changes and the timeline of till formation

holocene millennial scale summer temperature variability inferred from sediment parameters in a non glacial mountain lake danntjorn jotunheimen central southern norway holocene changes in summer temperature in the jotunheimen area have been inferred from variations in several sediment parameters from a composite combined from two overlapping sediment cores lake core record mean time resolution of 15 years from lake danntjorn a small mountain lake located close to the modern pine tree limit in jotunheimen central southern norway loss on ignition analysis at contiguous 0 5 cm intervals throughout the cores revealed that the variations in residue after ignition of the sediments at 5501c in the upper 260 cm 8500 calendar years were not associated with variations in magnetic susceptibility in the basal deglacial and early holocene sequence of the lake sediments however the two sediment parameters fluctuated mainly in phase in addition the biogenic silica bsi concentration is relatively high thus in the early part of the holocene the variations in the residue were probably primarily driven by input of minerogenic detrital material inwash and or windblown and biological productivity including bsi from diatoms in the lake itself and in the lake surroundings from approximately 8500 calendar years bp variations in the residue probably primarily reflect variations in low minerogenic low magnetic susceptibility with little variations and diatom bsi productivity as demonstrated with analysis of bsi concentration between 260 and 233 cm 8500 7760 calendar years bp the highest residue values probably mainly reflecting high diatom productivity occurred at 7800 7200 7000 6700 6200 5400 5050 4300 2500 1800 1550 900 700 and o100 calendar years bp the most significant o8000 calendar years bp residue minima mainly low diatom productivity were recorded at 7100 6800 6600 6000 5700 5000 4400 4200 3800 3600 3200 3000 2750 2300 1900 1700 1070 740 600 380 and 80 calendar years bp bp ad 2000 the lake record from jotunheimen is discussed in the context of holocene terrestrial and marine records from the north atlantic region and possible natural climate forcing factors r 2004 elsevier ltd all rights reserved

sediment characteristics and water physicochemical parameters of the lysimachia lake western greece in the present paper we present the sedimentological characteristics and the water physicochemical parameters of lysimachia lake which is one of the most important lakes of western greece as it is protected by international conventions and is listed in the natura 2000 european network sedimentological analysis involved grain size analyses moment measures total organic carbon toc total nitrogen tn and total phosphorus tp measurements as well as determination of the clay minerals content water physicochemical parameters such as ph temperature conductivity and dissolved oxygen were measured in situ with portable equipment while nutrients such as nitrates nitrites phosphates and ammonium ions as well as toc and tn were analyzed in a time period of 1 year seasonal monitoring geographical distribution of grain size and geochemical parameters indicated a clear partition in the northern and southern parts of the lake this phenomenon can related to the discharging of a channel into the lake the discharging of sewage effluents from agrinio city during the last years as well as the type of clay minerals distribution clay minerals analyses indicated that smectite predominates in the northern part of the lake whereas chlorite is more abundant in the southern parts this explain the higher amounts of toc and tn observed in the northern part of the lake and can be correlated with the higher external surface and adsorption capacity of minerals in the smectite rich sediments the four seasons monitoring of water physicochemical parameters indicates a relatively higher values of toc and tn in the northern part of the lake while nutrient concentrations indicate a uniform geographical distribution along the lake

sedimentation fracturing and sliding on a pelagic plateau margin the middle jurassic to lower cretaceous succession of rocca busambra western sicily italy the jurassic succession of rocca busambra consists of two lithostratigraphic units a pile of peritidal limestones several hundreds of metres thick inici formation hettangian to sinemurian and a 2 to 15 m thick sequence of rosso ammonitico type pelagic limestones toarcian to lowermost berriasian an extensive interval of non deposition is evidenced by a thick fe mn oxide crust on the bounding disconformity and is recorded partially in the material contained within a complex network of neptunian dykes and sills seven lithofacies are distinguished in the rosso ammonitico these lithofacies show that the rosso ammonitico limestones differ from most analogues both in sicily and elsewhere sediments are mostly grain supported and non nodular obviously bottom currents were important during deposition of these sediments these currents were pulsating at different frequencies and induced winnowing intraclast production and early cement precipitation other rosso ammonitico lithosomes of late jurassic to earliest cretaceous age usually decimetre thick and discontinuous overlie the inici formation without any fe mn crust their anomalous stratigraphical and geometrical relationships show that they were deposited on an inclined stepped erosional surface incised in the sub horizontal inici formation this ancient escarpment is interpreted as the result of a mainly gravitational collapse of the margin of a pelagic plateau such mass wasting was probably due to the backstepping of the tectonic plateau basin margin that is not observable directly but may be inferred from circumstantial evidence this observation clearly shows that tectonic activity affected the rocca busambra sector of the west tethys continental margins a few tens of millions of years after the end of the rifting stage the anomalous rosso ammonitico sediments are the only indication of the escarpment and their occurrence in the stratigraphic record is probably more widespread than reported in the literature more accurate palaeoenvironmental and palaeogeographic reconstructions may depend on the identification of these sediments

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

terrain changes caused by the 15 17 june 2013 heavy rainfall in the garhwal himalaya india a case study of alaknanda and mandakini basins abstract exceptional early high monsoon rains between 15 and 17 june 2013 combined with discharge from snowmelt water caused widespread floods in every major river of the garhwal himalaya this catastrophic event triggered widespread landslides and devastation in the region affecting the movement of the people that led to stranding of pilgrims in various pilgrimage routes this event caused many casualties and irreparable damage to the infrastructures and property in the garhwal himalaya a large volume of debris was deposited in kedarnath town 3 9 10 6 m 3 and a huge amount of debris was removed from rambara and surrounding areas 2 6 10 8 m 3 the study also found that villages like lambaghar bhyundar alaknanda river valley and rambara mandakini river valley were completely washed away leaving no trace of earlier settlement govindghat and pulna villages in the alaknanda river valley were also badly damaged approximately 0 3 10 6 and 0 72 10 6 m 3 of debris was deposited respectively similarly in the mandakini valley kedarnath and sonprayag towns were also badly damaged and 3 9 10 6 and 1 4 10 6 m 3 of debris was deposited in the area respectively simultaneously the moraine dammed chorabari lake breached releasing 6 1 10 5 m 3 of water with an average rate of 1429 m 3 s discharge of lake the towns of pandukeshwar in the alaknanda valley and gaurikund in the mandakini valley were partially damaged however no evidence of such magnitude of destruction was reported from the yamuna river valley during the same period this catastrophic event changed the landscape in many parts of uttarakhand making the whole region more fragile and vulnerable a disaster of such magnitude was perhaps not witnessed by the region for at least the last 100 years

widespread aggradation in the mountainous catchment of the alaknanda ganga river system timescales and implications to hinterland foreland relationships abstract cut and fill type fluvial terraces are ubiquitous in the lesser himalayan zone of the alaknanda ganga ganges rivers system which flows perpendicular to himalayan lithotectonic units and traverses a steep climatic gradient lithofacies analysis of the sedimentary sequences of cut and fill terraces indicated that the valley aggradation took place via 1 channel bar development and excess sediment supply 2 debris flows composed of mixed rounded to sub rounded lithoclasts resulting from episodic high intensity rainfalls in the upper catchment or 3 debris flows or rockfalls generated by local landslides the luminescence chronology indicates that valley aggradation took place in two phases 49 25 ka and 18 11 ka the incision of the fill started soon after 11 ka paleoclimatic records from marine sediments indicate that the aggradation and incision in the alaknanda ganga river has oscillated in phase with global climatic variations glaciation deglaciation processes in the upper catchment produced huge amounts of sediment between 63 and 11 ka which was fluvially transferred to the lower valley via several cycles of erosion and deposition leading to extensive aggradation the climatic amelioration at 11 ka and the completion of deglaciation processes led to increased fluvial discharge and decreased sediment supply conditions conducive for incision of the alluvial fills records from the indo gangetic plain and the ganga delta demonstrate that the phase of aggradation was regional but that incision in the foreland started at least 2 3 ka later after 7 ka bedrock incision rates as calculated from dated alluvial covers of terraces that are separated by bedrock steps are spatially variable and fall within the range of rates reported from across the himalaya these estimated rates however are higher than the basin average erosion rates calculated using isotopic mass balance in riverbed sediments this study suggests that during the last 50 ka river dynamics in the himalayas were dominated by monsoon variability and the role of tectonic activity was limited to bedrock incision in few reaches only

mesozoic tectonics and volcanism of tethyan rifted continental margins in western sicily abstract the paleotectonic and volcanic features of the jurassic cretaceous carbonate successions outcropping in central western sicily allow us to restore the tectono sedimentary evolution of a sector of the african continental margin these successions consist of shallow to deep water mesozoic deposits that have formed in the carbonate platform to pelagic plateau depositional setting of the so called trapanese paleogeographic domain fieldwork including structural analyses has indicated the occurrence of lateral facies changes resedimented materials volcanic products pillow lavas and tuffitic deposits unconformity surfaces and paleofaults of different trends and age these data combined with facies and a physical stratigraphic analysis allow one to distinguish between the different tectono stratigraphic settings a structural low filled with thick pillow lavas and reworked deposits appears bordered by two main structural highs an articulate carbonate pelagic platform with a stepped fault margin and the flank of a structural high where the volcanoclastic deposits are interlayered with reworked reef materials suggest the occurrence of a submarine volcano that evolved into an atoll type carbonate shelf setting tectonic and magmatic events punctuated the sedimentary evolution during the early jurassic middle late jurassic early and late cretaceous the horst and graben structures connected by steeped margins and the occurrence of distinctive types of volcanic products suggest that the study areas could represent a sector of the jurassic cretaceous southern tethyan passive continental margin situated at the edge of the continental platform bordering those basinal areas where rifting and possible spreading processes were active during the mesozoic

shallowing upward sequences in purbeckian peritidal carbonates lowermost cretaceous swiss and french jura mountains purbeckian carbonates in the swiss and french jura goldberg formation lower berriasian comprise shallow subtidal intertidal supratidal low energy high energy marine brackish freshwater and hypersaline facies these facies are arranged in small 0 2 1 5 m thick sequences which display a dominant shallowing upward component and which form the fundamental units of the highly structured purbeckian sedimentary record six types of small scale sequences can be recognized a intertidal to supratidal overprinting of shallow lagoonal facies b algal marsh sequence with frequent dolomitization c sabkha sequence often associated with collapse breccia d tidal flat sequence with desiccation features e lacustrine sequence f terrestrial overprinting of subtidal or intertidal facies episodic event deposits such as tempestites are superimposed thin transgressive beds which rework elements of the underlying facies are frequently found at the base of the sequences green marls and black pebbles are common at the top and indicate long subaerial exposure the sequences are often incomplete as subtidal facies may be absent or their upper part can be eroded lateral facies changes are common which is due to the very shallow and partly emergent purbeckian platform where various depositional environments were juxtaposed however many sequence boundaries are well developed and can be correlated over large parts of the study area the purbeckian shallowing upward sequences were generated by climatically controlled sea level changes autocyclic processes occurred locally but were overprinted by drops of sea level affecting the entire platform the small scale sequences are most probably related to the 20 000 year cycle of the precession of the equinoxes larger sequences with usually well developed emersion surfaces are attributed to the 100 000 and 400 000 year eccentricity cycles of the earth s orbit identification and correlation of sequence boundaries makes it possible to set up a framework of isochronous surfaces which often cut across facies boundaries and thus to interpret in detail the palaeogeographic sedimentological and diagenetic evolution of the purbeckian peritidal carbonate environments

early holocene monsoonal fluctuations in the garhwal higher himalaya as inferred from multi proxy data from the malari paleolake abstract a 4 9 m thick lake sequence formed due to the landslide damming of a stream in the semiarid garhwal himalaya was studied to understand past monsoonal variations in the region the optically stimulated luminescence osl chronology indicates that the lake existed between 12 and 7 ka ago chronologically constrained trends of sand percent organic phosphorus op apatite inorganic phosphorus aip and parameters of environmental magnetism were measured in the paleolake profile measured proxies indicate that the indian summer monsoon ameliorated in the early holocene after 12 ka cooling and it appears that all the proxies from the lake have captured this globally recognized early holocene warming four phases of wet conditions intensified monsoon are recognized at 11 5 ka 11 10 5 ka 10 9 ka and 8 7 ka with maximum uncertainties of 1000 years the wet phases are characterized by high magnetic susceptibility increased op and reduced aip in an attempt to understand the primary forcing of the sharp fluctuations in monsoonal activity in the region we show that changes in magnetic susceptibility match variations of residual atmospheric 14c suggesting a role for solar variability as an explanation of climatic variability

a 13 000 year record of environmental magnetic variations in the lake and peat deposits from the chandra valley lahaul implications to holocene monsoonal variability in the nw himalaya abstract an 13 000 year old record of in situ peat bog and lacustrine sediments from a post glacial lake in the chandra valley of the lahaul himalaya is studied to generate the record of environmental magnetic signatures in response to indian summer monsoon ism variability in the nw himalaya the chronology of studied chandra peat trench cpt profile is based on 9 ams 14c calibrated dates cal yr bp the piece wise linear regression analysis of age depth model indicates non linear sedimentation with higher rates from 4142 cal yr bp to the present and lower accumulation during 12 880 4142 cal yr bp the mineral magnetism showed three dominant assemblages of magnetic minerals with varying concentrations in peat lake sediment sequence i e 1 mixed ferri and antiferromagnetic minerals between 12 880 and 11 019 cal yr bp 2 dominant antiferromagnetic mineralogy from 11 019 to 3172 cal yr bp and 3 significantly increased concentrations of mixed ferri and antiferromagnetic minerals from 3172 cal yr bp to the present with characteristically increased ferrimagnetic concentrations after 2032 cal yr bp the characteristic increase in antiferromagnetic mineral concentration accompanied by decreased ferrimagnetic concentration from 10 398 to 5770 cal yr bp suggest possible oxidation of magnetite to hematite under warmer climate conditions and corresponds to increased ism intensity during early to mid holocene warm wet climate in the nw himalaya the distinctly increased concentration of antiferromagnetic minerals from 6732 to 5770 cal yr bp indicates mid holocene climate optimum hco in the lahaul himalaya the strengthening and weakening of ism recorded in environmental magnetic signatures during 1260 852 cal yr bp 690 1098 ad and between 852 and 239 cal yr bp 1098 1711 ad corresponds to medieval warm period mwp and little ice age lia events respectively

suspended sediment from the gangotri glacier quantification variability and associations with discharge and air temperature abstract to understand the sediment delivery variation for a himalayan glacier gangotri glacier garhwal himalayas and to determine its relationship with discharge and air temperature suspended sediment samples and discharge data were collected near the glacier snout 4000 m for four melt seasons during the period 2000 2003 these data were used to estimate suspended sediment concentration ssc suspended sediment load ssl sediment yield and erosion rate in the glacier melt stream bhagirathi the monthly distribution of suspended sediment and its variability from year to year have been examined mean monthly ssc for may june july august september and october were found to be 1942 2063 3658 2551 734 and 136 mg l 1 respectively maximum ssc in meltwater was observed in july followed by august it was found that the cumulative percentage delivery of ssc precedes discharge throughout the melt season mean monthly total ssl for may june july august september and october during the study period was found to be 149 423 1220 746 143 and 5 10 3 ton respectively the strong variability is found in ssl c v 1 1 than ssc c v 0 8 because computation of ssl includes both discharge c v 0 6 and ssc delivery response of ssl in terms of percentage of total load is less in the early part of the melt season than in the later stage in comparison to that of discharge this may be due to the fact that in the beginning of the melt season low melt rate conditions prevails and thus the low discharge velocity could not flush out stored glacial sediment it has been observed that 59 64 of the sediment passed through the channel by the time 50 of the total discharge passed the average suspended sediment yield for the whole melt season from the study area was estimated to be about 4834 ton km 2 and corresponding erosion rate was 1 8 mm the relationship between mean monthly ssc and discharge r 2 0 99 is much better than the daily ssc and discharge r 2 0 40 because variability of both parameters is averaged out on monthly scale mean monthly ssc and mean monthly ssl provide a good exponential relationship with mean monthly air temperature these results are relevant for planning and management of water resources in the high altitude areas and for designing hydropower projects

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

pattern of extensional faulting in pelagic carbonates of the umbria marche apennines of central italy the umbria marche apennines provide a new region in which the nature passive margin extensional faulting can be studied in outcrop in these dominantly pelagic carbonate rocks of jurassic and cretaceous age horsts acted as shallow nonvolcani seamounts while tilted half grabens formed deeper basins one well exposed seamount basin transition agrees in general with the model of listric normal faulting and tilted half grabens but shows interesting and significant divergences when studied in detail a small sedimentary wedge at the faulted margin of a horst block seamount thickens unexpectedly toward the adjacent basin this wedge developed because of local convex upward curvature of the shallowest part of a fault which at depth must have concave up listric geometry the local sedimentary wedge resulted from deposition on the hanging wall as it tilted followed by differential compaction of younger limestones that lapped onto the gentle slope leading from the horst block seamount toward the basin the map pattern of listric normal faulting in the umbria marche apennines suggests that both principal strain axes were extensional in contrast to the usual pattern of listric faults crossed by transfer faults

basin analysis in the southern tethyan margin facies sequences stratal pattern and subsidence history highlight extension to inversion processes in the cretaceous panormide carbonate platform nw sicily abstract in the mediterranean the south tethys paleomargin experienced polyphased tectonic episodes and paleoenvironmental perturbations during mesozoic time the cretaceous shallow water carbonate successions of the panormide platform outcropping in the northern edge of the palermo mountains nw sicily were studied by integrating facies and stratal pattern with backstripping analysis to recognize the tectonics vs carbonate sedimentation interaction the features of the requienid limestone including geometric configuration facies sequence lithological changes and significance of the top unconformity highlight that at the end of the lower cretaceous the carbonate platform was tectonically dismembered in various rotating fault blocks the variable trends of the subsidence curves testify to different responses both uplift and downthrow of various platform blocks impacted by extensional tectonics physical stratigraphic and facies analysis of the rudistid limestone highlight that during the upper cretaceous the previously carbonate platform faulted blocks were subjected to vertical movements in the direction opposite to the displacement produced by the extensional tectonics indicating a positive tectonic inversion comparisons with other sectors of the southern tethyan and adria paleomargins indicate that during the cretaceous these areas underwent the same extensional and compressional stages occurring in the panormide carbonate platform suggesting a regional scale significance in time and kinematics for these tectonic events

subglacial basins their origin and importance in glacial systems and landscapes closed topographic basins are found beneath contemporary ice masses and within the footprint of former ice masses in all glaciated regions we present the first integrated review of subglacial basin occurrence and formation and the implications of such basins for glaciological processes and the evolution of landscape our purpose is to motivate research in areas where understanding of basin origin and process significance is weak basins on the order of 10 102 m deep and 102 103 m long are produced by glacial erosion of subglacial rock and or sediment and are known as overdeepenings outlet and valley glaciers can overdeepen their beds far below sea level or local fluviatile base level larger basins typically in ice sheet contexts may have a pre glacial usually tectonic origin subglacial basins are important glaciologically because they require ice water and sediment to ascend an adverse subglacial slope in order to exit the glacial system the efficiency of which is dependent upon the gradient of the adverse slope and that of the ice surface basins thus influence subglacial drainage system morphology and transmissivity the thickness and distribution of basal ice and sediment layers and the mechanisms and dynamics of ice flow adverse gradients that exceed 11 times that of the ice surface may even permit the formation of subglacial lakes we speculate that in comparison to ice masses with few or no subglacial basins those with numerous or very large basins may respond to climatic changes with unexpected vigour in addition erosion rates and transport pathways of water and sediment through the glacial system and the expression of these processes in the sediment and landform record may be unexpectedly complex further our review shows that in a warming climate ice masses resting on adverse slopes will be vulnerable to rapid and potentially catastrophic retreat new lakes in subglacial basins exposed by mountain glacier retreat will present an increasing hazard and subglacial lakes may drain catastrophically on even longer time scales we speculate that the glacial excavation and post glacial filling of basins in mountainous regions should contribute importantly to climate related changes in isostasy and relief although the controls on overdeepening and their influence on other glacial and landscape processes remain uncertain we hypothesise that overdeepened glacial systems reflect an equilibrium ice bed geometry that maximises the efficiency of ice discharge improved understanding of overdeepening processes especially overdeepened bed hydrology is therefore necessary to understand fully the dynamic behaviour of valley and outlet glaciers and thus the fate of earth s largest ice masses

from rifting to drifting tectonic evolution of the south alpine upper crust from the triassic to the early cretaceous abstract the tectonic evolution of the south alpine rifted margin is discussed on the base of four palinspastic upper crustal profiles extension related to the movements between adria and europe began in the norian after variscan orogeny late carboniferous to middle permian orogenic collapse and continental scale wrenching from the late triassic to the early liassic stretching was mostly limited to the lombardian basin during this time extension was mainly controlled by four major listric faults symmetrically centred around the late carboniferous early permian collio grabens smaller faults which also started in the norian were progressively de activated during the late triassic after the middle liassic faulting in the lombardian basin gradually ceased and the site of extension shifted westwards i e towards the future site of crustal separation extension was then controlled by a set of west dipping normal faults oceanic crust was formed not later than 157 ma the overall extension along the profile which had a final length of 290 km was 52 km which corresponds to a stretching factor of 1 22 for the whole length of the preserved margin the strain rate is ca 1 10 16 s the sedimentation history suggests that the extension of the south alpine margin was a continuous process from the norian to the middle jurassic the changes in tectonic pattern are related to progressive hardening of the lithospheric segment undergoing slow extension

a liassic isolated platform controlled by tectonics south iberian margin southeast spain the middle and upper members of the gavilan formation near velez rubio almeria province southeast spain are interpreted as carbonate platform deposits the studied outcrops form geologically part of the external zones of the betic cordillera south iberian palaeomargin a genetic unit limited by intra sinemurian and intra upper carixian sedimentary breaks is defined the evolution of the parasequence sets in the area and the development of deeper sedimentation in its northern outcrops suggest that this platform was isolated with regard to the south iberian margin three distinct parasequence sets are proposed progradational parasequence set only locally present retrogradational parasequence set middle member of the gavilan formation and aggradational parasequence set basically composed of the upper member of the gavilan formation sedimentary features such as neptunian dykes sharp lithological changes thickness variations the presence of palaeofaults and the subsidence history all lead to the conclusion of a significant regional tectonic influence in the genetic unit evolution normal extensional faulting has been proposed as a major control on sedimentation on this isolated platform this regional factor has completely distorted the effect of the eustatic fluctuations for this period of time

influence of debris cover on terminus retreat and mass changes of chorabari glacier garhwal region central himalaya india recent studies of himalayan glacier recession indicate that there is wide variability in terminus retreat rate and mass balance in the different sectors of the mountain range primarily linked to the topography and climate of the region variable retreat rates of glacier termini and inadequate supporting field data e g mass balance ice thickness velocity etc in the himalayan glaciers make it difficult to develop a coherent picture of climate change impacts in this study the results of a detailed mapping campaign and ground based measurements of ablation rate terminus retreat and ice loss are reported for the period 2003 10 in addition background information from an old glacier map survey of india 1962 was compiled and terminus recession measurements were carried out from 1990 field photographs of chorabari glacier central himalaya our ablation stake network results suggest that the influence of debris cover is significant for chorabari glacier mass balance and terminus retreat the terminus survey finds that the glacier is retreating but at a lower rate than many other non debris covered glaciers in the region the recession and ablation data particularly in the upper ablation area at higher altitudes suggest that the ice volume loss of the glaciers is of greater magnitude than the slow terminus retreat and if the process continues the lowermost part of the glacier may reduce to a quasi stationary position while significant ice loss continues

subaerial exposure and drowning processes in a carbonate platform during the mesozoic tethyan rifting the case of the jurassic succession of western sicily central mediterranean abstract the liassic carbonate platform succession outcropping at monte maranfusa central western sicily consists of a shallowing upward sequence of peritidal carbonates with jurassic to paleogene pelagic limestone and siliciclastic tertiary covers above the cyclic sequences of subtidal wackestones packstones intertidal microcrystalline carbonates with bird s eye pores and supratidal bioclastic grainstones are interbedded with dark layers of the following composition 1 dark gray compact and well cemented limestone with blackish clasts interpreted as calcretes a type of carbonate soil and 2 reddish calcite laminae deformed by elongated cavities filled with vadose silt interpreted as paleokarst this succession is crossed by almost vertical faults of the late liassic to miocene which often coincides with neptunian dykes filled by several generations of toarcian early miocene pelagic sediments another system of dykes known as neptunian sills filled by injected upper lias dogger pelagic sediments lies parallel to the stratification the parallel dykes were caused by the flexure of the platform during the jurassic and presumably by a planar slip in the carbonate rocks whereas neptunian dykes are caused by faulting episodes here we present evidence that the dark layers in the liassic succession of monte maranfusa previously described by many authors only as parallel dykes can actually be interpreted as a neptunian sills b pedogenic calcretes and c paleospeleothems therefore we found evidence of exposure flooding intervals in the evolution of the carbonate platform during the liassic linked to different pulses in both the subsidence tectonic activity and the sea level oscillations at the top fe mn crusts hardgrounds seal the carbonate platform succession which is in turn overlain by condensed pelagic deposits confirming its drowning during rifting processes

fluid storage and migration properties of sheared neptunian dykes abstract neptunian dykes are widely reported along the tethyan carbonate platforms and are commonly considered as subsurface baffles or barriers to fluid flow however the fluid storage and migration properties of sheared neptunian dykes are poorly known for this reason we investigate the inner structure and fluid flow properties of two neptunian dykes which can be characterized by different architectures if involved or not in brittle shearing processes the dykes strike ca wnw ese and crosscutting the tight jurassic limestones exposed at maranfusa mt nw sicily italy the unsheared and sheared neptunian dykes are almost sub vertical and at high angle with respect to the horizontal plane respectively the first one includes a homogeneous pelagic limestone infill whereas the second one includes a heterogeneous marl rich pelagic limestone infill and also thin veneers of tectonic breccias vertically persistent throughout the investigated outcrop the sheared neptunian dyke shows evidences of transtensional faulting which likely occurred during the early jurassic up to middle cretaceous times with throw up to 2 m the amount of fracture porosity and equivalent permeability are computed by integrating geological and structural field data with petrographic data obtained from selected samples and discrete fracture network modelling of geocellular volumes representative of the study outcrops results are consistent with the sheared neptunian dyke forming a combined barrier conduit permeability structure in which the low permeability and low porosity cataclastic core is flanked by a fractured damage zone that enhance the dyke parallel fluid flow in the subsurface accordingly the amount of fluid storage in the fractured damage zone is sensitively higher than in the surrounding limestone host rock data we present highlight that the m offset sheared neptunian dyke due to its inherited sedimentary infill is characterized by a permeability structure that it is often associated to large fault zones made up of cataclastic fault cores that impede the cross fault fluid flow

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

the interpretation of cyclic successions of the middle and upper triassic of the northern and southern alps abstract theories regarding the formation of sedimentary cycles in the 3rd 4th and 5th order bands are reviewed with reference to the middle and upper triassic of the northern calcareous alps nca and southern alps milankovitch autocyclic and tectonic theories are discussed together with an evaluation of concepts of chaotic sedimentation and a case example from the nca concerning eustasy 3rd 4th and 5th order sea level fluctuations were probably a low amplitude low rate phenomenon caused by fluctuations in the volume of mountain glaciers and ocean water during the triassic the mid and late triassic was a non glacial interval in which polar regions may have been ice free so glacio eustasy can not be expected eustatic sea level variations in the 3rd 4th and 5th order bands seem to have left no useful imprint on cyclic successions in the region whatever record there may be is inextricably mixed with two other signals tectonic activity and autocycles the review shows how sedimentation in the triassic of the area was strongly influenced by tectonic activity this is as true for the middle and late triassic of the nca as it is for the southern alps tectonic activity may be responsible for large scale cyclicity 4th to 3rd order scale although seismogenic structures have yet to be identified and described in carbonate successions of the alps candidates do exist slumped and microfaulted layers in laminated sediments of the seefeld basin upper triassic nca have been described as the products of fault movements the sedimentary record from the nca and southern alps also leaves little doubt that autocyclic processes were important in all environments except perhaps the deep sediment starved basins most small scale platform cycles 5th order scale in the region can be related to autocyclic processes and in shallow basinal successions to events such as storms previous workers have not been consistent in their interpretation of cyclic successions in the area applying diverse theories to similar successions so far the steinplatte hochkonig platform with attached kossen basin is the only example interpreted with reference to tectonics and autocyclicity eustasy was probably not the most important factor in cycle generation in the triassic of the nca and southern alps such an approach could prove useful in future studies

reconstruction of last glacial to early holocene monsoon variability from relict lake sediments of the higher central himalaya uttrakhand india abstract proglacial lake sediments at goting in the higher central himalaya were analyzed to reconstruct the summer monsoon variability during the last glacial to early holocene sedimentary structures high resolution mineral magnetic and geochemical data suggest that the lacustrine environment experienced fluctuating monsoonal conditions optically stimulated luminescence osl dating indicates that the lake sedimentation occurred before 25 ka and continued after 13 ka during this period goting basin witnessed moderate to strengthened monsoon conditions around 25 ka 23 5 ka 22 5 ka 22 ka 18 ka 17 ka 16 5 ka and after14 5 13 ka the last glacial phase ended with the deposition of outwash gravel dated at 11 ka indicating glacial retreat and the onset of holocene condition additionally centennial scale fluctuations between 16 5 ka and 12 7 ka in the magnetic and geochemical data are seen a close correspondence at the millennial scale between our data and that of continental and marine records from the indian sub continent suggests that goting basin responded to periods of strengthened monsoon during the last glacial to early holocene we attribute the millennial scale monsoon variability to climatic instability in higher northern latitudes however centennial scale abrupt changes are attributed to the result of albedo changes on the himalaya and tibetan plateau

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

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

topographic control of asynchronous glacial advances a case study from annapurna nepal 1 differences in the timing of glacial advances which are commonly attributed to climatic changes can be due to variations in valley topography cosmogenic 10be dates from 24 glacial moraine boulders in 5 valleys define two age populations late glacial and early holocene moraine ages correlate with paleoglacier valley hypsometries moraines in valleys with lower maximum altitudes date to the late glacial whereas those in valleys with higher maximum altitudes are early holocene two valleys with similar equilibrium line altitudes elas but contrasting ages are 5 km apart and share the same aspect such that spatial differences in climate can be excluded a glacial mass balance cellular automata model of these two neighboring valleys predicts that change from a cooler drier to warmer wetter climate as at the holocene onset would lead to the glacier in the higher altitude catchment advancing while the lower one retreats or disappears even though the ela only shifted by 120 m

deglaciation and landscape history around annapurna nepal based on 10be surface exposure dating abstract the high himalaya is a key area for tectonic geomorphological and climate studies because of its extreme relief and location at the transition zone between areas with abundant monsoonal precipitation and the arid semiarid tibetan plateau we present 10be surface exposure ages on 22 boulders from the annapurna area in nepal the ages improve understanding of the late quaternary landscape history and the geomorphological processes operating in this part of the himalaya although our study is reconnaissance in nature it highlights the importance of catastrophic events such as landslides and debris flows for denudation of high mountains holocene exposure ages for the dhampu chooya landslide 4 1 0 6 ka and for 600 m of alluviation in kali gandaki valley 2 1 0 6 ka for example indicate the frequent occurrence and extent of catastrophic events and their implications for natural hazards we also offer an explanation for the differences in late quaternary glacial chronologies at closely spaced study sites in the nepal himalaya topographically controlled and spatially variable precipitation in the himalaya determines the sensitivity of glaciers to changes in temperature and precipitation accordingly some glaciers advanced in phase with northern hemisphere ice sheets whereas others reached their maximum extent at times of increased monsoonal precipitation during marine isotope stage 3 and the early holocene

the role of fungal biomineralization in the formation of early carboniferous soil fabrics paleosols in the lower carboniferous limestones of south wales commonly contain needle fibre calcite which is an unusual form of calcite recently shown to form by the calcification of fungal hyphae in present day soils the needle fibre calcite occurs in two associations in the paleosols as coatings on sediment grains and as rhizocretions the former can be compared with the microbial grain coatings of quaternary calcretes the latter represent the sites of fungal coats on roots and are interpreted as probable ectomycorrhizae a symbiotic fungal sheath root association these findings suggest that biomineralization was important in the formation of soil fabrics during the carboniferous as it is in present day soils

fe mn encrusted kamenitza and associated features in the jurassic of monte kumeta sicily subaerial and or submarine dissolution abstract an unusually jagged dissolution surface capped by a thick fe mn crust is well exposed in small quarry cuts of the jurassic of monte kumeta it was formed on a crinoidal limestone substrate of pliensbachian age and is covered by upper bajocian ammonitico rosso type sediments all cross cut by several generations of neptunian dykes this peculiar surface is more or less coeval with hardgrounds fe mn capped dissolution surfaces and associated neptunian dykes described from other localities of the western tethys and currently subject to fierce debates as to their purely submarine or perhaps partly subaerial origin the major goal of this paper is to add new arguments to this debate by revealing the finest details of field relationships at a site particularly adapted to the study of this phenomenon field observations are supported by petrography and to a lesser extent by geochemistry results are as follows i vertical dissolution grooves pointing to dissolution by gravitationally controlled waters were detected on the sides of several micro topographic highs ii extensive intergranular dissolution predating the formation of the fe mn crust was proved in the substrate both on the micro and meso scale iii intense micro bio erosion and local phosphate enrichment were detected immediately underneath the crust iv a toarcian fauna was identified from the hollows of the irregular surface v synsedimentary faults and fractures clearly predating the major fe mn encrusted surface were observed and vi a meso scale synsedimentary growth structure post dating the fe mn crust which controlled the liassic depositional environment of monte kumeta is documented our conclusion is that the studied surface records at least three separate events of dissolution and precipitation sedimentation each having either erased or overprinted the effects of the previous one and therefore not permitting the exact reconstruction of all the details of the complex story to form the irregular surface in addition to a transient phase of subaerial exposure a complex history of bio erosion and submarine dissolution by fluids of widely different chemical composition is proposed to permit the mixing of sea water with fault controlled waters of higher temperature and with groundwaters introduced by deep circulation a scenario of down faulted blocks and an adjoining distant subaerially exposed region is invoked such a region provided the hydraulic drive for the postulated circulation the ultimate cause for the unusual phenomena under scrutiny was the combined effect of tectonics the local manifestation of early liassic rifting in the western tethys and the well known pliensbachian toarcian sea level rise

low and high frequency sea level changes control peritidal carbonate cycles facies and dolomitization in the rock of gibraltar early jurassic iberian peninsula the rock of gibraltar comprises two tectonically separated limbs of an isolated klippe of liassic gibraltar limestone formation both limbs have similar c 400 m thick sequences of inner carbonate platform facies arranged in high frequency metre scale shallowing upward peritidal cycles with emergent caliche caps four cycle types are recognized on the basis of vertically repeated successions of different sedimentary structures lithologies facies and biota when compared with other liassic cycles from fault bound platforms of the western mediterranean region all are found to be of similar scale facies and cycle type likely common origins are through milankovitch band allocyclicity or autocyclic tidal flat progradation superimposed on regional subsidence within the gibraltar limestone high frequency cycles are superimposed on a low frequency third order cyclicity that is revealed through the use of fischer plots to control the occurrrence of facies biota high frequency cycle types and dolomitization falling sea level and lowstand phases with reduced accommodation space are typified by restricted inner platform facies and cycles and by early reflux dolomitization transgressive and highstand phases with more accommodation space are characterized by the absence of early dolomites the incoming of inner platform microfossils i e foraminifera and calcareous algae and by less restricted marine facies i e oncoids shelly rudstones packstones and grainstones fischer plots have demonstrable value in the correlation and analysis of tectonically separated and geographically isolated cyclic sequences that lack prominent marker beds or stratigraphically useful biotas

13c enrichment in the palaeoproterozoic carbonate rocks of the aravalli supergroup northwest india influence of depositional environment abstract the dolomitic carbonates from the jhamarkotra formation of the palaeoproterozoic aravalli supergroup are characterized by widely variable carbon isotope ratios 13 c ranging from near zero to as high as 12 v pdb the estimated maximum age ca 2150 ma of the aravalli carbonates help bracketing these with the coeval carbonate bodies of the world that show high positive carbon isotope values the intriguing existence of normal marine 13 c values in some pockets suggest influence of local scale depositional conditions prevailing in different sub basins amongst these two sub basins which showed high 13 c values a hypersaline evaporative condition is considered responsible for the necessary enrichment in one while methanogenesis possibly in conjunction with sulphate reduction processes might have caused such enrichment in the other from the empirical association of the sub basins with profuse stromatolitic phosphorite we infer that the depositional setting that favoured cyanobacterial growth leading to formation of stromatolites prevented growth of methanogenetic archaea in such anoxic environments our study therefore highlights the fact that the early palaeoproterozoic 13 c excursion in the aravalli supergroup is not essentially a time specific event but is greatly dependent on the variation in the depositional palaeoenvironment prevailing in different sub basins

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

sea level changes versus hydrothermal diagenesis origin of triassic carbonate platform cycles in the dolomites italy abstract the triassic platform carbonate cycles of the dolomites best developed and studied at the latemar have been considered key examples for the documentation of eustatic sea level changes the cycles appear to reflect a low energy lagoonal environment which is however difficult to reconcile with the small platforms lacking marginal energy barriers in a tropical stormy climate an alternative interpretation to eustatically controlled cyclicity and repeated subaerial exposure is provided by diagenesis in a hydrothermal field elevated heat flow 0 2 ma before the onset of the mafic igneous activity triggered the circulation of diagenetic fluids with a composition similar to seawater by intermittent opening of fractures through some platforms this caused tepee formation by precipitation of displacive cement pendant cement and pisolite formation and favoured cyanobacterial mat formation and their early dolomitization the abundance of cycles correlates with that of the somewhat younger volcanic dikes crosscutting some platforms diffuse venting or seeping in the upper unconsolidated sediment layers explains the stratiform occurrence of the diagenetic features and alternation with normal marine deposition in deep but photic water at the wave base

biogenic laminar calcretes evidence of calcified root mat horizons in paleosols laminar calcretes are described from the lower carboniferous of south wales the upper jurassic of southern england and the upper jurassic lower cretaceous of northern spain they are interpreted as calcified root mats horizontal root systems and are compared with other examples in the geological record and with possible modern analogues all three occurrences consist of virtually identical centimetre to decimetre thick locally organic carbon rich laminar micrites containing up to 50 by volume of millimetre sized typically calcite filled tubular fenestrae set in an irregular but very finely laminated matrix it is suggested that root mat calcretes are probably very common in the geological record in peritidal lacustrine margin and floodplain deposits but owing to their crudely biogenic microstructure they more closely resemble cryptalgal laminites than do other laminar calcretes the recognition of such root mat calcretes in sedimentary sequences not only provides evidence of subaerial exposure and vegetation cover but can also indicate positions of palaeo water tables in certain circumstances

climate and seismicity in the higher central himalaya during 20 10 ka evidence from the garbayang basin uttaranchal india abstract in the trans himalaya the trans himadri fault thf controlled the extent of past glaciers the rivers were impounded by glacial debris resulting in the formation of lakes that recorded regional climatic and seismic events one such lake formed at garbayang where the upper 28 m lacustrine succession spanned an age range of 20 10 ka magnetic susceptibility and sedimentological data suggest that the region experienced high amplitude low frequency millennial scale climate changes during the period 20 3 and 13 2 ka followed by low amplitude high frequency changes from 13 2 11 1 ka a sudden drop in magnetic susceptibility and elemental concentration of layers dated at 11 12 ka suggests cooling associated with the younger dryas occurrence of faulted strata seismites during 20 17 and 14 13 ka suggests recent activation of the thf this is noteworthy as the thf has been considered dormant since its last reactivation at 11 ma further the luminescence dates suggest that radiocarbon ages on organic carbon are grossly overestimated due to a hard water effect caused by the dominance of limestone in the lake catchment this implies that earlier radiocarbon based palaeoenvironmental reconstruction in the region will need revalidation

sicily s fold thrust belt and slab roll back the si ri pro seismic crustal transect sicily is a thick orogenic wedge formed by 1 the foreland african and its sicilian orogen and 2 the thick skinned calabrian peloritani wedge the crust under central sicily from the tyrrhenian margin to the coastline of the sicily channel has been investigated by the multidisciplinary si ri pro research project the project dealt with the nature and thickness of the crust and depth and geometry of the moho which is essential in formulating subduction models and improving the knowledge of african and tyrrhenian european lithospheres the results resolve features such as 1 the main orogenic wedge 2 the very steep nw se trending regional monocline suggesting inflection of the foreland crust 3 the deep caltanissetta synform imaged for the first time to about 25 km and 4 the top of the crystalline basement and the inferred crust mantle boundary the si ri pro transect confirmed that the nnw dipping autochthonous iblean platform of se sicily and its basement extends all the way into central sicily further nw towards the nnw end of the transect a large uplift involves the iblean platform and its underlying basement the associated gravity anomaly is interpreted as the southern wedge edge of the tyrrhenian mantle that splits the subducting iblean pelagian african continental slab from an overlying synformal stack of allochthonous thrust sheets supplementary materials additional data are available at www geolsoc org uk sup18594

late holocene climate response and glacial fluctuations revealed by the sediment record of the monsoon dominated chorabari lake central himalaya we studied a periglacial lake situated in the monsoon dominated central himalaya where an interplay of monsoonal precipitation and glacial fluctuations during the late holocene is well preserved a

misinterpreting proxy data for paleoclimate signals a comment on shukla et al 2020 shukla et al explored paleoclimatic signals from a 8 m thick profile of a moraine dammed lake in the central himalaya exposed due to lake burst from a flash flood in 2013 the main objective of t

interference between shallow and deep seated structures in the sicilian fold and thrust belt italy abstract the fold and thrust belt in western sicily is characterized by the presence and interference of shallow and deep seated compressional structures which were generated and developed at different structural levels the shallow structures consist of imbricated thrusts and asymmetric folds with a typical wavelength of 2 km involving relatively thin deep water units these units are superimposed on thick platform carbonate units along a wide and originally almost flat floor thrust the axial trend of the folds is variable as multi phase folding often occurred producing a characteristic interference pattern reflecting continuous variations of the apparent transport direction during the emplacement i e rotation of the allochthonous thrust sheets the deep seated structures consist of large double verging pop up structures with a typical wavelength of 5 10 km involving thicker platform carbonate successions the deep seated structures are characterized by large folds with vertical to overturned limbs caused by high angle transpressive ramps that reactivated previous i e mesozoic synsedimentary normal or transtensional faults the floor thrust of the shallow structures was passively deformed by the subsequent growth of the underlying younger deep seated structures large clockwise rotations of the tectonic units occurred during the compressional deformation and the amount of rotation is apparently related to the timing and amount of the tectonic transport

dating quaternary lacustrine sediments in the mcmurdo dry valleys antarctica abstract reports of erroneously old 14c dates for modern antarctic materials have thrown doubt into 14c chronologies the carbon reservoir effect purported to exist in quaternary lacustrine sediments of the mcmurdo dry valleys was investigated by studying 14c distribution and testing alternate dating techniques our results show that the carbon reservoir effect is not pervasive stream and near shore microbial mats and dissolved inorganic carbon dic in the surface waters of lake fryxell are in equilibrium with modern 14co2 the surface waters of lake hoare and lake bonney however have dic 14c ages of 1650 and 2080 yr b p respectively these older age estimates are suggested to be due to the direct input of large amounts of glacial melt with relict dic on the other hand lake fryxell receives only a minor component of its inflow directly from a glacier while a large component must travel long distances in numerous shallow ephemeral streams after leaving local valley glaciers this mode of melt water input allows the water to equilibrate with modern co2 before entering the lake bottom water 14c ages for lake hoare closely match surface sediment ages supporting the widely published period 1200 yr b p after a 1650 yr reservoir correction when most dry valley lakes apparently evaporated to small brine ponds and or disappeared completely lake bonney bottom water is 8000 yr b p carbon dating is shown to be a viable technique for lake edge deposits and possibly lake bottom deposits where a correction to the sediment surface age can be obtained however we conclude that deep water paleolake deposits can not be reliably dated using 14c alone because of an inability to determine the age of the reservoir correction i e accounting for the initial carbon reservoir plus the age of the bottom water a suite of alternative and complimentary dating techniques were tested on modern and late holocene lacustrine deposits these include thermoluminescence tl 210pb 137cs and paleomagnetism of these techniques tl or the more sensitive optically stimulated luminescence holds the most promise for correcting lake sediment 14c ages tl dating of the modern lake hoare sediments showed an 1000 yr relict signal this signal is unaffected by the age of the lake water both 210pb and 137cs occurred in very low levels in the sediments and do not appear to be viable dating techniques for the perennially ice covered lakes of the mcmurdo dry valleys paleomagnetism was not suited to the coarse grained nature of lake hoare bottom sediments but could be a useful alternative given a finer sediment type

tracing bottom water oxygenation with sedimentary mn fe ratios in lake zurich switzerland abstract redox dynamics of manganese mn were studied in the sediment of lake zurich using precise sediment core age models monthly long term oxygen o 2 monitoring data of the water column 1936 2010 and high resolution xrf core scanning the age models were based on bi annual lamination and calcite precipitation cycles if present mn exhibits distinct maxima which coincide with the annual maximum deep water o 2 concentrations in spring according to the monitoring data in contrast the iron fe signal is mainly the result of calcite dilution as indicated by a strong negative correlation between fe and calcium ca xrf data the mn fe ratio in the core from the maximum lake depth zh10 15 137 m revealed a moderate correlation with o 2 measurements in the lake bottom water confirming the successful application of the mn fe ratio to semi quantitatively reconstruct bottom water oxygenation in the lake mostly low ratios were observed between 1895 and the mid 1960s as a result of eutrophication however geochemical focusing and sedimentological factors can reduce the applicability of the mn fe ratio in reconstructing o 2 concentrations in the bottom water of lakes

sediment load characteristics of a proglacial stream of siachen glacier and the erosion rate in nubra valley in the karakoram himalayas india abstract this paper discusses the results of studies on sediment transport and the erosion rate in the nubra river carried out in hydrological years from 1986 to 1991 discharge data of proglacial stream of the siachen glacier shows seasonal variation ranging from 0 26 10 6 m 3 d 1 in the beginning of the ablation season to about 23 10 6 m 3 d 1 in the peak ablation season suspended sediment mass in the nubra river varies from 0 01 kg m 3 s 1 in the beginning of the ablation season to about 2 3 kg m 3 s 1 at its peak a relationship is developed between daily suspended sediment transport and daily discharge the total sediment load calculated from the data varies from 296 to 1287 tons km 2 of the glacier basin area per year the erosion rate calculated from total sediment load which includes suspended sediment and bedload varies from 0 11 to 0 46 mm year 1 the erosion rates in the nubra basin are much lower than the hunza basin in western karakoram himalayas 1 8 mm year 1 which may be due to its geological setting consisting of highly erosion resistant rocks like diorites grano diorites granites and granite gniesses tectonic upliftment and high relief give rise to comparatively higher erosion rates in karakoram himalayas

paleosols in shallow marine carbonate sequences abstract shallow water carbonate sequences in the geological record commonly exhibit numerous exposure surfaces reflecting emersion of sediment due to progradation processes and sealevel oscillations some ancient platform sequences contain hundreds of such surfaces associated with paleosols fossil soils typically calcretes a wide range of macro and microstructures are associated with these calcretes which are reviewed profile types and stages in profile development can be defined the nature of the exposure surface and associated paleosols can be used to identify the nature of the prevailing climate although hydromorphic effects related to marine flooding of the platforms can modify the paleosols a potentially important use of paleosols is to define the nature of sequence boundaries several studies have identified sets of paleosols with varying maturities reflecting changes in rates of accommodation space creation during sealevel rises and falls

late quaternary environmental changes in the taklamakan desert western china inferred from osl dated lacustrine and aeolian deposits sediment records from the tarim basin of western china are of great importance for understanding late quaternary climatic variability in central asia a chronology of aeolian and lacustrine deposits from the centre and southern margin of the taklamakan desert central tarim basin has been established using optical dating methods distinct variations in humidity during the last 40 000 a in this extremely arid inland basin have been identified lacustrine sediments were deposited in the centre of the taklamakan during two periods of wetter than present day conditions at around 2000 and 30 000 a ago another humid period is recorded between 40 000 and 30 000 a ago aeolian processes the development of large migrating dune fields dominated during periods of more arid conditions sand wedges at the southern margin of the taklamakan are dated at ca 40 000 a and ca 18 000 a and imply a significant temperature decrease in that area sedimentological evidence for a late holocene humid period are consistent with records in ancient chinese literature wetter environmental conditions in the past within the taklamakan as indicated by the presence of lacustrine deposits are also supported by data from adjacent regions it is assumed that changes of global westerlies and of the mobile polar high triggered the fluctuations of precipitation in the study area however variations in temperature in the taklamakan desert are presumed to be mainly controlled by the intensity of the winter monsoon

a multi parameter rock magnetic record of the last glacial interglacial paleoclimate from south central illinois usa pittsburg basin a small kettle lake in south central illinois was formed after the retreat of the illinoian ice sheet 130 ka b p and the sedimentary record includes the last interglacial glacial cycle curie temperature measurements xrd analyses and thermal demagnetization of a low temperature j indicate that the magnetic fraction is characterized by rs oxidized magnetite and magnetic iron sulfides the grain size of the magnetic fraction was estimated from armrj ratios rs frequency dependent susceptibility and hysteresis parameters these measurements show that glacial sediments contain coarse grained presumably detrital material while interglacial samples have an additional fine grained magnetic component which cannot be explained by a single catchment or climatic process early interglacial samples show magnetic properties characteristic of authigenic biogenically produced magnetite while late interglacial samples are probably influenced by pedogenesis around the basin q 1997 elsevier science b v

what do the hirm and s ratio really measure in environmental magnetism the hard isothermal remanent magnetization hirm and the s ratio are widely used in environmental magnetism to quantify the absolute and relative concentrations respectively of antiferromagnetic minerals hematite and goethite in mineral mixtures we demonstrate that synthetic al substituted hematite and goethite exhibit a wide range of coercivities which significantly influences the hirm and s ratio these parameters are therefore not necessarily straightforward indicators of the absolute and relative concentrations of hematite goethite to circumvent this problem we propose a new parameter the l ratio which is the ratio of two remanences after alternating field af demagnetization of an irm imparted in a 1 t field with a peak af of 100 mt and 300 mt irmaf 300mt irmaf 100mt these parameters are easily measured using modern vibrating sample or alternating gradient magnetometers changes in hirm only reflect changes in the absolute concentration of hematite and or goethite if the l ratio is relatively constant conversely l ratio fluctuations indicate variable coercivities that possibly reflect changes in the source of hematite goethite corresponding hirm and s ratio variations should be interpreted with caution in such cases the l ratio can be determined using equivalent terms depending on available instrumentation and measurement protocols for example the hirm is equivalent to irmaf 300mt likewise 0 5 sirm irm 100mt where irm 100mt represents the remanent magnetization obtained by first saturating the sample in a high field and then applying a back field of 100 mt is equivalent to irmaf 100mt the hirm 0 5 sirm irm 100mt ratio is therefore a suitable substitute for the l ratio when measurements are made with a long core magnetometer the newly proposed l ratio is straightforward to measure on a wide range of instruments and can provide significant new insights and reduce ambiguities associated with interpretation of two widely used parameters in environmental magnetism the hirm and s ratio

muddled or mixed inferring palaeoclimate from size distributions of deep sea clastics abstract one of the outstanding problems of palaeoclimate reconstruction from physico chemical properties of terrigenous deep sea sediments stems from the fact that most basin fills are mixtures of sediment populations derived from different sources and transported to the site of deposition by different mechanisms conventional approaches to palaeoclimate reconstruction from deep sea sediments do not distinguish between provenance and dispersal related variations and therefore often fail to recognise the true significance of variations in sediment properties we formulate a set of requirements that each proposed palaeo environmental indicator should fulfil and focus on the intrinsic coupling between grain size and chemical composition a critical review of past achievements in grain size analysis serves to introduce a conceptual model of spatio temporal grain size variation based on dynamic populations each dynamic population results from a characteristic combination of production and transport mechanisms that corresponds to a distinct subpopulation in the data analysed the mathematical statistical representation of the conceptual model can be obtained by means of the end member modelling algorithm emma applications of the model to several ocean basins are discussed as well as methods to examine the validity of grain size based palaeoclimate reconstructions palaeoclimate reconstructions of a high and low latitude basin illustrate the common degree of complexity of deep sea grain size records

characterization lateral variability and lateral extent of discontinuity surfaces on a carbonate platform barremian to lower aptian oman hiati of various duration in carbonates are commonly expressed as discontinuity surfaces the understanding of processes that form and affect these surfaces leads to an improved sequence stratigraphic interpretation a reliable outcrop correlation and better models for reservoir compartmentalization various intraformational discontinuities were analysed and interpreted in a well exposed study window 2 5 km in lateral length and 60 m in height comprising the barremian aptian qishn formation haushi huqf area central oman this study focuses on the lateral extent and morphology of the surfaces the petrography of the underlying rocks and the facies changes and geochemical trends across these discontinuities furthermore the lateral variability of discontinuity surfaces was documented three genetic types of discontinuities are differentiated i erosion surfaces ii omission surfaces hard and firmgrounds and iii composite surfaces with evidence for both subaerial exposure and submarine boring field observations combined with petrographic and geochemical data suggest that 17 surfaces are laterally extensive for at least 20 km and record relative sea level fluctuations of regional scale in contrast a large number of laterally limited surfaces 1 km are related to locally active processes such as waves and current erosion the lateral variability along extensive surfaces is the result of the depositional environment below the discontinuity the sea floor topography waves and currents and differential erosion the most pronounced lateral variability is present along six laterally extensive composite surfaces that record terrestrial exposure and subsequent flooding of a tidal flat environment this variability is caused by spatial variability in the tidal flat environment meteoric alteration and differential erosion this study emphasizes the spatial and temporal complexity of processes that form and modify discontinuity surfaces this variability must be kept in mind when interpretations and correlations are based on one dimensional sections or cores 2005 international association of sedimentologists

subglacial till formation sedimentary characteristics and classification we review the major subglacial till forming processes as presently understood by glacial researchers and define the parameters within which tills are produced and reconcile them with sedimentary end members processes of deformation flow sliding lodgement and ploughing coexist at the base of temperate glacier ice and act to mobilize and transport sediment and deposit it as various end members ranging from glacitectonically folded and faulted stratified material to texturally homogeneous diamicton the dominance of any one subglacial process varies both spatially and temporally giving rise to the possibility that a till or complex till sequence contains a superimposed signature of former transportation deposition at the ice bed interface we recommend that while glacial geologists and geomorphologists should be able to recognize the sedimentary imprints of various subglacial processes genetic fingerprinting of subglacial tills should be less process specific and till classification must reflect the range of products encompassed by the subglacial till production continuum glacial geologists can presently unequivocally identify a glacitectonite rock or sediment that has been deformed by subglacial shearing deformation but retains some of the structural characteristics of the parent material b subglacial traction till sediment deposited by a glacier sole either sliding over and or deforming its bed the sediment having been released directly from the ice by pressure melting and or liberated from the substrate and then disaggregated and completely or largely homogenised by shearing and support the theoretical case for c melt out till sediment released by the melting of stagnant or slowly moving debris rich glacier ice and directly deposited without subsequent transport or deformation because observations on contemporary glaciers reveal that their beds are most likely to be mosaics of deformation and sliding and warm based and cold based conditions the patterns of which change temporally and spatially it is extremely unlikely that subglacial till end members in the geological record will be anything but hybrids produced by the range of processes operative in the subglacial traction zone

late quaternary landscape evolution in the kunlun mountains and qaidam basin northern tibet a framework for examining the links between glaciation lake level changes and alluvial fan formation abstract the qaidam basin in northern tibet is one of the largest hyper arid intermontane basins on earth alluvial fans pediment surfaces shorelines and a thick succession of sediments within the basin coupled with moraines and associated landforms in the adjacent high mountain catchments of the kunlun mountains record a complex history of late quaternary paleoenvironmental change and landscape evolution the region provides an ideal natural laboratory to examine the interaction between tectonics and climate within a continent continent collision zone and to quantify rates of landscape evolution as controlled by climate and the associated glacial and hydrological changes in hyper arid and adjacent high altitude environments geomorphic mapping analysis of landforms and sediments and terrestrial cosmogenic radionuclide surface exposure and optically stimulated luminescence dating serve to define the timing of formation of late quaternary landforms along the southern and northwestern margins of the qaidam basin and in the burhan budai shan of the kunlun mountains adjacent to the basin on the south these dates provide a framework that suggests links between climatic amelioration deglaciation lake desiccation and alluvial fan evolution at least three glacial advances are defined in the burham budai shan of the kunlun mountains on the northern side of this range these occurred in the penultimate glacial cycle or early in the last glacial cycle during the last glacial maximum lgm lateglacial and during the holocene on the south side of the range advances occurred during the penultimate glacial cycle mis 3 and possibly the lgm lateglacial or holocene several distinct phases of alluvial fan sedimentation are likewise defined alluvial fans formed on the southern side of the kunlun mountains prior to 200 ka ice contact alluvial fans formed during the penultimate glacial and during mis 3 extensive incised alluvial fans that form the main valley fills north of the burham budai and extend into the qaidam basin are dated to 30 ka these ages suggest that there was a period of alluvial fan aggradation and valley filling that persisted until desiccation of the large lakes in the qaidam basin post 30 ka led to base level lowering and active incision of streams into the valley fills the continued lateglacial and holocene desiccation likely led to further degradation of the valley fills ice wedge casts in the qaidam basin date to 15 ka indicating significant lateglacial climatic amelioration while holocene loess deposits north of the burham bdudai suggest that aridity has increased in the region since the early holocene from these observations we infer that the major landscape changes within high glaciated mountains and their adjacent hyper arid intermontane basins such as the kunlun mountains and qaidam basin occur rapidly over millennial timescales during periods of climatic instability

mid to late holocene climate response from the triloknath palaeolake lahaul himalaya based on multiproxy data abstract a 2 13 m thick palaeolake sequence deposited between the right lateral moraine and the valley wall of triloknath glacier has been studied at high resolution to understand the past climatic changes in lahaul himalaya the osl and ams 14c chronology suggests that the lake building activity was initiated post cooling phase since 6484 cal ybp the combination of sedimentological geochemical and environmental magnetic parameters helped to infer five first order climatic zones the influx of magnetic minerals along with a notable increase in antiferromagnetic mineralogy appearance of hematite and higher chemical index of alteration cia values during 5925 cal ybp to 5676 cal ybp suggests warm and wet conditions owing to enhanced indian summer monsoon ism precipitation corresponding to the mid holocene warming further reduction in the magnetic mineral concentration with few peaks of antiferromagnetic mineralogy and higher cia values suggests warmer episodes within an overall cold climate and the finer ferrimagnetic grain size suggests intermittent low energy and ponding conditions during 3904 cal ybp to 2365 cal ybp this was followed by fluctuating cold arid conditions in response to reduced ism precipitation during 2365 cal ybp and 1758 cal ybp further between 1758 cal ybp to the present episodic warming pedogenic enhancement and increased monsoon precipitation have been recorded a major warm episode medieval warm period as depicted from enhanced antiferromagnetic mineralogy and higher cia values has been recorded between 742 cal yrs bp and 593 cal ybp the sudden drop in the magnetic mineral concentration as well as the cia value around 300 cal ybp 1650 ce is likely because of colder conditions prevailing during the little ice age lia the study illustrates high sensitivity of the lake sediment sequence to witness the climatic episodes experienced in the glaciated regime of the triloknath glacier

a new osl chronology for dust accumulation in the last 130 000 yr for the chinese loess plateau abstract a sensitivity corrected multiple aliquot regenerative dose protocol has been developed for fine grained quartz osl dating of chinese loess its reliability has been assessed on the basis of the methodology and by dating reference samples of known age close to the transition from the last interglacial paleosol s 1 to the last glacial loess l 1 which corresponds to the marine oxygen isotope stage mis 5 4 transition on the basis of the fine grained quartz osl age estimates for 33 loess samples from the upper part of the luochuan profile a detailed chronostratigraphy of continuous dust accumulation in the past 130 ka has been proposed changes in the accumulation rate occurred during the last glacial period mis 4 to mis 2 unexpectedly high accumulation rates were found in the weakly developed l 1 2 s paleosol of the last interstadial mis 3 rather than in the classic l 1 1 and l 1 3 loess of the cold dry glacial condition mis 2 and 4 the osl ages show some disagreement with the previous numerical chronology for the loess paleosol sequence based on correlation of variations in grain size with sedimentation rate the latter method resulted in an almost constant accumulation rate from 72 to 12 ka

paleogeography and structure of the central mediterranean sicily and its offshore area abstract the geology of the mainland and offshore of sicily is illustrated by a few geologic sections and seismic profiles across the late cenozoic orogenic belt of central and western sicily and across the sardinia channel and sicily straits this belt is the result of several tectonic events deformation involved mainly the sedimentary cover of the old african continental margin characterized by a broad basinal domain flanked along its external southern margin by a shallow water carbonate platform attached to africa in the triassic compressional deformation started in the more internal basinal rock assemblages overlying a thinned crust the most important structural characteristic of the early phase of thrusting is the duplex pile forming the bulk of the chain in central western sicily the structure consists of a basal allochthon made up of permian to middle triassic layers an intermediate duplex wedge composed of competent mesozoic carbonates and a roof complex including upper mesozoic lower tertiary less competent rocks large scale clockwise rotation of the thrusts accompanied transpressional movements in the hinterland during the pliocene right oblique reverse faults modified the previous tectonic contacts between the allochthons in the hinterland zones contemporaneous south directed imbrications affected the southern external areas progressively incorporating foreland and piggyback basins development of the gela thrust system appears to be linked to the transpressional event its accretion is also related to contemporaneous underthrusting at deeper levels of mesozoic carbonate substratum the older buried thrust sheets were pushed up to the surface breaching the deformed tertiary cover of the gela ts northwards in the belt post messinian normal growth faults opened half graben whose sedimentary fill underwent structural inversion alternation of extension and compression tectonics characterizes the sicilian continental margin in the last million years

equations for effective stress and permeability of soft mud sand mixtures equations for the terzaghi effective stress and permeability of clay silt sand mixtures are derived on the basis of a scale invariant structure of the soil to enhance physical interpretation of the empirical coefficients the behaviour of soft sediment is assumed to be dominated by the clay fraction but the sediment may also contain silt and sand a theoretical model is presented of the structure of the sediment based on the concept of a scale invariant structure of the clay silt matrix using this scale invariant model equations for effective stress and permeability are derived the equations take effects due to partial segregation into account the equations for effective stress and permeability are validated against data effective stress permeability and particle size distributions obtained from a consolidation experiment with a sandy soft mud it is shown that the equation for effective stress relates the effective stress to the clay and sand volume fraction accurately for the present data set