explosive volcanism during the holocene in the upper limay river basin the effects of ashfalls on human societies northern patagonia argentina abstract in order to understand human response to holocene ashfall events tephra layers found in archaeological sites along the upper limay river basin northern patagonia argentina were bracketed with radiocarbon dates and correlated with tephra from a lacustrine sediment core and from outcrops and the archaeological evidence was analyzed a dark tephra associated with seismic activity was identified in the el trebol rockshelter filling interstices between fallen blocks together with remains of human activity and bones of extinct fauna marking a seismo volcanic event occurring between 11 758 and 12 866 cal yr bp this same seismic event affected the cuyin manzano site where the roof collapse made the site uninhabitable for a time a white tephra present in epullan grande epullan chica and traful i caves is correlated with nahuel huapi tephra nht equivalent to laya s rio blanco and rio pereyra members rio pireco formation nht is considered to have been derived from the same eruptive event with dates ranging between ca 1950 2500 cal yr bp a dark tephra from ortega s cave and several tephra from puerto tranquilo i rockshelter ranging between 521 and 2069 cal yr bp show how the mobile hunters gatherers of northern patagonia were able to cope with the changing circumstances

correlation of changes in gravity elevation and strain in southern california measurements made once or twice a year from 1977 through 1982 show large correlated changes in gravity elevation and strain in several southern california networks precise gravity surveys indicate changes of as much as 25 microgals between surveys 6 months apart repeated surveys show that annual elevation changes as large as 100 millimeters occur along baselines 40 to 100 kilometers long laser ranging surveys reveal coherent changes in areal strain of 1 to 2 parts per million occurred over much of southern california during 1978 and 1979 although the precision of these measuring systems has been questioned the rather good agreement among them suggests that the observed changes reflect true crustal deformation

pressure core analysis of geomechanical and fluid flow properties of seals associated with gas hydrate bearing reservoirs in the krishna godavari basin offshore india abstract physical properties of the sediment directly overlying a gas hydrate reservoir provide important controls on the effectiveness of depressurizing that reservoir to extract methane from gas hydrate as an energy resource the permeability of overlying sediment determines if a gas hydrate reservoir s upper contact will provide an effective seal that enables efficient reservoir depressurization compressibility stiffness and strength indicate how overlying sediment will deform as the in situ stress changes during production providing engineering data for well designs assessing these properties requires minimally disturbed sediment india s national gas hydrates program expedition 2 nghp 02 provided an opportunity to study these seal sediment properties reducing disturbance from gas exsolution and bubble growth by collecting a pressure core from the seal sediment just above the primary gas hydrate reservoir at site nghp 02 08 in area c of the krishna godavari basin the effective stress chamber esc and the direct shear chamber dsc devices in the suite of pressure core characterization tools pccts were used to measure permeability compressibility stiffness and shear strength at the in situ vertical stress geotechnical properties of the predominantly fine grained seal layer at in situ vertical stress are in typical clay sediment ranges with low measured permeability 0 02 md high compressibility c c 0 26 0 33 and low shear strength 404 kpa though pressure and temperature were maintained throughout the collection and measurement process to stabilize gas hydrate the lack of effective stress in the pressure core storage chamber and the chamber pressurization with methane free water caused core expansion and gas hydrate in a thin coarser grained layer to dissolve the pccts can reapply in situ stress with incremental loading steps during a consolidation test to account for sediment compaction gas hydrate dissolution can be limited by storing cores just above freezing temperatures and by using solid spacers to reduce the storage chamber s free volume

india national gas hydrate program expedition 02 operational and technical summary abstract the india national gas hydrate program is being steered by the government of india s ministry of petroleum and natural gas mopng with participation of directorate general of hydrocarbons dgh oil and natural gas corporation limited ongc and the national oil companies and research institutes of india the india national gas hydrate program expedition 01 nghp 01 established the presence of gas hydrate in the krishna godavari kg and mahanadi basins and in the offshore area of the andaman sea basin however the gas hydrates discovered during nghp 01 were mainly distributed as fracture filling material in fine grained clay rich sediments the india national gas hydrate program expedition 02 nghp 02 was carried out with an objective to discover gas hydrate in sand rich sediment along the eastern offshore margin of india ongc planned and executed nghp 02 on the behalf of the mopng nghp 02 started on march 3 2015 and was completed on july 28 2015 total 147 days using the japanese scientific drilling vessel chikyu d v chikyu during nghp 02 42 holes at 25 sites were drilled cored and or surveyed with downhole logging tools these sites were located in four areas along the eastern margin of india and formally named area a mahanadi basin three sites area b northern part of the kg basin twelve sites area c central part of the kg basin six sites and area e southern part to the kg basin four sites all 25 sites established during nghp 02 were first drilled and logged with logging while drilling lwd tools and an additional 17 holes were then drilled and or cored with conventional coring tools hpcs escs or pressure coring tools pctb wireline logging was conducted in 10 holes and formation tests using a dual packer modular formation dynamics tester mdt tool were carried out in two holes the onboard science team used the laboratory facilities on the d v chikyu to examine and analyse the physical properties geochemistry and sedimentology of all the cores collected during the expedition core samples were also analysed in additional post expedition shore based studies conducted in numerous domestic and international gas hydrate research laboratories the nghp 02 sediment cores were archived at the national gas hydrate core repository in mumbai india which is associated with the ongc gas hydrate research and technology centre ghrtc the necessary data for characterizing the occurrence of gas hydrate such as interstitial water chlorinities core derived gas chemistry physical and sedimentological properties thermal images of the recovered cores pressure core and downhole measured logging data lwd and or conventional wireline log data were obtained from most of the drill sites established during nghp 02 almost all the drill sites yielded evidence for the occurrence of gas hydrate however the inferred in situ concentration of gas hydrate varied substantially from site to site for the most part the interpretation of downhole logging data core thermal images interstitial water analyses and pressure core images from the sites established during nghp 02 indicate that the occurrence of concentrated gas hydrate is mostly associated with coarser grained sand rich sediments this paper presents the operational and technical summary of nghp 02

stable isotopes reveal differential patterns of holocene environmental change among tuco tucos rodentia ctenomyidae ctenomys from patagonia abstract to explore the role of past environmental changes in shaping interspecific differences in genetic structure among tuco tucos rodentia ctenomyidae ctenomys from the limay valley of northern patagonia we compared 13c and 18o values for modern and historical tooth enamel from the colonial tuco tuco c sociabilis and the parapatric patagonian tuco tuco c haigi specifically we sought to test the hypothesis that a mid holocene loss of genetic variation in c sociabilis was associated with environmental change for both species the 13c composition of tooth enamel differed significantly 5 1 difference in mean 13c values between modern and holocene 0 5 12 kyr b p samples suggesting marked temporal changes in the vegetation consumed for c sociabilis no statistically significant differences in the 13c composition of teeth were found among individuals from the early middle and late holocene in contrast significant differences in 13c values were found between middle and late holocene samples from c haigi none of our analyses revealed statistically significant differences in 18o values thus although the diets of both study species have changed from the holocene to the present only c haigi experienced significant dietary changes during the holocene we suggest that the ecologically more specialized c sociabilis continued to consume the same food resources even as changing holocene conditions caused preferred habitats to disappear in contrast the more generalized c haigi altered its diet allowing populations of this species to remain widespread despite changing holocene environments

new technique for accurate porosity estimation from logging while drilling nuclear magnetic resonance data nghp 02 expedition offshore india abstract drilling and acquiring high quality downhole log data in the gas hydrate bearing sedimentary sections found mostly in deep marine environments and at low temperatures is often challenging because of the disseminated gas hydrates and mostly unconsolidated nature of the host sediments logging while drilling lwd technology was used in national gas hydrate program expedition 02 nghp 02 in 25 wellbores to acquire data needed for the comprehensive analysis of gas hydrate occurrences offshore eastern india the lwd tools deployed included a nuclear magnetic resonance nmr tool along with a density measurement tool for porosity computation a high resolution resistivity imaging tool for fracture evaluation and depositional system identification and a borehole acoustic tool for gas hydrate identification and pore pressure monitoring by measuring deviation of sonic velocity from normal compaction trend the nmr lwd tool measures transversely relaxing signal echoes decay which is calibrated and inverted into transverse relaxation times or a t2 distribution figure 2 the t2 distribution is then summed to compute nmr porosity due to the solid nature of gas hydrates at in situ conditions they are invisible to nmr it is fundamental for gas hydrate identification to look for zones with differences between the nmr porosity and density porosity this paper describes a new evaluation technique that addresses the porosity deficit problem due to the fast t2 relaxation observed in nmr data acquired during nghp 02 in the new algorithm the t1 t2 distributions are jointly inverted compared to conventional nmr processing which inverts a t2 distribution from the echo signal using a constant t1 t2 ratio it is observed that with the conventional method which assumes a constant t1 t2 ratio the nmr porosity in gas hydrate bearing zones is underestimated by about 3 6 porosity units and the derived gas hydrate saturations are overestimated by 8 10

recent volcanism in the puyehue cordon caulle region southern andes chile 40 5 s petrogenesis of evolved lavas

holocene tephra succession of puyehue cordon caulle and antillanca casablanca volcanic complexes southern andes 40 41 s abstract puyehue cordon caulle and antillanca volcanic complexes are two of at least 50 active frontal arc volcanoes that define the 1400 km long southern volcanic zone of chile holocene tephra deposits in chile and argentina 40 41 s up to 100 km east of these volcanoes comprise at least five voluminous 1 to 8 km 3 pyroclastic fall layers that preceded several recently deposited cordon caulle pumice fallouts field observations of proximal medium and distal facies of the deposits in conjunction with geochronology and geochemistry of the volcanic complexes indicate that three fall layers are derived from puyehue volcano puyehue 1 and 2 and mil hojas whereas two are sourced from the antillanca complex playas blanca negra and nahuel huapi tephra 20 km to the south the oldest tephra calibrated 14 c age 10 49 0 12 ka 2 found only at medium distal facies is deposited directly on granitic moraine boulders and consists of deeply weathered orange dacitic pumice lapilli the next prominent tephra at 7 ka comprises dacitic pumice and its age is equivalent to a rhyodacitic dome exposed in the puyehue summit crater above these deposits there are phases of a complex eruption consisting of a conspicuous compositionally zoned tephra it also comprises a pyroclastic density current together with lithic rich and scoriaceous fallout deposits mineralogical geochemical and sr isotope evidence plus the isopach maps confirm that this sequence of eruptive events is sourced from antillanca at 1932 68 yrbp the total volume of this eruptive sequence exceeds 8 km 3 making it the largest holocene eruption from either volcanic complex this eruption was likely responsible for the destruction of an ancestral antillanca volcano and the formation of a 4 5 km diameter caldera a distinctive younger unit in the region is a voluminous rhyodacitic pumice fall calibrated 14 c age 1 11 0 07 ka above which a series of several alternating dark lithic and pumice lapilli beds accumulated correlation with proximal deposits indicates that the 1 11 ka eruption was derived from puyehue and destroyed 3 km 3 of rhyodacitic domes at this volcano summit historic explosive activity at the nascent casablanca volcano and along cordon caulle including the 2011 2012 eruption 1 km 3 of uncompacted pumice the largest from this fissural zone emphasizes an increased risk for volcanic hazards in central chile and argentina

impact of the 1960 major subduction earthquake in northern patagonia chile argentina abstract the recent sedimentation processes in four contrasting lacustrine and marine basins of northern patagonia are documented by high resolution seismic reflection profiling and short cores at selected sites in deep lacustrine basins the regional correlation of the cores is provided by the combination of 137cs dating in lakes puyehue chile and frias argentina and by the identification of cordon caulle 1921 22 and 1960 tephras in lakes puyehue and nahuel huapi argentina and in their catchment areas this event stratigraphy allows correlation of the formation of striking sedimentary events in these basins with the consequences of the may june 1960 earthquakes and the induced cordon caulle eruption along the liquine ofqui fault zone lofz in the andes while this catastrophe induced a major hyperpycnal flood deposit of ca 3 106 m3 in the proximal basin of lago puyehue it only triggered an unusual organic rich layer in the proximal basin of lago frias as well as destructive waves and a large sub aqueous slide in the distal basin of lago nahuel huapi a very recent mega turbidite in the two distal basins of reloncavi fjord located close to the lofz suggests that 1960 co seismic movements in this area may have triggered the remobilization of ca 187 106 m3 of marine sediments

evaluation of the performance of the oceanic hydrate accumulation at site nghp 02 09 in the krishna godavari basin during a production test and during single and multi well production scenarios author s moridis gj reagan mt queiruga af boswell r abstract 2018 elsevier ltd the objective of this study is to quantify by means of numerical simulation the response of the complex system of gas hydrate accumulations at site nghp 02 09 krishna godavari basin indian ocean to different production conditions and to determine the technical feasibility of gas production through depressurization induced dissociation the study assesses the suitability of the site for a long term production test involving a single vertical well and the long term potential of the deposit under full field production using a system of multiple vertical wells we simulate gas and water flow estimate the production performance of the accumulation and separately investigate the corresponding geomechanical response of the system results indicate that production from site nghp 02 09 under the conditions of a long term field test involving a single vertical well is technically feasible and can yield high gas production rates however an inability to fully isolate the water bearing zones results in production that is largely from dissolved gas rather than hydrate dissociation and is thus burdened by excessive water production given the estimated physical properties of the reservoir system site nghp 02 09 does not appear to be a promising location for a single well field test of gas production but may be a promising production target for full field production operations using a multi well system in which exterior wells can mitigate water inflows to allow interior wells to more effectively depressurize the formation and capture methane from gas hydrate dissociation geomechanical issues need to be carefully considered as significant displacements are possible which can be challenging to well construction and stability

gas hydrate reservoir identification delineation and characterization in the krishna godavari basin using subsurface geologic and geophysical data from the national gas hydrate program 02 expedition offshore india abstract during the national gas hydrate program expedition 02 nghp 02 logging while drilling conventional coring and pressure coring wire line logging vertical seismic profiling and formation pressure measurements were carried out in deep water portions of the krishna godavari k g and mahanadi basins along the eastern continental margin of india a total of 42 research holes were completed for comprehensive data collection and measurements related to gas hydrate reservoir and host sediments properties with an objective to identify producible gas hydrate in sand rich reservoirs that would be suitable for a future pilot production test shipboard and post cruise evaluation of physical properties measurements pressure core dissociation studies and gas analysis of recovered core samples have confirmed the occurrence of sand hosted gas hydrate deposits in three operational areas named during nghp 02 as area b area c and area e in the deep water portion of the k g basin the energy resource potential of the discovered gas hydrate deposits in the k g basin depends on many factors including the quantity of available gas trapped as gas hydrate in the basin therefore this study was undertaken to identify characterize and delineate the discovered and confirmed gas hydrate prospects in the k g basin based on the integrated analysis of regional seismic data and nghp 02 acquired borehole data a total of 8 sand rich reservoir constrained gas hydrate prospects have been identified and mapped in the k g basin areas b c and e as described in this report

late quaternary tephrostratigraphy of southern chile and argentina abstract the southern and austral volcanic zones of the andes comprise 74 volcanic centres with known post glacial activity at least 21 of these have had one or more large explosive eruptions in the late quaternary dispersing tephra over vast areas these tephra layers therefore have great potential as tephrochronological marker horizons in palaeoenvironmental studies in southern chile and argentina a region that is particularly useful to study climate dynamics of the southern hemisphere however to date tephrochronology has rarely been fully utilised in this region as a correlation and dating tool here we review the existing post glacial tephrostratigraphic record of the southern and austral volcanic zones and compile a database of known occurrences of tephra from these volcanoes in ice and lacustrine marine peat and cave sediment records we address the inconsistencies in and revisions of the tephrostratigraphies presented in prior literature and discuss the challenges in correlating tephras and the limitations of the tephrostratigraphic record in this area this study highlights the many gaps that still exist in our knowledge of the eruptive histories of these volcanoes but also reveals the largely under utilised potential of tephra as a correlation tool in this region this is exemplified by the severe lack of adequate geochemical analysis of tephra layers preserved in many lacustrine and peat sediment sections which are particularly important tephrostratigraphic records in southern chile and argentina due to the paucity of surface preservation

techno economic forecasting of a hypothetical gas hydrate field in the offshore of india abstract the national gas hydrate program 01 expedition 2006 and the national gas hydrate program 02 expedition 2015 have established the presence of large deposits of gas hydrates in deep water areas offshore india this paper presents the results of a techno economic study carried out for the development of a hypothetical gas hydrate field in the krishna godavari kg basin located along the eastern margin of india standard industry approaches have been used to carry out capital cost and operational cost estimates based on initial reservoir simulation modelling results three cases have been considered to encompass the possible range of reservoir production responses in the first case 18 mmscmd of gas is envisaged to be produced from 120 wells for a production period of 10 years in the second case 12 mmscmd of gas is envisaged to be produced from the 120 wells for 16 years in the third case 6 mmscmd of gas is envisaged to be produced from the 120 wells for 30 years the production rates assumed in case 3 best represents what is believed to be the most reasonable production rates as modeled for a gas hydrate accumulation nghp 02 area b site nghp 02 16 drilled during nghp 02 for case 1 an initial determination is that field development is economically viable for prevailing gas price of usd 7 67 mmbtu with npv of 1921 mmusd and irr of 27 87 with a cost of production of usd 4 74 mmbtu for case 2 the study indicates that field development is viable with npv of usd 986 mmusd and irr of 20 27 and cost of production of usd 5 8 mmbtu for case 3 the cost of production is usd 9 mmbtu no production data is available for the gas hydrate accumulations discovered during nghp 02 in the offshore of india therefore these techno economic results generated in this study can only be validated after matching the results from future pilot production testing under actual field conditions

physical property characteristics of gas hydrate bearing reservoir and associated seal sediments collected during nghp 02 in the krishna godavari basin in the offshore of india abstract india s national gas hydrate program expedition 02 nghp 02 was conducted to better understand geologic controls on gas hydrate occurrence and morphology targeting coarse grained sediments along the lower continental slope offshore eastern india this study combines seismic logging while drilling data and a petroleum system approach to provide a regional geologic and lithologic context for 1 gas hydrate morphology and distribution and 2 effects of fine grained sediments clays and other grains smaller than 63 m on gas production in nghp 02 area b in the krishna godavari basin area b seismic data show a buried anticline syncline structure with strong reflectors r1 and r2 that delineate two of the five lithologic units unit i shallowest ii r1 iii iv r2 and v below the bas of gas hydrate stability throughout area b gas hydrate morphology depends on its placement within these units specifically core and grain scale measurements indicate fines content exerts a primary control on the gas hydrate distribution and morphology units i ii and iii are generally fine grained on the anticline crest these units host primarily grain displacing gas hydrate veins linked to pore occupying gas hydrate in thin localized coarser grained deposits diatoms in unit iii increase porosity with depth reaching 70 where it contacts unit iv the gas hydrate reservoir associated with reflector r2 the unit iii lithology and porosity allow fluid and dissolved phase methane to escape unit iv and form gas hydrate in the fine grained overburden within unit iv fine grained layers are interbedded with coarser grained gas hydrate reservoir sands and the fines content even in the sands is high enough to impact hydraulic and mechanical properties during gas production fluid motion during gas production can mobilize fines which can then clog pore throats limiting production rates pore water freshening during gas hydrate dissociation can increase fines mobilization particularly given the smectite identified in the fine grained interbeds

lithofacies characterization of gas hydrate prospects discovered during the national gas hydrate program expedition 02 offshore krishna godavari basin india abstract lithofacies of host sediments associated with gas hydrate reservoirs may have a significant influence on the formation of hydrates the type of sediments and the depositional processes responsible for the gas hydrate bearing sediments along the eastern margin of the india have been studied by integrating core data and logging while drilling downhole logs borehole data correlated with seismic data were used for the interpretation of geological process responsible for gas hydrate formation the acquired seismic profiles were correlated with the downhole logs by identifying the shape of the well logs curves that indicate finning up and blocky patterns turbidite sands and debris flows were also identified from the log and core sediment studies this study identified two prominent types of depositional systems 1 turbidity currents and 2 debris flows were mainly responsible for the deposition of gas hydrate bearing reservoirs in the study area based on these studies two well developed gas hydrate systems have been identified in the krishna godavari basin and hydrates were determined to be distributed mostly in sand dominated facies fine grained sand in the identified turbidite deposits were shown to be a good hydrate reservoir the hydrate bearing sediments in the central part of the krishna godavari basin area c in d6 block consist of mostly debris flows which is consistent with scattered gravel and sand silt sized grains in channel levee systems

postglacial vegetation climate and fire history along the east side of the andes lat 41 42 5 s argentina abstract the history of the low elevation forest and forest steppe ecotone on the east side of the andes is revealed in pollen and charcoal records obtained from mid latitude lakes prior to 15 000 cal yr bp the vegetation was characterized by steppe vegetation with isolated stands of nothofagus the climate was generally dry and the sparse vegetation apparently lacked sufficient fuels to burn extensively after 15 000 cal yr bp a mixture of nothofagus forest and shrubland steppe developed fire activity increased between 13 250 and 11 400 cal yr bp contemporaneous with a regionally defined cold dry period huelmo mascardi cold reversal the early holocene period was characterized by an open nothofagus forest shrubland mosaic and fire frequency was high in dry sites and low in wet sites the data suggest a sharp decrease in moisture eastward from the andes a shift to a surface fire regime occurred at 7500 cal yr bp at the wet site and at 4400 cal yr bp at the dry site preceding the expansion of austrocedrus by 1000 1500 yr the spread of austrocedrus is explained by a shift towards a cooler and wetter climate in the middle and late holocene the change to a surface fire regime is consistent with increased interannual climate variability and the onset or strengthening of enso the present day mixed forest dominated by nothofagus and austrocedrus was established in the last few millennia

estimates of vertical crustal movements along the coast of greece based on mean sea level data mean annual sea level masl data for 25 greek stations were analyzed for the time period 1969 1982 the data from 4 of these were unacceptably poor and the record of 3 stations showed unexplained step functions that were interpreted as errors relative masl between stations showed crustal stability at 10 of the 18 useful stations the standard deviation from the long term average of these stations was 1 8 cm we conclude that if station records are carefully kept in this area crustal movements in excess of 5 cm can be detected by relative masl a comparison of masl data with gravity changes measured in the peloponnese and central greece suggests that vertical movements occurred along a gradient equal to or larger than the free air gradient we conclude that the gravity network should be reoccupied frequently such that the non tectonic effects to be determined from the probable observed gravity changes and the tectonic vertical movements may be better understood a co seismic subsidence of about 5 cm is inferred to have taken place near korinth during the 1981 ms 6 8 earthquake which occurred 20 km n of this tide gauge posidonia during 2 5 years before the 1968 thessaloniki ms 6 6 earthquake sea level was lower than average suggesting possible crustal elevation of 3 6 cm at about 28 km epicentral distance because of the small amplitude of this change we are not certain that it represents crustal uplift at station myrina on limnos a strong and consistent trend of subsidence accumulated a 15 cm change between 1975 and 1980 chios showed a trend of emergence total accumulation about 5 cm while volos showed a trend of subsidence approximately 5 cm total kefalinia appears to have subsided about 10 cm during the data period the six stations along the hellenic arc plate boundary showed nearly constant masl suggesting that crustal stability existed there during the last 14 years

microgravimetry in greece applications to earthquake and volcano eruption prediction abstract the atalanti fault zone in central greece is an area of high seismic risk where destructive large magnitude earthquakes have taken place in the past the microgravimetric network set up in the region to detect gravity changes associated with big tremors has been monitored annually and the observations of the last five years from 1981 to 1986 are presented here all data were analyzed using a newly developed algorithm of network adjustment gravity changes of more than 40 gal were detected after 1982 in the region between atalanti and arkitsa and across the downthrow side of the fault these gravity changes implying uplift and observed only in this very closely monitored part of the network increased gradually in 1983 and 1984 and declined in 1985 the inferred uplift may exceed 200 mm at the center of the bulge applying the bouguer gravity gradient of 0 2 gal mm examination of the water table data from wells in the region suggests that the amplitude of the observed gravity changes is not likely to have been caused by changes in the water level only one third of the observed changes at the most could be thus accounted for since dilatancy cannot be established on the basis of the existing geophysical information there is no evidence for any association between the inferred uplift and the occurrence of a recent tremor in the region m l 4 3 june 6 1986 however it is possible that the aseismic movements monitored in the area after 1982 over a relatively small region in a small time period may offer some additional information about the deformation of the upper crustal layers another application of microgravimetry as part of a multidisciplinary project is being tried out on santonni island which has one of the most active volcanoes in the eastern mediterranean a network of 15 stations has been established there to try to detect upward movements of magma it was set up in 1984 using three lacoste and romberg gravity meters and has been monitored annually since then the rms error of adjustment was 7 0 3 2 and 2 6 gal in 1984 1985 and 1986 respectively small amplitude gravity changes were observed at spme stations in the network attempts to interpret these changes will be made if a clear pattern is confirmed by future observations and in the light of other available geophysical information

synchronisation of sedimentary records using tephra a postglacial tephrochronological model for the chilean lake district abstract well characterised tephra horizons deposited in various sedimentary environments provide a means of synchronising sedimentary archives the use of tephra as a chronological tool is however still widely underutilised in southern chile and argentina in this study we develop a postglacial tephrochronological model for the chilean lake district ca 38 to 42 s by integrating terrestrial and lacustrine records tephra deposits preserved in lake sediments record discrete events even if they do not correspond to primary fallout by combining terrestrial with lacustrine records we obtain the most complete tephrostratigraphic record for the area to date we present glass geochemical and chronological data for key marker horizons that may be used to synchronise sedimentary archives used for palaeoenvironmental palaeoclimatological and palaeoseismological purposes most volcanoes in the studied segment of the southern volcanic zone between llaima and calbuco have produced at least one regional marker deposit resulting from a large explosive eruption magnitude 4 some of which now have a significantly improved age estimate e g the 10 5 ka llaima pumice eruption from llaima volcano others including several units from puyehue cordon caulle are newly described here we also find tephra related to the cha1 eruption from chaiten volcano in lake sediments up to 400 km north from source several clear marker horizons are now identified that should help refine age model reconstructions for various sedimentary archives our chronological model suggests three distinct phases of eruptive activity impacting the area with an early to mid holocene period of relative quiescence extending our tephrochronological framework further south into patagonia will allow a more detailed evaluation of the controls on the occurrence and magnitude of explosive eruptions throughout the postglacial

implications for paleomobility studies of the effects of quaternary volcanism on bioavailable strontium a test case in north patagonia argentina abstract strontium isotopes 87sr 86sr are used as geochemical tracers for paleomobility studies because they display predictable and stable patterns in ecosystems primarily controlled by the underlying geological regimes while bedrock geology is stable over thousands of years geomorphological processes can influence the 87sr 86sr in ecosystems over archeologically relevant timescales among these geomorphological processes the deposition and reworking of volcanic sediments over quaternary timescales are little studied but could be an important control of 87sr 86sr variations in many archeological regions north patagonia is a key archeological region to address animal and human movements and an ideal location to test the influence of quaternary volcanism on 87sr 86sr variation as it is located downwind of major volcanic centers in this study we aim to assess the main environmental and geological controls of bioavailable 87sr 86sr and to build a high resolution isoscape using a machine learning regression framework for forthcoming paleomobility studies we sampled several locations and analyzed different types of samples n 94 the ratios show a limited range of variation which is not related to the bedrock geology rather bioavailable 87sr 86sr variations display a progressive increase going eastward away from the andes following dust aerosol deposition and elevation variations r2 0 71 rmse 0 00041 we argue that this trend relates to the deposition and reworking of unradiogenic volcanic sediments by aeolian fluvial and glacial erosion during the quaternary as most of this sediment reworking occurred during glacial periods the current bioavailable 87sr 86sr variations across the study area likely represent a long term average that varied little during the holocene consequently our isoscape provides a solid base for holocene paleomobility studies in north patagonia and underlines the importance of quaternary volcanism processes for interpreting 87sr 86sr data in paleomobility studies in volcanic regions

tephrostratigraphy of a deep sea sediment sequence off the south chilean margin new insight into the hudson volcanic activity since the last glacial period abstract a detailed tephrostratigraphy study supported by accelerator mass spectrometry ams 14 c dating stable isotope 18 o and geochemical analyses has been carried out from a deep sea core collected offshore the chonos taitao archipelago southern chile close to the main andean volcanic centres of the southern volcanic zone svz counting of glass shards in the drill core revealed the occurrence of twelve ash layers over the last 22 ka bp their provenance was determined by comparing the 14 c age and major element geochemistry of glass shards with tephra recovered in terrestrial fallout deposits from the southern south volcanic zone ssvz four cryptotephra layers in the uppermost part of the studied core 1 9 16 1 ka bp can be confidently correlated to the corresponding cerro hudson volcanic eruptive events hw7 hw3 hw2 and hw1 for the eight remaining tephra layers deposited between 16 1 ka and 20 ka bp no direct correlation is possible with onland volcanic products however the major element geochemistry of the glass shards strongly suggests the cerro hudson as the volcanic source for these tephra on the other hand the lack of two of the largest hudson holocene eruptions 3 6 and 7 5 ka bp in the uppermost part of deep sea core may be linked to changes in the position of the southern westerlies wind belt sww as a response to the climate variability in northern patagonia during the holocene

assessment of gas hydrate accumulations using velocities derived from vertical seismic profiles and acoustic log data in krishna godavari basin india abstract the second indian national gas hydrate program expedition nghp 02 was executed in 2015 in four areas termed as areas a b c and e during this expedition twenty five research sites were drilled and or cored in krishna godavari kg and mahanadi basins eastern indian offshore during nghp 02 zero offset vertical seismic profile vsp data were acquired at three sites sites nghp 02 17 19 and 22 in area b of the kg basin in this study we focus on the three sites in area b of the kg basin where zero offset vsp and downhole acoustic log data are used to assess and characterize the gas hydrate deposits zero offset vsp data are correlated with wireline log surface seismic and synthetic seismic data to characterize and delineate gas hydrate accumulations in the kg basin low velocities ranging from 1500 to 1650 m s are observed in the unconsolidated shallow sedimentary section above gas hydrate bearing units whereas very high velocities are observed in the acquired acoustic log and vsp data in the gas hydrate bearing sedimentary sections the vsp derived interval velocities range from 2000 to 3000 m s in the depth interval between 267 and 287 m below sea floor mbsf at site nghp 02 17 between 1650 and 1750 m s in the depth interval between 306 and 366 mbsf at site nghp 02 19 and between 1700 and 1800 m s in the depth interval between 198 and 290 mbsf at site nghp 02 22 gas hydrates are distributed both as pore filling and fracture filling at all three sites however high concentrations are only observed as pore filling morphology we estimate the amount of gas hydrate considering both isotropic pore filling and anisotropic fracture filling acoustic reservoir models our estimations of gas hydrate saturation match well with the available pressure core data and suggest that high gas hydrate concentrations to nearly 85 of pore space are distributed in a load bearing morphology

human subsistence and environmental stability during the last 2200 years in epullan chica cave northwestern patagonia argentina a perspective from the zooarchaeological record abstract the faunal content from epullan chica archaeological site ech thereafter a small cave located in northwestern patagonia argentina was studied from taphonomic and paleoenvironmental points of view this cave is placed in the ecotone between monte desert and the patagonian steppe in the middle limay river basin was occupied since the end of the late holocene zooarchaeological evidence retrieved from ech is diverse including fresh water mollusk shells diplodon chilensis eggshell and bone fragments of rheidae bones and teeth of large lama guanicoe medium e g chaetophractus villosus conepatus chinga and micro sized several species of sigmodontine and caviomorph rodents mammals most of the recorded taxa were the result of human exploitation however owl pellets preserved in the sediments and other taphonomic signatures clearly indicate that avian predators are responsible for part of the micromammal record micromammal abundances during the last 2 2 ka bp are suggestive of a relative environmental stability around ech at least until the beginning of the last century in this sense late holocene landscapes were dominated by open steppe areas and large rocky outcrops with minor changes in humidity and temperature during this period

holocene stability and recent dramatic changes in micromammalian communities of northwestern patagonia abstract micromammalian fossil sequences of two classical archaeological sites cueva traful i cti and cueva epullan grande ll both in the province of neuquen northwestern patagonia argentina were studied these sequences cover the entire holocene with assemblages mainly composed by rodent and marsupial remains accumulated by owls both sites are located near the ecotone fringes of the major vegetation units currently present in patagonia forest patagonian steppe cti and patagonian steppe monte desert ll comparisons between fossil and recent owl pellet samples in a regional approach indicated that micromammal communities remained stable over the major part of the last 10 ka with some minor expansion of desert adapted taxa to the west since the middle holocene and a dramatic change in the assemblages during the last 100 150 years two alternative but not contradictory explanations can be presented to interpret the stable period first climate environmental changes were not of sufficient magnitude to produce a clear reorganization of micromammal communities forest did not invade cti surroundings and monte did not reach around ll second the basic structure of northwestern patagonian steppe micromammal communities was resilient to minor or moderate climate environmental changes the strong shift depicted in the studied sequences in very recent times 100 150 years can be linked to human impact on the regional environment this change involves a deep restructuration of small mammal communities ranging from virtual extirpations of some species to dramatic increments of opportunistic taxa a century of sheep overgrazing coupled with the introduction of exotic shrubs was the main factor driving the configuration of present small mammal assemblages in northwestern patagonia

geologic implications of gas hydrates in the offshore of india krishna godavari basin mahanadi basin andaman sea kerala konkan basin gas hydrate resource assessments that indicate enormous global volumes of gas present within hydrate accumulations have been one of the primary driving forces behind the growing interest in gas hydrates gas hydrate volumetric estimates in recent years have focused on documenting the geologic parameters in the gas hydrate petroleum system that control the occurrence of gas hydrates in nature the primary goals of this report are to review our present understanding of the geologic controls on the occurrence of gas hydrate in the offshore of india and to document the application of the petroleum system approach to the study of gas hydrates national gas hydrate program of india executed the national gas hydrate program expedition 01 nghp 01 in 2006 in four areas located on the eastern and western margins of the indian peninsula and in the andaman sea these areas have experienced very different tectonic and depositional histories the peninsular margins are passive continental margins resulting from a series of rifting episodes during the breakup and dispersion of gondwanaland to form the present indian ocean the andaman sea is bounded on its western side by a convergent margin where the indian plate lithosphere is being subducted beneath southeast asia nghp 01 drilled logged and or cored 15 sites 31 holes in the krishna godavari basin 4 sites 5 holes in the mahanadi basin 1 site 2 holes in the andaman sea and 1 site 1 hole in the kerala konkan basin holes were drilled using standard drilling methods for the purpose of logging while drilling and dedicated wireline logging as well as through the use of a variety of standard coring systems and specialized pressure coring systems nghp 01 yielded evidence of gas hydrate from downhole log and core data obtained from all the sites in the krishna godavari basin the mahanadi basin and in the andaman sea the site drilled in the kerala konkan basin during nghp 01 did not yield any evidence of gas hydrate most of the downhole log inferred gas hydrate and core recovered gas hydrate were characterized as either fracture filling in clay dominated sediments or as pore filling or grain displacement particles disseminated in both fine and coarse grained sediments geochemical analyses of gases obtained from sediment cores recovered during nghp 01 indicated that the gas in most all of the hydrates in the offshore of india is derived from microbial sources only one site in the andaman sea exhibited limited evidence of a thermogenic gas source the gas hydrate petroleum system concept has been used to effectively characterize the geologic controls on the occurrence of gas hydrates in the offshore of india