preserved flora and organics in impact melt breccias impact cratering can destroy life from local to global scales and result in sudden turnovers of dominant genera and or species here we report that it can also preserve components of the local biology present at the time of impact we have investigated floral matter encapsulated within cenozoic era impact glasses produced by separate bolide impacts into the loessoid sediments of argentina that occurred between 9 2 ma miocene and 6 ka holocene the encapsulation preserved not only macro scale morphological biosignatures such as vascular bundles veins phytoliths and papillae but also structures down to the cellular level in the best preserved samples we also found evidence for organic matter while fossilization typically occurs over an extended time period as minerals slowly replace organic matter and the host rock lithifies under pressure the process documented here is instantaneous preservation of morphological and chemical biosignatures in impact events can provide snapshots of the ecology in environments that do not otherwise promote a diverse fossil record we suggest that this would provide a new strategy for identifying signs of possible early life on ancient mars where similar target conditions once existed

diversity of iron and silica precipitation by microbial mats in hydrothermal waters iceland implications for precambrian iron formations direct examination of microbial mats from icelandic hot springs with transmission electron microscopy and energy dispersive x ray spectroscopy revealed a consortium of bacterial cells in varying stages of mineralization differences in observed mineralogy largelyreflectdifferencesinthechemistryofthehydrothermalwaters silica richspheroids formedepicellularlyoncellwallsandsurroundingsheathsandcapsulesofmicroorganisms and insomecases intracellularlywhenpresumablythecell s hadlysed commonly these precipitateswereobservedcoalescingtoformamatrixofamorphoussilicathatcompletely encapsulated the cells and or replaced their cytoplasmic material however in other cells the precipitates were composed of amorphous granules made exclusively of iron and silica inapproximatelyequalproportions atonelocality thebacteriaformedseveralepicellular iron minerals ranging from iron mineralized capsules tofine grained spheroids of amorphous ferric hydroxide and acicular aggregates of goethite the complete encrustation of bacterial cells by silica iron or a combination of both may greatly enhance their preservation potential such that these mineralized microorganisms may conceivably represent future microfossils thus we may be witnessing contemporaneous biomineralization processes that are similar to those of the geologic past particularly with regard to the origin of some precambrian banded iron formations

pedogenic origin of dolomite in a basaltic weathering profile kohala peninsula hawaii we document stoichiometric dolomite occurring in a nonsaline quaternary soil on the kohala peninsula northwestern hawaii geologic constraints and geochemical and isotopic data confirm that this dolomite is not the result of marine influence or wind blown dust the strontium isotopic composition of the dolomite 87sr 87sr 0 7045 0 7048 is indicative of its derivation primarily from the weathering of basaltic parent material rather than from meteoric water or seawater infiltration of soil waters with elevated mg ca 1 derived from alteration of ferromagnesian minerals such as olivine likely led to dolomitization of early precipitated soil calcite and or to direct dolomite precipitation in the profile this demonstrates that well ordered dolomite can form in a nonmarine environment at temperatures 100 c without undergoing burial diagenesis

life on mars evaluation of the evidence within martian meteorites alh84001 nakhla and shergotty abstract analyses both support and are in opposition to the hypothesis that the martian meteorite alh84001 contains evidence for possible biogenic activity on mars new observations in two additional martian meteorites nakhla 1 3 ga old and shergotty 300 165 ma old indicate possible biogenic features features in the three martian meteorites compare favorably with the accepted criteria for terrestrial microfossils and evidence for early life on the earth there is strong evidence for the presence of indigenous reduced carbon biogenic magnetite and the low temperature formation of carbonate globules the morphological similarities between terrestrial microfossils biofilms and the features found in the three martian meteorites are intriguing but have not been conclusively proven every investigation must recognize the possibility of terrestrial contamination of the meteorites whether or not the meteorites are martian the search for evidence of ancient life in martian meteorites has emphasized the difficulties confronting the scientific community with the respect to the positive identification of evidence of past biogenic activity

multi scale study of the role of the biofilm in the formation of minerals and fabrics in calcareous tufa abstract three sites of actively forming tufa two barrage systems and one terraced slope system located in northern calabria italy and in north east england have been investigated with the purpose of studying the neo formed carbonate minerals at the interface with the organic components that compose the associated biofilms several depositional facies are distinguished notably peloidal to aphanitic laminar and dendrolitic fabrics composed of micrite and microsparite and isolated botryoids and continuous crusts composed of sparite all fabrics occurring in all depositional facies are organized into layers with a more or less well developed seasonal cyclicity low mg calcite precipitates more or less constantly during all seasons within the active depositional zone this extends for a few hundred microns upon the external surface of the deposits where the biofilm occurs the latter is composed of a heterogeneous community of green algae filamentous cyanobacteria and other types of prokaryotes actinobacteria and fungi with a variable amount of extracellular polymeric substances eps porous micro columns 50 to 150 m in size separated by interstitial spaces characterize the active depositional zone here precipitation always begins with organomineral nanospheres 10 to 20 nm diameter both along the external surfaces and within internal cavities of the micro columns by replacing degraded organic matter and at point sites suspended within living cyanobacterial tufts along the external surface of their sheaths indicating that the biological activities of the biofilm are crucial with its living organisms and non living organic matter organomineral nanospheres successively agglutinate to form irregular to rod shaped crystal aggregates 100 200 nm in size that with their further agglutination create two basic types of larger more ordered crystal structure polyhedrons in the range of 1 2 m and minute triads of calcite fibres varying in length from 0 4 short triads to 1 m long triads basic crystal structures coalesce to form larger crystals mainly tetrahedrons tens of microns in size that constitute the micro columns

a case study of an outbreak of twin tropical cyclones abstract previous studies have found that twin tropical cyclogenesis typically occurs 2 3 times a year in the pacific ocean during october 1997 however three sets of twin tropical cyclones developed in the central pacific within a single month tropical cyclone archives indicate that this is the only such outbreak from 1969 to 2006 this case study explores the background and synoptic conditions that led to this unique event all three twin tropical cyclogenesis events occurred within a broad and long lasting envelope of warm water low surface pressure active convection and weak or easterly vertical shear westerly winds at the equator and trade easterlies farther poleward created strips of cyclonic vorticity through a deep layer a low pass filter showed that these favorable conditions shifted eastward with time at 1 2 m s 1 in addition to the gradual eastward movement the equatorial westerlies and convection were modulated by higher frequency westward propagation these anomalies appear to have

the termination of the 1997 98 el nino part ii mechanisms of atmospheric change the mechanisms that drove zonal wind stress x changes in the near equatorial pacific at the end of the extreme 1997 98 el nino event are explored using a global atmospheric general circulation model the analysis focuses on three features of the x evolution between october 1997 and may 1998 that were fundamental in driving the oceanic changes at the end of this el nino event i the southward shift of near date line surface zonal wind stress x anomalies beginning november 1997 ii the disappearance of the easterly x from the eastern equatorial pacific eeqp in february 1998 and iii the reappearance of easterly x in the eeqp in may 1998 it is shown that these wind changes represent the deterministic response of the atmosphere to the observed sea surface temperature sst field resulting from changes in the meridional structure of atmospheric convective anomalies in response to the seasonally phase locked meridional movement of the warmest sst the southward shift of the near date line x anomalies at the end of this el nino event was controlled by the seasonal movement of the warmest sst south of the equator which both directly and through its influence on the atmospheric response to changes in sst anomaly brought the convective anomalies from being centered about the equator to being centered south of the equator the disappearance reappearance of easterly eeqp x has only been evident in extreme el nino events and has been associated with the development northward retreat of an equatorial intertropical convergence zone itcz the disappearance return of eeqp easterly x arises in the agcm as the deterministic response to changes in the sst field tied principally to the changes in climatological sst given time invariant extreme el nino ssta and not to changes in the underlying ssta field the disappearance return of eeqp easterly x in late boreal winter late boreal spring is a characteristic atmospheric response to idealized extreme el nino sst anomalies this suggests that the distinctive termination of the 1997 98 el nino event is that to be expected for extreme el nino events

morphological signatures of fault lines in an earthquake prone zone of southern baromura hill north east india a multi sources approach for spatial data analysis this paper aims to assess the morphological signatures of tectonic features faults on the basis of multi sources spatial data analysis for that purpose the present authors selected the southern part of baromura hill of tripura which has been discussed very little in the scientific literatures an extensive field work was done in the assumed faulted areas to understand the geomorphic signatures of faulting in the field gps was used for fixing the ground control points scanned survey of india soi topographical sheets spot pan and land sat band 5 was used for digital analysis an old dem on irs liss iii fcc was also consulted for final mapping two clear lineaments faults were detected from field observation on southern baromura hill apart from these another one was found in the outer part of this hill range an attempt was made to explain the morphological signatures of those faults by density slicing on radiometric data based on emittance of different physical components finally a geomorphic map with main tectonic features of baromura was prepared for future disaster management planning

metallic ion binding by bacillus subtilis implications for the fossilization of microorganisms the silicification of bacterial cells has been followed in a laboratory simulation by electron microscopy and energy dispersive x ray spectroscopy structural degradation of the bacteria was not influenced by silica availability but the remains of degraded cells did promote the precipitation of silica in contrast cells reacted with ferric iron before aging remained intact and structures conforming to the original morphology of the bacteria were preserved by silicification the binding of metallic ions by microbial cells in particular the retention of iron is therefore considered to be an important contributing factor to the fossilization of microorganisms

equatorial pacific easterly wind surges and the onset of la nina events abstractthe processes responsible for the onset of la nina events have not received the same attention as those responsible for the onset of el nino events for which westerly wind events wwes in the tropical pacific have been identified as important contributors results here show that synoptic scale surface easterly wind surges ewss play an important role in the onset of la nina events akin to the role of wwes in the onset of el nino events it is found that ewss are a substantial component of zonal wind stress variance along the equatorial pacific using reanalysis wind stress fields validated against buoy measurements 340 ews events are identified between 1986 and 2012 their distributions in space time and el nino southern oscillation enso state are described about 150 ewss occur during enso neutral conditions during the months associated with la nina initiation and growth april december composites of changes in sea surface temperature anomaly ssta following these 150 events show s

seismic assessment in southern baromura hill northeast india considering geophysical aspects this paper aims to assess the geophysical signatures like morphology and structure of a fault line which is situated in a part of southern baromura hill of tripura northeast india in this work manual observations and technical applications were adopted for understanding the morphological and structural characters of the fault line as tectonic mapping is one of the main objectives of this study the remote sensing technique was used to prepare a tectonic map of the study area geothermal range of the area was measured by unsupervised classification of landsat tm thermal infrared band band 6 the classified thermal band was overlaid by another classified shortwave infrared band band 7 of landsat tm which explains the structural evidences of the study area in addition an automated digital elevation model dem was prepared to assess the morphological characters of the study area particularly near the confluence of r maharani and r gumti to analyse the structural condition of the faulted zone resistivity characters of the rocks were measured by vertical electrical sounding ves method the electrical resistivity character of this area strongly supports that a displacement occurred in this place finally an attempt was made to explain the character of faulting on the basis of morphological signatures and structural evidences for future disaster management planning

sem imaging of bacteria and nannobacteria in carbonate sediments and rocks abstract bacteria and nannobacteria 0 1 m dwarfed forms are abundant in both non etched and gently etched travertines deposited by hot springs in viterbo italy they are also plainly visible in bahama ooids and hardgrounds and in great salt lake aragonite ooids and cements in addition nannobacteria are found in paleozoic and mesozoic rocks because of their extraordinary abundance in some specimens they probably play a prominent role in catalyzing the precipitation of carbonate materials

the association of the evolution of intraseasonal oscillations to enso phase abstract the pacific ocean intraseasonal kelvin wave is a leading oceanic mode that links intraseasonal tropical atmospheric variations with interannual variations in the coupled ocean atmosphere system this study considers the premise that these waves may evolve differently with their associated weather patterns during different phases of el nino southern oscillation enso if atmospheric and oceanic intraseasonal modes interact and evolve differently during various stages of enso this result may provide useful information with regard to the role of these intraseasonal processes in enso evolution this work utilizes signals of the oceanic kelvin wave as a statistical basis for a simple composite averaging technique that is applied during different phases of enso to objectively analyze the evolution of oceanic and the associated portions of atmospheric intraseasonal oscillations results confirm the above premise and suggest that coupling between kelvin waves and atmospheric convection evolves differen

self sedimented diatom mats as agents of exceptional fossil preservation in the oligocene florissant lake beds colorado united states microbial mats play a major role in the formation of exceptionally preserved fossil deposits by overgrowing and binding organic remains and sedimentary particles this minimizes hydrodynamic and biological disruption of dead organisms and sedimentary laminae but published works all implicate prokaryotic cyanobacteria as the microbial agent however exceptionally well preserved macrofossils of the oligocene florissant lake beds colorado united states are enveloped in matted aggregations of mucous secreting pennate diatom frustules it is suggested that the macrobiota became entrapped in mucous secreting mats of surface water blooms of planktonic diatoms in lake florissant as the mats and the incorporated macrobiota were sedimented out of the water column the mucosic mats and their associated bacterial communities arrested decay and promoted preservation of refractory tissues thus by a completely different mechanism the diatom mats fulfilled the same preservational role previously suggested for cyanobacterial mats this hitherto unrecognized mode of preservation may be an important causative factor in the formation of exceptionally preserved lacustrine fossil biotas

elemental mapping of exceptionally preserved carbonaceous compression fossils abstract elemental mapping offers rapid qualitative analysis of the mineralogy of exceptionally preserved fossils and importantly can be undertaken on unprepared samples the results of such analyses are sensitive to several variables including the operating conditions particularly accelerating voltage and the composition of the material analysed the higher the accelerating voltage employed and the lower the atomic number of the material impacted by the electron beam the larger the excitation volume in effect a greater thickness of the specimen that contributes to the resultant elemental map fossil non biomineralised arthropods are commonly preserved as carbonaceous compresssions the cuticle is organically preserved and in hand specimen essentially two dimensional the external and internal surfaces of this cuticle may be coated by authigenic minerals examples include arthropods from the middle cambrian burgess shale exceptional fauna it is theoretically possible that the proportion of the total counts generated by a thin surficial film of low atomic number e g a carbonaceous cuticle will be insufficient to distinguish it as a peak above the background spectrum i e it will be effectively transparent in elemental maps simulated energy dispersive x ray spectra for a windowless ed detector suggest that at an accelerating voltage of 15 kev a carbon layer less than about 0 2 m thick will be undetectable and at 5 kev a layer less than a few hundred angstroms thick these values will increase if the energy dispersive spectrometer is fitted with a super ultra thin window

a 250 000 year climatic record from great basin vein calcite implications for milankovitch theory a continuous record of oxygen 18 18o variations in the continental hydrosphere during the middle to late pleistocene has been obtained from a uranium series dated calcitic vein in the southern great basin the vein was deposited from ground water that moved through devils hole an open fault zone at ash meadows nevada between 50 and 310 ka thousand years ago the configuration of the 18o versus time curve closely resembles the marine and antarctic ice core vostok 18o curves however the u th dates indicate that the last interglacial stage marine oxygen isotope stage 5 began before 147 3 ka at least 17 000 years earlier than indicated by the marine 18o record and 7 000 years earlier than indicated by the less well dated antarctic 18o record this discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine 18o chronology may need revision and that orbital forcing may not be the principal cause of the pleistocene ice ages

massive ice of the tuktoyaktuk area western arctic coast canada the extensive coastal exposure of massive underground ice at peninsula point southwest of tuktoyaktuk northwest territories is believed to be intrasedimental ice the ice grew beneath a frozen d

permo pennsylvanian palaeotemperatures from fe oxide and phyllosilicate δ18o values abstract the oxygen isotope composition of fossil roots that have been permineralized by hematite are presented from eight different stratigraphic levels spanning the upper pennsylvanian and lower permian strata of north central texas hematite 18o values range from 0 4 to 3 7 the most negative 18o values occur in the upper pennsylvanian strata and there is a progressive trend toward more positive 18o values upward through the lower permian strata this stratigraphic pattern is similar in magnitude and style to 18o values reported for penecontemporaneous authigenic palaeosol phyllosilicates and calcites suggesting that all three minerals record similar paragenetic histories that are probably attributed to temporal palaeoenvironmental changes across the late pennsylvanian and early permian landscapes palaeotemperature estimates based on paired 18o values between penecontemporaneous hematite and phyllosilicate samples suggest these minerals co precipitated at relatively low temperatures that are consistent with a supergene origin in a low latitude soil forming environment hematite phyllosilicate 18o pairs indicate 1 relatively low soil temperatures 24 3 c during deposition of the upper pennsylvanian strata followed by 2 a considerable rise in soil temperatures 35 37 3 c during deposition of the lowermost permian strata significantly d and 18o values of contemporaneous phyllosilicates provide single mineral palaeotemperature estimates that are analytically indistinguishable from temperature estimates based on hematite phyllosilicate oxygen isotope pairs the results between the two temperature proxy methods suggest that the inferred large temperature change across the upper pennsylvanian lower permian boundary might be taken seriously if real such a significant climate change would have undoubtedly had far reaching ecological effects within this region of pangaea notably there are important lithological and palaeobotanical changes such as disappearance of coal and coal swamp floras across the upper pennsylvanian early permian boundary of north central texas that may be consistent with major climatic change toward warmer conditions

non destructive multiple approaches to interpret the preservation of plant fossils implications for calcium rich permineralizations permineralized fossil coniferous woods from the pliocene of dunarobba umbria italy and the jurassic of swindon wiltshire england were studied using non destructive techniques on uncoated polished thin sections to elucidate their preservational history specimens were observed using transmitted light polarized light reflected light under oil and cathodoluminescence selected areas were studied using a variable pressure sem in backscattered electron mode this allowed uncoated specimens to be examined and elemental distributions to be determined using an energy dispersive x ray microanalyser the data were used to interpret details of the permineralization history results reveal that anatomical interpretations based merely on observations of thin sections in transmitted light can be very misleading and could potentially affect the application of permineralized plant fossils for example in evolutionary biology palaeoclimate analysis and isotope geochemistry

late permian continental sediments in the se iberian ranges eastern spain petrological and mineralogical characteristics and palaeoenvironmental significance abstract a detailed mineralogical and petrological study and the analysis of paleosol profiles in continental alluvial sediments of the late permian in the se iberian ranges spain allow us to infer the significant environmental changes that occurred during this time period three parts have been distinguished in the late permian sediments alcotas formation the lower part includes abundant and well preserved carbonate paleosol profiles and fine grained sediments made up by quartz feldspar hematite and illite with scarce kaolinite the preservation of dolomicrite in some paleosols suggests that they originally developed as dolocretes in an arid to semi arid climate with marked seasonality a change towards more humid and acid conditions can be deduced from the presence of siderite and goethite in paleosols in the middle part of the alcotas formation moreover the presence of plant remains coal beds and or carbonaceous shales at the top of the middle part and the lack of carbonate paleosols in the upper part of the formation would indicate a further step towards acid conditions these conditions would increase until the early triassic as indicated by the lack of carbonates and the presence of sr rich aluminium phosphate sulphates aps minerals at the base of the triassic canizar formation which clearly indicates extreme acid conditions during the permian triassic transition of the study area

fossil wood from the middle cretaceous moreno hill formation unique expressions of wood mineralization and implications for the processes of wood preservation abstract the cretaceous turonian moreno hill formation of west central new mexico provides an opportune isotaphonomic setting to study wood preservation because both carbonized and mineralized wood are commonly found within the same sediments and often within individual specimens petrographic reflectance maceral and chemical analyses were used to compare and characterize mineralized and carbonized wood from the study site to investigate biases which influence mode of preservation coal in the form of coal inclusions is the most common form of fossil wood and mineralized wood is also widespread in the formation two striking specimens of in situ coalified stumps are particularly informative because each includes a mineralized ring that appears to represent the former location of sapwood most of the mineralized samples are primarily composed of quartz but a few specimens are predominantly mineralized with apatite calcite is present in charcoal samples where it permineralized but never replaced organic carbon this study points to two key factors that influence mineralization wood permeability and the chemical alteration of the wood prior to incorporation into the sediment the patterns of mineralization are consistent with hypothesized microbial involvement in the mineralization process the coexistence of coal and mineralized tissues in some samples suggests that the processes of silicification and phosphatization co occurred with coalification and that these processes are competitive within individual pieces of wood as such various stages of wood degradation have been preserved in mineralized samples from the moreno hill formation the study suggests that coal inclusions and mineralized wood coal associations may also be common in other ancient sediments even though weathering may obscure their presence such information is important for paleoecological and paleoenvironmental studies which utilize the occurrence of fossil wood to help reconstruct floral composition or climatic conditions

occurrence and significance of microbialites in the uplifted tasmaloum reef sw espiritu santo sw pacific abstract in the sw pacific ocean subduction of the d entrecasteaux ridge system has caused rapid uplift of the central new hebrides island arc the maximum uplift rate of 6 mm yr 1 occurs along the southwest coast of espiritu santo island near tasmaloum the tasmaloum uplifted reef sequence internal structure which is strongly linked to its tectonic context was investigated through a series of drill holes to depths up to 42 m although a stable tropical coast would undergo approximately 120 m of post glacial sea level rise the net relative sea level rise on such a rapidly uplifting coast is only about 20 m colonization of the tasmaloum fringing reef occurred by 24 ka upon a pre reef substrate composed of a thick bioclastic sand formation accumulated during the last glacial period during the post glacial sea level rise the vertical succession of reef assemblages reflects environmental and bathymetric variations controlled by the interplay of rapid but variable rates of sea level rise and more or less constant uplift of 5 6 mm yr 1 microbialite crusts composed of high magnesian calcite laminae occur in the tasmaloum reef from 20 to 6 ka and are particularly abundant from 16 to 10 ka the development of microbialite crusts is related to nutrient enrichment of interstitial waters through mixing with meteoric groundwater after 6 ka when sea level ceased rising in the region and continuing uplift caused rapid emergence of the reef microbialites disappear within the subtidal assemblages several explanations can be put forward for their disappearance in particular nutrient input changes are a likely cause a new hydrologic and oceanographic regime was established when sea level ceased rising this change was accompanied by warming of tropical waters

morphological signatures of fault lines in an earthquake prone zone of southern baromura hill north east india a multi source approach for spatial data analysis a critical review in a recent work dey et al environ earth sci 59 353 361 2009 presented some new observations on the southern part of one of the anticlinal ridges of tripura viz the baromura range the work incorporated a number of irregularities and misinterpretations that need to be addressed to avoid future confusion the present article critically reviews dey et al s paper to bring out its inaccuracies

permafrost response to surface temperature change and its implications for the 40 000 year surface temperature history at prudhoe bay alaska the geothermal data of lachenbruch et al 1982 in ice bearing permafrost at prudhoe bay are interpreted in terms of the temperature history on a time scale of 40 000 years or longer to this end two theories are developed a forward theory to calculate the response of ice bearing permafrost to a surface temperature disturbance and an inverse theory to calculate parameters characterizing the surface temperature history from suitable measurements in this permafrost the inverse theory shows that two pieces of information characterizing the surface temperature history on a long time scale and the equilibrium geothermal heat flux can usually be determined but the results depend upon the quality of the data the structure of the surface temperature disturbance and the timing of the measurements the memory of the permafrost may range from near zero to hundreds of thousands of years the geothermal data indicate that the prudhoe bay ground surface temperature has a 40 000 year average of minus 10 9 plus minus 3 0c and a value at glacial maximum of minus 10 9 plus minus 4 6c the limits correspond to the estimated uncertainties in the data and they depend somewhat on the structure of the surface temperature disturbance over the last 40 000 years or so the minus 10 9c temperaturemore is the same as that which prevailed before the 1 8 k warming of the past century the limits placed on the variation of the ground surface temperature by this interpretation are not in accord with limits placed by some existing interpretations of other paleoclimatic indicators it is concluded that a consistent understanding of climate history and geothermal regime in northern alaska does not yet exist less

estimates of interseismic deformation in northeast india from gps measurements abstract estimates of interseismic deformation in northeastern india based on gps measurements at eight permanent stations 2003 2006 and six campaign sites 1997 2006 are presented here the euler pole of rotation of indian tectonic plate in itrf2000 determined from the present data set is located at 51 7 0 5 n 15 1 1 5 e with angular velocity of 0 469 0 01 myr 1 the results show that there is a statistically insignificant present day active deformation within the shillong plateau and in the foreland spur north of the plateau in the brahmaputra valley convergence rate of the northeastern gps sites with respect to the igs station lhasa along baselines that are normal to the himalayan arc in this region is 16 0 5 mm yr this represents the arc normal indo eurasian convergence rate across the northeastern boundary similar to arc normal convergence rates determined in central nepal along the himalayan arc however unlike central nepal in the arunachal himalaya the 16 mm yr shortening is distributed between the lesser as well as higher and tethyan himalayas baselines between sites on the indo burmese fold and thrust belt ibftb and shillong plateau indicate variations in the shortening rate from 1 5 mm yr on the tripura mizoram salient trs south of the plateau to 6 mm yr in the imphal recess ir to the east and 8 mm yr in naga salient ns to the northeast this suggests that the deformation in the ibftb is segmented into n s blocks along e w transverse zones exhibiting dextral slip between ns ir and sinistral slip between ir and trs baselines between the ibftb sites also show 10 0 6 mm yr convergence pointing to the existence of an active transverse zone between aizawl and imphal

sedimentology of rock avalanche deposits case study and review abstract detailed sedimentological studies concerning different facies types and the factors influencing their development such as lithology topography substrates etc were carried out at the carbonate tschirgant rockslide rock avalanche deposit in the eastern alps of austria several depositional facies and sub facies have been identified at this and other sites by many researchers these facies are found throughout the debris regardless of depth or travel distance and result from highly heterogeneous stress distributions in time and space during emplacement one of the most important recent observations in terms of emplacement dynamics is that shear is not confined to the base but is distributed throughout the debris except the coarse carapace due to the preservation of source stratigraphy in these non turbulent mass movements any horizontal facies or grain size variations need to be regarded in context since they strongly depend on source stratigraphy and hence the spatial distribution of lithologies i e geological units of different mechanical properties for example some lithologies do not form a boulder carapace due to absence of large in situ blocks in the source rock mass however at tschirgant slight facies maturation with distance within the same lithology is observed i e clast fragmentation progresses to create the distinct facies characteristic grain size distribution only after some distance travelled these details are revealed through facies based sampling and analysis studies based on bulk sampling in some cases observed progressively reduced grain sizes with distance and depth which might be a function of added variations within different facies sampled together in this paper the wealth of observations on rockslide and rock avalanche sedimentology of the past decades is combined with a detailed case study of a lithologically relatively simple deposit to outline global and site specific depositional structures and facies with the aim to summarize review and refine the current state of knowledge on rock avalanche and rockslide emplacement processes

enhancement of leaf fossilization potential by bacterial biofilms terrestrial leaf fossils often form through authigenic preservation in which the leaf surface is coated by a variety of minerals especially iron oxides the mechanism of this fossilization is unclear because the largely hydrophobic leaf surfaces do not readily bind metal ions previously proposed mechanisms for mineral encrustation include precipitation of minerals in sediment pore space and precipitation of iron oxides at the surface by decay produced co 2 here we demonstrate that diverse bacterial species rapidly colonize leaf surfaces and form a biofilm within days of the leaf9s entry into a stream environment experimental mineralization of fresh and biofilm coated leaves indicates that leaves without biofilm do not mineralize but leaves with biofilms rapidly adsorb metal ions such as fe 3 onto the anionic biofilm surface where the ions form ferrihydrite once these mineralized leaves are buried by the sediment they are more likely to be converted to fossils than non mineralized leaves examination of a fossil leaf surface by scanning electron microscopy shows bacteria sized structures resembling those found in biofilms these experimental data imply that bacterial colonization of leaves may be an essential prerequisite for authigenic preservation

cambrian burgess shale animals replicated in clay minerals although the evolutionary importance of the burgess shale is universally acknowledged there is disagreement on the mode of preservation of the fossils after burial elemental mapping demonstrates that the relative abundance of elements varies between different anatomical features of the specimens these differences reflect the compositions of the minerals that replicated the decaying organism which were controlled by contrasts in tissue chemistry delicate morphological details are replicated in the elemental maps showing that authigenic mineralization was fundamental to preserving these fossils even though some organic remains are also present

organized convective systems in the tropical western pacific as a process in general circulation models a toga coare case study we examine the large scale effects of organized convective systems in the tropical western pacific observed during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare in a case study approach we examine realizations of a supercluster associated with the onset of the december 1992 westerly wind burst in the t213 operational medium range weather forecasting model of the european centre for medium range weather forecasts ecmwf we idealize a supercluster as a hierarchy of three interacting scales namely organized cumulonimbus c 1 mesoscale convective systems c 2 and the supercluster component c 3 it is shown that the ecmwf model represents this hierarchy as a c 3 like surrogate whose influence dominates the effect of parametrized convection this causes over prediction of the model tendencies which in the case of zonal momentum is explained in elementary terms the structure of the resolved scale momentum flux is explained by moncrieff s 1992 archetypal theory of organized convection which has been verified against observations and cloud resolving model data sets the parametrization of subgrid scale convective momentum flux in the ecmwf model based on a momentum mixing concept produces subgrid scale tendencies that are physically different from transports associated with cumulonimbus convection in a shear flow we outline a strategy for parametrizing the momentum flux by the c 1 component based on the archetypal model the c 2 component which is part resolved and part parametrized is at odds with the assumptions of scale separation underpinning parametrization it is argued that this component should be represented as part of the prognostic treatment of convectively generated cirrus finally we suggest cloud resolving modelling studies to further quantify the structure and large scale impact of superclusters in a westerly wind burst environment ranging from idealized models to models having data assimilation capability

dolomite mountains and the origin of the dolomite rock of which they mainly consist historical developments and new perspectives beginning in the late 18th century the dolomite mountains in northern italy have been the location for major sedimentological developments from the discovery of the mineral dolomite to the formulation of the coral reef hypothesis to explain the origin of the massive dolomite structures that define the splendid scenery of the region further the dolomite mountains have inspired voluminous research into the origin of dolomite questioning whether dolomite is a primary precipitate or a secondary replacement product recently with the recognition that microbes can mediate dolomite precipitation a new geomicrobiological approach combining the study of modern natural environments with bacterial culture experiments is now being used to calibrate or interpret microbial evidence derived from the dolomite rock record this three pronged methodology applied to the study of dolomite formation holds great promise for future research into the dolomite problem and provides a new impetus to revisit the dolomite mountains in the 21st century

chemosynthetic microbialites in the devonian carbonate mounds of hamar laghdad anti atlas morocco abstract veins cutting across the devonian conical mounds of the hamar laghdad ridge eastern anti atlas morocco were the carriers of geofluids although not completely determined the composition of these fluids seems related to hydrothermal and seepage fluxes that were the primary contributors to the establishment of sub seafloor cryptic environments linking deeper fluid sources to the seafloor the optical and scanning electron microscope investigation of the laminated carbonate infill of these veins has revealed that they consist of stromatolite and oncolite like fabrics in the early and middle devonian mounds the laminated carbonates contain morphologies that are attributable to microbially mediated processes that in turn suggest a direct biological contribution to the deposition of the veins infill microbial evidence include rod shaped and cocci clusters embedded in amorphous membranes iron rich filaments organized as mat like and biodictyon filamentous aggregates or isolated filaments microbial clotted textures and peloids moreover the oncoids from the veins of the middle devonian hollard mound have been interpreted as the mineral replacement of crypto microorganisms as frutexites other microbial evidence are biominerals and include carbonate with spheroids and pyrite framboids in which typifying hydrocarbon seep environments the hollard mound which is the only one with a well documented origin by hydrocarbon seepage shares a number of geomicrobiological evidence with other early devonian mounds these evidence which are supplemented by 13 c depleted data suggest that the infill of the veins system in the hamar laghdad mounds would be the product of chemotrophic chemosynthetic microbial communities that are adapted to crypto habitats sustained by hydrocarbon and other components fluid fluxes

sedimentation and basin fill history of the neogene clastic succession exposed in the southeastern fold belt of the bengal basin bangladesh a high resolution sequence stratigraphic approach abstract the tertiary basin fill history of the bengal basin suffers from oversimplification the interpretation of the sedimentary history of the basin should be consistent with the evolution of its three geo tectonic provinces namely western northeastern and eastern each province has its own basin generation and sediment fill history related mainly to the indo burmese and subordinately to the indo tibetan plate convergence this paper is mainly concerned with facies and facies sequence analysis of the neogene clastic succession within the subduction related active margin setting oblique convergence in the southeastern fold belt of the bengal basin detailed fieldwork was carried out in the sitapahar anticline of the rangamati area and the mirinja anticline of the lama area the study shows that the exposed neogene succession represents an overall basinward progradation from deep marine through shallow marine to continental fluvial environments based on regionally correlatable erosion surfaces the entire succession 3000 m thick has been grouped into three composite sequences c b and a from oldest to youngest composite sequence c begins with deep water base of slope clastics overlain by thick slope mud that passes upward into shallow marine and nearshore clastics composite sequence b characteristically depicts tide dominated open marine to coastal depositional systems with evidence of cyclic marine regression and transgression repetitive occurrence of incised channel tidal inlet tidal ridge shoal tidal flat and other tidal deposits is separated by shelfal mudstone most of the sandbodies contain a full spectrum of tide generated structures e g herringbone cross bedding bundle structure mud couplet bipolar cross lamination with reactivation surfaces tidal bedding storm activities appear to have played a subordinate role in the mid and inner shelf region rizocorallium rosselia planolites and zoophycos are the dominant ichnofacies within the shelfal mudstone this paralic sedimentation of neogene succession in the study area can serve as a good point of reference for tide dominated regressive shelf depositional systems the top of the composite sequence b is marked by a pronounced erosion surface indicating the final phase of marine regression followed by the gradual establishment of continental fluvial depositional systems represented by composite sequence a in this composite sequence stacked channel bars of low sinuosity braided rivers gradually pass upsequence into high sinuosity meandering river deposits a sequence stratigraphic approach has been adopted to interpret the basin fill history with respect to relative sea level changes and to subdivide the rock record into several sequences and units systems tracts and parasequences based on identified bounding discontinuities such as transgressive erosion surface tes regressive erosion surface res marine flooding surface mfs and incised valley floor ivf this approach provides new insight for both exploration and exploitation strategy for hydrocarbon plays that may prove vital to the oil companies engaged in exploration activities in the bengal basin it is strongly recommended here that the traditional lithostratigraphic classification of this part of the basin which is based on the assam stratigraphy be abandoned or at least revised a tentative allostratigraphic scheme is presented and it is suggested that to formalize the scheme further study both surface and subsurface is needed

goethite calcite and organic matter from permian and triassic soils carbon isotopes and co2 concentrations abstract pedogenic goethites in each of two early permian paleosols appear to record mixing of two isotopically distinct co2 components atmospheric co2 and co2 from in situ oxidation of organic matter the 13c values measured for the fe co3 oh component in solid solution in these permian goethites are 13 5 for the lower leonardian 283 ma bp paleosol mcgoeth and 13 9 for the upper leonardian 270 ma bp paleosol sap these goethites contain the most 13c rich fe co3 oh measured to date for pedogenic goethites crystallized in soils exhibiting mixing of the two aforementioned co2 components 13c measured for 43 organic matter samples in the lower leonardian waggoner ranch fm has an average value of 20 3 1 1 1s the average value yields a calculated early permian atmospheric p co 2 value of about 1 pal but the scatter in the measured 13c values of organic matter permits a calculated maximum p co 2 of 11 pal pal present atmospheric level measured values of the mole fraction of fe co3 oh in mcgoeth and sap correspond to soil co2 concentrations in the early permian paleosol profiles of 54 000 and 50 000 ppmv respectively such high soil co2 concentrations are similar to modern soils in warm wet environments the average 13c values of pedogenic calcite from 9 paleosol profiles stratigraphically associated with mcgoeth waggoner ranch fm range from 6 5 to 4 4 with a mean 13c value for all profiles of 5 4 thus the value of 13c between the pedogenic calcite data set and mcgoeth is 8 1 0 9 which is in reasonable accord with the value of 7 7 expected if atmospheric p co 2 and organic matter 13c values were the same for both paleosol types furthermore the atmospheric p co 2 calculated for the early permian from the average measured carbon isotopic compositions of the paleosol calcite and organic matter is also analytically indistinguishable from 1 pal with a maximum calculated atmospheric p co 2 permitted by one standard deviation of the organic matter 13c value of 5 pal if however measured average 13c values of the plant organic matter are more positive than the original soil organic matter as a result of diagenetic loss of 13c depleted labile organic compounds calculated permian atmospheric p co 2 using these 13c enriched organic values would underestimate the actual atmospheric p co 2 using either goethite or calcite this is the first stratigraphically constrained intrabasinal study to compare ancient atmospheric co2 concentrations calculated from pedogenic goethite and calcite these results demonstrate that the two different proxies record the same information about atmospheric co2 the fe co3 oh component in pedogenic goethite from a triassic paleosol in utah is significantly enriched in 13c relative to fe co3 oh in goethites from soils in which there are mixtures of two isotopic co2 components field relationships and the 13c value 1 9 of the triassic goethite indicate that this ancient paleosol profile experienced mixing of three isotopically distinct co2 components at the time of goethite crystallization the three components were probably atmospheric co2 co2 from in situ oxidation of organic matter and co2 from in situ dissolution of preexisting calcite although mixing of three isotopically distinct co2 components as recorded by fe co3 oh in goethite has been described in modern soil this is the first example from a documented paleosol its preservation affirms the need for careful case by case assessment of ancient paleosols to establish that goethite in any particular soil is likely to be a valid proxy of atmospheric p co 2

microscopic calcite dendrites in cold water tufa implications for nucleation of micrite and cement dendritic calcite forms in an active cold water tufa system in association with extracellular polymeric substances eps that discontinuously coat bryophytes and cyanobacteria dendrites consist of 100 200 nm thick calcite fibres that form 3d lattice like domains in each dendrite domain fibres have three structurally equal orientations which correspond in disposition to radii from the centre of a calcite unit cell to the convex triple face junctions on its surface fibres do not form in the orientation of the c axis the external form of each dendrite has the shape of half of a shortened octahedron with an upper triangular surface parallel to the substrate dendrite nucleation takes place on or in microbial eps whether microbial cells are present or not and is probably effected by attraction of ca 2 cations to negatively charged eps together with co2 degassing and concomitant ph increase of supersaturated spring water in stream splash zones ensuing dendrite growth is abiogenic and controlled by diffusion dendrite c axes are perpendicular to the substrate probably because the negative charge of eps forces the orientation of ca 2 and co 2 planes within the developing dendrite crystal to be parallel to the eps film surface dendrites are eventually filled and overgrown by solid syntaxial calcite which gradually and completely obliterates the dendrites as more familiar calcite crystal forms develop no trace of the dendritic nucleus remains in the rock record calcite crystal nucleation may take place by this mechanism in many marine and meteoric settings given that microbial eps is now assumed to be virtually ubiquitous in these environments this phenomenon could contribute to the development of familiar fabrics such as marine micrite cement and fibrous calcite cement radial ooids peloids abiogenic stromatolites sea floor precipitates microbialites tufa travertine speleothems and some meteoric cements it may also contribute to the substrate normal orientation of c axes of common cement fabrics

collision of the ganges brahmaputra delta with the burma arc implications for earthquake hazard abstract we take a fresh look at the topography structure and seismicity of the ganges brahmaputra delta gbd burma arc collision zone in order to reevaluate the nature of the accretionary prism and its seismic potential the gbd the world s largest delta has been built from sediments eroded from the himalayan collision these sediments prograded the continental margin of the indian subcontinent by 400 km forming a huge sediment pile that is now entering the burma arc subduction zone subduction of oceanic lithosphere with 20 km sediment thickness is fueling the growth of an active accretionary prism exposed on land the prism starts at an apex south of the gbd shelf edge at 18 n and widens northwards to form a broad triangle that may be up to 300 km wide at its northern limit the front of the prism is blind buried by the gbd sediments thus the deformation front extends 100 km west of the surface fold belt beneath the comilla tract which is uplifted by 3 4 m relative to the delta this accretionary prism has the lowest surface slope of any active subduction zone the gradient of the prism is only 0 1 rising to 0 5 in the forearc region to the east this low slope is consistent with the high level of overpressure found in the subsurface and indicates a very weak detachment since its onset the collision of the gbd and burma arc has expanded westward at 2 cm yr and propagated southwards at 5 cm yr seismic hazard in the gbd is largely unknown intermediate size earthquakes are associated with surface ruptures and fold growth in the external part of the prism however the possibility of large subduction ruptures has not been accounted for and may be higher than generally believed although sediment clogged systems are thought to not be able to sustain the stresses and strain weakening behavior required for great earthquakes some of the largest known earthquakes have occurred in heavily sedimented subduction zones a large earthquake in 1762 ruptured 250 km of the southern part of the gbd suggesting large earthquakes are possible there a large but poorly documented earthquake in 1548 damaged population centers at the northern and southern ends of the onshore prism and is the only known candidate for a rupture of the plate boundary along the subaerial part of the gbd burma arc collision zone

an abandoned channel fill with exquisitely preserved plants in redbeds of the clear fork formation texas usa an early permian water dependent habitat on the arid plains of pangea abstract a well preserved plant assemblage at the colwell creek pond locality of leonardian kungurian age provides an opportunity to evaluate taphonomic conditions in a dryland alluvial setting a narrow channel body incised to 5 m depth through red paleo vertisols contains 2 m of varicolored laminated mudstone with graded layers and plant material x ray diffraction analysis of individual laminae indicates the presence of chlorite illite kaolinite and mixed layer clay with hematite in red and gray layers and goethite in yellow brown laminae no carbonate was identified and the total organic carbon content is minimal the fine sediment accumulated in a shallow abandoned channel from suspension and gentle underflows probably linked to seasonal inflow and analysis of lamina thickness suggests that standing water may have persisted for up to a few millennia the preservation of lamination is attributed to a lack of bioturbation possibly linked to a paucity of subsurface oxygen low productivity elevated salinity rapid deposition or a combination of these factors minimal bioturbation may also reflect the limited use of freshwater ecospace during the early permian clay rich paleo vertisols complete the fill with drab root traces that indicate growth of vegetation in a strongly seasonal setting abundant plant material in the laminated beds includes branches of walchian conifers the possible cycadophyte taeniopteris spp and the comioid possible peltasperm auritifolia waggoneri they were derived from an adjacent riparian zone and preserved as 3d goethite petrifactions much of the foliage shows evidence of arthropod herbivory although a humid climatic episode cannot be ruled out the exceptional abundance and preservation of the plants probably reflects the persistence of an oxbow lake on a relatively arid alluvial plain where riparian plants experienced periodic moisture stress but had access to groundwater nearly year round rapid burial in standing water the lack of bioturbation in the laminated sediments and early biomineralization probably explain the exceptional preservation of the plant remains

permafrost heat flow and the geothermal regime at prudhoe bay alaska temperature measurements through permafrost in the oil field at prudhoe bay alaska combined with laboratory measurements of the thermal conductivity of drill cuttings permit an evaluation of in situ thermal properties and an understanding of the general factors that control the geothermal regime a sharp contrast in temperature gradient at approx 600 m represents a contrast in thermal conductivity caused by the downward change from interstitial ice to interstitial water at the base of permafrost under near steady state conditions interpretation of the gradient contrast in terms of a simple mode for the conductivity of an aggregate yields the mean ice content approx 39 and thermal conductivities for the frozen and thawed section 8 1 and 4 7 mcal cm s sup 0 c respectively these results yield a heat flow of approx 1 3 hfu which is similar to other values on the alaskan arctic coast the anomalously deep permafrost is a result of the anomalously high conductivity of the siliceous ice rich sediments curvature in the upper 160 m of the temperature profiles represents a warming of approx 1 8 sup 0 c of the mean surface temperature and a net accumulation of 5 6 kcal cm sup 2 by the solid earth surface during the last 100 years or so rising sea levelmore and thawing of ice rich sea cliffs probably caused the shoreline to advance tens of kilometers in the last 20 000 years inundating a portion of the continental shelf that is presently the target of intensive oil exploration a simple conduction model suggests that this recently inundated region is underlain by near melting ice rich permafrost to depths of 300 500 m its presence is important to seismic interpretations in oil exploration and to engineering considerations in oil production with confirmation of the permafrost configuration by offshore drilling heat conduction models can yield reliable new information on the chronology of arctic shorelines less

application of a proportional integral control for the estimation of static formation temperatures in oil wells a strategy based on proportional integral pi feedback control was applied to solve an inverse heat transfer problem for estimating static formation temperatures sfts from logged temperatures in oil wells the pi control feedbacks the error between logged and simulated temperatures during the shut in time process existing sft proposal thus mathematically speaking an inverse heat transfer problem was solved in this way since sft represents the initial conditions which are unknown to solve the partial differential equations governing the heat transfer process in the wellbore formation system the mathematical model considers transient convective heat transfer due to circulation losses to the rock surrounding a well the methodology was tested analyzing two oil wells mb 3007 and mb 3009 from the gulf of mexico and results were compared against two classic methods the method presented in this work needs only one temperature measurement for each fixed depth to estimate the sft

trench slope controlled deep sea clastics in the exposed lower surma group in the southeastern fold belt of the bengal basin bangladesh abstract deltaic to shallow marine neritic depositional settings have until now been the accepted interpretation for the neogene surma group of rocks exposed throughout the southeastern fold belt of the bengal basin the present study revises the earlier views and proposes some new insights on the basis of detailed field studies carried out in the sitapahar anticline rangamati area and in the mirinja anticline lama area it is here proposed that the surma group succession represents an overall basinward progradation from deep marine to coastal marine depositional settings sedimentological evidence strongly suggests that the lower part of the surma group represents a slope apron the growth of which is thought to have been governed by a westward migrating accretionary prism complex within the active margin setting of the indo burmese plate convergence thin packages of distinct turbidity current generated deposits together with some slump and debris flow deposits contained within thicker intervals of mudstone characterize the lowermost exposed unit of the surma group in the sitapahar anticline the overlying slope deposits are essentially mudstone dominated comparable deep sea clastics with thicker intervals of sandstone turbidites contained within a submarine canyon are present in the mirinja anticline this new model suggests that it may be timely to re evaluate the existing stratigraphic and tectonic framework of the eastern bengal basin

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr