a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

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

r selected benthic foraminifera with associated bacterial colonies in upper pleistocene sediments of the ross sea antarctica implications for calcium carbonate preservation investigations on foraminifera from upper pleistocene holocene sediments cored in the continental slope of the western ross sea 2383 m water depth revealed that the record of calcareous assemblages was restricted to a limited time interval approximately 6 kyr and characterized by a dominance of phytodetritus exploiting taxa such as alabaminella weddellensis and epistominella exigua rod shaped calcified fossil bacteria infest the partially dissolved calcareous foraminiferal surfaces either as clusters or as isolated cells suggesting that significant changes from underto oversaturated conditions with respect to calcium carbonate in the chemistry of the seawater developed before the final burial of the foraminiferal tests we postulate that bacterial activity on a microenvironmental scale interface and pore water in the sea floor could influence pore water conditions in such a way as to preserve carbonate in deep marine regions where environmental conditions usually prevent the establishment of carbonate secreting communities 1999 elsevier science b v all rights reserved

potential evidence of fossilised neoproterozoic deep life sem observations on calcite veins from oppaminda creek arkaroola south australia scanning electron microscopy revealed micron sized globular and coccoid objects associated with filaments and mucus like patches in antitaxial fibrous calcite veins from oppaminda creek northern flinders ranges south australia chemically the objects only differ from their calcite caco3 matrix by a higher sulphur content the 585 ma veins formed at about 3 6 km below the surface fluid inclusions indicate a temperature of formation of about 60 80 c and not exceeding 100 c a non biogenic origin of the objects is discussed but considered unlikely instead morphology chemistry and size distribution all indicate that the objects are fossilised microbes that lived in the veins at the time and depth of vein formation

the roussillon basin s france a case study to distinguish local and regional events between 6 and 3 ma the roussillon basin is a non silled miocene sedimentary basin filling a late oligocene early miocene graben the basin was intensively impacted by the 2 messinian fluvial erosion as evidenced in exposed sections in seismic profiles and in deep boreholes drilled for hydrocarbon exploration as the basin was open to the mediterranean sea the huge drop in sea level at the peak of the messinian salinity crisis is clearly recorded along with the subsequent sudden marine reflooding and the resulting prograding sedimentary filling particularly in gilbert type fan deltas here the messinian erosional surface mes is accurately mapped in a high resolution document which corrects the confusion resulting from the set of 1 50 000 scale regional maps aim of the 3d reconstruction of the mes is to modernize geological mapping a crucial challenge for mediterranean and peripheral areas thanks to a reliable chronostratigraphy provided by planktonic foraminifers calcareous nannofossils micro and macro mammal remains paleomagnetism and a 10 be cosmogenic nuclide derived study our reconstruction is one of the most comprehensive models of changes in sea level from 6 to 3 ma after the marine reflooding of the mediterranean basin at 5 46 ma the fluctuations in sea level recorded in the roussillon basin were forced by global changes following reflooding the prades large olistostrome collapsed prepared by the previous exhumation along the canigou fault the olistostrome is a good example of a local accident resulting from messinian events the exceptional changes in sea level at the peak of the messinian salinity crisis deeply marked the roussillon basin momentarily overprinting the pyrenean orogenesis key words roussillon basin messinian subaerial erosion zanclean sedimentary filling prades olistostrome

constitutive relationships and physical basis of fault strength due to flash heating 1 we develop a model of fault strength loss resulting from phase change at asperity contacts due to flash heating that considers a distribution of contact sizes and nonsteady state evolution of fault strength with displacement laboratory faulting experiments conducted at high sliding velocities which show dramatic strength reduction below the threshold for bulk melting are well fit by the model the predicted slip speed for the onset of weakening is in the range of 0 05 to 2 m s qualitatively consistent with the limited published observations for this model earthquake stress drops and effective shear fracture energy should be linearly pressure dependent whereas the onset speed may be pressure independent or weakly pressure dependent on the basis of the theory flash weakening is expected to produce large dynamic stress drops small effective shear fracture energy and undershoot estimates of the threshold slip speed stress drop and fracture energy are uncertain due to poor knowledge of the average contact dimension shear zone thickness and gouge particle size at seismogenic depths

issues involved in a martian sample return integrity preservation and the curation and analysis planning team for extraterrestrial materials captem position returning geological samples from mars is the next logical step as part of an integrated exploration program and is the critical subsequent stage in the search for evidence of life on the red planet analysis of such samples on earth will generally produce data of superior accuracy and precision than can be accomplished in situ on the martian surface and such data will be invaluable in providing ground truth for remotely sensed observations however obtaining meaningful data requires that the samples returned to earth suffer little or preferably no compositional or morphological changes during collection on mars transit to earth entry into earth s atmosphere impact on the surface and long term curation this paper presents recommendations from nasa s committee for curation and analysis planning team for extraterrestrial materials captem for preserving the integrity of martian samples during a return mission potential contaminants include dead bacteria on the outbound spacecraft and materials that come into contact with the samples during collection and storage therefore it is recommended that the spacecraft be sterilized and cleaned at least to pathfinder standards with the components that interact with the samples having a higher degree of cleanliness furthermore it is recommended that only pure homogeneous materials should be used for components that come into contact with the samples the adverse effects of temperature on the samples are explored and it is demonstrated that heat sterilization or undue temperature increases in transit or reentry have the potential to destroy important mineralogical and geochemical information concomitant with this will be degassing of the samples and stable isotopic fractionation therefore it is recommended that samples be kept at 240 k or below during transit reentry and curation it is further recommended that heat sterilization not be used except in extreme circumstances and other sterilization techniques such as radiation be explored while the purpose of this paper is not to design a sample return mission the recommendations presented here are intended to act as guidelines for returning martian samples in their pristine state in essence any procedure or piece of equipment that has the potential to compromise the pristinity of martian samples during the collection transportation or curation needs to be fully evaluated by a scientific committee with the requisite expertise prior to implementation captem is willing to serve in such a capacity if requested by nasa

temporal variation in calcification in marine cyanobacteria periods of widespread abundance of calcified cyanobacteria in marine environments are here termed cyanobacterial calcification episodes cces intense such episodes occurred in the cambrian early ordovician late devonian and mid late triassic mild episodes occurred during the early carboniferous and jurassic early cretaceous possible episodes during parts of the silurian and permian await confirmation cyanobacterial calcification is not obligate but is dependent upon environmental factors favouring carbonate precipitation cyanobacterial calcification episodes are therefore interpreted as reflecting periods of increased marine carbonate precipitation this is supported by the general abundance of marine carbonate cements and oolites during cyanobacterial calcification episodes cyanobacterial calcification episodes correspond with phanerozoic periods for which elevated global temperatures have been inferred they do not appear to correlate closely with inferred changes in aragonite calcite facilitation the sandberg curve and p co2 through time it is concluded that variations in the precipitation rates of abiotic and quasi abiotic marine carbonates through time have been controlled primarily by temperature the mineralogy of these precipitates appears instead to have been mainly influenced by p co2 and the mg ca ratio also linked to sea level through plate tectonic processes thus the controls on rate and mineralogy of precipitation were independent of one another

regional isostatic response to messinian salinity crisis events abstract the salinity crisis of the mediterranean during messinian time was one of the most dramatic episodes of oceanic change of the past 20 or so million years resulting in the deposition of kilometer thick evaporitic sequences a large and rapid drawdown of the mediterranean water level caused erosion and deposition of non marine sediments in a large lago mare basin both the surface loading by the lower messinian evaporites and the removal of the water load resulted in isostatic flexural rebound that significantly affected river canyons and topographic slopes we use flexure models to quantitatively predict possible signatures of these events and verify these expectations at well studied margins the highly irregular shape of the reconstructed basin calls for a three dimensional model near basin margins plate bending effects are most pronounced which is why flexure is particularly important for a relatively narrow basin like the mediterranean we focus on one specific sea level scenario for the messinian salinity crisis where most of the evaporite load was deposited during a sea level highstand followed by a rapid desiccation evaporite loading at current sea level is expected to cause subsidence of the deep basins by hundreds of meters and simultaneous uplift of continental parts of the margins differential uplift may lead to significant slope angle changes and thus gravity flows the relative scarcity of lower evaporite sequences along the margins may be a result of these phenomena normal faulting of lower evaporite and older sediments and rocks is expected on the margins desiccation enhances erosion of the freshly exposed continental shelf and slope subsidence and riverbed sedimentation occurs on the continental margins and significant uplift towards the basin center reverse faulting is predicted at the margins finally regional isostatic uplift following zanclean flooding is predicted to destabilize margin slope deposits and to cause marginal uplift river down cutting and normal faulting

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

biofilms microbial mats and microbe particle interactions electron microscope observations from diatomaceous sediments sediments and diatoms from the mudflats of the bay of bourgneuf in western france were examined in an electron microscope study of biofilms and microbial mats the sediments were kept in an aquarium for study and a diatom culture was made of the benthic diatoms the sediment biofilm was composed of exopolymeric substances eps incorporated clay particles and rarely bacteria this film coated all particles at the sediment water interface its surface morphology reflected its composition and internal structure thin films were smooth whilst a lumpy structure or incorporated fibrils produced either a mammillated or ropy surface and clays in the structure gave rise to a flaky morphology at shallow depths in the sediment column 0 5 cm the biofilm was already degraded the biofilm coating degraded diatom frustules in the benthic diatom culture consisted of eps and bacteria and presented a ragged appearance microbial mats occurred on the surface of the fresh littoral sediments as well as those in the aquarium and on the wall of the aquarium the mat on the surface of the aquarium sediments had an open structure with webs of fibrils and bacteria in the pore space it formed in a relatively quiet environment pore space was more limited in the mat from the surface of the fresh littoral sediments in which direct contact between biofilm coated particles was common in the exposed environment of the aquarium wall there was a thick resistant coating of eps in addition to binding particles together the presence of mats and biofilms in sediments affects sediment physical properties such as porosity and permeability the flux of dissolved substances in pore waters and the dissolution of particles and can therefore influence early diagenesis mats and biofilms seem to be more readily preserved in the geological record than the micro organisms such as bacteria which produce them their identification in the sedimentary record would greatly aid interpretation of sediment genesis and evaluation of the microbial role in sediment formation

microfossils and possible microfossils from the early archean onverwacht group barberton mountain land south africa there is widespread textural evidence for microbial activity in the cherts of the early archean onverwacht group layers with fine carbonaceous laminations resembling fossil microbial mats are abundant in the cherty metasediments of the predominantly basaltic hooggenoeg and kromberg formations in rare cases filamentous microfossils are associated with the laminae the morphologies of the fossils as well as the texture of the encompassing laminae suggest an affinity to modern mat dwelling cyanobacteria or bacteria a variety of spheroidal and ellipsoidal structures present in cherts of the hooggenoeg and kromberg formations resemble modern coccoidal bacteria and bacterial structures including spores the development of spores may have enabled early microorganisms to survive the relatively harsh surficial conditions including the effects of very large meteorite impacts on the young earth

microfossils or pseudofossils cu co sulphide microfeatures in the neoproterozoic katangan supergroup democratic republic of congo abstract in this paper we investigate a group of microfeatures discovered in the mineralised neoproterozoic mines subgroup of the katangan copperbelt democratic republic of congo drc at the mashitu south cu co deposit the features are bacillus shaped composed of cu co sulphides and occur within syn diagenetic apatite veins in a low grade metasedimentary shale they exhibit a range of evidence for biogenicity including indicators of cellular complexity and were therefore investigated as candidate microfossils of chasmoendolithic prokaryotes however our study found that the features are likely to be pseudofossils formed from abiogenic rutile crystals which have been replaced by sulphides in such a way as to mimic biogenicity indicators this method of sulphide replacement adds to the list of possible false positives in the search for early life and emphasises the importance for micropalaeontological studies to consider such features with a sceptical holistic approach and rigorous scientific method

paleoenvironmental and taphonomic controls on the occurrence of paleoproterozoic microbial communities in the 1 88ga ferriman group labrador trough canada abstract chert and iron formation from the ferriman group ca 1 88 ga labrador trough canada contain an exceptional assemblage of fossil bacteria and biofilms preserved within a well defined stratigraphic framework lithofacies associations suggest that microbes were restricted to suboxic shallow water environments through three sea level cycles microfossils are preserved as chert or sedimentary apatite francolite in hematite rich peritidal facies nearshore evaporation and fe redox pumping of silica drove rapid penecontemporaneous silicification of microbial mats in some communities breakdown of organic matter and fe redox pumping of pore water phosphate caused their syndepositional phosphatization preservation of bacteria was precluded in deeper settings because these processes could not operate at an anoxic seafloor filamentous forms dominate microbial morphologies secondary electron imaging of freshly broken surfaces shows filaments that are similar in size and shape to modern bacteria filaments vary from 0 5 and 1 m wide and reach tens of m in length they commonly envelop chert and iron oxide grains which stabilized the seafloor and contributed to firmground development the filamentous morphology similar mat forming behavior and suboxic paleoenvironments where these fossils lived are consistent to those of modern fe oxidizing bacteria and some cyanobacteria associated organic matter with low 13 c values is also present most values vary between ca 38 and 20 which is consistent with isotopic fractionation by such bacteria unlike modern settings however their distribution was restricted to shallow marine and peritidal environments where photosynthetically produced oxygen oases likely impinged on the seafloor although fe oxidizing bacteria were possibly important in forming some iron formation facies in the ferriman group physiochemical precipitation of fe oxyhydr oxides caused by photosynthetic oxygen was also probably widespread in the photic zone across the shelf this study demonstrates that a combined microanalytical sedimentologic and stratigraphic analysis of fossil bacteria not only yields a more detailed picture of the precambrian biosphere but also highlights the importance of taphonomy in the search for early life

biosignatures and microbial fossils in endolithic microbial communities colonizing ca sulfate crusts in the atacama desert abstract since the description of microbial communities colonizing ca sulfate crusts in the atacama desert there has been much interest in the mechanisms that could lead to the formation and preservation of biosignatures or microbial fossils of these communities a key to understanding physico chemical processes of taphonomy and early diagenesis is to examine microfossils in their natural environment in this study we characterize organomineral traces and microbial fossils found around microbial communities present in these ca sulfate crusts through scanning electron microscopy microanalytical eds and raman spectroscopy techniques calcium carbonate precipitates were detected around remnants of cryptoendolithic algae beneath the crust surface as what seems to be the final step in the organomineralization of these cryptoendolithic communities we also observed alga cell remains permineralized by mg si rich minerals inside gypsum crystals additionally mg si bearing minerals formed a web like structure within the hypoendolithic cyanobacterial habitat via permineralization of extracellular polymeric substances our observations indicate that despite the extremely hyperarid environment microenvironmental conditions may be appropriate for the formation of biosignatures and microbial fossils of extinct endolithic microbial communities a model of the possible organomineralization processes involved is presented

association between messinian drainage network formation and major tectonic activity in the marche apennines italy the marche apennines italy offer an excellent opportunity to constrain the temporal and spatial relationships between drainage network formation and tectonic activity using a combination of field data seismic lines and boreholes we show that the main deformation phase took place during the messinian when the area affected by the messinian sea level drop emerged and evolved from marine to continental conditions the results highlight that during the messinian emersion a drainage network developed contemporaneously with an increase in tectonic activity that could be related to sea level fall and river erosion the present day river system which is dominated by transverse rivers that cut straight across the tectonic grain is located in older messinian palaeovalleys even though the region was subsequently covered by water until the late pliocene early pleistocene

observational constraints on the fracture energy of subduction zone earthquakes we relate seismologically observable parameters such as radiated energy seismic moment rupture area and rupture speed to the dynamics of faulting to achieve this objective we computed the radiated energy for 23 subduction zone earthquakes recorded between 1992 and 2001 most of these earthquakes have a magnitude m w 7 5 but we also included some smaller m w 6 7 well studied subduction zone earthquakes and six crustal earthquakes we compiled static stress drop estimates for these 29 earthquakes from literature and used a slip weakening model to determine the radiation efficiency of these earthquakes we also determined the rupture speed of these earthquakes from literature from fracture mechanics fracture energy and hence radiation efficiency can be related to the rupture speed the radiation efficiencies estimated from the partitioning of energy as given by the slip weakening model are consistent with the rupture speed estimated for these earthquakes most earthquakes have radiation efficiencies between 0 25 and 1 and are hence efficient in generating seismic waves but tsunami earthquakes and two deep earthquakes the 1994 bolivia and the 1999 russia china border earthquakes have very small radiation efficiencies 0 25 and hence dissipate a large amount of energy during faulting we suggest that differences in the radiation efficiencies of different types of earthquakes could be due to fundamental differences in their rupture mechanics in deep events the energy is probably dissipated in thermal processes in the fault zone while it is possible that the morphology of the trench causes large energy dissipation during the rupture process of tsunami earthquakes

fracture surface energy of the punchbowl fault san andreas system the energetics of earthquake rupture slip weakening and rupture surface formation are poorly understood by measuring the energy associated with fracture damage along the punchbowl fault in the devil s punchbowl los angeles county park part of the san andreas system chester et al show that the fracture surface energy for rupture along a mature fault of this type accounts for only a small fraction of the energy released during large earthquakes as determined by seismologists this suggests that mechanisms such as melt lubrication and thermal pressurization are responsible for slip weakening fracture energy is a form of latent heat required to create an earthquake rupture surface and is related to parameters governing rupture propagation and processes of slip weakening1 2 3 fracture energy has been estimated from seismological and experimental rock deformation data4 5 6 7 8 yet its magnitude mechanisms of rupture surface formation and processes leading to slip weakening are not well defined8 9 10 here we quantify structural observations of the punchbowl fault a large displacement exhumed fault11 12 in the san andreas fault system and show that the energy required to create the fracture surface area in the fault is about 300 times greater than seismological estimates would predict for a single large earthquake if fracture energy is attributed entirely to the production of fracture surfaces then all of the fracture surface area in the punchbowl fault could have been produced by earthquake displacements totalling 1 km but this would only account for a small fraction of the total energy budget and therefore additional processes probably contributed to slip weakening during earthquake rupture

middle archean volcano hydrothermal sequence bacterial microfossil bearing 3 2 ga dixon island formation coastal pilbara terrane australia the 3 2 ga dixon island formation in the cleaverville group of the coastal pilbara terrane australia is one of the most complete and best preserved examples of middle archean oceanic stratigraphy and contains possible microbial material field observations and geochemical evidence suggest that this formation contains a low temperature hydrothermal vent system with a biogenic microbial colony from the archean ocean the dixon island formation is 350 m thick and consists of the rhyolite tuff black chert and varicolored chert members in ascending order the rhyolite tuff member contains many vein swarms such as quartz and black chert veins and highly altered rhyolite tuff layers which are identified as an underground bypass zone for circulating hydrothermal fluid many black chert vein swarms in the rhyolite tuff member imply intensive low temperature hydrothermal activity during deposition of the black chert member which is 10 15 m thick the black chert member is composed of massive black chert laminated black chert dark greenish siliceous shale and tuffaceous laminated chert which are mainly composed of very fine quartz abundant pseudomorphs of silica after aragonite barite and gypsum and a distinctly continuous stromatolite like biomat layer 10 20 cm thick are preserved within the laminated black chert bed the stromatolite like biomat bed is formed of fine iron or iron coated quartz pisolite within fine grained silica the absence of detrital sediment of continental origin and the many vein injections imply that this sedimentary facies represents a pelagic hydrothermal environment at 500 2000 m paleodepth and may have been on the slope of an immature island arc microbial material has been preserved well in the lower part of black chert member the massive black chert has carbonaceous peloids 0 3 2 0 mm in diameter which are similar to those in the black chert veins the massive black chert contains spiral rod and dendrite shaped bacterial material the total organic carbon toc value of massive black chert in the lower part of the black chert member is higher toc 0 15 0 45 than that of the overlying laminated chert section toc 0 02 0 15 and the black chert vein toc 0 1 0 13 and the carbon isotope 13 c values of this lithology 33 to 27 are also lighter than for the black chert veins 29 to 26 and the laminated black chert in the upper part of the black chert member and the varicolored chert member 27 to 13 this evidence suggests that the carbonaceous grains and bacteria shaped material in the lower part of the black chert member are of bio genic origin and were formed close to a low temperature hydrothermal vent system the microbial colony may have been rapidly fossilized by silicification related to hydrothermal activity laminated black chert in the upper part of the black chert and the varicolored chert members may have formed by cyanobacterial sedimentation from the ocean surface

coastal geomorphology of the martian northern plains the paper considers the question of the formation of the outflow channels and valley networks discovered on the martian northern plains during the mariner 9 mission parker and saunders 1987 and parker et al 1987 1989 data are used to describe key features common both in the lower reaches of the outflow channels and within and along the margins of the entire northern plains it is suggested that of the geological processes capable of producing similar morphologies on earth lacustrine or marine deposition and subsequent periglacial modification offer the simplest and most consistent explanation for the suit of features found on mars

stratigraphy and sedimentology of fault controlled backstepping shorefaces middle pliocene of crotone basin southern italy abstract the middle pliocene sedimentary succession of the crotone basin in the calabria peloritani terrane southern italy was deposited during extensional tectonism dominated by a system of horst and half grabens the studied succession spartizzo lagoonal clays and scandale shallow marine deposits is up to 250 m thick and represents a barrier lagoon system that spans a tectonically controlled transgressive phase the succession is internally organised into six higher frequency cycles 20 80 m thick most of these cycles are formed by transgressive lagoonal deposits separated from the overlying regressive shoreface units by a wave ravinement surface lowstand fluvial deposits were recognized locally at the base of the last cycle the shoreface units are up to 50 m thick and typically consist of a coarsening upward succession of isolated to amalgamated hummocky cross strata that merge upwards into swaley and trough cross strata ne trending synsedimentary normal faults strongly controlled the deposition and enhanced subsidence and thickness expansion within the half graben basins

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

evidence for late messinian seismites nijar basin south east spain the feos formation of the nijar basin comprises sediments deposited during the final stage of the messinian salinity crisis when the mediterranean was almost totally isolated levels of soft sediment deformation structures occur in both conglomeratic alluvial sediments deposited close to faults and the hyposaline lago mare facies a laminated and thin bedded succession of whitish chalky marls and intercalated sands alternating with non marine coastal plain deposits deformation structures in the coarse clastics include funnel shaped depressions filled with conglomerate liquefaction dykes terminating downwards in gravel pockets soft sediment mixing bodies chaotic intervals and flame structures evidence for soft sediment deformation in the fine grained lago mare facies comprises syndepositional faulting and fault grading sandstone dykes mixed layers slumping and sliding of sandstone beds convolute bedding and pillar and flame structures the soft sediment deformed intervals resemble those ascribed elsewhere to seismic shaking moreover the study area provides the appropriate conditions for the preservation of deformation structures induced by seismicity such as location in a tectonically active area variable sediment input to produce heterolithic deposits and an absence of bioturbation the vertical distribution of soft sediment deformation implies frequent seismic shocks underlining the importance of seismicity in the betic region during the late messinian when the nijar basin became separated from the sorbas basin to the north the presence of liquefied gravel injections in the marginal facies indicates strong earthquakes m 7 the identification of at least four separate fissured levels within a single lago mare interval suggests a recurrence interval for large magnitude earthquakes of the order of millennia assuming that the cyclicity of the alternating lago mare and continental intervals was precession controlled this suggestion is consistent with the present day seismic activity in se spain

filamentous fossil bacteria from the archean of western australia abstract four morphotypes of structurally preserved filamentous fossil bacteria have been discovered in petrographic thin sections of laminated carbonaceous cherts from the 3500 ma old warrawoona group of northwestern australia these tubular and septate microfossils are interpreted here as being syngenetic with warrawoona sedimentation as such they are apparently the oldest such fossils now known in the geological record the diversity of this assemblage and the evident complexity of its individual components suggest that the beginnings of life on earth may have appreciably pre dated the deposition of the warrawoona sediments

meridiani planum hematite deposit and the search for evidence of life on mars iron mineralization of microorganisms in rock varnish the extensive hematite deposit in meridiani planum was selected as the landing site for the mars exploration rover opportunity because the site may have been favorable to the preservation of evidence of possible prebiotic or biotic processes one of the proposed mechanisms for formation of this deposit involves surface weathering and coatings exemplified on earth by rock varnish microbial life including microcolonial fungi and bacteria is documented in rock varnish matrices from the southwestern united states and australia limited evidence of this life is preserved as cells and cell molds mineralized by iron oxides and hydroxides as well as by manganese oxides such mineralization of microbial cells has previously been demonstrated experimentally and documented in banded iron formations hot spring deposits and ferricrete soils these types of deposits are examples of the four water rock interaction scenarios proposed for formation of the hematite deposit on mars the instrument suite on opportunity has the capability to distinguish among these proposed formation scenarios and possibly to detect traces that are suggestive of preserved martian microbiota however the confirmation of microfossils or preserved biosignatures will likely require the return of samples to terrestrial laboratories

from sub rayleigh to supershear ruptures during stick slip experiments on crustal rocks supershear earthquake ruptures propagate faster than the shear wave velocity although there is evidence that this occurs in nature it has not been experimentally demonstrated with the use of crustal rocks we performed stick slip experiments with westerly granite under controlled upper crustal stress conditions supershear ruptures systematically occur when the normal stress exceeds 43 megapascals mpa with resulting stress drops on the order of 3 to 25 mpa comparable to the stress drops inferred by seismology for crustal earthquakes in our experiments the sub rayleigh to supershear transition length is a few centimeters at most suggesting that the rupture of asperities along a fault may propagate locally at supershear velocities in turn these sudden accelerations and decelerations could play an important role in the generation of high frequency radiation and the overall rupture energy budget

observation of microbial structures in rocks using 3d light microscopy real time 3d light microscopy provides a large depth of field and high resolution which have considerable advantages for the discovery and examination of microbial structures in rocks in highly translucent specimens real time 3d observation in transmitted light offers a greater capability for rapid recognition of microbial features than do other 3d imaging methods such as light microscopy of serial sections or tilted specimens scanning electron microscopy stereology confocal microscopy or computed tomography application of this new technique to samples of precambrian permian cretaceous and pleistocene age reveals an intriguing variety of probable microbial structures particularly in sparry calcites a direct view of the true spatial relationships among microbial structures and between microbial structures and mineral substrates provides essential clues for deciphering the controls on and timing of microbial activity relative to chemical and mechanical processes in rocks

frictional melt and seismic slip 1 frictional melt is implied in a variety of processes such as seismic slip ice skating and meteorite combustion a steady state can be reached when melt is continuously produced and extruded from the sliding interface as shown recently in a number of laboratory rock friction experiments a thin low viscosity high temperature melt layer is formed resulting in low shear resistance a theoretical solution describing the coupling of shear heating thermal diffusion and extrusion is obtained without imposing a priori the melt thickness the steady state shear traction can be approximated at high slip rates by the theoretical form ss n1 4 a under a normal stress n slip rate v radius of contact area r a is a dimensional normalizing factor and w is a characteristic rate although the model offers a rather simplified view of a complex process the predictions are compatible with experimental observations in particular we consider laboratory simulations of seismic slip on earthquake faults a series of high velocity rotary shear experiments on rocks performed for n in the range 1 20 mpa and slip rates in the range 0 5 2 m s 1 is confronted to the theoretical model the behavior is reasonably well reproduced though the effect of radiation loss taking place in the experiment somewhat alters the data the scaling of friction with n r and v in the presence of melt suggests that extrapolation of laboratory measures to real earth is a highly nonlinear nontrivial exercise

the formation of antitaxial calcite veins with well developed fibres oppaminda creek south australia abstract of the several vein types with elongate crystals we distinguish a class of veins with well developed fibres exposed at oppaminda creek south australia these calcite veins are characterised by very limited competition between growing crystals which leads to the development of fibrous crystals with smooth boundaries and which can attain extreme length width ratios fibres are often curved and track the opening trajectory the veins are also characterised by their outwards antitaxial growth starting from a narrow median zone these median zones contain wall rock inclusions and a distinctly different non fibrous internal microstructure such veins continue growing as long as extension is suitably oriented relative to the vein orientation multiple cross cutting vein sets can thus grow simultaneously and can together track over 90 rotation of the fibre growth direction the veins formed by calcite precipitation on both their outer surfaces we suggest that the term antitaxial should be redefined as applying only to those veins that have two simultaneous growth planes at their outer surfaces antitaxial veins grow without further fracturing which sets them apart from other veins that grew by precipitation inside a crack and which only have one single growth plane at the time the veins at oppaminda creek are about 585 ma in age and therefore formed at an estimated 4 6 km depth scanning electron microscope observations revealed about 1 m sized structures which we interpret as fossils of microbes that lived inside the veins at the time of their formation and which may even have played a role in the vein formation these structures would represent the first finds of fossilised life forms of such a combined age and depth

bacteria in the tatahouine meteorite nanometric scale life in rocks we present a study of the textural signature of terrestrial weathering and related biological activity in the tatahouine meteorite scanning and transmission electron microscopy images obtained on the weathered samples of the tatahouine meteorite and surrounding soil show two types of bacteria like forms lying on mineral surfaces 1 rod shaped forms rsf about 70 80 nm wide and ranging from 100 nm to 600 nm in length 2 ovoid forms ovf with diameters between 70 and 300 nm they look like single cells surrounded by a cell wall only na k c o and n with traces of p and s are observed in the bulk of these objects the chemical analyses and electron diffraction patterns confirm that the rsf and ovf cannot be magnetite or other iron oxides iron hydroxides silicates or carbonates the rites of the rsf and ovf are below those commonly observed for bacteria but are very similar to some bacteria like forms described in the martian meteorite alh84001 all the previous observations strongly suggest that they are bacteria or their remnants this conclusion is further supported by microbiological experiments in which pleomorphic bacteria with morphology similar to the ovf and rsf objects are obtained from biological culture of the soil surrounding the meteorite pieces the present results show that bacteriomorphs of diameter less than 100 nm may in fact represent real bacteria or their remnants c 2000 elsevier science b v all rights reserved

middle miocene out of sequence thrusting and successive exhumation in the peloritani mountains sicily late stage evolution of an orogen unraveled by apatite fission track and u th he thermochronometry 1 apatite fission track aft and u th he ahe thermochronometry are applied to constraint the thermal history of the basement rock forming the peloritani mountains in northeast sicily italy aft ages range between 29 0 5 5 ma and 5 5 0 9 ma while ahe ages vary from 19 4 ma to 3 3 ma most aft ages are younger than the overlying terrigenous sequence that in turn postdates the main orogenic phase through the coupling of the thermal modeling with the stratigraphic record a middle miocene thermal event is revealed this event affected an inner intermediate portion of the peloritani mountains and is confined by the distribution of the aft ages 15 ma the u shaped pattern of aft ages along n s transects across the mountain chain is consistent with burial below a thrust stack that is a few km thick created by an out of sequence thrusting phase that affected the inner portion of the belt the tectonic load was then removed initially by erosion enhanced by the high relief at 10 7 ma the difference between young aft and ahe ages is used to infer a rate of exhumation of 0 3 mm yr for this stage the gap between the youngest ahe ages and the sedimentary record above indicate a final exhumation stage with increasing rates of denudation 1 3 mm yr since the pliocene times due to extensional tectonics

the possible role of nannobacteria dwarf bacteria in clay mineral diagenesis and the importance of careful sample preparation in high magnification sem study abstract bacterial textures are present on clay minerals in oligocene frio formation sandstones from the subsurface of the corpus christi area texas in shallower samples beads 0 05 0 1 m in diameter rim the clay flakes at greater depths these beads become more abundant and eventually are perched on the ends of clay filaments of the same diameter we believe that the beads are nannobacteria dwarf forms that have precipitated or transformed the clay minerals during burial of the sediments rosettes of chlorite also contain after hcl etching rows of 0 1 m bodies in contrast kaolinite shows no evidence of bacterial precipitation we review other examples of bacterially precipitated clay minerals a danger present in interpretation of our earlier work and much work of other is the development of nannobacteria looking artifacts caused by gold coating times in excess of one minute we strongly recommend a 30 second coating time bacterial growth of clay minerals may be a very important process both in the surface and subsurface

origin and diagenesis of quaternary travertine shrub fabrics rapolano terme central italy millimetre to centimetre sized arborescent shrub like calcite precipitates are common constituents of hot water travertine shallow pool deposits of quaternary age at rapolano terme tuscany italy in the presently forming travertines the shrubs consist of apparently random associations of i micrite aggregates and ii subhedral to euhedral rhombic spar crystal aggregates in thin section the micrite aggregates appear dark and the spar rhomb aggregates light giving the shrubs a mottled appearance travertines are basically produced by caco3 precipitation due to degassing and evaporation of the spring waters although biological influence may also stimulate precipitation the formation of masses of erect shrubs rather than dense crystal crusts that form on slopes is probably due to limited water flow in the pool environments microbes including bacteria and diatoms are important influences on shrub microfabric and external shape the micrite aggregates are associated with bacteriform bodies seen as tiny rods and spheres the micrite precipitates around these bodies and in adjacent biofilm spar rhomb precipitation appears to be external to the biofilm and may be related to the presence of diatoms which are locally closely associated with the spar rhombs although an essentially inorganic origin particularly for the more euhedral rhombs cannot be ruled out in the older quaternary travertines the original microfabric of the shrubs has been diagenetically altered the original mottled appearance of the shrubs has become uniformly dark and micritic and the evidence for the dual micritic and spar rhomb origin of the shrubs is obscured or destroyed spar micritization of the shrubs is probably due to abiotic and locally biotic dissolution previous studies did not recognize the diagenetic micritization and attributed shrub formation entirely to bacterial activity

recent discoveries of proterozoic microfossils in south central brazil abstract twenty two precambrian microfossiliferous localities seven newly reported here are known from the sao francisco block and associated brasilia fold belt of south central brazil reported from outcrop and drill core samples of mesoand neoproterozoic cherts carbonates and siliciclastics of the 1170 to 950 ma old paranoa group and the 950 to 700 ma old sao francisco supergroup composed of the jequitai formation and the overlying bambui group representatives of nearly 30 genera of proterozoic microfossils chiefly cyanobacteria and subsidiary acritarchs have been reported from these strata preserved mostly within carbonaceous black chert in flat laminated and high relief stromatolites and represent a wide spectrum of environments evidently ranging from nearshore lagoonal to supratidal intertidal subtidal and offshore marine settings contrary to previously held views the microfossils are generally more abundant and better preserved in the older unit paranoa group than in the younger one sao francisco supergroup nevertheless among the newly reported assemblages one from the lower part of the bambui group stands out as probably the best preserved and most diverse microbiota known from any precambrian unit of south america although paleobiologic studies of the brazilian proterozoic are still in a formative stage recent discoveries are highly promising such as the detection in the work presented here of possible differences 1 between the microfossil sizes in stromatolites of the paranoa and bambui groups 2 in the abundance and size of acritarchs with respect to lithology and facies and 3 in the microfossil assemblages preserved in morphologically distinct stromatolites

contribution of bacterially induced oxidation of fe silicates in iron rich ore to laterite formation salobo iocg mine brazil abstract a diverse array of microorganisms found within the uppermost lithosphere can mediate the dissolution and precipitation of minerals and therefore contribute to the formation of laterites the salobo iron oxide copper gold iocg mine in brazil is an ideal environment to examine the specific interaction between iron oxidising bacteria and ferrous iron bearing minerals during formation of a 60 m thick laterite weathering profile we identified bacteria using dna extracted from samples in active weathering zones many of the identified species are capable of oxidising the ferrous iron and or reduced sulphur that occurred in minerals associated with the unweathered rocks of the deposit fe bearing phyllosilicates have been variably altered to clays along cleavage planes by bacterial iron oxidation accelerated weathering of fresh rocks in laboratory scale leaching column experiments was conducted using an endemic acidithiobacillus ferrooxidans ssp previously cultured from the salobo mine there were strong similarities between field samples from the salobo laterite zone and experimental leachate chemistry associated precipitates and fossilised bacteria remnants particularly with respect to ferric oxyhydr oxide formation groundwaters in the salobo laterite zone have circumneutral ph whereas some iron oxidising bacteria thrive in and locally create more acidic conditions ph 3 the leaching experiments showed that bacterially facilitated silicate weathering and bornite cu5fes4 oxidation can consume acid generated by bacterial oxidation reactions creating an effective equilibrium with ferric oxyhydr oxide precipitation however the current acid neutralisation capacity of the ferricrete horizon at the top of the laterite zone was minimal while bacterial activity promoted mineral oxidation and decomposition within the thick laterite at the salobo mine related iron mobility is restricted to the micrometre scale by essentially instantaneous precipitation of ferric oxyhydr oxide that eventually transforms via inorganic dehydration to goethite and hematite similar processes to those described in this study have likely occurred during the formation of many other iron rich laterites

upper messinian conglomerates in calabria southern italy response to orogenic wedge adjustment following mediterranean sea level changes widespread uppermost miocene conglomerate and sandstone along the apenninic maghrebian orogenic belt in the central mediterranean region cannot be explained as a result of the messinian base level falls along the ionian coast of calabria southern italy these rocks were deposited in marine fan deltas and rest in angular unconformity or disconformity upon the internal part of the calabrian accretionary wedge we propose that the upper messinian deposits were produced by internal shortening of the calabrian accretionary wedge as it compensated for the decrease in upper surface slope caused by flexural rebound as the 3 4 km thick ionian water mass evaporated latest miocene pliocene marine inundation reloaded the basin restored the wedge to a critical state and caused the rear part of the wedge again to become tectonically stable this isostatically driven mechanism could explain widespread latest messinian thrust faults and coarse siliciclastic deposits along much of the apenninic maghrebian orogen

exogenous carbonaceous microstructures in early archaean cherts and bifs from the isua greenstone belt implications for the search for life in ancient rocks abstract the microstructure of hf etched samples of early archaean banded iron formations bifs and cherts from the 3 7 b y old isua greenstone belt southwestern greenland was investigated using high resolution scanning electron microscopy equipped with an electron diffraction system capable of analysing light elements the rocks contain both endogenous of internal origin and exogenous of external origin carbonaceous microstructures the former consist of inclusions of graphite and possibly small amorphous carbonaceous particles both embedded in metacherts however further in situ tem studies are needed to verify the endogeneity of the amorphous particles moreover these rocks also contain endolithic microorganisms i e inhabiting cracks in rocks as well as undifferentiated carbonaceous matter that occur in fractures and cracks between grains the microorganisms include cyanobacteria filamentous microorganisms such as fungal hyphae and possibly bacteria as well as large unidentified cells or spores most of the microorganisms appear to have been fossilised the endoliths are evidently younger than the host rock but must have infiltrated at different periods most likely after the inland ice retreated 8000 years ago the presence of endolithic carbonaceous matter in cracks and microfissures in these rocks will affect any analyses of bulk samples such as carbon isotopes and chemical biomarkers as well as analyses of acid macerated residues thus previous isotope measurements made on bifs and cherts from isua may reflect younger contamination rather than an endogenous original signal likewise some of the previously described isuan microorganisms probably represent recent endolithic contamination

sedimentary evolution of the neogene quaternary crotone basin southern italy and relationships with large scale tectonics a sequence stratigraphic approach abstract the crotone basin is a neogene quaternary depocenter developed along the ionian margin of calabria southern italy the basin opening was concomitant with the onset of spreading of the tyrrhenian backarc basin during late serravallian and the subduction of the ionian lithosphere below the calabrian arc the adoption of modern sequence stratigraphic principles to subdivide the basin fill into stratigraphic sequences of different rank bounded by subaerial unconformities has allowed cycles of creation and loss of accommodation mainly related to tectonics to be recognized in particular an alternation between phases of basin subsidence concomitant with spreading of the tyrrhenian backarc basin and forward migration of the arc and phases of compressional or transpressional tectonics accompanied by basin uplift and stopping of arc migration are well recognizable in the basin fill in particular for the late messinian to late pleistocene part of the succession the present study highlights the effectiveness of the sequence stratigraphic method in basin analysis to decipher the effects of large scale tectonic events on sedimentation and ultimately to reconstruct the geodynamic evolution of the central mediterranean

distribution and diagenesis of microfossils from the lower proterozoic duck creek dolomite western australia two distinct generations of microfossils occur in silicified carbonates from a previously undescribed locality of the lower proterozoic duck creek dolomite western australia the earlier generation occurs in discrete organic rich clasts and clots characterized by microquartz anhedra it contains a variety of filamentous and coccoidal fossils in varying states of preservation second generation microfossils consist almost exclusively of well preserved gunflintia minuta filaments that drape clasts or appear to float in clear chalcedony these filaments appear to represent an ecologically distinct assemblage that colonized a substrate containing the partially degraded remains of the first generation community the two assemblages differ significantly in taxonomic frequency distribution from previously described duck creek florules taken together duck creek microfossils exhibit a range of assemblage variability comparable to that found in other lower proterozoic iron formations and ferruginous carbonates with increasing severity of post mortem alteration duck creek microfossils appear to converge morphologically on assemblages of simple microstructures described from early archean cherts two new species are described oscillatoriopsis majuscula and o cuboides the former is among the largest septate filamentous fossils described from any proterozoic formation

microbial pathways and palaeoenvironmental conditions involved in the formation of phosphorite grains safaga district egypt abstract phosphatic grains of the shallow marine phosphorite deposits of egypt are classified as either phosphatic bioclasts preserving biological structure e g skeletal fragments such as fish bones and teeth or phosphatic peloids and intraclasts this study describes the destructive and constructive microbial pathways represented by bioerosion of bones by endolithic cyanobacteria and accretion of phosphatic peloids by bacteria the palaeoenvironmental conditions and post depositional diagenetic history of these grains have also been considered scanning and transmission electron microscopy showed that the phosphatic peloids under transmitted light microscopy are composed mainly of microspheres 0 5 to 2 5 m similar in shape and size to coccoid like bacteria chemical mapping showed that these microspheres are composed of carbonate fluorapatite cfa and surrounded by degraded carbonaceous matrix these grains are suggested to be reworked from pre existing microbial mats during transgressive regressive cycles affecting the southern tethyan campanian maastrichtian shallow continental shelf the bioerosion of phosphatic bones is characterized by a network of meandering microborings that penetrated inward from the bone surface by endolithic cyanobacteria the bioerosion of bones resulted in a gradual centripetal digestion and conversion of bones into micritic phosphate peloids the bioerosion mechanism is probably started in the acidic sheath surrounding cyanobacteria followed by supersaturation of po 4 and reprecipitation of crystalline cfa as electron dense remineralized rims electron microprobe microanalyses showed that the remineralized microbored areas are higher in cao p 2 o 5 and f and depleted in cl relative to unaltered bones a gradual demineralization of remineralized rims followed by dissolution of cyanobacterial cells is probably occurred during diagenesis and meteoric water alteration leaving behind empty microborings bone exposed to meteoric water alteration is lower in cao and p 2 o 5 and higher in f and cl than the unaltered bones understanding bone bioerosion has significant implications for palaeoenvironmental and taphonomic reconstruction archaeological applications and a regional correlation of the late cretaceous to palaeogene phosphogenic province extending from middle east to north africa

neogene quaternary evolution of the forearc and backarc regions between the serre and aspromonte massifs calabria southern italy abstract the role of tectonics in the neogene quaternary evolution of the forearc basin between the serre and aspromonte massifs located in the southern calabria is widely documented in the exposed sedimentary successions the structuration of these different basins is due to the southeastward migration of the calabrian terranes which led to the subduction of the ionian lithosphere and the spreading of the tyrrhenian back arc basin the area is dominantly displaced by two nw se and ne sw oriented regional fault systems these fault systems were active during the infilling of the neogene quaternary basins and represent complex tear fault systems that accommodated stress generated in the accretionary prism during the subduction of the ionian lithosphere furthermore these structures play a relevant role as part of recent seismotectonic processes which controlled the late quaternary geodynamic evolution of the area

fast slip with inhibited temperature rise due to mineral dehydration evidence from experiments on gypsum anomalously low heat flow around active faults has been a recurrent subject of debate over past decades we present a series of high velocity friction experiments on gypsum rock cylinders showing that the temperature of the simulated fault plane is efficiently buffered due to large scale endothermic dehydration reaction the tests were performed at 1 mpa normal stress and a velocity of 1 3 m s 1 while measuring the temperature close to the sliding surface and the relative humidity around the sample the temperature close to the sliding surface is remarkably stable at 100 c during the dehydration reaction of gypsum microstructural and x ray diffraction investigations show that dehydration occurs at the very beginning of the test and progresses into the bulk as slip increases in the hottest parts of the sample anhydrite crystal growth is observed the half thickness of the dehydrated layer ranges from 160 m at 2 m slip to 5 mm at 68 m slip thermodynamic estimates of the energy needed for the dehydration to occur yield values ranging from 10 to 50 of the total mechanical work input the temperature plateau is thus well explained by the energy sink due to the dehydration reaction and the phase change from liquid water into steam we suggest that similar endothermic reactions can efficiently buffer the temperature of fault zones during an earthquake this is a way to explain the low heat flow around active faults and the apparent scarcity of frictional melts in nature

modeling dynamic rupture in a 3d earthquake fault model we propose a fourth order staggered grid finite difference method to study dynamic faulting in three dimensions the method uses an implementation of the boundary conditions on the fault that allows the use of general friction models including slip weakening and rate dependence because the staggered grid method defines stresses and particle velocities at different grid points we preserve symmetry by implementing a two grid row thick fault zone slip is computed between points located at the borders of the fault zone while the two components of shear traction on the fault are forced to be symmetric inside the fault zone we study the properties of the numerical method comparing our simulations with well known properties of seismic ruptures in 3d among the properties that are well modeled by our method are full elastic wave interactions frictional instability rupture initiation from a finite initial patch spontaneous rupture growth at subsonic and supersonic speeds as well as healing by either stopping phases or rate dependent friction we use this method for simulating spontaneous rupture propagation along an arbitrarily loaded planar fault starting from a localized asperity on circular and rectangular faults the shape of the rupture front is close to elliptical and is systematically elongated in the in plane direction of traction drop this elongation is due to the presence of a strong shear stress peak that moves ahead of the rupture in the in plane direction at high initial stresses the rupture front becomes unstable and jumps to super shear speeds in the direction of in plane shear another interesting effect is the development of relatively narrow rupture fronts due to the presence of rate weakening friction the solutions for the thick fault boundary conditions scale with the slip weakening distance do and are stable and reproducible for do greater than about 4 in terms of 2t t ax finally a comparison of scalar and vector boundary conditions for the friction shows that slip is dominant along the direction of the prestress with the largest deviations in slip rate direction occurring near the rupture front and the edges of the fault

detrital modes of the ionian forearc basin fill oligocene quaternary reflect the tectonic evolution of the calabria peloritani terrane southern italy abstract during oligocene neogene time the calabria peloritani terrane cpt a small block of continental lithosphere rifted from the southern margin of the eurasian continent and drifted southeastward to collide with the african continent along the leading edge of the cpt a late oligocene to quaternary mostly siliciclastic succession 2 000 meters thick was deposited in the ionian forearc basin the detritus forming the succession was derived directly from the erosion of the nearby cpt composed of hercynian plutons intruding metasedimentary host rocks contrary to most modern and ancient forearc basins penecontemporaneous volcanic detritus is virtually absent this results from rift related topographic barriers which separated the forearc basin from the associated volcanic arc in spite of an overall quartzofeldspathic continental block provenance the analysis of a large sandstone and conglomerate petrological dataset 228 samples points to three discrete detrital inputs of aphanitic lithic fragments in i late oligocene early miocene ii late messinian and iii quaternary times these petrological variations can be linked to independently determined tectonic events in the western mediterranean which likely modified the lithologic composition of the sediment source terranes input i documents the progressive widespread unroofing of the continental basement of the southern european margin when northwestward subduction of the remnants of the ligurian ocean began input ii is related to widespread intra messinian tectonism possibly due to out of sequence thrusting induced by isostatic readjustments of the perimediterranean orogenic wedges following the messinian drawdown input iii reflects the rapid vertical uplift experienced by the cpt since mid pleistocene time possibly the result of slab detachment along the ionian subduction zone this study indicates that detailed statistical analysis of the detrital modes of ancient terrigenous deposits can be used to identify the tectonic events affecting somewhat petrologically monotonous sediment source areas within small lithospheric terranes

a constitutive scaling law and a unified comprehension for frictional slip failure shear fracture of intact rock and earthquake rupture 1 it is widely recognized that some of the physical quantities inherent in a rupture are scale dependent and the scale dependence is one of the most no facts and features of rupture phenomena the paper addresses how such scale dependent shear rupture of a broad range from laboratory scale frictional slip failure and shear fracture of intact rock to field scale rupture as an earthquake source can be unified by a single constitutive law noting that the earthquake rupture is a mixed process between frictional slip failure and the shear fracture of intact rock it is concluded that the constitutive law for the earthquake rupture be formulated as a unifying law that governs both frictional slip failure and shear fracture of intact rock it is demonstrated that the slip dependent constitutive law is such a unifying law and a constitutive scaling law is derived from laboratory data on both frictional slip failure and shear fracture of intact rock this constitutive scaling law enables one to provide a consistent and unified comprehension for scale dependent physical quantities inherent in the rupture over a broad range from small scale frictional slip failure and shear fracture in the laboratory to large scale earthquake rupture in the field

sedimentary phosphate and associated fossil bacteria in a paleoproterozoic tidal flat in the 1 85 ga michigamme formation michigan usa abstract phosphorus is a nutrient fundamental to life and when it precipitates in modern environments bacteria are intimately involved in its release concentration and mineralization preserved fossil bacteria in phosphate crusts and grains from the ca 1850 million year old bijiki iron formation member of the michigamme formation michigan provide insight into the longevity and nature of this relationship the michigamme formation accumulated near the end of the earth s initial phosphogenic episode ca 2 2 and 1 8 ga to produce one of the first granular phosphorites phosphatic lithofacies consist of fine to medium sand sized francolite peloids concentrated on bedding surfaces in peritidal facies granular beds are up to 2 cm thick and peloids are often partially to completely replaced by dolomite and chert the grains contain organic matter and pyrite framboids that suggest bacterial breakdown of organic matter and bacterial sulfate reduction the peritidal nature of phosphorite in the michigamme formation is in sharp contrast to phanerozoic phosphogenic environments in deeper coastal upwelling settings peritidal settings were well suited for phosphogenesis under the very low oxygen and low dissolved sulfate levels of the paleoproterozoic as cyanobacteria produced oxygen in shallow water and evaporation led to increased sulfate concentrations such concomitant processes helped establish focused redox interfaces in the sediment that chemosynthetic bacterial communities sulfur oxidizers reducers forms that concentrate p and possibly iron oxidizers could exploit phosphate released from organic matter by heterotrophic bacteria and fe redox pumping was further concentrated by these chemotrophs a process that forms late neoproterozoic to phanerozoic phosphorites but on a much larger scale this early example of a granular phosphorite demonstrates that like their phanerozoic counterparts paleoproterozoic phosphorites are the concentrated indirectly biomineralized products of bacterial communities but unlike younger analogs which accumulated across subtidal shelves and shelf margins these ancient deposits formed only in tidal flat settings where phosphogenic redox processes could be established in the sediment from this early beginning the zone of phosphogenesis likely migrated into deeper water settings as oxygen and sulfate levels rose expanding the zone of chemosynthetic bacterial and associated phosphogenesis across the shelf

nanocrystalline slip zones in calcite fault gouge show intense crystallographic preferred orientation crystal plasticity at sub seismic slip rates at 18 150 c a central aim in fault mechanics is to understand the microphysical mechanisms controlling aseismic seismic transitions in fault gouges and to identify microstructural indicators for such transitions we present new data on the slip stability of calcite fault gouges and on microstructural development down to the nanometer scale our experiments consisted of direct shear tests performed dry at slip rates of 0 1 10 m s at a constant normal stress of 50 mpa at 18 150 c the results show a transition from stable to potentially unstable slip above 80 c all samples recovered showed an optical microstructure characterized by narrow 30 40 m wide riedel and boundary shear bands marked by extreme grain comminution and a crystallographic preferred orientation cpo boundary shear bands sectioned using fib sem focused ion beam scanning electron microscopy revealed angular grain fragments decreasing from 10 to 20 m at the outer margins to 0 3 m in the shear band core where dense aggregates of nanograins also occurred transmission electron microscopy applied to foils extracted from boundary shears using fib sem combined with the optical cpo showed that these aggregates consist of calcite nanocrystals 5 20 nm in size with the 104 201 dislocation glide system oriented parallel to the shear plane and direction our results suggest that the mechanisms controlling slip include cataclasis and localized crystal plasticity because crystal plasticity is strongly thermally activated we infer that the transition to velocity weakening slip is likely due to enhanced crystal plasticity at 80 c this implies that tectonically active limestone terrains will tend to be particularly prone to shallow focus seismicity

determination of paleocurrent direction from oblique sections of trough cross stratification a precise approach the study of paleoflow patterns is an essential part of basin analysis cross stratification both planar and trough is the principal directional structure used for paleocurrent analysis trough cross stratification is especially characteristic of fluvial deposits where it is typically formed by the primary current and correlates strongly with the flow direction harms and fahnestock 1965 wermund 1965 williams 1968 barrett 1970 mcgowen and garner 1970 dott 1973 michelson and dott 1973 high and picard 1974 the only exception reported by meckel 1967 is an artifact of an erroneous sampling technique high and picard 1974 however the paucity of three dimensional exposures of trough cross strata that are suitable for direct measurement of trough axis orientations quite often hinders the systematic collection of paleocurrent data with a view to overcoming this problem attempts have been made to estimate paleoflow directions from two dimensional exposures of trough cross strata slingerland and williams 1979 decelles et al 1983 because they are much more common slingerland and williams 1979 proposed two specific ways of determining the orientations of trough axes from two dimensional exposures according to their first method a single strike measured on a trough side can be corrected to give the trough axial azimuth with reference to the plunge of the trough measured from a quasi three dimensional exposure slingerland and williams 1979 p 731 the plunge direction itself after necessary tilt correction however indicates the flow direction and if it can be measured beyond doubt no further measurement of any other part of the trough is required this kind of exposure is also not qualitatively very different from a three dimensional one the second method proposed by slingerland and williams 1979 involves estimation of the trough axial azimuth by measuring on perfectly two dimensional vertical exposures the face azimuths and two

upper messinian siliciclastic rocks in southeastern calabria southern italy palaeotectonic and eustatic implications for the evolution of the central mediterranean region abstract the messinian stratigraphy of eastern calabria southern italy is characterised by a threefold subdivision 1 a pelite section with local limestone and gypsum deposited in a restricted marine environment is unconformably or disconformably overlain by 2 coarse grained alluvial conglomerate which is in turn locally overlain by 3 a thin and discontinuous ribbon shaped sedimentary body of sandstone and pelite commonly displaying a shallow marine to continental progradational trend the basal unconformity disconformity coarse grain size and abrupt compositional sedimentological change of unit 2 with respect to unit 1 can be explained as a response to tectonic instability and out of sequence thrusting in the calabrian orogenic wedge possibly induced by isostatic back tilting of the wedge following the desiccation of the mediterranean sea this mechanism could explain widespread late messinian thrusting and syntectonic sedimentation along the apenninic maghrebian orogenic belt the uppermost messinian continental to shallow marine siliciclastic deposits of unit 3 crop out today at elevations of up to 300 m similar age equivalent sedimentary deposits can be traced along the apennines and the sicilian maghrebides thus indicating that the mediterranean area was flooded before deposition of the trubi formation the base of which is traditionally regarded as marking the reestablishment of marine conditions in the mediterranean region

intact microbial fossils in the permian lucaogou formation oil shale junggar basin nw china abstract the permian lucaogou formation was deposited in a deep stratified lake with good preservation of the organic matter in the sediments likely due to anoxic bottom waters the lucaogou formation oil shale contains excellent source rocks with high toc contents 12 4 32 9 wt and high hi values 547 869 mg hc g toc the maceral compositions of the oil shales are dominated by lamalginite with some higher plant debris spherical structures about 75 150 m in diameter having yellow fluorescence were observed in the shale edx sem showed that these contained c o p and ca two kinds of well preserved microbial fossils with different morphology were found in these spherical structures using a confocal laser scanning microscope and sem ellipsoidal cells 1 1 5 m long and 0 5 1 m wide occurred inside the spherical structure whereas microspherical cells occur within the outer layers through excluding modern contaminants and endolithic microbes we propose that these microbial fossils are indigenous and syngenetic with oil shale deposition their close physical association in the sediments suggests a symbiotic relationship hydrocarbon extracts of these oil shales have relatively depleted carbon isotopic signatures which is suggestive of methane oxidation this was confirmed by analysis of abundant c 29 and c 30 17 21 h hopanes which show distinctly negative 13 c values typical of those found in methanotrophs several possibilities are presented for the identity of these microorganisms but it is not yet possible to state unequivocally that they are related to methane production and consumption

microbial structures and possible bacterial sulfide fossils in the giant jinding zn pb deposit yunnan sw china insights into the genesis of zn pb sulfide mineralization abstract the jinding zn pb sulfide deposit lanping yunnan china is one of the youngest sediment hosted giant zn pb deposit in the world it is also a well known deposit in china the large scale of the mineralization and especially the huge volume of h 2 s that was required to precipitate the zn pb sulfide are of great interest to ore geologists ore microscopy shows microbial structures such as framboidal sphalerite spherical aggregates of galena sphalerite oolite sphalerite dendritic colloidal sphalerite pyrite metacolloidal sphalerite pyrite multinuclear metacolloidalring like sphalerite pyrite botryoidal sphalerite pyrite framboidal pyrite and bacterial plate like of galena sphalerite detailed observations and analyses of the microbial structures at micron to nanometer scales by field emission scanning electron microscopy fesem and energy dispersive spectrometry eds reveal that the bacteria fossils are composed of sphalerite galena or pyrite or of multiple sulfide minerals with calcite and that they are distributed in bacterial colonies in the ore the individual bacteria fossils are spherical botryoidal or ring like with a diameter of 200 500 nm filamentous mucoid and tubular extracellular polymeric substances eps are commonly observed that are closely associated with and have the same composition as the bacteria fossils secondary ion microprobe analysis sims by in situ sulfur micro isotopic analysis of the microbial sulfide structures and bacteria fossils yield 34 s v cdt values varying from 48 6 to 9 5 per mil indicating that there was a high percentage of sulfate reducing bacteria in the zn pb sulfide mineralization process previous analyses have shown that the zn pb mineralization was formed at a shallow depth and low temperature with barely visible hydrothermal alteration the presence of evaporitic sulfate layers and paleo oil reservoir characteristics the authors believe that bacterial sulfate reduction might be the key h 2 s production mechanism in the jinding dome that was required to form this giant pb zn sulfide ore body

phase transformation and nanometric flow cause extreme weakening during fault slip faults weaken during earthquakes laboratory simulations of earthquake rupture show that the nanometric scale fault gouge created during slip is inherently weak and flows by grain boundary sliding providing a mechanism to weaken faults

earthquake slip weakening and asperities explained by thermal pressurization for the earth s crust to release accumulated stress in the form of an earthquake a fault must weaken and give way otherwise the movement would quickly grind to a halt due to the surrounding pressure this weakening is not really understood laboratory experiments simply don t match seismologists estimates of the distance a fault must slip before it becomes very weak a new study concludes that the missing ingredient is water geological studies and measurements show the slip zones to be narrow impermeable structures water already in the fault zone can quickly become pressurized by frictional heating as the rocks start to move catalysing large earthquakes from minor movements an earthquake occurs when a fault weakens during the early portion of its slip at a faster rate than the release of tectonic stress driving the fault motion1 2 this slip weakening occurs over a critical distance dc understanding the controls on dc in nature is severely limited however because the physical mechanism of weakening is unconstrained conventional friction experiments typically conducted at slow slip rates and small displacements have obtained dc values that are orders of magnitude lower than values estimated from modelling seismological data for natural earthquakes3 4 5 6 here we present data on fluid transport properties of slip zone rocks and on the slip zone width in the centre of the median tectonic line fault zone japan we show that the discrepancy between laboratory and seismological results can be resolved if thermal pressurization of the pore fluid7 8 9 10 is the slip weakening mechanism our analysis indicates that a planar fault segment with an impermeable and narrow slip zone will become very unstable during slip and is likely to be the site of a seismic asperity

precipitation and growth morphology of calcium carbonate induced by myxococcus xanthus implications for recognition of bacterial carbonates abstract it is thought that morphologies of bacterial carbonates can be used to identify microbial fossils and or precipitates in sediments and rocks this study shows that calcite and vaterite formed in a gel medium in the presence of myxococcus xanthus display a range of morphologies that depend on whether the bacteria are live or dead metabolic activity of the bacteria induced 1 aggregates of calcified bacteria formed at maximum supersaturation 2 vaterite spheres final growth stage of dumbbell fibrous radiated aggregates and 3 dipyramid and disphenoid like calcite crystals combination of 011 and 0001 forms morphologies 2 and 3 developed at a lower supersaturation and are typically found in gel like media dipyrimidal like calcite crystals were also obtained abiotically in gel medium dead m xanthus cells induced heterogeneous precipitation of calcite with rhombohedral morphologies at low supersaturation a growth mechanism resulting from self assembly of calcium carbonate nanocrystals may account for the observed morphologies crystal microstructure and crystallite size measurements all of the above mentioned morphologies of bacterial carbonate have been observed in other laboratory experiments and in continental and marine environments however all of them have also been produced abiotically with the exception of calcified bacterial cells this may make it more difficult to identify bacterial activity in the rock record nonetheless bacterially induced alkalinization appears to be a prerequisite for the development of spherulitic and dipyramid or disphenoid like forms in natural mucilaginous biofilms and microbial mats the morphologies reported here may facilitate the recognition of early and recent marine and continental microcrystalline bacterial carbonates and cements

pseudotachylytes in an ancient accretionary complex and implications for melt lubrication during subduction zone earthquakes abstract pseudotachylyte bearing fault zones found in the shimanto accretionary complex southwest japan developed during subduction or underplating at seismogenic depths the pseudotachylytes occur in narrow dark veins less than a few millimeters thick that are sharply bounded by foliated cataclasites that originated from a melange the microstructures of pseudotachylytes are represented by a fragment laden glass supported texture resulting from the rapid cooling of the frictional melt transmission electron microscopy reveals the presence of glass in which euhedral microcrystals of mullite are locally developed the compositions of the pseudotachylyte matrix and the characteristics of the unmelted grains and microlites in the matrix suggest that frictional melting occurred in an illite rich slip zone with a minimum melting temperature of 1100 c the viscosities of the frictional melt were calculated from the pseudotachylyte matrix composition as well as from the volume fraction and aspect ratio of the unmelted grains the viscosities at 1100 c range from 85 to 290 pa s and the corresponding shear resistance along a 1 mm thick melt layer at a slip rate of 1 m s was 0 1 0 3 mpa the formation of a melt layer in an illite rich slip zone can possibly induce large stress drops increase the slip rate and enhance rupture propagation which together could affect the earthquake magnitude in a subduction zone

metal fixation by bacterial cell walls all biomass contains a significant quantity of metallic constituents and mineralization in living and dead biodebris may contribute to element transport from the hydrosphere into sediments the anionic cell walls of bacteria are remarkable in their ability to fix metals and provide sites for nucleation and growth of minerals results presented show the types of cell wall polymers that are responsible for metal binding in walls of gram positive and gram negative bacteria

two stage growth of the calabrian accretionary wedge in the ionian sea central mediterranean constraints from depth migrated multichannel seismic data new structural images of the calabrian accretionary wedge are presented from depth migrated multichannel seismic data a combined interpretation swath mapping bathymetry allows us to identify five morphological domains on the basis of their tectonic style 1 beneath the undeformed abyssal plain a set of deep nw vergent reverse faults cuts the ionian oceanic crust and thick pre messinian sediments 2 towards the nw the low taper post messinian wedge overlying a shallow nw dipping decollement at the base of the messinian evaporites and exhibiting strong tectonic thickening 3 beneath the flat central transition zone a backthrust marks the contact between the post and pre messinian wedges here the decollement dip increases 3 cutting through deeper sediments to reach 10 km depth 4 beneath the pre messinian calabrian wedge some steep landward dipping features are imaged where underplating may occur 5 beneath the inner plateau a fore arc basin lies above the top of the calabrian continental basement imaged at 8 km depth the architecture of the calabrian accretionary complex is very similar to the mediterranean ridge both systems consist of a an external low taper post messinian wedge overlying a thick undeformed section of underthrust mesozoic sediments and b an internal pre messinian wedge where the decollement steps down and where the underthrust section is presumably underplated we perform area balancing and show that since the messinian the calabrian accretionary wedge has undergone extremely rapid outward growth at an average rate of 30 km ma which makes it the fastest growing accretionary wedge over the past 5 ma highlights relation between the pre and post messinian juxtaposed wedges contact between these wedges along a major backthrust the 130 km long outer calabrian prism a huge salt bearing body one of the fastest growing wedges 2 0 cm year in recent earth history 170 km amount of post messinian subduction subduction rate 3 4 cm year

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

estimation of radiated energy of finite source earthquake models we estimated seismically radiated energy for kinematic earthquake rupture models instead of integrating far field waveforms we used an expression for radiated energy with slip and stress on the fault plane using an analytic crack model of sato and hirasawa 1973 we show that the finite difference method can estimate the radiated energy fairly well however if the rupture propagation velocity is near the s wave velocity and the grid interval is coarse we may underestimate the radiated energy substantially we analyzed five models of three earthquakes of m w 5 7 for the 1995 kobe earthquake we used three different kinematic models and obtained consistent values of radiated energy of 2 4 3 6 1014 j there are common features among the three models 1 more efficient energy radiation from the deeper regions of the fault and 2 little energy radiation beneath the city of kobe the models of the kobe earthquake and the other two earthquakes show that energy radiation is concentrated near the hypocenter and the initiation point of asperities we also find the area of negative energy radiation energy absorption near the edge of large slipped areas although our estimates tend to be smaller by about a factor of 3 than previous estimates the difference is reasonable because the frequency range is not complete and we cannot deal with detailed rupture behavior such as rapid rupture acceleration and deceleration manuscript received 18 january 2002

in situ silicification of an icelandic hot spring microbial mat implications for microfossil formation transmission electron microscopy and energy dispersive x ray analysis revealed that filamentous phototrophic bacteria resembling chlorojlexus aurantiacus underwent rapid silicification in an icelandic hot spring microbial mat the mineralization associated with the cells occurred both extracellularly within and on the external sheaths of the bacteria and intracellularly within the cytoplasm the exceptional preservation of the bacterial sheaths is due to the presence of distinct mineral nucleation sites this results in the production of silica casts of the bacteria which bear a striking resemblance to microbial remains in ancient microfossil assemblages rcsumc les analyses par microscopie clectronique i transmission et par 1 6nergie dispersive des rayons x ont rcvcl6 que les bactkries filamenteuses phototrophes ressemblant b chlorojlexus aurantiacus ont subi une silicification rapide au sein d un tapis microbien de source therrnale en islande la mineralisation associee aux cellules se presente sous forme extracellulaire b l interieur de et sur la membrane externe des bacteries et sous forrne intracellulaire i l interieur du cytoplasme la preservation exceptionnelle de la membrane des bacteries est due b la presence de sites de nucleation minerale disperses le resultat est la production des moulages siliceux des bactkries affichant une resemblance remarquable avec les vestiges microbiens d anciens assemblages microfossiles traduit par la raaction fossil evidence of the earth s earliest biosphere shows that complex communities of microorganisms were abundant and well distributed throughout the precambrian era among the richest beds of microbial fossils are those found in the gunflint iron formation north of lake superior in canada barghoorn and tyler 1965 the early archaean apex chert of australia schopf and packer 1987 schopf 1993 and the riphean section of the anabar uplift in russia sergeev 1993 all ranging in age from 0 8 to 3 5 ga the distribution and types of microorganisms preserved as cellularly intact microfossils are remarkably similar to those in modern microbial mats in which organic rich layers formed by cyanobacteria and or other types of filamentous bacteria alternate with layers that are comprised of detrital inorganic sediment and authigenic mineral precipitates morse and mackenzie 1990 these benthic microbial communities are considered to be analogous and possibly homologous with those that were preserved billions of years ago as stromato

tracing acidification induced by deccan phase 2 volcanism abstract the deccan volcanic province dvp was built up by three major phases of eruptions the most voluminous of which the deccan phase 2 encompassed the cretaceous palaeogene kt boundary deccan eruptions have been implicated as a contributor to the end cretaceous mass extinction however mechanism by which volcanic activity affected biota remains poorly understood we applied a combination of rock magnetic techniques scanning electron microscopy to characterize mineral assemblages of three sections of intertrappean lacustrine sediments from the north western maharashtra deccan volcanic provinces our results indicate that in sediments deposited during the early stages of the deccan phase 2 the daiwal river and dhapewada sequences iron bearing mineral association is dominated by detrital iron oxides magnetite and hematite sourced from the weathering of the surrounding basaltic bedrocks with minor contribution form authigenic iron sulphides framboidal pyrite pyrrhotite and or greigite the sediments deposited during the final stages of phase 2 the podgawan sequence differ significantly in their characteristics in particular the podgawan sediments have 1 very low magnetic susceptibility values but higher terrigenous fraction clays and shales content 2 more complex assemblage of magnetic minerals 3 ubiquitous presence of fe ca ce vanadates and 4 unusual lithological variations in the middle part of the section represented by a charcoal rich level that is capped by a red clay layer containing fossilized bacterial colonies we suggest that these unusual characteristics reflect increased acidity in the region during the deposition of the podgawan sequence likely due to cumulative effects of volcanic aerosols released during the deccan phase 2 eruptions the combination of these features may be used to recognize episodes of increased acidity in the geological record our results also contribute to understanding of local vs global effects of the deccan volcanism

ancient microspheres abiogenic protobiogenic or biogenic criteria of biogenicity of microspheroidal objects which have been interpreted as microfossils are here reviewed in the light of additional data much weight has been placed by some commentators on constrained heterogeneity as a primary criterion of biogenicity the data from the field and laboratory suggest the need for continuing reservation in the interpretation of these objects on the basis of these and other data reasons are given for the alternative explanation that the objects are lithified relics of protobiotic assemblages the question remains open as to whether the early archean spheroidal objects are abiotic protobiotic or biotic in origin

the nature of fossil bacteria a guide to the search for extraterrestrial life in an attempt to establish reliable criteria for the identification of potential fossil life in extraterrestrial materials the fossilizable characteristics of bacteria namely size shape cell wall texture association and colony formation are described and an overview is given of the ways in which fossil bacteria are preserved as compressions in fine grained sediments preservation in amber permineralized by silica replacement by minerals such as silica pyrite fe mn oxides calcite phosphate and siderite or as molds in minerals the problem of confounding minerally replaced bacteria with non biological structures having a bacterial morphology is addressed examples of fossilized bacteria from the early archaean through to the recent are used to illustrate the various modes of preservation and the morphology of fossil bacteria

endolithic microorganisms in the antarctic cold desert in the frigid desert of the antarctic dry valleys there are no visible life forms on the surface of the soil or rocks yet in certain rock types a narrow subsurface zone has a favorable microclimate and is colonized by microorganisms dominant are lichens of unusual organization they survive not by physiological adaptation to lower temperatures but by changing their mode of growth being able to grow between the crystals of porous rocks their activity results in mobilization of iron compounds and in rock weatherning with a characteristic pattern of exfoliation this simple ecosystem lacks both higher consumers and predators

travertines depositional morphology and the bacterially constructed constituents abstract investigation of travertine accumulations throughout central italy and the west central u s has shown that the carbonate is precipitated in response to both inorganic and organic processes individual deposits range up to 85 m thick and hundreds of square kilometers in areal extent all of the carbonate is low magnesian calcite water chemistry temperature and morphology of the accumulation greatly influence the constituents comprising these deposits harsh environmental situations favor inorganic deposits while increasingly more moderate conditions result in the formation of a greater abundance of organically precipitated material morphological variations of travertine deposits recognized include 1 waterfall or cascade 2 lake fill 3 sloping mound fan or cone 4 terraced ound and 5 fissure ridge gross morphology internal stratification and constituents comprising these deposits vary systematically depending upon the type of accumulation and chemistry of the waters bacterially precipitated calcite forms a large percentage of the carbonate in many travertine accumulations exceeding 90 of the framework grains comprising some of the lake fill deposits bacteria are among the first taxa to inhabit and reproduce in harsh spring environments and produce a variety of fascinating constituents the bacteria are primarily rods generally 0 2 m in diameter and less than 1 0 m in length the rods readily decay resulting in calcite crystals loaded with micropores the basic building block of bacterially constructed travertine is a clump of bacteria averaging 20 m in diameter enclosed in a single crystal of calcite aggregates of these crystals produce a variety of deposits including 1 crudely laminated carbonate mud 2 finely laminat d layers of mud 3 intraclasts 4 foam rock and 5 shrubs the shrubs are most striking commonly forming layers 1 3 cm thick but also producing bacterial pisoids at some locales bacterial stromatolites composed of layers of shrubs alternating with finely laminated layers of bacterial mud comprise essentially the entire deposit the shrub layers are the result of flourishing summer growth of bacteria and furthermore show remarkable daily laminae 0 1 0 5 mm thick the importance of bacteria in the formation of travertine and their universally recognized abundance in modern sediments provides an impetus for a reexamination of the role of bacteria in the origin of other types of ancient deposits

polymeric substances and biofilms as biomarkers in terrestrial materials implications for extraterrestrial samples organic polymeric substances are a fundamental component of microbial biofilms microorganisms especially bacteria secrete extracellular polymeric substances eps to form slime layers in which they reproduce in the sedimentary environment biofilms commonly contain the products of degraded bacteria as well as allochthonous and autochthonous mineral components they are complex structures which serve as protection for the colonies of microorganisms living in them and also act as nutrient traps biofilms are almost ubiquitous wherever there is an interface and moisture liquid liquid liquid solid liquid gas solid gas in sedimentary rocks they are commonly recognized as stromatolites we also discuss the distinction between bacterial biofilms and prebiotic films the eps and cell components of the microbial biofilms contain many cation chelation sites which are implicated in the mineralization of the films eps biofilms and their related components thus have strong preservation potential in the rock record fossilized microbial polymeric substances fps and biofilms appear to retain the same morphological characteristics as the unfossilized material and have been recognized in rock formations dating back to the early archaean 3 5 b y we describe fps and biofilms from hot spring deep sea volcanic lake and shallow marine littoral environments ranging up to 3 5 b y in age fps and biofilms are more commonly observed than fossil bacteria themselves especially in the older part of the terrestrial record the widespread distribution of microbial biofilms and their great survival potential makes their fossilized remains a useful biomarker as a proxy for life with obvious application to the search for life in extraterrestrial materials

early archean fossil bacteria and biofilms in hydrothermally influenced sediments from the barberton greenstone belt south africa abstract sem imaging of hf etched 3 3 3 5 ga cherts from the onverwacht group south africa reveals small spherical 1 m diameter and rod shaped structures 2 3 8 m in length which are interpreted as probable fossil coccoid and bacillar bacteria prokaryotes respectively preserved by mineral replacement other possibly biogenic structures include smaller rod shaped bacteriomorphs 900 m textures in the sediments in which these biogenic structures occur suggest that they were probably deposited in a shallow water environment which was subjected to intermittent subaerial exposure pervasive hydrothermal activity is evidenced by oxygen isotope studies as well as the penecontemporaneous silicification of all rock types by low temperature 220 c hydrothermal solutions

mineral ecophysiological data provide growing evidence for microbial activity in banded iron formations the phosphorus composition of banded iron formations bifs has been used as a proxy for precambrian seawater composition and the paleoeredox state of earth s surface environment however it is unclear whether the phosphorus in bifs originally entered the sediment as a sorbed component of the iron oxyhydroxide particles or whether it was incorporated into the biomass of marine phytoplankton we conducted high resolution mineral analyses and report here the first detection of an fe iii acetate salt as well as nanocrystals of apatite in association with magnetite in the 2 48 ga dales gorge member of the brockman iron formation a bif hamersley western australia the clusters of apatite are similar in size and morphology to biogenic apatite crystals resulting from biomass decay in phanerozoic marine sediments while the formation of an fe iii acetate salt and magnetite not only implies the original presence of biomass in the bif sediments but also that organic carbon likely served as an electron donor during bacterial fe iii reduction this study is important because it suggests that phytoplankton may have played a key role in the transfer of phosphorus and other trace elements from the photic zone to the seafloor

earthquake fracture energy inferred from kinematic rupture models on extended faults 1 we estimate fracture energy on extended faults for several recent earthquakes by retrieving dynamic traction evolution at each point on the fault plane from slip history imaged by inverting ground motion waveforms we define the breakdown work wb as the excess of work over some minimum traction level achieved during slip wb is equivalent to seismological fracture energy g in previous investigations our numerical approach uses slip velocity as a boundary condition on the fault we employ a three dimensional finite difference algorithm to compute the dynamic traction evolution in the time domain during the earthquake rupture we estimate wb by calculating the scalar product between dynamic traction and slip velocity vectors this approach does not require specifying a constitutive law and assuming dynamic traction to be collinear with slip velocity if these vectors are not collinear the inferred breakdown work depends on the initial traction level we show that breakdown work depends on the square of slip the spatial distribution of breakdown work in a single earthquake is strongly correlated with the slip distribution breakdown work density and its integral over the fault breakdown energy scale with seismic moment according to a power law with exponent 0 59 and 1 18 respectively our estimates of breakdown work range between 4 105 and 2 107 j m2 for earthquakes having moment magnitudes between 5 6 and 7 2 we also compare our inferred values with geologic surface energies this comparison might suggest that breakdown work for large earthquakes goes primarily into heat production

large scale gravity driven phenomena in the crotone basin southern italy abstract the aim of this study is to better define the scale timing and driving mechanisms of a seaward gliding landmass currently affecting the crotone basin a forearc basin on the ionian side of calabria southern italy an integrated approach of seismic well and field data together with literature information have revealed that the slide includes an onshore updip extensional domain compatible with the presence of a curved seaward dipping fault system to the nw which is connected southward to an offshore downdip compressional domain through a buried detachment surface lying at a messinian halite layer the landmass which involves messinian pleistocene deposits has started to slide since the zanclean and experienced a paroxysmal episode between late zanclean and early piacenzian linked to transpressional tectonics after a phase of inactivity during the calabrian the gravitational collapse underwent a second reactivation since middle pleistocene due to regional uplift which seems to be restricted to the offshore sector the crotone peninsula and probably the eastern coastal area

depositional facies and diagenetic alteration in a relict siliceous hot spring accumulation examples from yellowstone national park u s a abstract siliceous precipitates from portions of an 11 m long core drilled through a relict yellowstone hot spring deposit provide valuable insights into the diagenetic facies in this hydrothermal environment most of the core consists of relatively low temperature siliceous sinter containing abundant plant diatom and microbial fossilized remains derived from the distal debris apron and discharge channel flowpath of the hot spring a few intervals contain stromatolitic horizons analogous to modern siliceous pool margin and discharge channel flowpath facies despite the abundance of silicified microbial remains e g silicified stromatolitic horizons as well as individual filamentous microbes diatoms distinctive organic biomarkers are not preserved in the core the apparent lack of distinctive organic biomarkers is attributable to pervasive diagenetic alteration in the presence of high temperature chemically reactive fluids numerous diagenetic features have been superimposed on the siliceous sinter especially considering the relatively shallow depths of burial the uppermost interval 0 to 1 2 m consists of highly porous siliceous sinter opal a and interbedded travertine amorphous manganese oxides and sparry calcite cements are present and are irregularly distributed throughout this interval below is a diagenetic facies 4 8 to 5 3 m that consists of opal ct and minor chalcedony the most pervasive diagenetic alteration in the core is the 6 8 to 11 2 m depth interval where abundant zeolites mordenite heulandite bladed cristobalite lepispheres chalcedony cements and calcite veins are present judging by the assemblage of plant and diatom remains most of this pervasive alteration is superimposed on relatively low temperature siliceous sinters and is likely the result of migration of hot waters through this interval the paragenesis of all these intervals is very complex involving numerous episodes of mineral precipitation and dissolution this diagenetic alteration is facilitated by the porous nature of the siliceous sinter thermal convection of superheated fluids or steam strongly oxidizing spring waters and fluctuating hydrochemical regimes rapid dissolution and or replacement of organic matter indicates that standard morphological means e g petrographic identification of body fossils may be the best method by which to identify that organisms were previously present in ancient hot spring accumulations

organic rich microfossils produced by oil infiltration of hollow silicified bacteria evidence from the ca 340 ma red dog zn pb deposit alaska

stromatolitic microbiota from the middle proterozoic wumishan formation jixian group of the ming tombs beijing china abstract a relatively diverse microbiota preserved in situ has been discovered in cherty stratiform stromatolites of the middle proterozoic wumishan formation c 1200 1300 maold jixian group in the ming tombs area of beijing this microfossil assemblage consists of two parts 1 the mat building and mat dwelling benthos which mostly belong to long lasting taxa and are mostly common with those of other proterozoic microbiotas and 2 allochthonous elements including some plankton and peculiar structures which are either new forms first described here or taxa shared with some contemporaneous or penecontemporaneous microbiotas elsewhere the latter may have more stratigraphic significance bivariate analysis on two characters measured length and width has been used in the classification of the elongate microfossils and the results demonstrate that biometrical methods are effective in the taxonomy of some precambrian microfossils the following new taxa are described archaeoellipsoides obesus sp nov archaeoellipsoides conjunctivus sp nov bactrophycus oblongum gen et sp nov bactrophycus dolichum gen et sp nov callosicoccus crauros gen et sp nov

filamentous microfossils from the 3 500 myr old onverwacht group barberton mountain land south africa the swaziland supergroup barberton mountain land south africa has long been regarded as a promising location for the earth s oldest fossils because it includes some of the most ancient well preserved sedimentary rocks many of which contain carbonaceous matter although there have been numerous reports of microfossils from swaziland group rocks1 7 the biogenicity of most of the structures has been questioned8 10 although some of the organic spheroids are probably biogenic10 11 the best early archaean simple spheroids are generally regarded as possible microfossils 10 because organic spheroids may form abiotically in several ways12 the discovery of less simple biological morphologies is therefore important in establishing the existence of early life forms in the early archaean uniformly sized curving filaments especially tubular ones are difficult to explain as anything other than the fossil remains of filamentous organisms here we report the discovery of numerous filaments from two different stratigraphical positions in the 3 500 myr old onverwacht group of the swaziland supergroup their morphologies and abundance provide convincing evidence for the existence of bacteria or cyanobacteria like organisms on the earth during the early archaean this supports recent reports of similar filamentous microfossils from 3 500 myr old rocks from western australia13