comment on weathering plants and the long term carbon cycle by robert a berner berner 1992 has asserted that jackson and keller 1970a misinterpreted the conspicuous reddish crust which forms on young lava flows in areas of rock surface colonised by the lichen stereocaulon vulcani but not in adjacent areas of bare rock in regions of high rain fall on the island of hawaii jackson 1968 and jackson and keller 1970a b concluded from the results of a thorough interdisiplinary investigation employing a wide spectrum of techniques and information that his reddish coating is an intensely leached weathering crust formed in situ and that biochemical activities of the lichen or its associated microflora not only accelerate the chemical weathering of the rock by orders of magnitude but also determine the specific mineralogical and chemical properties of the weathering products berner however maintained that the reddish crust is in reality a deposit of open quotes wind blown soil dust close quotes entrapped by a sticky organic substance secreted by the lichen berner fixed his attention on just one aspect of the many sided body of interrelated data on which the conclusions of jackson and keller are founded the observation that the weathering crust is much thicker on lichen covered rock surfaces than on lichen free open quotes control close quotes areas of the same rock more the totality of published evidence overwhelmingly supports the conclusions of jackson and keller an demonstrates that berner s rival hypothesis is untenable less

the effects of quartz dauphine twinning on strain localization in a mid crustal shear zone abstract we use microstructural electron backscatter diffraction ebsd and crystal vorticity axis cva analyses to evaluate the effects of quartz dauphine twinning on strain localization we compare a granodiorite mylonite and a tonalite mylonite from the grebe shear zone a mid crustal transpressional shear zone in fiordland new zealand ebsd analysis reveals identical quartz grain boundary migration dynamic recrystallization microstructures in both samples with abundant dauphine twinning only in the granodiorite mylonite bulk cva patterns further distinguish the untwinned and dauphine twinned samples indicating a transition from simple shear to pure shear dominated transpression respectively the quartz cva pattern from the dauphine twinned sample indicates that twinned and untwinned grains record a transition from simple shear to pure shear dominated deformation respectively pole figures of the dauphine twinned sample reveal high temperature slip systems in the untwinned and dauphine twinned grains we conclude that dauphine twinning formed early in transpression and rendered the twinned grains less deformable relative to the untwinned grains over time the effectiveness of dauphine twinning in localizing strain is therefore strongly influenced by its timing relative to the evolving shear zone kinematic deformation geometry

trace fossil evidence for late ordovician animals on land fossil burrows within newly recognized buried soils in the late ordovician juniata formation near potters mills in central pennsylvania represent the oldest reported nonmarine trace fossils they are thought to have been an original part of the soil because their greater density toward the top of the paleosols corresponds with mineralogical microstructural and chemical changes attributed to ancient weathering and because about half the burrows are encrusted with nodular carbonate interpreted as caliche associated fossil caliche the size distribution of the burrows and their w shaped backfills are evidence that the burrows may have been excavated by bilaterally symmetrical organisms that grew in well defined growth increments and were able to withstand desiccation among well known soil organisms millipedes are burrowing animals that satisfy these requirements but have a fossil record not quite this old this trace fossil evidence for animals on land together with recent palynological evidence for land plants of a bryophytic grade of evolution during late ordovician time are indications of terrestrial ecosystems of slightly greater antiquity and complexity than hitherto suspected

evidence for microbial life in synsedimentary cavities from 2 75 ga terrestrial environments fluviolacustrine sediments of the 2 75 ga hardey formation fortescue group australia preserve pendant columnar structures with stromatolitic lamination within synsedimentary cavities the millimeter sized finger like columns strongly resemble microbialites from modern basaltic caves and indicate the likely presence of microbial biofilms the ancient microbial columns are preserved by chert and locally occur as reworked clasts indicating a near depositional age for the structures sulfur isotopic analysis of pyrite in the columns and adjacent carbonaceous matrix yields 34scdt cdt canyon diablo troilite values between 8 5 and 19 showing significant fractionation characteristic of biological cycling of sulfur organic matter in cavity ceilings and shale matrix has 13cpdb pdb peedee belemnite values between 55 and 43 suggesting the presence of methanotrophs our results suggest that 2 75 ga terrestrial environments supported a microbial ecosystem including microbes that inhabited synsedimentary hollows extending the fossil record of coelobionts by 1 5 b y subsurface cavities represent a new habitable microenvironment for early life on earth and an analogue for ancient life on mars

continental paleoclimates from δd and δ18o of secondary silica in paleokarst chert lags approximate continental paleotemperatures can be inferred from oxygen and hydrogen isotopic analyses of authigenic silica that precipitated within chert lags on paleokarst surfaces data for two proterozoic examples suggest continental weathering temperatures that ranged from 30 to 43 c quantitative results appear possible for rocks at least as old as 1 1 ga

deformation thermometry based on quartz c axis fabrics and recrystallization microstructures a review abstract for quartz rich tectonites two types of deformation thermometer are currently commonly employed 1 the quartz c axis fabric opening angle thermometer that provides an estimate of deformation temperatures when fabrics were locked in during dislocation creep and dynamic recrystallization 2 the quartz recrystallization thermometer that indicates a range of likely deformation temperatures based on observed microstructures and inferred mechanisms of dynamic recrystallization a critically important caveat in applying both thermometers is the assumption that deformation temperature is the primary controlling factor in recrystallization mechanisms and fabric development however fabric opening angles and recrystallization mechanisms are also sensitive to other variables such as strain rate and water weakening in this paper the development of these thermometers is reviewed and their potential sensitivities to competing factors such as temperature strain rate water weakening and in the case of opening angles 3d strain type are discussed examples of the application of these potential thermometers to naturally deformed quartz rich rocks are given and case studies of correlations between deformation temperatures estimated by these thermometers and temperatures of synkinematic metamorphism determined by petrology based thermobarometers are highlighted in the review attention is focused on problems associated with applying these thermometers to natural deformation and examples of such problems are discussed

rheology of a coaxial shear zone in the virginia blue ridge wet quartzite dislocation creep at 250 280 c abstract cambrian quartzite along the western margin of the blue ridge near front royal virginia records significant penetrative strain under subgreenschist facies conditions strain analyses of the quartzite indicate general flattening and octahedral shear strain values up to 1 25 x z up to 5 7 1 samples with x z as low as 1 5 1 have crystallographic preferred orientations that record a dominance of basal slip and patterns consistent with coaxial flattening in most samples quartz has undergone minor amounts of dynamic recrystallization with mean grain sizes 4 5 m locally the quartzite is brittlely deformed and subgrains and recrystallized bulges are present along fractures and extinction bands fluid inclusion planes and fluid inclusions along deformation lamellae are abundant and quartz ftir analyses yield average h 106si values of 1100 3300 indicating fluid flow and high intragranular water content during deformation higher strain samples generally record lower water contents which may indicate that fluids migrated to grain boundaries during deformation dissolution microstructures are rare in high strain samples and we interpret most strain to have been accommodated by dislocation creep thermal modeling of zircon low temperature thermochronology data coupled with quartz c axis opening angle thermometry suggest deformation temperatures were likely 250 280 c these deformation temperatures are lower than what is typically considered the brittle plastic transition in quartz we attribute localization of this high strain zone and dislocation creep at these temperatures to hydrolytic weakening and a relatively low strain rate estimated to be 10 15 s 1

late precambrian tectonism in the kingston range southern california speculation on the early history of the cordilleran geosyncline of north america has relied in part on interpretation of the tectonic setting of the precambrian pahrump group recent mapping in the kingston range resulted in new data to aid our speculation specifically precambrian tectonic events involving folding and later low angle normal faulting affected the crystal spring formation beck spring dolomite and lower part of the kingston peak formation unconformably overlying these units is a relatively undeformed conglomerate diamictite occurs both above and below the unconformity hence cordilleran wide correlations of the kingston peak formation based on diamictite require reassessment the nature of boundaries localized deformation and outcrop distribution of the pahrump group suggest that these rocks may be preserved in transtensional basins associated with strike slip faulting possibly occurring during development of the late precambrian continental margin

weathering plants and the long term carbon cycle the chemical weathering of ca mg silicate rocks is the principal process whereby co2 is removed from the atmosphere on long or multimillion year time scales at present vascular land plants exert an important influence on weathering by recycling water and by bringing about the secretion of acids and the buildup of high levels of co2 in soils before the spread of vascular plants on the continents during the mid paleozoic chemical weathering must have been achieved by higher levels of atmospheric co2 and or by the intercession of primitive land biota such as lichens and cyanobacteria from examination of several pre vascular weathering scenarios it is concluded that in order to prohibit unreasonably high levels of atmospheric co2 weathering during the precambrian and early paleozoic must have taken place under essentially closed system abiotic conditions linear feedback or via strong regulation by primitive biota preliminary examination of modern weathering by lichens over tens to thousands of years militates against the latter possibility however much more work needs to be done on the quantitative effect of both primitive biota and vascular plants on the rate of weathering and their response to changes in atmospheric co2 before anything more definitive can be said

evidence for regional dauphine twinning in quartz from the santa rosa mylonite zone in southern california a neutron diffraction study preferred orientation in granitic mylonites from the santa rosa mylonite zone in southern california is investigated with time of flight neutron diffraction quartz and biotite display strong preferred orientation whereas feldspar alignment is weak for quartz a c axis maximum in the intermediate fabric direction is consistent with dynamic recrystallization pole figures for positive and negative rhombs such as rz 10 11 and zz 01 11 are distinct over a wide region suggesting that the pattern reflects tectonic deformation and was not

precambrian non marine stromatolites in alluvial fan deposits the copper harbor conglomerate upper michigan laminated cryptalgal carbonates occur in the precambrian copper harbor conglomerate of northern michigan which was deposited in the keweenawan trough an aborted proto oceanic rift this unit is composed of three major facies deposited by braided streams on a large alluvial fan complex coarse clastics were deposited in braided channels predominantly as longitudinal bars whereas cross bedded sandstones were deposited by migrating dunes or linguoid bars fine grained overbank deposits accumulated in abandoned channels gypsum moulds and carbonate filled cracks suggest an arid climate during deposition stromatolites interstratified with these clastic facies occur as laterally linked drapes over cobbles as laterally linked contorted beds in mudstone as oncolites and as poorly developed mats in coarse sandstones stromatolites also are interbedded with oolitic beds and intraclastic conglomerates stromatolitic microstructure consists of alternating detrital and carbonate laminae and open space structures radialfibrous calcite fans are superimposed on the laminae the laminae are interpreted as algal in origin whereas the origin of the radial fibrous calcite is problematic the stromatolites are inferred to have grown in lakes which occupied abandoned channels on the fan surface standing water on a permeable alluvial fan in an arid climate requires a high water table maintained by high precipitation or local elevation of the water table possibly due to the close proximity of a lake occurrence of stromatolites in the upper part of the copper harbor conglomerate near the base of the lacustrine nonesuch shale suggests that these depositional sites may have been near the nonesuch lake

the geochemistry of witwatersrand type gold deposits and the possible influence of ancient prokaryotic communities on gold dissolution and precipitation abstract compared to the prokaryote dominated lower proterozoic there are few environments now left on earth where prokaryotes are dominant by about 2 5 ga chemical conditions affecting the solution and precipitation of minerals were much influenced by microbial communities results of recent experiments show that modern living prokaryotes are capable of actively precipitating or flocculating gold this process goes far towards explaining the phenomenal extent to which gold is enriched in kerogenous marker seams on the witwatersrand neutron activation analyses confirm that gold is likewise anomalously enriched in kerogenous material present in the lower huronian metasediments of ontario long known as thucholite it appears from pyrolysis and x ray studies of a sample from a stratiform occurrence that it is a kerogen remarkably similar to kerogen from the vaal reef south africa a prokaryote precursor has been postulated for the vaal reef kerogen and the same may well be true of at least some of the stratiform occurrences of kerogen in the huronian simplifying solutions to the metallogeny of witwatersrand type gold that do not take into account the diverse types of gold in the deposits are unrealistic precipitated gold associated with kerogen is only one of four main types of witwatesrand gold but it may be the major one our proposed model to account for this gold involves the weathering of gold from archean source rock under anaerobic conditions and probably in the presence of s cycling microbial communities transported as a solution or colloid the gold was stabilized by humic acids or s cycle intermediates and was deposited onto braided alluvial plains there in the presence of extensive prokaryote microbial mats now preserved as kerogen gold was precipitated in forms characteristic of biologically induced biomineralization

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

the role of subgrain boundaries in partial melting abstract evidence for partial melting along subgrain boundaries in quartz and plagioclase is documented for rocks from the lost creek gneiss of the llano uplift central texas the wet mountains of central colorado and the albany fraser orogen southwestern australia domains of quartz or plagioclase crystals along subgrain boundaries are preferentially involved in partial melting over unstrained domains of these minerals material along subgrain boundaries in quartz and plagioclase has the same morphology as melt pseudomorphs present along grain boundaries and is commonly laterally continuous with this former grain boundary melt indicating the material along subgrain boundaries can also be categorized as a melt pseudomorph subgrain boundaries consist of arrays of dislocations within a crystal lattice and unlike fractures would not act as conduits for melt migration instead the presence of former melt along subgrain boundaries requires that partial melting occurred in these locations because it is kinetically more favorable for melting reactions to occur there preferential melting in high strain locations may be attributed to strain energy which provides a minor energetic contribution to the reaction and leads to preferential melting in locations with weakened bonds and or the presence of small quantities of water associated with dislocations which may enhance diffusion rates or locally lower the temperature needed for partial melting

the effect of dauphine twinning on plastic strain in quartz we present an electron backscatter diffraction analysis of five quartz porphyroclasts in a greenschist facies t 300 400 c granitoid protomylonite from the arolla unit of the nw alps mechanical dauphine twinning developed pervasively during the incipient stage of deformation within two porphyroclasts oriented with a negative rhomb plane z almost orthogonal to the compression direction z twin orientation twinning was driven by the anisotropy in the elastic compliance of quartz and resulted in the alignment of the poles of the planes of the more compliant positive rhomb r nearly parallel to the compression direction r twin orientation in contrast we report the lack of twinning in two porphyroclasts already oriented with one of the r planes orthogonal to the compression direction one twinned porphyroclast has been investigated with more detail it shows the localization of much of the plastic strain into discrete r twins as a consequence of the higher amount of elastic strain energy stored by r twins in comparison to z twins the presence of dauphine twins induced a switch in the dominant active slip systems during plastic deformation from basal regions without twinning to and pervasively twinned regions dynamic recrystallization is localized along an r twin and occurred dominantly by progressive subgrain rotation with a local component of bulging recrystallization part of the recrystallized grains underwent rigid body rotation approximately about the bulk vorticity axis which accounts for the development of large misorientation angles the recrystallized grain size piezometer for quartz yields differential stress of 100 mpa the comparison of this palaeostress estimate with literature data suggests that mechanical dauphine twinning could have a potential use as palaeopiezometer in quartz bearing rocks

diagenesis of late proterozoic carbonates the beck spring dolomite of eastern california abstract petrographic and compositional attributes of limestone and dolostone in the beck spring dolomite of eastern california indicate that late proterozoic mineralogies isotopic compositions and diagenetic processes were similar to those inferred for younger phanerozoic marine carbonate sequences allochems in limestones include strontium rich ooids with well preserved concentric banding and cortices of equant neomorphic calcite that commonly exhibit dissolution and compaction features cements include microdolomite rich columnar marine calcite and equant spar calcites are depleted relative to dolomites and become enriched with stratigraphic depth acicular and columnar marine cement and allochems in dolostones display fabrics identical to those in limestones but are isotopically distinct dolomite ooids columnar and acicular cement crystal silt and early luminescent spar cement from four stratigraphic sections define overlapping positive oxygen carbon covariant fields that trend toward depleted calcite compositions early luminescent dolomite spar cement is unconformably overlain by depleted ferroan dolospar fabric data suggest that marine cement and ooids were precipitated as magnesian calcite and aragonite isotopic data suggest that metastable components locally stabilized to calcite during subaerial exposure while laterally dolomitization took place in mixed marine meteoric waters early dolospar precipitation began during replacive dolomitization and late ferroan dolospar precipitated during burial lack of evidence for hypersaline conditions suggests that late proterozoic normal marine carbonate isotopic composition was 0 5 2 018o and 5 3 0 5913c

the janda cavity at fruska gora the first cave assemblage from the southeast pannonian lowland vojvodina serbia abstract the recently discovered janda cavity yielded the first large mammal fossil assemblage of the late pleistocene age in the southeast pannonian lowland vojvodina outside the karst region of serbia the cavity is formed in the badenian reef limestone on the northern hillside of the fruska gora mountain the paper provides a paleontological description and taphonomic data on mammal remains collected from the loose sediments or scree herbivores are represented by bison priscus bojanus 1827 which is the most abundant species followed by megaloceros giganteus blumenbach 1803 and equus germanicus nehring 1884 with several remains of mammuthus sp and coelodonta antiquitatis blumenbach 1799 carnivores are represented by ursus spelaeus ingressus rabeder et al 2004 crocuta crocuta spelaea goldfuss 1823 panthera leo spelaea goldfuss 1810 as well as canis lupus linnaeus 1758 wolf remains are characterized by their large size almost reaching the size of hyenas which is in contrast with the finds of rather small pleistocene wolves from the caves in the mountainous part of serbia the faunal composition and the presence of mostly grazing forms among the herbivores indicate glacial conditions and an open landscape in the surroundings of the site during the formation of the janda cavity infill taphonomic observations indicate the cave hyena as a dominant bone accumulating agent in contrast to other cave hyena sites in serbia where mostly small and medium sized prey remains were accumulated prey preference for large and extra large mammals is noted it is supposed that this is the consequence of the differences between mountainous and lowland landscapes and environments climatic conditions different composition of animal and plant associations and also in different modes of competitions between predators

calcite twins their geometry appearance and significance as stress strain markers and indicators of tectonic regime a review twin lamellae are a widespread feature in calcites of any type and origin twinning in calcite is an important intracrystalline deformation mechanism with low critical resolved shear stress and virtually no temperature dependence in contrast to most slip systems in rock forming minerals twinning therefore permits intracrystalline deformation at very low temperature and very little confining pressure twinning alone however cannot lead to large strains because only one independent slip system is effectively available twins lead to discontinuous shearing on the grain scale which gives rise to considerable strain incompatibilities at grain boundaries twinning consequently leads to strain hardening detailed observations of the geometry of twin lamellae show that incompatibilities at grain boundaries are eliminated by pressure solution on the grain scale at low temperature and dynamic recovery processes at higher temperatures twins are found in various tectonic environments and record very small strains in rocks deformed under very little cover different twinning strain and twinning stress methods and palaeopiezometers are critically reviewed all methods are limited to strains of less than 15 shortening or extension by twinning twinning nevertheless is an important although not directly measurable contribution to the total strain in highly strained calcite rocks at least up to middle greenschist facies under which conditions it is the most effective contributor to the formation of strong lattice preferred orientations in calcite tectonites the appearance of calcite twin lamellae changes systematically as a function of deformation temperature micro twins and straight narrow 1 5 m but fewer twins are developed above approximately 200 c curved twins twinned twins and completely twinned grains indicate the progressive importance of other slip systems and larger intracrystalline strains are possible at ca 250 c and above ancient straight twin lamellae are modified into irregular geometries by recrystallization and grain boundary migration the appearance of calcite twins is proposed as an approximate but rapid and easy to use geothermometer in low temperature environments

life on land in the precambrian microfossils have been discovered in cavity fill and replacement silica that occurs between chert breccia clasts in 1200 million year old paleokarst at the top of the mescal limestone central arizona and in 800 million year old paleokarst at the top of the beck spring dolomite southeastern california microbial communities on precambrian g550 million years ago land may have been extensive enough to affect weathering erosion sedimentation and geochemical processes