diverse thrombolites from the c 2 4 ga turee creek group western australia abstract observations from a stromatolite thrombolite reef complex of the c 2 4 ga turee creek group western australia indicate diversity in stromatolite and microfossil morphology in addition to the appearance of clotted thrombolite like microbialites barlow et al 2016 barlow and van kranendonk 2018 here we document the diverse morphologies and textures of clotted microbialites from the turee creek group reef complex that occur interbedded and interlayered with stromatolites and sediments in the supratidal to subtidal facies the clotted microbialites consist of four types with distinct gross morphology mesostructure and microtextures including 1 an aggregate of isolated millimetre scale organic rich clots that accumulated following storm events and were cemented by coarsely crystalline radiating carbonate 2 domal bioherms composed of a framework of non laminated branching columns 3 stratiform clotted microbialites consisting of fine grained clots that form both an interconnected framework surrounded by coarsely crystalline cement or comprise a poorly defined mixture of fine and coarsely crystalline textural components and 4 thrombolites that comprise lobate bioherms with non layered internal textures variations in thrombolite texture and morphology are likely driven by a combination of environmental and biological factors as is the case in modern microbial carbonate environments such as shark bay and the bahamas these findings show that the turee creek group clotted microbialites are significantly more diverse than first recognised adding to previously documented expressions of microbialite complexity from this microbialite reef complex

trapping and binding a review of the factors controlling the development of fossil agglutinated microbialites and their distribution in space and time trapping and binding of allochthonous grains by benthic microbial communities has been considered a fundamental process of microbialite accretion since its discovery in popular shallow marine modern examples bahamas and shark bay however agglutinated textures are rare in fossil microbialites and thus the role of trapping and binding has been debated in the last four decades recently renewed attention on this subject has produced new findings of fossil agglutinated microbialites those mainly formed by trapping and binding and analogous to modern examples but they are still few and geologically recent mainly post paleozoic when compared to the 3 5 gyr long record of microbialites in order to better understand this discrepancy between modern and fossil examples an extensive literature review is presented here providing the first thorough database of agglutinated microbialites which shows that all of them are formed in shallow marine environments and most under tidal influence in addition a lower cretaceous example is described including very diverse microbialites each of them formed in a particular paleoenvironment some of these microbialites developed in grainy settings but only those formed in marginal marine tide influenced environments accreted mainly by trapping and binding the surrounding grains being analogous of modern agglutinated microbialites and matching the environmental pattern observed in the literature database the combination of the literature review with the case study allows to discuss the factors that control and enhance trapping and binding a occurrence of grains in the microbialite environment b frequent currents that mobilize the grains and supply them onto the microbialite surface c high concentration and diversity of electrolytes in the water to increase the adhesiveness of the extracellular polymeric substances eps of the microbialite surface and d a caco3 saturation state not high enough to promote early and strong carbonate precipitation within eps which would eventually decrease its availability to adhere grains therefore this review shows that the keys to solve the trapping and binding debate may be environmental because the conjuction of these hydrodynamic and hydrochemical parameters is preferentially achieved in shallow marine settings and especially in those influenced by tides at least since mesozoic times this explains the limited environmental and stratigraphic distribution of microbialites mainly formed by trapping and binding and opens new ways to look geologically and microbiologically at this process so often cited and yet so rare

quantitative identification of erosional lake bonneville shorelines utah abstract although the major shorelines of pleistocene lake bonneville have been recognized for more than 100 years less prominent shorelines have proven difficult to quantitatively identify and correlate since the time of g k gilbert by applying the savitzky golay filter and methodology of hare et al to high resolution lidar data of selected erosional shorelines five distinct correlatable shorelines between the well described bonneville and provo shorelines on the transgressive limb of the lake bonneville hydrograph are documented the results provide a framework for determining whether these transgressive features represent lake oscillations or stillstands during the height of the last glacial maximum in the eastern great basin of the western united states with possible attendant paleoclimate implications

quaternary palaeolakes in the evolution of semidesert basins with special emphasis on lake bonneville and the great basin u s a abstract this paper reviews attributes of quaternary lakes and lake basins which are often important in the environmental prehistory of semideserts basin floor and basin closure morphometry have set limits on palaeolake sizes lake morphometry and basin drainage patterns have influenced lacustrine processes and water and sediment loads have influenced basin neotectonics information regarding inundated runoff producing and extra basin spatial domains is acquired directly from the palaeolake record including the littoral morphostratigraphic record and indirectly by reconstruction increasingly detailed hypotheses regarding lake bonneville the largest late pleistocene palaeolake in the great basin are subjects for further testing and refinement oscillating transgression of lake bonneville began about 28 ka the highest stage occurred about 15 ka and termination occurred abruptly about 13 ka a final resurgence of perennial lakes probably occurred in many subbasins of the great basin between 11 and 10 ka when the highest stage of great salt lake successor to lake bonneville developed the gilbert shoreline and when the russell shoreline formed 500 600 km away in the carson desert of the lake lahontan basin the highest post gilbert stage of great salt lake which has been one of the few permanent lakes in the great basin during holocene time probably occurred between 3 and 2 ka a set of eighteen general observations regarding geologic aspects of the palaeolake record in semidesert basins is helping to guide quaternary studies in the great basin

3 d architecture depositional patterns and climate triggered sediment fluxes of an alpine alluvial fan samedan switzerland the sedimentary architecture of an alpine alluvial fan with a surface of 300 000 m2 near samedan switzerland was three dimensionally investigated using 9 km of ground penetrating radar sections with a penetration depth of 10 m radar facies patterns could be very well calibrated to sedimentology and dated horizons due to a 300 m long outcrop section at the foot of the fan six major reflectors have been identified and represent first order fan wide palaeosurfaces they are made up of up to 20 cm thick fine grained deposits partly with initial pedogenetic structures and wood remains which yielded ages between 5670 60 and 7515 65 a 14c bp between these surfaces different depositional lobes and specific architectural elements like channels levees or snouts of debris flows could be identified all these data were geo referenced to establish a complete quantitative 3 d time stratigraphic framework this allowed us to calculate deposited sediment volumes and sediment fluxes for different time slices between the dated palaeosurfaces sediment fluxes show an overall decline during the holocene which we interpret as the decling sediment production in the catchment area a function of the paraglacial cycle since the middle atlantic period the aggradation of the fan almost ceased and climate perturbations are no longer reflected in the sedimentary record since then within the aggradation period distinct peaks of high sediment fluxes could be correlated with known periods of glacier retreats in the swiss alps which points to a high sensitivity of the system to climate changes the results of our study give valuable new insights into thresholds of activity and quiescence of an alpine catchment fan system and its stage in the course of a paraglacial cycle although very important for the understanding of such dynamic systems under global warming scenarios and geo risk assessment such data sets are rarely available

palaeoshorelines of glacial lake kuray chuja south central siberia form sediments and process glacial lake kuray chuja which occupied the kuray and chuja basins during the quaternary period marine isotope stages 2 and 3 left distinct shoreline features around the basin margins at the greatest extent the lake had a surface area of 2951 km2 with wind fetches up to 70 km wind waves constructed erosional erosional accumulative and accumulative strandlines the latter including spits tombolos barrier beaches and offshore bars strandlines range in altitude between c 1600 and 2100 m the range in altitudes demonstrating lake level variations through time the shoreline forms and stratigraphy are detailed particular attention is given to the presence of pocket beaches on rock coasts the alluvial strandlines of which have distinctive alongshore gradients although reasonably ascribed to regional differential tectonic uplift the possibility that the local alongshore gradients are augmented as a process response to alongshore drift of sediment in a sediment starved system of closed coastal cells is explored using a simple numerical model

microbial mats as bioreactors populations processes and products microbial mats are dynamic and complex ecosystems exhibiting spatial and temporal heterogeneity the physical chemical environment is typified by steep gradients and distinct microenvironments these microenvironments support a great diversity of species with a wide range of metabolic processes these processes often result in coupled reactions and biogeochemical cycles and produce important end products such as trace gases and mineral precipitates the latter can impact the composition and character of the sediment imparting a biosignature these biosignatures can be preserved in the rock record and are useful in the interpretation of fossil record on earth and possibly as an indication of life on other planetary bodies the modern marine stromatolites of the exuma cays bahamas provide an ideal system for studying the populations processes and products in a microbial ecosystem using a multidisciplinary approach in order to acquire redox energy microbial populations need to carry out metabolic reactions at rates faster than the equivalent chemical abiotic reactions as such microbes can be viewed as bioreactors that preferably oxidize carbon to co2 to maximize the energy yield the study of the microbial role in carbonate sedimentation and lithification in these stromatolites provides a picture of microbial mats as bioreactors producing a biosignature

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

controls on microbial activity and tidal flat evolution in shark bay western australia microbial deposits at shark bay constitute a diverse living microbial carbonate system developed in a semi arid highly evaporative marine setting three tidal flats located in different embayments within the world heritage area were investigated in order to compare microbial deposits and their holocene evolution the stressing conditions in the intertidal subtidal environment have produced a microbial ecosystem that is trapping binding and biologically inducing caco3 precipitation producing laminated stromatolites tufted smooth and colloform non laminated thrombolitic forms pustular and cryptomicrobial non laminated forms microbial pavement a general shallowing upwards sedimentary cycle was recognized and correlated with holocene sea level variations where microbial deposits constitute the younger 2360 years bp and shallower sedimentary veneer in addition sediments have been documented with evidence of exposure during the holocene from 1040 to 940 14c years bp when sea level was apparently lower than present filamentous bacteria constitute the dominant group in the blister tufted and smooth mat types and coccus bacteria dominate the pustular colloform and microbial pavement deposit types in the subtidal environment within colloform and pavement structures microbial communities coexist with organisms such as bivalves serpulids diatoms green algae acetabularia crustaceans foraminifera and micro gastropods which are responsible for exoskeleton supply and extensive bioturbation the internal fabric of the microbial deposits is laminated sub laminar scalloped irregular or clotted depending on the amount of fine grained carbonate and the natural ability of microbial communities to trap and bind particles or induce carbonate precipitation nilemah tidal flat contains the thickest 1 3 m and best developed microbial sedimentary system its deposition pre dated the rocky point and garden point tidal flats with the most positive isotope values for 13c and 18o reflecting strong microbial activity in a highly evaporative environment there is an evolutionary series preserved within the tidal flats reflecting relative ages and degree of salinity elevation

morphology and paleoclimatic significance of pleistocene lake bonneville spits abstract pleistocene lake bonneville of western utah contains a variety of spits associated with shorelines and other features that formed between 21 000 and 12 000 14 c yr bp field studies in the low lying mountain ranges of the central portion of lake bonneville identified 17 spits of various types the spits are connected to small mountain ranges and islands vary in size from 0 02 to 0 5 km 2 and are composed of coarse grained well rounded poorly sorted sedimentary material sixteen of the 17 spits have a northeasterly to southwesterly orientation implying that winds were from the northwest to northeast approximately 180 out of phase with modern winds in the eastern great basin lake bonneville spit orientation is best explained as the result of persistent northerly winds caused by the high atmospheric pressure cell of the continental ice sheet and passage of low pressure extratropical storms south of the lake similar strong persistent winds are a common feature of modern continental ice sheets and passing low pressure systems if so the north american jet stream tracked south of lake bonneville as recently as 12 000 14 c yr bp well past the height of the last glacial maximum

sediment generation and delivery from large historic landslides in the southern alps new zealand abstract there is much variability of sediment yield in mountain river systems because it is influenced by both periodic e g snowmelt monsoonal circulation and episodic high intensity rainstorms earthquakes controls in the southern alps of new zealand landslides are dominant mechanisms of conveying large amounts of debris to river channels this paper attempts to quantify catastrophic modes of sediment delivery by presenting three recent examples of large landslides on the western slopes of the southern alps a combination of ground surveys dem based volume calculations and air photo interpretation attributes immediate postfailure sediment yields in excess of 70 000 t km 2 a 1 in the short term such landslide derived sediment pulses pose significant hazards to downstream settlements and infrastructure on alluvial fans where they cause massive aggradation increased flooding frequency and large scale channel avulsion in addition to intramontane valley floor obliteration or channel metamorphosis these geomorphic impacts may thus occur far beyond the initial locations of slope failure these catastrophic off site effects involve apparent net sediment delivery rates in the order of 10 5 10 6 m 3 a 1 the accurate quantification of the relative contribution of debris from the disturbing landslide to overall sediment flux is extremely difficult nonetheless are quantitative estimates of landslide derived sediment production and delivery important data to develop a more comprehensive understanding of the variability in alpine sediment flux such data are essential not only for use in hydraulic engineering or catchment management but also in gauging potential future impacts from rainstorm and earthquake induced landsliding in the southern alps

new evidence for an extended occupation of the provo shoreline and implications for regional climate change pleistocene lake bonneville utah usa abstract lake bonneville was a climatically sensitive closed basin lake that occupied the eastern great basin during the late pleistocene ongoing efforts to refine the record of lake level history are important for deciphering climate conditions in the bonneville basin and for facilitating correlations with regional and global records of climate change radiocarbon data from this and other studies suggest that the lake oscillated at or near the provo level much longer than depicted by current models of lake level change radiocarbon data also suggest that the lake dropped from threshold control much more rapidly than previously supposed these revisions to the lake bonneville hydrograph coupled with independent evidence of climate change from vegetation and glacial records have important implications for conditions in the bonneville basin and during the pleistocene to holocene transition

paleowind 11 000 bp directions derived from lake spits in northern michigan we report on the characteristics of several previously unstudied late pleistocene spits in northern lower michigan each spit developed as strong waves eroded a headland or island within the main and or later stages of glacial lake algonquin most have ese to wnw orientations with prominent recurved hooks at their ends some are as long as 20 km sedimentologically the spits contain thick several meters or more sequences of sand and well rounded gravel we suggest that summertime winds during the spits formation 11 800 to 10 500 bp were both very strong and dominantly from the e and se based on the following data 1 their ese source or head of the spit to wnw orientation 2 the presence of steep wave cut bluffs on the east sides of the islands and headlands and 3 spit locations on the northeastern shore of michigan s lower peninsula coupled with their absence on the northwestern shore just 100 km away wind direction data provided by these spits agree with paleoclimatic models that suggest that the laurentide ice sheet had developed a strong anticyclonic circulation the near lack of archeological sites from this time period in the northern lower peninsula which was surrounded by lake algonquin at that time supports the notion that the climate of northern lower michigan was inhospitably cold and very windy in the late pleistocene

from supratidal to subtidal an integrated characterisation of carbla beach shallow microbial mats hamelin pool shark bay wa lipid biomarkers stable carbon isotopes and microfabrics abstract modern microbial mats from shark bay are commonly regarded as robust analogues for precambrian stromatolites these microbial mats are complex ecosystems that exhibit intense biogeochemical recycling in this study a multi proxy approach including lipids compound specific carbon isotope analysis and petrography is used to characterise microbial communities in three different types of mats tufted pustular and smooth along the shallowest section of a tidal flat gradient cyanobacterial lipids were present in all three mats petrographical optical and scanning electron microscopy investigations also revealed that ooids in the tufted mat were larger and more common compared to the pustular and smooth mats biomarkers specific to sulfate reducing bacteria were detected in all mats the diatom specific c25 1 highly branched isoprenoid hbi alkene was most abundant in the smooth mat however imaging revealed that the smooth mat only contained rare diatoms of small size 10 m whereas the pustular mat contained a variety of larger diatoms 50 m the c25 1 hbi alkene marker is only produced by four diatom genera which were most likely more represented in the smooth mat additionally the smooth mat contained a greater contribution from aquatic macrophytes paq 0 38 compared to the shallower mats which is corroborated by the presence of 13c enriched seagrass lipids i e c29 steradiene in all the mats a major eukaryotic contribution was revealed via imaging techniques and supported by a high sterol content this eukaryotic component e g benthic foraminifera diatoms can impact the cohesive structure of the mats the lithification processes and the lipid distribution potentially complicating comparisons with precambrian microbialites that were not affected by eukaryotic activity this study reemphasizes the complexity of microbial ecosystems and therefore highlights the benefit of multi proxy approaches to characterise these biological systems

the role of endolithic cyanobacteria in the formation of lithified laminae in bahamian stromatolites the microboring activity of endolithic cyanobacteria plays a major role in the formation of the dominant lithified laminae in modern marine stromatolites in the exuma cays bahamas these stromatolites are composed primarily of fine grained carbonate sand that is trapped and bound by the filamentous cyanobacteria schizothrix sp periodic introduction of coccoid endolithic cyanobacteria solentia sp during hiatuses in stromatolite growth associated with very low rates of sedimentation results in the formation of lithified horizons 200 1000 lm thick these layers consist of micritized grains that are welded together at point contacts the micritization is caused by extensive microboring and carbonate precipitation within boreholes concurrent with endolithic activity grain welding occurs when boreholes cross from one grain to another at point contacts thus microboring destroys original grain textures but at the same time plays a constructional role in stromatolite growth by forming lithified layers of welded grains these lateral bands of fused carbonate grains help to stabilize and preserve the stromatolite deposits

age and paleoclimatic significance of the stansbury shoreline of lake bonneville northeastern great basin abstract the stansbury shoreline one of the conspicuous late pleistocene shorelines of lake bonneville consists of tufa cemented gravel and barrier beaches within a vertical zone of about 45 m the lower limit of which is 70 m above the modern average level of great salt lake stratigraphic evidence at a number of localities including new evidence from crater island on the west side of the great salt lake desert shows that the stansbury shoreline formed during the transgressive phase of late pleistocene lake bonneville sometime between about 22 000 and 20 000 yr b p tufa cemented gravel and barrier beaches were deposited in the stansbury shorezone during one or more fluctuations in water level with a maximum total amplitude of 45 m we refer to the fluctuations as the stansbury oscillation the stansbury oscillation cannot have been caused by basin hypsometric factors such as stabilization of lake level at an external overflow threshold or by expansion into an interior subbasin or by changes in drainage basin size therefore changes in climate must have caused the lake level to reverse its general rise to drop about 45 m in altitude reducing its surface area by about 18 5000 km2 and later to resume its rise if the sizes of great basin lakes are controlled by the mean position of storm tracks and the jetstream which as recently postulated may be controlled by the size of the continental ice sheets the stansbury oscillation may have been caused by a shift in the jetstream during a major interstade of the laurentide ice sheet

tectonics mantle spread across the sea floor the sea floor around mid ocean ridges is often carpeted by hummocky lava flows images from the southwest indian ridge sea floor however show a smooth texture created by exhumation and widespread exposure of altered mantle rocks

paleowind velocity and paleocurrents of pluvial lake manly death valley usa pluvial lake deposits are found throughout western north america and are frequently used to reconstruct regional paleoclimate in death valley california usa we apply the beach particle technique bpt of adams 2003 sedimentology 50 565 577 and adams 2004 sedimentology 51 671 673 to lake manly deposits at the beatty junction bar complex bjbc desolation canyon and manly terraces and calculate paleowind velocities of 14 27 m s these wind velocities are within the range of present day wind velocities recorded in the surrounding area sedimentary structures and clast provenance at desolation canyon and the manly terraces indicate sediment transport from north to south lake level based on the elevation of constructional features indicates that the hill west of the bjbc was an island and that the bjbc spits formed during simple lake regression the data are consistent with the hypothesis that the present wind regime velocity and direction formed the pluvial lake manly features

sequence stratigraphy of the red river formation williston basin usa stratigraphic signature of the ordovician katian greenhouse to icehouse transition abstract the upper katian upper ordovician red river formation is a carbonate evaporite supersequence that formed in the epicratonic williston basin of western north america this study focuses on the upper part of the formation in the southern us part of the basin the studied succession is made up of three transgressive regressive sequences rr1 rr2 and rr3 each 0 5 1 m y in duration and composed of relatively few meter scale high frequency cycles parasequences sequence boundaries are characterized by intraclastic breccia laminated dolomite successions that have been truncated and capped by evaporite deposits subaqueous anhydrites within each sequence represent evaporite lowstand systems tracts lsts that formed during relative sea level lows that lead to the precipitation of gypsum later recrystallized into anhydrite in a quiet salina type environment transgressive tst and early highstand systems tracts hst are composed of subtidal facies of predominantly skeletal mudstone to wackestone packstone with abundant burrow mottling late hsts are predominantly composed of peritidal porous laminated dolomite the study illustrates how the sequence stratigraphic framework of carbonate evaporite deposits from the williston basin relates to the late ordovician glacio eustasy transitional climates and low basin subsidence in an arid setting

characteristics distribution and morphogenesis of subtidal microbial systems in shark bay australia abstract the distribution nature and extent of microbial deposits in hamelin pool shark bay have been investigated and mapped with emphasis on the occurrence external morphologies internal fabrics constructional mechanisms microbial communities growth rates and sediment associations in the intertidal and previously little researched subtidal zone detailed georeferenced substrate mapping revealed extensive subtidal microbial deposits occupying approximately 300 km 2 of the total holocene 1400 km 2 area of hamelin pool the microbial pavement covers 227 km 2 of the subtidal substrate that together with columnar structures reveals a subtidal microbial habitat which occupies an area 10 times larger than the area of the intertidal deposits microbial carbonate is composed of aragonite 80 98 that reveals high positive values of 13 c 4 46 to 5 88 and 18 o 3 06 to 3 88 as a characteristic of the highly evaporative environment with extensive microbial activity oldest dated heads are 1915 and 1680 14 c years bp and the overall system was deposited in two stages the first between 2000 and 1200 and the last from 900 years bp to the present slow growth rates vary from less than 0 1 mm year to 0 5 mm year different internal fabrics were constructed according to their position in relation to the littoral zone by distinct microbial communities and lateral fabric relations have been established evidence of shallowing upward fabric sequences of microbial origin reflects relative falling sea levels during the late holocene and is likely useful in ancient environmental interpretation a sequence of events and mechanisms are described emphasizing differences between the stromatolitic thrombolitic and cryptomicrobial deposits in shark bay the new substrate map and depositional history for this distinctive and peculiar microbial habitat establish the significance of subtidal structures and emphasize the geoscientific importance of hamelin pool especially with respect to early life studies and ancient analogues for understanding microbial activity deposit characteristics fenestral fabrics and distribution

evaluation of wasatch fault segmentation and slip rates using lake bonneville shorelines 1 analysis of lake bonneville shorelines using lidar digital elevation data challenges accepted models of wasatch fault deformation since the late pleistocene while footwall deformation of the weber segment of the wasatch fault is consistent with back rotation of the footwall block and greatest displacement rate toward the center of the segment shorelines along the footwall of the salt lake city segment decrease in elevation toward the interior and are highest at the segment boundaries an opposite pattern of footwall deformation than predicted for boundaries arresting or strongly inhibiting displacement during earthquakes the spatial pattern of footwall rebound implies that some of the proposed persistent fault segment boundaries do not stop earthquake ruptures that originate on adjacent fault segments nor constrain ruptures initiated within the salt lake city segment net vertical fault displacement at the boundary between the salt lake and provo segments is 16 20 m over the past 16 3 18 5 ka corresponding to a vertical displacement rate of 0 8 1 2 mm yr a net fault slip rate of 2 0 2 8 mm yr and horizontal extension rate of 1 8 2 6 mm yr on the 25 west southwest dipping fault that forms the southern salt lake city segment boundary shoreline analysis suggests isostatic rebound caused by a drop in lake level was concentrated during a relatively short 2000 year time period following the bonneville flood at 16 ka lidar derived topography in conjunction with robust geomorphic datums improves our ability to map deformation associated with lithospheric flexure and faulting while demonstrating the limitation of lacustrine shorelines in this type of analysis

bipolar changes in atmospheric circulation during the little ice age annually dated ice cores from siple dome west antarctica and central greenland indicate that meridional atmospheric circulation intensity increased in the polar south pacific and north atlantic at the beginning 1400 a d of the most recent holocene rapid climate change event the little ice age lia as deduced from chemical concentrations at these core sites the lia was characterized by substantial meridional circulation strength variability and this variability persists today despite strong evidence for an end to lia cooling thus increased late 20th century storm variability may be in part a result of the continuation of these climatic fluctuations

microbial biomineralization processes forming modern ca mg carbonate stromatolites abstract modern ca mg carbonate stromatolites form in association with the microbialmat in the hypersaline coastal lagoon lagoa vermelha brazil thestromatolites although showing diversi ed fabrics characterized by thin orcrude lamination and or thrombolitic clotting exhibit a pervasive peloidalmicrofabric the peloidal texture consists of dark micritic aggregates of veryhigh mg calcite and or ca dolomite formed by an iso oriented assemblage ofsub micron trigonal polyhedrons and organic matter limpid acicular crystalsof aragonite arranged in spherulites surround these aggregates unlike thearagonite crystals organic matter is present consistently in the dark micriticcarbonate comprising the peloids this organic matter is observed as sub micron at and lamentous mucus like structures inside the interspaces of thehigh mg calcite and ca dolomite crystals and is interpreted as the remains ofdegraded extracellular polymeric substances moreover many fossilizedbacterial cells are associated strictly with both carbonate phases these cellsconsist mainly of 0ae2to4lm in diameter sub spherical rod like and lamentous forms isolated or in colony like clusters the co existence offossil extracellular polymeric substances and bacterial bodies associated withthe polyhedrons of ca mg carbonate implies that the organic matter andmicrobial metabolism played a fundamental role in the precipitation of theminerals that form the peloids by contrast the lack of extracellular polymericsubstances in the aragonitic phase indicates an additional precipitationmechanism the complex processes that induce mineral precipitation in themodern lagoa vermelha microbial mat appear to be recorded in the studiedlithi ed stromatolites sub micron polyhedral crystal formation of high mgcalcite and or ca dolomite results from the coalescence of carbonatenanoglobules around degraded organic matter nuclei sub micron polyhedralcrystals aggregate to form larger ovoidal crystals that constitute peloids subsequent precipitation of aragonitic spherulites around peloids occurs asmicro environmental water conditions around the peloids change keywords bacterial fossils biomineralization microbialite nanoglobules peloids stromatolites

defining biominerals and organominerals direct and indirect indicators of life abstract by introducing the new term organomineral to apply to minerals that are affected by organics mostly life related but not directly produced by living cells we hope to increase the accuracy of the terminology in present usage we believe that the term biomineral does not describe all mineral deposits precisely enough and offer case studies to support instances where the use of the new term organomineral is more appropriate we provide examples of some materials that are biominerals such as those in diatoms and human bones and which perform a functional purpose we then attempt to show that terminology can sometimes mislead investigators drive the direction and prejudice interpretations of scientific investigation this is achieved by presenting case studies of minerals that have been investigated as biominerals although they may not actually be directly controlled by biology for this reason we pay special attention to desert varnish hot spring siliceous deposits stromatolites and bacterial encrustations we go on to explain why we regard biominerals as direct indictors of life whereas organominerals should be treated as indirect indicators of life that require careful characterization to establish the origin of contained organics and whether these are biotic in origin how organic compounds are preserved and transformed in sedimentary environments and in the mineral matrix is as highly relevant to the study of modern earth environments as it is in the search for the oldest evidence of life in the terrestrial rock record it is also important to many disciplines such as microbiology and archaeology and especially to scientists planning missions to look for evidence of life on other planetary surfaces

the composite nature of the provo level of lake bonneville great basin western north america abstract deposits of a transgressive phase lake bonneville stillstand or oscillation are found just below the elevation of the regressive phase provo shoreline at numerous exposures throughout the bonneville basin existence of these subprovo shoreline deposits provides a new explanation for the massive size of provo depositional and erosional landforms which can no longer be explained by a long stillstand at the provo shoreline provo coastal landforms are large because they are superimposed on subprovo landforms results also help to clarify divergent interpretations regarding the relative age of the provo shoreline and the number of times it was occupied by the water plane occupation of approximately the same level during both the transgressive and the regressive phase of lake bonneville may be coincidental or it may indicate that a bedrock sill controlled outflow at subprovo as well as provo time rise to the bonneville level could have occurred after massive slope failure plugged the outlet pass

quantitative characterization and elevation estimation of lake lahontan shoreline terraces from high resolution digital elevation models the precision with which the elevation of a feature such as a terrace can be measured depends on the characterization of the noise contaminating the measurement a method for identification and extraction of terrace feature elevations is presented and the topographic noise due to erosion as well as measurement error is quantified high resolution digital elevation models dem are acquired at six wave cut volcanic bedrock terrace sites from around the highstand of paleo lake lahontan in the western great basin local dems which are tied to regional geodetic control were acquired using conventional total station rapid postprocessed and real time kinematic global positioning system methods the topographic signal is processed with derivative filters for geomorphic feature recognition and averaging for noise reduction results indicate that noise levels for identifiable features such as riser crest knickpoint and slope inflection point are statistically equivalent and on the order of 0 5 m standard deviation averaging within topographic bins spanning 50 m along terrace strike yields feature elevation estimates with standard errors on the order of 0 12 m the mean bench window elevation between the riser crest and knickpoint has the lowest standard error and is systematically related to water level propagation of surveying geoid estimation and terrace feature elevation estimation errors indicates that displacements on the order of 0 5 m may be resolved using these methods elevation estimate interpretation involves terrace development degradation and neotectonics but this new methodology has significant advantages in studies of neotectonic or geomorphic processes using local terrace elevation measurements

morphological signatures of microbial activity across sediment and light microenvironments of lake vanda antarctica abstract cyanobacteria dominated microbial mats in lake vanda grow with pinnacles and ridges separated by prostrate mat rocks protrude over microbial mats on the lake bottom to create localized dm scale gradients in sedimentation and irradiance the effects of sedimentation on pinnacle and ridge growth were isolated from photosynthetic activity by contrasting growth across microenvironmental gradients sedimentation rate was measured as the mass of sand and mud sized sediment in mat that accumulated over 11 years and the incident light was modeled near and under rocks by reconstructing topography using structure from motion techniques morphologically diverse pinnacles and ridges were documented in both exposed and sheltered mat microenvironments in addition to growing downward from the underside of overhanging rocks mat that grew with 40 irradiance under overhangs did not have consistent differences in pinnacle density or ridge abundance as a function of sedimentation rates or irradiance when compared to exposed mat however their morphology did change significantly with changes in the direction of incident irradiance where irradiance was

oligo miocene lacustrine microbial and metazoan buildups from the limagne basin french massif central the limagne basin french massif central is an extensive continental lacustrine system accommodating microbial and metazoan buildups from chattian to aquitanian age a description of these buildups and their associated biotic components in grand gandaillat and crechy quarries provides insights into their spatio temporal distribution patterns flats cauliflowers domes cones and coalescent columnar morphologies have been identified with a main laminated mesofabric and laminated columnar filamentous and caddisfly coated microfabrics two low gradient margin models emerged based on the changes in the distribution morphology and size of the microbial and metazoan rich deposits through time the first model applies to the chattian deposits in the grand gandaillat quarry and the second to the aquitanian deposits in the crechy quarry this study emphasizes the heterogeneity of marginal lacustrine carbonate siliciclastic cycles the lacustrine palustrine cycles of the limagne basin record i lacustrine deposits composed of microbial and metazoan buildups and organic matter rich marls indicating periods of high accommodation and ii palustrine deposits composed of mudstone and clayey paleosoils indicative of periods of low accommodation the cycles differ with thin and symmetrical deposits that dominate the chattian cycles whereas thicker and asymmetrical deposits mark the aquitanian cycles in addition the chattian buildups are exclusively microbial and only a few centimeters thick whereas the aquitanian ones are multiple meters in height and are composed of both microbes and metazoans climatic tectonism volcanic and local parameters are involved in the deposition of buildups and their organization in each different cycle climate may control the long term arid humid sedimentary succession tectonic may explain the difference in the deposit thickness between two cycles of different ages and localizations as well as the specific distribution of the buildups throughout the basin volcanism may control the chemical lacustrine conditions and local physiography may impact the soil removal ability of the lake margin

the biogeomorphology of shark bay s microbialite coasts abstract the world heritage microbialites coquinas and microbialitic sediments of hamelin pool shark bay western australia form through complex community and environmental interactions resulting in surficial co2 sequestration predicted climate change impacts threaten the stability of this setting and the balance of biogeomorphological processes that generate them in this setting long term surficial co2 sequestration occurs through the combination of biomineralisation organomineralisation and lithification which locks atmospheric co2 into caco3 rocks and sediments biogeomorphological processes that control the distribution and effectiveness of these mechanisms including biostabilisation bioconstruction bioerosion and bioturbation have not been addressed in this setting to date a three dimensional biogemorphological mapping unit framework is defined at three locations in hamelin pool within the shallow subtidal to supratidal zones based on historical and recent multiscale datasets this framework is used to review the complex distribution of geomorphological and biogeomorphological processes the distribution of lithification within a biogeomorphological process context is examined and current geological analogue models of microbialite and coquina development are expanded to include biogeomorphological processes the framework is used to understand the impacts of increased water elevation in response to intensification of the leeuwin current during the 2010 2012 ningaloo nino event potential climate change impacts are identified including reduced intertidal bioconstruction and a shift from microbialitic structure generation to increased grain generation reducing stromatolite development review of the uncertainty of impacts of ocean acidification and temperature shifts on biomineralisation organomineralisation and lithification processes crucial to the maintenance of the outstanding universal values in this world heritage location suggests urgent research is required

challenges to carbonate evaporite peritidal facies models and cycles insights from lower cretaceous stromatolite bearing deposits oncala group n spain abstract peritidal carbonate evaporite successions since they are developed in the transition between continental and marine realms provide essential keys for palaeobathymetric and palaeoclimatic interpretations as a result several facies models have been proposed to assist on the interpretation of ancient tidal flat deposits and peritidal successions have been extensively used for cyclicity analyses in this study well exposed lower cretaceous peritidal deposits oncala group cameros basin n spain are analysed and compared with the most commonly used present day analogues from shark bay the arabian gulf and the bahamas and with ancient peritidal successions providing their palaeoenvironmental and palaeoclimatic interpretation assessing the usefulness and limitations of the facies models and evaluating the suitability of these deposits for analysis of decimetre to metre scale cycles the studied peritidal deposits consist of thinly bedded to laminated dolostones dolomitic stromatolites stromatolite breccias flat pebble and edgewise breccias and calcite and quartz pseudomorphs after anhydrite nodules abundant resemblances of the peritidal deposits of the oncala group with those of shark bay including that they are largely composed of microbialites and intraclasts makes the peritidal deposits of the oncala group one of the best fossil analogues of this present day setting however the presence of anhydrite nodules indicates pervasive evaporite precipitation in the supratidal zone which is a feature that does not occur in supratidal flats of shark bay but is characteristic of arid sabkhas of the arabian gulf nevertheless the fact that carbonate evaporite tidal flats of the oncala group were laterally related with siliciclastic tidal flats with large freshwater input and broadly inhabited by dinosaurs suggests that anhydrites precipitated under less arid climates than those of the arabian gulf nowadays pointing to semiarid climatic conditions during deposition moreover the fact that peritidal deposits with anhydrite nodules were exclusively formed in a low subsidence area of the cameros basin suggests that the rate of accommodation space creation also played an important role in their development regarding the comparison with other fossil peritidal sediments the studied deposits show more abundant similarities with proterozoic and cambrian successions composed mainly of stromatolites microbial laminites and intraclasts than with other mesozoic peritidal deposits in which bioclasts and burrowing are usually more abundant this highlights the difficulties for assigning specific features to certain geological ages finally peritidal facies of the oncala group may change laterally and vertically to any other facies showing a patchy lateral distribution of facies and an unsystematic vertical stacking pattern the sedimentary features of the stromatolite breccia and thinly bedded to laminated dolostone facies do not allow their assignment to a unique tidal zone moreover sedimentary features indicative of subaerial exposure such as anhydrite nodules formed in the capillary zone occur within any of the carbonate facies and show limited lateral extent this results in a succession that cannot be clearly subdivided into subsequent shallowing upward cycles not even by using erosive surfaces or the anhydrite nodule layers as marker horizons of the upper part of the cycles because their limited lateral extent prevents reliable correlations similar composite lateral and vertical facies relationships have been documented both in the present day analogues and in ancient successions which suggests that this kind of facies relationships may be common in peritidal successions and highlights the caution that must be taken when trying to perform cyclicity analysis on them

chronology of lake bonneville 30 000 to 10 000 yr b p abstract 368 radiocarbon ages between 30 and 10 cal ka for samples collected from outcrops and shorelines from the lake bonneville basin have been compiled for this paper samples include 1 organic materials from sources outside the lake such as wood charcoal plant fragments from emergent aquatics and dispersed wetland organics and 2 carbonate materials deposited in the lake such as mollusk shells tufa charophyte debris ooids and marl in general organic materials provide rather than precise ages for lacustrine events but their interpretation is less complicated than interpretation of results from carbonate samples the data set shows evidence of contamination of different carbonate samples with both younger carbon and older carbon for example a radiocarbon reservoir at certain places within the lake during the middle transgressive phase accounts for ages of mollusk shells that are older than basal wood ages at similar altitudes the large number of ages permits an accurate reconstruction of the lake chronology conflicts between ages can be detected and reliable ages can be meaningfully integrated in interpretations if fewer ages were available the chronology might look simpler but its accuracy would be unknown

stratigraphy and chronology of offshore to nearshore deposits associated with the provo shoreline pleistocene lake bonneville utah abstract stratigraphic descriptions and radiocarbon data from eleven field locations are presented in this paper to establish a chronostratigraphic framework for offshore to nearshore deposits of lake bonneville based on key marker beds and geomorphic position the deposits are interpreted to have accumulated during the period from the late transgressive phase through the overflowing phase into the regressive phase of the lake radiocarbon ages of sediments associated with the provo shoreline indicate that lake bonneville dropped rapidly from the provo shoreline at about 12 600 14c yr bp 15 000 cal yr b p the presence of one or more sand beds in the upper part of the provo aged marl indicates rapid lowering of lake level or storm events at the end of the provo episode an accurate understanding of the timing and nature of lake bonneville s climate driven regression from the provo shoreline is critical to correlations with records of regional and hemispheric climate change the rapid descent of the lake from the provo shoreline correlates with the decline of lakes lahontan and estancia and with the onset of the b o lling aller o d warming event

transgressive stratigraphic record and possible oscillations of late pleistocene lake bonneville northern hogup mountains utah u s a abstract distinct mappable facies changes make the stratigraphic record of the shorezone of late pleistocene lake bonneville the most robust indicator for past lake level oscillations unfortunately clear stratigraphic evidence of transgressive and regressive deposits has been generally lacking new stratigraphic and chronological data within the lacustrine shorezone sediments of the hogup mountains of northwestern utah provide some of the best evidence yet for oscillations within the overall transgressive phase of the lake this study documents two previously unknown oscillations hereby named the lower hogup 22 cal ka and upper hogup 20 6 cal ka oscillations and provides further evidence for the previously proposed u2 oscillation 21 3 cal ka the study suggests that the water level of the lake changed dramatically up to 25 of the lake s total volume during the transgressive phase 30 15 cal ka with the additional oscillations documented in this study there are seven proposed oscillatory events during the transgressive phase of the lake these events likely correlate to rapid but short term regional climatic fluctuations during the broader climatic trends of the last glacial maximum however it is still unknown what specific climatic drivers are causing these oscillations and if these events can be correlated to other global climatic events

lithifying microbial mats in lagoa vermelha brazil modern precambrian relics abstract bacterial populations microbial and mineral forming processes and their products were analyzed in lagoa vermelha brazil the microbial mat and underlying sediment were studied as a unique system to define the boundary conditions responsible for high mg calcite and dolomite formation in the uppermost layers of the microbial mat oxygenic photosynthesis and aerobic respiration resulted in calcite precipitation whereas in the underlying anoxic layers of the mat sulfide oxidation and sulfate reduction induced formation of a range of carbonate minerals with increasing mg concentrations the chemical mineralogical and biological conditions presently found in lagoa vermelha may have been more common in the precambrian the microorganisms performing the metabolic processes related to carbonate mineral formation within lagoa vermelha s hypersaline microbial mat may have already been present in the precambrian thus microbial carbonate as a biomineral could be a record of metabolism throughout geological time

shrub morpho types as indicator for the water flow energy tivoli travertine case central italy abstract travertines from tivoli area central italy possess abundant shrub like fabrics that are laterally continuous over hundreds of square meters they occur dominantly in horizontal layers with aggradational and progradational stacking patterns their fabrics and morphologies are remarkably similar to the shrubs lithotypes reported in literature for the pre salt reservoirs offshore brazil and angola with huge oil accumulations petrographic and micro computer tomography analyses allowed the identification of six shrub morpho types i e narrow dendriform wide dendriform fili dendriform arborescent arbustiform and pustular dendriform shrubs are the most common lithotype in tivoli area and three different subtypes could be distinguished according to the arrangement of their branches the shrubs consist largely of peloidal micritic aggregates engulfed in spar calcite ranging in average from 1 to 3 cm in height the shrubs are interpreted to have developed in very shallow extensive waterlogged slightly inclined flat areas changing laterally into a slope system with crusts as the main lithotype changes in the hydrodynamic conditions with episodes of stagnancy influenced the shrub morpho types making them very variegated shrub morphologies likely reflect specific micro environments that are controlled by water flow rates evaporation and microbial activity the latter processes influenced shrub fabric and morphology under high flow conditions co 2 degassing is the main process leading to carbonate precipitation consequently denser and tightly packed morphologies will precipitate composing mainly the crust lithotype in this scenario microbes are less dominant dendriform shrubs with narrow wide and fili morphologies are interpreted to occur in moderate to low energy water flows narrow dendriform shrubs reflect faster flowing conditions with decreasing impact of flow on the morphological aspects from wide dendriform shrubs to fili dendriform shrubs slow to very slow flowing waters are more characteristic for the arborescent arbustiform and pustular shrubs that possibly are highly influenced by evaporation a decrease of water flow likely allows higher microbial activity and consequently shrub morphologies become more fragile and enriched in peloidal micritic aggregate fabrics

alternation of microbial mounds and ooid shoals middle jurasssic morocco response to paleoenvironmental changes abstract the occurrence of neritic microbial carbonates is often related to ecological refuges where grazers and other competitors are reduced by environmental conditions or to post extinction events e g in the late devonian early triassic here we present evidence for middle jurassic bajocian microbial mounds formed in the normal marine shallow neritic setting of an inner ramp system from the high atlas of morocco the microbial mounds are embedded in cross bedded oolitic facies individual mounds show low relief domal geometries up to 3 m high and 4 5 m across but occasionally a second generation of mounds exhibits tabular geometries

lake bonneville constraints on lithospheric thickness and upper mantle viscosity from isostatic warping of bonneville provo and gilbert stage shorelines the deformed shorelines of the late pleistocene lake bonneville provide an excellent opportunity to analyze the response of the earth to surface loads of relatively short wavelengths 400 km and short duration 30 kyr recently revised estimates of the lake loading history and an expanded compilation of shoreline elevations for the bonneville 1550 m provo 1440 m and gilbert 1300 m shorelines have prompted us to reexamine the deflection the earth model we use is identical with that employed by nakiboglu and lambeck and consists of an elastic plate overlying a maxwell viscoelastic channel and a rigid base our calculation differs from that of nakiboglu and lambeck in two respects we used a significantly more detailed load model and we compared our results with observations from three distinct shorelines the lake elevation history spans 32 kyr in 18 piecewise linear segments the water load is computed at each time step from a digital terrain model 4 4 km cell size and a specified lake elevation we find that the use of three separate shorelines significantly reduces the acceptable region of parameter space the effective elastic lithospheric thickness is 23 2 km the mantle viscosity is 1 2 0 2 1020 pa s and the depth to a significant viscosity increase is no less than 300 km though it might be much more examination of the residual deflections differences between observed and computed shoreline elevations reveals a regional tilt down to the ne of 6 10 5 which we attribute to collapse of the peripheral bulge produced by the laurentide ice sheet

transgressive phase barriers as indicators of basin wide lake level changes in late pleistocene lake bonneville utah usa abstract lake bonneville was the largest of the late pleistocene pluvial lakes that once filled part of the great basin of the interior western united states as the lake reached its highest level at the bonneville shoreline and overflowed it eroded through landslide deposits and alluvium near red rock pass idaho and quickly dropped over 100 m to the provo shoreline this unique flooding history and resulting rapid lake level fall allows us to assume that all shorelines with elevations between the bonneville and provo levels the intermediate shorelines formed during the lake s transgressive phase various types of depositional features characterize the transgressive phase shorelines including barrier spits and bayhead barriers this study uses 5 m auto correlated digital elevation models dems airborne light detection and ranging lidar and ground penetrating radar gpr surveys to measure the internal and external structure of intermediate barriers analysis of 102 barriers at 26 different locations further documents the lake s constructional shorelines while employing a statistical approach to show patterns in basin wide lake levels these methods identify only one confidently correlatable intermediate shoreline at an adjusted elevation of 1530 m 4 m providing evidence of a still water level during the late transgressive phase of lake bonneville the variability of elevations along barrier crests indicates that the formation of depositional features is highly dependent on local wave climate in addition to basin scale climatic controls

late pleistocene and holocene sea level change in the australian region and mantle rheology summary spatial and temporal variations in sea level are produced by the melting of the late pleistocene ice and by the earth s response to the redistribution in surface loads by examining different parts of the sea level curves of the past 20 000 yr from geographically widely distributed regions it becomes possible to constrain models of the melting history of the ice sheets and of the earth s rheology observations from sites away from the former arctic ice sheets such as the australian and south pacific region are particularly important for constraining the total meltwater volumes added into the oceans in the past 20 000 yr and the rates at which this occurred these observations indicate that the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9000 6000 yr ago when it may have lagged behind minor melting of the antarctic ice sheet appears to have continued throughout the late holocene differential observations of the late holocene sea level change recorded at sites in the same region are particularly useful for estimating parameters describing the earth s non elastic response to surface loading the effective parameters used here are a lithospheric thickness an upper mantle viscosity and a lower mantle viscosity describing the response below 670 km depth with the observations used here it is not possible to separate the lithospheric thickness h from the upper mantle viscosity and the viscosity results are based on the assumption that 50 h 100 km neither do these observations provide a resolution of the depth dependence of viscosity in the upper mantle and the resulting estimates are effective parameters only differential sea levels along continental margins and along the shores of large gulfs and bays constrain the effective upper mantle viscosity to be about 1 2 1020 pa s 1 while differential values from islands of different sizes are suggestive of a somewhat lower value the lower mantle taken to be below 670 km depth viscosity is about two orders of magnitude greater than this the estimated ice and rheological models explain many of the holocene sea level observations throughout the australian and southern pacific region the tilting of continental margins as exemplified by observations of variable amplitudes of the holocene high stands and the variable times at which sea levels first reached their present level along the north queensland coast and great barrier reef is well represented by these models differential holocene sea levels observed along the narrow spencers gulf of south australia are also well explained by the models and in neither case is it necessary to invoke tectonic motions predicted late holocene sea levels at small to medium sized islands are characterized by small amplitude high stands that reached their maximum values about 4000 2000 yr ago consistent with observations from the society cook and tuamotu islands

microbialite fields developed in a protected rocky coastline the shallow carbonate ramp of the aptian romualdo formation araripe basin ne brazil abstract the aptian romualdo formation is a siliciclastic dominated sedimentary unit recording the last marine ingression within the cretaceous interior basins of northeastern brazil at the western margin of the araripe basin rocks of the romualdo formation are mainly represented by carbonates resting abruptly over the proterozoic crystalline basement detailed mapping and stratigraphic analysis revealed two stromatolite fields that were described and discussed for the first time several bioherms biostromes and isolated stromatolites characterized by distinct microbialite morphologies associated with echinoid rich strata have been identified suggesting that hypersalinity water depth and hydraulic conditions were the main factors controlling stromatolite morphogenesis a cm thick amalgamated bivalve rudstone resting directly on the basement and representing a shell concentration formed above the fair weather wave base was also recorded based on the regional distribution of the stromatolite types and associated sedimentary facies we interpret the depositional environment as a local low gradient carbonate ramp deepening to the east our data robustly indicated that the western rocky shorelines of the araripe basin during the aptian were populated by microbial mats and stromatolites in a condition analogous to the modern world famous hamelin pool shark bay western australia finally the development of stromatolites and echinoid bearing microbialites at the western margin of the basin may be correlated with the formation of bakevelliid and cassiopid rich shell beds in the upper part of the romualdo formation at the eastern margin

shrub and pore type classification petrography of travertine shrubs from the ballik belevi area denizli sw turkey petrographical and petrophysical properties of the turkish ballik belevi travertine shrubs demonstrate the necessity of reservoir oriented classifications for shrub related lithotypes and associated pore types the presented shrub related lithotype classification incorporates morphology size and fabric which are linked to specific pore types and sizes the travertines show highly complex pore networks as observed from computed tomography reconstructions making them of interest for the development and optimization of pore characterization methodologies and techniques following an upscaling approach porosity 3 15 and permeability 0 505 md strongly vary for the ballik belevi travertines the highest porosities and permeabilities are measured for horizontal samples dominated by slightly dissolution enlarged intershrub and interdigit growth framework porosity mostly found for dendritic shrubs the presented shrub and pore type classification can be applied to shrubs worldwide studying outcrop analogues of continental carbonates helps to better understand heterogeneities lateral variability and properties of pre salt cretaceous continental carbonate reservoirs offshore brazil and angola

revisiting the deformed high shoreline of lake bonneville abstract since g k gilbert s foundational work in the eastern great basin during the late 1800s the late pleistocene lake bonneville 30 10 ka has been recognized as a natural laboratory for various quaternary studies including lithospheric deformation due to surface loading and climate forced water balance changes such studies rely on knowledge of the elevations of lake bonneville s paleoshoreline features and depositional landforms which record a complex history of lake level variations induced by deglacial climate change in this paper we present 1 a new compilation of 178 elevation measurements of shoreline features marking lake bonneville s greatest areal extent measured using high precision differential gps dgps and 2 a reconstructed outline of the highest shoreline based on dgps measurements submeter resolution aerial imagery topographic digital elevation models dems and field observations we also 3 devise a simplified classification scheme and method for standardizing shoreline elevation measurement for different shoreline morphologies that includes constraints on the position of the still water level swl relative to each feature type the deformation pattern described by these shoreline features can help resolve the relative effects of local hydro isostasy due to the lake load and regional solid earth deflection due to the laurentide ice sheet with potential implications for earth rheology glacial isostatic adjustment and eustatic sea level change

ordovician metre scale cycles implications for climate and eustatic fluctuations in the central appalachians during a global greenhouse non glacial to glacial transition abstract metre scale shallowing upward cycles in ordovician carbonates of the central appalachian basin record climate and eustatic fluctuations during a transition from early ordovician global greenhouse to late ordovician icehouse conditions peritidal facies and shale abundance suggest a long term trend in this area from semi arid early ordovician to more humid middle to early late ordovician conditions with a return to semi arid conditions during the late ordovician the climatic fluctuations were most likely produced by tectonics uplift and erosion related to taconic orogenesis plate motion of north america and the areal extent of water covering the shelf peritidal cyclic facies indicate that high frequency relative sea level fluctuations were of small amplitude 20 m relative sea level fluctuations that decreased into the later ordovician if these sea level changes are eustatic then the increased amplitude may mark the early initiation of continental glaciation on gondwana in the late middle ordovician followed by waning of ice sheets prior to the latest ordovician glaciation

the evolution of microbialite forms during the early triassic transgression a case study in chongyang of hubei province south china abstract the widespread development of microbialites in shallow areas of the tethys ocean at the start of the early triassic reflects the deterioration of marine ecosystems in the aftermath of the extinction that marked the demise of the majority of palaeozoic marine faunas here we present a study of the evolving microbialite forms and associated biotic assemblages of this pioneering microbialite interval from exposures at chongyang hubei province china this research provides a perspective on the effects of eustatic transgression on marine ecosystems as water depths increased at the beginning of mesozoic through the study of the changing forms microfacies and distribution of microbialites microbialite forms evolved from stratiform stromatolites to a sequence of tabular thrombolites with an intercalated layer of columnar stromatolites followed by domical thrombolites that were overlain in turn by oolites the stratiform stromatolites contain poorly preserved remains of calcified cyanobacteria but microfossils with chambered structure can also be seen metazoan fossils increased from the base of the overlying tabular thrombolite reflecting increasing biodiversity with deepening of seawater the occurrence of columnar stromatolites within the tabular thrombolite may indicate a temporary sea level shallowing foraminiferans and other metazoans are absent within the columnar stromatolites but spherical cyanobacterial remains are extremely abundant well preserved calcified cyanobacteria may reflect an absence of metazoan predation and or carbonate supersaturation of seawater as water deepened domical thrombolites developed and the more complex seafloor relief created varied niches between and within the domes that harboured more ecologically diverse communities during the process of transgression within the microbialite interval carbon isotopes exhibit a negative relationship with biodiversity implying that upwelling of anoxic deep ocean water if associated with the negative excursion of carbon isotope values did not inhibit the diversification of benthic organisms at least on shallow carbonate platforms in the period immediately after the end permian mass extinction

decadal record of climate variability spanning the past 700 yr in the southern tropics of east africa biogenic silica profiles in varved sediments from northern lake malawi nyasa east africa span the past 700 yr and reflect past primary productivity in the overlying waters on a centennial scale this has been influenced by lake level and a consequent shift in the location of high diatom productivity within the lake basin primary production was higher during the little ice age an arid period from about a d 1570 to 1850 when lake level was about 120 m lower than during the previous three centuries or the past 150 yr

radiocarbon chronology of lake bonneville eastern great basin usa abstract lake bonneville occupied a series of connected topographically closed structural basins in the eastern great basin from about 30 ka to 12 ka the following synthesis of lake bonneville history is based on a critical evaluation of the stratigraphic and geomorphic contexts of 83 radiocarbon ages of a variety of samples including wood charcoal dispersed organic matter mollusk shells and tufa the lake began to rise from levels close to average holocene levels after about 28 ka by 22 ka it had transgressed approximately 100 m between 22 and 20 ka it regressed about 45 m in the stansbury oscillation and the stansbury shoreline was formed transgression after 20 ka proceeded in two phases a rapid phase from 20 to 18 ka and a slower phase from 18 to 15 ka the lake overflowed intermittently at its highest level the bonneville shoreline from about 15 to 14 5 ka then catastrophically dropped 100 m during the bonneville flood to the level of the provo shoreline which it occupied until about 14 ka subsequent closed basin regression was rapid and complete by 12 ka and was followed by a modest transgression to form the gilbert shoreline between 10 9 and 10 3 ka the lake bonneville record is an accurate proxy of the changing water balance in the bonneville basin during the late pleistocene although the nature of the climatic changes during this period are still uncertain

lake bonneville fluctuations and global climate change lake bonneville the largest late pleistocene closed basin lake in the north american great basin fluctuated widely in response to changes in climate the geochemistry and mineralogy of endogenic calcium carbonate deposited in deep water and stratigraphic studies of shore zone deposits provide evidence of millennial scale lake level fluctuations that had amplitudes of about 50 m between 30 and 10 ka falling lake events occurred at 21 18 5 19 17 5 16 15 5 14 13 and 10 ka radiocarbon years synchronously with the terminations of heinrich events h1 and h2 and other smaller scale iceberg rafting events a b c and younger dryas in the north atlantic ocean the lake bonneville results thus support other climate records that suggest that late pleistocene millennial scale climate change was global in extent the size and shape of the northern hemisphere ice sheets which determined the mean positions of storm tracks may have been the primary control on late pleistocene water budgets of great basin lakes

kalkowsky s stromatolites revisited lower triassic buntsandstein harz mountains germany abstract the term stromatolite was proposed by kalkowsky 1908 z dt geol ges 60 68 125 for structures he discovered in the carbonates of the lower triassic buntsandstein of the harz mountains in central germany we have re examined these localities to clarify kalkowsky s descriptions and to deduce the environmental conditions of stromatolitic growth the lower buntsandstein was deposited in a closed lacustrine basin the central european permo triassic basin the depositional environment was a playa lake with variable salinity in the centre of the basin oolite beds are intercalated in the mainly siliciclastic succession which is composed of 20 fining upward cycles thought to have been produced by climatic variations stromatolites occur almost exclusively on the surface of oolite beds stromatolitic structures consist of millimetre thick laminated crusts and centimetre high branching columnar forms smaller and bigger 2 m high domes are composed of secondary order columns and intercalated crusts occasionally upper surfaces of the domes are pitted due to syndepositional dissolution despite of the overall intense sparitization two groups of stromatolitic microstructures can be distinguished spongy fenestrate and fan like fabrics the spongy fenestrate fabric is similar to that one caused by the recent cyanobacteria phormidium calothrix and dichothrix and the fan like fabric to rivularia laminated crusts called stromatoid by kalkowsky are interpreted as being of cement origin and formed by quick precipitation the change from columnar to domical forms may reflect changes of hydrodynamic conditions clear photoautotrophism suggests that cyanobacteria or eukaryotes were the dominant organisms involved in the formation of kalkowsky s stromatolites influx of ooids or siliciclastic mud interrupted or terminated the stromatolitic growth the morphology growth pattern and fabrics of stromatolites were most likely controlled by ecological factors which all seem to be related to the general hydro climatic evolution of the lower buntsandstein

earliest life on earth evidence from the barberton greenstone belt south africa abstract studies investigating the structure and diversity of earth s record of life older than 3 2 ga are restricted to two locations worldwide in which sedimentary rocks have escaped regional high grade metamorphism and penetrative deformation the pilbara craton of western australia and the barberton greenstone belt in the kaapvaal craton of south africa this paper provides a south african perspective on the evidence of paleoarchean life a record that is often overlooked in the literature it aims to summarize and critically review previously reported claims of early life in the bgb gives an overview of the latest findings and provides an outlook on potential future discoveries the 15 km thick volcanic sedimentary succession making up the barberton supergroup was deposited between 3 55 to ca 3 20 ga and can be subdivided in three stratigraphic units that provide a unique window into a diverse and widespread paleoarchean microbial ecosystem landscape putative biosignatures occur almost throughout the entire bgb stratigraphy and range from carbonaceous cherts containing filamentous spheroidal and lenticular microstructures traces of hydrothermal biofilms photosynthetic microbial mats remnants of pseudocolumnar stromatolites and large organic walled spheroidal microfossils of currently unknown affinity the bgb also contains one of the world s oldest known record of tufted microbial mats which extensively colonized tidally influenced siliciclastic shorelines and were most likely formed by filamentous photosynthesizers other mat associated biosignatures include silicified gas bubbles domes and lenses that likely formed due to metabolic activity or the decay of buried organic matter some of these subsurface voids beneath the cohesive mats were inhabited by the earliest known forms of cavity dwelling microbial communities that were probably dominated by chemotrophic or photosynthetic microbes recently discovered terrestrial microbial mats once thriving in a fluvial dominated setting represent the oldest macroscopically visible fossil traces of life on land which is also supported by the occurrence of nearby paleosols that carry signals of biogenic sulfur fractionation the wealth of preserved microbial biosignatures from marine fluvial hydrothermal and possibly planktonic settings combined with the high spatial and temporal resolution of the barberton greenstone belt deposits is truly exceptional consequently the bgb deserves an equal level of attention and protection for future generations like its australian counterpart

computational fluid dynamics simulations of the late pleistocene lake bonneville flood abstract at approximately 18 0 ka pluvial lake bonneville reached its maximum level at its northeastern extent it was impounded by alluvium of the marsh creek fan which breached at some point north of red rock pass idaho leading to one of the largest floods on earth about 5320 km3 of water was discharged into the snake river drainage and ultimately into the columbia river we use a 0d model and a 2d non linear depth averaged hydrodynamic model to aid understanding of outflow dynamics specifically evaluating controls on the amount of water exiting the lake bonneville basin exerted by the red rock pass outlet lithology and geometry as well as those imposed by the internal lake geometry of the bonneville basin these models are based on field evidence of prominent lake levels hypsometry and terrain elevations corrected for post flood isostatic deformation of the lake basin as well as reconstructions of the topography at the outlet for both the initial and final stages of the flood internal flow dynamics in the northern lake bonneville basin during the flood were affected by the narrow passages separating the cache valley from the main body of lake bonneville this constriction imposed a water level drop of up to 2 7 m at the time of peak flow conditions and likely reduced the peak discharge at the lake outlet by about 6 the modeled peak outlet flow is 0 85 106 m3 s 1 energy balance calculations give an estimate for the erodibility coefficient for the alluvial marsh creek divide of 0 005 m y 1 pa 1 5 at least two orders of magnitude greater than for the underlying bedrock at the outlet computing quasi steady state water flows water elevations water currents and shear stresses as a function of the water level drop in the lake and for the sequential stages of erosion in the outlet gives estimates of the incision rates and an estimate of the outflow hydrograph during the bonneville flood about 18 days would have been required for the outflow to grow from 10 to 100 of its peak value at the time of peak flow about 10 of the lake volume would have already exited eroding about 1 km3 of alluvium from the outlet and the lake level would have dropped by about 10 6 m

a high precision record of mid late holocene sea level events from emergent coral pavements in the houtman abrolhos islands southwest australia early work on sea levels in southwest australia claimed to recognise a holocene sea level highstand which was not seen in better known sea level records elsewhere at the time more recent work has confirmed that a mid holocene highstand occurred about 6 kyr ago as new data on oscillating sea levels from the region have recently been published a high continuity precisely dated and accurately surveyed record was obtained from emergent coral pavements in the leeward houtman abrolhos islands serventy island a tectonically stable region from where good quality holocene sea level data have been previously obtained from corals from the mid holocene highstand ca 7 u th kyr ago sea level declined linearly during the remainder of the holocene as the carbonate platform prograded leewards hydro isostatic controls are probably significant in the record c 2005 elsevier ltd and inqua all rights reserved

viscosity estimates for the crust and upper mantle from patterns of lacustrine shoreline deformation in the eastern great basin the deformed shorelines of lake bonneville constitute a classic source of information on lithospheric elastic thickness and upper mantle viscosity we describe and apply a new model to a recently augmented data set new data better constrain both the complex spatio temporal pattern of the lake load and the crustal deformation response to that load the history of lake level fluctuations has been significantly refined and somewhat modified this is due to both more radiocarbon dates from within the bonneville basin and to an improved calibration of the radiocarbon timescale itself the data which constrain the crustal deformation pattern consist of ages and shoreline elevations from several hundred points which sample three major levels of lake bonneville and corresponding elevations from the high stands of three smaller lakes situated to the west of lake bonneville the data from the smaller lakes help elucidate the pattern of deflection which occurred beyond the edge of the big lake the geometry of the earth model incorporates an arbitrary number of layers overlying a half space and the rheology of each level can accommodate an arbitrary number of maxwell viscoelastic elements in parallel the inverse modeling comprises three complementary approaches for the simplest configurations we performed a direct search of the parameter space and delineated the irregular boundary of the subspace of acceptable models for more complex configurations we constrained the elastic parameters to their seismically determined values and then solved for viscosity versus depth profiles by either expressing the log viscosity versus log depth profile as a series of specially constructed orthogonal polynomials or by allowing each of 8 10 layers plus the half space to have an independently determined viscosity we found that the data do not strongly support nor can they conclusively exclude a more complex rheology than simple maxwell viscoelasticity the orthogonal polynomial solution exhibits an essentially monotonic decrease in viscosity with depth the most rapid change occurs at shallow depths decreasing from 1023 pa s at 3 km to 102o pa s at 30 km the decrease is much more gradual below with only another factor of 5 decrease between 30 and 300 km depth the unconstrained solution exhibits a rapid decrease in viscosity with depth from 2x 10 24 pa s in the top 10 km to 4x 1017 pa s at a depth of 40 km a nearly isoviscous asthenospheric region extends from 40 to 150 km and is underlain by a mantle lithospheric region with increased viscosity 2x 102o pa s extending from 150 to 300 km depth and by a uniform viscosity 1019 pa s half space below

estimating palaeowind strength from beach deposits abstract the geological record of past wind conditions is well expressed in the coarse gravel cobble and boulder beach deposits of quaternary palaeolakes in the great basin of the western usa and elsewhere this paper describes a technique using the particle size distribution of beach deposits to reconstruct palaeowind conditions when the lakes were present the beach particle technique bpt is first developed using coarse beach deposits from the 1986 87 highstand of the great salt lake in utah combined with instrumental wind records from the same time period next the bpt is used to test the hypothesis that wind conditions were more severe than at present during the last highstand of lake lahontan 13 ka which only lasted a decade or two at most the largest 50 beach clasts were measured at nine beach sites located along the north west and south sides of antelope island in the great salt lake all of which formed in 1986 87 at these sites the largest clast sizes range from 10 to 28 cm b axis and fetch lengths range from 25 to 55 km nearshore wave height was calculated by assuming that the critical threshold velocity required to move the largest clasts represents a minimum estimate of the breaking wave velocity which is controlled by wave height shoaling transformations are undertaken to estimate deep water wave heights and ultimately wind velocity wind estimates for the nine sites using the bpt range from 6 5 to 17 4 m s 1 which is in reasonable agreement with the instrumental record from salt lake city airport the same technique was applied to eight late pleistocene beaches surrounding the carson sink sub basin of lake lahontan nevada using the bpt estimated winds for the eight sites range from 9 7 to 27 1 m s 1 the strongest winds were calculated for a cobble boulder beach with a fetch of 25 km instrumental wind records for the 1992 99 period indicate that wind events of 9 12 m s 1 are common and that the strongest significant wind event 9 m s 1 for 3 h reached an average velocity of 15 5 m s 1 based on this preliminary comparison it appears that the late pleistocene western great basin was a windier place than at present at least for a brief time