intercontinental correlation by sea level events in the early silurian of north america and china yangtze platform potential for eustatic sea level changes on continental platforms during early silurian llandovery time was highly propitious due to the double effects of lingering glaciation in gondwana and the rapid rate of sea floor spreading which assisted the general dispersion of many era tonic realms through middle paleozoic oceans following the initial mass melting of the late ordovician early silurian glaciers in north africa and arabia four smaller cycles of sea level fluctuation were recorded by recurrent shelly communities in a predominantly carbonate setting on the north american platform peaks in sea level rise occurred in late rhuddanian or early idwian a 4 b 1 positions early fronian c 1 position early telychian c 4 position and late telychian c 6 position times although absolute time control is poor the periodicity of these events may have been every 2 5 m y in the more submerged regions of the north american platform such as iowa and anticosti island diverse faunal associations distinguished by the presence of stricklandiid brachiopods were especially productive at peak times of transgression co occurrence of the calcareous green alga cyclocrinites with certain of these faunas indicates that maximum water depth was still within the photic zone at the other extreme low stands in sea level are identified by diminished faunal diversity as well as a combination of typical sedimentary structures and evaporite indicators located on a well defined precambrian craton the yangtze platform is now a large region in central and southwestern china during successive stages of the early silurian a thick sequence of graptolitic shales shelly carbonates and red beds were deposited on the platform of the four sea level peaks defined in north america three are recognized in the yangtze region there is very good evidence for a latest llandovery or earliest wenlock transgression based on the extensive distribution of the salopinella coronocephalus sichuanoceras fauna another clear and well dated sea level peak involves the occurrence of faunas with characteristic stricklandiid and pentamerid brachiopods at a level equivalent to the lower telychian c 4 position the initial silurian transgression appears to have reached its peak on the yangtze platform primarily during early idwian time b 1 position but this is based less surely on changing patterns in graptolite diversity at present there is no compelling evidence for a widespread early fronian c 1 position transgression in china successful matching of the other sea level events however substantially refines intercontinental correlation for lower silurian strata in the yangtze region of china and the central regions of north america

timing of the avalonia baltica plate convergence as inferred from palaeogeographic and stratigraphic data of chitinozoan assemblages in west pomerania northern poland timing of the avalonia baltica plate convergence as inferred from palaeogeographic and stratigraphic data of chitinozoan assemblages in west pomerania northern poland

intact phospholipids microbial life markers in marine deep subsurface sediments abstract deep subsurface sediments from the nankai trough japan sea odp leg 190 sites 1173 1174 1177 and near surface sediments from hydrate ridge ne pacific have been analysed by high performance liquid chromatography hplc electrospray ionisation esi mass spectrometry ms the main objective was to utilize the presence of intact phospholipids as a direct indicator of viable microorganisms the extracts of nankai trough sediments were found to contain a variety of phospholipid pl structures well known to stem from microorganisms to depths as great as 745 mbsf and in situ temperatures as high as 85 c in addition high relative amounts of lysophospholipids e g lysophosphatidylcholines exceeding those of the regular phospholipids were detected diglyceride mass fragments of various pls have been assigned to fatty acyl side chains of typical chain length c14 c16 c18 c20 and degree of unsaturation zero one or two double bonds similar results were obtained for the phospholipid distribution in extracts of organic matter rich hydrate ridge sediments to date the enhanced occurrence of lysophospholipids cannot be explained completely but a response to increasing thermal and ecological stress seems probable

volatile organic acids produced during kerogen maturation amounts composition and role in migration of oil abstract maturation dependent generation of organic compounds from north sea source rocks has been investigated by hydrous pyrolysis of powdered source rock samples the generation of water soluble organic acids is emphasised and their composition compared with oil field water samples similar compositions are found matrix adsorption effects are not found to be quantitatively important timing of acid generation relative to oil generation is discussed effects of realistic concentrations of a volatile organic acid in the water phase on interfacial tension is determined and effects on fluid flow of crude oil through water saturated sandstone is investigated using a long core flow rig

present and past microbial life in continental pan sediments and its response to climate variability in the southern kalahari abstract terrestrial climate archives are rare in the arid southwestern african region which makes paleoclimate and paleoenvironmental studies difficult since there are only ephemeral lacustrine systems in the area in this study a continental pan playa is evaluated as a climate archive climate has a strong impact on the pan ecosystem causing adaptation of indigenous microorganisms to varying temperature precipitation and salinity conditions here a combined approach of inorganic and organic geochemical investigations including lipid biomarker analyses was carried out to examine the response of indigenous microbial communities to environmental changes and to characterize the nature abundance and depth distribution of recent phospholipids and past glycerol dialkyl glycerol tetraethers gdgts microbial life within the sediments of witpan located in the southern kalahari lipid biomarkers contain information about changes in biogeochemical processes and climate variation therefore we tested here whether they can be used to reconstruct paleoclimatic changes such as past precipitation periods in arid terrestrial ecosystems despite the extreme environmental conditions with rather low toc values restricted availability of water and substrates in the pan system bacterial life was observed along the depth profile of witpan bacterial membrane phospholipid life markers showed their highest abundance in the surface layers indicating that microbial life in witpan is strongly influenced by near surface processes a series of saturated branched and unsaturated phospholipid fatty acids plfas were detected and several phyla of bacteria such as gram positive and gram negative bacteria were present some plfas and intact archaeal membrane lipids point to the presence of a halophilic microbial community in the surface layers biomarkers for past microbial life archaeol branched and isoprenoid gdgts were absent or had very low concentrations during the dry holocene sequence below the surface sediments however during the last glacial maximum lgm considered to represent a period with increased precipitation an increased abundance of these biomarkers was observed thus these results demonstrate the potential of microbial biomarkers in pan systems to preserve climate signals over geologic timescales the data indicates that microbial biomarkers can be used to trace paleo precipitation periods in semi arid to arid environments and that pan structures can form suitable geo archives for biomolecules in areas where other terrestrial archives are missing

the impacts of land plant evolution on earth s climate and oxygenation state an interdisciplinary review abstract the paleozoic emergence of terrestrial plants has been linked to a stepwise increase in earth s o2 levels and a cooling of earth s climate by drawdown of atmospheric co2 vegetation affects the earth s o2 and co2 levels in multiple ways including preferential organic carbon preservation by decay resistant biopolymers e g lignin and changing the continental weathering regime that governs oceanic nutrient supply and marine biological production over shorter time scales 1 myr land plant evolution is hypothesized to have occasionally enhanced p weathering and fertilized the oceans expanding marine anoxia and causing marine extinctions oceanic anoxia would eventually become limited by oceanic o2 uptake as oxygen accumulates in the atmosphere and surface oceans when excess organic carbon is buried in marine sediments here we review hypotheses and evidence for how the evolving terrestrial ecosystems impacted atmospheric and oceanic o2 and co2 from the ordovician and into the carboniferous 485 298 9 ma five major ecological stages in the terrestrial realm occurred during the prolonged time interval when land was colonized by plants animals and fungi marked by the evolution of 1 non vascular plants 2 vascular plants with lignified tissue 3 plants with shallow roots 4 arborescent and perennial vegetation with deep and complex root systems and 5 seed plants the prediction that land vegetation profoundly impacted the earth system is justified although it is still debated how the individual transitions affected the earth s o2 and co2 levels the geological record preserves multiple lines of indirect evidence for environmental transitions that can help us to reconstruct and quantify global controls on earth s oxygenation and climate state

climatic and oceanic changes during the middle late ordovician transition in the tarim basin nw china and implications for the great ordovician biodiversification event abstract the middle late ordovician transition darriwilian to sandbian age witnessed a major pulse of the great ordovician biodiversification event gobe and distinctive oceanic geochemical fluctuations such as coeval negative c and sr isotope excursions in this study investigations into geochemical variations notably the hg abundance or hg toc have been carried upon the organic rich black shale of the middle upper ordovician saergan formation to unravel the causes of this pulse based on these data three phases were identified phase 1 0 to 3 m is characterized by rising hg toc up to 138 ppb wt and ti al values as well as high ciacorr corrected chemical index of alteration values 68 9 72 3 with negligible enrichment of redox sensitive elements rse and nutrient elements e g u 5 2 ppm v 153 ppm mo 1 8 ppm p2o5 0 2 suggesting intensified volcanism which could have emitted significant amounts of greenhouse gases thereby leading to climate warming in contrast phase 2 3 to 11 m is characterized by decreasing hg toc and ti al ratios relatively low though slightly fluctuating ciacorr values generally depleted in rse except moderately enriched u up to 14 6 ppm and increased p al and ba al ratios implying weakening volcanic activity and subsequent climate cooling and the potential for improved seawater ventilation as a result of oceanic upwelling phase 3 sandbian age 11 13 m witnessed continuous decrease in hg toc ratio an increase in ti al and ciacorr values fairly low values of rse enrichment and p al and ba al ratios indicating recurrent climate warming and the potential for slowed oceanic circulation and attenuated upwelling of nutrient rich deep waters onto the shallow shelf these changes could have diminished bioproductivity and organic output onto the seafloor this study offers insights into volcanic climatic oceanic interactions during a major pulse of the gobe around the middle late ordovician transition while black shales were extensively deposited

lipid biomarker and stable isotopic profiles through early middle ordovician carbonates from spitsbergen norway abstract one of the most dramatic episodes of sustained diversification of marine ecosystems in earth history took place during the early to middle ordovician period changes in climate oceanographic conditions and trophic structure are hypothesised to have been major drivers of these biotic events but relatively little is known about the composition and stability of marine microbial communities controlling biogeochemical cycles at the base of the food chain this study examines well preserved carbonate rich strata spanning the tremadocian through upper dapingian stages from the oslobreen group in spitsbergen norway abundant bacterial lipid markers elevated hopane sterane ratios average 4 8 maximum of 13 1 detection of chlorobi markers in organic rich strata and bulk nitrogen isotopes 15ntotal averaging 0 to 1 for the open marine facies suggest episodes of water column redox stratification and that primary production was likely limited by fixed nitrogen availability in the photic zone near absence of the c30 sterane marine algal biomarker 24 n propylcholestane 24 npc in most samples supports and extends the previously observed hiatus of 24 npc in early paleozoic late cambrian to early silurian marine environments very high abundances of 3 methylhopanes average 9 9 maximum of 16 8 extends this biomarker characteristic to early ordovician strata for the first time and may reflect enhanced and sustained marine methane cycling during this interval of fluctuating climatic and low sulfate marine conditions olenid trilobite fossils are prominent in strata deposited during an interval of marine transgression with biomarker evidence for episodic euxinia anoxia extending into the photic zone of the water column

searching for travertines calcretes and speleothems in deep time processes appearances predictions and the impact of plants common models for modern calcite precipitation in and around caves soils springs and streams involve co 2 supplied by thick high p co 2 biogenic soils which were probably thin or non existent before vascular plants indeed plant influenced chemical weathering might have caused accelerated terrestrial carbonate production from the devonian onwards however terrestrial carbonates have also been documented from the archaean proterozoic cambrian ordovician and silurian mechanisms which could have caused non marine carbonates to precipitate without organic rich soils are described and some geological events likely to have influenced non marine carbonate precipitation up to the origin of vascular plants are highlighted as organisms have evolved so have the petrographic characteristics of non marine carbonates some examples of this are also given here

water extraction of coals potential for estimating low molecular weight organic acids as carbon feedstock for the deep terrestrial biosphere abstract with the recent increasing interest in the deep biosphere the question arises as to where the carbon sources that support deep microbial communities are derived from our research was focussed on the water soluble low molecular weight lmw organic acids that are potentially available from different sedimentary lithologies to serve as a carbon source to feed the deep biosphere a series of eocene pleistocene coals mudstones and sandstones of varying rank maturity and total organic carbon toc content from the waikato basin new zealand has been soxhlet extracted using water the combined concentration of recovered formate acetate and oxalate range from 366 to 2499 g g sediment and appear to be dependent on rank organofacies and toc the yields indicate the potential of carbonaceous sediments to feed the local deep terrestrial biosphere over geological periods of time the existence of living microbial organisms in the mudstones and sandstones was proved by the identification of intact phospholipids pls

the climate change caused by the land plant invasion in the devonian land plants invaded continents during the mid paleozoic their spreading and diversification have been compared to the cambrian explosion in terms of intensity and impact on the diversification of life on earth whereas prior studies were focused on the evolution of the root system and its weathering contribution here we used a coupled climate carbon vegetation model to investigate the biophysical impacts of plant colonization on the surface climate through changes in continental albedo roughness thermal properties and potential evaporation from the early to the late devonian our model simulates a significant atmospheric co2 drop from 6300 to 2100ppmv that is due to an increase in the consumption of co2 though continental silicate weathering the continental drift and the climatic changes promoted by land plants explain this trend the simulated co2 drawdown is paradoxically associated with unchanged temperatures we show here that the co2 drop is counteracted by a large warming resulting from the surface albedo reduction caused by the appearance of an extended plant cover if co2 is consensually assumed as the main driver of the phanerozoic climate this paper demonstrates that during land plant invasion the modifications of soil properties could have played in the opposite direction of the carbon dioxide fall hence maintaining warm temperatures during part of the devonian

first record of rellimia leclercq bonamo aneurophytales from gondwana with comments on the earliest lignophytes

biodegradation of oil in uplifted basins prevented by deep burial sterilization biodegradation of crude oil by bacterial activity which has occurred in the majority of the earth s oil reserves is known to reduce greatly the quality of petroleum in reservoirs for economically successful prospecting for oil it is therefore important to understand the processes and conditions in geological formations that lead to oil biodegradation although recent studies speculate that bacterial activity can potentially occur up to temperatures as high as 150 degrees c refs 3 4 it is generally accepted that effective petroleum biodegradation over geological timescales generally occurs in reservoirs with temperatures below 80 degrees c ref 2 this appears however to be at odds with the observation that non degraded oils can still be found in reservoirs below this temperature here we compile data regarding the extent of oil biodegradation in several oil reservoirs and find that the extensive occurrence of non biodegraded oil in shallow cool basins is restricted to those that have been uplifted from deeper hotter regions of the earth we suggest that these petroleum reservoirs were sterilized by heating to a temperature around 80 90 degrees c during deep burial inactivating hydrocarbon degrading organisms that occur in the deep biosphere even when such reservoirs are subsequently uplifted to much cooler regions and filled with oil degradation does not occur implying that the sterilized sediments are not recolonized by hydrocarbon degrading bacteria

microbial cycling migration and leakage of light alkanes in the nile delta tertiary fan abstract we present a geochemical dataset which helps unravel the complex set of processes by which light alkanes are sourced charged mixed leaked and altered in the plio pleistocene nile delta thermogenic gas derives from a sub messinian source and mixes with microbial hydrogenotrophic methane rich gas in the plio pleistocene section there is strong isotopic evidence for both microbial generation and microbial degradation of ethane and propane but these signals are only recorded where the rates of biological processes outstrip the rate of thermogenic charge high resolution gas geochemistry profiles through four 500 1100 m sequences of mixed channel channel levee mass flow deposits and hemipelagites shed light on migration and leakage pathways we see limited geochemical evidence for migration along or across faults which cross cut mud rich sequences lateral migration along sands silts delivers gas to structural highs where leakage occurs vertically along focussed pathways through heterogeneous mud rich sediments we propose that in situ generation of microbial gas within mud rich sequences facilitates percolation of migrating gases that replenishes c2 components and sustains the biodegradation pathway in syntrophic microbial communities high resolution changes in gas composition suggest an unequilibrated system which is being actively charged in some structures rates of charge and of microbial alteration of gas are broadly similar in others rates of charge exceed rates of microbial alteration our results have important implications for the understanding of both basin wide fluid flow and the ecology of the deep biosphere

paired isotope records of carbonate and organic matter from the middle ordovician of argentina intrabasinal variation and effects of the marine chemocline abstract we investigate the expression of the middle darriwilian isotope carbon excursion mdice across marine shelf environments in the argentine precordillera previous work identified the mdice in the las chacritas formation in argentina but did not recognize the expression of the mdice in time equivalent strata of the deeper water las aguaditas formation albanesi et al 2013 palaeogeography palaeoclimatology palaeoecology v 398 p 48 66 recent biostratigraphic investigations of these units have for the first time provided the opportunity for high resolution correlation which suggest that the mdice or at least the initiation of the mdice should be observed in both the las chacritas and las aguaditas formations here we present new paired carbon isotope data of carbonate and organic carbon from the las chacritas and las aguaditas formations we identify a 2 positive shift in the isotopic composition of marine carbonate in the las chacritas formation whereas values abruptly fall to

sensitivity of the epeiric sea carbon isotope record to local scale carbon cycle processes tales from the mohawkian sea ancient marine carbon isotope records derived from epeiric sea carbonates can bear a strong influence of local scale carbon cycling processes across the late ordovician mohawkian sea of eastern laurentia the carbon isotope compositions d 13 c of contemporaneous sediments range from 2x in the interior of the sea to 2 5x along the margin here we use a box model to explore the relative importance of carbon fluxes within the mohawkian sea from a mass balance perspective in the model the mohawkian sea carbon reservoir is coupled to but distinct from the ocean and atmosphere carbon reservoirs at initial steady state conditions the residence time of carbon in the mohawkian sea is less than 10 years we find that to produce model d 13 c values representative of the range in d 13 c across the mohawkian sea we must divide the sea into an inner region and an outer region and limit dissolved inorganic carbon dic exchange between the two to 15 of the initial steady state unrestricted exchange rate it is also necessary to supply low d 13 c carbon 29x to the inner region of the sea at a rate of 17 4 10 12 mol c yr 1 the required flux of low d 13 c carbon could not have been sustained over the long term by remineralization of organic carbon stored in sediments of the inner region of the mohawkian sea and the geographic d 13 c pattern is unlikely to have been generated by upwelling along the sebree trough rather the low d 13 c flux might have been derived from bryophytedominated terrestrial ecosystems suggesting an important role for terrestrial carbon cycling prior to the advent of vascular plants aninterestingfeatureofthemodelisthattheisotopiccompositionsofboththeepeiric seaandthelargerocean atmospheresystem are sensitive to changes in exchange rates within the epeiric sea this has important implications for interpreting global d 13 c

further evidence for diversity in late silurian land vegetation small coalified plant fragments from basal pridoli silurian strata at perton near hereford england comprise isotomously branching smooth axes terminating in vertically elongate sporangia the latter which occasionally bifurcate are characterized by prominent distally concentrated spinous emergences and contain trilete retusoid smooth walled isospores the plants are placed in a new genus and species caia langii comparisons are made with a number of silurian and lower devonian plants with elongate sporangia and particularly with horneophyton a hypothesis is developed that spines on sporangia had a nutritive function the spores are discussed in terms of other records of late silurian early devonian in situ spores

the use of rbsr and kar dating methods as a stratigraphic tool applied to sedimentary rocks and minerals abstract rb sr and k ar methods can be used for direct numerical chronostratigraphy of sediments using the clay silicates they contain the interpretation of the ages calculated depends on the satisfaction of the following requirements 1 1 the series studied must include diagenetic clay sediments coarsely detrital or alightly metamorphic formations must be excluded studies in progress concerning decarbonatation may lead to the application of direct dating of sediments being extended to carbonate sediments 2 2 careful mineralogical study of the clay minerals must prove early diagenetic recrystallization or new formation this part of the study must precede any isotopic work 3 3 the isotopic study must involve the use of both rb sr and k ar methods the extreme sensibility of the k ar isotopic system to late diagenesis helps to choose between early or late diagenesis a younger k ar age may generally be regarded as that of the late diagenesis whereas the rb sr age may be that of the early diagenesis 4 4 the initial 87sr 86sr isotopic ratio is not always a reliable criterion owing to the effects of the dilution of the radiogenic 87sr by the great amounts of primary sr contained in carbonates 5 5 the regularly decreasing succession of isotopic ages must follow the stratigraphic succession when this condition is satisfied there is a high probability that the calculated ages are indeed those of the deposition dates

mid late holocene climate variability in the indian monsoon evidence from continental shelf sediments adjacent to rushikulya river eastern india we present elemental and grain size distributions obtained from the sediment core of the continental shelf adjacent to the rushikulya river mouth eastern india to quantify the paleoclimatic changes the retrieved 1 60 m long well dated core spans the past ca 6800 cal bp the modern spatial distribution of grain size and geochemistry of the inner mid shelf sediments has been carried out to understand the seafloor morphology and sedimentary processes based on the modern investigations the proportion of particle size clay vs sand and variation in elemental values tio2 vs al2o3 has been used to interpret the changes in terrigenous supply the grain size and elemental distribution data from the core sediments indicates a period of enhanced surface water runoff from 6800 to 3100 cal bp followed by a drier condition 3100 cal bp to present suggesting weakening of monsoon the weakening of the monsoonal strength is coeval with other records from the indian sub continent and suggests response of indian monsoon to changing solar insolation during late holocene

late ordovician early silurian cryptospore occurrences on anticosti island ile d anticosti quebec canada residues from hirnantian upper ordovician and aeronian lower silurian strata of anticosti island quebec canada have yielded the oldest occurrence of terrestrial based palynomorphs cryptospores from eastern north america a low abundance low diversity cryptospore assemblage containing specimens of pseudodyadospora velatitetras and alete monads has been recovered from the velleda member of the ellis bay formation upper ordovician hirnantian the gun river formation lower silurian aeronian contains a low abundance low diversity assemblage composed of specimens of velatitetras laevolcancis and alete monads the occurrence of these assemblages provides evidence for early land plants in this part of north america during the late ordovician and early silurian and documents the existence of a terrestrial based flora during and after the saharan late ordovician glaciation

paired δ13ccarb and δ13corg records of upper ordovician sandbian katian carbonates in north america and china implications for paleoceanographic change late sandbian early katian marine carbonates from two sections in north america and one in south china were analyzed for paired 13ccarb and 13corg and revealed similar 13ccarb but varying trends in 13corg stratigraphy while all sections recorded a well known positive 13ccarb shift these 13corg records are the first through the guttenberg 13ccarb excursion gice in china oklahoma and west virginia in south china a positive excursion in 13corg is associated with the latter part of the positive 13ccarb excursion and closely resembles trends from iowa and pennsylvania that have been interpreted to reflect a lowering of atmospheric pco2 levels the 13corg trends from oklahoma and west virginia differ significantly from what is observed in china this likely indicates that local changes in nutrient cycling and phytoplankton growth rates were the dominant control on 12c fractionation in oklahoma and west virginia masking a possible global signal of lowered atmospheric pco2 levels observed in china

flooding of sinking creek garretts spring karst drainage basin jessamine and woodford counties kentucky usa tashamingo subdivision in sinking creek karst valley a tributary of the garretts spring drainage basin in jessamine and woodford counties kentucky was flooded in february 1989 to determine the cause of flooding the groundwater basin boundary was mapped discharge data were measured to determine intake capacity of swallets and hydrologic modeling of the basin was conducted swallet capacity was determined to be limited by the hydraulic parameters of the conduit rather than by obstruction by trash flooding from a precipitation event is more likely and will be higher when antecedent soil moisture conditions in the watershed are near saturation hydrologic modeling shows that suburban development of 20 percent of the southeast basin will cause a small increase in flood stage at tashamingo subdivision

early silurian glaciations in brazil abstract the opening of the brazilian paleozoic basins during the late ordovician was followed by a tectonic stabilization in the silurian at the time of the early silurian glaciations deposition of continental sandstones prevailed in the basins offshore environments were present in the amazonas basin and to a smaller extent in the parana basin the ice sheets advanced over fluviatile and littoral sediments except for the south margin of the amazonas basin where the glacial diamictites immediately overlie marine facies the ice produced much meltwater even when advancing and this was probably climatically controlled the ice movements were from the northwest at the northern margin of the amazonas basin and towards the northeast at the southern margin in the parnaiba basin and its outliers the jatoba basin and cariri valley the ice came from southeast and probably also from east further to the south in the parana basin it came from the north and northeast four glaciations have been dated to the early silurian the oldest is dated as latest ashgill and or earliest llandovery in the parana basin as evidenced from tillites in the upper rio ivai and lower vila maria formations including the former iapo formation it is contemporaneous with a glaciation in the cape basin south africa the next glaciation is dated as early middle llandovery gregarius graptolite zone and is present in the amazonas basin and the andean belt and probably also in the parnaiba basin and its outliers the two youngest tillites were widespread in the northern brazilian basins amazonas parnaiba and jatoba basins and cariri valley as well as in the andean belt and are dated as early late llandovery possibly starting already in the late middle llandovery and latest llandovery to earliest wenlock the latter tillite is the most widespread one assuming these glaciations are related to polar positions the apparent migration of the south pole ice cap must have been quite rapid from central north africa in late ashgill towards central brazil in the middle late llandovery the glaciation in the parana basin took place up to 45 from the late ashgillian south pole the cool climate continued during the silurian but no new glaciations are known before latest devonian

aliphatic and aromatic biomarkers from gondwanan sediments of late ordovician to early devonian age an early terrestrialization approach abstract twenty one core samples of late ordovician to early devonian age from sections in southern tunisia north african platform gondwana and containing marine and terrestrial organic matter with microbial input were investigated to link the aliphatic and aromatic hydrocarbon distributions with the terrestrial and marine palynomorph content e g acritarchs prasinophytes chitinozoans cryptospores and trilete spores in addition to several biomarkers of algal bacterial origin long chain n alkanes that might be derived from land plants as well as the terrestrial diterpane norabietane were found several land plant derived biomarkers such as retene cadalene simonellite tetrahydroretene and c19 isohexylalkyl naphthalene were observed in the aromatic fractions while these terrestrial biomarkers could be clearly recognized in the middle silurian lower devonian samples their presence in the upper ordovician lower silurian sediments is more doubtful because of much lower relative abundances the land plant biomarkers show a fairly good correlation with the occurrence and abundance of cryptospores and trilete spores derived from bryophytes and tracheophytes which covered the emerged areas around the ghadamis basin during the silurian and devonian the early tracheophytes e g cooksonia lycophytes and zosterophylls are therefore suggested as a new terrestrial source for most of the saturated and aromatic biomarkers found in sediments of middle silurian to early devonian age

the moesian terrane during the lochkovian a new palaeogeographic and phytogeographic hypothesis based on miospore assemblages abstract the relative position of terranes during the palaeozoic can be indicated by a combination of palaeomagnetic and floral faunal evaluation palaeomagnetic data are absent from the moesian terrane south eastern europe and its position is here estimated thanks to palaeophytogeographic considerations based on miospore assemblages miospore assemblages have been studied in two boreholes from northern bulgaria preliminary analyses of chitinozoans acritarchs and phytodebris have already been published the oldest samples were considered to be of pridoli age based on chitinozoan data but here we provide new miospore evidence suggesting a lochkovian age this age determination is in accordance with the new interpretations based on previously published acritarch data it is likely that the previous pridoli age determination was influenced by pridoli chitinozoans being reworked into the lochkovian the miospores are typical of assemblages only present in a small area of avalonia and the western part of the baltica plate and belong to the sinuosus zavallatus s z phytogeographic province defined here on the contrary to the miospores marine palynomorphs have affinity with gondwanan assemblages the different palaeogeographic affinities of the different palynomorph groups are not necessarily in contradiction as it has recently been suggested that the rheic ocean did not act around the silurian devonian boundary as a hermetic barrier for transoceanic chitinozoan and acritarch exchange therefore the results are tentatively interpreted as indicating that the moesian terrane belonging to the s z province was close to southern laurussia during the lower devonian this northern position of the moesian terrane during the lower devonian conflicts with most current palaeogeographic reconstructions but partially supports the hypothesis of a migration of this terrane from gondwana to laurussia during the palaeozoic the possible presence of reworked palynomorphs in the lochkovian may reflect early tectonic events associated with the close proximity of the moesian terrane and the dobrudgea periphery of palaeo europe

drainage and flooding in karst terranes flooding in karst terranes is a commonly occurring geo hazard it causes damage to property businesses and roadways it can lead to the formation of cover collapse sinkholes and groundwater contamination generally three types of flooding or their combinations are related to karst recharge related sinkhole flooding flow related flooding and discharge related flooding understanding of the type of flooding is essential for solving the flooding problem areas prone to karst flooding should be recognized and restrictions and laws on land use should be implemented runoff and erosion control plans should address the unique characteristics of karst features digging out clogged sinkholes creating retention basins or installing class v injection wells are possible solutions to improve drainage of storm water solutions to flooding problems in karst areas should also be coordinated with the water quality control to prevent groundwater contamination

revisiting the great ordovician diversification of land plants recent data and perspectives abstract recent molecular clock data suggest with high probability a cambrian origin of embryophyta also called land plants indicating that their terrestrialization most probably started about 500 ma the fossil record of the cambrian explosion was limited to marine organisms and not visible in the plant fossil record the most significant changes in early land plant evolution occurred during the ordovician for instance the earliest bryophyte like cryptospores and the oldest fragments of the earliest land plants are from the middle and late ordovician respectively organic geochemistry studies on biomarker compositions hint at a transition from green algae to land plants during the great ordovician biodiversification event gobe the colonization of the terrestrial realms by land plants clearly had an impact on marine ecosystems interactions between the terrestrial and marine biospheres have been proposed and the radiation of land plants potentially impacted on co2 and o2 concentrations and on global climate in addition the shift of strontium isotopes during the ordovician is probably linked to changing terrestrial landscapes affected by the first massive land invasion of eukaryotic terrestrial life the land plants seem unaffected by the first global mass extinction at the end of the ordovician that eliminated many marine invertebrate taxa

new evidence for land plants from the lower middle ordovician of saudi arabia macerations of middle ordovician llanvirnian shales from saudi arabia yield an assemblage of spores of probable land plants cryptospores acritarchs and chitinozoa the production of sporopollenin containing sporelike tetrads is considered a fundamental character of the embryophytes because no extant algae produce spores of this type no trilete spores were found at this horizon reinforcing previous assertions that obligate meiotic tetrads predate the earliest trilete spores sporomorph tetrads and dyads in conjunction with cuticlelike fragments were probably derived from terrestrial plants at a bryophyte grade although there are reports of possibly older cryptospores the hanadir assemblage described herein clearly establishes their presence by llanvirnian time

an organic geochemical perspective on terrestrialization the colonization of land required new strategies for safe gamete diaspore dispersal and to cope with desiccation harmful radiation fire and gravity accordingly the morphology behaviour and physiology of the organisms changed here we explore to what extent physiological adaptations reflected in the molecular content of the sediments add to our understanding of the terrestrialization many compounds considered characteristic of land organisms do not provide valuable information from the fossil record since 1 they were not preserved 2 they occur or correspond to substances that evolved prior to the terrestrialization e g cutan vs algaenan cellulose or 3 they have been changed diagenetically and or catagenetically the latter leads to geo macro molecules without a chemical fingerprint relating them to their original bio macro molecules despite sometimes excellent morphological preservation of the organic remains nevertheless some molecular markers and their stable isotopes provide independent information on the terrestrialization process the odd predominance of n alkane surface waxes is a feature already apparent in early land plants and could with caution be used as such furthermore fossil terpenoids and their derivatives are valuable for reconstructing the evolution of major plant groups the radiation of the phenylpropanoid pathway with for example sporopollenin and lignin seems to be closely related to the evolution of land plants as for other disciplines occupied with unravelling past life and environment organic geochemistry relies heavily on the paradigm that the present provides a key to the past for organic geochemistry the biosynthetic pathways of living organisms provide such a key the biosynthetic differences between organisms provide insight into the evolution of biosynthetic pathways and this can be applied to and calibrated against the fossil record evolution also implies adaptation and by linking species ecology to their biochemistry the adaptive value of the biosynthetic pathways and the biomolecules produced may be resolved this biosynthetic link to environment can also be applied to the past for instance the notion that oxygen is required in steroid and non hopanoid triterpenoid synthesis implies that analysis of steroids in ancient sediments may help to unravel the early evolution of the atmosphere summons et al 2006 analogous to the oxygenation of the earth s atmosphere terrestrialization also required major adaptations of the terrestrializing organisms to the living conditions on land the conquest of land required the development or strengthening of supportive structures such as skeletons stems and roots to withstand earth s gravity without the support of water and to resist wind it also demanded water saving strategies such as arthropod and plant cuticles vertebrate skin and cork to survive low humidity environments and sometimes fire as well as the development of water conducting tissues in plants roots tracheids finally the higher exposure to harmful radiation required sunscreens such as pigments aromatic and other substances as uv filters whereas the endoand exoskeletal adaptations are intrinsically based on the formation of large biopolymers water saving and uv protection may be also realized by means of smaller molecules our working hypothesis is that the major changes in biosynthetic pathways which accompanied the terrestrialization of organisms are reflected in the molecular composition of the organic matter present in palaeozoic sedimentary rocks for instance a minor change in the biosynthesis of sporopollenin may have led to lignin in return we can expect the changes in composition of the organic matter om in palaeozoic rocks to help determine following evolutionary trends the question being asked is to what extent is our working hypothesis valid and what does this provide us with to understand terrestrialization we restrict ourselves to primary producers and arthropods since they have a rich fossil record both organic geochemically and as microand macroscopic remains we exclude other terrestrial heterotrophic life forms worms snails vertebrates etc since they do not usually leave a chemically characteristic signature in the sediments from vecoli m clement g meyer berthaud b eds the terrestrialization process modelling complex interactions at the biosphere geosphere interface geological society london special publications 339 11 36 doi 10 1144 sp339 3 0305 8719 10 15 00 the geological society of london 2010 organic matter analysis lipids and

water resource management in karstic catchments the case of the asso torrent basin southern italy in karstic endorheic basins the hydraulic works for runoff regulation marshland reclaiming and defense from inundations usually consist of channels tributary to sinkholes vertically connected to aquifers through karstic conduits and fractures the drainage capacity of such basins reduces as conduits and fractures are progressively clogged by sediments thus floodings may occur during heavy rains the sinks may also be utilized to inject treated wastewater underground this note concerns the management issues of the asso torrent basin italy where the recharge through water sinks preserves the deep aquifer from saltwater intrusion the basin represents a controversial case for which the sequence of infrastructures produced a critical system and nowadays it is difficult to find a compromise among mitigation of flood hazard safeguard of groundwater resources and preservation of human health the hydrogeological framework and the hydraulic works executed in the basin are described followed by considerations on the environmental effects of the decision making process finally statements concerning alternative measures for the management of the water resources are given management actions conforming to the integrated water resources management recommendations fail in the studied case because there is an intrinsic difficulty to transform the related concepts to practical and robust solutions

palynological dating of low grade metamorphosed rocks applications to early paleozoic rocks of the central maine aroostook matapedia basin and fredericton trough northern appalachians in eastern and east central maine u s a identification of spores acritarchs and chitinozoans in weakly metamorphosed 300 c turbidites demonstrates the usefulness of palynological dating for hitherto unfossiliferous strata that underlie much of the gander terrane in maine combined with sparse macrofossil ages and geochronologic data from detrital zircons volcanic horizons and plutons the fossils constrain the ages of strata in the central maine aroostook matapedia cmam basin and fredericton trough and help to resolve paleogeographic and tectonic problems ages for the provisional brewer upper ordovician to llandovery and bangor wenlock formations in the bangor area fill the last remaining gap in cmam basin stratigraphy and permit correlation across the entire basin from western maine to the new brunswick border resulting lithofacies patterns document basinward facies changes from both eastern and western external sources and also indicate internal sources within the basin a progressive decrease in carbonate sediment in the cmam basin toward the south suggests interaction between axial and basinward currents in which micrite transported by axial currents from the matapedia platform in northern new brunswick was progressively overwhelmed to the south by clastic sedimentation from flanking highland sources middle to late silurian age ranges for the flume ridge formation the most extensive unit in the fredericton trough and the newly named county road formation permit correlation with rocks in similar structural positions in new brunswick recent geologic mapping the new age control and improved understanding of facies relationships show that the cmam basin was perhaps as wide as 800 to 1000 km prior to deformation developed on continental crust after mid ordovician plate accretion contained a body of deep water with anoxic bottom conditions and mostly pelagic organisms and contains a series of overlapping submarine fans derived from multiple sources

local and global perspectives on carbon and nitrogen cycling during the hirnantian glaciation abstract the impact of climate and ocean circulation changes on marine carbon and nitrogen cycling was investigated for a period covering the late ordovician hirnantian glaciation three sections were studied two from nevada one proximal and one distal and one from the yukon the opportunity to compare 13 c carb 13 c org and 13 c grap profiles between ocean and epeiric platform settings enabled a more thorough assessment of environmental and diagenetic factors influencing the preservation of seawater 13 c values at each stratigraphic section using the best preserved sedimentary components from the two nevada sections a lowstand sedimentary gradient of 4 was found between platform and ocean settings during the hirnantian glaciation gradients of similar magnitude have been reported from hirnantian platforms in the canadian arctic and baltic basins taking the outboard sections as the most representative of the ocean carbon pool a mean positive 13 c shift of just 2 7 0 4 is calculated which is significantly smaller than the 5 7 positive shifts recorded in epeiric platform settings the discrepancy is attributed to the effects of local carbon cycling in tropical and subtropical epeiric seas it is hypothesized that increased carbonate weathering caused 13 c values of local carbon weathering fluxes to increase which in turn caused seawater 13 c values to increase in basin proximal settings in addition nutrient dust fluxes may have contributed to increased levels of photosynthetic activity in proximal settings driving sedimentary 13 c values even higher much higher than sediment deposited in outboard settings where carbon exchanges with the surface ocean were less restrictive a 15 n profile reconstructed from deposits of the distal vinini creek section records a 1 5 positive shift through the hirnantian glacial interval interpreted as a major late ordovician upwelling zone high organic carbon 1 wt and high hydrogen indices 400 600 make the vinini creek section a suitable candidate for the preservation of original sedimentary 15 n records to explain the results a conceptual model of ocean nitrogen cycling under greenhouse climate conditions is presented that highlights the role of cyanobacteria as both primary producers and nitrogen fixers it is hypothesized that in greenhouse climates the fixed nitrogen inventory of the abyssal ocean was low due to efficient denitrification in the ocean s expansive oxygen minimum zones this caused algal productivity to become strongly dependent on continuous supplies of fixed nitrogen from cyanobacteria in the photic zone yielding sedimentary 15 n values between 0 and 2 by contrast the cooler icehouse climate of the hirnantian led to increased ocean ventilation greater partitioning of atmospheric oxygen into downwelling surface waters and oxygen minimum zone shrinkage as a result fixed nitrogen levels climbed in the ocean s abyssal depths due to the lower denitrification rates this in turn allowed nitrogen with high 15 n values to recycle back into the photic zone driving sedimentary 15 n values higher during the hirnantian glaciation

chronometric calibration of mid ordovician to tournaisian conodont zones a compilation from recent graphic correlation and isotope studies three available graphic correlation analyses are used to calibrate mid palaeozoic conodont zonations sweet s scheme for the mid to upper ordovician kleffner s for the mid to upper silurian and murphy berry s for the lower and middle lower devonian the scheme of sweet is scaled by applying the high precision u pb zircon date of tucker and others for the rocklandian and linked with that of kleffner by scaling the graptolite sequence of the ordovician silurian global stratotype section to fit two similarly derived dates from this sequence the top of kleffner s scheme all of murphy berry s as well as standard zones to the frasnian are calibrated by using tie points of the latest cambridge bp time scale gts 89 however the recent microbeam zircon date by claoue long and others for the hasselbachtal devonian carboniferous auxiliary stratotype is used to calibrate the standard famennian zones also the similarly derived but preliminary determination reported by roberts and others from the isismurra formation of new south wales is tentatively taken as the top of the tournaisian and so used to calibrate tournaisian zones despite the considerable extrapolation required to compile these schemes and their inherent errors the resultant time scale closely agrees with other dates of tucker and others from the llanvirn as well as the gts 89 homerian gorstian tie point this suggests that stratigraphic methods can be usefully applied to geochronometry the llandovery appears to have lasted longer 16 m y than usually envisaged and the ordovician silurian boundary may need to be lowered to approximately 443 5 ma certainly chrons varied widely in duration and further stratigraphic studies to estimate their relative durations as well as high resolution dating for their calibration will be crucial to more accurate biochronometries

silurian age fossils from the paleozoic parana basin southern brazil this paper is the first example of how middle ordovician to lower silurian land plant microfossils commonly present in otherwise unfossiliferous or poorly fossiliferous nonmarine or nearshore facies may be used for biostratigraphic purposes this new information permits the recognition of a broad regional unconformity extending from the parana basin to arabia conclusive evidence for the presence of silurian rocks in the parana basin of southeastern brazil is developed the age is based on organic microfossils including tetrahedral tetrads of land plant spores and phytoplankton acritarchs and prasinophytes that were recovered from body and trace fossil bearing rocks of the northeastern parana basin both the plant spores and phytoplankton indicate an early silurian early llandoverian age and support the previous permissive silurian age assignment based on the trace fossil arthrophycus and invertebrate body fossils

extent and bathymetry of north american platform seas in the early silurian the north american craton is 25 covered by lower silurian llandovery rocks based strictly upon the geographic area of surviving marine strata preserved in outcrop and the subsurface this figure does not take into account extensive post silurian tectonics and erosion isolated structural basins in which these strata are found today were not necessarily defined as corresponding topographic basins in the silurian analysis of interbasin structural arches and outliers provides important clues as to the actual extent of early silurian seas information on the age of tectonic origin for 15 prominent arches is reviewed the placement and significance of 11 key outliers is also discussed evidence of this kind indicates early silurian platform seas were among the most extensive of the paleozoic probably more than 65 of the north american craton was then flooded nothing on so vast a scale serves as a recent guide to the past the pliocene holocene bahamian banks do provide however worthy models for the role of bathymetry and water circulation as related to the changeover from laterally monotonous blanket deposits to a more complex mosaic of facies the original bathymetry of early silurian environments may be determined correlated and mapped on the basis of widespread carbonate cycles linked to sea level fluctuations the range of fully integrated facies patterns includes 1 coral stromatoporoid stromatolite paleosol cycles williston basin 2 pentamerid brachiopod coral stromatoporoid stromatolite cycles michigan basin and 3 stricklandiid brachiopod pentamerid brachiopod coral stromatoporoid cycles east iowa basin with shallow bathymetries of 0 30 m the williston class tends to represent mosaic facies while with bathymetries of 0 60 m and 10 90 m the deeper water michigan and iowa classes typically involve blanket deposits bathymetry of other basin deposits generally fits one of these three classes maximum and minimum stands in sea level during late llandovery time are represented by bathymetric maps

the early land plants from the armorican massif sedimentological and palynological considerations on age and environment the ch teaupanne unit belongs to the south armorican domain of the armorican massif france which is part of the variscan belt this unit includes two lower devonian plant levels and one of them corresponds to the basal member of the chalonnes formation a sedimentological and palaeontological analysis of these fossiliferous deposits from the ch teaupanne quarry montjean loire maine et loire france is presented here for the first time the age determination based on palynology indicates that the locality records the earliest occurrence of plant megafossils in the armorican massif their presence suggests an emergence event that has never been described before our study highlights the promising potential of the basal member of the chalonnes formation to aid in understanding these occurrences and provides new insights into the history of the variscan belt

vila maria formation silurian parana basin brazil integrated radiometric and palynological age determinations fresh shale samples taken from a well known outcrop section of the silurian vila maria formation located on the northeastern margin of the parana basin tres barras farm goias state central western brazil have been analysed for both palynological and radiometric age determi nations the rocks yielded a fairly diverse age definitive cryptospore assemblage and the same samples proved suitable for rb sr analysis despite silurian sedimentary rocks being rarely suited to radiometric dating techniques this study thus introduces an alternative independent method for estimating the minimum depositional age of the vila maria formation the rb sr age value has been calculated via an isochron diagram that yields 435 9 7 8 ma accordingly the latter value is inter preted as the minimum depositional age of the analysed vila maria strata implying their deposition during llandovery times this concurs with the palynological results which indicate an age no older than early silurian and more particularly favour an early to middle llandovery rhuddanian early aeronian attribution

carbon isotopes support the presence of extensive land floras pre dating the origin of vascular plants abstract multiple lines of evidence indicate that earth s land masses became green some 2 7 ga ago about 1 billion years after the advent of life about 2 2 billion years later land plants abruptly appear in the fossil record and diversify marking the onset of ecologically complex terrestrial communities that persist to the present day given this long history of land colonization surprisingly few studies report direct fossil evidence of emergent vegetation prior to the continuous record of life on land that starts in the mid silurian ca 420 425 ma ago here we compare stable carbon isotope signatures of fossils from seven ordovician silurian 450 420 ma old appalachian biotas with signatures of coeval marine organic matter and with stable carbon isotope values predicted for ordovician and silurian liverworts bryocarb model the comparisons support a terrestrial origin for fossils in six of the biotas analyzed and indicate that some of the fossils represent bryophyte grade plants our results demonstrate that extensive land floras pre dated the advent of vascular plants by at least 25 ma the appalachian fossils represent the oldest direct evidence of widespread colonization of continents these findings provide a new search image for macrofossil assemblages that contain the earliest stages of land plant evolution we anticipate they will fuel renewed efforts to search for direct fossil evidence to track the origin of land plants and eukaryotic life on continents further back in geologic time

palaeophytogeographical and palaeoecological implications of a miospore assemblage of earliest devonian lochkovian age from saudi arabia abstract palynological samples from two boreholes drilled in the eastern part of saudi arabia contain a rich assemblage of cryptospores and trilete spores they are dated as most probably lochkovian in age intriguingly the cryptospores are very similar to those from a coeval continental palynomorph assemblage from the old red sandstone continent whereas the trilete spores show a strong affinity with miospore assemblages from western gondwana it is suggested that cryptospore producing plants inhabited confined damp biotopes and had a wide range of climatic tolerance on the other hand trilete spore producing plants inhabited a wider variety of biotopes but were more sensitive to climatic variations the high degree of similarity between old red sandstone and saudi arabian cryptospore assemblages favours palaeogeographic reconstructions where there is close proximity between western gondwana and euramerica and or a land connection between these palaeoplates climatic differences between the old red sandstone continent and the northern part of western gondwana can be invoked to explain the variations in the trilete spore assemblages

living microbial ecosystems within the active zone of catagenesis implications for feeding the deep biosphere earth s largest reactive carbon pool marine sedimentary organic matter becomes increasingly recalcitrant during burial making it almost inaccessible as a substrate for microorganisms and thereby limiting metabolic activity in the deep biosphere because elevated temperature acting over geological time leads to the massive thermal breakdown of the organic matter into volatiles including petroleum the question arises whether microorganisms can directly utilize these maturation products as a substrate while migrated thermogenic fluids are known to sustain microbial consortia in shallow sediments an in situ coupling of abiotic generation and microbial utilization has not been demonstrated here we show using a combination of basin modelling kinetic modelling geomicrobiology and biogeochemistry that microorganisms inhabit the active generation zone in the nankai trough offshore japan three sites from odp leg 190 have been evaluated namely 1173 1174 and 1177 drilled in nearly undeformed quaternary and tertiary sedimentary sequences seaward of the nankai trough itself paleotemperatures were reconstructed based on subsidence profiles compaction modelling present day heat flow downhole temperature measurements and organic maturity parameters today s heat flow distribution can be considered mainly conductive and is extremely high in places reaching 180 mw m2 the kinetic parameters describing total hydrocarbon generation determined by laboratory pyrolysis experiments were utilized by the model in order to predict the timing of generation in time and space the model predicts that the onset of present day generation lies between 300 and 500mbelow sea floor 5100 5300mbelow mean sea level depending on well location in the case of site 1174 5 10 conversion has taken place by a present day temperature of ca 85 c predictions were largely validated by on site hydrocarbon gas measurements viable organisms in the same depth range have been proven using 14c radiolabelled substrates for methanogenesis bacterial cell counts and intact phospholipids altogether these results point to an overlap of abiotic thermal degradation reactions going on in the same part of the sedimentary column as where a deep biosphere exists the organic matter preserved in nankai trough sediments is of the type that generates putative feedstocks for microbial activity namely oxygenated compounds and hydrocarbons furthermore the rates of thermal degradation calculated from the kinetic model closely resemble ratesof respiration and electron donor consumption independently measured in other deep biosphere environments we deduce that abiotically driven degradation reactions have provided substrates for microbial activity in deep sediments at this convergent continental margin

paleozoic lake faunas establishing aquatic life on land abstract lakes are important archives for continental records of paleoenvironmental as well as paleoclimatic change they also record a unique macroevolutionary pattern that occurred when faunas invaded the continental realm in order to document that pattern we compiled a database of over one hundred and six lake basins from the neoproterozoic to permian looking at this critical time in lacustrine evolution several patterns emerge for the neoproterozoic through silurian time there is a paucity of documented lake deposits and lake faunal records however the records that are available indicate that lakes were oligotrophic and their nutrient cycling regimes primitive it is not until the establishment of land plants in the silurian that lakes began to respond with higher diversities and more complex physical and chemical conditions during the devonian carboniferous periods diversity was on the rise as trophic structure became more complex most lakes of the devonian and carboniferous formed along continental margins or in tectonic basins with occasional connection to the marine realm the faunas from these types of lakes were commonly comprised of mixed marine and freshwater elements and were far more diverse than other more inland lakes this estuary effect created a gateway or filter through which faunas invaded the continental realm the early history of lake faunas is one of opportunity and amelioration the feedback loops created by the establishment of vascular plants altered the nutrient cycle on land and in lakes all trophic levels were established early but became increasingly complex throughout the paleozoic as roles changed and faunal elements became established groups invading the continents via the estuary effect did so numerous times before establishing themselves permanently this was linked with the episodic re establishment in marine freshwater connections along these continental margins

palynology and palynofacies analysis of a silurian llandovery wenlock marine succession from the precordillera of western argentina palaeobiogeographical and palaeoenvironmental significance abstract a comprehensive survey of the marine and terrestrial palynomorphs from the la chilca formation exposed in the central precordillera of san juan argentina is presented twenty four samples from the quebrada ancha section were analysed marine phytoplankton predominated in the entire stratigraphic unit while the contribution of terrestrial palynomorphs was much less acritarchs and chlorophytes represent a highly diversified assemblage including stratigraphically relevant taxa such as domasia trispinosa tylotopalla caelamenicutis tylotopalla digitifera crassiangulina variacornuta stellinium rabians and percultisphaera cf stiphrospinata terrestrial palynomorphs are exclusively represented by six cryptospore species namely gneudnaspora divellomedia pseudodyadospora laevigata rugosphaera cerebra tetrahedraletes medinensis cf imperfectotriletes vavdovae and velatitetras retimembrana comparisons with coeval phytoplankton assemblages from gondwana and other palaeoplates such as laurentia baltica and avalonia show strong similarities suggesting a cosmopolitan distribution pattern during the llandovery and wenlock the first palynofacies analysis for the early silurian of argentina was performed depositional environments based on palynofacies match with those previously suggested based on sedimentological data two main palynofacies associations are recognised association b occurs in the lower part of the la chilca formation and is mostly composed of amorphous organic matter aom representative of low energy inner shelf environments association a is recognised in the upper part of the formation where sandstone beds become more frequent and is characterised by a greater amount of possible palynomorph remains ppr indicating a proximal platform to shoreface environment three excursions of total organic carbon toc were identified in the section probably as a result of sea level rise episodes that produced anoxic conditions and preservation of organic matter