terrestrial and marine extinction at the triassic jurassic boundary synchronized with major carbon cycle perturbation a link to initiation of massive volcanism mass extinction at the triassic jurassic tr j boundary occurred about the same time 200 ma as one of the largest volcanic eruptive events known that which characterized the central atlantic magmatic province organic carbon isotope data from the uk and greenland demonstrate that changes in flora and fauna from terrestrial and marine environments occurred synchronously with a light carbon isotope excursion and that this happened earlier than the tr j boundary marked by ammonites in the uk the results also point toward synchronicity between extinctions and eruption of the first central atlantic magmatic province lavas suggesting a causal link between loss of taxa and the very earliest eruptive phases the initial isotopic excursion potentially provides a widely correlatable marker for the base of the jurassic a temporary return to heavier values followed but relatively light carbon dominated the shallow oceanic and atmospheric reservoirs for at least 600 k y

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

vertical roughness of mars from the mars orbiter laser altimeter the vertical roughness of the martian surface at 250 m spatial scales has been determined in two global latitude bands an equatorial and a high northern band acquired from 18 tracks of data by the mars orbiter laser altimeter mola during the fall of 1997 the distribution of rms vertical roughness as derived from mola pulse widths for the equatorial band is non gaussian with an overall mean of 2 8 m rms but with secondary populations at 1 5 m and 2 6 m rms the higher latitude northern plains of mars are almost uniformly 1 m rms in their vertical roughness characteristics suggesting that they are smoother than virtually any terrestrial deserts we suggest that dust mantling has muted the local topography of mars rendering it as smooth as 1 2 m rms heavily cratered uplands near the martian equator are noticeably rougher indicating more rugged and less mantled local topography

paleoatmospheric pco2 fluctuations across the cretaceous tertiary boundary recorded from paleosol carbonates in ne china abstract a dramatic change in atmospheric composition has been postulated because of global carbon cycle disruption during the cretaceous k tertiary t transition following the chicxulub impact and deccan trap eruptions here pedogenic carbonates were collected from drill core of a borehole sk 1 n straddling the late cretaceous and early paleocene strata in the songliao basin northeast china to reconstruct atmospheric co 2 concentrations using a paleosol paleobarometer our estimates for atmospheric pco 2 from paleosol carbonates range between 277 115 ppmv and 837 164 ppmv between 67 8 ma and 63 1 ma one large 66 65 5 ma and several small co 2 spikes 64 7 64 2 ma during the latest maastrichtian to earliest danian are reported here and incorporated with previously published pco 2 estimates also estimated from paleosol carbonates these co 2 spikes are attributed to one million year long emplacement of the large deccan flood basalts along with the extraterrestrial impact at the k t boundary

chronology of the central atlantic magmatic province implications for the central atlantic rifting processes and the triassic jurassic biotic crisis abstract the central atlantic magmatic province camp is among the largest igneous provinces on earth emplaced synchronously with or just prior to the triassic jurassic t j boundary ca 200 ma in great part due to the controversial connection between the occurrence of camp and the events of the t j boundary the demand for better constraints on the duration and eruptive chronology of this province has increased more than 100 new 40 ar 39 ar ages have been published in the last 15 years with more than half of these in the last 3 years a careful review and selection of available ages as well as the publication of 16 new ages from the carolinas newark basin usa french guyana and morocco are presented judicious selection yields a total of 58 accepted age determinations for camp magmatism ranging from 202 to 190 ma covering every part of the camp a more complete picture develops with intrusive camp magmatism commencing as early as 202 ma extrusive activity initiated abruptly 200 ma reaching peak volume and intensity around 199 ma on the african margin the main period of camp magmatism is confirmed as brief but is suggested to consist of at least two phases over 1 5 ma with magmatism commencing along the africa north american margins and slightly later along the south american margin two volumetrically minor but distinctive magmatic peaks centered at 195 and 192 ma are mirrored in data from all three continents and highlighted by our statistical approach models describing rifting and thermal input and magma production on these timescales are explored despite significant advances in our understanding of the chronology of camp more data of better quality and broader geographical coverage are needed to completely characterize the evolution of the camp and infer its geodynamic origin in addition lack of a well defined t j boundary age as well as the absence of a relevant basis for comparison between u pb and 40 ar 39 ar data for this time period remain limiting factors to unambiguously linking camp in time with the events of the t j boundary

combining soil water balance and clumped isotopes to understand the nature and timing of pedogenic carbonate formation abstract pedogenic carbonate is an important archive for paleoclimate paleoecology and paleoelevation studies however it can form under seasonal environmental conditions that differ significantly from the mean growing season environment or mean annual conditions potentially complicating its use for proxy reconstructions the observed seasonal temperature is typically but not always biased high relative to mean annual air temperature mat to evaluate the annual timing of pedogenic carbonate formation ten different soils were sampled across the western united states sites were selected to span a variety of precipitation regimes and soil orders precipitation regimes ranged from arid sites mean annual precipitation map 50 cm dominated by summer precipitation pedogenic carbonate formation temperatures derived from clumped isotope measurements ranged between 6 and 22 c with most samples falling at or below mat clumped isotope temperatures were compared to monthly precipitation normals and modeled monthly values of evapotranspiration and soil water content results show that carbonate formation temperatures agree with the annual timing of soil water depletion suggesting soil moisture content is a primary control on the timing of pedogenic carbonate formation although the seasonal bias is a function of environmental factors that are difficult to reconstruct in paleo studies the use of other paleosol proxies can help to assess if changes in clumped isotope temperatures are a function of changes in air temperature or hydrology these results have important implications for the production of accurate paleoclimate and paleoelevation estimates

assessing the record and causes of late triassic extinctions accelerated biotic turnover during the late triassic has led to the perception of an end triassic mass extinction event now regarded as one of the big five extinctions close examination of the fossil record reveals that many groups thought to be affected severely by this event such as ammonoids bivalves and conodonts instead were in decline throughout the late triassic and that other groups were relatively unaffected or subject to only regional effects explanations for the biotic turnover have included both gradualistic and catastrophic mechanisms regression during the rhaetian with consequent habitat loss is compatible with the disappearance of some marine faunal groups but may be regional not global in scale and cannot explain apparent synchronous decline in the terrestrial realm gradual widespread aridification of the pangaean supercontinent could explain a decline in terrestrial diversity during the late triassic although evidence for an impact precisely at the boundary is lacking the presence of impact structures with late triassic ages suggests the possibility of bolide impact induced environmental degradation prior to the end triassic widespread eruptions of flood basalts of the central atlantic magmatic province camp were synchronous with or slightly postdate the system boundary emissions of co2 and so2 during these eruptions were substantial but the contradictory evidence for the environmental effects of outgassing of these lavas remains to be resolved a substantial excursion in the marine carbon isotope record of both carbonate and organic matter suggests a significant disturbance of the global carbon cycle at the system boundary release of methane hydrates from seafloor sediments is a possible cause for this isotope excursion although the triggering mechanism and climatic effects of such a release remain uncertain d 2003 elsevier b v all rights reserved

stratigraphic record of the early mesozoic breakup of pangea in the laurasia gondwana rift system rift basins of the central atlantic margins cam of north america and morocco preserve largely continental sequences of sedimentary strata and less important minor basalt flows spanning much of the early mesozoic the best known is the newark basin of new jersey new york and pennsylvania where an astronomically calibrated magnetic polarity time scale is developed lacustrine cycles of milankovitch origin are commonly present in cam basins with the period changing from 10 ky paleoequator with coals to 20 ky 4 10n to perhaps 40 ky northward with evaporites cycles of100 ky 413 ky and2 my are also important four mostly unconformity bounded tectonostratigraphic sequences are present the anisian ts i is fluvial and eolian ts ii ts iv late triassic to early jurassic consist of tripartite lacustrine sequences caused by extension pulses the newark basin accumulation rate history allows comparison with quantitative rift basin models the north american plate s slow northward drift resulted in a relative shift of climate although the rapid humidification during the latest triassic and early jurassic is associated with a sea level rise the triassic jurassic mass extinction is of independent origin plausibly impact related

late triassic and early jurassic palaeogeography of the world abstract a new version of global and regional palaeogeographic maps is presented for two time intervals these maps depict the plate tectonic configuration palaeoenvironment and lithofacies during the late triassic carnian norian and early jurassic hettangian toarcian time the individual maps illustrate the general conditions present during the maximum marine transgressions of higher frequency cyclicity within the absaroka sequence of sloss during triassic time pangaea began to stretch initiating the rifting and future break up of the supercontinent the continued northward drift of the cimmerian continent corresponded with the progressive closure and consumption of palaeotethys oceanic crust and the opening of the neotethys ocean the most significant late triassic convergent event was the indosinian orogeny occurring as a result of the consolidation of south china and north china blocks also indochina and indonesia were sutured to south china at the same time the qiangtang block approached the eurasian margin the consolidation of the north chinese and amurian blocks left open a large embayment of panthalassa between amuria and laurasia the so called mongol okhotsk ocean active subduction existed along the margin of this ocean dipping cratonwards towards east siberia the last collisional events of the uralian orogeny took place during the triassic and early jurassic time the conclusion of the uralian orogeny was accompanied by uplift of the adjacent areas of eastern europe and western siberia during the early jurassic the palaeotethys ocean was finally closed and the cimmerian continent collided with asia causing the cimmerian orogeny the time around the triassic jurassic boundary marked an important biotic extinction event plate tectonic activity caused palaeogeographic and palaeoclimatic change which may have contributed to the mass extinction from the plate tectonic and palaeogeographic point of view the following events could have influenced the extinction 1 the closure of palaeotethys and assembly of the asian part of pangaea 2 the break up of pangaea in the future central atlantic area and transition from rifting to drifting and 3 the very extensive basaltic volcanism of the central atlantic magmatic province

determining terrestrial paleotemperatures using the oxygen isotopic composition of pedogenic carbonate abstract quantifying terrestrial paleotemperatures has proven to be a challenging endeavor this paper explores the use of the oxygen isotopic composition of pedogenic calcite for terrestrial paleotemperature reconstructions we generate three paleotemperature equations two of them derived by simultaneous solution of equations that describe the fractionation of oxygen isotopes in the exogenic cycle while the third equation is derived using a linear regression through modern 18occ mat oxygen isotopic composition of pedogenic calcite versus mean annual temperature data we use the paleotemperature equations to evaluate climate change across the k t boundary by analyzing the oxygen isotopic composition of pedogenic carbonates from a series of stacked paleosols in west texas the fabrics in the calcite nodules were evaluated in order to identify soil carbonate components that have the best chance of containing isotopic information that represents ancient pedogenic conditions the average temperature for west texas during the time period studied is 18 0 5 c two temperature excursions are recognized prior to the k t boundary in which terrestrial temperatures increase by about 4 c for relatively short periods of time these short greenhouse events documented in west texas correlate with changes in marine temperatures as well as terrestrial temperatures in north dakota during the same time period latitudinal temperature gradients generated using the west texas and north dakota data indicate that the spatial simultaneous solution yields the most reliable temperature reconstructions of the three equations considered in this study

a method to estimate the longshore sediment transport at ebb tidal deltas based on their volumetric growth application to the guadiana spain portugal border

triassic jurassic atmospheric co2 spike i question the claim by tanner et al 1 that atmospheric co2 levels remained constant across the triassic jurassic boundary on the grounds of problems with stratigraphic completeness and contamination with atmospheric methane because methanogenic ch4 has a light isotope composition and oxidizes readily to co2 methane clathrate dissociation and oxidation events cannot be detected by palaeobarometers that use the carbon isotope composition of palaeosol carbonate

reef expansion during the triassic spread of photosymbiosis balancing climatic cooling the paleoreefs database indicates that reef abundance increased profoundly during the triassic period from a pronounced low in the early triassic to a major peak in the norian this expansion is also evident when standardizing for sampling corresponding to the reef expansion is a relative increase of scleractinian corals as reef builders whereas the contribution of hypercalcifying sponges and microbes decreased during the triassic the numerical expansion of corals is paralleled by a proportional increase of morphological features that are suggestive of photosymbiosis such that the norian reef boom might be explained by the spread of photosymbiosis in corals the geographical expansion of reefs was far less pronounced especially concerning palaeolatitude late triassic reef growth was limited to more or less the same latitudinal range as modern reefs as oxygen isotope data and new modeling results indicate declining temperatures and co2 concentrations during the late triassic the lack of latitudinal expansion might be attributed to global cooling reef development during the triassic can thus be explained by the evolutionary spread of photosymbiosis balancing the effects of climatic cooling

stability of atmospheric co2 levels across the triassic jurassic boundary the triassic jurassic boundary 208 million years ago is associated with widespread extinctions in both the marine and terrestrial biota the cause of these extinctions has been widely attributed to the eruption of flood basalts of the central atlantic magmatic province this volcanic event is thought to have released significant amounts of co2 into the atmosphere which could have led to catastrophic greenhouse warming but the evidence for co2 induced extinction remains equivocal here we present the carbon isotope compositions of pedogenic calcite from palaeosol formations spanning a 20 myr period across the triassic jurassic boundary using a standard diffusion model we interpret these isotopic data to represent a rise in atmospheric co2 concentrations of about 250 p p m across the boundary as compared with previous estimates of a 2 000 4 000 p p m increase the relative stability of atmospheric co2 across this boundary suggests that environmental degradation and extinctions during the early jurassic were not caused by volcanic outgassing of co2 other volcanic effects such as the release of atmospheric aerosols or tectonically driven sea level change may have been responsible for this event

co2 and the end triassic mass extinction the end of the triassic period was marked by one of the largest and most enigmatic mass extinction events in earth s history1 and with few reliable marine geochemical records terrestrial sediments offer an important means of deciphering environmental changes at this time tanner et al 2 describe an isotopic study of mesozoic fossil soils which suggests that the atmospheric concentration of carbon dioxide pco2 across the triassic jurassic boundary was relatively constant within 250 p p m v but this is inconsistent with high resolution evidence from the stomatal characters of fossil leaves3 here i show that the temporal resolution of the fossil soil samples may have been inadequate for detecting a transient rise in pco2 i also show that the fossil soil data are consistent with a large increase in pco2 across the triassic jurassic boundary when variations in the stable carbon isotope denoted as 13c in terrestrial plant leaves are taken into account these factors suggest that the linkage between pco2 global warming and the end triassic mass extinction remains intact

rising atmospheric co2 as a possible trigger for the end triassic mass extinction the end triassic mass extinction one of the five largest extinctions in earth history was a severe catastrophe in which 80 of all species were wiped out the cause of the extinction is controversial but any mechanism must account for mass extinction in both marine and terrestrial environments one smoking gun the eruption of the central atlantic magmatic province camp has prompted the hypothesis that co2 degassing to the atmosphere may have induced an environmental catastrophe at the end triassic in this study we use a numerical coupled ocean atmosphere climate model of the late triassic to determine environmental stresses associated with a rapid increase in atmospheric co2 a series of sensitivity experiments with co2 levels that bracket estimated end triassic pco2 estimates 2 8 pre industrial levels predict extreme environmental conditions on land increasing co2 from 2 to 8 pre industrial levels causes an increase in the number and severity of hot days and days without precipitation an exponential increase in continental area experiencing hot days and enhanced seasonal fluctuation in the ocean wind driven circulation decreases and meridional overturning diminishes by a factor of 4 leading to enhanced ocean stratification a three box model of the deep ocean predicts a decline of 85 mol l in deep ocean oxygen concentration with a 4 fold increase in atmospheric co2 consequently while terrestrial organisms would have been subject to severe heat and water stress marine fauna would have experienced oxygen deprivation additional sensitivity experiments indicate that variations in milankovitch orbital parameters may further contribute to faunal stress by intensifying continental heating and seasonal fluctuations in sum model results predict that rising atmospheric co2 would have significantly impacted both marine and continental environments providing a link between turnover on land and ocean during the late triassic

paleosols trace fossils and precipitation estimates of the uppermost triassic strata in northern new mexico abstract this study provides a detailed pedogenic evaluation of two upper triassic late norian through rhaetian stratigraphic intervals in new mexico in order to assess the climate and ecology of the latest triassic which ended in a mass extinction the two study areas are located in north central and east central new mexico and are separated by 200 km each section contains abundant paleosols of varying maturity with features that reflect an arid to semiarid climate there is little pedogenic variation throughout the strata at each location and a typical paleosol profile is about 1 m thick and has an ab bw bk bc horizon succession bkm bss bssk or bssg horizons are present in some paleosols micromorphological features suggest dominantly well drained sola e g abundant carbonate nodules illuviated clay with minor periods of moist or saturated conditions e g femn concretions femn coatings and hypocoatings sepic plasmic fabrics trace fossils are abundant in these strata and are dominated by taenidium serpentinum and root traces depth to carbonate functions estimate that mean annual precipitation was between 200 and 450 95 mm relative to location 1 eastern new mexico location 2 north central new mexico produced higher paleo precipitation estimates and has stronger and more abundant sepic plasmic fabrics in thin sections the presence of a gleyed paleosol camborygma eumnkenomos and slickensides at location 2 also suggests conditions wetter than at location 1 taxonomically all of the paleosols in this study appear to be entisols or aridisols and can be grouped into seven representative pedotypes of varying maturity by comparing these paleosols to modern soils this study demonstrates that the late triassic western interior during the late norian to rhaetian was arid to semiarid and supported a desert shrub environment that had localized and periodic moist or saturated soil conditions

pedogenic carbonate isotopes as evidence for extreme climatic events preceding the triassic jurassic boundary implications for the biotic crisis the triassic jurassic boundary is associated with widespread marine and terrestrial extinctions but there is disagreement regarding the existence and extent of climatic changes that may have driven the biotic crisis here we apply quantitative isotopic climate proxies in order to construct two age equivalent relatively continuous temperature and p co 2 records that span the eight million years preceding the triassic jurassic boundary and that supersede previous terrestrial records in temporal resolution the 18 o data suggest that mean annual temperatures mat increased by 7 9 c from the late norian to the rhaetian in association with the peak increases in p co 2 levels the 13 c data suggest relatively low late norian p co 2 levels 1500 ppmv and at least two periods of extreme p co 2 levels 3000 ppmv preceding the triassic jurassic boundary these estimates are consistent with a recent late triassic climate model that suggests the effects of increased p co 2 levels on pangea would cause severe climatic consequences including a global mat increase of 6 c 10 c in some regions while it is possible that periods of increased aridity could have resulted in erroneously high estimates of both temperature and p co 2 levels it is likely that climate was still fluctuating during the end of the triassic although our data precede the triassic jurassic boundary many studies conclude that the mass extinction took place over a more prolonged period beginning in the late triassic thus climate may have been a significant driving mechanism of the late triassic extinctions

shoreline accretion and sand transport at groynes inside the port of richards bay the south western shoreline along the entrance channel inside the port of richards bay has experienced continued erosion four groynes were constructed to stabilise the shoreline monitoring of shoreline evolution provided valuable data on the accretion adjacent to two of the groynes and on the sediment transport rates at these groynes tides beach slopes winds wave climate current regime and sand grain sizes were documented the one site is moderately protected from wave action while the other is protected according to the wiegel wiegel r l 1964 oceanographical engineering prentice hall inc englewood cliffs nj classification the shoreline accreted progressively at the two groyne sa t 0 065 m day and 0 021 m day respectively the shorelines accreted right up to the most seaward extremity of the groynes equilibrium shorelines were reached within about 3 5 years to 4 years which compare well with other sites around the world the mean wave incidence angle is large and was found to be about 22 the median sand grain sizes were 0 33 mm and 0 37 mm the groynes acted as total traps the beach surveys were extended to an adequate depth and cross shore sediment transport did not cause appreciable net sand losses into the entrance channel the net longshore transport rate along the study area which is north westbound is only slightly lower than the gross longshore transport the actual net longshore transport rates are 18 000 m 3 year and 4 600 m 3 year respectively at the two groynes a rocky area limits the availability of sand at one

new constraints on using paleosols to reconstruct atmospheric pco2 ecosystem and climatic changes due to anthro po genic emissions of co 2 are of increasing importance to society one way to predict these changes in the future is to study warming events in the geologic past the main control of earth s temperature over geologic time is the concentration of atmospheric co 2 however the precise relationship between co 2 and temperature is not fully understood therefore it is essential to be able to quantify atmospheric co 2 concentrations in the geologic past especially at times of rapid climate change analogous to current atmospheric changes one widely applied proxy relates the carbon isotopic composition of pedogenic carbonates to atmospheric pco 2 but one of the key variables soil respired co 2 s z is not well constrained this study presents a new proxy where soil respired co 2 is related to mean annual precipitation map by the following equation s z 5 67 map 269 9 r 2 0 59 se 681 ppm this proxy validated for modern atmospheric pco 2 levels constrains the primary source of uncertainty in the soil carbonate paleobarometer we apply this proxy to make atmospheric pco 2 reconstructions for examples from the cenozoic mesozoic and paleozoic and calculate co 2 estimates that are in better agreement with estimates from other independent proxies and model results than previous pedogenic carbonate reconstructions the implications of the uncertainties attributed to pedogenic carbonate paleobarometry as well as guidelines for using this method are discussed by making individual measurements rather than assumptions for each isotopic value and combining those analyses with an s z estimate for each paleosol considered using our new proxy described herein we can obtain increased precision for atmospheric pco 2 reconstructions

multi proxy paleosol evidence for middle and late triassic climate trends in eastern utah abstract prior investigations suggest that alluvial lowlands of pangea in the southwestern u s a during the middle to late triassic experienced an arid to semiarid climate with significant seasonality our investigation finds evidence for a global pluvial episode from paleosols in the middle to late triassic section of eastern utah multi proxy paleosol evidence is used to quantify rainfall amounts ambient temperatures and atmospheric co 2 concentrations and infer associated plant formations related to ecosystem persistence rainfall estimates are derived from geochemical molecular weathering ratios temperature and atmospheric co 2 levels from stable oxygen and carbon isotopes of pedogenic carbonate respectively and ecosystem reconstruction by a combination of climate indexes and paleosol characteristics eight pedotypes were identified and include poorly drained aquic entisols fisher well drained non aquic entisols salt valley calcic aridisols castle valley calcic inceptisols moab cambic ute and calcic la sal vertisols dystric inceptisols kokopeli and argillic alfisols slickrock the middle triassic moenkopi formation anisian was dominated by castle valley paleosols with mean annual rainfall between 300 and 400 mm and mean annual temperature between 13 and 23 c mesic to hyperthermic based on these climate indexes and root traces the associated plant formation was most likely desert shrub or dry woodland the lower chinle formation carnian contains a succession of ute and la sal paleosols that changed up section to kokopeli fisher and slickrock paleosols in accordance with geochemical and isotopic signatures from these pedotypes rainfall amounts initially increased to between 700 and 900 mm and then to between 1300 and 1400 mm temperatures estimated from the la sal paleosol are approximately 18 c thermic at this time the lower chinle marks a transition from dry woodland to open forest that appears to correlate with the formation of the petrified forest member in arizona the upper chinle formation carnian norian reveals a return to semiarid to subhumid conditions and the formation of castle valley moab and salt valley paleosols all of which appear to have supported desert shrub or dry woodlands rainfall amounts decreased to between 400 and 600 mm with temperatures eventually increasing to 29 c hyperthermic using the paleosol isotopic barometer atmospheric co 2 estimates generally correlate with other proxy for the triassic the well developed alfisols and noncalcareous inceptisols identified during the carnian of the lower chinle correlate with a previously identified global pluvial episode based on sedimentological and marine isotopic evidence possibly in response to rifting of pangea it should not be assumed that the middle to late triassic in continental alluvial lowlands supported a uniform semiarid to arid climate with strong seasonality

on the application of static equilibrium bay formulations to natural and man made beaches crenulate shaped bays are common features found all around the world the most widely used formulation for representing this kind of bay is the parabolic approach proposed by hsu and evans institution of civil engineers proc london england 87 1989 556 who suggested a methodology to test and predict the stability of static equilibrium shapes in natural and man made bays based on an analytical model of null drift current and using an empirical approach a modified methodology is proposed the new procedure is able to locate the downcoast starting point of the static equilibrium beach from which the parabolic plan form of hsu and evans is valid this methodology is applied with good results to different natural and man made beaches along the atlantic and mediterranean coasts of spain including tombolo shaped beaches

multiple phases of carbon cycle disturbance from large igneous province formation at the triassic jurassic transition the end triassic mass extinction ca 201 4 ma coincided with a major carbon cycle perturbation based on an 5 6 negative excursion in 13 c toc total organic carbon records both events coincided directly with the onset of massive flood basalt volcanism in the central atlantic magmatic province camp organic carbon isotope data from the western tethys ocean austria and the germanic basin uk and germany however demonstrate earlier disruption of the global carbon cycle preceding camp eruptions a 2 3 late rhaetian precursor negative excursion in marine and continental 13 c toc records is matched by a negative perturbation in 13 c leaf data suggesting multiple events of rhaetian atmospheric 13 c depletion intruding dike and sill systems preceding camp eruptive volcanic activity may have released 3000 7000 gt of isotopically light carbon as thermogenic methane from subsurface organic rich strata this possibly caused an end triassic atmospheric p co 2 increase and reduced ecosystem stability before the actual onset of eruptive volcanic activity in the camp region we present a model that identifies three phases of disturbances in global biogeochemical cycles related to the formation of this large igneous province

isotopic imprint of climate and hydrogeochemistry on terrestrial strata of the triassic jurassic hartford and fundy rift basins abstract late triassic to early jurassic terrestrial sequences in the hartford and fundy rift basins have distinctive carbon and oxygen isotopic compositions of calcite and dolomite the isotopic data mostly reflect paleoclimatic fluctuations and hydrogeochemistry of the lacustrine playa and fluvial environments dolomites from laminae in three sequences of playa red mudstones and lacustrine gray to black mudstones in the hartford basin have variable isotopic compositions 13c 5 8 to 1 8 pdb 18o 7 2 to 0 7 pdb within any single symmetrical cycle of playa red mudstone lacustrine gray black gray mudstone playa red mudstone there is a systematic change to relatively enriched 13c compositions in dolomite in the grayish black and black mudstones in the center of the cycle these carbon isotopic data suggest that the lacustrine sequences formed as the lakes changed from well mixed with anoxic bottom waters to stratified with anoxic bottom waters where 13c depleted carbon was concentrated in organic matter that was then buried calcites from lacustrine micritic and biomicritic limestones of the scots bay formation of the fundy basin have stable isotopic compositions 13c 4 6 to 2 2 pdb 18o 6 1 to 3 0 pdb that become more enriched in 18o and 13c upward in shallowing depositional sequences these isotopic data reflect initial calcite precipitation when a high inflow of fresh water produced high lake levels followed by progressively lower inflow resulting in lower lake stands and higher salinity due to continuing evaporative loss of surface wat r the lake waters were well oxygenated at all times in the hartford basin caliche calcites in fluvial mudstones and sandstones have isotopic compositions 13c 7 3 to 3 8 pdb 18o 8 0 to 5 6 pdb that reflect paleosol processes during climatic conditions that varied from warm and dry in late triassic time to relatively cooler and probably wetter in the early jurassic isotopic compositions of caliche calcites in redbeds in the fundy basin indicate a parallel climate change from late triassic to early jurassic time but also that the climate was relatively hotter and probably drier over the entir interval as compared to the hartford basin

the correlation between 18o 16o ratios of meteoric water and surface temperature its use in investigating terrestrial climate change over geologic time abstract correlations between mean annual temperature mat and the weighted average oxygen isotope composition of yearly precipitation 18opt are well known but the utility of modern relations to make reliable estimates of temperature change over geological time is uncertain this question has been addressed by using seasonal subsets of the global data base of temperature and isotopic measurements to represent two different climate modes a comparison of middle to high latitude 18opt temperature relations for each climate mode reveals 1 a significant offset between them and 2 a difference in the strength of their correlations the offset in relations is due to differences in temperature and water vapor budget in the tropics and can lead to serious underestimates of temperature change differences in the strength of correlations arise from the influence of climate mode specific non temperature factors on 18opt the overall result is that no single relation can be used in all cases to make unambiguous temperature estimates using a temporal record of 18opt values one way to overcome these problems is to reconstruct 18opt temperature relations for the time periods being investigated if an appropriate proxy for 18opt is available it may also be possible to estimate temperature without relying on 18opt temperature relations a promising alternative to these options is to use records of 18opt to test predictions of global climate models an approach that may allow a reliable and more complete reconstruction to be made of climate change over geologic time

continental sequence stratigraphy of the upper triassic norian rhaetian chinle strata northern new mexico u s a allocyclic and autocyclic origins of paleosol bearing alluvial successions abstract two age equivalent upper triassic fluvial successions deposited on the continental interior of the southwestern united states were evaluated using an adapted marine stacking pattern analysis methodology a three tier cyclic hierarchy is present in the strata at both study areas meter scale fining upward fluival aggradation cycles facs comprise fluvial aggradational cycle sets facsets 4 15 m thick avg 8 4 m facsets in turn stack into four fluvial sequences 26 48 m thick avg 41 m within these sequences transgressive systems tract equivalents te are characterized by channel sands and associated minor overbank deposits and relatively immature paleosols i e high rates of deposition whereas highstand to falling stage systems tract equivalents hfe are dominated by overbank muds and relatively well developed paleosols i e lower rates of deposition these two fluvial successions which are 200 km apart contain age equivalent fluvial sequences that record similar histories of deposition and pedogenesis sequence 1 contains only an incomplete hfe sequence 2 includes both the te and hfe sequence 3 is an hfe and sequence 4 contains only a te fluvial sequences likely accumulated in response to pulses of source area uplift and or basin subsidence which resulted in changes in accommodation conversely higher frequency facs and facsets that occur within sequences do not correlate between study areas and are likely the products of autocyclic processes such as channel avulsion floodplain aggradation and channel migration these results suggest that regionally significant tectonic episodes may be discernible in suspended load fluvial deposits that accumulated over a broad area

carbonate to biosilica transition at the norian rhaetian boundary controlled by rift related subsidence in the western tethyan lagonegro basin southern italy abstract the lagonegro basin located in the southern apennines italy records a transition from carbonate sediments of the calcari con selce fm cherty limestone to biosiliceous sediments of the scisti silicei fm siliceous shale around the norian rhaetian boundary nrb upper triassic sedimentologic and chemostratigraphic analysis of three sections pignola abriola monte volturino and madonna del sirino representing a proximal to distal transect across the basin document marine productivity redox and chemical weathering conditions the basin was characterized by low to moderate productivity and mainly oxic deep waters with no systematic secular variation throughout the 10 myr long study interval a weathering proxy the chemical index of alteration cia shifts toward higher values from 0 70 to 0 80 in all three study sections suggesting development of warmer and or more humid conditions just before the nrb the lack of evidence for changes in marine productivity or redox conditions and the time transgressive nature of the carbonate biosilica transition suggests that the latter was caused not by changes in planktonic communities but rather by a rise in the ccd the most likely cause of which was seafloor subsidence within the actively rifting ionian ocean i e the westernmost branch of the tethys ocean the tectonically active character of the lagonegro basin is also reflected in evidence of synsedimentary paleoseismic activity e g numerous debris flows around the basin margins the present study thus documents sedimentologic changes within a marginal basin in a geologically young ocean

eogenetic diagenesis of chinle sandstones petrified forest national park arizona usa a record of late triassic climate change fluvially derived tuffaceous chinle sandstones from petrified forest national park provide a well preserved late triassic archive of climate information petrographic analysis of 38 chinle sandstones provides new insight into the depositional history and evolution of palaeoclimate during chinle deposition this study focuses on the relationship between climate and meteoric diagenesis as a guide for constraining climate change in western equatorial pangea during the late triassic petrographic analysis of chinle sandstones reveals their wide range of textural attributes as well as pedogenic and shallow burial diagenetic features that occurred during the late triassic these diverse petrological characteristics are indicative of the evolving late triassic climate when placed into a well constrained stratigraphic and geochronological framework the stratigraphic succession is characterized by variations in the abundance of framework grains detrital matrix weathering intensity of feldspar and volcanic rock fragments and the mineralogy of clay cements climate records from chinle palaeosol geochemistry indicate a progression from wet to dry conditions this trend is also reflected in the meteoric diagenetic features of chinle sandstones during deposition of the lower chinle elevated rainfall promoted the weathering of labile volcanic detritus to kaolinite whereas feldspars especially plagioclase were partially or completely dissolved in the upper chinle a trend towards drier conditions favoured the formation of smectite and less feldspar dissolution resulting in a higher abundance of well preserved plagioclase grains shallow burial meteoric weathering reactions in chinle sandstones reflect the evolving climate during the late triassic