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The Upper Pennsylvanian to lowermost Permian El Cobre Canyon and Arroyo del Agua formations are well exposed in a 250+ m section in the Chama Basin in northern New Mexico. This is one of the few known successions of fossiliferous red-bed siliciclastic sediments encompassing the Pennsylvanian-Permian boundary in the American Southwest and thus may inform questions regarding changing paleoclimate in tropical Pangea across the Pennsylvanian-Permian boundary. The section consists mainly of silty mudstones and sandstones with sheet-like to ribbon geometry and very minor limestones and records an upward transition from mainly braided stream deposition in the El Cobre Canyon Formation to anastomosing stream deposition in the Arroyo del Agua Formation. We recognized multiple paleosol types within these strata, including calcic Protosols, calcic Argillisols, argillic Calcisols and Calcisols, all generally consistent with the interpretation of a seasonal sub-humid to semi-arid climate. The calcretes in these paleosols occur primarily as truncated profiles. Although Calcisols occur in both formations, we note that Protosols are more common in the El Cobre Canyon Formation, and Argillisols dominate in the Arroyo del Agua Formation. Also, we find that the calcretes in the Arroyo del Agua Formation are generally thicker than those in the underlying El Cobre Canyon Formation. The difference in calcrete maturity could be explained by changes in source-area relief and sedimentation rate. However, stable isotope analyses of pedogenic carbonate indicate that a significant enrichment of δ 18 O occurs near the transition between the two formations, which approximates the Virgilian-Wolfcampian (equals Gzhelian-Asselian) boundary. Although the δ 13 C data suggest that p CO 2 remained stable during the interval of deposition, the δ 18 O data are consistent with the interpretation of climate aridification across the Pennsylvanian-Permian transition, potentially related to the onset of Gondwanan glaciation in the earliest Permian. [ABSTRACT FROM AUTHOR]

Carbonate lithofacies of the lower member of the El Hefhuf Formation (Turonian, Coniasian-Santonian) in the Bahariya Oases, Western Desert of Egypt comprise dolostone, burrowed dolostone, cherty dolostone, calcareous dedolostone, dolomitic quartzose lime-mudstone, and caliche. The dolostone and cherty dolostone formed in intertidal to supratidal environments, while dedolostone and caliche were formed during subaerial exposure. The dolomitic quartzose lime-mudstone was deposited in a restricted subtidal environment. Stable isotope analyses of the dolostone lithofacies are consistent with dolomitization by normal marine to evaporatively enriched dolomitizing fluids with only slight mixing of meteoric water. Therefore, dolomitization occurred in the intertidal and supratidal environments immediately following deposition. The dolostone and cherty dolostone lithofacies display pronounced cyclicity at the sub-meter scale, with individual cycles consisting of one (monolithic), two (diad) or at most three (triad) lithofacies. Most of all cycles show evidence of subaerial exposure at the top, such as brecciations, and many cycles are capped by calcareous palaeosol layers (caliche). In the absence of evidence for cycle periods at Milankovitch-scale frequencies, we reject orbital forcing as the cause of the cyclicity and suggest instead autocyclic depositional processes in the peritidal environment as the primary control on cyclicity, possibly modified by eustatic fluctuations at periods longer than the cycles recorded here. The significance of this study is to suggest formation of dolomite cycles due to high-frequency in sea level with intermittent subaerial exposure. [ABSTRACT FROM AUTHOR]

We document the occurrence of Upper Triassic fusain in northern Arizona, southern Utah and northern New Mexico in latest Carnian(?) to Norian-age alluvial strata of the Monitor Butte Formation and the Sonsela and Painted Desert members of the Petrified Forest Formation (Chinle Group). The fusain, identified by standard techniques of macroscopic and microscopic morphology, and resistance to chemical oxidation, is present at multiple stratigraphic horizons at several locations that are approximately correlative, although separated by several hundred km. The morphology of this fossil charcoal includes large, partially charred silicified to coalified logs, completely charred smaller limbs, charcoal fragments reworked in fluvial deposits, and particulate fusain disseminated in sediments. The apparent rarity of fusain in Triassic strata previously was cited as evidence for relatively low levels (compared to modern) of atmospheric oxygen and the consequent infrequent occurrence of wildfire during this time interval. However, our findings demonstrate a significantly greater abundance of fusain in Upper Triassic strata than previously acknowledged. Therefore, we suggest that wildfire was not an unusual occurrence during the Late Triassic. This conclusion supports recent experimental studies and geochemical models that indicate atmospheric oxygen levels at or above modern levels during the Late Triassic. [ABSTRACT FROM AUTHOR]

TheUpper Permian? – Lower Jurassic Newark Supergroup of eastern North America has a strikingly uniform succession of lithologic units. This uniformity is seen regardless of whether these units are characterized on the basis of their lithostratigraphy, allostratigraphy, biostratigraphy, or chemostratigraphy. After deposition, these units were broken up tectonically and attacked erosionally; parts of them survive today only within localized, down-faulted areas. Many lines of evidence compellingly demonstrate that most or all of these remnant units once were physically continuous between remaining outcrops. It is needlessly confusing to give every remnant of each unit a different name in each area where it persists simply because it is now physically isolated by erosion from other portions of the same unit. Instead, these units should be defined within a regional lithostratigraphic framework that emphasizes their common origins and original stratigraphic continuity. To this end, the formation-level stratigraphy of the Newark Supergroup is reduced from 58 locally applied and locally defined formations to a succession of only 16 uniformly defined and regionally recognizable formations. In all cases the oldest name validly applied to each formation is given priority over more recently erected synonymous names, which are either abandoned or, in a few cases, changed in rank to a member of one of the formations recognized here. The Newark Supergroup is here organized into four regionally recognizable groups, each subdivided into regionally recognizable formations. In ascending order, the Upper Permian?-Middle Triassic Acadia Group (new name) includes the Honeycomb Point Formation, Chedabucto Formation, Economy Formation, and Evangeline Formation. This group is preserved only in the Canadian Fundy and Chedabucto basins. The Upper Triassic (Carnian-Norian) Chatham Group includes the Doswell Formation, Stockton Formation, Lockatong Formation, and Passaic Formation. The Upper Triassic-Lower Jurassic (upper Rhaetian-lower Hettangian) Meriden Group includes the Talcott Formation, Shuttle Meadow Formation, Holyoke Formation, East Berlin Formation, and Hampden Formation. The term “Agawam Group,” previously proposed to encompass all Newark Supergroup strata above the highest basalt of the Meriden Group, is here abandoned and replaced with the name “Portland Group” for the same suite of strata. The Lower Jurassic (upper Hettangian-lower Sinemurian) Portland Group includes a lower Boonton Formation, an overlying Longmeadow Sandstone (here reinstated), and the Mount Toby Conglomerate, which laterally intertongues with both the Boonton Formation and the Longmeadow Sandstone. [ABSTRACT FROM AUTHOR]

Samples from strata spanning the Triassic–Jurassic boundary at the GSSP at Kuhjoch and at Kendlbachgraben were studied by NAA, XRF and combustion analysis to determine Ir levels and associated geochemistry. The results are compared to previously determined carbon isotope stratigraphy at these sections. Ir concentrations in the limestones of the Kössen Formation at Kuhjoch are very low (< 10 pg/g) below the top of the formation, rising to 26 pg/g, in the T-bed at the top of the Eiberg Member. The Tiefengraben Member of the Kendlbach Formation exhibits higher concentrations of Ir in general relative to the strata below. The shift to higher levels is abrupt at the base of the member, coinciding with a decrease in carbonate content. Concentrations of 60 to 80 pg/g are typical through the entire thickness of the Schattwald Beds and into the gray Tiefengraben Member strata, peaking at 145 pg/g. Concentrations decline to 30–40 pg/g above 680 cm from the formation base, coinciding with increasing carbonate content. The analyses from the Kendlbachgraben section compare well with those from Kuhjoch, with similar difference in Ir concentration between the Kössen and Kendlbach formations. In both sections, the initial increase in Ir corresponds to the initial carbon isotope excursion. Concentrations of redox-sensitive elements indicate transient reducing conditions during deposition of the uppermost Kössen Formation, but oxidizing conditions during Tiefengraben Member deposition. The Al/Ti ratio indicates more intense weathering during deposition of the lowermost 20 cm of the Tiefengraben Member, but otherwise consistently humid to sub-humid climate prevailed during deposition. The primary control on Ir concentration in the sampled section is formation lithology, although there are variations within the Tiefengraben Member that are independent of carbonate content. Enrichment of Ir at the top of the T-bed is associated with a redox boundary, but the cause of other variations is undetermined. [ABSTRACT FROM AUTHOR]

A spectacular example of columnar-jointed basalt occurs at Svartifoss in the Vatnajökull National Park of southern Iceland. The columns are notable for a variety of features on the vertical joint surfaces and the horizontal parting surfaces. The jointed surfaces of the columns display horizontal striations at a spacing of centimeters to decimeters. The individual striations exhibit crescentic hackles with a plumose pattern, the orientation of which varies between adjacent striations. Also present are gently dipping, millimeter-scale laminations not previously described. Horizontal parting surfaces of the columns display a circular ring that inscribes most of the diameter column. The ring features alternately positive or negative relief against the perimeter of the column and exhibits a radiating pattern of hackles originating at the center of the ring. Petrographic examination reveals that the basalt contains an interlocking network of plagioclase laths preferentially aligned perpendicular to the column axes. The circular features have been described previously and attributed to late-stage melt migration driven by a load-induced pressure gradient. The striations were formed from stepwise, downward propagation of the polygonal fracture system, and the plumose structures were formed from tensile stresses during fracture propagation. The small-scale laminations may result from preferential grain alignment of plagioclase laths. [ABSTRACT FROM AUTHOR]

Abstract: The Upper Triassic (Adamanian LVF) Ojo Huelos Member of the San Pedro Arroyo Formation (Chinle Group) is a distinctive, carbonate-rich unit that occurs in the lower Chinle section of central New Mexico. The member consists mainly of micritic lime mudstones, ostracodal wackestones to grainstones, peloidal grainstones and distinctive pisolitic rudstones, interbedded with fine-grained siliciclastic mudstones. Most limestones exhibit some evidence of pedogenic brecciation and root penetration, and porous fabrics similar to those of modern limestone tufas occur locally. The interbedded mudstones are typically lenticular and commonly display a blocky ped fabric in which subequant peds are separated by sparry calcite veins. Fossils from the Ojo Huelos Member are freshwater (darwinulid) ostracodes, various freshwater fishes and aquatic/amphibious tetrapods–metoposaurs and phytosaurs. We interpret the carbonate facies as the deposits of carbonate lakes, ponds and wetlands that were partly spring-fed, whereas the interbedded and surrounding mudstones were alluvial in origin. The groundwater and overland hydrology of the region was likely controlled by the relative proximity to an upland recharge area in the Mogollon Highlands to the south, but sedimentary fabrics record strong overprinting by desiccation and pedogenic reworking. Consequently, we interpret the Ojo Huelos Member as recording a climate that varied from subhumid to semi-arid, which caused episodic falls in the hydrologic base-level. This resulted in landscape degradation, exemplified by significant pedogenic and erosional reworking of the carbonate sediments and fluvial incision. [Copyright &y& Elsevier]

In this paper we present a model for the growth of a maar-diatreme complex in a shallow marine environment. The Miocene-age Costa Giardini diatreme near Sortino, in the region of the Iblei Mountains of southern Sicily, has an outer tuff ring formed by the accumulation of debris flows and surge deposits during hydromagmatic eruptions. Vesicular lava clasts, accretionary lapilli and bombs in the older ejecta indicate that initial eruptions were of gas-rich magma. Abundant xenoliths in the upper, late-deposited beds of the ring suggest rapid magma ascent, and deepening of the eruptive vent is shown by the change in slope of the country rock. The interior of the diatreme contains nonbedded breccia composed of both volcanic and country rock clasts of variable size and amount. The occurrence of bedded hyaloclastite breccia in an isolated outcrop in the middle-lower part of the diatreme suggests subaqueous effusion at a low rate following the end of explosive activity. Intrusions of nonvesicular magma, forming plugs and dikes, occur on the western side of the diatreme, and at the margins, close to the contact between breccia deposits and country rock; they indicate involvement of volatile-poor magma, possibly during late stages of activity. We propose that initial hydromagmatic explosive activity occurred in a shallow marine environment and the ejecta created a rampart that isolated for a short time the inner crater from the surrounding marine environment. This allowed explosive activity to draw down the water table in the vicinity of the vent and caused deepening of the explosive center. A subsequent decrease in the effusion rate and cessation of explosive eruptions allowed the crater to refill with water, at which time the hyaloclastite was deposited. Emplacement of dikes and plugs occurred nonexplosively while the breccia sediment was mostly still soft and unconsolidated, locally forming peperites. The sheltered, low-energy lagoon filled with marine limestones mixed with volcaniclastic material eroded from the surrounding ramparts. Ultimately, lagoonal sediments accumulated in the crater until subsidence or erosion of the tuff ring caused a return to normal shallow marine conditions. [ABSTRACT FROM AUTHOR]

Abstract: The type section of the Lower Cenomanian Bahariya Formation at Gebel El-Dist (Bahariya Oasis, Western Desert), Egypt, comprises claystones, mudstones, siltstones and sandstones deposited in fluvial-deltaic coastal plain, lagoonal, estuarine and shallow marine environments. The formation is characterized by an abundance of ferruginous sandstones that locally weather to form prominent iron crusts. These centimeter to decimeter-scale ferruginous horizons display a continuum of features ranging from unaltered sandstone with a pervasive ferruginous matrix to distinct ironstone beds with massive, nodular, vesicular and pisolitic textures. Ferruginous sandstone typically occurs at the tops of sandstone beds, or bracketing the base and top of beds, in the fining-upward cycles of deltaic plain deposits in the lower part of the formation and on a low-energy fluvial floodplain in the middle of the formation. Indurated ironstone beds occur mainly as the caps of coarsening-upward cycles of prograding shoreface sediments through much of the formation. We interpret the ironstone crusts as ferricretes, formed by iron accumulation that resulted from the oxidation and precipitation of soluble iron or colloids transported in the sediment load or by groundwater. This accumulation possibly took place at the water table or possibly below the water table at the fresh water/saline water interface. However, base-level fall and subsequent subaerial exposure of the sediments resulted in reworking and pedogenic modification of some of the iron-impregnated horizons. [Copyright &y& Elsevier]

Abstract: The stratigraphic section of the Upper Triassic–Lower Jurassic Whitmore Point Member of the Moenave Formation at Potter Canyon, Arizona, comprises c. 26m of gray to black shales and red mudstones interbedded with mainly sheet-like siltstones and sandstones. These strata represent deposition from suspension and sheetflow processes in shallow, perennial meromictic to ephemeral lakes, and on dry mudflats of the terminal floodout of the northward-flowing Moenave stream system. The lakes were small, as indicated by the lack of shoreline features and limited evidence for deltas. Changes in base level, likely forced by climate change, drove the variations between mudflat and perennial lacustrine conditions. Lenticular sandstones that occur across the outcrop face in the same stratigraphic interval in the lower part of the sequence represent the bedload fill of channels incised into a coarsening-upward lacustrine sequence following a fall in base level. These sandstones are distinctive for the common presence of over-steepened bedding, dewatering structures, and less commonly, folding. Deformation of these sandstones is interpreted as aseismic due to the lack of features typically associated with seismicity, such as fault-graded bedding, diapirs, brecciated fabrics and clastic dikes. Rapid deposition of the sands on a fluid-rich substrate produced a reverse density gradient that destabilized, and potentially fluidized the underlying, finer-grained sediments. This destabilization allowed synsedimentary subsidence of most of the channel sands, accompanied by longitudinal rotation and/or ductile deformation of the sand bodies. [Copyright &y& Elsevier]

Abstract: A detailed profile of Ir concentrations in continental strata of the Blomidon Formation ostensibly spanning the Triassic–Jurassic boundary confirms the existence of multiple anomalies, with a peak Ir concentration of 450 pg/g. The total amount of Ir deposited exceeds 4 ng/cm2, a value that requires an external source other than typical terrestrial sediment. Of the 10 other elements measure, only Zn and organic carbon are correlated to Ir. The organic carbon appears to be concentrated in mm-thick kerogenous laminae in greenish-grey to dark grey sediment layers that also host the Ir anomalies. The stratigraphic distribution of Ir and probably Zn appears to be controlled largely by redox boundaries conditions, with Ir probably forming organo-metallic complexes. We find no specific geochemical or sedimentological evidence for an extraterrestrial source for this enrichment, although we cannot exclude an impact origin. However, the close spatial and temporal relationship of the Ir anomalies in the Fundy and Newark basins to the basalts of the Central Atlantic Magmatic Province suggests alternative working hypotheses. Potentially, the volcanic rocks sourced the Ir through post-eruptive fluid mobilization into the surrounding sediments. Conversely, mantle outgassing and aerosol deposition during early stages of the eruptions may have been the source for the Ir anomalies. At this time, the data are insufficient to eliminate any of these hypotheses conclusively. [Copyright &y& Elsevier]

Abstract: Nonmarine fluvial, eolian and lacustrine strata of the Chinle and Glen Canyon groups on the southern Colorado Plateau preserve tetrapod body fossils and footprints that are one of the world''s most extensive tetrapod fossil records across the Triassic–Jurassic boundary. We organize these tetrapod fossils into five, time-successive biostratigraphic assemblages (in ascending order, Owl Rock, Rock Point, Dinosaur Canyon, Whitmore Point and Kayenta) that we assign to the (ascending order) Revueltian, Apachean, Wassonian and Dawan land-vertebrate faunachrons (LVF). In doing so, we redefine the Wassonian and the Dawan LVFs. The Apachean–Wassonian boundary approximates the Triassic–Jurassic boundary. This tetrapod biostratigraphy and biochronology of the Triassic–Jurassic transition on the southern Colorado Plateau confirms that crurotarsan extinction closely corresponds to the end of the Triassic, and that a dramatic increase in dinosaur diversity, abundance and body size preceded the end of the Triassic. [Copyright &y& Elsevier]

Abstract: The Moenave Formation was deposited during latest Triassic to earliest Jurassic time in a mosaic of fluvial, lacustrine, and eolian subenvironments. Ephemeral streams that flowed north-northwest (relative to modern geographic position) deposited single- and multi-storeyed trough cross-bedded sands on an open floodplain. Sheet flow deposited mainly silt across broad interchannel flats. Perennial lakes, in which mud, silt and carbonate were deposited, formed on the terminal floodplain; these deposits experienced episodic desiccation. Winds that blew dominantly east to south-southeast formed migrating dunes and sand sheets that were covered by low-amplitude ripples. The facies distribution varies greatly across the outcrop belt. The lacustrine facies of the terminal floodplain are limited to the northern part of the study area. In a southward direction along the outcrop belt (along the Echo Cliffs and Ward Terrace in Arizona), dominantly fluvial–lacustrine and subordinate eolian facies grade mainly to eolian dune and interdune facies. This transition records the encroachment of the Wingate erg. Moenave outcrops expose a north–south lithofacies gradient from distal, (erg margin) to proximal (erg interior). The presence of ephemeral stream and lake deposits, abundant burrowing and vegetative activity, and the general lack of strongly developed aridisols or evaporites suggest a climate that was seasonally arid both before and during deposition of the Moenave and the laterally equivalent Wingate Sandstone. We interpret growth of the erg as a consequence of marine regression during the latest Triassic through earliest Jurassic that exposed sediments on the coast of the back-arc sea to eolian reworking. Tectonic processes that created accommodation space enhanced preservation of the erg. [Copyright &y& Elsevier]

The Dinosaur Canyon Member of the Moenave Formation, of Late Triassic to Early Jurassic (Rhaetian-Hettangian) age, consists predominantly of sandstones and mudstones deposited by sheet and channelized flow and by eolian processes. We document several previously undescribed biogenic structures in these strata. At one location, eolian dune sandstone hosts the lined, smooth-walled burrow Palaeophycus heberti (Saporta); these may be the nesting burrows of small sand wasps, or alternatively, the burrows of sand-treader camel crickets. Eolian dune facies that host abundant rhizoliths also are typically bioturbated. Circular markings that are convex in epirelief are assigned to Pustulichnus gregarious Ekdale and Picard. Unlined, non-ornamented burrows are unassigned. We speculate that both of these also were formed by the burrowing activity of one of the many species of sand wasp. Rhizoliths are particularly prominent at the tops of eolian dune sandstone beds and locally may host termite nests. Stabilization of the landscape by plants permitted pedogenic alteration of the sediments. [ABSTRACT FROM AUTHOR]

Abstract: We present new analyses that confirm Ir enrichment (up to 0.31 ng/g) in close proximity to the palynological Triassic–Jurassic boundary in strata near the top of the Blomidon Formation at Partridge Island, Nova Scotia. High Ir concentrations have been found in at least two samples within the uppermost 70 cm of the formation. Ratios of other PGEs and Au to Ir are generally higher by an order of magnitude than in ordinary chondrites. No impact-related materials have been identified at this horizon in the Blomidon Formation, therefore we cannot confirm an extraterrestrial source for the anomalous Ir levels. We consider, however, the possibility that regional basaltic volcanism is a potential source for the Ir in these sediments. The elevated Ir concentrations are found in reduced, grey colored mudstones, so redox concentration is a possible explanation for the distribution of Ir in these strata. [Copyright &y& Elsevier]

The role of sector collapse in the generation of catastrophic volcanigenic tsunami has become well understood only recently, in part because of the problems in the preservation and recognition of tsunami deposits. Tinti et al. [Tinti, S., Bortolucci, E., Romagnoli, C., 2000. Computer simulations of tsunamis due to sector collapse at Stromboli, Italy. J. Volcanol. Geotherm. Res. 96, 103–128] modeled a tsunami produced by the c. 5,000 years BP collapse of the Sciara del Fuoco on the island volcano Stromboli. Although deposits associated with this event are generally lacking on the island, volcaniclastic breccias on the SE side of the island extending to an elevation above 120 m a.s.l. may have been generated by this tsunami. Deposits above 100 m are dominated by coarse breccias comprising disorganized, poorly sorted, nonbedded, angular to subangular lava blocks in a matrix of finer pyroclastic debris. These breccias are interpreted as a water-induced mass flow, possibly a noncohesive debris flow, generated as colluvial material on steep slopes was remobilized by the return flow of the tsunami wave, the run-up of which reached an elevation exceeding 120 m a.s.l. Finer breccias of subrounded to rounded lava blocks cropping out at 15 m a.s.l. are similar to modern high-energy beach deposits and are interpreted as beach material redeposited by the advancing tsunami wave. The location of these deposits matches the predicted location of the maximum tsunami wave amplitude as calculated by modeling studies of Tinti et al. [Tinti, S., Bortolucci, E., Romagnoli, C., 2000. Computer simulations of tsunamis due to sector collapse at Stromboli, Italy. J. Volcanol. Geotherm. Res. 96, 103–128]. Whereas the identification and modeling of paleo-tsunami events is typically based on the observation of the sedimentary deposits of the tsunami run-up, return flow may be equally or more important in controlling patterns of sedimentation. [Copyright &y& Elsevier]

The Miocene–Pliocene Furnace Creek Formation was deposited in marginal lacustrine and lacustrine environments in an extensional setting. Laminated facies comprising marlstone/limestone and mudstone/marlstone laminites lack features of surficial or shallow water deposition, indicating that sediment accumulated on the floor of a deep, perennial lake. Meter-scale mounds of porous limestone with a clotted-micritic fabric are spring-apron tufas that formed where groundwater discharged into more saline lake-bottom waters.The bedded borate facies comprises meter-scale bodies of borate, mainly colemanite, interbedded with laminated mudstone. The massive borate facies comprises thick, nonbedded borate layers, locally containing host rock clasts with sharp to diffuse boundaries. Borate formation took place at or below the sediment/water interface at the bottom of a permanently stratified carbonate lake. The composition of the borate deposits varies from mainly colemanite to zoned, with colemanite surrounding a core of probertite and ulexite. High Ca2+/Na+ ratios favored primary deposition of hydrated Ca-borates, which subsequently transformed by diagenetic dehydration to colemanite. Gradual depletion of Ca2+ and decreasing Ca2+/Na+ ratios resulted in NaCa-borate precipitation. Finally, renewed onset of elevated Ca2+/Na+ ratios again caused Ca-borate deposition. [Copyright &y& Elsevier]

Examines the carbon isotope compositions of pedogenic calcite from paleosol formations spanning across the Triassic/Jurassic boundary to represent a rise in atmospheric carbon dioxide concentrations. Effects of the eruptions of the Central Atlantic Magmatic Province; Factors controlling carbon isotopic composition of soil carbonate; Stratigraphic units sampled; Calculation findings of atmospheric paleo-carbon dioxide.

Anomalous levels of iridium in sedimentary strata are associated with mass extinction events caused by impact events. In the case of the end-Triassic extinction event, the anomalies as well as the extinctions are linked to the eruption of the Central Atlantic Magmatic Province (CAMP) flood basalts. We report new data on concentrations of iridium in continental strata of the Fundy, Deerfield, Hartford and Newark basins, both above and below the oldest CAMP flows in these basins, that demonstrate that these anomalies are more common than previously known. We conclude that the enrichments were at least in some instances likely derived locally by concentration due to leaching directly from the lavas into sediments proximal to the CAMP flows due to post-eruptive hydrothermal activity. In other instances, the enrichments likely record the global fallout of aerosols and/or ash particles during the eruptions of the CAMP basalts. The common association of the highest levels of enrichment with organic matter suggests either redox control or stabilization by formation of organometallic complexes following post-eruptive redistribution. These findings demonstrate the importance of considering the distribution and magnitude of iridium anomalies in considering the source of the iridium and possible extinction mechanisms. [ABSTRACT FROM AUTHOR]

The latest Triassic was an interval of prolonged biotic extinction culminating in the end-Triassic Extinction (ETE). The ETE is now associated with a perturbation of the global carbon cycle just before the end of the Triassic that has been attributed to the extensive volcanism of the Circum-Atlantic Magmatic Province (CAMP). However, we attribute the onset of declining latest Triassic diversity to an older perturbation of the carbon cycle (δ13C org) of global extent at or very close to the Norian/Rhaetian boundary (NRB). The NRB appears to be the culmination of stepwise biotic turnovers that characterize the latest Triassic and includes global extinctions of significant marine and terrestrial fossil groups. These biotic events across the NRB have been largely under-appreciated, yet together with a coeval disturbance of the carbon cycle were pivotal in the history of the Late Triassic. Here, we present new and published δ13C org data from widespread sections (Italy, Greece, ODP, Australia, New Zealand, USA, Canada). These sections document a previously unknown perturbation in the carbon cycle of global extent that spanned the NRB. The disturbance extended across the Panthalassa Ocean to both sides of the Pangaean supercontinent and is recorded in both the Northern and Southern Hemispheres. The onset of stepwise Late Triassic extinctions coincides with carbon perturbation (δ13C org) at the NRB, indicating that a combination of climatic and environmental changes impacted the biota at a global scale. The NRB event may have been triggered either by gas emissions from the eruption of a large igneous province pre-dating the NRB, by a bolide impact of significant size or by some alternative source of greenhouse gas emissions. As yet, it has not been possible to clearly determine which of these trigger scenarios was responsible; the evidence is insufficient to decisively identify the causal mechanism and merits further study. [ABSTRACT FROM AUTHOR]

Abstract: New major and trace element data and 40Ar/39Ar plateau ages constrain the timing, duration and time-related geochemical evolution of the Central Atlantic magmatic province in the U.S.A. (Newark and Culpeper basins) and refine correlations with basaltic lava flows from other Late Triassic–Early Jurassic circum-Atlantic basins. The precise, statistically robust 40Ar/39Ar plateau ages were obtained on biotite and on fresh plagioclase and calculated using the latest 40K decay constants. These ages are supported by a general consistency of the Ca/K calculated from 37Ar/39Ar of the plateau steps and the Ca/K obtained by detailed electron microprobe analyses on plagioclase phenocrysts. The ages of five analyzed basalt lava flows, from all three lava flow units in the Newark basins, and the ages of two sill samples are indistinguishable, indicating a brief magmatic peak phase at 201.8±0.7Ma. Recalibrated 40Ar/39Ar plateau ages from the entire province indicate a near-synchronous onset and peak volcanic activity at the Triassic–Jurassic boundary within the circum-Atlantic basins from the U.S.A., Canada and Morocco. The early erupted magmas (Moroccan Lower to Upper basalts, the Fundy basin North Mountain Basalt, and Orange Mountain and equivalent U.S.A. flows) yield an enriched geochemical signature (e.g., with relatively high La/Yb), whereas late magmas in the U.S.A. (Hook Mountain and Hampden basalts) and Morocco (Recurrent basalt) yield relatively depleted geochemical compositions (low La/Yb). A slight, but significant age difference for eruption of Hook Mountain and Hampden basalts (200.3±0.9Ma) and Recurrent basalts (198.2±1.1Ma) is interpreted as evidence of a diachronous northward rift–drift transition during break-up of Pangea. Our data indicate also a prolonged intrusive sequence that continued until about 195Ma at the Palisades sill and is consistent with sporadic late CAMP magmatism for dykes from the south-eastern U.S.A. and for intrusions from Guinea. [Copyright &y& Elsevier]