Is the transition impact to post-impact rock complete? Some remarks based on XRF scanning, electron microprobe, and thin section analyses of the Yaxcopoil-1 core in the Chicxulub crater

The transition from impact to post-impact rocks in the Yaxcopoil-1 (Yax-1) core is marked by a 2 cm-thick clay layer characterized by dissolution features. The clay overlies a 9 cm-thick hardground, overlying a 66 cm-thick crossbedded unit, consisting of dolomite sandstone alternating with thin micro-conglomerate layers with litho- and bioclasts and the altered remains of impact glass, now smectite. The micro-conglomerates mark erosion surfaces. Microprobe and backscatter SEM analysis of the dolomite rhombs show an early diagenetic, complex-zoned, idiomorphic overgrowth, with Mn-rich zones, possibly formed by hot fluids related to cooling melt sheet in the crater. The pore spaces are filled with several generations of coelestite, barite, K-feldpar, and sparry calcite. XRF core scanning analysis detected high Mn values in the crossbedded sediments but no anomalous enrichment of the siderophile elements Cr, Co, Fe, and Ni in the clay layer. Shocked quartz occurs in the crossbedded unit but is absent in the clay layer. The basal Paleocene marls are strongly dissolved and do not contain a basal Paleocene fauna. The presence of a hardground, the lack of siderophile elements, shocked quartz, or Ni-rich spinels in the clay layer, and the absence of basal Paleocene biozones P0 and Pa all suggest that the top of the ejecta sequence and a significant part of the lower Paleocene is missing. Due to the high energy sedimentation infill, a hiatus at the top of the impactite is not unexpected, but there is nothing in the biostratigraphy, geochemistry, and petrology of the Yax- 1 core that can be used to argue against the synchroneity of the end-Cretaceous mass-extinctions and the Chicxulub crater.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

The section of the Barranco del Gredero (Caravaca, SE Spain): a crucial section for the Cretaceous/Tertiary boundary impact extinction hypothesis

Abstract The Barranco del Gredero section is one of the most complete, expanded and well exposed Cretaceous Tertiary (K/T) boundary sections in the world. Therefore, the Gredero section has played a key role in the development and testing of the impact extinction hypothesis, and has a significant number of “first discoveries “ to its name: The first discovered intact ejecta layer, microkrystites with K-spar pseudomorphs after clinopyroxene and Cr-rich spinels, abundant soot, carbonaceous chondritic 53Cr/52Cr ratios in the ejecta layer, the foraminiferal P0 Zone in the boundary clay, and the adaptive radiation of planktic foraminifers. Also, stable isotope, trace element analysis and the magneto- and cyclo stratigraphy, and the history of burrowing adds to the importance of the Gredero section. Recently urban and road-building development has threatened the excellent exposures, and the lower 100 meters of the upper Maastrichtian are already not longer accessible. The status of geological monument of the Region of Murcia would guarantee that the section will remain accessible for scientific investigation in the future. Resumen La sección del Barranco del Gredero es una de las secciones del límite Cretácico/Terciario (K/T) más completas, expandidas y bien expuestas en el mundo. Por tanto, la sección del Gredero ha jugado un papel clave en el desarrollo y la comprobación de la hipótesis de extinción por impacto, y tiene asociados a su nombre un número considerable de ‘primeros descubrimientos’: el primer lecho con ejecta intacto, con microkrystitas con seudomorfos en sanidina de clinopiroxeno y espinelas ricas en Cr, con abundante hollín, con proporciones de 53Cr/52Cr como los condritos carbonáceos en el nivel de ejecta, con la Zona P0 de los foraminíferos planctónicos en la arcilla del límite, y con el registro de la radiación adaptativa de los foraminíferos planctónicos. También aumentan la importancia de la sección del Gredero, el análisis de isótopos estables y de elementos traza, la magneto- y cicloestratigrafía, así como la historia de la bioturbación. El desarrollo reciente urbano y de carreteras ha puesto en peligro los excelentes afloramientos, de hecho los 100 m inferiores del Maastrichtiense superior no son ya accesibles. El estatus de monumento geológico de la Región de Murcia garantizaría que la sección permaneciera accesible a los investigadores en el futuro

The structure of disordered mackinawite

Synthetic Fe2+ monosulfide, FeSam, displays a disordered tetragonal mackinawite structure. It is nanocrystalline, with an average primary particle size equivalent to a crystallite, size of 4 nm and a corresponding specific surface area of 350 m(2)/g. It can be described in terms of a mixture of two end-member phases with different long-range ordering, which we refer to as MkA and MkB. MkA has an average primary particle size of 2.2 x 1.7 nm and lattice parameters a = b = 4.0 Angstrom, c = 6.6 +/- 0.1 Angstrom. MkB has an average primary particle size of 7.4 x 2.9 nm and lattice parameters a = b = 3.7 Angstrom, c = 5.5 +/- 0.2 Angstrom. A typical disordered mackinawite precipitate consist of 30% MkA and 70% MkB and the proportion of MkA decreases with age. Lattice expansions relative to crystalline mackinawite (a = b = 3.7 Angstrom, c = 5.0 Angstrom) may be explained by intercalation of water molecules between the tetrahedral sheets and by lattice relaxation due to small crystallite size. The formation of two phases of FeSam is consistent with competing pathways involved in its formation from aqueous solution. MkA may be equivalent to sheet-like precipitated aqueous FeS clusters. The reactivity of FeSam is dependent on the proportion of the two end-member phases. These in turn are dependent on the conditions of formation, especially pH, and the age of the precipitate. These observations partly explain the reported differences in FeSam reactivity in experimentation and in the environment. The structural model has implications for the behavior of natural acid volatile sulfides in scavenging elements from solution in natural environments

The section of the Barranco del Gredero (Caravaca, SE Spain): a crucial section for the Cretaceous/Tertiary boundary impact extinction hypothesis

Abstract The Barranco del Gredero section is one of the most complete, expanded and well exposed Cretaceous Tertiary (K/T) boundary sections in the world. Therefore, the Gredero section has played a key role in the development and testing of the impact extinction hypothesis, and has a significant number of “first discoveries “ to its name: The first discovered intact ejecta layer, microkrystites with K-spar pseudomorphs after clinopyroxene and Cr-rich spinels, abundant soot, carbonaceous chondritic 53Cr/52Cr ratios in the ejecta layer, the foraminiferal P0 Zone in the boundary clay, and the adaptive radiation of planktic foraminifers. Also, stable isotope, trace element analysis and the magneto- and cyclo stratigraphy, and the history of burrowing adds to the importance of the Gredero section. Recently urban and road-building development has threatened the excellent exposures, and the lower 100 meters of the upper Maastrichtian are already not longer accessible. The status of geological monument of the Region of Murcia would guarantee that the section will remain accessible for scientific investigation in the future. Resumen La sección del Barranco del Gredero es una de las secciones del límite Cretácico/Terciario (K/T) más completas, expandidas y bien expuestas en el mundo. Por tanto, la sección del Gredero ha jugado un papel clave en el desarrollo y la comprobación de la hipótesis de extinción por impacto, y tiene asociados a su nombre un número considerable de ‘primeros descubrimientos’: el primer lecho con ejecta intacto, con microkrystitas con seudomorfos en sanidina de clinopiroxeno y espinelas ricas en Cr, con abundante hollín, con proporciones de 53Cr/52Cr como los condritos carbonáceos en el nivel de ejecta, con la Zona P0 de los foraminíferos planctónicos en la arcilla del límite, y con el registro de la radiación adaptativa de los foraminíferos planctónicos. También aumentan la importancia de la sección del Gredero, el análisis de isótopos estables y de elementos traza, la magneto- y cicloestratigrafía, así como la historia de la bioturbación. El desarrollo reciente urbano y de carreteras ha puesto en peligro los excelentes afloramientos, de hecho los 100 m inferiores del Maastrichtiense superior no son ya accesibles. El estatus de monumento geológico de la Región de Murcia garantizaría que la sección permaneciera accesible a los investigadores en el futuro

Synthesis and properties of di-n-dodecyl alpha,omega-alkyl bisphosphate surfactants

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Wetting-induced layer contraction in illite and mica-family relatives

When dry illite is wetted, its layer structure contracts along the c-axis by up to 0.2 Å. This behavior contrasts with that of smectite which shows interlayer swelling on wetting. Layer contraction has also been found to occur in glauconite and celadonite that are structurally more disordered than illite, as well as with phengite and artificially degraded hydromuscovite. In contrast, muscovite proper does not show contraction. The contraction is ascribed to the deprotonation of hydronium ions (H3O+ → H2O + H+) occupying interlayer K+ positions. The hydronium ion is approximately 5% larger than the neutral water molecule. This difference in size is proportional to the magnitude of contraction. The change in molecular volume and interlayer separation of illite particles may explain the anomalous decrease in density after dehydration under pressure. This paper reports on wetting-induced contraction in illite and related layer silicates, using humidity-controlled X-ray diffraction