Trace element concentrations in the Mexico-Belize ejecta layer: A link between the Chicxulub impact and the global Cretaceous-Paleogene boundary

From the proceedings of the Workshop on Impact Craters as Indicators for Planetary Environmental Evolution and Astrobiology held in June 2006 in Östersund, Sweden.Four exposures of Chicxulub impact ejecta along the Mexico-Belize border have been sampled and analyzed for major and trace element abundances. The ejecta deposits consist of a lower spheroid bed, containing clay and dolomite spheroids, and an upper diamictite bed with boulders and clasts of limestone and dolomite. The matrix of both beds is composed of clay and micritic dolomite. The rare earth element (REE) compositions in the matrix of both units show strong similarities in concentrations and pattern. Furthermore, the Zr/TiO2 scatter plot shows a linear correlation indicating one source. These results indicate that the basal spheroid bed has the same source and was generated during the same event as the overlying diamictite bed, which lends support to a single-impact scenario for the Albion Formation ejecta deposits. The elevated concentrations of non-meteoritic elements such as Sb, As, U, and Zn in the matrix of the lower spheroid bed are regarded to have been derived from the sedimentary target rocks at the Chicxulub impact site. The positive Eu and Ce anomalies in clay concretion and in the matrix of the lower part of the spheroid bed in Albion Island quarry is probably related to processes involved in the impact, such as high temperature and oxidizing conditions. Analogous trace element anomalies have been reported from the distal Cretaceous-Paleogene (K/T) boundary clay layer at different sites. Thus, the trace element signals, reported herein, are regarded to support a genetic link between the Chicxulub impact, the ejecta deposits along the Mexico-Belize border, and the global K/T boundary layer.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

Late Ludfordian correlations and the Lau Event

Changes in whole conodont faunas and δ13C values are combined to achieve highresolution correlations of Upper Silurian successions in many areas (primarily Gotland, Skåne, Lithuania, Bohemia, Austria, Sardinia and Queensland); other areas are correlated with lower precision. Four of the widely recognised subzones average considerably less than 0.1 Ma and a fifth interval less than 0.01 Ma. The main constraints on resolution and precision now achievable are the amount of, and the precision in, new or previously published data from each local section; centimetric scale collecting would be worthwhile in many sections. Some stratal characters are more widespread during certain intervals than might have been expected, for example, the presence of oncolites and algal coatings in the Icriodontid Zone and the lower part of the O. snajdri Zone. Similarly, the Dayia navicula bloom in the Upper P. siluricus Subzone was widespread. So also were muddy-sandy sediments followed by oolite low in the O. snajdri Zone; crinoids flourished widely when the lower part of the Lower Icriodontid Subzone was formed. Closely spaced samples show that, in some intervals, the now well-known δ13C spike was modified considerably by fluctuations; that is, it is not a smooth plateau. The best-documented fluctuations (19 analyses) are 2.5 smooth cycles with up to 2.7‰ in amplitude during ca 12,000 years or less in the base of the O. snajdri Zone. An enigma is the depletion of the spike in some sections, especially in the best Bohemian section

Late Ludfordian correlations and the Lau event

Changes in whole conodont faunas and δ¹³C values are combined to achieve high-resolution correlations of Upper Silurian successions in many areas (primarily Gotland, Skåne, Lithuania, Bohemia, Austria, Sardinia and Queensland); other areas are correlated with lower precision. Four of the widely recognised subzones average considerably less than 0.1 Ma and a fifth interval less than 0.01 Ma. The main constraints on resolution and precision now achievable are the amount of, and the precision in, new or previously published data from each local section; centimetric scale collecting would be worthwhile in many sections. Some stratal characters are more widespread during certain intervals than might have been expected, for example, the presence of oncolites and algal coatings in the Icriodontid Zone and the lower part of the O. snajdri Zone. Similarly, the Dayia navicula bloom in the Upper P. siluricus Subzone was widespread. So also were muddy-sandy sediments followed by oolite low in the O. snajdri Zone; crinoids flourished widely when the lower part of the Lower Icriodontid Subzone was formed. Closely spaced samples show that, in some intervals, the now well-known δ¹³C spike was modified considerably by fluctuations; that is, it is not a smooth plateau. The best-documented fluctuations (19 analyses) are 2.5 smooth cycles with up to 2.7‰ in amplitude during ca 12,000 years or less in the base of the O. snajdri Zone. An enigma is the depletion of the spike in some sections, especially in the best Bohemian section.23 page(s

Facies development across the Late Silurian Lau Event based on temperate carbonates of the Prague Basin (Czech Republic)

The facies development through the stratigraphical interval of the Silurian (late Ludlow) Lau Event and the associated major δ13C record excursion have been studied in the Prague Basin. The investigated sections consist of temperate-water carbonates (Kopanina Formation) that were deposited in shallow as well as deeper parts of the basin. In both areas, the facies evolution reflects a major shallowing of sea-level during the early part of the event, which resulted in weathering (karstification) and erosion in the shallower parts of the basin, leading to stratigraphic gaps there. Paleokarst features and dolomitization are associated with these strata in the vicinity of Prague, where the δ13C record displays a strong diagenetic overprint and palynomorphs are very poorly preserved. A transition from deep-water shale to subtidal, thick-bedded limestone facies in the deeper parts of the basin, close to Kosov, signals the same sea-level drop, indicating that it was basin-wide. Detailed lithologic descriptions for the studied sections are provided and the development in the Prague Basin is compared with the coeval succession on Gotland, Sweden, which was located in the tropical realm at this times

Onshore Jurassic of Scandinavia and related areas

Jurassic strata are extensively distributed in offshore areas of Scandinavia, but onshore exposures are mostly restricted to southern Sweden (Skane), the Danish island of Bornholm, East Greenland, northern Norway (Andoya) and Svalbard. The latest Triassic and Jurassic saw active tectonism in Scandinavia associated with the break-up of Pangaea and rifting in the North Atlantic region and the North Sea. Rifting and the gradual rise in sea level controlled the structural and sedimentological architecture of Scandinavian basins throughout the Jurassic. The Upper Triassic is represented by continental red beds (claystones and arkosic conglomerates) indicative of arid conditions (until the Norian) and by coal measures characteristic of humid conditions (in the Rhaetian). Early Jurassic sedimentation in the region was dominated by fluvial-estuarine systems. Basin subsidence combined with the supply of huge volumes of sediments led to the accumulation of thick sand units on vast coastal plains in the Early and Middle Jurassic. During the Late Jurassic, transgressions led to deposition of extensive marine mud, although sandstones are locally preserved. Paralic depositional environments prevailed during the Late Jurassic and into the Early Cretaceous in southern Scandinavia. Scandinavia hosts a rich Jurassic palaeontological record including fossil plants, sharks, dinosaur footprints, ammonites, belemnites, ichthyosaurs and pliosaurs. Miospores provide the primary tool for biostratigraphic subdivision and correlation of the continental Jurassic sediments, whereas ammonites, dinoflagellates and foraminifera are the main groups employed for marine biostratigraphy. However, much work remains to be completed to achieve a highly resolved zonation scheme that integrates both marine and terrestrial indices

Palynostratigraphy of dinosaur footprint-bearing deposits from theTriassic–Jurassic boundary interval of Sweden

The Triassic–Jurassic boundary (c. 200 Ma) marks one of the five largest Phanerozoic mass extinction events and is characterized by a major turnover in biotas. A palynological study of sedimentary rock slabs bearing dinosaur footprints from Rhaeto–Hettangian strata of Skåne, Sweden was carried out. The theropod dinosaur footprints (Kayentapus soltykovensis) derive from the southern part of the abandoned Vallåkra quarry (Höganäs Formation) and were originally dated as earliest Jurassic (Hettangian) based on lithostratigraphy. Our results reveal that two of the footprints are correlative with the latest Triassic (latest Rhaetian) disaster zone typified by a high abundance of the enigmatic gymnosperm pollen Ricciisporites tuberculatus and Perinopollenites elatoides together with the key taxon Limbosporites lundbladii and fern spores. Two footprints are dated to correlate with the Transitional Spore-spike Interval. One footprint is interpreted as Hettangian in age based on the relatively high abundance of Pinuspollenites spp. together with the presence of the key taxa Retitriletes semimuris and Zebrasporites intercriptus. Our new palynological study suggests that the Kayentapus ichnogenus already appeared in the end of Triassic, and our study highlights the use of palynology as a powerful tool to date historical collections of fossils in museums, universities and elsewhere. The Hettangian footprint reflects a marine influence while all other studied ichnofossil specimens occur in non-marine (floodplain and delta interdistributary) sediments. The sediments associated with the Hettangian footprint include a significant proportion of charcoal transported from land after wildfires. The Rhaeto–Hettangian vegetation was otherwise characterized by multi-storey gymnosperm–pteridophyte communities