Blow Hole Cave: An Unroofed Cave on San Salvador Island, the Bahamas, and its Importance for Detection of Paleokarst Caves on Fossil Carbonate Platforms

Prispevek obravnava podobnosti v razvoju krasa kvartarne karbonatne platforme na otoku San Salvador in devonske karbonatne platforme na platoju Krásná na Moravskem. Za obe območji so značilne jame, katerih nastanek lahko razložimo s "flank margin" modelom in so nastale v območju sladkovodnih leč med obdobji relativno visoke morske gladine, v času relativno stabilne halokline, kar potrjujejo različne študije jamskih zapolnitev. V obeh primerih so jamske sedimentne zapolnitve genetsko primerljive - obalni in eolski sedimenti ter breče.The comparative study of a Quaternary carbonate platform (San Salvador Island, the Bahamas) and a Devonian Carbonate Platform (Krásná Elevation, Moravia) indicates a great similarity in karst evolution. Caves on both sites are interpreted as flank margin caves associated with a freshwater lens and halocline stabilised during sea-level highstands. The sedimentary fill of both caves is genetically comparable - beach and aeolian sediments with bodies of breccias

Osmium and lithium isotope evidence for weathering feedbacks linked to orbitally paced organic carbon burial and Silurian glaciations

The Ordovician (∼487 to 443 Ma) ended with the formation of extensive Southern Hemisphere ice sheets, known as the Hirnantian glaciation, and the second largest mass extinction in Earth History. It was followed by the Silurian (∼443 to 419 Ma), one of the most climatically unstable periods of the Phanerozoic as evidenced by several large scale (>5‰) carbon isotope (δ13C) perturbations associated with further extinction events. Despite several decades of research, the cause of these environmental instabilities remains enigmatic. Here, we provide osmium (187Os/188Os) and lithium (δ7Li) isotope measurements of marine sedimentary rocks that cover four Silurian δ13C excursions. Osmium and Li isotope records resemble those previously recorded for the Hirnantian glaciation suggesting a similar causal mechanism. When combined with a new dynamic carbon-osmium-lithium biogeochemical model we suggest that astronomical forcing of the marine organic carbon cycle, as opposed to a decline in volcanic arc degassing or the rise of early land plants, resulted in drawdown of atmospheric CO2, triggering continental scale glaciation, intense global cooling and eustatic sea-level lows recognised in the geological record. Lower atmospheric pCO2 and temperatures during the Hirnantian and Silurian glaciations suppressed CO2 removal by silicate weathering, driving 187Os/188Os and δ7Li variability, supporting the existence of climate-regulating feedbacks

Palaeozoic Basement of the Pyrenees

International audienceIn the Pyrenees, the Cambrian-Lower Ordovician strata represent a quiescent time span with no remarkable tectonic activity, followed by a late Early-Mid Ordovician episode of uplift and erosion that led to the formation of the Sardic unconformity. Silurian sedimentation was widespread and transgressive followed by a Devonian succession characterized by a complex mosaic of sedi-mentary facies. Carboniferous pre-Variscan sediments (Tournaisian-Viséan cherts and limestones) precede the arrival of the synorogenic siliciclastic supplies of the Culm flysch at the Late Serpukhovian. All this succession was subsequently affected by the Serpukhovian-Bashkirian (Variscan) collision, as a result of which, the Palaeozoic rocks were incorporated into the northeastern branch of the Ibero-Armorican Arc

Přínosné užívání závlahové vody

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Principles for utilization of progressive systems in hop irrigation under the condition of hop regions in Czech Republic

Metodika pro praxi, která řeší hlavní zásady pro využití progresivních systémů závlah chmele v podmínkách chmelařských oblastí ČR

Wenlock-Ludlow boundary interval revisited: New insights from the off-shore facies of the Prague Synform, Czech Republic

Abstract: Wenlock-Ludlow boundary beds exposed near NesvaÄ ily in the Prague Synform are documented in terms of their lithology, faunal content, high-resolution record of 19 graptolite species, graptolite biostratigraphy and conodont record. This is the first time in Bohemia and peri-Gondwanan Europe that a continuous graptolite-bearing section through upper ludensisâ middle nilssoni biozones is described in detail in order to refine high-resolution biostratigraphy and correlation of the Wenlock-Ludlow boundary. Organic-rich shale, relatively rare non-graptolite fauna and absence of bioturbation indicate a stable deep-water off-shore setting with sporadic, low level bottom oxygenation. The uninterrupted succession revealed a series of origination events of principal graptolite taxa employed in determination of the Wenlock-Ludlow boundary strata world-wide. Bohemograptus represented by B. praecox appeared as early as in the uppermost Wenlock ludensis Biozone. B. praecox is later accompanied and replaced by B. bohemicus associated with Uncinatograptus uncinatus. The lowest Neodiversograptus nilssoni marked the base of the Ludlow nilssoni Biozone. Speciation within Bohemograptus continued in the middle nilssoni Biozone when the robust B. butovicensis evolved from B. bohemicus. Colonograptus colonus shows its lowest occurrence in the middle part of the nilssoni Biozone together with the latest C. gerhardi. The monograptids are associated with abundant and diverse plectograptids that are at present mostly known from Baltica. B. praecox sp. nov. and B. butovicensis (BouÄ ek, 1937) are described in the systematic part. The conodont Kockelella ortus absidata, found in the lower-middle part of the nilssoni Biozone, is consistent with a stratigraphic interval within Oz. bohemica and K. crassa conodont biozones.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Running across the Silurian/Devonian Boundary along Northern Gondwana: A Conodont Perspective

The Global Stratotype Section and Point (GSSP) of the Silurian/Devonian boundary, Lower Devonian Series and Lochkovian Stage was formally placed in 1977 at Klonk, in the Czech Republic, at the first appearance of the graptolite Uncinatograptus uniformis uniformis (Přibyl). However, since then, correlation of this limit has been often hampered in carbonate facies where graptolites are uncommon or totally absent. A large calcareous deposition occurred at the Silurian/Devonian boundary along the northern and peri-Gondwana margin, thus representing an ideal location to select and test a possible additional biostratigraphic marker of the limit among conodonts. The first appearance of Caudicriodus hesperius almost simultaneously at the base of the Devonian in Bohemia, the Carnic Alps, Sardinia, Morocco and elsewhere indicates that this taxon is the conodont that best approximates the beginning of the Period. The first or last appearance of other species (e.g., Ozarkodina confluens, Zieglerodina klonkensis, Z. remscheidensis and Caudicriodus woschmidti) may help to recognise the boundary as well