Academic literature on the topic 'Givetian S.E'

The names proposed world-wide for Devonian bryozoans have been evaluated with respect to replaced names, synonyms, and nomina dubia [Horowitz and Pachut (1993), Journal of Paleontology, in press]. The resulting list contains 1738 specific names assigned to 199 genera in 45 families. Approximately 75% of Devonian bryozoan species are reported from a single stage. Not more than 10%, and usually 4–6%, of the species reported in any Devonian stage are also reported in the succeeding stage.The largest decrease in observed bryozoan diversity occurs between the Givetian and Frasnian stages, reducing the number of species by 77%, genera by 64%, and families by 42%. These values are less than those reported for the range-through method for the entire fauna of the Permian mass extinction (Raup, 1979) but larger than percentage extinctions (presumably based on range-though data) for four other Phanerozoic mass extinctions tabulated by Valentine and Walker (1987).The range-through method dampens the observed differences in taxonomic diversity among Devonian stages at all taxonomic levels. The range-through number of species/stage is based upon both direct applications of the range-through method and on the assignment of ranges known only to early, middle and late Devonian to include appropriate Devonian stages. Generic and familial diversity increases monotonically from Lochkovian through Givetian stages. Thereafter (Givetian to Frasnian), range-through values for specific (69%), generic (31%), and familial diversity (10%) decrease. Specific and familial decreases across the Givetian-Frasnian boundary are comparable to those reported for non-Permian mass extinctions by Valentine and Walker, but the generic decrease is not as great. These results are consistent with Valentine and Walker's random mass extinction model.Observed bryozoan diversity across the Frasnian-Famennian boundary increases while values calculated using the range-through method decrease by approximately 5–15%. This does not suggest a major bryozoan extinction event. Conversely, the decrease in bryozoan diversity across the Givetian-Frasnian interval is similar to an important Devonian extinction among rugose corals. The reason(s) for these extinctions is not yet clear. With respect to Devonian bryozoans, our inadequate understanding of the cause(s) of mass extinctions and the relatively coarse resolution of the stadial timescale does not permit differentiating between gradual or catastrophic scenarios.

Many species, subspecies and forms assigned to Ripidiorhynchus SARTENAER 1966 do not belong to it and give it an overextended published stratigraphic range of Givetian to Lower Carboniferous. Eight new genera are proposed: Kedridorhynchus [type species K. cedarensis (STAINBROOK 1942); late Givetian], Poleomesorhynchus [type species P. gregeri (BRANSON 1923); early Frasnian], Hypselororhynchus [type species H. farsani (BRICE 1977); middle-late Frasnian], Porthmorhynchus [type species P. ferquensis (GOSSELET 1887); middle-late Frasnian], Paropamisorhynchus [type species P. kotalensis (BRICE 1971); late Frasnian], Saxulirostrum [type species S. saxatile (HALL 1867); late Frasnian], Piridiorhynchus [type species P. confinium n. sp.; earliest Famennian], Orophomesorhynchus [type species O. huotinus (de VERNEUIL 1845); early Famennian]. Following revision of Ripidiorhynchus a new zone is introduced at the base of the Famennian based on Piridiorhynchus confinium in the southeastern and eastern parts of Dinant Basin. Some attention is also devoted to the alleged overlapping of the Frasnian/ Famennian boundary by Ripidiorhynchus.

The Ahnet and Mouydir regions of southern Algeria are part of one of the world's largest, almost undeformed exposures of Palaeozoic rocks which exemplify a hitherto poorly known early Variscan development of a Devonian basin and ridge system. This area includes a series of intracratonic basins along the northern margin of the West African Craton which consists (from W to E) of the Reggane Basin, Azel Matti Ridge, Ahnet Basin, Foum Belrem Ridge and Mouydir Basin. The depositional and palaeogeographic interpretation is based on 71 sections in this region, which for the first time were biostratigraphically calibrated by means of conodonts, goniatites and brachiopods. The structural evolution during Devonian times was probably controlled by reactivation of ancient N–S- to NW–SE-running faults in the Precambrian basement, which caused differential subsidence and uplift of a previously largely unstructured siliciclastic shelf. A hiatus during Emsian times indicates widespread emergence during this interval. The entire area was flooded during the earliest Eifelian, when the first vestiges of the Azel Matti Ridge become evident by stratigraphic condensation. The palaeogeographic differentiation is most apparent during the Givetian, when a shoal with reduced carbonate sedimentation was established on the Azel Matti Ridge passing towards the west and east into basinal environments of the Reggane and Ahnet basins, respectively. The Foum Belrem Ridge is distinguished by increased subsidence during the early Givetian and by revived uplift during the late Givetian. In the Mouydir Basin further east, up to 1000 m of shales were deposited during the Givetian. The early Frasnian is marked by the ubiquitous sedimentation of black shales and bituminous styliolinites. These lithologies occur repeatedly already during the Middle Devonian and document intermittent anoxic conditions. The basin and ridge topography is levelled by the shallowing-up sequence of up to 1400 m thick upper Frasnian and Famennian shales which grade into a deltaic sequence of uppermost Famennian/Tournaisian sandstones. The up to now only vaguely discriminated lithostratigraphic formations of the Devonian have been biostratigraphically defined in suitable type sections.

The Oñate Formation of Middle Devonian (Givetian) age is exposed in the Mud Springs Mountains of New Mexico, where it is represented by an unusually shaly and extremely fossiliferous facies. Tabulophyllum traversensis (Winchell) found here is the only rugose coral species known thus far from Middle Devonian rocks of New Mexico and is of special interest as evidence of migration between the area of the Oñate occurrence and those in the Cedar Valley Limestone in Iowa and the Traverse Group of Michigan. The occurrence is also of interest because of the association of the Oñate coral with the receptaculitid Sphaerospongia sp. cf. S. tessellata (also known from Canada, Australia, and New York). The corals apparently utilized receptaculitids as a solid substrate for post-larval growth and developed an extremely broad flat base, fixed to the upper surface of Sphaerospongia.

Accurate palyno-analysis by S. Loboziak (from 1980 to 1983) of 28 samples from the Upper Givetian to the Middle Frasnian Blacourt, Beaulieu and Ferques Formations and of 44 samples of the Upper Frasnian to the Lower Famennian Hydrequent Formation are re-evaluated. Chelinospora concinna, Verrucosisporites bulliferus, Cirratriradites jekhowskyi, Lophozonotriletes media first occurrences are major criteria for Lower and Middle Frasnian, well calibrated by conodonts. Cymbosporites acanthaceus, Rugospora bricei, Grandispora gracilis, Diducites plicabilis, Corbulispora vimineus first occurrences allow to subdivide the Upper Frasnian where conodonts are poorly present. Samarisporites triangulatus versus Auroraspora pseudocrista taxonomy and stratigraphic significance are discussed. The reconnaissance borehole Nieuwkerke-De Seule (95W152), near the limit of the Upper Palaeozoic subcrop on the Brabant Massif (West Flanders, Belgium, 75 km east of the Boulonnais), which has intersected conodont-dated Givetian/Frasnian boundary at the transition between the Bois de Bordeaux and Bovesse Formations, contained poorly preserved miospores attributed to the triangulatus–concinna (TCo) Oppel Zones. In the nearby Nieuwkerke-Noordhoek borehole (95W153), strata also assigned to the Bovesse Formation yielded better preserved miospores which demonstrate a close succession of triangulatus–concinna (TCo) and bulliferus–jekhowskyi (BJ) Oppel Zones at the transition Lower–Middle Frasnian, also known in the Beaulieu Formation in the Boulonnais. Samples from the Heuvelland groundwater monitoring well (95W175), 10 km north of Nieuwkerke, contain the bricei-acanthaceus (BA) Oppel Zone suggesting a late Frasnian age, also known in the Hydrequent Formation in the Boulonnais area and in the Booischot Formation in the Booischot borehole (59E146) from the Campine Basin (Belgium). International correlation using Frasnian miospore zonation is attempted between the Pripyat Depression in Belarus, the Timan–Pechora province in Russia and North-West China.

The geological substrate of the town of Marche-en-Famenne, and its surrounding area, consists mainly of Givetian limestone and Frasnian to Emsian siliciclastics. The soil geochemistry within and around the town was studied by the collection of 214 samples from the urban area, and from a section of 3.5 by 20 km to the SW of the town. These samples were analysed for Ca, Cd, Cu, Fe, K, Mg, Mn, Ni, Pb and Zn by AAS. One of the most remarkable feature is that the contrast between limestone and sandstone is only weakly reflected in the major and trace element distribution patterns. This may be explained by the presence of loamy soils, which develop on limestone after weathering, which are very comparable to loamy soils developed on top of sandy shale and shale. A clear relation between geological substrate, soil-type and Fe-K-Ni content is apparent, and is also reflected in the bivariate correlation matrix. Further, red coloured lithologies of the so-called Burnotian age (i.e., Emsian) display an increase in Fe-content. Some particular dispersion patterns are clearly geogenetic in origin (e.g., in relation with mineralised faults, presence of overbank sediments, etc.), while in and around industrial sites, elevated heavy metal concentrations have been recorded and reflect an anthropogenic influence on the natural environment. Highest recorded Zn, Pb and Cd concentrations are respectively about 1300 mg/kg, 500 mg/kg and 4 mg/kg. However, values do not exceed trigger values, commonly used in environmental studies (e.g., Flemish Soil Sanitation Act). A speciation study, based on selective extraction, showed that about 20% of Zn and Pb are relatively easily dissolved; Cd can also potentially be leached, since more than 40% relates to the operationally defined "carbonate fraction". However, the Cd concentration is generally low. More important here is that overall heavy metals are dominantly bound to Mn- and/or Fe oxyhydroxides and to a fraction, which is only dissolved by strong acids (HClconc-HNO3 conc-HFconc). This aspect, together with the absence of real anomalous concentrations in heavy metals, suggest that the eco- and human toxicological risk in the studied area is low.

From the beginning of the Late Ordovician (Sandbian: 460.9myr) through end Devonian (Famennian: 359.2myr), coral-stromatoporoid sponge reefs formed a remarkable, evolving ecosystem that dominated sediment production on tropical carbonate platforms in a calcitic ocean. This was a time of maximal and unparalleled reef development in the Phanerozoic, with reef tracts vastly exceeding in size and biodiversity of those in the Holocene (e.g., the Great Barrier Reef). Within this circum-equatorial niche, the calcitic tabulate and rugose corals, and the aragonitic (or high Mg calcite) stromatoporoid sponges, were the primary Middle Paleozoic reef frame builders. These were supplemented ecologically and skeletally by now extinct groups of calcitic bryozoans, crinoids, brachiopods, and red algae, alongside aragonitic green algae, and enigmatic CaCO3precipitating and binding calcimicrobes. This 100 myr long Middle Paleozoic reef consortium thrived under SST averages of 30°+, to latitudes as high as 45°–55°, under high atmospheric CO2conditions of 6000+ ppm, and sealevels 150–200 m higher than today. This reef ecosystem was disrupted by several relatively short duration south polar glacial episodes, centered around northern Gondwana, defining the O/S boundary Mass Extinction Events (MEEs). Nearly all coral and stromatoporoid families survived this MEE: there were losses at the genus level. Reef-building stopped nearly everywhere, and during the ‘recovery’ interval, solitary rugose corals initially prevailed, and stromatoporoids were small. Full global re-establishment of the reef ecosystem, and biodiversity, took another 3–4 million years (not until the late Aeronian, Early Silurian). This was followed by a remarkable reef expansion in the Middle Silurian (Wenlock), then by declines in the latest Silurian (Ludlow-Pridoli), and earliest Devonian (Lochkovian) possibly due to sealevel lowstands, tectonic plate re-assembly, and ocean current re-direction. Maximal Phanerozoic reef success was during the Emsian-Givetian, when some 15 barrier reef tracts more than 1100 km long flourished in tropical shallow seas. Reef-building coral diversity exceeded 200 genera, and the calcifying stromatoporoids evolved 60+ genera, especially in the ‘Old World’ faunal province (Euramerica, Cathaysia, northern Australia). Near the end of the Middle Devonian (mid- to late Givetian), the primary reef dwellers declined sharply in diversity, marked generally by sealevel lowstand, followed in the Frasnian (Late Devonian) by shrinking latitudes for carbonate platforms, and reduced reef accommodation space. Sharp cooling, with the arrival of a global Icehouse climate, and aragonitic oceans, led to the second largest Phanerozoic Mass extinction around the Frasnian/Famennian boundary, with reef builder and reef inhabitant losses exceeding those of the O/S MEE. The global absence of coral-sponge reefs persisted for nearly all of the 16 myr long Famennian, as total CaCO3production fell some 60–90%, as aragonitic oceans took over. Only small and scattered Famennian coral-stromatoporoid patch reefs are known, with the last of these in the late Famennian (Strunian), punctuated by total disappearance of the whole keystone reef-building order. Famennian and Strunian corals belonged to Carboniferous families. During the Famennian, calcimicrobes, the first calcifying foraminiferans, and select ‘lithistid’ calcareous sponges dominated a highly stressed reef ecosystem, lacking barrier reef tracts. Biodiversity and reef construction were decoupled under global climatic stress during the succeeding icehouse Late Paleozoic.

AbstractUnderstanding the life orientation of fossil organisms, such as brachiopods, is not only important for understanding the biology of the organism in question, but it also can be used to interpret paleoecological information about the assemblages from which the specimens were derived. The dorsibiconvex brachiopod morphology is particularly common, especially among the Order Atrypida, yet there have been few independent, biomechanical studies to assess the life orientation of these brachiopods. In this study, we assess potential orientations of two end-member morphologies of a dorsibiconvex brachiopod, Pseudoatrypa lineata, from the Mid–Late Devonian of North America by placing realistic models in a flume.Using materials with the specific gravity of calcium carbonate, we modeled two well-preserved Pseudoatrypa lineata from the Waterways Formation (Givetian–Frasnian, Alberta, Canada) to represent the original shell. The hydrodynamic stability of the models was assessed by placing the models in a recirculating flume in one of three initial orientations: (1) anterior commissure upstream, (2) umbo upstream, and (3) lateral (specimen perpendicular to flow), each with the dorsal and ventral valve topmost. The entire process was conducted both on a Plexiglas substrate and on well-sorted, mediumgrained sand. All scenarios were repeated five times for a total of sixty trials per specimen (120 total).Flume trials indicate that neither brachiopod had a true hydrodynamically stable orientation.Reorientations occurred at low velocities (~0.2 m/s), with transport occurring soon after (~0.3 m/s).Assuming that a juvenile, pedunculate, dorsibiconvex brachiopod would initially have been oriented with its ventral valve topmost, our results suggest two outcomes: the brachiopods either (1) were attached via pedicles throughout their lives or (2) lived in quiet, undisturbed waters. Given the abundance of dorsibiconvex brachiopods in observed high-energy environments, our results indicate it is more conservative to assume dorsibiconvex brachiopods retained pedicles throughout their lives.

The basin of the Mokra Volnovaha River, from the Mykolaivka village to the place where it flows into the Kalmius River, exposes an extremely informative geological cross-section of the conjunction of the Pryazov block of the Ukrainian Shield (US) with the complexly located Donetsk Hercynian structure. The results of the survey of this area are presented and the perspectives for creation of the MafHaia Geological Park named after the important paleo-volcanic structure are substantiated. The most significant events related to the geological studies of the regions from the academic expeditions of Pierre Guillaume Frédéric Le Play, P. S. Pallas to nowadays are considered in historic sequence. The structural-tectonic position of the territories, mineral-petrographic peculiarities of the rocks of the prospective geopark were studied and great geodiversity important for the development of the geotourism as an important component of functioning of geopark was determined. We followed sequential change in the geological cross-section from the association of Maksymivski granodiorites of the Middle Archean East-Pryazovska StructuralFormation Zones of the Ukrainian Shield in Mykolaivka village, terrigenous and volcanic formations of the Devonian system which are embedded on them and belong to the Eifelian, Givetian, Frasnian and Famennian stages, to terrigenous carbon-bearing deposits of Carboniferous system which form large rock outcrops on the Left Bank of the Styla water reservoir and outcrops in the quarries for extraction of flux limes and dolomites. It is proposed to consider as highly relevant the principally new “Balanced structural-geologic map of the Southern Donbass” proposed by V. V. Yudin, based on fracture-block tectonics, thrust faults which caused pre-fault mélanges and duplexes. The most characteristic peculiarities of the geological structure of the Rozdolne Geological Reserve as the main location of the future geopark were determined. As the one of the main attractions of geotourism itineraries, we evaluated the unique Devonian flora of global significance in the Velyka Karakuba (Rozdolne) village, particularly Archaeopteris archaetypus Schm., Archaeopteris fissilis Schm., Lepidodendron karakubense Schm., Demeripteris fasciculate Schm. and others, first in history discovered in 1894 by I. O. Shmal’gauzen. An important peculiarity of the zone of the junction of the US and the folded Donbas is its attractiveness for collecting minerals, including crystals and druse amethyst, smoky quartz, druses of pyrite, pseudomorph on corals, chalcedony, pseudo stalactites with marcasite, small agates, pink quartz, sanjuanite, fulgurite and others.