Temat: reefs - Katalog OPAC zbiorów

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Tytuł:: The Early Sarmatian bryozoan Celleporina medoborensis sp. nov. from the Medobory reefs of western Ukraine (Central Paratethys)
Autorzy:: Hara, U.
Jasionowski, M.
Powiązania:: https://bibliotekanauki.pl/articles/2060494.pdf
Data publikacji:: 2012
Wydawca:: Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
Tematy:: Bryozoa
taxonomy
serpulid-microbialite reefs
Lower Sarmatian
Middle Miocene
Ukraine
Paratethys
Opis:: Moundlike, globular to hemispherical bryozoan colonies of Celleporina medoborensis sp. nov. are documented from the calcareous organodetrital, slightly marly facies of the Lower Sarmatian (Volhynian) serpulid-microbialite reefs, in the Polupanivka and Ditkivtsi quarries (Medobory Hills), located at the northeastern margin of the Carpathian Foreland Basin (Central Paratethys) in western Ukraine. The colonies of C. medoborensis are multilamellar, often with a subcircular hole and occur together with numerous cyclostome bryozoans (crisiids, tubuliporinids, branching colonies of entalophoroids) as well as schizoporellid and cryptosulid cheilostomes, accompanied by a few macro- and micro-fossil taxa. The combination of morphological characters such as: thick radial ribs in the pseudoporous, variably-shaped area of the ovicell, and one or two small adventitious oral, as well as large vicarious avicularia are the main characteristic features of species. The rich occurrence of the celleporiform colonies of C. medoborensis sp. nov. within the fine-grained calcareous sands of Polupanivka and Ditkivtsi suggests a shallow-water setting and high availability of soft substrates, probably dominated by calcareous algae upon which the bryozoans may have settled in the Medobory reef biota during the Early Sarmatian.
Źródło:: Geological Quarterly; 2012, 56, 4; 895--906
1641-7291
Pojawia się w:: Geological Quarterly
Dostawca treści:: Biblioteka Nauki

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Tytuł:: Facje i geochemia dolnosarmackich raf z północnych obrzeży Paratetydy na Roztoczu (Polska) i Miodoborach (Ukraina): implikacje paleoorodowiskowe
Facies and geochemistry of Lower Sarmatian reefs along the northern margins of the Paratethys in Roztocze (Poland) and Medobory (Ukraine) regions: paleoenvironmental implications
Autorzy:: Jasionowski, M.
Powiązania:: https://bibliotekanauki.pl/articles/2074462.pdf
Data publikacji:: 2006
Wydawca:: Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
Tematy:: rafy sarmackie
facje
geochemia
paleośrodowisko
zapadlisko przedkarpackie
Paratethys
Carpathian Foredeep
Sarmatian
reefs
microbialite
serpulid
paleoenvironment
Opis:: The Middle Miocene (Lower Sarmatian = Middle Serravallian) carbonate buildups called “serpulid-microbialite reefs” that occur in the Medobory and Roztocze regions (Paratethys Basin, western Ukraine and southeastern Poland) are composed mainly of calcite precipitates. Skeletal organisms represented by serpulid tubes and bryozoans (in places) are of minor importance and comprise merely a few percent of the rock volume. They are overgrown with micritic peloidal microbialites that are the major reef component. The microbialites and serpulids/bryozoans make together a porous reef framework that is usually filled up with abundant synsedimentary fibrous cements and micritic internal sediments. Other biota is taxonomically impoverished but often rich in individuals and comprises few species of bivalves, gastropods, benthic foraminifers. In places, the serpulid-microbialite limestone masses are incrusted with coralline algae, bryozoans and nubeculariid foraminifers. Bivalve coquinas, bioclastic limestones, breccias and conglomerates are associated with the reefs. The synsedimentary precipitates represented by microbialites and fibrous cements have quite unusual geochemical characteristics. They are composed of Mg-calcite with 5–6 mole % MgCO3 in average with a very high content of strontium (1000–1650 ppm Sr). The precipitates are enriched in heavy oxygen and carbon isotopes. Fibrous cements exhibit the highest values (18O ca. +1.5 [PDB] and 13C 2.8 [PDB]. It is generally believed that in the Early Sarmatian the Paratethys was a brackish basin due to restricted connections to theWorld Ocean. This is indicated by taxonomically poor biotic assemblages that inhabited the basin. On the other hand, however, the predominance of calcitic precipitates (such as microbialites and synsedimentary cements) is indicative of water highly supersaturated in respect to calcite due to high carbonate alkalinity content. Oxygen isotopic composition of the precipitates indicates that the brackish water, in which the reefs originated, had to be enriched in the heavy oxygen isotope due to strong evaporation. The low Mg content in calcite (if compared to modern tropical settings) could be the result of a relatively low precipitation temperature coupled with lower Mg/Ca ratio in Miocene than today, and the elevated Sr content may be indicative of a high precipitation rate resulting from high supersaturation. It seems therefore that the origin of the serpulid-microbialite buildups is related to a peculiar interplay of regional and local controls in the Sarmatian Paratethys. First, the relative isolation of the entire Paratethys basin resulted in the brackish water environment that could be inhabited by taxonomically poor opportunistic biota only and simultaneously enabled blooming of microbial communities. Second, a strong evaporation of the brackish water with high alkalinity content caused a supersaturation in respect to calcium carbonate and consequently a widespread precipitation of calcite (including calcification of microbial mats).
Źródło:: Przegląd Geologiczny; 2006, 54, 5; 445-454
0033-2151
Pojawia się w:: Przegląd Geologiczny
Dostawca treści:: Biblioteka Nauki

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