Depositional and palaeoenvironmental variation of lower Turonian nearshore facies in the Bohemian Cretaceous Basin, Czech Republic

0446085 - GLÚ 2016 RIV GB eng J - Článek v odborném periodiku
Žítt, Jiří - Vodrážka, R. - Hradecká, L. - Svobodová, Marcela - Šťastný, Martin - Švábenická, L.
Depositional and palaeoenvironmental variation of lower Turonian nearshore facies in the Bohemian Cretaceous Basin, Czech Republic.
Cretaceous Research. Roč. 56, September/December (2015), s. 293-315. ISSN 0195-6671. E-ISSN 1095-998X
Institucionální podpora: RVO:67985831
Klíčová slova: phosphatic particle accumulations * organic matter * micropalaeontology * biostratigraphy * condensed sedimentation * Upper Cretaceous
Kód oboru RIV: DB - Geologie a mineralogie
Impakt faktor: 2.196, rok: 2015

The relief of the rocky bottom (about 14.000 m²) was reconstructed and two overlying sedimentologic and palaeoecological settings (lower Turonian) were recognized in the area of Plaňany (Bohemian Cretaceous Basin). Dark grey deposits form part of the first setting, representing a fill of deep depressions on the northern foot of the Plaňany elevation (UC6a and particularly UC6b nannoplankton zones). The second setting with a phosphatic lag is located on the elevated part of the area. The enrichment of C_org and S, clay minerals with an important kaolinite peak, formation of framboidal pyrite and the enrichment of macrofauna and phosphatic particles (mainly coprolites) are characteristic of the basal portions of the dark deposits. The sulphate reduction zone is suggested for this sedimentary environment. No phosphatic lag is developed. On the other hand, the phosphatic lag is most characteristic of the second setting developed in elevated parts of the bottom. This lag is a product of sedimentary condensation, characterized by a long-lasting concentration of phosphatic particles and phosphogenesis, accompanied by encrustation of adjacent rock surfaces by a faunal community with Terebella. Biostratigraphic data (foraminifera, palynomorphs, nannoplankton) indicate that the phosphatic lag and basal dark grey deposits may be approximately coeval. The stagnant depositional conditions with only very slow sea-level rise are thought to have lasted for a significant part of the Whiteinella archaeocretacea Zone (lowermost Turonian). In elevated parts, condensation could proceed under conditions of prevailingly weak currents and strong oxidation of organic matter, while decomposition of organic matter was probably very slow and incomplete in depressions below the elevation. The sedimentary condensation in both settings is highlighted by the remarkable formation of abundant glauconite in local deposits.
Trvalý link: http://hdl.handle.net/11104/0248060