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Aptian foraminiferal stratigraphy and Nannoconus assemblages from the Kopka section (Western Tatra Mountains, Poland)

Pszczółkowski A.

Annales Societatis Geologorum Poloniae

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2015

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Vol. 85, No. 1

123--138

EN

In the Kopka section (Dolina Kościeliska valley, Western Tatra Mountains), the upper part of the Kościeliska Marl Formation consists of biomicrites with marly interbeds. These deposits, 76 m thick, are assigned to the Praehedbergella excelsa and Leupoldina cabri zones, of Aptian age. The taxa identified belong mainly to the genera Praehedbergella Gorbachik and Moullade, 1973, Globigerinelloides Cushman and Ten Dam, 1948 (emended by Longoria 1974 and Verga and Premoli Silva, 2003a) and Gorbachikella Banner and Desai, 1988. Nineteen Nannoconus taxa were identified during an SEM study of 34 samples. The occurrence of N. vocontiensis in the higher part of the section allows the nannoconid assemblages in the upper part of the section to be distinguished from those in the lower part. Four Nannoconus assemblages were recognized in these limestones: (1) Nannoconus bucheri-N. steinmannii, (2) N. truitti frequens, (3) N. vocontiensis and (4) N. aff. regularis. The wide-canal Nannoconus specimens are more frequent than the narrow-canal ones in the limestones of earliest Aptian age (Praehedbergella excelsa Zone), but the wide-canal forms predominate consistently in the upper part of the section, still within the L. cabri Zone.

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The OAE1a in Cuchía (Early Aptian, Spain): C and O geochemistry and global correlation

García-Mondéjar J., Fernández-Mendiola P. A., Owen H. G.

Acta Geologica Polonica

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2015

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Vol. 65, no. 4

525--543

EN

C-isotopes, TOC and O geochemical data from the lower Aptian Cuchía section in the western Basque-Cantabrian basin (BCB) allow an accurate delimitation of the OAE1a-equivalent and its geochemical Menegatti´s segments, a detailed δ13Ccarb correlation with regional and interregional sections, and a high-resolution construction of TOC and bulk-rock δ18Ocarb curves and their interpretation. The δ13Ccarb values range from -2‰ and +4‰ (VPDB). They agree with previous data from the eastern BCB sections (Aralar) confirming the ammonite age of the OAE1a in the Basque-Cantabrian basin: Deshayesites forbesi, Deshayesites deshayesi, and Deshayesites deshayesi-Dufrenoyia furcata transition Zones. Interregional δ13Ccarb correlation with pelagic (Cismon, Italy, and Mid-Pacific Mountains, DSDP Site 463) and neritic (Roquefort-La Bédoule, France) core sections, reveals a common profile of a wide negative excursion characteristic of the OAE1a. It consists of a double trough separated by a flat relative maximum, with two negative spikes in the upper trough of neritic sections. TOC absolute values range from 0.12% to 1.37%. Segments of the TOC curve with persistent low values closely correspond with descending segments of the δ13Ccarb curve, and are attributed to lesser organic productivity in the BCB. Detailed bulk-rock δ18Ocarb data (-5.71‰ to -1.05 ‰ PDB) and variation curve show two main positive O-isotope shifts and three minor positive inflections, within a general negative trend characteristic of the OAE1a. The two major positive shifts correspond to both shallowing upwards sequences and the lowermost can be related to a eustatic sea level fall. Independent interregional correlation of the O-isotope shifts with C-isotopes supports their interpretation as punctuating colder events within a general warming trend.

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Early Aptian bay deposits at the southern margin of the Lower Saxony Basin : Integrated stratigraphy, palaeoenvironment and OAE 1a

Lehmann J., Friedrich O., Bargen D., Hemker T.

Acta Geologica Polonica

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2012

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Vol. 62, no. 1

35-62

EN

The present study establishes a lithostratigraphic subdivision, a bio- and chemostratigraphy and describes the sedimentology of the Alstatte Bay at the southern margin of the Lower Saxony Basin in northern Germany. The socalled Fischschiefer is developed in the lower part of the section, a 2.1 m thick laminated interval that shows TOC values of up to 2 % and is interpreted as local expression of the global Oceanic Anoxic Event 1a (OAE 1a). The basal part of the Fischschiefer is fairly continuously laminated, whereas its upper part is characterized by an alternation of laminated and non-laminated beds. Stable carbon isotopes ([delta^13]C[carb]) show a characteristic pattern for the Fischschiefer interval that can be correlated with sections from the Tethyan Realm. Immediately above the Fischschiefer, however, the studied section might reveal a diagenetic overprint as indicated by very negative carbon stable isotope values. The remaining part of the section is characterized by a rather monotonous claystone succession, terminated by a greenish layer rich in glauconite overlain by glacial till of Pleistocene age. The fauna is typically Boreal in the lower part of the section, but changes around 2 m above the Fischschiefer towards an assemblage indicating a distinct Tethyan influx. The faunal shift is considered to be due to the maximum flooding of the continuous, long-term sea level rise of the Early Aptian which led also to a supposed shift from a restricted to open bay environment.