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Ammonite stratigraphy and organic matter of the Pałuki Fm.n(Upper Kimmeridgian–Lower Tithonian) from the central-eastern part of the Łódź Synclinorium (Central Poland)

Wierzbowski Andrzej, Wierzbowski Hubert

Volumina Jurassica

2019

Vol. 17, no. 1

49--80

The ammonite biostratigraphy as well as the organic matter content, its type and maturity of the Pałuki Formation, belonging to the fine, siliciclastic Kimmeridge Clay type facies, were investigated in five deep boreholes from the central-eastern part of the Łódź Synclinorium in Central Poland. The studied deposits are assigned to the Eudoxus and Autissiodorensis zones of the Upper Kimmeridgian as well as the Klimovi, Sokolovi, Pseudoscythica and Puschi (=Tenuicostata) zones of the Lower Tithonian (“Lower Volgian”). The Pałuki Formation shows in its lower and middle parts average TOC concentrations of ca. 2.5 wt.% and prominent, restricted increases in organic matter content, which are found in the mid-Eudoxus Zone, the lowermost part of the Autisiodorensis Zone, and at the Sokolovi–Pseudoscythica zone boundary. These stratigraphical intervals correlate well with rich in organic matter levels present in the Kimmeridge Clay Formation of NW Europe. The periodic expansions of Submediterranean and Subboreal-Boreal ammonites corresponded mostly to the transgressive phases, often correlated with a higher content of organic matter. The development of special morphologies of ammonites, such as the small-sized, nectopelagic forms of Nannocardioceras in the Late Kimmeridgian, has also been related to the deposition of shales rich in organic matter during the transgression maxima. The organic matter present in the Pałuki Formation mostly consists of Type II kerogen and is immature or early mature with respect to hydrocarbon generation, which is in agreement with previously published data. Evaluation of the new and published geochemical, lithological and structural data from the Pałuki Formation in the central-eastern part of the Łódź Synclinorium shows that these deposits could not have been a considerable source of crude oil or gas.

New studies on perisphinctids from the Lower Tithonian (Hybonotum Zone) of S Germany and SE France

Scherzinger A., Atrops F., Schweigert G.

Volumina Jurassica

2006

Vol. 4, no. 1

244-245

New extensive collections from the Hybonotum Zone of Liptingen (SW Germany), Canjuers (Dpt. Var, France) and Crussol (Dpt. Ardeche, France), together with already published material from Laisacker (Franconia, S Germany, Schairer & Barthel 1981) give deep insights in ontogeny, intraspecific variation, dimorphism, and evolution of several Late Jurassic perisphinctid ammonite genera, as a basis for future revisions. In older studies perisphinctids were often problematic due to little material, erroneous interpretations of type species, incompletely or poorly preserved specimens, disregarding of dimorphism, and widespread homeomorphism. After our recent study the perisphinctids are much more diverse than previously thought. A correlation with French biohorizons established in the Paris and Aquitaine basins is possible due to the occurrence of Gravesia M+m and Tolvericeras M+m?, especially at Liptingen. Besides the two latter genera we can distinguish five other dimorphic pairs which are coupled as follows: Lithacoceras Hyatt (M) + Silicisphinctes Schweigert & Zeiss (m); group of "Virgatosphinctes" eystettensis Schneid (M) + Subplanites group A (m); Euvirgalithacoceras Zeiss, Schweigert & Scherzinger (M) + Subplanites group B, S. rueppellianus sensu Schairer & Barthel non Quenstedt (m); Hegovisphinctes Zeiss, Schweigert & Scherzinger (M) + group of "Torquatisphinctes" filiplex Schairer & Barthel non Quenstedt (m); Hoelderia Ohmert & Zeiss (M) + group of "Subdichotomoceras" sp. in Schairer & Barthel 1981, pl. 5, fig. 4 only (m). Some of these dimorphic pairs can be recognized also in SE Spain (Calanda area) and in the Balkans (Bulgaria, Croatia) and thus permit correlations across the Submediterranean Province. The rich perisphinctid fauna, together with other excellently preserved ammonites underlines the potential of the French sections as key sections for long-distance and high time-resolution correlations as well as the understanding of the Kimmeridgian-Tithonian transition.