Taphonomic differentiation of Oxfordian ammonites from the Cracow Upland, Poland

Abstract

Taphonomic analysis of Lower and Middle Oxfordian ammonites from the Cracow Upland, southern Poland (localities at Podłę _ ze, Zalas, Młynka) revealed differences in ammonite preservation. The studied ammonites, usually termed as external and internal moulds, show a more complex state of preservation. In the Middle Oxfordian glauconitic marls, ammonites are preserved as internal moulds with neomorphic calcite shells showing relics of the original internal structure. In the Middle Oxfordian platy peloidal limestones, ammonites are preserved mostly as external moulds, without septal suture, however under microscope might show relics of internal whorls and septa and/or subtle differences in sediment filling phragmocone chambers. In sponge-microbial bioherms and biostromes, ammonite internal moulds have shells, which in contrast to ammonites from glauconitic marls are not strictly neomorphic ones, but originated by shell dissolution and subsequent filling of moldic porosity by calcite cement. In sponge-microbial nodular limestones, the ammonites are strongly deformed and the outer wall is usually removed by dissolution under pressure. Other important taphonomic differences include the rate of compaction (highest in platy limestones), sedimentary infillings, microborings, encrustations and preservation of siphuncular tubes. The majority of the ammonites appear to be phragmocones; aptychi in all facies are rare. Siphuncular tubes are fossilized exclusively in oppeliids, only in specimens from glauconitic marls and platy limestones, although their other taphonomic attributes are different. Tubes seem to have fossilized due to microbially mediated phosphatization that could be favoured by a set of parameters which operated rather at the scale of ammonoid carcasses: closed, poorly oxygenated conditions, and reduced pH. Taphonomic processes were controlled by the sedimentary environment (fragmentation, sedimentary filling, phosphatization of siphuncular tubes), as well as by early and late diagenesis (neomorphic transformation, dissolution, cementation, compaction) influenced by lithology.

Oxfordian neptunian dykes with brachiopods from the southern part of the Kraków-Częstochowa Upland (southern Poland) and their links to hydrothermal vents

“…1). The exposed Lower and Middle Oxfordian succession includes zones from the Cordatum to the Transversarium (Głowniak 2006;Jurkowska and Kołodziej 2013). The Upper Jurassic sequence begins with marls with sponges and ammonites which grade upward into thin-bedded, pelitic limestones with marl intercalations (Fig.…”

“…2). A horizon of glauconitic marls occurs in the upper part of the pelitic limestones (Jurkowska and Kołodziej 2013), followed by massive limestones representing the Plicatilis-Transversarium zones and developed as microbial-sponge facies with siliceous sponges, bivalves, brachiopods, ammonites, bryozoans, and fragments of echinoderms, sometimes accompanied by numerous specimens of Crescentiella sp. (Hoffmann and Matyszkiewicz 1989).…”

Jurassic planktic foraminifera from the Polish Basin

“…Jurassic strata in the Wrzosowa Quarry (50 • 45 25.4 N, 19 • 08 51.9 E) are represented by a succession, approximately 5 m thick, of Cordatum Zone (lower Oxfordian) marl-limestone rhythmites with the dominant limestone of the Jasna Góra beds, yielding numerous sponges, belemnites, ammonites, and brachiopods (Trammer, 1985;Matyja et al, 2006a;Wierzbowski et al, 2009;Głowniak, 2012). Some isolated samples of Callovian and Oxfordian strata were additionally collected from little-known sections such as Bolęcin (lower Callovian) (Różycki, 1953), Czatkowice (Lamberti Zone, upper Callovian) (Dayczak-Calikowska and Kopik, 1973a;Salata, 2013), Gorenice (lower Oxfordian) (Różycki, 1953), and Podłęże (middle Oxfordian) (Giżejewska and Wieczorek, 1977;Jurkowska and Kołodziej, 2013).…”

The first plesiosaurian (Sauropterygia, Pliosauridae) remains described from the Jurassic of Poland

“…The biostratigraphy of the Zalas Quarry has been well recorded. For an overview and further detailed description of the geology of the area please refer to Matyja and Tarkowski (1981) and Jurkowska and Kolodziej (2012); a general overview is given by Molenda (1997) and Borszcz and Zatoń (2009).…”

“…This fossil fauna includes brachiopods, bivalves, nautiloids, ammonites, gastropods, belemnites, corals, bryozoans, serpulids, sponges, echinoids, crinoids, brittle stars, stromatolites, polychaetes, crabs and radiolarians (Gizejewska and Wieczorek, 1976;Matyja and Tarkowski, 1981;Trammer, 1989;Molenda, 1997;Górka and Bak, 2000;Borszcz and Zatoń, 2009;Jurkowska and Kolodziej, 2012;Zatoń et al, 2013). In contrast, there is a severe lack of vertebrate remains.…”