The oceanic "Metis Geotectonic Event" (Callovian/Oxfordian) and its implications for the peri-Tethyan area of Poland

Condensed deposits of the Middle/Upper Callovian and/or lowermost Oxfordian are spread over vast areas of peri-Tethyan Europe from Portugal, and Spain through France, Switzerland, Germany, Poland, to Romania. A number of hypotheses for the origin of these deposits have been presented. Melendez et al. (1983) suggested that they originated due to the rise of CCD in relation to increased igneous activity. Other proposed explanations include: an extra-terrestrial event (Brochwicz-Lewifski et al. 1989) and erosional events and related taphonomic reworking of fossils during long episodes of subaerial exposure (Aurell et al. 1991). Palaeomagnetic data from the Pieniny Klippen Belt (Carpathians) of southwestern Ukraine (Lewandowski et al. 2005), and western Slovakia (Lewandowski et al. 2006) indicate that during Middle Callovian - Early Oxfordian time span a relatively fast opening of the oceanic domain took place in the outer part of the Tethys. This newly open basin (possibly corresponding to the Magura Basin in the Carpathian domain) attained 1100-1400 km in width. The rocks that formed during the Middle Callovian - Early Oxfordian in the epi-platform area of Poland bear witness to this geotectonic event. It is highly probable that the total spatial range of the geo-tectonic event within the Tethys (cf. Lewandowski et al. 2006) has been much greater, however, which indicates that the obtained results can be applied to the whole peri-Tethyan Europe. Thus, to distinguish this phenomenon independently of which particular part of the Tethys it affected, we propose to name it the "Metis Geotectonic Event"(Metis in Greek mythology was the Oceanid, and the daughter of Tethys). The appearance of condensed deposits in the epi-platform area of Poland (Giżejewska & Wieczorek 1974; Dembicz & Praszkier 2003, and other papers cited therein) remains in close time relation with recognized extension in the Tethyan domain. The short time interval of the extension (about 5 Ma) plus a large-scale displacement could have resulted in a sudden change in deposition from shallow-marine to pelagic environment, as well as in chemical corrosion of earlier accumulated carbonates. This change of deposition was controlled by relative sea-level rise as well as by upwelling of cold oceanic waters into the epi-platform area. This interpretation is consistent with recognized isotopic thermometry results indicating drastic cooling of sea water at lower middle latitudes (Dromart et al. 2003). The development of the sponge megafacies covering the peri-Tethyan part of the Late Jurassic shelf of Europe remains in close relationship with discussed phenomena. These deposits showed during Oxfordian similar spatial distribution as older condensed deposits, and represent the non-actualistic deep environment of the Late Jurassic shelf (Matyja & Pisera 1991; Matyja & Wierzbowski 1996).