Zdarzenia jura środkowa-jura górna i ich implikacje
Abstract
MIDDLE- UPPER JURASSIC EVENTS AND THEIR IMPLICATIONS
Summary
The hitherto obtained results of studies of the Middle/ Upper Jurassic boundary events (M-UJ) appear fairly important for the continuing discussion on the hypothesis (15) linking mass extinction events with catastrophic ones caused by impacts of large cosmic bodies. Iridium and isotope anomalies from M-UJ boundary appear to be of the same order as those from the Cretaceous/Tertiary boundary, shocked quartz was found in Polish and Spanish sections, and boundary were layers shown to be highly enriched in ablation spherules. There remains a question whether we are dealing with effects of cosmic catastrophe resulting from impact of one or more large cosmic bodies and leading to significant global changes or merely minor meteorite showers leading to local changes.
Up to the present, effects of redeposition used to be underestimated or even completely neglected in stratigraphic studies of the boundary section. This makes it necessary to carry out reanalyses of the sections in order to obtain more firm time brackets for the events. On the basis of the available data and using approach similar to that of R.R. Brooks et al. (8) we are inclined to date the major events at the Lamberti subzone of the Lamberti zone. The scale of extinction also appears underestimated and it would need to carry out revisions of individual fossils to eliminate Callovian taxa from lists of the Oxfordian to obtain more appropriate estimates.
Summary
The hitherto obtained results of studies of the Middle/ Upper Jurassic boundary events (M-UJ) appear fairly important for the continuing discussion on the hypothesis (15) linking mass extinction events with catastrophic ones caused by impacts of large cosmic bodies. Iridium and isotope anomalies from M-UJ boundary appear to be of the same order as those from the Cretaceous/Tertiary boundary, shocked quartz was found in Polish and Spanish sections, and boundary were layers shown to be highly enriched in ablation spherules. There remains a question whether we are dealing with effects of cosmic catastrophe resulting from impact of one or more large cosmic bodies and leading to significant global changes or merely minor meteorite showers leading to local changes.
Up to the present, effects of redeposition used to be underestimated or even completely neglected in stratigraphic studies of the boundary section. This makes it necessary to carry out reanalyses of the sections in order to obtain more firm time brackets for the events. On the basis of the available data and using approach similar to that of R.R. Brooks et al. (8) we are inclined to date the major events at the Lamberti subzone of the Lamberti zone. The scale of extinction also appears underestimated and it would need to carry out revisions of individual fossils to eliminate Callovian taxa from lists of the Oxfordian to obtain more appropriate estimates.