The Kimmeridgian of the south-western margin of the Holy Cross Mts., central Poland: stratigraphy and facies development. Part I. From deep-neritic sponge megafacies to shallow water carbonates

Abstract

The stratigraphical interval of the Kimmeridgian between the Bimammatum and the Hypselocylum zones in the SW margin of the Holy Cross Mts. shows a transition from the open shelf deep-neritic sponge megafacies to the shallow-water carbonate platform, including its development and decline. The uniform progradation of the shallow-water carbonate platform occurred at the end of the Planula Chron. Development of the shallow-water carbonate platform was controlled by climatic and tectonic factors. The former induced by orbital cyclicity resulted in changes of sea-level, revealed i.a. by the incoming of open-marine ammonite faunas, the latter were related to the synsedimentary activity of faults which resulted in contrasted facies changes. The episodically occurring strong influx of siliciclastic material was at least partly controlled by the tectonic activity. The newly elaborated formal lithostratigraphic subdivision takes into account the facies development of the succession in relation to climatically and tectonically induced changes. Such is e.g. the Małogoszcz Oolite Formation, corresponding to a single 100-kyr eccentricity cycle from the late Platynota Chron to the earliest Hypselocyclum Chron, bordered from the base and top by two transgressive climatically-controlled levels. The final stage of the shallow-water platform development at the end of the Hypselocyclum Chron was marked by the successive limitation of restricted environments, and the appearance of more open-marine conditions related to tectonic subsidence of the area of study. Comparison between the carbonate platform development of the Holy Cross Mts. in central Poland, and the coeval shallow-water carbonates of the Jura Mts. in northern Switzerland and south-eastern France provides an opportunity to consider similarities in the successions which can be attributed to the climatically-controlled sedimentary cyclicity and/or the wide-ranged tectonic phenomena. The palaeontological part of the study gives comments on the classification and phylogeny of ammonites of the families Ataxioceratidae and Aulacostephanidae.