Ammonites and stratigraphy of the uppermost Bajocian and Lower Bathonian between Częstochowa and Wieluń, Central Poland

Abstract

A detailed biostratigraphical study of the black clays and siltstones with ironstone nodules of the Ore Bearing Częstochowa Clay Formation in the brick-pits at Częstochowa and Wieluń resulted in recognition of the following standard ammonite zones and subzones: the Parkinsoni and Bomfordi subzones of the Parkinsoni Zone of the uppermost Bajocian; the Convergens, Macrescens and Yeovilensis subzones of the Zigzag Zone, and the Tenuiplicatus Zone of the Lower Bathonian. The ammonite faunas are of Submediterranean character, although markedly impoverished when compared with those of the most classic areas of the province. This impoverishment is especially well seen in the uppermost Bajocian – lowermost Bathonian part of the succession, where the only numerous ammonites are these of the genus Parkinsonia, together with rare representatives of Cadomites; and in the uppermost part of the Lower Bathonian, where representatives of the corresponding macro- and microconchs – Asphinctites tenuiplicatus (BRAUNS), and Polysphinctites secundus (WETZEL) – predominate. In the palaeontological part of the paper 14 species belonging to the genera Oxycerites, Parkinsonia, Cadomites, Wagnericeras, Asphinctites and Polysphinctites are described. Of these, particular attention is paid to a form referred to as Parkinsonia (Parkinsonia) aff. dorni ARKELL from the uppermost Bajocian, represented by several specimens of various growth stages, which may be tentatively compared with the poorly diagnostic small, incomplete type-specimens of P. dorni.