Jura górna i kreda dolna okolic Zacharza (NE skrzydło niecki łódzkiej)

Andrzej Witkowski




The article presents some new geological data from the north-eastern limb of the Lódź trough (Fig. 1). Clayey-marly deposits of the Upper Kimmeridgian, belonging to the horizon Virgataxioceras fallax and the horizon Aulacostephanus pseudomutabilis, are the oldest formations found so far in the vicinity of Zacharz. The Upper Kimmeridgian deposits gradually pass into marly limestones of the Volgian stage, which belong to the horizon Subplanites sp. and Zaraiskites scythicus.
Higher up, the Lower Cretaceous deposits rest penaccordantly, represented by the Infravalanginian and Valanginian deposits developed in siltstone-clayey facies. Hauterivian deposits are lacking in this area. Above the Upper Valanginian are found arenaceous deposits of the Biała Góra series, referred, according to J. Lewinski (1932), to the younger Lower Cretaceous I(Fig. 2). To the Upper Cretaceous belong siltstone-marly deposits of Middle and Upper Albian age, which contain subordinate phosphorites. Quaternary formations make here a sedimentary cover, ranging from 26 m to 6l,2 m in thickness. This area lacks Tertiary formations.
Tectonics of the area considered is simple. Dip of the Upper Jurassic Sub-Cretaceous surface, that makes the NE limb of the Lódź trough, amounts to 8–10° towards SW, and that of the Upper Cretaceous surface, above the Biała Góra series – 5–7° (Fig. 3).
On the basis of the detailed studies the author gives petrographic and chemical characteristics of the Lower Cretaceous deposits. The ascertained paragenesis of ferruginous minerals allowed to state that most of the Neocomian deposits at Zacharz had been formed under reducing conditions of sedimentary environment. According to the classification of geochemical fades by G. I. Teodorowitsh (1964), based on rH profile, these deposits belong to 1–4 type.
Among the Neocomian deposits from Zacharz a slight, unpayable iron mineralization occurs. Here, ferruginous oolites are built up of chamoisite and siderite (Tab. I, Figs 4 and 5; Tab. III, Figs. 8 and 9), and secondary iron hydroxides and iron oxides (Tab. IV, Fig. 10) are epigenetic minerals. Thus, these oolites are similar to the Middle Jurassic ones, and differ from most of the known Lower Cretaceous ferruginous oolites, which are built up mainly of iron oxides and iron hydroxides.

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