Facje i paleogeografia cechsztyńskiego anhydrytu dolnego (A1d) w Polsce

Tadeusz Marek Peryt, Lech Antonowicz



At the end of the Zechstein Limestone deposition the sealevel felt. The sequence of Lower Werra Anhydrite is transgressive. The pro gradation of sulfate deposits which, in the peripheral part of the sedimentary basin, took place along with the transgression, led to the development of a sulphate platfonn which was attached to the carbonate platform of the Zechstein Limestone. A depositional pattern of the Lower Werra Anhydrite is quite complex as it results from the interaction of several factors; the most important were: the rate of sulfate deposition, fine differences of subsidence rate, both regional and local, and, as evidenced by the findings in other parts of the Zechstein basin, eustatic fluctuations of sea level. The result was that in the peripheral parts of the basin isolated lagoons could originate in which chloride deposition took place. The faster rate of deposition in the peripheral part of the basin where on the vast evaporitic flats of small depth (a few tens of centimetres to a few tens of metres) bottom-nucleated crystals were formed, compared to the central part of the basin where mechanically- deposited laminated deposits ("rain" of crystals precipitated on the water-air boundary) originated, resulted in the differentiation of the relief between these both major areas. Considering that graded-bedded deposits, which are interpreted as turbidites, appeared during a rather early phase of the deposition of Lower Werra Anhydrite, that differentiation was early but the relief difference was smaller than it is suggested by the difference of thickness of the Lower Werra Anhydrite sequences in both major zones.

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