Comment on “Relative bathymetric position of opoka and chalk in the Late Cretaceous European Basin” by M. Machalski and O. Malchyk [Cretaceous Res. 102 (2019) 30–36]

Abstract

© 2020 Elsevier Ltd In their recent paper, Machalski and Malchyk, 2019, present a paleobathymetric model proposed relations among main facies types, including opoka and chalk, along a perpendicular to the shore. The model is seemed to be a pioneering one based on paleoecological and taphonomical data from the successions from Poland and western Ukraine. However, speaking about lithofacies, the authors do not take into account such crucial factors as mineral composition of rocks and origin of silica in the basin. “Camouflaged” pyroclastic material which is evidence of volcanic ash falls, could be among major contributors to mineral composition of opokas and among minors of chalks. Thus, considering this factor could be essential to sediment accumulation the paleobathymetric model would not face mismatches revealed in different parts of the basin. More research (including quantitative XRD and electron microscopy analysis) is necessary to study precise mineral composition and peculiarities of rock microfabrics in order to understand the proper origin of opokas and chalks, making a basis for more reliable paleobathymetric model of distribution of chalks and opokas in the Late Cretaceous European Basin.