Rutile to tourmaline index – a tool for the recognition of the hydrodynamics of the depositional environment; a case study from the Campanian Szozdy Delta System, SE Poland

Abstract

The newly discovered mid-Campanian Szozdy Delta System (Roztocze Hills, SE Poland) located in the southern part of the Polish Cretaceous Basin, at the northern edge of the Łysogóry-Dobrogea Land, has revealed interesting features concerning the relationship between the abundance of rutile and tourmaline. A distinct inverse relationship between rutile and tourmaline can be readily recognised in the succeeding units of the tripartite cyclothems (calcareous mudstone, calcareous sandstone, and calcareous gaize) representing the submarine part of the Szozdy Delta System. In the Szozdy section, both minerals are of similar shape (highly rounded), durability, and size; they are, however, characterised by markedly different densities. Therefore, it might be expected that these two mineral phases will be strongly dependent, both vertically and spatially, on the local energy of the sedimentary environment hydrodynamic power that existed during the deposition of the succeeding units of the cyclothems. The lighter tourmaline was likely transported further to the more quiescent prodelta environment, rendering the prodelta facies overrepresented in this mineral, whereas the heavier rutile was deposited closer to the river discharge. Such relative change in the abundance of these two mineral phases, emphasised by a standardised Z-score statistics, is referred here to as rutile to tourmaline index (RuTidx). Accordingly, as the RuTidx increases, the hydrodynamic power in the sedimentary environment increases as well. Since these two mineral phases are comparatively immune to alteration during the sedimentary cycle, the RuTidx is considered here to be an independent tool in recognising the hydrodynamics of the depositional environments of any age.