Torreites milovanovici Grubić, 1979 in the Iranian Upper Cretaceous succession: Paleoenvironmental characteristics

Abstract

Genus Torreites shows different features in comparison to other types of rudists, making them important to interpret paleoenvironmental circumstances. In the study area which is located north of Shiraz (Zagros Basin, Interior Fars) (i.e. the northwesternmost section of Torreites-bearing sections of the Middle East) about 40 specimens from the Iranian section were analyzed to interpret the paleoecological characteristics of the Campanian monospecific layer. At first sight, their morphotypes reveal the substrate, hydrodynamic energy, and other factors. Except for a limited number of specimens, they predominantly function as elevators, indicating a relatively quiet surrounding environment. There are minor organisms, including corals, gastropods, sponges, other non-rudist bivalve groups, and polychaeta, helping for more precise interpretations. The Torreites-bearing carbonate layer is situated on a soft shaly and marly siliciclastic bed, and other organisms colonized a considerable proportion of the surface of Torreites specimens. As they are photosymbiont-bearing bivalves, they may play a significant role in interpreting environmental characteristics such as trophic conditions. In addition, as surface bioerosion increases in response to elevated nutrient levels, the prevailing trophic condition is supposed to be oligotrophic to mesotrophic. Also, based on marine constituents, and previous studies, the studied interval must be deposited in a tropical environment. Based on various interpretations, hydrodynamic energy has transitioned from low to moderate levels. Besides, bioerosion rates observed on different sides and coupled specimens imply that Torreites samples should have preferred directions.