Community structure of the late Cenomanian Neolobites vibrayeanus bioevent in the Batna Mountains (Northeastern Algeria)

Neolobites vibrayeanus (d'Orbigny) is a well-known bioevent in North Africa and the Middle East. It is equivalents to the marker early-late Cenomanian Calyoceras guerangeri biozone (∼95.2–94.8; my = 400ky). This well-dated event was used to analyze minor variations in the macrobenthic communities within Algeria's Batna Mountains. In the study area, the Neolobites bioevent is often accompanied by the nautiloid Angulithes mermeti (Coquand). Quantitative analyses of the benthic fauna from four sections indicated gradual changes in the composition and function of the macrobenthic faunal community. These vertical faunal changes coincide with the stocking pattern of a fourth-order (20-m thick) depositional cycle. Epifauna and suspension feeders decreased gradually and reached a minimum at the maximum flooding surface (mfs), while infauna and deposit-feeders such as irregular echinoids increased and reached a peak at the mfs. Diversity indices show gradual biodiversity decrease and dominance increase upward, which was attributed to deepening, flourishing of the irregular echinoids, and increasing bulldozing activities. These activities may have resulted in a soft substrate, where epifaunal taxa were negatively affected. In contrast to significant vertical faunal changes, geographic variations were minor suggesting lateral extent of similar environmental setting, and thus, the stratigraphic features of this bioevent have been simultaneously recorded. Our analysis reveals that faunal shifts extend beyond sequence boundaries, particularly during late TST and early HST, highlighting the effectiveness of biosequence stratigraphy in low-energy environments with minimal lithofacies variation.