Paucispecific invertebrate associations in the Coniacian (Upper Cretaceous) Essen Formation (Tébessa Mountains, northeast Algeria)

Abstract

The Coniacian strata of the Tébessa Mountains in northern Algeria are predominantly marly facies that have received few studies. The present study is the first one to be carried out at Djebel Essen (west of Tébessa) to reveal the paleoenvironmental setting. The macrofossil taxa identified herein include fifteen bivalve species, three gastropods, and one cephalopod species, in addition to four irregular echinoid species. Quantitative analysis of these macrofossils indicates the occurrence of three benthic Coniacian macrofaunal associations, which include: 1) Agelasina plenodonta, 2) Cucullaea, and 3) Oscillopha-Plicatula. Both Agelasina plenodonta and Cucullaea associations are dominated by infauna. However, Cucullaea Association contains only suspension-feeders, where deposit-feeders are completely absent, suggesting oligotrophic conditions, that might have resulted in the lowest diversity level. In contrast, epifaunal taxa dominated the Oscillopha-Plicatula association. All the three associations are paucispecific. This low diversity of the Coniacian associations at study area and in other North African countries, can be attributed to the retreat of the sea and the shrinking of shallower habitats’ area. Probably, these associations lived within restricted marginal marine environments. The absence of any potential indicator of the middle-upper Coniacian anoxic event (OAE-3) agrees with the case in nearby sections and confirms a restricted extent of this event. The occurrence of many taxa of either regional or cosmopolitan affinity suggests episodic connection with the Tethyan Ocean.