Significance of the trace fossil Macaronichnus from the Cenomanian low-latitude nearshore deposits of the Saharan Atlas, Algeria

Abstract

The Cenomanian deposits of the Eastern Saharan Atlas are characterised by gypsum-dominated series interpreted as coastal sabkha deposits, indicating low-latitude, and tropical to subtropical settings. The evaporitic conditions are interrupted by rapid marine ingressions allowed the deposition of carbonate beds. In the Djebel Ousigna section, fine sandy limestone bed shows abundant burrows of Macaronichnus. These traces indicate the upper shoreface–foreshore contact, affected by storm events, which show similarities with recent huge tsunami waves that facilitated the proliferation of Travisia polychaete populations (Macaronichnus tracemaker). This Macaronichnus-suite represents the most proximal marine setting during a regressive phase. Also, this unique occurrence of Macaronichnus in the North African Cenomanian low-latitude, subtropical to tropical evaporites is interpreted as related to upwelling of cold nutrient rich-waters. The latter seemingly challenge the view that this trace fossil is restricted to colder climatic zones. From an ethological viewpoint, studied Macaronichnus specimens are considered to be a sequorichnial trace (exploratory behaviour) produced by polychaete annelids.