Characterization and paleoenvironment of the Anembalemba Member in the Kinkony Lake sector (Mahajanga Basin)

Earth sciences

The Campanian of the Mahajanga Basin is recognized by many authors as a very fossiliferous stage of the Upper Cretaceous. A large number of terrestrial vertebrates that flourished in the basin at this time have been discovered there, including dinosaurs. Previous taphonomic studies concluded that the majority of these large vertebrate fossils were collected from Facies 2 of the Anembalemba Member of the Maevarano Formation considered Campanian in age in this study. The investigations were carried out in the Lake Kinkony sector, a study area still little explored compared to that of Berivotra where outcrops of Upper Cretaceous layers including those of the Anembalemba Member abound and where dinosaur fossils and other terrestrial vertebrates are well preserved. The Anembalemba Member of the Lake Kinkony sector was then the subject of morphoscopic, mineralogical and geochemical analyses. It was deduced that the Anembalemba Member was deposited during a period of continental transgression in an alluvial plain. The climate there was hot and subtropical, as in the entire Mahajanga Basin. Following the morphology of the basin, the Maevarano Formation becomes thinner in this westernmost part of the basin, generating insufficient accommodation space for the effective burial of large terrestrial vertebrates. Also, the results of the geochemical analysis revealed that the deposits of the Anembalemba Member were exposed to the air for a quite long period, which does not allow good conservation of the fossils they contain.

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