Chad Basin: Paleoenvironments of the Sahara since the Late Miocene

Abstract

Since the mid 1990s, the Mission paléoanthropologique francotchadienne (MPFT) conducts yearly paleontological field investigations of the Miocene-Pliocene of the Chad Basin. This article synthesizes some of the results of the MPFT, with focus on the Chad Basin development during the Neogene. We propose an overview of the depositional paleoenvironments of this part of Africa at different scales of time and space, based on a multidisciplinary approach (sedimentary geology, geomorphology, geophysic, numerical simulations and geochronology). The Miocene-Pliocene paleoenvironments are examined through the sedimentary archives of the early hominids levels and the Holocene Lake Mega-Chad episode illustrates the last major paleoenvironmental change in this area. The sedimentary record of the Chad Basin since the Late Miocene can be schematized as the result of recurrent interactions from lake to desert environments. To cite this article: M. Schuster et al., C. R. Geoscience 341 (2009). # 2009 Published by Elsevier Masson SAS on behalf of Académie des sciences. RésuméBassin du Tchad : paléoenvironnements du Sahara depuis le Miocène supérieur. Depuis le milieu des années 1990, la Mission paléoanthropologique francotchadienne (MPFT) conduit chaque année des recherches paléontologiques de terrain dans le Mio-Pliocène du Bassin du Tchad. Cet article synthétise certains résultats de la MPFT concernant l'évolution du Bassin du Tchad au Néogène. Nous proposons un aperçu des paléoenvironnements de dépôt de cette partie de l'Afrique, à différentes échelles, à partir d'une approche multidisciplinaire (géologie sédimentaire, géomorphologie, géophysique, simulations numériques et géochronologie). Les paléoenvironnements du Mio-Pliocène ont été étudiés, notamment à partir des archives sédimentaires des séries à hominidés anciens, et le Lac Méga-Tchad holocène illustre le dernier changement paléoenvironnemental majeur dans cette région.

Diatom, phytolith, and pollen records from a 10Be/9Be dated lacustrine succession in the Chad basin: Insight on the Miocene–Pliocene paleoenvironmental changes in Central Africa

“…Paleoenvironmental studies at Chadian hominin sites (faunal composition and structure, dental mesowear and isotopes) concluded to the existence of a diversified vegetation cover, with a mosaic of forests, woodlands, grasslands, up to desert conditions, in close relationship with aquatic/lacustrine areas in northern Chad during the Messinian Schuster et al, 2006;Jacques, 2007;LeFur et al, 2009;Schuster et al, 2009;Blondel et al, 2010;Otero et al, 2010), and open C 4 -vegetations later on during the Pliocene (Brunet et al, 1997;Zazzo et al, 2000;Geraads et al, 2001;Lee-Thorp et al, 2012), in association with large lake occurrences (Schuster et al, 2009). Paleovegetation modeling for the Messinian does not support the existence of mosaic vegetation in northern Chad, but rather a spread of the tropical savanna biome (Pound et al, 2012).…”

Pliocene hominin biogeography and ecology

“…The Chad Basin is bounded in the south by the Bongo massif, separating it from the Congo Basin, and by the Darfour mountains in the east, separating it from the Sudan (Schuster et al, 2009). This intersection of mountainous regions now marks the watershed between the Nile, the Congo, and the Chad Basin (Goudie, 2005) and constitutes a potential bottleneck for any dispersing mammal from the East (Fig.…”

“…afarensis and were suggested to represent a local population of a widely dispersed A. afarensis (Brunet et al, 1995); only later were the fossils assigned to a new species (Brunet et al, 1996). The well-vegetated green belt, which repeatedly extended across the Sahara from the Atlantic to East Africa during the Pliocene (Larrasoaña et al, 2013) and the successive wet and arid periods in Northern Chad (Schuster et al, 2009), could have led East African hominins to periodically expand and contract their ranges. Whether the morphological differences in the cross-sectional shape of the mandibular symphysis and in tooth root morphology (Brunet et al, 1996;Guy et al, 2008) between the specimens from Koro Toro and A. afarensis (Fig.…”

Climate impact of high northern vegetation: Late Miocene and present

“…The aridification of northern Africa principally seems to be realistic since the proxy record indicates repeated aridification of this region in the last 11 Ma (e.g. Senut et al 2009;Schuster et al 2006Schuster et al , 2009. Many mechanisms causing aridification in North Africa are discussed in literature ranging from orbital forcing (e.g.…”