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Radiocarbon Chronology of Holocene Hydrologic Changes in Northeastern Mali

Published online by Cambridge University Press:  20 January 2017

C. Hillaire-Marcel ,
J. Riser ,
P. Rognon ,
N. Petit-Maire ,
J.C. Rosso  and
I. Soulie-Marche
C. Hillaire-Marcel
Affiliation:
Département des Sciences de la Terre, Université du Québec à Montréal, B.P. 8888, Succ. A, Montréal, Quebec H3C 3P8, Canada
J. Riser
Affiliation:
Section Géographie, Faculté des Lettres, Université d'Avignon, 1 rue Violette, 84000 Avignon, France
P. Rognon
Affiliation:
ERA 684, Départment de Géographie Physique, Université P. et M. Curie, 4, Place Jussieu, 75230 Paris Cedex 05 France
N. Petit-Maire
Affiliation:
Laboratoire de Géologie du Quaternaire, Centre de Luminy, 13288 Marseille Cedex 2 France
J.C. Rosso
Affiliation:
Laboratoire de Géologie du Quaternaire, Centre de Luminy, 13288 Marseille Cedex 2 France
I. Soulie-Marche
Affiliation:
ERA 114, Paléobotanique, Faculté des Sciences, Place Eugène Bataillon, 34000 Montpellier, France
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Abstract

A detailed chronology of hydrological changes that occurred in northeastern Mali during the Holocene is based on approximately 30 14C dates of molluscs which were collected from the lacustrine and paludal deposits of the Ine Sakane sand sea. The presence of cemented paleodunes indicates that the end of the Pleistocene was and arid period. This was followed by an early Holocene lacustrine episode (ca. 9500–6500 yr B.P.) during which numerous lakes occupied depressions formed in the Cretaceous limestones and between the sand ridges. These lakes reflect a significant rise in the water table. Between ca. 6500 and 5500 yr B.P. the lakes dried up, although the water table remained close to the ground surface in several areas. Calcareous concretions formed at the water table fringe during this time, thereby “fossilizing” some of the middle Holocene dunes. A second lacustrine episode is dated between ca. 5500 and 4500 yr B.P.; it corresponds to the establishment of numerous Neolithic settlements in the area. Arid conditions have developed since about 4500 yr B.P. to attain the conditions of the present day. The isotopic composition (18O and 13C) of the fauna reflects highly variable hydrological conditions. Groundwaters were recharged by precipitation which was occasionally very depleted in heavy oxygen (δ18O ≅ −13%.). Evaporation induced an enrichment in 18O; high concentrations characterize some lakes. The 13C content of fossil shells reflect: (1) species ecological requirements, (2) isotopic composition of the total inorganic dissolved carbon (TIDC) in groundwaters, and (3) the lake metabolism.

Type
Original Articles
Information
Quaternary Research , Volume 20 , Issue 2 , September 1983 , pp. 145 - 164
Copyright
University of Washington

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