F. Paris et al., FIRST RECORD OF CHITINOZOANS FROM THE ORDOVICIAN-SILURIAN BOUNDARY BEDS OF MAURITANIA - PALAEOGEOGRPHIC IMPLICATIONS, Comptes rendus de l'Academie des sciences. Serie II. Sciences de la terre et des planetes, 326(7), 1998, pp. 499-504
In the Hodh area (SE Mauritania), siltstones and shales overlying glac
ial deposits yield numerous chitinozoans. They provide a high resoluti
on biostratigraphy for these Upper Hirnantian and Lower Rhuddnian depo
sits. Glacial evidence disappears in the Upper Hirnantian along with t
he development of the first marine faunas indicative of an opening tow
ard the Rheic Ocean. This opening appears to be younger in the Hodh th
an in the northern Sahara Basins. The exceptional development of the H
irnantian and of part of the Rhuddanian in the Hodh area, compared wit
h the highly condensed sequences representing the contemporaneous depo
sits in the northern Sahara Basins, suggests an end-glacial transgress
ive event followed by a northward progradational event. (C) Academic d
es sciences/Elsevier, Paris.