Cj. Underwood et al., HIGH PALEOLATITUDE (HODH, MAURITANIA) RECOVERY OF GRAPTOLITE FAUNAS AFTER THE HIRNANTIAN (END ORDOVICIAN) EXTINCTION EVENT, Palaeogeography, palaeoclimatology, palaeoecology, 142(3-4), 1998, pp. 91-105
Marine shales directly overlying lower Hirnantian (uppernost Ordovicia
n) glacially related sediments in Mauritania (northwest Africa) have p
roduced a rich graptolite fauna spanning the Ordovician-Silurian bound
ary in an area of high palaeolatitude. The lowermost transgressive san
dy shales are barren of graptolites, but overlying shales show a sudde
n appearance of a diverse fauna indicative of the terminal Ordovician
persculptus Zone, suggesting that with improving conditions, colonisat
ion by a relatively cold-tolerant fauna was possible. This. fauna is r
eplaced by a low-diversity assemblage dominated by long-ranging taxa,
probably representing the basal Silurian acuminatus and atavus Zones.
With the extinction of the persculptus Zone fauna, conditions were sti
ll hostile to warm water Silurian graptolites, and a Normalograptus fa
una was again established. A sudden influx of fairly diverse taxa mark
s the base of the acinaces Zone and the establishment of a typical Low
er Silurian fauna with the establishment of warmer water conditions. (
C) 1998 Elsevier Science B.V. All rights reserved.