Profound biotic changes accompanied the late Cenomanian delta C-13
excursion and OAE2 in planktic foraminifera in the Tarfaya Basin of
Morocco. Planktic foraminifera. experienced a severe turnover, though no
mass extinction, beginning with the rapid delta C-13 excursion and
accelerating with the influx of oxic bottom waters during the first peak
and trough of the excursion. Species extinctions equaled the number of
evolving species, though only the disaster opportunists Guembelitria and
Hedbergella thrived along with a low oxygen tolerant benthic assemblage.
The succeeding delta C-13 plateau and organic-rich black shale
deposition marks the anoxic event and maximum biotic stress accompanied
by a prolonged drop in diversity to just two species, the dominant
(80-90%) low oxygen tolerant Heterohelix moremani and surface dweller
Hedbergella planispira. After the anoxic event other species returned,
but remained rare and sporadically present well into the lower Turonian,
whereas Heterohelix moremani remained the single dominant species. The
OAE2 biotic turnover suggests that the stress to calcareous plankton was
related to changes in the watermass stratification, intensity of
upwelling, nutrient flux and oxic levels in the water column driven by
changes in climate and oceanic circulation. Results presented here
demonstrate a 4-stage pattern of biotic response to the onset, duration,
and recovery of OAE2 that is observed widely across the Tethys and its
bordering epicontinental seas. Published by Elsevier Ltd.