A high-resolution micropalaeontological study, combined with geochemical
and sedimentological analyses was performed on the Tiefengraben,
Schlossgraben and Eiberg sections (Austrian Alps) in order to
characterize sea-surface carbonate production during the end-Triassic
crisis. At the end-Rhaetian, the dominant calcareous nannofossil
Prinsiosphaera triassica shows a decrease in abundance and size and this
is correlated with a increase in delta O-18 and a gradual decline in
delta C-13(carb) values. Simultaneously, benthic foraminiferal
assemblages show a decrease in diversity and abundance of calcareous
taxa and a dominance of infaunal agglutinated taxa. The smaller size of
calcareous nannofossils disturbed the vertical export balance of the
biological carbon pump towards the sea-bottom, resulting in changes in
feeding strategies within the benthic foraminiferal assemblages from
deposit feeders to detritus feeders and bacterial scavengers. These
micropalaeontological data combined with geochemical proxies suggest
that changes in seawater chemistry and/or cooling episodes might have
occurred in the latest Triassic, leading to a marked decrease of
carbonate production. This in turn culminated in the quasi-absence of
calcareous nannofossils and benthic foraminifers in the latest Triassic.
The aftermath (latest Triassic earliest Jurassic) was characterised by
abundance peaks of ``disaster'' epifaunal agglutinated foraminifera
Trochammina on the sea-floor. Central Atlantic Magmatic Province (CAMP)
paroxysmal activity, superimposed on a major worldwide regressive phase,
is assumed to be responsible for a deterioration in marine
palaeoenvironments. CAMP sulfuric emissions might have been the trigger
for cooling episodes and seawater acidification leading to disturbance
of the surface carbonate production at the very end-Triassic.