50 research outputs found
Environmental changes across the Triassic–Jurassic boundary and coeval volcanism inferred from elemental geochemistry and mineralogy in the Kendlbachgraben section (Northern Calcareous Alps, Austria)
The end-Triassic extinction (ETE), one of the five largest Phanerozoic mass extinctions, is associated
with rapid and severe environmental change, but existing data permit alternative models of causation.
Volcanism in the Central Atlantic Magmatic Province (CAMP) has been proposed as the main trigger,
but direct evidence for this linkage is scarce. To help constrain scenarios for the ETE and other Triassic–
Jurassic boundary (TJB) events, we obtained a temporally highly resolved, multidisciplinary dataset
from the Kendlbachgraben section in the Northern Calcareous Alps in Austria. The section belongs to
the same paleogeographic unit (Eiberg Basin) and share similar stratigraphy with the recently selected
base Jurassic Global Stratotype Section and Point at Kuhjoch.
Micromineralogic study of the topmost bed of the Rhaetian K¨ ossen Formation revealed pseudomorphs
of altered, euhedral pyroxene and amphibole crystals. Their well-faceted morphology is
consistent with their origin from distal mafic volcanic ash fallout. Spherical grains were also observed
in the same bed, likely representing clay-altered volcanic glass. Clay minerals of this bed include lowto
medium-charged smectite and Mg-vermiculite, both typical alteration products of mafic rocks. The
same bed yielded a rare earth element pattern that differs from all other levels in an enrichment of
heavy REEs, hinting at some minor contribution from mafic magmatic material. These features from a
layer that was deposited very near to the TJB are interpreted as direct evidence of CAMP volcanism,
coeval or immediately preceding the ETE and the initial negative carbon isotope anomaly.
The kaolinite-dominated clay mineral spectrum of the overlying boundary mudstone records
intensive weathering under hot and humid greenhouse conditions. Redox-sensitive minor and trace
elements do not support the development of widespread anoxia in the studied section. Although pyrite
is common in several layers, framboid size indicates formation within a reductive zone, below the
sediment/water interface, rather than in an anoxic water column.
Our data provide a direct link between uppermost Triassic marine strata and CAMP-derived
material. They support scenarios where CAMP volcanism induced climate and other environmental
change, which in turn triggered the ETE and that is also reflected in the carbon isotope anomalies