Аннотация:New Sr isotope data from well-preserved aragonite ammonoid shell material from the
Mesozoic are compared with that from a living Nautilus shell. The prominent negative Sr
isotope excursions known from the Middle Permian, Jurassic and Cretaceous probably have
their origins in intensive plate tectonic activity, followed by enhanced hydrothermal activity
at the mid-ocean ridges (mantle volcanism) which supplied low radiogenic Sr to seawater.
The maximum positive (radiogenic) shift in the lower Mesozoic Sr isotope curve (Lower
Triassic peak) was likely caused by a significant expansion of dry land surfaces (Dabie-Sulu
Triassic orogeny) and their intensive silicate weathering in conditions of extreme warming
and aridity in the very end of the Smithian, followed by warm and humid conditions in the
late Spathian, which apparently resulted in a significant oceanic input of radiogenic Sr
through riverine flux. The comparatively high 87Sr/86Sr ratio obtained from the living Nautilus
shell is probably a function of both the Alpine orogeny, which was accompanied by
significant continental weathering and input of radiogenic Sr to the oceans, and the weakening
of mantle volcanism