Boron systematics of authigenic carbonates: a new approach to identify fluid processes in accretionary prisms

A magnetostratigraphic study has been performed on the paleontologically well constrained pelagic Middle Triassic (Lower/Upper Ladinian boundary) section at Margon (Trento, Southern Alps, Italy). Rock magnetic investigations indicate the presence of both, high and low coercivity minerals. Specimens subjected to progressive thermal demagnetization procedures show that nearly all of them exhibit a low temperature magnetization component, parallel to the present-day field before bedding correction, and a high temperature one, characterized by either positive or negative and opposite polarity, considered as the characteristic Triassic magnetization. The comparison of the Margon magnetic polarity zonation with those of two coeval sections poses some problems when ammonoid- and conodont-based stratigraphies have to be correlated. However, good correlation has been obtained for the recognized Middle Triassic ammonoid biozones in the Tethyan realm. Valuable data to the construction of a standard magnetostratigraphic and paleontological scale are contributed by the results from the Margon section.