CARG UNIFE/PAB. Rilevamento geologico Foglio 016 Dobbiaco alla scala 1:50.000.

Rilevamento geologico Foglio 016 Dobbiaco alla scala 1:50.000 secondo le metodologie CARG. Allestimento note illustrative e database. Convenzione Dipartimento di Scienze della Terra - Provincia Autonoma di Bolzano

Emplacement modes of the Ladinian plutonic rocks of the Dolomites. Insights from anisotropy of magnetic susceptibility

In the Dolomites (Eastern Southern Alps, Italy), a diffuse Middle Triassic igneous activity is now present mostly as lava flow and pyroclastic successions, with rare shallow-depth intrusive bodies cropping out at Predazzo, Monzoni and Cima Pape areas. In this work, the emplacement modes of the Predazzo and Monzoni bodies were investigated by means of petrographic and anisotropy of magnetic susceptibility (AMS) data coupled with a field geological study. The presence of intrusive rocks in between these two bodies and the continuity of the metamorphic aureola from west of the Predazzo to east of the Monzoni body suggest that they are parts of a ∼20 km wide SW-NE oriented continuous pluton, sub-parallel to Ladinian strike-slip faults. AMS and petrographic data from the Predazzo body are consistent with a multistage ring-dyke emplacement mode, with areas of upward flow of the magma located in the NW and ESE part of the intrusion, whereas in the southern sector of the pluton our data suggest prevalently horizontal flows. In general, the Predazzo sheets indicate either upward magma flow or along-strike lateral magma transport, and the round shape suggests no influence of Ladinian tectonic structures. On the contrary, the ENE-WSW elongated shape of the Monzoni body was controlled by the occurrence of strike-slip faults associated with Ladinian-tectonics, the feeder being likely located at the NE edge of the body. However, the absence of deformation at the field- and micro-scale is consistent with a post Ladinian-tectonics timing of emplacement, as for the Predazzo pluton

Weathering and sea level control on siliciclastic deposition during the Carnian Pluvial Episode (Southern Alps, Italy)

A higher precipitation regime during the early Late Triassic Carnian Pluvial Episode (CPE; 232–234 Ma) in many marine basins is evidenced by thick siliciclastic deposits, which are coeval with C-cycle perturbations and global warming. However, the mechanisms driving higher siliciclastic deposition are still not fully explored and could be linked to different effects of the climate change on depositional environments. Here, we present the first major, minor and trace elements, and mineralogical data from fine-grained sediments across the CPE in the Dolomites (Southern Alps, Western Tethys). Combining weathering indices (CPA and Rb/K2O), and qualitative and quantitative mineralogical analysis, we recognize two main phases during the CPE. Pre-CPE conditions show no significant weathering variations and some peaks of clay minerals referable to the weathering of Ladinian igneous material. The first C-isotope excursion of the CPE is coincident with an increase of CPA, Rb/K2O and kaolinite, with no change in the sediment-source and depositional setting, that indicate an enhancement of chemical weathering and confirm a shift to more humid conditions at the onset of the CPE. Such a signal from the Dolomites can be correlated with other similar observations from marine and terrestrial settings worldwide. After this first phase, a major sea level fall, probably linked to aquifer-eustasy and/or limno-eustatism, and following important transgression led to the erosion and recycling of older rocks marked by a decoupling of CPA and Rb/K2O and a substantial increase of K-feldspar from older volcanic rocks. The eustatic signal overwhelmed the humid climatic signal that is inferred by independent palynological and paleosol data within the same interval. After the CPE, data show high physical weathering under arid climate. Our results are compatible with the general view that the CPE was linked to injections of volcanic CO2 from Large Igneous Province activity and consequent global warming and enhanced hydrological cycle. This first intensified rock chemical weathering at the onset of the CPE, then promoted higher storage of freshwater on land and a substantial increase of erosion and transport of unweathered material into the basins of the western Tethys, that were rapidly infilled

Magnetostratigraphy and biostratigraphy of the Middle Triassic Margon section (Southern Apls, Italy)

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.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 conodontbased 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. © 2001 Elsevier Science B.V. All rights reserved