Aragonite dissolution, sedimentation rates and carbon isotopes in deep-water hemipelagites (Livinallongo formation, Middle Triassic, northern Italy)

Abstract

In a recent contribution to this journal Preto et al. (2005) present stratigraphic results and correlations of sediments of the Middle Triassic Buchenstein basin (Buchenstein/Livinallongo Fm.) of the Southern Alps. The data are then used for quantifying the rates of pelagic sedimentation and for the interpretation of observed dissolution features. Because we feel that some relevant conclusions presented therein are either not supported by field evidence or have been proposed previously, with this discussion we intend to clarify some aspects of the geology of the hemipelagic Buchenstein basin. The aspects discussed here address the following points: 1) the reliability of the proposed stratigraphic correlations and the importance of the post-depositional diagenetic modification for assessing the variations in rates of sedimentation; 2) the origin and rates of sediment accumulation of the Plattenkalke versus the Knollenkalke; 3) aragonite dissolution versus compation-driven diagenesis and the bias of the fossil record. Graphical logs of the Buchenstein sediments along with stratigraphic and sedimentologic analysis demonstrate that the Buchenstein basin was fed from different sediment sources whose relative importance has changed through time and space (e.g., Ogilvie Gordon, 1927; Viel, 1979; Bosellini and Stefani, 1991; Brack and Rieber, 1993; Maurer and Schlager, 2003). Relevant for the assessment of basinal sedimentation rates proposed in Preto et al. (2005) are the new data presented for two basinal sections (Rio Sacuz, San Marco) along with information mainly adapted from the literature (Seceda, Bagolino).