RICERCA ITALIANA     

LATE PALEOZOIC/MESOZOIC HERITAGE IN THE STRUCTURE OF THE ALPINE OROGEN

Università degli Studi di Pavia

Abstract

The research project is aimed to the investigation of depositional and deformational structures of pre-alpine age (mostly mesozoic but also earlier) responsible for the following build up of the alpine orogen, especially in the Dauphinois, Briançonnais, Prepiemontese and eastern Southalpine domains.. For this purpose studies concerning both depositional (corniolas, gaps, hardgrounds) and tectonic (block tiltings, unconformities, synsedimentary faulting) events will be enhanced to reconstruct their evolutionary trend and the present-day geology. The comparison amongst the gathered results in the different sectors will allow the reconstruction of the sindepositional kinematic evolution of the two opposite continental margins. The final goal will be the elaboration of a model for the whole chain where the single elements of the nappes could be inserted.

Principal Investigator

Alberto LUALDI Università degli Studi di PAVIA

Research Objectives

As the obiective of the research program, common to the three local Units, a full "modern" revision of the stratigraphy and sedimentology of the Jurassic-Paleogene succession will be done, and it will have the following goals:
- Check of the extension and characters of the Liassic emersion. In particular the study of the sediments associated to the discontinuity will provide information both on the sedimentary environments and on the degree of the associated erosion and gaps due to the rifting and preceding the drowning;
- Detailed control of the stratigraphy of the Upper Triassic and Middle-Upper Jurassic, in order to improve the biostratigraphic knowledges, highlight the facies and thickness variations, find stratigraphic evidence for synsedimentary tectonics (sedimentary dykes, anomalous stratigraphic characters of pelagic sediments leaning on paleoslopes,etc);
- Acquisition of data and sedimentological reinterpretation of the Cretaceous-Paleogene succession, keeping in mind the existence of an unconformity of fundamental importance at the Cretaceous - Cenozoic boundary in the adjoining Provençal Dauphinois domain. Thereby the relationships between tectonics and sedimentation during the Eocene will be explained and some hypotheses on the sandy sediments provenance and the benthic platform foraminifera associations will be formulated.
The final goal will be moreover in the elaboration of a model for all the sector of the chain where every single >>>

First Results

The main results which are expected from this research are:
- reconstruction of the tectono-sedimentary evolution of the Ligurian Briançonnais and Provençal Dauphinois domains between the Late Triassic and Eocene and of the Mesozoic for the eastern Southalpine, with production of original mappings in key sectors;
- comparison between the different evolutions of the studied domains and interpretation of the paleogeographic relationships both during the Mesozoic structuration of the continental passive margins and during the birth of the alpine foreland basin;
- comparison between the deformational styles of the two studied domains in order to evaluate the role of the preceding stratigraphic and structural heritages;
- verification of the validity of a multidisciplinary approach to the study of sedimentary successions involved in orogenic chains and affected by an intense polyphase tectonization.

As to the temporal organization of the program geological mapping, structural analysis, stratigraphic section measurement will be concentrated in the first year; the second year will be devoted to map and structural data processing and to laboratory analyses (petrography, micropaleontology, possibly geochemistry) and to control of field data.

Timescale

24 months

National and international background

A paleogeographical reconstruction of an area, by means of analyses of sedimentary successions, is a fundamental step for understanding its geological structure.
The recent reconstructions of the Western Alps chain have been mainly focused on the identification of the deformational processes due to the subduction and exhumation phases and considerable progresses have been achieved in the knowledge of phenomena and reconstruction of geometries.
The same detail has not been applied to the study of the deformational history which influenced the formation and evolution of the basins where the sedimentary covers, subsequently involved in the alpine orogenesis, were deposited.
Some unquestionable examples of Mesozoic, if not earlier, heritage where the history and the sequence of the events could be surely reconstructed, demonstrates how the existence of major sindepositional tectonic lines, early detachment from mother-areas, reduced or no sedimentation zones are the signal of a not exhausted geodynamic behaviour that for a long time drove the building of the alpine orogen.
The complex synsedimentary tectonic evolution of the paleoeuropean passive margin led to a structuration characterized by significative litostratigraphic lateral variations at all scales, which represented a fundamental heritage for the alpine chain formation. More in detail, both paleotectonic heritages, repeatedly influencing facies and depositional geometries, and >>>