Stratigraphy, Sedimentology and Syndepositional
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Rivista Italiana di Paleontologia e Stratigrafia (Research in Paleontology and Stratigraphy) vol. 123(3): 355-378. November 2017 STRATIGRAPHY, SEDIMENTOLOGY AND SYNDEPOSITIONAL TECTONICS OF THE JURASSIC-CRETACEOUS SUCCESSION AT THE TRANSITION BETWEEN PROVENÇAL AND DAUPHINOIS DOMAINS (MARITIME ALPS, NW ITALY) LUCA BARALE1*, CARLO BERTOK2, ANNA D’ATRI2, LUCA MARTIRE2 & FABRIZIO PIANA1 1*Corresponding author. Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse - Unità di Torino, Via Valperga Caluso 35, 10125 Torino (Italy). E-mail: [email protected], [email protected] 2Dipartimento di Scienze della Terra, Università di Torino, Via Valperga Caluso 35, 10125 Torino (Italy). E-mail: [email protected], [email protected], [email protected] To cite this article: Barale L., Bertok C., d’Atri A., Martire L. & Piana F. (2017) - Stratigraphy, sedimentology and syndepositional tectonics of the Jurassic-Cretaceous succession at the transition between Provençal and Dauphinois domains (Maritime Alps, NW Italy). Riv. It. Paleontol. Strat., 123(3): 355-378. Keywords: syndepositional tectonics; palaeoescarpment; Jurassic-Cretaceous; Dauphinois Domain; Provençal Domain; Maritime Alps. Abstract. The Provençal and Dauphinois Mesozoic successions cropping out at the southeastern margin of the Argentera Massif (Maritime Alps, NW Italy) were deposited at the transition between the Provençal platform and the Dauphinois basin, marked in the study area by a partly preserved Mesozoic palaeoescarpment. These successions show important lateral variations occurring over relatively short distances, probably related to synde- positional tectonics. Different stratigraphic intervals of the pelagic-hemipelagic Dauphinois succession contain resedimented deposits, made up of both intra- and extrabasinal material, which provide a twofold evidence of syndepositional tectonics indicating both tectonically-triggered gravitational processes and a tectonically-driven evolution of the source areas. Two stages of syndepositional tectonics have been recognized: the first in the earliest Cretaceous, which is related to the deposition of carbonate breccias in the Dauphinois succession and to hydro- thermal dolomitization of the Middle Triassic-Jurassic Provençal carbonates, and the second in the Late Cretaceous, which triggered the deposition of different detrital lithozones in the Upper Cretaceous Puriac Limestone. The cited evidence indicates that syndepositional tectonics continued to influence the evolution of the Alpine Tethys European passive margin long after the Late Triassic-Early Jurassic syn-rift stage, which caused the differentiation between the Dauphinois basin and the Provençal platform. INTRODUCTION Mesozoic syndepositional tectonics have been in- creasingly recognized in the last decades in several Syndepositional tectonics plays a major role sectors of the Western Alpine chain, often revising in the evolution of modern passive continental previous interpretations that overestimated the role margins, where high-resolution seismic methods of Alpine deformation in generating complex geo- and deep-drilling data allow detailed reconstruc- metries (e.g., Barféty & Gidon 1983, 1984; Dardeau tion of the geometries of faults and sedimentary & De Graciansky 1987; Dardeau 1988; Hibsch et bodies (e.g., Favre & Stampfli 1992; Karner & - Dri al. 1992; Montenat et al. 1997, 2004; Claudel et al. scoll 2000; Moulin et al. 2005; Péron-Pinvidic et 1997; Claudel & Dumont 1999; Bertok et al. 2011, al. 2007; Afilhado et al. 2008; Aslanian et al. 2009).2012; Cardello & Mancktelow 2014). Conversely, in fossil continental margins presently The Mesozoic stratigraphic successions crop- involved in orogenic chains, the direct observation ping out at the southeastern margin of the Argen- of preserved palaeostructures is rare and the recon- tera Crystalline Massif (Maritime Alps, NW Italy) struction of syndepositional tectonics commonly were deposited on the Alpine Tethys European pa- relies on the recognition of indirect evidence, both laeomargin, at the transition between the Provençal stratigraphic and sedimentologic. In the case of the platform and the Dauphinois basin. The present- Alpine Tethys European palaeomargin, currently day geological knowledge about these stratigraphic incorporated in the Alpine orogen, the effects of successions substantially derives from studies ear- lier than 1970, and is summarized in the Geological Received: November 09, 2016; accepted: June 27, 2017 Map of the Argentera Massif at 1:50,000 (Malaroda 356 Barale L., Bertok C., d’Atri A., Martire L. & Piana F. 1970, explanatory notes by Carraro et al. 1970). The gna valleys (Fig. 1). This sector is composed of a set study of the sedimentary successions on the Italian of tectonic units, whose stratigraphic successions side of the Argentera Massif has been resumed in have been referred to the Dauphinois and Provençal recent years by Bersezio et al. (2002), Barale et al. palaeogeographic domains (d’Atri et al. 2016): the (2016a, b) and d’Atri et al. (2016). Entracque Unit, the Roaschia Unit, the Limone-Vio- Detailed stratigraphic and sedimentologic zene Zone (LiVZ), and the Refrey Zone. They form analyses show that syndepositional tectonics play- a SE-NW trending narrow belt, comprised between ed a key-role in the evolution of this part of the the Argentera Massif to the SW and the more inter- European margin throughout the Mesozoic. The nal Briançonnais and Western Ligurian Flysch units Provençal and Dauphinois successions are cha- to the NE (Fig. 1). The Italian side of the Argentera racterized by important lateral variations, occurring Massif and the adjoining sedimentary successions over relatively short distances. Moreover, different have been mapped at 1:50,000 by Malaroda (1970; stratigraphic intervals of the pelagic-hemipelagic explanatory notes by Carraro et al. 1970). More- re Dauphinois succession contain resedimented depo- cently, Barale et al. (2016a) published a detailed map sits, made up of both intrabasinal and extrabasinal of the study area, which the reader is addressed to material, which provide a twofold evidence of syn- for all the cited toponyms and names of lithostrati- depositional tectonics both pointing to tectonically- graphic units. triggered gravitational processes and documenting The Dauphinois and Provençal domains re- tectonically-driven changes in the source and di- present the most internal part of the Alpine Tethys spersal of sediments. European palaeomargin, developed on continental The aim of this paper is twofold: crust. The two domains started to differentiate in the • to describe the Jurassic-Lower Cretaceous Early Jurassic, in response to the extensional tecto- Provençal and Dauphinois stratigraphic succes- nics related to the opening of the Alpine Tethys (e.g., sions, and the overlying Upper Cretaceous succes- Lemoine et al. 1986; Dardeau 1988; De Graciansky sion, cropping out at the southeastern margin of & Lemoine 1988). The stratigraphic successions the Argentera Massif, providing new stratigraphic of the study area (Carraro et al. 1970; Barale et al. and sedimentologic interpretations based on origi- 2016a) start with Permian continental siliciclastic de- nal data; posits, which rest on the crystalline basement of the • to document the multiple stratigraphic and Argentera Massif, and are characterized by marked sedimentologic evidence of syndepositional tecto- thickness changes, reaching a maximum thickness nics recorded in these successions, reconstructing of up to 4000 meters (Faure-Muret 1955; Malaroda the major phases of Mesozoic tectonic activity. 1999). They are followed by Lower Triassic coastal siliciclastic deposits (Valette du Sabion quartzareni- tes) and Middle Triassic peritidal carbonates (Mont METHODS Agnelet Formation). Upper Triassic-Lower Juras- sic deposits consist of a thin stratigraphic interval, Geological mapping at 1:10,000 scale was performed to iden- tify the main tectonic and lithostratigraphic units, and to reconstruct commonly involved in tectonic slicing. This interval primary geometries and stratigraphic relationships. The resulting ge- is present in the Roaschia Unit and in the northern ological map was recently published at 1:25,000 scale by Barale et al. part of the Entracque Unit, whereas it is absent in (2016a). Petrographic studies on 60 uncovered thin sections (30 μm thick) of the collected samples were carried out by optical micro- the southern part of the Entracque Unit (see Barale scopy and cathodoluminescence (CL) with the aim of characterizing et al. 2016a). It consists of (Malaroda 1957; Carraro the main microfacies. CL observations were carried out on polished et al. 1970; Barale et al. 2016a): red and green shales thin sections using CITL 8200 mk3 equipment (operating conditions: (Bec Matlas shales, Late Triassic); fine grained lime- 17 kV, 400 μA). stones and dolomitic limestones, locally with algal lamination, containing beds of flat pebble breccias GEOLOGICAL SETTING and bivalve coquinas (Monte Servatun Formation, Rhaetian-Hettangian); bioclastic packstones and The study area is located at the southeastern wackestones with abundant echinoderm fragments, margin of the Argentera Massif (Maritime Alps, NW cephalopods and bivalves (Costa Balmera Limesto- Italy), between the Gesso and the upper Vermena- ne, Sinemurian). These units indicate a progressive Jurassic-Cretaceous succession of Provençal and Dauphinois domains (Maritime Alps, NW Italy) 357 Fig. 1 - a) Schematic geographical