The Miocene Saint-Florent Basin in Northern Corsica: Stratigraphy, Sedimentology, and Tectonic Implications William Cavazza,N Peter G
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Basin Research (2007) 19, 507–527, doi: 10.1111/j.1365-2117.2007.00334.x The Miocene Saint-Florent Basin in northern Corsica: stratigraphy, sedimentology, and tectonic implications William Cavazza,n Peter G. DeCelles,w Maria Giuditta Fellin,n 1 and Luigi Paganellin z nDepartment of Earth and Geoenvironmental Sciences, University of Bologna, Bologna, Italy wDepartment of Geosciences, University of Arizona,Tucson, Arizona, USA Department of Geology, Palaeontology and Geophysics, University of Padua, Padua, Italy z ABSTRACT Late early^early middle Miocene (Burdigalian^Langhian) time on the island of Corsica (western Mediterranean) was characterized by a combination of (i) postcollisional structural inversion of the main boundary thrust system between the Alpine orogenic wedge and the foreland, (ii) eustatic sealevel rise and (iii) subsidence related to the development of the Ligurian-Provenc° al basin.These processes created the accommodation for a distinctive continental to shallow-marine sedimentary succession along narrow and elongated basins. Much of these deposits have been eroded and presently only a few scattered outcrop areas remain, most notably at Saint-Florent and Francardo.The Burdigalian^Langhian sedimentary succession at Saint-Florent is composed of three distinguishing detrital components: (i) siliciclastic detritus derived from erosion of the nearby Alpine orogenic wedge, (ii) carbonate intrabasinal detritus (bioclasts of shallow-marine and pelagic organisms), and (iii) siliciclastic detritus derived from Hercynian-age foreland terraines.The basal deposits (Fium Albino Formation) are £uvial and composed of Alpine-derived detritus, with subordinate foreland- derived volcanic detritus. All three detrital components are present in the middle portion of the succession (Torra and Monte Sant’Angelo Formations), which is characterized by thin transitional deposits evolving vertically into fully marine deposits, although the carbonate intrabasinal component is predominant.The Monte Sant’Angelo Formation is characteristically dominated by the deposits of large gravel and sandwaves, possibly the result of current ampli¢cation in narrow seaways that developed between the foreland and the tectonically collapsing Alpine orogenic wedge.The laterally equivalent Saint-Florent conglomerate is composed of clasts derived from the late Permian Cinto volcanic district within the foreland.The uppermost unit (Farinole Formation) is dominated by bioclasts of pelagic organisms.The Saint-Florent succession was deposited during the last phase of the counterclockwise rotation of the Corsica^Sardinia^Calabria continental block and the resulting development of the Provenc° al oceanic basin.The succession sits at the paleogeographic boundary between the Alpine orogenic wedge (to the east), its foreland (to the west), and the Ligurian-Provenc° al basin (to the northwest). Abrupt compositional changes in the succession resulted from the complex, varying interplay of post-collisional extensional tectonism, eustacy and competing drainage systems. INTRODUCTION that rifting of Corsica^Sardinia^Calabria from Europe was the result of upper plate extension related to slab The islands of Corsica and Sardinia and the surrounding roll-back along the Ionian subduction zone. Although continental shelves are a fragment of European^Iberian the exact timing is still far from precisely known (see lithosphere, which, together with Calabria, rifted o¡ the Speranza, 1999, for a discussion), rifting started as early southern continental margin of Europe during Oligo- as the early Oligocene (Vially & Tre¤ molie' res, 1996) cene^Miocene time and drifted southeastward by coun- whereas drifting occurred between ca. 22 and 15 Ma terclockwise rotation (Alvarez, 1972, 1976; Alvarez et al., (Ferrandini etal., 2003). Rifting reactivated Pyrenean com- 1974) of about 45 . Malinverno & Ryan (1986) ¢rst proposed 1 pressional structures of the Late Cretaceous^Early Eocene Provenc° al foldbelt (Vially & Tre¤ molie' res, 1996). Subse- Correspondence: William Cavazza, Department of Earth and quent rifting of Calabria from Corsica^Sardinia during Geoenvironmental Sciences, University of Bologna, Piazza di the late Miocene isolated Corsica^Sardinia between the Porta S. Donato 1, 40126 Bologna, Italy. E-mail: william.cavazza @unibo.it Ligurian-Provenc° al basin to the northwest and theTyrrhe- 1 Present address: Geologisches Institut, ETH Zˇrich, Switzer- nian Sea to the east (see Cavazza et al., 2004a, b, for a re- land. view) (Fig.1). r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd 507 W. Cavazza et al. s lp 45¼N A Francardo in Ap s en Pyrenees a n B in Alpine l e a s ç Hercynian Corsica n e T v yr Corsica ough o rh Tr r e P n Aleria ia Iberia n Plain 40¼N lencia S a e V a 0 100 200 Km Neogene Bonifacio 0¼ 10¼E 20¼E sediments 5 km Marine de Farinole Cima di Gratera Gulf 1026 of St. Florent Bastia Monte Genova 421 Col de Teghime St-Florent 536 Casta Nebbio Tenda Massif Balagne Continental and Metamonzogranite coastal deposits Monte Asto T e of Monte Asto Unit Quaternary 1535 n Metagranodiorite - St. Florent Fm d Metatonalite of L. Langhian a Casta Unit Mt. S.Angelo- and Monzogranite- M Torra Fms Metamonzogranite a Burdigalian- s of Monte Genova Unit s L. Langhian Late Carboniferous - i Fiume Albino Fm f Permian Volcanic Succession Burdigalian Lower Schistes Neogene fault S Lustrés Autochtonous c L u foreland sediments Balagne Nebbio Nappes h Upper Schistes thrust i s Eocene Mesozoic-Paleogene t Lustrés thrust reactivated as sediments s an extensional fault Hercynian granitoid t r Farinole, Oletta and é rock and pre-Hercynian Jurassic Ophiolite- e Serra di Pigno thrust reactivated as s s a strike slip fault crystalline country rock bearing unit orthogneiss Fig.1. Schematic geologic map of northern Corsica within the framework of the Mediterranean region. Modi¢ed after Cavazza et al. (2001) and Fellin et al. (2005). As the Corsica^Sardinia^Calabria block rifted away components. Remnants of the older portions of this basin from Europe, the progressively widening Ligurian-Pro- ¢ll are preserved in Corsica and are referred to as the venc° al basin was £ooded by marine water. Situated be- Saint-Florent Basin (Fig.1). Most striking are stacked de- tween the extending Provenc° al margin of Europe and a posits of very large-scale gravelly and sandy bedforms and fragment of the collapsing western Alpine orogenic wedge intercalated sediment-gravity £ows. The tectonic setting (Fig. 2), the basin was ¢lled with a diverse assemblage of of the Saint-Florent Basin between the extending orogenic lithofacies that include both carbonate and siliciclastic wedge and the foreland produced a narrow paleostrait 508 r 2007 The Authors. Journal compilation r 2007 Blackwell Publishing Ltd, Basin Research, 19, 507^527 Miocene Saint-Florent Basin WSW Balagne Tenda massif St. Florent ENE s.l. 5 km St. Florent succession Hercynian basement Schistes Lustrés s.l. Nebbio and Balagne Nappes Eocene foreland sediments Tectonised Hercynian basement Farinole-Oletta orthogneiss Fig. 2. Schematic cross-section across northern Corsica (see Fig.1for location of trace of section). Solid arrows indicate Alpine-age contractional faulting; open arrows indicate (i) late Oligocene normal faults that reactivated Alpine thrust faults, and (ii) Neogene high- angle normal faults. Modi¢ed after Cavazza et al. (2001). where oceanic (probably tidal) currents were strongly am- Florent, Francardo, the Aleria plain and Bonifacio (Fig. 1) pli¢ed. The purpose of this paper is to document the (e.g. Orszag-Sperber & Pilot, 1976; Alesandri et al., 1977; Saint-Florent Basin ¢ll and to assess its potential signi¢ - Groupe Francais d’Etude du Neogene, 1989; Cubells et al., cance for understanding the history of rifting and orogenic 1994; Ferrandini et al., 1998, 2002, 2003; Loy« e-Pilot et al., collapse in northern Corsica, as well as its implications for 2004; Fellin et al., 2005).The successions at Saint-Florent, the Oligocene^Neogene tectonic evolution of the western Francardo and Bonifacio are thin and cover almost pre- Mediterranean. Our results should be useful for evaluating cisely the same time span (Burdigalian-Langhian).The se- other Neogene basins in the Mediterranean region, where dimentary succession of the Aleria Plain spans Burdigalian upper plate (or back-arc) rifting events in response to sub- to Pliocene time and represents the onland portion of the duction zone retreat (Royden, 1993) are widespread (e.g. 48 km-thick o¡shore Corsica basin to the east (Mau¡ret Jolivet & Faccenna, 2000; Cavazza et al., 2004a). et al., 1999), which developed during rifting of Calabria from the Corsica^Sardinia block. This paper describes and interprets the Miocene succession at Saint-Florent within the framework of the post-collisional evolution of GEOLOGIC SETTING Corsica and the western Mediterranean. Corsica is divided into two distinct geologic terranes (Fig. 1). The western part of the island is characterized by Carboniferous^Permian granitoid rocks and acid volcanic STRUCTURE OF THE BALAGNE ^ rocks related to the Hercynian orogeny, with Precambrian^ BASTIA TRAVERSE middle Palaeozoic metamorphic host rocks and scattered outcrops of Palaeozoic sedimentary rocks.The northeast- The Saint-Florent Basin lies along the Balagne^Bastia tra- ern portion of the island (‘Alpine Corsica’) is a nappe stack verse (Fig. 2), which arguably constitutes the best-studied dominated by Jurassic oceanic crust and its sedimentary part of