The Middle Jurassic Alpine Tethyan Unconformity and the Eastern Sardinia - Corsica Jurassic High: A sedimentary and regional analysis

Abstract

Investigations performed along the Middle Jurassic Alpine Tethyan unconformity surface of E Sardinia evidenced an elaborate surface that developed over older Late Paleozoic to Triassic rocks. This surface is covered by the Middle Jurassic Genna Selole Fm, which has different sedimentological and petrographical characteristics and thicknesses according to its location and the morphology and evolution of the lower substrate.An analysis of the unconformity and the rocks located above and below it revealed that a tectonic high emerged early during the Middle Jurassic from E Sardinia to Corsica in response to the extensional tectonics leading to the Alpine Tethys opening. This high was almost immediately fragmented in secondary blocks, and an irregular morphology of minor lows and highs thus formed upon it. The high was, on the whole, subjected to strong erosion. Its deposits accumulated along the rims of the high and in the lows of its surface, smoothing the landscape and preparing it for the marine transgression that followed. The tectonic high rapidly collapsed starting from its North side as show the older age of the marine deposits first investigated.A similar rise-and-collapse tectosedimentary evolution can be seen in some of the W Mediterranean domains next to the Sardinia-Corsica block. Indeed, they are all related to the Alpine Tethys opening and may mark a discontinuous high separating the Paleoeuropa from the Tethyan domain. Consequently, a comparison with all of these domains has been attempted by trying to set the Sardinia-Corsica block in this extensional margin scenario.Keywords: Alpine Tethys, Unconformity, Jurassic, Paleogeography, Sedimentology, Eastern Sardinia-Corsica Tectonic high ResumenInvestigaciones llevadas a cabo en la superficie discordante del Jurásico Medio del Tetis alpino evidencia que esta superficie está muy elaborada y se desarrolló sobre rocas que abarcan desde un registro Paleozoico Superior a Triásico. Esta superficie está cubierta por la Fm Genna Selole, de edad Jurásico Medio, que tiene diferentes características sedimentológicas y petrológicas y una potencia que depende de su localización y la morfología y evolución del substrato inferior.Un análisis de esta discordancia y de las rocas localizadas por encima y debajo de la misma revela que hubo un importante alto tectónico in etapas iniciales del Jurásico Medio que afectaba desde el E de Cerdeña a Córcega en respuesta a una tectónica extensional relacionada con la apertura del Tetis alpino. Esta área elevada fue rápidamente fragmentada en bloques desarrollándose una morfología de zonas altas y deprimidas previa a la transgresión marina que llegó seguidamente. Por los datos que muestran los primeros registros marinos se puede deducir que la fragmentación del citado alto tectónico se inició por su parte norte. Una evolución similar en zonas altas y bajas puede observarse igualmente en otras zonas del Mediterráneo occidental próximas al bloque de Córcega-Cerdeña. De hecho, todas ellas están relacionadas con la apertura de...

A palaeoenvironmental reconstruction of the Middle Jurassic of Sardinia (Italy) based on integrated palaeobotanical, palynological and lithofacies data assessment

“…1) are restricted to the Genna Selole Formation (Scanu et al 2012;Costamagna 2015Costamagna , 2016. The more than 700 rock slabs with Jurassic plant macrofossils discussed in this paper come from three fossil collections.…”

“…The alluvial fans were covered by palustrine-coastal plains, the plains by transitional to marine lagoons and bars. At the end, sea covered them all and the carbonate Jurassic shelf sedimentation recovered (Costamagna 2015(Costamagna , 2016.…”

“…9). During the Early Jurassic, the area was covered by a shallow sea with carbonate sedimentation (Cherchi 1986;Costamagna 2016). During the early Middle Jurassic, the opening of the Alpine extension of the Tethys triggered the ephemeral rise of the Eastern Sardinia block, and the gradual shallowing of the western part of the island (Costamagna 2016).…”

“…The thickness of the Genna Selole Fig. 2 Stratigraphy of the Monte Rosé Quarry with evidenced the sampled area (modified after Cherchi and Schroeder 1986) Formation varies, depending on its geographical position (Dieni et al 1983;Costamagna 2016). In the Tacchi area (Central Sardinia), it reaches up to 78 m in thickness but decreases northwards to a few metres in the Supramonte and Baronie area (NE Sardinia) and tends to disappear totally.…”

“…During the Early Jurassic, the area was covered by a shallow sea with carbonate sedimentation (Cherchi 1986;Costamagna 2016). During the early Middle Jurassic, the opening of the Alpine extension of the Tethys triggered the ephemeral rise of the Eastern Sardinia block, and the gradual shallowing of the western part of the island (Costamagna 2016). The rise of the eastern part of Sardinia triggered the erosion of part of the older successions down to the Paleozoic Variscan basement, the Middle Triassic-Early Jurassic carbonate deposits and the remains of the Carboniferous to Permian rocks left behind by the former erosive events.…”