Sedimentary response to intra-arc extension: controls on Oligo-Miocene deposition, Sarcidano sub-basin, Sardinia

Abstract

The Oligo-Miocene Sardinian rift is a rare example of a well exposed intra-arc basin comprising several independent depocentres. Synthesis of field observations from one such depocentre, the Sarcidano sub-basin in central Sardinia, not only allows a new and integrated sedimentological and tectonostratigraphic history for the area, but also provides insights into controls on syn- and post-rift sedimentation in intra-arc settings. Initial rifting during the late Rupelian–early Chattian (Oligocene) occurred on NW–SE-trending normal faults and produced a half-graben topography which controlled the dispersal of locally supplied coarse continental clastic sediments. Latest Chattian–Aquitanian (Miocene) NE–SW-trending normal faulting defined a more complex ‘block’ topography that remained underfilled in all areas except those which received voluminous ignimbritic volcanic material. Subsequent marginal- and shallow-marine sedimentation progressively infilled the fault topography as sea level rose. Deposition of coarse clastic sediments eroded from fault scarps was focused in the hanging-wall depocentres of the intersecting fault trends, whilst platform carbonates became established in topographically higher areas protected from clastic sedimentary supply. Finally, as the relative rise in sea level drowned sediment source areas in the Burdigalian, deeper-marine marlstones dominated sedimentation. The results demonstrate that the Sarcidano sub-basin was dominated by a mixed volcanic–siliciclastic–carbonate basin fill with abrupt facies changes developed in response to complex fault-defined topography, relative rise in sea level and an episodic volcanic supply. Whilst the rift structure largely controlled the provenance, supply and accumulation of sediments, relative sea level primarily controlled the types of facies that developed.