Siliciclastic-carbonate sequences of Miocene grabens of northern Sardinia, western Mediterranean sea

Abstract

The small crustal block of Sardinia Island (western Mediterranean) underwent major rifting events during Oligocene-Early Miocene (Aquitanian), Early Burdigalian, and Plio-Pleistocene times. Sedimentation in the resulting extensional and transtensional basins was affected by both local tectonic and worldwide sea-level changes. The mixed siliciclastic-carbonate sequences which developed, are readily comparable with those predicted by sequence stratigraphy. This paper focuses on the post-volcanic, Uppermost Burdigalian to Lower Messinian (?) sedimentation at the confluence between a main N-S trending basin and a secondary SW-NE trending graben, in northern Sardinia. Silty marlstones of Late Burdigalian-Early Langhian age characterize the central part of the main basin, whereas variable siliciclastic and carbonate sequences affected by up to three major transgression and regression cycles developed at its margins and at the confluence with the smaller graben. Differential movements along the main boundary fault led to rotation of blocks which localized narrow, elongated offshore algal carbonate platforms. Low sea-level stand led to deep erosion (type 2 sequence boundary) of these carbonates and to the formation of siliciclastic sandy lowstand wedges. High sea-level stand led to re-establishment of algal platforms at the shelf margin which were bounded farther inland by siliciclastic-carbonate mixed parasequences. Although it is not possible to date directly every stratigraphic unit, local sequences are well structured and can be tentatively correlated with reported worldwide transgressive-regressive events.