Facies types and depositional cyclicity of a Toarcian–Aalenian(?) carbonate-siliciclastic mixed succession (Cabo Carvoeiro Formation) in the Lusitanian Basin, Portugal

The Toarcian–Aalenian(?) Cabo Carvoeiro Formation in the Lusitanian Basin (LB), Portugal, is characterized by a succession of mixed carbonate–siliciclastic sediments deposited under the influence of an active horst-graben system caused by the progressive tectonic uplift of the Berlengas basement block. Towards the top of the succession, this formation is characterized exclusively by grainstone facies (CC5 member), in contrast with the overall marly hemipelagic sediments of the coeval Sao Giao and Povoa da Lomba Formations in the onshore LB region. A new subdivision of the CC5 member is here proposed based on outcrop observations and petrographic analysis, with three new subdivisions being identified, in addition to two pre-existing ones, and leading to the definition of the CC5a to CC5e sub-units. These are generally characterized by grainstone facies containing varying quantities of intraclasts, ooids, skeletal grains and quartz extraclasts. A detailed facies scheme was developed to allow for an interpretation of spatial facies variability and facies cyclicity inserted in a sequence stratigraphy framework. The CC5c to CC5e sub-units are interpreted to mark a departure from point-source deposition in a submarine fan-like setting to line-source deposition closer to the Berlengas platform edge, with the development of infralittoral prograding wedges. Deposition of these sub-units occurs during the late stages of a 2nd order regression phase, which culminates in a regionally recognizable discontinuity. Minor tectonic pulses accompanying the gradual decrease in relative sea-level influence the accommodation space variability, which is infilled by high sediment production/influx from the nearby high energy depositional settings of the Berlengas platform margin.