Depositional biofacies model for post-OAE1a Aptian carbonate platforms of the western Maestrat Basin (Iberian Chain, Spain)

• Rudist clingers dominated internal platform tops, elevators margins and upper slopes.
• Distribution of different rudist morphotypes reflects the influence of sedimentation.
• Prevalence of polyconitids in Aptian platform heralds their widespread proliferation.

Two well exposed platform successions of late Early Aptian age developed in the central part of the Galve sub-basin of the Maestrat Basin: the highstand ‘Camarillas–El Morrón’ platform, and the succeeding ‘Las Mingachas’ small lowstand platform, built out downslope in the former basin. Both platforms had a flat-topped non-rimmed depositional profile, showing similar platform-top to slope biofacies, which are described here in both qualitative and quantitative terms. The proximal platform top succession is characterized by a Toucasia-dominated rudist association. The margins of the two platforms consist of massive limestone characterized by a Polyconites-dominated association, in which clusters of Polyconites hadriani in life position are joined by both branching and domal corals, as well as the oyster-like Chondrodonta and nerineid gastropods. In Las Mingachas platform, where the massive rudist- and coral-rich platform limestones pass laterally into the slightly more marly and recessive clinoforms of the upper slope facies, Polyconites is especially abundant. Basinwards these slope deposits pass into basinal marls with orbitolinids and ammonoids. The distribution of the two distinct rudist associations recognized here is attributed to the different environmental tolerances of the rudists with respect to such factors as current regime and rate of sedimentation. The prevalence of polyconitids, in place of caprinids, in these late Early Aptian platform margin facies makes a striking contrast with older, earliest Aptian platforms.