The Middle‑Upper Jurassic unconformity in the South Iberian Palaeomargin, Western Tethysa history of carbonate platform fragmentation, emersion and subsequent drowning

Zusammenfassung

A wide diversity of processes occurred during the fragmentation of the shallow carbonate platform of the Middle Jurassic in the South Iberian Palaeomargin. A detailed study of the Middle-Upper Jurassic discontinuity from the Prebetic (Betic Cordillera) has allowed identifying the formation of hardgrounds and the emersion, erosion and formation of hydromorphic soils. The contact between oolithic and oncolithic limestones of the Middle Jurassic and the spongiolithic limestones of the Middle and Upper Oxfordian is represented by a palaeorelief that suggests the emersion and erosion of the carbonate platform. Locally, erosive palaeorelief is not developed and a hardground characterized by an iron crusts and abundant borings is preserved on the top of the Middle Jurassic oolithic and oncolithic limestones. In other localities, iron crusts were recorded on the top of the Middle Jurassic limestones, which include iron ooids and pisoids and shows an Al-substitution in goethites of 10%. This is an indicator of hydromorphic soils (plinthite) as well as of the presence of kaolinite. This kind of soils developed in coastal plains under tropical climate. The subsequent drowning of the platform in the Middle Oxfordian is recorded by a bed of ferruginous oolithic limestone with abundant planktic foraminifera and ammonites, also bearing iron ooids and pisoids reworked from eroded palaeosoils. Following drowning, sponge meadows proliferated resulting in spongiolithic limestones in the Middle-Upper Oxfordian. This was a mid-shelf environment with hemipelagic infuence as evidenced by the occurrence of siliceous sponges (hexactinellids), planktic foraminifera and ammonites. The comparison of the Prebetic sections studied in this work with other records of the Western Tethys during the same interval highlights the wide variability of features related to this discontinuity in the South Iberian Palaeomargin.