A fossil flora of Miocene age has been preserved by karstic agencies in a solution subsidence complex developed in a large exotic block of limestone, part of the Gwna Group mélange (?Cambrian), at Trwyn y Parc, Cemaes Bay, Anglesey. The flora suggests that the Menaian Surface and the Snowdonian Mountain block were already well established landscape features by the end of the Miocene. The wider geomorphological implications of the find are briefly discussed.

A fossil flora of Miocene age has been preserved by karstic agencies in a solution subsidence complex developed in a large exotic block of limestone, part of the Gwna Group mélange (?Cambrian), at Trwyn y Parc, Cemaes Bay, Anglesey. The flora suggests that the Menaian Surface and the Snowdonian Mountain block were already well established landscape features by the end of the Miocene. The wider geomorphological implications of the find are briefly discussed.

Dolomites formed in upper Turonian–lower Coniacian Cueva Formation carbonates in the El Ribero area (Burgos province, northern Spain) have been investigated. Carbonate banks up to 30 m thick are massive or poorly structured along several kilometres, but at this location they contain clinoforms that dip away from the central area of the Rosío diapir, producing a dome-like structure. Three main diagenetic processes affected the El Ribero carbonates: silicification, dolomitization and subsequent dedolomitization. Silicification was mainly early, producing chert nodules from Thalassinoides burrows and replacing anhydrite cauliflower-type geodes, converting them into quartz geodes and silicified fossils (corals, echinoderms and oysters). Dolomite occurs immediately below the first order Coniacian Sequence Boundary (CSB) and is restricted to the diapiric area of influence. The dolomite has a flat top, whereas its base is irregular, suggesting downward movement of dolomitic fluids. Isotopic data from the dolomite (δ18O=−3.4‰PDB and δ13C= 1.1‰PDB) are similar to values reported from both evaporative and mixing zone dolomite. Finally, an intense and locally destructive dedolomitization produced significant dissolution. This affected the unsilicified organisms, and was followed by the development of meteoric-water poikilotopic calcite cements and radiaxial calcite geodes infilling dissolution cavities (isotopic values for later calcite are δ18O=−7.4‰PDB and δ13C=−9.0‰PDB). In addition, palaeokarstic horizons formed as a result of diapiric uplifts that caused collapse structures and vugs of several centimetres in size infilled by laminated sediments. All these features suggest that the diapiric movements could have been synsedimentary and particularly active during the Cueva Formation deposition.