http://www.ceemar.org/dspace/handle/11099/209 http://www.ceemar.org/dspace/retrieve/116 http://www.ceemar.org/dspace/handle/11099/209 Search the Channel search http://www.ceemar.org/dspace/simple-search http://www.ceemar.org/dspace/handle/11099/246 Title: Mn-crust todorokite mineralization on SW backshore Cretaceous limestones from the island of Dugi Otok (Central Adriatic, Croatia) <br/> <br/>Authors: LUGOVIĆ, Boško; ŠEGVIĆ, Branimir <br/> <br/>Abstract: The southwest shore of the island of Dugi Otok is characterized by the unusual sample occurrence of Mn-hydrated oxide mineralization in the form of botryoidally and globular, fine-laminated concentric aggregates, crusting the Upper Cretaceous backshore limestones. The mineralization consists mainly of Fe impoverished 10-Å tecto-manganate todorokite (enriched in Mg and transition metals) accompanied by accessory MnO·OH. Todorokite chemical composition is typical of a hydrogenous origin in an oxic shallow marine environment. According to our model, Mn has been recurrently leached and mobilized from the Late Pleistocene sea floor sediments located around 50 nautical miles south of Dugi Otok. We propose a link between the Mn-geochemical anomaly of these sediments and the alteration of distinct, spatial close pre-Holocene tephra, dispersed over the entire recent Adriatic area. Key words: 10-Å manganates, todorokite, hydrogenous origin, pre-Holocene tephra, Dugi Otok island, Adriatic INTRODUCTION The island of Dugi Otok is a part of the Adriatic carbonate platform and belongs to the Dinaridic orogenic mountain chain. The coastal outline of the orogenic topography was ultimately reshaped by extensive sea level rise during Holocene deglaciation (Fig. 1). The island consists entirely of gastropods fosiliferous Upper Cretaceous limestone and minor dolomite (MAMUŽIĆ et al., 1967) showing various karstification morphology phenomena (DŽAJA, 2003). The Mn-mineralization presented by the predominant todorokite and accessory Mon, 29 Oct 2007 22:58:59 GMT