Island dolostones: Genesis by time-transgressive or event dolomitization

Thick Cenozoic dolostone successions found on many isolated carbonate islands have commonly been attributed to dolomitization events, whereby time-restricted dolomitization processes repeatedly affected the original limestone successions. Any model invoked to explain dolomitization of these successions depends on accurate dating of the events because that may allow correlation with other processes such as sea level oscillations or climate change. The Sr-87/Sr-86 ratios available from island dolostones throughout the world, which have been used to date dolomitization under the premise that seawater mediated its formation, indicate that most of these island dolostones developed between the late Miocene and late Pleistocene (similar to 10 to <0.5 Ma). Analysis of available Sr-87/Sr-88 ratios (n = 348) shows that (semi-)continuous time-transgressive dolomitization processes linked to tectonic subsidence and sea level changes underpinned the development of island dolostones. Islands that experienced rapid subsidence generally have much thicker dolostone successions than those islands that experienced minimal subsidence and/or uplift. It is readily apparent that the tectonic history of an island must be factored into any model developed to explain the evolution of the dolostones. Further refinement of the time-transgressive dolomitization genesis model of island dolostones will require more Sr-87/Sr-86 ratios from the thick dolostone successions found on islands that experienced substantial tectonic subsidence. (C) 2019 Elsevier B.V. All rights reserved.