Spongy-like porosity in peritidal carbonates: An interaction of cyclic sea-level oscillations, fresh water supply and sediment texture

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• 作者：S. Todaro^a ; ^{simona.todaro@unipa.it" class="auth_mail" title="E-mail the corresponding author} ; C. Hollis^b ; ^{cathy.hollis@manchester.ac.uk" class="auth_mail" title="E-mail the corresponding author} ; P. Di Stefano^a ; ^{pietro.distefano@unipa.it" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Carbonate platform ; Diagenesis ; Stratabound dissolution ; Spongy-like pattern ; Triassic ; Sicily
• 刊名：Sedimentary Geology
• 出版年：2016
• 出版时间：15 March 2016
• 年：2016
• 卷：333
• 期：Complete
• 页码：70-83
• 全文大小：5402 K

文摘

This paper focuses upon the analysis of a complex paleokarstic system recorded within uppermost Triassic peritidal cycles in northwestern Sicily. Besides documenting spectacular karstification at the Triassic/Jurassic boundary, it provides an example of stratabound ‘spongy’ or ‘swiss-cheese’ dissolution. On the base of field observations, microfacies analysis, transmitted-light and cathodoluminescence petrography and stable-isotope analyses we put forward an original model for the formation of this peculiar stratabound dissolution. It implies a complex interaction of several controlling factors at the interface between the marine and meteoric diagenetic realms during the relative cyclic oscillations of sea-level.

The presence of a fresh water supply from an adjacent emerged area is the key for the periodic formation of a mixing water lens during the relative sea level lowstand that brought about the subaerial exposure of the platform. The resulting dissolution pattern in the subtidal unit of a specific cycle is strongly controlled by the textural features of the sediments. In the case of bioturbated wackestones the ‘spongy’ or ‘swiss-cheese’ pattern develops, while in mollusk-rich beds biomoldic porosity occurs. In well-sorted subtidal members, such as algal grainstones, the dissolution originates as randomly distributed vuggy porosity. During periodic flooding of the platform, a new subtidal unit is formed and the dissolution stops as fully marine phreatic conditions are re-established.