Page 1 - Spongy-like

Page 1 - Spongy-like_2016

P. 1

Sedimentary Geology 333 (2016) 70–83

Contents lists available at ScienceDirect

Sedimentary Geology

journal homepage: www.elsevier.com/locate/sedgeo

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

a,
b
S. Todaro ⁎, C. Hollis , P. Di Stefano a
a
Department of Earth and Marine Sciences, University of Palermo, Via Archiraﬁ 22, Palermo, Italy
b
School of Earth, Environmental and Atmospheric Science, University of Manchester, Manchester M13 9PL, United Kingdom
article i nfo abstract

Article history: This paper focuses upon the analysis of a complex paleokarstic system recorded within uppermost Triassic
Received 21 September 2015 peritidal cycles in northwestern Sicily. Besides documenting spectacular karstiﬁcation at the Triassic/Jurassic
Received in revised form 10 December 2015
boundary, it provides an example of stratabound ‘spongy’ or ‘swiss-cheese’ dissolution. On the base of ﬁeld ob-
Accepted 11 December 2015 servations, microfacies analysis, transmitted-light and cathodoluminescence petrography and stable-isotope
Available online 23 December 2015
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
Editor: B. Jones
realms during the relative cyclic oscillations of sea-level.
Keywords: The presence of a fresh water supply from an adjacent emerged area is the key for the periodic formation of a
Carbonate platform mixing water lens during the relative sea level lowstand that brought about the subaerial exposure of the plat-
Diagenesis form. The resulting dissolution pattern in the subtidal unit of a speciﬁc cycle is strongly controlled by the textural
Stratabound dissolution features of the sediments. In the case of bioturbated wackestones the ‘spongy’ or ‘swiss-cheese’ pattern develops,
Spongy-like pattern while in mollusk-rich beds biomoldic porosity occurs. In well-sorted subtidal members, such as algal grainstones,
Triassic the dissolution originates as randomly distributed vuggy porosity. During periodic ﬂooding of the platform, a new
Sicily
subtidal unit is formed and the dissolution stops as fully marine phreatic conditions are re-established.
© 2015 Elsevier B.V. All rights reserved.

1. Introduction dissolution pattern. The morphological comparison between swiss-
cheese and spongy-like cavities seems appropriate. The latter authors
Dissolution processes in modern and ancient carbonate platforms favor dissolution from the formation of a marine-meteoric mixing
are very variable in shape and size as a result of different forcing factors zone. Moreover, the presence of CO 2 from bacterial sulfate reduction
(James and Choquette, 1988). Climate, sea-level ﬂuctuations, texture, and/or root action can increase the water's potential for dissolution
diagenetic features and tectonism, are among the most important con- (Back et al., 1986; Smart et al., 1988; Walter and Burton, 1990).
trolling factors in the generation of different scales of dissolution from Bioturbation may also facilitate dissolution; several authors have de-
microkarstic cavities to giant blue-holes (Esteban and Klappa, 1983; scribed traces of bioturbation expressed by tunnels, vugs and channels
Mylroie and Carew, 1995; Whitaker and Smart, 1998; Moore, 2001; in modern (e.g. Beach, 1995) and Mesozoic carbonate limestones
Smart et al., 2006). (Droser and O'connell, 1992; Lehmann, 1974; Scheweigert et al., 1997;
The literature contains numerous examples of dissolution features in Tonkin et al., 2010, among others). Bioturbators create their burrows,
modern (Smart et al., 1988; Beach, 1995) and ancient carbonate plat- which can have widely varying dimensions, in sub-lithiﬁed muddy ho-
forms (Choquette and Pray, 1970; James and Choquette, 1988; Christ rizons. Burrows also have a distinct shape and are generally ﬁlled by
et al., 2012 and references therein). However, one of the features that sediments and microcrystalline calcite. These networks appear to form
are less discussed is a particular type of porosity named “swiss-cheese” a template for subsequent diagenetic modiﬁcation and can therefore
solution, which results in stratabound, centimeter-sized, rounded cavi- have an important impact on hydrocarbon charge and productivity in
ties forming a complex pore network (Back et al., 1986). Baceta et al. oil and gas ﬁelds (e.g. Hollis, 2011).
(2001, 2007) described a similar type of porosity from upper Danian The aim of this paper is to analyze an intense, stratabound dissolu-
platform limestones in the western Pyrenees, Spain, as a “spongy-like” tion that affects the uppermost Triassic peritidal cycles cropping out in
northwestern Sicily (Italy), with the purpose of contributing to the dis-
cussion on the processes that leads to the particular dissolution mor-
⁎ Corresponding author.
E-mail addresses: simona.todaro@unipa.it (S. Todaro), cathy.hollis@manchester.ac.uk phology hereafter named “spongy-like”. Based on ﬁeld observations,
(C. Hollis), pietro.distefano@unipa.it (P. Di Stefano). microfacies analysis, transmitted-light and cathodoluminescence

1 2 3 4 5 6