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S. Todaro et al. / Sedimentary Geology 333 (2016) 70–83 81

Fig. 12. Reconstructed profile of the carbonate platform showing a mixing water lens, floating on the marine phreatic zone, that is created by a fresh water recharge from an adjacent
exposed landmass. The position of the lens varies during lowstand and highstand stages. Not to scale.

textural features of the subtidal facies occurring along the succession: carbonate platforms supports the influence of a mixing water lens.
i) bioturbated mudstone–wackestone, ii) mollusk-shell mudstone– Field and petrographic observations tie the formation of this lens to
wackestone, and iii) skeletal grainstone to packstone. the cyclic exposure of the platform.
Keeping in mind the conceptual model (Fig. 13), when the lowstand The limited areal extent of the observed dissolution morphologies as
mixing-water lens was stationed in bioturbated horizons the spongy compared to the entire carbonate platform points to the importance of a
dissolution was created. In contrast, when the mixing zone was posi- fresh water recharge from an adjacent exposed land for the mixing zone
tioned on mollusk beds, biomoldic dissolution occurred and in the ab- formation.
sence of both textures, other forms of dissolution (e.g. vuggy) were Sediments and microcrystalline calcite that usually filled tunnels
most likely created. All pores interpreted to have formed in the mixing and burrows, were subsequently dissolved and replaced by several gen-
zone have at least a basal layer of reddish silt (Fig. 5B–C). erations of radiaxial fibrous cements, polychrome sediments and later
A final, interesting point is the occurrence of Mg-inclusions in RFC blocky calcite.
cements. These most likely represent residual high Mg concentrations Our data highlight the strong textural control exerted by the biotur-
from a high Mg-calcite precursor, which has since stabilized to low bation, by the fossil content or by the absence of both in determining the
Mg calcite. Sandberg (1983) interpreted oscillations between seawater resulting solution patterns.
that preferentially precipitated calcite, versus an aragonitic and high In other words, when the mixing zone was stationed on the biotur-
Mg-calcite sea, to be controlled by global concentrations of CO 2 . In par- bated mud, where a differential porosity and permeability existed, the
ticular, calcite seas corresponding to times of high CO 2 and aragonite dissolution preferentially assumed the spongy shape. In the presence
seas to times of low CO 2 , correlate respectively with Fischer's (1984) of abundant mollusk shells, dissolution operated by the mixing waters
greenhouse and icehouse conditions. The Triassic/Jurassic boundary re- preferentially created biomoldic porosity, while without a strong
cords such a transition from icehouse (aragonitic and high Mg calcite macrotextural control a vuggy porosity developed.
seas) to greenhouse (calcitic seas) conditions (Taylor, 2007)due to an
increase of magmatic activity, related to the Central Atlantic Magmatic
Province (McElwain et al., 1999; Hesselbo et al., 2002). Our data demon- Acknowledgments
strate that high Mg calcite was still dominant as a seawater precipitate
immediately beneath this important stratigraphic boundary. Data presented here were performed in the frame of the PhD of S.T.
We are deeply indebted with Andrea Mindszenty, Budapest, for the
8. Conclusions training of S.T. in carbonate diagenesis in the frame of a grant provided
by the University of Palermo. We thank Giuseppe Zarcone (Palermo) for
The analysis of the intense stratabound dissolution recorded by the the generous support in field mapping, sampling and discussions on the
uppermost Triassic peritidal cycles in northwestern Sicily allowed us dynamics of the Panormide Carbonate Platform. Gyori Orsi (Budapest)
to put forward some data and interpretations about the possible mech- for the discussions and photographs on the field. Constructive reviews
anism of formation of the peculiar pattern of dissolution known as by Alessandro Iannace (University of Naples) and Luca Martire (Univer-
spongy-like or swiss-cheese. sity of Turin) helped improve the manuscript. Many thanks also to the
This peculiar pattern is interpreted to have formed in response to Williamson Resource Centre at the School of Earth and Atmospheric Sci-
dissolution, overprinting a texture determined by an intense precursor ence of University of Manchester in which S.T. has had the possibility to
bioturbation by decapods, favoring a differential and faster dissolution use the equipment for CL observations and electron probe microanaly-
of the burrows infill. The morphological comparison of the spongy- sis. Financial support provided by Miur/Prin 2008 and by the University
cavities with similar dissolution patterns in modern and ancient of Palermo (PJ_AUTF_005550) granted to P.D.