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S. Todaro et al. / Sedimentary Geology 333 (2016) 70–83 75

Fig. 5. Schematic columns of the most common elementary cycles (left) affected by stratabound dissolution and field photographs (right) as observed along a quarry wall; A) biomoldic
dissolution of megalodont shell. Notice the geopetal filling of the molds. B) Vug porosity in well-sorted algal grainstones. Cavities filled up by RFC cements and reddish sediment.
C) Spongy-like dissolution in a bioturbated subtidal unit.

centimeter-scale (5–10 cm in width and length) cavities filled by calcite calcite cement that points to periods of interruption in sediment decan-
cements and reddish sediments that give rise to geopetal structures tation. The composition of the internal sediment is 63.2% calcite with a
(Fig. 5C). The cavities display a clear stratabound thickness that ranges small percentage of quartz, hematite and siderite. Ostracods and Fe-
from 40 cm to more than 1 m of thickness. Up-section the spongy hori- oxide pellets also occur. It is worth noting that the red sediment laminae
zons became less frequent. can be correlated laterally across several pores, suggesting an intercon-
nection between cavities. Isotopic values of two samples have isotopic
18
13
6. Petrographic Observations and Geochemistry values of δ C= −1.13 to 2.29‰ and δ O= −2.26 to −0.61‰ (sam-
ples TS 118 D and CU 48 B in Table 1 and Fig. 9A).
Within the subtidal units affected by spongy-like stratabound disso- Radiaxial fibrous calcite cements (RFC) occur as a rim in the lateral
lution, we differentiate three principle, superimposed zones (Fig. 6): and upper zone of the dissolution cavities (Fig. 6B, C). They are charac-
terized by the diagnostic criteria defined by Kendall (1985), i.e. crystals
1) A lower zone that consists of irregular cavities that are filled up by an that diverge away from the substrate, convergence of optic axes to give
equi-dimensional microcrystalline sediment made of particles of undulose extinction in cross-polarized light and a marked cleavage. In
about 150 μm in diameter (zone 1 in Fig. 6A).
2) An intermediate zone consisting of cavities, or parts of cavities filled the RFC we observed dark zones of reddish silt that represent events
of sedimentation during the crystal growth (Fig. 7B), indicating that
up either by laminated reddish sediments or by radiaxial fibrous ce- the accretion of RFC is almost contemporaneous with the slow and dis-
ments (zone 2 in Fig. 6A).
continuous decantation of the laminated internal sediment (Fig. 6B).
The reddish sediment consists of alternating laminae with different The presence of twin lamellae (Fig. 7E) in some crystals implies recrys-
textures, from muddy to peloidal with, in places, a reverse grading tallization during burial diagenesis (Railsback, 1993). Under CL, the RFC
(Fig. 7A). The individual laminae show a variable color from light cements have a moderate to dull luminescence with some thin, lumi-
cream to dark red in relation to the amount of hematite. The laminae nescing zones, suggesting precipitation under oxidizing conditions
are commonly separated by a thin (100 to 200 μm) rim of isopachous with periods of suboxic crystal growth (Fig. 7C, D). Moreover the