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

Fig. 4. A) Subtidal member consisting of a coral boundstone (Rethiophillia sp.) growing on a bioeroded surface. B) Erosional surface capped by a black pebble lag at the base of a muddy
subtidal member. C) Mudstone–wackestone with Triasina hantkeni. D) Grainstone–packstone with characean gyrogonites. Burrows with retextured sediment fill are evident.
E) Mudstone–wackestone with Favreina sp. F) Particular of a burrow infill with “tramples” that are interpreted as the successive burrow floor (Gingras et al., 2007).

(Fig. 5). Finally, on the macroscale a cavernous porosity formed by calcispheres, and very rare benthic foraminifers. The burrows, created
decameter-scale collapsed breccia bodies, particularly close to the Trias- by sediment-dwelling organisms, are often branched or interconnected.
sic/Jurassic (T/J) transition. We focus here only on the spongy-like hori- The organisms modified the original texture of the sediments so that the
zons to understand the mechanism of their formation, bearing in mind burrow fill exhibits an inhomogeneous micrite fabric with a greenish/
that the cavernous porosity is clearly related to successive dissolution grayish color. In some cases, the burrows can be infilled with coarse-
episodes, as large fragments of the spongy-like beds are common ele- grained sediments transported during storms or hurricanes (Wanless
ments in the collapse breccias. et al., 1988; Tedesco and Walness, 1991). The intense bioturbation of
the muddy sediment is also seen in thin section (e.g. sample CU35,
5. The Spongy-like Horizons Fig. 4D), where frequent, irregular burrows up to 8–10 mm in diameter
are filled by a finely crystalline carbonate sediment which is coarser and
The spongy-like horizons occur only in the subtidal facies, within a well sorted compared to the non-burrowed part of the limestone. In
few cycles of Rhaetian age. The best exposures are observed in an aban- some cases the burrow infills show irregular laminae known as “tram-
doned quarry (here named as Quarry D) along walls cut by diamond ples” that are interpreted as the successive burrow floor (Gingras
wire. et al., 2007).
The host rock consists of a bioturbated mudstone with rare skeletal The dissolution cavities forming the spongy-like pattern occur in the
grains and fecal pellets such as decapod coprolites (Fig. 4E), ostracods, upper zone of the bioturbated sediment and appear as a network of