Page 6 - Tondietall2015

Italian Journal of Geosciences Accepted manuscript

planar and cross-beds from 20 cm to 1 m thick, dipping 5-10° ESE (fig. 2a). As a whole, the
grainstones are made up of a variety of sub-rounded bioclasts (i.e., Vermetus, Serpula, bivalves,
echinoids, red algae and corals) ranging in size from about 100 microns to a few centimeters (fig.
2b; TONDI et alii, 2012). Calcite cements are volumetrically scarce (less than 2% of the total rock
volume) and consist of microsparry cement at the grain contacts and/or within intragranular pores,
and syntaxial overgrowth cement around echinoid plates and spines.

MAJELLA CARBONATE GRAINSTONES
The Orfento Formation strata (~15 m in thickness) exposed along the Madonna della Mazza
quarry consist of bioclastic proximal turbidites (MUTTI et alii, 1996; CILONA et alii, 2012) in form
of normal graded, planar beds, tens of decimeters thick and dipping 10-20° NE (fig. 2c). Turbidite
beds largely consist of poor-to-fair consolidated grainstones, white in color (gray-weathering) and
grading upward to well-consolidated packstones, wackestones and mudstones at the top (uppermost
a few centimeters) of individual beds. A few calcareous breccia layers, tens of centimeters thick,
also occur.
Grainstones are made up of subangular to subrounded rudist fragments, and minor micritic
intraclasts, ranging in size from about 20 microns to a few centimeters (fig. 2d). Echinoid plates and
spines, as well as Orbitoides are occasional. Cements account only for less than 2% of the total rock
volume, and consist of discontinuous rims of microsparry calcite crystals around individual pores
(CILONA et alii, 2012).

POROSITY AND PORE STRUCTURE OF THE TWO CARBONATE GRAINSTONES
Favignana grainstones are very heterogeneous and their porosity (mostly intergranular) may
drastically vary lithofacies-by-lithofacies. TONDI et alii (2012) reported porosity ranging between
30% (2D) and 50 % (triple weight method). Helium pycnometer measurements we performed in