Borello Formation

Fig. 2. Sketch showing the diverse patterns of calcite cement in sandstones of this study (from McBride el al., 1995). (A) Sandstone beds inteibedded with mudrock are completely cemented by calcite (1), cemented in two rows of spheroidal concretions (Borello Formation only, 2), cemented only in the lower one-third (3), or are cemented in concretions located chiefly at the base of the beds (4). (B) Stacked sandstone beds are cemented in tabular concretions parallel with bedding (2) or parallel with faults...

Fig. 4. Localization of authigenic calcite (c) on dissolving silicate grains. Back-scattered electron images. (A) Calcite replaces parts of two K-feldspar grains (K) from the M. Cervarola Formation. (B) Partial calcitization of an epidote grain (e) in the Borello Formation.

Fig. 5. Authigenic ferroan dolomite overgrowth (o) on a core of fractured detrital dolomite (d) from the Bismantova Formation. Overgrowth development preceded precipitation of calcite cement. Similar dolomite overgrowths are observed in the Borello Formation. Back-scattered electron image.

Fig. 6. Pressure dissolution ofForaminifera. Dark grey grains are quartz. Calcite cements the grains and also fills the intraskeletal pores. Back-scattered electron images. (A) Bismantova Formation. Large grain in lower right is a mica. (B) Borello Formation.

The lA Pliocene, Ranzano and Antognola formations were cemented by meteoric water the Bismantova Formation was cemented in part by water with a meteoric component the Loiano and the Borello formations were cemented by slightly modified marine pore water and all the foreland basin units (except the Borello) were cemented by water variably enriched in 0 (8 0 = -2 to +8) generated from silicate reactions. The most 0-enriched values for S 0, a,er are compatible with depths and temperatures of cementation of the three deepest formations, but not for the less deeply buried Loiano and upper part of the Mamoso-arenacea formations. 0-enriched fluids in these latter formations were more probably derived from underlying, more deeply buried rocks apd expelled by compaction. Possibly, the calcite in the deepest buried formations re-equilibrated with hot water after precipitation. 

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