Arenites turbiditic

The turbiditic arenites of S3 (Petrofacies B2) contain fewer carbonate intrabasinal grains (silici-clastic arkosic arenites) (Figs 4A,B and 5C). The siliciclastic fraction is qualitatively similar to that of sequences S1 and S2 (Fig. 4B,C) and came from the same source. 

The heavy mineral composition in the Vetto-Carpineti area (Fig. 1) (Zuffa, 1969 Fontana Spadafora, 1994) shows that metamorphic minerals such as allanite, pistacite, chloritoid, glaucophane, hornblende, orthopyroxene and augite are abundant in shelf arenites from the basal members, whereas in Vetto turbidites they are very minor constituents. Ultrastable minerals such as tourmaline, zircon and rutile are ubiquitous, but the greater amounts occur... 

Generally the calcite cements are characterized by relatively low average mol% of Fe (1.0%), Mg (0.6%) and Mn (0.2%) (Table 2). Cements in the turbiditic arenites have somewhat more Fe than those in the shelf hybrid arenites (av. 1.4% and 0.6%, respectively) (Table 2). Bioclasts such as echinoderms, originally composed of high-Mg calcite, show low Mg contents, which confirms their pseudomorphic replacement. Calcite which replaced feldspar grains is occasionally Sr rich (up to 2.1% SrC03) (Fig. 6F Table 2). 

K-feldspar occurs as overgrowths and fracturehealing of detrital K-feldspar, and as discrete K-feldspar crystals (Fig. 9A) disseminated in both shelf and turbidite arenites in trace amounts. K-feldspar overgrowths and discrete crystals are covered and engulfed by, and therefore pre-date, calcite cement (Fig. 9A). The diagenetic K-feldspar shows a near stoichiometric KAlSijOg end-member composition. 

Fig. 10. Generalized paragenetic sequence in the shelf hybrid arenites and in turbidite feldspathic litharenites.

Fig. 12. Plot of carbonate grains% versus intergranular calcite cement% showing the positive correlation between amounts of bioclasts and cement in S1 and S2 arenites and between carbonate fragments and cement in S4 turbidites.

---