Sandstone central, composition

In marine turbidite sandstones of the central basin, following minor siderite precipitation, dolomites formed early in the zone of methanogenesis. These have Ca-rich compositions similar to dolomites reported from contemporaneous fine-grained rocks of the Monterey Formation, coastal California. The dolomites are an example of young (< 6 Ma) dolomite formation at shallow burial depth in marine pore water, and they may have undergone some recrystallization during shallow burial without resetting their initial Sr/ Sr values. 

Fig. 5. Oxygen and carbon isotopic composition of early-formed dolomite cements in sandstones of the central San Joaquin basin.

In the central part of the Illizi Basin and over the Ghadames Depression (WT-i, HD-i, RYB-i, AKF-i) we observe sediments characteristic of deeper marine environments, i.e. fine-grained sandstones with intercalations of clays and silts. The characteristic feature of these Siegenian sandstones is the chloritic composition of the clay fraction of their cements and the chloritic-illitic nature of the argillaceous intercalations. Because of this situation, these deposits could have been derived from a hard substrate (effusive or metamorphic rocks) inundated by the Siegenian sea and open into the direction of the present Libyan coast. 

Table 10.9 Averagechemical composition to fourvolcaniclastic sandstones from the upper Buckley Formation (Permian) in the central Transantarctic Mountains (Barrett et al. 1986 Table 11)...

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