Carbonate rock fragments

Carbonate rock fragments could also be a source of calcite cement if they are available in the source area and if they survive transport. In the Palaeogene sandstones of the North Sea we have found intervals containing up to 55 vol% chalk clasts, for instance, and carbonate rock fragments have also been reported from sandstones in other basins (e.g. Richmann et al., 1980 Dickinson, 1988 Taylor, 1990). However, carbonate rock fragments are probably more stable than biogenic carbonate because of their low-Mg-calcite composition and coarser crystal size. 

Fig. 3. QFL triangle for 10 stratigraphical units. Data from Valloni et al. (1991), Bruni et al. (1994) and this study. Dashed lines indicate foreland basin units. Q, quartz F, feldspar, L, lithics, including extrabasinal carbonate rock fragments.

Assessment of intraconcretion variations in minor and trace element concentrations of calcite was undertaken in nine vein samples, three host rocks (carbonate content dominantly carbonate rock fragments, CRFs), and 29 other samples of concretions and generalized cements, including seven concretions for which multiple analyses were performed at different places relative to the centre of the concretion (Table 5). 

This study aims to decipher and compare the dia-genetic evolution of hybrid arenites and arenites rich in carbonate rock fragments belonging to the Bismantova-Termina succession, a synorogenic sequence of the northern Apennines (Fig. 1). Special emphasis is given to the roles of the complex detrital composition, provenance and facies organization of the arenites in their carbonate cementation. 

Fig. 8. 6 CpDB versus 5 Opdb plot of representative diagenetic and detrital calcite in the various depositional sequences of the Bismantova-Termina succession. Arrow denotes the probable derivation of S4 cements from marine carbonate rock fragments.

Arrowsmith, J.R., Rice, G.E. Hower, J.C. (1998) Documentation of carbon-rich fragments in varnish-covered rocks from central Arizona using electron microscopy and coal petrography. Science. 

Furthermore, carbonate rocks are susceptible to dissolution, which commonly removes shell fragments. Many limestones exhibit evidence of increases in grain size and crystallinity with increasing age of deposit. 

CBKT Quartz, feldispar, muscovite, rock fragments Very few carbonate Fine Subarkose... 

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