Sedimentary mudrocks

The geological record shows that this material-transport mechanism has operated for at least 3.8 billion years. New sediments are derived either from older sedimentary rocks or from newly generated or ancient igneous and metamorphic rock. The average chemical composition of suspended sediment in rivers, sedimentary mudrock and the upper continental crust is quite similar (Table 4.1). 

Table 4.1 Average chemical composition of upper continental crust, sedimentary mudrock and suspended load of rivers. Data from Wedepohl (1995) and Taylor and McLennan (1985).

This suggests that rivers represent an important pathway of material transport (Table 4.2) and that sedimentary mudrocks record crustal composition during material cycling. 

Sedimentary rocks within the lower (mainly felsic) part of the volcanic pile are highly variable and not voluminous. Greenish grey to dark grey mudrocks and volcaniclastic rocks occur locally in the FLB, MB, NF, SL and SR formations (Fig. 

Sedimentary rocks in the upper (mainly mafic) part of the pile are predominantly mudrocks, but they have an exhalative component. Maroon shale and chert are present in the BB, LR, and SK formations (Fig. 1). Notably, maroon shale and chert are abundant in the CLL Formation and also occur locally near the top of the FLB and SR formations. Caradocian black shale and pelagic chert of the BB, LR, and SK formations mark the end of volcanic activity in the BMC. In places, these rocks grade upward into flysch of the M or T formations (Fig. 1). 

Potter, P. E. 2003. Mudrocks. In Middleton, G. V. (ed) Encyclopedia of Sediments and Sedimentary Rocks. Kluwer Academic Publishers, Dordrecht, 451-459. 

Milliken K. L. (1995) Petrographic evidence of open-system chemical reactions in mudrocks in the Gulf of Mexico sedimentary basin. Geological Society of American Annual Meeting 27(6), p. 461. 

Most sedimentary kaolinite is detrital in origin and forms in the soil. But it is also found in mudrocks, clastie sediments and eoal as an authigenic mineral, formed at shallow depth where temperature is low. 

Numerous researchers have published variants of the Castagna mudrock equation (Fig. 6.19). In 1993, Castagna et al. compiled an analysis of data for different sedimentary rocks. The following consideration gives a part of the results. Table 6.12 lists a selection of the modified equations based on a compilation by Mavko et al. (1998). 

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