Root mats, calcified

Platy Consists of centimetre-thick plates, up to tens of centimetres in diameter, commonly found above hardpan or chalky layers. Plates may be tabular or wavy in form and may exhibit crude lamination. Some are fragmented calcified root mats. Distinguished from brecciated laminar calcrete by a lack of strong laminations... 

Figure 2.5 (A) Laminar calcrete (arrowed) overlain by an oolitic—pisolitic layer associated with a calcified root-mat layer, Holocene soil. La Mora area, Tarragona, northeast Spain (see Calvet and Julia, 1983). (B) Stage V-VI profile with hardpan layer overlain by pisolitic and brecciated level with a prominent calcified root-mat layer (arrowed), from San Miguel salinas area, Torrevieja, Alicante, southeast Spain. Such a profile would correspond to a thickened, polyphase profile as shown on the right of Figure 2.8.

Wright et al. (1995), based on studies of rhizogenic palaeosol calcrete profiles from southern Europe, proposed the rhizogenic model (Figure 2.7C). In Mesozoic palaeosols from northern Spain, they identified progressive profile development by calcified root mats from a few isolated laminar levels to thick (>2m) dense carbonate sheets. In early Cenozoic successions in southern France they noted stages of development from scattered Microcodium remains to entire sheets composed almost wholly of this component. 

Wright, V.P., Platt, N.H. Wimbledon, W.A. (1988) Biogenic laminar calcretes evidence of calcified root-mat horizons in palaeosols. Sedimentology 35, 603-620. 

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