Calcrete laminar

Verrecchia, E.P., Freytet, P., Verrecchia, K.E. Dumont, J.L. (1995) Spherulites in calcrete laminar crusts biogenic CaC03 precipitation as a major contributor to crust formation. Journal of Sedimentary Research 65, 690-700. 

The significance of the calcrete tongue became apparent after geochemical analysis of samples from the test pits showed elevated Au concentrations. Importantly, the highest concentrations (>50 ppb Au) were confined to the laminar... 

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... 

Laminar Consists of sheets of laminated carbonate, in which the laminae are on a millimetre-scale. The term is synonymous with soilstone crust . Some forms are dark in colour. They commonly occur capping hardpan layers but can also occur within chalky layers or in the host sediment or soil. They can be interlayered with pisolitic calcretes on a centimetre-scale. Most are only a few centimetres thick but some forms can reach 2 m and can be... 

Stringer domal in form. This type of calcrete is strongly polygenetic in nature Closely related to laminar calcretes but not all forms are well laminated. These are sheets of carbonate, usually only a few centimetres thick, of subvertical to sub-horizontal form, that penetrate into carbonate-rich hosts and are related to root mats. They can occur singly or at multiple levels and varied orientations, extending for metres, and can cross-cut each other... 

Pisolitic Millimetre- to centimetre-sized coated grains in layers typically only a few centimetres thick but up to metres thick at the bases of slopes. Can develop in a variety of hosts but are common on coarse-grained hosts. Laminae are generally micritic. Inverse grading is commonly seen. Commonly occur above laminar calcretes... 

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. 

Pulsed sedimentation stabilization with laminar calcrete development... 

Figure 2.9 Characteristics of groundwater calcretes. (A) Generalised macroscopic features based on various sources. Some workers, such as Carlisle (1980), identify two zones in the massive phreatic unit an upper earthy zone with remnant soil and alluvium, and a lower, dense porcellaneous zone with abundant cracks and cavities. Phreatophytic plants may also produce features such as rhizocretions and laminar rhi-zolite crusts (Seminiukand Meagher, 1981). (B) Generalised model for the evolution of groundwaters and their precipitates in semi-arid to arid alluvial systems based on Arakel (1986).

Alonso-Zarza, A.M. (1999) Initial stages of laminar calcrete formation by roots examples from the Neogene of central Spain. Sedimentary Geology 126, 177-191. 

Alonso-Zarza, A.M. Silva P.G. (2002) Quaternary laminar calcretes with bees nests evidence of small-scale climatic fluctuations, Eastern Canary Islands, Spain. Palaeogeography, Palaeoclimatology, Palaeoecology 178, 119-135. 

Klappa, C.F. (1979) Lichen stromatolites criterion for subaerial exposure and a mechanism for the formation of laminar calcrete (caliche). Journal of Sedimentary Petrology 49, 387-400. 

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

---