Clay cutan

Clay Cutans are a geologic fabric that develop around ancient cavities (such as peds) within paleosols.

Formation

Clay Cutans form by the coating of ancient open spaces by colloidal materials that were elluviated down from overlying horizons - and are commonly stained by iron oxides such as hematite. While the originally openings are commonly lost through geologic time and diagenesis, the cutanic fabric remains as evidence. Cutans also often contain relics of nodules and skeleton grains. ^[1]

They are one of the most diagnostic features of paleosols.

Recognition

Clay Cutans are most easily recognized under cross polarized light where they anisotropic. Cutans usually show lineations caused by the preferred orientation of clay minerals.

Practical Significance

Clay Cutans inherently indicate illuviation and therefore may indicate the presence of a petroleum seal in an underlying layer if silica had been transported to that depth. The J2 sandstone in Medicine River Gas Field in Alberta, Canada was cemented in such a manner. ^[2]

References

1. ^ Retallack, G.J., 1988. Field recognition of paleosols. In: Paleosols and weathering through geologic time: Principles and Applications, Reinhardt, J. and Sigleo, W.R. (eds.). Geological Society of America, Special Paper, 18 pp.
2. ^ Wright, V.P., 1992. Paleosol recognition: A guide to early diagenesis in terrestrial settings. In K.H. Wolf and G.V. Chilingarian: Diagenesis III, Developments in Sedimentology 47, Elsevier Science Publishers B.V., 591-619.