Abstract

Chertified oolite in the lower part of the Precambrian Bhander Limestones, around Maihar, Madhya Pradesh, India, shows extensive compaction-deformation of ooids into oblate bodies, lying preferably parallel to bedding. Chertification, though begun locally when compaction was only slight, continued through and outlasted compaction-deformation in most parts. Unusual deformation of ooids is caused by overpressurization of ooids against a preburial rigid emersion surface below the chertified oolite. Unlike common fabrics of tectonically deformed rocks, compaction-deformation fabrics are uneven with respect to both shape and orientation of ooids. Though there is a strong tendency for preferred orientation of the deformed ooids parallel to bedding, directional variability is not uncommon. This difference of soft-sediment deformation fabric from that of tectonically deformed rocks mainly stems from the fact that overburden stress is transmitted heterogeneously from grain to grain in unconsolidated sediments. Lithification, on the other hand, homogenizes stress distribution leading to greater uniformity of shape and orientation of fabric elements in tectonically deformed rocks. In addition, the soft-sediment deformation fabric lacks relationship with the external geometry of the rocks.

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