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Dahanayake, Kapila
- Study of Red and Brown Earth Deposits of North-West Sri Lanka
Authors
1 Department of Geology, University of Sri Lanka, Peradeniya, LK
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 20, No 9 (1979), Pagination: 433-440Abstract
Geological, mineralogical and chemical studies of Red and Brown Earth deposits of Northwest Sri Lanka reveal both fluvial and aeolian origins. It has been established that the colour of sediments change from brown, reddish brown to red in that order with increasing Fe+++ content.
- Upward Regressing Energy Sequences in a Limestone Section from the French Jura
Authors
1 Ecole Nationale Superieure de Geologie, Appliquee et de prospection miniere, Nancy, FR
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 20, No 12 (1979), Pagination: 587-597Abstract
Textural and compositional studies of a limestone section from the Upper Jurassic of the French Jura Mountains reveal a series of sequences of lithofacies, each sequence marking a progressive reduction of water turbulence (energy). The Limestones are oolitic, pelletiferous and oncolitic packstones, wackestones and mudstones.- Formation of Phosphatic Coated Grains and Peloids by Grain Diminution of Precambrian Apatite Crystals
Authors
1 Institute of Fundamental Studies, Hantana Road, Kandy, Sri Lanka, LK
2 Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka, LK
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 35, No 2 (1990), Pagination: 189-197Abstract
Due to tropical physical and chemical processes active on a Precambrian apatite marble formation, primary apatite crystals were removed from the parent rock and deposited in different types of depressions within a thick weathering profile. The primary apatite crystal margins show a microcrystalline envelope characteristic of coated grains. The envelope may extend towards the centre of the grain eventually forming a wholly microcrystalline apatite body out of the initial coated grain, thus producing a peloid by the process of grain diminution.
Microbial mats grow within the depressions engulfing the primary apatite crystals. coated grains and peloids of variable size. Continuous surficial processes together with subsurface percolation of sediment and nutrient-rich waters help to maintain the growth of the laminated stromatolitic groundrnass. Grain diminution seems to play an important role during diagenetic process in the phosphate micro-sedimentary environment of the depressions within the apatite marble formation. The grain diminution of Precambrian single apatite crystals to form a phoscrete-type phosphorite is perhaps a unique phenomenon.