CARBONATE DEPOSITS THROUGH AGES SOUMYABRATA BISWAS UG-III GEOLOGICAL SCIENCES JADAVPUR UNIVERSITY
<ul><li>“ Present is the key to the past”. </li></ul><ul><li>Does not true always. </li></ul><ul><li>“ Present is the key to the Pleistocene”. </li></ul>
Why law of UNIFORMITARIANISM is not applicable? The major controls on carbonate facies are geotectonics and climate. Some evidences CARBONATE SAND REEF COMPLEXES TEMPORAL FLUCTUATION IN MARINE CARBONATE DEPOSITION DOLOMITE PROBLEM <ul><li>Why PLEISTOCENE? </li></ul>Holocene carbonate sediment reflects recent changes in sea level that can be used to interpret PLEISTOCENE carbonate formations.
CARBONATE SAND Deposited high energy environment Relative abundance of marine carbonate rocks during the Phanerozoic Pattern of global sea-level change during Phanerozoic
OOLITE IS NON SKELETAL CARBONATE GRAINSTONES.IT’S ABUNDANCE ALSO DEPENDS ON GLOBAL SEA-LEVEL. Abundance of Oolite in Phanerozoic limestone sequences.
SKELETAL GRAINSTONES PALEOZOIC dominated by brachiopod,crinoidal,bryozoans and corals . MESOZOIC dominated by bivalves CAINOZOIC dominated by mollusc,brachiopod and echinoderm Diversity,abundance and composition of calcareous marine organisms
REEF COMPLEXES Occurrences of major reef complexes
TEMPORAL VARIATION IN PHANEROZOIC MARINE PRESIPITATES TWO MAJOR CONTROLS ON MARINE PRESIPITATES PCO 2 Mg/Ca ratio MARINE PRECIPITATES- High Mg Calcite and Aragonite Calcite-Mg content generally low Mineralogy of marine carbonate precipitates through Phanerozoic
DOLOMITE PROBLEM Why dolomites are much more common than limestones in Precambrian compared with the Phanerozoic? The relative abundance of limestones and dolomites through time.
ABUNDANCE OF DOLOMITES MOSTLY DEPENDS ON CA/MG RATIOS. Ca/Mg ratio in carbonate rocks.