CARBONATE DEPOSITS CARBONATE DEPOSITS THROUGH AGESTHROUGH AGES

SOUMYABRATA BISWASSOUMYABRATA BISWASUG-IIIUG-III

GEOLOGICAL SCIENCESGEOLOGICAL SCIENCESJADAVPUR UNIVERSITYJADAVPUR UNIVERSITY

•“Present is the key to the past”.

•Does not true always.

•“Present is the key to the Pleistocene”.

Why law of UNIFORMITARIANISM is not applicable?The major controls on carbonate facies are geotectonics and climate.

Some evidencesCARBONATE SANDREEF COMPLEXESTEMPORAL FLUCTUATION IN MARINE CARBONATEDEPOSITIONDOLOMITE PROBLEM

•Why PLEISTOCENE?

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 PRESIPITATESPCO2 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.