Abstract

Oolitic ironstones or glauco-phosphorites were deposited all along the northern India continental margin during major tectonically enhanced transgressions in Frasnian, Permian, Norian, Callovian, Early Cretaceous, and Paleocene time. These regional events of starvation and drowning were commonly associated with alkalic to tholeiitic magmatism and invariably coincided in time with multiple rifting events that punctuated the progressive disintegration of Gondwana. Deposition of major condensed horizons enriched in iron, silica, and phosphorus was fostered by global factors such as eustatic rise, warm "greenhouse" climates, sluggish circulation, increased fertility, and poor ventilation in the oceans. Such anomalous sedimentary conditions recurred synchronously during magnetic quiet zones, pointing to successive episodes of global fast spreading and accelerated terrestrial heat loss. Multiple "pulsations" of Earth are inferred to have triggered supercontinent breakup and widespread volcanism, thus altering the atmosphere and hydrosphere, and dramatically affecting sedimentary and biological systems.

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