Anomalous phosphorus episodes during Callovian-Oxfordian times in the Kachchh Basin, western India: Implications for palaeoclimate, productivity, and weathering

The Upper Callovian-Oxfordian strata of the Kachchh Basin, western India, record three positive excursions of phosphorus. They have been documented in three sections of the Chari Formation from different parts of the basin. Corroboration of field and petrographic data with trends of major and trace elemental data and elemental ratios of the strata revealed that these excursions were coeval with reduced chemical weathering in the source area and significant reduction of siliciclastic influx to the depositional sites. The study also revealed the intrabasinal source of P, and minor sea-level fluctuations and resultant episodic sediment recycling as the causative factors. Considering the geographic locations of the three sections, the phosphorus anomalies seem to be controlled by a regional and/or basin-scale process, if not linked with global signals. Temporal resolution of these anomalies suggests that the processes were episodic and related to short term climate/relative sea-level cycles, the durations of which could be unraveled with high-resolution biostratigraphic data.