The 5th International Conference of Geobiology

The Ediacaran and its transition into the Cambrian period are characterized by significant disruptions in the global carbon cycle, highlighted by major carbon isotope excursions that serve as critical markers for chronostratigraphic subdivision and correlation. Much of our current understanding of these global carbon cycle perturbations has stemmed from geochemical studies of marine carbonates from this period. In this study, we investigate the least studied Ediacaran – early Cambrian mixed-siliciclastic and carbonate sequence in the Hazara Basin of the Western Lesser Himalaya in North Pakistan, which provides a unique geological archive for refining the chemostratigraphic framework and for gaining deeper insights into carbon cycle dynamics. We present new δ¹³C_carb data from three stratigraphic sections in the Hazara Basin, which reveal the presence of global carbon cycle perturbations in the form of three notable negative δ¹³C_carb excursions, each exceeding –5‰. The first excursion, with a nadir of –5‰, which is found within a newly identified Ediacaran cap-carbonate in the basal Tanakki Member of the Kakul Formation, corresponds to global cap carbonate negative excursion (CANCE). The second excursion, located in the upper part of the Mahmdagali Member and extending into the overlying Sirban Member of the Abbottabad Formation, reaches a nadir of –9‰ and bears a close resemblance to the globally recognized Shuram/DOUNCE excursion, as observed in sections from Oman, Australia, and South China. The third excursion, although locally expressed, occurs in the upper part of the Sirban Member of the Abbottabad Formation with a nadir of –5‰ and may correlate with basal Cambrian carbon isotope excursion (BACE). Combine with recent biostratigraphic data, the upper Sirban negative excursion further suggest that the Ediacaran – Cambrian boundary lies within the upper part of the Sirban Member. Our findings not only reveal significant global carbon cycle perturbations—likely analogous to the Shuram/DOUNCE and BACE events—in the Hazara Basin but also refine the chronostratigraphic framework for the successions in question. However, further chemostratigraphic data integrated with radioisotopic dating are needed to advance the understanding of the spatial and temporal calibrations of these negative excursions. Ultimately, these future efforts will contribute to a more comprehensive understanding of carbon isotope dynamics and the associated biogeochemical change across the pre-Himalayan northwestern margin of the Indian Plate.
 

Ediacaran, Cambrian, Carbon isotope excursions, Western Lesser Himalaya, Pakistan, Shuram, DOUNCE, BACE, Chronostratigraphic framework