Revised palynological correlations of the lower Potomac group (USA) and the cocobeach sequence of Gabon (Barremian-Aptian)

Abstract

Dating of the lower Potomac Group (Zone I), the oldest exposed Cretaceous unit of the Atlantic Coastal Plain of the USA, has relied on palynological correlations with marine sections elsewhere in Southern Laurasia. Correlation with sections in Northern Gondwana, such as the Cocobeach sequence of Gabon, has been hampered by differences due to climate. However, recently described palynofloras from intermediate areas show more overlap of elements, allowing stepwise correlations between the two provinces. A key element is the coarsely reticulate monosulcate angiosperm Brenneripollis, which appears near the base of the Aptian in England. Brenneripollis occurs in basal Potomac samples from Delaware City well D12 and outcrop localities previously dated as Barremian, favoring an early Aptian age. Other lower Zone I angiosperms include ‘Clavatipollenites’, Stellatopollis, Similipollis, Afropollis and very rare tricolpates. Upper Zone I, which contains more reticulate tricolpate pollen, has been dated as early Albian, but associated Brenneripollis grains correlate better with the middle Aptian of Egypt. This age is also favored by the presence of the zonasulculate genus Schrankipollis in upper Zone I and the Aptian of Egypt. Zone C-VII of Gabon, which contains the first reticulate tricolpates and zonasulculate species of Afropollis, has been dated as early Aptian. However, it seems older than the presumed basal Aptian of Egypt, which contains Brenneripollis and striate tricolpates, not seen until Zone C-VIII, and there are putative late Barremian occurrences of Afropollis in Nova Scotia, England, Morocco, Libya and Israel. Together with reports of tricolpates from the Barremian and Aptian of England, these results eliminate the supposed lag in migration of tricolpate-producing plants from Gondwana into Laurasia, but Northern Gondwana does appear to have been their main center of diversification.