Upper Cretaceous radiolarians reworked in the Eocene London Clay Formation, SE England

Abstract

Radiolarians were recently discovered in the lower Eocene London Clay Formation of the London Basin from samples in a drainage borehole in the River Thames. They come from a c. 10 m thick sequence of silty shales in the lower part of the formation. The radiolarians are, in general, rather poorly preserved, with the exception of six samples that yielded moderately preserved radiolarians that allowed the identification of eighteen taxa. All radiolarians observed are of Late Cretaceous age and they are therefore reworked into the lower part of the Eocene London Clay Formation. The best preserved sample yielded an assemblage of twelve morphospecies, including Diacanthocapsa ovoidea, Theocapsomma amphora and Theocapsomma sp. aff. T. amphora sensu Popova-Goll et al. 2005, suggesting an original Santonian-Campanian age, and more likely only the Campanian. However, the stratigraphic origin of these radiolarians from the Upper Cretaceous sequence of the London Basin is uncertain.

Reworked Mesozoic Radiolarians in Miocene-Pliocene Foreland Sediments in the Zagros Belt, Iran

“…Smaller fragments might also have been lost during the sieving process in a 63 µm sieve. The observation of strong sorting of radiolarians contrasts with a report of reworked Upper Cretaceous radiolarians described in the Eocene marine London clay formation, where no such sorting has been observed (Fer et al 2016). While the authors described a generally poor preservation of radiolarians as also found in this study, the source and mode of transport of these reworked radiolarians was uncertain.…”

“…Differences could also apply as the radiolarians in this study were deposited within a mudstone of a fluvial environment. In contrast, the assemblage reported by Fer et al (2016) was deposited in a marine environment.…”

Strengthening the argument for a large Greater India

“…S2.1, S2.11, and S3 ). Third, hypothetically reworked Early Cretaceous radiolarians should be more poorly preserved than the Late Paleocene radiolarians ( 26 ), which is obviously not the case as the Early Cretaceous radiolarian in units 6 and 17 are moderately to well preserved. Fourth, even in the work of Hu et al (2015), Cretaceous calcareous nannofossils show no signs of reworking ( 11 ), which contradicts their own statements that reworking of microfossils is common throughout the Sangdanlin section.…”