African Natural History
versión On-line ISSN 1816-8396
MCMILLAN, I.K.. Early Campanian Foraminifera of the Igoda Formation and Needs Camp upper and lower quarries, Eastern Cape, South Africa, and comparison with Mzamba and the KwaZulu Basin. Afr. nat. history (Online) [online]. 2009, vol.5, pp. 133-154. ISSN 1816-8396.
Four outcrops of Late Cretaceous rocks are known in the East London region of the Eastern Cape Province, discovered at different times during the 20th century. These are at the Needs Camp upper and lower quarries, inland of East London; and at Igoda River mouth and a nearby road cutting close to the estuary, located to the south of East London, designated the Igoda Formation. All four sites contain similar foraminiferal assemblages, and the successions are interpreted as roughly coeval. The published record from the two Igoda Formation outcrops up to now consists of just one foraminifera species (Spiroplectinella sp.), and about 20 Cretaceous species have been reported from the Needs Camp quarries. However, examination of additional samples, as well as repeated reprocessing of previously-studied limestone samples from the four outcrops has led to the discovery of 87 species of foraminifera. Only five of these are planktic species, mainly very rare Heterohelix globulosa (Ehrenberg), Hedbergella spp., Hedbergella cf. H. simplex (Morrow), Globigerinelloides asper (Ehrenberg) and Rugoglobigerina rugosa (Plummer), the last-named indicating a Campanian-Maastrichtian age. These planktics indicate that surface waters were slightly better oxygenated, but the complete absence of keeled planktics yet diverse benthics suggests the majority of the lower water column, but not the sea-floor, was experiencing dysoxic conditions. Because of the different circumstances in the discovery of each of these outcrops, their contained foraminiferal assemblages and their interpreted foraminiferal ages and depositional environments have never before been effectively compared and contrasted. The Igoda/Needs Camp foraminiferal assemblages detailed here are compared with a greatly revised biostratigraphy for the southern African Campanian succession. The distinctive Igoda benthic assemblages, composed in the main of Gavelinella and Lenticulina species, are marked by small numbers of the age-diagnostic early Campanian (Campanian I and lowest Campanian II) benthic species, Valvulineria sp., and the Early Campanian (Campanian I) benthic species, thin Dorothia sp. The four outcrops are considered to expose parts of a somewhat siliciclastic-poor, carbonate-rich deposit. This accumulated in an inner (Needs Camp limestones) to middle (Needs Camp limey claystones) to outer neritic (Igoda limey claystones) setting on a relatively well-oxygenated sea-floor experiencing periodic inflows of inner neritic siliciclastics and shell hash. The majority of foraminifera tests preserved in these rocks have been the focus of post-depositional ferric iron precipitation, probably derived from oxidation and deterioration of pyrite, so that they are now a strong orange-red colour.
Palabras clave : foraminifera; Needs Camp; Igoda; planktic; benthic; Cretaceous; Campanian; biostratigraphy.