Lower Oligocene ice rafted debris of the Kerguelen Plateau, supplement to: Breza, James R; Wise, Sherwood W (1992): Lower Oligocene ice-rafted debris on the Kerguelen Plateau: evidence for East Antarctic Continental Glaciation. In: Wise, SW; Schlich, R; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 120, 161-178

• Main Authors: Breza, James R, Wise, Sherwood W
• Format: Article in Journal/Newspaper
• Language: English
• Published: PANGAEA - Data Publisher for Earth & Environmental Science 1992
• Subjects: Drilling/drill rig; Leg120; Joides Resolution; Ocean Drilling Program ODP; Antarctic; Banzare Bank; Indian; Kerguelen; Ross Sea; The Antarctic; Antarc*; Ice Sheet
• Online Access: https://dx.doi.org/10.1594/pangaea.758569; https://doi.pangaea.de/10.1594/PANGAEA.758569

Appreciable lower Oligocene clastic detritus interpreted to be ice-rafted debris (IRD) was recovered at Ocean Drilling Program (ODP) Site 748 on the Central Kerguelen Plateau in the southern Indian Ocean. Site 748 is located in the western part of the Raggatt Basin, east of Banzare Bank at 58∞26.45'S, 78∞58.89'E (water depth = 1250 m). The physiologic and tectonic setting of the site and the coarse size of the material rule out transport of the elastics by turbidity currents, nepheloid layers, or wind.The IRD occurs between 115.45 and 115.77 mbsf within a stratum of siliceous nannofossil ooze in an Oligocene sequence otherwise composed exclusively of nannofossil ooze with foraminifers and siliceous debris. Glauconite and fish skeletal debris (ichthyolith fragments) occur in association with the IRD. According to planktonic foraminifer, diatom, and nannofossil biostratigraphy and magnetostratigraphy, the IRD interval is earliest Oligocene in age (35.8-36.0 Ma). The sedimentation rate throughout this interval was rather low (approximately 6.3 m/m.y.). The IRD consists of predominately fine to coarse sand composed of quartz, altered feldspars, and mica. A large portion of the quartz and feldspar grains is highly angular, and fresh conchoidal fractures on the quartz grains are characteristic of glacially derived material. Scanning electron microscope and energy-dispersive X-ray studies plus light microscope observations document the presence of a heavy-mineral suite characteristic of metamorphic or plutonic source rocks rather than that derived from the devitrification of a volcanic ash. Benthic foraminifer d18O values across this interval show a marked enrichment.This direct physical evidence of lower Oligocene IRD this far north of the Antarctic continent (the lowest latitudinal occurrence known) and the association of the IRD with the globally recognized shift in d18O argue strongly for the presence of an earliest Oligocene ice sheet on the Antarctic continent. This corroborates other recent drilling evidence of coeval glacial activity along the Antarctic margin (ODP Legs 113 and 119) and in the Ross Sea (CIROS-1), as well as previous indirect evidence based on stable isotope studies from the world's oceans.The co-occurrence of the IRD, biosiliceous-rich nannofossil ooze, fish skeletal debris, and glauconite probably denotes changes in patterns and/or intensity of oceanic circulation associated with a profound climatic cooling. These changes apparently enhanced upwelling and surface-water productivity and the development of a trophic structure that supported abundant vertebrate marine life, perhaps an important step in the evolution of vertebrate marine faunas.