Early development of the southern Kerguelen Plateau (Indian Ocean) from shallow wide‐angle ocean bottom seismometer and multichannel seismic reflection data

Abstract

We examine the early geological history of the southern Kerguelen Plateau (Indian Ocean) using ocean bottom seismometer (OBS), multichannel seismic (MCS), and Ocean Drilling Program data. Velocity‐depth models in the sedimentary Raggatt Basin are constrained by near‐range OBS data (refractions and reflections, including multiples and converted shear waves) and migrated MCS data. The models elucidate the significance of Lower Cretaceous lava flows, Albian to Coniacian/Santonian terrestrial and terrigenous sediment, and Maastrichtian and Paleocene seismic sequences. The Albian/Aptian basaltic basement complex consists of an upper and a lower series. The upper series is characterized by average Vps of 4.6–4.7 km/s, an upward increase of intercalated terrestrial sediment and altered flowtops, and a concomitant decrease in flow thickness; the lower series is marked by average Vps of 5.3–5.5 km/s, and contains thicker flows and less sediment. A volcanic center in the Raggatt Basin shows relatively low Vps (3.7–3.9 km/s for the upper series, 4.7–4.9 km/s for the lower series), and dipping reflections on the Raggatt Basin's flanks are also recorded as refractions. Terrestrial and terrigenous sediment of the Raggatt Basin, immediately overlying basement, is characterized by a seismic low‐velocity layer with Vps ranging from 2.2–2.9 km/s and a thickness of >1100 m in the central basin. Nearby source regions (e.g., Banzare Bank and other elevated areas south of the basin) account for a terrestrial and terrigenous sediment volume of ∼12,500 km3, deposited over ∼20 m.y. The depocenter of the Raggatt Basin began shifting in Santonian to early Maastrichtian time, and concluded by early late Paleocene time.