Southern hemisphere palaeobathymetry

Abstract

Digital grids, with a spatial resolution of 0.5 °, were compiled using batbymetry, sediment thickness and oceanic crustal ages for the southern hemisphere to calculate sedimentfree palaeobathymetric charts for late Cretaceous (110 Ma) to the present. These reconstructions allow the definition and quantification of the bathymetric evolution of the seaways and gateways within this region. Pre-60 Ma the palaeobathymetry and the interconnection of the deeper ocean basin was dominated by the formation of hotspot-related ridges and plateaux. Between 40 Ma and the present the palaeobathymetry is characterized by the opening of numerous gateways as the Tasman Rise separated from Antarctica, the Mascarene Plateau split from the Chagos-Laccadive Ridge, Broken Ridge rifted from the northern Kerguelen Plateau, the Crozet Plateau separated from the Madagascar Ridge, and the Scotia Sea opened.The validity of these palaeobathymetric reconstructions is demonstrated by comparing the digital gridded data sets, from which they were calculated, with data derived from 39 Deep Sea Drilling Project and Ocean Drilling Program drill sites. Comparison of drill site data with the gridded data revealed positive correlations between crustal ages and bathymetry, whereas the sediment thickness data showed no correlation. The lack of any correlation for the sediment thickness data, however, did not preclude a positive correlation between sediment-flee bathymetries.The difference between expected 'true' palaeobathymetry, that is with sediments older than the time of reconstruction decompacted and reloaded back onto oceanic crust, and the sediment-free palaeobathymetry was shown to be less than 600 m for 87.5% of the data. The greatest differences occur where sediment thicknesses are greatest, i.e. within the deep ocean basins which are in close proximity to the continental margin.

GlobSed: Updated Total Sediment Thickness in the World's Oceans

“…Our modeled age of the oceanic lithosphere correlates well with the dated samples from the drill sites (Figure b). We do not see a perfect one‐to‐one correlation, which may partly be influenced by inaccuracies in dating, as some of the drill site ages are based on the oldest sediment age (Sykes et al, ). However, this is not significant as seen from Figure b, the scatter of data may rather suggest that random uncertainty dominates.…”

“…(section 3.4). The location of drill sites used bySykes et al (1998) and for comparison with our results are shown in yellow on the map. For reference, we show all other DSDP/ODP/IODP sites in the Indian Ocean (red circles).…”

South Atlantic paleobathymetry since early Cretaceous

“…More recently, Sykes et al . 5 calculated sediment-free paleobathymetric reconstructions at 0.5 degrees resolution for the southern hemisphere using present-day bathymetry, sediment thickness and seafloor age grids. They were able to show acceptable correlations (∼500–700 m) with paleobathymetric estimates from a handful (6 in the South Atlantic) of DSDP and ODP drill sites.…”

Gridded isopach maps from the South Pacific and their use in interpreting the sedimentation history of the West Antarctic continental margin

“…Several studies have shown that the ACC and Antarctic Bottom Water (AABW) are strongly guided by seafloor topography [e.g., Lazarus and Caulet, 1993;Rack, 1993]. Recent palaeobathymetric models were based on the kinematics and thermal subsidence rates of oceanic crust [e.g., Sykes et al, 1998;Brown et al, 2006], but lack any consideration of the effects of sediment distribution. For greater accuracy, sediment accumulations should also be taken into account in the next generation of paleobathymetric reconstructions.…”