Late Cretaceous and Cenozoic seafloor and oceanic basement roughness: Spreading rate, crustal age and sediment thickness correlations

Abstract

Single-channel seismic data from the South Australian Basin and Argentine Basin, and bathymetry data from the flanks of the Mid-Atlantic Ridge, East Pacific Rise and Southwest Indian Ridge are analysed to determine the root-mean-square (RMS) roughness of the seafloor and oceanic basement created at seafloor spreading rates ranging from 3 to 80 km/Ma (half-rate). For these data, crustal ages range from near zero to 85 Ma and sediment thicknesses range from near zero to over 2 km. Our results are consistent with a negative correlation of basement roughness and spreading rate where roughness decreases dramatically through the slow-spreading regime (< 20–25 km/Ma), then passes an intermediate-rate transition (25–50 km/Ma) where roughness decreases more gradually. At faster rates, a minimum roughness is reached after which roughness appears to increase slightly. The negative correlation of oceanic basement roughness and spreading rate appears to have existed since the late Cretaceous for slow and intermediate spreading rates, suggesting that the fundamental processes creating abyssal hill topography may have remained the same for this time period. Basement roughness does not appear to decrease (smooth) with increasing crustal age, and therefore off-ridge degradation of abyssal hill topography by mass wasting is not detected by our data. Seismic data reveal that sediment thickness increases with increasing crustal age in the South Australian Basin and Argentine Basin, but not monotonically and with significant regional variation. We show that minor accumulations of sediment can affect roughness significantly. Average sediment accumulations of less that 50 m (for our 100 km long sample seismic profiles and half-spreading rates < 47 km/Ma) can reduce the seafloor roughness to less than 80% of the measured basement roughness. For sediment thicknesses averaging 50–550 m, the seafloor roughness measured is 80% to a low 6% of the actual basement roughness. For average accumulations greater than 550 m, seafloor roughness values are consistently between 10 and 30% of the basement roughness. Thus, results from roughness and other statistical studies of sedimented seafloor must be interpreted with caution, especially if conclusions are made concerning the accretionary process at mid-ocean ridges.