Submarine channel asymmetry in a gravel-rich system, Cerro Toro Fm, Chile
One of the main purposes of publishing research is to get as many eyes on your results as soon as possible. A recent work that my co-authors (Anne Bernhardt and Don Lowe) and I published and would like the world to know about concerns some outcrops of submarine channels in the the Magallanes Basin, Chile. For a pdf of this work, click here. The exposures are wonderful due to recent glaciation, and the scale of the channel system is immense. For an intro to the basin go here and for an intro to the Cerro Toro channel belt, see this pdf.
See a few of the photos below to see the scale and architecture of the channel complex – it’s kind of like Where’s Waldo, only you are looking for a ‘geologist for scale’!
Abstract and a few figures to entice you to download the pdf.
Facies and architectural asymmetry in a conglomerate-rich submarine channel fill, Cerro Toro Formation, Sierra del Toro, Magallanes Basin, Chile
Cross-sectional asymmetry is characteristic of sinuous channels, in both fluvial and submarine settings. Less well documented are the facies distributions of asymmetric channels, particularly in submarine settings. Exposures of the axial channel-belt in the Magallanes retro-arc foreland basin on Sierra del Toro represent the fill of a 3.5 km wide, 300 m thick channel complex, here termed the “Wildcat,” that displays an asymmetric cross section and facies distribution. Measured sections and mapping demonstrate that facies proportion, degree of amalgamation, and margin architecture vary laterally from east to west across the Wildcat channel complex. The eastern side is characterized by thick-bedded, amalgamated sandstone and clast- and matrix-supported conglomerate that onlap a steep, simple margin adjacent to sandy overbank deposits. The western side contains thin-bedded, sandy and muddy strata that onlap a shallow composite margin adjacent to mud-rich out-of-channel strata.
The observed asymmetry is likely due to centrifugal flow forces and was caused by a low-sinuosity right-hand meander bend of the Cerro Toro axial channel-belt. The facies and architecture of the opposing margins indicate that the eastern and western sides constitute the outer and inner bends of the Wildcat channel complex, respectively. The modest cross-sectional asymmetry of the Wildcat complex is likely a product of the low channel-belt sinuosity. The absence of lateral accretion surfaces and deposits suggests that the channel did not migrate during filling. Flows depositing the uppermost channel fill were only weakly confined, resulting in flow divergence and overbank deposition.
A depositional model that incorporates the asymmetric facies distributions and the contrasting outer-bend and inner-bend architecture of the Wildcat channel complex is also presented. Similar facies distributions exist in other low-sinuosity submarine channels, and even more extreme facies and cross-sectional asymmetry probably characterize more highly sinuous channels. Data on facies distributions presented here represents a useful resource for constraining numerical and experimental models of the evolution of sinuous submarine channels as well as reservoir models of sinuous submarine channels.
Figure 1. Overview of the Magallanes retro-arc foreland basin, located in southern Chile.