Abstract

More than 844,000 km² of the northern Line Islands Ridge mapped with multibeam bathymetry and backscatter provide unprecedented views of the geomorphology of this isolated area in the central equatorial Pacific Ocean. A compilation of all available multibeam data in the area reveals six extensive submarine dendritic channel systems that encompass a combined drainage area that exceeds 60,000 km². The channel systems occur in a predominately carbonate environment and are the longest calciclastic submarine channel systems mapped in the oceans to date. The channel systems occur in a carbonate-dominated region well above the carbonate compensation depth and have developed into the surface of basins that are surrounded by small guyots and seamounts that make up a discontinuous rim around the summit of the northern Line Island Ridge. The channels have mostly straight or gently curved well-developed tributaries and main reaches. Although the Line Island Ridge has been dated at 86 to 68 Ma old, the channels occur on the surface and are not buried by any significant sediment accumulations. Levees are very rare along the channel banks and no bathymetric expression of submarine fans was found where the channels exit onto the adjacent abyssal basins. There is sparse evidence of landslide deposits throughout the ridge although the flanks of the guyots exhibit numerous headwall scarps. The presence of plunge pools below the northwest escarpment, together with well-defined channels meters to hundreds of meters deep relative to the surrounding seafloor, suggests the channels might be relatively recent (perhaps late Neogene or even younger) features developed long after the ridge subsided more than a kilometer below sea level.

Highlights

  • Multibeam echosounder (MBES) bathymetry mapping has revealed that submarine channels are common on continental margins; e.g., Chaytor et al (2009); Gardner et al (2016), and Mosher et al (2017) as well as on flanks of some oceanic islands and oceanic ridges; e.g., Canary Islands (Mitchell et al, 2003), Azores (Quartau et al, 2012), West Mariana Ridge (Gardner, 2010), and Northern Line Islands Ridge Channels

  • Many studies have focused on submarine channels on continental margins, few have focused on the geomorphology of submarine channels on aseismic oceanic ridges, channels that Peakall and Sumner (2015) describe as “nonmargin ocean channels.”

  • The objective of this study is to analyze the available MBES bathymetry and acoustic backscatter data to provide for the first time a comprehensive view of the geomorphology of this area and to provide a detailed quantitative description of the extensive submarine channel systems found in this terrain

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Summary

Introduction

Multibeam echosounder (MBES) bathymetry mapping has revealed that submarine channels are common on continental margins; e.g., Chaytor et al (2009); Gardner et al (2016), and Mosher et al (2017) as well as on flanks of some oceanic islands and oceanic ridges; e.g., Canary Islands (Mitchell et al, 2003), Azores (Quartau et al, 2012), West Mariana Ridge (Gardner, 2010), and Northern Line Islands Ridge ChannelsMendocino Ridge (Gardner, 2017) to name just a few recent studies. Many studies have focused on submarine channels on continental margins, few have focused on the geomorphology of submarine channels on aseismic oceanic ridges, channels that Peakall and Sumner (2015) describe as “nonmargin ocean channels.”. Such channels likely act as the main sediment transport pathways that help shape the geomorphology and sedimentary deposits of these non-margin environments. A comment by Lyle et al (2016) in a study of sedimentation of an interior basin on the NLIR stated that, in their opinion, what is needed in the Line Island Ridge area is multibeam bathymetry mapping to help understand the sediment-dynamics processes. The objective of this study is to analyze the available MBES bathymetry and acoustic backscatter data to provide for the first time a comprehensive view of the geomorphology of this area and to provide a detailed quantitative description of the extensive submarine channel systems found in this terrain

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