Erosion and Sedimentation on the Carnegie Ridge, Eastern Equatorial Pacific
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The Carnegie Ridge is an aseismic ridge that bounds the south flank of the Panama Basin. Dynamic sedimentation around Carnegie Ridge is shown by evidence of erosion, dissolution and re-deposition of pelagic sediments where erosive episodes have carved out relict landscapes. I examine three aspects of these features: 1) What are the mechanisms involved in the erosive episodes; 2) Can the ages of the erosive events be constrained; and finally 3) Can the transport mechanism be identified? The extent of erosion and re-deposition was studied during the R/V Melville cruise MV1014 from October to November 2010 to compare with geochemical estimates of sediment focusing. The MV1014 cruise acquired geochemical, geological and geophysical data to compare with earlier surveys and scientific drilling. Large-scale erosion, presumably driven by massive, density-driven deepwater spillover events from the Peru Basin, created a prominent valley named Sand Dune Valley in the study area. A second, smaller valley, known as Western Valley, was likely formed by medium-scale erosion catalyzed by a ridge jump with subsequent normal faulting forming a fault scarp which has intensified near-bottom currents. Smaller-scale erosional events created small-scale surface sediment truncation. Utilizing a seismic stratigraphy developed by comparing seismic horizons to the sediment columns at DSDP Site 157 and ODP Site 846, and exposure of diagenetic chalk along the valley floors allowed a reconstruction of the timing of these highly erosive episodes. Two major erosive episodes are proposed to have occurred at ~5 Ma and ~3Ma which removed as much as 75 km3 of sediment. The erosive episodes may be linked to a ridge jump of the Galapagos hotspot at ~5-4 Ma and the final closing of the Isthmus of Panama ~3Ma. Sediment transport regimes for the Quaternary were determined using horizons dated at 2 Ma (PL-2), 1.7 Ma (PL-1) and 84 ka (Q-84). Isopachs created using the three horizons concluded that the dominant transport regime occurs to the NW of the study area with strong lateral transport to the sides of the valleys.
Brooks, Caroline Kelly (2014). Erosion and Sedimentation on the Carnegie Ridge, Eastern Equatorial Pacific. Master's thesis, Texas A & M University. Available electronically from