Formation and Evolution of Valdivia Bank, Walvis Ridge, South Atlantic Ocean from Geophysical Data and International Ocean Discovery Program Expedition 391 Drilling Results

Valdivia Bank is an oceanic plateau in the South Atlantic, part of the Walvis Ridge hotspot track, that was formed at the Mid-Atlantic Ridge by plume-ridge volcanism during the Late Cretaceous. Oceanic plateaus are shallow rises on the ocean floor that are emplaced by thick accumulations of lava. Their history provides insights into paleo-oceanography, the nature of plume volcanism, and regional plate tectonics. Despite this importance, Valdivia Bank has until recently lacked detailed geophysical investigation and coring, obscuring the formation history and evolution of this plateau. Geochemical and paleomagnetic studies suggest that Valdivia Bank is complex, revealing a potential microplate and ridge reorganization in the Late Cretaceous, and late-stage volcanism in the Eocene. In 2019, geophysical surveys of Valdivia Bank were carried out on expedition TN-373 and TN-374 aboard the R/V Thomas G. Thompson. In 2021, the plateau was scored by IODP Expedition 391. In my research, I produce a detailed bathymetry map of Valdivia Bank and interpret the morphology and seafloor geologic processes on the plateau. Then, I utilize IODP Expedition 391 coring results to develop an age model of Valdivia Bank sediments and apply principles of seismic stratigraphy to multichannel seismic data to understand the sedimentation history of the plateau and the nature and timing of late-stage volcanism. Finally, I perform a structural assessment of Valdivia Bank to uncover the faulting and rifting history as observed in seismic and seafloor datasets to understand deformation of an oceanic plateau. The results suggest that Valdivia Bank experienced a multi-phased evolution in which the plateau was rifted and faulted in the Late Cretaceous due to ridge jumps. Microplate kinematics reactivated faults and rotated magnetic lineation to the east of the edifice in the Paleocene. In the Eocene,thermal rejuvenation uplifted the edifice as a short-lived island and emplaced volcanoes along rift faults, promoting coral growth atop shallow pinnacles. As the plateau subsided at a new thermal age, sediment was shed off the shallow areas through debris flows, slides, gullies, and channels. Ocean bottom current intensification in the Cenozoic developed moats and contourite deposits adjacent to the platforms.

Name thesis:degree_name

Doctor of Philosophy

Discipline thesis:degree_discipline

Geophysics

Grantor

University of Houston

Year dc:date.issued

2024

Author dc:creator

• Contreras, Edgar 1996-

Advisor dc:contributor.advisor

• Sager, William

Committee members dc:contributor.committeemember

• Mann, Paul
• Gharib, Jim
• Zhou, Hua-wei

Language dc:language.iso

English

Handle dc:identifier.uri

https://hdl.handle.net/10657/18303

OAI identifier oai:identifier

oai:uh-ir.tdl.org:10657/18303