Submarine dissolution during the late-Miocene carbonate crash and subsequent mega-pockmark formation on the Cocos Ridge

Author(s): Kluesner, J.; Silver, E. A.; Bangs, N. L.; McIntosh, K. D.
Author Affiliation(s): Primary:
University of California, Santa Cruz, Santa Cruz, CA, United States
Other:
University of Texas, Austin, United States
Volume Title: AGU 2014 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2014; American Geophysical Union 2014 fall meeting, San Francisco, CA, Dec. 15-19, 2014. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: A large field (245km2) seabed mega-pockmarks (∼1 km to 4 km in diameter) was recently imaged on the western edge of the Cocos Ridge near the Middle American Trench. The pockmarks are part of a vast mega-pockmark field (∼10×150 km) and were imaged using high-resolution multibeam bathymetry and backscatter and 3D seismic reflection data. On the seafloor, multiple pockmarks exhibit a two-tiered geomorphology, some of which contain small high-backscatter mounds, possibly indicating recent seafloor seepage. 3D seismic data reveal that the two-tiered morphology is caused by collapse structures at depth with large pockmarks above the walls of the former. Observed collapse structures are characterized by steep walls that truncate surrounding strata, apparent normal "ring" faults, chaotic internal reflections interpreted as infill, and circular morphologies. Younger pockmarks located above the walls of the collapse structures are larger in diameter, have gently dipping walls that do not truncate surrounding strata, and typically show elliptical morphologies. Physical properties results at IODP Site U1414 that intersects the 3D seismic volume suggest that observed reverse polarity lens-shaped zones, which are truncated by the deeper collapse structures, represent anomalous regions of high porosity and low density. In addition, a rapid drop in Ca concentrations observed within this interval at Site U1414 suggests a relationship with possible carbonate dissolution. Correlation of the collapse structures stratigraphic timing with nanno-fossil data at Site U1414 suggests formation occurred ∼8-10 Ma, approximately during the Late Miocene eastern Pacific carbonate crash. Based on 3D seismic analysis and recent drilling results, we propose a two-stage formation process that consists of initial collapse caused by carbonate dissolution during the late Miocene, followed by sustained fluid-flow along the walls of established collapse features, resulting in pockmark formation. This process resulted in a two-tiered seafloor geomorphology along the western flank of the Cocos Ridge, similar to that observed on the Carnegie Ridge (see Michaud et al., Mar. Geol., 216:205-219).
Year of Publication: 2014
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Cenozoic; Cocos Ridge; Costa Rica Seismogenesis Project; East Pacific; Expedition 344; Geophysical methods; Geophysical surveys; IODP Site U1414; Integrated Ocean Drilling Program; Miocene; Neogene; North Pacific; Northeast Pacific; Pacific Ocean; Seismic methods; Surveys; Tertiary; Upper Miocene
Coordinates: N083014 N083014 W0841332 W0841332
Record ID: 2015097866
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