Tiny Fossils, Big Impact: The Role of Foraminifera-Enriched Condensed Section in Arresting the Movement of a Large Retrogressive Submarine Landslide in the Gulf of Mexico
A 3.4-m thick condensed section enriched in foraminifera formed the final detachment horizon of a retrogressive submarine landslide, in the Ursa Basin, northern Gulf of Mexico. The high concentration of foraminifera produces a high porosity (up to five porosity units) layer distinct from the background clay. Integrated Ocean Drilling Program Expedition 308 Site U1324 cored and logged this layer. We conducted a sedimentological analysis on 31 samples across this zone and the overlying and underlying background clay. CT images show that foraminifera are individuals dispersed within the clay, unbroken, and have retained a significant amount of intraskeletal void space. The assemblage is expected for this time interval in the Late Pleistocene (~24 kya). We interpret the layer is a result of a pause in terrigenous sedimentation. The condensed section was a preferred detachment horizon but only minimal sliding occurred before further movement ceased. One possible mechanism to explain this is the presence of foraminifera results in a dilational shear strengthening behavior, which arrested movement. Further work will be required to test this, however. On a broader scale, condensed sections with abundant microfossils, may play a key role in landslide mechanics because they can alter the shearing properties of the background material.
KeywordsUrsa Basin Retrogressive Slip zone Microfossils Expedition 308
We thank John Firth (Gulf Coast Core Repository) for conducting CT scan s of samples. This study relied on core samples from Integrated Ocean Drilling Program Expedition 308. We thank David Harris (Kentucky Geological Survey) for access to microscope. We thank Peter Talling and Morelia Urlaub for constructive and thoughtful reviews that improved this paper.
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