[S-CG51] Hard-Rock Drilling Science: Continental and Deep-Sea Drilling, and Ophiolite

[SCG51-P01] Hydraulic properties of pre-Mediterranean Salinity Crisis (MSC) and early-MSC sediments recovered from the Gulf of Cádiz and the Alborán Basin

*Xunhui XU¹, Weiren LIN¹, Erika TANAKA², Jiaming ZHU¹, Go-Ichiro Uramoto², Yuhi SAKAI¹, Clara BLÄTTLER³, Fadl RAAD⁴, Jonathan STINE⁵, Manuel TEIXEIRA⁶, Shaoru YIN⁷, Kosuke EGAWA⁸, Rachel FLECKER⁹, Emmanuelle DUCASSOU¹⁰, Trevor WILLIAMS¹¹, IODP Expedition 401 Scientists (1.Kyoto University, 2.Kochi University, 3.University of Chicago, 4.Università di Corsica Pasquale Paoli, 5.University of Minnesota - Twin Cities, 6.University of Lisbon, 7.Second Institute of Oceanography-Ministry of Natural Resources, 8.Kyushu University, 9.University of Bristol, 10.University of Bordeaux, 11.Texas A&M University)

Keywords:Mediterranean-Atlantic seawater exchange, MSC (Messinian Salinity Crisis), Gulf of Cádiz, Alborán Basin, sediment microstructures, hydraulic properties

Evaporite sedimentation in the Western Mediterranean within a short period might potentially trigger overpressure within and below low permeability evaporite layers[1]. Additionally, fluid expulsion events in the km-thick Messinian evaporites in the depocentres of the Mediterranean Basin illustrate the evidence of subseafloor fluid flow partly driven by salt dissolution[2]. In the Gulf of Cádiz, a combination fine-grained low-permeability sealing formations and rapid contour current or mass transport deposition following the reopening of Atlantic-Mediterranean gateway were reported[3]. Heavy deformed Miocene succession in the western Gulf of Cádiz was also observed according to the seismic models[4]. Fluid release by overpressure could be consequently triggered due to the low permeability of sediments and increasingly applied environmental stresses[5]. However, it is rare to see the submarine hydraulic-property results in Pre-Mediterranean Salinity Crisis (MSC) and MSC sediments in either offshore side of Gibraltar, since previous drilling projects targeted the Plio-Pleistocene boundaries[6], or focused less on the available hydraulic parameters of potential fluid flow in the sediments deep under the seafloor.
Given the critical roles of microstructural features in controlling the hydraulic response, micro-X-ray CT scans with resolution of 10, 22, 35 µm were conducted on 62 lithified mini-core samples from the Pre-MSC and early-MSC successions in the Gulf of Cádiz (Site U1610) and Alborán Basin (Site U1611) that were recovered during IODP Expedition 401[7]. Mean CT numbers of the concentrated distribution were obtained from the double-peaked histogram based on a denoising operation. Gradual changes in sediment components, which are challenging to be observed on the sediment core surface, were unveiled by CT-number distributions, providing additional insights into the bulk physical properties of these sediments. Flow pump tests using pure water at a constant flow rate of 0.001 ml/min were subsequently carried out on 10 mini core samples. Hydraulic conductivity and specific storage were produced based on Esaki’s model [8] for exploring the correlations between hydraulic properties, structural characteristics, and onboard physical/chemical properties. Results presented herein provide an accessible hydraulic record of the Atlantic-Mediterranean region, suggesting an explanation for the migration of evaporites in the Alboran Sea Basin since the early MSC, and unveiling potential mechanisms of downcore compactions under different drainage conditions at both sites.

References
[1] Dale et al. (2021) Basin Research, 33(4):2202-2228. [2] Bertoni & Cartwright (2015) Marine and Petroleum Geology, 66:165-176. [3] Mencaroni et al. (2020) Geological Society, London, Special Publications, 500(1):289-300. [4] Brackenridge et al. (2013) Marine and Petroleum Geology, 46, 36-50. [5] Dugan & Sheahan (2012) Reviews of Geophysics, 50(3). [6] Hernández-Molina et al. (2016) Marine Geology, 377:7-39. [7] Flecker et al. (2024) Expedition 401 Preliminary Report: Mediterranean–Atlantic Gateway Exchange. International Ocean Discovery Program. [8] Esaki et al. (1996) Geotechnical Testing Journal, 19(3), 241-246.