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Contrasting log and seismic expression of evaporitic deposits along the Valencia Basin

AuthorsOchoa, Diana; Sierro, Francisco Javier; Lofi, J.; Maillard, Agnès; Urgeles, Roger ; Flores, José Abel; Suárez, Mercedes
Issue Date5-May-2015
PublisherMicropalaeontological Society
CitationAbstract Book : RCMNS Interim Colloquium: 39 (2015)
AbstractDuring the Messinian Salinity Crisis (MSC), the Mediterranean Sea became a giant saline basin, which led to the precipitation of thick evaporitic deposits. Deep sediments, including evaporites, were first studied after the recovery of few cores during the Deep Sea Drilling Project‐Leg 13. However, characterization of those deep deposits has been limited by the lack of complete cored sequences; consequently, their study is currently mostly based on seismic interpretation. Seismic imaging efficiently provides information on the three‐dimensional geometry, variability and disposition of horizons, depositional sequences, and structures. Nonetheless, seismic interpretations often lack lithological and chronostratigraphical controls, thus they need to be combined with biostratigraphic and lithostratigraphic well data. In this study, we integrate drilling and seismic data gathered from the Valencia Basin, where significant oil‐related subsurface research has been done. In this basin, studies described the presence of a seismic unit accumulated during a low‐stand phase, known as the Upper Unit (UU). The UU is generally characterized by having parallel and continuous internal reflections of relatively high amplitude. Our aim was to complement existing interpretations of the UU with lithological and stratigraphical data from boreholes drilled at different depths. We specifically focused on those intervals corresponding to the UU, which were chosen and calibrated after performing time‐depth conversions of the sonic logs. X‐ray diffraction and cutting inspection show that none of the lithological intervals is entirely composed of evaporitic phases. By contrast, mineral content is completely dominated by calcite and phyllosilicates (clays), with less than 15% of gyspum. Abundance of calcite explains low sonic and gamma rays values, which initially were interpreted as resulting from gypsum/anhydrite beds. Comparison of logs (sonic, gamma ray and resistivity) and seismic reflectors show that logging signal has different patterns across the Valencia basin, whereas the seismic expression of the UU is more homogeneous. These observations could reflect the diverse depositional nature of the deposits containing evaporitic mineral phases, and thus of the UU. Differences between observed log patterns suggest the presence of lateral and/or basinward variations in the lithology. Nonetheless, further research detailing depositional settings at each drill site still needs to be carried out
DescriptionRegional Committee on Mediterranean Neogene Stratigraphy (RCMNS) Interim Colloquium 2015 - Mediterranean-Atlantic Gateways (Neogene to present), 5-8 May 2015, Rabat, Marocco.-- 1 page
Appears in Collections:(ICM) Comunicaciones congresos
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