%0 Journal Article
%A Fortuin, A.R.
%A Dabrio, Cristino J.
%T Evidence for Late Messinian seismites, Nijar Basin, south-eastSpain
%D 2008
%@ 0037-0746
%U https://hdl.handle.net/20.500.14352/49362
%X The Feos Formation of the Nijar Basin comprises sediments deposited duringthe final stage of the Messinian salinity crisis when the Mediterranean wasalmost totally isolated. Levels of soft-sediment deformation structures occur inboth conglomeratic alluvial sediments deposited close to faults and thehyposaline Lago Mare facies, a laminated and thin-bedded succession ofwhitish chalky marls and intercalated sands alternating with non-marinecoastal plain deposits. Deformation structures in the coarse clastics includefunnel-shaped depressions filled with conglomerate, liquefaction dykesterminating downwards in gravel pockets, soft-sediment mixing bodies,chaotic intervals and flame structures. Evidence for soft-sedimentdeformation in the fine-grained Lago Mare facies comprises syndepositionalfaulting and fault-grading, sandstone dykes, mixed layers, slumping andsliding of sandstone beds, convolute bedding, and pillar and flame structures.The soft-sediment deformed intervals resemble those ascribed elsewhere toseismic shaking. Moreover, the study area provides the appropriate conditionsfor the preservation of deformation structures induced by seismicity; such aslocation in a tectonically active area, variable sediment input to produceheterolithic deposits and an absence of bioturbation. The vertical distributionof soft-sediment deformation implies frequent seismic shocks, underlining theimportance of seismicity in the Betic region during the Late Messinian whenthe Nijar Basin became separated from the Sorbas Basin to the north. Thepresence of liquefied gravel injections in the marginal facies indicates strongearthquakes (M≥7). The identification of at least four separate fissured levelswithin a single Lago Mare interval suggests a recurrence interval for largemagnitude earthquakes of the order of millennia, assuming that the cyclicity ofthe alternating Lago Mare and continental intervals was precession-controlled.This suggestion is consistent with the present-day seismic activity in SE Spain.
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