Publication: Evidence for Late Messinian seismites, Nijar Basin, south-east
Spain
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Publication Date
2008
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Blackwell Publishing Ltd
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Abstract
The Feos Formation of the Nijar Basin comprises sediments deposited during
the final stage of the Messinian salinity crisis when the Mediterranean was
almost totally isolated. Levels of soft-sediment deformation structures occur in
both conglomeratic alluvial sediments deposited close to faults and the
hyposaline Lago Mare facies, a laminated and thin-bedded succession of
whitish chalky marls and intercalated sands alternating with non-marine
coastal plain deposits. Deformation structures in the coarse clastics include
funnel-shaped depressions filled with conglomerate, liquefaction dykes
terminating downwards in gravel pockets, soft-sediment mixing bodies,
chaotic intervals and flame structures. Evidence for soft-sediment
deformation in the fine-grained Lago Mare facies comprises syndepositional
faulting and fault-grading, sandstone dykes, mixed layers, slumping and
sliding of sandstone beds, convolute bedding, and pillar and flame structures.
The soft-sediment deformed intervals resemble those ascribed elsewhere to
seismic shaking. Moreover, the study area provides the appropriate conditions
for the preservation of deformation structures induced by seismicity; such as
location in a tectonically active area, variable sediment input to produce
heterolithic deposits and an absence of bioturbation. The vertical distribution
of soft-sediment deformation implies frequent seismic shocks, underlining the
importance of seismicity in the Betic region during the Late Messinian when
the Nijar Basin became separated from the Sorbas Basin to the north. The
presence of liquefied gravel injections in the marginal facies indicates strong
earthquakes (M≥7). The identification of at least four separate fissured levels
within a single Lago Mare interval suggests a recurrence interval for large
magnitude earthquakes of the order of millennia, assuming that the cyclicity of
the 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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