y flow density exceeding bed density. The flows produce unique deposits, called turbidites, with internal mud layers, mixed cohesive-noncohesive sediment layers, and various soft-sediment deformation structures. A depositional model for intrabed turbidites is proposed, comprising from base to top: (I1) sand-bearing mud, with an eroded base, dispersed mud, and mud clasts; (I2) muddy sand from the intrabed portion of the turbidity current; (I3) sandy mud with a speckled appearance; and (I4) mud-poor sand from the suprabed portion of the flow. Complete I1I4 turbidites are inferred to dominate locations in nature where the currents mix with the bed and deep erosional scours form, filled with deformed or chaotic sand-mud mixtures. Further downflow, base-missing I2-I4 and I4 sequences signify gradual deceleration, loss of erosivity and termination of intrabed flow.
Major earthquake at the Pleistocene-Holocene transition in Lake Vttern, southern Sweden
Martin Jakobsson et al., Department of Geological Sciences, Stockholm University, 106 91 Stockholm, Sweden. Published online 17 Mar. 2014, http://dx.doi.org/10.1130/G35499.1. Open Access.
Lake Vttern is located in southern Sweden and is the second largest lake in the country. Geophysical mapping and geological coring show striking deformation structures in the soft sediment accumulated on the lake floor. The bottom sediments have drastically been bent downwards in response to vertical tectonic displacements below the lake floor. The vertical displacements reach in places as much as 13 m. The new geological and geophysical data suggest that an earthquake took place in Lake Vttern with an estimated seismic moment magnitudes of about 7.5. Analysis of pollen in sediment infilling of the mapped collapse structures suggest that this major seismic event occurred at about 11,500 years before present. Authors Martin Jakobsson aPage: 1 2 3 4 5 6 Related biology news :1
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