Geologos, 2014, 20, 2
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Browsing Geologos, 2014, 20, 2 by Author "van Loon, A.J. (Tom)"
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Item Seismic and non-seismic soft-sediment deformation structures in the Proterozoic Bhander Limestone, central India(Bogucki Wydawnictwo Naukowe, 2014-06-30) Sarkar, Subir; Choudhuri, Adrita; Banerjee, Santanu; van Loon, A.J. (Tom); Bose, Pradip K.Numerous soft-sediment deformation structures occur within the Proterozoic Bhander Limestone of an intracratonic sag basin in a 750 m long section along the Thomas River, near Maihar, central India. Part of these deformation structu -res have most probably a non-seismic origin, but other structures are interpreted as resulting from earthquake-induced shocks. These seismic structures are concentrated in a 60 cm thick interval, which is interpreted as three stacked seismi -tes. These three seismites are traceable over the entire length of the section. They divide the sedimentary succession in a lower part (including the seismites) deposited in a hypersaline lagoon, and an upper open-marine (shelf) part. Most of the soft-sediment deformations outside the seismite interval occur in a lagoonal intraclastic and muddy facies asso -ciation. The SSDS within the seismite interval show a lateral continuity. They record simultaneous fluidisation and liquefaction. The bases of each of the three composing seismite bands are defined by small-scale shear folds, probably recording an earthquake and aftershocks. The presence of the three seismite bands at the boundary between the lagoonal and the overlying open-marine oolitic facies association suggests that the seismic event also triggered basin subsidence.Item The life cycle of seismite research(Bogucki Wydawnictwo Naukowe, 2014-06-30) van Loon, A.J. (Tom)Item The Mesoproterozoic ‘seismite’ at Laiyuan (Hebei Province, E China) re-interpreted(Bogucki Wydawnictwo Naukowe, 2014-06-30) van Loon, A.J. (Tom)A 1-million m3 breccia near Laiyuan (Hebei Province, E China) occurs as a block-like lithological unit between dolo -stones of the 1.55–1.45 Ga (Early Mesoproterozoic) Wumishan Formation. It has previously been interpreted as a seis -mite, but it appears not to fulfil any of the commonly accepted criteria that jointly are considered diagnostic for seis -mites. Its presence in a graben-like structure with almost vertical bounding fault planes rather indicates an origin as a (submarine) valley fill. As the valley originated by tectonic activity in the form of faulting, the breccia can be consid-ered as a secondary effect of seismic activity, but it does not represent a seismite.