Geologos, 2014, 20, 2
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Item Late Pleistocene-Holocene earthquake-induced slumps and soft-sediment deformation structures in the Acequion River valley, Central Precordillera, Argentina(Bogucki Wydawnictwo Naukowe, 2014-06-30) Perucca, Laura P.; Godoy, Enrique; Pantano, AnaEvidence of earthquake-induced liquefaction features in the Acequión river valley, central western Argentina, is ana -lysed. Well-preserved soft-sediment deformation structures are present in Late Pleistocene deposits; they include two large slumps and several sand dikes, convolutions, pseudonodules, faults, dish structures and diapirs in the basal part of a shallow-lacustrine succession in the El Acequión River area. The water-saturated state of these sediments favoured deformation. All structures were studied in a natural trench created as a result of erosion by a tributary of the Acequión River, called El Mono Creek. They form part of a large-scale slump system. Two slumps occur in the western portion of the trench and must have moved towards the ENE (70°), where the depocentre of the Boca del Acequión area is situated. Consid -ering the spatial relationship with Quaternary faults, the slumps are interpreted as being due to a seismic event. The thickest dikes in the El Mono Creek trench occur in the eastern portion of the trench, indicating that the responsible earthquake was located to the east of the study area, probably at the Cerro Salinas fault system zone. The slumps, sand dikes and other soft-sediment deformation features are interpreted as having been triggered by earth -quakes, thus providing a preliminary palaeoseismic record of the Cerro Salinas fault system and extending the record of moderate- to high-magnitude earthquakes in central western Argentina to the Late Pleistocene.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.Item Neogene seismites and seismic volcanic rocks in the Linqu area, Shandong Province, E China(Bogucki Wydawnictwo Naukowe, 2014-06-30) Tian, H.S.; Zhang, B.H.; Zhang, S.H.; Lü, M.Y.The Yishu Fault Zone runs through the centre of Shandong Province (E China); it is a deep-seated large fault system that still is active. Two volcanic faulted basins (the Shanwang and Linqu Basins) in the Linqu area, west of the fault zone, are exposed to rifting, which process is accompanied by a series of tectonic and volcanic earthquakes with a magnitude of 5–8. Lacustrine sediments in the basins were affected by these earthquakes so that seismites with a variety of soft -sediment deformation structures originated. The seismites form part of the Shanwang Formation of the Linqu Group. Semi-consolidated fluvial conglomerates became deformed in a brittle way; these seismites are present at the base of the Yaoshan Formation. Intense earthquakes triggered by volcanic activity left their traces in the form of seismic volcanic rocks associated with liquefied-sand veins in the basalt/sand intercalations at the base of the Yaoshan Formation. The -se palaeo-earthquake records are dated around 14–10 Ma; they are responses to the intense tectonic extension and the basin rifting in this area and even the activity of the Yishu Fault Zone in the Himalayan tectonic cycle.Item Palaeo-earthquake events during the late Early Palaeozoic in the central Tarim Basin (NW China): evidence from deep drilling cores(Bogucki Wydawnictwo Naukowe, 2014-06-30) He, Bizhu; Qiao, Xiufu; Jiao, Cunli; Xu, Zhiqin; Cai, Zhihui; Guo, Xianpu; Zhang, YinliVarious millimetre-, centimetre- and metre-scale soft-sediment deformation structures (SSDS) have been identified in the Upper Ordovician and Lower-Middle Silurian from deep drilling cores in the Tarim Basin (NW China). These struc -tures include liquefied-sand veins, liquefaction-induced breccias, boudinage-like structures, load and diapir- or flame --like structures, dish and mixed-layer structures, hydroplastic convolutions and seismic unconformities. The deformed layers are intercalated by undeformed layers of varying thicknesses that are petrologically and sedimentologically similar to the deformed layers. The SSDS developed in a shelf environment during the early Late Ordovician and formed initially under shear tensile stress conditions, as indicated by boudinage-like structures; during the latest Ordovician, SSDS formed under a com -pressional regime. The SSDS in the Lower-Middle Silurian consist mainly of mixed layers and sand veins; they formed in shoreline and tidal-flat settings with liquefaction features indicating an origin under a compressional stress regime. By Silurian times, the centre of tectonic activity had shifted to the south-eastern part of the basin. The SSDS occur at different depths in wells that are close to the syn-sedimentary Tazhong 1 Fault (TZ1F) and associated reversed-thrust secondary faults. Based on their characteristics, the inferred formation mechanism and the spatial asso -ciation with faults, the SSDS are interpreted as seismites. The Tazhong 1 fault was a seismogenic fault during the later Ordovician, whereas the reversed-direction secondary faults became active in the Early-Middle Silurian. Multiple palaeo-earthquake records reflect pulses and cyclicity, which supports secondary tectonic activity within the main tectonic movement. The range of SSDS structures reflects different developments of tectonic activity with time for the various tectonic units of the centralbasin. The effects of the strong palaeo-earthquake activity coincide with uplift, fault activity and syn-tectonic sedimentation in the study area during the Late Ordovician to Middle Silurian.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 Seismogenic structures in Quaternary lacustrine deposits of Lake Van (eastern Turkey)(Bogucki Wydawnictwo Naukowe, 2014-06-30) Üner, SerkanSoft-sediment deformation structures formed by liquefaction and/or fluidisation of unconsolidated sediments due to seismic shocks are frequent in the Quaternary sandy, silty and clayey deposits of Lake Van. They are present in both marginal and deep lacustrine facies. Their morphology and interpreted genesis imply that they should be considered as fluid-escape structures (dish and pillar structures, flame structures and sand volcanoes), contorted structures (simple and complex convolutions and ball-and-pillow structures) and other structures (disturbed layers and slump structures). The most recently formed structures are related to the October 23rd, 2011 Van-Tabanlı (M w 7.2) earthquake. The exist -ence of seismites at various stratigraphic levels in the lacustrine deposits is indicative of tectonic activity that frequently triggered earthquakes with magnitudes of 5 or more, affecting the Lake Van Basin.Item Soft-sediment deformation structures in seismically affected deep-sea Miocene turbidites (Cilento Basin, southern Italy)(Bogucki Wydawnictwo Naukowe, 2014-06-30) Valente, Alessio; Ślączka, Andrzej; Cavuoto, GiuseppeSoft-sediment deformation structures (SSDS) are widespread in the upper part of the S. Mauro Formation (Cilento Group, Middle-Late Miocene). The succession is represented mainly by thick and very thick, massive, coarse-grained sandstones, deposited by rapid sedimentation of high-density turbidity currents. The most common SSDS are short pillars, dishes, sedimentary sills and convolutions. They occur mostly in the upper parts of sandstone beds. Vertical tubes of 4–5 cm in diameter and up to 50 cm long constitute the most striking structures. They begin in the middle part of sandstone beds, which are basically massive or contain faint dish structures. These tubes can bifurcate upwards and/ or pass into bedding-parallel veins or dikes. The vertical tubes sometimes form sand volcanoes on the then sedimentary surface. The SSDS are interpreted as the result of earthquake-triggered liquefaction and/or fluidisation of the turbidites that were affected by the seismic shocks. This implies that the deformed layers should be considered as seismites.Item The life cycle of seismite research(Bogucki Wydawnictwo Naukowe, 2014-06-30) van Loon, A.J. (Tom)