标题：Enigmatic gravity-flow deposits at Ujscie (western Poland), triggered by earthquakes (as evidenced by seismites) caused by Saalian glacioisostatic crustal rebound
作者：Pisarska-Jamrozy, Malgorzata; Van Loon, A. J. (Tom); Mleczak, Mateusz; Roman, Malgorzata
通讯作者：Van Loon, AJ
作者机构：[Pisarska-Jamrozy, Malgorzata; Mleczak, Mateusz] Adam Mickiewicz Univ, Inst Geol, B Krygowskiego 12, PL-61680 Poznan, Poland.; [Van Loon, A. J. (Tom 更多
会议名称：7th PATA Days Workshop on Paleoseismology, Active Tectonics, and Archaeoseismology
会议日期：MAY 30-JUN 04, 2016
关键词：Seismites; Soft-sediment clasts; Gravity-flow deposits; Glacioisostatic; rebound
摘要：Two breccia layers occur directly stacked upon each other in a silty/sandy Saalian glaciolacustrine succession near Ujgcie (western Poland). This complex is exceptional because of two aspects: the two breccia layers consist of distinctly more fine-grained material (mainly silt) than the rest of the succession, and they contain numerous soft sediment clasts of sandy silt with irregular shapes. The silty clasts are interpreted to represent fragments of eroded sediment from the more marginal (proximal) bottom of the lake. The fine-grained character of the breccia matrix excludes that the process responsible for their deposition had a sufficiently high erosional capability to erode the embedded clasts. The only feasible explanation is that this enigmatic breccia consists of a mixture of sediments: the silty matrix must first have been deposited on the bottom of a lake and afterward have been eroded and redeposited by gravity flows that initially had sufficient power to erode the lake margin over which they ran down. The source of the gravity-flow silt remains enigmatic because no sediments with similar lithology are currently present nearby at a higher topographic level. We must therefore deduce that such sediments existed previously but were entirely eroded away, probably by the Weichselian ice mass that had reached this area during the next glaciation.; The probable trigger of the gravity flows is evidenced by the presence of soft-sediment deformation structures in two levels around 4.5 m below the breccias. These two levels show intense folding, collapse, and load structures indicative of liquefaction and fluidization. The deformation is ascribed to shocks, most probably resulting from earthquakes that were induced by glacioisostatic rebound during the Saalian deglaciation. Similar seismic shocks are likely to have triggered the mass flows that resulted in the breccia layers. (C) 2018 Elsevier B.V. All rights reserved.