Palaeo-earthquake events during the late Early Palaeozoic in the central Tarim Basin (NW China): evidence from deep drilling cores

Abstract

Various 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 structures 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 association 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.

Seismites from a well core of palustrine deposits as a tool for reconstructing the palaeoseismic history of a fault

“…In this situation, it can be difficult to distinguish the influence of climate and tectonic activity on both the sedimentation rate and re-suspension processes . Nice examples of ancient seismically-induced SSDSs in well cores have been described by El Taki and Pratt (2012) and He et al (2014). The scarcity of literature on soft-sediment deformation structures in well cores with a palaeoseismic perspective is difficult to explain since, generally, the continuous cores show a good preservation of the delicate primary lamination and bedding, soft-sediment deformation structures and trace fossils, especially in fine-grained deposits (Alfaro et al, 1995;Weimer and Tillman, 1980).…”

The Mesoproterozoic ‘seismite’ at Laiyuan (Hebei Province, E China) re-interpreted

“…Van Loon & Pisarska-Jamroży, 2014), which commonly affects only the uppermost few decimetres of sediment, in exceptional cases a metre or somewhat more, which can result in 'giant' seismites (Alfaro et al, 2010). No such deformations are present in the sediments under study, however, although they are common in seismites (see, for instance, He, 2014;Perruca et al, 2014;Sarkar et al, 2014, Valente et al, 2014, Uner, 2014 all in this issue). It should be kept in mind, however, that Liang et al (2002a) apparently used the term 'seismite' not in the sense in which Seilacher (1969Seilacher ( , 1984 introduced it, viz.…”

Soft Sediment Deformation Structures in the Maastrichtian Patti Formation, Southern Bida Basin Nigeria: Implications for the Assessment of Endogenic Triggers in the Maastrichtian Sedimentary Record

“…Interpretation: In this deformed layers the load casts originated in response to gravitational instabilities caused by unstable density gradient which allowed denser sediment to sink into less dense sediment. This process is related to liquefaction and drastic reduction in shear strength of the sediments [37]- [40] and [41].…”