Home  |  About JOP  |  Editorial Committee  |  Subscription  |  Message  |  Meetings  |  Call for Papers  |  Contact

For Reviewer   Review Policy   Reviewer Login   EC Member Login   Editorial Office Login   Editor-in-Chief Login   Online First   Current Issue   Archive   Advanced Search   Most Read   Most Download   Free Email Alert   RSS

Current Issue   2016 Vol.  5 No.  4 Published: 2016-09-15 311 Researches of soft-sediment deformation structures and seismites in China — A brief review Zeng-Zhao Feng, Zhi-Dong Bao, Xiu-Juan Zheng, Yuan Wang During the past 30 years (1987–2016), a great progress has been made in researches of soft-sediment deformation structures (SSDS), seismites and palaeoearthquakes in China. However, the research thought of this academic ?eld is not open enough. It is almost with one viewpoint or one voice, i.e., almost all the papers published in journals of China considered the layers with SSDS as seismites. On the other hand, the authors are very glad to learn that the professors and students of China University of Petroleum (East China) have proposed different academic viewpoints on the origin of SSDS in Lingshan Island, Qingdao, Shandong Province, China. It is a very active academic atmosphere. The authors' ideas are as follows: (1) The SSDS are sedimentary structures with multi-origin. The term “SSDS” is a good sedimentary and geological term and should be utilized continually. (2) The term “seismites” is a term which is de?nitely assigned to the layers with SSDS induced by earthquakes. It is one type of the layers with SSDS. It is not equal to SSDS. (3) Some geologists suggested obsoleting the term “seismites”. These suggestions are rational. However, since the term “seismites” has been utilized for a long time in China and worldwide, to obsolete this term should be discussed and agreement should be acquired from numerous geologists in China and worldwide. It may be suitable that let the geological practice decide whether to obsolete it or not. (4) Hopefully, further progress will be made in the researches of SSDS. 2016 Vol. 5 (4): 311-317 [Abstract] ( 277 ) [HTML 1KB] PDF (237 KB)   ( 61 ) 318 The seismite problem G. Shanmugam During a period of 82 years (1931–2013), 39 genetic terms were introduced for various deposits. Of the 39 terms, only ten are meaningful in understanding the true depositional origin (e.g., turbidites), the remaining 29 are just jargons (e.g., seismites, tsunamites, etc.). The genetic term “seismites”, introduced by Seilacher (1969) for recognizing palaeoearthquakes in the sedimentary record, is a misnomer. The term was introduced in haste, based on an examination of a single exposure of the Miocene Monterey Formation (10 m) in California, without a rigorous scienti?c analysis. The fundamental problem is that earthquake is a triggering mechanism, not a depositional process. Type of triggers cannot be recognized in the ancient sedimentary record because evidence for triggers is not preserved by nature. Soft-sediment deformation structures (SSDS), commonly used as the criteria for interpreting seismites, are a product of liquefaction. However, liquefaction can be induced by any one of 21 triggers, which include earthquakes, meteorite impacts, tsunamis, sediment loading, among others. Brecciated clasts, typically associated with earthquake-induced deposits in the Dead Sea Basin, are also common depositional products of debris ?ows (i.e., synsedimentary product unrelated to earthquakes). Also, various types of SSDS, such as duplex-like structures and clastic injections, can be explained by synsedimentary processes unrelated to earthquakes. Case studies of sandstone petroleum reservoirs worldwide, which include Gulf of Mexico, North Sea, Norwegian Sea, Nigeria, Equatorial Guinea, Gabon, and Bay of Bengal, reveal that there is compelling empirical evidence for sediment loading being the primary cause of SSDS. The Krishna–Godavari Basin, located on the eastern continental margin of India, is ideal for sediment failures by multiple triggering mechanisms where overpressure and liquefaction have led to multi-origin SSDS. Because tsunamis and meteorite impacts are important phenomena in developing extensive deposits, lateral extent of SSDS cannot be used as a unique distinguishing attribute of earthquakes. For these reasons, the genetic term “seismites”, which has no redeemable scienti?c value, is obsolete. 2016 Vol. 5 (4): 318-362 [Abstract] ( 312 ) [HTML 1KB] PDF (18436 KB)   ( 67 ) 363 Seismites resulting from high-frequency, high-magnitude earthquakes in Latvia caused by Late Glacial glacio-isostatic uplift A.J. (Tom) van Loon, Ma?gorzata Pisarska-Jamro?y,Māris Narti?s, Māris Krievāns, Juris Soms Geologically extremely rapid changes in altitude by glacial rebound of the Earth crust after retreat of the Scandinavian Ice Sheet at the end of the last Weichselian glaciation in?uenced the palaeogeography of northern Europe. The uplift of the Earth crust apparently was not gradual, but shock-wise, as the uplift was accompanied by frequent, high-magnitude earthquakes. This can be deduced from strongly deformed layers which are interpreted as seismites. Such seismites have been described from several countries around the Baltic Sea, including Sweden, Germany and Poland.Now similarly deformed layers that must also be interpreted as seismites, have been discovered also in Latvia, a Baltic country that was covered by an ice sheet during the last glaciation. The seismites were found at two sites: Near Valmiera in the NE part and near Rakuti in the SE part of the country. The seismites were found in sections of about 7 m and 4.5 m high, respectively, that consist mainly of glacio?uvial and glaciolacustrine sands and silts. At the Valmiera site, 7 seismites were found, and at the Rakuti site these were even 12 seismites.The two sections have not been dated precisely up till now, but lithological correlations and geomorphological characteristics suggest that the sediments at the Valmiera site cannot be older than 14.5 ka. Because the accumulation of the section did not take more than about 1000 years, the average recurrence time of the high-magnitude (M ≥ 4.5–5.0) earthquakes must have been maximally only 100–150 years, possibly only 6–7 years. The sediments at Rakuti must also have formed within approx. 1000 years (17–16 ka), implying a recurrence time of high-magnitude earthquakes of maximally once per 100–200 years. 2016 Vol. 5 (4): 363-380 [Abstract] ( 292 ) [HTML 1KB] PDF (6718 KB)   ( 59 ) 381 The response of stromatolites to seismic shocks: Tomboliths from the Palaeoproterozoic Chaibasa Formation, E India A.J. (Tom) van Loon, Rajat Mazumder, Shuvabrata De It is demonstrated here for the ?rst time how Palaeoproterozoic stromatolites survived seismic disturbance of their substrate. The stromatolites under study could have been cyanobacteria or any other photoautotrophic microbes, which formed mats that covered a substrate of very ?ne-grained sandstones and mudstones of the Chaibasa Fm. in eastern India. The sediments represent a shelf environment. The local abundance of the stromatolites suggests that the low-energy environment formed a suitable habitat. The common phases of tectonic quiescence were, however, occasionally interrupted by seismic shocks. These were suf?ciently strong to deform the mat layers, the lower parts of which might already have been (semi-) consolidated. The mats became partly folded, partly faulted, and already consolidated parts of the stromatolite layers broke off. This can be deduced from the angular shapes of part of the broken-off fragments. It appears, however, that part of these fragments were still suf?ciently soft to become rounded and deformed by rolling over the sea?oor, probably under the in?uence of tidal currents. When come to rest, these fragments served as a new substrate for new generations of the microorganisms. These micro-organisms thus survived by continued growth on the reworked fragments and built up new stromatolites that may show an ‘angular disconformity’ with the stromatolites of their substrate. It thus is shown that stromatolites have an adequate response to a sudden disturbance of their habitat, and that they survive earthquakes by colonization of broken-off fragments. We call the ‘healed’ fragments ‘tomboliths’ (tumbled stones). 2016 Vol. 5 (4): 381-390 [Abstract] ( 306 ) [HTML 1KB] PDF (5492 KB)   ( 58 ) 391 A new ‘superassemblage’ model explaining proximal-to-distal and lateral facies changes in ?uvial environments, based on the Proterozoic Sanjauli Formation (Lesser Himalaya, India) Ananya Mukhopadhyay, Priyanka Mazumdar, A.J. (Tom) van Loon Facies analysis of ?uvial deposits of the Proterozoic Sanjauli Formation in the Lesser Himalaya was combined with an architectural analysis. On this basis, a model was developed that may be applied to other ?uvial systems as well, whether old or recent. The new model, which might be considered as an assemblage of previous models, explains lateral variations in architecture and facies but is not in all respects consistent with the standard ?uvial models. The Sanjauli ?uvial model is unique in that it deals with lateral facies variations due to shifts of the base-level along with ?uctuations in accommodation space owing to changes in palaeoclimate. 2016 Vol. 5 (4): 391-408 [Abstract] ( 207 ) [HTML 1KB] PDF (7414 KB)   ( 66 ) 409 Growth characteristics and sedimentary mode of Permian reefs, Lengwu, Tonglu, Zhejiang Province, southern China Ling Liu, Ya-Sheng Wu, Hong-Xia Jiang, Hong Liu Organic reefs are favourable accumulation spaces for hydrocarbons and various mineral resources. A complete Permian organic reef pro?le about 44 m thick with distribution area no more than 1 km2 is exposed near Lengwu, Tonglu, Zhejiang Province. Examination of outcrops and thin sections revealed that the main reef-building organisms are calcisponges, with inozoans as dominant type. Five types of rocks have been recognized in the reef, and they are calcisponge framestone, calcisponge baf?estone, bindstone, rudstone and bioclastic wackestone. The pro?le was constructed in three reef-building stages. The thickness of the second stage is largest, followed by the ?rst stage and the third stage is smallest. Each stage started with a framestone or baf?estone, ended as the reef grew near the sea-level, and died because of in?ux of terrigenous sediments. The development of the Lengwu reef is controlled by biological factors and sea-level changes. Based on the study a reef sedimentary model is established. 2016 Vol. 5 (4): 409-422 [Abstract] ( 292 ) [HTML 1KB] PDF (7412 KB)   ( 66 )

Copyright © 2014 JOURNAL OF PALAEOGEOGRAPHY Editorial Office of Journal of Palaeogeography, 20 Xueyuan Road, P. O. Box 902, Beijing 100083, China Tel: +86-10-62394320; +86–10–62396149     Email: Jpalaeo2012@163.com