新元古代沂沭海峡地震引发的软沉积物变形及其微量元素信息

新元古代沂沭海峡位于郯庐断裂带昌邑—大店断层西侧宽60~90km、长300km的区域内,其分布范围基本与郯庐断裂带中段一致。新元古代,该海峡盆地先后沉积了青白口系、南华系及震旦系的滨—浅海相陆源碎屑、泥质及碳酸盐沉积物,其岩石地层称之为土门群。本次研究从该海峡盆地土门群佟家庄组(由石英砂岩、泥灰岩和页岩组成,属南华系)、浮来山组(由细—粉砂岩夹页岩组成,属震旦系)及石旺庄组(主要由碳酸盐岩组成,下部夹页岩,属震旦系)中鉴别出了一系列地震触动软沉积物形成的变形构造,包括液化砂墙和砂脉、负载构造、火焰构造、球枕构造、软布丁构造、底辟构造、滑塌褶曲和同沉积断层等。它们是地震事件的记录——震积岩。新元古代中晚期(约800—600Ma)沂沭海峡盆地拉张裂陷是它们形成的动力机制。根据石旺庄组中的微亮晶方解石脉与地震成因的变形构造(如负载、火焰、软布丁及同沉积断层等)共(伴)生的事实,并结合模拟地震试验结果分析,认为微亮晶方解石脉很可能是地震引发的饱和灰泥(方解石微粒)液化脉。微量化学元素分析结果表明,这些震积岩中的w(La)/w(Sc)和w(La)/w(Th)值高于上地壳平均值和正常沉积层,而w(Th)/w(Sc)值则较低,深源微量元素Ni和Cr的含量也高于上地壳平均值及正常沉积层。这些微量元素特征是当时的盆地基底不稳定、快速沉积且伴有深部物质元素混入的反映,强地震很可能是快速沉积和促进深源物质混入的主要动力。土门群中发育的一系列地震引起的软沉积物变形(震积岩),再次证明了古郯庐断裂带的存在,由它们记录的地震事件也是晋宁运动乃至Rodinia超大陆的裂解的响应。

Siliceous Cementation of Chlorite-Coated Grains in the Permian Sandstone Gas Reservoirs,Ordos Basin

Objective It has long been controversial that whether authigenic chlorite coatings in sandstone reservoirs can prevent precipitation of siliceous cements. It is commonly believed that chlorite coatings （also called chlorite films, chlorite linings, or chlorite rims） may prevent quartz overgrowth, and thus help the preservation of original pores in sandstone reservoirs. Recently, however, this assumption has been challenged by reservoir geologists. This dispute cannot be solved by mere analysis of thin sections, nor by chemical equations and diagenesis analysis. The main objective of the present contribution is to shed light on this problem on the basis of sandstone samples from the Permian Shanxi and Shihezi Formations in the eastern part of the Sulige gas field, Ordos Basin in central China.

Neogene Paleoseismic Events and the Shanwang Biota's Burial in the Linqu Area,Shandong Province,China

Several paleoseismic events are recorded in the Neogene Linqu Group, exposed in the Linqu area, Shandong Province, China. The events were interpreted on the basis of fleldwork and laboratory analysis, which showed the presence of seismites with plastically deformed soft-sediment deformation structures in the Shanwang Formation, and of seismic volcanic rocks in the Yaoshan Formation which show brittle deformation. The earthquake-triggered soft-sediment deformations in the seismites include load structures, ball-and-pillow structures, flame structures, piUow-like beds, boudinage structures, slump folds, syn-depositional faults, veins of liquefied sand, and dikes of liquefied sandy lime-mud. The seismic activity is also reflected in what might be called ＇brittle seismites＇; these originated when, under the influence of seismic vibrations, semi-consolidated conglomerate was shattered. Moreover, volcanic activity is related to intense earthquakes that affected basalts intercalated with sand layers; these successions are known as ＇seismic volcanic rocks＇, which are characterized by veins of liquefied sand intruding the basalts. AH above traces of paleoseismic activity were left from one single time span of 4 Ma with active seismicity that took place 14-10 Ma. This time span is known as ＇the Linqu Neogene Paleoseismic Active Period＇, which is divided into four paleoseismic episodes, which were responses to tectonic extension and basin rifting in this area. It even includes the activity of the Yishu Fault Zone during the Miocene and the Neogene. The ratios of trace elements in the seismites, w（La）/w（Sc） and w （La）/w（Th） are higher than the average value of the upper crust, but w（Th）/w（Sc） is lower; this is geochemical evidence for the basin rifting that resulted in a high sedimentation rate. The intense and frequent paleo-earthquakes are held responsible for the rapid burial of the Shanwang Biota. Secondary earthquake-induced processes （e.g. slumping of a lake shore and the strongly increased lacustrine sedimentation rate） contributed to the rapid burial of the biota.

An Upward Shallowing Succession of Gravity Flow Deposits in the Early Cretaceous Lingshandao Formation,Western Yellow Sea

Objective Several well-exposed gravity flow deposits in the Early Cretaceous Lingshandao Formation provide a rare opportunity to study deep-water processes. The main objective of this work is to establish the spatial and temporal relationships between the various gravity flow deposits, and thus to establish their sequence stratigraphic patterns and depositional conditions.

Geochemical,mineralogical,and petrological analyses for the interpretation of the sedimentary environment of the Middle-Late Ordovician Majiagou Formation(northern China)as a tool for more effective gas exploration

Core samples from the deeply buried Ordovician Majiagou Formation below the Huainan Coalfield(E China) have been investigated for their carbonate types,major and trace elements(including rare earth elements) and C and O isotopes,The objective was to get a better insight into the possible occurrences of gas(and possibly oil) derived from Carboniferous coals.It was found that the carbonates are dolomites with strongly varying amounts of CaO and MgO.The low concentrations of SiO_(2),Al_(2)O_(3),and Fe_(2)O_(3)indicate deposition in a normal marine environment with little terrigenous input,The Na_(2)O/K_(2)O,Fe/Mn and Sr/Ba ratios,as well as the Ga values indicate mainly a marine salinity and a hot and humid climate.The slight depletion of Ce and Eu,the depletion of heavy rare earth elements(HREE) and the enrichment of light rare earth elements(LREE) indicate deposition in a reducing environment.It thus appears that the Majiagou Formation below the Huainan Coalfield closely resembles that in the eastern part of the Ordos Basin,where several gas reservoirs are present,so that the Majiagou Formation under the Huainan Coalfield represents a promising target for hydrocarbon exploration.

Restrictions to the application of 'diagnostic'criteria for recognizing ancient seismites

Soft-sediment deformation structures induced by seismic liquefaction and/or fluidization receive much attention in sedimentological,structural and palaeoseismic studies.The direct record of larger earthquakes is restricted to instrumental and historical data; the recognition of prehistoric earthquakes requires criteria to recognize seismites in the geological record.The areal distribution of seismites can sometimes be related to active faults since distances to the epicenter(for a given magnitude) tend to be related to the liquefaction effects of seismic shocks.The use of soft-sediment deformation structures for palaeoseismic studies has limitations,however.Hardly anything is known,for instance,about the effects that modern seismic events have on the sediments in most environments.Moreover,criteria for the recognition of seismites are still under discussion.The following characteristics seem,particularly in combination,the most reliable:(1) Soft-sediment deformation structures should occur in laterally continuous,preferably recurring horizons,separated by undeformed beds;(2) These deformation structures should be comparable with structures known to have been triggered by modern seismic activity;(3) The sedimentary basin should have experienced tectonic activity at the time when the deformations were formed; and(4) The intensity or abundance of the soft-sediment deformation structures in a presumed seismite should change laterally,depending on the distance to the epicenter.It turns out that all of these four criteria have important exceptions.(1) Soft-sediment deformation structures occurring over large lateral distances in a specific layer can be triggered also by other processes.Moreover,in environments with a low sedimentation rate,the time between successive earthquakes is often too short to allow accumulation of beds that remain undisturbed.Furthermore,total liquefaction of a sandy bed may result in the absence of deformation features.(2) No truly diagnostic soft-sediment deformation structures exist to prove seismic activity.Moreover,the final configuration of a soft-sediment deformation structure is independent of the type of trigger.(3) Seismites occur frequently in areas where seismic activity is low today.(4) The lateral changes in the intensity of soft-sediment deformation structures in seismites as a factor presumed to depend on the distances to the epicenter,pose a complicated problem.The 2012 Emilia earthquakes,for instance,affected sandy fluvial channels but not the fine-grained floodplains.It must thus be deduced that specific soft-sediment deformation structures cannot be used without additional evidence to identify seismites.In particular,the magnitude of seismic shocks and the recurrence time of main events(the most important features that allow recognition of seismites) seem to be sedimentological in nature:facies changes in space and time seem theparameters that most strongly control the occurrence,morphology,lateral extent and the vertical repetition of seismites.

Deformed stromatolites in marbles of the Mesoproterozoic Wumishan Formation as evidence for synsedimentary seismic activity

The Mesoproterozoic Wumishan Formation consists mainly of dolomites that represent diagenetically transformed limestones deposited in a shallow peritidal environment.Although the environment was tectonically stable,the study area in the Changping District(north of the Beijing area) was affected by synsedimentary earthquakes.Later,the dolomites in the study area were intruded by a granite.This resulted in contact metamorphism of the dolomites,changing them in a halo around the intrusion into marble.This marble,which is exposed near Taoyukou Village,shows some levels with well-developed stromatolites.The stromatolites contain structures that point at deformation when the stromatolites had not yet been lithified,and thus represent soft-sediment deformation structures.The stromatolites apparently built up during a time-span when repeated deformational processes affected the still unlithified sediment,from the sedimentary surface down to maximally a few decimeters.The deformed stromatolites thus represent seismites,which feature is exceptionally rarely recognizable in marble.

The Vérard et al.(2015) method for 3D palaeogeographic reconstructions:How solid is its base?

Verard and co-workers proposed in an earlier issue of this journal a method to reconstruct the 3D palaeogeography ＂anywhere in the world at any time＂. The present contribution is a discussion of some of the assumptions on which the method of Verard et al. is based. The reason for this discussion is that the method will give, at least seemingly, illogical outcomes for numerous situations. Moreover, some assumptions used by Verard and his team pose theoretical probtems. It is deduced that the method developed by Verard and co-workers may occasionally help, indeed, to obtain a rough picture of the altitude of the sedimentary surface on the continents and of the depth of the sedimentary surface in the oceans in the geological past. The outcomes should, however, be treated with utmost care as severat of the assumptions on which the interpretative 3D method is based have no solid basis, so that even the rough outcomes of the method must be considered questionable.

Genesis of an unusual clastic dike in an uncommon braided river deposit

A clastic dike containing unusually large clasts occurs in the Quaternary deposits that unconformably cover the Mesoproterozoic sediments in the Fangshan District,Beijing area,China.The material into which the dike intruded is also uncommon because it consists mainly of loess-type silts that were deposited by braided rivers.The intrusion of the dike is explained as the result of the expulsion of pore water into the coarse,gravel-containing layers of a braided river system.The large size of the clasts in the dike is explained by an exceptionally strong upwards directed flow which owed its high energy to a high hydrostatic pressure that had been built up because pore water could not gradually seep through the impermeable silt-sized material during ongoing burial.This uncommon dike is compared with a second example,in similar Quaternary sediments covering the Mesozoic rocks in the Huairou District.

Were sauropod dinosaurs responsible for the warm Mesozoic climate?

It was recently postulated that methane production by the giant Mesozoic sauropod dinosaurs was larger than the present-day release of this greenhouse gas by nature and man-induced activities jointly, thus contributing to the warm Mesozoic climate. This conclusion was reached by correct calculations, but these calculations were based on unrealistic assumptions:the researchers who postulated this dinosaur-induced warm climate did take into account neither the biomass production required for the sauropods’ food, nor the constraints for the habitats in which the dinosaurs lived, thus neglecting the palaeogeographic conditions. This underlines the importance of palaeogeography for a good understanding of the Earth’s geological history.

The hyperpycnite problem: comment

A recent review article("The hyperpycnite problem") by Shanmugam(Journal of Palaeogeography 7(3):197–238,2018) in this journal has some shortcomings, comes to scientifically incorrect conclusions, and calls for student education in a way that would significantly diminish the students’ changes for a geological career. Having studied--and still studying--hyperpycnites in the field, it seems only appropriate to inform the readers of this journal about our concerns regarding the review article mentioned above.Actually, the article by Shanmugam(Journal of Palaeogeography 7(3):197–238, 2018) is not a review paper but rather a comment, criticizing al researchers who have come to the conclusion, on the basis of both field research and theory,that hyperpycnal flows result in sediments(hyperpycnites) with characteristics that make it possible to distinguish them from deposits formed in another way. This is also the essence of Shanmugam’s comment: as he states himself, he is"an ardent critic of al genetic facies models".

Book Review

【正】Microbial mats in siliciclastic depositional systems through time,edited by Nora Noffke & Henry Chafetz, 2012.SEPM Special Publication 101.Society for Sedimentary Geology(SEPM),Tulsa,OK,USA(order through https://members.sepm.org/iMISpublic/Core/Orders/).

Book Review

Atlas of sedimentary structures in estuarine and tidally-influenced river deposits of the Rhine-Meuse-Scheldt system and their application to the interpretation of analogous