Lower Cretaceous lacustrine successions,North Yellow Sea Basin,eastern China: Rift basin sequence stratigraphy and stacking patterns in response to magmatic activity

A series of Mesozoic rift basins formed in eastern China were associated with magmatic activity and subduction along the Eurasia, Izanagi and Pacific plate margins. The impact of magmatic activity on lacustrine sequence development was documented with well-log and 3-D seismic data from the Jupiter Depression in the North Yellow Sea Basin. We identified key surfaces, retrogradational and progradational parasequence sets, and defined the characteristics of systems tracts and the internal sequence components for the Lower Cretaceous (K₁SQ1). A 2-D SEDPAK numerical stratigraphic forward modeling was used to further constrain sequence development in the Jupiter Depression by considering different modeling parameters and the spatial-temporal characteristics of magmatic activity. Modeling results were compared and matched with the sequence architecture observed from seismic and well interpretations. Magmatic activity impacts on the development of the K₁SQ1 sequence in the North Yellow Sea Basin include topographic variation, lake level fluctuation, and sediment supply ratios. Results suggest that magmatic upwelling uplifted the northwestern area of the Jupiter Depression and formed its slope break during the late Jurassic or early Cretaceous. Along with uplifting, relative lake level dropped sharply and lake accommodation was reduced, but with increased sediment supply. Therefore, sediment accumulated along the slope break as a lowstand systems tract. Later on, as lake level continuously rose, transgressive and highstand systems tracts were developed. The proposed stacking pattern provides an analog, and a useful model, for lacustrine sequence development in response to magmatic activities in eastern China and other rift basins of similar tectonic setting.     

Long lasting interactions between tectonic loading, unroofing, post-rift thermal subsidence and sedimentary transfers along the western margin of the Gulf of Mexico: Some insights from integrated quantitative studies

After Jurassic rifting, numerous carbonate platforms (i.e., the Orizaba, Cordoba and Golden Lane-Tuxpan platforms) developed during the Lower and Middle Cretaceous episode of thermal subsidence along the western passive margin of the Gulf of Mexico, with intervening basinal domains (i.e., the Tampico-Misantla, Zongolica, Veracruz and Deep Gulf of Mexico - DGM - basins).During the Late Cretaceous-Paleocene, the east-verging Sierra Madre Oriental thrust belt developed, resulting in tectonic uplift and unroofing of the allochthonous units (i.e. tectonic units made up of former Orizaba and Cordoba platforms and Zongolica Basin series). This new topography provided also an important source of clastics to feed the adjacent foredeep, where coeval tectonic loading accounted for the bending of the foreland lithosphere. However, shallow water facies or even emersion persisted until the Eocene in the forebulge area (at the present location of the Golden Lane), preventing locally the clastics to reach the DGM. This topographic barrier was ultimately bypassed by the clastics only during the Oligocene and Neogene, once (1) the prograding clastic wedge had exceeded accommodation, and (2) the long lasting thermal subsidence of the passive margin could overpass the effect of the bending and force the former bulge to sink.Numerous paleo-thermo-meters (Tmax, Ro), paleo-thermo-barometers (fluid inclusions), PVT and coupled forward kinematic and thermal modeling have been used to calibrate and date the progressive unroofing of the thrust belt. Coupled tectonic and sedimentologic modeling was applied in the foreland to predict the distribution of sand versus shale ratios in the Oligocene to Plio-Quaternary clastic sedimentary wedge of the passive margin, where gravitational gliding of post-Eocene series occurred during the Neogene along major listric faults.Mantle dynamics are advocated as the main process accounting for post-orogenic uplift and regional tilting of the basement, which initiated a massive transfer of sediments from the Cordillera towards the Gulf of Mexico, from Oligocene onward, resulting in a destabilization and gravitational collapse of the western slope of the Gulf of Mexico in Neogene times.     

三门海游构造火山盆地之火山─沉积岩系层位归属讨论

本文根据天台测区1：5万区域地质调查工作成果，综合测区构造，岩石组合，岩石化学、化石，接触关系特征等资料分析，对三门海游构造火山盆内龙珠山─下路朱一带及芹溪、三门中学等地出露约70km2的火山─沉积岩系地层，进行层位归属讨论。指出海游盆地内龙珠山、里金、下路朱一带及芹溪、三门中学等地出露的火山─沉积岩地层，其层位应归属下白垩统永康群馆头组和朝川组，系属北北东向展布的早白垩世临海断陷地的组成部分。     

Analysis and application of ichnofabrics

Bioturbation at all scales, which tends to replace the primary fabric of a sediment by the ichnofabric (the overall fabric of a sediment that has been bioturbated), is now recognised as playing a major role in facies interpretation. The manner in which the substrate may be colonized, and the physical, chemical and ecological controls (grainsize, sedimentation rate, oxygenation, nutrition, salinity, ethology, community structure and succession), together with the several ways in which the substrate is tiered by bioturbators, are the factors and processes that determine the nature of the ichnofabric. Eleven main styles of substrate tiering are described, ranging from single, pioneer colonization to complex tiering under equilibria, their modification under environmental deterioration and amelioration, and diagenetic enhancement or obscuration. Ichnofabrics may be assessed by four attributes: primary sedimentary factors, Bioturbation Index (BI), burrow size and frequency, and ichnological diversity. Construction of tier and ichnofabric constituent diagrams aid visualization and comparison. The breaks or changes in colonization and style of tiering at key stratal surfaces accentuate the surfaces, and many reflect a major environmental shift of the trace-forming biota due to change in hydrodynamic regime (leading to non-deposition and/or erosion and/or lithification), change in salinity regime, or subaerial exposure. The succession of gradational or abrupt changes in ichnofabric through genetically related successions, together with changes in colonization and tiering across event beds, may also be interpreted in terms of changes in environmental parameters. It is not the ichnotaxa per se that are important in discriminating between ichnofabrics, but rather the environmental conditions that determine the overall style of colonization. Fabrics composed of different ichnotaxa (and different taphonomies) but similar tier structure and ichnoguild may form in similar environments of different age or different latitude. Appreciation of colonization and tiering styles places ancient ichnofabrics on a sound process-related basis for environmental interpretation.     

四川盆地下中三叠统盐系地层古地磁研究与成盐条件有关问题探讨

四川盆地下中三叠统嘉陵江组—雷口坡组(T1j-T2L)盐系地层蒸发岩发育,是我国海相碳酸盐岩沉积区探盐找钾的重要地区层位。现通过四川盆地下中三叠统盐系地层古地磁样品的系统采集和测试工作,首次在我国建立了古地磁磁性地层剖面,并根据测定结果,结合地质资料,探索了四川盆地下中三叠统(T1j-T2L)成盐古气候条件及其时代归属等有关问题。     

造山带断片型地层层序恢复实例剖析

南皮河组和怕拍组分布于昌宁一孟连带西缘的耿马、沧源、澜沧地区,前人将其分别划归晚二叠世和早三叠世。新的研究表明,它们不是连续地层,而是由多个地层断片组成。通过逐个地层断片研究,恢复了该区被动陆缘的地层序列。在此基础上,重新进行地层划分,厘定了弄巴组、南皮河组和怕拍组。进而探讨了该被动陆缘的演化历史。     

Stratigraphic evidence for millennial-scale temporal clustering of earthquakes on a continental-interior fault: Holocene Mississippi River floodplain deposits, New Madrid seismic zone, USA

The earthquake cycles that characterize continental-interior areas that are far from active plate boundaries have proven highly cryptic and difficult to resolve. We used a novel paleoseismic proxy to address this issue. Namely, we reconstructed Holocene Mississippi River channels from maps of floodplain strata in order to identify channel perturbations reflective of major displacement events on the high-hazard and mid-plate Reelfoot thrust fault, New Madrid seismic zone, U.S.A. Only three discrete slip events are currently documented for the Reelfoot fault ( AD 900,  AD 1450, and AD 1812). This study extends this record and, thus, illustrates the utility of stratigraphic proxies as paleoseismic tools. We concurrently offer here some of the first quantified response times for tectonically induced channel pattern changes in large alluvial rivers.

We identified at least two cycles of pervasive meandering that were interrupted by channel-straightening responses occurring upstream of the Reelfoot fault scarp. These straightening responses initiated at 2244 BC +/− 269 to 1620 BC +/− 220 and  AD 900, respectively, and each records initiation of a period of Reelfoot fault slip after millennia of relative tectonic quiescence. The second (or New Madrid) straightening response was triggered by the previously known  AD 900 fault slip event, and this initial low sinuosity has been protracted until the modern day by the latter  AD 1450 and AD 1812 events. The first (or Bondurant) straightening response began a period of several hundred to  1400 years of low river sinuosity which evidences a similar period of multiple recurrent displacement events on the Reelfoot fault. These Bondurant events predate the existing paleoseismic record for the Reelfoot fault.

These data offer initial evidence that slip events on the Reelfoot fault were temporally clustered on millennial scales and, thus, offers the first direct evidence for millennial-scale clustering of earthquakes on a continental-interior fault. This carries additional ramifications. Namely, faults that have been quiescent and non-hazardous for millennia could re-enter an enduring period of recurrent hazardous earthquakes with little warning. Likewise, the Reelfoot fault also reveals evidence of temporal clustering of earthquakes on short-term cycles (months), as well as evidence for longer-term reactivation cycles (10⁴–10⁶ years). This introduces the possibility that temporal clustering could be hierarchical on some continental-interior faults.     

华北克拉通古元古代地层划分与对比

华北克拉通古元古代地层分布广泛,主要集中于胶辽吉带、中部带和西部孔兹岩带三个带状区域。近年来华北克拉通古元古代地层研究取得了很大的进展,根据作者的研究和前人的大量工作,本文对华北克拉通主要的古元古代地层的组成、时代、形成的构造背景等进行了总结。发现华北克拉通古元古代底部2.47～2.35Ga间的地层普遍缺失,反映了华北克拉通地质演化历史上的一个静寂时期。～2.3Ga在华北克拉通中条山及鲁山等地发育了少量的冷口变质火山岩以及上太华岩群变质地层。大量的年代学资料表明华北克拉通以往认为时代大致始于2.5Ga的滹沱群、甘陶河群、辽河岩群、绛县群、中条群等众多地层实际年龄多集中在2.2～1.9Ga之间,而且大多数地区所划分的不同的古元古代地层在时间上是并置或叠合的,没有新老或上下关系,仅在中条山地区和五台地区的古元古代地层具有从老到新连续演化的特征。目前,古元古代早期2.4～2.3Ga的地层研究程度还不高,形成的构造背景存在岛弧和裂谷两种不同的认识,我们倾向于活动大陆边缘环境,推测在鲁山-华山-中条山-吕梁山一带存在古元古代早期的岛弧与活动大陆边缘的相互作用。2.2～1.9Ga这一阶段的地层除孔兹岩系外,通常为变质火山-沉积岩系,且火山岩基本都具有双峰式火山岩特征,表明它们应该形成于伸展环境,但对伸展的机制还存在裂谷与弧后盆地的争议,根据作者等的工作本文倾向于它们形成于陆内裂谷环境,反映了华北克拉通可能从2.2Ga开始经历了强烈的伸展活动,最终导致了原有基底的裂解。     

Diagenetic signatures in the deltaic and fluvial-estuarine Messinian sandstone reservoirs in the Nile Delta as a tool for high-resolution stratigraphic correlations

The current study utilizes a range of diagenetic fingerprints to differentiate between sandstone facies deposited in the Nile Delta before and during the Messinian salinity crisis (MSC), which is normally a challenging task considering the complex bio- and lithostratigraphic subdivisions of Messinian rock units. Subaerial exposure of the pre-MSC (Qawasim deltaic sandstone), during drawdown of the Mediterranean Sea at the time of the MSC, triggered pervasive dissolution of unstable rock fragments, kaolinization of feldspar, and meteoric dolomitization of carbonate. This was followed by mesogenetic calcite cementation and kaolinite transformation into dickite in deeply buried Qawasim sandstone. Comparatively, the Abu Madi estuarine facies, deposited during transgression after drawdown related to the MSC, is characterized by eogenetic iron (Fe)-calcite, glauconite, and pyrite (averages of 14.5%, 6%, and 2%, respectively). This facies transition is marked by abundance of mature glauconite (with potassium oxide (K₂O) at about 8%) whose content abates upward from the transgression surface. Moreover, the compositional variability of the Abu Madi sandstone gave rise to multiple diagenetic trajectories that resulted in chlorite formation presumably following smectite and kaolinite. Listed diagenetic variations in the studied Messinian sandstone resulted from a complex interplay between rocks’ compositional, depositional, and burial attributes, ultimately serving as a basis for high-resolution stratigraphic correlation in continental and marginal marine settings with poor biostratigraphic controls.     

苏南地区三叠纪地层格架

根据关键界面识别,苏南地区三叠纪地层可划分为3个层序。时限分别为早三叠世印度期、早三叠世奥伦期—中三叠世安尼期、中三叠世拉丁期—晚三叠世卡尼期。岩相和地层结构分析表明,本区存在碳酸盐缓坡沉积、镶边碳酸盐台地沉积、碳酸盐潮坪—泻湖沉积、陆缘近海湖泊沉积、湖泊—沼泽沉积等5个沉积体系。经历了3次海平面升降