Normal faulting as a control on the stratigraphic development of shallow marine syn-rift sequences: the Nukhul and Lower Rudeis Formations, Hammam Faraun fault block, Suez Rift, Egypt

Tectono-stratigraphic analysis of the East Tanka fault zone (ETFZ), Suez Rift, indicates that the evolution of normal fault segments was an important control on syn-rift depositional patterns and sequence stratigraphy. Sedimentological and stratigraphic analysis of the Nukhul Formation indicates that it was deposited in a narrow (ca 1–2 km), elongate (ca 5 km), fault-bounded, tidally influenced embayment during the low subsidence rift-initiation phase. The Nukhul Formation is composed of transgressive (TST) and highstand (HST) systems tract couplets interpreted as reflecting fault-driven subsidence and the continuous creation of accommodation in the hangingwall to the ETFZ. The overlying Lower Rudeis Formation was deposited during the high subsidence rift-climax phase, and is composed of forced regressive systems tract (FRST) shallow marine sandbodies, and TST to HST offshore mudstones. Activity on the ETFZ led to marked spatial variability in stratal stacking patterns, systems tracts and key stratal surfaces, as footwall uplift, coupled with regressive marine erosion during deposition of FRST sandbodies, led to the removal of intervening TST–HST mudstone-dominated units, and the amalgamation of FRST sandbodies and the stratal surfaces bounding these units in the footwall. This study indicates that the evolution of normal fault segments over relatively short (i.e. <1 km) length-scales has the potential to enhance or suppress a eustatic sea-level signal, leading to marked spatial variations in stratal stacking patterns, systems tracts and key stratal surfaces. Crucially, these variations in sequence stratigraphic evolution may occur within time-equivalent stratal units, thus caution must be exercised when attempting to correlate syn-rift depositional units based solely on stratal stacking patterns. Furthermore, local, tectonically controlled variations in relative sea level can give rise to syn-rift stacking patterns which are counterintuitive in the context of the structural setting and perceived regional subsidence rates.     

Paleoenvironmental records of water level and climatic changes from the middle to late Holocene at a Lake Erie coastal wetland, Ontario, Canada

Pollen and diatom assemblages, and peat stratigraphies, from a coastal wetland on the northern shore of Lake Erie were used to analyze water level and climatic changes since the middle Holocene and their effects on wetland plant communities. Peat deposition began 4700 cal yr B.P. during the Nipissing II transgression, which was driven by isostatic rebound. At that time, a diatom-rich wild rice marsh existed at the site. Water level dropped at the end of the Nipissing rise at least 2 m within 200 yr, leading to the development of shallower-water plant communities and an environment too dry for most diatoms to persist. The sharp decline in water level was probably driven primarily by outlet incision, but climate likely played some role. The paleoecological records provide evidence for post-Nipissing century-scale transgressions occurring around 2300, 1160, 700 and 450 cal yr B.P. The chronology for these transgressions correlates with other studies from the region and implies climatic forcing. Peat inception in shallow sloughs across part of the study area around 700 cal yr B.P. coincides with the Little Ice Age. These records, considered alongside others from the region, suggest that the Little Ice Age may have resulted in a wetter climate across the eastern Great Lakes region.     

深时全球海平面变化重建方法的回顾与展望

全球海平面变化对古地理、古生物、古气候演化以及能源矿产分布具有重要的控制作用。然而,目前学界对深时海平面变化的驱动机制尚不清楚,部分归因于缺乏高精度全球海平面变化的恢复。文章回顾了全球海平面变化研究的起始与发展过程,归纳出五种类型的深时海平面变化重建方法和技术,即地层学、沉积学、洋盆动力学、同位素地球化学方法和大数据技术。并总结了上述研究方法的原理、优势和不足,并以白垩纪全球海平面重建为实例,讨论了当前深时全球海平面重建的难点和争议点,并对未来深时全球海平面变化重建进行了展望。     

同位素地层和土壤地层及其在第四纪研究中的应用

同位素地层和土壤地层是在多元地层划分理论的基础上,为适应第四纪高分辨率古环境研究的需要而建立起来的两种地层划分的方法。这两种地层划分方法在第四纪古环境的研究中显示了很强的生命力。     

东准噶尔造山带非史密斯地层类型划分及等级体制建立

在研究东准噶尔造带类型及发展历史的基础上建立区域构造格架、组合形式 ,划分出构造 -地层体类、构造 -岩层体类、构造 -混杂体类的非史密斯地层。按照所划分类型的各自特征 ,能够满足造山带 1∶ 2 5万填图精度的要求 ,对全部无序或局部无序的地 (岩 )层建立“岩群、岩组、岩段、岩层”等级体制 ;对那些总体有序、局部无序或总体无序、局部有序的地层 ,能通过各种手段恢复原始层序 ,服从史密斯地层层序律的 ,按“群、组、段、层”建立等级体制     

Facies and sequence stratigraphic architecture of the Mural Limestone (Albian), Arizona: Carbonate response to global and local factors and implications for reservoir characterization

This study documents the detailed facies and sequence stratigraphic architecture of a multi-cyclic patch-reef and its associated ramp interior facies that formed during Oceanic Anoxic Event 1b in the Mural Limestone, Arizona, USA. Ramp interior facies are comprised of bedded wackestone/packstone, rudist build-up and coral–algal patch-reef facies located north of Bisbee, Arizona, at the Grassy Hill locality. The larger multi-cyclic patch-reef that developed coevally ca 5 km to the south of Grassy Hill consists of a high-angle windward margin with a narrow ca 70 m long reef frame containing vertically zonated Microsolena, Actinastrea, diverse branching coral and rudist assemblages, and an 870 m long low-angle leeward margin comprised of reef debris rudstone and grainstone shoal facies. Similar reef geomorphology and orientation is documented across the Gulf of Mexico and reflects the shelf-wide north to north-east-trending prevailing wind and current energies. Controls affecting reef formation and growth patterns include changes in accommodation space associated with low-amplitude global sea-level rise and regional thermotectonic subsidence, local accommodation space and nutrient fluctuations associated with the inner shelf depositional setting within a humid and siliciclastic-rich environment. Four aggradational to retrogradational high-frequency sequences are documented in Arizona: High-frequency sequences 1 and 2 represent the first pulse of patch-reef development in an overall second-order marine transgression over the Sonora/Bisbee Shelf. These sequences correlate to δ¹³C signatures associated with Oceanic Anoxic Event 1b across the Gulf of Mexico and suggest that carbonate reefs persisted on the ramp interior during this time. High-frequency sequences 3 and 4 record a second brief transgression and backstepping of reef facies followed by the final regression of shallow shelf carbonates that correlates to more robust patch-reef development in Sonora, Mexico. The patch-reef at Paul Spur is an excellent outcrop analogue for productive patch-reefs in the Maverick Basin (Comanche Shelf) of Texas. Detailed facies mapping of this outcrop analogue shows that the greatest reservoir potential is contained within the backreef grainstone shoals where primary porosity of up to 15% is observed.     

Capability of constitutive models to simulate soils with different OCR using a single set of parameters

Incorporation of void ratio as a state variable into constitutive models allows, in principle, to use a single set of parameters for soils with different OCRs. Two sets of experimental data on reconstituted clays are used for evaluation of three constitutive models of different complexity (Modified Cam clay model, 3SKH model, hypoplastic model for clays). Although all the models predict the influence of OCR correctly from the qualitative point of view, quantitative comparison using a suitable scalar error measure reveals merits and shortcomings of different models.     

Section of Permian deposits and fusulinids in the Halvan Mountains, Yazd province, Central Iran

The Permian section situated northwest of Tabas in the Halvan Mountains is studied and fusulinids occurring in the section are described. The Chili, Sartakht, and Hermez formations distinguished in the section are separated by horizons of bauxitic laterite and belong to the Khan Group formerly ranked as a synonymous formation. Fusulinids occur at two levels in the section. The lower one confined to the Chili Formation yields the so-called Kalaktash fusulinid assemblage of the late Sakmarian age. The second late Asselian assemblage has been discovered in pebbles from conglomerate-breccia in the basal laterite of the Sartakht Formation. A brief characterization of fusulinids is presented and three new species are described. The new Benshiella genus is discriminated from the Rugosofusulinidae family. As Skinner and Wilde (1965, 1966) changed the original diagnosis of the Pseudofusulina genus, we suggest, regarding all species, which have been attributed to this genus but do not satisfy the new diagnosis, as representing the new Nonpseudofusulina genus.     

Aims and Scope

正Acta Geologica Sinica(English Edition)mainly reports the latest and most important achievements in the theoretical and basic research in geological sciences,together with new technologies,in the world.Papers published involve various aspects of research concerning geosciences and related disciplines,such as stratigraphy,paleontology,     

Stabilization of swelling clays by Mg(OH)2. Changes in clay properties after addition of Mg-hydroxide

Stabilization of the swelling clay structure is attempted by intercalation of Mg(OH)₂ and the development of a brucite interlayer between the clay layers. The properties of the product obtained by applying the technique, formulated as described in a previous work, are considered here. The materials used were Wyoming bentonite (USA), Fuller's Earth (UK), kaolinite, illite, lignite, and silica gels. The Mg(OH)₂-clay products were examined by the methylene blue dye test, X-ray diffraction analysis (XRD), differential thermal analysis (DTA), and derivative thermogravimetry analysis (DTGA). From the results obtained it is concluded that: the Mg-hydroxide is adsorbed by swelling clays both on their external and internal surface, whereas it is adsorbed on the external surface by non-swelling clays. The internally adsorbed phase of Mg-hydroxide forms an ill-defined interlayer of brucite, retarding swelling, whereas the external phase covers the particles modifying drastically their surface properties, like the adsorption of the MB dye. The material produced after precipitation of Mg-hydroxide on swelling clays (smectites) did not re-expand on wetting or after glycolation. The adsorption of MB dye was also reduced by some 80–90%, due to coating effect, preventing the measurements of the external surface area of the clay by polar molecules. The principal forces involved in the process are believed to be physical adsorption on the external surface, along with chemisorption and some chemical bonding, mostly in the internal surface. Cementation due to crystallization and, in the long term, some pozzolanic reactions take also place. Internal adsorption of the Mg-hydroxide is postulated to be in the form of positively charged mono- and/or small polymers and it is, chiefly, diffusion controlled. Since Mg-hydroxide is internally adsorbed by swelling clays, whereas Ca-hydroxide(lime) is not, and the (Mg, Ca)-clay aggregates are more stable than the Ca-clay or the Mg-one, the combination of the two hydroxides could give better results in soil stabilization than each hydroxide alone.