The Byers Basin: Jurassic-Cretaceous tectonic and depositional evolution of the forearc deposits of the South Shetland Islands and its implications for the northern Antarctic Peninsula

ABSTRACT

This paper addresses the Jurassic–Cretaceous stratigraphic evolution of fore-arc deposits exposed along the west coast of the northern Antarctic Peninsula. In the South Shetland Islands, Upper Jurassic deep-marine sediments are uncomformably overlain by a Lower Cretaceous volcaniclastic sequence that crops out on Livingston, Snow and Low islands. U-Pb zircon ages are presented for the upper Anchorage Formation (153.1 ± 1.7 Ma) and the Cape Wallace granodiorite of Low Island (137.1 ± 1.7 Ma) as well as ⁴⁰Ar/³⁹Ar ages of 136–139 Ma for Low Island andesites. Data are also presented for a U-Pb age of 109.0 ± 1.4 Ma for the upper volcanic succession of Snow Island. In combination with published stratigraphy, these data provide a refined chrono- and litho-stratigraphic framework for the deposits herein referred to as the Byers Basin. Tentative correlation is explored with previously described deposits on Adelaide and Alexander islands, which could suggest further continuation of the Byers Basin towards the south. We also discuss possible correlation of the Byers Basin with the Larsen Basin, a sequence that shows the evolution of foreland to back-arc deposits more or less contemporaneously with the fore-arc to intra-arc evolution of the Byers Basin.     

High-resolution sequence stratigraphy,sedimentology and reservoir quality evaluation of the Yaojia Formation in the Longxi area of the Western Slope,Songliao Basin,China

Delta-front sand bodies with large remaining hydrocarbon reserves are widespread in the Upper Cretaceous Yaojia Formation in the Longxi area of the Western Slope, Songliao Basin, China. High-resolution sequence stratigraphy and sedimentology are performed based on core observations, well logs, and seismic profile interpretations. An evaluation of the reservoir quality of the Yaojia Formation is critical for further petroleum exploration and development. The Yaojia Formation is interpreted as a third-order sequence, comprising a transgressive systems tract (TST) and a regressive systems tract (RST), which spans 4.5 Myr during the Late Cretaceous. Within this third-order sequence, nine fourth-order sequences (FS9–FS1) are recognized. The average duration of a fourth-order sequence is approximately 0.5 Myr. The TST (FS9–FS5) mostly comprises subaqueous distributary channel fills, mouth bars, and distal bars, which pass upward into shallow-lake facies of the TST top (FS5). The RST (FS4–FS1) mainly contains subaqueous distributary-channel and interdistributary-bay deposits. Based on thin-sections, X-ray diffraction (XRD), scanning electron microscope (SEM) and high-pressure mercury-intrusion (HPMI) analyses, a petrographic study is conducted to explore the impact of the sedimentary cyclicity and facies changes on reservoir quality. The Yaojia sandstones are mainly composed of lithic arkoses and feldspathic litharenites. The sandstone cements mostly include calcite, illite, chlorite, and secondary quartz, occurring as grain coating or filling pores. The Yaojia sandstones have average core plug porosity of 18.55% and permeability of 100.77 × 10⁻³ μm², which results from abundant intergranular pores and dissolved pores with good connectivity. Due to the relatively coarser sediments and abundant dissolved pores in the feldspars, the FS4–FS1 sandstones have better reservoir quality than the FS9–FS5 sandstones, developing relatively higher porosity and permeability, especially the FS1 and FS2 sandstones. The source–reservoir–cap-rock assemblages were formed with the adjoining semi-deep lake mudstones that were developed in the Nenjiang and Qingshankou Formations. This study reveals the deposition and distribution of the delta-front sand bodies of the Yaojia Formation within a sequence stratigraphic framework as well as the factors controlling the Yaojia sandstones reservoir quality. The research is of great significance for the further exploration of the Yaojia Formation in the Longxi area, as well as in other similar lacustrine contexts.     

北京地区大灰厂组孢粉组合及其地质意义

大灰厂组沉积在北京西部大灰厂一带发育良好。该组由陆相火山碎屑砂岩、粉砂岩、页岩及砾岩组成，富含狼翅鱼、叶肢介、拟蜉蝣等动物化石和孢子花粉化石，厚度１２０－２００米。与下伏东狼沟组整合接触，与上覆辛庄组假整合接触。其孢粉组合是以ｃｌａｓｓｏｐｏｌｌｉｓ占显著优势为特征（６０－８０％）．含有较多Ｃｉｃａｔｒｉｃｏｓｉｓｐｏｒｉｔｅｓ，Ｌｙｇｏｄｉｕｍｓｐｏｒｉｔｅｓ及少量Ｃｉｃａｔｒｉｃｏｓｉｓｐｏｒｉｔｅｓ、Ａｐｐｅｎｄｉｃｉｓｐｏｒｉｔｅｓ、Ａｅｑｕｉｔｒｉｒａｄｉｔｅｓ、Ｈｓｕｉｓｐｏｒｉｔｅｓ及Ｄｅｎｓｏｉｓｐｏｒｉｔｅｓｖｅｌａｔｕｓ，Ｄ．ｍｉｃｒｏｒｕｇｕｌａｔｕｓ等。与国内外早白垩世的孢粉组合比较，时代为早白垩世韦尔登期。属于旱的热带和亚热带气候。     

藏南白垩系黑-红层沉积岩有机质组成分布特征

对藏南江孜县床得剖面白垩系黑层和红层沉积岩进行的有机地球化学研究表明,黑层有机碳含量高于红层5～10倍,红层和黑层饱和烃主峰碳数分别为nC25和nC23;黑层和红层沉积有机质的母质来源都以水生植物和菌藻类等低等生物为主,陆源有机质的输入非常有限;但饱和烃的分布和主峰碳数的差异可能反映了有机母源物质在种群方面的差异,而这种差异可能主要是水体温度存在差异造成的,即红层发育时期水体温度可能高于黑层沉积时期.而在高温度条件下,水生生物和陆生植物的生长发育受到限制,造成原始有机质产率和有机质沉积保存量低可能是红层沉积岩形成的主要原因.     

长春地区白垩系地层地铁勘察参数的确定

白垩系砾岩及泥岩地层在长春地区普遍存在,但由于砾岩地层现场钻探难以取样进行室内土工试验,泥岩地层由于存在水稳性、膨胀性、崩解性等因素影响,砾岩和泥岩的承载力值、抗剪强度参数指标、渗透系数以及基床系数等参数多以经验数据评估方法为主,在合理准确确定相关参数的问题上存在较大分歧。通过对长春地区白垩系砾岩及泥岩进行原位平板载荷试验、浸水载荷试验以及现场原位剪切试验,获取砾岩、泥岩的承载力值、抗剪强度指标、渗透系数以及现场基床系数值等,为地铁建设工程地质问题分析及设计提供充足的地质依据。     

西藏努林晚白垩世花岗闪长岩地球化学特征及成因

南冈底斯晚白垩世岩浆岩的成因及地球动力学机制一直存在争议。本文对冈底斯南缘努林花岗闪长岩开展地球化学、锆石U-Pb年代学及同位素示踪研究。结果显示,该岩体具有富SiO₂（66.62%～67.81%）、高Al₂O₃（15.11%～15.66%）、高Sr（>481×10^-6）,低Y（≤8.13×10^-6）和低Yb（≤0.73×10^-6）特征,Sr/Y比值达59～111,显示埃达克岩的特征;岩石轻稀土富集,重稀土亏损,具有显著的Eu正异常;富集大离子亲石元素,亏损高场强元素。（⁸⁷Sr/⁸⁶Sr）_i=0.704011～0.704244,ε_Nd（t）=＋3.61～＋5.75,总体反映地幔源区的Sr、Nd同位素特征。锆石U-Pb LA-ICP-MS测年显示存在83Ma和89Ma两组年龄。结合地质及地球化学分析,认为努林花岗闪长岩是新特提斯洋洋脊俯冲引起的镁铁质新生下地壳部分熔融的产物。     

白垩系饱和冻结砂岩蠕变试验及本构模型研究

冻结法作为穿越富水软岩地层的重要施工方法,冻结壁的长期稳定性对于工程安全有着至关重要的作用。蠕变破坏是诱发冻结壁变形的显著特点之一,对研究冻结岩石蠕变的特性有重要的理论和工程意义。以白垩系饱和冻结砂岩为研究对象,开展–10℃低温冻结条件下,不同围压(0、2、4、6 MPa)的三轴蠕变力学试验。分析了饱和冻结砂岩蠕变变形,根据现有黏弹塑性模型开展了参数辨识并探究蠕变参数的变化规律,基于此提出考虑温度及损伤效应的蠕变本构模型。研究结果表明:低温冻结削弱蠕变过程中颗粒间的相互胶结力,使其蠕变特征明显;而围压却在一定程度上抑制饱和冻结砂岩内部损伤的发展,导致稳态蠕变速率随围压的升高出现明显的下降趋势。随围压的增加饱和冻结砂岩的蠕变破坏形态呈现出从剪切破坏到张拉破坏再到局部塑形硬化破坏的变化过程。在黏弹塑性模型的基础上,总结蠕变参数E₁、E₂和η₂随荷载的增加呈现先增后减的趋势,拐点为屈服应力;而参数η₀在大于屈服应力后出现并呈现先增后减的趋势。结合冻结岩石蠕变数据对定义的应力-低温耦合蠕变本构模型进行了参数...     

Bivalves and oncoids as palaeoenvironmental indicators at Late Jurassic and Early Cretaceous dinosaur sites from Spain

Bivalves from the Late Jurassic and Early Cretaceous stratigraphic section at Las Zabacheras (Galve Sub-basin Teruel, northern Spain), are reviewed from both systematic and palaeoautoecological perspectives. For this study the Villar del Arzobispo Formation, well known for important dinosaur occurrences, was sampled from the boundary with the underlying Higueruelas Formation (Late Jurassic), to the first levels of the overlying El Castellar Formation (Early Cretaceous). The bivalve taxa have Late Jurassic affinity, pointing to a possible Jurassic-Cretaceous boundary towards the top of the Villar del Arzobispo Formation. We have sampled oncoids, whose nuclei are bivalves, through the section to study environment change in this lithostratigraphical formation. Geochemical trace elements and δ¹³C and δ¹⁸O stable isotope analysis of the oncoids enable us to determine the conditions in which the microbialites were formed and provide further palaeoenvironmental data from the deposits containing the bivalves. Bivalve taxa change from the lower part of the Villar del Arzobispo Formation, where Ceratomya excentrica and Unicardium cf. subregulare are characteristic of marine conditions, becoming more continental towards the top of the formation with the presence of Unionoidean bivalves, and in the “Wealden” facies of the El Castellar Formation, where Teruella gautieri, has been found. Bivalves and oncoids allow us to recognize continental conditions where the first dinosaur of Spain, the sauropod Aragosaurus ischiatus was found, in an open water system, where there was limited evaporation, and with enough energy to produce well oxygenated water.