Impact of dynamic sedimentation on facies heterogeneities in Lower Cretaceous peritidal deposits of central east Oman

This study, based in the Haushi‐Huqf area of central east Oman, aims to characterize the controls on facies distribution and geometries of some of the best preserved examples of Lower Cretaceous tidal flat facies within the Tethyan epeiric platform. Field, petrographic and geochemical data were acquired from the Barremian–Aptian Jurf and Qishn formations that crop out in a 500 × 1000 m² butte, thus allowing for pseudo three‐dimensional quantitative data acquisition of the dimensions and spatial distributions of discontinuity surfaces and sedimentary bodies. The interpretation presented here suggests that the main processes impacting sedimentation in the Lower Cretaceous peritidal environment of the Haushi‐Huqf were transport and erosion processes related to storm waves and currents. The vertical evolution of the carbonate system is organized into six types of metre‐scale depositional sequences, from subtidal dominated sequences to supratidal‐capped sequences, which are bounded by regional discontinuity surfaces. At subaerial exposure and submarine erosion surfaces associated with a base level shift, sedimentary horizons along the entire depositional profile are cut by scours possibly created by storm events. Chemostratigraphy allows correlation between the Haushi‐Huqf and the age‐equivalent sections logged in the interior of the platform in Oman. The correlation suggests that the change from subtidal to intertidal depositional sequences during the late highstand is coeval with the development of rudist dominated shoals on the shelf. This study is the first to discuss the controls on Lower Cretaceous peritidal carbonate cyclicity of the Arabian epeiric platform. The results presented here also offer a unique quantitative dataset of the distribution and dimensions of peritidal carbonate shoals and storm scours in a regional sequence stratigraphic context.     

Biostratigraphy of the Garau Formation (Berriasian?–lower Cenomanian) in central part of Lurestan zone,northwest of Zagros,Iran

Deposition of organic rich black shales and dark gray argillaceous limestones in the Berriasian–Turonian interval has been documented in many parts of the world. Northwest of Zagros, Iran (Lurestan zone), thin bedded black shales and marls, dark gray argillaceous limestones and fissile limestone layers, having bitumen, of the Garau Formation are deposited. For biostratigraphic studies two stratigraphic sections including one surface section (Kuzaran) and one subsurface section (Naft well) were selected, respectively. In this study, 61 foraminiferal species belonging to 17 genera have been identified, and 12 biozones were recognized. Based on fossils distribution and biozones identification, the age of the Garau Formation is Berriasian?–early Cenomanian. In addition, the micropalaeontological study demonstrated a variety of widespread morphological changes in planktonic foraminifera assemblages (e.g., the elongation of the final chambers, appearance of twin chambers in the last whorl). These changes coincide with deposition of argillaceous limestones and marls rich in organic matter, indicating oceanic anoxic events. On this basis, three oceanic anoxic events such as OAE1a, OAE1b and OAE1d were recognized in Naft well section and two (OAE1b and OAE1d) in Kuzaran section.     

四川盆地元坝地区上三叠统须家河组的潮控河口湾与潮控三角洲沉积

通过盆地边缘地表剖面,以及元坝区岩芯的研究,发现须家河组并非长期以来人们普遍认定的陆相沉积,而是海岸系统产物。须二段属潮控河口湾环境,包括冲积河道、潮汐—河流水道、UFR沙坪、潮汐沙坝、泥坪和盐沼等相。须四段属潮控三角洲环境,包括三角洲平原河道、分流河口潮汐沙坝、三角洲前缘与前三角洲、泥坪与盐沼等相。这两种环境（沉积）,都是海侵的产物,都是地史上的暂时现象。当其被充满时（海退）,就变为潮坪—海岸平原环境,分别对应于须三段、须五段的细粒含煤序列。基于储层质量与原始沉积环境密切相关,划分了5类储层相。根据我们研究安岳地区须家河组的成功经验,提出了勘探建议。     

蓟县中元古界下马岭组地层中菱铁矿的发现及其意义

蓟县剖面中元古界下马岭组地层下部黑色岩系中发现丰富的铁质结核,经X射线粉晶衍射、显微镜下观察、能谱分析等方法鉴定,确定铁质结核主要由菱铁矿构成.这些菱铁矿可能具有经济意义.另外,野外和室内研究表明,无论是铁质结核还是黑色岩系本身,都匮乏硫化物.这一发现说明中元古代下马岭期的燕辽海盆水体贫氧、富铁、贫硫,不是硫化的海洋.     

鄂尔多斯盆地延长组物源与成岩耦合关系研究

随着油气勘探的逐渐深入,致密低渗油气藏所占比例越来越高,将是今后油气勘探的一个重要领域。颗粒成分不同导致的成岩差别对致密低渗储层的储集物性具有明显的控制作用。本文以鄂尔多斯盆地上三叠统延长组长8-长6段致密砂岩为例,研究砂岩骨架颗粒、孔隙类型与成岩作用之间的关系。在此基础上,分析由不同类型母岩形成的砂岩成岩作用差别。结果表明,鄂尔多斯盆地长8-长6段物源对砂岩成岩作用具有非常明显的控制作用:(1)石英、长石等刚性颗粒的含量直接影响着压实作用的强度;(2)火山岩屑可以导致绿泥石环边和浊沸石胶结物的形成,火山岩屑和浊沸石胶结物的溶蚀较强,易形成次生孔隙;(3)黑云母可以导致强压实形成致密层,但黑云母水解可以提供大量的铁和镁,利于绿泥石环边的形成;(4)碳酸盐岩岩屑的溶解可以为碳酸盐胶结物的形成提供额外的物质来源。所以,物源研究可以有效地预测深层致密碎屑储层的成岩作用及成岩强度,进而对高效储层的发育作出预测。     

Biological and abiological processes in a simulated sedimentary system

A simulated sedimentary system, capable of being controlled and monitored for a considerable length of time without undue disturbance, has been assembled and applied to specific problems of the genesis of stratiform Pb‐Zn ore deposits. Results have been obtained relevant to: (i) the concentration of Pb and Zn from brines to underlying sediments; (ii) the behaviour of microorganisms in metal‐rich, highly saline environments; (iii) the precipitation diagenesis of calcium and magnesium carbonates; and (iv) the diagenesis of organic matter.

The experiment has demonstrated the feasibility of simulating a complex sedimentary environment in the laboratory and has indicated the potential of such systems for the investigation of geobiological problems.     

A reinterpretation of seismic data in the Laura Basin,Queensland

The results of the seismic surveys recorded during 1963 and 1968 for Marathon Petroleum and Crusader Oil in the Laura Basin, north Queensland, have been reinterpreted. Seismic reflections which dip almost continuously from 0.6 to 4.0 seconds reflection time may come from the base of and within an 8000 m sequence of Permo‐Carboniferous sediments, which may underlie the flat‐lying Mesozoic Laura Basin sediments and overlie the heavily folded Carboniferous‐Devonian sediments in the Hodgkinson Basin. Further seismic investigation of this area is recommended since a thick Permo‐Carboniferous sedimentary section here could be prospective for hydrocarbons.     

Geology and age of the Glikson impact structure,Western Australia

The Glikson structure is an aeromagnetic and structural anomaly located in the Little Sandy Desert of Western Australia (23°59'S, 121°34′E). Shatter cones and planar microstructures in quartz grains are present in a highly deformed central region, suggesting an impact origin. Circumferential shortening folds and chaotically disposed bedding define a 19 km-diameter area of deformation. Glikson is located in the northwestern Officer Basin in otherwise nearly flat-lying sandstone, siltstone and conglomerate of the Neoproterozoic Mundadjini Formation, intruded by dolerite sills. The structure would not have been detected if not for its strong ring-shaped aeromagnetic anomaly, which has a 10 km inner diameter and a 14 km outer diameter. We interpret the circular magnetic signature as the product of truncation and folding of mafic sills into a ring syncline. The sills most likely correlate with dolerites that intrude the Boondawari Formation ～25 km to the north, for which we report a SHRIMP U?–?Pb baddeleyite and zircon age of 508?±?5 Ma, providing a precise older limit for the impact event that formed the Glikson structure.     

Vines 1 revisited: are older Neoproterozoic glacial deposits preserved in Western Australia?

The stratigraphy in Vines 1, a 2017.5 m-deep cored stratigraphic hole drilled by the Geological Survey of Western Australia in 2001 near the Western Australian – South Australian border, has been reinterpreted with implications for the Neoproterozoic to Cambrian geological history of the Officer Basin. A previous interpretation considered the intersected succession as a conformable stratigraphic package, the Vines Formation. An assemblage of palynomorphs, found throughout the hole and previously used to infer an age of no older than earliest Cambrian, is now thought to consist of contaminants. An older assemblage, which is considered to be reworked and inherited from underlying rocks, provides a new maximum age constraint of mid-Neoproterozoic. Based on sedimentological interpretations and comparisons with other drillholes in the western Officer Basin, and the succession in the eastern Officer Basin, the Vines 1 succession is reinterpreted as four discrete sedimentary packages, the Pirrilyungka (new name), Wahlgu, Lungkarta and Vines (redefined) Formations, in ascending order. The Pirrilyungka and Wahlgu Formations include glacigenic sediments and may correlate with similar glacial successions in Supersequences 2 and 3 (mid to late Cryogenian) of the Centralian Superbasin, and the Sturt Tillite and Elatina Formation and their equivalents in the Adelaide Rift Complex of South Australia, respectively. The eolian Lungkarta Formation and fluvial Vines Formation are considered, on regional evidence, to be most likely of Ediacaran to earliest Cambrian age.     

Nature and significance of the Neoproterozoic Sturtian–Marinoan Boundary,Northern Adelaide Geosyncline,South Australia

The Cryogenian succession of the Northern Flinders Ranges reveals a complex sedimentary record between the Sturtian and Marinoan glacial deposits. A major unconformity separates the Sturtian and Marinoan-aged sedimentary successions in the area. This forms a subaerial erosion surface with terrestrial and marginal marine infill directly above the Angepena and Balcanoona Formations in their respective localities. This exposure surface is here correlated with the previously documented submarine unconformity between the Yankaninna Formation and the underlying deep marine Tapley Hill Formation. This erosional event provides a chronostratigraphic marker horizon that coincides approximately with thepreviously defined Sturtian–Marinoan Time Series boundary in the Northern Flinders Ranges. These stratigraphic relationships also constrain lateral facies relationships between the Oodnaminta ReefComplex (Balcanoona Formation) and the Angepena Formation. Similarly, the shallow-water Weetootla Dolomite is correlated with the deeper water carbonates of the Yankaninna Formation.