A sequence stratigraphic model for the Lower Coal Measures (Upper Carboniferous) of the Ruhr district, north-west Germany

Upper Carboniferous Coal Measures strata have been interpreted traditionally in terms of cyclothems bounded by marine flooding surfaces (marine bands) and coal seams. Correlation of such cyclothems in an extensive grid of closely spaced coal exploration boreholes provides a robust stratigraphic framework in which to study the Lower Coal Measures (Namurian C–Westphalian A) of the Ruhr district, north-west Germany. Three distinct types of cyclothem are recognized, based on their bounding surfaces and internal facies architecture. (1) Type 1 cyclothems are bounded by marine bands. Each cyclothem comprises a thick (30–80 m), regionally extensive, coarsening-upward delta front succession of interbedded shales, siltstones and sandstones, which may be deeply incised by a major fluvial sandstone complex. The delta front succession is capped by a thin (<1 m), regionally extensive coal seam and an overlying marine band defining the top of the cyclothem. (2) Type 2 cyclothems are bounded by thick (≈1 m), regionally extensive coal seams with few splits. The basal part of a typical cyclothem comprises a thick (15–50 m), widespread, coarsening-upward delta front or lake infill succession consisting of interbedded shales, siltstones and sandstones. Networks of major (>5 km wide, 20–40 m thick), steep-sided, multistorey fluvial sandstone complexes erode deeply into and, in some cases, through these successions and are overlain by the coal seam defining the cyclothem top. (3) Type 3 cyclothems are bounded by regionally extensive coal seam groups, characterized by numerous seam splits on a local (0·1–10 km) scale. Intervening strata vary in thickness (15–60 m) and are characterized by strong local facies variability. Root-penetrated, aggradational floodplain heteroliths pass laterally into single-storey fluvial channel-fill sandstones and coarsening-upward, shallow lake infill successions of interbedded shales, siltstones and sandstones over distances of several hundred metres to a few kilometres. Narrow (<2 km) but thick (20–50 m) multistorey fluvial sandstone complexes are rare, but occur in a few type 3 cyclothems. Several cyclothems are observed to change character from type 1 to type 2 and from type 2 to type 3 up the regional palaeoslope. Consequently, we envisage a model in which each cyclothem type represents a different palaeogeographic belt within the same, idealized delta system, subject to the same allogenic and autogenic controls on facies architecture. Type 1 cyclothems are dominated by deltaic shorelines deposited during a falling stage and lowstand of sea level. Type 2 cyclothems represent the coeval lower delta plain, which was deeply eroded by incised valleys that fed the falling stage and lowstand deltas. Type 3 cyclothems comprise mainly upper delta plain deposits in which the allogenic sea-level control was secondary to autogenic controls on facies architecture. The marine bands, widespread coals and coal seam groups that bound these three cyclothem types record abandonment of the delta system during periods of rapid sea-level rise. The model suggests that the extant cyclothem paradigm does not adequately describe the detailed facies architecture of Lower Coal Measures strata. Instead, these architectures may be better understood within a high-resolution stratigraphic framework incorporating sequence stratigraphic key surfaces, integrated with depositional models derived from analogous Pleistocene–Holocene fluvio-deltaic strata.     

Strategic elements in the Fort Cooper Coal Measures: potential rare earth elements and other multi-product targets

Abstract

Mineral matter in coals has been found to host valuable elements including germanium, lithium and rare-earth elements (REE), but such content of Australian coals remains under-explored. The aim of this paper is to provide a proof-of-concept study that determines elemental concentrations in the mineral matter of the high-ash, Fort Cooper Coal Measures (FCCM), Bowen Basin, Queensland. Coal in the FCCM has good coking properties but has not been extensively explored owing to its high ash content. This study performs a preliminary assessment of the elements from the coal portion that would typically become waste after washing or combustion. Given that the needs for industrial extraction methods will change over time, cataloguing and documenting the elemental composition of coal may assist future development of multiple products for the benefit of both the coal and mineral industries. This preliminary study has revealed similar elevations of REE and higher-than-average crustal concentrations of lithium, bismuth and scandium in some of the samples. Further analyses will be required on a larger dataset to better understand elemental associations and explore spatial patterns of elemental content that may indicate localised enrichments. Understanding the potential of valuable elements in the FCCM may stimulate interest in multiple-product-coal (or elemental-coal) mining in this under-exploited resource and further encourage the reduction of waste from other Australian coals at the wash-plant stage.     

Age and significance of the Platypus Tuff Bed,a regional reference horizon in the Upper Permian Moranbah Coal Measures,north Bowen Basin

The Platypus Tuff Bed in the Permian Moranbah Coal Measures provides a basin‐wide marker horizon traceable for over 300 km along strike. The bed is a tephra event unit, the product of a large‐scale volcanic eruptive episode involving a pyroclastic volume > 10 km³. The relatively even thickness (～1–1.5 m) of the tuff across the entire northern Bowen Basin (～10 000 km²) implies a distant source. The tuff is ash‐rich and its original geochemistry has been compromised by diagenetic alteration. Crystal content (10–15%) is dominated by quartz, suggesting a rhyolitic association. SHRIMP U–Pb analysis of zircons indicates an age of 258.9 ± 2.7 Ma for the Platypus Tuff Bed, confirming the Late Permian age that has generally been assigned to the Blackwater Group. The age framework now apparent for the coal‐bearing Blackwater Group suggests an average depositional rate ranging from ～133 m/10⁶ years for its eastern depocentre in the northern Bowen Basin to ～70 m/10⁶ years in more marginal settings to the west.     

基于烧失量与氧化铝含量关系的红土型三水铝土矿快速勘查

文章通过论述烧失量中的成分与氧化铝含量之间关系,建立了LOI与Al_2O_3的经验公式;经过在几内亚某红土型三水铝土矿地质勘探过程中实地验证,该经验关系公式合理。此方法具有较强的实践应用性,对类似条件的铝土矿床现场勘查评价具有一定的参考价值。     

达里湖沉积粒度组分-湖面状况定量模型

湖泊碎屑沉积物的粒度分布可以提供与区域气候变化相关的湖泊水文变化信息。然而, 由于湖泊沉积物多峰分布固有的复杂性, 其粒度组分成因的解释仍存在很大的不确定性。本文利用对数正态分布函数对内蒙古达里湖36个表层沉积物样品的粒度组分进行了分离, 并探讨了各组分特性与特定沉积环境(包括每个采样点位的离岸距离和水深)之间的关系。结果表明, 达里湖现代碎屑沉积物包含5个截然不同的单峰粒度分布, 分别代表5个不同的粒度组分。虽然其相对百分含量随湖泊水动力条件而变化, 但每个组分均保留着各自的众数粒径、搬运方式、沉积环境等特性。这些组分自细而粗可分为: 长期悬移粘土组分、离岸带悬移细粉砂组分、离岸带悬移中粗粉砂组分、近岸带悬移细砂组分、近岸带跃移中砂组分。近岸带环境两个组分的百分含量与现今湖泊水深呈负相关, 揭示出沉积岩芯近岸带组分与地质历史时期湖面状况相关联的数值模型。该模型在达里湖沉积岩芯中的应用显示, 近岸带组分百分含量增加与同岩芯孢粉序列重建的区域降水减少相对应。两种独立的代用指标在时间上的一致性, 不仅展示了对数正态分布函数分离多峰沉积物的有效性, 而且揭示出利用粒度组分-湖面状况模型重建湖泊古水文的潜力。     

低渗油气储层物理参数解释模型——以宝浪油田煤系粗粒低渗储层为例

为了建立宝浪油田粗粒低渗储层的精确渗透率解释模型,从储层物性的影响因素分析入手,确定影响此类储层物性的关键属性参数.从表征岩石结构参数的流动带指数的角度建立了孔隙度和渗透率的关系模型,逐步建立以测井数据为基础的流动单元的判别函数.在流动单元判别的基础上,根据孔隙度和渗透率的关系模型进行了从测井数据到渗透率参数的计算.宝浪油田三工河组储层Ⅲ油组划分出5类流动单元类型,在流动单元控制下解释的储层渗透率值,经实际应用能够满足储层精细描述的要求.     

A methodology for the study of the relation between coastal cliff erosion and the mechanical strength of soils and rock masses

A methodology is proposed to make approximate estimates of the destructive force of waves at the bottoms of cliffs where no accurate bathymetric data are available, by means of correlation between the erosion rate of rocky coasts and the mechanical strength of soils and rock masses. The correlation used makes it possible to obtain a linear semi-logarithmic expression between the long-term average erosion rate (from an engineering standpoint) of coasts consisting of different lithologies, wave energy, and the uniaxial compressive strength of soils and rock masses forming the cliffs. The uniaxial compressive strength of soils consisting of landslide debris was measured using a pocket penetrometer and the Rock Mass index (RMi) method was used for rock masses. These methods were chosen after critical analysis of the methodologies currently available. The proposed approach was tested in the Cilento area of southern Italy, and in particular along a 6 km stretch of coast typified by rock masses and landslide debris that are particularly susceptible to erosion. This coastline is exposed to south-westerly waves which in deep water reach significant heights (between 1 and 3 m) and significant wave periods (between 4 and 7 s). Estimates of the coastal erosion rates were made by studying the variations, especially in restricted headland areas, occurring over two time spans, 30 and 45 years, respectively by comparing topographic maps and aerial photographs taken at different times. These comparisons give approximate indications of retreats of 15 m over the time span of 30 years (average erosion rate of 0.5 m year⁻¹) and of 35 m over the time span of 45 years (average erosion rate of ca 0.8 m year⁻¹). These data do have a local significance but clearly show how quick these processes sometimes are. Lastly, the study of a notch incised by wave action on a concrete sea wall built to protect a terrace made it possible to quantify the impact of erosion on concrete. It was possible to obtain RMi-values through field observations. Furthermore, it was possible to obtain the constants of the Hoek and Brown failure criterion using RMi. On the basis of RMi-values, the rock masses studied were defined as ‘moderately strong’ to ‘strong’ and, according to the Hoek and Brown criterion, as ‘poor’ to ‘fair’. A semilogarithmic linear relation was found between the strength of landslide debris, rock masses and concrete, as well as their respective long-term erosion. Consequently, a rough estimate of the destructive force of waves (ca 24 MPa) was calculated. This value is given by the product of the mean value of their hydraulic pressure for a non-dimensional constant which, in turn, takes into account the sandy-pebbly beach sediment at the foot of the cliffs that acts as an abrasive on the rock mass.     

Distribution Characteristics and Accumulation Model for the Coal‐formed Gas Generated from Permo‐Carboniferous Coal Measures in Bohai Bay Basin,China: A Review

Coal-formed gas generated from the Permo-Carboniferous coal measures has become one of the most important targets for deep hydrocarbon exploration in the Bohai Bay Basin, offshore eastern China. However, the proven gas reserves from this source rock remain low to date, and the distribution characteristics and accumulation model for the coal-formed gas are not clear. Here we review the coal-formed gas deposits formed from the Permo-Carboniferous coal measures in the Bohai Bay Basin. The accumulations are scattered, and dominated by middle-small sized gas fields, of which the proven reserves ranging from 0.002 to 149.4×108 m3 with an average of 44.30×108 m3 and a mid-point of 8.16×108 m3. The commercially valuable gas fields are mainly found in the central and southern parts of the basin. Vertically, the coal-formed gas is accumulated at multiple stratigraphic levels from Paleogene to Archaeozoic, among which the Paleogene and PermoCarboniferous are the main reservoir strata. According to the transporting pathway, filling mechanism and the relationship between source rocks and reservoir, the coal-formed gas accumulation model can be defined into three types: "Upward migrated, fault transported gas" accumulation model, "Laterally migrated, sandbody transported gas" accumulation model, and "Downward migrated, sub-source, fracture transported gas" accumulation model. Source rock distribution, thermal evolution and hydrocarbon generation capacity are the fundamental controlling factors for the macro distribution and enrichment of the coal-formed gas. The fault activity and the configuration of fault and caprock control the vertical enrichment pattern.