Seismic facies analysis of Westphalian sequences of the southern North Sea

Differing seismic facies are observed from within the Westphalian sequences of the southern North Sea. A review of published synthetic seismograms and seismic data from known coal-bearing basins establishes seismic facies types and their relationships. Similar reflection character is recognized from Westphalian sequences in the southern North Sea and lithologies confirmed by borehole information. Probable sand/silt or clastic-prone Upper Coal Measures (Westphalian C/D) stages and coal-prone Lower and Middle Coal Measures (Westphalian A, B and part C) stages can be defined and mapped, providing information on the regional distribution of source and reservoir rocks and stratigraphic plays. It is suggested that sand-prone channel complexes or clastic dominated areas within the mainly A/B stages can be recognized and mapped, providing information on migration pathways and stratigraphic plays.     

鲁西北平原可持续农业发展的机制与途径——以东昌府区为例

以鲁西北平原东昌府区为典型案例,通过动态分析和典型调查,揭示东昌府区农业可持续发展的投入机制、市场机制、科技应用、经营管理和决策调控机制的运行规律。在此基础上,针对性提出了农业可持续发展的产业结构调整;农业市场化、企业化和专业化基地发展,推动农业产业化进程;发展农业科技,提高农民素质,加强农业人力资本建设和建立农业可持续发展的调控机制四个方面的发展对策。     

洛阳市张庄地热井地热资源开发利用与保护浅析

张庄地热井已完工两年多,至今尚未开发利用.针对张庄地热井地热流体化学特征,对地热资源和地热水可开采资源量进行了计算与评价,对地热流体质量进行了七项水质评价,提出了地热资源的开发利用方向,并对地热资源的开发利用可能引发的环境问题及保护措施提出了建议.     

临清市地下水漏斗区与地面沉降研究

随着经济的发展和人口的不断增加,城区用水量大幅度上升.临清市城区生活及工业用水全部为地下水,由于大量超采地下水,造成了地下水位埋深大幅度下降,形成了以城区为中心的大面积地下水漏斗区.地下水位大幅度下降,势必引起地面沉降等环境地质问题.因此摸清临清城区地下水的下降规律及地质状况、漏斗区的范围、地面沉降的状况并提出阻止地面沉降的措施,对地上建筑物、地下构筑物保护等都具有十分重要的意义.     

广西合浦包墩水库工程地质问题分析及对策

对包墩水库建成运行以来的工程地质、水文地质及大坝渗漏、稳定作出评价,归纳存在的工程地质问题,提出相应的防渗漏处理措施。     

Geology and mining practice in relation to shallow subsidence in the Northern Coalfield,New South Wales

The former Northern Coalfield, comprising much of the Newcastle‐Maitland‐Cessnock‐Lake Macquarie region, has now been mined for two hundred years. Most of the twenty‐odd seams in the Newcastle, Tomago and Greta Coal Measures have been worked, but the bulk of production has been drawn from just four coalbeds: the Borehole, Greta, Homeville and Great Northern Seams. Literally hundreds of mine names are on record for the coalfield, the great majority working these seams at depths of less than 30 m. This paper reviews regional subsidence problems in the context of mining history, past mining practices and coal measures geology. Subsidence over shallow bord‐and‐pillar workings may result in highly disturbed ground, open fissures, cratering, seam fires and ‘creeps’ (slow surface movements caused by gradual closure of mine cavities). This form of subsidence differs from that over modern longwall mines in being less predictable, affecting much smaller areas, and occurring sometimes decades after mine abandonment. The geological factors contributing to this subsidence hazard include the multiplicity of seams, the strong roof sandstones, stiff coal and relatively soft floors, and the presence of faults and dykes. The working of thick seams like the Borehole Coal in up to three phases, leaving high, slender pillars, also contributed to later ground instability. Contrary to expectation, the main problem areas are not over haphazardly laid‐out convict‐era pits, but rather above small hand‐worked scavenger mines (‘ratholes’) which operated as late as the 1950s. Many of these short‐lived collieries still contain large voids at shallow depth, sometimes only a few metres, which must eventually collapse or be backfilled.     

Alternating episodes of extension and contraction during the Triassic: evidence from Mesozoic sedimentary basins in eastern Australia

Triassic to Lower Cretaceous continental sedimentary basins occur in eastern Australia, but the tectonic and structural evolution of these basins is not fully understood. Using gridded aeromagnetic data, seismic reflection data and field observations, we conducted a structural analysis aimed at characterising major faults and deformation style in these sedimentary basins. Our results show evidence for two alternating episodes of rifting during the Triassic. An earlier episode of rifting, which took place in the Early Triassic to early Late Triassic, is inferred based on synsedimentary normal faults in the Nymboida Coal Measures and the boundary West Ipswich Fault System in the Esk Trough. This phase of rifting was followed by a contractional event that resulted in tilting, folding, and thrust faulting. Evidence of synsedimentary normal faults and bimodal volcanism indicates that another rifting phase occurred during the Late Triassic and resulted in the development of the Ipswich Basin. From the latest Late Triassic to the Early Cretaceous, the accumulation of continental sediments in the Clarence-Moreton Basin was accompanied by subsidence. We suggest that the alternating rifting episodes and contraction were ultimately controlled by plate boundary migration and switches between trench retreat and advance during the Triassic.     

Age of the Yarrabee and accessory tuffs: implications for the upper Permian sediment-accumulation rates across the Bowen Basin

The Yarrabee Tuff is a stratigraphically significant marker across the Bowen Basin separating the Fort Cooper–Burngrove–Fair Hill formations from the overlying Rangal and equivalent coal measures. At least three to four persistent tuffs (referred here as accessary tuffs) beneath the Yarrabee Tuff were recognised in the Fort Cooper Coal Measures as suitable for regional stratigraphic correlations. In this study, we determined the ages of the Yarrabee and accessary tuffs across different morphotectonic zones of the basin through high-precision U–Pb dating of zircon with the CA-IDTIMS technique. The age of the Yarrabee Tuff is found to be 252.69 ± 0.16 Ma in the Duckworth 11 well, 253.07 ± 0.22 Ma in the Crocker Gully 2 well and <252.58 ± 0.23 Ma in the Peat 1 well. The age range of the Yarrabee Tuff coincides with the previously published date of the Kaloola Tuff Member in Meeleebee 5 suggesting that the tuffs are stratigraphically equivalent. The age range for the accessory tuff 1 is 253.12 ± 0.12 Ma to 252.85 ± 0.16 Ma, 253.45 ± 0.08 Ma for accessory tuff 2 and 253.77 ± 0.17 Ma to 253.57± 0.18 Ma for accessory tuff 3, placing them in the upper Changhsingian Stage. The age of the accessory tuff 6 (less laterally consistent in the basin) from the Fair Hill Formation is 254.03 ± 0.03 Ma, placing it in the lower Changhsingian Stage. The age-constrained intervals allow the estimation of sedimentation rates using decompacted coal and clastic sediment thickness. In the Taroom Trough, the temporal variation in sedimentation rates is found to be 902 m/Ma in the Fair Hill Formation decreasing to 234.5 m/Ma in the overlying Burngrove Formation, reflecting a decrease in accommodation or sediment supply upwards in the sequence. Across the basin, the sedimentation rates for the Burngrove Formation are consistently higher in the Taroom Trough ranging between 234.5 and 224.5 m/Ma and lower rates of 112 m/Ma in the Roma Shelf. This regional variation reflects areas of high sedimentation rates that are high accommodation sites recognised by split coal seams and increased interburden. Conversely, low sedimentation rates reflect low accommodation sites, such as the Roma Shelf and the Burunga Anticline that are characterised by coalesced coal seams. The results help to understand stratal relationships across variable accommodation sites, basin-fill history of the basin including extent of sediment supply and paleotopographic controls during the evolution of the Bowen Basin. We also discuss criteria for interpreting the results of CA-IDTIMS U–Pb dating and consider the possible geological uncertainties related to either the primary magmatic processes or secondary reworking of tuffs at the site of deposition.     

The anatomy of a coal seam split,Durham coalfield,Northeast England

A pronounced coal seam split, one of many within the Lower Westphalian B (Upper Carboniferous) sequence of the Durham coalfield, northeast England, occurs in the vicinity of the village of Burnhope. This feature involves the division of the combined Main/Fivequarter coal into its two component parts, which become separated by up to 8 m of clastic sedimentary rocks over a horizontal distance of 150 m. Three-dimensional outcrop data from an opencast (surface) coal mine straddling the split, supported by extensive subsurface information, have allowed detailed study of the seam split geometry, in addition to that of three overlying coal seams and intervening clastic facies. The study suggests that deposition of the interval as a whole, including the split, was strongly influenced by compaction-controlled subsidence, and not by either contemporary fault movements or channel sedimentation. A substantially greater aggregate thickness of coal is preserved over the five seam interval where the Main/Fivequarter is unsplit than where split. This relationship is consistent with the coal depositional model proposed by Fielding (1984a), which proposed that thick coals in the Durham area are located adjacent to, but not within, coal seam splits. It further implies that attractive sites for future opencast development in the area may be predicted from a regional knowledge of coal seam splits.     

A relation between abrasiveness and quartz content for some Coal Measures sediments

Conclusions 1. For a limited range of Coal Measures sediments, it has been shown that a good relation exists between the abrasiveness of the rocks and their quartz content.2. In this instance it was not possible to make any correlation with cutter wear, but it would be expected from the above result that the higher the quartz content of the rock the greater would be the wear on the cutters.