Diagenesis of Triassic Sherwood Sandstone Group rocks, Preston, Lancashire, UK: a possible evaporitic cement precursor to secondary porosity?
Diagenesis of Triassic Sherwood Sandstone Group rocks, Preston, Lancashire, UK: a possible evaporitic cement precursor to secondary porosity?
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英国兰开夏郡普雷斯顿三叠纪舍伍德砂岩群岩石的成岩作用：可能是次生孔隙的蒸发胶结物前体？
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发表时间：
1993
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通讯作者：
G. E. Strong
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作者：
G. E. Strong
兰开夏郡Kirkham [SD 4324 3247]和Weeton Camp [SD 3888 3603]的钻孔穿透了位于Manx-Furness（东爱尔兰海）盆地东缘附近的舍伍德砂岩群的三叠纪砂岩。对岩心砂岩样品进行岩石学分析，以确定成岩特征。一些孔隙度为25-30%的非常多孔的砂岩具有胶结物溶解纹理，表明早期大量的胶结物很大程度上被侵蚀性孔隙流体去除，可能是在三叠纪。这些早期胶结物是方解石和非铁白云石，可能是在麦西亚泥岩沉积期间引入的后来的碳酸盐胶结物（硬石膏、石膏、岩盐）。非铁白云石的形成时间晚于早期方解石，并局部取代早期方解石。少量含铁白云石、晚期方解石和黄铁矿。在某些石英砂屑岩中，发育了广泛的早期石英增生和胶结物。孔隙度值约为10 - 13%，但渗透率可能较低。这些石英胶结的石英砂岩单元可以在钻孔之间相互关联。各钻孔砂岩的粘土矿物组合差异较大。Kirkham序列的特征是伊利石，含有富含Fe的绿泥石和少量蒙皂石，而Weeton Camp序列则以高岭石为主，含有少量伊利石和蒙皂石。这些差异归因于不同的孔隙流体历史，可能是结构控制。
Abstract Boreholes at Kirkham [SD 4324 3247] and Weeton Camp [SD 3888 3603] in Lancashire penetrate Triassic sandstones of the Sherwood Sandstone Group that occur near the eastern margins of the Manx-Furness (East Irish Sea) Basin. Petrological analysis of sandstone samples from cores was undertaken to determine diagenetic characteristics. Some very porous sandstones with porosities of the order of 25–30% have cement dissolution textures indicating that earlier extensive cements have largely been removed by aggressive pore fluids, probably during the Triassic. These early cements were calcite and non-ferroan dolomite, and possibly later evaporitic cements (anhydrite, gypsum, halite) introduced during the period of deposition of the Mercia Mudstones. Non-ferroan dolomite post-dates and locally replaces early calcite. There is minor ferroan dolomite, late calcite and pyrite. Extensive early quartz overgrowths and cements have developed in some quartz arenites. Porosity values are about 10 to 13%, but permeabilities are likely to be low. These quartzcemented quartz arenite units may correlate between the boreholes. The clay mineral assemblages of the sandstones of each borehole are significantly different. The Kirkham sequence is characterized by illite with Fe-rich chlorite and minor smectite, whereas the Weeton Camp sequence is dominated by kaolinite with minor illite and smectite. These differences are attributed to different pore fluid histories, possibly structurally controlled.