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Alison Searl 《Geological Journal》1992,27(3):243-270
The Broadford Beds comprise a basal carbonate-dominated unit overlain by dark muddy sandstones and an upper cross-bedded sandstone unit. The limestones include coralliferous and oolitic lithologies and the sandstones include pisolitic berthierine ironstones and abundant phosphate nodules. The Broadford Beds have a maximum thickness of 140 m and can be subdivided into 17 parasequences, each initiated by an approximately 20 m rise in relative sea level. Marine flooding surfaces are most readily recognized in the lower parts of the succession, where diagenetic data can be utilized to locate emergence surfaces. There is no diagenetic evidence of early emergence in the upper parts of the sequence, but a variety of sedimentological data can be used to identify parasequence boundaries. Deposition of the Broadford Beds occurred largely around the shores of a number of islands in the northern Hebridean area. These islands partly isolated the Skye–Applecross area from a deeper marine basin to the west, and this may have enhanced the formation of authigenic phosphates and iron silicates. It is possible to use the regional variability of parasequence thicknesses to investigate the role of active local tectonism in governing differential subsidence and sediment supply. 相似文献
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J.M. Huggett A.S. Gale C. Hazell 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(6):782-789
The Vectis Formation was deposited in a restricted lagoonal environment that periodically dried up, as indicated by the presence of desiccation surfaces. The fauna indicates that salinities fluctuated significantly during deposition, from fresh to brackish-marine. Pre-burial berthierine-rich clay replaced faecal pellets in the sediment, infilling desiccation cracks, during re-flooding of the lagoon. Concretions formed by early pyrite and apatite cementation during initial burial in lake sediment, with organic debris of fish and wood, acting as nuclei and a trigger for cementation. With subsequent partial or complete exhumation oxidation of the pyrite occurred, prior to cementation by Mn siderite. All further concretion cementation occurred within the oxic to sub-oxic diagenetic zones. Textural relationships indicate that commonly occurring baryte formedafter pyrite oxidation and represents the last diagenetic mineral phase. 相似文献
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Jesper Stokkendal Henrik Friis Johan B. Svendsen Mette Lise K. Poulsen Lars Hamberg 《Marine and Petroleum Geology》2009
The Hermod sand of the Stine Segments, Siri Field, Danish North Sea, displays large permeability variations (1–600 mD). These permeability variations represent horizontal layering in the reservoir, largely formed by diagenetic processes. They have a significant impact on reservoir performance, because horizontal producers in fairly thin reservoirs (∼30 m) are protected against bottom-water influx and can produce water-free for long periods of time. 相似文献
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