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293.
微生物白云石模式评述 总被引:2,自引:2,他引:2
Vasconcelos等在实验室模拟巴西Lagoa Vermelha潟湖条件,成功地沉淀出白云石,由此提出了微生物白云石模式。该模式在南澳大利亚、阿拉伯海湾、西印度外陆棚边缘以及意大利南部等地区得到了不同研究者的肯定,我国鄂尔多斯盆地奥陶系马家沟组五段白云岩也可以解释为微生物成因。此模式对白云石形成机理的研究具有突破性的意义。当硫酸盐还原细菌利用SO42-时,也吸收了Mg2+,因为Mg2+与SO42-形成了很强的离子对。微生物由于其新陈代谢作用利用SO42-而克服了动力障碍,同时从离子对中释放出Mg2+。在白云石形成的化学反应中,微生物因素把硫酸根离子从反应的抑制剂变成了催化剂。白云石一旦成核,就会在埋藏过程中长大。尽管不是所有的白云石都可以用微生物白云石模式来解释,但野外研究和模拟实验都证明这一模式是有说服力和生命力的。 相似文献
294.
Beyene G.Haile Urszula Czarniecka Kelai Xi Aleksandra Smyrak-Sikora Jens Jahren Alvar Braathen Helge Hellevang 《地学前缘(英文版)》2019,10(2):629-649
Sedimentary basins containing igneous intrusions within sedimentary reservoir units represent an important risk in petroleum exploration. The Upper Triassic to Lower Jurassic sediments at Wilhelm?ya(Svalbard) contains reservoir heterogeneity as a result of sill emplacement and represent a unique case study to better understand the effect of magmatic intrusions on the general burial diagenesis of siliciclastic sediments. Sills develop contact metamorphic aureoles by conduction as presented in many earlier studies. However, there is significant impact of localized hydrothermal circulation systems affecting reservoir sediments at considerable distance from the sill intrusions. Dolerite sill intrusions in the studied area are of limited vertical extent(~12 m thick), but created localized hydrothermal convection cells affecting sediments at considerable distance(more than five times the thickness of the sill)from the intrusions. We present evidence that the sedimentary sequence can be divided into two units:(1) the bulk poorly lithified sediment with a maximum burial temperature much lower than 60-70 ℃,and(2) thinner intervals outside the contact zone that have experienced hydrothermal temperatures(around 140 ℃). The main diagenetic alteration associated with normal burial diagenesis is minor mechanical plastic deformation of ductile grains such as mica. Mineral grain contacts show no evidence of pressure dissolution and the vitrinite reflectance suggests a maximum temperature of ~40 ℃. Contrary to this, part of the sediment, preferentially along calcite cemented flow baffles, show evidence of hydrothermal alteration. These hydrothermally altered sediment sections are characterized by recrystallized carbonate cemented intervals. Further, the hydrothermal solutions have resulted in localized sericitization(illitization) of feldspars, albitization of both K-feldspar and plagioclase and the formation of fibrous illite nucleated on kaolinite. These observations suggest hydrothermal alteration at T 120-140 ℃ at distances considerably further away than expected from sill heat dissipation by conduction only, which commonly affect sediments about twice the thickness of the sill intrusion. We propose that carbonate-cemented sections acted as flow baffles already during the hydrothermal fluid mobility and controlled the migration pathways of the buoyant hot fluids. Significant hydrothermally induced diagenetic alterations affecting the porosity and hence reservoir quality was not noted in the noncarbonate-cemented reservoir intervals. 相似文献
295.
城口锰矿是成岩作用的产物,除叠层石外其它如鲕粒、豆粒、球粒等主要源自碳酸盐台地,由合适的海流搬运而来,后被原地生长的微生物韵律性包覆而构成稳定的“滩”。Mn2+主要来源于下部富含有机质、形成于深水还原环境之泥岩的粒间水,其极有利于来自陆地和海底喷发的锰质的富集和保存,在成岩作用时受上覆重荷影响使富含Mn2+的酸性粒间水被排驱,向压力较小的孔隙度大、渗秀性好的“滩”内转移,使“滩”相弱碱性碳酸盐层的Ca2+、Mg2+被Mn2+交代而成矿。 相似文献
296.
L. Macchi 《Geological Journal》1987,22(4):333-345
Current understanding of the origin of illite cements within the pore systems of sandstone reservoirs is at best speculative whilst knowledge of the control of illite morpholoy is, to all practical purposes, non-existent. This is unfortunate considering the widespread occurrence of illite and the often disastrous decrease in reservoir performance associated with its presence (up to 200-fold decreases in permeability have been recorded from aeolian sandstones of the U.K. southern North Sea for example). An advanced knowledge of the origin of this clay mineral is thus of considerable importance to the future of the hydrocarbon exploration and production industry. This paper presents an assessment of sandstone illite morphotypes and reviews the mechanisms which have been proposed for their formation. 相似文献
297.
Diatomite associated with the Kolubara Coal Basin was studied to better understand early stage silica diagenesis of shallow water deposits. The Kolubara Basin consists of Neogene siliciclastic rocks, diatomite, marlstone and rare carbonates. Palaeozoic metamorphic and Mesozoic sedimentary and igneous basement rocks are transgressively overlain by Upper Miocene sandstone, siltstone, shale and mudstone. This Upper Miocene section is transgressively overlain by the Pontian section, which contains diatomite and coal beds. White and grey diatomite forms beds 0.7-2.2 m thick that are continuous over an area of about 2 km2. Siliceous rocks vary in composition from diatomite (81-89 per cent SiO2) to diatom-bearing shale (58-60 per cent SiO2). Siliceous deposits are laminated in places, with the laminae defined by variations in clay minerals, organic matter and diatoms. Diatomite shows only incipient diagenesis characterized by the fragmentation of diatom frustules, the minor to moderate corrosion of frustules and the formation of minor amounts of opal-A' (X-ray amorphous inorganic opal) cement. The low degree of diagenesis results from the young age of the deposits, low burial temperatures and possibly also from the presence of abundant organic matter and the dissolution of kaolinite. The presence of only weak diagenesis is also reflected by the characteristically poor consolidation of the rocks and low rank of the associated coal. 相似文献