Anatomy of the marginal zone of the Waulsortian Carbonate bank (mudmound) complex, North Co. Galway

Q4 Earth and Planetary Sciences
A. Lees
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Abstract

Abstract:Two closely-spaced drill-cores through the marginal zone of the Waulsortian Complex in north Co. Galway have been studied petrographically to help identify factors that limited spread of the banks and led to their demise. The Waulsortian limestones found there have textural and structural characters and skeletal-grain content of Waulsortian Phase C, indicating a relatively shallow-water environment but below the depths colonised by calcareous chlorophyte algae. Bank depositional structures of both flat-lying and clinoform type are present. Four associated limestone facies are distinguished: off-bank, precursor (beneath and around the banks), cap (directly overlying banks) and cover facies. Spatial relationships between these are used to construct a depositional model. Five developmental stages are recognised through the sequence and used to correlate the two sections. The distribution of biostratigraphically significant foraminifera supports the sedimentological correlation. Throughout the sequence there was unusual physical disturbance of the sediments by water movement. There is evidence of progressively increasing damage to the polymud-forming processes. Formation of cryptofibrous cements and micritisation were affected at a late stage. Interference in development of precursor muds, probably more vulnerable than the banks, could have ‘killed’ the Complex by halting bank-initiation. The timing of these changes correlates with a sea-level fall identified elsewhere in Ireland and abroad.
北戈尔韦公司沃尔索田碳酸盐岩滩(泥丘)杂岩边缘带解剖
摘要:对戈尔韦州北部Waulsortian杂岩边缘带的两个紧密间隔的岩芯进行了岩石学研究,以帮助确定限制河岸扩展并导致其消亡的因素。在那里发现的沃氏石灰岩具有沃氏C相的质地和结构特征以及骨骼颗粒含量,表明其水环境相对较浅,但低于钙质绿藻定殖的深度。存在平坦型和斜坡型的河岸沉积结构。有四种相关的石灰岩相可区分:离岸相、前体相(河岸下方和周围)、盖层相(直接覆盖河岸)和盖层相。它们之间的空间关系用于构建沉积模型。通过序列识别出五个发育阶段,并用于将这两个部分关联起来。具有生物地层学意义的有孔虫的分布支持了沉积学对比。在整个序列中,水的运动对沉积物产生了不寻常的物理干扰。有证据表明,多泥形成过程中的损伤逐渐增加。隐纤维胶结物的形成和泥化在晚期受到影响。对前体泥浆开发的干扰,可能比河岸更脆弱,可能会通过停止河岸启动来“杀死”综合体。这些变化的时间与爱尔兰其他地方和国外发现的海平面下降有关。
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来源期刊
Irish Journal of Earth Sciences
Irish Journal of Earth Sciences Earth and Planetary Sciences-Earth and Planetary Sciences (all)
CiteScore
0.90
自引率
0.00%
发文量
2
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