加拿大西部阿萨巴斯卡油砂矿床下白垩统McMurray组Mn - Fe -方解石和Mn -菱铁矿微球晶结构的盐溶构造和湖相碳酸盐层成因

IF 1.9 3区 地球科学 Q1 GEOLOGY
Paul L. Broughton
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引用次数: 0

摘要

在加拿大西部阿萨巴斯卡油砂矿床北部的下白垩统麦克默里组地层中,首次发现了几个湖相碳酸盐岩层,每个层厚达1米,由密集排列的富锰菱铁矿微球粒或富锰铁方解石微球粒组成。下麦克默里湖相碳酸盐矿床以一米厚的富锰菱铁矿微球晶为特征。中上部McMurray层发育富锰方解石微球粒结构。这些碳酸盐层代表了盐碱化湖泊沉积环境,是由湖底沉积物由富含Mn2+ - Fe2+的碳酸盐饱和盐水从下面侵入而形成的。这些泥盆纪地层水的上剖面迁移来自于阿尔伯塔盆地前陆科迪勒拉变形期间下伏泥盆纪草原蒸发岩的灰岩和盐硬石膏层的溶解趋势。这些盐水沿着角砾岩管道、陷落孔和不同沉降的上泥盆统断块边缘等溶蚀崩塌构造上升到上覆的McMurray组沉积物中。硫酸盐饱和的富Fe2+和Mn2+盐水的向上迁移导致McMurray湖底沉积物进入与泥炭沼泽地形发育有关的地点。湖底沉积物的微生物氧化还原作用形成了由富锰菱铁矿和黄铁矿层状交织而成的微球粒结构碳酸盐层。随后的盐溶解事件和泥盆纪盐水在McMurray中上段沉积期间的上剖面迁移导致了类似的碳酸盐饱和但硫酸盐缺乏的化学性质。这些盐水流也进入了湖底沉积物,形成了由锰铁方解石而不是菱铁矿组成的密集球状结构的石灰岩床。这些沉积物提供了对阿萨巴斯卡油砂下方盐溶解趋势导致的大量盐水分布的深入了解,并进一步加深了我们对有争议的麦克默里沉积过程的理解。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

Salt dissolution tectonism and origin of lacustrine carbonate beds: Mn-Fe-calcite and Mn-siderite micro-spherulite fabrics of the Lower Cretaceous McMurray Formation, Athabasca Oil Sands deposit, western Canada

Salt dissolution tectonism and origin of lacustrine carbonate beds: Mn-Fe-calcite and Mn-siderite micro-spherulite fabrics of the Lower Cretaceous McMurray Formation, Athabasca Oil Sands deposit, western Canada

Several lacustrine carbonate beds, each a metre-thick interval of densely packed Mn-rich sideritic micro-spherulites or Mn-rich ferroan calcite micro-spherulites, are recorded for the first time within strata of the Lower Cretaceous McMurray Formation of the northern Athabasca Oil Sands deposit, western Canada. A lower McMurray lacustrine carbonate deposit is characterised by a metre-thick bed fabric of Mn-rich siderite micro-spherulites. The middle and upper interval McMurray beds developed fabrics of Mn2+-rich ferroan calcite micro-spherulites. These carbonate beds represent saline lacustrine depositional environments that resulted from the lake bottom sediments ingressed from below by Mn2+-Fe2+-rich carbonate-saturated brines. These up-section migrations of Devonian formation water were sourced from dissolution trends developed in limestone and halite-anhydrite beds of the underlying Devonian Prairie Evaporite during Cordilleran deformation of the Alberta Basin foreland. These brines ascended to the overlying McMurray Formation sediments along dissolution-collapse structures such as breccia pipes, sinkholes and margins of differentially subsided Upper Devonian fault blocks. The up-section migration of a sulphate-saturated Fe2+ and Mn2+-rich brine resulted in the ingress of a lower McMurray lacustrine bottom sediment at a site associated with the development of a peat mire terrain. Microbial redox of the lake bottom sediment resulted in a carbonate bed of micro-spherulitic fabrics of Mn-rich siderite interwoven with pyrite laminae. Subsequent salt dissolution events and up-section migrations of Devonian brine during deposition of the middle and upper McMurray intervals resulted in similar carbonate-saturated but sulphate-poor chemistry. These saline flows also ingressed lacustrine bottom sediments below, and resulted in limestone beds of densely packed spherulitic fabrics of Mn-ferroan calcite, not siderite. These deposits provide insight into largely unknown dispositions of voluminous brine resulting from salt dissolution trends below the Athabasca Oil Sands and further our understanding of controversial McMurray depositional processes.

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