Depositional Environments and Cycles in the Jurassic Fernie Formation, Southern Canadian Rocky Mountains
Depositional Environments and Cycles in the Jurassic Fernie Formation, Southern Canadian Rocky Mountains
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加拿大南部落基山脉侏罗纪弗尼组的沉积环境和旋回
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发表时间：
1984
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通讯作者：
N. Stronach
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作者：
N. Stronach
摘要 落基山脉南部的弗尼组（侏罗系）主要为页岩，根据粒度、沉积结构、有机碳含量以及宏观和微观动物群可分为沉积相。 “厌氧”沉积物积聚在缺氧的底层水中，是富含有机物的纸质页岩，有孔虫或放射虫微型动物的多样性较低； “好氧”沉积物碳含量贫乏，含有大型动物、生物扰动和多种有孔虫组合。中间的“缺氧”相主要是凝集的有孔虫动物群。扑克筹码页岩（下侏罗统）富含有机物的页岩堆积在浅且缓坡的陆架上，能量在陆架边缘衰减。在 Highwood 和 Ribbon Creek 成员（中侏罗世），类似的沉积物起源于风暴波基底下方，通过厚层序列与浅水沉积物分开，显示出中间氧化的证据。岩溪段（中侏罗统下部）的砂岩沉积在浅陆架上，并不断受到潮流的改造。更多的间歇性风暴和重力流导致了 Pigeon Creek 层和 Corbula munda 层（中侏罗统上部）的互层砂岩和页岩的沉积。沉积环境的变化可能反映了晚巴约世期间该地区西北部沉降加深而演变的盆地结构。隆起导致中巴通阶的西风沉积物来源。沉积物分为五个浅层向上旋回，每个旋回中“厌氧”泥岩向上进入“厌氧”泥岩，然后进入“需氧”泥岩和砂岩。循环由密集的海侵单元终止，其中较低的沉积速率导致丰富的动物群集中和早期成岩方解石、磷酸盐和贝蒂林的形成。周期结束时海平面相对上升发生在最早的巴约世、早期巴约世、中晚期巴通世和早期牛津时代。第五个周期是通道床周期，以库特尼群为上限。海平面的突然上升或沉降的增加似乎控制了周期，并且与全球稳定模式存在一定的相关性。
Abstract The Fernie Formation (Jurassic) in the southern Rocky Mountains is predominantly shaly and can be classified into depositional facies on the basis of grain size, sedimentary structures, organic carbon contents and macro-and micro-fauna. “Anaerobic” sediments accumulated in oxygen-poor bottom waters and are papery, organic-rich shales with a low diversity foraminiferal or radiolarian microfauna; “aerobic” sediments are poor in carbon and contain macrofauna, bioturbation and a diverse foraminiferal assemblage. Intermediate, “dysaerobic” facies have a mainly agglutinated foraminiferal fauna. Organic-rich shales of the Poker Chip Shale (Lower Jurassic) accumulated on a shallow, gently-sloping shelf where energy was damped at the shelf edge. In the Highwood and Ribbon Creek Members (Middle Jurassic), similar sediments originated well below storm wave base, separated from shallow water deposits by a thick sequence showing evidence of intermediate oxygenation. Sandstones of the Rock Creek Member (lower Middle Jurassic) were deposited on a shallow shelf, where they were constantly reworked by tidal currents. More episodic storm and gravity flows were responsible for the deposition of the interbedded sandstones and shales of the Pigeon Creek Member and Corbula munda Beds (upper Middle Jurassic). Changes in sedimentary environment may reflect an evolving basin configuration as subsidence deepened the northwest of the area during the Late Bajocian. Uplift led to westerly sediment sources in the Middle Bathonian. Sediments group into five shallowing-upward cycles in each of which “anaerobic” mudstones pass upward into “dysaerobic” and thence into “aerobic” mudstones and sandstones. Cycles are terminated by condensed transgressive units where lower sedimentation rate led to abundant faunal concentrations and early diagenetic calcite, phosphate and berthierine formation. Relative sea-level rises at the end of cycles occurred in earliest Bajocian, Early Bajocian, Middle-Late Bathonian and Early Oxfordian times. The fifth cycle is that of the Passage Beds, capped by the Kootenay Group. Sudden rises in sea-level or increments of subsidence appear to have controlled the cycles and there is some correlation with global patterns of eustasy.