Parasequence-scale organic facies variations through an Early Carboniferous Yoredale cyclothem, Middle Limestone Group, Scremerston, Northumberland
Parasequence-scale organic facies variations through an Early Carboniferous Yoredale cyclothem, Middle Limestone Group, Scremerston, Northumberland
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DOI：
10.1144/gsjgs.152.1.0041
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发表时间：
1995-02
影响因子：
2.7
通讯作者：
Michael C. Frank;R. Tyson
中科院分区：
文献类型：
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作者：
Michael C. Frank;R. Tyson
早石炭世（Brigantian）中灰岩群诺森伯兰代表了一个长期的节奏约勒代尔型三角洲沉积。对次要的贝里克石灰岩旋回层进行了光学和地球化学分析，这是主要的牛津石灰岩旋回层内的一个向上变粗变浅的旋回（准层序）。这表明III-IV型陆生植物来源的干酪根（木本植物碎屑）占压倒性优势。氢指数与孢粉学测定的黑色：棕色碎植体比率呈极强的负相关。细粒岩性的总有机碳含量通过循环向上增加，并与粉砂含量呈正相关，可能是由于水动力等效性和共同的河流来源的碎植体和粉砂颗粒。黑色碎植体的第一个：equant比增加向上通过循环（即在近端方向），这种模式是“非典型的”，结果从板条形的碎植体大于equant的。该剖面为边缘成熟（约0.64%镜质组反射率）;反射率与氢指数相关。黄铁矿和菱铁矿的分布显然与沉积物积累速率有关，菱铁矿最常见于石灰岩上方旋回层下半部可能最高沉积的区间。该旋回底部的海泛面覆盖着黑色页岩，而不是石灰岩;旋回层的传统（石灰岩）基底与真正的基底不一致。
The Early Carboniferous (Brigantian) Middle Limestone Group of Northumberland represents a prolonged period of rhythmic Yoredale-type deltaic sedimentation. Optical and geochemical analyses were undertaken on the minor Berwick Limestone Cyclothem, a prograding coarsening- and shallowing-upward cycle (parasequence) within the major Oxford Limestone Cyclothem. These indicate an overwhelming dominance of Type III–IV land-plant derived kerogen (woody phytoclasts). The hydrogen index shows a strong negative correlation with the palynologically determined b1ack: brown phytoclast ratio. The total organic carbon content of the fine-grained lithologies increases upwards through the cycle and is positively correlated with silt content, presumably due to the hydrodynamic equivalence and common fluvial source of phytoclasts and silt particles. The 1ath:equant ratio of the black phytoclasts increases upwards through the cycle (i.e. in a proximal direction); this pattern is ‘atypical’ and results from the lath-shaped phytoclasts being larger than the equant ones. The section is marginally mature (about 0.64% vitrinite reflectance); reflectance is correlated with hydrogen index. The distribution of pyrite and siderite is apparently related to sediment accumulation rate, with siderite most common in the interval of probable highest sedimentation in the lower half of the cyclothem above the limestone. The marine flooding surface at the base of the cycle is overlain by black shale, not limestone; the traditional (limestone) base of the cyclothem does not correspond to the true base.