Stratigraphic and ecologic implications of late Precambrian microfossils from Utah
Stratigraphic and ecologic implications of late Precambrian microfossils from Utah
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犹他州晚前寒武纪微化石的地层学和生态学意义
DOI：
10.2475/ajs.281.3.247
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发表时间：
1981
影响因子：
2.9
通讯作者：
S. Awramik
中科院分区：
文献类型：
--
作者：
A. Knoll;N. Blick;S. Awramik
在犹他州盐湖冰碛成因的上前寒武纪矿叉组的黑色页岩和粉砂岩中发现了大量保存完好的微体化石。这些岩石被解释为在冰川退缩期间沉积在一个浅的、受限制的海洋海湾中的冰缘附近。几种不同的形态型是可辨别的，但根据Moorman（1974），我们将其中大多数解释为单一的孢子化的内孢菌Bavlillellll Jllveolllta（Shepeicva）Vidal的生活史阶段。该群落的分类多样性较低，加上种群规模较大以及Bavlillella几乎完全占主导地位，表明环境受到生态压力。这种压力的来源可能是冰川融化。根据地层位置和岩性与\Vashington的放射性测年序列的对比，Mineral Fork Formation被认为约为8亿年。古老;然而，Bavlillella的最好的日期发生在Vendian（650-570百万年）的岩石中。年龄Bavlillella Javeolata在Mineral }-'ork地层中的存在提出了关于这一假定的Vendian指数化石的地层范围和美国北部Conlillera晚前寒武纪冰川作用时间的重要问题。
Abundant and well preserved microfossils have been discovered in black shales and siltstones of the glaciogenic upper Precambrian Mineral Fork Forma tion ncar Salt Lake City, Utah. The rocks are interpreted to have been deposited close to an ice margin in a shallow, restricted marine embayment during glacial retreat. Several distinct morphotypes are discernible, but following Moorman (1974), we interpret most of these as stages in the life cycle of a single planktonic, endosporulating alga, Bavlillellll Jllveolllta (Shepeicva) Vidal. The low taxonomic diversity of this assemblage, coupled with the large population size and almost complete dominance by Bavlillella, suggests an ecologically stressed environment. The source of this stress was probably the melting glacier. On the basis of stratigraphic position and lithological correlation with a radio metrically dated sequence in \Vashington, the Mineral Fork Formation has been considered to be about 800 m.y. old; however, most well dated occurrences of Bavlillella are in rocks of Vendian (650-570 m.y.) age. The presence of Bavlillella Javeolata in Mineral }-'ork strata raises significant questions concerning both the stratigraphic range of this presumed Vendian index fossil and the timing of Late Precambrian glaciation in the l\'orth American Conlillera.