Reconstructing the paleoenvironment of an oxygenated Mesoproterozoic shoreline and its record of life
Reconstructing the paleoenvironment of an oxygenated Mesoproterozoic shoreline and its record of life
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DOI：
10.1130/b36634.1
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发表时间：
2024-03-01
影响因子：
4.9
通讯作者：
Strother，Paul K.
中科院分区：
文献类型：
--
作者：
Slotznick，Sarah P.;Swanson-Hysell，Nicholas L.;Strother，Paul K.
Nonesuch地层微生物群提供了一个窗口。1075 Ma生活在古代北美的内部。诺纳苏赫水体是在中大陆裂谷内广泛的火山活动停止后形成的，因为盆地继续下沉。在美国密歇根州北方和威斯康星州，铜港砾岩记录了陆地冲积扇和河流平原环境，过渡到Nonesuch组的水下湖泊沉积。这些单元向与布朗斯通福尔斯角不整合相关的古地形高点变薄。由于这些“褐石高地”，我们能够在同生沉积物的不同深度横向探索古环境。岩石磁性数据限制，当湖浅，它是氧化的氧化矿物组合证明。氧气水平在更深的地方更低在水体的最深处，记录了缺氧条件。中间相的深度和氧化还原之间的这些端元保存碎屑磁铁矿和赤铁矿，这可能是目前在高丰度由于近端的火山高地。这一磁相使得基于碎屑磁铁矿和赤铁矿的古磁极得以发展，将湖泊的古纬度限制在7.1 ± 2.8°N。中间相的沉积物保存了精美的有机质壁微化石，微化石在缺氧相中的多样性较低，甚至不存在，无定形有机物更有可能被保存下来。蓝藻和真核生物（光合自养和异养生物）的组合生活在这个热带中元古代水体的含氧沃茨。
The Nonesuch Formation microbiota provide a window into ca. 1075 Ma life within the interior of ancient North America. The Nonesuch water body formed following the cessation of widespread volcanism within the Midcontinent Rift as the basin continued to subside. In northern Michigan and Wisconsin, USA, the Copper Harbor Conglomerate records terrestrial alluvial fan and fluvial plain environments that transitioned into subaqueous lacustrine deposition of the Nonesuch Formation. These units thin toward a paleotopographic high associated with the Brownstone Falls angular unconformity. Due to these “Brownstone Highlands,” we were able to explore the paleoenvironment laterally at different depths in contemporaneous deposits. Rock magnetic data constrain that when the lake was shallow, it was oxygenated as evidenced by an oxidized mineral assemblage. Oxygen levels were lower at greater depth—in the deepest portions of the water body, anoxic conditions are recorded. An intermediate facies in depth and redox between these endmembers preserves detrital magnetite and hematite, which can be present in high abundance due to the proximal volcanic highlands. This magnetic facies enabled the development of a paleomagnetic pole based on both detrital magnetite and hematite that constrains the paleolatitude of the lake to 7.1 ± 2.8°N. Sediments of the intermediate facies preserve exquisite organic-walled microfossils, with microfossils being less diverse to absent in the anoxic facies where amorphous organic matter is more likely to be preserved. The assemblage of cyanobacteria and eukaryotes (both photoautotrophs and heterotrophs) lived within the oxygenated waters of this tropical Mesoproterozoic water body.