Spring origin of Eocene carbonate mounds in the Green River Formation, Northern Bridger Basin, Wyoming, USA
Spring origin of Eocene carbonate mounds in the Green River Formation, Northern Bridger Basin, Wyoming, USA
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DOI：
10.1111/sed.12852
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发表时间：
2021-02
期刊：
影响因子：
3.5
通讯作者：
E. Jagniecki;T. Lowenstein;R. V. Demicco;M’bark Baddouh;A. Carroll;B. Beard;C. Johnson
中科院分区：
文献类型：
--
作者：
E. Jagniecki;T. Lowenstein;R. V. Demicco;M’bark Baddouh;A. Carroll;B. Beard;C. Johnson
现代和古代湖相碳酸盐沉积为了解构造、过去气候和局部和区域尺度盆地水文之间的相互作用提供了独特敏感的沉积和地球化学记录。在始新世湖泊（Gosiute湖）的边缘，人们早就发现了绿河组中发育良好的大型（一米至十米）碳酸盐丘。然而，它们的起源方式和古水文学意义仍有争议。新的沉积学、锶同位素数据和构造证据表明，在美国怀俄明州briger盆地的Little Mesa及邻近地区，明显的春季泄油导致了绿河组Wilkins峰上段10米大小的岸线碳酸盐丘群的形成。沉积学证据表明，泉水的流量主要是水下的，但有时也有水下的，这产生了凝灰岩瀑布和微边缘岩大坝结构。与同时期的古湖泊碳酸盐（87Sr/86Sr = 0.71195 ~ 0.71561）相比，这些陆上温泉沉积物的87Sr/86Sr比值（87Sr/86Sr = 0.71040 ~ 0.71101）的放射性成因较低，因为它们的母质地下水可能与放射性成因较低的古生代碳酸盐相互作用。泉水矿床正下方Wasatch组的方解石胶结砂岩锥状和尖塔状（87Sr/86Sr = 0.71037 ~ 0.71057）表明，古生代碳酸盐岩的地下水优先沿逆冲断层流动。这些结果表明，高泉水流量与威尔金斯峰上部的湖高水位一致，表明布里杰盆地西北缘的补给有助于戈斯特湖的水收支，并降低了一个未填满的蒸发湖盆的盐度。研究结果为识别古湖泊系统的地下水排放提供了依据，为其他古湖泊沉积中发现古泉系统提供了依据。
Modern and ancient lacustrine carbonate build‐ups provide uniquely sensitive sedimentary and geochemical records for understanding the interaction between tectonics, past climates, and local and regional scale basin hydrology. Large (metre to decametre), well‐developed carbonate mounds in the Green River Formation have long been recognized along the margins of an Eocene lake, known as Lake Gosiute. However, their mode of origin and significance with respect to palaeohydrology remain controversial. Here, new sedimentological, Sr isotope data and structural evidence show that significant spring discharge led to the formation of a decametre size complex of shoreline carbonate mounds in the upper Wilkins Peak Member of the Green River Formation at Little Mesa and adjacent areas in the Bridger Basin, Wyoming, USA. Sedimentological evidence indicates that spring discharge was predominantly subaqueous but was, at times, also subaerial, which produced tufa cascades and micro‐rimstone dam structures. The 87Sr/86Sr ratios measured from these subaerial spring deposits are less radiogenic (87Sr/86Sr = 0.71040 to 0.71101) than contemporaneous palaeolake carbonates (87Sr/86Sr = 0.71195 to 0.71561) because their parent groundwaters likely interacted with less‐radiogenic Palaeozoic carbonate. Calcite‐cemented sandstone cones and spires (87Sr/86Sr = 0.71037 to 0.71057) in the Wasatch Formation directly below the spring deposits suggest that groundwaters derived from Palaeozoic carbonates preferentially flowed along thrust faults. These results imply that high spring discharge coincided with lake high stands of the upper Wilkins Peak Member, suggesting that recharge at the north‐west margin of the Bridger Basin contributed to Lake Gosiute’s water budget and lowered the salinity of an underfilled, evaporative lake basin. The findings of this study provide criteria for the recognition of groundwater discharge in palaeolake systems which may lead to the discovery of palaeospring systems in other ancient lake deposits.