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Devonian to Carboniferous continental-scale carbonate turnover in Western Laurentia (North America): upwelling or climate cooling?
Facies ( IF 1.8 ) Pub Date : 2022-07-25 , DOI: 10.1007/s10347-022-00653-4
Makram Hedhli 1, 2 , Keith Dewing 1 , Benoit Beauchamp 2 , Stephen E Grasby 1, 2 , Rudi Meyer 2
Affiliation  

The Devonian to Carboniferous (DC) transition coincided with a green-to-ice house climatic shift, anoxia, disappearance of lower latitude carbonate banks, and turnover from warm-to-cool water carbonate factories. In western Laurentia, the switch to carbonate factories dominated by cool-water biota was contemporaneous with a tectonically driven palaeogeographic change. To investigate this depositional shift and infer the relative impact of climate vs tectonics, a continental-scale sedimentological and geochemical study was conducted on twelve stratigraphic sections of DC strata from western Canada to southern Nevada (USA). The spatial–temporal distribution of microfacies records the turnover from [i] a Famennian lime mud-rich, shallow warm-water carbonate ramp with low sedimentation rates, mesotrophic conditions and tabular geometry to [ii] Tournaisian to Viséan lime mud-depleted and grainstone dominated cool-water carbonate ramp with anomalous high sedimentation rates, oligotrophic conditions and a pronounced slope. Positive excursions of δ18Ocarb (+ 2‰ V-PDB) and δ13Ccarb (+ 4‰ V-PDB) of Lower Mississippian carbonates likely correspond to the first cooling peak of the Carboniferous-Permian icehouse climate, following carbon withdrawal during black shale deposition during the late Famennian and early Tournaisian. However, late Tournaisian return of photozoan elements and their persistence throughout the Viséan suggests that warmer surface water existed, revealing a decoupling of the lower latitude ocean and the atmosphere. Shoaling of the thermocline was likely a result of cold-water upwelling along an open coast, as the Antler orogen no longer provided an oceanic obstruction to the west. This study shows that carbonate platforms are more susceptible to regional changes than global shifts.



中文翻译:

西劳伦西亚(北美)泥盆纪到石炭纪的大陆级碳酸盐转换:上升流还是气候变冷?

泥盆纪到石炭纪(DC)的转变恰逢绿色到冰室气候转变、缺氧、低纬度碳酸盐岩岸的消失以及从温水到冷水碳酸盐工厂的转变。在劳伦西亚西部,向以冷水生物群为主的碳酸盐工厂的转变与构造驱动的古地理变化同时发生。为了研究这种沉积变化并推断气候与构造的相对影响,对从加拿大西部到美国内华达州南部的 DC 地层的 12 个地层剖面进行了大陆尺度的沉积学和地球化学研究。微相的时空分布记录了从[i]富含法门期石灰泥、沉积速率低、中营养条件和板状几何的浅层温水碳酸盐斜坡到[ii]图尔奈期到维塞期石灰泥贫化和粒岩的转换以冷水碳酸盐坡道为主,具有异常高的沉积速率、贫营养条件和明显的坡度。密西西比河下游碳酸盐岩δ 18 O碳水化合物(+ 2‰ V-PDB) 和δ 13 C碳水化合物(+ 4‰ V-PDB)的正偏移可能对应于碳回收后石炭纪-二叠纪冰室气候的第一个冷却峰值法门纪晚期和图尔奈早期黑色页岩沉积时期。然而,图尔奈晚期光虫元素的回归及其在整个维塞安地区的持续存在表明存在较温暖的地表水,揭示了低纬度海洋和大气的脱钩。温跃层的浅滩很可能是冷水沿开放海岸上升的结果,因为鹿角造山带不再对西部构成海洋障碍。这项研究表明,碳酸盐台地比全球变化更容易受到区域变化的影响。

更新日期:2022-07-25
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