The source of reworked Devonian algal “cysts” in last glacial maximum (LGM) sediment in the Gulf of Mexico is traced to their host black shales, which ring the southwestern Great Lakes. The source-to-sink pathway includes intermediate storage in fine-grained LGM glacial lacustrine sediment and till. The “cysts” are pelagic chlorophyllous algae (Tasmanites and Leiosphaeridia), collectively referred to herein as tasmanitids. Radiocarbon dates of syndepositional Gulf of Mexico foraminifera, derived from accelerator mass spectrometry, bracket the Gulf of Mexico sediment age with common tasmanitids from 28.5 ± 0.6–17.8 ± 0.2 cal kyr B.P.Approximately 1400 km north of the Gulf of Mexico, tasmanitids are abundant in Upper Devonian black shales (New Albany, Antrim, and Ohio Shales) that ring the Michigan, Illinois, and Appalachian intracratonic basins. Tasmanitids were eroded from bedrock and incorporated in glacial sediment dating from ca. 28.0–17.6 cal kyr B.P. by the Lake Michigan, and Huron-Erie lobes of the Laurentide Ice Sheet. The physical characteristics of tasmanitids are ideal for long-distance transport as suspended sediment (density: 1.1–1.3 g/cc, size ranging from 63 µm to 300 µm), and these sand-sized tasmanitids traveled with the silt-clay fraction. Thus, the source-to-sink journey of tasmanitids was initiated by subglacial erosion by water or friction, sequestering in till or glaciolacustrine sediment, re-entrainment and suspension in meltwater, and final delivery in meltwater plumes to the Gulf of Mexico. River routes included the Mississippi, Illinois, Ohio, Wabash, Kaskaskia, and many of their tributaries.Reworked Devonian tasmanitids are a previously unrecognized link between their occurrence in deep-water deposits of the Gulf of Mexico and the late Wisconsin glacial history of the Upper Mississippi Valley. We propose that tracking occurrences of tasmanitid concentrations from the source area to sink, along with adjunct proxies such as clay minerals, will facilitate a more refined analysis of the timing and duration of megafloods. This study also demonstrates that isotopically dead carbon, from reworked Devonian tasmanitid “cysts,” can contaminate radiocarbon dating of LGM bulk sediment samples toward older ages.

中文翻译：

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从源头到汇点：上一次冰川最大期冰川末期泥盆纪藻类“囊肿”（塔斯曼人）被运往墨西哥湾

墨西哥湾最后一次冰期最大（LGM）沉积物中重造的泥盆纪藻类“囊肿”的来源可追溯到其宿主的黑色页岩，这些页岩环绕西南大湖。源到汇路径包括在细粒LGM冰川湖沉积物和耕层中的中间存储。“囊肿”是上层叶绿素藻类（塔斯马尼亚人和Leiosphaeridia），在本文中统称为塔斯马尼德。源自加速器质谱的墨西哥湾有孔虫的共沉积放射性碳日期，与28.5±0.6–17.8±0.2 cal kyr BP的常见塔斯马尼提斯形成了墨西哥湾的沉积年龄，大约在墨西哥湾以北约1400 km，塔斯马尼提斯的碳含量较高泥盆纪黑色页岩（新奥尔巴尼，安特里姆和俄亥俄页岩）环绕密歇根州，伊利诺伊州和阿巴拉契亚克拉通盆地。塔斯马尼迪特人从基岩中被侵蚀，并被整合到大约自公元前的冰川沉积物中。密歇根湖的BP年代为28.0–17.6千里，和Laurentide冰盖的Huron-Erie裂片。塔斯曼尼鳄的物理特性非常适合作为悬浮沉积物（密度：1.1–1.3 g / cc，尺寸从63 µm至300 µm）进行长距离运输，并且这些沙粒大小的塔斯曼尼鳄随淤泥-粘土组分一起移动。因此，塔斯曼尼特人从源头到汇地的旅程是由水或摩擦作用对冰川下的侵蚀，隔离在耕层或冰川湖沉积物中，重新夹带和悬浮在融化水中以及最后以融化水羽流最终输送到墨西哥湾而开始的。河流路线包括密西西比州，伊利诺伊州，俄亥俄州，瓦巴什，卡斯卡斯基亚及其许多支流。重新构造的泥盆纪塔斯马尼特人是它们在墨西哥湾深水沉积物中的发生与威斯康星州上密西西比河谷冰川晚期的历史之间从未被认识到的联系。我们建议跟踪从源区到下沉的塔斯马尼迪浓度的发生，以及诸如粘土矿物的辅助代理，将有助于对特大洪水的时间和持续时间进行更精细的分析。这项研究还表明，来自泥盆纪塔斯马尼特斯“囊肿”的同位素死碳会污染年龄较大的LGM大量沉积物样品的放射性碳年代。连同诸如粘土矿物的辅助代理，将有助于对特大洪水的时间和持续时间进行更精细的分析。这项研究还表明，来自泥盆纪塔斯马尼特斯“囊肿”的同位素死碳会污染年龄较大的LGM大量沉积物样品的放射性碳年代。连同诸如粘土矿物的辅助代理，将有助于对特大洪水的时间和持续时间进行更精细的分析。这项研究还表明，来自泥盆纪塔斯马尼特斯“囊肿”的同位素死碳会污染年龄较大的LGM大量沉积物样品的放射性碳年代。