U–Pb detrital zircon evidence of transcontinental sediment dispersal: provenance of Late Mississippian Wedington Sandstone member, NW Arkansas

U–Pb ages of detrital zircons from the Wedington Sandstone member in northwest Arkansas provide evidence for Late Mississippian westward transcontinental sediment transport from the Appalachian foreland. The Late Mississippian Wedington Sandstone member of the Fayetteville Shale is a fine- to medium-grained quartzarenite. It separates the Fayetteville Shale into informal lower and upper intervals, and was deposited as a small constructive delta complex that prograded towards the south and southeast during the Late Mississippian. As a major influx of clastic sediments, the Wedington Sandstone member records the sediment source and dispersal in the mid-continent during the Late Mississippian. A total of 559 detrital zircon grains from six Wedington samples were recovered for U–Pb detrital zircon geochronological analysis. Results show that age distributions can be subdivided into six groups: ~350–500, ~900–1350, ~1360–1500, ~1600–1800, ~1800–2300, and > ~2500 Ma, and are characterized by a prominent peak for the age group of ~900–1350 Ma, a major peak at ~1600–1800 Ma, and a few other minor age clusters. Regional correlation and geological evidence from surrounding areas suggest that the transcontinental sediment dispersal started as early as the Late Mississippian. U–Pb detrital zircon age distribution suggests that the Wedington Sandstone member was likely derived from the Appalachian foreland with contributions from the Nemaha Ridge to the west where the Yavapai–Mazatzal sources were exposed during the Late Mississippian. Sediment was likely transported westward through or around the Illinois Basin, merged with mid-continent sediment, and then entered into its current location in northwest Arkansas. Transportation of this sediment from mixed sources continued along its course to the south, forming a delta on the Northern Arkansas Structural Platform.

采自阿肯色州西北部（northwest Arkansas）的韦丁顿砂岩段（Wedington Sandstone member）碎屑锆石（detrital zircons）铀-铅（U–Pb）年龄数据，为密西西比世晚期（Late Mississippian）源自阿巴拉契亚前陆（Appalachian foreland）的跨大陆西向沉积物搬运（westward transcontinental sediment transport）提供了直接证据。费耶特维尔页岩（Fayetteville Shale）的密西西比世晚期韦丁顿砂岩段为细-中粒石英砂岩（fine- to medium-grained quartzarenite），可将费耶特维尔页岩划分为非正式的上下两段，其沉积时为小型建设性三角洲复合体（constructive delta complex），于密西西比世晚期向南东方向进积（prograded）。作为一次规模可观的碎屑沉积物（clastic sediments）输入事件，韦丁顿砂岩段记录了密西西比世晚期北美中大陆（mid-continent）的沉积物物源与扩散路径。本次研究从6件韦丁顿砂岩样品中共分选获得559颗碎屑锆石，用于铀-铅碎屑锆石年代学分析（U–Pb detrital zircon geochronological analysis）。分析结果显示，年龄分布可划分为6个区间：~350–500 Ma、~900–1350 Ma、~1360–1500 Ma、~1600–1800 Ma、~1800–2300 Ma及> ~2500 Ma，其特征为~900–1350 Ma年龄区间存在显著峰值（prominent peak），~1600–1800 Ma区间存在主峰值（major peak），同时伴随少量次要年龄簇（minor age clusters）。区域对比（regional correlation）结果与周边地区的地质证据共同表明，此次跨大陆沉积物搬运早在密西西比世晚期就已启动。铀-铅碎屑锆石年龄分布特征显示，韦丁顿砂岩段的物源大概率源自阿巴拉契亚前陆，同时受到西侧内哈马岭（Nemaha Ridge）的物源补给——该区域在密西西比世晚期暴露了亚瓦派-马扎扎尔物源区（Yavapai–Mazatzal sources）。沉积物可能通过伊利诺伊盆地（Illinois Basin）内部或其周边区域向西搬运，与北美中大陆原有沉积物混合后，最终抵达现今的阿肯色州西北部沉积位置。来自混合物源的沉积物沿搬运路径持续向南推进，最终在阿肯色州北部构造台地（Northern Arkansas Structural Platform）上形成了三角洲沉积体。