Paleozoic Biogeographic Signals from Southeastern Alaska

亚历山大地体具有阿拉斯加可疑地体中最长、最完整的古生代地层，其地层和化石记录可追溯到早奥陶世。它位于几个年轻地块的外侧，是了解北美西北部增生史的关键部分之一。许多研究人员认为，它的悠久历史始于西部的“原太平洋”，直到中生代晚期才到达北美附近。从正在进行的研究中获得的动物证据并不支持这一观点，但表明亚历山大地体与北美大陆的关系比与澳大利亚或亚洲的关系更密切。动物群属于旧大陆界，与澳大利亚东部和中国动物群的类群形成鲜明对比，主要表现为科迪勒拉地区类群。然而，这种亲缘关系并不完全是科迪勒山脉的，还有一些西伯利亚的方面需要进一步解释。P.I.将收集和描述泥盆纪、密西西比纪和宾夕法尼亚纪的腕足动物，看看它们是否也显示出北美的亲缘关系，或者它们是否表明西伯利亚的持续影响。中国和苏联的工作人员正在迅速填补亚洲动物知识的空白，以便一旦我们在自己的部门收集到足够的资料，就可以进行比较。这项工作将集中在腕足类动物上，因为它们是底栖动物，对生物地理因素很敏感，但也将利用我们最近对阿拉斯加东南部齿状动物的研究，因为这些齿状动物在这些钙质剖面中提供了最好的年龄控制。

The Alexander terrane has the longest and most complete Paleozoic stratigraphy of the Alaskan suspect terranes, with a stratigraphic and fossil record extending back to the early Ordovician. It lies outboard of several younger terranes and it is one of the key sections in understanding the accretionary history of northwestern North America. Many workers believe it began its long history in the western "Protopacific" and only arrived in the vicinity of North America in late Mesozoic time. Faunal evidence gained from ongoing studies does not support this view but suggests that the Alexander terrane was more closely associated with the continent of North America than with Australia or Asia. The faunas belong to the Old World Realm and show mainly Cordilleran Region affinities that contrast with the affinities of faunas in eastern Australia and China. However, the affinities are not wholly Cordilleran and there are some Siberian aspects that need further explanation. P.I. will collect and describe brachiopods of Devonian, Mississippian, and Pennsylvanian age to see if these also show a North American affinity or if they indicate a continuing Siberian influence. The gaps in knowledge of Asiatic faunas are being rapidly filled by workers in China and the USSR so that comparisons are possible once we have collected adequate material in our own sections. The work will concentrate on brachiopods, because these are benthic and sensitive to biogeographic factors, but will make use of our recent work on donodonts from southeastern Alaska because these provide the best available age control in these calcareous sections.