东秦岭南部奥陶-志留系界线附近腕足动物群演替及生态

东秦岭南部淅川、内乡一带奥陶-志留纪界线附近地层中的腕足类目前已发现20属.晚奥陶世寺岗组的腕足动物可分为中、下部的Catazyga群落和上部的Zygospira群落,前者生态域为BA5或BA4-5,后者生态域为BA2-3.早志留世石燕河组的腕足类以无洞贝类的Nalivkinia占绝对优势,称Nalivkinia群落,其生态域可能在BA1和BA2之间;刘家坡组的腕足动物可称Salopina群落,以德姆贝类Salopina等占主导地位,Nalivkina已消失,Sowerbyella又重新出现,它们的生态域可能为BA2;张湾组的腕足动物以Eospirifer, Strispirifer等为主,称Eospirifer群落,其中在本区首次出现的有Eospirifer, "Plaesiomys", Leptostrophia等属,它们的生态域可能在BA3.根据腕足类资料,本区奥陶-志留系界线应置于寺岗组与石燕河组之间.

SUCCESSION AND ECOLOGY OF BRACHIOPOD FAUNAS ACROSS ORDOVICIAN-SILURIAN BOUNDARY SOUTH OF EASTERN QINLING MOUNTAINS

The rocks across the Ordovician-Silurian Boundary are subdivided into the Sigang, Shiyanhe, Liujiapo, Zhangwan and other formations in the outh of Eastern Qinling Mountains. The Sigang Formation belongs to the Late Ashgillian age, mainly composed of grey to greyish-green medium-bedded clayrocks and nodular biolithlte. The Catazyga Community from the lower and middle parts of the Sigang Formation contains Catazyga, Skenidioides, Sowerbyella, Rostricellula, Aegiromena and Dinorthis. Among them, Catazyga is most abundant, while Catazyga and Skenidioides inhabiting the deeper-water environment are typical representatives of Benthic Assemblage 5 or Benthic Assemblages 4-5 (Copper, 1977; Boucot, 1975), and therefore the ecology of the middle and lower parts of the Sigang Formation belongs to BA5 or BA4-5. The Zygospira Community from the upper part of the Sigang Formation with a low diversity only contains Zygospira, Dinorthis, Pionorthis, Sowerbyella, Rhynchotrema, Rostricellula and Catazyga, the last genus being very rare at that time. This community lived in a shallow-water environment roughly corresponding to the ecological niches of the Pentamerus to Eocoelia Communities in Silurian (Copper, 1977), and therefore the ecology of the upper part of the Sigang Formation may be assigned to Benthic Assemblages 2-3, indicating a great regression in this area at that time.