摘要
通过对牙形石器官的对称性、相分布和地球化学特征的研究,探讨湘西北晚二叠世至三叠纪初牙形动物的生态分布.按器官所包括不同对称型分子的比例,牙形动物器官的对称性可分为4级,器官的对称性越高,动物运动能力越强.湘西北晚二叠世一三叠纪初地层可分为6种沉积相,即盆地相、盆缘-台坡相、开阔台地相、边缘浅滩相、局限台地相和泥坪相.具不同对称级器官的属种在6种沉积相中的差异分布,反映了牙形动物的3种生态类型:自由游泳型、浮游型和底栖型.牙形石地球化学组分的变化与当时环境演变相吻合.随水深增加,化石中的P含量升高,而Ca、s、sr的含量降低;Al、Fe和Ba在近岸浅水环境的牙形石中富集;而Mg的富集指示高盐环境.基于上述研究,划分了4个牙形石相,建立了一个组合横向替代的牙形动物生态分布模式.
Northwestern Hunan is one of the best areas for studying conodont palaeoecology, provided with abundant conodonts and other kinds of fossils, well-developed Permian and Triassic strata under varied sedimentary anvironmaents. This paper makes a discourse on the conodont biofacies distribution and the available geochemical characters.
Based on the apparatus classification of conodonts, the symmetries of the apparatus series have been divided into four grades. The former three grades are erected for gondolellids, including the first-grade symmetric series arranged by the units only with the symmetric posterior-end of platform, the second-grade symmetric series formed by two kinds of units with symmetrio and asymmetric posterior-ends of platforms; and the third grade symmetric series composed of three kinds of units with symmetric, asymmetric and extra-asymmetric posterior-ends of platforms. The fourth-grade symmetric series includes some complex series, i.e. the six-element series of Hindeodus and the multielement series of Isarcicella with different oral ornaments. The apparatus symmetry can reflect moving abilities of the animal.
Six facies have been recognized in the working area based on characters of fossil assemblages, rocks and sedhnentary structures, namely, basin f cies, b sin margin and slope facies, open platform facies, tidal bank facies, rescricted platform facies and mud flat facies.
By observing the distribution of conodonts in the four symmetric grades (Tables II, III, IV), it can be found that the four symmetric grades represent three ecologic types, i.e. free swimmer type (first-grade), plankton-benthonic swimmer type (second and third grades), and benthonic swimmer type (fourth grade). Moreover, four conodont biofacies have been distinguished as follows: I. Hindeodus-lsarcicella biofacies, II. Hindeodus biofacies, III. free swimming gondoMlids biofacies and IV. plaktonic gondolellids biofacies. The distributional model of these bioracles is shown in Text-fig. 3. As for the model, this paper considers that there exists the bemhonic swimming community among the conodonts, and one conodont assemblage can be replaced by another horizontally.
Through probing the chemical elements of conodonts, a study have been made on their geochemical characters. The phosphorus content of concdonts is getting higher with the deepening of water mass, while the contents of calcium, sulphur and stronium are rising with the shallowing of sea water. The contents of aluminium, iron and barium are rich only in the nearshore shallow Water, and the abundance of magnesium content indicates the high salt contained in the water body. The content curves coincide with the curves of environment changes. In short, to make clear the geochemical characters of conodonts is an important method in palaeoecological research.
出处
《古生物学报》
CAS
CSCD
北大核心
1993年第3期332-345,409-411,共14页
Acta Palaeontologica Sinica
关键词
牙形石
地球化学
古生态
conodont
facies
geochemistry
palaeoecology
