新生代浮游有孔虫整体变化趋势

新生代浮游有孔虫在确定地层时代和推断古沉积环境等方面有着极其重要的实用价值,本文利用新生代浮游有孔虫数据库,对其中的属种资料进行了大量的分析和总结,初步了解了新生代浮游有孔虫整体特征的变化趋势及其在各地史时期中的面貌,使我们有可能建立一种以浮游有孔虫分类特征为基础的“模式”。这样,我们不仅把握了新生代浮游有孔虫的宏观特征,而且有可能找到一种只要对某些特征组合面貌进行判断即可大致确定地层时代的快速方法。

SOME GENERAL TRENDS OF MORPHOLOGIC VARIATION IN CENOZOIC PLANKTONIC FORAMINIFERA

The Cenozoic planktonic foraminifera has been widely applied for the study of biostratigraphy and paleoenvironment. On the basis of a database of the Cenozoic planktonic foraminifera, some general trends in morphologic variation and the combina- tion of major characters of the planktonic foraminifera from Paleocene to Holocene have been summarized up. It is possible to establish some "character patterns"for the Cenozoic planktonic foraminifera, which are helpful for finding a quick and simple way to date strata. It's well known that there is some extent of incongruity in the classification of the planktonic foraminifera owing to different viewpoints and personal experiences. Therefore, it's necessary to base the "batterns"on the elementary characters in order to hold the main features of the planktonic foraminifera. Taking the early Oligocene fauna of planktonic foraminifera which shows an extensive decline in diversity and types of morphological variation as compared with that of Late Eocene, as an example,its "character patterns"can be summarized into: (1) shape of cham- bers--many types (including digitate, wedge--shape, apiculate) disappeared; a new type with last chamber digitate appeared. (2) coiling pattern--many types (including involute planispiral, biserial planispiral, early biserial and later uniserial, early trochospiral with final chamber enveloping a large part of earlier test) disappeared. (3) gross shape--dominated by Unequally biconvex type and some types (including stellate, bilobate, elongate pyramidal) disappeared. (4) periphery--the extinction of keeled types is an excellent marker for these strata; subangular and truncated types reduce markedly. (5) umbilicus--the type with umbilicus covered by final chamber disappeared. (6) primary aperture--many types (in- cluding extraumbilical slit--like,umbilical to dorsal slit--like,triradiate,terminal oval---shaped) disappeared. (7) apertural modification--the types with lateral flanges and spatulate flap disappeared. a few of types with porticus and short neck appeared. (8) nonprimary aperture--the types with various nonprimary aperture are rare. (9) bulla--the types with sutural and umbilical--sutural bulla disappeared. (10) surface structure--the types with spinose or cancellate surface structure decreased markedly; rugose types and cancellate type with spinose disappeared. Based on the "character patterns", some general trends in morphologic variation have been recognized in the planktonic foraminifera from the Paleocene to Holocene: (1) The axial periphery varied from rounded shape to truncated then to keeled from Paleocene to Late Eocene, the keeled types disappeared and truncated types reduced markedly in the Oligocene, and after Late Oligocene this changed from rounded to keeled periphery had al- so taken place. (2) the chamber seemed to vary in many aspects, for example, one was from globular (or ovate) shape to central apiculate then to anterior apiculate from Early Eocene to Late Eocene; the another was from ovate--shaped to wedge--shaped from Paleocene to Eocene, in Early Oligocene the wedge--shaped types disappeared, and after Late Oligocene this changed from ovate to wedge--shape had also taken place. (3) the gross shape varied from biconvex to plano--convex from Paleocene to Early Eocene, it varied from plano--con- vex to biconvex from Middle Eocene to Middle Oligocene, and after Late Oligocene this process from biconvex to'plano--convex had also occurred. (4) the primary aperture varied from extraumbilical--umbilical type to umbilical one from Paleocene to Middle Oligocene, after Miocene it varied from umbilical to extraumbilical--umbilical, and the shapes of aper- ture was from slit--like to lower arched to highly arched. (5) the rate of aperture modifica- tions increased gradually from Paleocene to Holocene.