广东南雄盆地上湖组介形类动物群及白垩-第三系界线

A STUDY ON OSTRACOD FAUNA OF SHANGHU FORMATION AND CRETACEOUS-TERTIARY BOUNDARY IN NANXIONG BASIN, GUANGDONG

南雄盆地上湖组介形类可划分为2个性质不同的动物群及4个化石带:下部为 Porpocypris 动物群,是以中生代属种为主,中、新生代属种混生的过渡性动物群,时代为晚白垩世最晚期;上部为 Cypris 动物群,以 Cypris 属占优势, Sinocypris 属开始出现, Cypridea 等古老属种绝灭为主要特征,时代为早—中古新世.根据介形类演化发展阶段和白垩纪末生物绝灭事件,南雄盆地白垩系与第三系的界线应划在 Porpocypris 与 Cypris 动物群之间,即上湖组坪岭段与下惠段之间.

The ostracod faunas described in this paper were collected from the Pingling and Fengmenao sections. The ostracods were separated from 411 samples, including 57 species assigned to 17 genera, with the establishment of 12 new species. They may be divided into 2 faunas and 4 zones as follows: 1. Porpocypris Fauna I. Porpocypris orbiculata Zone; II. Porpocypris sphaeroidalis Zone. 2. Cypris Fauna III. Cypris jiangxiensis-C, concina-llyorypris subhuangqiaoensis Zone; IV. Cypris jiangxiensis-Parailyocypris changzhouensis-Ilyocypris hengyangensis Zone The depositional time of the Shanghu Formation is a turning period in the evolution of the Mesozoic-Cenozoic nonmarine ostracod faunas. These two ostracod faunas are different in characters. The Porpocypris Fauna is dominated by the Late Mesozoic genera Cypridea, Nanxiongium, Porpocypris, etc. mixed with Cenozoic elements, such as a transitional fauna with a distinct successional character to the Talicypridea Fauna of the Nanxiong Formation (Late Cretaceous in age). This fauna was found from the Pingling Member of the Shanghu Formation, belonging to Late Cretaceous in age. The Cypris Fauna contains abnndant Cenozoic elements with the disappearance of Mesozoic ostracod genera and species. It is coincident with the full prosperity period of the Bemalambda Fauna. This fauna was acqutred from the Xiahui and Nilongkeng Members of the Shanghu Formation (Early and Middle Paleocene in age). The Cretaceous-Tertiary boundary should beplaced between the Cypris Fauna and the Porpocypris Fauna, i. e., between the Xiahui Member and the Pingling Member. DESCRIPTION OF NEW SPECIES Eucypris pinglingensis sp. nov. (Pl. l, figs. 9-11) Description Carapace short, subrenifo m in lateral view. Dorsal margin strongly arched and highest medially; ventral margin concave. Anterior end rounded, while posterior end obliquely rounded, with the former slightly higher than the latter. Left valve larger than the right, strongly overlapping it along anterior dorsal and ventral margins. Shell lenticular in dorsal view. Surface smooth. Comparison This new species differs from Eucypris jiangnianensis Yang in the short carapace, the subequal ends in height or slightly higher anterior end than posterior. Eucypris praelongata sp. nov. (Pl. I, figs. 14-17) Description Carapace elongate, subreniform in lateral view. Dorsal margin convex, highest in front of the middle; ventral margin conspicuously incurred. Anterior end broadly rounded and higher; posterior end narrow. Left valve larger than the right, slightly overlapping it along the free margins. Maximum thickness located medially in dorsal view. Surface smooth. Comparison This new species differs from Eucypris glabra in the very narrowly elongate carapace, and the height/Iength ratio <0.45. Eucypris sinualis sp. nov. (Pl. I, figs. 12, 13) Description Carapace short, reniform in lateral view. Dorsal margin convex and highest medially; ventral margin concave. Both ends rounded; anterior end nearly equal to or higher than posterior. Left valve longer than the right, overlapping it along the free margins. Maximum thickness located medially in dorsal view. Surface smooth. Comparison This new species differs from Eucypris glabra Bodina in the very short carapace, and the height/length ratio>0.55. Nanxiongium dalangshanense sp. nov. (Pl. II, figs. 4-6) Description Carapace short, elliptical in lateral view. Dorsal margin slightly convex and highest in front of the middle; ventral margin nearly straight or slightly concave medially. Both ends rounded and equal in height. Anterodorsal region compressed. Surface finely pitted and reticulate. Comparison This new species differs from Nanxiongium xuanchengense (Cao et Guo) in the short carapace, and the height/length ratio>0.6. Candoniella majuscula sp. nov. (Pl. II, figs. 14-16) Description Carapace rather large, subelliptical in lateral view. Dorsal margin straight and highest at posterior one-third, slightly inclined toward anterior; ventral margin slightly concave. Anterior end rounded; posterior end obliquely rounded, truncated in upper part. Left valve larger than the right, overlapping it along the free margins. Thickest part located medially to post- medially in dorsal view. Surface smooth. Comparison This new species differs from Candoniella candida Hao in the large carapace, the posterior end obliquely rounded and truncated in upper part, and the dorsal margin slightly inclined towards anterior. Candoniella peculiaris sp. nov. (Pl. II, figs. 24, 25) Description Carapace short, subtrapezoid in lateral view. Dorsal margin straight; ventral margin concave. Anterior end rounded; posterior end obliquely rounded, truncated in upper part. Both ends subquel in height. Surface smooth. Comparison This new species differs from Candoniella minuta Ye in the subtrapezoid carapace, the straight dorsal margin and the posterior end truncated in upper part. Cypria longior sp. nov. (Pl. II, figs. 30-32) Description Carapace small, elongate, elliptical or elongate-ovate in lateral view. Dorsal margin convex and highest medially; ventral margin slightly convex. Both ends rounded and subequal in height. Left valve larger than the right, overlapping it weakly on ventral margin. Thi- ckest part located medially to postmedially in dorsal view. Surface smooth. Comparison This new species differs from Cypria minuta Yang in the elongate carapace, and the height/length ratio< 0.7. Parailyocypris protensa sp. nov. (Pl. III, figs. 14-17) 1979 Parailyocypris taizhouensis Yang, He dunde, p. 253, pl. 4, figs. 3,4. Description Carapace elongate, elliptical in lateral view. Dorsal margin slightly convex and highest medially to postmedially; ventral margin nearly straight or slightly concave. Anterior end rounded; posterior end slightly narrowly rounded, Both ends subequal in height or with anterior end higher than posterior. Thickest part at posterior half. Two furrows in median-anterodor-sal position. Surface weakly reticulate, with knobs and 2-4 nodes. Comparison This new species is very similar to Parailyocypris taizhouensis Yang from the Taizhou Formation of Jiangsu, but differs from the latter in the elongate carapace, and the height length ratio <0.6. Cypridea (Morinina) diplonoda sp. nov. (Pl. IV, figs. 6, 7) Description Carapace short, subrectangular in lateral view. Dorsal margin straight and slightly rapidly sloping to posterior, highest at anterior cardinal angle; ventral margin straight. Left valve larger, strongly over lapping around the ventral margin of the right valve. Both ends rounded. Maximum thickness median in dorsal view. A very shallow depression occurring dorsomedially. Surface roughly pitted and reticulated, covered with knobs and nodes, parallel to posterior and ventral margins in arrangement. Comparison This new species differs from Cypridea (Morinina) nanxiongensis Guan in the short carapace and the height/length ratio>0.6. Cypridea (Guangdongia) longibinoda sp. nov. (Pl. IV, figs. 10-12) Description Carapace large, elongate-elliptical in lateral view. Dorsal margin straight, sloping to poserior end, distinguished by anterior cardinal angle; ventral margin slightly concave. Both ends rounded. Beak and notch somewhat slight in anteroventral part. Two transectional furrows appearing backwards in dorsal position; posterior furrow branched, with two big nodes situated on each side of the furrow. Surface covered with knobs around posterior and ventral margins in arrangement. Comparison This new species differs from Cypridea (Guangdongia) speciosa Guan in the surface ornamented with two big nodes and many knobs. In outline and ornamentation, this species closely resemble Cypridea (Morinina) elongata Guan, but it can be distinguished from the latter by the furrows in dorsal position. Cypridea (Guangdongia) brevibinoda sp. nov. (Pl. IV, figs. 14, 15) Description Carapace large, subrectangular in lateral view. Dorsal margin straight and sloping to posterior end, with highest part at anterior cardinal angle; ventral margin concave. An- terior end broadly rounded and higher than posterior. Two transectional furrows in dorsal position; posterior furrow branched, with two big nodes situated on each side of the furrows. Surface finely reticulate, covered with knobs. Comparison This new species differs from Cypridea (Guangdongia) longibinoda sp. nov. in the short carapace, and the height/length ratio>0.6. Limnocythere dalangshanensis sp. nov. (PI. II, figs. 39-43) Description Female: Carapace tumid, subelliptical in lateral view. Dorsal margin nearly straight; ventral margin concave. Anterior end rounded; posterior end truncated in upper part and extending strongly downward. Two sulci well pronounced dorsomedially, with anterior sulcus short and shallow, while posterior sulcus deep and long. Surface finely reticulated. Male: Carapace elongated, tumid. Posterior end broadly rounded and higher than anterior. Dorsal margin straight; anteroventral margin slightly concave, while postroventral margin strongly convex. Maximum height at posterior one-third. Comparison This new species differs from other species of the genus in the tumid surface, the compressed anterior margin, and the posterior end extending strongly downward.