浙江长兴煤山地区二叠-三叠系界线底粘土中动物化石的发现及其意义

<正> 浙江长兴煤山地区是我国南部上二叠统长兴阶及二叠-三叠系界线候选层型剖面的所在地。近十年来,我们先后在本区测制了6条上二叠统长兴阶及二叠-三叠系界线剖面,即剖面A.B.C.D.E和Z(Sheng et al.,1984)把下三叠统下青龙组底部的混生动物群层自下而上分成混生层1、2和3三层,混生层1包括两部分,下部为伊利石-蒙脱石粘土层,亦称底粘土(basal clay),上部为黑色泥岩,当时没有在底粘土发现化石。此后,一

Discovery of fossil animals from the basal clay of Permian-Triassic boundary in the Meishan area of Changxing, Zhejiang and its significance

The marine continuous strata across the Permian-Triassic boundary are well exposed in the Meishan area of Changxing, Zhejiang. The lowermost Triassi known as the mixed fauna] horizon can be ascen-dingly subdivided into Mixed beds 1,2 and 3- Mixed bed 1 is composed of basal clay below and dark grey mudstone above. Before 1986, most Chinese scholars regarded the base of the basal clay as the Permian-Triassic boundary, because no fossils have been found in it, however, based on the characters of clay minerals and the change of sedimentary environment, He Jinwen (1981) held that the basal clay should be referred to the uppermost Changhsing and the Permian-Triassic boundary may be placed at the top of the basal clay. Since then, a few conodont specimens (four specimens per kilogram) obtained from the basal clay bave been identified by Clark and others as follows: Neogondolella changxingensis, N. de-flecta, N. carinata and Hindeodella minutus. Recently, a great number of marine fossils were discovered in the basal clay by writers. They comprise non-fusulinacean foraminifers Bradyina sp., Globivalvulina sp., Gcinitzina sp., Hemigordius spp., Giomospira sp., Tetrataxis sp., Nodosaria sp., Textularia sp.; conodonts Neogondolclla changxingcnsis, N. deflecta, N. subcannata, Hindeodclla sp.; ostracodes Basslcrella obesa and brachiopod Crvrithyris sp.. Among them, most are the typical forms of late Late Permian age in South China, while the index fossils of Triassic have not yet been seen. Apparently, this fauna exhibits a distinct aspect of late Late Permian age. As a whole, the palaeontological data available in the present paper may prove that the basal clay is formed in the restricted shallow sea in which the sea water is quiet and stagnant, belonging to a slightly reductive and low energy environment and is late Late Permian in age. Accordingly, the Permian-Triassic boundary should be drawn at the top of the basal clay.