摘要
湘西北特马豆克期的地层,以台地相和斜坡相碳酸盐岩沉积为主。属盆地边缘相或开阔浅海相的沉积,仅在泸溪小章至白洋溪一带和桃源基隆、畲田坪等地零星分布,是一套以褐黄、灰绿色泥质岩(钙质页岩、泥岩)为主,夹深灰色薄层灰岩的地层,含有与浙西相似的三叶虫动物群。它们对于确定特马豆克期江南海盆的西界和东南类型三叶虫的分布范围有较重要的地质意义。
Sixteen species assigned to 14 genera of trilobites are described from the section of the Guotang Formation near Xiaozhang, Luxi County, western Hunan. Among them, 2 new species, Acrocephalina xiaozhangensis sp. nov. and Parabolinella hunanensis sp. nov. are erected, and 9 species belonging to Hysterolenus, Niobella, Macropyge, Promacropyge, Proteuloma, Rhadinopleura and Shurnardia (Conophrys) respectively are left under open nomenclature. A revision of the species Dichelepyge lata Peng, 1984 is given based on the newly discovered material. Two zones, the Hysterolenus Zone and the Dichelepyge lata Zone, are recognized within the Formation. The Guotang faunas are early Tremadocian in age, showing affinities to other early Tremadocian faunas of West Zhejiang, Tianshan,, and Inner Mongolia in China and to those of South Wales, central England, Kazakhstan, southern France, Bavaria and Argentina. The zones of the Guotang Formation can be separately correlated with the Hysterolenus Zone and the Dichelepyge sinensis Zone of the Yinchupu Formation in the Jiangshan-Changshan area, West Zhejiang (Lu and Lin, 1984). Sedimentary series and faunas of the Guotang Formation suggest that during the early Tremadocian the Luxi area stood on the western edge of the Jiangnan Basin, near the Jiangnan Slope on the west and was under a deep water environment.Description of new and revised species Acrocephalina xiaozhangensis sp. nov. (P1. Ⅱ, figs. 1—3; P1. Ⅳ, fig. 6; Text-fig. 3)Diagnosis Species of Acrocephalina with anterior border furrow deeply incised laterally; preglabellar area wide (sag.); median lateral glabellar lobe isolated; median lateral furrow isolated and deflective; librigena bearing incised but incomplete lateral border furrow and long spine.Description Length of cranidium (excluding frontal and occipital spines) equivalent to the width at palpebral lobe. Well defined glabella tapering forward, trapezoidal in outline, obtusely rounded anteriorly, with 3 pairs of deeply incised lateral furrows. Preoccipital furrow gently curved, almost connecting with occipital furrow. Median furrow running inward and slightly rearward initially, then sharply deflected rearward at midway to meet the preoccipital furrow and to isolate the median lateral lobe from glabella; anterior furrow pit-like, located at anterolateral corners, isolated from the axial furrow. Occipital furrow slightly sinuate, deepened laterally. Occipital ring nearly as wide (tr.) as preoccipital lobes, widest (sag.) mesially with a slender median spine. Palpebral lobe strongIy arcuate,, occupying 2/5 the glabellar length. Ocular ridge very prominent. Anterior border furrow gently curved and deeply notched at anterolateral corners of cranidium, becoming feeble in front of the glabella. Anterior border bearing a strong and long frontal spine which upturns gradually forward. Preocular sections of facial sutures diverging forward, turning inward after running across the anterior border furrow to meet anterior margin at a short distance. Posterior section running diagonally from the posterior end of palpebral lobe onto posterior border furrow, then turning abruptly inward and rearward to cut the strip-like posterior border.Librigena with a long gently inward-curved genal spine, a slightly convex genal field, and narrow, flat lateral border which is slightly widened anteriorly. Border furrow as deeply incised as the lateral portions of the anterior border furrow, becoming very faint near the genal angle. Posterior border furrow almost obliterated.Surface of glabella, fixigenae, occipital ring, preglabellar area, and genal field of the librigenae covered with both densely spaced fine granules and scattered coarse granules. Fine granules also visible in the posterior part of the frontal spine.Remarks The type species A. armata Troedsson differs from the new species in having a narrower (sag.) preglabellar field, and shorter, straight median glabellar furrows, with no anterior cranidial border furrow. A. reticulata Chien (1961, pl. 4,. figs. 13--15) is distinguished by its smaller palpebral lobes, less developed cephalic borders, and the absence of the anterior lateral glabellar furrows, while A. cf. acuta (Peng, 1984, pl. 8, figs. 6, 7) is different in having narrower fixigenae, less defined ocular ridges, with no surface granules.Parabolinella hunanensis sp. nov. (P1. Ⅱ, figs. 4, 5)Diagnosis Species of Parabolinella with slightly converging preocular sections of facial sutures, tiny palpebral lobes, rounded anterolateral corners of cranidium, and narrow (tr. sag.) anrerior border. Description Glabella (excluding occipital ring) rectangular, 1.3 times as long as wide, with flanks slightly expanded outward,, eve.nly rounded anteriorly. Three pairs of glabellar furrows equal ly spaced and inward-rearward directed. Occipital, furrowslightly bowed rearward; Occipital equally wide (sag.), with a tiny median node. Ocular ridge bar-like, transverse or slightly oblique rearward with its inner end opposite the anterior lateral glabellar furrow. Small palpebral lobe lying anterior to the median glabellar furrow. Preglabellar field occupying 0.2--0.25 of total cranidial length, ornamented with fine radiating ridges. Anterior sections of facial sutures converging slightly and curved smoothly to form rounded cranidial anterolateral corners. Anterior sutures running transversely after crossing anterior border, meeting each other sagittally to define a wirelike anterior border. Posterior sections of facial sutures slightly sinuous, enclosing large, triangular posterior limbs.Remarks The new species is similar to P. constricta (Lu et al., 1981, p. 7, pl. 2, figs. 2, 3) and P. latilimbata Lu et Chien (in Yin and Li, 1978, p. 478 pl. 164, fig. 7) but both of the latter two species have relatively wider pleural regions and deeper and more sinuous preoccipital furrows. In addition, P. constricta differs in having a shorter but broader glabella with a more arched anterior end, and P. latilimbata in having a relatively wider (sag.) preglabellar field and forward rather than rearward oblique ocular ridges.Dichelepyge lata Peng, 1984 (P1. Ⅳ, figs. 1—4)1982 Hysterolenus asiaticus Lu, Liu, p. 334, pl. 230, fig. 1.1984 Dichelepyge lata Peng, p. 374, pl. 4, figs. la, b; pl. 5, fig. 11.Diagnosis i Species of Dichelepyge with broad (sag.) preglabellar area, smoothly rounded preocular sections of facial sutures, gently tapering and laterally constricted glabella with 4 pairs of lateral furrows isolated from axial furrows, pleural region of thorax 2/3 as wide (tr.) as the axis, very gently swollen anterior pleural band of thoracic segment and transverse triangular pygidium with wide (tr.) axis.Description Exoskeleton ovate, 2 times as long as wide. Glabellar cylinder in outline, expanded gently outward at its base and constricted at lp, rounded anteriorly with truncated apex. Four pairs of glabellar furrows isolated from axial furrows with the preoccipital pair bifurcated and the anterior pair weakly impressed. Occipital furrow shallow mesially, very incised laterally, not connected with axial furrows. Small palpebral lobe semicircular, situated close to glabella and immediately in front of the mid-point of the glabella. Ocular ridge weak and short. Preglabellar area with short paradoublural lines, enclosed by smoothly rounded preocular sections of facial sutures, occupying some 0.3 of the total cranidial length. Posterior sections sinuous, diverging outward rapidly, enclosing blade-like posterior limbs. Posterior border bearing a fulcral socket about 2/3 of its length (tr.) from axial furrow.Librigena with ridge-like eye socle, paradoublural line, narrow and convex border, short and slender genal spine. Doublure wide and flat.Thorax of six segments with pointed tips. Ring furrows deepened laterally. Pleural lobe with anterior band gently swollen,, wider (exsag.) than the posterior band.Pygidium transversely triangular, with rounded anterolateral corners and narrow posterolateral borders. Axis broadly conical, with four or five rings and a terminal piece, continuing rearward as postaxial ridge. Two pairs of border spines.Remarks This species was first described on the basis of a more or less vertically compressed pygidium yielded from the Panjiazui Formation, Taoyuan, Hunan. The new material with cranidia and exoskeleton enables a revision of diagnosis and a full description of the species. An exoskeleton, which is also from the Panjiazui Formation in Taoyuan and has been described as Hysterolenus asiaticus Lu by Liu (1982, pl. 230, fig. 1), is certainly conspecific with the present form. D. lata is most similar to D. phylax Hutchson et Ingham (1967, pl. 8, figs. 6, 8—10, 12, 15, 16), but in the latter, the preglabellar area is shorter (sag.) and the pleura1 region is proportionally much narrower than. that of the former. The less segmented pygidial axis can distinguish the present species from D. pascuali, the type species from the Lower Tremadocian Kaillena meridionalis Zone of Argentina (Harrington and Leanza, 1957), D. biconis (Lisogor, 1961) from the Kendyiktas Formation of Kazakhstan and D. sinensis from the D. sinensis Zone of the Yinchupu Formation of West Zhejiang (Lu and Lin, 1984).
出处
《古生物学报》
CAS
CSCD
北大核心
1991年第2期141-166,277-280,共26页
Acta Palaeontologica Sinica
