福建宁化禾口盆地早白垩世禾口组的褶珠蚌化石——兼论Plicatounionidae的分类

PLICATOUNIO FROM HEKOU FORMATION OF HEKOU BASIN, NINGHUA, FUJIAN, WITH DISCUSSION ON CLASSIFICATION OF PLICATOUNIONIDAE

前言福建宁化禾口盆地位于我国东部闽赣交界的武夷山脉中段或新华夏构造带的西南段。其四周多被断层所隔,成一狭长的断陷盆地,长近40km,最宽约10km,整个盆地均由坂头组、禾口组、沙县组和赤石组组成,前三组中含有丰富的动物和植物化石(福建省区测队,1972;福建省石油地质队地层古生物组,1979;王国平,1984;曹美珍,1986)。1980年。

This paper describes 3 nonmarine bivalves, Plicatounio (Plicatounio) naktongensis Kobayashi et Suzuki, 1936, P. (P.) aff. naktongensis and P. (P.) fujianensis Gu et Ma, 1976, from the Early Cretaceous Hekou Formation of the Hekou Basin, Ninghua, Fujian, with a detailed discussion on the classification of Plicatounionidae. The key character of the Trigonioidacea lies in the anterior retractor pedal scar which is distinctly separated from the anterior adductor scar. The general pattern of ornament can be regardedas the taxonomical criteria at family or subfamily level. In Plicatounionidae Kobayashi, the shell surface is only ornamented with radial ribs, except the concentric growth sculpture, which differs from the concentric growth lines on the shell surface in Nakamuranaiidae Guo, the V-shaped ribs in Trigouioididae Cox and the reversed V-shaped or cheveron ribs on the posterior shell surface in Pseudohyriidae Kobayashi. The family Plicatounioinidae Kobayashi probably include 6 genera (subgenera) and 1 group which can be defined as follows: Plicatounio (s. s.) Kobayashi et Suzuki, 1936 (=Plicatounio (Kwanmonia) Ota, 1963), ornamented with less than 25 radial ribs on the whole shell surface and crenulation on the whole interior ventral margin; submedian tooth absent; crenulation on teeth generally medium in strength. Range, probably limited to the Early Cretaceous of Asia. Plicatounio (Guangxiconcha) Yao et Yu 1985 (=Plicatounio (Tamuraia) Guo,1986), oramented with more than 24 radial ribs on the whole shell surface and crenulation on the interior margin; submedian tooth absent; crenulation on hinge teeth weak to strong. Range, Late Jurassic?—Creta-ceous of Asia. Plicatounio latiplicatus Gu et Yu 1976 group, ornamented with about 8 radial ribs which are wide and scarcely spaced on the whole shell surface and with crenulation on the interior margin, submedian tooth absent; crenulation on teeth fairly strong. Range, Cretaceous of China. Lioplicatounio Ma, 1983, ornamented with several radial ribs and marginal crenulations in posterior part; no submedian tooth and not any crenulation on teech. Range, Late Jurassic-Late Cretaceous of China. Buginella (s. s.) Basbold, 1969, sculptured with radial ribs extending to venter in anterior and middle parts, but smooth in the posterior part, no submedian tooth. Range, Late Cretaceous of Russian Asia and Mongolia. Buginella (Weichangella) Yu et Yao, 1980, sculptured with radial ribs which are fine, densely spaced, not extending to the venter, but smooth in posterior part; no submedian tooth. Range, Late Jurassic?—Early Cretaceous of China. Rongxiania Liu, 1982, with submedian teeth and the same ornament as that of Plicatounio (s.s.). Range, Cretaceous of China. Plicatounio (Acclinoplicatounio) Ma et Huang, 1979, belonging to Pseudohyriidae for its ornaments of reversed V-shaped or cheveron ribs on the posterior shell surface. Plicatounio (Entotrigonioides) Guo, 1986, not belonging to Trigonioidacea due to the absence of anterior retractor pedal scar separated from the anterior adductor scar. The species of the so-called Plicatounio from Africa are misidentified, such as P radidei Gouward, 1956 from the Upper Cretaceous of Sudan and P. flattersensis Mongin, 1963 from the Lower Cretaceous of Fort Flatters of the Sahara desert. They are not genuine Plicatounio and Trigonioi-dacea for their anterior retractor pedal scar is joined with, rather than separated from, the anterior adductor scar, which is a typical pattern of muscle scar in Unionidae rather than in Trigonioidid. Plicatounio (Plicatounio) naktongensis, occurring abundantly in the Sengoku Formation (W1) but rarely in the Lower Wakamiya Formation (W3) of the Wakino subgroup in Japan, and commonly in the Kinbu or Kasando Formation but rarely in the Shinshu Formation of the Naktong subgroup in South Korea. This species is very abundant in the Hekou Formation of Ninghua, Fujian and therefore it appears that the Hekou Formation corresponds to the Sengoku Formation (W1) and the Lower Wakamiya Formation (W3) of the Wakino subgroup in Japan, and to the Kinbu or Kasando and Shinshu Formation of the Naktong subgroup in South Korea, and very probably to the Sengoku (W1) and Kinbu or Kasando Formations, which are definitely earlier than late Albian and very probably of Neocomian in age.