摘要
东海陆架盆地西南部海相始新统富含钙质超微化石,经初步分类描述,计60种,其中57种分别隶属11科,有3种的科级分类未定。依据标志种的存在,自下至上划分出4个钙质超微化石带,即Tribraciatus orthostylus带(NP12),Discoaster lodoensis带(NP13),Discoaster sublodoen-sis带(NP14)和Nannotetrina fulgens/Chiasmolithus solitus联合带(NP15/NP16)。据钙质超微化石的分布情况,讨论了地层的时代,其中瓯江组至温州组下部含泥质灰岩与其上覆钙质泥岩分界处(NP14带底部)定为早始新世,由该分层界线至平湖组之顶归入中始新世。通过钙质超微化石组合特征分析,及其与邻近的台湾西部近海盆地和大西洋等洋域的对比,论证本区海相始新统代表一次完整的海侵旋回,旋回内部有过三次小规模的海平面升降活动;同时,沉积区处于中纬度偏南地带,属于陆棚海近岸环境。
The marine Eocene in the southwestern Continental Shelf Basin of the EastChina Sea has been discovered in the 'course of exploratory drillings for oil andgas. According to lithologic characters, these rocks may be divided into threeformations in conformable contact with each other, which, in descending order,are as follows: 1.Pinghu Formation This formation, about 128m thick, underlies unconfor-mably the Lower Miocene strata and consists of brownish mudstones in the upperpart and light grey mudstones and siltstones intercalated with sandstones in thelower part. 2.Wenzhou Formation This formation with a total thickness of 756.5m maybe subdivided into three parts, the upper part contains unequally thick interbed-dings of grey-light grey mudstones,siltstonas and sandstones;the middle part con-tains sandstones with gravels; silty mudstones intercalated with thin-beddedbioclastic limestones and marlites; the lower part consists of grey mudstonesand bioclastic limestones. 3.Oujiang Formation This formation with a total thickness of 505m is com-posed of two different parts in lithological character:the upper part of grey mud-stones intercalated with siltstones and the lower part of sandstones intercalatedwith mudstones and carbonaceous mudstone deposits. It is in unconformable con-tact with the underlying Paleocene strata. A total of more than 60 samples, including 52 ditch cuttings, 2 sidewallcores and 6 cores, have been collected from throughout the above sequence du-ring this investigation. Distinctly abundant and diversified calcareous nannofossilassemblages are mainly found in some of the calcareous mudstone samples. Fourcalcareous nannoplankton datum levels can be recognized from the Upper OujiangFormation to the Pinghu Formation, namely, the last occurrence of Tribrachiatusorthostylus, the first occurrence of Discoaster sublodoensis and Rhabdosphaera inflata,the last occurrence of R. inflata, and the last occurrence of Chiasmolithus solitusand Sphenolithus furcatolithoides. The intervals of these datum levels are approxi-mately coincident with NP12,NP13,NP14 and NP15/NP16 in the 'Standard zonation'(Martini, 1971) respectively (Fig. 2). The base of the Tribrachiatus orthostylus zone (NP12), however, can not be delimited due to the barrenness of calcareousnannofossils in the middle part of the Oujiang Formation.Some of the well-known forms representing offshore conditions frequently occur in the presentassemblage, such as Braarudosphaera, Micrantholithus, Pemma, Rhabdosphaera,Transversopontis and Zygrhablithus. In addition, the boundary between LowerEocene and Middle Eocene is drawn near the base of the Discoaster sublodoensiszone(NP14); this recent opinion (Haq et al., 1986) is followed here. The dino-flagellates also support this conclusion (He Cheng-quan, this volume). The result of the present study may directly apply to the western Taiwanand adjacent offshore basins; according to Huang (1982), the Lower Eocene andMiddle Eocene nannofossil zones NP12 through NP16 have proved to be ubiqui-tous beneath the Miocene or Oligocene in the Taihsi, Penghu,South Pengchiahsu,and other basins. By supposition, therefore, it is reasonably suggested that thesebasins have linked up with the southwestern part of the East China Sea ShelfBasin as a source of intruding sea water, and have been situated in the near-shore environments in the marginal sea. Results of study during this investigation show that the known ranges ofseveral species can possibly be extended. For example, Ericsonia subdisticha (Rothet Hay) Roth, Helicosphaera bramlettei (Muller) Jafar et Martini and Reticulofene--stra hillae Bukry et Percival have been found in the Pinghu and Upper WenzhouFormations (Upper NP15/NP16). This can not be the result of contaminationfrom overlying rocks, because in the present drill hole section, there are nomarine Upper Eocene and Oligocene based on the date of foraminifera, calcare-ous nannofossils and dinoflagellates. On the other hand, the appearance of scarceDiscoaster diastypus Bramlette et Sullivan and D. monstratus Martini in the
出处
《微体古生物学报》
CSCD
北大核心
1990年第4期311-344,432-438,共34页
Acta Micropalaeontologica Sinica
