摘要
该文报道了松辽盆地白垩纪丰富的非海相微体浮游植物群,主要是沟鞭藻类及一些绿藻和疑源类;论述了藻类的生物地层特征,自下而上初步划分出10个组合带;结合微量元素和古地磁等资料,较详细地讨论了含微体浮游植物组段的沉积环境,认为松辽盆地在白垩纪至少遭受过两次重要的海侵(分别在青山口组一段及嫩江组一、二段沉积时期),导致古松辽湖泊五种不同水体环境的演替,指出微体浮游植物组合的变化是受古盐度、古温度和古水深等因素控制的。此外,对有关组段的地质时代也进行了讨论,进一步补充了新的浮游植物化石证据。
Abundant non--marine microphytoplankton is found from the Cretaceous sediments of the Songliaobesin including dinoflagellates with ten algal assemblage zones recognized in this paper. The following five sets of the algal assemblages represent five different depositional environments controlled bypalaeosalinity, palaeotemperature and water depth,and the two important transgressions. 1. The freshwater dinoflagellate assemblage from the Shahezi Formation (Berriasian--Valanginian) and the Yingcheng Formation (Hauterivian) is considered as originating from afreshwater lake; it is dominated by the ceratioid cysts of the genera Vesperopsis and Balmula,with lowdiversity and high abundance. 2. The slightly brackish water dinoflagellate to freshwater chlorophyte assemblage from Member 3(Albian) of the Quantou Formation and Members 2--3 (possibly Santonian) of the YaojiaFormation, formed close to the seashore, is characterized by the dominance of Operculodinium andNyktericysta, the latter being associated with the freshwater Scenedesmus. 3. The brackish dinoflagellate assemblage from Member 1 (Cenomanian) of the QingshankouFormation and Members 1--2 (possibly Campanian) of the Nenjiang Formation, in fluented by twotransgressions on the ancient Songliao lake,is chiefly dominated by two types of cysts: the proximatecysts referable to the genus Dinogymniopsis and the chorate cysts belonging to Kiokansium andCleistosphaeridium. The dinoflagellate flora from the former formation dominated by Kiokansiumpossibly represents a deep--water lagoon phase, while that from the latter formation dominated byCleistosphaeridium and characterized by higher diversity represents a depositional environment of theopen lake--type. 4. The slightly brackish to freshwater algal assemblage from Members 2--3 of the QingshankouFormation was formed in the regression stage after the transgressive deposition stage of Member 1 ofthe Qingshankou Formation,and is characterized by the disappearance of a lot of dinoflagellate taxa,the then undeveloped freshwater chlorophyte, and by the appearance of a lot of acritarchs such asGranodiscus and Filisphaeridium. 5. The limnetic freshwater algal aasemblage from Member 1 of the Yaojia Formation, theSifangtai and Mingshui Formations was deposited in the smallest lake waters after regression, and ismainly characterized by the fresh water chlorococcalean Pediastrum and the dinoflagellates Aquadulcumand Tetranguladinium. Dinoflagellate cysts have been used as indicators of palaeotemperature and palaeo--water depth.Generally speaking, the abundance of cavate cysts indicates cool or cold waters; the chorate dinocystsare usually dominant in warmer waters; the cysts with short spines or proximate thick walls usuallyoccur in nearshore shallow water environment, while the cysts with complex and dense processesrepresent deep water environment. The dinoflagellates from Member 3 of the Quantou Formation isdominated by the genus Nyktericysta with cornucavate cysts, possibly representing cooler waterconditions, while those from Member 1 of the Qingshankou Formation and Members 1--2 of theNenjiang Formation are dominated by Kiokansium with relatively long, dense processes or byOperculodinium and Cleistosphaeridium with very long and thinner processes, indicating a relatively warmand deep water environment. Such interpretations of palaeotemperature are correlatable with that ofpalaeomagnetism and oxygen isotope from the Cretaceous in the Songliao Basin. In addition, this paper makes a brief discussion on geological ages of the strata containingdinocysts in the Songliao Basin; new genera and new species will be described in other articles.
出处
《微体古生物学报》
CSCD
北大核心
1992年第2期111-126,235-238,共16页
Acta Micropalaeontologica Sinica
关键词
白垩纪
松辽盆地
微体浮游植物
microphytoplankton
Cretaceous
biostratigraphy
palaeoenvironment
Songliao Basin
