105 / 2022-02-16 15:25:32

海拉尔盆地Hong-6井铜钵庙组孢粉组合及其古气候意义

the Hailar Basin, Well Hong-6, Tongbomiao Formation, Palynological Assemblages, Berriasian-Valanginian, Palaeovegetation and Palaeoclimate

Abstract Two palynological assemblages are recognized for the first time from the Tongbomiao Formation in the Hongqi Sag of the Hailar Basin, Inner Mongolia. A palynological assemblage from the lower of the Tongbomiao Formation is named as Bayanhuasporites–Cycadopites–Protoconiferus; The assemblage is characterized by abundant gymnosperm pollen and diverse fern spores, among the gymnosperm pollen, Paleoconifer is dominant (4.98-31.62%); and Cycadopites (8.55-25.23%) is common. Some important elements, such as Classopollis，Parcisporites，Erlianpollis，Callialasporites and Jiaohepollis, etc. Among the fern spores, Bayanhuasporite (0-8.96%); and Granulatisporites (0.93-6.97%) is common. The other critical categories are Cicatricosisporites, Concavissimisporites, Densoisporites, Hsuisporites, Foraminisporis and Leptolepidites, ect. The palynological assemblage from the upper of the Tongbomiao Formation is named as Cicatricosisporites- Cedripites - Perinopollenites , gymnosperm pollen is dominant accounting 77.30% of the palynomorphs, while the rest percentage 22 .70% is fern spores. Among the angiosperm pollen, Pinaceae is dominant (31.9%); and Paleoconifer (19.02%) is common, some important elements, such as Quadraeculina，Erlianpollis and Jiaohepollis, ect. Among the fern spores, Cicatricosisporites (4.29%) is abount, Paleoconifer (19.02%) is common, some important elements, such as Concavissimisporites, Aequitriradites and Leptolepidites, ect. There is no angiosperm pollen found in above two palynological assemblages. The discovery of these palynological assemblages provides important biomarkers for stratigraphic division in southern Hongqi Sag and adjacent areas, and also provides critical evidence for paleoclimate analysis in this district. The geological age of Tongbomiao Formation in Well Hong-6 is assigned to Berriasian-Valanginian of Early Cretaceous based on the palynological data, because there exists diverse distribution of Paleoconifer, meanwhile the Lygodiaceae is rare in the assemblage. The vegetation reconstructed on the palynological data of the Tongbomiao Formation in Well Hong-6 from conifer forest or conifer broad-leaved mixed forest to conifer forest with shrubs and grassland, the climate belongs to warm temperate and warm - subtropicalt. At the top of the Tongbomiao Formation 1601.36m depth, the vegetation type is conifer forest, and its paleoclimate is sub-humid warm temperate. However, the interval between the sample at 2286.98m and the sample at 2281.58m above and the sample at 2290.85m below was only 5.4m and 3.87m respectively, indicating that a short cataclysmic event, and the event caused the vegetation landscape to change from conifers and broad-leaved mixed forest to herbs and conifers forest from bottom to top, and then quickly recovered to conifers forest and herbs vegetation landscape dominated by conifers forest, and the forest fire event was the most likely to lead to this event.