Systematic Classification And Stratigraphy Of Triprojectacites In The Upper Cretaceous Of The Songliao Basin,NE China

Triprojectacites Mtchedlishvili,1961 emend.Stanley,1970 is a group of angiosperm pollen widely distributed in the Upper Cretaceous-Paleocene in Northern Hemisphere.Their distinctive characteristics,high diversity,short geological distribution and rapid evolution make them important index fossils for the division and correlation of strata.Triprojectacites is diagnosed by the projections with colpate apertures.Due to the complex and varied morphology,there are many difficulties in the measurement and description of this kind of pollen,and there is no clear and uniform standard.The uncertainty of description leads to the divergence of the definition and division of genera and species.Up till now,38 genera and more than 300 species have been proposed as in relation to Triprojectacites,many of which are synonymous and need to be combined or revised.There are still many confusions and controversies in systematic classification of Triproj ectacites,which needs further study.In the present study,the morphology,systematic classification of Triprojectacites and its stratigraphy are studied based on the material of the upper Cretaceous core profile SK-1 by the Continental Scientific Drilling Project of Songliao Basin in China.The combined observation techniques of single pollen grain under both optical microscope and scanning electron microscope(SEM)or transmission electron microscope(TEM)were used to observe pollen grains from the second member of the Nenjiang Formation to the second member of the Mingshui Formation in the north and south boreholes of SK-1.Based on the observation of a large number of specimens and the review of the former researches,the meaning and scope of Triproj ectacites are well defined as the pollen having three projections with colpus at their terminals against the main body.A new classification system of Triprojectacites is established after the revision of the genera and species.The morphological characteristics of Triproj ectacites,such as body and projections,wall structure,projection thickening,sculptures,appendices and polarity,are described in great detail.It is considered that sculpture and polarity are not suitable as the primary criteria for classification,because there are transitional types in between.Appendices(such as collar ring,secondary projection,and equatorial lateral fissure)are stable and easy to identify,which can be used as keys to the differentiation of genera.Aiming to solve the problems existing in the measurement,description and classification of Triprojectacites,a universally applicable measurement method is proposed,including a set of indices,based on a mass observation of Triprojectacites in SK-1.The application of this method shows that it can help avoid various errors in measurements to realize an accurate description of the morphological characteristics.The method is also applicable for specimens preserved at different views,which makes them comparable.It is a scientific and rational morphological measurement and description standard for classification.A total of 101 samples were analyzed and observed,of which 34(32 in the north borehole and 2 in the south borehole)are rich in Triprojectacites.7 genera and 35 species of Triprojectacites are systematically described from SK-1.Five development stages of Triprojectacites are recognized in the Songliao Basin ascendingly,based on its occurrence and distribution through SK-1 core:?.occurrence stage(the earliest Campanian);?.radiation stage(the early Campanian);?.steady stage(the mid-late Campanian);?.flourishing stage(the latest Campanian-the early Maastrichtian);?.fading stage(the mid-late Maastrichtian).Five palynozones are established accordingly:the Aquilapollenites kentii-A.stelckii,Aquilapollenites striatolongus-Integricorpus scolpulensis,Fibulapollis mirificus-Aquilapollenites spinulosus Zone,Aquilapollenites attenuatus-Bratzevaea amurensis and Bratzevaea cliva-Pseudoaquilapollenites conatus zones.The morphological evolution trend and phylogeny of Triprojectacites are presumed,based on the occurrence order of genera and species and morphological features through the profile.It shows a tendency for Triproj ectacites to be larger in size,stronger in projection and more prominent in sculpture,and to evolve appendices.Regional correlation shows that Triproj ectacites palynoflora in the Songliao Basin is comparable to that of Japan and South Korea in composition and evolution whilst somewhat different from that of North America and Siberia.Aquilapollenites quadricretae,Bratzevaea amurensis are good stratigraphic indicators for Maastrichtian Period,which can be used for regional stratigraphic correlation at a large scale.