Late Cretaceous-Paleocene Ostracod Faunas From The Jiaolai Basin And Pingyi Basin In Shandong,China And Their Biostratigraphic And Palaeoenvironmental Significance

The Cretaceous was a period with a typical greenhouse climate.Against such a background,the Earth's climate underwent significant changes,with transition from a very warm mid-Cretaceous greenhouse world to a period of long-term cooling during the Late Cretaceous(including the early Paleocene).The end-Cretaceous mass extinction(ca.66 Ma)is one of the big five mass extinctions.The relationship between climate changes and the biological evolution during the Cretaceous-Paleogene,and the end-Cretaceous mass extinction have long been research hotspots.The Jiaolai Basin and Pingyi Basin are respectively located on the eastern and western sides of the Yishu Fault Zone,with well developed Late Cretaceous-Paleocene non-marine strata containing abundant fossils and the Cretaceous/Paleogene boundary(K/Pg boundary).Therefore they become important areas for scientists to study the Cretaceous-Paleogene terrestrial ecosystem and its palaeoenvironmental background.Ostracods are small bivalved crustacean arthropods equally(palaeo)environmentally informative in both the marine and non-marine realm.They are widely used in the palaeoenvironmental and biostratigraphic research.In this thesis,the Late Cretaceous-Paleocene ostracods from the Jiaolai and Pingyi basins are studied from the perspectives of taxonomy,taphonomy,biostratigraphy and palaeoenvironment.Additonally,the family Talicyprididae,a Cretaceous-Paleogene cypridoid group with a cockscomb-like beak at anteroventral portion,is detailedly reviewed for the first time concerning its taxonomy,diversity and palaeobiogeography.In the Jiaolai Basin,samples from the upper part of the Jiaozhou Formation in the Jiankou Village Section,Zhucheng yielded abundant non-marine ostracods,which are assigned to 27 species(including 9 indeterminate species)within 12 genera and reported for the first time from the Zhucheng area.Among these ostraocds,Cypris ectypa(Stankevitch,1974)is combined as Talicypris ectypa(Stankevitch,1974)comb.nov.Comparison of the ostracod assemblage from the Jiankou Village Section with the known eastern Asian ones indicates a Late Cretaceous Campanian to early Maastrichtian age for the upper part of the Jiaozhou Formation.It further suggests the K/Pg boundary very probably within the upper Jiaozhou Formation in Zhucheng.Palaeoenvironmental analysis of the species composition and taphonomic study of the above ostracods,combined with a study of valve ornamentation,suggest that an ephemeral pond(or a small ephemeral lake)alternated with a permanent lake in the studied area during the late Campanian,and there was a seasonally expanding and shrinking lake accompanied by both permanent and ephemeral basins in the latest Campanian to earliest Maastrichtian.In the Pingyi Basin,the Gucheng Formation and the first member of Bianqiao Formation crop out in the Gejiazhuang Section,Pingyi,yielding abundant non-marine ostracods assigned to 18 species(including 7 indeterminate species)within 10 genera.Comparison of the ostracod assemblages obtained here with the known ones in East Asia suggests a Campanian to Maastrichtian age for the middle-upper part of the Gucheng Formation(interval between the first occurrence of Cypridea cavernosa and the first occurrence of Ilyocypris),and a latest Maastrichtian to early Danian age for the first member of Bianqiao Formation(interval between the first occurrence of Ilyocypris and the last occurrence of ostracods).Additionally,this comparison indicates the K/Pg boundary just within the first member of Bianqiao Formation,0.8-4 m above the top of the Gucheng Formation,which further constrains on the occurrence of the K/Pg boundary in the Gejiazhuang Section.Palaeoenvironmental analysis of the ostracod species composition,combined with previous sedimentological analyses and charophyte taphonomic studies,indicates that a small freshwater lake was accompanied by ephemeral basins in the Gejiazhuang area during the Campanian to Maastrichtian interval,and changed into a large lake in the latest Maastrichtian,A review of the family Talicyprididae for the first time indicates a total of 114 species within 9 genera(Altanicypris,Bogdocypris,Chinocypridea,Cristocypris,Khandia,Ovalicypridea,Rhombicypridea,Talicypridea and Talicypris).Among these genera,Rhombicypridea may be a younger synonym of Talicypridea,which,however,needs a further study.An analysis of Talicyprididae in diversity through time shows that this family underwent a great change.Talicyprididae remained a very low diversity during the whole Early Cretaceous although appearing in the Aptian at the latest,but increased quickly in diversity in the Late Cretaceous,culminating in the Maastrichtian.After the Cretaceous,it suddenly fell in diversity with only two genera and species left in the Paleocene,and disappeared completely by the end of Eocene.A palaeogeographical review of Talicyprididae,combined with the fact that this family first appeared in Gondwana and then in Asia,indicates the migration and dispersal of this family are basically in agreement with the "Eurogondwana hypothesis".The migration and dispersal process of Talicyprididae is speculated as follows.The family originated in Gondwana in the Early Cretaceous(no later than Aptian),then migrated to Europe and successively to Asia in the Albian at the latest.And meanwhile,it spread in Gondwana although fossil records are insufficient.During the Late Cretaceous,its geographical distribution broadened and reached the peak in the Campanian-Maastrichtian with fossils found in main Gondwanan landmasses and Asia.Into the Paleogene,its distribution greatly shrank rapidly with a few components confined to some places in China and Mongolia in the Paleocene and only a species in Hunan,China in the Eocene.Both rapid evolutionary radiation and great palaeogeographical expansion of Talicyprididae in the Late Cretaceous is herein considered to be closely related with the warm climate and its reproductive strategies(producing resting and desiccation-resistant eggs which facilitate the widespread dispersal).The sudden decreasing diversity and shrinking palaeogeographical distribution occurring in Talicyprididae just into the Paleogene very probably resulted from the end-Cretaceous mass extinction.