Oligocene-Miocene Dinoflagellates Biostratigraphy And Palaeoenvironmental Interpretation In Northern South China Sea, Panyu Uplift Of Pearl River Mouth Basin

In Panyu uplifts, located in Pearl River Mouth Basin of the South China Sea,there are some different idea about the boundary between the Zhuhai and ZhujiangFormation, the present thesis is focused on biostratigraphy and paleoenvironmentalinterpretation, in order to provide some new proof about the expanding of the SouthChina Sea and some useful dinoflagellate cyst data of early Miocene-late Oligocene inmiddle-low latitude area.The 61 samples studied in the thesis were collected from the Well PY34-1-1frominterval 3546-3894m and the Well LH19-5-1 from the interval 2475-2718m. Bothqualitative and quantitative approaches were used for above purpose. Nearly allsamples contain moderate to few and well-preserved dinoflagellate cysts. Fortydinoflagellate species/subspecies of twenty-nine genera were identified and choratecysts overwhelmingly dominant dinoflagellate assemblages .The boundary between Miocene and Oligocene and two assemblages weredefined based on characters of assemblages and the highest occurrences ofCleistosphaeridium diversispinosum , Cordosphaeridium gracile and the lowestoccurrences of Hystrichosphaeropsis obsura,Malitasphaeridium choanophorum,Tuberculodinium vancampoae in Well PY34-1-1. The boundary Miocene / Oligocenewas located at 3822m-3834m. Late Oligocene: Cleistosphaeridium diversispinosum-Cordosphaeridium gracil;Early Miocene: Polysphaeridium zoharyi—Lingulodiniummachaerophorum. The boundary between Miocene and Oligocene and twoassemblages defined based on characters of assemblages and the highest occurrencesof Cleistosphaeridium diversispinosum,Cordosphaeridium gracile in Well LH19-5-1.The boundary Miocene / Oligocene was located at 2685m-2691m .Late Oligocene:Cordosphaeridium gracile;Early Miocene: Cleistosphaeridium placacanthum—Lingulodinium machaerophorum. So the age of the Zhuhai Formation is assigned toOligocene, the age of the bottom of the Zhujiang Formation is also Oligocene, and therest of the Zhujiang Formation is Miocene.Based on some key species, two environment stages may be recognizedin WellPY34-1-1. In Late Oligocene, its environment was the inner neritic sea, interpreted bydinoflagellate assemblage dominanted by species of Polysphaeridium;In EarlyMiocene, the outer neritic sea was envidenced by the sudden decrease ofPolysphaeridium, the increase of Cleistosphaeridium , Spiniferites andHystrichokolpoma which are regarded to represent the outer neritic, and the startingoccurrence of a very small amount of Leptodinium, Nematosphaeropsis andImpagidinium which may be the neritic/oceanic boundary environment indicator. SoPanyu region experienced a significant environment change from the inner neritic toouter neritic sea during late Oligocene to early Miocene, which can prove theexpanding of SCS at that times.