我國中、新生代主要陸地生物群的年代框架和沉積環境演變研究報告

鄧成龍+鞏恩普+姜寶玉+王旭

摘要：建立了榆社盆地的高分辨率磁性地層年代學框架，厘定了高莊動物群和麻則溝動物群的準確年代，建立了中國陸相上新統高莊階和麻則溝階的高分辨率磁性地層年代學框架。高莊動物群和高莊階的時代為早上新世，麻則溝動物群和麻則溝階的時代為晚上新世。目前已對臨夏盆地牛家村、丫溝、楊家山、后山和郭泥溝剖面等五個含有重要化石層位的剖面以約20 cm間距采集了古地磁定向手標本樣品。結合巖石地層學、磁性地層學和生物年代學的制約，確定了下沙溝動物群的年代為2.2-1.7 Ma；將上新統/更新統界線確定于下沙溝剖面的底部。此外，結合研究組近年來在泥河灣盆地的其他磁性地層學定年結果，建立了泥河灣盆地哺乳動物群的年代序列。建立了大理盆地三營組的高分辨率磁性地層年代學框架，揭示出大理盆地記錄了C4n.1r負極性時到C2n正極性時之間的沉積，其中三營植物群產于上新世地層中，從而準確厘定了三營植物群的年代。課題組建立了昭通盆地的高分辨率磁性地層年代學框架，揭示出昭通盆地記錄了C3Br負極性時到C2An.1n正極性時之間的沉積，其中昭通古猿化石及其伴生哺乳動物群產于C3An.1n正極性時早期，年代為6.1 Ma。 此外，對遼西建昌玲瓏塔大西山剖面含化石沉積層中的3 個凝灰巖樣品進行了詳細的SIMS 鋯石U-Pb 定年， 獲得了160.7±1.7， 159.5±2.3 和158.9±1.7 Ma 的年齡結果。 通過對義縣組各個沉積層展開精細的研究，確定各沉積層的古環境特征，并對熱河生物群開展古生物學研究，命名Microraptor一新種。對遼西四合屯早白堊世古湖泊邊緣區和深水區的各種巖相的分布范圍和厚度變化趨勢進行調查，分析了各種巖相和相組合在時間和空間的分布規律，恢復了湖泊形成、演化和消亡規律，探討了各種巖相和相組合中化石埋葬的方式，從而尋找有利于化石特異埋藏的環境。對富含珍稀動植物化石的、遼西四合屯早白堊世古湖泊演化的第二和第三階段的沉積物進行了高分辨率、微米級的沉積微相分析，從而劃分了6個微相。 通過有機碳同位素、碳酸鹽碳氧同位素等地球化學手段在我國由南至北三個沉積盆地的地層中確定PETM事件的存在，并通過四醚膜類脂物（GDGTs）組分重建古溫度等信息，進而恢復PETM時期我國陸地氣候的空間格局和環境特征。本課題選取了內蒙古岱海地區全新世以來的湖泊沉積物DH99a鉆孔，進行了黑碳的提取和碳同位素（δ13C）分析。 在揭西縣灰寨、河源黃村和瀏陽澄潭江發現了三條出露完整、化石豐富的新剖面。對這三條剖面以及宜章心田門剖面進行了詳細的研究，初步建立了南嶺地區晚三疊世-早侏羅世的巖石地層和生物地層的層序。

關鍵詞：高分辨率磁性地層學；陸地生物群；古環境；古湖泊；古新世-始新世極熱事件；沉積盆地

Chronology and sedimentary environment of terrestrial biota during the Mesozoic and Cenozoic

Abstract：High-resolution magnetostratigraphic investigations were conducted on a series of sedimentary basins and associated mammalian faunas. Results show that： The age of the sedimentary sequence in the Yushe Basin can be constrained to an interval from late Miocene to early Pleistocene. The Gaozhuang Fauna and the Mazegou Fauna have ages of Early Pliocene and Late Pliocene， respectively. The sedimentary profile in the Dali Basin spans from Chron C4n.1r to Chron C2n. The age can be constrained to an interval from late Miocene to early Pleistocene. The sedimentary profile in the Zhaotong Basin spans from Chron C3Br to Chron C2An.1n. The age of the sedimentary sequence in the basin can thus be constrained to an interval from late Miocene to late Pliocene. The hominoid fossil in the Zhaotong Basin has an age of ～6.1 Ma， the terminal Miocene. The Nihewan faunas can be placed between the Gauss–Matuyama geomagnetic reversal and the Matuyama–Brunhes geomagnetic reversal （2.58-0.78 Ma）， leading to a time range of ca. 2.6-0.8 Ma for the Nihewan mammalian faunas. The Pliocene–Pleistocene boundary is located in the lower part of the Xiashagou section. High-resolution paleomagnetic sampling has been conducted in the Linxia Basin， yielding more than 5000 samples at intervals of ～20 cm. The SIMS U-Pb zircon analyses of zircons derived from three tuff layers in Daxishan section in Linglongta yield （160.7±1.7）， （159.5±2.3） and （158.9±1.7） Ma， indicating that they were formed at early Late Jurassic. Sedimentary properties of the fossil-bearing deposits of Lake Sihetun （Yixian Formation， Lower Cretaceous） were investigated on a high-resolution， submillimetric scale. Lake evolution is subdivided into four phases， of which Phases 2 and 3 provided suitable conditions for excellent fossil preservation. Six microfacies are recognized within these two phases. Detailed geochemical analyses were carried out on three basin sequences along a north-south transect demonstrate the presence of the PETM. Carbon isotope ratio of black carbon was measured on the Daihai Lake sediment core with an objective to examine the effectiveness and sensitivity of the δ13C values of black carbon as a potential indicator of terrestrial environmental changes. Three well outcropped Mesozoic profiles rich in faunas at Huizhai， Huangcun and Chengtan were found. Lithostratigraphic and biostratigraphic sequences were established.

Keywords：High-resolution magnetic stratigraphy； terrestrial biota； paleoenvironments； paleolake； Paleocene-Eocene Thermal Maximum （PETM）； sedimentary basin

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