新疆北部中–晚泥盆世植物稳定碳同位素研究

对新疆北部和布克赛尔地区呼吉尔斯特组上段中—晚泥盆世7属9种植物,206个样品开展了植物稳定碳同位素分析,包括草本石松类Haskinsia、Leclercqia,乔木状石松Hoxtolgaya,工蕨类Serrulacaulis,前裸子植物Tetraxylopteris,原始真蕨类Compsocradus,带蕨Taneocrada等,时代跨度从中泥盆世Eifelian期至晚泥盆世Frasnian期。新疆北部泥盆纪陆生植物δ13C值分布范围在?26‰~?19‰之间,与现代C3植物δ13C值分布范围一致。不同类群植物稳定碳同位素组成存在一定的差距,这与植物水分利用效率大小有一定的对应关系。同一植物属种不同器官的δ13C值并不完全相同,δ13C茎轴 >δ13C孢子叶。从Givetian期至Frasnian期,植物δ13C值下降3‰左右,推测与其对应的是CO2浓度的小规模上升,气候变暖。中泥盆世Eifelian期至Givetian期,植物δ13C值并未表现出明显的变化趋势,反映了整个中泥盆世气候可能相对稳定。

山东中新世山旺组葛属(豆科)小叶的形态及其古生态学意义

葛属Pueraria是豆科蝶形花亚科、菜豆族大豆亚族中最大的、具有三小叶复叶的属,其大多数种为攀援性藤本植物,分布于东亚、南亚、东南亚和大洋洲。化石记录表明,葛属早在中新世就已出现在东亚、巴尔干半岛和高加索地区的亚热带和温带植物群中,目前已知有3个化石种,即中国山旺中新世的荚果化石山旺葛藤P. shanwangensis、山旺和日本数个中、上新世产地的叶、小叶化石鲁葛藤P. miothunbergiana以及克罗地亚和格鲁吉亚阿布哈兹中新世的小叶化石大葛藤P. maxima。本文基于对中新世山旺组最近采集的葛属小叶印痕化石的观察和对现生种葛P. montana小叶的形态比较,研究了该属化石种的小叶形态和发育变异。结果表明,现生种葛与化石种鲁葛藤和大葛藤的小叶都具有不甚发育的间二级脉,这个特征在先前报道的鲁葛藤小叶化石中未见保存。另外,它们的主脉和二级脉远轴侧有时都会分别发出两条挨得很近、角度不同的二级脉和二级脉梳脉,这个特征过去在葛属中则被忽视了。总体上,葛属小叶化石的叶脉特征在中新世广阔的欧亚中纬度地区显示了高度的相似性。目前,仅在中国中新世山旺植物群和日本中新世高峰山组植物群中发现了与现生的葛小叶相似的、具有裂瓣的鲁葛藤小叶化石,但现生葛比化石葛的小叶更大些、似乎发育了更多具有裂瓣的小叶,这可能与中新世以来大气二氧化碳浓度的变化有关。现生葛长在荫蔽生境以及攀援于支持物(如藤架或其他木本植物)上的植株比生于开阔生境以及蔓生的植株发育了更多的、具有裂瓣的小叶,这可能有效促进了整株植物的叶片和冠层中的光照截取和通风散热。据此推测,中国和日本中、上新世的鲁葛藤居群可能比克罗地亚和阿布哈兹中新世的大葛藤居群的生态耐受性更加宽泛,东亚的居群既生于荫蔽的、更多依赖森林的生境中,也长在开阔的、较少依赖森林生境中,甚至蔓生。

Devonian integrative stratigraphy,biotas,and paleogeographical evolution of the Qinghai-Tibetan Plateau and its surrounding areas

The Devonian System in the Qinghai-Tibetan Plateau and its surrounding areas is widely distributed,diverse in lithotypes and rich in fossils.It records the crucial processes of continuous subduction and reduction of the Paleo-Asian Ocean in the northern hemisphere and the transformation of the Proto-Tethys Ocean into the Paleo-Tethys Ocean in the southern hemisphere.Thus,it is of great significance for explaining the global paleogeographic evolution,tectonic activities and biodiversity changes during this critical period.The blocks on both sides of the southern Tienshan suture zone and the Longmu Co-ShuanghuChangning-Menglian suture zone belong to different sedimentary systems and paleobiogeographic realms and regions,showing important tectonic paleogeographic partitioning significance.The two suture zones represent the main branches of the PaleoAsian Ocean and the Paleo-Tethys Ocean,respectively,and on this basis the Devonian System can be subdivided into three types:the Tienshan type,the Tethys type and the Gondwana type.Based on recent research progress on the Devonian stratigraphy and paleontology in combining provenance analysis and biotic characteristics in the Qinghai-Tibetan Plateau and surrounding areas,this paper aims to establish the latest integrative stratigraphic framework and conduct paleogeographic reconstruction,providing foundation for exploring the geological evolution and dynamic mechanisms of various terranes and blocks in the northern margin of Gondwana.The results indicate that the North Qiangtang,South Qiangtang,Simao,Baoshan and Tengchong terranes,as well as the Himalaya Tethys Zone and the South China Block have affinities with the Indian Block,while the Lhasa Terrane has affinities with the Australian Block,and may be located between the South China and Australian blocks.In the Emsian(Early Devonian),the South China Block separated from the northern margin of Gondwana,a process that was accompanied by the opening of the Jinshajiang-Ailaoshan Ocean.In the Middle Devonian,the mid-oceanic ridge of the Paleo-Tethys Ocean expanded rapidly,corresponding with a global sea-level rise,the widespread development of carbonate platforms and nadir values of Devonian seawater strontium isotopes.By the Late Devonian,the Paleo-Tethys Ocean had reached a considerable size,leading to abundant occurrences of Upper Devonian radiolarian cherts in the Paleo-Tethys suture zones.

Devonian integrative stratigraphy and timescale of China

The Global Boundary Stratotype Sections and Points(GSSPs) for the bases of all seven international Devonian stages have been formally defined and ratified by IUGS till 1996, and nowadays, the main tasks for Devonian stratigraphers include further subdivision of these standard stages, strictly constrained absolute ages for the boundaries, and precise neritic-pelagic and marine-terrestrial correlations using multidisciplinary stratigraphy methods. Establishment of high-resolution Devonian integrative stratigraphy framework and timescale of China would play an important role in improving regional and international correlation, facilitating the recognition of important stratigraphic levels in different paleogeographic settings, and understanding the evolution pattern of biota, paleoclimate and paleoenvironment during this critical interval. Based on well-studied bio-and chronostratigraphy of Devonian in South China and adjacent areas, in combination with recent achievements in carbon isotope stratigraphy, event stratigraphy and radioactive isotope ages, this paper briefly summarize the research history and current status of Devonian chronostratigraphy of China, and for the first time introduce Devonian integrative stratigraphy framework of China.Up to date, few studies have been conducted on the astronomical cyclostratigraphy and high-resolution radioactive isotope dating in Devonian of China, which should be our main focuses in the near future.

The evolution of Paleozoic vascular land plant diversity of South China

Data of Paleozoic and some Early Triassic vascular land plant fossils from South China are synthetically analyzed,revealing evolutionary characteristics of Paleozoic vascular land plant diversity.Vascular land plant diversity keeps increasing in the Paleozoic as a whole.The Silurian witnessed the earliest evolution and initial diversification of land plants.From the Early Devonian to the Early Carboniferous(Mississippian),the great development,diversification,and differentiation really occurred in vascular land plants,with fluctuations of diversity,rapid replacement of the plant types,and an all-out takeover of terrestrial ecological niches.From the Early Permian,land plant diversity dramatically increased,and reached a climax in the Middle-Late Permian.Comparisons between late Paleozoic marine and terrestrial biodiversity reveal co-evolution of the late Paleozoic animals and plants as well as the individual evolutionary patterns of sea/land ecosystems.Vascular land plant diversity dramatically declined in the Frasnian as a result of the F/F event,and the end-Permian mass extinctions completely turned over the phytogroups.