中国-中新世湖泊的古生态:根据山旺盆地植硅体的初步解释

山东山旺中新世山旺组湖相沉积中富含保存精美的古生物化石。对于湖相沉积中的昆虫、植物和哺乳动物化石,前人已经做了大量的研究工作。其中植物大化石和孢粉的研究结果表明,中新世山旺组在沉积期间,山旺湖周围的植被处于湿润的暖温带到亚热带的古生态环境下。哺乳动物蝙蝠和貘化石的研究结果也支持这个结论。然而,迄今为止,还没有关于草本植物的种类组成及含量的研究报道。本文首次对山旺组样品中的植硅体进行了研究,为山旺中新世植被的研究提供了新的证据。对从6块山旺组样品中分析出的植硅体进行研究的结果表明,山旺中新世植硅体组合含有丰富的保存极好的草本植物植硅体,代表森林成分的双子叶植物植硅体,以及偶尔出现的棕榈科植硅体。草本植物的植硅体主要来自于C_3/C_4禾本科的PACCAD类群和早熟禾亚科的植物,少数可能来自于在林下封闭生活环境中生长的草本植物。山旺中新世植硅体组合显示,在湖边森林生活环境下,伴生大量的适合沼生到中生环境的草本植物,在较干旱的地区生长着早熟禾(和PACCAD)的草本植物。本文的研究结果进一步支持山旺中新世气候比现在更加湿润而且变动较小的观点。山旺中新世植硅体组合与土耳其和北美大平原中新世湖相沉积中的植硅体组合不同,后者的植硅体组合主要是由多种C_3早熟禾亚科草本和不同种类的PACCAD类群草本植物组成。今后的研究工作将进一步揭示这种差异是否反映了草本植物群落在大尺度的生物地理上的差异,或者是由于地区性的局部气候不同所导致。

PALAEOECOLOGY OF AN EARLY-MIDDLE MIOCENE LAKE IN CHINA: PRELIMINARY INTERPRETATIONS BASED ON PHYTOLITHS FROM THE SHANWANG BASIN

The lacustrine Early to Middle Miocene Shanwang Formation contains an exceptionally well- preserved biota including insects,plants,and vertebrates that has been subject to intense study.Palaeo- ecological work on plant macrofossils and palynofloras indicate that the locality represents a forest under a humid,warm-temperate to subtropical climate that remained rather stable during the deposition of the formation.This interpretation is supported by fossil vertebrates such as bats and tapirs discovered in the Shanwang section.However,to date no information has been available on the presence,abundance, and taxonomic composition of grasses at this locality.Here,we report on phytoliths extracted from six samples from the Shanwang Formation,providing new evidence of the vegetation that grew around the lake.The phytolith assemblages contain well-preserved and abundant grass phytoliths,forest indicator phytoliths from dicotyledonous plants,and infrequent palm phytoliths.The grass phytoliths consist of forms produced by C_3/C_4 PACCAD grasses and pooids,with a minor component of morphotypes thought to derive from closed-habitat grasses.Our preliminary interpretation of these phytolith assemblages is that they reflect a lake-side wooded habitat and abundant helophytic to mesophytic grasses,with drier areas supporting pooid (and PACCAD) grasses.The data support the reconstruction of the Miocene Shanwang region as more humid and equable than presently.The Shanwang phytolith assemblages con- trast with Miocene lacustrine phytolith assemblages from Turkey and the Great Plains of North America, which indicate grass communities characterized by diverse C_3 pooids and different types of PACCAD grasses.Future research will determine whether this variability reflects large-scale biogeographic differ- ences in grass communities or local,microclimate-related variation.