Magnetostratigraphy of Plio-Pleistocene Lake Sediments from Armenia (Magnetostratigraphie Plio-Pleistozäner Seesedimente aus Armenien)

亚美尼亚的更新世地质以广泛存在的湖泊沉积为主导，这证明至少在过去200万年里，环境条件发生了反复、迅速和剧烈的变化。这些沉积物中含有种类繁多的化石遗迹，可以重建动植物以及气候条件，特别是在像地球古人类(1.8 Ma)这样的早期人类扩散到欧亚大陆期间。然而，不幸的是，这些层序的准确测年仍然是一个有争议的问题，到目前为止，唯一可用的绝对年龄是来自覆盖在湖相硅藻岩上的玄武岩，范围从1.2 Ma到0.935 Ma。为了解决年龄问题，联合调查员在靠近Sisian镇的Vorotan河地区进行了详细的磁性地层试验性研究，迄今在该地区总共获得了250个定向钻芯。采样覆盖了5个地层厚度约70米的剖面。详细的古地磁分析表明，在一个以逆磁化为主的层序中存在一个正极性带。这些结果与估计的湖泊沉积速率相结合，被初步解释为反映了Matuyama计时器内的Olduvai正态亚时。如果这一解释被证明是可靠的，那么这项研究代表着在为该序列分配绝对年龄方面向前迈出了重要的一步。到目前为止，所研究的材料在磁性上的极高质量值得进一步取样，以增加样品密度。这将产生过去300万年的高分辨率磁性地层学，并为这些沉积物在区域和全球尺度上的对比做出重要贡献。此外，对正常到反向和反向到正常转变的详细研究将产生关于地球S磁场在磁场逆转之前不久、期间和之后不久的精细结构的宝贵信息。该项目计划的研究还将涉及相对古强度以及对过去三百万年气候条件的岩磁指标的分析。将古地磁、岩石磁学研究与古生物学、古植物学相结合，将有助于全面了解小高加索地区早期人类活动的环境条件，进而有助于对地球S磁场的认识。

The Pleistocene geology of Armenia is dominated by the widespread occurrence of lake sediments testifying repeated rapid and drastic changes of the environmental conditions during at least the last 2 million years. These sediments contain a huge variety of various fossil remains allowing the reconstruction of flora, fauna as well as the climatic conditions especially during dispersal of early man like homo georgicus (1.8 Ma) into Eurasia. Unfortunately, however, precise dating of these sequences is still a matter of debate and the only absolute ages available up to date have been derived from basalts overlaying the lacustrine diatomites and ranging from 1.2 to 0.935 Ma. Addressing the age debate, a detailed magnetostratigraphic pilot study has been carried out in the Vorotan river area near the town of Sisian, where a total number of 250 orientated drill cores has been obtained so far by the co- investigator. Sampling covered 5 sections with roughly 70 meters in stratigraphic thickness. Detailed palaeomagnetic analysis reveals the presence of a zone of normal polarity within a sequence which is dominated by inverse magnetizations. These results, in combination with estimated sedimentation rates for lake sediments, are tentatively interpreted to reflect the Olduvai normal subchron within the Matuyama chron of inverse polarity. If this interpretation proves to be robust, this study represents a major step forward in assigning absolute ages to the sequence. The extremely high quality of the material studied so far magnetically merits further sampling in order to increase the sample density. This will result in a high resolution magnetostratigraphy for the last 3 million years and provide important contributions for correlation of these sediments on regional and global scales. Furthermore, detailed studies of the Normal to Reverse and Reverse to Normal transitions will yield valuable information with regards to the fine structure of the Earth s magnetic filed shortly before, during and shortly after field reversals. The studies planned in this project will also address relative palaeointensities as well as analysis of rockmagnetic proxies for climate conditions during the last three million years. Combining palaeomagnetic and rockmagnetic studies with palaeontology and palaeobotany will result in a comprehensive picture of the environmental conditions during the occurrence of early man in the Lesser Caucasus and furthermore, significantly contribute to the understanding of the Earth s Magnetic Field.