Abstract Samples from 12 drillhole-cores from the Urals-Emba region to the north-east of the Caspian Sea were analysed for pollen and spores. The records reveal vegetation and climate changes for the late Pliocene to early Pleistocene within the time interval from ca. 3.6 to ca. 1.65 Ma. According to the results of the pollen analysis, at the beginning of the Akchagylian stage (3.6–3.4 Ma) there was a cooling and change in structure of the dendroflora, and steppe-dominated landscapes were present. At the end of the early Akchagylian, and continuing into the middle Akchagylian, a maximum variety of pollen from tree species occurred. The presence of mesophilic and thermophilic elements signifies a moderately warm and humid climate occurred at around 3.2 Ma, probably related to the ‘Mid-Pliocene Warm Period’. A second major cooling occurred at around 2.5 Ma coinciding with the onset of northern hemisphere glaciations. During this time, coniferous forests dominated by Picea, Pinus and Abies with lesser numbers of broad-leaved trees were established. At the end of the Akchagylian, at around 1.8 Ma, the climate became more arid and steppe landscapes were re-established. During the Akchagylian, alternations between forest- and steppe-dominated landscapes occurred at least three times in the Urals-Emba region. Results are compared with pollen spectra in surface samples, and with ostracods and foraminiferal assemblages in cores from the study region.

中文翻译：

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北里海地区的 Akchagylian 阶段（上新世晚期-更新世早期）：乌拉尔-恩巴地区植被和气候变化的花粉证据

摘要 对来自乌拉尔-恩巴地区到里海东北部的 12 个钻孔岩心样品进行了花粉和孢子分析。记录揭示了上新世晚期到更新世早期的植被和气候变化，从大约 20 年开始。3.6 到大约 1.65 马。根据花粉分析结果，在阿克恰吉阶初期（3.6~3.4 Ma），林木植物群出现降温和结构变化，呈现以草原为主的景观。在早期 Akchagylian 末期，并继续到中期 Akchagylian，来自树种的花粉种类最多。中温和高温元素的存在意味着在 3.2 Ma 左右发生的温和温暖和潮湿的气候，可能与“中上新世暖期”有关。第二次大冷却发生在 2.5 Ma 左右，与北半球冰川作用的开始一致。在此期间，建立了以云杉、松树和冷杉为主，阔叶树数量较少的针叶林。在 Akchagylian 末期，大约 1.8 Ma，气候变得更加干旱，草原景观重新建立。在 Akchagylian 期间，以森林和草原为主的景观在乌拉尔-恩巴地区至少发生了 3 次交替。结果与表面样品中的花粉光谱以及研究区域核心中的介形虫和有孔虫组合进行了比较。在 Akchagylian 末期，大约 1.8 Ma，气候变得更加干旱，草原景观重新建立。在 Akchagylian 期间，以森林和草原为主的景观在乌拉尔-恩巴地区至少发生了 3 次交替。结果与表面样品中的花粉光谱以及研究区域核心中的介形虫和有孔虫组合进行了比较。在 Akchagylian 末期，大约 1.8 Ma，气候变得更加干旱，草原景观重新建立。在 Akchagylian 期间，以森林和草原为主的景观在乌拉尔-恩巴地区至少发生了 3 次交替。结果与表面样品中的花粉光谱以及研究区域核心中的介形虫和有孔虫组合进行了比较。