Vegetation response to early Pleistocene climatic cycles in the Lamone valley (Northern Apennines, Italy)

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• 作者：Fabio Fusco
• 关键词：pollen ; vegetation cycles ; climate ; Lamone ; Pleistocene ; Italy
• 刊名：Review of Palaeobotany and Palynology
• 出版年：2007
• 出版时间：June 2007
• 年：2007
• 卷：145
• 期：1-2
• 页码：1-23
• 全文大小：731 K

文摘

The vegetation response to cyclic climatic changes has been investigated by means of pollen analysis carried out on marine deposits outcropping in the Lamone valley (Northern Italy). The deposits consist of grey–blue silty–clays of the “Argille Azzurre” Formation. Three sedimentary successions, which form the Lamone section, have been analysed. These successions, according to previous studies, have been referred to the first two substages of the lower Pleistocene, the Santernian and the Emilian.

Pollen data from sixty-nine samples document vegetation dynamics consisting of a temporal spread of three distinct forest formations: mixed-deciduous forest (with Quercus dominating), Juglandaceae forest (with Carya dominating) and mountain coniferous forest (with Picea dominating). Each forest formation formed a vegetation belt, characterized by distinct temperature and precipitation conditions. The spread of the mixed deciduous forest indicates that the temperature increases whereas the humidity is low. The transition to a Juglandaceae forest indicates the increase of humidity; this phase is characterized by “optimum” of temperature and precipitations. The spread of mountain coniferous forest points out temperature drop and humidity still high. When forest dynamics is interrupted by the spread of open vegetation, indicating decrease of humidity, a complete vegetation cycle occurs. Such cycle suggests that temperature and humidity independently vary, with minimum and maximum of temperature generally preceding humidity extremes. Each vegetation cycle, therefore, reveals the response of vegetation to cyclic climatic changes occurring during the early Pleistocene (glacial/interglacial cycles).

Comparison with coeval pollen series from other Italian sites shows wider spread of Picea and minor expansion of open vegetation in Northern Italy with respect to Central and Southern Italy, suggesting the hypothesis of more humid conditions at the North (as also documented by previous works). Taxodium pollen-type is continuously represented in the Lamone pollen record, exhibiting values of 7 % on average excluding Pinus ( 4 % including pine). Sciadopitys shows a discontinuous presence and very low percentages. Local and peculiar climate conditions may have favoured the long survival of these taxa into the Pleistocene.

On the basis of a comparison between the profile of Picea + Tsuga pollen curve (recorded at Lamone) and the δ¹⁸O signal established at Site 607 (North Atlantic), the vegetation cycles documented in the Lamone valley have been tentatively correlated to oxygen isotope stages from 64 to 46. Stages 59 and 51 seem to be partially recorded, whereas, stages 58, 57, 50 and 49 are not recorded.