Mid- to Late Holocene (5200–980 cal YR BP) paleoenvironmental dynamics in the Ilha Grande, Brazil, assessed by terrestrial and marine microfossils

Ilha Grande is a Brazilian island that has a high vegetal biodiversity with a well-documented prehistoric human occupation but has few paleoenvironmental studies developed in this area. In view of this, multiproxy analysis of lagoonal sediments including radiocarbon dating were carried out on a 139 cm-long continental sediment core. The aim of our study was to recognise and explain environmental dynamics in this region during the Holocene (∼5200 cal yr BP). The palynomorphs indicate the continuous presence of Atlantic Forest under humid conditions during the last Holocene sea-level highstand, after 5200 cal yr BP. A phase of low palynomorph concentrations was followed by a marked increase in palynomorph accumulation and diversity which may be linked to the subsequent drop of the sea-level. Dinoflagellate cysts showed a higher accumulation at the base of the sediment core. The high accumulation of charcoal particles identified between approximately 3700 and 3000 cal years BP might indicate human activity related to the long-lasting bonfires kept burning by the inhabitants of the archaeological site of Ilhote do Leste.

格兰德岛（Ilha Grande）是巴西的一座岛屿，其植物生物多样性极高，史前人类活动遗迹已有详实记录，但该区域开展的古环境研究相对匮乏。鉴于此，研究团队对一根长139厘米的大陆沉积岩芯开展了包含放射性碳定年（radiocarbon dating）在内的泻湖沉积物（lagoonal sediments）多代用指标分析（multiproxy analysis）。本研究旨在识别并阐释全新世（Holocene，约5200校正距今年（cal yr BP））以来该区域的环境动态变化。孢粉（palynomorphs）结果显示，在5200校正距今年之后的全新世海平面高位期，该区域始终处于湿润环境，大西洋森林持续存在。一段孢粉浓度较低的阶段之后，孢粉堆积量与多样性显著升高，这可能与随后的海平面下降有关。甲藻孢囊（dinoflagellate cysts）在沉积岩芯底部的堆积量更高。在约3700至3000校正距今年之间识别出的大量木炭颗粒，可能反映了与东小岛（Ilhote do Leste）考古遗址居民持续燃烧篝火相关的人类活动。