Central Santa Catarina coastal dunefields chronology and their relation to relative sea level and climatic changes

ABSTRACTDuring the past decades, there have been contrarian explanations for the formation and stabilization of coastal dunefields: while many authors believe the dunes formation would be enhanced by falling sea level, others argue that a rising or stable sea level context would be favorable. For Brazilian coastal dunefields, the second hypothesis seems to be more consistent with the luminescence ages found so far; however, most of these data were obtained without using the SAR protocol. Another point of concern is the role of climate change in the aeolian system, which is still not very clear. The aim of this paper is to try to clarify these two questions. To this end, five coastal dunefields were selected in central Santa Catarina coast. The remote sensing and dating results allowed the discrimination and mapping of at least four aeolian generations. Their age distribution in relation to the global curve of relative sea level variation during the Late Pleistocene allows us to suggest that the formation of Aeolian dunefields in the coastal context is supported by stable relative sea level. However, relative sea level is not the only determinant for the formation and preservation of the aeolian coastal dunes. Evidences of climatic control indicate that the initiation of dunefields would be favored by periods of less humidity while their stabilization would occur preferably during the periods of rain intensification, connected to monsoon activity.摘要：近数十年来，学界对海岸沙丘场（coastal dunefields）的形成与稳定机制存在相悖的学术解释：诸多学者认为海平面下降会促进沙丘发育，而另有观点则提出，海平面上升或稳定的环境背景更有利于沙丘形成。针对巴西海岸沙丘场，后一种假说似乎更契合迄今已获取的光释光年代（luminescence ages）数据，但其中绝大多数年代结果均未采用单片再生剂量法（SAR protocol）进行测试。此外，气候变化在风成系统中的作用仍不甚明晰。本研究旨在厘清上述两个科学问题。为此，研究团队在圣卡塔琳娜州中部海岸选取了5处海岸沙丘场。通过遥感分析与年代学测试，研究人员得以识别并绘制至少4期风成沉积序列。结合晚更新世全球相对海平面变化曲线的年代分布特征，本研究提出：海岸环境下风成沙丘场的形成受相对海平面稳定的条件支撑，但海平面并非控制海岸风成沙丘形成与保存的唯一因素。气候调控的证据表明，沙丘场的发育更易在湿度较低的时期启动，而其稳定过程则多发生在与季风活动相关的降雨增强时段。