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迥异的解释：诸多学者认为海平面下降会促进沙丘形成，另有一派观点则提出，海平面上升或相对稳定的环境更有利于沙丘发育。针对巴西海岸沙丘场而言，第二种假说似乎更契合迄今已获取的光释光年代（luminescence ages）数据，但其中绝大多数测年结果均未采用SAR程序（SAR protocol）进行分析。此外，气候变化在风成系统（aeolian system）中的作用仍未得到清晰阐释，亦是学界关注的焦点之一。本研究旨在厘清上述两个核心问题。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。借助遥感（remote sensing）与测年分析结果，研究人员得以识别并圈定至少4期风成沉积期次。结合晚更新世（Late Pleistocene）全球相对海平面变化曲线，对这些风成沉积期次的年代分布进行分析后，我们提出：海岸环境下风成沙丘场的形成，以相对海平面稳定为支撑条件。但相对海平面并非决定海岸风成沙丘形成与保存的唯一因素。气候调控的相关证据表明，海岸沙丘场的起始发育更适宜在湿度较低的时段发生，而其稳定阶段则多出现于与季风活动相关的降雨增强时期。