首页> 外文期刊>Journal of paleolimnology >Early Holocene brackish closed basin conditions in Georgian Bay, Ontario, Canada: Microfossil (thecamoebian and pollen) evidence
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Early Holocene brackish closed basin conditions in Georgian Bay, Ontario, Canada: Microfossil (thecamoebian and pollen) evidence

机译:加拿大安大略省佐治亚湾的全新世微咸封闭盆地条件:微化石(花胶和花粉)证据

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Microfossils have been critical in unravelling the complex postglacial history of Georgian Bay. Thecamoebians (testate amoebae/rhizopods) record paleolimnological conditions, and pollen stratigraphy allows correlation across the basin, where sedimentation has been spatially and temporally discontinuous. Because parts of Georgian Bay have been non-depositional or erosional since the end of the Nipissing transgression (~5,000 (5,800 cal) BP), early Holocene features are exposed on the lakebed. Among these are shoreline features, such as submerged beaches and relict channels, associated with low-level Lake Hough that was driven far below the level of basin overflow. Cores taken throughout Georgian Bay record the existence of closed basin conditions that persisted several centuries around 7,500 (8,300 cal) BP, corresponding to the late Lake Hough lowstand. Evidence for hydrologic closure includes a low-diversity centropyxid-dominated thecamoebian fauna around the boundary between pollen subzones 2a and 2b in the Flowerpot Beach core, Flowerpot and Killarney basins, and in Severn Sound. This low-diversity centropyxid-dominated fauna is interpreted as recording the development of slightly brackish conditions as a result of a hydrologic deficit associated with relatively arid conditions in the Great Lakes basin during the early Holocene pine zone (~8,800-7,200 (9,900-8,050 cal) BP). The rest of the Holocene record in Georgian Bay (where it is preserved) is more diverse and dominated by difflugiid thecamoebians: predominantly Difflugia oblonga prior to human settlement, and Cucurbitella tricuspis since high-density human occupation and agriculture (and resulting eutrophication) began with the Wendat First Nations people around Severn Sound about 750 years ago. The implication that water budget fluctuations leading to discernible variations in lake level and water chemistry occurred in the relatively recent geologic past is significant to studies of global climate change and resource management in the Great Lakes, one of the world's largest freshwater resources.
机译:微化石对于揭示乔治亚湾复杂的冰川后历史至关重要。附生动物(有遗迹的变形虫/根瘤菌)记录了古湖泊学条件,花粉地层学使得整个盆地都具有相关性,而沉积在空间和时间上都是不连续的。由于自从Nipissing海侵(〜5,000(5,800 cal)BP)结束以来,乔治亚湾的部分地区一直没有沉积或侵蚀,所以全新世的早期特征暴露在湖床上。其中包括海岸线特征,例如淹没的海滩和遗物通道,与低层的霍夫湖有关,而后者被远远低于盆地溢流的水平。整个乔治亚湾的岩心记录了闭合盆地条件的存在,该条件一直存在约7500(8300 cal)个BP,持续了几个世纪,相当于晚期的霍夫湖低水位。水文关闭的证据包括在花盆海滩核心,花盆和基拉尼盆地以及塞文海峡中,在花粉分区2a和2b之间的边界附近,存在着一个以低多样性为中心的,以虫草为主导的camoebian动物群。这种低多样性以人种为主导的动物系被解释为记录了全新世早期松树带早期大湖流域与干旱条件相关的水文赤字导致的微咸状态的发展(〜8,800-7,200(9,900-8,050 cal)BP)。格鲁吉亚湾(保存有该地区)的全新世记录的其余部分更加多样化,并以散漫的camoebians为主:主要是人类定居之前的长满通水,以及自高密度人类占领和农业(及由此产生的富营养化)开始的Tricurapis tricuspis。大约在750年前,塞文峡湾附近的温达特第一民族人民。在相对较近的地质历史中发生的水预算波动导致湖泊水位和水化学发生明显变化,这对于研究全球最大的淡水资源之一的大湖地区的全球气候变化和资源管理具有重要意义。

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