Impact of long-term climate change and sea-level fluctuation on Mississippian to Permian mid-oceanic atoll sedimentation (Akiyoshi Limestone Group, Japan)
Impact of long-term climate change and sea-level fluctuation on Mississippian to Permian mid-oceanic atoll sedimentation (Akiyoshi Limestone Group, Japan)
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DOI：
10.1016/j.palaeo.2005.11.009
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发表时间：
2006-06
期刊：
影响因子：
--
通讯作者：
H. Sano
中科院分区：
文献类型：
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作者：
H. Sano
为了了解长期气候事件和海平面变化对大洋中环礁沉积的影响，回顾了秋吉石灰岩群(上文山至上首都)的岩相、生物相地层变化、淡水成岩蚀变和生物地层不连续的水平。这个群记录了大约7000万年来潘塔拉萨大洋中部海域的环礁沉积，它几乎与晚古生代冈瓦纳冰川同步发展。Akiyoshi灰岩群的整个层序可划分为四个相组合：骨架-蚝粒灰岩组合、泥质灰岩组合、泥灰岩-骨架灰岩组合和礁灰岩组合。上Viséan-Bashkirian发育丰富的橄榄砂砾屑岩和珊瑚礁灰岩组合，以温暖适应的后生动物造礁生物(珊瑚、毛虫和苔藓虫)为礁相。其特征表明它们是在海平面升高的温暖气候中沉积的。泥质石灰岩协会(莫斯科到卡西莫万)记录了适应温暖的后生动物生物礁建造者的消亡和频繁的堆积事件。许多地球化学数据支持莫斯科纪至卡西莫夫期气温的显著下降。这些泥质灰岩组合的沉积和生物事件表明，其沉积作用受气候凉爽和海平面普遍较低的强烈影响。泥质灰岩-骨灰岩组合的特征是钙质微生物、钙质藻类和钙质藻类的重要性向上递增。与泥质灰岩组合II相比，演替记录的浮现事件较少，这些特征反映了吉赫勒-首都时代气候变暖和海平面上升。Akiyoshi石灰岩群解释的气候幕和海平面变化一般对应于密西西比纪到二叠纪的全球气候变化趋势和与冈瓦那冰川重大冰川事件有关的海平面波动。明代造山带记录的晚Viséan至Bashkirian暖气候和海平面升高、莫斯科至Kasimovan降温和海平面下降、Gzhelian至Capitana变暖和海平面上升与全球气候模式和海平面波动相似，其中包含密西西比纪早至中冰期前温暖气候和高位、宾夕法尼亚中期至晚宾夕法尼亚降温和冈瓦纳冰盖退缩时相关的冰川-海平面波动，以及早至中二叠世全球变暖和海平面上升。明代环礁沉积对宾夕法尼亚的全球变冷和相关的海平面下降影响最大，但它们的影响是短暂的。Akiyoshi堆积物中的冷却和频繁的浮现事件发生的时间延迟，大约比盘根海陆架上的类似事件晚1000万年。Akiyoshi堆积物的冰后变暖比泛古大陆的陆表海至少早了数百万年。这种现象可能是由于Akiyoshi积聚在大洋中部的潘塔拉萨大洋的古位置造成的。
To understand the impacts of long-term climatic episodes and sea-level changes on mid-oceanic atoll sedimentation, the stratigraphic changes of litho- and bio-facies, and stratigraphic levels of freshwater diagenetic alteration and biostratigraphic discontinuity of the Akiyoshi Limestone Group (upper Viséan to upper Capitanian) were reviewed. This group records approximately 70 million years of atoll sedimentation in a mid-oceanic realm of the Panthalassa Ocean, which developed nearly synchronously with the Late Paleozoic Gondwana glaciation. The entire succession of the Akiyoshi Limestone Group was divided into four facies associations; skeletal-oolitic grainstone, muddy limestone, muddy limestone–skeletal grainstone, and reefal limestone associations. Skeletal-oolitic grainstone and reefal limestone associations (upper Viséan to Bashkirian) are characterized by an abundance of oolite and crinoidal grainstone, and reef facies of warm-adapted metazoan reef-builders (corals, Chaetetes, and bryozoans), respectively. Characteristics of skeletal-oolitic grainstone and reefal limestone associations indicate their deposition in a warm climate with elevated sea-level. Muddy limestone association (Moscovian to Kasimovian) records the demise of the warm-adapted metazoan reef builders and frequent emergence events of the buildup. Many geochemical data support the significant drop in temperature during Moscovian through Kasimovian time. These depositional and biotic events of muddy limestone association indicate that its sedimentation was strongly affected by cool climate and generally low sea-level. Muddy limestone–skeletal grainstone association is characterized by an upward-increasing significance of calcimicrobes, calcareous algae, and calcisponges. The succession records less frequent emergence events than that of muddy limestone association II. These characters reflect a warming climate and sea-level rise in Gzhelian to Capitanian time. The climate episodes and sea-level changes interpreted from the Akiyoshi Limestone Group generally correspond to the global trend of Mississippian to Permian long-term climatic change and sea-level fluctuation related to the major glacial events of Gondwana glaciation. The late Viséan to Bashkirian warm climate and elevated sea-levels, Moscovian to Kasimovian cooling and sea-level lowering, and Gzhelian to Capitanian warming and sea-level rise recorded in the Akiyoshi buildup are comparable to the global climate model and sea-level fluctuation, which contain Early to Middle Mississippian pre-glacial warm climate and highstands, Middle to Late Pennsylvanian cooling and related glacio-eustatic sea-level fluctuation at the culmination of Gondwana glaciation, and Early to Middle Permian global warming and sea-level rise due to the retreat of Gondwana ice sheets. Akiyoshi atoll sedimentation was most significantly affected Pennsylvanian global cooling and related sea-level lowering, but their impact was short-lived. The onset of the cooling and frequent emergence events in the Akiyoshi buildup occurred delayed, approximately 10 millions years later than that of comparable episodes on the Pangean shelves. The post-glacial warming in the Akiyoshi buildup started at least several millions of years earlier than in epicontinental seas of the Pangea. This phenomenon may be due to the palaeoposition of the Akiyoshi buildup in a mid-oceanic realm of the Panthalassa Ocean.