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首页> 外文期刊>Paleoceanography >A 26 million year gap in the central Arctic record at the greenhouse-icehouse transition: Looking for clues
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A 26 million year gap in the central Arctic record at the greenhouse-icehouse transition: Looking for clues

机译：从温室到冰屋的过渡，北极中央记录的差距为2600万年：寻找线索

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摘要

The Cenozoic record of the Lomonosov Ridge (central Arctic Ocean) recovered during Integrated Ocean Drilling Program (IODP) Expedition 302 revealed an unexpected 26 Ma hiatus, separating middle Eocene (similar to 44.4 Ma) from lower Miocene sediments (similar to 18.2 Ma). To elucidate the nature of this unconformity, we performed a multiproxy palynological (dinoflagellate cysts, pollen, and spores), micropaleontological (siliceous microfossils), inorganic, and organic (Tetra Ether Index of lipids with 86 carbon atoms (TEX86) and Branched and Isoprenoid Tetraether (BIT)) geochemical analysis of the sediments from similar to 5 m below to similar to 7 m above the hiatus. Four main paleoenvironmental phases (A-D) are recognized in the sediments encompassing the unconformity, two below (A-B) and two above (C-D): (A) Below the hiatus, proxies show relatively warm temperatures, with Sea Surface Temperatures (TEX86-derived SSTs) of about 8 degrees C and high fresh to brackish water influence. (B) Approaching the hiatus, proxies indicate a cooling trend (TEX86-derived SSTs of similar to 5 degrees C), increased freshwater influence, and progressive shoaling of the Lomonosov Ridge drilling site, located close to or at sea level. (C) The interval directly above the unconformity contains sparse reworked Cretaceous to Oligocene dinoflagellate cysts. Sediments were deposited in a relatively shallow, restricted marine environment. Proxies show the simultaneous influence of both fresh and marine waters, with alternating oxic and anoxic conditions. Pollen indicates a relatively cold climate. Intriguingly, TEX86-derived SSTs are unexpectedly high, similar to 15-19 degrees C. Such warm surface waters may be partially explained by the ingression of warmer North Atlantic waters after the opening of the Fram Strait during the early Miocene. (D) Sediments of the uppermost interval indicate a phase of extreme oxic conditions, and a well-ventilated environment, which occurred after the complete opening of the Fram Strait. Importantly, and in contrast with classical postrifting thermal subsidence models for passive margins, our data suggest that sediment erosion and/or nondeposition that generated the hiatus was likely due to a progressive shoaling of the Lomonosov Ridge. A shallow water setting both before and after the hiatus suggests that the Lomonosov Ridge remained at or near sea level for the duration of the gap in the sedimentary record. Interacting sea level changes and/or tectonic activity (possibly uplift) must be invoked as possible causes for such a long hiatus.
机译：在综合海洋钻探计划（IODP）远征302期间恢复的罗蒙诺索夫海岭（北冰洋中部）的新生代记录显示，出乎意料的26 Ma裂隙，使中始新世（约44.4 Ma）与中新世下部沉积物（约18.2 Ma）分开。为了阐明这种不整合的性质，我们进行了多代理孢粉虫学（恐龙鞭毛囊肿，花粉和孢子），微古生物学（硅质微化石），无机和有机（脂醚具有86个碳原子的四醚指数（TEX86）以及支链和类异戊二烯）沉积物的四醚（BIT）地球化学分析，其范围从低于裂隙以下5 m到高于裂隙以上7 m。在沉积物中发现了四个主要的古环境相（AD），包括不整合面，下面两个（AB）和上面两个（CD）：（A）在裂隙下方，代理显示相对温暖的温度，海面温度（TEX86衍生出的SST） ）约8摄氏度，对淡咸水的影响较高。 （B）接近裂隙时，代理表明冷却趋势（TEX86衍生的SST接近5摄氏度），淡水影响增加以及Lomonosov Ridge钻探地点（靠近海平面或在海平面上）的浅滩。 （C）不整合面正上方的间隔包含稀疏的返修白垩纪至渐新世的二鞭毛囊肿。沉积物沉积在相对较浅，受限制的海洋环境中。代理显示出淡水和海水的同时影响，以及有氧和无氧条件的交替。花粉表明气候相对寒冷。有趣的是，源自TEX86的SST异常高，接近15-19摄氏度。这种中部温暖的地表水可能部分由中新世初期Fram海峡开放后北大西洋中较温暖的水侵入所引起。 （D）最上层间隔的沉积物表示极端的有氧条件和通风良好的环境，这是在弗拉姆海峡完全开放之后发生的。重要的是，与经典的裂隙后被动沉降的热沉降模型相比，我们的数据表明，造成裂孔的沉积物侵蚀和/或非沉积可能是由于罗蒙诺索夫海岭的逐渐浅滩。裂隙前后的浅水环境表明，罗蒙诺索夫海岭在沉积记录的间隙期间一直保持在海平面或附近。相互作用的海平面变化和/或构造活动（可能是隆升）必须作为造成如此长裂隙的可能原因。

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