Neoarchean deep marine paleotemperature: Evidence from turbidite successions
Neoarchean deep marine paleotemperature: Evidence from turbidite successions
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DOI：
10.1016/j.precamres.2011.09.004
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发表时间：
2011-11-01
影响因子：
3.8
通讯作者：
Carter, James E.
中科院分区：
文献类型：
--
作者：
Fralick, Philip;Carter, James E.
为了确定太古宙海洋的温度，已经进行了许多使用各种替代物的研究。如果正如其中一些研究表明的那样，太古宙海洋相对较热，随着时间的推移，显生界有冷却的趋势，这将对沉积物的侵蚀、运输和沉积产生影响。更高的表面温度将导致水的粘度降低，这是定义流动流体动力学的一个重要变量。特别是，粘度较低的水会影响洋流涟漪的发展。这些取决于层流亚层的存在，因为撞击这一层的湍流涡流的扫掠形成了小土丘，然后演变成涟漪。层流亚层在较高的温度下变薄，允许较小尺寸的沙粒破坏它。在现代地表温度下，海流波纹不能在粗粒砂岩中形成，如果太古宙存在更热的海洋，它就会阻止中粒砂岩甚至细粒砂岩中海流波纹的形成。对西部苏必利尔省的许多新太古代、深水、浊积层序的研究表明，波纹交错层理在所有这些单元中都是罕见的。由于海流波纹的形成取决于以下几个方面：沉积合适粒度的沉积物的水流，合适范围内的流速，以及粘性底层的存在，而前两个前提条件在这些减速浑浊洋流的沉积过程中都得到了满足，因此在大多数水流中是否存在粘性亚层是值得怀疑的。对新太古代麦凯拉港组暴露良好的浊积岩中的海流波纹交错层理的出现进行了量化，发现波纹交错层理的丰度大大低于显生界浊积岩中的波纹交错层理的丰度，表明新太古代深海可能比今天的深海温暖得多。(C)2011爱思唯尔B.V.保留所有权利。
Numerous studies using various proxies have been conducted to ascertain the temperature of the Archean ocean. If, as some of these investigations indicate, the Archean ocean was relatively hot, with a cooling trend through time to the Phanerozoic, this would have had consequences for sediment erosion, transport and deposition. Substantially higher surface temperatures would cause the viscosity of water, an important variable in defining flow hydrodynamics, to be lowered. In particular, less viscous water would have affected the development of current ripples. These are dependent on the existence of the laminar sublayer, as the sweeps of turbulent eddies impinging on this layer build small mounds that evolve into ripples. The laminar sublayer thins at higher temperatures allowing sand grains of smaller sizes to destroy it. At modern surface temperatures current ripples cannot form in coarse-grained sands, and if a hotter ocean existed in the Archean it would have inhibited current ripple formation in medium-grained sands, and possibly even fine-grained sands.Examination of numerous Neoarchean, deep-water, turbiditic successions in western Superior Province led to the realization that ripple cross-lamination is rare in all these units. As the formation of current ripples is dependent on: the flow depositing sediment of the proper grainsize, velocities in the appropriate range, and existence of a viscous sublayer, and the first two prerequisites were met during deposition from these decelerating turbidity currents, the existence of the viscous sublayer during the majority of flows must be questioned. The occurrence of current ripple cross-lamination in well exposed turbidites of the Neoarchean, McKellar Harbour Formation was quantified and found to be substantially less than the abundance of ripple cross-lamination present in Phanerozoic turbidites, indicating that the Neoarchean deep ocean may have been considerably warmer than the deep ocean of today. (C) 2011 Elsevier B.V. All rights reserved.