Middle Miocene oceanographic event in the eastern Gulf of Mexico: Implications for seismic stratigraphic succession and Loop Current/Gulf Stream circulation
Middle Miocene oceanographic event in the eastern Gulf of Mexico: Implications for seismic stratigraphic succession and Loop Current/Gulf Stream circulation
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DOI：
10.1130/0016-7606(1987)98
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发表时间：
1987-06
影响因子：
4.9
通讯作者：
H. T. Mullins;A. Gardulski;S. Wise;J. Applegate
中科院分区：
文献类型：
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作者：
H. T. Mullins;A. Gardulski;S. Wise;J. Applegate
通过对与两个岩芯相关的101 500公里高分辨率单道气枪地震反射剖面的分析，表明佛罗里达中西部碳酸盐斜坡在中新世中期经历了一次海洋事件，导致了一次主要的地层断裂或沉积序列的连续。在中新世早期至中期的长期海平面上升过程中，碳酸盐陆棚边缘沉积的特征是向海延伸，横向和纵向上都建立了S形斜坡。陆架边缘沉积物粒度较细，富含白云石、总有机物和粘土矿物。约12-15百万年在1990年代以前，构造控制的巴拿马地峡的海洋学封闭和/或气候梯度的增加导致了海洋环流的加强。增加流速的环路电流截断先行斜坡沿着中新世中期的陆架边缘的环路电流，第一次，成为一个动态的海洋学障碍，陆架沉积物运输。碳酸盐沉积沿着西佛罗里达斜坡发生了巨大的变化，从一系列覆盖的斜坡到一个远洋斜坡-前缘-充填系统，其向陆边缘由一个封闭的环流的等深流限定。陆棚边缘沉积物，目前代表为一个凝聚的序列，变得更加丰富的碳酸盐，粗粒，有机含量较低，并在白云岩亏损。我们的研究结果表明，海洋事件可以产生主要的地震地层中断，导致沉积序列和系统的继承沿着大陆边缘，他们可能是一样重要的海平面振荡。我们的数据还表明，“现代”环流/墨西哥湾流环流开始于中新世中期，由构造海洋学和/或气候过程控制。现在的挑战是识别岩石记录中的地震地层尺度海洋事件，将其与海平面变化响应区分开来，并评估其古环境意义。
Analysis of ∼1,500 km of high-resolution, single-channel air-gun seismic-reflection profiles, correlated with two drill cores, demonstrates that the central west Florida carbonate-ramp slope experienced an oceanographic event in the middle Miocene that resulted in a major stratigraphic break or succession of depositional sequences. During the long-term eustatic sea-level rise in the early to middle Miocene, carbonate shelf-margin deposition was characterized by seaward-prograding, sigmoidal clinoforms that built both laterally and vertically. Shelf-margin sediments were relatively fine grained and rich in dolomite, total organics, and clay minerals. Approximately 12–15 m.y. ago, tectonically controlled oceanographic closure of the Isthmus of Panama, and/or increased climatic gradients, resulted in an intensification of oceanic circulation. Increased flow velocity of the Loop Current truncated antecedant clinoforms along the mid-Miocene shelf margin as the Loop Current, for the first time, became a dynamic oceanographic barrier to off-shelf sediment transport. Carbonate deposition along the west Florida slope changed dramatically from a series of prograding clinoforms to a pelagic slope-front-fill system bounded on its landward margin by contour-current flow of an invigorated Loop Current. Shelf-margin sediments, presently represented as a condensed sequence, became more carbonate rich, coarser grained, lower in organic content, and depleted in dolomite. Our results suggest that oceanographic events can generate major seismic stratigraphic breaks that result in the succession of depositional sequences and systems along continental margins and that they may be as important as eustatic oscillations. Our data also suggest that “modern” Loop Current/Gulf Stream circulation was initiated in the middle Miocene, controlled by tectono-oceanographic and/or climatic processes. The challenge now is to identify seismic stratigraphic-scale oceanographic events in the rock record, differentiate them from eustatic responses, and evaluate their paleoenvironmental significance.