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首页> 外文期刊>Facies >Contrasts between wave- and tide-dominated oolitic systems: Holocene of Crooked–Acklins Platform, southern Bahamas
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Contrasts between wave- and tide-dominated oolitic systems: Holocene of Crooked–Acklins Platform, southern Bahamas

机译：波浪和潮汐主导的橄榄岩系统之间的对比：巴哈马南部的弯曲–阿克林斯平台全新世

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摘要

As the stratigraphic record is neither homogenous nor isotropic, a fundamental challenge in sedimentary geology is characterizing and predicting the nature of variability. Although many nearshore to shallow-marine siliciclastic depositional systems have been grouped into wave-dominated and tide-dominated classes, many facies models of carbonate systems have not recognized or applied this distinction. To fill this gap, the purpose of this study is to compare and contrast the hydrodynamic processes, sedimentology, geomorphology, and stratigraphy of an oolitic tide-dominated shoal complex and an oolitic wave-dominated shoreline system from the same area (Crooked–Acklins Platform, southern Bahamas). Field, petrographic, granulometric, remote-sensing, and hydrodynamic data illustrate marked contrasts between the two end members. The wave-dominated shoreface system near French Wells on the leeward margin is influenced by small (H_s<30 cm) waves and only weak, wave-driven currents (<15 cm/s, net southward flow); the passage of Hurricane Irene (in 2011) had only a local impact on the shoreface. The low-energy setting favors generation and alongshore transport of ooids and peloids of fine- to medium-sized sand, and has facilitated nearly 1 km of shoreface progradation, forming geomorphic bodies with margin-parallel geometry. The stratigraphic record of the area includes a coarsening- and shoaling-upward succession. In contrast, the ~7-km-wide, tide-dominated shoal on the southwestern margin is dominated by vigorous tidal currents (in excess of 50 cm/s, and reversing twice daily). These currents generate margin-normal bars and channels consisting of oolitically coated grains of medium to coarse sand size. Stratigraphically, above a basal clast-rich deposit, sediment size and sorting vary across the shoal. The open-ocean and the platformward flanks of the shoal, most impacted by tide and wave energy, include the cleanest oolitic sand, with fines accumulating in the stabilized shoal interior. Overall, the oolitic shoal aggraded and expanded platformward over bioturbated peloid–ooid sand. These results reveal how sediment, geomorphology, and stratigraphy differ between tide- and wave-dominated end members, patterns broadly analogous to several ancient examples. These data collectively illustrate the processes that create multi-scale linkages among stratigraphic patterns, geological facies bodies, and granulometry (e.g., depositional porosity and permeability). These linkages provide information that could be used to predict sedimentological and geomorphical trends in ancient analogues.
机译：由于地层记录既不是均质的也不是各向同性的，因此沉积地质学的根本挑战是表征和预测变化性。尽管许多近岸到浅海的硅质碎屑沉积系统已被划分为以波浪为主和以潮汐为主的类别，但是许多碳酸盐岩相的相模型并没有认识或应用这种区别。为了填补这一空白，本研究的目的是比较和对比同一地区的一个以潮汐为主的浅滩复合体和以波浪为主的海岸线系统的水动力过程，沉积学，地貌学和地层学（Crooked-Acklins平台，巴哈马南部）。现场，岩相，粒度，遥感和水动力数据说明了两个端部构件之间的明显对比。在背风边缘的法国维尔斯附近，波浪主导的岸面系统受小（H_s <30 cm）的波浪影响，并且仅受波浪驱动的弱流（<15 cm / s，净南流）影响;艾琳飓风（2011年）的通过仅对海岸面产生了局部影响。低能环境有利于中小型砂土的卵石和类胶体的生成和沿岸运输，并促进了近1 km的海面扩展，形成了边缘平行几何形状的地貌体。该地区的地层记录包括粗化和浅滩向上演替。相比之下，西南边缘约7公里宽的以潮汐为主的浅滩被强劲的潮流（超过50厘米/秒，每天反转两次）所控制。这些电流会生成由中等至粗砂尺寸的经过油膜涂覆的晶粒组成的正常边界条和通道。地层学上，在基层丰富的沉积物之上，浅滩的沉积物大小和分类是不同的。受到潮汐和波浪能影响最大的浅海和浅滩侧腹包括最干净的橄榄石砂，细粉会积聚在稳定的浅滩内部。总体而言，在生物扰动的类胶体-类卵石砂上，鲕粒浅滩向平台上方扩展和扩展。这些结果揭示了在以潮汐为主和以波浪为主的端段之间的沉积物，地貌和地层是如何不同的，其模式大体上类似于几个古代实例。这些数据共同说明了在地层模式，地质相体和粒度（例如沉积孔隙度和渗透率）之间建立多尺度联系的过程。这些联系提供了可用于预测古代类似物中的沉积学和地貌趋势的信息。

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