Anatomy of a late Quaternary carbonate island: Constraints on timing and magnitude of sea-level fluctuations, West Caicos, Turks and Caicos Islands, BWI
Anatomy of a late Quaternary carbonate island: Constraints on timing and magnitude of sea-level fluctuations, West Caicos, Turks and Caicos Islands, BWI
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晚第四纪碳酸盐岛的解剖：对海平面波动时间和幅度的限制，西凯科斯群岛、特克斯和凯科斯群岛、BWI
DOI：
10.1016/j.quascirev.2018.12.010
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发表时间：
2019
影响因子：
4
通讯作者：
Cheng, Hai
中科院分区：
文献类型：
--
作者：
Kerans, Charles;Zahm, Chris;Bachtel, Steven L.;Hearty, Paul;Cheng, Hai
西凯科斯岛的数据集包括高分辨率激光雷达和数字图像、辐射测量数据、氨基酸外消旋化（AAR） D/L值，以及岛上沉积和生物构造沉积物的非凡保存。西凯科斯数据集与邻近巴哈马岛链的成熟区域地层框架和详细的野外测绘相结合，为我们进一步了解碳酸盐地层与海平面、沉积物供应、构造和气候等控制参数之间的联系提供了机会。西凯科斯岛保存异常完好的中晚更新世地层记录可以识别海洋同位素阶段（MIS） 9/11、5e和全新世。该岛西海岸提供了连续8.4 km的MIS 5e记录暴露，增强了我们对该地区MIS 5e内部两部分演替的理解，并支持了末次间冰期（LIG）期间发生的海平面下降。西凯科斯群岛形成了一系列风成相、前滨-滨面相、堡礁相和边缘礁相。除MIS 7和MIS 5a/c矿床外，其他所有矿床的海岸线位置现在都在亚米级大地测量质量的地形深潜激光雷达测量中获得。MIS 9/11时代的星城单元形成了岛的南缘和中央岩溶变质脊，铀钍（使用单键th）珊瑚年龄在36.8至36.5万年前（ka）之间，D/L Glu平均值为bb0.60。早期MIS 5e地层包括位于岛屿中心的Railroad Ridge单元，该单元先前被确定为较老的单元之一。铁路山脊单元是一个南北线状沙丘山脊，其D/L Glu平均值为0.52，表明泥沙来源来自东部，与被淹没的凯科斯台地中部有关。早期MIS 5e South Reef单元（+ 3.75-4 m海平面高度）在西凯科斯群岛西海岸几乎同步成核，与更新世中期Star Town单元相连。南礁珊瑚的平均单键年龄为126.5 ka，骨骼基质的平均D/L Glu为0.46。这个过渡性屏障/边缘礁不整合地被MIS 5e船湾单元覆盖。在这个上层5e船湾单元的基底海侵阶段，珊瑚平均产生120.6的单键th和平均D/L Glu为0.45。MIS 5e晚期的浅海相、前滨相和风成相位于一个波浪切割阶地上，该阶地将MIS 5e早期的南礁单元切割了3米，降低到比目前海平面高0.5米。上层的MIS 5e船湾单元显示，从前海岸的中间测量，最大海拔高于现在的海平面+4.5米。这一估计可能是一个最小值，因为西海岸的暴露是强迫退前海岸序列的一部分。MIS 5e上部沉积的最后阶段出现在一系列退退的沙丘-海滩脊沉积中，被称为东北脊单元，海平面位置从西凯科斯群岛中部早期的+4.5米到东北海岸的+0.5米，最终下降到今天的海平面以下。这一海平面历史与巴哈马和全球之前记录的记录非常吻合，广泛的侵蚀支持了短暂的（在126至120 ka之间）mis 5e内的相对海平面下降。西凯科斯群岛的全新世沉积仅限于岛屿的北部和东部边缘，是滩平原和沙丘脊混合的骨架-鲕粒单元的组合。利用高分辨率数字高程模型（DEM）和链接…
The data set of the island of West Caicos consists of a combination of high-resolution lidar and digital imagery, radiometric data, and amino acid racemization (AAR) D/L values as well as extraordinary preservation of sedimentary and bio-constructed deposits on the island. Together with a well-established regional stratigraphic framework from the neighboring Bahamian island chain and detailed field mapping, the West Caicos data set provides an opportunity to advance our understanding of the link between carbonate stratigraphy and the controlling parameters of sea level, sediment supply, tectonics, and climate. The exceptionally well-preserved stratigraphic record of the mid–late Pleistocene from West Caicos allows recognition of marine isotope stages (MIS) 9/11, 5e, and Holocene. The west coast of the island provides a continuous 8.4 km exposure of the MIS 5e record that enhances our understanding of the intra-MIS 5e bipartite succession in this region and supports a sea-level lowering that occurred during the last interglacial (LIG).West Caicos accreted as a series of eolian, foreshore–shoreface, barrier-reef, and fringing-reef facies. Shoreline positions for all but the MIS 7 and MIS 5a/c deposits are now captured in the sub-meter geodetic-quality topobathy lidar survey. The Star Town unit of MIS 9/11 age forms the southern margin of the island as well as the central karst-modified spine, with uranium–thorium (Usingle bondTh) coral ages of between 368 and 365 thousand years ago (ka) and a D/L Glu average of >0.60. Early MIS 5e strata include the Railroad Ridge unit in the center of the island, which was previously identified as one of the older units. The Railroad Ridge unit is a north–south linear dune ridge that has a D/L Glu average of 0.52 and indicates the onset of sediment sources from the east associated with a flooded central Caicos Platform. Approximately synchronously, the early MIS 5e South Reef unit (+3.75–4 m sea-level elevation) nucleated on the western coast of West Caicos, attached to the middle Pleistocene Star Town unit. The South Reef corals yield an average coral Usingle bondTh age of126.5 ka, with an average D/L Glu from skeletal matrix of 0.46. This transitional barrier/fringing reef is unconformably overlain by the late MIS 5e Boat Cove unit. Corals in the basal transgressive phase of thisupperMIS 5e Boat Cove unit yield an average120.6 kaUsingle bondTh and average D/L Glu of 0.45. Shallow-marine, foreshore, and eolian facies of the late MIS 5e rest on a wave-cut terrace that cuts the early MIS 5e South Reef unit by as much as 3 m down to a +0.5 m above present sea-level elevation. The upper MIS 5e Boat Cove unit displays a maximum of +4.5 m elevation above present-day sea level, measured from the middle of the foreshore. This estimate may be a minimum value as the exposures on the west coast are part of a forced regressive foreshore sequence. Last stages of the upper MIS 5e deposition are seen in a series of regressive dune-beach ridge deposits referred to as the Northeast Ridges unit, with sea-level positions ranging from +4.5 m early in the central part of West Caicos, to +0.5 m on the far northeast coast, eventually building down below present-day sea level. This sea-level history fits well with previously documented records in the Bahamas and globally, and the extensive erosion supports a short-lived (between 126 and 120 ka) intra-MIS 5e relative-sea-level fall. Holocene deposition on West Caicos is restricted to northern and eastern margins of the island as a combination of strandplain and dune ridge mixed skeletal–oolitic units.Using the high-resolution digital elevation model (DEM) and linked …
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