Evolution of the barrier islands of southern Long Island, New York
Evolution of the barrier islands of southern Long Island, New York
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纽约长岛南部堰洲岛的演变
DOI：
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发表时间：
1981
期刊：
影响因子：
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通讯作者：
J. E. Sanders
中科院分区：
文献类型：
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作者：
M. Rampino;J. E. Sanders
根据400多个钻孔和可控震芯的数据，利用三条证据重建了纽约长岛南部全新世海侵期间堰塞岛的演化：(1)现今屏障背后的全新世海侵地层序列；(2)内陆架的地层模式；(3)现已埋藏的晚更新世海岸地物的形态。
长岛南部内陆架上广泛保存的屏障后沉积物的放射性碳年代为7000至8000年，这表明屏障不仅通过持续的岸面侵蚀而后退，而且还通过就地‘淹没’屏障和海浪带的逐步后退而经历了不连续的后退。冲浪带的这种逐级后退阻止了后屏障沉积物的重新加工。
根据地震记录中潜堤砂体的存在，推测9000年前，当海平面低于现今海平面约24m时，在距今屏障约7公里处的现今陆架上发育了一系列屏障。随着海平面的持续上升，-24米的屏障向上修建，直到海平面达到-15米，恰好在公元7000年前。然后，这些屏障被迅速上升的海平面淹没，冲浪区迅速向陆地移动到距离目前海岸线约2公里的位置。冲浪区越过了老泻湖向陆地的边缘，它已经固定在威斯康星州中部陡峭的海面上(？)或者桑加米亚海岸屏障。在过去的五六千年间，海岸面连续后退了约2公里。
来自长岛南部和沿海潜水地区其他地区的证据表明，海平面快速上升和沙粒供应不足似乎有利于障碍物的逐步撤退，而较慢的潜水速度和更多的沙子供应通常有利于持续的海面撤退。当沙的供应量很大，和/或淹没速度减缓或逆转时，可能会发生静止的堆积，或屏障向海推进。无论是连续撤退，还是逐步撤退，海侵前表面(如老障壁海脊)上的地貌高位往往会固定迁移障碍物的岸线。
Three lines of evidence based on data from more than 400 boreholes and vibrocores have been used to reconstruct the evolution of the barrier islands during the Holocene transgression in southern Long Island, New York: (1) the Holocene transgressive stratigraphic sequence behind the present barriers, (2) the stratigraphic patterns of the inner shelf, and (3) the morphology of the now-buried late Pleistocene coastal features.
The extensive preservation of backbarrier sediments, radiocarbon dated between 7000 and 8000 yr BP, on the inner shelf of southern Long Island suggests that the barriers have not retreated by continuous shoreface erosion alone, but have also undergone discontinuous retreat by in-place ‘drowning’ of barriers and stepwise retreat of the surf zone. Such stepwise retreat of the surf zone has prevented the backbarrier sediments from being reworked.
Based on the presence of submerged barrier sand bodies in seismic records, it is inferred that about 9000 years ago, when the sea stood about 24 m below the present sea level, a chain of barriers developed on the present shelf about 7 km offshore of the present barriers. With continued sea-level rise, the – 24 m barrier built upward until the sea reached about – 15 m MSL, just prior to 7000 yr BP. The barriers were then submerged by the rapidly rising sea, and the surf zone shifted rapidly landward to a position about 2 km from the present shoreline. The surf zone overstepped to the landward margin of the old lagoon, which had become fixed at the steep seaward face of mid-Wisconsinan (?) or Sangamonian coastal barriers. During the past 5000 or 6000 years, the shoreface has retreated continuously by about 2 km.
Evidence from southern Long Island and elsewhere in regions of coastal submergence indicates that rapid sea-level rise and low sand supply seem to favour the stepwise retreat of barriers, whereas slow rates of submergence and a greater supply of sand generally favour continuous shoreface retreat. Stationary upbuilding, or seaward progradation of barriers may occur when supply of sand is great, and/or submergence is slowed or reversed. Morphologic highs on the pretransgression surface (such as old barrier ridges) tend to fix the migrating barrier shoreline during either continuous retreat, or stepwise retreat of barriers.