Rhodoliths and coralliths of Muri Lagoon, Rarotonga, Cook Islands
Rhodoliths and coralliths of Muri Lagoon, Rarotonga, Cook Islands
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库克群岛拉罗汤加穆里泻湖的红石和珊瑚
DOI：
10.1007/bf00300865
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发表时间：
1985
期刊：
影响因子：
3.5
通讯作者：
C. Woodroffe
中科院分区：
文献类型：
--
作者：
T. Scoffin;D. Stoddart;A. Tudhope;C. Woodroffe
在拉罗汤加岛礁坪上的浅穆里泻湖海床上，大量生长着大量自由生长的块状和分枝状球状石灰质红藻（红柱石）和珊瑚（珊瑚石）（直径约5厘米）。红柱石由一种或多种Neogoniolithon、Lithophyllum、Tenarea和Porolithon组成;珊瑚石是Pavona varians（Verrill）和Porites lutea（Milne-Edwards和Haime）。穆里泻湖是拉罗汤加岛上唯一一个被珊瑚礁岛挡住海浪的地区。潮流，这主要是单向的穆里泻湖，集中的珊瑚礁岛屿进入渠道，通过砂和砾石沉积物定期运输。然而，这些主要的电流通常不会滚动的rhodoliths和珊瑚石。对各种类型的球状结构的拾取速度进行实地实验的结果，结合对大块珊瑚石生长历史的观察，如骨骼密度带的非同心性质所揭示的，表明红柱石和珊瑚石可能会在长达几个月的时间内保持静止，但仍保持完整的活组织包膜。这种向下的生存可能取决于强大的电流。水不仅冲刷过沉积物基底的上部毫米左右，而且还能够移动侧向支撑红柱石和珊瑚石的砂和砾石颗粒，因此球状结构的任何一点都不会与基底直接接触致命的时间长度。块状的红柱石作为离散的球状结构具有很高的保存潜力;相反，分支的红柱石和珊瑚石容易破碎，块状的珊瑚石会长成稳定的微环礁。我们的结论是，一个类似的组合中的红柱石，珊瑚石和微环礁的化石记录可能表明前存在的当代礁坪岛屿。
Free-living massive and branching spheroidal growths (about 5 cm diameter) of calcareous red algae (rhodoliths) and corals (coralliths) occur in abundance on the sea bed of shallow Muri Lagoon on Rarotonga's reef flat. The rhodoliths are composed of one or more species ofNeogoniolithon, Lithophyllum, Tenarea, andPorolithon; the coralliths arePavona varians(Verrill) andPorites lutea(Milne-Edwards and Haime). Muri Lagoon is the only area on Rarotonga's reef flat that is sheltered by reef islands from ocean waves. The tidal currents, which are predominantly unidirectional in Muri Lagoon, are concentrated by the reef islands into channels through which sand and gravel sediment is regularly transported. However, these prevailing currents do not normally roll the rhodoliths and coralliths. The results of field experiments on the pick-up velocity of the various types of spheroidal structure, combined with observations on growth histories of massive coralliths as revealed by the non-concentric nature of skeletal density banding, indicate that the rhodoliths and coralliths may remain static for periods up to several months yet maintain a complete envelope of living tissue. This downward survival may depend on the strong currents. Not only is the water flushing through the upper millimetre or so of the sediment substrate, but it is also capable of moving the sand and gravel grains which laterally support the rhodoliths and coralliths so that no one point of a spheroidal structure is in direct contact with the substrate for a fatal length of time. Massive rhodoliths have a high preservation potential as discrete spheroidal structures; in contrast, branching rhodoliths and coralliths are prone to fragmentation, and massive coralliths grow into stable microatolls. We conclude that a similar assemblage of rhodoliths, coralliths and microatolls in the fossil record may be indicative of the former existence of contemporary reef flat islands.