Sedimentation control on growth of stromatoporoid reefs in the Silurian of Gotland, Sweden
Sedimentation control on growth of stromatoporoid reefs in the Silurian of Gotland, Sweden
复制标题
瑞典哥特兰岛志留纪沉积物对层孔生物礁生长的控制
DOI：
10.1144/gsjgs.150.1.0197
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发表时间：
1993
影响因子：
2.7
通讯作者：
S. Kershaw
中科院分区：
文献类型：
--
作者：
S. Kershaw
瑞典哥特兰岛志留系以层孔虫为主的生物礁是碎屑供给减少时期形成的生物礁和生物层。在Wenlock Högklint组早期和Ludlow Hemse组中期均有出露。珊瑚礁的发育在浅水生物层中达到顶峰，在稳定的基底上横向扩展，并与频繁的侵蚀表面有关。Högklint珊瑚礁开始是生物礁，随着水变浅，被生物基质阶段所取代，具有垂直分区的群落。生物基质相被认为相当于Hemse群中单个的基质-多孔生物基质（不含生物热相）的整体，它们在稳定的基质上发育于浅层、低至中等能量的水中。与这些珊瑚礁相关的低碎屑供应不仅减少了粘土的输入，这在哥特兰岛的大多数非珊瑚礁环境中很常见，而且还被解释为降低了可用营养水平。现代珊瑚礁在低营养条件下发育最好，并且还显示(a)抑制生物侵蚀，(b)珊瑚和藻类之间的共生关系增加，从而保存了珊瑚礁生物群中的营养。Högklint珊瑚礁显示生物侵蚀减少，而Hemse珊瑚礁几乎完全没有生物侵蚀。叠层孔虫和珊瑚之间的共生，被解释为对营养保护需求的反应，发生在珊瑚礁中，但在Hemse珊瑚礁中更为常见。Högklint和Hemse珊瑚礁都被认为是在与现代珊瑚礁一致的营养缺乏条件下生长的，尽管对Hemse珊瑚礁的影响被认为更大，因为它们似乎是在广阔的大陆架上安静的条件下生长的，并且在整个勒德洛的退化制度下可能减少了对营养物质的获取。哥特兰礁石生长时碎屑供应减少可能是由于区域构造运动控制了当地海平面变化。然而，Högklint组和Hemse群的礁相与海平面上升下降的时间一致。因此，哥特兰岛上的珊瑚礁生长可能与俯冲相关的上升构造作用或板块弯曲过程或气候控制有关。志留纪的海洋学模型提出了干湿交替的时期，解释为二氧化碳驱动，可能控制了碎屑的输入，允许化石礁和碳酸盐台地的发展。这些解释为研究珊瑚礁生长提供了一个修订的框架。
Silurian stromatoporoid-dominated reefs of Gotland, Sweden, are bioherms and biostromes formed during phases of reduced clastic supply. Well-exposed examples are in the early Wenlock Högklint Formation and middle Ludlow Hemse Group. Reef development culminated in shallow water biostromes, laterally expanded over a stabilized substrate and associated with frequent erosion surfaces. Högklint reefs began as bioherms, to be replaced by biostromal phases as water shallowed, with vertically zoned communities. Biostromal phases are considered equivalent to the whole of individual stromato-poroid biostromes (without biohermal phases) of the Hemse Group, which developed in shallow, low to moderate energy water, on stabilized substrate. Low clastic supply associated with these reefs reduced not only the clay input, which is otherwise common in most non-reef environments on Gotland, but also is interpreted to have lowered available nutrient levels. Modern reefs develop best in conditions of low nutrients and also show (a) suppressed bioerosion, and (b) increased symbiosis between corals and algae which conserves nutrients in the reef biota. Högklint reefs show reduced bioerosion while Hemse reefs show almost complete lack of bioerosion. Symbiosis between stromatoporoids and corals, interpreted as a response to the need for nutrient conservation, occurs in the reefs, but is much more common in Hemse reefs. Both Högklint and Hemse reefs are regarded as having grown in nutrient-deficient conditions in line with modern reefs although the effect on Hemse reefs is believed to have been greater because they appear to have grown in quieter conditions on a broad shelf and may have had reduced access to nutrients in a regressive regime throughout the Ludlow. Reduced clastic supply while the Gotland reefs grew could have been due to regional tectonism controlling local sea-level change. However, the Högklint Formation and Hemse Group reef phases coincide with times of proposed eustatic sea-level falls. Reef growth on Gotland could therefore relate to eustatic tectonism by subduction-related or plate flexure processes, or climatic control. An oceanographic model for the Silurian proposed alternating wet and dry episodes, interpreted as CO2-driven, and could have controlled clastic input, permitting the development of fossiliferous reefs and the carbonate platforms on which they formed. These interpretations provide a revised framework for examining the reef growth.