Bryozoan-rich stromatolites (bryostromatolites) from the Silurian of Gotland and their relation to climate-related perturbations of the global carbon cycle
Bryozoan-rich stromatolites (bryostromatolites) from the Silurian of Gotland and their relation to climate-related perturbations of the global carbon cycle
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DOI：
10.1111/sed.12863
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发表时间：
2021-05-12
期刊：
影响因子：
3.5
通讯作者：
Ernst, Andrej
中科院分区：
文献类型：
--
作者：
Claussen, Anna Lene;Munnecke, Axel;Ernst, Andrej
苔藓虫-叠层石组合（bryostromatite）在哥特兰岛的Sheinwoodian（Wenlock）至Ludfordian（卢德洛）地层中形成了明显的礁结构，但迄今为止尚未被描述。它们主要由结壳苔藓虫组成，与孔层和海绵层微生物形成复杂的共生体，与丰富的层孔珊瑚藻礁的组成不同。在苔藓叠层石中可以识别出不同的生长阶段。这种演替过程可以作为生物礁形成过程中环境变化的证据。棘皮动物、海绵动物、珊瑚和三叶虫等狭盐性珊瑚礁生物显示出完全的海洋盐度。发现了10个暴露苔藓层菌病的地方。个别的苔藓虫体积很小，只有几分米，最大可达一米，只出现在浅海地区。哥特兰岛上这些珊瑚礁的共同特征是菜花状生长，苔藓虫多样性高，磷质化石和组分丰富，如苔藓虫珍珠和无节磷质腕足动物，生物侵蚀增强，Palaeomicrocodium结壳，渗流粉砂和石膏假形。Palaeomicrocodium的高丰度以及与其他地壳形成贡献者的交替表明，它可能直接在古海面形成，可能是在海平面波动较小但频率较高的时期。在礁腔中石膏之后的渗流粉砂和假晶表明在礁生长后不久陆上暴露。大量的磷酸盐成分表明高营养输入，可能是灰尘。所有的苔藓层瘤都是在δ C-13值强烈升高的时候形成的。沉积学和古生态学特征的不寻常的组合，以及它们的发生只在强阳性三角洲C-13游览，是证据表明，苔藓层岩的发展响应气候/海洋学的变化，这可能发挥了重要作用，在珊瑚礁控制。
Bryozoan-stromatolite associations (bryostromatolites) formed conspicuous reef structures throughout the Sheinwoodian (Wenlock) to Ludfordian (Ludlow) stratigraphy on Gotland but have not been described so far. They are mainly composed of encrusting bryozoans forming a complex intergrowth with porostromate and spongiostromate microbes and are different from the abundant stromatoporoid-coral-algal reefs with respect to their composition. In the bryostromatolite different growth stages can be identified. The observed succession can be taken as evidence for cyclic environmental changes during reef formation. Stenohaline reef-dwelling organisms, such as echinoderms, sponges, corals and trilobites, indicate fully marine salinities. Ten localities exposing bryostromatolites were discovered. Individual bryostromatolites are small with few decimetres up to one metre in size, and occur solely in shallow marine areas. Common features of these reefs on Gotland are cauliflower-like growth, a high bryozoan diversity, a high abundance of phosphatic fossils and components such as bryozoan pearls and inarticulate phosphatic brachiopods, enhanced bioerosion, Palaeomicrocodium crusts, vadose silt and gypsum pseudomorphs. The high abundance of Palaeomicrocodium, as well as the alternation with other crust-forming contributors, suggest that it could have been formed directly at the palaeo-sea surface, probably in times of minor but high-frequency sea-level fluctuations. Vadose silt and pseudomorphs after gypsum in reef cavities indicate subaerial exposure shortly after reef growth. The high amount of phosphatic components indicates a high nutrient input, probably by dust. All bryostromatolites were formed in times of strongly elevated delta C-13 values. The unusual combination of sedimentological and palaeoecological features, as well as their occurrence exclusively during strong positive delta C-13 excursions, are evidence that the bryostromatolite development responded to climatic/oceanographic changes, which may have played an important role in reef control.