Facies architecture, palaeoecology and biotic spatial self-organization of a Devonian, sediment-impacted carpet reef

中、晚泥盆世可能是古生代最大的陆表台地碳酸盐岩扩张时期。在这里，我们展示了德国西部Klutert洞穴中异常暴露的泥盆纪珊瑚礁生物层。我们认为，该洞穴代表了一个令人信服的测试案例，可以研究Givetian （387-382 Ma）沉积影响的珊瑚礁的相结构、古生态和生物空间自组织。Klutert洞穴之所以吸引人，有几个原因：(1)礁体在地层上很薄（<12.3米），符合“地毯礁”的标准，与许多全新世的礁没有什么不同。岩礁嵌在碎屑单元和岩心之间，侧翼在洞穴内横向暴露约450 x 200米。岩礁侧翼的末端在洞穴附近的道路切割处掐出。（ii）礁体在横向和地层上都极为暴露。最近清理的岩壁提供了26000平方米的连续岩石表面，以精美的细节暴露了礁体的底部、核心、侧翼和顶部。（iii）寄主基质沉积物表明，在相对较短的礁生长期间，大量碎屑（浊度）进入陆架。根据岩壁的详细相图，我们打算对这些露头进行数值测试，以确定消费者（这里是叠层孔虫、表状珊瑚和波纹珊瑚）与其资源（营养物质、照明、空间等）之间相互作用所产生的内在生物自组织的特征。这是特别有趣的，因为随着海平面变化，沉积物流入的上升水平可以放在生物自组织模式的背景下，在珊瑚礁形成，顶峰和消亡期间。我们将进一步测试自组织过程的工作假设，该假设允许比较泥盆纪和全新世生物基质演替，这些生物基质演替来自边缘地区，如波斯/阿拉伯湾，那里的珊瑚礁系统以相对较低的动物多样性发展。对基质中细粒碎屑物质的粘土矿物谱和物源的分析将有助于揭示沉积物的流入。该项目的一个重要组成部分是珊瑚礁生物群的详细分类框架，为沉积物胁迫环境下的生物多样性提供证据。我们将比较和对比生物（方解石）档案（珊瑚，层孔类，腕足类）的超微结构和地球化学性质对成岩蚀变的响应。以此为泥盆纪古环境研究的代用数据提供基准。我们特意选择专注于一个研究区域，并将在很大的空间分辨率下工作。目前还不清楚这个毯状礁在多大程度上是例外的，或者，作为一个基准，其他同时期（通常是沉积物影响的毯状礁）的珊瑚礁可以进行比较。本文提出的研究旨在回答这些问题。

The Middle and Late Devonian time interval witnessed the perhaps largest Palaeozoic expansion of epeiric platform carbonates. Here, we present an exceptionally exposed Devonian reefal biostrome in the Klutert Cave, Western Germany. We argue that this cave represents a compelling test case to investigate the facies architecture, palaeoecology and biotic spatial self-organization of a Givetian (387-382 Ma) sediment-impacted reef. The Klutert Cave is intriguing for several reasons: (i) the reefal body is stratigraphically thin (<12.3 metres) and qualifies as a ‘carpet-reef’, not unlike many Holocene reefs. The reef is intercalated between clastic units and its core and flanks are exposed laterally for about 450 x 200 m within the cave. The extremities of the reef flanks pinch out in road cuts in the vicinity of the cave. (ii) The reef is extremely well-exposed both laterally as well as stratigraphically. The recently-cleaned cave walls provide access to 26,000 m2 of continuous rock surfaces exposing the base, core, flanks and top of the reefal body in exquisite detail. (iii) The host matrix sediment indicates significant clastic input (turbidity) onto the shelf during the comparably short interval of reef growth. Based on detailed facies maps of cave walls, we intend to numerically test these outcrops for the hallmarks of intrinsic biotic self-organization arising out of the interaction between consumers (here stromatoporoids, tabulate and rugose corals) and their resources (nutrients, illumination, space etc.). This is particularly interesting, as upsection increasing levels of sediment influx along with sea-level change can be placed within the context of patterns in biotic self-organization during reef initiation, acme and demise. We will further test the work hypothesis that self-organization processes allow for a comparison between Devonian and Holocene biostromal successions from marginal locations, such as the Persian/Arabian Gulf, where reef systems develop with a relatively low faunal diversity. The analysis of the clay mineral spectrum and provenance of fine-grained clastic material in the matrix will shed light on sediment influx. An important component of this project is a detailed taxonomic framework of reefal biota, providing evidence on biotic diversity in a sediment-stressed environment. We will compare and contrast biotic (calcite) archives (corals, stromatoporoids, brachiopods) for the response of their ultrastructure and geochemical properties exposed to diagenetic alteration. By this we intend to provide benchmarks for proxy data in Devonian palaeoenvironmental research. We have deliberately chosen to focus on one study area and will work in great spatial resolution. It is, at present, unclear to what degree this carpet reef is exceptional or, alternatively, serves as a benchmark against which other coeval (generally, sediment-impacted carpet-reefs) reefs can be compared. Research presented here aims to answer these questions.