Transgressive oolites onlapping a Silurian rocky shoreline unconformity, Gotland, Sweden
Transgressive oolites onlapping a Silurian rocky shoreline unconformity, Gotland, Sweden
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瑞典哥特兰岛志留纪岩石海岸线不整合面上的海侵鲕粒岩
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发表时间：
1999
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影响因子：
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通讯作者：
Ewa Säll
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作者：
M. Calner;Ewa Säll
地层关系、岩相和岩石学证据确定了哥特兰岛温洛克晚期的岩石海岸线。形成岩石海岸线的主要相元素是：1）几个在地表下暴露的礁，它们在基准面下降期间受到侵蚀，并形成地形; 2）在基准面随后上升期间沉积的鲕粒岩的上超。这里详细讨论了沿着岩石海岸线的五个地点，即，Svalings 1（不整合边界可进入）和Bara 1-4（上覆鲕粒岩岩相学已研究）。在最新的Cyrtograptus lundarii生物带的结束时的回归导致了哥特兰碳酸盐台地的部分露出。最低水位（C. lundeli生物带）造成了这条岩石海岸线的地形，并导致了暴露的珊瑚礁中的截断、腐蚀和渗流淤泥。下面的小纳萨生物带开始于海侵的巴拉鲕粒岩段（最低的Halla组），它覆盖着Slite群最年轻的礁代的南翼。岩石海岸线可以追溯到11公里，走向西南-东北。计算得出的侵蚀基准面位于一个Slite珊瑚礁最高保存部分顶部以下16米以上，表明海平面下降的可能最小幅度。详细的岩相学工作上重叠的鲕粒是一致的解释，它是在海岸接壤的古海岸的潮汐带形成的。Slite Rocky Shoreline不整合面（SRSU）在此被视为相当于分隔西哥特兰岛Klintehamn地区海退Frojel组和海侵Bara Oolite段（最低Halla组）的层序边界的近台地。岩石海岸线的发展被认为是最可靠的证据，一个快速的海退-海侵循环在中荷马的哥特兰。（减）
Stratigraphical relationships, facies and petrographical evidences define a rocky shoreline in the Late Wenlock of Gotland. The major facies-elements forming the rocky shoreline are 1) several subaerially exposed reefs, which were eroded during falling base-level and which form the topography, and 2), onlap of oolite grainstones which were deposited during the subsequent rise of the base-level. Five localities along the rocky shoreline are discussed in detail here, viz., Svalings 1 where the unconformable boundary is accessible, and Bara 1-4 where the petrography of the onlapping oolite has been studied. A regression at the end of the latest Cyrtograptus lundgreni Biozone resulted in emersion of parts of the Gotland carbonate platform. Erosion during the short time interval of maximum lowstand (top C. lundgreni Biozone) caused the topography of this rocky shoreline and resulted in truncations, corrosion and vadose silt in the exposed reefs. The following parvus-nassa Biozone starts with the transgressive Bara Oolite Member (lowermost Halla Formation) which onlaps the southern flanks of the youngest reef generation of the Slite Group. The rocky shoreline can be traced for 11 km striking SW-NE. Calculated base-level for the erosion is situated more than 16 metres below the top of the highest preserved part of one Slite reef, indicating the probable minimum magnitude of the sea-level drop. Detailed petrographic work on the onlapping oolite is consistent with the interpretation that it was formed in the tidal zone of the shores bordering the palaeocoast. The Slite Rocky Shoreline Unconformity (SRSU) is herein considered as the platform-proximal equivalent to the sequence boundary separating the regressive Frojel Formation and the transgressive Bara Oolite Member (lowermost Halla Formation) in the Klintehamn area on western Gotland. The rocky shoreline development is taken as the most reliable evidence of a rapid regressive-transgressive cycle in the mid-Homerian of Gotland. (Less)