Abstract The lack of modern analogues for the thick primary selenite gypsum deposits formed in the Mediterranean area limits the understanding of the Messinian (Miocene) evaporitic systems and particularly of their lateral relationships, their evolution through time and their related ecosystems. Some complex stratigraphic relationships of these extreme environments are revealed in the Messinian Canos Formation along the northern flank of the Sierra Alhamilla at the southern boundary of the Sorbas Basin (southern Spain). Here, the bottom-grown selenite gypsum beds pinch-out against graded clastic carbonate beds (ooid grainstones, rudstones and mudstones) emplaced by gravity flows. We infer that these tabular bodies formed along a low gradient ramp, derived from the periodic erosion of coeval shallow-water to coastal carbonate factories located on top of the Sierra Alhamilla ridge. The carbonate deposits bear many similarities with the Terminal Carbonate Complex described in the northern, steeper margin of the basin; both deposits show a cyclical pattern given by the repetition of couplets consisting of coarser- and finer-grained deposits. This rhythmic facies organization recalls the precessional-controlled cyclic pattern of the gypsum unit. Clastic carbonates and gypsum were deposited during the same precessional hemicycle but appear to be mutually exclusive. In fact, the clastic carbonates represent the lateral equivalent of the gypsum beds, or are occasionally found at their base or at both their base and top, but never interstratified with them. Such an arrangement suggests that during the peak of the evaporitic phases a strong pycnocline acted as the top boundary for gypsum and the lower boundary for carbonate-bearing gravity flows, with the exception of debrites, high-density gravity flows and slumps. These facies architectures appear to be mainly controlled by the interplay between the variable depth of the pycnocline and the density of the brine within the evaporitic cycle.

中文翻译：

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浅水碳酸盐岩和原生石膏之间的地层关系：对 Sorbas 盆地（Betic Cordillera，西班牙南部）Messinian 演替的见解

摘要 地中海地区形成的厚的原生亚硒酸盐石膏矿床缺乏现代类似物，这限制了对墨西拿（中新世）蒸发系统的理解，特别是对它们的横向关系、它们随时间的演变及其相关生态系统的理解。这些极端环境的一些复杂地层关系在 Sorbas 盆地（西班牙南部）南部边界沿 Sierra Alhamilla 北侧的 Messinian Canos 组中得到揭示。在这里，底部生长的亚硒酸盐石膏层在重力流包围的分级碎屑碳酸盐岩层（鲕粒岩、砂岩和泥岩）上尖尖向外。我们推断这些板状体沿着低梯度斜坡形成，源于同时期浅水对位于 Sierra Alhamilla 山脊顶部的沿海碳酸盐工厂的周期性侵蚀。碳酸盐矿床与盆地北部较陡峭边缘的终端碳酸盐岩复合体有许多相似之处；两种矿床都显示出周期性模式，由粗粒度和细粒度矿床组成的对联重复出现。这种有节奏的相组织让人想起石膏单元的岁差控制循环模式。碎屑碳酸盐和石膏沉积在同一个岁差半周期中，但似乎是相互排斥的。事实上，碎屑碳酸盐代表了石膏床的横向等效物，或者偶尔在它们的底部或它们的底部和顶部发现，但从未与它们分层。这样的排列表明，在蒸发相的高峰期，强烈的pycnocline 作为石膏的顶部边界和含碳酸盐重力流的下边界，但碎屑、高密度重力流和坍塌除外。这些相结构似乎主要受蒸发循环中不同的密斜层深度和卤水密度之间的相互作用控制。