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首页> 外文期刊>Facies >Slope breccias colonized by bivalves and serpulids during the Middle Jurassic (Subbetic, SE Spain)
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Slope breccias colonized by bivalves and serpulids during the Middle Jurassic (Subbetic, SE Spain)

机译：侏罗纪中期（西班牙东南部，贝贝特），双壳类和蛇形类菌落形成的坡角砾岩。

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The Middle Jurassic of the Intermediate Domain, in the northern Subbetic (External zones of the Betic Cordillera, SE, Spain), reveals the transition from hemipelagic limestones (Banos Formation) to overlying shallow-water oolitic limestones (Jabalcuz Formation). Near La Guardia (Jaen), the basal part of the succession that records this transition comprises clast-supported calcareous breccias 24 m thick. Transverse sections reveal a fan shape close to a normal fault. The upper parts of some breccia beds were colonized by bivalve patches that locally evolve to bivalve-serpulid bioherms. The bioherms are massive, with low relief and a metre-scale lenticular shape. Two main parts have been differentiated: a bivalve bioherm and a serpulid bioherm. The bivalve bioherm consists of densely packed mytiloids in life position with secondary serpulids, where the matrix is a grainstone of bioclasts, peloids, and ooids. Laterally, there are accumulations of reworked bivalves. The serpulid bioherm is made up of serpulid aggregates in a bioclast wackestone. On an unstable slope with abundant breccias, bioherm development took place in favourable periods of low sedimentation rate. The pioneer colonisers of the sea-bottom were mytiloid bivalves in relatively high-energy waters. Shell comissures were aligned parallel to the dip of the slope as an adaptation to feeding from the plankton and seston inputs associated with palaeocurrents. The intercalation of reworked bivalve beds likely indicates brief periods of higher-energy storm events. The serpulid bloom in the upper part of the buildups was probably related to a stage of low-energy conditions (as evidenced by the delicacy of these structures), which is congruent with the wackestone texture. The relief provided by the bivalves favoured the development of the serpulid bioherm phase in an elevated and advantageous position for suspension-feeding. The dense packing in these bioherms offered clear advantages in this unstable palaeoenvironment: (1) dense populations are less susceptible than isolated individuals to overgrowth by other sessile organisms or predator attacks; and (2) the interconnection among individuals enhances stability and resistance against high-energy events, and increases the growth potential of future generations. The interruption of bioherm growth was probably related to the deposition of new breccia beds and reworked oolitic limestones.
机译：中亚侏罗纪的中亚侏罗纪，在北亚贝贝特（西班牙东南部的比蒂科迪勒拉的外部带）中，揭示了从半海生石灰岩（班诺斯组）到上覆浅水橄榄岩石灰石（贾巴尔库兹组）的过渡。在拉瓜迪亚（哈恩）附近，记录了这一过渡的演替的基部包括碎裂支撑的24 m厚的钙质角砾岩。横向截面显示风扇形状接近正常故障。一些角砾岩床的上部被双壳类斑块定殖，该双壳类斑块局部进化成双壳类-Serpulid生物体。生物herms巨大，浮雕低且具有米尺度的凸状形状。区分了两个主要部分：双壳生物hermlid和塞尔皮利德bioherm。双壳类生物herm由生活中密集堆积的类髓生物和次生serpulids组成，其中基质是破骨细胞，类胶体和卵石的结石。在侧面，有重做的双壳类动物的堆积。 Serpulid生物herm由在bioclast wackestone中的serpulid聚集体组成。在角砾岩丰富的不稳定斜坡上，生物沉积发育发生在低沉积速率的有利时期。海底的先驱定居者是能量相对较高的水域中的髓类双壳类。壳壳平行于坡度的倾斜方向排列，以适应与古洋流相关的浮游生物和塞斯顿输入的进食。返工的双壳层床的插入可能表明短暂的高能风暴事件。堆积物上部的蛇绿石水华可能与低能状态有关（如这些结构的美味所证明），这与毛泥岩的质地是一致的。双壳类动物提供的缓解作用有利于在悬浮饲料的高位有利位置开发蛇皮草生物hermherm相。这些生物群落中的密集堆积在这种不稳定的古环境中提供了明显的优势：（1）密集种群比其他个体更不容易受到其他无性生物或捕食者攻击的过度生长; （2）人与人之间的相互联系增强了对高能事件的稳定性和抵抗力，并增加了后代的增长潜力。生物礁生长的中断可能与新角砾岩床和重做的橄榄岩灰岩的沉积有关。

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