ABSTRACT While spatial facies patterns can be observed in modern systems, only vertical facies successions can usually be examined in ancient deposits. Lateral facies relationships (depositional models) and relative sea-level changes throughout time are traditionally deduced from correlation of vertical facies successions along transects perpendicular to inferred paleo-shorelines. Establishing vertical facies successions and their corresponding time-equivalent proximal to distal facies patterns are, therefore, paramount in reconstructing ancient carbonate depositional systems and their response to sea-level change. In the present study of well-exposed panoramics of late Tortonian (8.1 Ma) mixed heterozoan carbonate and terrigenous deposits in La Chanata area in Sierra de Gádor, Almería, SE Spain, we show that frequent changes in facies width make it difficult to predict how variation in sea level impacts the facies distribution. The following facies are recognized: shoreline conglomerates directly overlie an erosion surface on the basement; terrigenous coralline-algal packstones extend basinwards from the conglomerates and are interpreted as shallow-water deposits stabilized by seagrass. There exist three types of facies consisting of relatively well-preserved, parautochthonous bioclasts, which occur generally seawards of the packstones: a) branching-coralline rudstones that formed from rhodolith (maërl) beds, both shorewards and basinwards from seagrass meadows where b) foliose-coralline rudstones to floatstones accumulated, and c) lenses of Heterostegina rudstones to floatstones changing laterally to any of the coralline algal facies. The factory facies of a–c show a patchy distribution with no definite arrangement in shoreline-parallel belts. The evolution of the depositional system is as follows: after filling paleovalleys in the erosion surface, deposition took place on a homoclinal ramp. The hybrid heterozoan carbonate–terrigenous deposits show a general retrogradation altered by one episode of proximal facies progradation. The width of facies across the ramp changes markedly in different episodes of relative sea-level rise: in several episodes of transgression, terrigenous coralline-algal packstones spread across the ramp locally overlying more distal facies, such as branching-coralline rudstones, thus generating regressive vertical patterns during relative sea-level rise. In other transgressive episodes packstones disappear, and the a–b factory facies pass laterally into conglomerate. The stratigraphic changes in facies width might be due to changes in general energy caused by climate variations or, alternatively, to the amount of relative sea-level rise. Large sea-level rise would result in relatively deep and calm conditions, thus favoring little fragmentation of large bioclasts during accumulation of the factory facies. Conversely, little change in accommodation would have resulted in higher-energy environments with concomitant increased physical erosion of the coralline-algae factories, thus resulting in mostly sand-size bioclasts in the packstones. In this environmental context, vertical change from distal to proximal facies can result from relative sea-level rise with increased mobilization and lateral expansion of proximal facies across the ramp. This outcome challenges the adequacy of using vertical lithofacies successions to reconstruct relative sea-level change in carbonate depositional systems.

中文翻译：

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上中新世异生动物碳酸盐陆源沉积物（Sierra de Gádor, Almería, SE Spain）的矛盾同代垂直相变化

摘要 虽然在现代系统中可以观察到空间相模式，但在古代沉积物中通常只能检查垂直相序列。横向相关系（沉积模型）和随时间的相对海平面变化传统上是从沿垂直于推断的古海岸线的横断面的垂直相序列的相关性推导出来的。因此，建立垂直相序及其对应的近端到远端相模式的时间当量对于重建古代碳酸盐沉积系统及其对海平面变化的响应至关重要。在目前对西班牙东南部阿尔梅里亚的塞拉德加多尔的拉查纳塔地区晚托尔托世 (8.1 Ma) 混合异生碳酸盐和陆源沉积物的曝光良好的全景研究中，我们表明，相宽度的频繁变化使得很难预测海平面的变化如何影响相分布。识别出以下相： 海岸线砾岩直接覆盖在基底上的侵蚀表面上；陆源珊瑚藻包岩从砾岩向盆地延伸，被解释为由海草稳定的浅水沉积物。存在三种类型的相，由保存相对完好的副陆生生物碎屑组成，它们通常发生在堆积岩的向海方向：a）由红石（maërl）床形成的分枝珊瑚状地壳岩，从海草草甸向海岸和盆地延伸，其中 b）叶状- 累积的珊瑚陆基岩到浮石，以及 c) 异体陆基岩到浮石的透镜体横向变化到任何珊瑚藻相。a—c厂相呈片状分布，在平行岸线带中没有明确的排列。沉积体系的演变过程如下：在侵蚀面填满古河谷后，沉积发生在同斜斜坡上。杂虫碳酸盐-陆源沉积物显示出由近端相进积改变的一般回积。在相对海平面上升的不同阶段，斜坡上的相宽度显着变化：在几次海侵事件中，陆源珊瑚藻包岩在斜坡上散布，局部覆盖更远的相，如分支珊瑚礁岩，从而产生海退相对海平面上升期间的垂直模式。在其他违规情节中，包装石消失了，a-b 工厂相横向进入砾岩。相宽度的地层变化可能是由于气候变化引起的一般能量变化，或者是相对海平面上升的量。海平面大幅上升将导致相对较深和平静的条件，因此在工厂相的积累过程中有利于大型生物碎屑的碎裂。相反，住宿条件的微小变化会导致更高能量的环境，伴随着对珊瑚藻工厂的物理侵蚀增加，从而导致石块中大部分是沙子大小的生物碎屑。在这种环境背景下，从远端到近端相的垂直变化可能是由于相对海平面上升，随着近端相在斜坡上的流动性增加和横向扩展。