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首页> 外文期刊>Facies >Discontinuity surfaces recorded in shallow-marine platform carbonates: An example from the Early Jurassic of the Velebit Mt. (Croatia)
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Discontinuity surfaces recorded in shallow-marine platform carbonates: An example from the Early Jurassic of the Velebit Mt. (Croatia)

机译：浅海平台碳酸盐岩中记录的间断面：Velebit山早期侏罗纪的一个例子。 （克罗地亚）

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Discontinuity surfaces of different types and scales are common in successions of shallow-marine carbonate platforms because sediments there are deposited close to the sea level and therefore are sensitive to any significant physico-chemical changes of environmental factors. Discontinuity surfaces indicate breaks in sedimentation under subaqueous or subaerial conditions. Most discontinuities in shallow-marine carbonate successions are on a bed-scale, and can be determined only by analysis of sedimentologic, diagenetic, taphonomic, and ichnologic features of the rock. The study of small-scale discontinuities has been carried out on two Lower Jurassic successions of the Velebit Mt. Depending upon their common features and environment of formation, three groups of discontinuities are distinguished on simple bedding planes: subaerial exposure surfaces, erosion surfaces, and omission surfaces. The distribution of discontinuity types in both successions is evaluated. Exposure surfaces prevail in both sections, and four units (relatively thin intervals of the sedimentary record) with abundant subaerial exposures are recognized. Dated by biostratigraphy, these units are of earliest Sinemurian, middle Early Sinemurian, earliest Pliensbachian, and late Early Pliensbachian age. Omission surfaces are the least common type of discontinuity. Thickness variations of high-frequency peritidal and shallow subtidal shallowing-upward cycles, highlighted by the Fischer plots show a very similar long-term trend for the two sections. The units with common subaerial exposure surfaces coincide with the falling limb of the Fischer plots and the section with common omission surfaces coincides with the rising limb of the plots. The studied discontinuities are formed by autocyclic and/or allocyclic processes operating on the shallow platform, but the units with abundant subaerial exposures invoke allogenic forcing of the sedimentary record. The use of the units with abundant discontinuities instead of a single surface has proven useful for the correlation of the studied shallow-platform deposits because one type of discontinuity may change laterally into another type or features of different discontinuity types can be superimposed.
机译：在浅海碳酸盐岩平台中，不同类型和规模的不连续面是常见的，因为那里的沉积物沉积在靠近海平面的位置，因此对环境因素的任何重大物理化学变化敏感。不连续的表面表明在水下或水下条件下的沉积物破裂。浅海碳酸盐岩演替过程中的大多数不连续性都是在床尺度上，并且只能通过分析岩石的沉积学，成岩作用，透声学和水力学特征来确定。小规模不连续性的研究是在韦勒比特山的两个下侏罗统演替中进行的。根据它们的共同特征和形成环境，在简单的层理平面上可分为三类间断点：地下暴露面，侵蚀面和遗漏面。评估了两个连续的不连续类型的分布。两个部分均以暴露面为主，并识别出具有大量地下暴露量的四个单位（相对较薄的沉积记录间隔）。根据生物地​​层学日期，这些单位是最早的Sinemurian，中早期Sinemurian，最早的Pliensbachian和晚期Pliensbachian年龄。遗漏表面是最不常见的不连续类型。 Fischer图突出显示了高频围生期和浅潮下浅层向上上升周期的厚度变化，表明这两个部分的长期趋势非常相似。具有共同的地下暴露面的单位与菲舍尔图的下降肢体重合，具有共同的遗漏表面的截面与地块的上升肢体重合。所研究的不连续性是由在浅平台上进行的自旋和/或同构环过程形成的，但是具有大量地下暴露的单元调用了沉积记录的异体强迫。已证明使用具有大量不连续性的单元而不是单个表面对于研究的浅平台沉积物的相关性很有用，因为一种类型的间断性可能会横向改变为另一种类型，或者可以叠加不同不连续性类型的特征。

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