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Sedimentology and sequence stratigraphy of the Early Cretaceous Centenario Formation (upper member) in the north-eastern border of the Neuquén Basin, Argentina
Journal of South American Earth Sciences ( IF 1.704 ) Pub Date : 2021-02-12 , DOI: 10.1016/j.jsames.2021.103203
Pablo J. Pazos; María E. Novara; Juan Iñigo; Marcos Comerio

The Centenario Formation is a unit known in literature by the content of oil reservoirs in the Productive Trend Río Colorado (PTRC) situated in the north-eastern border of the Neuquén Basin. The formation is composed of a lower and upper member, the latter being the object of this study. The analysis of five wells distributed in a cross section of 10 km length, allowed the analysis of 150 m of cored succession that cover almost all the stratigraphic extent of the upper member. Facies analysis allowed defining ten of them (A–J), recording storm, tidal, and fluvial processes, as well as trace-fossils mainly of the Cruziana and Cruziana-Skolithos ichnofacies and microbialites distributed in different parts of the succession. Nine Facies Associations (I–IX) were defined and them account for marine, marginal-marine and fluvial environments. The marine record documents deposits from the offshore to shoreface that form part of a first and thickest stratigraphic sequence (Sequence I) dominated by a starved transgression (TST), followed by a shallow and wave-dominated delta system (HST) evidencing multiple directions of progradation, and showing quartz dominated composition derived from old sedimentary units. An erosive sequence boundary denotes the beginning of a new depositional cycle (Sequence II). It starts with estuarine facies (TST) containing the coarsest deposits in the entire succession (conglomerates) that are probably correlatable with incised valleys and fluvial deposits documented in outcrops and subsurface. A remarkable change to a lithic composition with abundant volcaniclastic fragments evidences a supply from younger units than the underlying sequence; additionally, tidal action is amplified by a non-lineal coast. A marine interval records the end of the transgression (MFZ), and later a coarsening upward arrangement (HST) product of bay head deltas grading laterally into mud flats. The uppermost part of the unit records the change in the coast line with the advance of fluvial deposits denoting the new sedimentary change with the reorganization of the depositional system (Sequence III). It starts with unconfined fluvial deposits (LST) that present the peculiarity of bimodal grain-size deposits and well-sorting as a result of reworking of previous eolian deposits. The abundant kaolinite contrasts with the underlying sequence and indicates meteoric water input. The fluvial deposits, oil reservoirs, are sealed by marginal marine deposits on top (TST). The succession is incomplete by erosion of the intra-Senonian unconformity, but the stacked sequences exhibit a similar staking trend as in the outcropping Agua de la Mula Member of the Agrio Formation. The last one is a good surface analog unit for comparing sedimentary processes, sequence stratigraphy and ichnology. Taking into account previous studies and outcrops and subsurface correlations, this study restricts the upper member of the Centenario Formation time-equivalent to the Agua de la Mula Member of the Agrio Formation; a post-earliest Barremian age is disregarded. The integration of all available information confirms that conglomerates recorded in subsurface, and also outcrops are the result of incised valleys related to sea level drops. In this sense the Chachauén volcano outcrops are probably the exposed records of the Centenario Formation, rather than the Agrio Formation. Finally, this study confirms a complex sedimentary evolution of the north-eastern basin border, with tectonic controls and a variable coastal line that allows explaining short distance facies changes. This study demonstrates the usefulness of ichnological approaches with sedimentology, particularly in intervals completely oil-impregnated where sedimentary features are frequently difficult to analyze for paleoenvironmental interpretations.



中文翻译:

阿根廷内乌肯盆地东北边界早白垩世百年纪念层(上部)的沉积学和层序地层学

Centenario组是文献中已知的一个单元,位于内乌肯盆地东北边界的科罗拉多州生产趋势里的石油储层中。地层由下部和上部组成,后者是本研究的对象。对分布在10 km长的横截面上的5口井的分析允许对150 m的有芯演替进行分析,这些岩心演替几乎覆盖了上层地层的所有地层范围。通过相分析,可以定义其中的十个(A–J),记录风暴,潮汐和河流过程,以及主要是CruzianaCruziana - Skolithos的痕迹化石。岩相和微辉石分布在演替的不同部分。定义了九个相协会(I–IX),它们解释了海洋,边缘海洋和河流环境。海洋记录文件记录了从海上到岸面的沉积物,这些沉积物是第一个也是最厚的地层层序(序列I)的一部分,该层序由饥饿的海侵(TST)主导,然后是一个浅海和波浪为主的三角洲系统(HST),表现出多个方向的变化。沉积,并显示出源自旧沉积单元的石英为主成分。侵蚀性序列边界表示新的沉积周期(序列II)的开始。它始于河口相(TST),其中包含整个演替过程中最粗的沉积物(砾岩),可能与切开的谷底和露头和地下记录的河流相沉积有关。具有丰富火山碎屑碎片的岩性成分发生了显着变化,这表明来自年轻单元的供给要低于其基础层序。另外,潮汐作用被非线性海岸放大了。一个海洋间隔记录了海侵的结束(MFZ),随后记录了一个海湾头三角洲的向上粗化向上排列(HST)的产物,该产物侧向地分为泥滩。该单元的最上部分记录了沿岸线的变化以及河流沉积的发展,这表明随着沉积系统的重组而出现了新的沉积变化(序列III)。它始于无限制河床沉积物(LST),这是双峰粒度沉积物的奇特之处,并且由于对先前的风积沉积物进行了重新加工而得到了很好的分选。丰富的高岭石与下面的层序形成对比,表明水流输入。河流沉积物,储油层被顶部的边缘海相沉积物(TST)封闭。塞内亚内部不整合面的侵蚀使演替不完全,但是堆积的层序显示出与阿格里奥组露头的阿瓜德拉穆拉成员相似的下注趋势。最后一个是一个很好的地表模拟单元,用于比较沉积过程,层序地层学和岩石学。考虑到先前的研究以及露头和地下相关性,这项研究将百日纳里奥组上部的时间限制为与阿格里奥组的阿瓜德拉穆拉组的时间相等。后最早的巴里米亚时代被忽略了。所有可用信息的整合证实了砾岩记录在地下,而且露头是与海平面下降有关的切开的山谷的结果。从这个意义上说,Chachauén火山露头可能是Centenario组而不是Agrio组的裸露记录。最后,这项研究证实了东北盆地边界的复杂沉积演化,构造控制和变化的海岸线,可以解释近距离相的变化。这项研究证明了鱼类学方法对沉积学的有用性,

更新日期:2021-02-22
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