Sedimentology of the tide-dominated Jurassic Lajas Formation, Neuquén Basin, Argentina
Sedimentology of the tide-dominated Jurassic Lajas Formation, Neuquén Basin, Argentina
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DOI：
10.1144/gsl.sp.2005.252.01.05
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
D. McIlroy;S. Flint;J. Howell;Nick Timms
中科院分区：
文献类型：
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作者：
D. McIlroy;S. Flint;J. Howell;Nick Timms
摘要潮汐沉积体系通常被解释为高水位时期以波浪或河流为主的层序中的低水位/海侵河口沉积。阿根廷Neuquén盆地中侏罗世Lajas组由4个跨度约4.5 Ma的不整合面层序中600米裸露的潮汐控制相组成。相组合包括潮控三角洲、砂质-异石器潮汐河道充填和广泛的进积潮坪序列，它们被异石器潮汐河道充填物局部切割。尽管测深沉积范围狭窄，相变化复杂，但可以沿着48公里长的露头带确定和绘制洪泛面。这些泛面可以定义三种不同类型的准序列，它们表现出向上粗化、向上细化和向上粗化的主题。层序界面以广泛但浅的切割为标志，堆积的河流/潮汐河道并列充填在各种潮下相和潮间相上。在层序界面上可能发生非常规的粒度变化，其特征是异石器-泥质潮间带/潮上泥滩沉积并置在潮下砂滩相上的盆地向内相转移。通过完整的基准面旋回维持大潮条件，被解释为由于裂谷作用继承的构造地形，导致整个次盆地表现为一个受构造控制的海湾。
Abstract Tidal depositional systems are often interpreted as lowstand/transgressive estuarine deposits within sequences that are either wave or river dominated during highstand times. The Middle Jurassic Lajas Formation of the Neuquén Basin, Argentina, comprises 600 m of well-exposed tide-dominated facies deposited within four unconformitybounded sequences, spanning approximately 4.5 Ma. Facies associations include tidedominated deltas, sandy-heterolithic tidal channel fills and extensive progradational tidal-flat successions, which are locally cut by heterolithic tidal channel fills. Despite the narrow bathymetric depositional range and the complex facies variability, flooding surfaces can be defined and mapped along a 48 km-long outcrop belt. These flooding surfaces allow definition of three distinct types of parasequence that exhibit coarsening-upwards, finingupwards and coarsening- to fining-upwards motifs. Sequence boundaries are marked by widespread, but shallow, incision, and the juxtaposition of stacked fluvial/tidal channel fills on a variety of subtidal and intertidal facies. Unconventional grain-size changes at sequence boundaries can occur where basinward facies shifts are marked by juxtaposition of heterolithic-argillaceous intertidal/supratidal mudflat deposits on subtidal sandflat facies. The maintenance of macrotidal conditions through complete base-level cycles is interpreted as being due to the structural topography inherited from rifting, causing the whole sub-basin to behave as a structurally controlled embayment.