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Seismic record of a cyclic turbidite-contourite system in the Northern Campos Basin, SE Brazil
Marine Geology ( IF 2.6 ) Pub Date : 2021-01-13 , DOI: 10.1016/j.margeo.2021.106422
Bruna Teixeira Pandolpho , Antonio Henrique da Fontoura Klein , Isadora Dutra , Michel M. Mahiques , Adriano R. Viana , Gilmar Vital Bueno , Arthur Antonio Machado , Yuri L. Camargo , Cízia M. Hercos , Yhaohannah Lima , Antonio Fernando H.F. Filho , Carlos E. Theodoro

A new mixed turbidite-contourite system is described in the northern Campos Basin, southeastern Brazilian margin. This system is developed in a middle slope setting, and was formed through non-synchronous interaction between the turbidity current and a contour current in the same stratigraphic interval (Miocene). Depositional cycles were differentiated based on diagnostic seismic features. Seismic attributes, seismic facies, and isochron maps were used to identify alternating cycles of downslope and alongslope processes in the study area, along with the intermediate stage with features from both processes (mixed system). Seismic units were then associated with the dominant type of current. Alongslope current activity can be distinguished from the downslope current based on its acoustic characteristics (mainly low root-mean-square (RMS) amplitude values), internal architecture (clinoforms), and external geometry pattern (alongslope trend).

On the other hand, downslope gravity currents develop deposits with high-amplitude or chaotic seismic facies, usually higher values of RMS amplitude, channel or channel-lobe features, erosive surfaces, and a basinward depositional trend. The first and oldest seismic unit (S1) was interpreted as a dominantly alongslope system, with vertical aggrading sigmoidal clinoforms and high-frequency, low-amplitude reflections commonly associated with fine-grained sedimentary deposits, typical of a plastered drift, along with a basinward mass transport deposit (MTD) from previous drift instability. Seismic unit S2 represents the intermediate stage where both gravity-driven and along-slope currents act asynchronously. Its is refered to as a mixed turbidite-contourite sequence that shows high-amplitude sediment waves migrating upslope and a moat feature that is carved in its upslope front. The interfingering between high- and low-amplitude reflectors, distal chaotic facies, together with sediment waves and a channel moat, points to a sand-rich deposit reworked by northward-flowing contour currents. Seismic units S3 and S4 show downslope features with chaotic facies (S3) and paleochannels with coarse basal lag deposits (high RMS amplitude values) (S4). In S4, a series of long-lived submarine channels formed. Last, seismic unit S5, referred to as the second plastered drift sequence, is marked by low-amplitude clinoforms that thin basinward. At the seafloor, submarine channel banks (formed at S4) covered by fine sediment deposits (from S5) show asymmetrical features with a slight northward depositional trend, indicating a northward-flowing bottom current, as the deposits are known to pile up in a downcurrent trend. Important information on the paleocurrents' direction was also made based on the final deposits display (e.g. terraces, sediment waves, paleochannels). Research on alternating dominant processes and transitional stages or mixed depositional systems, with both turbidites and contour currents, may provide a better understanding of deep-water depositional processes. Because these processes do not always fit previous depositional models that are mainly described for synchronous systems, new insights on cyclic non-synchronous mixed systems can improve our understanding of how mixed systems are organized through time and space. Being able to determine which were the dominant processes that controlled the sedimentation by indicating periods where the margin was mostly submitted to sediment transfer from continent to the basin and periods where the oceanic currents prevailed by redistributing sediments along the isobaths and replacing the axis of downslope transfer conduits. Setting new models on cyclic deposits and intermediate stages can have a future economic impact on potential hydrocarbon reservoir architecture.



中文翻译:

巴西东南部坎波斯盆地北部一个周期性浊积-共生体系的地震记录

在巴西东南部边缘的北部Campos盆地描述了一种新的混浊-混浊-杂岩系统。该系统是在中斜率环境下开发的,是通过在相同地层间隔(中新世)中浊度电流和轮廓电流之间的非同步相互作用形成的。根据诊断地震特征区分沉积周期。地震属性,地震相和等时线图被用来确定研究区域的下坡和顺坡过程的交替周期,以及具有两个过程特征的中间阶段(混合系统)。然后,地震单位与电流的主要类型相关。

另一方面,下坡重力流形成具有高振幅或混沌地震相的沉积物,通常具有较高的RMS振幅值,通道或通道瓣特征,侵蚀性表面和盆地向沉积趋势。第一个也是最古老的地震单元(S1)被解释为主要为斜坡系统,具有垂直渐进的S型斜线形和高频,低振幅反射,通常与细颗粒沉积物(通常为灰泥漂移)相关,并伴有盆地向以前的漂移不稳定引起的大规模运输沉积物(MTD)。地震单元S2代表中间阶段,在此阶段,重力驱动的电流和沿斜坡的电流均异步作用。它被称为混浊-辉石混合序列,显示出高振幅的泥沙波向上坡迁移,并在其上坡前刻有护城河特征。高振幅反射器和低振幅反射器,远侧混沌相以及沉积波和沟mo之间的相互指责指向了富砂矿床,该矿床由向北流动的轮廓流重做。地震单元S3和S4表现出具有混沌相的下坡特征(S3)和具有较粗的基底滞后沉积物(高RMS振幅值)的古河道(S4)。在S4中,形成了一系列长寿命的海底通道。最后,地震单元S5(称为第二膏状漂移序列)的特征是向后变薄的低振幅斜形。在海底 细沙沉积物(来自S5)覆盖的海底河道堤(形成于S4)显示出不对称特征,并具有轻微的北向沉积趋势,表明向北流动的底流,因为已知沉积物会以顺流趋势堆积。还根据最终的沉积物显示(例如阶地,沉积波,古河道)获得了有关古流向的重要信息。对交替的主要过程和过渡阶段或混合沉积系统(包括浊流和等高线流)的研究可能会更好地理解深水沉积过程。由于这些过程并不总是适合以前主要针对同步系统描述的沉积模型,关于循环非同步混合系统的新见解可以增进我们对如何通过时间和空间组织混合系统的理解。能够通过指示边缘主要用于沉积物从大陆到盆地的转移以及洋流占优势的时期(决定等速控制沉积的主要过程),洋流是通过沿等压线重新分配沉积物并替换下坡转移轴来占优势导管。在循环沉积和中间阶段建立新模型可能会对潜在的油气藏构架产生未来的经济影响。能够通过指示边缘主要用于沉积物从大陆到盆地的转移以及洋流占优势的时期(决定等速控制沉积的主要过程),洋流是通过沿等压线重新分配沉积物并替换下坡转移轴来占优势导管。在循环沉积和中间阶段建立新模型可能会对潜在的油气藏构架产生未来的经济影响。能够通过指示边缘主要用于沉积物从大陆到盆地的转移以及洋流占优势的时期(决定等速控制沉积的主要过程),洋流是通过沿等压线重新分配沉积物并替换下坡转移轴来占优势导管。在循环沉积和中间阶段建立新模型可能会对潜在的油气藏结构产生未来的经济影响。

更新日期:2021-01-28
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