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Seismic stratigraphy of a partially filled incised valley on a semi-arid continental shelf, Northeast Brazil
Geo-Marine Letters ( IF 2.1 ) Pub Date : 2021-03-18 , DOI: 10.1007/s00367-021-00687-7
Antonio Rodrigues Ximenes Neto , Paulo Roberto Silva Pessoa , Lidriana de Souza Pinheiro , Jáder Onofre de Morais

This study aimed to understand the key surfaces and the sedimentary filling pattern of the Coreaú incised valley (CIV) system (NE Brazil) using high-resolution seismic stratigraphy. Six key surfaces (Ss) and five seismic units (SUs) were identified. The difference in the basal reflector (S1) and the paleointerfluve (modern sea floor) was verified to be up to 40 m of incision, of which only 20 m are filled. S1 (sequence boundary—SB) was associated with the acoustic basement (Tibau Formation/Barreiras Group) and presented strong control (antecedent topography) in the incision (re-incisions in the Pleistocene lowstands) and sedimentary stacking pattern. The CIV fill showed lowstand system tract, LST (chaotic facies)–transgressive system tract, TST (horizontal layers to chaotic facies)–highstand system tract, HST (chaotic facies) from the base to top. Thin fluvial deposits above SB correspond to LST. Overlapping this system tract is the first marine flooding surface—transgressive surface. Afterwards, the largest seismic unit (lateral and vertical) with sub-parallel and parallel (onlap) seismic facies, interpreted as related to a low energy system, with shallow gas, and vertical accretion (central basin of estuary) occurred. This environment is related to the drowning of the shelf from the shelf break (a decrease in gradient). A tide ravinement surface truncated the top of SU3 and favored coastal to shallow marine deposition. The transgressive system tract (TST) is thicker in the middle (mainly) and outer sectors in the fluvial troughs (depocenter). The maximum flooding surface appears near the sea floor and favored the development above of carbonate sedimentation in the HST. These seimostratigraphic stacking patterns showed a strong influence of semi-arid climate and antecedent topography/structural inheritance. Thus, it is evident that the filling of the CIV differs from other valleys on semi-arid systems and/or influenced by paleotopography (e.g., South Africa and Texas Shelf), which demonstrates the importance of local settings. The great influence of estuarine to coastal sediments in the valley infilling is also observed in the modern Coreaú coastal plain incised valley.



中文翻译:

巴西东北部半干旱大陆架上部分充满切口的山谷的地震地层

这项研究旨在利用高分辨率地震地层学来了解Coreaú切谷(CIV)系统(巴西东北)的关键表面和沉积物填充模式。确定了六个关键表面(Ss)和五个地震单位(SU)。基底反射器(S1)和古界面流(现代海床)之间的差异经验证可达到40 m的切口,其中只有20 m被填满。S1(序列边界-SB)与声学基底(Tibau组/ Barreiras组)相关联,并且在切口(更新世低层台地的再次切口)和沉积物堆积模式中表现出较强的控制能力(前地形)。CIV填充从底部到顶部显示低位系统道LST(混沌相)-海侵系统道TST(水平层到混沌相)-高位系统道HST(混沌相)。SB上方较薄的河流沉积物对应于LST。与该系统域重叠的是第一个海洋洪水表面—海侵表面。此后,出现了最大的地震单元(横向和垂直),具有亚平行和平行(重叠)地震相,被解释为与低能量系统有关,具有浅层天然气和垂直沉积物(河口中央盆地)。这种环境与架子破裂造成的架子淹没(坡度降低)有关。潮汐起伏的表面截断了SU3的顶部,有利于沿海到浅海的沉积。海侵系统道(TST)在河流槽的中部(主要是)和外部部分(沉积中心)较厚。最大的洪水面出现在海床附近,有利于HST碳酸盐岩沉降以上的发育。这些地层叠加模式显示出半干旱气候和前期地形/结构继承的强烈影响。因此,很明显,CIV的充填不同于半干旱系统上的其他山谷和/或受古地形学(例如南非和德克萨斯架)的影响,这表明了当地环境的重要性。在现代Coreaú沿海平原切割山谷中,也观察到河口对河谷填充物中沿海沉积物的巨大影响。

更新日期:2021-03-19
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