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The arrival of the paleo–Orinoco Delta at Trinidad: The Cruse Formation delta lobes and delivery to deepwater Atlantic
Journal of Sedimentary Research ( IF 2 ) Pub Date : 2020-08-19 , DOI: 10.2110/jsr.2020.47
Ariana Osman 1 , Ronald J. Steel 2 , Ryan Ramsook 1 , Cornel Olariu 2 , Si Chen 3
Affiliation  

Icehouse continental-shelf-margin accretion is typically driven by high-sediment-supply deltas and repeated glacio-eustatic, climate-driven sea-level changes on a ca. 100 ky time scale. The paleo–Orinoco margin is no exception to this, as the paleo–Orinoco River Delta with its high sediment load prograded across Venezuela, then into the Southern and Columbus basins of Trinidad since the late Miocene, depositing a continental-margin sedimentary prism that is > 12 km thick, 200 km wide, and 500 km along dip.The Cruse Formation (> 800 m thick; 3 My duration) records the first arrival of the paleo–Orinoco Delta into the Trinidad area. It then accreted eastwards, outwards onto the Atlantic margin, by shallow to deepwater clinoform increments since the late Miocene and is capped by a major, thick flooding interval (the Lower Forest Clay). Previous research has provided an understanding of the paleo–Orinoco Delta depositional system at seismic and outcrop scales, but a clinoform framework detailing proximal to distal reaches through the main fairway of the Southern Basin has never been built. We integrate data from 58 wells and outcrop observations to present a 3-D illustration of 15 mapped Cruse clinoforms, in order to understand the changing character of the first Orinoco clastic wedge on Trinidad. The clinoforms have an undecompacted average height of 550 m, estimated continental slope of 2.5° tapering to 1°, and a distance from shelf edge to near-base of slope of > 10 km. The clinoform framework shows trajectory changes from strong shelf-margin progradation (C10–C13) to aggradation (C14–C20) and to renewed progradation (C21–24). Cruse margin progradational phases illustrate oblique clinothem geometries that lack well-developed topsets but contain up to 70 m (200 ft) thick, deepwater slope channels. This suggests a high supply of sediment during periods of repeated icehouse rise and fall of eustatic sea level, with fall outpacing subsidence rates at times, and delivery of sand to the deepwater region of the embryonic Columbus channel region. Also, evidence of wholesale shelf-edge collapse and canyon features seen in outcrop strongly suggest that deepwater conduits for sediment dispersal and bypass surfaces for Cruse basin-floor fans do exist. The change to a topset aggradational pattern with a rising shelf trajectory may be linked to increased subsidence associated with eastward migration of the Caribbean plate. The Cruse-margin topsets were dominated by mixed fluvial–wave delta lobes that were effective in delivery of sands to the basin floor. The preservation of a fluvial regime of the delta may have been impacted by basin geometry which partly sheltered the area from the open Atlantic wave energy at the shelf edge. Ultimately, understanding shelf-edge migration style as well as process-regime changes during cross-shelf transits of the delta will help to predict the location of bypassed sands and their delivery to deepwater areas.

中文翻译:

古奥里诺科三角洲到达特立尼达:克鲁斯组三角洲裂片并输送到深水大西洋

冰室大陆架边缘的积聚通常是由高沉积物供应三角洲和反复的冰川消融,气候驱动的海平面变化引起的。100 ky时间刻度。古奥里诺科河边缘也不例外,因为其高沉积物负荷的古奥里诺科河三角洲从委内瑞拉开始发展,然后从中新世晚期进入特立尼达的南部和哥伦布盆地,沉积了一个大陆边缘的沉积棱柱。 > 12 km厚,200 km宽,沿垂线500km。Cruse组(> 800 m厚; 3 My的持续时间)记录了古奥里诺科三角洲首次进入特立尼达地区。然后从中新世晚期开始,它由东向东,向外扩展到大西洋边缘,由浅水到深水的斜形逐渐增加,并被一个大而厚的洪水间隔(低森林粘土)所覆盖。先前的研究已经了解了地震和露头尺度的古奥里诺科三角洲沉积系统,但从未构造过倾斜形框架,详细描述了通过南部盆地主航道向近端延伸的近端。为了了解特立尼达第一个奥里诺科碎屑楔的变化特征,我们整合了58口井和露头观测的数据,以提供15种映射的克鲁斯斜形的3-D插图。斜形平均高度为550 m,未估计的大陆坡度为2.5°逐渐减小至1°,从大陆架边缘到坡度近于底部的距离> 10 km。斜形框架显示了轨迹的变化,从强大的货架边缘扩展(C10–C13)到扩展(C14–C20)以及更新的扩展(C21–24)。残缘渐进阶段表明倾斜的斜面几何形状缺乏发达的顶部,但包含多达70 m(200 ft)厚的深水斜坡通道。这表明,在冰屋反复上升和下降时(正常海平面不断上升)期间,沉积物供应量很高,有时下降速度超过了沉降速度,并且将沙子输送到了胚胎哥伦布通道区域的深水区域。同样,在露头处看到大量的架子边缘塌陷和峡谷特征的证据强烈表明,确实存在用于沉积物分散的深水管道和克鲁斯盆地风扇的旁路表面。架子轨迹上升到顶部集聚模式的变化可能与与加勒比板块东移相关的沉降增加有关。Cruse-margin顶部是河流-波浪混合三角波的主导,有效地将沙子输送到盆地底部。三角洲河流形态的保存可能受到盆地几何形状的影响,盆地的几何形状部分地使该区域避开了架子边缘的开放大西洋波能量。最终,了解三角洲跨架运输过程中的陆架边缘迁移方式以及过程条件的变化,将有助于预测绕过的沙子的位置及其向深水区域的输送。
更新日期:2020-09-28
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