墨西哥湾古新世下威尔科克斯群最早三角洲岸线的沉积学与地层学

IF 2 4区 地球科学 Q1 GEOLOGY
Mariana I. Olariu
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引用次数: 0

摘要

在区域二维地震数据中,陆架到斜坡边缘的大规模增长得到了很好的记录,但它很少与较小规模的沉积学过程和详细的地层结构联系在一起。本研究通过使用824口井的数据、4口井的80m岩芯和3750km3地震数据,通过连续的海岸线回归和海侵,记录了陆架-斜坡边缘顶集的构建,重点是重复跨陆架过渡期间海岸线行为的复杂性。我们的组合数据集可以理解陆架上沉积过程在单个海退-海侵旋回(小于105年)尺度上的可变性,并表明墨西哥湾北部威尔科克斯群的古地理比通常描述的更为多样。在四级尺度上,主要过程(河流、波浪和潮汐)控制着海岸线形态,因此对于理解陆架上的砂岩体分布以及向陆架边缘和深水输送沉积物至关重要。Lower Wilcox最早的三角洲在相对海平面上升的条件下向南推进,跨越50公里宽的陆架,但富含砂岩的三角洲距离陆架边缘仍保持10-20公里的上升趋势,陆架边缘通过富含泥浆的斜坡岩的堆积而增长。平面形态和内部结构反映了内陆架和中陆架上具有受波浪影响和潮汐改造的三角洲的沉积体系,以及外陆架上的河流泛滥和波浪改造的超密度岩沉积。在岩芯中观察到大量的正级配和反级配地层,块状到扁平到波状的分层交替,以及低强度的生物扰动,表明陆架砂岩体是由超密度流沉积的。总体而言,研究表明,德克萨斯州下威尔科克斯群的三角洲沉积体系比之前解释的更具结构复杂性和过程可变性。波浪修饰的超孢子虫首次在威尔科克斯发现,被认为是泥架演替的重要组成部分。与陆架上先前的研究相比,超孢子虫叶位于三角洲供应航道的横向位置,位置更远。沉积物的这种沿海岸重新分布表明,三角洲到达陆架边缘所需的时间比许多陆架到斜坡边缘所推断的要长,并且向深水输送的沉积物可能相应减少。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Sedimentology and stratigraphy of the earliest deltaic shorelines of the Paleocene Lower Wilcox Group in the Gulf of Mexico
Large-scale growth of shelf-to-slope margins is well documented in regional 2-D seismic data, but it is only rarely linked to sedimentological processes and detailed stratigraphic architecture at smaller scales. This study documents the building of a shelf-to-slope margin topset through successive shoreline regressions and transgressions by using data from 824 wells, 80 m of core from 4 wells, and 3750 km3 of seismic data with a focus on the complexities of shoreline behavior during repeated cross-shelf transits. Our combined data set allows understanding of the variability of depositional processes on the shelf at the scale of individual regressive–transgressive cycles (less than 105 years), and shows that the paleogeography of the Wilcox Group in the northern Gulf of Mexico is more diverse than commonly depicted. At a fourth-order scale dominant processes (river, wave, and tide) control shoreline morphology and as a result are critical to understanding sandstone body distribution on the shelf and sediment delivery to the shelf margin and deep water. The earliest deltas of the Lower Wilcox prograded southward under conditions of rising relative sea level across a 50-km-wide shelf, but the sandstone rich deltas remained 10–20 km updip from the shelf edge, and the shelf margin grew through accretion of mud-rich clinothems. The plan-view morphology and internal architecture reflect depositional systems with wave-influenced and tide-modified deltas on the inner and mid shelf, and river flood and wave-reworked hyperpycnite deposits on the outer shelf. An abundance of normal and inverse graded beds, alternation of massive to flat to undulating lamination, and low intensities of bioturbation observed in cores indicate that the shelf sandstone bodies were deposited from hyperpycnal flows. Overall the study shows that the deltaic depositional systems of the Lower Wilcox Group in Texas have a greater architectural complexity and process variability than previously interpreted. Wave-modified hyperpycnites were identified for the first time in the Wilcox and are considered to form a significant component of the muddy shelf succession. The hyperpycnite lobes are located laterally from the deltaic supply fairway in more distal positions than previous studies identified on the shelf. This along-shore redistribution of sediment suggests that it takes more time for deltas to reach the shelf edge than is inferred for many shelf-to-slope margins, and there is likely to be correspondingly less delivery of sediment to deep water.
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来源期刊
CiteScore
3.80
自引率
5.00%
发文量
50
审稿时长
3 months
期刊介绍: The journal is broad and international in scope and welcomes contributions that further the fundamental understanding of sedimentary processes, the origin of sedimentary deposits, the workings of sedimentary systems, and the records of earth history contained within sedimentary rocks.
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