Lithostratigraphy Versus Chronostratigraphy in Facies Correlations of Quaternary Deltas: Application of Bedding Correlation
Lithostratigraphy Versus Chronostratigraphy in Facies Correlations of Quaternary Deltas: Application of Bedding Correlation
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第四纪三角洲相对比中的岩石地层学与年代地层学：层理对比的应用
DOI：
10.2110/pec.05.83.0031
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发表时间：
2005
影响因子：
4.9
通讯作者：
J. Bhattacharya
中科院分区：
文献类型：
--
作者：
M. Gani;J. Bhattacharya
露头和高分辨率地震研究表明，进积的三角洲沉积物由向海倾斜的倾斜斜状地层组成。尽管如此，许多第四纪三角洲的研究，特别是那些基于沉积物岩心对比的研究，通常描绘了尖锐到平缓起伏的相边界，类似于斯克鲁顿在 1960 年最初显示的那些。斯克鲁顿模型强调“层状”岩石地层学，将外观相似但高度穿时的环境相关联起来，以跨越时间线的实线为界。相比之下，古代地下三角洲的相建筑和层序地层研究基本上放弃了这种岩石地层学方法。另一种“年代地层”方法使用露头和地震示例作为训练图像，用于导出驱动地下地层内部相结构相关性的概念模型。这些露头和地震实例表明，斯克鲁顿的历时相单元之间不存在可观察到的物理边界。概念性的“标准”将进积三角洲描述为向海倾斜的斜状地层。倾斜的三角洲前缘砂岩层与时间线大致平行，并与泥质前三角洲底组交错。如果无法解析单个地层，则通常会以表明这种类型的边界是渐变的而不是尖锐的方式绘制历时过渡相边界，特别是通过使用闪电型“shazam”线。我们使用从露头和地震模拟中观察到的几何形状得出的层理关联方法（即地层和床组的关联）作为概念指南，对最近发表的几个现代实例的地层和相进行重新关联，其中数据仅限于少数、间距较远的岩心。新的相关性虽然由于相关距离较长而不精确，但可能更准确地描述了地层规模相结构，并且在涉及三角洲地层规模生长建模或需要预测三角洲储层和含水层的 3D 流体流动行为的应用中可能更有用。河流三角洲——概念、模型和实例 SEPM 特别出版物第 83 号，版权所有 © 2005 SEPM（沉积地质学会），ISBN 1-56576-113-8，第 11 页。 31-48。引言 露头相结构研究始于河流沉积物的研究（例如，Allen，1983；Miall，1985）。由于最近全球对深水勘探的重视，最近的露头研究强调深海沉积系统（Pickering 等，1995；Bouma 和 Stone，2000）。相比之下，三角洲砂体的二维相结构研究受到的关注要少得多，并且还没有整合这些系统的露头和地下数据的 3D 研究，尽管三角洲沉积物对于能源资源和环境科学非常重要。通常，三角洲前缘砂岩体具有复杂的准层序内几何形状和形状，其特征是向海倾斜的砂岩夹有页岩（例如，Barrell，1912；Busch，1971；Berg，1982；Frazier，1974；Van Wagoner 等，1990；Bhattacharya，1991；Bhattacharya 和沃克，1992；威利斯等人，1999；奇德西，2001）。准确确定这些复杂的几何形状是解决三角洲地床规模演化历史的关键。此外，页岩互层的分布、方向和整体相结构对于控制三角洲前缘砂体的储层和含水层行为尤其重要（例如，Willis 和 White，2000）。在说明沉积体的内部相结构时，通常使用实线来表示物理表面（例如，Van Wagoner 等，1990；Bhattacharya，1993；Posamentier 和 Allen，1999），包括边界面和地床边界。历时相边界不是物理表面，通常用“shazam 线”来描述（例如，Rich，1951；Van Wagoner 等，1990；Posamentier 和 Allen，1999）。 Shazam 线是不规则的线，这意味着代表相互通的渐变边界。现代密西西比三角洲最有影响力的早期剖面描述之一（Scruton，1960）试图说明三角洲进积过程中相与沉积时间之间的关系（图 1）。在该描述中（图 1A），相边界显示为纯黑色，大致水平到轻微起伏的表面，这意味着它们代表水平床或层之间的边界。这代表了一种岩石地层学解释，缺乏有关岩性和层理几何形状内部变化的任何信息。随着相建筑和层序地层概念的出现，Scruton 模型在古代三角洲的研究中已基本被放弃（例如，Van Wagoner 等，1990；Bhattacharya，1991；Bhattacharya，1993；Posamentier 和 Allen，1993；Tye 等，1999；Ainsworth 等，1999），但它仍在继续可应用于许多现代三角洲系统的研究，这些系统的解释是基于几个钻孔，以及在不存在高分辨率地球物理图像或无法获得露头的情况下（例如，Cumming 和 Al-Aasm，1999 年；Woodroffe，2000 年；Hori 等人，2001 年；Ta 等人，2002b；Jones 等人，2003 年；Staub 和加斯塔尔多，2003；田边等人，2003）。本文的目的是说明使用层理相关性（即地层和床组边界的相关性）和相建筑概念建立的模型与使用更传统的岩石地层学方法建立的相相关性模型之间的差异。我们首先简要回顾地层规模结构的露头和地下示例，然后展示如何将这些示例应用于最近发布的几个第四纪示例中提供的岩心数据的重新关联。 M. Royhan GANI 和 JANOK P. BHATTACHARYA 32
Outcrop and high-resolution seismic studies show that prograding delta deposits consist of seaward-dipping, offlapping clinoform strata. Despite this, many studies of Quaternary deltas, particularly those based on correlation of sediment cores, commonly depict sharp to gently undulating facies boundaries, similar to those originally shown by Scruton in 1960. The Scruton model emphasizes “layer-cake” lithostratigraphy that correlates similar-appearing but highly diachronous environmental facies, bounded by solid lines that cut across time lines. In contrast, facies architectural and sequence stratigraphic studies of ancient subsurface deltas have largely abandoned this lithostratigraphic approach. The alternate “chronostratigraphic” approach uses outcrop and seismic examples as training images that are used to derive conceptual models that drive the correlation of the internal facies architecture of subsurface strata. These outcrop and seismic examples suggest that there is no observable physical boundary between Scruton’s diachronous facies units. The conceptual “norm” depicts prograding deltas as seaward-dipping clinoform strata. Dipping delta-front sandstone beds roughly parallel time lines and interfinger with muddy prodelta bottomsets. If individual beds cannot be resolved, then diachronous, transitional facies boundaries are routinely drawn in a way that indicates that boundaries of this type are gradational rather than sharp, specifically by using lightning-stroketype “shazam” lines. We use the method of bedding correlation (i.e., correlation of beds and bedsets) derived from geometries observed in outcrops and seismic analogs as a conceptual guide to recorrelate beds and facies for several recently published modern examples, where data are limited to a few, widely spaced cores. The new correlations, although imprecise because of long correlation distances, are potentially more accurate depictions of the bed-scale facies architecture, and may be more useful in applications that involve modeling bed-scale growth of deltas or that require prediction of 3-D fluid-flow behavior of deltaic reservoirs and aquifers. River Deltas—Concepts, Models, and Examples SEPM Special Publication No. 83, Copyright © 2005 SEPM (Society for Sedimentary Geology), ISBN 1-56576-113-8, p. 31–48. INTRODUCTION Outcrop facies architectural studies began with the study of fluvial deposits (e.g., Allen, 1983; Miall, 1985). More recent outcrop studies emphasize deep-marine depositional systems, because of the recent global emphasis on deep-water exploration (Pickering et al., 1995; Bouma and Stone, 2000). Two-dimensional facies architectural studies of deltaic sand bodies, in contrast, have received much less attention, and there have been no 3-D studies integrating outcrop and subsurface data of these systems, despite the importance of delta deposits for energy resources and in environmental sciences. Typically, delta-front sandstone bodies have complex intra-parasequence geometries and shapes, characterized by seaward-dipping inclined sandstones interbedded with shales (e.g., Barrell, 1912; Busch, 1971; Berg, 1982; Frazier, 1974; Van Wagoner et al., 1990; Bhattacharya, 1991; Bhattacharya and Walker, 1992; Willis et al., 1999; Chidsey, 2001). Accurate determination of these complex geometries is the key to addressing the bed-scale evolutionary history of a delta. Also, the distribution, orientation, and overall facies architecture of shale interbeds are especially important in controlling reservoir and aquifer behavior in delta-front sand bodies (e.g., Willis and White, 2000). In illustrating the internal facies architecture of a sedimentary body, solid lines are generally used to refer to physical surfaces (e.g., Van Wagoner et al., 1990; Bhattacharya, 1993; Posamentier and Allen, 1999), which include bounding surfaces and bed boundaries. Diachronous facies boundaries, which are not physical surfaces, are commonly depicted with a “shazam line” (e.g., Rich, 1951; Van Wagoner et al., 1990; Posamentier and Allen, 1999). Shazam lines are irregular lines, which imply gradational boundaries that represent facies intertonguing. One of the most influential early cross-sectional depictions through the modern Mississippi delta (Scruton, 1960) attempted to illustrate the relationship between facies and time of deposition during progradation of a delta (Fig. 1). In this depiction (Fig 1A), facies boundaries are shown as solid black, broadly horizontal to gently undulating surfaces, implying that they represent the boundaries between horizontal beds or layers. This represents a lithostratigraphic interpretation that lacks any information about internal variations of lithology and bedding geometry. The Scruton model has largely been abandoned in studies of ancient deltas with the advent of facies architectural and sequence stratigraphic concepts (e.g., Van Wagoner et al., 1990; Bhattacharya, 1991; Bhattacharya, 1993; Posamentier and Allen, 1993; Tye et al., 1999; Ainsworth et al., 1999), but it continues to be applied in studies of many modern deltaic systems where interpretations are based on a few boreholes, and in cases where high-resolution geophysical images do not exist or there is no access to outcrops (e.g., Cumming and Al-Aasm, 1999; Woodroffe, 2000; Hori et al., 2001; Ta et al., 2002b; Jones et al., 2003; Staub and Gastaldo, 2003; Tanabe et al., 2003). The objective of this paper is to illustrate the differences in models built using bedding correlation (i.e., correlation of beds and bedsets boundaries) and facies architectural concepts, versus facies correlation models built using the more traditional lithostratigraphic approach. We begin with a brief review of outcrop and subsurface examples of bed-scale architecture and then show how these examples can be applied to recorrelation of core data presented in several recently published Quaternary examples. M. ROYHAN GANI AND JANOK P. BHATTACHARYA 32