Tide-Dominated Han River Delta, Korea (eBook)

Geomorphology, Sedimentology, and Stratigraphic Architecture

Kyungsik Choi, Don Cummings, Robert Dalrymple, Jaehwa Jin (Autoren)

eBook Download: PDF | EPUB

2015 | 1. Auflage
382 Seiten
Elsevier Science (Verlag)
978-0-12-801081-5 (ISBN)

Infos

The Tide-Dominated Han River Delta provides a thorough analysis of a river delta in which tidal currents have reworked the river-borne sediment, generating characteristic geomorphological and sedimentological signatures in the process. Such 'tide-dominated' deltas are common in the modern ocean, forming the substrate upon which entire populations are built. Furthermore, ancient examples contain enormous volumes of hydrocarbon. Despite this, tide-dominated deltas remain less well understood than their wave- and river-dominated counterparts, largely because processes within them are inherently more complex and fewer modern examples have been investigated in detail. This multi-year study by a team of experts in coastal geoscience represents the most complete documentation of a tide-dominated delta to date. Results help advance, and are applicable to, a broad range of fields within sedimentary geology, including clastic sedimentology, seismic and sequence stratigraphy, and coastal geomorphology, in addition to petroleum geology and reservoir engineering. - Offers new access to results of a multi-year hydrocarbon-reservoir analogue study not available elsewhere - Features 75 full-color figures and illustrations to emphasize critical aspects of the delta's sedimentology, geomorphology, and stratigraphy - Provides basic data that better define what tide-dominated deltas are, how these complex systems behave over time, and why this is so - Aids petroleum geologists and reservoir engineers in predicting the distribution of baffles and barriers in tide-dominated sediment bodies, helping in the successful development of reservoirs

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The Tide-Dominated Han River Delta provides a thorough analysis of a river delta in which tidal currents have reworked the river-borne sediment, generating characteristic geomorphological and sedimentological signatures in the process. Such "e;tide-dominated"e; deltas are common in the modern ocean, forming the substrate upon which entire populations are built. Furthermore, ancient examples contain enormous volumes of hydrocarbon. Despite this, tide-dominated deltas remain less well understood than their wave- and river-dominated counterparts, largely because processes within them are inherently more complex and fewer modern examples have been investigated in detail. This multi-year study by a team of experts in coastal geoscience represents the most complete documentation of a tide-dominated delta to date. Results help advance, and are applicable to, a broad range of fields within sedimentary geology, including clastic sedimentology, seismic and sequence stratigraphy, and coastal geomorphology, in addition to petroleum geology and reservoir engineering. - Offers new access to results of a multi-year hydrocarbon-reservoir analogue study not available elsewhere- Features 75 full-color figures and illustrations to emphasize critical aspects of the delta's sedimentology, geomorphology, and stratigraphy- Provides basic data that better define what tide-dominated deltas are, how these complex systems behave over time, and why this is so- Aids petroleum geologists and reservoir engineers in predicting the distribution of baffles and barriers in tide-dominated sediment bodies, helping in the successful development of reservoirs

Textauszug

Chapter 1

Introduction

Abstract

To fill a significant gap in our understanding of tide-dominated deltas, this book presents a multi-faceted exploration of the Han River Delta, located on the east coast of the Yellow Sea, Korea. Topics covered are the geologic and process setting, delta morphology, the distribution of surficial sediment types, the facies present in short and long cores, stratal architecture, and the sequence-stratigraphic organization of the Holocene succession. The results will have application for the management of such deltas and for petroleum exploration in the deposits of ancient analogues.

Keywords

Facies model; Macrotidal; Petroleum; River delta; Sedimentary geology; Sequence stratigraphy; Subaqueous delta platform; Tide-dominated

Chapter Points

• Tide-dominated deltas are the most common type of large delta in the world today

• Few have been studied

• Within them, proximal–distal trends in hydraulic energy, facies, and architecture are complex

• A well-accepted facies model does not exist

• The Han River delta was studied to help fill this knowledge gap

• It has the largest tidal range of any delta studied to date

River deltas are some of the most beautiful, complex features on Earth. Viewed from space, they almost look alive, their channels branching across the land surface like air passages in a lung or the limbs of a tree. In addition to looking alive, deltas help sustain life. Hundreds of millions of people live on them, commonly within meters of sea level (Goodbred and Saito, 2012). To the farmer, the delta is the field; to the engineer, the substrate of the city; to the geologist, the reservoir for drinking water and petroleum. To the ocean, the delta is like a security gate, a macroscopic physical, biological, and chemical filter through which most sediment, nutrients, and water-borne pollutants from the continent must pass. Deltas were one of the first sedimentary environments to be studied in detail (Gilbert, 1885; Fisk, 1944) and they remain the focus of intense study today (Bhattacharya, 2010).

All deltas share two fundamental traits. First, they consist primarily of fluvial sediment: deltas owe their existence to deposition from decelerating, expanding river flow issuing into a body of water. The sediment may be reworked by non-fluvial processes following initial deposition (Wright and Nittrouer, 1995), but ultimately the delta exists because a river supplied it with sediment. Second, deltas are progradational: they build outward into the body of water. The outbuilding typically occurs by accretion of sediment onto the distal (i.e., seaward) face of the delta, which in mature systems takes the form of a sloping depositional surface known as a clinoform. The term progradational is used somewhat loosely here. Deltaic outbuilding typically involves shoreline progradation, but for many of the larger and more strongly tidally influenced deltas, most of the outbuilding takes place far from shore, beneath the water surface (Figure 1.1). In these systems, the top (“topset”) of the delta, across which most sediment is bypassed, is largely subaqueous, the prograding clinoform∗ displaced 40–120 km offshore and submerged in 10–50 m of water (Friedrichs and Wright, 2004; Walsh et al., 2004).

Figure 1.1 The Han River subaqueous delta platform compared to that of other tide-dominated and strongly tide-influenced deltas. Basinward is to the right. The sediment load, tidal range, and wave height values quoted should be thought of as average and approximate because they are inherently spatially and temporally variable. Data from Milliman and Meade (1983), Hong et al. (2002), and Hori et al. (2002).

Beyond these two common traits, variability is the norm. Grain size, basin physiography, tectonic setting, climate, and physical oceanography all play a role in determining delta physiography (Coleman and Wright, 1975), leading to a conceivably infinite number of possible outcomes. However, for large marine deltas, which tend to be fine grained because of inland trapping of coarse sediment, variability is often primarily a function of the physical oceanography of the receiving basin, and in particular the degree to which waves versus tidal currents rework the fluvial sediment in the coastal zone. Recognizing this, Galloway (1975) proposed a geomorphological classification of deltas with three end-member types: (1) river-dominated deltas, whose mouth bars—the fundamental deposit of river outflow (Bates, 1953)—experience little reworking by waves or tides; (2) wave-dominated deltas, within which waves and wave-generated currents perform most geomorphic work, reworking the mouth-bar sediment alongshore into beaches; and (3) tide-dominated deltas, within which tidal currents perform most geomorphic work, reworking mouth bars into shore-normal tidal bars. Significant advances in understanding have been made since Galloway’s publication, thanks in part to numerical modeling (Pirmez et al., 1998; Swenson et al., 2005), flume experiments (Southard, 1991; Dumas et al., 2005), integration of ichnology (MacEachern et al., 2005) and hydrodynamic data (Kineke and Steinberg, 1995; Geyer et al., 2004), and, perhaps most importantly, the study of deltas themselves (Wright and Nittrouer, 1995; Goodbred and Saito, 2012). However, Galloway’s simple yet elegant scheme remains the de facto starting point for discussion.

Of Galloway’s three end-member delta types, tide-dominated deltas remain the least well understood, despite the fact that five of the 10 largest rivers in the world today have tide-dominated or strongly tide-influenced deltas (Middleton, 1991; Goodbred and Saito, 2012). There are several reasons for this. At the time of Galloway’s publication, several of the tide-dominated deltas he listed had not been studied in detail. Subsequent work has shown that some of these may actually be drowned river mouths still undergoing transgression (i.e., they are “estuaries” sensu Dalrymple et al. (1992)), not progradational sediment bodies that are actively outbuilding onto the shelf (i.e., deltas). The presence of very broad shallow water areas on the subaqueous delta plain (Figure 1.1), coupled with the presence of strong tidal currents, makes access difficult and dangerous. Thus, to this day, few modern examples of tide-dominated deltas have been studied in detail (for a summary, see Goodbred and Saito (2012)). Furthermore, within tide-dominated deltaic environments, proximal–distal variations in hydraulic energy, and thus facies, tend to be more complex and less well understood than in their river- and wave-dominated counterparts (Dalrymple and Choi, 2007). The morphologic complexity of tide-dominated deltas with their multitude of channels and bars further compounds the problem of characterizing such deltas. Consequently, a comprehensive tide-dominated delta facies model has not taken root in the geological community. This may explain why so few ancient examples have been identified despite their abundance in modern settings (Willis, 2005; Bhattacharya, 2010).

To help fill this knowledge gap, the Han River delta, a tide-dominated delta along Korea’s west coast, was studied using a large integrated dataset of short cores, long drill cores, and seismic data (Figure 1.2). The study represents the most comprehensive investigation of a tide-dominated delta to date. Straddling the border between North and South Korea, the Han is the Korean peninsula’s largest river. It debouches into Gyeonggi Bay (alternative spelling: Kyunggi Bay), a shallow (∼40 m depth), rocky, wide-mouthed embayment fringed by tidal flats, dotted by bedrock islands, and characterized by an extreme tidal range (Figure 1.3), which exceeds 9 m at the very head of the bay during spring tides. The river mouth lacks a distinct shoreline protruberance, which has led some to refer to it as an estuary (Lee et al., 2013). However, as is common to all tide-dominated deltas studied to date (Figure 1.1), most of the action has taken place out of sight, beneath the water surface: previous data show that an aerially extensive, heterolithic package of sediment has aggraded and then prograded offshore of the river mouth, with upward of 60 m of sediment having accumulated since the last glacial maximum lowstand (Jin, 2001). The Han’s subaqueous delta platform is not flat-topped like those of other deltas. Rather, it consists of several broad, shore-attached, finger-like protrusions. The protrusions are larger—and especially wider—than “typical” tidal bars observed in previously studied deltas. We therefore refer to them as large tidal bars. In the mid-2000s, an extensive dataset was collected from the centermost large tidal bar by a government–industry–academic consortium. These data, along with older, unpublished data from the inner large tidal bar (Jin, 2001), form the focus of this book. In later chapters, data from other subenvironments, such as distributary channels and tidal...

Produkt-Details

• Erscheint lt. Verlag: 25.9.2015
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Geologie
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Geophysik
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Hydrologie / Ozeanografie
• Themenwelt: Naturwissenschaften ► Physik / Astronomie
• Themenwelt: Technik
• ISBN-10: 0-12-801081-9 / 0128010819
• ISBN-13: 978-0-12-801081-5 / 9780128010815