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Abyssal channels are channels in Earth's sea floor. They are formed by fast-flowing floods of turbid water caused by avalanches near the channel's head, with the sediment carried by the water causing a build-up of the surrounding abyssal plains. Submarine channels and the turbidite systems which form them are responsible for the accumulation of most sandstone deposits found on continental slopes and have proven to be one of the most common types of hydrocarbon reservoirs found in these regions (Weimer et al., 2000). Submarine channels and their flanking levees are commonly referred to as channel levee systems (Flood and Damuth, 1987). They are significant geomorphological features that may run for thousands of kilometres across the ocean floor. Often, they coalesce and overlap to form channel levee complexes which are the building blocks of many major submarine fans. (Kane, 2010) This makes them one of several geological processes responsible for the transport of coarse grained sediment into deep water as well as being a chief conduit for the transfer of carbon from continental shelf to the deeper parts of the continental margins. (Bull et al., 2009; Frey- Martinez et al., 2005; Gee et al., 2006; Masson et al., 2006; Shipp et al., 2004). They do however remain one of the least understood sedimentary processes. (Kane, 2010) The effect of Earth's rotation causes more sediment to build up on one side of the channel than on the other.〔(【引用サイトリンク】 title=Sea floor geology - Hikurangi Channel )〕 What constitutes a channel is not straight forward. Different terms are used on a per study basis all of which have similar but not quite interchangeable definitions. There have been efforts by both Wynn et al. (2007) and Mayall et al. (2006) to produce an up to date, holistic view but even since then there has been a significant number of papers which take concepts, models and ideas even further. There are numerous terms that are used to describe the features contained in this study including geo-body, channel complex, channel storey, channel complex set, confined channel complex system (Kane, 2011). These cover single channels, a single channel and associated sediments or multiple channels grouped. Flood (2001) defines a channel-levee system as a single channel with a levee at each side. These levees are formed by the overspilling and flow stripping of turbidity currents. These are most likely to occur during sea level lowstands. A collection of these channels and levees along with overbank sediments form a channel-levee complex. They can be V or U in shape, have the presence or lack of depositional margins, highly sinuous or straight (Mayall et al. 2006). ==Architecture and nomenclature== Kane et al. (2010) advocates the use of the terms ‘internal levee’ and ‘external levee’ to avoid confusion in the literature concerning the use of ‘inner’ and ‘outer’ levees. To help encourage this unification of phrases into a clearer architectural hierarchy, this study will use Kane’s nomenclature. External levees are a dominantly depositional body forming a constructional wedge of sediment that thins perpendicularly away from a channel-belt. (Figure 2.1) The external levee forms during the evolution of a genetically related channel-belt (or slope valley, channel fairway) by flows that partially spill out of their confinement. External levees can confine adjacent channel belts to form levee-confined systems. External levees may be much less sinuous than the levees of an individual channel-levee system as they do not follow one particular channel but may be the product of overspill from one or more channels or channel-levee systems meandering within the wider channel-belt (Deptuck et al., 2003; Posamentier, 2003). The levee crest is the highest point of the external levee, and runs parallel to the course of the channel-belt, separating the external levees into outer external levees and inner external levees. Internal levees are constructional features fed by flows that partially spilled out of channelised confinement, but were largely unable to escape the confinement of the channel-belt. The flows which build internal levees may interact with the main confining surface, i.e., the external levees, and/or the channel-belt erosion surface, and are liable to erosion by the migration or avulsions of channel thalwegs, and the overbank passage of large flows not confined by the internal levees. As a consequence of lateral migration, internal levees may be better preserved on inner bends (Schwarz and Arnott, 2007). Internal levees form only when confinement has been established, through the construction of external levees and/or the degradation and entrenchment of the composite erosion surface of the channel-belt, or within canyon confinement (Deptuck et al., 2003). Internal levees may form distinct wedges of sediment where enough space is available; where space is limited, i.e., where overspill from underfit channels interacts with external levees or erosional confinement, overspill deposits may appear superficially similar to terrace deposits, which are widely identified in the subsurface (Damuth et al., 1988; Babonneau et al., 2004). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「abyssal channel」の詳細全文を読む スポンサード リンク
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