The Hunghae Formation, SE Korea: Miocene debris aprons in a back‐arc intraslope basin

Abstract

During early to middle Miocene times a sudden opening of the Ulleung (Tsushima) back‐arc basin in the East Sea (Sea of Japan) led to the development of intraslope basins along the rifted southwestern margin (southeast Korea). Abrupt subsidence resulted in the deposition of the 200 m thick Hunghae Formation (middle Miocene), a sand/mudstone sequence that can be divided into five facies. Facies I (sand and mudstone couplet) and II (coarse sand) are turbiditic in origin, as evidenced by massive, graded, crudely‐layered and parallel‐laminated sand beds. Facies III (homogeneous mudstone) is characterized by various lignite and plant fragments, clastic and biogenic grains that are randomly oriented, suggestive of hemipelagic deposition. Facies IV (chaotic deposit) is characterized by the disruption of beds, the presence of isolated siltstone blocks (or balls) and large clasts in the muddy matrix, indicative of retrogressive rockfall and slide/slump. Facies V (conglomerate) is of debris flow origin, as evidenced by clast‐ and matrix‐supported features, floating large clasts and absence of traction structures. Individual facies are organized into two types of facies association: (1) homogeneous mudstone (facies III) associated randomly with the rest (facies I, II, IV and V), indicative of hemipelagic and episodic sediment‐gravity flow processes, respectively; (2) conglomerate (facies V), coarse sand (facies II) and sand/mudstone couplet (facies I), representing the flow transformation from debris flow to high‐ and low‐concentration turbidity currents. These facies associations are similar in many respects to modern and ancient debris (or slope) aprons found elsewhere. Numerous isolated slide/slump blocks, wedged conglomerates with armoured mudstone balls, discontinuous lignite‐containing sand/mudstone beds, chaotic structure and growth faults suggest that the deposition occurred on a steep slope (intraslope basin) off coalescing fan‐deltas, mainly by unchannellized sediment‐gravity flows. Ancient deposits with irregular facies sequences can be viewed as debris‐apron systems, which provide alternatives to submarine‐fan models in many clastic basins with a line rather than point source.

Quaternary colluvium in west‐central Anatolia: sedimentary facies and palaeoclimatic significance

“…For example, deposits qualifying as colluvial, although not necessarily described as such, have been reported from the Tertiary of Arizona ( Yarnold, 1993), Spanish Betics ( Midtun, 1991; Kjærefjord, 1992), SW Turkey ( Nemec et al. , 1998b ), SE Cyprus ( Murton & MacLeod, 1987; Eaton & Robertson, 1993) and SE Korea ( Choe & Chough, 1988); the Cretaceous of NE Scotland ( Andrews et al. , 1990 ; Lawrence, 1993), the Canadian Queen Charlotte Islands ( Higgs, 1990) and Baja California ( White & Busby‐Spera, 1987; Busby‐Spera, 1988; Morris et al.…”

Relationships between high‐magnitude relative sea‐level changes and filling of a coarse‐grained submarine canyon (Pleistocene, Ionian Calabria, Southern Italy)

“…The evidence above precludes other interpretations such as a linear‐sourced slope apron (e.g. Choe & Chough, 1988; Ineson, 1989; Stow et al. , 1996), or an intraslope minibasin (e.g.…”

“…The local presence of fresh water ostracods and leaves in Facies M2 units of the upper part of the succession indicate the vicinity of the mainland and of fluvial point sources discharging continental material into the open sea (e.g. Choe & Chough, 1988; Drexler et al. , 2006).…”

Distinct sedimentary processes reflected in the isotopic signatures of dolomitic concretions in the Miocene Pohang Basin (southwestern East Sea)

“…Several fan deltas began to form along the western basin margin (Hwang et al, 1995;Sohn et al, 2001;Sohn and Son, 2004). As a result, the sedimentary succession, named the Yeonil Group, exhibits the intercalation of deltaic sediments and hemipelagic mudstones (Choe and Chough, 1988;Chough et al, 1990;Hwang and Chough, 1990;Hwang et al, 1995), is more than 1 km thick, and contains abundant fossil faunas of late Early to Middle Miocene age. Palaeontologic ages based on molluscs, foraminifers, nannofossils, and dinoXagellate cysts are generally between 17 and 11 Ma (Kim, 1990;Yi and Yun, 1995;Bak et al, 1996).…”