Primary versus secondary and subaerial versus submarine hydrovolcanic deposits in the subsurface of Jeju Island, Korea

Abstract

Jeju Island is a Quaternary shield volcano built upon the Yellow Sea continental shelf off the Korean Peninsula. Decades of borehole drilling reveals that the shield-forming lavas of the island are underlain by extensive hydrovolcanic deposits (the Seoguipo Formation), which are about 100 m thick and show diverse depositional features. This study provides criteria for distinguishing between hydrovolcanic deposits formed by primary (pyroclastic) and secondary (resedimentation) processes in subaerial and submarine settings based on the observations of several selected cores from the formation. Five facies associations are identified, including: (i) primary hydrovolcanic deposits formed by pyroclastic surges and co-surge fallouts in tuff rings (facies association PH TR ); (ii) primary hydrovolcanic deposits formed by Surtseyan fallout and related pyroclastic transport processes in tuff cones (facies association PH TC ); (iii) secondary hydrovolcanic deposits formed by debris flows, hyperconcentrated flood flows, sheet floods and rill flows in subaerial settings (facies association RH AE ); (iv) secondary hydrovolcanic deposits formed in submarine settings under the influence of waves, tides and occasional mass flows (facies association RH MAR ); and (v) non-volcaniclastic and fine-grained deposits formed in nearshore to offshore settings (facies association NV MAR ). The primary hydrovolcanic facies associations (PH TR and PH TC ) are distinguished from one another on the basis of distinct lithofacies characteristics and vertical sequence profiles. These facies differ from the secondary hydrovolcanic and non-volcaniclastic facies associations (RH AE , RH MAR and NV MAR ) because of their distinctive sedimentary structures, textures and compositions. The depositional processes and settings of some massive and crudely stratified volcaniclastic deposits, which occur in many facies associations, could not be discriminated unambiguously even with microscopic observations. Nevertheless, these facies associations could generally be distinguished because they occur typically in packets or sequences, several metres to tens of metres thick and bounded by distinct stratigraphic discontinuities, and comprise generally distinct sets of lithofacies. The overall characteristics of the Seoguipo Formation suggest that it is composed of numerous superposed phreatomagmatic volcanoes intercalated with marine or non-marine, volcaniclastic or non-volcaniclastic deposits. Widespread and continual hydrovolcanic activity, together with volcaniclastic sedimentation, is inferred to have persisted for more than a million years in Jeju Island under the influence of fluctuating Quaternary sealevels, before effusion of the shield-forming lavas. Extensive distribution of hydrovolcanic deposits in the subsurface of Jeju Island highlights that Sedimentology (2008) 55, 899-924 899 there can be significant differences in the eruption style, growth history and internal structure between shelfal shield volcanoes and oceanic island volcanoes.

“Bottomsets” of the lava−fed delta of James Ross Island Volcanic Group, Ulu Peninsula, James Ross Island, Antarctica

“…non−JRIVG or Cretaceous provenance) clasts was very low. They might be derived from local diamictite substratum and incorporated into the overriding gravity flows (Porębski and Gradziński 1990; Walker and Plint 1992; Sohn et al 2008). We found no evidences of marine reworking.…”

A Keleti-Bakony triász időszaki vulkanogén képződményeinek petrográfiai vizsgálata és képződési körülményeik értelmezése

“…Mindkét egység ben nagy elterjedés -ben jelennek meg az anisusi-kora-ladin intermediersavanyú finomszem csés vulkáni rétegek, ún. "pietra verde" képződ mények (SZABÓ & RAVASZ 1970, RAVASZ 1973, BRUSCA et al 1981, OBENHOLZNER 1991, STAMPFLI et al 1991, PÁLFY et al 2003, BUDAI 2004. A késő-ladin-korakarni korszakban a bázi sos-intermedier kőzeteket produ ká ló vulkanizmus vált ural kodóvá a Neotethys-óceán kinyí lásá -hoz kapcsolódva.…”

“…A késő-anisusi-kora-ladin során intenzív vulkaniz mus ját szó -dott le a Tethys nyugati területén. Ennek a sava nyú-intermedier vulkanizmusnak a finomszemcsés tufarétegei ("pietra verde") igen nagy területi elterjedésben ismertek a Déli-Alpok (elsősorban a Dolomitok és a Karni-Alpok) területén (többek közt BRUSCA et al 1981, OBENHOLZNER 1991, STAMPFLI et al 1991, és a Dunántúli-középhegy ségben is megtalálhatók (többek közt SZABÓ & RAVASZ 1970, RAVASZ 1973, PÁLFY et al 2003, BUDAI 2004. A ladin során tovább mélyültek a platformok közötti pelágikus medencék, amelyekben döntően kovás karboná -tokból álló, egyre kevesebb vulkáni anyagot tartalmazó rétegsorok rakódtak le (MAURER & SCHLAGER 2003).…”

“…Hasonló bélyegeket figyelt meg kis mértékben átülepített freatomagmás rétegsorokban pl. SOHN et al (2008) Koreában, Jeju szigetén. Az átalakulási termékek nem csak szemcsefajtánként megfigyelt különbözősége (intermedier szemcsék kevésbé átalakultak, míg a savanyú törmelékszemcsék erőteljesen) szintén jelezheti a különböző környezetekben, különböző időkben leülepedett, ezért különbözőképpen mállott törmelékanyag későbbi összekerülését.…”

Simulation of Pyroclastic Density Current by Lava Dome Collapse at Jeju Island Using TITAN2D

“…Korea 화성쇄설밀도류에 대한 재난을 모의하기 위하여 TITAN2D (Sheridan et al, 2005), VolcFlow (Kelfoun and Druitt, 2005;Kelfoun et al, 2008;)나 Flow3D (Sheridan et al, 2000) 등과 같은 수치모의 프로그램들이 개발되어 왔으며, 이들 중 국내에서는 백두산에서 발생 가능한 화쇄류의 모의를 위하여 TITAN2D (Yun et al, 2013;와 VolcFlow (Chang and Yun, 2015)가 사용되었다. 본 연구에서는 백두산 의 화쇄류 수치모의를 위해 Yun et al(2013Yun et al( , 2014 (Lee and Yun, 2012 (Kim and Lee, 2000;Sohn and Park, 2004;Sohn et al, 2008;Sohn and Yoon, 2010;Brenna et al, 2012aBrenna et al, , 2012b. 크게 4단계로 분류되는 제주도의 형성 과정 (Lee, 1982 …”