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Recognition of stratigraphic sequence in the northeast Asian continent: a critical essay
Sung Kwun Chough 한국지질과학협의회 2018 Geosciences Journal Vol.22 No.5
This paper discusses the equivocal nature of the refined definition of stratigraphic sequence for universal recognition. The current definition requires a couple of inferences to be drawn: diagnosis of “a full cycle of base-level change” and, in turn, evaluation of stratal lapout “systems tract”. In the initial depositional models, the inferences were made in vertically exaggerated seismic profiles of passive continental margins with condensed clinoform geometry and bounding surfaces. In ancient outcrop sections, which are devoid of the clinoforms, the inferences are practically implausible. On the other hand, the cycle change is not always in phase with the unconformity, especially with the upper unconformity affected by tectonic movements. For these reasons, a sequence is limited for universal recognition. Intercontinental correlation of stratigraphic sequence is implausible. An alternative sequence can be defined by “a basin-wide correlation of recurrent facies succession bounded at the base by distinctive lithologic discontinuity or erosion surface”. A sequence in alluvial deposits can be identified on the basis of its bounding discontinuities. The evolving definition of stratigraphic sequence signals the demise of the initial concept of sequence stratigraphy and leads to a new avenue for the recognition of stratigraphic sequence. A distinctive sequence can be recognized based on the descriptive characteristics and scale of the succession.
Origin of deep-water sediment waves in the Ulleung Interplain Gap, East Sea
Sang Hoon Lee,Jang Jun Bahk,Sung Kwun Chough 한국지질과학협의회 2003 Geosciences Journal Vol.7 No.1
A detailed analysis of Chirp (2-7 kHz) subbottomprofiles and a long (ca. 10 m) piston core reveals origin of deep-water sediment waves in the Ulleung Interplain Gap (UIG). Onthe basis of acoustic and lithologic characters, the sediments aredivided into two units: 1) upper transparent unit (UTU) and 2)lower wavy stratified unit (LWSU). The LWSU is characterized bya few regular wavy reflectors with upslope migration. Also, itgradually decreases downslope in wave height, wave asymmetryand thickness, and consists dominantly of fine-grained turbiditeswith subordinate pelagic and hemipelagic sediments. These sedi-mentary features indicate that the LWSU was most likely gener-ated by turbidity currents, rather than bottom currents. The UTU,discordant to the reflectors of the underlying LWSU, mostly com-prises muddy contourites and manganiferous contourites withrare fine-grained turbidites, reflecting intensified bottom-currentactivity and infrequent input of turbidity currents from the slopesof the Oki Bank and Dok Island. Under these conditions, a thin(3-6 m thick), elongate mound of bottom-current deposits (UTU)formed on the fine-grained turbidity current waves (LWSU).
CHEN, JITAO,CHOUGH, SUNG KWUN,CHUN, SEUNG SOO,HAN, ZUOZHEN Blackwell Publishing Ltd 2009 Sedimentology Vol.56 No.4
<P>Abstract</P><P>This paper focuses on the formative processes of limestone pseudoconglomerates in the Gushan and Chaomidian Formations (Late Cambrian) of the North China Platform, Shandong Province, China. The Gushan and Chaomidian Formations consist mainly of limestone and shale (marlstone) interlayers, wackestone to packstone, grainstone and microbialite as well as numerous limestone conglomerates. Seventy-three beds of limestone pseudoconglomerate in the Gushan and Chaomidian Formations were analysed based on clast and matrix compositions, internal fabric, sedimentary structures and bed geometry. These pseudoconglomerates are characterized by oligomictic to polymictic limestone clasts of various shapes (i.e. flat to undulatory disc, blade and sheet), marlstone and/or grainstone matrix and various internal fabrics (i.e. intact, thrusted, edgewise and disorganized), as well as transitional boundaries. Limestone pseudoconglomerates formed as a result of soft-sediment deformation of carbonate and argillaceous interlayers at a shallow burial depth. Differential early cementation of carbonate and argillaceous sediments provided the requisite conditions for the formation of pseudoconglomerates. Initial deformation (i.e. burial fragmentation, liquefaction and injection) and subsequent mobilization and disruption of fragmented clasts are two important processes for the formation of pseudoconglomerates. Burial fragmentation resulted from mechanical rupture of cohesive carbonate mud, whereas subsequent mobilization of fragmented clasts was due to the injection of fluid materials (liquefied carbonate sand and water-saturated argillaceous mud) under increased stress. Storm-wave loading was the most probable deformation mechanism, as an external triggering force. Subsequent re-orientation and rounding of clasts were probably prolonged under normal compactional stress. Eventually, disrupted clasts, along with matrix materials, were transformed into pseudoconglomerates by progressive lithification. Soft-sediment deformation is prevalent in alternate layers of limestone and mud(marl)stone and/or grainstone, regardless of their depositional environments.</P>
LEE, HYUN SUK,CHOUGH, SUNG KWUN Blackwell Publishing Ltd 2011 Sedimentology Vol.58 No.6
<P><B>Abstract</B></P><P>To understand the depositional processes and environmental changes during the initial flooding of the North China Platform, this study focuses on the Lower to Middle Cambrian Zhushadong and Mantou formations in Shandong Province, China. The succession in the Jinan and Laiwu areas comprises mixed carbonate and siliciclastic deposits composed of limestone, dolostone, stromatolite, thrombolite, purple and grey mudstone, and sandstone. A detailed sedimentary facies analysis of seven well‐exposed sections suggests that five facies associations are the result of an intercalation of carbonate and siliciclastic depositional environments, including local alluvial fans, shallowing‐upward carbonate–siliciclastic peritidal cycles, oolite dominant shoals, shoreface and lagoonal environments. These facies associations successively show a transition from an initially inundated tide‐dominated carbonate platform to a wave‐dominated shallow marine environment. In particular, the peritidal sediments were deposited during a large number of depositional cycles. These sediments consist of lime mudstone, dolomite, stromatolite and purple and grey mudstones. These shallowing‐upward cycles generally resulted from carbonate production in response to an increase of accommodation during rising sea‐level. The carbonate production was, however, interrupted by frequent siliciclastic input from the adjacent emergent archipelago. The depositional cycles thus formed under the influence of both autogenetic changes, including sediment supply from the archipelago, and allogenic control of relative sea‐level rise in the carbonate factory. A low‐relief archipelago with an active tidal regime allowed the development of tide‐dominated siliciclastic and carbonate environments on the vast platform. Siliciclastic input to these tidal environments terminated when most of the archipelago became submerged due to a rapid rise in sea‐level. This study provides insights on how a vast Cambrian carbonate platform maintained synchronous sedimentation under a tidal regime, forming distinct cycles of mixed carbonates and siliciclastics as the system kept up with rising relative sea‐level during the early stage of basin development in the North China Platform.</P>