Byong-Kwon Park

Sediments and Sedimentary Sequences on a Modern Macrotidal Flat, Inchon, Korea

ABSTRACT Enormous, unbarred tidal flats fringe the west coast of Korea. Near Inchon, where spring tides range between 8 and 9 m, the intertidal expanse is more than 4 km wide. This low-energy regime results in three broadly intergradationai modern subfacies: l) an intensely bioturbated inner flat of slightly sandy mud; 2) a wavy-bedded middle flat of clayey sandy silt; and 3) a ripple-laminated outer flat of bioturbated sandy silt to silty sand. The mid-flat region is less distinctive sedimentologically than the mixed-flat subfacies of North Sea tidal flats, and flaser and lenticular bedding are rare. Well-developed intertidal drainage networks and landward salt marshes are absent. Vibracores reveal two additional sequences underneath the modern sequence, their contacts defined by scour horizons and shell concentrations. The basal sequence is characterized by irregularly oxidized, intensely-to-totally bioturbated argillaceous sediment with scattered wavy beds and abundant in-situ plant roots. These deposits suggest a transition from a shallow subtidal or low intertidal environment to a salt marsh developed in a protected intracoastal setting. The overlying intermediate sequence also consists principally of bioturbated fine sediment with scattered wavy beds, but plant roots are absent. Stratigraphic distributions of mollusk shells and other features ally this sequence with landward parts of the modern sequence.

Glaciomarine sedimentation and its paleoclimatic implications on the Antarctic Peninsula shelf over the last 15 000 years

Abstract Analyses of sedimentological, geochemical and micropaleontological parameters from radiocarbon-dated sediment cores retrieved from the Antarctic Peninsula’s western continental shelf reveal a detailed paleoclimatic and/or paleoceanographic history over the last 15 000 radiocarbon years. Deglaciation of the outer shelf off Anvers Island commenced prior to at least 15 000 yr BP, marked by the deposition of distal glaciomarine diamicton (facies 2) beneath a floating ice shelf, and lasted for 3800 years with increasing diatom abundance and total organic carbon (TOC) over time. A return to colder conditions occurred between 12 800 and 11 600 yr BP with a drop in TOC content and diatom abundance, which is coincident with the Younger Dryas event in the North Atlantic region. At this time, an abrupt increase in percentage sea-ice taxa as well as in the ratio of (Fragilariopsis curta+Fragilariopsis cylindrus)/Thalassiosira antarctica suggests renewed ice-shelf advance. In contrast, the inner shelf was deglaciated somewhat later about 11 000 yr BP, that is, 3000 years after the outer shelf. Prior to 11 000 yr BP, deposition of proximal glaciomarine diamicton (facies 1) close to the grounding line under a floating ice shelf and/or persistent sea ice may have occurred on the inner shelf. After this date, deposition of distal glaciomarine diamicton (facies 2) followed. A climatic optimum is recognized between 6000 and 2500 yr BP, coinciding with a ‘mid-Holocene climatic optimum’ from several other Antarctic sites, e.g. the Palmer Deep. During this time, as the glacial system receded from the shelf, greatly enhanced primary productivity occurred in open marine conditions, resulting in the deposition of diatomaceous mud (facies 3) and causing post-depositional dissolution of calcareous benthic and planktonic foraminifers in sediment. Around 2500 yr BP (the onset of the Neoglacial), diatomaceous sandy mud (facies 4), characterized by a decrease in TOC and diatom abundance, reflects the formation of more extensive and seasonally persistent sea ice, as evidenced by an increase in percentage of sea-ice taxa and in the ratio of (F. curta+F. cylindrus)/T. antarctica. Our results provide evidence of climatic change on the Antarctic Peninsula’s western shelf that helps to refine the existence and timing of late Pleistocene and Holocene millennial-scale climatic events in the Southern Hemisphere.

DISTRIBUTION AND DISPERSAL PATTERN OF SUSPENDED PARTICULATE MATTER IN MAXWELL BAY AND ITS TRIBUTARY, MARIAN COVE, IN THE SOUTH SHETLAND ISLANDS, WEST ANTARCTICA

Abstract Water property casting data (SPM and CTDT) have been obtained from ice-influenced fjords, Maxwell Bay and Marian Cove, in the South Shetland Islands, Antarctica to describe the configuration of turbid meltwater plumes in detail and to elucidate the dispersal pattern of the plumes in the areas. Of the primary sediment pathways, only ice-contact processes are unique in ice-influenced fjords. The effect of glaciofluvial discharges has been overwhelmed by the influences of subglacial discharge and ice-front melting. Fluvial discharge from side-entry glaciers that commonly end on land and/or supraglacial discharge from ice surface are, however, more responsible for the overflow plumes in Maxwell Bay and Marian Cove. Subglacial meltwater discharge, which is almost always in the form of vertically rising buoyant jets, is considered rare. Active glaciofluvial and/or supraglacial input from Marian Cove causes most suspended particulate matter to be concentrated near the mid-point of Maxwell Bay. Thus, even though closer to fjord-head trunk glaciers, SPM concentration in Collins Bay is comparatively low, largely due to clean tidewater glaciers and absence of meltwater streams around Collins Bay. Strong bottom current flowing along the continental shelf off the South Shetland Islands may import and export sediment from the outside of Maxwell Bay, influencing the distribution of bottom sediment as well as benthic community.

Depositional environment of near-surface sediments, King George Basin, Bransfield Strait, Antarctica

Four sediment cores were collected to determine the depositional environments of the King George Basin northeast of Bransfield Strait, Antarctica. The cored section revealed three distinct lithofacies: laminated siliceous ooze derived from an increased paleoproductivity near the receding sea-ice edges, massive muds that resulted from hemipelagic sedimentation in open water, and graded sediments that originated from nearby local seamounts by turbidity currents. Clay mineral data of the cores indicate a decreasing importance of volcanic activity through time. Active volcanism and hydrothermal activity appear to be responsible for the enrichment of smectite near the Penguin and Bridgeman Islands.

Distribution, provenance, and dispersal pattern of clay minerals in surface sediments, Bransfield Strait, Antarctica

Clay minerals of the surface sediments of Bransfield Strait, Antarctica, exhibit distinctive geographical distributions: kaolinite has the highest concentration near the shore of the South Shetland Islands in the northern strait (20%); chlorite, near Smith Island in the northwestern strait; illite, on the continental shelf off the Antarctic Peninsula in the southern strait (80%); and smectite, close to the Penguin and Bridgeman islands in the northeastern strait (25%). This distribution pattern, combined with hydrographic and climatic data for the strait, are used to infer clay mineral provenance and dispersal patterns.

The distribution of clay minerals in recent sediments of the Korea Strait

Abstract The bottom sediments of the Korea Strait contain, on average, 50% illite, 21% kaolinite, 17% intergrade clay, 8% chlorite, and 4% smectite. The geographical distribution of the clay minerals shows an increase in illite, a decrease in kaolinite and a slight decrease in chlorite seawards. The distributional patterns of smectite and intergrade clay are irregular. The clay fractions of the sediments near the land are supplied by river-borne sediments and are mixed with sediments transported landwards from offshore. The distribution of clay minerals in the Korea Strait appears to have been influenced by the supply or/and redistribution of fine-grained sediments by the Tsushima Warm Current from the East China Sea. Kaolinite seems to be transported mainly by river runoff; and illite, chlorite and smectite might have been derived partly from the East China Sea by the Tsushima Warm Current. Intergrade clay seems to have a complex origin.

The origin of massive diamicton in Marian and Potter coves, King George Island, West Antarctica

Marine sediment cores were obtained from in front of the tidewater glaciers in Marian and Potter coves in the South Shetland Islands in the austral summer of 1998–1999. Sedimentological and geochemical data from these cores document an advance of ice tongue for the deposition of clast-supported, massive diamicton, interpreted as having been produced by ice rafting in front of glacier margin and/or releasing of clasts from basal debris zones in the sub-ice tongue setting. A C-14 chronology for a core indicates that glacial advance took place ca. 1450–1700 yrs B.P., coincident with warm, humid phase in the study area. During this period, the glacier margin was likely to advance and release diamicton clasts, inferred from a reduction in the total organic carbon content, and an increase in sand and clasts within the diamicton facies. The glacial advance probably caused enhanced ice-edge blooms near the core sites, resulting in increased abundance of sea-ice related diatoms i.e.,Fragilariopsis curta andFragilariopsis cylindrus in the diamicton. The warm and humid conditions between 1450–1700 yrs B.P. might allow the intrusion of warm circumpolar deep water within the fjords, bringing about increased abundance of warm water form, i.e.,Fragilariposis kerguelensis. On the other hands, this warming condition probably prohibited the intrusion of Weddell Ice shelf water from the fjord, as evidenced by lack of cold water form,Thalassiosira antarctica, in the diamicton. Clearly, the response of the outlet glacier system along the periphery of the South Shetland Islands Ice Sheet during the late Holocene warm, humid period (1450–1700 yrs B.P.) was expansion. Thus the process of clast-supported massive diamicton formation is likely to be applicable to a number of areas of the modern and Quaternary Antarctic Peninsula.

Petrology and Geochemistry of Dokdo Valcanic Rocks, East Sea

Petrological, geochemical, and geochronological studies of Dokdo volcanic rocks, East Sea, have been carried out to understand their petrogenesis. Dokdo volcanic activity is divided into three stages according to occurrences and eruption ages of rocks. The second-stage activity is accompanied by large volume of pyroclastics and lavas of intermediate composition, and occupies most of the East and West islets. K-Ar biotite and whole-rock ages indicate that Dokdo volcanic activity occurred during late Pliocene and became systematically younger toward later stages: namely, 2.7-2.4 Ma for the first-stage trachyte, 2.4-2.3Ma for the second-stage trachyandesite and 2.2-2.1 Ma for the last-stage trachyte and dikes. Dokdo volcanic rocks are of intermediate to felsic compostions, and have OIB-like alkaline nature. The geochemical similarities between Dokdo and Ulleungdo volcanic rocks suggest that they were formed from the same mantle plume. However, considering the difference of eruption ages between Dokdo (2.7-2.1 Ma) and Ulleungdo (1.4-0.01 Ma) volcanic rocks, the former seems to have been formed by earlier hot spot activity.

Clay mineralogy of bottom sediment in the Jinhae Bay, Korea

The bottom sediments of Jinhae Bay area contain, on average, 45 % illite, 23 % kaolinite, 17 % intergrade clay, 10 % chlorite, and 5 % smectite. The geographical distribution of the clay minerals shows, in general, an it crease in illite, a decrease in kaolinite, and a slight decrease in chlorite seawards. The distributional trends of smectite and intergrade clay are irregular. The clay fractions of the sediments of Jinhae Bay are supplied from stream-borne sediments and are mixed with sediments transported landwards from the East China Sea. Local erosion and redeposition of the clay fractions of the bottom sediments is caused by rapid tidal currents.

The geological age and paleoenvironment of the lower Seogwipo Formation, Cheju Island, Korea

The marine deposits of the lower Seogwipo Formation, Cheju Island are very important materials to reconstruct the paleoenvironment and the evolution of the island. Analysis of planktonic foraminifera from fifteen samples of the lower Seogwipo Formation indicates that its geological age is Middle Pleistocene (late N22 Zone, i.e.,Globigerina calida calida Subzone, and older than 400 Ka) based on the occurrences ofGlobigerina calida calida, Beella digitata, Globigerina bermudezi, andGloboquadrina conglomerata in the section.The ratio of planktonic to total foraminiferal fauna decreases from the lower to the upper parts in the section. At the same time, warm water speciesGlobigerinoides ruber andG. trilobus also decrease while the temperate water speciesNeogloboquadrina dutertrei, Globigerina quinqueloba increase. Quantitative analyses of both the benthic and planktonic foraminifera disclosed the changes of paleoenvironment: A warm middle shelf (or offshore) water might be dominant during the deposition of the lower part and then the paleoenvironment changed to a shallower inner shelf (or nearshore) with a temperate water in the upper part of the section. With the paleoenvironment varying from the offshore to the nearshore, the lower Seogwipo Formation recorded a sedimentary history of regression (including three sub-regressions and two subtransgressions).