Kaoru Kashima

An earthquake history derived from stratigraphic and microfossil evidence of relative sea-level change at Coos Bay, southern coastal Oregon

Much of the uncertainty in determining the number and magnitude of past great earthquakes in the Cascadia subduction zone of western North America stems from difficulties in using estuarine stratigraphy to infer the size and rate of late Holocene relative sea-level changes. A sequence of interbedded peaty and muddy intertidal sediment beneath a small, protected tidal marsh in a narrow inlet of Coos Bay, Oregon, records ten rapid to instantaneous rises in relative sea level. Each rise is marked by a contact that records an upward transition from peaty to muddy sediment. But only two contacts, dating from about 1700 and 2300 yr ago, show the site-wide extent and abrupt changes in lithology and foraminiferal and diatom assemblages that can be used to infer at least half a meter of sudden coseismic subsidence. Although the characteristics of a third, gradual contact do not differ from those of some contacts produced by nonseismic processes, regional correlation with other similar sequences and high-precision 14 C dating suggest that the third contact records a great plate-boundary earthquake about 300 yr ago. A fourth contact formed too slowly to have been caused by coseismic subsidence. Because lithologic and microfossil data are not sufficient to distinguish a coseismic from a nonseismic origin for the other six peat-mud contacts, we cannot determine earthquake recurrence intervals at this site. Similar uncertainties in great earthquake recurrence and magnitude prevail at similar sites elsewhere in the Cascadia subduction zone, except those with sequences showing changes in fossils indicative of >1 m of sudden subsidence, sand sheets deposited by tsunamis, or liquefaction features.

Reconstruction of climatic changes during the Late Pleistocene, based on sediment records from the Konya Basin (Central Anatolia, Turkey)

Climatic changes during the last climatic cycle have been studied using three sediment cores from the Konya plain, a now dry, closed and semi-arid lacustrine basin at 1000 m altitude in central Anatolia, Turkey. The reconstruction of regional climatic characteristics and evolution is based on mineral, diatom, pollen and molluscan content of sediments. Correlations are made between cores using 14C and U-Th ages, stratigraphy and drought levels shown by changes in mineral contents. Environmental responses to local and regional climatic changes are traced by trends in authigenic carbonates, evaporites, detrital mineral content and by diatom-inferred salinity levels. Our data have shown that, during the period covering the end of the previous Glacial (Termination II) and the last Interglacial (between c. 150 and 117 ka), peat and freshwater shallow lakes expanded. From 117 to 66 ka, the plain was occupied by lakes, the salinity and existence of which varied in time and space. Specific events are marked by mineralogic and stratigraphic signals at (i) c. 101 ka and (ii) 66 ka. From 66 ka to 30 ka, desiccation of the lake is marked by a hiatus. At c. 27 ka, milder climatic conditions led to the extension of freshwater marshes and lakes in the central depressions while palaeosols developed on the emerged parts of the plain. From 25 to 20·5 ka 14C cal., the sediments of a freshwater to brackish lake are present in one core only. From 20·5 ka 14C cal. onwards, strong evaporitic conditions occurred, the lake edges being transformed into playas. Upper parts of the sequences registered other lacustrine short phases, both before the Younger Dryas and during the Holocene. Copyright

Seismic or hydrodynamic control of rapid late-holocene sea-level rises in Southern coastal Oregon, USA?

Intertidal stratigraphy has been instrumental in demonstrating the hazard posed by great earthquakes at the Cascadia subduction zone, but inferring an earthquake history from interbedded sequences of peat and mud is complicated by many factors that influence sedimentation and relative sea-level change on both tectonic and nontectonic coasts. Rapid-to-sudden rises in relative sea level marked by sharp contacts between intertidal peat and overlying mud or sand may reflect coseismic coastal subsidence and tsunami deposition or, alternatively, nonseismic hydrodynamic changes in estuaries. Reconnaissance coring at 16 sites in the marshes fringing a narrow, protected tidal inlet of Coos Bay, supplemented by diatom and 14C analyses at four sites, reveals a stratigraphic record too fragmentary and ambiguous to distinguish seismic from hydrodynamic causes for more than three of the 10 rises in relative sea-level identified. Only three sharp contacts have the wide extent and evidence of substantial (>0.5 m) submergence that distinguish them from similar contacts produced by nonseismic processes. Correlation with stratigraphic sequences at other estuaries shows that the fringing marshes suddenly subsided and were partially buried by tsunami sand during a great plate-boundary earthquake about 300 years ago. Similar contacts were produced by earthquakes about 1500–1800 years ago, and perhaps about 2400–2700 years ago. Other earthquakes with substantially less subsidence may also have occurred, but evidence is too ambiguous to reconstruct a more complete history.

Environmental and climatic changes during the last 20,000 years at Lake Tuz, central Turkey

Abstract Our study demonstrates the importance of detailed lithostratigraphic and biostratigraphic analyses of deposits of lake-side terraces and alluvial fans in attempts to identify fluctuations of climate characteristics such as precipitation and evaporation rates, and of local conditions for water balance changes in the central part of Turkey during the last 20,000 years. Lake Tuz basin, central part of the Anatolian Plateau, Turkey, had two high lake-level stages dated as about 20,000–17,000 years ago and about 13,000 years ago. At the high lake stages, water level rose more than 15 m higher than the present lake level, and the lake area spread widely to near the southern edge of the basin, as inferred by lithologic and chronological investigation of drilling cores. In the Holocene, lake level fell and the southeast part of the basin became extensive lake terraces. Alluvial fans have formed along the edge of the upland area on the terraces in the Holocene. Stratigraphy and dating of the fan deposits show the fluctuations in the depositional rates of the fans. Major formative stages of the fans are dated about 7000–5500 and 2500–2000 years BP, and several times of minor stages (probably 4300 and 3000 years BP) occurred between the two major stages. Our archaeological research shows that there are strong relationships between the distributions of archaeological sites of this area and the above geo-environmental histories.

Vertical tectonic movement in northeastern Marlborough: Stratigraphic, radiocarbon, and paleoecological data from Holocene estuaries

Abstract Height and age information from Holocene estuarine deposits along the northeastern Marlborough coast provide a database to evaluate coastal vertical tectonics. These data are related to the postglacial marine transgression and coastal geomorphic features formed since the culmination of sea‐level rise. Four tectonic domains are recognised. The Wairau domain is characterised by subsidence at rates over 4 mm/yr. About 60% of this subsidence is tectonic and may be related to Marlborough Sounds subsidence, and 40% is a result of compaction. The Vernon Fault at the south side of the lower Wairau plain separates the Wairau domain from the high‐standing Vernon domain. The Awatere Fault marks the southern boundary between the Vernon domain and the Grassmere domain, which extends from the Awatere River valley to Mussel Point. Slight uplift (c. 1 m in 6500 yr) characterises the Grassmere domain, based on data obtained from Blind River, Lake Grassmere, and, to a lesser extent, from Awatere River fluvial terr...

Fragmentary Evidence of Great-Earthquake Subsidence during Holocene Emergence, Valdivia Estuary, South Central Chile

A reconnaissance of Holocene stratigraphy beneath fringing marshes of the Valdivia estuary, where an M 9:5 earthquake caused 1-2 m of regional coseismic subsidence in 1960, shows only fragmentary evidence of prehistoric coseismic sub- sidence. In most of the 150 hand-driven cores that were examined, a distinct uncon- formity separates 0.5-1.5 m of late Holocene tidal and floodplain mud, peat, and sand from underlying middle Holocene subtidal mud and sand. At the Las Coloradas site, where stratigraphy is best preserved, two A horizons of marsh and meadow soils abruptly overlain by sand and mud probably record coseismic subsidence shortly fol- lowed by tsunamis. The amount of subsidence during the earthquakes proved difficult to reconstruct with a diatom transfer function because of differences between modern and fossil diatom assemblages. Maximum 14 C ages on macrofossils from the two A horizons at the Las Coloradas site of 1.7-1.3 ka and 2.7-1.7 ka allow correlation of the younger horizon with either of two of six 14 C-dated A horizons buried by tsunami sand or post-tsunami tidal sand 200 km to the south at Maullin, and with a lake-wide mass wasting event in Lago Puyehue, 100 km to the southeast. Tidal records of prehistoric coseismic subsidence at Valdivia are scarce because of a sea-level fall of 3-8 m over the past 6000 years, erosion of marsh and meadow soils during subsidence-induced flooding of the estuary, and largely complete land-level recovery during cycles of coseismic subsidence and postseismic uplift. Online Material: Diatom species data from the Las Coloradas site, Valdivia estuary.

The quantitative reconstruction of salinity changes using diatom assemblages in inland saline lakes in the central part of Turkey during the Late Quaternary

Abstract Climatic changes during the Late Quaternary have been studied using three sediment cores from closed and semi-arid lacustrine basins in central Anatolia, Turkey, based on diatom assemblages of sediments. The first step in using diatoms as salinity indicators is to obtain quantitative data concerning their ecological characteristics along salinity gradients. Using 51 samples of living diatoms from 38 lakes and rivers in Turkey, an abundance-weighted mean salinity was calculated for each taxon. On the basis of a strong relationship between diatom composition and salinity, the diatom-based transfer functions were defined for the salinity reconstruction, and then applied to three drill cores from Late Quaternary lacustrine sediments from Konya Basin. The oscillations of the diatom-inferred salinity of the cores generally indicate “glacial-pluvial” correlations. High salinity levels were associated with inter-glacial stages, and low sanity levels indicate glacial stages. The curves also included the phases of shorter oscillations ranging from 10,000 to 20,000 years, presumably caused by global climate changes and local environmental changes.

Holocene sediments and vertical tectonic downwarping near Wairoa, Northern Hawke's Bay, New Zealand

Abstract Depositional environments for Holocene terrestrial, estuarine, and marine sediments on the Wairoa River floodplain at Wairoa and coastal plain east of Wairoa, were determined from an analysis of stratigraphy, lithologies, and diatom assemblages obtained from auger holes and foundation and water-well drillholes. The sediments were deposited during the postglacial sea-level rise which started sometime prior to c. 9200 years ago and ended at c. 4000 years ago, when the shoreline was at least 2 km landward of the present position, and a ria-like morphology had developed at the innermost edge of the present-day coastal plain. The postglacial marine sediments usually occur slightly below the present sea level (down to -4 m a.m.s.l.) indicating net tectonic subsidence during the Holocene. Other evidence suggests that this tectonic subsidence may extend back into the middle Pleistocene.

Factors controlling typhoons and storm rain on the Korean Peninsula during the Little Ice Age

Documenting multi-decadal typhoon and storm-rain variability is useful to prevent future typhoon and flood disasters. We present the history of typhoon and storm-rain activity in East Asia inferred from multi-proxy analyses of Lagoon Hwajin-po sediments along the eastern coast of Korea. Anthropogenic effects were enhanced in Lagoon Hwajin-po since ca. AD 1900, by increasing farming in the catchment. To avoid these human-induced effects, we reconstructed the history of typhoon and storm-rain activity only for the interval AD 1400–1900. The record indicates that typhoon frequency throughout the Korean Peninsula varied in response to the state of the El Niño/Southern Oscillation. Typhoon variability was likely modulated further by the state of the East Asia summer monsoon (EASM) pattern, associated with variation in the magnitude of solar irradiance. During periods of minimum solar activity, such as the early Maunder Minimum (AD 1650–1675), typhoons struck the east China coast and Korean Peninsula more frequently because of a strengthened EASM.

Holocene paleolimnological changes of Lake Oyako-ike in the Soya Kaigan of East Antarctica

Abstract We studied Holocene paleolimnological changes as a part of studies of global change in Lake Oyako-ike in the Soya Kaigan of Lützow-Holm Bay region in East Antarctica, inferred from organic components and microscopic observation of microalgae and cyanobacteria in a sediment core (Ok4C-01, core length 135 cm), along with sedimentary facies and accelerator mass spectrometry (AMS) 14C dating. The Ok4C-01 core was composed mainly of silt and fine sand containing laminae between 135 and 65.5 cm, overlain by cyanobacterial mud between 65.5 and 0 cm. The mean sedimentation rate and crustal uplift rate were estimated to be 0.69 mm/y and 2.2 mm/y, respectively. The crustal uplift rate of Lake Oyako-ike basin is similar to those of present uplift rates but is somewhat greater than those estimated in the Lambert Glacier region, East Antarctica. The low biological production with diatoms in coastal marine environments (135–74.75 cm, ca. 2170–1300 cal BP) changes into green sulfur bacteria in stratified saline lake environments (74.75–60.95 cm, ca.1300–1100 cal BP), and then high biological production with cyanobacteria and green algae in freshwater environments (60.95–0 cm, ca.1100–220 cal BP). The ongoing retreat of glaciers and ongoing isostatic uplift during the mid-Holocene Hypsithermal (4000–2000 years ago) and thereafter are the main reasons for this isolation, whereas eustatic sea level change is believed to have played only a minor role.