Ages Of Terraces Research Articles

Late Quaternary slip rates across the central Tien Shan, Kyrgyzstan, central Asia

Slip rates across active faults and folds show that late Quaternary faulting is distributed across the central Tien Shan, not concentrated at its margins. Nearly every intermontane basin contains Neogene and Quaternary syntectonic strata deformed by Holocene north‐south shortening on thrust or reverse faults. In a region that spans two thirds of the north‐south width of the central Tien Shan, slip rates on eight faults in five basins range from ∼0.1 to ∼3 mm/yr. Fault slip rates are derived from faulted and folded river terraces and from trenches. Radiocarbon, optically stimulated luminescence, and thermoluminescence ages limit ages of terraces and aid in their regional correlation. Monte Carlo simulations that sample from normally distributed and discrete probability distributions for each variable in the slip rate calculations generate most likely slip rate values and 95% confidence limits. Faults in basins appear to merge at relatively shallow depths with crustal‐scale ramps that underlie mountain ranges composed of pre‐Cenozoic rocks. The sum and overall pattern of late Quaternary rates of shortening are similar to current rates of north‐south shortening measured using Global Positioning System geodesy. This similarity suggests that deformation is concentrated along major fault zones near range‐basin margins. Such faults, separated by rigid blocks, accommodate most of the shortening in the upper crust.

Numerical modeling of fluvial strath-terrace formation in response to oscillating climate

AbstractMany river systems in western North America retain a fluvial strath-terrace rec ord of discontinuous downcutting into bedrock through the Quaternary. Their importance lies in their use to interpret climatic events in the headwaters and to determine long-term incision rates. Terrace formation has been ascribed to changes in sediment supply and/or water discharge produced by late Quaternary climatic fluctuations. We use a one-dimensional channel- evolution model to explore whether temporal variations in sediment and water discharge can generate terrace sequences. The model includes sediment transport, vertical bedrock erosion limited by alluvial cover, and lateral valley-wall erosion. We set limits on our modeling by using data collected from the terraced Wind River basin. Two types of experiments were performed: constant- period sinusoidal input histories and variable-period inputs scaled by the marine δ18O rec ord. Our simulations indicate that strath-terrace formation requires input variability that produces a changing ratio of vertical to lateral erosion rates. Straths are cut when the channel floor is protected from erosion by sediment and are abandoned—and terraces formed—when incision can resume following sediment-cover thinning. High sediment supply promotes wide valley floors that are abandoned as sediment supply decreases. In contrast, wide valleys are promoted by low effective water discharge and are abandoned as discharge increases. Widening of the valley floors that become terraces occurs over many thousands of years. The transition from valley widening to downcutting and terrace creation occurs in response to subtle input changes affecting local divergence of sediment-transport capacity. Formation of terraces lags by several thousand years the input changes that cause their formation.Our results suggest that use of terrace ages to set limits on the timing of a specific event must be done with the knowledge that the system can take thousands of years to respond to a perturbation. The incision rate calculated in the field from the lowest terrace in these systems will likely be higher than the rate calculated by using older terraces, because the most recent fluvial response in the field is commonly downcutting associated with declining sediment input since the Last Glacial Maximum. This apparent increase in incision rates is observed in many river systems and should not necessarily be interpreted as a response to an increase in rock-uplift rate.

21Ne versus 10Be and 26Al exposure ages of fluvial terraces: the influence of crustal Ne in quartz

The accuracy of 21Ne surface exposure ages depends critically on the correction for a trapped Ne component. Commonly, the amount of cosmogenic Ne used to calculate 21Ne exposure ages is considered to be the Ne excess relative to a trapped component of atmospheric composition ( 21Ne/ 20Ne=0.00296). Here, we document a trapped Ne component in quartz samples from a series of river terraces at the northern margin of Tibet [Hetzel et al., Nature 417 (2002) 428–432], which has a non-atmospheric 21Ne/ 20Ne ratio varying from 0.00299 to 0.00398. Vacuum crushing of amalgamated samples, each derived from 30–80 quartz clasts, revealed that the non-atmospheric trapped component is present in fluid inclusions. It has probably been incorporated into the quartz crystals during their growth in veins at low-grade metamorphic conditions. Only if the amount of cosmogenic 21Ne is determined relative to this trapped component are the calculated 21Ne exposure ages consistent with the relative ages of the tectonically induced terraces and in agreement with independent 10Be and 26Al exposure ages of the fluvial terraces. A significant in situ production of nucleogenic 21Ne by the reaction 18O(α,n) 21Ne in the Paleozoic quartz minerals is ruled out by extremely low U contents of the order of 1–5 ppb. All ages have been corrected for an inherited cosmogenic component that results from cosmic ray exposure during erosion of the host rock and transport of the clasts to the terraces. The origin of the trapped component from crustal fluids is supported by high 40Ar/ 36Ar ratios of 2000–6000 and slightly elevated 136Xe/ 132Xe ratios relative to air, which can be explained by radioactive decay of 40K and spontaneous fission of U in the crust.

Holocene strath terraces, climate change, and active tectonics: The Clearwater River basin, Olympic Peninsula, Washington State

Research Article| June 01, 2002 Holocene strath terraces, climate change, and active tectonics: The Clearwater River basin, Olympic Peninsula, Washington State Karl W. Wegmann; Karl W. Wegmann 1Division of Geology and Earth Resources, Washington State Department of Natural Resources, Olympia, Washington 98504, USA Search for other works by this author on: GSW Google Scholar Frank J. Pazzaglia Frank J. Pazzaglia 1Division of Geology and Earth Resources, Washington State Department of Natural Resources, Olympia, Washington 98504, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2002) 114 (6): 731–744. https://doi.org/10.1130/0016-7606(2002)114<0731:HSTCCA>2.0.CO;2 Article history received: 30 Mar 2001 rev-recd: 18 Jan 2002 accepted: 05 Feb 2002 first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Karl W. Wegmann, Frank J. Pazzaglia; Holocene strath terraces, climate change, and active tectonics: The Clearwater River basin, Olympic Peninsula, Washington State. GSA Bulletin 2002;; 114 (6): 731–744. doi: https://doi.org/10.1130/0016-7606(2002)114<0731:HSTCCA>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The ∼400 km2 Clearwater River basin, located on the Pacific flank of the actively uplifting Olympic Mountains of western Washington State, contains a well-preserved flight of Holocene fluvial terraces. We have collected a large data set of numeric ages from these terraces that is used to elucidate the geomorphic, fluvial, active tectonic, and climatic processes that operate at Holocene spatial and temporal scales. Detailed field mapping reveals three prominent Holocene straths and their overlying terrace deposits. Terrace ages fall into three broad ranges: ca. 9000–11 000 yr B.P. (Qt4), 4000–8000 yr B.P. (Qt5), and 0–3000 yr B.P. (Qt6). Terrace deposit stratigraphy, sedimentology, and age distributions allow us to consider two alternative models for their genesis. The favored model states that the terrace ages are coincident with lateral incision of the Clearwater channel, emplacement of the terrace alluvium, and the carving of the straths. Vertical incision of the Clearwater channel was primarily relegated to the brief (∼1000 yr) intervals when we have no record of terraces. Alternatively, the straths were carved as the channel incised vertically during the brief time periods between dated terrace deposits, and the terrace ages record a subsequent long time of alluviation atop the straths and concomitant termination of vertical incision. In both models, we envision a Clearwater River channel at or near capacity with a temporally variable rate of both lateral and vertical incision. Small deviations from this at-capacity condition are driven by variations in the liberation and delivery of hillslope sediment to the channel. We consider several causes for variable hillslope sediment flux in this tectonically active setting including Holocene climate change and ground accelerations related to earthquakes. Holocene rates of vertical incision are reconstructed along nearly the entire Clearwater Valley from the wide distribution of dated terraces. Incision rates clearly increase upstream, mimicking a pattern documented for Pleistocene terraces in the same basin; however, the rates are 2–3 times those determined for the Pleistocene terraces. The faster Holocene incision rates may be interpreted in terms of an increase in the rates of rock uplift. However, we favor an alternative explanation in which the Holocene rates represent a channel rapidly reacquiring its stable, graded concavity following protracted periods of time in the Pleistocene when it could not accomplish any vertical incision into tectonically uplifted bedrock because the channel was raised above the bedrock valley bottom by climatically induced alluviation. These results illustrate how, even in tectonically active settings, representative rates of rock uplift inferred from studies of river incision should be integrated over at least one glacial-interglacial cycle. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Dated speleothem evidence for uplift rates and terrace ages on the Tasmanian south coast

Seaward-facing terraces along the south-western coastline of Tasmania are suggestive of late Cainozoic uplift. Dating of speleothems from two caves at New River Lagoon on the south coast appears to constrain coastal uplift since the Last Interglacial to less than 10m and possibly less than 4 m. Caves and terraces at 70-80 m are unlikely to be less than 600 ka old and are probably much older.

A Fluvial Record of Long-term Steady-state Uplift and Erosion Across the Cascadia Forearc High, Western Washington State

Six late Quaternary river terraces, preserved along the Clearwater River in northwestern Washington State, provide a ∼140 ka record of long-term incision and uplift across the western side of the Cascadia forearc high. Terrace ages are constrained by weathering rind and radiocarbon dating and by correlation to dated coastal glacio-fluvial deposits and the global eustatic curve. The terraces overlie flat bedrock surfaces, called straths, which represent uplifted segments of the river channel. Bedrock incision is measured by the height of a strath relative to the adjacent modern river channel. The straths along the Clearwater show an upstream increase in bedrock incision, ranging from ∼0 at the coast to a maximum of 110 m in the headwaters. The incision at any point along the profile increases systematically with strath age. The calculated incision rates range from ∼10 ky) the Clearwater River valley has maintained a steady-state profile defined by a long-term balance in the rates of incision and rock uplift. Upstream divergence of terraces is best explained by an increase in the rate of rock uplift from the coast toward the central part of the range. These results are consistent with other evidence indicating a long-term steady-state balance between the accretionary influx and the erosional outflux for this part of the Cascadia subduction wedge since ∼14 Ma. These results help show how terrace deposits form in tectonically active landscapes. The dominantly fluvial Clearwater drainage was forming straths while alpine glaciers were advancing in adjacent drainages. In turn, the straths were buried during the transition to interglacial times because of increased sediment supply due to local deglaciation and because of eustatic highstands that forced aggradation in the lower reach of the drainage and across the continental shelf as well. The fluvial system shows strong forcing by the glacial climate cycle. Even so, the river appears to have returned to the same valley profile during each cycle of strath cutting. Thus, bedrock incision is clearly unsteady at time scales shorter than the glacial climate cycle (∼100 Ky) but appears to be relatively steady when averaged over longer time scales. A simple kinematic model is used to examine how uplift of the Cl. Our analysis indicates that the accretionary flux into the wedge occurs mainly by frontal accretion and not by underplating. If accretion occurred entirely at the front of the wedge, the present west coast should be moving to the northeast at ∼3 m/ky, relative to a fixed Puget Sound. This prediction is in good agreement with offset of a ∼122 ka sea cliff preserved at the southwest side of the Clearwater valley profile. In this case, the long-term margin-perpendicular shortening would account for 20 to 35 percent of the geodetically-measured northeast-southwest shortening across the Olympic Mountains.

The impact of episodic fault‐related folding on late Holocene degradation terraces along Waipara River, New Zealand

The Waipara River flows eastwards through growing folds in the tectonically active foothills of New Zealand's Southern Alps. In the middle Waipara region, flights of degradation terraces are widespread and rise to 55 m above river channels. Ages of terrace surfaces and paleoearthquakes on four faults are constrained by radiocarbon samples and weathering‐rind dates from surface cobbles of Torl esse Group sandstone. Terrace ages indicate rapid incision (c. 30–100 mm/yr) of Waipara River and three tributaries during the late Holocene. Cumulative‐incision curves suggest a 15–25 m lowering of regional base level over the last thousand years and an additional 20–25 m of local incision 200–600 yr BP along Waipara River where it crosses Doctors Anticline. Rapid river incision was strongly influenced by rock uplift on the anticline associated with fault rupture during an earthquake 300–400 yr BP. From incision data we infer that the earthquake was preceded and followed by aseismic fold growth. Tectonic uplift during folding was probably, at most, one‐third of local river incision; this discrepancy may relate to the short sample period and to locally elevated stream erosive power due in part to a reduction in floodplain width.

Use of a new 10Be and 26Al inventory method to date marine terraces, Santa Cruz, California, USA

Marine terraces along active continental margins reflect the interplay between sea-level oscillations and rock uplift. Well-dated marine terraces record the timing of sea-level highstands and delimit both uplift and geomorphic rates. Cosmogenic radionuclides provide a new tool for dating previously undatable terraces. Because the five marine terraces north of Santa Cruz, California, are capped by well-developed soils formed in regressive marine sands, both predepositional cosmogenic radionuclide inheritance and bioturbation of the profile must be accounted for. We present a new cosmogenic radionuclide inventory method that uses the depth-integrated cosmogenic radionuclide concentration to determine the terrace age. This method yields terrace ages that correlate well with sea-level highstands of marine oxygen isotope stages 3, 5a, 5c, 5e, and 7. The implied uplift rate is steady at 1.1 mm/yr, and is two to three times higher than rates suggested by earlier studies.

PRIME lab AMS performance, upgrades and research applications

The Purdue Rare Isotope Measurement Laboratory (PRIME Lab) is a dedicated research and service facility for AMS that provides the scientific community with timely, reliable and high quality chemical processing (∼600 samples/year) and AMS measurements (∼3000 samples/year) of 10Be, 14C, 26Al, 36Cl, 41Ca and 129I. The AMS system is based on an upgraded FN (7 MV) tandem accelerator that has recently been modified to improve performance. The precision is 1% for 14C and it is 3–5% for the other nuclides for radioisotope/stable isotope ratios at the 10 −12 levels. System background for 10Be, 14C, 26Al, 36Cl and 41Ca is 1–10×10 −15 while for 129I the natural abundance limits it to 20×10 −15. Research is being carried out in Earth, planetary, and biomedical sciences. Geoscience applications include determination of exposure ages of glacial moraines, volcanic eruptions, river terraces, and fault scarps. Burial histories of sand are being determined to decipher the timing of human expansion and climatic history. Environmental applications are tracing the release of radioactivity from nuclear fuel reprocessing plants, water tracing, and neutron dosimetry. The applications using meteoric nuclides are oil field brines, sediment subduction, radiocarbon dating, and groundwater 36Cl mapping. Radionuclide concentrations are also determined in meteorites and tektites for deciphering space and terrestrial exposure histories.

Geometry and rate of faulting in the North Baikal Rift, Siberia

We present a detailed morphotectonic analysis of late Quaternary faulting in the North Baikal Rift (NBR), a region characterized by ranges and basins distributed over more than 800 km along strike in eastern Siberia. Remote sensing techniques (SPOT, METEOR scenes, and aerial photographs) are used to map the active fault network which displays a general en échelon distribution from the northern Lake Baikal to the easternmost basin, with ∼30‐km‐spaced overstepping segments of 10–80 km in length. Most faults have a dominant dip‐slip component over their Cenozoic history. The inherited crustal fabric strongly influences the overall geometry of the rifted basins. We use 54 14C ages of postglacial terraces near the foot scarps of the Muya basin to date offsets measured inside alluvial fans. The last main postglacial event in this area appears to be the early Holocene optimum dated at ∼10 ± 2 ka, following the onset of deglaciation at ∼13 ka. Using these time constraints, a detailed leveling across two terraces offset by the Taksimo fault (West Muya basin) shows consistent minimum vertical slip rates of 1.6±0.6 mm yr−1. Using 30 other active scarps analyzed in the field, we find a lower bound for horizontal velocity of 3.2±0.5 mm yr−1 across the NBR, a rate close to the one found in the southern rift from Global Positioning System measurements. We then compare directions of slip vectors from Holocene field data and slip directions from earthquake fault plane solutions: although local discrepancies appear, the mean directions of lesser horizontal stress (σ3) inverted from theses values are ∼N130°E and ∼N155°E, respectively, which are comparable within uncertainties and favor a rifting obliquity of ∼30°–40°. Extrapolating our Holocene rates, we estimate basin ages younger than those generally believed (less than 7 Ma) and propose a spatial and temporal evolution of rifted basins consistent with experimental models of oblique rifting. Total amounts of extension and vertical throw (∼7 and ∼12 km, respectively) across major faults appear rather constant from the central to the northern rift. These results favor a progressive development of asymmetric grabens in a rift zone that widens with times and they indicate a strong rheological control on deformation which seems enhanced by other contributions than the far‐field effects of the Indo‐Eurasian collision.

Growth folding and active thrusting in the Montello region, Veneto, northern Italy

The Montello is an elongated hill about 15 km long and 5 km wide located south of the Venetian Alps front and ∼100 km southwest of Gemona, site of the destructive Ms ∼6, 1976 earthquake sequence. Mio‐Pliocene strata in the core of the hill are folded. Seven Quaternary terraces across the western termination of the anticline have also been folded and uplifted. The terraces flank the abandoned Biadene valley, a former course of the Piave river which now flows eastwards along the north side of the hill. Topographic profiles along and transverse to the valley and terraces are used to measure the progressive development of the anticline. Fossil remains and archaeological sites dated with 14C suggest that the Biadene paleovalley was abandoned between 14 and 8 ka (11±3 ka). The successive terraces appear to have been emplaced at the onset of interglacials and interstadials, since about 350 ka. The best fitting terrace ages suggest vertical uplift rates of about 0.5 mm/yr before 172 ka and of about 1 mm/yr after 121 ka. The Montello thus appears to be a growing ramp anticline on top of an active, north dipping thrust that has migrated south of the mountain into the foreland. Modeling the deformation of the terraces as a result of motion on such a thrust ramp requires that it propagated both south and upwards with time but with a constant slip rate (1.8–2 mm/yr). For at least 300 kyr the lateral growth of the anticline kept pushing the course of the Piave river southwestwards, at a rate at first of 10 mm/yr, and then 20 mm/yr. Though the growth rate doubled more than 120 kyr ago, the anticline kept a constant height/length growth ratio (≃20) implying self‐similar depth/length growth of the thrust underneath. The clustering of historical earthquakes north of Treviso suggests that the thrust responsible for ongoing folding of the Montello slipped seismically three times (778, 1268, 1859 A.D.; intensity I ≥ VIII) in the last 2000 years, with events of maximum magnitude close to 6 and with average recurrence time between 500 and 1000 years. NW shortening on NE‐SW trending thrusts along the Venetian Alps front is compatible with the direction of convergence between Africa and Europe but does not suffice to absorb this convergence.

APPLICATION OF 40Ar/39Ar AND 230Th DATING METHODS TO THE CHRONOSTRATIGRAPHY OF QUATERNARY BASALTIC VOLCANIC AREAS: THE USTICA ISLAND CASE HISTORY

Abstract The island of Ustica has been the site of coeval volcanism and transgressive–regressive marine cycles. The volcanic history can be subdivided into five periods of activity according to stratigraphical and compositional data. Basaltic magmas were extruded during most of these periods and only one period was characterized by the emplacement of trachytic rocks. Sea level high-stands generated five orders of marine terraces with related level surfaces at variable elevation and sedimentary deposits. A geochronological study was carried out by means of 40 Ar/ 39 Ar and 230 Th dating methods on magmatic and marine sedimentary rocks, respectively. The results obtained allow us to give temporal constraints for the geological history of the island. Volcanism took place between about 750 and 130 ka BP. Until about 500 ka BP, Ustica was a seamount with subaqueous eruptions. The sole trachytic explosive eruption occurred about 424 ka BP, after a long period of rest during which the conditions for formation and evolution of a shallow magma chamber were established. The ages of the marine terraces are in very good agreement with those obtained for correlatable level surfaces along the coasts of the southern Tyrrhenian sea. The I-order marine terrace (80–120 m a.s.l.) was created about 350 ka BP, while the III-order terrace (20–30 m a.s.l.), which is the youngest dated, formed around 130 ka BP. According to geomorphological constraints, the IV-(10 m a.s.l.) and V-order terraces (5 m a.s.l.) are correlated with level surfaces dated at 105 and 80 ka BP.

Unspiked K–Ar dating of Pleistocene tholeiitic basalts from the deep core SOH-4, Kilauea, Hawaii

Tholeiitic subaerial lava flows from Kilauea (SOH-4 deep core) were successfully dated by unspiked K–Ar with 40Ar * contents as low as ≈0.1%. Ages between 436 and 42 ka were found on lavas between the depths of 1650 and 468 m. All subaerial ages are consistent with their stratigraphic position and allow us to derive a lava accumulation rate of 3.07±0.44 mm/a, which is within the range of rates determined in high 40Ar * OIBs. Age determinations on dike samples yield ages that are younger than those of the enclosing lavas. The validity of the ages was cross-checked with U-series ages of coral terraces on the northwest flank of Hawaii as determined by Ludwig et al. (1991). Dating problems seem to be restricted to a submarine pillow lava sample from level 1808 m, which gives an apparent age of ≈1 Ma, which is an overestimate with respect both to rate of construction of Kilauea and the Hawaiian plume history.

Late Quaternary paleolandslides on the coral terraces of Huon Peninsula, Papua New Guinea

Many landslides disrupt the coral terraces at northeast Huon Peninsula, Papua New Guinea. Each landslide is younger than the youngest terrace which it intersects and is older than the oldest coral reef or shoreline that overlies it. The ages of the raised coral reefs and terraces were established by previous studies using radiocarbon and uranium-series dating. The times of occurrence of 26 late Quaternary landslides are reported here; 7 are based on new radiocarbon dates from in situ corals or molluscs associated with landslide deposits, and the remainder are based on terrace ages that were established previously. The landslides include slumps, block slides and block flows which mostly involve failure of coral limestones of the terraces, and debris flows which originate from large landslides that cut through the coral limestones into underlying fan-delta and tuffaceous sedimentary rocks. The proportion of terrace area affected by Late Quaternary landslides ranges from < 1% to > 50% per km2 and depends on average gradient of the landsurface, tectonic uplift rate, and the thickness and geometry of the raised reefs and terraces. Clusters of landslides, which occurred at about 800–1250 and 6300–7800 yr BP, may have been triggered by large earthquakes which also caused metre-scale coseismic uplift. However, we did not identify landslides that could have been associated with every large coseimic uplift that has been documented in this region.

Quaternary soil chronosequences on terraces of the Susquehanna river, Pennsylvania

Susquehanna River terraces are used to establish time lines along a 150 km reach of the river, from the Lower Piedmont to the edge of the Appalachian Plateau. This is achieved by generating soil chronosequences at two locations — Marietta, PA, in the Lower Piedmont, and Muncy, PA, near the glacial border on the boundary between the Valley and Ridge province and the Appalachian Plateau. These sites preserve the most complete record of fluvial incision on the Susquehanna River with flights of seven Quaternary terraces ranging in elevation from 3 m to 51 m above the modern river. Soil characteristics used to develop the soil chronosequences include complexity of horizonization, thickness of B horizon, clay content of B horizon, soil color, CBD extractable Fe, Al, and Mn, total extractable Fe, and clay mineralogy. Terrace age constraints are based on soil development, correlation to regional glacial stratigraphy, correlation to dated fluvial and glaciofluvial deposits, and by paleomagnetic analysis of sediments. Terrace ages at the Muncy site range from modern (< 150 ybp) to Middle Middle through Early Middle Pleistocene (∼ 300 ka to ∼ 770 ka). Marietta has terrace ages ranging from modern (< 150 ybp) to Early Pleistocene through Late Pliocene (∼ 770 ka to ∼ 2400 ka).

Die glazifluvialen Sedimente im unteren Günztal (Bayerisch Schwaben/ Deutschland) nach morpho- und pedostratigraphischen Befunden sowie TL-Daten

Abstract. Until now in the lower valley of the river "Günz" the glaciofluvial gravel deposits were interpreted as an accumulation of the same glaciation (Riss). But the result of the stratigraphic investigation of loess cover sediments and glaciofluvial gravel layers - in connection with TL (Thermoluminescence)-datings - show that a mindelian gravel body lies beside the gravel deposits of the rissian upper high-terrace. The comparison of both subfaces of the gravel layers demonstrate that the older mindelian gravel deposits can be found on a higher level. Moreover, it is possible to connect the subface of the mindelian gravel with the subface of the "Grönenbach-Schwaighausener" gravel (it is the mindelian gravel of A. PENCK'S classical subdivision of the Ice Age with four glaciations in the area of Memmingen) in the south of the "Iller-Lech”-region. Furthermore, the stratigraphie division of the aeolian cover sediments at the localities of "Autenried" and "Günzburg" indicates the different ages of both gravel terraces (rissian and mindelian age). In that case the development of both gravel terraces do not belong to the same glaciation; they represent the main gravel deposits of two different glaciation periods.

パプアニューギニア北東部のサンゴ礁段丘の総合研究 パプアニューギニア，ヒュオン半島の更新世後期サンゴ礁段丘に関するαスペクトル｀２３０´Ｔｈ／｀２３４´Ｕ年代の再評価

Total number of fifty-four Pleistocene corals collected during the 1988 and 1992 international expeditions, were dated by the α-spectrometric 230Th/234U method, and the similar dates reported previously were critically reevaluated after the five-step screening by the following criteria : (1) The sample has no evidence of recrystallization of coral skeleton and/or cementation with the secondary calcite or aragonite ; (2) Skeletal textures have not changed through their diagenetic history ; (3) The sample should be free of the initial 230Th ; (4) The uranium concentration should be the same (2 to 4 ppm) as those in the present-day counterparts ; and (5) The initial 234U/238U activity ratio should be consistent with that in the present sea water, 1.144±0.002 (Chen et al., 1986). Most of the α-spectrometric dates evaluated to be fully reliable, were consistent with the TIMS (thermal ionization mass-spectrometer) 230Th/234U date of the same sample.One of the most salient observations is that many corals occurring in the Pleistocene terraces of Huon Peninsula have not necessarily preserved the closed system for uranium isotopes, even though they are composed of 100% aragonite without any textural alteration of original skeleton. For the reason, only half of α-spectrometric 230Th/234U dates were proven to be reliable in this study.On the basis of the precise α-spectrometric 230Th/234U dating, ages of terraces correlated with oxygen isotope stage 3 (Shackleton and Opdyke, 1973) become a little older than the former assignment (e.g., Bloom et al., 1974). Terrace IV of Chappell (1974) was assigned to ca. 73 ka ; and Terrace IIIa, IIIa middle, IIIIa lower, IIIb, IIIc lower, to ca. 52 ka, ca. 51 ka, ca. 46 ka, ca. 45 ka, ca. 44 ka, respectively. Ages of Terrace II b (ca. 38 ka) and II c (ca. 33 ka) are newly revised to ca. 41 ka of Terrace II a. Such increase of the age-values for Terraces II to IV works to lower the paleo sealevel estimated by Chappell and Shackleton (1986) to that from the oxygen isotopic records (Shackleton, 1987). Three α-spectrometric and one TIMS 230Th/234U dates corresponding to the last interglacial maximum were obtained from the basal part of coral limestone beneath Terrace VIb. This observation indicates decidedly that lower Pleistocene terraces such as Terraces VI to N are underlain by the limestone formed during the isotope stage 5e.

パプアニューギニア北東部のサンゴ礁段丘の総合研究 パプアニューギニア，ヒュオン半島の古崩壊地の年代・分布・形成過程に関する研究

Landsides occur widely on the coral terraces of the tectonically active Huon Peninsula, Papua New Guinea. Large historic earthquakes in Papua New Guinea have frequently triggered large landslides. Landslide that disrupt the coral terraces at Huon Peninsula have a variety of forms including ; 1) large translational block slide features that carry essentially intact coral terrace remnants along, without large debris flows ; 2) complex slides that may begin as rockslide or deep-seated rotational slide features that continue downslope as debris flow features. In addition, small rockfall and rockslide features that commonly occur on steep valley walls and headwall (type III). Large scale landslides of types I and II occur more frequently in the southeast of the study area where uplift rate is high, up to 3.5 m/ka.Approximate ages of 26 large, late Quaternary landslides of types I and II have been obtained by radiocarbon dating of corals from immediately above or below the debris flow units that have extended and across the Holocene reef sequence, or by U-series ages of older coral terraces that have been disrupted by landslides or where terrace have developed on older landslide debris. The youngest debris flow (type I) directly overlies a coseismically uplifted terrace dated at ca. 1, 250 yr BP. At three sites, at least, an older debris flow is intercalated with reef material that was forming during a late stage of the post-glacial transgression about 7-8 ka. More than 10 large blockslides without debris flow (type I) disrupt ca. 33 ka terrace, but these are trimmed at outer edge by the ca. 6.5 ka Holocene terrace, thus providing bracketing ages.Historic precedent of large landslides generated by major earthquakes, and the close association of debris flow deposits with coseismically uplifted terraces of Holocene age lead us to propose that many, and perhaps most, o f the large scale landslides on Huon Peninsula are earthquakegenerated.

Climatic, eustatic, and tectonic controls on Quaternary deposits and landforms, Red Sea Coast, Egypt

The degree to which local climatic variations, eustatic sea level fluctuations, and tectonic uplift have influenced the development of Quaternary marine and fluvial landforms and deposits along the Red Sea coast, Eastern Desert, Egypt was investigated using a combination of remote sensing and field data, age determinations of corals, and numerical simulations. False color composites generated from Landsat Thematic Mapper and SPOT image data, digital elevation models derived from steieophotogrammetric analysis of SPOT data, and field observations document that a ∼10‐km‐wide swath inland from the coast is covered in many places with coalescing alluvial fans of Quaternary age. Wadis cutting through the fans exhibit several pairs of fluvial terraces, and wadi walls expose alluvium interbedded with coralline limestone deposits. Further, three distinct coral terraces are evident along the coastline. Climatic, eustatic, and tectonic uplift controls on the overall system were simulated using a cellular automata algorithm with the following characteristics: (1) uplift as a function of position and time, as defined by the elevations and ages of corals; (2) climatic variations driven by insolation changes associated with Milankovitch cycles; (3) sea level fluctuations based on U/Tb ages of coral terraces and eustatic data; and (4) parameterized fluvial erosion and deposition. Results imply that the fans and coralline limestones were generated in a setting in which the tectonic uplift rate decreased over the Quaternary to negligible values at present. Coralline limestones formed during eustatic highstands when alluvium was trapped upstream and wadis filled with debris. During lowstands, wadis cut into sedimentary deposits; coupled with continuing uplift, fans were dissected, leaving remnant surfaces, and wadirelated terraces were generated by down cutting. Only landforms from the past three to four eustatic sea level cycles (i.e., ∼300 to 400 kyr) are likely to have survived erosion and deposition associated with fluvial processes.

Active Fault Topography and Trench Survey in the Central Part of the Yangsan Fault, Southeast Korea

Many distinct lineaments have been recognized by Landsat images in Korean Peninsula. The Yangsan fault system situated in the southeastern part of Korea is especially linear, continuously traceable for a long distance (about 200km), and particularly remarkable among these lineaments. The topographic expression of the Yangsan fault system is derived from the straightly stretching fault valley with wide shattered zones in the direction of NNE-SSW. This fault system extends for about 200km from the mouth of the Nagdong River west of Busan in the south to Yeondong in the north, and geologically separates Korean Peninsula from the Japan Sea. The amount of horizontal displacement may reach 30km. It is recognized as one of the most important faults in Korean Peninsula.From the interpretations of aerial photographs, and field surveys along the central part of the Yangsan fault system, the main results are summarized as follows:1. The Yangsan fault system has repeatedly moved in the late Quaternary. The lower to higher river terrace surfaces on this system show cumulative vertical offsets.2. The vertical component is upthrown on the east side from considering the terrace offset and the distribution of the mountainous lands. This vertical movement is reverse to the topographical situation on the meso-scale.3. The fault trace is extremely straight. The fault plane is almost vertical. The shatteredzone exceeds tens of meters in width with a remarkable fault gouge.4. The longer axis of flat clasts within the gravel observed in excavated the exploratory trench showed the re-arrangement along the fault. The predominantly right-lateral movements were recognized as the elongation of clayey parts and breccias in the fault gouge.5. From these characteristics, the Yangsan fault was clarified to be active with predominantly right-lateral movement. Estimated ages of terraces and its deposits give average rates of vertical and right slip on the Yangsan fault system at about 0.02-0.03mm/y, and at least 0.05-0.1mm/y, respectively.6. The fault topography is not found on the lower and lowest terraces. As the surface of the terrace has widely been cultivated as paddy fields for long historical time, lower fault scarplets less than a few meters high might have been modified or destroyed by the human actions. Therefore, we cannot mention the existence of the younger movement on the lower and lowest terraces.