Late Pleistocene-Holocene Sediments Research Articles

Establishing the Late Pleistocene–Holocene sedimentation boundary in the southern North Sea using OSL dating of shallow continental shelf sediments

This paper provides insight into the fate of Late Weichselian and Early Holocene sediments accumulated in the German sector of the southern North Sea. A combination of optically stimulated luminescence (OSL) dating and radiocarbon dating was applied to set up the chronology. Seven cores were studied to obtain ten quartz OSL samples and ten radiocarbon samples. The core locations were chosen along a southeast to northwest transect along the western side of the Elbe palaeovalley, giving a good coverage of the entire German North Sea area. All samples for OSL dating showed a significant scatter in the equivalent dose (De) distribution of quartz due to heterogeneous bleaching. The Minimum Age Model (MAM-3) was found to be the most suitable to extract true burial ages. It was inferred from the study that sedimentation did still occur during the late deglaciation period in many areas. These are mainly Late Weichselian glaciofluvial or glaciolacustrine sediments directly overlain by early Holocene fluvial and/or transgressive deposits and followed by modern marine sands. However, considerable late Weichselian erosion or a possible period of non-deposition was observed in the highland area to the northeast of the Dogger Bank and a small discontinuity in the near-shore region was noticed, probably due to early Holocene fluvial erosion. Relicts of a palaeo-river bank or terrace were identified in core 14VC to the east of the Dogger Bank. A possible interpretation of the Pleistocene–Holocene interface along the core transect is provided based on lithology and measured OSL and radiocarbon ages.

Active faults and related Late Quaternary deformation along the Northwestern Himalayan Frontal Zone, India

Numerous newly-identified traces of active faults in the Himalayan foothill zone along the HFF around Chandigarh, in Pinjore Dun, along the piedmont zone of the Lower Siwalik hill front and within the Lower Tertiary hill range reveal the pattern of thrust and strike-slip faulting, striking parallel to the principal structural trend (NNW-SSE) of the orogenic belt. The active Chandigarh Fault, Pinjore Garden Fault and Barsar thrust have vertically dislocated, warped and backtilted fluvial and alluvial-fan surfaces made up of Late Pleistocene-Holocene sediments. West- and southwest-facing fault scarplets with heights ranging from 12 to 50 m along these faults suggest continued tectonic movement through Late Pleistocene to recent times. Gentle warping and backtilting of the terraces on the hanging wall sides of the faults indicate fault-bend folding. These active faults are the manifestation of north-dipping imbricated thrust faults branching out from the major fault systems like the Main Boundary Fault (MBF) and Himalayan Frontal Fault (HFF), probably merging down northward into a decollement. The Taksal Fault, striking NNW-SSE, shows prominent right-lateral movement marked by lateral offset of streams and younger Quaternary terraces and occupies a narrow deep linear valley along the fault trace. Right stepping along this fault has resulted in formation of a small pull-apart basin. Fault scarplets facing ENE and WSW are the manifestation of dip-slip movement. This fault is an example of slip-partitioning between the strike-slip and thrust faults, suggesting ongoing oblique convergence of the Indian plate and northward migration of a tectonic sliver. Slip rate along the Taksal Fault has been calculated as 2.8 mm/yr. Preliminary trench investigation at the base of the Chandigarh Fault Scarp has revealed total displacement of 3.5 m along a low angle thrust fault with variable dip of 20° to 46° due northeast, possibly the result of one large magnitude (Mw 7) prehistoric earthquake. Taking into consideration the height of the Pinjore surface (20 to 25 m), tentative age (8.9 ± 1.9 ka), displacement during one event and average angle of fault dip (25°) gives slip rate of about 6.3 ± 2 mm/yr, a rate of horizontal shortening of 5.8 ± 1.8 mm/yr and recurrence of faulting of 555 ± 118 years along the Himalayan Frontal Fault.

Foraminifers in late Pleistocene-Holocene sediments of the Deryugin Basin of the Sea of Okhotsk

The study of foraminifers from sediments accumulated during the last 30 ky revealed their similar distribution in the central and marginal parts of the Deryugin Basin, which implies similar environmental changes throughout this morphological structure. The lack or extreme taxonomical impoverishment of the benthic foraminiferal assemblages during the Last Glacial Maximum indicates a combination of several factors: the significant deterioration of the parameters controlling their bioproductivity in response to the general cooling; the development of anoxic bottom conditions; and, probably, the unfavorable influence of cold barite-methane seeps on the geochemical parameters of the bottom waters. The weaker activity of these seeps in the central part of the basin during the Holocene is evident from some deviations in the structure of the benthic foraminiferal assemblages against the background of their general taxonomic similarity.

History of Sedimentation on the Voring Plateau (Norwegian Sea) during the Last 25 ka

Based on sedimentological, mineralogical, geochemical, and micropaleontological data on the comprehensively investigated Core ASV 1372, the late Pleistocene-Holocene sedimentation history is reconstructed for the Voring marginal plateau (continental margin of the Norwegian Sea). The age model is constructed based on the correlation with several adjacent cores, for which the AMS radiocarbon dates are available. Lithostratigraphic correlation made it possible to compare stratigraphic division of Core ASV 1372 with other cores recovered from the Voring Plateau and the shelf and continental slope off the central Norway. It is concluded that the compositional and structural features of sediments are correlated with paleoclimatic and paleoceanographic changes, variations in provenances, as well as agents and pathways of sedimentary material transport.

過去１３万年間にわたる大阪湾東部沿岸地域の層序，堆積シークエンスと堆積環境

大阪平野西部で採取された住之江コア(A～F孔)を用いて, 大阪湾東部沿岸地域の過去13万年間の層序, 堆積シークエンスおよび堆積環境の検討を行った.その結果, 以下の3項目が明確となった.(1)住之江コアは7つの堆積ユニット(Sm-1～Sm-7)に区分される.このうちSm-7～Sm-5は上町累層(中位段丘堆積層), Sm-4～Sm-2は難波累層(沖積層)に区分される.(2)住之江コアには2つの礫質網状河川システム(Sm-5およびSm-4)ならびに2つの内湾～デルタシステム(Sm-7～Sm-6およびSm-3～Sm-2)が認定される.(3)住之江コアをシークエンス層序学的に解釈するならば, 過去13万年間に3つの第5から第6オーダーの堆積シークエンス(DS1～DS3)の認定が可能である.

Preliminary Results from Paleomagnetic Records on Lake Sediments from South America

The preliminary results of paleomagnetic and radiocarbon dating of late pleistocene-holocene sediments from two lakes of south-western Argentina (41°S, 71.5°W) are presented. The magnetic susceptibility, intensity and direction of the natural remanent magnetisation were measured. The stability of the natural remanent magnetisation was investigated by alternating field demagnetisation. The magnetic parameters allowed the cores within each lake to be correlated. δ 13 C analysis, total organic content measurements and C 14 dating were carried out. A model of sedimentation is suggested. Using this model and the correlation, curves of variations of magnetic inclination and declination in time are shown.

Rock-magnetic study of Late Pleistocene-Holocene sediments from the Babícora lacustrine basin, Chihuahua, northern Mexico

Se reportan los resultados del estudio de propiedades magnéticas y sedimentología en dos perfiles de la secuencia lacustre Cuaternaria de Babícora (29.4° N, 107.7° W; 2,100 m a.s.l.), Estado de Chihuahua, México. Las variaciones de susceptibilidad magnética e intensidades de magnetización remanente natural (NRM) e isotermal (IRM) correlacionan con los contenidos relativos de arenas, arcillas y limos en los sedimentos. Estas relaciones estratigráficas sugieren que los minerales magnéticos son de origen externo y transportados al lago por procesos erosivos. Las curvas de adquisición de IRM y el espectro de coercitividad de campos alternos indican la ocurrencia de titanomagnetitas ricas en hierro, hematitas e hidróxidos de hierro. Las fluctuaciones en el aporte de sedimentos correlacionan con cambios en los procesos de erosión, clima. y tectonismo en la cuenca. Cinco fechas de radiocarbono en el rango entre 4,346 y 16,343 años A.P. permiten un control cronológico preliminar. El perfil en el sector sur cubre un periodo mayor que el perfil del sector oeste, que cubre el intervalo entre 11,000 y 6,000 años cuando el lago se extendió en la cuenca. Dos periodos mayores de incremento en la precipitación caracterizados por niveles altos del lago ocurren en el Pleistoceno Tardío y en el Holoceno Tempqmo. El periodo húmedo del Wisconsin Tardío es seguido por un periodo de aridez gradual hacia los 6,000 años A.P. Entre los 11,000 y los 8,000 años, se tiene otro periodo de incremento en la precipitación de verano. El intervalo árido entre los 3,000 y los 2,000 años es seguido por una etapa de incremento regional en la erosión.doi: Sin doi

A palaeomagnetic secular variation record from late Pleistocene-Holocene lacustrine sediments from Chalco Lake, Basin of Mexico

Palaeomagnetic secular variation is reported for the past 25,000 years from the lacustrine sequence of Chalco Lake, Basin of Mexico. The rock magnetic and palaeodirectional record is obtained from a 11.27 m core drilled in the central sector of the lake (19.25 ° N, 99 ° W). Detailed stratigraphy, pollen and diatom studies provide a reconstruction of the environmental evolution. The depth-time scale transformation is derived from nine 14C dates, which give depositional rates of 0.28 mm/year for the first 3.5 m and 0.80 mm/year between 3.5 m and 11.27 m. Spectral analysis of intensity and directional records shows low frequency components with characteristic periods of 10,500, 3200–3400, 2900–3000, 1400–1500 and 800–900 years. In phase oscillations of inclination and intensity records point to drifting non dipole field anomalies. Mean inclination anomaly is −2.4 °, which is similar to results from volcanic rocks of the Basin of Mexico and Hawaii, and which support a zonal character of the non dipole field. The palaeomagnetic vectors describe characteristic loops, with dominant clockwise sense in the intervals 2000–5600, 12,000–15,000 and 18,600–24,000 years, and dominant counterclockwise sense in the intervals from 6500 to 11,000 and 16,600–18,500 years. Clockwise vector rotation may represent westward drift of non dipole field anomalies, though westward drift may also result in counterclockwise vector motion. Major declination swings are related to environmental and depositional disturbances, and without further confirmation they cannot be considered as geomagnetic variations.

Late Pleistocene-Holocene sediments on the Spanish continental shelves: Model for very high resolution sequence stratigraphy

Sequence stratigraphy analysis of high resolution seismic profiles (Geopulse, Uniboom and 3.5 kHz) of late Pleistocene-Holocene sediments has been carried out on five sectors of the Spanish continental margin. Four types of depositional settings are distinguished in these sectors: (1) low subsident ramps (Alborán Margin-Cádiz Gulf); (2) high subsident (2m/kyr) ramps (Alicante-Valencia); (3) “Ria”-type morphology on the Atlantic passive margin (Ria de Muros); and (4) fault-scarp morphology systems with subsidence (Balearic Margin). A Type 1 sequence is interpreted in all these sectors, being composed of lowstand systems tract, transgressive systems tract and highstand systems tract. This conforms to the basic concepts of sequence stratigraphy and each systems tract correlates with a particular part of the last eustatic hemicycle. Characteristic shelf features such as terraces, terraces with beach deposits and progradational sediment wedges evidence a complex stacking of lesser sub-sequences in all the systems tracts, which must be related to very-short period sea-level stillstands and fall. We propose a very high resolution sequence stratigraphy model in which the last sea-level hemicycle is punctuated by: “P” cycles (4500 years), which give rise to the neo-glacial events; “h” cycles (2200-950 years), and “c” cycles (500-50 years). These cycles interact with each other, thus establishing the placing of the high and low sea levels. This attention to detail: (1) explains sedimentary evolution on both the shelf and upper slope during late Pleistocene-Holocene time; (2) illustrates some departures from the classical sequence stratigraphy model; and (3) also demonstrates that the late Pleistocene-Holocene eustatic curve is not one simple transgression but is modulated by three differing-period cycle groups below the Milankovitch band. Our model is delimited by fluctuating sea level during Pleistocene-Holocene times. Such features should be identifiable on any continental margin. However, localized features occur due to subsidence and continental shelf morphology which determ ine the location and depth of sedimentary bodies generated in each eustatic cycle.

Processes of Late Quaternary Turbidity Current Flow and Deposition on the Var Deep Sea Fan, Northwest Mediterranean Sea

Late Quaternary sedimentation patterns on the Var deep-sea fan are known from high-resolution seismic boomer profiles (vertical resolution 120 m, where it spilled over the eastern Var sedimentary ridge at a velocity of 2.5 ms[sup [minus]1]. Other Holocene turbidity currents (with a 103-yr recurrence interval) were muddier and thicker, but also deposited sand on middle fan-valley levees and are inferred to have had a similar slide-related origin. Late Pleistocene turbidity currents deposited on the high Var sedimentary ridge. The presence of sediment waves and the cross-flow slope inferred from levee asymmetry indicate that some flow were hundreds of meters thick, with velocities of 0.35 ms[sup [minus]1].more » Estimated times for deposition of thick levee mud beds are many days or weeks. Late Pleistocene flows therefore are interpreted to result from hyperpycnal flow of glacial outwash in the Var River. Variation in late Pleistocene-Holocene turbidite sedimentation thus is controlled more by changes in sediment supply than by sea level.« less

濃尾活断層系から発生した古地震の考察 梅原断層のトレンチ調査

The Nobi Active Fault System, one of the most active fault systems in Japan, is composed of a series of active faults extending 80 km in the NW-SE direction with en echelon arrange-ment. These faults display predominantly left-lateral displacement. In 1891, major strands within the system were ruptured during the great (M=a8.0) seismic event (the Nobi earthquake) of 1891. The magnitude of this event was extraordinarily large for normal intraplate earth-quakes.In order to clarify the long-term behavior of the fault system, the activity of each segment or strand has been examined by geological and geomorphological methods. A section of the Late Pleistocene-Holocene sediments broken by one of the segmented faults (Umehara Fault) was studied to establish the timing of faulting mainly by trench excavation The results are summarized as follows:(1) An accumulated displacement ensures that the Neodani Fault lying at the middle of whole length of the Nobi Fault System is the most active and longest strand. The Neodani Fault has ruptured at least, once every few thousand years with higher frequency than other strands.(2) The entrenchment across the Umehara Fault provided recognition of the horizons on which paleo-seismic events had taken place on the fault zone. The six events were inferred within trench logs. The ages are 1891 A. D.(Event 1), 20, 000 y. B. P.(Event 2), 28, 000 y. B. P.(Event 3) and prior to 30. 000 y. B. P.(Event 4-6). The ages of Events 2, 3 and 6 are not conclusive.(3) The recurrence intervals of the Umehara Fault between the last three events are over 10, 000 years, which are ten times longer than that of the Neodani Fault.(4) Thus, other strands in this fault system are inferred to have been dormant even when the Neodani Fault ruptured. It is likely that very large earthquake seldom occurred in association with faulting not only along the Neodani Fault but also along the other less active strand such as the Umehara Fault.(5) The 1891 Nobi earthquake was an extraordinarily large one. However, the record of the great Nobi earthquake should be used in evaluating future seismic hazards. especially in areas where long active faults are densely distributed.

Geochemistry of uranium in the late Pleistocene-Holocene sediments from the southern part of the Black Sea basin

A total of 53 cores from the southern part of the Black Sea was used to investigate the geochemical distribution of uranium in three units of late Pleistocene-Holocene sediments. Vertical and areal distribution of U, together with selective extraction studies, suggest that in the reduced sediments of units 1 and 2, deposited on the abyssal plain, U is mainly associated with organic matter. High concentrations of U (> 5 ppm) occur characteristically in sediments having > 2% organic carbon and in those deposited on abyssal plains with low sedimentation rates. High carbonate contents appear to have a dilution effect on the U concentrations in the sediments. Of the total uranium, the ionexchangeable uranium constitutes an average of ∼50%; organic uranium, tightly bound as “organo-uranium” complexes, 25%; and, the residual uranium, bound in the silicates, the remaining 25%. The relative proportions of the residual U in the clastic-rich unit- 1 sediments collected on the continental slope and in unit- 3 sediments are generally higher than 25% of the total U. Vertical distribution of U, together with the presence of mobile U - with an average of 15% of the total U - suggest that some U has been mobilized from U-rich unit 2 into the overlying unit 1 and the underlying unit 3.

Control of Clay-Mineral Stratigraphy by Selective Transport in Late Pleistocene-Holocene Sediments of Northern Cascadia Basin--Juan De Fuca Abyssal Plain: Implications for Studies of Clay-Mineral Provenance

ABSTRACT Previous investigations (Duncan and others, 1970; Stokke and Carson, 1974) of Cascadia Basin clay mineralogy indicate a general trend in which montmorillonoids (smectites, 17 A) are enriched relative to illite (10 A) and chlorite (7 A) in Holocene lutites, whereas illite and chlorite dominate in Late Pleistocene deposits. The apparent of all clay-mineral groups declines from Pleistocene to Holocene (Russell, 1967). There exist, however, numerous local exceptions to these general patterns which are not readily explained by the previous works. Fifteen samples from 5 cores in Northern Cascadia Basin and Juan de Fuca Abyssal Plain were fractionated into 6 size classes. Semi-quantitative determinations of clay mineralogy and crystallinity were made on each of the 90 subsamples. The results indicate a definite size-dependency in clay mineralogy and which is consistent both areally and temporally. Discriminant-function analysis indicates that clay mineralogy and of some individual size fractions are statistically distinct but that the stratigraphic units (Late Holocene, Early Holocene, and Late Pleistocene) are not statistically discernible. Textural variations within and between Holocene and Pleistocene parallel sediment clay-mineral changes. and mineralogy can be predicted on the basis of clay-min ral size-dependency and grain-size distribution. It is inferred that the stratigraphic textural-mineralogic variations result from selective transport and deposition and not from contrasting source areas or weathering conditions, as had previously been suggested (Duncan and others. 1970; Stokke and Carson. 1974). Future investigations of clay-mineral provenance, dispersal, or correlation, in any area, should be based upon data which has been corrected for the effects of clay-mineral size-dependency.

Differentiating Sediments from Different Sources in Gulf Basin by Grain-Shape Analysis: Example from Late Pleistocene-Holocene Sediments of Northwestern Gulf of Mexico Continental Shelf: ABSTRACT

ABSTRACT It has been shown previously that different source rocks produce quartz sand grains with unique gross shape characteristics. These gross shape characteristics cannot be altered by abrasion, and are thus an immutable record of sediment source. Therefore, sand grains in a sedimentary basin should contain in the gross shape a fingerprint of their source unaffected by the amount of reworking to which the sands have been subjected. In order to test this idea, the shapes of late Pleistocene-Holocene sands grains from two sources in the northwest Gulf of Mexico (the Rio Grande and Western Gulf Province) were analyzed with the Fourier grain shape technique. The results indicate that two gross grain shape assemblages are present in the sands of these two provinces. One assemblage is associated with a mineralogical suite typical of relatively mature coastal plain sediments, and thus probably represents the contribution of sediment from such a Coastal Plain Source Terrane. The other assemblage is associated with a relatively immature mineralogical suite more typical of sediments derived from crystalline sources, and thus probably represents the contribution from such a Source Terrane. Both assemblages are found in sands of both provinces, inasmuch as the major rivers in these provinces which act as conduits for these sediments drain both source terrane types. However, the amount of area of these terranes drained by the rivers differs between the provinces, and so the relative proportions of these assemblages in the sands of the two provinces also differ. Rio Grande Province sands contain on the average 59% of the assemblage associated with the Highland Source Terrance, while Western Gulf Province sands contain only 34% of this assemblage. Thus, it is the difference in the relative proportion of these two assemblages in the samples which can be used to identify and distinguish the sands from the two provinces. All in all, the results of this pilot project indicate that the analysis of gross grain shape can indeed differentiate sediments from different sources in the Gulf of Mexico.

Paleomagnetism of Late Pleistocene-Holocene Sediments, Gulf of Mexico: ABSTRACT

Detailed paleomagnetic studies have been made on 15 sediment cores selected along north-south lines in the eastern and western Gulf of Mexico. The piston cores were sampled at 20-cm intervals immediately upon extrusion and measurements of natural remanent magnetization (NRM) were made using a 5hZ spinner magnetometer. Excursions of the geomagnetic field are recorded at 2 levels in many cores. Extrapolation of the ZY boundary in the western Gulf indicates that the younger feature is between 13.5 and 17.5 × 103 years BP, and is consistent with the age determination of the Laschamp event. Dates are not available for the eastern Gulf cores, but the depth of the paleomagnetic feature correlates with the expected sedimentation rates. The older feature is less di tinct and further extrapolation of the ZY boundary places it between 20.0 and 24.0 × 103 years BP. This age is within the range of a geomagnetic feature that is not the Laschamp. These results show that with extreme care, paleomagnetic measurements may be used as a stratigraphic tool in the Gulf of Mexico. Several points should be considered. First, because of the high sedimentation rates, the 2 young features described herein are the only ones expected in piston cores from this region. Second, direction scatter is quite pronounced in the upper 1/2 m and lower few centimeters of several cores. Correlations at these levels are difficult. Finally, as measurement of the geomagnetic features described lasted for only a short time and did not traverse a full 180°, dense sampling is recommended to assure their definition. End_of_Article - Last_Page 1897------------