Anachronistic facies in the Lower Triassic of South China and their implications to the ecosystems during the recovery time

The end-Permian mass extinction not only severely distressed the Paleozoic ecosystems but also dramatically changed the sedimentary systems, resulting in a peculiar Early Triassic ecosystem and submarine environment during the recovery time following the mass extinction. The Lower Triassic is characteristic of the wide occurrence of various distinctive sediments and related sedimentary structures, such as flatpebble conglomerates, vermicular limestone, subtidal wrinkle structures, microbialite, carbonate seafloor fans, thin-bedded limestone and zebra limestone-mudstone. These sediments were common in the Precambrian to Early Ordovician marine settings, and then they occurred only in some extreme and unusual environments with the expansion of metazoan faunas. However, the Early Triassic witnessed an "anachronistic" reappearance of some distinctive sedimentary records in normal shallow marine settings. The study of these anachronistic facies should be of great importance for the understanding of the unique ecosystem and marine environment through the great Paleozoic-Mesozoic transition. The anachronistic facies characterized by vermicular limestone have been documented in many localities in South China and occur at various horizons of the Lower Triassic. Most types of re- ported distinctive sediments over the world have been observed in the Lower Triassic of South China. This provides an excellent opportunity for understanding the Early Triassic environment and its co- evolution with the biotic recovery. Among the anachronistic facies the vermicular limestone is the most characteristic and common distinctive sediments in the Lower Triassic of South China but has received relatively few investigations. Taking it as a case study, we will detail the variation of vermicular limestone and its stratigraphic distribution in the Three Gorges area, Hubei Province. The investigation on the vermicular limestone and other distinctive sediments from the Lower Triassic of South China further indicates that the appearance of anachronistic facies immediately following the mass extinction and the elimination from normal shallow marine facies with the radiation of Mesozoic marine faunas imply the natural response of the sedimentary systems and ecosystems to the great Paleozoic-Mesozoic transitional events and their induced harsh environments. Therefore, the ups and downs of the anachronistic facies may act as a proxy for the evolution of ecosystems independent of fossil analyses.     

A magnetic polarity time scale for the Early Cretaceous and Late Jurassic

The ages of polarity chrons in previous M-sequence magnetic polarity time scales were interpolated using basal sediment ages in suitably drilled DSDP holes. This method is subject to several sources of error, including often large paleontological age ranges. Magnetostratigraphic results have now tied the Early Cretaceous and Late Jurassic paleontological stage boundaries to the M-sequence of magnetic polarity. The numeric ages of most of these boundaries are inadequately known and some have been determined largely by intuition. An examination of relevant data suggests that 114 Ma, 136 Ma and 146 Ma are optimum estimates for the ages of the Aptian/Barremian, Cretaceous/Jurassic and Kimmeridgian/Oxfordian stage boundaries, respectively. Each of these boundaries has a good correlation to the M-sequence of magnetic reversals. The magnetostratigraphic tie-level ages are linearly related to the spreading distance and have been used to calculate a new magnetic polarity time scale for the Early Cretaceous and Late Jurassic. All stage boundaries in this time interval were correlated by magnetic stratigraphy to the proposed new time scale which was then used to estimate their numeric ages. These are, with the approximate relative errors of placement within the M-sequence:The absolute errors of these interpolated stage boundary ages depend on the accuracy of the tie-level ages.     

Refined Early to Middle Miocene diatom biochronology for the middle- to high-latitude North Pacific

Abstract   Refined numerical ages of the diatom biohorizons of the Early to Middle Miocene (11–18 Ma) period in the Neogene North Pacific are presented based on the direct correlation between biostratigraphy and magnetostratigraphy at Site 887 on the Patton–Murray Seamount in the northeastern Pacific. Sampling intervals of 0.02–0.04 my allowed the determination of the ages of the biohorizons to be more precise than previous studies. The secondary biohorizons established in the northwestern Pacific have been proven to be useful also in the northeastern Pacific, and are linked to magnetostratigraphy directly for the first time. The refined diatom biochronology established in this study will provide a vital basis for the study of the Neogene marine sediments of the middle- to high-latitude North Pacific, which rarely yield calcareous microfossils. Denticulopsis praedimorpha var. prima n. var. is described.     

Astronomical calibration of the Matuyama-Brunhes boundary: Consequences for magnetic remanence acquisition in marine carbonates and the Asian loess sequences

We have compiled 19 records from marine carbonate cores in which the Matuyama-Brunhes boundary (MBB) has been reasonably well constrained within the astronomically forced stratigraphic framework using oxygen isotopes. By correlation of the δ¹⁸O data to a timescale based on astronomical forcing, we estimate astronomical ages for each of the MBB horizons. In all but one record the MBB occurs within Stage 19.

Most magnetostratigraphic sections in Asian Loess place the MBB within a loess interval. Since loess deposition is presumed to be associated with glacial intervals, loess horizons should correspond to even-numbered oxygen isotope stages. A glacial age for the MBB is at odds with the results presented here, which firmly place the MBB within interglacial Stage 19. Inconsistency among the many loess sections and between the loess and the marine records suggests that the magnetic interpretation of loess sections may be more complicated than hitherto supposed.

The mean of the Stage 19 age estimates for the MBB is 777.9 ± 1.8 (N = 18). Inclusion of the single Stage 20 age results in a mean of 778.8 ± 2.5 (N = 19). The astronomical age estimate of the MBB compares favorably with an (unweighted) mean of 778.2 ± 3.5 (N = 10) from a compilation of ⁴⁰Ar/39^Ar results of transitional lava flows. Combining the two independent data sets yields a grand mean of 778.0 ± 1.7 (N = 28).

The new compilation shows virtually no trend in placement of the MBB within isotope Stage 19 as a function of sediment accumulation rate. We interpret this to mean that the average depth of remanence acquisition is within a few centimeters of the sediment-water interface.

Separating the cores into two geographic regions (an Indo-Pacific-Caribbean [IPC] Group and an Atlantic Group) results in a significant difference in the position of the mid-point of the reversal with respect to the astronomical time scale. The data presented here suggest a difference of several thousand years between the two regions. This observation could be caused by systematic differences between the two regions in sedimentation rate within the interval of interest, systematic differences in remanence acquisition, or by genuine differences in the timing of the directional changes between the two regions.     

Possible configurations of the magnetic field in the outer magnetosphere during geomagnetic polarity reversals

Possible configurations of the magnetic field in the outer magnetosphere during geomagnetic polarity reversals are investigated by considering the idealized problem of a magnetic multipole of order m and degree n located at the centre of a spherical cavity surrounded by a boundless perfect diamagnetic medium. In this illustrative idealization, the fixed spherical (magnetopause) boundary layer behaves as a perfectly conducting surface that shields the external diamagnetic medium from the compressed multipole magnetic field, which is therefore confined within the spherical cavity. For a general magnetic multipole of degree n, the non-radial components of magnetic induction just inside the magnetopause are increased by the factor 1 + [(n + 1)/n] relative to their corresponding values in the absence of the perfectly conducting spherical magnetopause. An exact equation is derived for the magnetic field lines of an individual zonal (m = 0), or axisymmetric, magnetic multipole of arbitrary degree n located at the centre of the magnetospheric cavity. For such a zonal magnetic multipole, there are always two neutral points and n – 1 neutral rings on the spherical magnetopause surface. The two neutral points are located at the poles of the spherical magnetopause. If n is even, one of the neutral rings is coincident with the equator; otherwise, the neutral rings are located symmetrically with respect to the equator. The actual existence of idealized higher-degree (n > 1) axisymmetric magnetospheres would necessarily imply multiple (n + 1) magnetospheric cusps and multiple (n) ring currents. Exact equations are also derived for the magnetic field lines of an individual non-axisymmetric magnetic multipole, confined by a perfectly conducting spherical magnetopause, in two special cases; namely, a symmetric sectorial multipole (m = n) and an antisymmetric sectorial multipole (m = n – 1). For both these non-axisymmetric magnetic multipoles, there exists on the spherical magnetopause surface a set of neutral points linked by a network of magnetic field lines. Novel magnetospheric processes are likely to arise from the existence of magnetic neutral lines that extend from the magnetopause to the surface of the Earth. Finally, magnetic field lines that are confined to, or perpendicular to, either special meridional planes or the equatorial plane, when the multipole is in free space, continue to be confined to, or perpendicular to, these same planes when the perfectly conducting magnetopause is present.Also Honorary Research Associate, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK and Visiting Reader in Physics. University of Sussex, Falmer, Brighton BN1 9QH, UK     

Integrated Radiolaria,benthic foraminifera and conodont biochronology of the pelagic Permian blocks/tectonic slices and geochemistry of associated volcanic rocks from the Mersin Mélange,southern Turkey: Implications for the Permian evolution of the northern Neotethys

Blocks and tectonic slices within the Mersin Mélange (southern Turkey), which are of Northern Neotethyan origin (Izmir–Ankara–Erzincan Ocean (IAE)), were studied in detail by using radiolarian, conodont, and foraminiferal assemblages on six different stratigraphic sections with well‐preserved Permian succesions. The basal part of the Permian sequence, composed of alternating chert and mudstone with basic volcanics, is assigned to the late Asselian (Early Permian) based on radiolarians. The next basaltic interval in the sequence is dated as Kungurian. The highly alkaline basic volcanics in the sequence are extremely enriched, similar to kimberlitic/lamprophyric magmas generated at continental intraplate settings. Trace element systematics suggest that these lavas were generated in a continental margin involving a metasomatized subcontinental lithospheric mantle source (SCLM). The middle part of the Permian sequences, dated by benthic foraminifera and conodont assemblages, includes detrital limestones with chert interlayers and neptunian dykes of middle Wordian to earliest Wuchiapingian age. Higher in the sequence, detrital limestones are overlain by alternating chert and mudstone with intermittent microbrecciated beds of early Wuchiapingian to middle Changhsingian (Late Permian) age based on the radiolarians. A large negative shift at the base of the Lopingian at the upper part of section is correlated to negative shifts at the Guadalupian/Lopingian boundary associated with the end‐Guadalupian mass extinction event. All these findings indicate that a continental rift system associated with a possible mantle plume existed during the late Early to Late Permian period. This event was responsible for the rupturing of the northern Gondwanan margin related to the opening of the IAE Ocean. When the deep basinal features of the Early Permian volcano‐sedimentary sequence are considered, the proto IAE oceanic crust formed possibly before the end of the Permian. This, in turn, suggests that the opening of the IAE Ocean dates back to as early as the Permian.     

Astronomical forcing in Upper Miocene continental sequences: implications for the Geomagnetic Polarity Time Scale

We present an integrated stratigraphic study of cyclically bedded distal alluvial fan to lacustrine deposits in the late Miocene continental sections of Cascante and Cañizar (Teruel basin, NE Spain). The cyclostratigraphic analysis reveals that different scales of sedimentary cyclicity are present with a thickness ratio of about 1:2:5. Spectral analysis of colour records in the depth domain indicates the presence of a significant peak at ∼2.2 m, which corresponds to the average thickness of the basic, mudstone-carbonate, cycle. Other peaks correspond to the large-scale cycle, which consists of clusters of five basic cycles, and to a cycle twice the average thickness of the basic cycle. Magnetostratigraphic results, in combination with small-mammal biostratigraphy, indicate that the three normal polarity intervals recorded in our sections correspond to C5n.2n, C5n.1n and C4Ar.2n. Assigning the ages of CK95 to the polarity reversals implies significant changes in sedimentation rate, which is not in agreement with the regularity of the sedimentary cyclicity. Thus, spectral analysis of high-resolution colour records in the time domain only produce a spectrum that is consistent with Milankovitch climate forcing, if several of the assigned age tie points are excluded. This indicates that the sedimentary cyclicity in these sections is related to astronomical variations in climate and that the ages of reversal boundaries are in error. Hence, we have calculated the astronomical durations for C4Ar.2n (87 ky), C4Ar.3r (54 ky), C5n.1n (141 ky), and C5n.1r (33 ky), which indeed show significant discrepancies with CK95. The duration pattern of our polarity intervals is confirmed by seafloor anomaly profiles and magnetostratigraphic records of deep-sea cores. Consequently, this study demonstrates that astronomically forcing in continental sequences can be a powerful tool to improve the fundamental dating of the geological record.     

Magnetostratigraphy of Upper Permian sediments in the southwestern slope of Pai-Khoi (Khei-Yaga River section): Evidence for the global Permian-Triassic crisis

The study of rock samples from the Upper Permian Khei-Yaga River section revealed an r-n-r-n-r magnetic polarity succession based on the prefolding characteristic component of natural remanent magnetization. With account for stratigraphic and previous magnetostratigraphic data on Lower Triassic rocks from the Khei-Yaga River section, the examined strata of the Pechora Group (Silova Formation) may be compared with magnetic zones R₁P₂u and N₁P₃t in the magnetostratigraphic scale of European Russia. The gap in the paleomagnetic record, which corresponds in the examined section to the interval of the mid-Severodvinian Stage to basal Induan Stage, Zone N₁T included, is estimated to be 10 Ma long. It is assumed that this hiatus represents one of the local signs of the global Permian-Triassic crisis.     

Deep-water sediments and evolution of the Lower Triassic Xikou Formation in southwestern Fujian, China

The Lower Triassic Xikou Formation in southwestern Fujian, China is a set of complex deep-water sediments which includes turbidites, sandy contourites and isolated olistoliths. Five facies and seven subfacies are recognized in the deep-water turbidites, which are considered to belong to five facies associations of upper, middle and lower fans, respectively. The sandy contourites, which occur within turbidites as isolated thin layers with structures of traction current, are formed by reworking turbidites. They occur in discrete units, not as a part of a vertical sequence of structures, such as Bouma sequence. Paleocurrent directions derived from sandy contourites are perpendicular to or at a large angle of those derived from turbidites. In some areas, within the Formation there exist large oolitic limestone blocks slided from shallow sea. The temporal-spatial distribution of three types of sediments mentioned above and the related evidences could indicate that a passive continental margin from shallow sea to bathyal-abyssal region, dipping toward southeast, once occurred in study area during the early Triassic. The early Triassic represents a period of sealevel uprising. The uprising of sea level and the development of isolated olistoliths probably imply gradual shrinking of an ocean basin at that time. Project supported by the National Natural Science Foundation of China (Grant Nos. 49490011, 49702036).     

High‐resolution lithostratigraphy and organic carbon isotope stratigraphy of the Lower Triassic pelagic sequence in central Japan

After the severest mass extinction event in the Phanerozoic, biotic recovery from the extinction at the Permian–Triassic boundary required approximately 5 my, which covers the entire Early Triassic. It is important to obtain information on the superocean Panthalassa, which occupied most of the world ocean, to explore paleoenvironmental changes during the Early Triassic at the global scale. In order to establish the continuous lithostratigraphy of pelagic sediments in Panthalassa during the Early Triassic, high‐resolution reconstruction of the Lower Triassic pelagic sequence in Japan was conducted for the first time based on detailed field mapping and lithostratigraphic correlation in the Inuyama area, central Japan. The reconstructed Early Triassic sequence is approximately 9.5 m thick, consists of five rock types, and is divided into eight lithological units. For the reconstructed continuous sequence, measurement of carbon isotopic composition of sedimentary organic matter (δ¹³C_org) was carried out. Stratigraphic variation of the δ¹³C_org value shows large‐amplitude fluctuations between ?34.4 and ?21.0‰ throughout the sequence. In order to establish a higher resolution age model for the reconstructed Lower Triassic pelagic sequence, we correlated δ¹³C_org records in the Inuyama area with high‐resolution isotopic profiles of carbonate carbon (δ¹³C_carb) from shallow‐marine carbonate sequences in southern China based on the similarity in general variation patterns with age constraints by radiolarian and conodont biostratigraphy. The result provides a high‐resolution time scale for the pelagic sequence of Panthalassa during the Smithian and Spathian. The age model suggests a drastic increase in sedimentation rate during the late Smithian, which should have been caused by the increase in terrigenous input to this site.     

Numerical evaluation of hydrodynamic damping due to the Upper Mounted Baffles in real scale tanks

In this study, the hydrodynamic damping effects of Upper Mounted Baffles (UMB) used in the real scale liquid tanks are numerically investigated. In this regard, the paper follows three main purposes. First, the accuracy of the analytical model developed by the author is examined for full scale applications. In this regard, the tanks equipped by UMB with various dimensions and locations are numerically analyzed in free vibration mode. Then, the numerical results are compared with an analytical solution results, and the validity of the analytical formulation for using in real applications is discussed. Second, the seismic efficiency of UMB is considered, and the reduction of the sloshing wave height due to the presence of the UMB is examined under several earthquake excitations. Finally, a seismic design procedure is proposed to evaluate the effect of UMB on the suppression of sloshing in a liquid tank, and its predictions are compared with the results of numerical analysis.     

青藏高原拉萨地块中部上三叠统多布日组沉积岩古地磁研究及其构造意义

拉萨地块晚古生代至早新生代期间的演化历史对理解青藏高原的形成和演化至关重要.本文报道了青藏高原中部申扎地区上三叠统多布日组沉积岩的古地磁学、岩石磁学和岩相学分析结果.岩石磁学结果显示红层、灰岩和灰绿色砂岩分别以赤铁矿,赤铁矿与磁铁矿,以及磁铁矿为主要载磁矿物.岩相学结果表明红层、灰岩和灰绿色砂岩中的磁性矿物主要为自生成因.对60个采点（602块样品）进行系统热退磁实验,结果揭示出多布日组沉积岩的特征剩磁方向在地理坐标系下为D_g=13.9°,I_g=38.9°（α_95g=0.9°）,在地层坐标系下为D_s=16.7°,I_s=8.4°（α_95s=1.5°）.进一步对其特征剩磁方向进行逐步褶皱展平检验,结果显示精度参数k的极大值在9.9%展平状态下最大,对应的特征剩磁方向为D=14.4°,I=35.9°（α₉₅=0.9°）,古地磁极为72.9°N,216.2°E（dp=0.6°,dm=1°）.这一古地磁极与拉萨地块54~47 Ma的古地磁极接近,表明其重磁化时间可能发生在54~47 Ma期间.结合前人获得的拉萨地块新生代早期古地磁数据以及同期的欧亚大陆古纬度数据,我们推断拉萨地块在56~44 Ma时相对欧亚大陆发生了1676±577 km的南北向构造缩短.

     

Spathian to Aegean (upper Lower Triassic to lower Middle Triassic) carbon isotope stratigraphy constrained by the conodont biostratigraphy of carbonates on top of a mid-oceanic seamount formed in the Panthalassic Ocean

The Taho Formation in western Shikoku Island, Japan, consists of Triassic carbonates that formed on a seamount in the Panthalassic Ocean. In order to investigate the stratigraphy and paleoceanography of this carbonate succession, we analyzed the biostratigraphy and chemostratigraphy of a 17.6 m-thick section of the upper Taho Formation at the stratotype area in Tahokamigumi, Seiyo City. This section comprises bioclastic limestone containing Triassic bivalves, ammonoids, and conodonts. We recognized six conodont zones (in ascending order): the Novispathodus pingdingshanensis, Novispathodus brevissimus, Triassospathodus symmetricus, Triassospathodus homeri, Chiosella timorensis, and Magnigondolella cf. alexanderi zones. Thus, the studied carbonate succession is latest Smithian to Aegean in age. A δ¹³C profile of this section shows elevated values during the lowest Spathian followed by a gradual negative excursion, a subsequent positive excursion near the Spathian–Aegean boundary, and relatively constant values during the Aegean. The characteristic series of negative and positive excursions correlates with other δ¹³C records for this period, including the peak of the upper Smithian–lowest Spathian positive excursion (P3), lower to middle Spathian negative excursion (N4), and middle Spathian–lowest Aegean positive excursion (P4). This represents a new high-resolution Spathian–Aegean δ¹³C record of the Panthalassic Ocean, for which ages are constrained by conodont biostratigraphy. The Taho δ¹³C profile exhibits a consistent positive offset of ~2 ‰ as compared with those from other regions (i.e., mostly in the Tethyan Ocean). This can be explained by preferential removal of ¹²C from seawater during photosynthesis and calcification by marine organisms over the platform, and/or the relatively high δ¹³C values of dissolved inorganic carbon in the Panthalassic Ocean due to less influence of ¹²C-enriched terrestrial waters and high marine organic production/burial as compared with the more restricted Tethyan Ocean.     

Triassic magmatism and its relation to decratonization in the eastern North China Craton

Lithospheric removal and destruction of the North China Craton have been hotly discussed recently. It has been confirmed that the timing of a strong lithospheric removal took place in Late Mesozoic; however, little is known about when the lithospheric removal was initiated and how the Late Permian to Early Triassic deep subduction of Yangtze continental crust affected the cratonic destruction. This paper presents an overview on the temporal and spatial framework and geochemical characteristics of the Triass...     

Thermal maturity assessment of the Upper Triassic to Lower Jurassic Nampo Group, mid-west Korea: Reconstruction of thermal history

Abstract   Thermal maturity of the Upper Triassic to Lower Jurassic Nampo Group, a sediment-fill of the Chungnam Basin located in the central western part of South Korea, was assessed by illite crystallinity measurement and sandstone microtexture analysis. The Nampo Group consists of a fluvio-lacustrine deposit bearing meta-anthracitic coals and was over-thrusted by the basement rocks. Sandstones are characterized by down sequence increasing illite crystallinity, from anchizone to epizone, which is strongly suggestive of burial heating. Deep-burial diagenesis and deformation are evidenced by well-developed pressure solution textures, whose intensity tends to increase down sequence, and by ductile deformation in the lowermost strata. On the basis of the result of illite crystallinity measurement, the maximum paleo-temperature and total burial depth of the Nampo Group are estimated to be ca 340°C and 10 km, respectively; these conditions are in good agreement with the observed ductile deformation features. The absence of strata younger than the Nampo Group in and around the Chungnam Basin suggests that deep burial of the Nampo Group was caused by tectonic crustal loading. The tectonic overload was because of basement over-thrusting that occurred during the Jurassic Daebo orogeny, which is closely related to the orthogonal subduction of the Izanagi Plate beneath the East Asian continent. Subsequent hydrothermal alteration disturbed the thermal maturity pattern, resulting in anomalously high illite crystallinity and meta-anthracitization.     

Magnetostratigraphy of the late Cenozoic Laojunmiao anticline in the northern Qilian Mountains and its implications for the northern Tibetan Plateau uplift

The uplift process of the Qinghai-Tibetan Plateau holds the key to understand the dynamic mechanisms of continental crust shortening and mountain-building and to test the relationship between the Tibetan uplift and tectonic-climatic coupling and environmental im-pacts[1―4].However,there are still many debates in the process and mechanism of how the Tibetan Plateau uplifted to the present configuration.Among various approaches to solve these key questions,dating of the Cenozoic stratigraphy …     

Late Triassic ammonoid Sirenites from the Sabudani Formation in Tokushima,Southwest Japan,and its biostratigraphic and paleobiogeographic implications

Discovery of Sirenites senticosus (Dittmar) in the upper part of the Sabudani Formation of the Kurosegawa Belt, Kito area, Tokushima Prefecture, Japan, establishes a late Early Carnian age for this part of the stratigraphic unit. Because S. senticosus was mainly distributed in the Tethyan region, its occurrence provides evidence that Late Triassic ammonoids of Japan had strong affinities with those of the Tethyan faunas. This finding clearly differs from the biogeographic distribution of contemporary bivalves in the region, which are referred to as the Kochigatani bivalve faunas, and show strong affinities to faunas of the Boreal region.     

A methodology to estimate renewal time scales in estuaries: the Tagus Estuary case

High-resolution hydrodynamic models are a common tool to simulate water dynamics in estuaries. Results from these models are, however, difficult to interpret without the aid of additional parameters to integrate the information. In this paper a methodology to understand the transport patterns in the Tagus Estuary is proposed. It is based on the computation of two renewal time scales: residence time and integrated water fraction. This last parameter is used to build a dependency matrix that gives the integrated influence of each region of the estuary at a selected point. The parameters are computed using a Lagrangian transport model coupled to the hydrodynamic model. Results show that Tagus Estuary has two different types of regions: the central part of the estuary, with low renewal efficiency, and three regions with higher renewal efficiency. Renewal mechanisms are, however, different for each region as shown by the dependency matrix. Comparison of renewal time scales with results from a water-quality model revealed that residence time is not a limiting parameter for primary production in the Tagus Estuary.Responsible Editor: Hans Burchard     

Multiple temporal scale relationships of bankfull discharge with streamflow and sediment transport in the Yellow River in China

This paper presents a study on the characteristics of multiple time scales of bankfull discharge and its delayed response to changes of flow conditions using continuous wavelet analysis for data from selected hydrological stations in the Yellow River basin. Results showed that bankfull discharge series had one or two dominant time scales. For example, the Huayuankou station in the lower reach of the Yellow River had two dominant time scales of 19-20 years and 545 years. The dominant time scales of the bankfull discharge series were generally consistent with the dominant time scales of water discharge and sediment concentration series, indicating that the channel morphology inherits the characteristics of the hydrological system in terms of multiple time scales. In addition, the wavelet coefficients of the bankfull discharge series had a phase difference in relation to those of the sediment concentration series, with a delay time that varied from 3 to 16 years at different sites. This delay time or relaxation time is a result of the delayed response of bankfull discharge to flow conditions, which was significant for channel adjustments in response to changes of flow conditions. The findings of the multiple time scales and the delayed response are of importance for further study of channel morphology of fluvial systems.     

Multiple time scale evaluation of the energy balance during the maize growing season,and a new reason for energy imbalance

Energy imbalance is a common problem associated with the measurement of surface energy using the eddy covariance method. In the evaluation of the energy balance, people usually pay more attention to the statistical result that the effective energy (the sum of sensible and latent heat) is systematically lower than the available energy (the difference of net radiation and ground heat flux). However, little attention has been paid to the existence of the reversed situation when the effective energy is larger than the available energy or their contribution to the overall energy closure rate. In this paper, based on the analysis of the energy balance on multiple time scales across the maize growth season, we conclude that the non-synchronization of energy components is the main reason for the existence of the reversed case. By shifting the phase of the effective energy components half an hour ahead, the rates of energy closure over all time scales are improved and dramatically reduce the number of the half-hourly samples when the energy ratio exceeds 1 or is below 0.5. According to the characteristics of the energy distribution and transformation over multiple time scales, latent heat is always the main type of energy cost, and the residual of the energy balance increases with the growth of the maize plant surpassing the sensible heat for seventy days. It is suggested that the heat storage and photosynthetic energy play an important role in the energy balance during the growing period of maize. Supported by National Basic Research Program of China (Grant No.2007CB714402) and State Key Laboratory of Remote Sensing Science (Beijing Normal University)