Red Clay Sequence Research Articles

Terrestrial mollusk evidence for the origin and sedimentary environment of the Late Tertiary Red Clay Formation in the Loess Plateau, China

The origin and sedimentary environment of the Late Tertiary (Neogene) Red Clay Formation in northern China had long been controversial. A new mollusk record from the Xifeng red clay (red-earth) sequence in the central Loess Plateau provides the biological evidence for addressing questions of its origin and environmental implication. The study of composition and preservation condition of seventy mollusk fossil assemblages reveals the initial ecological condition of the red clay formation, avoiding the effect of post-deposited alteration. The result shows that all of identifiable mollusk species are composed of terrestrial taxa, most of them are the common species found in the overlying Quaternary loess-paleosol sequence. Most of fossil individuals preserved in the red clay strata are in living conditions based on the investigation of fieldwork, indicating the original population. Thus, the mollusk fossil assemblages can be used as an indicator of primary environment of the red clay formation. The mollusk record from the Xifeng red clay sequence supports the view that the red clay is an aeolian origin, similar to the overlying Quaternary loess deposits. Our data also reveal the history of environmental changes at Xifeng from 6.2–2.4 Ma, which is coupled in phase with the formation and development of the Arctic ice sheets and the process of the Tibetan Plateau uplift. Both may be the major cause and forcing mechanisms of the late Tertiary environmental changes in the Loess Plateau.

Physical and chemical features of red clays in Northern Hungary

In this paper, data on the mineralogical composition of samples and a summary of those results are given (through a more detailed analysis of measurement data by using instrumental phase analytical methods concerning the examined boreholes of the two areas) that allow for the characterization of the loess and red clay sequences. The aim of our study was to characterize and correlate rocks in both areas using instrumental tests performed on samples from borehole drilled in the Hegyhat and Uveghuta areas.

Ichthyolith strontium isotope stratigraphy of a Neogene red clay sequence: calibrating eolian dust accumulation rates in the central North Pacific

Cenozoic pelagic (‘red’) clays of predominantly eolian and hydrogenous origin blanket much of the central North Pacific ocean basin. The eolian component is a key indicator of past paleoclimatic conditions; thus, Cenozoic atmospheric circulation can potentially be reconstructed through provenance studies of Pacific red clays, provided there are precise age controls. Methods commonly employed in the past to date red clay cores have included cobalt accumulation rates, ichthyolith biostratigraphy, magnetostratigraphy, and ichthyolith strontium isotope stratigraphy. The first two dating methods yield ages with large uncertainties, while magnetostratigraphy is only relevant to cores with accumulation rates in excess of 1 mm/kyr. Ichthyolith strontium isotope stratigraphy has shown promise as a chronological tool in marine studies, but has been only sparingly employed in the dating of marine red clay sequences. In this study, we present a complete age–depth profile for a large diameter piston core from the central North Pacific Ocean (EW9709 PC-01, 32.5°N, 141.2°W), consisting of 11 m of primarily wind-deposited dust. To generate this age–depth profile, strontium isotopic compositions were determined on fish teeth ichthyoliths previously cleaned of contaminants using a newly modified reductive cleaning procedure. Ages were determined by reference to the recently refined Sr isotope curve for Neogene seawater. Comparison with nearby giant piston core LL44-GPC3 reinforces the accuracy of our methods. The data for EW9709 PC-01 indicate a fairly constant sediment accumulation rate of ∼0.45 mm/kyr over most of the 24 Myr time period represented by this core.

Abrupt shifts in the late Cenozoic environment of north‐western China recorded in loess–palaeosol–red clay sequences

Aeolian deposits can provide a sensitive record of climatic change. Two abrupt changes in grain size and accumulation rate have been identified at c. 2.4–2.6 Ma and 1.1–1.2 Ma in the loess–palaeosol–red clay sequences from the Loess Plateau of China. These changes are apparent in two major stepwise increases in grain size and accumulation rate following two abrupt prominent change events of grain size, implying a two‐step reorganization that was probably connected with two abrupt environmental change events. The correlation among different sections suggests that regional rather than local environmental processes are responsible for these changes. These changes likely record abrupt fluctuations in winter monsoon and the provenance of sediments associated with renewed Plio‐Pleistocene uplift of the Tibetan plateau, and its role on climate and detrital sediment yield.

Magnetostratigraphy and sedimentology of the Jingchuan red clay section and correlation of the Tertiary eolian red clay sediments of the Chinese Loess Plateau

A 325‐m‐thick loess and red clay sequence was recently discovered at Jingchuan, which is situated about 45 km north of the previously studied Lingtai section in the middle part of the Chinese Loess Plateau. The Jingchuan section is composed of 199 m of Pleistocene loess and 126 m of Tertiary red clay deposits. Paleomagnetic studies show that the Jingchuan red clay has a basal age of at least 7.7 Ma, which represents the oldest red clay deposits presently known in the Loess Plateau. Field observations and grain size analyses both suggest an eolian origin of the red clay, thus extending available records of the eolian deposits in the Loess Plateau from about 7.0 Ma to 7.7 Ma. Correlation of both pedostratigraphy and magnetic susceptibility records suggests that the late Cenozoic red clay records in the Loess Plateau have a general continuous nature, thereby providing potential for deriving long‐term climatic evolution signals from this eolian loess and red clay sequence.

Seven million-year iron geochemistry record from a thick eolian red clay-loess sequence in Chinese Loess Plateau and the implications for paleomonsoon evolution

Recently, the Tertiary red clay sequence underlying Pleistocene loess has attracted much attention. The remarkable progress is the recognition that the Tertiary red clay sequence is also wind-blown in origin, thus providing a good opportunity to reconstruct long-term monsoon changes. In contrast to the loess deposits, the magnetic susceptibility and the pedogenic characteristics are almost independent of each other in the red clay, thus challenging the validity of the readily measurable magnetic susceptibility in describing the monsoon history recorded by the red clay. With the objective to address the long-term East Asia summer monsoon evolution, the free to total Fe2O3 ratios were calculated in a continuous eolian red clay-loess sequence at Lingtai, the Chinese Loess Plateau, which has a thickness of 305 m and a basal age of 7.0 Ma. The seven million-year Fe2O3 ratio record from the red clay-loess sequence indicates that (i) variations of the free to total Fe2O3 ratios of the loess can correlate generally with the alternations of the loess and paleosol horizons; (ii) the East Asia summer monsoon was stronger as a whole in Neogene than that in Quaternary; (iii) the strongest East Asia summer monsoon may occur between 4.0 and 4.8 Ma. The relatively small ice volume and high global temperature may be responsible for the strong summer monsoon during the early Pliocene.

Iron geochemistry of loess and red clay deposits in the Chinese Loess Plateau and implications for long-term Asian monsoon evolution in the last 7.0 Ma

Abstract Recently, some groups of authors have demonstrated that the Tertiary red clay deposits underlying the Pleistocene loess–paleosol sequence in the Chinese Loess Plateau are wind-blown in origin, thus extending the eolian record in the Plateau from 2.6 Ma back to about 7.0 Ma, and providing a good opportunity to reconstruct long-term monsoon changes. As magnetic susceptibility, the widely used paleomonsoon proxy of loess deposits, is problematic in reconstructing the monsoon history recorded in the red clay, the development of other proxies is urgently needed. In this study, we analyzed the ratios of citrate–bicarbonate–dithionite (CBD)-extractable Fe2O3 to total Fe2O3 concentrations in four loess sections along a north–south transect of the Loess Plateau, and in the Lingtai loess–red clay sequence of ∼305 m thick. The Fe2O3 ratio in the loess sections clearly shows higher values in soil units than in loess horizons, and a southward increase in this ratio is also remarkable along the transect. These are in good agreement with the temporal–spatial variations in the East Asia summer monsoon intensity identified by other monsoon proxies and soil development observations. The Fe2O3 ratio thus attests to being a good proxy indicator of the summer monsoon evolution. The Lingtai Fe2O3 ratio record shows high values over three time intervals: ∼4.8–4.1 Ma, ∼3.4–2.6 Ma, and during the interglacial periods of the past 0.8 Ma. The increase in summer monsoon intensity over the three intervals also coincides with the well-developed soil characteristics. It is therefore concluded that the East Asia summer monsoon has experienced a non-linear evolution since the late Miocene. The occurrence of a monsoon prime at about 4.8–4.1 Ma implies that the Tibetan Plateau, one of the most important boundary conditions in maintaining the monsoon circulation, must have been uplifted to a critical height at that time.

C 3/C 4 vegetation evolution over the last 7.0 Myr in the Chinese Loess Plateau: evidence from pedogenic carbonate δ 13C

The stable carbon and oxygen isotopic compositions of soil carbonate were measured on an eolian loess and red clay sequence at Lingtai, the Chinese Loess Plateau. This sequence is composed of 130 m of Tertiary red clay deposits with a basal age of 7.05 Ma overlain by 175 m of Pleistocene loess. In the field we identified ca. 110 carbonate nodule horizons in the red clay and 27 nodule horizons in the loess. These carbonate nodule horizons are formed by leaching and re-precipitation of carbonate from the eolian material. The δ 13C record of soil carbonate indicates a major expansion of C 4 plants at ca. 4.0 Myr in the Loess Plateau. This event is comparable in timing with the expansion of C 4 plants in northern North America ( Cerling et al., 1997. Nature 389, 153–158) but is ca. 3 million years later than the C 4 biomass expansion in Pakistan ( Quade et al., 1989. Nature 342, 163–166). The pedogenic characteristics of the soils and the δ 18O record in the red clay suggest that the C 4 plant expansion in the Loess Plateau was not driven by local climatic changes, which may support Cerling et al.'s (1997) assertion that the decline of atmospheric CO 2 levels in the Neogene is responsible for this global vegetation change. Our record also implies that the Tibetan Plateau could have been uplifted to a critical height in the late Miocene, thus resulting in the formation of the atmospheric Great East-Asia Trough.

Re-arrangement of atmospheric circulation at about 2.6 Ma over northern China: evidence from grain size records of loess-palaeosol and red clay sequences

Recent studies have shown that the red clay sequence underlying the Quaternary loess of the Chinese Loess Plateau is wind-blown in origin. Continuous atmospheric dust deposition in the past 7.0 Ma has been documented. To address the wind system that transported the Tertiary red clay, two north–south transects were studied in the Chinese Loess Plateau. One of the transects was designed to study spatial changes in grain size of the last glacial–interglacial loess records, and the other to observe particle changes of the Tertiary red clay underlying the Quaternary loess. The loess transect consists of nine sections, and the red clay transect of four sections. Analyses of closely spaced samples show that there is a strong southward decrease in grain size of both loess and palaeosol horizons of the Late Pleistocene, which is consistent with the idea that the aeolian materials of the Quaternary in the Loess Plateau are transported by the northerly winter monsoonal winds. Grain size distribution of the red clay sequences, however, does not show such a change. From north to south along the red clay transect, the particle size distribution is almost identical in the four sections, suggesting that the winter monsoonal winds might have played a less important role in transporting the red clay material. It is suggested that the red clay may have been transported by the westerlies from the dust-source regions of northwestern China onto the Loess Plateau. A remarkable re-arrangement of atmospheric patterns at about 2.6 Ma, therefore, has been recorded by the red clay-loess shift. It is speculated that this re-arrangement of atmospheric patterns may have been caused by the onset of glaciation in the Northern Hemisphere.

Pedostratigraphy and paleomagnetism of a ∼7.0 Ma eolian loess–red clay sequence at Lingtai, Loess Plateau, north-central China and the implications for paleomonsoon evolution

A 305-m-thick loess–red clay sequence was discovered recently at Lingtai, which is located in the middle part of the Chinese Loess Plateau. It consists of a complete Pleistocene loess–soil sequence with a thickness of about 175 m and 130 m of Tertiary red clay deposits. The red clay sequence at Lingtai is the thickest one presently known in the Loess Plateau. Field observations show that the Lingtai red clay contains over 110 couplets of pedogenic B horizons and horizontal carbonate nodule horizons, and that it can be regarded as an extremely thick soil complex. Paleomagnetic studies of 680 samples suggest that the basal age of the Lingtai loess–red clay sequence is about 7.05 Ma. Grain size analysis of samples taken at 3.3 cm intervals indicates that the red clay has the same sedimentological characteristics as those observed in the loess, thus suggesting a wind-blown origin of the Tertiary red clay and continuous atmospheric dust deposition in the Loess Plateau during the last 7.05 Ma. The pedogenic characteristics of the paleosols within the Pleistocene loess and the B horizons in the red clay suggest that the East-Asia summer monsoon in the latest Miocene may have already been slightly stronger than that during the Holocene. This implies that at about 7.5 Ma BP, the Tibetan Plateau could have been uplifted to a critical height in maintaining the East-Asia summer monsoon system. Observations of the loess–red clay sequence also suggest that the long-term changes in the East-Asia summer monsoon strength have been nonlinear since the latest Miocene.

Magnetostratigraphy and palaeoclimatic significance of Late Tertiary aeolian sequences in the Chinese Loess Plateau

The aeolian Red Clay sequence in the central part of the Chinese Loess Plateau was investigated in an attempt to obtain magnetostratigraphic and palaeoclimatic records. From the results, we deduce that aeolian dust accumulation and the related East Asia palaeomonsoon system began at least 7.6 Myr ago, and that the Tibetan Plateau had reached a significant elevation by that time. The Late Tertiary palaeoclimatic history of the Red Clay as reflected by magnetic susceptibility is reconstructed for the time period 7.6–2.5 Ma. Increases in aeolian dust accumulation for the last 7.6 Myr appear to have a close relation with the uplift processes of the Tibetan Plateau. The remarkable increase of aeolian dust accumulation beginning at 3.2 Ma appears to reflect the influence of an increasing global ice volume on the East Asian monsoon and aeolian dust accumulation.

Magnetostratigraphy and palaeoclimate of Red Clay sequences from Chinese Loess Plateau

Two Red Clay profiles near Xi’an and Xifeng were investigated in an attempt to determine magnetostratigraphic and palaeoclimatic records. The results show that aeolian dust accumulation and the related East Asia palaeomonsoon system had begun by 6.5 Ma, and it is deduced that the Tibetan Plateau had reached a significant elevation at that time. The late Tertiary palaeoclimatic history of the Red Clay as reflected by magnetic susceptibility is reconstructed during the period of 6.5–2.5 Ma. Stepwise increase in susceptibility of aeolian dust accumulation appears to have a close correlation to the uplift processes of the Tibetan Plateau. The remarkable increase of aeolian dust accumulation at 3.2 Ma appears to be due to the influence of global ice volume on the East Asia monsoon. Palaeomonsoon variation during the late Tertiary as recorded in the Red Clay sequences from the Chinese Loess Plateau can be regarded as the product of a number of interacting factors, such as uplift of the Tibetan Plateau, solar radiation, global ice volume, etc.

Paleocene to lower Eocene clay sedimentation in the Bay of Biscay

A study of the mineralogy of red clay sequences overlying basalt in the Bay of Biscay revealed two successive units: unit one (lower unit) indicates that clay minerals are the result of subaerial weathering of acid or basic continental rocks, occurring in the Galice province (northwest Spain); and unit two (upper unit) consists of fine-grained particles which suggest distinct volcanic activity. Clay materials from the first unit (Paleocene) are deposited in shallow environments, whereas the second unit materials (lower Eocene) Occur in deeper environments followed by neoformation of clay Minerals and concentration of chemical elements (cobalt, nickel, lead, zinc, and barium).

The use of phillipsite in test construction of agglutinated deep‐sea benthonic foraminifera*

ABSTRACTAgglutinated deep‐sea benthonic foraminifera with tests composed of phillipsite are documented and illustrated from a red clay sequence in a Giant Piston Core from the central North Pacific. Associated with the benthonic foraminifera are phillipsite crystal rosettes and aggregates of phiilipsite crystals. The benthonic foraminifera and phillipsite crystals constitute most of the > 38 μm fraction, but have little effect upon the mean size of the red clay sediments.