Yongqiang Zong

Mid-Holocene sea-level highstand along the Southeast Coast of China

Various sea-level curves have been proposed for the coast of China in the past two decades. These sea-level curves indicate a complex history of Holocene sea level, and so the debate on whether or not a higher mid-Holocene sea-level highstand exists in the coast of China has continued. This paper aims to re-examine the Holocene sea-level history for the low latitude part of the China coast (between 18°N and 32°N) by re-assessing all the sea-level data available from the east to south coasts and separating them according to geological settings in order to examine the influences of global and local factors. The reconstructed sea-level histories from different coastal sectors of the China coast reveal a certain degree of variability in the timing and height of mid-Holocene sea-level highstand. Within large river deltas, the mid-Holocene sea-level highstand occurred earlier by almost 1000 years than that from other coastal sites. The highstand from large river deltas appears also lower in altitude (a few metres below the present-day sea level) due probably to the local factors of subsidence and sediment consolidation. In geologically stable coastal sites, the highstand is recorded at the same altitude as the present-day sea level. A 1–2 m higher highstand is found from sites where tectonic uplift is observed.

Tidal marsh stratigraphy, sea-level change and large earthquakes, i: a 5000 year record in washington, U.S.A.☆

Abstract Many of the estuaries of the Pacific Northwest of the U.S.A. and Canada contain stratigraphic sequences typified by alternating peat-mud couplets. Recent studies in this region interpret such couplets as the product of repeated large (magnitude S or 9) earthquakes on the Cascadia subduction zone. The resultant pattern of land-level movements is described by a model, the ‘earthquake deformation cycle’, of coseismic land subsidence followed by land uplift during interseismic strain accumulation. However, peat-mud couplets similar to those recorded in the Pacific Northwest are found on other less tectonically active temperate-latitude coasts, such as northwest Europe and the Atlantic coast of the U.S.A., where they have been interpreted as the product of non-seismic coastal processes. In this paper we apply the methods and scientific framework common to sea-level investigations in northwest Europe to a sequence of peat-mud couplets recorded in the lower Johns River, an estuary in southern Washington, to provide a test of the ‘earthquake deformation cycle’. Stratigraphic investigations of the intertidal sediments along the lower Johns River, using lithological, pollen, diatom and foraminiferal data, show evidence for eight coastal submergence events during the last 5000 years. To evaluate the ‘earthquake deformation cycle’ we assess the lateral extent of peat-mud couplets, the synchroneity of submergence, the presence of tsunami deposits accompanying submergence, and the suddenness and amount of submergence. Each submergence is shown to be accompanied by changes in coastal sedimentation broadly commensurate with those predicted by the ‘earthquake deformation cycle’, demonstrating the continued intermittent seismic activity of the Cascadia subduction zone throughout the mid and late-Holocene. Quantitative analyses of contemporary and fossil biostratigraphic data, using TWINSPAN and Detrended Correspondence Analysis, enable us to estimate the magnitude of submergence accompanying each peat-mud couplet. One event was accompanied by submergence of about 1.5 m or more, four events by intermediate submergence of about 1±0.5 m, and a further three events by submergence of

Diatom-based tidal-level transfer functions as an aid in reconstructing Quaternary history of sea-level movements in the UK

This research analyses the diatom asssemblages recorded from six UK coastal sites and relates these diatom assemblages to tidal levels. The relationship between diatom assemblages and tidal levels is examined statistically in order to develop a diatom-based tidal-level transfer function. The results suggest that there is highly significant correlation between the diatom assemblages and water levels from mean high water of neap tides to highest astronomical tide (p = 0.01, 99 random permutations). A weighted average (WA) transfer function is thus established, and the predictive ability of this transfer function is highly satisfactory. Finally, this transfer function is applied successfully to estimate palaeotidal-levels from fossil diatom data recorded in late Holocene coastal sequences. Copyright

IMPLICATIONS OF PARALIA SULCATA ABUNDANCE IN SCOTTISH ISOLATION BASINS

Diatom assemblages from eight basins of northwest Scotland, isolated from the sea during the Late Devensian and Holocene, show Paralia sulcata abundant towards the ingression and isolation contacts of the sedimentary sequences. Across the contacts, Paralia sulcata is commonly replaced by, or associated with, salt-tolerant freshwater species, in particular Fragilaria spp. Such a Paralia sulcata-Fragilaria spp. transition indicates a gradual reduction in marine influence and highly fluctuating water salinities. Optimal growth of Paralia sulcata occurred as a result of the favoured conditions in isolation basins, under which many other marine and brackish taxa were disadvantaged. Notwithstanding the typical transition, there are other smaller variations in the diatom assemblages, reflecting morphological features and aquatic and saltmarsh vegetation development. Most importantly, Paralia sulcata was abundant during warmer periods and disappeared when the nutrient supply, water chemistry, vegetation and sedim...

Late Devensian and Holocene relative sea-level changes in northwestern Scotland: New data to test existing models

Abstract Pollen, diatom, lithostratigraphic and radiocarbon data from five sites in northwestern Scotland provide new data from an area previously devoid of reliable and precise information on Late Devensian and Holocene sea-level changes. The sites cover a range of palaeoenvironments, indicative of diversity in coastal evolution since deglaciation. For each site and palaeoenvironment the reference water (tide) level, indicative range, age and tendency of sea-level movement of all sea-level index points are quantified to enable correlation of the diverse coastal environments. The data record patterns of relative sea-level change and tendencies of sea-level movement from 12 ka BP to 1 ka BP. This is the longest and most comprehensive published record of relative sea-level change from the area. The information is used to test the accuracy of existing models of relative sea-level change. The results are only broadly consistent with a quantitative rebound model, and there is significant disagreement with empirical models during the Late Devensian and the early Holocene.

DIATOM ZONES ACROSS INTERTIDAL FLATS AND COASTAL SALTMARSHES IN BRITAIN

The distributional patterns of diatom assemblages across the upper intertidal zone are examined in a number of British coastal sites which differ in morphological and hydrological conditions. The relationships between diatom assemblage composition and a number of environmental variables, including vascular vegetation cover, organic content and particle size of the surface sediments, and ground altitude which is related to the frequency and duration of tidal inundation are investigated. Three diatom groups common to most sites are identified. The first group is associated with the high marsh environment, where tidal inundation is infrequent and of short duration, organic content of the sediments is high and vascular vegetation cover is dense. The second group is related to low marsh conditions characterized by longer duration and higher frequency of tidal inundation, much lower organic content and variable density of vascular vegetation cover. In this zone, water salinity and particle size of the surface s...

Holocene sea-level changes and crustal movements in Morecambe Bay, northwest England

Holocene stratigraphy from Skelwith Pool, on the northern side of Morecambe Bay, is described. Diatom and pollen analyses and radiocarbon dating have been undertaken for three sampling sites, from which eight sea-level index points have been obtained. These index points come from a small homogeneous area and similar palaeoenvironments. Some published sea-level index points from Morecambe Bay have been re-evaluated and validated by means of diatom analysis. An enhanced sea-level database with 28 index points has been used for the reconstruction of Holocene sea-level history. Relative sea-level rose rapidly around 6870–6510 BC at a maximum rate of +36.7 mm yr−1. Subsequently, the rate of sea-level change has varied between −8 mm yr−1 and +12 mm yr−1. The rate of relative sea-level changes for the last 3500 years is not clear. Uplift driven by deglaciation is believed to have been interrupted in the early Holocene by a rapid rise in relative sea-level. Uplift restarted at 6510 BC but soon declined as glacio-isostatic recovery ended around 3800 BC in the Morecambe Bay area. Since then, crustal movements in the Morecambe Bay area have been minimal. Factors affecting the attitudes of the index points such as sediment compaction of the basal peat and variations in palaeotidal range during the Holocene have been considered.

Holocene relative sea-level changes and coastal vegetation history at Kentra Moss, Argyll, northwest Scotland

Abstract A late-Holocene fall in relative sea level in northwest Scotland, from ca. 1.3mm yr−1 to ca. 1.0 mm yr−1, is interpreted from lithostratigraphic, biostratigraphic, chronostratigraphic and numerical analyses of fossil tidal marsh and acidic peat bog communities elevated by isostatic uplift. Pollen, diatom and stratigraphic data from contemporary depositional environments are used to define the indicative range (±0.2 m) and reference water level (mean high water of spring tides or highest astronomical tide) of thirteen dated sea-level index points. No Holocene intertidal sediments are recorded above + 7.7 m OD and all sea-level index points are younger than ca. 4 kyr B.P. In parts of Kentra Moss, beyond the limit of Holocene intertidal clastic sedimentation, raised bog communities were established by at least 8.3 kyr B.P. These age and altitude parameters differ from those interpolated for the “Main Postglacial Shoreline”, but support a regional model in which isostatic uplift continues at present in the Kentra Moss area.

Mid-holocene variability of the East Asian monsoon based on bulk organic δ13C and C/N records from the Pearl River estuary, southern China

Understanding the mid-Holocene dynamics of the East Asian monsoon (EAM) is integral to improving models of the Holocene development of the global climate system. Here we reconstruct the mid-Holocene EAM history from the Pearl River estuary, southern China, using bulk organic carbon isotopes (δ13C), total carbon to total nitrogen (C/N) ratios and total organic carbon (TOC) concentration. Sedimentary δ13C, C/N and TOC are potentially good indicators of changes in monsoonal precipitation strength. Sediments buried during a period of high precipitation exhibit a high proportion of terrigenous material, and have low δ13C and high C/N, and vice versa during a period of low precipitation. Results suggest a general decreasing trend in monsoonal precipitation from 6650 to 2150 cal. yr BP because of the weakening Northern Hemisphere insolation most likely related to the current precession circle. Superimposed on this trend are apparent dry–wet oscillations at centennial to millennial timescales most likely in response to solar activity. Mismatches between our δ13C record and results from the Dongge Cave in southern China at millennial timescales may indicate that the δ13C from the Pearl River estuary reveals changes in precipitation over a broader area than the δ18O from Dongge Cave.

Modern pollen assemblages from cultivated rice fields and rice pollen morphology: Application to a study of ancient land use and agriculture in the Pearl River Delta, China

Pollen from a series of surface soil samples collected along a transect spanning southeast China was investigated to better understand palynological signals of ancient agriculture and other human activity. The transect surface samples consist of pairs taken inside and outside rice paddy fields. Pollen assemblages from these samples are valuable as modern analogs of human-altered environments and rice agriculture. Our measurements of Poaceae pollen grains from inside the modern rice fields discovered that 34–40 µm is the statistically significant size range for identifying domesticated rice in fossil pollen samples. This conclusion is also based on a size comparison of raw and chemically treated modern pollen grains from the plants. Pollen measurements for local wild grasses show that most native weeds have pollen grains less than 30 µm in size. The modern analogs and our study of the influence of chemical treatment on pollen grain size made it possible to examine a sediment core from the Pearl River delta for evidence of anthropogenic influence, including rice farming. Pollen assemblages from around 2200 cal. yr BP are highly similar to those of our modern analogs representing disturbed landscapes outside modern rice fields. The pollen spectra reveal abrupt increases in Poaceae, Dicranopteris, Artemisia and Pinus indicative of rice farming and forest clearance, at around 2200 cal. yr BP. Major factors associated with this abrupt transition were the rapid formation of the deltaic flood plain and massive increases in the Pearl River delta area population during the Qin Dynasty.