Holocene Sedimentary Sequence Research Articles

Analysis and interpretation of Holocene sedimentary sequences in the Humber Estuary

Abstract The interpretation of the Holocene evolution of the Humber Estuary has been made possible only through integrated multidisciplinary studies involving inter alia : drilling, to obtain sedimentary records of the Holocene Estuary fill; multi-element, carbon-nitrogen-sulphur and stable carbon isotope geochemistry; heavy and clay mineralogy; palaeomagnetism; radio-carbon dating; and pollen, diatom and foraminiferal studies. Eight chemostratigraphic suites and 14 palaeo-environments have been recognized. Sediment types, environments of deposition and provenance change in response to rising sea-level, showing a range from freshwater fluvial deposition of locally derived terrestrial sediment to intertidal and subtidal deposition of sediments from marine sources. The methods used are illustrated with reference to sediment cores from inner and outer estuary locations. The results show that Holocene environmental characterization is most secure when a number of different, but complementary, techniques are used. The integration of radiocarbon dates with palaeomagnetic and geochemical data improves the understanding of the presence and significance of time breaks, which is crucial to constraining sedimentation rates and material budgets.

Flux and fate of fluvial sediments leaving large islands in the East Indies

Because of their generally small drainage basin areas, high topographic relief, relatively young and erodible rocks, and heavy rainfall, rivers draining the high-standing islands of the East Indies transport a disproportionately large amount of sediment to the ocean. Rivers on the islands of Sumatera (Sumatra), Jawa (Java), Borneo, Sulawesi (Celebes), Timor and New Guinea are calculated to discharge about 4.2×10 9 t of sediment annually. Although these six islands only account for about 2% of the land area draining into the global ocean, they may be responsible for as much as 20 to 25% of the sediment export. Fluvial sediment leaving these islands is discharged into several distinctly different provinces: shallow epicontinental seas such as the Sunda Shelf, Gulf of Papua and Sea of Arafura; and narrow-shelf, active margins along the western and southern sides of Sumatra and Java, and the north coast of New Guinea. High-resolution seismic profiles in the Gulf of Papua (New Guinea) show a clinoform sequence of Holocene sediments pinching out on the mid- to outer shelf, with sediment thickness locally greater than 40 m near the coast; some — but perhaps not much — sediment escapes to the outer shelf and the deeper Papua Trough beyond. In contrast, seismic profiles off northern New Guinea show river-derived sediment prograding over and by-passing a narrow shelf that locally has buried a relict barrier reef. A small fraction of the sediment escaping the northern shelf may be transported to the eastern equatorial Pacific by way of the Equatorial Counter Current, where it may help fertilize equatorial upwelling.

Birch pollen measurements and the history of birch at Bruvatnet, Norwegian Lapland

Birch pollen measurements were carried out on a Holocene sediment sequence from lake Bruvatnet, in the birch‐forest region of Norwegian Lapland. Betula pollen diameters were measured systematically from samples that were taken at 5 cm intervals. The resulting size‐frequency distributions were analysed statistically to infer their species composition and to reconstruct the local history of birch. Birch catkin scales and fruits were used as an independent supplementary evidence. According to the vegetation reconstruction based on these results shows that Betula tortuosa has grown in the area throughout the Holocene. In the beginning of the Holocene B. pubescens was also present and its occurrence reached a peak in the birch‐pine woodland phase prior to the onset of pine decline. While pine receeded southwards, 5000–3000 BP, B. pubescens also gradually ceased to grow around the lake and the vegetation became more open.

Holocene Sea-Level Change in the Bilbao Estuary (North Spain): Foraminiferal Evidence

Benthic foraminiferal assemblages in Holocene sedimentary sequences of 4 boreholes from the Bilbao estuary (Bay of Biscay, northern Spain) have been analyzed. Estuarine indigenous and open-sea exotic foraminifera have been distinguished in order to interpret the environments of deposition (inter/supratidal sand dune and beach, low marsh, brackish intertidal, near-marine intertidal and fresh water) with varying amounts of open-sea influence. Two distinct upward-shallowing sequences, with a variable succession of envi- ronments depending on the distance to the estuary entrance, have been identified (- 8000 BP and - 3000 BP by comparison with other coastal deposits) and interpreted as showing episodic increase of sea level.

A microfaunal and sedimentary record of environmental change within the late Holocene sediments of Boca do Rio (Algarve, Portugal)

The foraminifera and ostracods observed in a late Holocene sedimentary sequence within a fluvial valley at Boca do Rio in the coastal zone of the western Algarve, Portugal, reveal a general, though not smooth transition from marine to fluvial conditions. The relative influence of these two environments appears to depend on the degree of permeability of the barrier system at the coast. Optically stimulated luminescence dates and palaeoecological information obtained from the sequence suggest that barrier formation may be related to changes in climate and/or patterns of ocean current circulation. An unusual deposit rich in sand and gravel found within the otherwise mud-dominated sequence has been dated at AD 1801 ± 76 years. This deposit contains foraminifera and ostracods which indicate marine conditions, and which contrast markedly with the brackish-water, estuarine assemblages found in the mud deposits. The rapid transition in the foraminifera and ostracod assemblages indicates a short-lived coastal flooding, which may represent the tsunami associated with the Lisbon earthquake of AD 1755. The variations in the foraminifera and ostracod assemblages also suggest subsidence during the earthquake, with uplift having occurred in the period since then.

Magnetic properties of sediments in a Polish lake: evidence of a relation between the rock-magnetic record and environmental changes in Late Pleistocene and Holocene sediments

A study of mineral magnetic parameters was carried out on a Late Pleistocene and Holocene sedimentary sequence (of nearly 18 m) from Lake Bledowo (central Poland). Sediments of Lake Bledowo have already been analysed for bulk sediment mineralogy and biogenic materials. The mineral magnetic stratigraphy confirms the major changes in palaeo-environmental conditions that have been deduced from other methods. The most important mineral magnetic change results from the authigenetic formation of ferrimagnetic greigite, Fe3S4, during the beginning of lacustrine conditions (± 12 000 yr BP). Our data also indicate a detrital origin of overlying ferrimagnetic iron oxides. It is suggested that they originate from brown soils developed on the boulder clay constituting the west side of the lake shore. Variations of ferrimagnetic iron oxide size are related to the early diagenetic processes in the sediment. Larger particles are present in periods with early diagenesis of organic matter in anoxic conditions. This indicates the dissolution of fine magnetic particles by iron-oxide-reducing bacteria and results in homogeneous magnetic grain sizes, despite their origin from soils, characterized by a multimodal grain-size distribution.

Infrared stimulation spectra of sediments containing feldspars

High resolution infrared stimulation spectra have been measured for feldspar-bearing samples from a sequence of intertidal Holocene sediments at Downholland Moss, Lancashire, U.K. To allow comparison, spectra were also measured for a range of well characterized feldspar specimens. The spectra from sediment samples show a broad resonance peaking at ∼1.44 eV with an average FWHM of 0.196 ± 0.028 eV. Fitting the sum of two Gaussian functions to the stimulation spectra of both sediment samples and mineral specimens indicate that two component bands at 1.442 eV (860 nm) and ∼1.6 eV (∼775 nm) are present. The position of the low energy band at 1.44 eV is independent of feldspar composition in the suite of feldspars studied. The ratio of the 1.6 to the 1.44 eV band appears to increase with increasing potassium content of the feldspar samples, although this is not exclusively the case. It is the relative intensities of these two bands which results in the asymmetry observed in the spectra of some feldspars.

An early Holocene record of rising sea level along a bathymetrically complex coast in southwestern Australia

The Holocene sedimentary sequence in the Bouvard Reefs area, southwestern Australia is located in a transitional zone between two contrasting coastal sectors. It contains a complex stratigraphic sequence recording a dramatic coastal change associated with a rising, then falling, Holocene sea level. With a rising sea level, during the early Holocene, sedimentation and progradation of seagrass bank, beach, and beachridges were abruptly terminated, and succeeded by the development of a retrograding barrier dune with its associated barred lagoon. The reason for the change in sedimentation style (i.e., sedimentation processes and patterns) relates to the inundation of the offshore limestone ridge. At 8000 14C yrs B.P., sea level coincided with, or was below, the top of an offshore limestone ridge, and a cuspate foreland accumulated leeward of the rocky reefs. Continuing sea-level rise inundated the reefs to sufficient water depth (i.e., more than 2 m) such that they ceased to shelter the coast, which became more exposed, and a barrier dune developed. The barrier dune then retrograded over the cuspate foreland plain. The dramatic change in sedimentation style within 500 years indicates that marked changes in coastal sedimentation can also in a relatively short time. This paper also illustrates the contrasting sedimentary style that may be superimposed and juxtaposed as sedimentation continues with rising sea levels along a bathymetrically complex coast, and provides insight into coastal response where a sea rises into a bathymetrically complex area.

Holocene environmental change in the Abisko region of northern Sweden recorded by the mineral magnetic stratigraphy of lake sediments

Abstract Combined mineral magnetic, geochemical and palynological analyses were undertaken on Holocene sediment sequences recovered from lakes in the Abisko region of northern Sweden. The absence of the Kårsa glacier in the Early and Mid‐Holocene is reflected in downstream lake sediment sequences by zones of gyttja clay that experienced post‐depositional magnetite (Fe3O4) dissolution and greigite (Fe3S4) authi‐genesis, due to organic matter decomposition and sulphate reduction. Between 3,000 and 2,500 14C yrs BP the Kårsa glacier reformed and the accumulation of sediment with a higher minerogenic content took place, with the result that magnetite was preserved in the sediments. The mineral magnetic properties of different sediment types (algal/detrital gyttja) deposited in two lakes in the Abisko valley record the same climatic deterioration between 3,000 and 2,500 14C yrs BP, although these lakes have been isolated from a glacial influence during the Holocene. Gyttja deposited during the Early and Mid‐Holocene was also subjected to magnetite dissolution (and greigite authigenesis in one lake) until the regional climate deteriorated between 3,000 and 2,50014C years BP. Due to climate induced alterations in vegetation the limnology of the lakes changed and magnetite became preserved in the sediments. Snowball, I.F., 1996: Holocene environmental change in the Abisko region of northern Sweden recorded by the mineral magnetic stratigraphy of lake sediments. GFF, Vol. 118 (Pt. 1, March), pp. 9–17. Stockholm. ISSN 1103–5897.

The lithostratigraphy and biostratigraphy of a holocene coastal sediment sequence in Marazion Marsh, west Cornwall, U.K. with reference to relative sea-level movements

A Holocene sedimentary sequence at Marazion Marsh, Mount's Bay, west Cornwall, U.K. is examined with reference to coastal evolution and relative sea-level change. A sample core analyzed in this paper shows the base of the sedimentary sequence rests on weathered bedrock material. Basal organic-rich deposits are overlain by minerogenic materials dominated by sand. A sharp contact separates these two sedimentary units. Changing coastal conditions are reconstructed using lithostratigraphic, biostratigraphic and Chronometric data from this sequence. The lower organic-rich unit accumulated between ca. 5420 ± 60 and 4380 ± 55 yrs B.P. Substantial changes in the marsh environment, involving vegetation succession from initial herb domination to mesophytic woodland and eventually to fen-carr/reed-marsh development, is indicated by pollen records from this unit. Diatom data show increased salinity within the basal sequence as arboreal pollen values decline and fen-carr/reed-marsh becomes established. Radiocarbon dates from this and other cores from west Cornwall are used to construct a local time/altitude plot of relative sea level (RSL). It is concluded that the sediment sequence at Marazion Marsh appears to have accumulated in an embayed environment. The sequence was both indirectly and directly affected by changes in relative sea-level position and the influence of protective/transgressive coastal morpho-sedimentary structures and associated processes of sedimentation during the mid-Holocene period.

Mineral magnetic record of environment in Late Pleistocene and Holocene sediments, Lake Manas, Xinjiang, China

A study of magnetic parameters was carried out on a Late Pleistocene and Holocene sedimentary sequence (5 m) from Lake Manas (northern Xinjiang, China), that has already been analysed for bulk sediment mineralogy, stables isotopes from carbonates and biogenic material. Magnetic minerals confirm major changes in palaeoenvironmental and palaeohydrological conditions that were deduced from other methods. They also provide complementary information on changes in the lake system during the early and middle Holocene. The most important mineral magnetic change results from the authigenic formation of ferrimagnetic greigite, Fe3S4 during the lacustrine episodes dated from ∼8.7 kyr B.P. to ∼5.5 kyr B.P. (380–335 cm) and from ∼4.5 kyr B.P. to ∼3.5 kyr B.P. (320–285 cm) respectively. Our data also indicate an abrupt break in sedimentary conditions which coincides with a short‐term return towards dry climatic conditions around 3.5 kyr B.P., which was only suggested from other proxy data.

Holocene sedimentary sequence, foraminifera and ostracoda in west coastal lowland of Bohai Sea, China

The Holocene sedimentary sequences in the west coastal lowland of the Bohai Sea consists in ascending order of: pre-transgression river and lake sediments, transgressive tidal flat and estuarine sediments, shelf sediments, and prograding delta and river deposits. The delta deposits are the thickest and are typically composed of two imbricating Yellow River delta superlobes that acted at different periods. There are three marker horizons in the sequence at: (1) the bottom of marine sediments; (2) the bottom of shelf deposits; and (3) the boundary between two imbricating delta superlobes. Environmental changes were mainly controlled by a rising sea level prior to 6000 BP and by delta progradation after 6000 BP. Stratigraphic distribution of foraminifera and ostracoda vary according to variations in salinity and sedimentation rate. There is no evidence that the Yellow River delta developed during the Holocene transgression but rather during a later prograding phase. An understanding of the shelly ridges in the coastal lowland indicates that the ridges were formed at a similar level to the present and there is no evidence for Holocene sea levels 1–2 m higher than the present sea level.

Mud-bank destruction and the formation of a transgressive sand sheet, southwest Florida inner shelf

The Holocene sediment sequence immediately seaward of the Florida Bay mud-bank complex consists of a thin (<0.25 m) skeletal-sand sheet and skeletal-sand banks as much as 2.0 m thick. This is in marked contrast to the myriad carbonate mud banks within the bay. Sedimentologic, stratigraphic, and radiocarbon data suggest that the skeletal sands are partly the product of physical and biological degradation of precursor mud banks which existed at least 3500 yr B.P. During degradation of mud banks, most of the skeletal material is locally reworked, whereas mud is transported onshore (eastward) where it contributes to the buildup of younger constructional banks. Active mud-bank destruction is presently occurring in a transitional zone between the transgressive sand sheet and accretionary mud-bank complex. In this zone, bank stratigraphy consists of a lower mud-bank core and upper skeletal sand or entirely of skeletal sand. The sands diminish toward the interior of the bay, whereas the basal mud-bank facies disappears to the west. Continued sea-level rise at its present long-term rate of ∼4 cm/100 yr should be accompanied by a landward shift in the destructional zone and expansion of the transgressive sand sheet. Hence, it is hypothesized that much of the western Florida Bay mud-bank complex may ultimately be preserved as a thin skeletal-sand sheet and not as a muddy carbonate sequence as previously suggested. Paleoenvironmental reconstructions of Pliocene and Pleistocene transgressive sediment sequences from the south Florida peninsula support this hypothesis.

The Holocene climatic record of the salt caves of Mount Sedom Israel

Mount Sedom is a salt diapir, on the southwestern shore of the Dead Sea, which has been rising above the local base level throughout the Holocene. Karst development within the salt body has kept pace with the rise forming subhorizontal cave passages with vertical shafts. Wood fragments found embedded in flood sediments that were deposited in the cave passages yielded 14C ages ranging from c. 7100 to 200 BP. A palaeoclimatic sequence was constructed, based on parameters that include: relative abundance of plant types or floral communities, the elevations of the corresponding cave passages and the ratio of their width to present passage width. The results were correlated to the Holocene sedimentary sequence of the Dead Sea Basin, and other features associated with shifting lake levels. Moister climatic stages are indicated by relatively abundant wood remains, by wide cave passages and by elevated outlets indicating high Dead Sea level. Arid periods are marked by a scarcity of wood remains, by narrow cave passages and by low-level outlets. The Holocene sequence of Mount Sedom is subdivided into 10 climatic stages: A moist stage in the early Holocene, older than 7000 BP, and nine subsequent stages of drier climate, fluctuating between conditions that are somewhat drier, up to somewhat moister than those of today. The Dead Sea level dropped from c. -300 MSL during the early moist period to -400 MSL or lower during the subsequent arid periods.

Holocene deltaic sequence in the Saloum estuary, Senegal

The 2250 km 2 Saloum delta, south of Dakar, Senegal, consists of a Holocene sedimentary sequence deposited during five evolutionary stages: submerged postglacial ria, funnel-like estuary, barred estuary, cuspate delta, and reverse estuary. The passage from one stage to another was marked by the deposition of sedimentary units consisting of shelly sands, silty or sandy clays, and an extensive thick green mud. Muds in the lower strata, dating between 6130 and 3500 yr B.P., were deposited on a subtidal mudflat, while fine sands and silty clays characterize intertidal deposits. A drastic change in sedimentation patterns, resulting in the accumulation of a series of beach barriers, likely was associated with a major climatic change. The regional climate was then very dry, and silt and sand were trapped in the water behind the barriers in two stages, from 1990 to 1510 and 1020 to 600 yr B.P. Each event was accompanied by construction of shell middens that demonstrate the presence of humans who exploited newly available shallows and banks. Relative sea level did not change significantly between 6000 yr B.P. and the present. Morphological and sedimentological changes observed in the late Holocene sequences were apparently induced by a constraining climatic background.

Geologic evidence of net onshore sand transport throughout the Holocene marine transgression, southwest Florida

The Holocene sediment sequence within the Ten Thousand Islands area of southwest Florida consists of more than 3 m of marine shelly quartz sand which overlies a thin layer (<1 m) of paralic and freshwater sediment. Although this transgressive sequence is similar to that produced during the erosional shoreface retreat of sandy, storm dominated shorelines, sedimentologic and stratigraphic features suggest the southwest Florida shoreline retreated landward primarily by submergence. The shelly quartz sand was derived from an offshore source subsequent to the initial stages of marine transgression. The specific mechanism responsible for onshore sand transport can only be speculated at the present time as climatic and wave data are essentially nonexistent for this remote area. However, net onshore sand transport implies that low steepness waves have mobilized a larger volume of sediment than waves of high steepness. Low steepness waves are generated under prevailing wave conditions and by the swell of distant tropical cyclones. High steepness waves are associated with winter cold fronts or the direct landfall of a tropical cyclone. Because wave heights average only 10 cm along this low energy coastline it is entirely possible that the swell of distant tropical cyclones is the principle mechanism by which sand is transported onshore and incorporated into the Holocene sediment sequence of the Ten Thousand Islands area.

Sedimentology, Paleoflow Dynamics and Flood History of JoKulhlaup Deposits: Paleohydrology of Holocene Sediment Sequences in Southern Iceland Sandur Deposits

ABSTRACT This paper examines the sedimentology of a series of deposits associated with catastrophic floods caused by subglacial volcanic eruptions in southern Iceland. A simple model is proposed for the interpretation of the sediments in terms of changes in flow characteristics of the fluid-sediment mix. A range of sediment types characteristic of these flood flows is identified, the predominant one being thick, massive, homogeneous, poorly structured, black pumice, fine gravels, with 65 p rcent silt + clay (Type E); and single lithology boulder deposits (Type F). These flood deposits alternate with, or are channeled into, more 'normal' sandur deposits, comprising heterogeneous, poorly sorted, clast-supported, imbricated, rounded cobble and pebble gravels (Type G). The dominant sediment sequences are interpreted as representing hyperconcentrated fluid-sediment mixtures, with dispersive stresses acting to create massive, poorly sorted, nongraded or inversely graded sediments, the latter characterized by large surface boulders. The vertical changes in sediment type reflect significant changes in flow conditions during transport and subsequent deposition, with an initial massive flood surge followed by flow deceleration, sediment 'freezing' and dewatering, producing a more fluid series of flows. The more fluid phases were associated with extensive erosion and channelization, cutting deep scour channels marked by residual streamlined hummocks, boulder lags, and fields of 'megaripples', leading downstream to a 'washed' sandur plain. The paper examines some of the problems associated with the application of paleoflow models for determining former flow dynamics. The models adopted suggest that most of the flows occurred as relatively mobile, low viscosity flows, with little internal resistance to shear. While sediment concentrations are estimated to have reached about 50 percent by weight, with maximum yield strengths between 2.9 103 and 4.2 105 dn cm -2, maximum viscosities ranged between only about 2 and 8 102 poises. A range of paleovelocity models applied to the flood sediment indicates flow rates of between abo t 4 and 13 ms-1, with peak discharges reaching a maximum of 3.3 105 m3 s -1. Dating of the deposits by 14C dating and tephrochronology indicates that at least 8 major sediment-producing jokulhlaups occurred over a 4,000-year period, between c 4500 yr BP and 1357 AD. Hence, although relatively rare, the effects of these floods still dominate the proglacial landscape, probably producing > 85 percent of the total thickness of proglacial sandur sediments.

Rate of Sea Level Rise as a Control on Physical versus Biological Sedimentation: Examples from Holocene of South Florida: ABSTRACT

Decelerating late Holocene sea level rise over the south Florida platform has been accompanied by changes in sediment composition which reflect a transition from physically emplaced (allochthonous) sediment to biologically emplaced (autochthonous) sediment. This interpretation is based on a south Florida submergence curve which suggests that the rate of sea level rise has decreased from 26 cm/100 years, prior to 3200 y.B.P., to 3.5 cm/100 years thereafter. These compositional changes are recognizable within both mixed siliciclastic/carbonate and pure carbonate depositional systems. For example, mangrove islands located in the Ten Thousand Islands area of southwest Florida are overlain by a Holocene sediment sequence which consists of (in ascending order) (1) thin basal mangrove peat, (2) thin oyster zone, (3) shelly quartz packstone, (4) oyster or vermetid packstone to boundstone, and (5) mangrove peat. The lower sequence (units 1 through 3) reflects an early deepening phase which accompanied a rapid rise in sea level. Biological sediment production was not rapid enough to keep up with rising sea level and, as such, the mangrove-fringed shoreline was overstepped. The overlying subtidal shelly quartz packstones reflect local reworking of Pleistocene quartz sands and, later, the introduction of quartz sand by suspension from offshore. As seamore » level rise slowed, biological sediment production and accumulation began to exceed rates of sea level rise and subsequently deposits built up to and kept pace with rising sea level (units 4 and 5). Carbon-14 dates confirm this interpretation as the thin basal peats date at 4000 y.B.P. (rapid rise) and oysters at the base of unit 4 date at 1000 y.B.P. (slow rise).« less

Batchawana Bay, Lake Superior: late Quaternary sedimentary fill and paleomagnetic record

The lake-bottom sediments of the shelf area of Batchawana Bay are composed of sands, and the basinal sediments grade from silts to coarse-grained clay basin ward. There is a significant relationship of decreasing mean grain size to increasing water depth for the sediments of the basinal areas. Although the sediments of Batchawana Bay would appear to be formed by the variable mixing of sand and clay, hydraulic action probably removed the clay end member and ultimately deposited it in the lake proper.Grains of magnetic minerals deposited on a lake bottom tend to align in the direction of the Earth's magnetic field at the time of deposition, imparting a remanent magnetic direction to the sediments. The late Holocene sedimentary sequence of Batchawana Bay provides a record of the secular changes of the Earth's magnetic field. "Type" paleodeclination and paleoinclination logs plotted against time can be utilized to date the sedimentary sequence of Batchawana Bay. This paleomagnetic time scale indicates that glacial outwash and varve deposition continued for approximately 600 years after glacial retreat from the lake basin to about 8700 years BP.

Preservation of diatoms in glacial to Holocene deep-sea sediments of the equatorial Pacific

Siliceous diatom valves exhibit better preservation in surface sediments of the eastern than of the western equatorial Pacific. The preservation noticeably decreases westward and is enhanced with increasing depth of water. Diatom preservation generally improves from glacial through Holocene sediment sequences. Superimposed on this trend are two zones of poorer preservation within the last 20,000 yr. Preservation of diatoms appears to be inverse to that of calcareous Foraminifera throughout the sequences studied in the equatorial Pacific.