Holocene Facies Research Articles

Late Pleistocene to Holocene facies architecture and sedimentary evolution of the Zhejiang coast, East China Sea

The Holocene mud wedge that extends from the Yangtze River mouth to the Taiwan Strait along the Zhejiang–Fujian coast, East China Sea, has attracted considerable research attention; however, the pre-Holocene sedimentary evolution of the same area has been less well documented owing to limited data. We conducted an integrated analysis of 7000 km of high-resolution shallow seismic profiles and two ∼60–80-m-long borehole cores from the Zhejiang coast of eastern China to improve our understanding of the formation of the mud wedge in the context of the post-Late Pleistocene sedimentary evolution of the coastal area. Five major seismic units (numbered SU 1 to SU 5 in descending order) and various subunits that have formed since Marine Oxygen Isotope Stage (MIS) 5 were identified in the study area. SU 5 is recognizable only in the southeastern part of the study area and is interpreted to comprise subtidal to inner-shelf deposits (SU 5b) that were formed during MIS 5 and littoral to tidal-flat deposits (SU 5a) that were formed during the overall sea-level fall of MIS 4 and early MIS 3 (∼60–40 ka). These two subunits are divided by an intervening erosional surface that was likely generated by subaerial exposure of the study area during the sea-level lowstand of MIS 4. During the period from late MIS 3 to MIS 2, the study area was gradually exposed subaerially owing to further sea-level fall, with numerous small rivers incising the underlying strata to form a subaerial unconformity surface (T4). During the early postglacial transgression between ∼15.0 and ∼ 14.0 ka, the study area was progressively flooded, and the river channels were transformed into small estuaries (tidal rivers) that then coalesced into a large-scale, wave-dominated estuary during sea-level rise from ∼14.0 to ∼10.0 ka. The sandy fluvial and/or tidal-river deposits above T4 constitute SU 4. The wave-dominated estuary included a central estuarine bay on the landward side and an estuary-mouth complex on the seaward side, corresponding to fine-grained (muddy) deposits (SU 3a) and coarse-grained (sandy) deposits (SU 3b), respectively. The estuarine deposition concluded with the formation of a transgressive ravinement surface by erosional shoreface retreat during the rising sea level in the early MIS 1 from ∼13.5 ka in the southeasternmost part of the study area to ∼10.0 ka in the area closer to the shore. During the following transgressive phase, the study area was under coastal to shelf sedimentary environments during deposition of SU 2a. Tidal sand ridges (SU 2b) in the eastern part of the study area were formed at ∼11.5 ka and have been active since then. The maximum flooding surface was formed at ∼7.6 ka, and a mud wedge (SU 1) in the study area (except in the eastern part) has been developing since that time and is interpreted to have resulted from the deposition of sediments derived predominantly from the Yangtze River under the modern current system established since the maximum flooding in the Middle Holocene. The study provides new insights into the paleoenvironmental and paleogeographic evolution and facies architecture of the Zhejiang coast since MIS 5, which were controlled by preexisting geomorphological conditions and changes in sea level, hydrodynamics, and sediment supply.

Tsunami deposits and recurrence on a typhoon-prone coast of northern Taiwan from the last millennium

Widely known for its hazardous history, Taiwan holds valuable records of NW Pacific tsunamis and typhoons. Despite the similarity between tsunami and typhoon deposits, historical accounts enabled the identification of the 1867 tsunami deposit on the northern coast through matching with the record-setting inundation. However, the identification of prehistoric tsunami deposits has been hindered by severe sediment reworking and post-depositional changes produced by the typhoon-prone, tropical, and humid climate. In this study, we investigated the upper Holocene facies and their sediment sources and radiocarbon ages on distal floodplains and rocky backshores of the northern coast, where sediment reworking is less intense. Four decimetre-thick gravelly layers were identified, intercalated with fluvial mud and colluvium. The gravelly layers are composed of beach-derived quartz-rich sand and rounded gravels of the sedimentary basement rocks, longshore-drift andesite and stranded pumice. The remarkable layer thickness, gravel size, and quartz richness were determined to have endured post-depositional changes. The event layers are sharp-based, matrix-supported, and poorly sorted and have recorded scouring, sediment entrainment and rapid fallout of suspension-rich turbulent flows that probably originated with tsunamis. The event layers occur 0.5–0.8 km inland and 3–11.5 m above sea level, matching the 1867 tsunami inundation and wave height, respectively. Radiocarbon dating tied the event layers to the 1867 tsunami and three prehistoric events that occurred in the periods: 1545 to 1810, 1293 to 1414 and 1090 to 1235, representing a recurrence interval of 83–436 years over the last millennium.

Holocene sedimentation in a blue hole surrounded by carbonate tidal flats in The Bahamas: Autogenic versus allogenic processes

The sediment in North Atlantic blue holes preserves paleoclimate records. However, accurate paleoclimate reconstructions require an improved understanding of allogenic versus autogenic processes controlling blue hole sedimentation. Here we provide a detailed case study of the Holocene stratigraphy within Freshwater River Blue Hole, which is currently surrounded by carbonate tidal flats in the northern Bahamas (Abaco Island). During the Holocene, concomitant coastal aquifer elevation and relative sea-level rise controlled internal blue hole depositional environments. The general Holocene facies succession observed is: (i) basal detrital and freshwater peat, (ii) palustrine to lacustrine marl, (iii) algal sapropel, and finally (iv) bedded carbonate mud. During the middle Holocene when groundwater levels were lower, small changes in accommodation space that were inherited from the bedrock surface below (<1 m) were able to promote significant lateral facies changes. Multiple cores are needed to characterize these lateral facies changes. Hydrographic characteristics of the coastal aquifer (e.g., vertical position, stratification, salinity) relative to the blue hole benthos exert a fundamental control on (a) benthic flora and meiofauna (e.g., charophytes, ostracodes, foraminifera, gastropods) and (b) organic matter production and preservation from pelagic productivity. Over the last 5000 years, water column stratification in Freshwater River Blue Hole was interrupted on millennial to sub-decadal timescales , which are potentially linked to changing aquifer recharge and rainfall. Lastly, historical intense hurricanes passing closely to the west of the site may have promoted deposition of coarse beds at the site. However, the lack of carbonate tidal flat microfaunal remains (foraminifera: Peneroplis) within these coarse intervals indicates that Freshwater River Blue Hole does not preserve a reliable record of hurricane-induced overwash deposition from the carbonate tidal flats during the last 2300 years.

Sediment composition, provenance, and Holocene paleoenvironmental evolution of the Southern Po River coastal plain (Italy)

Geochemistry, sediment provenance, and the Holocene paleoenvironmental evolution of the Southern Po River coastal plain (Italy) were examined based on the geochemical analysis of 279 sediment samples from 35 cores. The Holocene succession is subdivided into four major facies associations: back‐barrier, transgressive barrier, shallow‐marine, and beach‐ridge deposits. Bulk chemical composition shows remarkable differences between facies associations, and the poly‐modal behavior in the related frequency curves suggests distinct sources of sediment. Using MgO and Ni as geochemical tracers, changes in sediment provenance were assessed with the aim to reconstruct the Holocene paleoenvironmental evolution of the area. The Po River and the Apenninic rivers represented the main sources of sediment during the early stages of transgression and highstand sea‐level conditions, whereas transgressive barrier and early shallow‐marine facies associations exhibit a clear North Adriatic river (eastern Alpine) provenance. The Holocene paleoenvironmental evolution of the study area, between about 10 ky and the present, indicates the presence of a bypass zone in front of the Po River mouth between 9 and 6 ky BP. At that time, sediment supplied by the North Adriatic rivers was transported southward by the longshore drift, bypassed the weak Po River influx and accumulated close to the Apennines. Comparison between Holocene facies associations and current back‐barrier and shallow‐marine sediments confirms that the present‐day basin circulation is similar to the one that acted during the last episode of sea‐level rise.

A new device to mount portable energy-dispersive X-ray fluorescence spectrometers (p-ED-XRF) for semi-continuous analyses of split (sediment) cores and solid samples

Abstract. Portable energy-dispersive X-ray fluorescence spectrometers (p-ED-XRF) have become increasingly popular in sedimentary laboratories to quantify the chemical composition of a range of materials such as sediments, soils, solid samples, and artefacts. Here, we introduce a low-cost, clearly arranged unit that functions as a sample chamber (German industrial property rights no. 20 2014 106 048.0) for p-ED-XRF devices to facilitate economic, non-destructive, fast, and semi-continuous analysis of (sediment) cores or other solid samples. The spatial resolution of the measurements is limited to the specifications of the applied p-ED-XRF device – in our case a Thermo Scientific Niton XL3t p-ED-XRF spectrometer with a maximum spatial resolution of 0.3 cm and equipped with a charge-coupled device (CCD) camera to document the measurement spot. We demonstrate the strength of combining p-ED-XRF analyses with this new sample chamber to identify Holocene facies changes (e.g. marine vs. terrestrial sedimentary facies) using a sediment core from an estuarine environment in the context of a geoarchaeological investigation at the Atlantic coast of southern Spain.

Revision of Platte River Alluvial Facies Model Through Observations of Extant Channels and Barforms, and Subsurface Alluvial Valley Fills

Abstract The Platte River of Nebraska, central USA, has been used by sedimentologists as a type example of a sandy, braided river system for some forty years. Despite this designation, however, the details of the river’s subsurface stratigraphy have never been evaluated, and so the extant facies model for the Platte River remains unvalidated. This paper analyzes the Holocene stratigraphy of the central and lower Platte River. It utilizes newly acquired data from wireline logs, sediment cores, aerial photography, and ground-penetrating radar (GPR) traverses to characterize subsurface geology, in addition to surface sediment and geomorphic mapping, sampling, and analysis of serial aerial imagery. Cores and GPR profiles show that the lithosome of the active Platte is 6–8 m in thickness and consists predominantly of medium sand. Although macroform features are common on the surface of the modern (active) central and lower Platte River in Nebraska, the shallow subsurface stratigraphy is dominated by mesoform cross-bedding and planar stratification overlying channel scour fills. This differs markedly from the vertical succession predicted by the Platte River facies model of Miall (1977). Data from inactive portions of the central and lower Platte River, however, show macroform cross-bedding indicative of the downstream and cross-stream migration of linguoid and transverse bars, which would be predicted by the published model. The typical architecture of the Holocene channel-belt sand body in the areas studied thus comprises a lower unit dominated by macroform-scale cross-bedding, overlain by an upper unit dominated by mesoform-scale cross-bedding and scour fills. Furthermore, time-series analysis of aerial photography of the river in the vicinity of Grand Island, Nebraska, shows that: (1) the river has become dominated by aggressively vegetated subaerially exposed channel-bed domains (termed “vegetated channel islands”) that superficially resemble bars; and (2) that this stretch is no longer dominated by downstream-accreting macroform bars, which were abundant in the 1960s and 1970s. Contraction of the active channel in this region has accompanied these changes, somewhat independently of discharge variation. New vertical sequence facies models are presented to account for these differences. Our data show the futility of seeking to characterize a fluvial system by means of a single vertical sequence model, and furthermore indicate that the Holocene facies architecture of the sandy, braided Platte River varies both in space and in time. The dominance of mesoform-scale structure in the shallow subsurface of the central and lower Platte River likely reflects the ongoing process of gradual abandonment of the system. It further highlights the need for caution in interpreting subsurface structure from surface geomorphology in fluvial systems.

Holocene coral reef development under windward and leeward locations at Ishigaki Island, Ryukyu Islands, Japan

Coral reef growth is largely controlled by the wave energy associated with ocean swells and local winds. This growth has responded to changes in wave conditions that evolved in concert with Holocene sea-level changes. We analyzed Holocene facies of the Ibaruma and Fukido reefs of Ishigaki Island, southern Ryukyu Islands, in the context of temporal and spatial changes in wave conditions by comparing present-day coral assemblages and internal (fossil) reef facies. Four major coral assemblages that developed under different wave-energy conditions were recognized. Six cores recorded a Holocene reef sequence consisting of four sedimentary facies that differed in the relative volumes of four coral taxa: Acropora digitifera and Acropora hyacinthus, and lesser amounts of Favia stelligera and Montastrea curta. Holocene windward reef growth began at 7820 cal. years BP after flooding of the Pleistocene reef limestone surface; the ensuing reef growth kept up with the rapid sea-level rise. A vertical growth rate of 7.5 m/1000 years during reef nucleation and early growth stages decreased to 3.5 m/1000 years during the main stage of reef framework development. The uppermost part of the windward reef consisted of a very robust framework, unlike the open framework of the leeward reef. Ages indicated that the uppermost leeward reef was ca. 3000 years younger than the uppermost windward reef. These variations in facies development and timing were caused by differences in local wind-driven wave conditions.

Late Pliocene to Holocene platform evolution in northern Belize, and comparison with coeval deposits in southern Belize and the Bahamas

AbstractLithostratigraphy, depositional facies architecture, and diagenesis of upper Pliocene to Holocene carbonates in northern Belize are evaluated based on a ca 290 m, continuous section of samples from a well drilled on Ambergris Caye that can be linked directly to outcrops of Pleistocene limestone, and of overlying Holocene sediments. Upper Pliocene outer‐ramp deposits are overlain unconformably by Pleistocene and Holocene reef‐rimmed platforms devoid of lowstand siliciclastics. Tectonism controlled the location of the oldest Pleistocene platform margin and coralgal barrier reef, and periodically affected deposition in the Holocene. A shallow, flat‐topped, mostly aggradational platform was maintained in the Holocene by alternating periods of highstand barrier‐reef growth and lowstand karstification, differential subsidence, and the low magnitude of accommodation space increases during highstands. Facies in Pleistocene rocks to the lee of the barrier reef include: (i) outer‐shelf coralgal sands with scattered coral patch reefs; (ii) a shoal–water transition zone comprising nearshore skeletal and oolitic sands amidst scattered islands and tidal flats; and (iii) micritic inner‐shelf deposits. Four glacio‐eustatically forced sequences are recognized in the Pleistocene section, and component subtidal cycles probably include forced cycles and autocycles. Excluding oolites, Holocene facies are similar to those in the Pleistocene and include mud‐mounds, foraminiferal sand shoals in the inner shelf, and within the interiors of Ambergris and surrounding cayes, mangrove swamps, shallow lagoons, and tidal and sea‐marginal flats. Meteoric diagenesis of Pliocene and Pleistocene rocks is indicated by variable degrees of mineralogic stabilization, generally depleted whole‐rock δ18O and δ13C values, and meniscus and whisker‐crystal cements. Differences in the mineralogy and geochemistry of the Pliocene and Pleistocene rocks are attributed to variable extent of meteoric alteration. Dolomitization in the Pliocene carbonates may have begun syndepositionally and continued into the marine shallow‐burial environment. Positive dolomite δ18O and δ13C values suggest precipitation from circulating, near‐normal marine fluids that probably were modified somewhat by methanogenesis. Sedimentologic and diagenetic attributes of the Pliocene–Pleistocene rocks in the study area are similar to those in the Bahamas with which they share a common history of sea‐level fluctuations and climate change.

Facies system of the Eastern Barents Sea since the last glaciation to present

Twenty-two sediment cores raised from the central and eastern parts of the Barents Sea have been studied to reconstruct the evolution of the facies system since the Late Weichselian glaciation. Multiproxy records reveal four lithostratigraphic units, which reflect major development stages of paleoenvironments. Age control is provided by 23 AMS 14C dates for Holocene sections of four cores. Continental moraine deposits of the last glaciation are overlain by proximal glaciomarine facies of the initial deglaciation phase. During this phase, the Barents Sea ice sheet detached from the ground resulting in seawater penetration into troughs, iceberg calving, deposition of IRD and fine-grained glacier meltwater load in newly formed marine basins. The main deglaciation phase is characterized by pulsed sedimentation from various gravity flows resulting in accumulation of distal glaciomarine facies comprising laminated clay and sand sequences with minor IRD. Redistribution of fine-grained suspended matter by bottom currents and brine-induced nepheloid flows combined with biogenic processes and minor ice rafting caused facies diversity of the Holocene marine sediments. The Holocene facies of shelf depressions reflect rather high, but variable productivity responding to climate changes and variations of Atlantic water inflow into the Barents Sea.

The Belize margin revisited. 2. Origin of Holocene antecedent topography

The importance of antecedent topography in dictating Holocene facies patterns has been generally recognized. There is, however, disagreement as to origin or lithology of the antecedent topography, particularly with respect to the siliciclastic or carbonate nature of the underlying topography and structural patterns. To help resolve these problems, published and unpublished information have been compiled to produce a structural fabric map of onshore and offshore Belize that includes a new geologic map of the country. The map, along with illustrated seismic lines, demonstrates the occurrence of a number of NNE-trending transpressional faults in which landward directed thrusting is consistently displayed along with tectonic inversion. Offshore wells in conjunction with the seismic lines document the inversion as post-Eocene, suggesting a similar age for transpressional fault movement. Presumably, the landward-directed thrusting reflects the opposing force of eastward-directed subduction along the western margin of Central America relative to the westward seafloor spreading of the Caribbean Cayman Ridge. The Belize faults show little current seismicity, but, nevertheless, the resulting structures have affected Quaternary carbonate deposition as evidenced on an illustrated seismic line by both seaward and landward (bi-directional) progradation of the reef margin from an underlying structural high. The structural influence on the development of Holocene antecedent topography is further suggested by the occurrence of a Bouguer gravity plateau in the same shelf area that marks the occurrence of the Belize lagoon rhomboid shelf atolls. The youngest documented lithology of 12 illustrated offshore exploration wells is Miocene carbonate. In some wells, the carbonate is interpreted as extending into the Pliocene and Holocene although no age diagnostic criteria are in evidence. In other wells, siliciclastics of unknown age and thickness are identified as overlying Neogene carbonates. The regional distribution and age of onshore limestones suggests that unroofing of the Cretaceous carbonate cap of the Maya Mountains siliciclastic sediment source did not occur until late in Neogene time, perhaps no earlier than late Pliocene. Consequently, the Maya Mountains could not have been a major offshore source of siliciclastics until the Quaternary. Information on the lithology of the immediately underlying pre-Holocene is provided by limited penetration core data and shallow resolution seismic lines. These show that antecedent Pleistocene limestones beneath the Holocene reefs were deposited around 130,000 b.p. (isotope stage 5e). The thickness of the overlying Holocene, shelf margin, reef-capped carbonates increases along depositional strike from a few meters in the north to more than 25 m in the south. In contrast, piston cores and seismic data from the southern shelf lagoon collectively document the occurrence of antecedent siliciclastic topography. The southward dip of both carbonate and siliciclastic antecedent surfaces is presumably a reflection of increasing southerly subsidence. Increasing antecedent erosional relief in the same direction reflects the pronounced southerly increase in paleo-rainfall that presumably paralleled that of present-day rainfall.

The Belize margin revisited: 1. Holocene marine facies

Belize is best known for its 260-km-long barrier reef and associated lagoon reef shoals, but also exhibits a complete transition from near-shore siliciclastics to pure carbonate deposits across a narrow shelf lagoon and, in addition, has three of the very few occurrences of Caribbean atolls. Published Holocene facies relationships on the Belize shelf have been semi-quantitative in that they are based on quantitative point count thin section data in the northern shelf lagoon and on qualitative estimates of thin section composition in the southern shelf lagoon. This contrast has been rectified by point counting southern shelf lagoon thin sections and incorporating the result with published point count data from the northern shelf, supplemented by additional information, to produce a modified factor analysis facies distribution for the entire shelf. The resulting nine facies are extended seaward to include previously published analysis of sediment on the three Belize off-shelf atolls, resulting in a total of 11 facies. In addition, the carbonate mud distribution has been mapped over both the shelf and atolls with the not unexpected result that, in places, the distribution pattern clearly indicates a barrier platform source of lagoon-deposited carbonate mud. Dunham's limestone classification terminology has been used as a basis for description to make these relationships more useful to those reconstructing ancient limestone depositional environments.

14C Ages of Tephra Layers from the Holocene Deposits of Kunashir Island (Russian Far East)

Holocene deposits from the central and southern regions of the Kunashir Island contain tephra from 12 volcanic eruptions (Kn1–12). We studied radiocarbon data, mineralogical composition, and distribution of the tephra layers in different Holocene facies. The main sources of the Holocene tephra samples were the volcanoes of Hokkaido Island. The distribution of ash layers on Kunashir Island allows us to estimate their direction. Ash layers can be reliable markers for age determination of different coastal landforms on open oceanic shores. We propose here a tephrastratigraphical scheme for different Middle-Late Holocene facies.

Facies deposicionales Holocenas de la Costa de Huelva: propuesta de nomenclatura para litofacies estuarinas

Depositionail holocene facies identified along the Huelva coast, southwestern Spain, are joined mb nine sets: (1.) lateral-fluvial bars, (2> fluvial flood plain, (3> estuarine channel, (4> tidal channel, channel-margin, (6> tidal fiat, (7> tidal delta, (8> salt-marsh and (9) sandy spit. A nomenclature of estuarine lithofacies, descriptive terrninology, as identified in different and rdated coastal environments is proposed. Estuarine lithofacies can be classified according to capital letters to represent lit.hology, small letters for physical sedimentary structures, a Greek letter for burrowing type ane, finally, a number to indicate trw burrowing degree. Nine estuarine lithofacies groups with vanous assoeiations of individual litliofacics aire distinguished: (1) gravels, (2) plant-derived organic accumulations, (~> shell accumulations, (4> burrowed clean sands, (5) unburrowed clean sands, (6> muddy sands, (7> sandy muds, (8> unburrowcd muds and (9> burrowed muds. Depositional facies occurred along the Huelva coast, with indication of every associated estuarine lithofacies group, are interpreted showing their lateral, vertical and longitudinal variability as occurred along the different estuarine domains. The application of the proposed nomenclature contribute to: (1> make the synthesis of the facies showed on the modem estuaries and (2) to facilitate the facies description in the oid estuaries as well as its comparison with thc modern ones.

Stratigraphic control of the geochemistry of Holocene inner-shelf facies, Great Barrier Reef

Cleveland Bay and Halifax Bay are adjacent embayments, situated on the inner-shelf region (0–20 m) of the central Great Barrier Reef shelf off Townsville, northeast Australia. These bays contain Holocene sediments up to 5 m in thickness, deposited during the last stages of the post-glacial sea-level rise. X-ray diffraction and X-ray fluorescence techniques were used to examine the mineralogy and geochemistry of the main Holocene facies, sampled in 40 vibrocores. The sediments of southern Halifax Bay and Cleveland Bay consist mainly of quartz (ca. 50%), alkali feldspars (ca. 20%), clay minerals (ca. 20%) consisting of mixed-layer clays, smectite, kaolinite and illite, and carbonate (ca. 10%) including aragonite and calcite. The Holocene facies sequence comprises, in order of increasing age, modern bay, shoreline and mangrove sediments. The oxides of the major components (SiO 2, Al 2O 3, Fe 2O 3, MgO, CaO, K 2O, Na 2O, P 2O 5) in Halifax Bay show the predicted linear correlations with geochemically related minor elements (Pb, Rb, Sr, Y, Zr, Ga, Zn, Ni, Co, Mn, Cr, Ti, Sc, V, Ba), and can be used to discriminate Holocene facies. However, in Cleveland Bay these elements are poorly correlated within each facies and provide very poor facies discrimination. These findings probably result from the presence of sandy shoreline sediments up to 2 m in thickness in the Holocene sequence of Cleveland Bay, with the consequent development of a weak oxic zone and migration of elements between adjacent facies. A similar oxic zone is poorly developed in Halifax Bay because the shoreline facies there is either thin or absent. That the chemical signatures of Holocene inner-shelf facies are spatially-variable, and are strongly influenced by the stratigraphy, has wide implications for geochemical studies of marine sediments.

Late quaternary sediments in incised coastal valleys in Benin: A preliminary sequence-stratigraphic interpretation

Abstract The incised coastal valley fill of the Mono and Oueme Rivers in Benin comprises several Late Pleistocene and Holocene facies that have been interpreted in sequence-stratigraphic terms. The study shows the existence of lowstand, transgressive and highstand systems tracts related to the last 120,000 year eustatic cycle and the subsequent still-stand since around 5500 BP. The lowstand systems tract consists of Late Pleistocene alluvial sediments overlying an earlier sequence in the Oueme valley. This tract has not been identified in the Mono Valley mouth where the lower sequence boundary directly separates the transgressive systems tract from the underlying substratum. The transgressive systems tract is represented by lagoonal mud and bay-mouth shoal/flood-tidal delta sands. This tract may also subsist as a thin shoreface lag or overwash sandy gravel deposit. The lagoonal muds are separated in places from the overlying estuary-mouth sands by tidal or wave ravinement surfaces. The highstand systems tract comprises the following: prograded sand barrier beach/shoreface sands, a non-prograding barrier associated with a migrating inlet, lagoonal muds and bay-head delta sands and muds. This tract has been partly reworked by tidally-influenced migration of the Mono channel and includes highstand fluvial-tidal, tidal and wave ravinement surfaces. Fine-scale differentiation of early highstand and late transgressive systems tracts and the maximum flooding surface, especially in the Oueme Valley, is rendered difficult by the essentially similar nature of their facies. This is notably the case of muddy backbarrier lagoonal sediments. It is hoped that future work will enable a finer resolution of these sequence tracts and stratigraphic surfaces.

Stratigraphy and Holocene Evolution of Mobile Bay in Southwestern Alabama

ABSTRACT Mobile Bay is a large (1058 km2) estuarine system in southwestern Alabama. On the basis of borings, vibracores, radiocarbon dating, and high resolution seismic lines, Holocene inundation of the bay has been reconstructed. A paleotopographic map delineates an entrenched river valley that occupied the present-day bay area during the last Pleistocene lowstand. Vertical stacking of Holocene facies seen in vibracores and boring logs records the evolution of the bay during postglacial sea-level rise and the resumption of deposition above the Late Pleistocene exposure surface. Two types of vertical sequences are present in Mobile Bay sediments. The first type is a fining-upward sequence that formed as beach, marsh, and near-shore sediments were covered by open-bay muds. Local progradation of the bay-head delta and the Dauphin Island-Morgan Peninsula barrier complex has produced the second type, a fining then coarsening-upward sequence. A disconformable contact with the pre-Holocene sediments is recognizable on seismic lines by erosional truncation and in cores by coloration, root mottling, and radiocarbon ages greater than 17,500 years before present (Y. B. P.). Bay inundation commenced approximately 7,500 Y. B. P. and proceeded in two phases. The first phase, from 7,500 to 6,000 Y. B. P., was a time of rapid relative sea level rise in which 70% of the bay was inundated. Rapid submergence below normal wave base produced a low energy, open-bay setting in the central part of the bay. In this area, vertical sequences are characterized by thin near-shore and beach deposits ( 5 m). By 6,000 Y. B. P., the bay extended farther to the north and was slightly deeper than the present-day bay. The second phase, from 6,000 Y. B. P. to present, was a time of slow relative sea-level rise. Slow inundation resulted in more time for sediments to be reworked and to accumulate above normal wave base. Thus, vertical sequences from the slowly inundated bay margins contain thick sections of near-shore and beach facies (> 5 m) overlain by thin sections of open-bay mud (< 1 m). Both length and depth of the bay decreased as the bay-head delta prograded and the bay filled. Decreasing length and shallowing of the bay over this time resulted in increasing riverine dominance and a diminishing of the northward intrusion of high salinity Gulf of Mexico waters.

The significance of high-boreal to subarctic maerl deposits in northern Norway to reconstruct holocene climatic changes and sea level oscillations

This paper describes (i) the Recent distribution pattern of various types of carbonate sediments in Troms county (northern Norway), and (ii) the onset of carbonate sedimentation after the final deglaciation of the Fennoscandian ice-shield. The distribution of major facies belts is strongly dependent on hydrographic and topographic constraints. The main bulk of carbonate deposits is derived from maerl-producing coralline algal biotopes that are restricted to the photic zone of waveprotected areas and influenced by tidal currents. Furthermore, extended mollusc and echinoderm-rich arenites are present in the area investigated. In deeper subtidal areas, terrigenous sediments of Late Weichselian to Early Holocene age are preserved. However, these are strongly influenced by later winnowing processes, generating a coquina lag deposit that serves as a secondary hardground for a diverse fouling community. The Holocene facies successions can be seen in several raised outcrops, containing the transition from glacigenic to Recent non-glacigenic depositional conditions. Autochthonous radiocarbon dated rhodolith banks, which mark the onset of carbonate sedimentation, yielded surprisingly young ages of 5,500 YBP. Around 5,500 YBP, present-day oceanographic and climatic conditions had already been firmly established. This time-lag can be explained with the behaviour of postglacial sea level fluctuations in the area. From 10,000 their cooperation in this project. We address our sincere thanks specifically to Prof. T.O. Vorren, Dr. M. Hald, Dr. B. Gulliksen, Dr. J. Hansen, Dr. J.J. Moller, Dr. E. Thomsen, and Dr. G. Corner for their dedicate help in organizing our field trips in Troms and for extensive scientific discussions. Special thanks to capitain K. Bendiksen for his patience and professional skill while operating the vessel ‘OTTAR’ in the skerry area even under bad weather conditions. S. Rasmussen and G. Ellingsen assisted during the cruises and very kindly introduced us to the Norwegian way of life. Special thanks to the two reviewers (Prof. Dr. W.-Ch. Dullo and anonymus) for their critical but constructive remarks. J. Welling and Dr. M. Kaminski improved the language of the final version of the manuscript. This project is part of the German Science Foundation’s main research program ‘Globale und regionale Steuerungsprozesse biogener Sedimentation”. Financial support was kindly provided by the Deutsche Forschungs-gemeinschaft (He 1671/1-1, 2).

Late Quaternary evolution of the Burullus lagoon region, north-central Nile delta, Egypt

The evolution of late Quaternary stratigraphic sequences in the Burullus lagoon region of the north-central Nile delta, Egypt is determined by petrological analysis of radiocarbon-dated sediment borings. Shallow marine, lagoonal and fluvial deposits accumulated during the late Pleistocene, and delta plain to coastal facies during the Holocene (since about 7500 yrs B.P.). The latter sequence is characterized primarily by an irregular succession of delta plain deposits, i.e. distributary channel fill, marsh and lagoon. Complete coarsening upward sequences, formed by prodelta to coastal units and previously defined in the northeastern Nile delta, are not observed in this region. Long-term sediment accumulation rates for Holocene facies during the build-up of the delta range from about 100 to 300 cm 1000 yrs . The location and ages of three Nile distributary channel systems are recognized by means of cores, from east to west: Sebennitic, Saitic, and Bolbitine/Rosetta. The mouth of the Sebennitic, which is oldest of the three, was located on what is now the inner to middle shelf. This would explain the absence of prodelta and delta-front sequences and a presence of a belt of medium- to coarse-grained sands extending seaward of the coast. The distribution in time and space of the Holocene facies is interpreted in terms of the interplay of factors controlling sedimentation, i.e. eustatic sea-level oscillations, climatic changes and land subsidence (minor in this region: 0.04 cm/yr). Of the three, sea-level changes dominate. Paleogeographic maps show, through a series of time slices, the changing configuration of this region during the past 30,000 years. Maps indicate the shifting channel systems and the major displacement of associated marshes and lagoons. This study suggests that, without the emplacement of coastal protection barriers and containment structures, an expansion of Burullus lagoon may be expected in the near future.

Holocene Sequences Distributed across the Northern Nile Delta, Egypt, as a Function of Tectonic, Eustatic, and Climatic Controls

Analysis of the laterally variable lithofacies distributions in the Nile delta, Egypt, in recent time provides an opportunity to model the evolution of a very active depocenter, the largest on the North African margin. Of particular interest is the interplay of major factors controlling sedimentation. The changes of Holocene facies in time and space across the northern Nile delta have been mapped by means of sediment cores. This study is based on extensive petrological, geochemical, and biogenic analyses of more than 2000 samples in 65 cores. Most cores (length to 60 m) are radiocarbon dated, indicating that Holocene deltaic progradational sequences began to accumulate about 7500 years ago. The delta plain has been subsiding (from 0.04 to 0.50 cm/yr) and also tilting toward the northeast during this period. As a consequence, sediments have accumulated at long-term averaged rates of 0.1 to 0.5 cm/year, from west to east. Marked variations in temporal and lateral lithofacies distributions and sequence thicknesses are in part a direct consequence of asymmetric lowering of the delta plain surface during the period of sediment accumulation. On the one hand, classic complete deltaic coarsening-upward sequences consisting of open marine prodelta to coastal facies are restricted to the northeasternmore » delta; this is largely a response to accelerated subsidence in this region. In contrast, sediment sections are reduced in thickness and comprise lithologically more irregular successions of delta plain deposits (distributary channel, marsh, lagoon) over most of the tectonically more stable north-central sector of the delta.« less

Carbonate Facies and Landsat Imagery of Shelf Off Belize, Central America: ABSTRACT

A reevaluation of Holocene sediments on the Belize shelf is based on (1) a newly constructed composite of 7 Landsat images, enhanced and registered to form a regional base map, and (2) a Holocene facies map based on a rigorous treatment of compositional and textural parameters for approximately 600 bottom samples. The sediments are mapped in terms usually applied to lithified carbonate rocks, allowing direct comparisons with carbonate facies in the subsurface. By combining Landsat imagery with this facies map, it is possible to point out the following geologic features: (1) major tectonic elements, such as the Maya Mountains, the Yucatan Plateau, several offshore ridges, and 3 large atolls, (2) major physiographic features such as the Belize barrier reef with its reef platform and crest, middle-shelf shoal deposits, middle-shelf patch reefs (including lagoon reefs or rhomboid reefs), (3) Holocene facies patterns with potential reservoir facies of foraminifera-grainstone bars, Halimeda grainstones, and branching-coral, encrusting red-algae boundstones, and (4) nearshore clastics and a sharp transition eastward to carbonate sediments. An understanding of Holocene facies patterns on the Belize shelf is important to the explorationist, because these facies patterns are living examples of exploration fairways and invite comparisons with several petroleum provinces: (1) Cretaceous reefs of Texas, (2) upper Paleozoic skeletal-grainstone bars in west Texas, and (3) Devonian reefs of the Alberta basin. End_of_Article - Last_Page 271------------