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Journal Articles: River Deltas and Geology

Articles  :   Geology  |   Ecosystems  |   Climate Change  |   Sea Level Rise  |   Fauna  |   Birds  |   Fish

Adams, R. S. and R. M. Bustin (2001). "The effects of surface area, grain size and mineralogy on organic matter sedimentation and preservation across the modern Squamish Delta, British Columbia: the potential role of sediment surface area in the formation of petroleum source rocks." International Journal of Coal Geology 46(2-4): 93-112.

Surface sediment samples were collected from the Squamish River Delta, British Columbia, in order to determine the role of sediment surface area in the preservation of organic matter (OM) in a paralic sedimentary environment. The Squamish Delta is an actively prograding delta, located at the head of Howe Sound. Bulk total organic carbon (TOC) values across the Squamish Delta are low, ranging from 0.1 to 1.0 wt.%. The carbon/total nitrogen ratio (C-org/N) ranges from 6 to 17, which is attributed to changes in OM type and facies variations. The < 25-mum fraction has TOC concentrations up to 2.0 wt.%, and a C-org/N ratio that ranges from 14 to 16. The 53-106-mum fraction has higher TOC concentrations and Corg/N ratios relative to the 25-53-mum fraction. The C-org/N ratio ranges from 9 to 18 in the 53-106-mum fraction and 5.5-10.5 in the 25-53-mum fraction. Surface area values for bulk sediments are low (0.5-3.0 m(2)/g) due to the large proportion of silt size material. Good correlation between surface area and TOC in bulk samples suggests that OM is adsorbed to mineral surfaces. Similar relationships between surface area and TOC were observed in size-fractionated samples. Mineralogy and elemental composition did not correlate with TOC concentration. The relationships between surface area, TOC and total nitrogen (TN) can be linked to the hydrodynamic and sedimentological conditions of the Squamish Delta. As a result, the Squamish Delta is a useful modern analogue for the formation of petroleum source rocks in ancient deltaic environments, where TOC concentrations are often significantly lower than those in source rocks, formed in other geological settings. (C) 2001 Elsevier Science B.V. All rights reserved.

Alfaro, A., L. G. Pujades, et al. (2001). "Preliminary map of soil's predominant periods in Barcelona using microtremors." Pure and Applied Geophysics 158(12): 2499-2511.

In order to evaluate soil effects in the urban area of Barcelona, the Nakamura's technique has been used to estimate the predominant periods of soils. Noise measurements for 195 sites were performed using a strong motion accelerograph and a velocimeter. In this work, the resulting preliminary map of predominant periods is presented. The obtained predominant periods are coherent with the geological and geotechnical features of the area. The analysis of the information has allowed the distinctions among several types of soil and underlying materials. A predominant period of about 0.06 s is evaluated for sites located over outcrop Paleozoic rock in the Tibidabo-Collserola Mountains. For sites consisting of material named tricycle, that is the most extensive and also the most heterogeneous zone, predominant period range from 0.10 s up to 2.0 s depending on the thickness of the surface materials and the kind and thickness of the underlying materials. In the Besos river two zones are observed: the riverside with periods between 0.50 s and 0.83 s and a second area with periods between 1.0 and 2.1 s. In the Llobregat river delta the obtained periods are quite homogeneous with values around 0.72 s. Other predominant periods are found in some tertiary rock outcrop.

Are, F. and E. Reimnitz (2000). "An overview of the Lena River Delta setting: Geology, tectonics, geomorphology, and hydrology." Journal of Coastal Research 16(4): 1083-1093.

The Lena River Delta, largest in the Arctic, occupies 32,000 km(2). It has a complicated structure caused by neoitectonic block-movements, which formed an island archipelago with elevation differences as large as 60 m of distinct geological units. The modern active delta occupies spaces between older islands of the archipelago, and is just beginning to protrude into the open sea. The hydrologic pattern in the delta also shows the influence of tectonism. Numerous earthquakes during last century with magnitudes as large as 6 suggest that tectonic movement is continuing. Radiocarbon dating shows that the modern delta has been built during the second half of the Holocene. The total advance of the delta during this time was 120-150 km. The Lena River is considered the main sediment source for the Laptev Sea. The latest investigations give the suspended sediment load in the lower Lena River at 21 Mt/y, but only < 30% of this load is thought to reach the sea. The bed load transport is considerable but its value is unknown. The active sub-aerial delta is bordered by a shallow platform as wide as 18 km, which turns into a relatively steep slope at the 2 m isobath. This feature, corresponding in depth to the thickness of the seasonal ice cover, is observed only off Arctic rivers and is not understood. Some sections of the modern delta have morphological features characteristic for advancing shores, others show signs of retreat. However no measurements of delta shore dynamics are available. Thus the general direction of the process is disputable. The western part of the Lena Delta is formed by a large, 20-m-high sand island fringed by a unique lace coast formed by narrow estuary-like bays deeply penetrating the land. This unique coast undergoes intensive erosion not only on promontories but also inside of estuaries due to storm surges reaching to >2 m height. The sand island is characterized by typical lake-thermokarst relief, but no volumes of underground ice large enough to explain this relief are known. The elongated lake depressions and lakes are oriented about 2-8 degrees True. In the middle of generally 1- to a-m-deep lakes are equally oriented hollows as deep as 25 m. The lakes are degrading because of erosion by stream channels draining them. The lake-thermokarst relief on the north slope of the island is partly or totally destroyed by erosion processes. Thus the Lena Delta is characterized by several unique features that are either poorly understood or unexplained.

Aslan, A., W. A. White, et al. (2003). "Holocene evolution of the western Orinoco Delta, Venezuela." Geological Society of America Bulletin 115(4): 479-498.

The pristine nature of the Orinoco Delta of eastern Venezuela provides unique opportunities to study the geologic processes and environments of a major tropical delta. Remote-sensing images, shallow cores, and radiocarbon-dating of organic remains form the basis for describing deltaic environments and interpreting the Holocene history of the delta. The Orinoco Delta can be subdivided into two major sectors. The southeast sector is dominated by the Rio Grande-the principal distributary-and complex networks of anastomosing fluvial and tidal channels. The abundance of siliciclastic deposits suggests that fluvial processes such as overbank flooding strongly influence this part of the delta. In contrast, the northwest sector is represented by few major distributaries, and overbank sedimentation is less widespread relative to the southeast sector. Peat is abundant and occurs in herbaceous and forested swamps that are individually up to 200 km(2) in area. Northwest-directed littoral currents transport large volumes of suspended sediment and produce prominent mudcapes along the northwest coast. Mapping of surface sediments, vegetation, and major landforms identified four principal geomorphic systems within the western delta plain: (1) distributary channels, (2) interdistributary flood basins, (3) fluvial-marine transitional environments, and (4) marine-influenced coastal environments. Coring and radiocarbon dating of deltaic deposits show that the northern delta shoreline has prograded 20-30 km during the late Holocene sea-level highstand. Progradation has been accomplished by a combination of distributary avulsion and mudcape progradation. This style of deltaic progradation differs markedly from other deltas such as the Mississippi where distributary avulsion leads to coastal land loss, rather than shoreline progradation. The key difference is that the Orinoco Delta coastal zone receives prodigious amounts of sediment from northwest-moving littoral currents that transport sediment from as far away as the Amazon system (similar to1600 km). Late Holocene progradation of the delta has decreased delta-plain gradients, increased water levels, and minimized overbank flooding and siliciclastic sedimentation in the northwest sector. These conditions, coupled with large amounts of direct precipitation, have led to widespread peat accumulation in interdistributary basins. Because peat-forming environments cover up to 5000 km(2) of the delta plain, the Orinoco may be an excellent analogue for interpreting ancient deltaic peat deposits.

Britsch, L. D. and J. B. Dunbar (1993). "Land Loss Rates - Louisiana Coastal-Plain." Journal of Coastal Research 9(2): 324-338.

Land loss mapping and rate curve development for 62 quadrangles in the Mississippi River deltaic and chenier plains shows that land loss rates and trends vary significantly throughout coastal Louisiana. Land loss rates were defined for each quadrangle for 4 time periods (1930's to 1956-1958, 1956-1958 to 1974, 1974 to 1983, and 1983 to 1990). Differences in land loss rates among the individual quadrangles are a function of the geologic and hydrologic setting and the factors which contribute to land loss such as subsidence, storm induced erosion, channelization of streams and rivers, and canal dredging. Of the 62 quadrangles mapped, 8 quadrangles are losing more than 1 percent of their land area each year, while 21 quadrangles are losing more than 0.5 percent per year during the 1983 to 1990 period. On a regional scale, the land loss rate for the entire Louisiana Coastal Plain has decreased from an average yearly rate of 41.83 square miles in the 1956-1958 to 1974 period to 25.34 square miles during the 1983 to 1990 period. The percentage of land being lost is also decreasing from 0.51 percent per year in the 1956-1958 to 1974 period to 0.35 percent per year during the 1983 to 1990 period. The regional land loss rate will probably continue to decrease slowly until a background rate is reached.

Brooks, G. R., J. L. Kindinger, et al. (1995). "East Louisiana Continental-Shelf Sediments - a Product of Delta Reworking." Journal of Coastal Research 11(4): 1026-1036.

Data from 77 vibracores were integrated with 6,700 line-km of high-resolution seismic reflection profiles collected off the eastern Louisiana coast in the region of the St. Bernard Delta, the first of the Holocene highstand deltas of the Mississippi River. Seismic facies and sediment facies were integrated in order to establish the stratigraphic details within this relict delta. Results provide a regional geologic framework from which comparisons can be made with other areas. Holocene deposits in the study area overlie a heavily dissected surface interpreted to represent a lowstand erosional surface. Resting on this surface is a thin unit of relatively clean, quartz sand interpreted to have been deposited during early transgression. This unit is overlain by sediments of the St. Bernard Delta, a seaward-prograding. coarsening-upward wedge of sands and muds that contain vertically-stacked unite of deltaic succession. Two or more prograding units separated by an unconformity, delineated from regional seismic profiles, may represent laterally shifting subdelta lobes. Surficial sediments consist of a thin unit of sands and muds derived from and reflecting the individual subenvirons of the underlying delta. Holocene inner-shelf development off eastern Louisiana has been controlled by relative sea-level rise and sediment supply. Sediment supply and deposition are a product of delta progradation and delta lobe switching. The modern shelf configuration and surficial sediment distribution patterns reflect reworking of underlying deltaic deposits. The lack of modern sediment input helps to maintain the imprint of this ancient delta on the modern shelf surface.

Butenko, J. and J. P. Barbot (1980). "Geologic Hazards Related to Offshore Drilling and Construction in the Orinoco River Delta of Venezuela." Journal of Petroleum Technology 32(5): 764-770.

Chen, X. Q. (1998). "Changjiang (Yangtze) River delta, China." Journal of Coastal Research 14(3): 838-858.

After a brief review of the previous studies and a description of the geographical setting of the Changjiang River, the Changjiang River delta, and the Changjiang River estuary, this paper first summarizes the geological framework in which the recent vertical tectonic movement is emphasized because of its close connection with relative sea level changes and earthquakes. A systematic description of the stratigraphy reveals the local geologic history. Sedimentary sequences, facies and structures since the Holocene are next briefly reviewed. The historical delta and coast development is examined, with special reference to the coastal response to sediment supply. Recent achievements on the physical and biological processes in estuarine and coastal waters are presented. These processes are found to greatly influence the temporal and spatial variation of water salinity, suspended sediment concentration, sedimentation rate, and primary productivity. The interaction of natural processes with socioeconomic development is discussed in detail, with an emphasis on the major problems of estuarine freshwater resources and the impact of water diversion, harbors and navigation channels, land shortage and the impact of land reclamation, subsiding ground surface, rising sea level and flood hazards. Finally, the probable delta development in the coming decades in response to several large scale engineering works is discussed, such as the Three-Gorges Dam, the planned water transfer to North China, and the Deep Water Navigation Channel.

Coleman, J. M., H. H. Roberts, et al. (1998). "Mississippi River delta: an overview." Journal of Coastal Research 14(3): 698-716.

Over the last century, the river-dominated Mississippi delta has received increasing attention from geoscientists, biologists, engineers, and environmental planners because of the importance of the river and its deltaic environments to the economic well-being of the state of Louisiana and the nation. Population growth, subsurface resource extraction, and increased land-water use have placed demands on the delta's natural geologic, biologic, and chemical systems, therefore modifying the time and spatial scales of natural processes within the delta and its lower alluvial valley. As a result, the combined effects of natural and human-induced processes, such as subsidence, eustatic sea level rise, salt water intrusion, and wetland loss, have produced a dynamically changing landscape and socioeconomic framework for this complex delta. Under natural conditions, the fundamental changes that result in land-building and land loss in the Holocene Mississippi River delta plain are rooted in the systematic diversion of water and sediment associated with major shifts in the river's course-the process of delta switching. Research over the last half century has shown that major relocations of the Mississippi's course have resulted in five Holocene delta complexes and a sixth one in an early stage of development as a product of the latest Atchafalaya River diversion. Collectively, these Holocene deltas have produced a delta plain that covers an area of similar to 30,000 km(2) and accounts for 41% of the coastal wetlands in the United States. After a river diversion takes place, the resulting delta evolves through a systematic and semipredictable set of stages generally characterized by: (a) rapid progradation with increasing-to-stable discharge, (b) relative stability during initial stages of waning discharge, (c) abandonment by the river in favor of a higher gradient course to the receiving basin, and (d) marine reworking of a sediment-starved delta as it undergoes progressive submergence by the combined processes of subsidence. Delta switching has taken place every 1000 to 2000 years during Holocene times, and resulting deltas have an average thickness of approximately 35 m. Within a single delta there are subdeltas, bayfills, and crevasse-splays that have higher frequency delta cycles ranging from several hundred years to a few decades. These depositional features are usually less than 10 m thick, and some have produced marshland areas of over 300 km2. The net result of these delta-building events is a low-lying landscape with components that are changing(building and deteriorating) at different rates. Geologically, these depositional cycles produce a thick accumulation of coarsening, upward deltaic deposits that have various thicknesses in response to development on a variety of temporal and spatial scales. In this river-dominated delta system, distributaries can prograde seaward at rates of over 100 m/year. The cumulative effect of the Holocene depository has been to depress the underlying Pleistocene surface. In a local setting, e.g., the modern Balize Lobe, differential loading causes the vertical displacement of underlying clay-rich facies (shale diapirs-mudlumps). The delta front of this lobe, which has prograded into deep water of the outer continental shelf, is characterized by rapid deposition of silt- and clay-rich sediments and slope instability, which results in seaward displacement of sediments by a variety of mass-movement processes. Superimposed on the natural processes and forms of the Mississippi deltaic plain and its associated estuarine environments, are human impacts, most of which have been imposed in this century. The most significant impacts have resulted from a decrease in sediment input to the river from its tributaries and the alteration of the river's natural sediment dispersal processes through the construction of levees. Measures are now being taken to reinstate some of the delta's natural processes, thereby mitigating landless so that decline in animal and plant productivity can be mitigated.

Correa, I. D. and J. L. Gonzalez (2000). "Coastal erosion and village relocation: a Colombian case study." Ocean & Coastal Management 43(1): 51-64.

Because of its tectonic setting, the Pacific coast of Colombia is subject to a variety of geological hazards, including earthquakes, tsunamis and associated phenomena such as regional and local coastal subsidence, flooding and soil liquefaction. Erosional trends are prevalent along much of the 700 km long, low barrier island's shorelines of the Pacific littoral and land losses are enhanced by factors such as 30 cm regional sea level rises associated to the occurrence of El Nino. Marine erosion is threatening more seashore littoral villages and worsening the already difficult socioeconomic conditions of most part of the inhabitants. Because of diverse and strong motivations to stay near the sea, the responses of barriers island's inhabitants to marine erosion has consisted in most cases of repetitive in-shore and along-shore directed relocations of villages, rather than definitive abandonment of the islands. In the long run, this procedure only has postponed the problem and led to repetitive relocations and economical losses. The recent inland relocation of El Choncho village, on the San Juan River delta, illustrates a different response to marine erosion. Although a new along-shore relocation was physically possible, inhabitants decided to abandon the barrier island and migrate to an interior, ancient beach ridge complex, applying a prudent solution which will be the most appropriate for other threatened villages of the Pacific littoral. A detailed geomorphologic mapping program must be conducted in order to identify appropriate sites for inland relocation of existing villages on the barriers islands of the Colombian Pacific coast. (C) 2000 Elsevier Science Ltd. All rights reserved.

Demets, C. (1992). "A Test of Present-Day Plate Geometries for Northeast Asia and Japan." Journal of Geophysical Research-Solid Earth 97(B12): 17627-17635.

Alternative geometries for the present-day configuration of plate boundaries in northeast Asia and Japan are tested using NUVEL-1 and 256 horizontal earthquake slip vectors from the Japan and northern Kuril trenches. Statistical analysis of the slip vectors is used to determine whether the North American, Eurasian, or Okhotsk plate overlies the trench. Along the northern Kuril trench, slip vectors are well-fit by the NUVEL-1 Pacific-North America Euler pole, but are poorly fit by the Pacific-Eurasia Euler pole. Results for the Japan trench are less conclusive, but suggest that much of Honshu and Hokkaido are also pan of the North American plate. The simplest geometry consistent with the trench slip vectors is a geometry in which the North American plate extends south to 41-degrees-N, and possibly includes northern Honshu and southern Hokkaido. Although these results imply that the diffuse seismicity that connects the Lena River delta to Sakhalin Island and the eastern Sea of Japan records motion between Eurasia and North America, onshore geologic and seismic data define an additional belt of seismicity in Siberia that cannot be explained with this geometry. Assuming that these two seismic belts constitute evidence for an Okhotsk block, two published kinematic models for motion of the Okhotsk block are tested. The first model, which predicts motion of up to 15 mm yr-1 relative to North America, is rejected because Kuril and Japan trench slip vectors are fit more poorly than for the simpler geometry described above. The second model gives a good fit to the trench slip vectors, but only if Okhotsk-North America motion is slower than 5 mm yr-1.

Deniau, I., S. Derenne, et al. (2004). "Occurrence and nature of thermolabile compounds in the Boom Clay kerogen (Oligocene, underground Mol Laboratory, Belgium)." Organic Geochemistry 35(2): 91-107.

The Boom Clay Formation has been selected as a model for studying the long term disposal of high activity nuclear waste in clay. During the resulting storage, the immature kerogen in the clay would be subjected to thermal stress and some of the products which could be generated might affect the efficiency of the geological barrier. The kerogen isolated from a representative clay sample, collected in the underground laboratory of the Nuclear Energy Research Centre at Mol (Belgium), was subjected to short heating at 300 degreesC to examine the thermolabile fraction released. The fraction contains a wide variety of components including hydrocarbons, ketones, alkanoic acids, phenols, furans and pyrroles. Information about the origin of these compounds was obtained through comparison with the bitumen and with the previously examined pyrolysis products generated from the kerogen at higher temperature (400 degreesC). The thermolabile fraction appears to correspond to "free" compounds trapped in the macromolecular structure of the kerogen and "labile" moieties linked by covalent bonds with a relatively low thermal stability. The study affords additional information on the sources and composition of the kerogen. Furthermore, the thermolabile components in the Boom Clay kerogen might affect the effectiveness of the clay barrier when subjected to thermal stress, especially through the release of oxygen-containing products, like carboxylic acids and phenols, that might complex released radioactive elements. (C) 2003 Elsevier Ltd. All rights reserved.

Echelle, A. A., R. A. Van den Bussche, et al. (2000). "Mitochondrial DNA variation in pupfishes assigned to the species Cyprinodon macularius (Atherinomorpha  :  Cyprinodontidae): Taxonomic implications and conservation genetics." Copeia(2): 353-364.

Variation in mitochondrial DNA (mtDNA) was assessed in a captive stock and 11 wild populations (n = 259) from throughout the native range of Desert Pupfish Cyprinodon macularius as traditionally understood. Using PCR-SSCP, 18 composite haplotypes were identified from a 333-bp segment of the mitochondrial D-loop and two segments of the ND2 gene (333 and 325 bp). Representatives of each haplotype were sequenced for the entire ND2 gene and the 337-bp segment of the D-loop. Phylogenetic analyses revealed that haplotypes form two monophyletic groups, one in the Rio Sonoyta/Qllitobaquito Springs area and one in the Salton Sea/Colorado River Delta. This, with previous observations on morphology, color pattern, and geological history, supports recognition of the Rio Sonoyta/Quitobaquito populations as a separate species, the Quitobaquito Pupfish C. eremus Miller and Fuiman, from the more widespread desert pupfish C. macularius Baird and Chard. More than 70% of mtDNA diversity across all populations was attributable to differences between the two species. Within species, the average local population contains 94% and 97% of the diversity in, respectively, C. eremus and C. macularius. Differences between the Salton Sea and Colorado River Delta populations of C. macularius ex plain a small (3.7%), but statistically significant, portion of mtDNA diversity in this species. This and the history of connections between Salton Sea and the delta suggest that the two regions should be managed separately with no intermixing of pupfish other than what occurs when the present, human-regulated hydrology is overcome by natural flooding. Haplotype frequencies in C. eremus from Quitobaquito Springs and Rio Sonoyta were not significantly different. However, the potentially long history of isolation between these two populations and evidence of some degree of morphological divergence indicate a need for conservative management with no intermixing The captive stock exhibited reduced mtDNA variation relative to its wild parent population from a locality on the delta. Variacion de ADNmt fue examinado por una cepa de cautivo y 11 poblaciones silvestres (n = 259) de todas partes del rango natural del cachorrito del desierto Cyprinodon macularius como entendido tradicionalmente. Utilizando PCR-SSCP, 18 haplotipos compuestos fueron identificados desde un segmento de 337-pb del D-loop mitocondrial y dos segmentos del gene DN2 (333 ph y 325 pb). Representantes de cada haplotipo fueron sequenciados por el gene DN2 entero y el segmento de 337-pb del D-loop. Analisis filogenetico mostro una relacion monofiletica reciproca ent-e poblaciones de dos regiones generales, Rio Sonoyta/Quitobaquito y Salton Sea/Delta del Rio Colorado. Esto, con observaciones previas de morfologia, patron de color, y la historia geologica, sostiene el reconocimiento de las poblaciones de Rio Sonoyta/Quitobaquito come ma especie distinta, el cachorrito de Quitobaquito C. eremus Miller and Fuiman, de la especie con una distribucion mb amplia, el cachorrito del desierto C. macularius Baird and Chard. Mb de 70% de la diversidad ADNmt de todas las poblaciones fue atribuida a diferencias entre las dos especies. Dentro de cada especie, la poblacion promedia local contiene 94% y 97% de la diversidad de, respectivamente, C. eremus y C. macularius. Las diferencias entre las poblaciones de C. macularius del Salton Sea y las de la Delta del Rio Colorado explican una pequena (3.7%) pero ma porcion estadisticamente significativa de la diversidad ADNmt de esta especie. Esto y la historia de conecciones entre el Salton Sea y la delta sugieren que los dos regiones deben ser manejadas aparte sin mezclar a los cachorritos mb que lo que ya ocurre cuando la hidrologia actual controlada por los humanos, esta conquistada por inundaciones naturales. Frequencias de los haplotipos en C. eremus del Quitobaquito Springs y el Rio Sonoyta no fueron sig-. (C) 2000 by the American Society of Ichthyologists and Herpetologists

Evans, K. G., A. W. Stephens, et al. (1992). "Quaternary Sequence Stratigraphy of the Brisbane River Delta, Moreton Bay, Australia." Marine Geology 107(1-2): 61-79.

The Quarternary geological history of the Brisbane River delta front and prodelta was interpreted using seismic stratigraphic and sequence stratigraphic principles. During the last major glacial sea level episode, the floor of the bay was exposed and eroded by stream channels. In the subsequent postglacial marine transgression, the palaeochannels of the Brisbane and Pine Rivers were backfilled with mud. Sea level continued rising until about 6500 years ago and a highstand has persisted since then. During the Quarternary, sediment deposition in Moreton Bay was controlled by sea-level fluctuations, channel migration, and palaeotopography. There were at least four depositional episodes prior to the last glacial period, plus the present postglacial episode. Periods of low sea level occurred between highstands and the sea bed exposed and eroded. Eight major seismic reflectors were recognised and six seismic sequences defined. The seismic sequences represent five highstand systems tracts and one transgressive systems tract. The relationships between eustacy and system tract type were applied to glacio-eustatic sea-level curves to determine relative ages of sequences in Moreton Bay. The application of sequence stratigraphy to high frequency sea-level fluctuations was demonstrated. The stratigraphic system established within the context of sequence stratigraphy will provide a reference for future work within the region.

Gambolati, G., P. Teatini, et al. (1999). "Coastline regression of the Romagna region, Italy, due to natural and anthropogenic land subsidence and sea level rise." Water Resources Research 35(1): 163-184.

The Romagna coastal area in the Northern Adriatic Sea has experienced in recent times continuous changes because of its precarious environment and low ground elevation above mean sea level (msl). Major processes that may influence the stability of the coast profile include land subsidence of both natural and anthropogenic origin and the msl rise caused by global climate change. According to the most accredited modeling predictions msl is expected to rise by almost 0.5 m over the next century because of the greenhouse effect. Natural land subsidence is the result of deep downward tectonic movement and consolidation of geologically recent deposits. It may be estimated in the range of 2-2.5 mm/yr in the Ravenna area and twice as much in the Po River delta. Anthropogenic land subsidence is primarily related to groundwater pumping from the upper fresh water aquifer system and gas production from Plio-Pleistocene reservoirs. Geodetic surveys from 1953 to 1990 provide documentary evidence of cumulative land settlement exceeding 0.8 m and 1.2 m at Marina di Ravenna and Cesenatico, respectively. In this study we estimate both natural and anthropogenic land subsidence for the years 2015, 2050, and 2100 with the aid of ad hoc finite element simulation models. The use of these predictions together with the expected msl rise shows that many present lowlands may be permanently submerged at the end of the next century. The extent of the flooded area of the Romagna coastal region can be as much as 690 and 910 km(2), using optimistic and pessimistic land subsidence scenarios, respectively. A local detailed analysis indicates that the areas around the cities of Ravenna and Cesenatico may be seriously affected by sea water ingression while the city of Rimini is well protected because of its relatively high elevation above msl.

Gastaldo, R. A. and J. R. Staub (1999). "A mechanism to explain the preservation of leaf litter lenses in coals derived from raised mires." Palaeogeography Palaeoclimatology Palaeoecology 149(1-4): 1-14.

Leaves and other non-woody canopy parts are rarely preserved in coals. Although the pH of pore waters within peat swamps is usually relatively low (less than or equal to 3.5), providing geochemical conditions that would promote preservation after burial, shed canopy parts may remain at the air-soil interface for periods of up to several months prior to burial by additional organic detritus. Leaf half-life in tropical forests has been reported to range from several weeks to months, depending upon species histology. During this time of exposure on the forest floor, catabolic (internal enzymatic), fungal, bacterial and root degradation, as well as saprophagous scavenging, act upon the least resistant parts to promote decay into hemic and sapric macerals. It is unusual, then, to find well-preserved leaves in peats or coals. When such accumulations are encountered, either permineralized in coal balls or duripartically preserved in lignites, the bedded leaves generally are spatially isolated. Several explanations have been proposed to account for such fossil Lagerstatten that require temporal changes in accumulation or degradation rates. Neither of these mechanisms is required to account for such accumulations. Bedded leaves, showing minimal evidence of subaerial exposure and degradation, have been recovered at depth from a vibracore taken 1 km into the interior of a peat swamp in the Rajang River delta, Sarawak, East Malaysia. Evidence is provided to indicate that such accumulations form within peat substrate depressions resulting from the displacement of rootstocks as trees either die and fall over, or are blown down in severe storms. These localized, acidic water-filled pools act as a natural buffer to the degradation of fallen canopy parts that accumulate therein. (C) 1999 Elsevier Science B.V. All rights reserved.

Hanson, P. J., D. W. Evans, et al. (1993). "Assessment of Elemental Contamination in Estuarine and Coastal Environments Based on Geochemical and Statistical Modeling of Sediments." Marine Environmental Research 36(4): 237-266.

Sediment of variable mineralogical, textural and metal contaminant composition was collected from 38 estuaries along the Atlantic and Gulf of Mexico coasts of the United States and analyzed for total Al, Ag, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Si, Sn, Tl and Zn concentrations. Based on observed covariation of elements at 15 estuaries remote from contaminant inputs, linear regressions of metals on Al were used to model the metal content in baseline sediments. A geochemical model for the covariation was developed, verified and used to guide the statistical modelling approach. Comparison of metal concentrations predicted by the models with those occurring in uncontaminated geological materials suggests that baseline relationships are valid for the entire region sampled Using these baseline relationships, sediment metal concentrations can be partitioned into natural and anthropogenic fractions. Models improve the comparability of metal levels in sediments by correcting for variable background concentrations that, if left uncorrected, only serve to increase total data variability and reduce detection of spatial and temporal differences. Examples of the application of baseline models to pollution studies are provided. A continuing decline in Pb concentrations in Mississippi River delta sediments is observed consistent with the declining use of Pb additives in gasoline since 1970. Major spatial trends in contaminant metals in sediments along the Atlantic and Gulf of Mexico coasts are noted.

Hart, B. S. and J. V. Barrie (1995). "Environmental geology of the Fraser delta, Vancouver." Geoscience Canada 22(4): 172-183.

Environmental geological and geophysical studies of the submarine portions of the Fraser delta at Vancouver reveal complex patterns of sedimentation, erosion and slope instability resulting from natural and industrial activity. Knowledge of the spatial and temporal variability of these processes is needed to help identify sea-floor hazards in areas of significant economic importance, and to monitor environmental contamination and changes to the physical environment due to industrial activity. Portions of the delta slope adjacent to the main fluvial distributary are prone to downslope mass movement in response to sediment loading, accentuated by the development of steep subaqueous slopes and interstitial (biogenic) gas. The presence of Canada's largest coal export facility, ferry terminals, and submarine high-voltage cables in close proximity to areas of mass movement are causes for concern. Triggering events for other large slope failure complexes (several tens of square kilometres in areal extent) include large earthquakes.

Hart, B. S., T. S. Hamilton, et al. (1998). "Sedimentation rates and patterns on a deep-water delta (Fraser Delta, Canada): Integration of high-resolution seismic stratigraphy, core lithofacies, and Cs-137 fallout stratigraphy." Journal of Sedimentary Research 68(4): 556-568.

The Fraser Delta is a Holocene feature with complex surficial geology that has built into the deep (> 300 m) water of the Strait of Georgia on Canada's Nest coast. We used high-resolution marine geophysical data, core lithofacies, and fallout stratigraphy to examine modern sedimentation rates on the delta slope and prodelta, Modern sedimentation rates, measured by the peak and onset of Cs-137 in cores, are in excess of 13 cm yr(-1) near the mouth of the main fluvial distributary but drop to less than 3 cm yr(-1) farther than 4 km offshore. Asymmetry to the pattern of sedimentation rates reflects both the prevailing oceanographic circulation and human influence. The map of modern sedimentation provides a synoptic view of this deltaic system that is of value to understanding older deltaic systems as well as the modern offshore environments on this populous and heavily used delta. In attempting to estimate the annual sediment discharge of the river from our sedimentation-rate map, we were able to account for slightly less than 40% of the measured river discharge. Our inability to adequately characterize the deposition and resedimentation of the sand fraction is probably responsible for most of the discrepancy.

Hole, J. A., T. M. Brocher, et al. (2000). "Three-dimensional seismic velocity structure of the San Francisco Bay area." Journal of Geophysical Research-Solid Earth 105(B6): 13859-13873.

Seismic travel times from the northern California earthquake catalogue and from the 1991 Bay Area Seismic Imaging Experiment (BASIX) refraction survey were used to obtain a three-dimensional model of the seismic velocity structure of the San Francisco Bay area. Nonlinear tomography was used to simultaneously invert for both velocity and hypocenters. The new hypocenter inversion algorithm uses finite difference travel times and is an extension of an existing velocity tomography algorithm. Numerous inversions were performed with different parameters to test the reliability of the resulting velocity model. Most hypocenters were relocated <2 km from their catalogue locations. Large lateral velocity variations at shallow (<4 km) depth correlate with known surface geology, including low-velocity Cenozoic sedimentary basins, high-velocity Cenozoic volcanic rocks, and outcrop patterns of the major Mesozoic geologic terranes. Salinian are rocks have higher velocities than the Franciscan melange, which in turn are faster than Great Valley Sequence forearc rocks. The thickess of low-velocity sediment is defined, including >12 km under the Sacramento River Delta, 6 km beneath Livermore Valley, 5 km beneath the Santa Clara Valley, and 4 km beneath eastern San Pablo Bay. The Great Valley Sequence east of San Francisco Bay is 4-6 km thick. A relatively high velocity body exists in the upper 10 km beneath the Sonoma volcanic field, but no evidence for a large intrusion or magma chamber exists in the crust under The Geysers or the Clear Lake volcanic center. Lateral velocity contrasts indicate that the major strike-slip faults extend subvertically beneath their surface locations through most of the crust. Strong lateral velocity contrasts of 0.3-0.6 km/s are observed across the San Andreas Fault in the middle crust and across the Hayward, Rogers Creek, Calaveras, and Greenville Faults at shallow depth. Weaker velocity contrasts (0.1-0.3 km/s) exist across the San Andreas, Hayward, and Rogers Creek Faults at all other depths. Low spatial resolution evidence in the lower crust suggests that the top of high-velocity mafic rocks gets deeper from west to east and may be offset under the major faults. The data suggest that the major strike-slip faults extend subvertically through the middle and perhaps the lower crust and juxtapose differing lithology due to accumulated strike-slip motion. The extent and physical properties of the major geologic units as constrained by the model should be used to improve studies of seismicity, strong ground motion, and regional stress.

Huang, Z. G., Y. Q. Zong, et al. (2004). "Coastal inundation due to sea level rise in the Pearl River Delta, China." Natural Hazards 33(2): 247-264.

This paper examines the increased potential risk of tidal inundations in the Pearl River delta, China, due to future rises in sea level. The research is based on tidal records of 54 tide gauges distributed across the delta plain, and employs mathematical calculations to predict potential rises of water level in different parts of the delta under a number of flood scenarios. After assessing a 72-year tidal record of Hong Kong and factors such as estuarine backwater effects and long-term geological subsidence, it suggests that a 30 cm rise in relative sea level at the mouth of the estuary is possible by 2030. Based on the prediction and five freshwater discharge scenarios, the potential impacts on water levels across the delta plain are calculated. Three zones are identified as least affected, heavily affected and severely affected. The impacts are also translated into return periods of water level. It is suggested that in a large part of the delta plain, return periods will be shortened and hence will be increasingly vulnerable to tidal inundation. Finally, management implications are discussed along with assessment of the adequacy of the existing tidal flood defences, as well as evaluation of the cost implications if they are to be improved.

Innocenti, L. and E. Pranzini (1993). "Geomorphological Evolution and Sedimentology of the Ombrone River Delta, Italy." Journal of Coastal Research 9(2): 481-493.

The geomorphological evolution and nearshore sediments textural characteristics of the Ombrone River delta are here described. The delta evolution, as deduced from archaeological and historical sources as well as from traditional geological studies, has been influenced by changes in land use that occurred during the last 2,500 years within the Ombrone River catchment area. The sedimentological study has been carried out using different granulometric data analysis techniques, such as the comparison of graphic parameters, grain-size spectra map analysis, and cluster analysis. These results are concordant with data coming from numerical modelling of longshore transport energy. The resulting sediment grain-size uniformity is explained on the basis of the recent Ombrone River plain evolution, which prevented coarse sediments from reaching the outlet, and also by wave energy which attacks the beach and removes the fines even at greater depths.

Jiang, Y. H., J. D. Wang, et al. (2004). "Analysis of the geomorphology and environmental geological problems of Huzhou on the Yangtze River delta." Acta Geologica Sinica-English Edition 78(3): 808-812.

Geomorphically, Huzhou, which is on the Yangtze River delta is characterized mainly by plains, with small hills. This paper presents a detailed analysis of the environmental geological hazards both natural and those incurred by human activities in different morphologic units. The authors point out that most of the regional environmental geological problems in the natural geologic-morphologic conditions, such as crustal stability, foundation of soft soil, soil waterlogging and soil erosion, have insignificant effects to the society, or related countermeasures of prevention and control have been adopted. But environmental geological problems incurred by human being's economic activities become more and more severe, for example, water and soil pollution and land subsidence in plain areas resulting from overexploitation of groundwater, and landslides, karst collapses and water and soil loss etc. caused by quarrying in hilly areas.

Koutitonsky, V. G., B. Long, et al. (1991). "The Influence of Hydrodynamical Processes on Sediment Transport in the Northern Gulf of St-Lawrence." Continental Shelf Research 11(8-10): 1209-1221.

Sediment transport on continental shelves occurs in response to a wide spectrum of hydrodynamical factors each acting at particular temporal scales. We document in this study one such factor, namely the quasi-periodic passage of large-scale meteorological storms over a region at synoptic frequencies (3-20 days). Our case study focuses on the geological evolution of the Natashquan river delta on the northern Gulf of St Lawrence shelf in relation to nearshore currents. Airgun seismic measurements show that the main deltaic lobe has migrated towards the west in a series of transient events. Time-series analysis of current measurements in the region reveals the presence of energetic current fluctuations occurring at synoptic frequencies; predominantly oriented alongshore and towards the west. These fluctuations are coherent with the large-scale winds. and the highest coherence is found around 15 days. Their amplitudes usually exceed 0.4 m s-1. And are thus capable of transporting the sediments found in the region. Tidal currents are less energetic (0.15-0.2 m s-1), are mainly semi-diurnal in nature and their amplitudes are modulated at the Mm periodicity (27.55 days). It is suspected that the Natashquan marine delta progressed towards the west mainly as a result of the transport of sediments by wind-driven current transients that occur during the progression of intense extra-tropical cyclones along the eastern boundary of the Gulf of St Lawrence.

Mathers, S. and J. Zalasiewicz (1999). "Holocene sedimentary architecture of the Red River Delta, Vietnam." Journal of Coastal Research 15(2): 314-325.

Remotely sensed satellite images, integrated with compilations of shallow geological data, enable elucidation of the Holocene facies architecture of the Red River Delta of Vietnam. The Holocene delta sediments are relatively fine-grained, up to 30 m thick, and represent rapid progradation during the current high sea level stand; they overlie a coarse-grained Pleistocene sequence of braided river and alluvial fan deposits formed during glacial low sea level stands. The Holocene delta shows roughly equal influence by fluvial, wave and tidal processes. In this it resembles the Niger Delta, but with the crucial difference that the facies belts are sectorial rather than concentric, being governed along the coast by differing amounts of shelter from wave action in a uniformly mesotidal setting. The wave-dominated sector appears to have advanced by leapfrogging' seawards, perhaps under the influence of episodic high-discharge fluvial flood events, producing lateral alternations of stacked sandy beach ridges and intervening fine-grained lagoonal deposits in chenier-like architectures.

Mathewes, R. W. and J. J. Clague (1994). "Detection of Large Prehistoric Earthquakes in the Pacific-Northwest by Microfossil Analysis." Science 264(5159): 688-691.

Geologic and palynological evidence for rapid sea level change similar to 3400 and similar to 2000 carbon-14 years ago (3600 and 1900 calendar years ago) has been found at sites up to 110 kilometers apart in southwestern British Columbia. Submergence on southern Vancouver Island and slight emergence on the mainland during the older event are consistent with a great (magnitude M greater than or equal to 8) earthquake on the Cascadia subduction zone. The younger event is characterized by submergence throughout the region and may also record a plate-boundary earthquake or a very large crustal or intraplate earthquake. Microfossil analysis can detect small amounts of coseismic uplift and subsidence that leave little or no lithostratigraphic signature.

Reed, D. J. (2002). "Sea-level rise and coastal marsh sustainability: geological and ecological factors in the Mississippi delta plain." Geomorphology 48(1-3): 233-243.

Chronostratigraphic approaches to coastal geomorphology frequently include consideration of salt marsh deposits as indicators of past sea-level positions. Continuous horizons of such deposits can be used to infer that salt marshes were keeping pace with local rates of relative sea-level rise (RSLR). Rates of past accumulation, estimated using dating techniques, are then used to hindcast the rate of sea-level rise in that area. Estimates of contemporary sea-level rise rates are often derived from tide gauge records. This approach allows identification of subdecadal variations in mean water level. Accumulation rates of both organic and inorganic sediments can also be derived at these time scales and studies from many coastal marshes demonstrate the episodic nature of inorganic sediment deposition. The frequency and spacing of these events does not necessarily coincide with periods of increased local sea level. In addition, short-term increases in sea level could result in marsh deterioration as soils become excessively waterlogged. A conceptual model of changes in geomorphic and ecological processes contributing to marsh sustainability during the Holocene has been developed for the Mississippi delta plain (MDP). The survival of some marshes in this area, despite high rates of subsidence, indicates that the combined effect of organic and inorganic accumulation processes can be adequate to sustain coastal marshes in the face of sea-level rise. (C) 2002 Elsevier Science B.V. All rights reserved.

Reinhardt, E. G., D. J. Stanley, et al. (1998). "Strontium isotopic-paleontological method as a high-resolution paleosalinity tool for lagoonal environments." Geology 26(11): 1003-1006.

A combined strontium isotopic (Sr-87/Sr-86) and paleontological method is newly applied to a modern lagoon in Egypt's Nile River delta to test its applicability as a paleosalinity proxy. Analyses of 22 surficial samples collected throughout the lagoon include 81 Sr isotopic analyses of mollusks, foraminifera, ostracods, barnacles, bryozoans, serpulid worm tubes, pore water, and gypsum crystals. Two salinity groups are distinguished in each sample: a lower salinity group (similar to 1 ppt) mixed with a higher salinity group (similar to 3-10 ppt) that, respectively, are interpreted as the modern biocoenosis and an older relict fauna. The relict fauna denotes higher salinity conditions in the lagoon prior to closure of the Aswan High Dam (1964), and the modern fauna records freshening of the lagoon. Recent decreased salinity is a response to regulated Nile River flow and increased discharge into Manzala of fresh water via canals and drains. Quantification of this short-term salinity change holds promise for study of modern lagoons in other world settings, and may provide paleoclimatic information for older lagoon sequences in the Nile River delta and the geologic record.

Roberts, M. C. and T. S. Murty (1989). "Influence of Delta Growth on Paleo-Tidal Flow - Fraser-River Delta, British-Columbia .1. Geological Framework and Evolution of the Delta." Marine Geodesy 13(3): 221-228.

Roberts, H. H. and J. M. Coleman (1996). "Holocene evolution of the deltaic plain: A perspective - From Fisk to present." Engineering Geology 45(1-4): 113-138.

Before publication of Fisk's classic scientific papers dealing with the Mississippi River alluvial valley and deltaic plain, geological knowledge of the Holocene deltaic plain was the product of surficial geomorphological studies with a temporal framework provided by archaeology. Fisk and his co-workers provided the third and fourth dimensions, the three-dimensional characteristics of sediment bodies, by numerous deep borings and better chronostratigraphy through C-14 dating. This research, and the emphasis of his work on fluvial processes, was largely responsible for the form-process approach in sedimentary geology and the awareness that depositional environments are represented by unique sedimentary sequences and properties. Although Fisk made many contributions to deltaic geology, six major areas are noteworthy: delta response to base level changes, sedimentary loading, processes of delta switching, delta abandonment and formation of transgressive sands, river diversion (Atchafalaya distributary), and deltaic sedimentary architecture. In order to comprehend the complexly structured Holocene deltaic plain, the processes of channel migration, meander belt formation, avulsion, and delta switching must be understood. Preceding the work of Fisk, landforms resultant from these processes were recognized by geomorphologists, and this body of research formed the foundation for Fisk's major contributions. Using the concept of changing sea levels during the Quaternary, Fisk was one of the initial scientists to recognize the importance of a changing base level and its effect on valley cutting and filling episodes, particularly during the process of valley filling by fluvial and deltaic sediments during rising sea level. In documenting these cyclic processes, he first postulated the development of canyons or trenches carved across the continental shelf, the development of shelf-edge deltas, and the feeding of the deep-sea fans during periods of lowered sea level. Trowbridge (1930) and Russell and Russell (1939) described the dendritic shape of delta lobes and indicated that they were offset and overlapping, resulting in the Holocene deltaic plain configuration; delta chronology was provided by utilizing archeological methods (McIntire, 1954). The pioneering work of Fisk and McFarlan (1955) on the Mississippi delta set the stage for refinement of delta lobe chronology. Details regarding the timing of important depositional events have been added by McFarlan (1961), Frazier (1967), Morgan (1970), Penland and Suter(1989) and, most recently, Autin et al. (1991). In collecting data on offshore Mississippi River delta deposits, Fisk documented the regional subsidence associated with loading by continuous delta deposition as well, as the localized subsidence associated with delta-front deposition and the formation of mud diapirs. He later applied this concept to the accumulation of peat deposits in interdistributary regions and the development of interdistributary bays. This research was the foundation for work by later scientists dealing with wetland loss in the deltaic plain. Fisk was the first major contributor to our current understanding of the stratigraphic-sedimentological architecture of the modern deltaic plain of the Mississippi River. The first cross-sections of the deltaic plain were published by Fisk (1947), prior to which there were little data for establishing the geometry of sediment bodies and spatial relationships of facies beneath the modern surface. Classic examples of this approach were the point bar and backswamp studies in the alluvial valley of the Lower Mississippi River (Fisk, 1944), his bar-finger sand paper (Fisk, 1961), and his more comprehensive sand facies paper (Fisk, 1955). This body of work on sedimentary facies relationships and specifically sand body geometries found wide acceptance among both academic and industry groups. At the time Fisk prepared his appraisal of sand facies in the Mississippi delta he was an employee of Humble Oil and Refining Company, and the paper was obviously directed toward understanding reservoir geometries and spatial relationships in a deltaic complex. In addition to the sedimentary architecture of the delta, Fisk also contributed to understanding of both the constructive and destructive cycles, the geotechnical properties of various delta facies, and subsidence, all of which helped establish an awareness of the critical need for geological knowledge in engineering applications. Since Fisk's contributions, the major advances in understanding the Holocene deltaic plain have been primarily in the realm of filling in the details of Fisk's sedimentary architecture. The mudlump studies of Morgan (1961) and work on crevasse splays and bay-fill sequences by Welder (1959), Coleman and Gagliano (1964), and Morgan (1970), as well as others, are good examples. Later, work on the new lobe of the deltaic plain, the Atchafalaya-Wax Lake delta complex (Shlemon, 1975; Roberts et al., 1980a, van Heerden and Roberts, 1980; van Heerden et al., 1983), added an element to the deltaic plain evolutionary story that was not available during Fisk's era. However, regardless of future research on the Mississippi River deltaic plain, the body of work produced by Fisk and his co-workers will always be recognized as the cornerstone of our understanding of this complex depositional system.

Roberts, H. H. (1997). "Dynamic changes of the Holocene Mississippi River delta plain: The delta cycle." Journal of Coastal Research 13(3): 605-627.

Previous geologic research on Holocene Mississippi River deltaic deposits has verified that the present delta plain and associated nearshore barrier islands and submarine shoals are either direct or indirect products of cyclic delta-building events that have operated on a variety of temporal and spatial scales. A major depositional element of the modern delta plain is the delta complex, of which there are six: (1) Maringouin, (2) Teche, (3) St. Bernard, (4) Lafourche, (5) Balize, and (6) Atchafalaya. Major delta-building events have occurred at a frequency of one every 1-2 kyr. Deposits associated with the six major delta complexes are fundamental constructional units of the delta plain, which collectively covers an area of similar to 30,000 km(2). Sedimentary deposits associated with these delta-building events range in thickness from about 10 to 100 m. Their construction is modulated by stream capture, which develops a new delta complex by way of a new river course. Delta complexes may be comprised of one or more delta lobes. As a product of this delta switching, the depositional architecture of the delta plain consists of laterally offset and stacked delta lobes. Within delta lobes are subdeltas and even smaller crevasse-splays. These smaller scale deltas sedimentologically and geomorphically mimic their larger delta lobe counterparts, but they are considerably thinner, cover less area, and have a shorter period of development and abandonment. Subdeltas are usually < 10 m thick and may fill shallow bays that cover over 300 km(2). They build and deteriorate on time-scales of 150-200 years. Crevasse-splays or overbank splays are < 5 m thick, cover only a few square kilometers, and are abandoned after several decades of active growth. Each delta evolves through a rapid regressional phase as water and sediment are captured from an antecedent river course. If highstand conditions persist long enough, deltas may prograde to the outer shelf to form wedges of deltaic sediment much thicker than their inner shelf counterparts. The delta-building process starts with the filling of interior lakes (lacustrine deltas), which is followed by bayhead delta-building at the coast, and finally by progradation across the marine shelf(shelf delta). Delta complexes and delta lobes, as well as their smaller counterparts, experience three phases of growth and abandonment: (1) rapid growth with increasing-to-stable discharge, (2) relative stability during initial stages of waning discharge, when sediment input balances the collective effects of subsidence, and (3) abandonment, followed by rapid subsidence-driven subaerial delta deterioration. In the rapid growth stage, formerly eroding-subsiding coastal environments experience delta plain accretion and coastal progradation from renewed sediment input. On the abandonment side of the cycle, marine processes overwhelm fluvial processes and rework the delta perimeter. Forced by the combined processes of subsidence, the delta surface undergoes progressive submergence. Transgressive sand bodies created by wave reworking of the delta evolve from headland beaches and spits, to barrier islands, and finally to submarine shoals as the abandonment phase is completed.

Saito, Y., H. L. Wei, et al. (2000). "Delta progradation and chenier formation in the Huanghe (Yellow River) Delta, China." Journal of Asian Earth Sciences 18(4): 489-497.

To clarify Holocene development of the Huanghe (Yellow River) delta and the relationship between delta progradation and chenier formation, detailed sediment analyses and high-resolution radiocarbon dating were done on borehole samples taken from two sites on the present Huanghe; H9601 (Latitude 37 degrees 40.5'N and Longitude 118 degrees 28.7'E with an altitude of + 5.5 m) and H9602 (Lat. 37 degrees 47.8'N and Long. 118 degrees 54.3'E, + 4.8 m). Downcore changes of sediment facies and accumulation rate show that delta progradation occurred at least twice during ca 2.6-1.2 C-14 yrBP and 1855-present at the two borehole sites. These phases of progradation correlate with Superlobes 6 and 7 and Superlobe 10 respectively, of ten superlobes composing the Holocene Huanghe Delta shown by C. Xue (Historical changes in the Yellow River delta, China, Marine Geology 113, 321-329, 1993). The boundary of these sediments at H9602 is sharp and erosional, and correlates with cheniers located between borehole sites on the delta plain. The diastem period between these phases of progradation almost coincides with the periods when the river mouth of the Huanghe was located in the northwestern part of the Bohai Sea during 1048-1128 AD (Superlobe 8), and the jiangsu region facing the Yellow Sea during 1128-1855 (Superlobe 9). This suggests that chenier formation and delta progradation are linked, and controlled by sediment supply and river course shifts of the lower reaches of the Huanghe. (C) 2000 Elsevier Science Ltd. All rights reserved.

Saleh, A., F. Al-Ruwaih, et al. (1999). "A reconnaissance study of a elastic coastal sabkha in Northern Kuwait, Arabian Gulf." Journal of Arid Environments 43(1): 1-19.

A elastic, tidal flat-sabkha complex characterizes the mesotidal coastline of Northern Kuwait. The Holocene tidal sediments of this area represent the western-most limit of the Shatt Al-Arab delta sediments. The area under study in Bahrah is subdivided according to its geomorphological features and depositional setting into eight sub-environments. The sediments are characterized by two distinct size populations; a coarse fraction of siliciclastic sand derived from a local source area (the Jal-Az-Zor escarpment); and a dominant, mud-size mode of more distinct origin. The mud-size, elastic fraction is dominated by detrital carbonates (low-Mg calcite with minor dolomite). The latter sediments are brought to the area through direct aeolian fallout and through the reworking of the delta sediments by counterclockwise currents in the northern Arabian Gulf. Since the coastal areas are bordered by the hypersaline basin of the Arabian Gulf, biological activity is limited in the tidal zones. As a result, most of the internal sedimentary structures are preserved, with minor disruption caused by intra-sedimentary gypsum growth. Progradation of the coastline has been going on since about 3040 years B.P. at the rate of 1.5 to 2 m per year. The 'early Holocene' transgressive sediments are made up of patchily distributed, autochtonous carbonates (aragonitic oolites, pellets and micrite) similar to those of other Recent carbonate provinces on the southern coast of the Arabian Gulf. A unique tidal regime characterizes the northern coastal zone. Maximum flooding of the supratidal area is dependent on the coincidence of high water spring and/or storm tides with south-easterly winds. This results in a very small area (0.6-0.7 km) of the tidal zone being subjected to flood recharge during the normal tidal cycle. The study area therefore, can be described as a 'wind tidal flat'. This area is unique among modern sedimentary environments and a similar example is not known from either modern sedimentary settings elsewhere or from ancient analogues. The closest comparable example is the Colorado River delta. Bahrah area contrasts with the southern shoreline of Kuwait and the southern Arabian Gulf coastline which are characterized by carbonate-hosted sabkhas. The semi-quantitative model developed in this study may be used to characterize similar ancient analogues from the geological record. (C) 1999 Academic Press.

Tanabe, S., K. Hori, et al. (2003). "Song Hong (Red River) delta evolution related to millennium-scale Holocene sea-level changes." Quaternary Science Reviews 22(21-22): 2345-2361.

The Song Hong (Red River) delta occurs on the northwest coast of the South China Sea. Its evolution in response to Holocene sea-level changes was clarified on the basis of sedimentary facies and 14 radiocarbon dates from the 40 m long Duy Tien core from the delta plain, and using previously reported geological, geomorphological, and archaeological data. The delta prograded into the drowned valley as a result of early Holocene inundation from 9 to 6 cal. kyr BP, as sea-level rise decelerated. The sea-level highstand at + 2-3 m from 6 to 4 cal. kyr BP allowed widespread mangrove development on the delta plain and the formation of marine notches in the Ha Long Bay and Ninh Binh areas. During sea-level lowering after 4 cal. kyr BP, the former delta plain emerged as a marine terrace, and the delta changed into the present tide- and wave-influenced delta with accompanying beach ridges. Delta morphology, depositional pattern, and sedimentary facies are closely related to Holocene sea-level changes. In particular, falling sea level at 4 cal. kyr BP had a major impact on the evolution of the Song Hong delta, and is considered to be linked to climate changes. (C) 2003 Elsevier Ltd. All rights reserved.

Thurlow, J. G., C. P. Spencer, et al. (1992). "Geological Interpretation of a High-Resolution Reflection Seismic Survey at the Buchans Mine, Newfoundland." Canadian Journal of Earth Sciences 29(9): 2022-2037.

Sixteen kilometres of high resolution Vibroseis reflection seismic data have been acquired in the vicinity of the former Buchans mine. Direct identification of the cause of several reflectors is possible because the geology is tightly constrained by underground workings and drill holes both of which locally exceed 1 km depth. Many of the mine-scale thrust faults are imaged as reflectors but conformable and intrusive contacts generally responded poorly. A significant shallow-dipping thrust, the Powerline Fault, is recognized below the orebodies and traced throughout the Buchans area, primarily as a result of the seismic survey. It truncates ore stratigraphy and forms the floor thrust of a large duplex - stack, which hosts all the orebodies. Its presence has negative implications for exploration in the immediate mine area. Several lines of evidence suggest that this fault has a significant component of out-of-sequence movement. A strong reflector 4.5 km below Buchans is correlated with the surface expression of the Victoria River Delta Fault, an important regional structure, newly recognized southeast of Red Indian Lake. This shallow, north-dipping sole thrust forms the structural base of the Buchans Group and brings it above a younger fossiliferous Llanvirn volcanic sequence. This fault is not itself the Red Indian Line but is one of a series of faults that collectively effect substantial geological contrasts in central Newfoundland. The seismic survey was a cost-efficient means of gaining knowledge of Buchans structure, which might otherwise have been acquired at much higher cost and over a longer period of time.

Todd, B. J. and S. R. Dallimore (1998). "Electromagnetic and geological transect across permafrost terrain, Mackenzie River delta, Canada." Geophysics 63(6): 1914-1924.

The time-domain electromagnetic (TDEM) method provides a surface geophysical technique suitable for interpreting deep permafrost conditions. This paper describes profiles collected in early spring in a transitional area of the Mackenzie Delta, Arctic Canada, with differing permafrost conditions and surficial geology. These data augment previously published profiles and allow the construction of a 30-km-long TDEM transect from the Holocene-age Mackenzie Delta in the southwest to the Pleistocene-age Tuktoyaktuk Coastlands in the northeast. The geoelectric section produced from the TDEM data is interpreted in terms of permafrost distribution. This interpretation provided a basis for inferring lithologic changes. Unconsolidated, non-ice-bonded (unfrozen) sediment has resistivities less than 10 ohm-m. partially ice-bonded sediment ranges in resistivity from 10 Co 40 ohm-m. Ice-bonded (frozen) sediment has resistivities from 30 to 300 ohm-m. Bedrock has low resistivities (from 5 to 15 ohm-m). Interpretation of the geoelectric section derived from both the shallow (<200 m) and deep (>500 m) TDEM data suggests that the main body of permafrost increases in thickness from 50 to 500 m over a few kilometers. A horizontally persistent unfrozen zone (taIik) is situated from 50 to 100 m in depth within the main body of permafrost. Ice-bonding models derived from the TDEM surveys provide constraints on the geologic history of the Mackenzie Delta.

Tugarova, M. A., A. V. Goncharov, et al. (1999). "The transformation of dynamic parameters of oil-contaminated sediments of north European Russia." Physics and Chemistry of the Earth Part B-Hydrology Oceans and Atmosphere 24(7): 875-878.

The study of dynamic parameters of terrigenious material was carried out in subaqueous areas of the North European Russia and in the coastal Pechorskoe sea including Pechora river delta. The areas are characterized by extremely wide spreading of fluxes, lakes, terrigenious material was carried out in subaqueous areas of the North European Russia and in the coastal Pechorskoe characterized by extremely wide spreading of fluxes, lakes, marshes. This is the intensive exploited oil-gas area. The geological survey and the existence of pooled recoverable hydrocarbons are accompanied by the pollution of the natural environments and upper lithosphere. The main oil-pollution is accumulated in soils and sediments of small flows. The periodic processes (high-flood, snow thaw) include the contaminated sediments in transfer. According by the natural investigations of the spreading range of oil-pollutions connected with terrigenious material can be highly essential. The experimental work was based on the comparison of structural and dynamic characteristics of polluted sediments and the same sediments purified from oil-products. The average breaking and accumulated velocities for the sediments of different lithology with various concentrations of oil-products were determined. Parallel we determined  :  the character of interaction of mineral and oil parts (morphological forms of oil-contaminents), the quantitive and qualitative composition of oil-products in different size fractions of sediments. The dynamic of moderately oil-contaminated sediments is governed by natural dynamical processes. At 10 and more times background concentrations, oil-products influence to the structural changes of sediments and as a result to the processes of transfer and accumulation. The results of investigations allow us to predict the distance of migration, possible zones of accumulation and the scale of oil-pollution in bottom sediments. (C) 1999 Elsevier Science Ltd. All rights reserved.

van Heijst, M., G. Postma, et al. (2001). "Quantitative analogue flume-model study of river-shelf systems: principles and verification exemplified by the Late Quaternary Colorado river-delta evolution." Basin Research 13(3): 243-268.

Physical modelling of clastic sedimentary systems over geological time spans has to resort to analogue modelling since full scaling cannot be achieved within the spatial and temporal restrictions that are imposed by a laboratory set-up, Such analogue models are suitable for systematic investigation of a sedimentary system's sensitivity to allocyclic changes by isolating governing parameters. Until now, analogue models of landscape evolution were mainly qualitative in nature. In this paper, we present a quantitative approach. The quantitative experimental results are verified and discussed by comparison with high-resolution data from the Colorado river-shelf system of the Texas shelf that we used as a prototype. The model's dimensions are proportionally scaled to the prototype, except for a vertical exaggeration. Time is scaled using a Basin Response factor to maintain a similar ratio between the period of change and the system's equilibrium time for model and prototype. A Basin Fill factor was used to compare the ratio between the time-averaged sedimentation rate and the rate of change in accommodation space of model and prototype. The flume-model results are in the form of sediment budgets that are related to shelf cannibalism and fluvial supply, which are compared with the ancestral Colorado river-delta evolution of the last 40 kyr. Model and prototype have similarities in delta evolution in response to one cycle of sea-level change. With sea-level change as the isolated variable, the flume model generates a significant supply pulse caused by headward erosion of the shelf in response to the sea-level fall. This pulse adds to the yield of the hinterland. The supply induced by sea-level change persists during the early rise, although its rate declines. A similar trend is observed on the east Texas shelf. We argue that shelfal and fluvial degradation cycles induced by sea-level changes can significantly influence the timing and amount of sediment supply to basins and Must therefore be taken into consideration.

Vernberg, F. J. (1993). "Salt-Marsh Processes - a Review." Environmental Toxicology and Chemistry 12(12): 2167-2195.

Salt marshes are found between the high tide and the near-shore sublittoral zones along the coasts and up estuaries of continents, primarily in the temperate zone. They flourish in regions where much silt is carried to the coastal regions by rivers or where geological processes favor erosion and suspension of silt. Salt marshes have multiple ecological and economic values. They have a high rate of primary productivity; provide habitats for many marine species (including commercially important organisms); assist in flood and erosion control; lessen the effects of stormwater surges; and improve water quality by filtering pollutants, excess nutrients, and disease-causing microorganisms. In addition, this habitat is used for recreational and educational purposes by millions of people who spend millions of dollars. Although the myriad functions and uses of this habitat attest to its tremendous importance, legal protection of salt marshes varies significantly throughout the world. Salt-marsh processes are governed by the interactions between ''natural'' physical, chemical, geological, and biological factors. Of importance to ecotoxicologists and other scientists is understanding the intimate interaction between these various abiotic and biotic factors. This paper reviews the functional processes of salt marshes and discusses recent research advances under the following major headings: (a) physical, geological, and chemical factors; (b) biotic factors (including productivity of vascular plants, phytoplankton, epibenthic algae, and attached macrophytes; secondary production of primary and secondary consumers; and decomposition; (c) material cycling, biogeochemical cycling, and nutrients; (d) long-term changes; and (e) interaction with adjacent ecosystems.

Walker, H. J. (1998). "Arctic deltas." Journal of Coastal Research 14(3): 718-738.

Arctic river deltas are among the most unique annd fragile of deltas to be found on earth. Leading to this uniqueness and fragility are the interactions between geologic, oceanographic, climatologic, biologic, and cryospheric activities that occur in high latitudes. These interactions are analyzed at both regional and local levels with respect to their influence on delta formation. Specific morphological forms, such as ice-wedge polygons, and processes, such as thermoerosion, that are associated with permafrost are identified. Arctic deltas, including the Ob, Lena, Yenisey, Mackenzie, Yukon and Colville, are discussed illustrating the diverse range of variables affecting deltaic processes. Variables considered include age, size, shape, discharge, sediment load and surface forms. Current anthropogenic impacts on deltaic resources, such as construction associated with hydrocarbon production, are considered as is the potential for change that could result from a rising sea level.

Zong, Y. Q. (2004). "Mid-holocene sea-level highstand along the southeast coast of China." Quaternary International 117: 55-67.

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 18degreesN and 32degreesN) 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 sealevel 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 1-2m higher highstand is found from sites where tectonic uplift is observed. (C) 2003 Elsevier Ltd and INQUA. All rights reserved.