Land-derived Sediments Research Articles

Early extensional salt tectonics controls deep-water sediment dispersal

Predicting the distribution of sedimentary facies during the early stages of deformation of salt-detached continental margins is key to constraining the location and stratigraphic architecture of hydrocarbon and CO2 reservoirs, as well as to understanding the oceanic carbon cycle. Despite its importance, we still have a relatively poor understanding of salt-sediment interactions during the early phases of extensional salt tectonics, mainly because subsequent salt-related deformation and/or deep burial of the related stratigraphic succession means the related deposits are poorly imaged in seismic reflection data and/or not penetrated by borehole data. We investigated the interplay between early extension-related salt deformation and deep-water sediment dispersal using 3-D seismic reflection data from the northern Levant Basin offshore Lebanon. Our results indicate that salt tectonics has two contrasting impacts: Whereas slope-parallel faults favor early sediment transfer along downslope-oriented corridors to the abyssal plain, slope-normal faults and ramp-syncline basins trap land-derived sediments, hampering or delaying their transport to the abyssal plain. These results help refine source-to-sink models of turbidite systems developing in young salt basins, highlighting the crucial role of extensional tectonics in controlling sediment dispersal and the development of intra-slope depocenters and emphasizing the impact of fault strike, ramp-syncline basin evolution, and salt thinning. Our study has significant implications for predicting the location of deep-water coarse-grained sediment and the preservation of land-derived organic carbon in mature, more structurally complex, salt basins.

Coastal morphology and heavy mineral accumulation in an upper-macrotidal environment – A geological-mineralogical approach from source to trap site in a natural placer laboratory (Channel Islands, Great Britain)

The Isles of Jersey and Guernsey, GB, are situated in the Bight of St. Malo which ranks among the upper-macrotidal environments with one of the highest tidal ranges ever measured on the globe. They are built up of metasedimentary and –magmatic basement rocks followed by a suite of gabbro-diorite-granite intrusive rocks. Based on sedimentological, geomorphological and mineralogical investigations focused on heavy minerals (HM) the coastal environment has been subdivided into three principal coastal types headland-, headland-bay and bay types. Chemical and physical weathering, neotectonics, eustatic sea level changes, wave action, land-derived sediment supply and aeolian processes had not only a strong impact on the various coastal landform series (CLFS) established but also on the variegated HM assemblages casting them into the role of markers for the coastal environment and some kind of an ore guide for marine placer deposits. Tidal-dominated coastal environments under study sculptured exclusively out of crystalline bedrocks are conservative with regard to the economic geology and potential of HM placer-type deposits provided while physical weathering predominates over the chemical one. The tidal processes in context with the other land-forming processes are special importance for the diversity of coastal features within the environment hosting HM on a small- and large-scale. Neotectonics may accentuated or suppress tidally-controlled features in that strong uplift and provokes typical tidal features to get suppressed so that vast tidal flats are missing in a great deal of coastal areas and rocky coasts formed instead with consequences for the accumulation of HM. The “GMS tool (granulometry-morphology-situmetry) has methodologically proved to be very effective for the study of the coastal zones hosting HM in two principal ways. Granulometric and the morphological variation of HM can successfully be used for the host rock environment analysis (“ore guide”). Morphometric studies and situmetric measurements of gravel clasts in the coastal sediments bearing HM accompanied by similar measurement of joints and faults cutting through the bedrock can assist in the localization of HM trap sites in shoreline platforms and their rock veneer. The HM associations in upper-macrotidal environments are variegated in terms of morphology, mineralogical composition and their geomorphological trap sites so that they constitute a natural laboratory for environment analysis in terms of hydrodynamic and (paleo) climate along marine terrigenous shorelines and help better understand the way of HM from source to trap site in modern and paleoplacers.

Biostratigraphy of acritarchs, chitinozoans, and miospores from Upper Ordovician sequences in Kuh-e Boghou, southwest of Kashmar, eastern central Iran: Stratigraphic and paleogeographic implications

A siliciclastic succession is well exposed at Kuh-e Boghou, located in eastern-central Iran. To verify the exact age and paleogeographic position of this section of the Iranian Platform, a detailed, high-resolution palynological analysis of the Ghelli Formation was performed. Sixty-nine surface samples of the sedimentary succession were collected and analyzed. Most samples yielded abundant and well-preserved acritarchs (34 species of 24 genera), euglenids (3 species of a single genus), chitinozoans (36 species of 19 genera), and cryptospores (25 species of 10 genera). Based on the presence of well known chitinozoan species, a Late Ordovician (Katian–Hirnantian) age was assigned to this succession. The identified chitinozoan fauna allowed recognition of the Belonechitina robusta, Tanuchitina fistulosa, Armoricochitina nigerica, Ancyrochitina merga, Tanuchitina elongata, and Spinachitina oulebsiri biozones in ascending stratigraphic order as was previously established for the northern Gondwanan Domain. These results indicate that eastern-central Iran was part of the peri-Gondwana domain during the Late Ordovician. Seven morphotypes were recorded for the first time, and five of them were established as new species, namely Abditusdyadus khayyammii, Alhajrichitina spinifera, Dyadospora ferdowsii, Lophosphaeridium bulbosumensis and Moyeria hafezii, and two were left in open nomenclature (e.g. Eisenackitina sp. and Moyeria sp. A). The abundant cryptospore taxa in the Late Ordovician might be related to land-derived sediments acquired during the global sea level fall in the Late Ordovician glaciation or to the adaptation of primitive land plants in a wide range of climatic conditions. The association of terrestrial miospores with marine palynomorphs suggests a nearshore marine environment.

Significance to hydrocarbon exploration of terrestrial organic matter introduced into deep marine systems: Insights from the Lower Cretaceous in the Levant Basin

Oil shows from wells in the Levant Basin and Egypt are suggestive of potential economic discoveries within unpenetrated Mesozoic reservoirs in the Eastern Mediterranean. Analysis of some of these oils indicate a non-marine source of mixed deltaic-terrestrial or lacustrine origin for the organic matter. Data from Barremian-Aptian sediments from the MNUPH-1 core in northern Israel opens a window on potential importance of terrestrial-sourced kerogen deposited in source rocks in a marine depositional environment.Core analyses of the Barremian Nabi Sa'id Fm. demonstrate the occurrence of a gas-prone immature source rock of >77 m gross thickness averaging 4.6% TOC, peaking at 37% TOC. Rock-Eval pyrolysis, biomarker n-alkane, sterane, and tricyclic terpane indices, atomic C/N ratios, and δ13Corg ranges indicate mixed terrestrial-marine organic source rocks for the Barremian, while higher up, the Aptian Hidra Fm. contains source rocks with organic matter derived dominantly from carbohydrate-rich land plants. The interval at MNUPH-1 includes abundant evidence for off-shelf mass transport of terrestrial and proximal marine sediments into the deep marine basin. These features are used to explain the anomaly of a terrestrial source for organic matter in this setting. Mass transport and consequent mixing of distal marine, proximal marine and land-derived sediment is, in fact, the norm at the foot of continental slopes globally.The dominantly type III source rocks described here would be unlikely to expel oil but might produce thermogenic gas. Thermogenic gas identified in similar marine settings might wrongly be interpreted as having been generated from marine organic matter, misleadingly indicative of a prospective oil source. When prospecting for deep-rooted hydrocarbon accumulations in offshore marine settings, an alternative system dominated by basinward sediment transport of gas-prone ‘terrestrial’ source rocks into strategically-positioned toe-of-slope marine settings, is supported here, and could well be producing gas in the Levant Basin.

Widespread Deposition in a Coastal Bay Following Three Major 2017 Hurricanes (Irma, Jose, and Maria)

In 2017, three major hurricanes (Irma, Jose, and Maria) impacted the Northeastern Caribbean within a 2-week span. Hurricane waves can cause physical damage to coastal ecosystems, re-suspend and transport antecedent seafloor sediment, while the associated intense rainfall can yield large influxes of land-derived sediment to the coast (e.g. burial of ecosystems). To understand sedimentation provenance (terrestrial or marine) and changes induced by the hurricanes, we collected bathymetry surveys and sediment samples of Coral Bay, St. John, US Virgin Islands in August 2017, (pre-storms) and repeated it in November 2017 (post-storms). Comparison reveals morphologic seafloor changes and widespread aggradation with an average of ~25 cm of sediment deposited over a 1.28 km2 benthic zone. Despite an annual amount of precipitation between surveys, sediment yield modeling suggests watersheds contributed <0.2% of the total depositional volume. Considering locally established accumulation rates, this multi-hurricane event equates to ~1–3 centuries of deposition. Critical benthic communities (corals, seagrasses) can be partially or fully buried by deposits of this thickness and previous studies demonstrate that prolonged burial of similar organisms often leads to mortality. This study illuminates how storm events can result in major sediment deposition, which can significantly impact seafloor morphology and composition and benthic ecosystems.

Giant kelp forests at critical light thresholds show compromised ecological resilience to environmental and biological drivers

Replacement of kelp and fucoid forests by low biomass turfing communities or urchin barrens has been identified in temperate marine ecosystems worldwide. Variation in the mechanisms of decline (e.g., urchin grazing, temperature stress) and apparent driving stressors (e.g., overfishing, sedimentation, global warming) has greatly limited the development of generalized management strategies. Thresholds of urchin density and thermal tolerance for habitat-forming seaweeds are increasingly well established, yet thresholds of turbidity are rarely considered. Given the universal requirement for light in aquatic macrophytes, estimation of photosynthetically active radiation (PAR) limits may help underpin frameworks for better management of terrestrial stressors. Here I have examined spatial and temporal variability of PAR in forests of the giant kelp Macrocystis pyrifera across a gradient of exposure to land-derived sediments. Exposure to excess suspended sediments pushed PAR below critical thresholds for net sporophyte growth (<1.0 mol m−2 day−1), affecting giant kelp densities, but also impacting a range of ecological metrics including: fucoid density; laminarian density; beta diversity metrics; subcanopy composition; and urchin density. While kelps and fucoids responded to similar light thresholds, kelps appear to be vulnerable to physical disruption by sediments whereas fucoids are tolerant of physical disruption mechanisms, but vulnerable to declining light availability. Light thresholds of 1.0 mol m−2 day−1 may be a useful target for management of stressors affecting water clarity (e.g., sedimentation, eutrophication), with universal applicability across diverse groups of aquatic photoautotrophs.

An environmental magnetism approach to assess impacts of land-derived sediment disturbances on coral reef ecosystems (Cartagena, Colombia)

We used environmental magnetism methods to study recently deposited marine sediments from the estuarine ecosystems on the Caribbean coast of Colombia. Cartagena region has undergone an increasing sediment load during the last decades via sediment plumes from Magdalena River and its distributary man-made channel. Concentration dependent magnetic parameters show an increasing abundance of ferrimagnetic minerals on the uppermost sediments on sites located close to the continent (remanent magnetization SIRM = 5.4–9.5 × 10−3Am2 kg−1) as well as faraway sites (SIRM = 0.5–1.7 × 10−3Am2 kg−1 near Rosario Islands coral reef complex). The magnetic grain size and mineralogy along the cores are variable, showing the dominance of the magnetite-like minerals (remanent coercivity Hcr = 34.3–45.3 mT), with a minor contribution of high-coercivity minerals (Hcr = 472–588 mT). In addition, there is a moderate enrichment of elements Cu, Mo, and Zn (enrichment factor EF = 1.5–3.8) that indicates the additional land-derived contribution on sediments. The environmental magnetism approach, which shows significant signals of magnetic minerals and trace elements, is a reliable tool to prove the presence of continental sediment supply in coral reef ecosystems.

Exposure of coastal ecosystems to river plume spreading across a near-equatorial continental shelf

The Berau Continental Shelf (BCS) in East Kalimantan, Indonesia, harbours various tropical marine ecosystems, including mangroves, seagrass meadows and coral reefs. These ecosystem are located partly within reach of the Berau River plume, which may affect ecosystem health through exposure to land-derived sediments, nutrients and pollutants carried by the plume. This study aims (1) to assess the exposure risk of the BCS coastal ecosystems to river plume water, measured as exposure time to three different salinity levels, (2) to identify the relationships between these salinity levels and the abundance and diversity of coral and seagrass ecosystems, and (3) to determine a suitable indicator for the impacts of salinity on coral reef and seagrass health. We analysed hydrodynamic models, classified salinity levels, and quantified the correlations between the salinity model parameters and ecological metrics for the BCS systems. An Empirical Orthogonal Functions (EOF) analysis revealed three modes of river plume dispersal patterns, which strongly reflect monsoon seasonality. The first mode, explaining 39% of the variability, was associated with the southward movement of the plume due to northerly winds, while the second and third modes (explaining 29% and 26% of the variability, respectively) were associated with the northeastward migration of the plume related to southwesterly and southerly winds. Exposure to low salinity showed higher correlations with biological indicators than mean salinity, indicating that low salinity is a more suitable indicator for coastal ecosystem health. Significant correlations (R2) were found between exposure time to low salinity (days with salinity values below 25 PSU) with coral cover, coral species richness, seagrass cover, the number of seagrass species, seagrass leaf phosphorus, nitrogen, C:N ratio and iron content. By comparing the correlation coefficients and the slopes of the regression lines, our study suggests that coral reefs are more susceptible to low salinity levels exposure than seagrass meadows. Regarding the risk of corals being exposed to low salinity, nearshore and northern barrier reefs were classified as “high risk”, the middle barrier reef as “medium to high risk” and southern barrier reefs as “medium risk”. Further offshore, the oceanic reefs were classified as “low risk”. Regarding the seagrass meadows, the nearshore region was categorized as “high risk”, the barrier reef as “medium to low risk” and oceanic reefs as “low risk”. This study contributes to assessing the potential impacts of salinity on the BCS ecosystems, and further provides a knowledge base for marine conservation planning.

Diverse and durophagous: Early Carboniferous chondrichthyans from the Scottish Borders

ABSTRACTChondrichthyan teeth from a new locality in the Scottish Borders supply additional evidence of Early Carboniferous chondrichthyans in the UK. The interbedded dolostones and siltstones of the Ballagan Formation exposed along Whitrope Burn are interpreted as representing a restricted lagoonal environment that received significant amounts of land-derived sediment. This site is palynologically dated to the latest Tournaisian–early Viséan. The diverse dental fauna documented here is dominated by large crushing holocephalan toothplates, with very few, small non-crushing chondrichthyan teeth. Two new taxa are named and described. Our samples are consistent with worldwide evidence that chondrichthyan crushing faunas are common following the Hangenberg extinction event. The lagoonal habitat represented by Whitrope Burn may represent a temporary refugium that was host to a near-relict fauna dominated by large holocephalan chondrichthyans with crushing dentitions. Many of these had already become scarce in other localities by the Viséan and become extinct later in the Carboniferous. This fauna provides evidence of early endemism or niche separation within European chondrichthyan faunas at this time. This evidence points to a complex picture in which the diversity of durophagous chondrichthyans is controlled by narrow spatial shifts in niche availability over time.

Cryptospore and trilete spore assemblages from the Late Ordovician (Katian–Hirnantian) Ghelli Formation, Alborz Mountain Range, Northeastern Iran: Palaeophytogeographic and palaeoclimatic implications

Well-preserved miospore assemblages are recorded from the Late Ordovician (Katian–Hirnantian) Ghelli Formation in the Pelmis Gorge, located in the Alborz Mountain Range, Northeastern Iran. The palynomorphs were extracted from siliciclastic deposits that are accurately dated using marine palynomorphs (acritarchs and chitinozoans). The spore assemblages consist of 14 genera and 28 species (26 cryptospores and 2 trilete spore species). Six new cryptospore species are described: Rimosotetras punctata n.sp., Rimosotetras granulata n.sp., Dyadospora asymmetrica n.sp., Dyadospora verrucata n.sp., Segestrespora iranense n.sp., and Imperfectotriletes persianense n.sp. The study furthers knowledge of the development of the vegetative cover during the Late Ordovician. Various and abundant cryptospores in the Late Ordovician (Katian–Hirnantian) Ghelli Formation are probably related to the augmentation of land-derived sediments either during the global sea-level fall linked to the Late Ordovician glaciation or adaptation of the primitive land plants in a wide range of climatic conditions. These miospore taxa were produced by the earliest primitive land plants, which probably grew close to the shoreline and were washed in from adjacent areas, producing a high volume of miospores. The associated marine palynomorphs consist of acritarchs (13 genera and 18 species), chitinozoans (9 genera and 10 species), prasinophycean algae, scolecodonts, and graptolite remains, which are not discussed in detail herein. The established chitinozoan biozones of this part of the Palaeozoic sequence are the Armoricochitina nigerica Biozone, the Ancyrochitina merga Biozone, the Tanuchitina elongata Biozone, and the Spinachitina oulebsiri Biozone, suggesting a Late Ordovician age (Katian–Hirnantian). These chitinozoan biozones are widely evidenced only in the peri-Gondwanan Domain, indicating that the study area was part of this palaeo-continent in the Late Ordovician.

Miospore assemblages from Late Ordovician (Katian-Hirnantian), Ghelli Formation, Alborz Mountain Range North-eastern Iran: Palaeophytogeographic and palaeoclimatic implications

Well-preserved miospore assemblages are recorded from the Late Ordovician (Katian-Hirnantian), Ghelli Formation in Pelmis-gorge at the north-eastern Alborz Mountain The palynomorphs were extracted from siliciclastic deposits which are well-dated by using of marine palynomorphs (acritarchs and chitinozoans). The encountered miospore assemblages consist of 14 genera (28 species: 26 cryptospores and 2 trilete spores). Six new cryptospore taxa are described: Rimosotetras punctata, Rimosotetras granulata, Dyadospora asymmetrica, Dyadospora verrucata, Segestrespora iranense and Imperfectotriletes persianense. The present findings contribute to improving knowledge of origin and onset of development of vegetative cover during the Late Ordovician. The recovery of diverse and abundant cryptospores in the Late Ordovician (Katian-Hirnantian) Ghelli Formation are probably related to increasing input of land-derived sediments during the global sea-level fall linked to the Late Ordovician glaciation, and tolerance of the primitive land plants in a wide range of climatic conditions. These miospore taxa were produced by earliest primitive land plants which probably grew close to the shoreline and washed in from the adjacent areas and produced high amount of miospores. The associated marine palynomorphs consist of acritarchs (13 genera and 18 species), chitinozoans (9 genera and 10 species), prasinophycean algae, scolecodonts and graptolite remains which are not discussed in detail herein. The established chitinozoan biozones of this part of Palaeozoic sequences are Armoricochitina nigerica, Ancyrochitina merga, Tanuchitina elongata and Spinachitina oulebsiri, suggesting the Late Ordovician (Katian-Hirnantian). These chitinozoan biozones are well-known only in peri-Gondwanan Domain, indicating that the study area has been part of this palaeo-continent during the Late Ordovician.

An exploratory model study of sediment transport sources and deposits in the Bohai Sea, Yellow Sea, and East China Sea

A regional ocean circulation model (ROMS) is used to simulate the Chinese land-derived sediment transport in the Bohai Sea, Yellow Sea, and East China Sea (BYECS). The model includes the effect of currents, tides, and waves on the sediment transport and is used to study the pathway and dynamic mechanisms of the fine-grain sediment transport from the Huanghe River (Yellow River), the Old Huanghe Delta, and the Changjiang River (Yangtze River) in the BYECS. The seasonal variability of the sediment transport in the BYECS and the sources of the Yellow Sea Trough mud patch, the mud patch southwest of Cheju Island, the mud patch offshore from the Zhejiang and Fujian provinces and the Okinawa Trough mud patch are discussed. The results show that the Huanghe River sediment can be transported to the Yellow Sea Trough, but little makes it to the outer shelf while the Old Huanghe Delta sediment is mainly transported to the Yellow Sea Trough. Most of the sediment from the Changjiang River mouth is carried to the mud patch off the coast of the Zhejiang and Fujian provinces but with part of this sediment also transported to the Yellow Sea Trough. The model shows that it is difficult to transport land-derived sediment to the Okinawa Trough mud patch under normal conditions. The model also has difficulty accounting for the deposition of sediment in the region to the southwest of Cheju Island and offshore from the Zhejiang and Fujian provinces, an issue requiring further study.

Cryptospore assemblages from Upper Ordovician (Katian–Hirnantian) strata of Anticosti Island, Québec, Canada, and Estonia: Palaeophytogeographic and palaeoclimatic implications

Rich palynological assemblages have been recovered from deposits of Hirnantian age in Anticosti Island (Québec, Canada), and in borehole Valga-10 in southern Estonia. The assemblages are well preserved, and include acritarchs, chitinozoans, and cryptospores. The age of the deposits is well constrained by means of palynomorphs (acritarchs and chitinozoans) as well as sequence stratigraphic and chemostratigraphic correlations. Cryptospore assemblages from the two localities are similar and are also broadly comparable to the few known coeval assemblages described elsewhere. They include 11 genera and 20 species, and testify to the presence of an extended and diverse flora during Hirnantian times in Laurentia and, for the first time, also in Baltica. The present findings contribute to an improved knowledge of origin and early development of vegetative cover. The recovery of diverse and abundant cryptospores in Hirnantian deposits may be related to increased input of land-derived sediment during the global sea-level fall linked to the Late Ordovician glaciation, but it also demonstrates that the early land plants may have tolerated a wide range of climatic conditions.

Major perturbation in sulfur cycling at the Triassic-Jurassic boundary

Research Article| September 01, 2009 Major perturbation in sulfur cycling at the Triassic-Jurassic boundary Kenneth H. Williford; Kenneth H. Williford 1University of Washington, Seattle, Washington 98195, USA *Current address: Curtin University of Technology, Perth, Australia; E-mail: k.williford@curtin.edu.au. Search for other works by this author on: GSW Google Scholar Julien Foriel; Julien Foriel 1University of Washington, Seattle, Washington 98195, USA Search for other works by this author on: GSW Google Scholar Peter D. Ward; Peter D. Ward 1University of Washington, Seattle, Washington 98195, USA Search for other works by this author on: GSW Google Scholar Eric J. Steig Eric J. Steig 1University of Washington, Seattle, Washington 98195, USA Search for other works by this author on: GSW Google Scholar Geology (2009) 37 (9): 835–838. https://doi.org/10.1130/G30054A.1 Article history received: 21 Jan 2009 rev-recd: 09 Apr 2009 accepted: 28 Apr 2009 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Kenneth H. Williford, Julien Foriel, Peter D. Ward, Eric J. Steig; Major perturbation in sulfur cycling at the Triassic-Jurassic boundary. Geology 2009;; 37 (9): 835–838. doi: https://doi.org/10.1130/G30054A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Stable sulfur isotopes from the reduced sulfur fraction of Late Triassic–Early Jurassic marine sediments at Kennecott Point in British Columbia, Canada, show evidence for a major perturbation in sulfur cycling coincident with a major carbon cycle perturbation in the wake of a mass extinction event at the Triassic-Jurassic boundary. The δ34S of reduced sulfur shifts from values consistent with open system bacterial sulfate reduction (−30‰) to values higher than any previously reported for Early Jurassic sulfates (20‰) and consistent with complete utilization of sulfate and Rayleigh fractionation in a closed system. We suggest that this isotopic shift was initiated by declining seawater sulfate concentration due to evaporite deposition in nascent Atlantic rift zones and enhanced by a local mechanism, such as a decoupling of the zone of sulfate reduction from the sulfate supply due to a catastrophic increase in the flux of land-derived sediments reaching the sea in the wake of massive terrestrial plant die-off during the Triassic–Jurassic mass extinction. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Continental and marine contributions to formation of mangrove sediments in an Eastern Amazonian mudplain: The case of the Marapanim Estuary

The coastline of the state of Pará in the Eastern Amazon is formed by submerged valleys occupied partially with mangroves, such as the estuary of the Marapanim River. The sediments of these mangroves are silty-clays, composed of quartz, kaolinite, illite, smectite, K-feldspar, pyrite, hematite, jarosite and halite with accessory zircon, estaurolite, tourmaline, rarely kyanite, rutile, ilmenite, sillimanite, andaluzite, topaz and anatase. Quartz, kaolinite, hematite and most accessories like zircon, estaurolite, tourmaline, rutile, kyanite, topaz, anatase and opaque minerals are inherited from the surrounding rocks (source area). The smectite, K-feldspar, pyrite, halite and jarosite are authigenic (neoformed). Halite and jarosite are currently and locally formed by intense evaporation. The sediments are formed mainly of SiO2, Al2O3 and Fe2O3, which indicates that they were subjected to intense chemical weathering, like the sediments of the Barreiras Formation. This is reinforced by the trace elements, with concentration of residual elements Zr, Cr, V, Nb, among others, while other trace elements are impoverished. The formation of K-feldspar, illite, smectite, halite and pyrite were linked to the environment of sedimentation of the mangrove, rich in organic matter and under the influence of sea water which contributed SO42-, Cl, Na+, K+, Ca2+, and Mg2+ for the formation of these minerals. In conclusion the inherited minerals, chemical composition and concentration of residual trace elements show the Barreiras Formation to be the main source of the land-derived sediments of the Marapanim mangroves.

Sediment characteristics and hydrodynamic setting of reef platform sediments of Kunduchi, north of Dar es Salaam harbour

Sediment grain size distribution, carbonate content and current velocities for the Kunduchi area are used to determine its hydrodynamic setting and sediment characteristics. The sediment mean grain size generally decreases northward. The sediments consist of medium to coarse sand south of the Tegeta River and fine sand further north. The sediment sorting values, which lack a north-south trend, vary from moderately well sorted to poorly sorted. The skewness of the sediment vary from near-symmetrical to very negatively skewed while the peakedness (kurtosis) varies from platykurtic to leptokurtic. The carbonate content increases with distance offshore, whereas the siliciclastic component decreases with distance offshore. The siliciclastic/carbonate transition of the investigated area is characterized by a narrow transition with no inter-fingering of the two facies. The lack of inter-fingering of the two facies suggests that there is a limited offshore transport of land-derived sediments. This is further supported by the drogue experiment results, which shows that the predominant surface current flows northward irrespective of the tidal phase Tanzania Journal of Science Vol. 32 (1) 2006: pp. 37-52

Coupled anthropogenic anomalies of radionuclides and major elements in estuarine sediments

Concentrations of fertilizer industry-derived P (up to 3.4%), Ca (up to 6.1%), 226Ra (up to 744 Bq kg −1) and 210Pb (up to 1317 Bq kg −1) at least one order of magnitude above natural levels were recorded in a sediment core from Morrão River estuary (SE Brazil). Unsupported 210Pb (=total 210Pb − 226Ra) activities unexplained by atmospheric fallout and deviations from the radionuclides secular equilibrium also indicated strong anomalies. Anomalous constituents were positively correlated with each other and negatively correlated with clay mineral-bearing elements. These negative correlations were explained by a depletion of natural sediment constituents due to a dilution caused by elevated inputs of steel industry-derived elements (mainly by Fe levels up to 24%). Absolute data and normalizations by a proxy for clays (Al) and anthropogenic Fe evidenced variabilities in the quality of coastal and land-derived sediment inputs, mainly due to changes in the relative contributions from industrial sources.

Quantity, composition, and source of sediment collected in sediment traps along the fringing coral reef off Molokai, Hawaii

Sediment traps were used to evaluate the frequency, cause, and relative intensity of sediment mobility/resuspension along the fringing coral reef off southern Molokai (February 2000–May 2002). Two storms with high rainfall, floods, and exceptionally high waves resulted in sediment collection rates > 1000 times higher than during non-storm periods, primarily because of sediment resuspension by waves. Based on quantity and composition of trapped sediment, floods recharged the reef flat with land-derived sediment, but had a low potential for burying coral on the fore reef when accompanied by high waves. The trapped sediments have low concentrations of anthropogenic metals. The magnetic properties of trapped sediment may provide information about the sources of land-derived sediment reaching the fore reef. The high trapping rate and low sediment cover indicate that coral surfaces on the fore reef are exposed to transient resuspended sediment, and that the traps do not measure net sediment accumulation on the reef surface.

Skeletal-Carbonate Neptunian Dikes of the Capitan Reef: Permian, Guadalupe Mountains, Texas, U.S.A.

Sedimentary dikes in the Permian (Guadalupian) Capitan Reef of West Texas and New Mexico are composed of siliceous sand, skeletal carbonate, or cement. Skeletal-carbonate neptunian dikes appear to be a relatively uncommon type; only four are known by the authors, but they are important in providing information about platform growth, sediment sources, and dispersal on the platform, and the biota that were present on the platform. The dikes occur within massive poorly sorted skeletal grainstones typical of the reefal part of the Capitan Formation (the Capitan-massive) that is correlative with upper Guadalupian Yates B strata on the platform. They formed during later Yates B, Yates C, and Tansill deposition on the platform, following closely a major period of progradation of the platform margin. The dikes are approximately vertical, and parallel to and within about 100 m of the platform margin. Fissure formation was a probable consequence of flexing and fracturing of lithified shallow-water Capitan-massive over compacting unconsolidated slope and basinal sediment. At least three stages of opening and filling are recorded in the largest and most complex dike, with each sequential fissure opening forming on the basinward side of the previous cemented filling. In two of the dikes, centimeter-thick deposits of vertically laminated peloidal grainstone, which formed in situ within microbial films on the fissure wall, preceded filling by skeletal sediment. Skeletal fossils within two of the dikes are well preserved and represent organisms that either were living within the fissures or were living on the adjacent sea floor and were washed into the fissures soon after death. Other skeletal grains in these dikes, and all of those in the other two dikes, are abraded, strongly micritized, and encrusted with microbial micrite, indicative of having lain on the sea floor for a considerable time before being deposited in the fissures. Fossils in the dikes are characteristic of the reefal and adjacent outer-shelf facies tracts, but they are a biased record of the biota of that depositional area in that they consist largely of vagile or only weakly attached members of the dweller and baffler guilds living on the reef surface and of organisms living within the fissures; members of the reefal framework communities are largely absent. The absence in the dikes of fossils diagnostic of more distant facies tracts indicates that there was little across-platform movement of carbonate sediment on the platform. Deposition of terrigenous sediment is correlated with a sea-level low-stand, indicating that land-derived sediment moved across the platform otherwise infrequently.

Mixing, trapping and outwelling in the Klong Ngao mangrove swamp, Thailand

The Klong Ngao estuary in Thailand is a 7-5-km long tidal creek facing the Andaman Sea and drains 11.5 km 2 of mangrove swamps. Physical processes in the estuary differ greatly from the wet season to the dry season. In the dry season, vertical homogeneity prevails and the swamp behaves like an evaporation pond. Salt and water are trapped upstream, longitudinal gradients result and, through tidal dispersion, nutrient outwelling may result for SiO 2, possibly NO 2 and NO3, but not PO 4. The outflow is trapped in a coastal boundary layer. In the wet season, short-lived local floods generate a strong stratification in salinity and episodical flushing of the estuary and may make measurements of nutrient budgets inconclusive. The Klong Ngao mangrove swamp traps land-derived sediments in the wet season.