RESUMEN

Rapidly spreading industrialization since the 19th century has led to a drastic increase in trace metal deposition in coastal sediments. Provided that these trace metals have remained relatively immobile after deposition, their sedimentary enrichments can serve as records of local-regional pollution histories. Factors controlling this proxy potential include trace metal geochemistry (carrier-, and host phase affinity), and depositional environmental factors (redox variability, particulate shuttling, organic matter loading, bathymetry). Yet, the relative importance and interactions between these controls are still poorly understood, hampering the reliable use of trace metal-based environmental proxies. By summarizing nine site-specific correlation matrices of 16 metal (loid) s (Pb, Cd, Cu, Zn, Sb, Sn, Ni, As, Tl, V, Mo, U, Re, Fe, Mn, Al), total organic C, and S contents in short sediment cores into a single meta-matrix, we test a novel approach for quickly detecting common and contrasting trace metal enrichment patterns across different study locations. Our meta-matrix shows two trace metal groups, within which positive correlations of e.g., Pb, Cd, Zn, Cu, Sb suggest a primary "anthropogenically sourced" (group I) control, whereas known "redox-sensitive" (group II) trace metals (Mo, U, Re) are characterized by fewer positive correlations. However, some group I metals (Cd, Zn, Cu, Sb) also covary with group II metals, inferring that redox variability may obscure primary anthropogenic signals; Sb even shows advantages over Mo and U under oxic conditions. As a more robust pollution indicator we identified Pb; yet for reconstructing historical Pb atmospheric pollution signals (1970s Pb peak), it is crucial to consider the distance from shore. In near-shore environments, local (fluvial) pollution signals may overprint large-scale (atmospheric) signals. Our findings demonstrate that combining site-specific sedimentary correlation and distribution patterns with a meta-matrix considerably aids the understanding of trace metal sequestration in different coastal sedimentary environments, which thereby improves trace metal proxy reliability.

RESUMEN

This study focuses on the comprehensive reservoir characterization of the 'Kukih' Field within the onshore northeastern Niger Delta region, Nigeria. The absence of its detailed description with delineated reservoir properties, lateral continuity, and their use to identify potential reservoir quality and heterogeneity necessitated this study. Integrating well log and 3D seismic data, the investigation aims to elucidate reservoir properties, lithofacies, and depositional environments to unravel hydrocarbon potential. The geological setting, encompassing the Agbada Formation of Early and Middle Miocene age, is scrutinized through detailed geologic analysis. Petrophysical evaluation of four well logs (Kukih-1, Kukih-2, Kukih-3, and Kukih-4) facilitated the determination of key parameters such as shale volume, effective porosity, and water saturation. Seismic interpretation further enriched the structural characterization of the field. Results showcase three predominant reservoir sands (A, B, and C) with distinct lithofacies and thickness variations. Effective porosity ranges from Fair to Excellent, with permeability exhibiting high values for hydrocarbon reservoir potential. Water saturation trends, lithofacies distributions, and structural features were illuminated through iso-parametric maps and seismic analyses. Depositional environments were inferred through facies analysis, revealing the presence of funnel-, cylinder-, and bell-shaped successions that hint at intricate marine sedimentary processes. Challenges owing to limited core data were acknowledged, and the integration of methodologies emerged as a pivotal strategy for enhanced reservoir understanding. This study underscores the 'Kukih' Field's hydrocarbon potential, accentuating the significance of multidisciplinary approaches in deciphering complex reservoir systems. In light of the petrophysical analysis derived from the well logs and the identification of structural highs through the structural maps, this study recommends the drilling of unexplored zones exhibiting promising structural characteristics.

RESUMEN

Reconstruction of the depositional environment of the Paleocene-Eocene Sinjar Formation from two outcrop sections in northwestern and northeastern Iraq has been evaluated using the traditional petrographic and facies analysis supported by X-ray diffraction and scanning electron microscopy with a focus on the Paleocene-Eocene (P-E) transition boundary. To this end, major and trace elemental geochemistry was conducted and various paleoenvironmental proxies for the paleoredox, paleoclimate, paleosalinity and paleoproductivity were determined in order to evaluate the changes in widely acknowledged environmental and climatic indicators and the elemental enrichment/depletion across the P-E boundary. The redox-sensitive trace element enrichment and the ir ratios (V/V + Ni, V/Cr, and U/Th) indicate that normal oxygenated circumstances prevailed during the late Paleocene deposition, and that anoxic conditions and a gradual commencement of oxygen depletion occurred during the early Eocene deposition. The coeval increase in the P2O5 content, P/Ti, and P/Al ratios in the Eocene sediments suggests an increase in nutrients and primary productivity due to the effect of upwelling currents during early Eocene. The conditions can be verified by observing a small change in salinity levels from low to high across the P-E boundary, which can be indicated by the Sr/Ba ratios. In addition, certain minerals such as Mg-calcite, dolomite, and palygorskite are commonly present, and paleoclimatic changes can be observed across the P-E transition from arid to semiarid and then to humid conditions, which can be recorded from C-values, Sr-Cu, Rb/Sr ratios, and clay mineralogy. These conditions were noted in the Sinjar Formation, which is made up of many microfacies such as lime mudstone, wackstone, packstone, grainstone and boundstone. These microfacies were deposited in a shallow marine environment that extended from tidal flats to reef slopes, with a developed reef environment that included back reef, reef core, and fore reef environments.

RESUMEN

Petrographical characterization and field observations were caried out to evaluate Kamlial Formation in Bagh district, Azad Jammu and Kashmir. Based on detailed petrography, the lithic arenite consisted of quartz (20-25%), feldspar (7-11%), rock fragments (20-37%), cementing materials (11-21%), and accessory minerals. Grains are mostly angular to subrounded and poorly to moderately sorted. The analysis revealed that the lithic arenite is mineralogically immature; also, the current activity during the time of deposition was low. Polycrystalline quartz indicates that the sandstone was derived from metamorphic source, while monocrystalline quartz indicates a granitic origin. Quartz having an angular shape suggests the source rock was near the depositional site, while quartz having a rounded shape represents long transportation. The presence of feldspar in the lithic arenite suggests the rocks were deposited at high relief or cold temperatures. Primary porosity in sandstone was reduced by calcite cements around the grain, while secondary porosity was developed by fracturing of quartz and feldspar. Tectonic uplift in the study area was demonstrated by fractured quartz and mica in thin sections. Field observations of various sedimentary structures were observed such as load casts, ripple marks, and mud cracks, etc. The presence of conglomerates and load casts in the study area indicates that the Kamlial sandstone was deposited by fluvial and shallow marine environment. Furthermore, the ripple marks indicate that the tidal flat environment controlled the deposition of the sediments.

RESUMEN

The alluvial-lacustrine strata that were formed by the evolution of rivers and lakes in the Hetao Plain during the Late Quaternary have an important influence on the formation and distribution of shallow high-arsenic groundwater. This study analyzed the distribution characteristics and depositional environments of shallow high-arsenic groundwater in study area using 1179 groundwater samples and more than 1100 pieces of drilling data. The indicator kriging statistics and the study results of the Quaternary lithofacies paleogeography show that the study area can be divided into three high-arsenic probabilistic distribution areas, namely, the Houtao Plain (HTP), the Yellow River Channel Belt (YRCB), and the Eastern Hubao Plain (EHBP). The depositional environment of the HTP was shaped by the alluviation of the Yellow River during the Late Pleistocene-Holocene. The YRCB is still affected by the alluviation of the Yellow River presently, and the EHBP was almost unaffected by the Yellow River. The high-arsenic groundwater in the EHBP is mostly distributed in the relatively continuous alluvial-lacustrine strata and has a typical hydrochemical type of HCO3, with the highest Meq(HCO3-/SO42-) and the highest reduction degree of SO42-. By contrast, the high-arsenic groundwater in the alluvial-lacustrine environments of the HTP and the YRCB accounts for only 14.77% and 20.13%, respectively, and has only less than 40% of HCO3 dominant type water. The high-arsenic groundwater in these two areas is generally located in the alluvial or alternating fluvial-lacustrine strata. However, the two areas exist more than three alluvial-lacustrine layers with a thickness of over 2 m each, which play a critical role in the formation of high-arsenic groundwater. Moreover, affected by alluvial aquifers in the same system, the high-arsenic groundwater in both the HTP and the YRCB is not intensively distributed and does not represent a typical HCO3 dominant type. The S2- produced by the massive reduction of SO42- might co-precipitate with Fe and As, which may explain why the EHBP has lower arsenic concentration than the HTP and the YRCB, both of which have a lower reduction degree of SO42-.

Asunto(s)

RESUMEN

Coal, being one of the major energy sources for power generation, contains several critical trace elements. There is a growing scarcity and expense of these critical elements as a result of the increased demand and limitation of mining sources. To explore the geochemical characteristics of the rare-metal, rare-dispersed (scattered), and rare-earth elements (TREs) in coal, 25 coal seam samples of the Shanxi Formation in the Huainan coalfield were collected. The major element oxides, minerals, and TREs were analyzed by X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), and inductively coupled plasma-mass spectrometry (ICP-MS). The results revealed that the coal of the Shanxi Formation had ultra-low moisture and low ash yield and was medium-high-volatility with low sulfur content and high calorific value. Concerning minerals, the coal was mainly composed of kaolinite, illite, quartz, calcite, dolomite, and pyrite. Compared with Chinese coal and world hard coal, rare-metal element Li and rare-dispersed element Se were enriched, whereas Ga and Ta were only slightly enriched. The average content of REYs was 51.34 µg/g, which is lower than the average content of REYs in Chinese coal. It has the enrichment characteristics of light REYs. In the vertical direction, the content of most TREs was higher in the roof and floor of the coal seam and the parting, indicating that the sedimentary microenvironment plays an important role in controlling the migration and enrichment of elements. The experimental results of sequential chemical extraction and correlation analysis showed that the TREs in the Shanxi Formation coal mainly exist in a residual and carbonate bound state, and occur in clay minerals and carbonate minerals. The enrichment of Se may be due to its high organic form ratio. The C-value, B content, w(Sr)/w(Ba), and REY geochemical parameters indicated that the Shanxi Formation Coal seam was developed in a transitional, semi-saline, deltaic sedimentary environment. With their development affected by seawater, REYs in coal are greatly supplied by terrigenous clastics. The complex sedimentary environment is an important reason for the varying occurrence states of TREs in the Shanxi Formation coals.

RESUMEN

The Cretaceous and Neogene deposits from the Mamfe Basin consisting of sandstone, shale and claystone were studied using petrography, and major, traces and REEs analyses to address sediment source, environment setting, prevailing paleoclimate as well as tectonic regime of the basin. The angular to subangular shape of detrital grains reflects the mineralogical and textural immaturity of sediments and the proximity of the sediment supply source. Sedimentary rocks are composed of a significant number of lithic debris, organic matter, ostracods as well as subrounded heavy minerals referring to notable igneous and metamorphic rocks bordering the Mamfe Basin. The plots of major element ratios including iron oxide/potasium oxide (Fe2O/K2O) against silicium oxide/aluminium oxide (SiO2/Al2O3) combined with that of sodium oxide/potassium oxide (Na2O/K2O) compared to silicium oxide/aluminium oxide (SiO2/Al2O3) are characteristic of greywacke and shale with few arkoses. The pronounced Eu negative anomaly of chondrite normalized REEs along with the plot of La/Th vs Hf and Co/Th vs La/Sc suggest that sediments are in general from felsic and intermediate source rock provenance, only subordinated contribution of mafic source. The negative anomaly of Yb suggests igneous fractionation under highly reducing conditions. The chemical index of alteration values of 47-70 combined with chemical index of weathering values of 0.6-84 suggest low to moderate weathering process of the sediment in the basin. This result is further confirmed by an index of chemical variability values of 0.6-100 and Zr/Sc ratio of 0.06-2.96. The REEs distribution displays a substantial content in LREE, low content in HREE and noticible proportion of (La/Yb)N ratio (mean >9), poor (Gd/Yb)N ratio in the Cross River Formation (mean <2) and slightly moderate (Gd/Yb)N ratio in the other formations (mean >2). This result implies that sediments from the Ngeme, Nfaitok and Baso formations derived from post-Archean rocks. Geochemical paleoenvironmental proxies including Sr/Cu, Sr/Ba, Ga/Rb vs Sr/Cu and SiO2 vs K2O + NaO2+Al2O3 are in favor of arid to semi-arid conditions during the deposition. Trace Elemental ratios such as Sr/Cu, Sr/Ba, V/Ni, U/Th, Ni/Co, V/Sc, and V/Cr values indicate a predominance of oxic conditions during deposition. In contrast, some authigenic pyrite, hematite, siderite and vivianite which are iron-rich minerals suggests episodic reducing conditions in the basin. The study provides a valuable information in evaluating sediments source, depositional environment, tectonic regime as well as the paleoclimatic conditions prevailing in the basin during the depositional period. The geochemistry of rocks of the Ngeme and Baso formations suggest passive continental margin setting and Ngeme, Nfaitok and Cross River formations suggest oceanic island Arc tectonic setting.

RESUMEN

We investigated the Mianagish Formation's potentiality as a Lower Cretaceous source rock and the included reservoir facies zone in the Umm Gudair oil field. The Middle Oolitic grainstone is the only producing zone in the formation. The wireline logs were used to trace the reservoir characteristics and calculate the total percentage of organic carbon (TOC) in the lithotype of the Minagish Formation. The commercial software, thin sections, and laboratory measurements are used to provide an integrated study. Integration of burial history, calculated TOC values, thermal maturity, depositional model, structural elements, and reservoir characterization were used to take a thoughtful look at the Minagish Formation's role in oil production in the field and as Lower Cretaceous source rock for the Cretaceous reservoirs. The reservoir facies are characterized by 16% average clay content, 16.7% average porosity, 420 millidarcys (mD) average permeability, and the average oil saturation is about 62%. The reservoir's quality reaches its maximum at the crest of the anticline in the west, south, and east, whereas the reservoir facies are deposited on the pre-existing structurally high shoal, while the quality decrease away from the shoal into the relatively deep water. The oil feeds the reservoir from the Lower Minagish Formation and maybe the Sulaiy Formation. According to the thermal model, the oil is heavy because of falling the TOC in the early maturation stage. The depositional environment and sequence stratigraphy are similar in the nearby Dharif and Abduliyah oil fields, and the study can be applied.

RESUMEN

As the strata sedimentary process proceeds, considerable amounts of nitrogen (N) is buried in sediments, which controls the sources and fate of N in the "groundwater-sediment" system. However, there is little concern regarding N burial characteristics in continuous sediment profiles from surface layer to deep aquifer thus far. In this study, lithology, grain size, geochronology, exchangeable N contents and geochemical proxies of sediments were analyzed to reveal the controlling mechanisms of N burial characteristics in Quaternary sediments and to interpret the enrichment of N in groundwater of central Yangtze River Basin. The results demonstrated a similar distribution trend for buried N in two sedimentary cores, which were high in the surface layer and decreased to stable in the deep aquifer. Excessive exchangeable N (EX-N) contents in sediments were mainly attributed to geologic origin. The N burial characteristics were controlled by the evolution of depositional environment: sedimentary facies determined the concentrations of total organic nitrogen (TON), further affecting the mineralization capacity of sediments; while paleoclimate regulated the intensity of the N transformation processes, ultimately influencing the actual concentrations of EX-N in sediments. In addition, due to the fast accumulation of alluvial deposits after Last Glacial Maximum and rapid development of Jianghan Lake Groups during Holocene, abundant organic matter (with high TON contents) was buried in sediments, which were still able to produce more ammonium or nitrate, and further posing continuous threats to groundwater quality. This study provided a new interpretation for the formation of high-ammonium aquifer in terms of depositional evolution.

Asunto(s)

RESUMEN

Montney Formation (MF) source rock located in northeastern British Columbia (BC), Canada, was analyzed to determine its depositional conditions and organic matter source input other than to determine their level of thermal maturity. The high total sulfur (TS) (2.23-20.86 wt.%) and good to very good total organic carbon (TOC) content (0.3-5.87 wt.%) in the analyzed samples give good evidence that the deposition of MF source rock was in a marine environment under reducing conditions. A mixed marine-terrestrial derived organic matter (OM) for the Montney source rock that was deposited in a marine dysoxic environment is deduced from the composition and distribution of different biomarker traces. Thus, the previous result is supported by the high short-chain n-alkanes ratio, accompanied by carbon preference index (CPI) around unity, high concentration of tricyclic terpanes, high C24 tricyclic/C24 tetracyclic, hopane/sterane ratios ranging from low to moderate, as well as the relationship between regular sterane compositions. During deposition of the MF source rock, it can be noticed that more land organic materials this was deduced according to the high waxiness index. From maturity ratios of Ts/(Ts + Tm), C32 22S/(22S + 22R) homohopane, moretane/hopane and 20S/(20S + 20R) and ßß/(ßß + αα) C29 it can give a conclusion that the source rock is mature to postmature of hydrocarbon generation.

RESUMEN

The present study evaluates the enrichment and distribution of radioelements along the eastern coast of India. India possesses the second largest reserve of thorium bearing monazite in the world, in terms of heavy minerals present primarily along its long coastline. Radioelement estimation of about 30 km long beach area along the eastern coast of India is reported and implications discussed. A total number of 822 data points were studied using a portable Geiger Muller counter, to estimate the variation of dose rates, due to the ambient radionuclides along two different trends. One was parallel (northeast-southwest) and the second one perpendicular to the coastline. Pre-selected samples from in-situ radiometric surveys on the heavy mineral placers were studied further, for quantitative estimation of the abundance of radioactive elements primarily uranium and thorium, using a High Purity Germanium detector. Radioelement concentration assessment of core samples (depth ~2 m), were studied from two different beaches. Radiological parameters like radium equivalent, annual effective doserate and absorbed dose rate has been calculated based on the 238U, 232Th and 40K concentrations. Heavy mineral placers along the shoreline indicate a very high thorium (avg - 2990.22 Bq kg-1) which is due to the extensive distribution indicative of monazite. The coastal area also exhibits relatively low uranium (avg - 319.1 Bq kg-1). Based on its high thorium concentration, the area can be considered as a high natural background radiation area. Based on the concentrations of uranium and thorium, the weathering conditions and depositional environment prevalent along the beach areas have been discussed.

Asunto(s)

RESUMEN

In this study, we explore the variability of sedimentation conditions (e.g., grain-size, accumulation rate, contamination) according to fluvial depositional environments. Indeed, sediment cores are commonly used as archives of natural and anthropogenic activities in hydrosystems, but their interpretation is often complex, especially in a fluvial context where many factors may affect the quality, continuity, and resolution of the record. It is therefore critical to thoroughly understand the nature and dynamics of an environment in which a sediment core is sampled to be able to interpret it. To that end, four depositional environments from a bypassed reach of the Rhône River were comparatively investigated through geophysics in order to assess the range of sedimentation conditions: a floodplain, a semi-active secondary channel, an active secondary channel, and a dam reservoir. Sediment cores were retrieved from each environment and thoroughly characterised (e.g., grain-size, Total Organic Carbon, organic contaminants). Robust age-depth models were elaborated for each core based on 137Cs, 210Pbex, and Persistent Organic Pollutants (POPs) trends. The results show that each depositional environment recorded a different time-period, and therefore different contamination levels and trends. In particular, a shift from polychlorinated biphenyls (PCBs) to polybrominated diphenyl ethers (PBDEs) as the predominant POP in the sediments can be observed, the tipping point being set in the 1970s. Two types of infrastructure-induced legacy sediments related to two periods of river engineering in the reach were also identified using grain-size analysis. The combination of geophysical methods (Ground Penetrating Radar) and sediment cores is therefore confirmed as a relevant methodology that should be promoted in fluvial contexts in order to reconstruct the sedimentary evolution of fluvial corridors. The study also highlights the challenges of dating recent fluvial sediments and proposes a multi-proxy dating methodology using POPs contamination trends.

RESUMEN

A sedimentological investigation was carried out in Agu-Awka and Umunya localities to interpret the facies, depositional environment, sequence stratigraphy, reservoir potential, and architecture of the outcropping Eocene Nanka Formation of the Ameki Group in southeast Nigeria. Petrographic analysis reveals that the sediments are composed of predominantly subangular to subrounded recycled quartz grains with a minor amount of rock fragments. It indicates that the sediments are texturally submature and mineralogically mature. Lithofacies analysis indicates that the formation is composed of fine to coarse-grained, trough and planar cross-bedded sandstone with clay-drape units, interpreted to be a subtidal bar facies, and a minor mudstone interval with sand to muddy heterolith interpreted to be a tidal mudflat facies. This suggests that the formation is of mixed environments, such as a tidally influenced high-energy fluvial and low-energy marsh to lagoonal settings. The lower sand unit of the subtidal bar facies (fine to coarse-grained cross-bedded sandstone with clay-drape) represents a highstand systems tract. The sharp base sandy heterolith lithofacies that forms the upper unit of the subtidal facies, and the overlying tidal mudflat facies that comprises a bedded mudstone and overlying wave rippled sandy heterolith intervals represent a transgressive systems tract. The reservoir quality of the sandstone facies is predicted to be moderate to good based on textural statistical analysis. The various relationships of the sedimentological parameters of the outcrops revealed by this study may assist and contribute to the prediction and understanding of the reservoir stratigraphic heterogeneity and properties of the subsurface depositional facies of the Nanka Formation.

RESUMEN

Microplastic is a ubiquitous environmental contaminant, but large gaps still exist in our knowledge of its distribution. We conducted a detailed assessment of the extent and variability of microplastic pollution in the Bristol Channel, UK. Sand samples were collected between the 5th and 30th August 2017, with microplastic recovered from 15 of the 16 beaches sampled along a coastal extent of ~230 km. In total, 1446 particles of suspected microplastic were extracted using a cascade of sieves and visual identification. The most common microplastics recovered were fragments (74%) and industrial plastic pellets (13%). We used Fourier-Transform Infrared (FTIR) spectroscopy to analyse 25% of recovered particles, 96.5% of which were confirmed as plastic, with polyethylene (61%) and polypropylene (26%) the most common polymers. Our analysis of local beach environments indicates microplastic burdens were higher on lower energy beaches with finer sediments, highlighting the importance of depositional environment in determining microplastic abundance.

Asunto(s)

RESUMEN

Gammacerane is one of the major biomarkers widely used in depositional environment diagnosis, oil family classification, and oil-source correlation. It is generally accepted that gammacerane is more resistant to biodegradation than regular hopanes. However, whether it is biodegradable as well has not been reported in literatures. In order to investigate the effect of biodegradation on gammacerane in crude oils, 69 core samples from two biodegraded petroleum accumulations were geochemically characterized by quantitative GC-MS analysis. All samples are originated from lacustrine source rocks in China and have experienced at least level 8 degree of biodegradation on the scale of Peters and Moldowan (The biomarker guide: interpreting molecular fossils in petroleum and ancient sediments, Prentice Hall, Englewood Cliffs, 1993). Both case histories showed the concentration of gammacerane decrease with increasing severity of biodegradation, indicating the destruction of gammacerane by biodegradation. A whole series of 25-norhopanes paralleling the 17α,21ß-hopanes (up to C34), together with C28 18-α-25,30-bisnorneohopane, C29 25-nordiahopane and C29 25-norgammacerane, is found in the Liaohe sample suite but C33, C34 25-norhopane and 25-norgammacerane are almost undetectable in the Junggar case. The gammacerane in the Liaohe case study appear to be altered simultaneously with hopanes, although the rate of gammacerane alteration is slower. Its susceptibility to biodegradation is similar to 18α(H)-22,29,30-trisnorneohopane (Ts) and 17α(H)-22,29,30-trisnorhopane (Tm) but more vulnerable than 18α-30-norneohopane (C29 Ts), 15α-methyl-17α(H)-27-norhopane (C30 diahopane) and pregnanes. The gammacerane in the Junggar oils appear to be less biodegradable than the Liaohe case history. It was altered simultaneously with pregnanes and C29 Ts but faster than C30 diahopane. The present data suggest that biodegradation sequence is not universal since the relative rates of biodegradation of different compound classes depend upon specific environmental conditions. Like the case of hopane demethylation, the mechanism of gammacerane biodegradation is not straightforward. While the conversion of gammacerane to 25-norgammacerane is not quantitatively balanced in the Liaohe case history, no 25-norgammacerane has been formed from the degradation of gammacerane in the Junggar case history. The ratio of gammacerane to regular hopanes increases with biodegradation degree especially at extreme levels of degradation, gammacerane index is no longer valid for depositional environment assessment or oil-source correlation.

Asunto(s)

RESUMEN

A planície costeira de Soure, na margem leste da ilha de Marajó (Pará), é constituída por áreas de acumulação lamosa e arenosa, de baixo gradiente, sujeitas a processos gerados por marés e ondas. Suas feições morfológicas são caracterizadas por planícies de maré, estuários, canais de maré e praias-barreiras. A análise faciológica e estratigráfica de seis testemunhos a vibração, com profundidade média de 4 m, e de afloramentos de campo permitiu a caracterização dos ambientes deposicionais, sua sucessão temporal e sua correlação lateral, a elaboração de seções estratigráficas e a definição de uma coluna estratigráfica. Foram identificadas cinco associações de facies: (1) facies de planície de maré, (2) facies de manguezal, (3) facies de barra de canal de maré, (4) facies de praia e (5) facies de duna. A história sedimentar da planície costeira de Soure é representada por duas sucessões estratigráficas: (1) a sucessão progradacional, constituída pelas associações de facies de planície de maré, manguezal e barra de canal de maré; e (2) a sucessão retrogradacional, formada pelas associações de facies de praia e de duna. Essas sucessões retratam uma fase de expansão das planícies de maré e manguezais, com progradação da linha de costa (Holoceno médio a superior), e uma posterior fase de retrogradação, com migração dos ambientes de praias e dunas sobre depósitos lamosos de manguezal e planície de maré, no Holoceno atual. A história deposicional da planície costeira de Soure é condizente com o modelo de evolução holocênica das planícies costeiras do nordeste paraense.

Soures's coastal plain, eastern Marajó island (Pará), is formed by muddy and sandy deposits, low gradient areas submitted to tidal and wave processes. The morphological features are tidal flats, estuaries, tidal channels and barrier-beach ridges . The faciological and stratigraphical analysis of six vibra-core with medium deph of four meters and from outcrops allowed a caracterization of depositional environments, temporal sequence and spacial corelation, the elaboration of stratigraphical seccions and column. Were identified five facies associations: (1) tidal flat facies, (2) mangrove facies, (3) tidal channel bar facies, (4) beach facies and (5) dune facies. The sedimentary history of the Soure coastal plain is represented by two stratigraphical successions: (1) progradational succession (tidal flat, mangrove and channel bar facies association) and (2) retrogradational succession (beach and dune facies association). These successions are related to a expansion phase of tidal flats and mangroves with progradation of the coastline (Middle/Late Holocene) and a posterior retrogradation phase with landward migration of the shoreline (Late Holocene). The depositional history of the Soure coastal plain is related to the holocenic evolution model of the northeast coastal plains of Pará.

Asunto(s)