Flandrian Research Articles

Mixed siliciclastic-carbonate-evaporite sedimentation in an arid eolian landscape: The Khor Al Adaid tide-dominated coastal embayment, Qatar

The Khor Al Adaid embayment of southern Qatar represents a unique shallow-water mixed siliciclastic‑carbonate coastal depositional system that developed in a hyper-arid climatic setting over the past 6000 years. The embayment, which was formed during the Flandrian transgression as a result of flooding across a partially fault-controlled incised fluvial drainage, is supplied by quartz-rich sands delivered by wind-blown dunes migrating southward across the surface of Qatar. These offshore-migrating eolian-derived sediments are being redistributed by tidal currents in an otherwise low-energy coastal zone, where in situ formation of carbonate mud and a low-diversity skeletal assemblage is ongoing within salinity-restricted environments. Three depositional sectors are delineated: 1) an energetic, linear, fault-controlled Entrance Channel into which the eolian dunes spill directly; 2) a relatively deep (up to 20 m) Outer Lagoon, interpreted to represent a flooded karst-collapse structure; and 3) a sprawling, low-energy, shallow (<2 m) Inner Lagoon occupying low-lying areas between deflated eolian dunes.Physical oceanographic modeling, integrating multi-seasonal current meter and tidal gage measurements, demonstrates tidal current flow velocities are relatively high in both the Entrance Channel and at the constricted entrance to the Inner Lagoon. Associated flow expansion into less confined areas results in deposition of the eolian-derived sands as flood-tidal deltas, one in the Outer, and two in the Inner Lagoon. A weakly-developed ebb-tidal delta occurs where the Entrance Channel debouches into the Arabian Gulf. Flood-tide dominance is also apparent in Entrance Channel deposits, where sand accumulates in seaward-terminating “ebb barbs” along the margins of the flood-dominant thalweg. Such flood-tide dominance of the thalweg is unusual and likely reflects the absence of river discharge. Evidence of significant inverse estuarine circulation (seaward flow of a brine along the embayment floor) is mostly absent in spite of the landward increase of salinity, where concentrations reach more than double normal seawater salinity in the Inner Lagoon. Modeling results show that seaward-flowing brines formed in the Inner Lagoon are trapped in the relatively deep Outer Lagoon, and that mixing by tidal currents in the energetic Entrance Channel precludes the formation of vertical density gradients there. Because siliciclastic mud is essentially absent, and most of the sediment forming the deltas consists of sand, upper intertidal deltaic deposits that would normally consist of mud are absent, resulting in the flood-tide deltas having a pronounced lobate geometry similar to that of fluvial deltas formed predominantly of sand.Away from tidal deltas, low-energy lagoons are floored by carbonate mud of local production, with minor gypsum precipitating in the Inner Lagoon. Wind-generated waves only locally influence sedimentation, forming complex nearshore bars along some lagoonal shorelines. The overall landward increase in salinity is accompanied by a decrease in the diversity of benthic fauna and their skeletal remains. A fairly diverse faunal assemblage is observed in the Entrance Channel near the Arabian Gulf, including colonial corals, whereas the inner lagoon assemblage is dominated gastropods belonging to Pirenella cingulata. The remnants of large eolian dunes are preserved in the low-energy setting of the Inner Lagoon, segmenting the waterbody, and locally increasing restriction. The sedimentology of the arid-zone coastal Khor Al Adaid embayment may serve as an analogue for environmental settings that were perhaps more commonplace in arid zones of flooded continents during greenhouse times.

General aspects of continental margin sediments of the Ceará State, northeast Brazil, from mineralogy and principal component analysis

Granulometry, mineralogy, portable X-ray fluorescence (XRFp), portable X-ray diffractometry (XRDp), and principal component analysis (PCA) have been made in samples of two deep cores of the continental margin of the Ceara State, northeast Brazil, aiming to detail the general aspects of deep sedimentation, including mechanical dispersion of continental minerals, environmental chemistry, and clay identification. The samples comprised biogenic oozes, clays, coarse silt, and fine sand to a lesser extent. The granulometric composition suggests slow and calm sediment accumulation over time. XRDp analysis pointed out that pelagic clays consist of chlorite, kaolinite, nontronite, and vermiculite. High oxidation levels are suggested for the two core samples, represented by the light brown color 5YR 6/4 of the sediments. Traces of minerals existing at the continental shelf were found, although in the core SIS-454 at 160 to 164 cm depth, there is a total absence of both heavy and light continental minerals. In core SIS-515, the total absence of heavy and light minerals was found at the depth of 87 to 92 cm. The levels with absence of continental minerals are probably associated with the absence of mechanical dispersion due to transgression and regression events in the Ceara continental shelf. The high oxidation levels can probably be linked to shallow waters caused by sea level changes, or to large period of sedimentation in the slope. From the statistical analysis, it is suggested that element contents are related to each other according to the provenance setting, whereas the pelagic sediment has provenance from marine water, resurgence currents, wind transport, cosmic dust, and from slow transportation, originated from the continent. It was deduced that sedimentation in the area was affected by at least two events with absence of mechanical dispersion of continental sediments, associated with geochemical characteristics represented by antagonism between elements of terrigenous and biogenic origin. These events are possibly associated with small-scale regressions occurred during the Flandrian Transgression in the Ceara Basin.

Age and forming conditions of groundwater in the middle Pliocene aquifer in the Mekong Delta, Vietnam, based on the results of carbon radioactive isotope study

The results of studying and assessment of the impact of climate change on the groundwater in the Mekong delta have indicated that the exploitation of quaternary aquifers is not enough to solve the task of water supply in the region. Therefore, in the exploitation plan of groundwater in the Mekong Delta, the greatest prospects are bound with Pliocene aquifers. So, by using of carbon radioactive isotope to determine the age and forming conditions of groundwater in the middle Pliocene aquifer in the Mekong Delta, the important information for planning exploitation and zoning of areas subject to restrained exploitation of groundwater is retrieved. The determination of the age with the use of carbon radioactive isotope study in the complex with the geostatistical interpolation techniques allowed creation age map of middle-Pliocene aquifer with high accuracy nad determination the recharge area on the north-east of the Mekong delta (South-Eastern area). From the recharge area, groundwater flows in the south-west direction at a flow velocity of 8 m/year and discharges into the sea (Siam Golf and Eastern sea). It is the first time by using geostatistical interpolation «cokriging» of two parameters (age - key parameter and depth of sampling - extra parameter). The tasks to improve the accuracy of specialized maps in Vietnam have been solved. The age map has been made with the correlation parameter 0,9, that justifies the high efficiency of the studies. Furthermore, results of the correlation between age and concentration chlorine of groundwater in the middle-Pliocene aquifer (n22) allowed making a suggestion, that formation of mineralized water is a result of mixing of meteoric water with the sedimentation waters of initial sea genesis, which were formed during Flandrian transgression which began about 21000 years ago and ended 4200 years ago.

Influence of the paleogeographic evolution on the groundwater salinity in a coastal aquifer. Cabo de Gata aquifer, SE Spain

The groundwater of the Cabo de Gata detritic aquifer, in southeastern Spain, exhibit salinities of between 70–726 mmol/L of Cl− (brackish-salt to hypersaline waters). We have investigated the causes of the high salinity anomaly, which at certain points exceeds that of present-day seawater (600 mmol/L). Two hypotheses are considered as possible sources for the saline water: (1) The deeper, more saline groundwater date back to an old marine intrusion that occurred at the end of the last Ice Age (14–17 ka), when seawater salinity was higher than in the present day. This hypothesis is supported by the values of 14C measured in this water (∼6–10 pmc), which indicate old water of up to 17 ka. However, the values of 18O and 2H are lower than would be expected. (2) The water is the result of mixing between fresh groundwater and seawater. The latter explanation agrees well with the low values of 18O and 2H. This mixture is later subject to evaporation, explaining its high salinity. Hydrogeochemical modelling was carried out for the most saline samples, assuming such mixing between freshwater and seawater followed by evaporation, and the results show a very good agreement between the measured and simulated values. According to the model calculation, the original mixture contained approximately 60% seawater and its volume subsequently was reduced through evaporation by around 30%. This mixing and evaporation could occur during the Flandrian Transgression (6000–8000 y), when this area accommodated a coastal lagoon.

LA LÍNEA DE COSTA FLANDRIENSE EN EL PALEOESTUARIO DEL RÍO GUADALQUIVIR (C. 6500 BP

This work presents a brief sinthesis of the theoretical starting points and the investigative results of the doctoral dissertation The Flandrian Transgression in the alluvial plain near Sevilla. The Guadalquivir river palaeoestuary, which includes the mapping of the coastline of the paleoestuary generated by the Flandrian Transgression circa 6500 years ago in the Guadalquivir valley in the area of Sevilla, north of the present-day marshlands. Also, data have been collected which allow to make approaches and produce work hypothesis about the fill process of the palaeoestuary. The gnoseological aim, according with the theoretical and methodological framework of the Dialectical Geoarchaeology, is to contribute to the explication, in the south of the Iberian Peninsula, of the causes of the historical development of the double dialectic between the social systems and the natural systems, in the transition from the neolithic tribal socioeconomic formation to the initial classist socioeconomic formation between the IVth and the IIIrd milennium BC.

Evolutionary trend of paleoshorelines in the Coastal Makran zone (Southeast Iran) since the mid-Holocene

The Coastal Makrn (CM) is the outermost part of the Makran zone, which is one of few intact areas to study the evolutionary trend of raised beaches and also to estimate the rate of coastal progradation since the late Holocene. The Makran zone is an accretionary wedge that has formed by the subduction of oceanic crust of Arabian Plate under the Eurasian Plate. The CM range in Iran is located between the eastern corner of the Hormuz Strait and the middle of the Guwader Bay at the Iran–Pakistan boundary. This research method utilized remote sensing (RS) techniques and geographic information system (GIS), field survey and radiocarbon dating of fossils The data indicate the effective limit of the Flandrian transgression (18,000 BP) and paleo-geographical features in the mid-Holocene. Sequences and time periods of fossil beach development and the mean rate of shoreline mobility and uplift in omega-shaped bays were obtained. Coastal progradation from the oldest fossil beach in the Kerian area started from 4329 ± 64 Cal BP, and in Chabahar and Guwader Bay from 5438 ± 87 Cal BP and 5389 ± 58 Cal BP, respectively. Different rates of uplift result from tectonic movements of various scales. Development of fossil beaches in the Chabahar and Pozm Bays since the mid-Holocene coincided with a clear increase in rate of uplift from 0.71 mm y−1 to 5.02 mm y−1. The highest rate of uplift of fossil beaches (5.02 mm y−1) occurred at Darango Bay. Tombolos were identified as a main paleo-geographic feature of the CM zone in the early Holocene. Such landforms were gradually converted to Omega-shaped bays from the mid-Holocene. Developments of Omega-shaped bays are continuously in progress by a regional mechanism, in which wave regimes and sediment supply from hinterlands are relatively stable. Paleo-geographic features of the area in the mid-Holocene were built based on land progradation rate, tectonic events, and trend of sea level changes.

Morphodynamic Change of Fraserganj and Bakkhali Coastal Stretch of Indian Sundarban, South 24 Parganas, West Bengal, India

The Bengal plain is characterized by the presence of an extensive coastal tract bordered by the Bay of Bengal in the south. Two contrasting coastal environments are prevailing in the area, namely; the macro tidal Hooghly estuary in the east; and the mesotidal Midnapore Coastal plain to the west. A morphogenetic study based on the terrain mapping unit (TMU) concept reveals the form- process-material interactions of these two contrasting coastal environments with a possible geo-history model of the coastal Quaternaries. It has been established that the entire process-response system of the coastal tract of the Bengal plain started operating after the rise of sea level around 6000yrs B.P. (i.e., optimum of flandrian transgression) and the Hooghly estuary, the mangrove vegetation plays a significant role as the dominant geomorphic agent in the evolution of the tidal shoals and their eventual accretion to the main landmass resulting in delta progradation. In the present-day scenario, the Hooghly estuary becomes the abandoned part of the Ganga-Brahmaputra delta in India, and is also turning destructive and forming erosional regime in the mesotidal Midnapore coastal area.

A semi-automated approach for mapping geomorphology of El Bardawil Lake, Northern Sinai, Egypt, using integrated remote sensing and GIS techniques

Among the other coastal lakes of the Mediterranean northern coast of Egypt, Bardawil Lake is a unique lagoon, as it is fed only by seawater. The lagoon is composed of two main basins, and several other internal small basins interconnected to one another. Although the general geomorphologic characteristics are treated in some regional studies, we used a semi-automated approach based on a wide variety of digital image processing for mapping the major geomorphological landforms of the lake on a medium scale of 1:250,000. The approach is based primarily on data fusion of Landsat ETM+ image, and validated by other ancillary spatial data (e.g. topographic maps, Google images and GPS in situ data). Interpretations of high resolution space images by Google Earth and the large-scale topographic maps (1:25,000), in specific, revealed new microforms and some detailed geomorphologic aspects with the aid of GPS measurements. Small sand barriers, submerged sand dunes, tidal channels, fans and flats, and micro-lagoons are the recurrent forms in the lake. The approach used in this study could be widely applied to study the low-lying coastal lands along the Nile Delta. However, it is concluded from geological data and geomorphologic aspects that Bardawil Lake is of a tectonic origin; it was much deeper than it is currently, and has been filled with sediments mostly since the Flandrian transgression (∼8–6kabp).

Origin of groundwater salinity (current seawater vs. saline deep water) in a coastal karst aquifer based on Sr and Cl isotopes. Case study of the La Clape massif (southern France)

In this study a typical coastal karst aquifer, developed in lower Cretaceous limestones, on the western Mediterranean seashore (La Clape massif, southern France) was investigated. A combination of geochemical and isotopic approaches was used to investigate the origin of salinity in the aquifer. Water samples were collected between 2009 and 2011. Three groundwater groups (A, B and C) were identified based on the hydrogeological setting and on the Cl− concentrations. Average and maximum Cl− concentrations in the recharge waters were calculated (ClRef. and ClRef.Max) to be 0.51 and 2.85mmol/L, respectively). Group A includes spring waters with Cl− concentrations that are within the same order of magnitude as the ClRef concentration. Group B includes groundwater with Cl− concentrations that range between the ClRef and ClRef.Max concentrations. Group C includes brackish groundwater with Cl− concentrations that are significantly greater than the ClRef.Max concentration. Overall, the chemistry of the La Clape groundwater evolves from dominantly Ca–HCO3 to NaCl type. On binary diagrams of the major ions vs. Cl, most of the La Clape waters plot along mixing lines. The mixing end-members include spring waters and a saline component (current seawater or fossil saline water). Based on the Br/Clmolar ratio, the hypothesis of halite dissolution from Triassic evaporites is rejected to explain the origin of salinity in the brackish groundwater.Groundwaters display 87Sr/86Sr ratios intermediate between those of the limestone aquifer matrix and current Mediterranean seawater. On a Sr mixing diagram, most of the La Clape waters plot on a mixing line. The end-members include the La Clape spring waters and saline waters, which are similar to the deep geothermal waters that were identified at the nearby Balaruc site. The 36Cl/Cl ratios of a few groundwater samples from group C are in agreement with the mixing hypothesis of local recharge water with deep saline water at secular equilibrium within a carbonate matrix. Finally, PHREEQC modelling was run based on calcite dissolution in an open system prior to mixing with the Balaruc type saline waters. Modelled data are consistent with the observed data that were obtained from the group C groundwater. Based on several tracers (i.e. concentrations and isotopic compositions of Cl and Sr), calculated ratios of deep saline water in the mixture are coherent and range from 3% to 16% and 0% to 3% for groundwater of groups C and B, respectively.With regard to the La Clape karst aquifer, the extension of a lithospheric fault in the study area may favour the rise of deep saline water. Such rises occur at the nearby geothermal Balaruc site along another lithospheric fault. At the regional scale, several coastal karst aquifers are located along the Gulf of Lion and occur in Mezosoic limestones of similar ages. The 87Sr/86Sr ratios of these aquifers tend toward values of 0.708557, which suggests a general mixing process of shallow karst waters with deep saline fossil waters. The occurrence of these fossil saline waters may be related to the introduction of seawater during and after the Flandrian transgression, when the highly karstified massifs invaded by seawater, formed islands and peninsulas along the Mediterranean coast.

Inventory of Quaternary Geology and the Evolution of the Oguta Lake, Southeastern Nigeria

ENGLISH/ANGLAIS] Affiliations: 1 Department of Geology, Anambra State University, Uli Anambra State, NIGERIA 2 Department of Geology, University of Ibadan, Ibadan, NIGERIA Address for Correspondence/ Adresse pour la Correspondanc e: nforbng@yahoo.c om Accepted/Accepte : December, 2011 Citation: Nfor BN, Akaegbobi IM. Inventory of the Quaternary Geology and the Evolution of the Oguta Lake, Southeastern Nigeria. World Journal of Engineering and Pure and Applied Sciences 2012;2:16. Individual and/or combined contributions of globally accepted processes of natural lake formation were investigated and used in consonance with field observations to propose a geologic setting for the genesis and evolution of the Oguta Lake. Results suggest that combined structural and fluvio/hydrodynamic forces initiated its formation during the WurmWisconsin (10,000 YBP) eustatic low sea level that affected the Guinea Coast. The resultant base level incision of the Niger and Njaba Rivers and subsequent aggradations of thick sandy alluvium during eustatic Flandrian transgression, would have caused, the Njaba R. to erode its valley into a ‘U’ shape around the Oguta area. The valley was further aggravated by instability, resulting from subsurface growth faults common within the Niger Delta. Around Oguta, both Rivers could have deposited enough sediments to choke their passage, resulting in meandering, braiding and ox-bow lakes. The depressions formed by natural levees and the outer margins of the floodplains then became filled with water, and then the coalescence of a number of ox-bow lakes from the wailing Niger and Orashi Rivers resulted in the Oguta Lake. Alternatively, the Awbuna and Utu Rivers could have built deposits across the Njaba R. valley to pond it or the latter could have aggravated its valley flow more rapidly than its two tributaries and ended up being ponded. Hydrodynamics between sedimentation and erosion under varying climatic conditions broke the empoundment at the western end into an outflow route, which eventually was captured by a fast flowing Orashi R., giving birth to the Oguta Lake System.

Trace elements in Holocene sediments of the southern Doñana National Park (SW Spain): historical pollution and applications

The multidisciplinary analysis of core sediments from Donana National Park, south Spain, permits to delimitate both the paleoenvironmental changes and the geochemical evolution of this area during the Holocene. In a first phase (10–6.5 kyr cal), this area was occupied by freshwater/brackish marshes with periodical alternation of dry periods and humid intervals. In a second phase, these marshes were inundated during the Flandrian transgression (~6.5 kyr cal), with the deposition of bioclastic sands. The third phase (6.5–3.6 kyr cal) is characterized by the transition to an old lagoon, with unpolluted, bottom sediments. The geochemical concentrations of these clayey sediments can be used as a geochemical background for present-day and future environmental evaluations of this area. In the following 600 years approximately, two tsunamis caused the partial infilling of this area with bioclastic, marine sediments. In the interval comprised between these two tsunamis, this lagoon was polluted with heavy metals derived from historical mining activities. This environmental contamination represents one of the oldest evidences of mining pollution in the world (>3 kyr cal BP).

The Holocene sea level changes as evidenced from palaeontological data: A case study from Glauconome sculpta (Bivalvia) along the eastern coast of India

The coastal areas of the world are undergoing severe erosion due to a rapid transgression starting 3000 years ago. The erosion leads to exhumation of an ancient marsh at many places along the eastern coast of India. This marsh supported rich mangrove vegetation and a monospecific bivalve community, Glauconome sculpta (Sowerby), typical of estuarine facies. The bivalves are semi-infaunally positioned in their life mode within the sediments and they apparently monopolized the entire low water belt as opportunists. Present exhumation and exposure of the mud sediments lead to reworking of the bivalve shells and admixing with modern beach fauna. Extensive time-averaging of biota and development of condensed zone are thus in the making. The extermination of the bivalve community and preservation of numerous dead shells in life position point to a rapid rise of sea level that results in quick burial and consequent changes in substrate and salinity. These factors presumably were directly responsible for the evident regional mass mortality of G. sculpta. This palaeontological proxy has been used to understand the post Flandrian transgression during the past 3 ka.

The Emergence of Muge Mesolithic Shell Middens in Central Portugal and the 8200 cal yr BP Cold Event

ABSTRACT The emergence of Portugal's Muge Mesolithic, with its characteristic shell middens and human burials, is widely seen as a response to the formation of a highly diverse terrestrial and aquatic ecotone in the Tagus basin by the Flandrian transgression. Recently, some have suggested that this was an adaptive response to the 8200 cal yr BP event. Using the available radiocarbon data for the shell middens, paleoclimatic data, and paleoceanographic data we present a new model for the appearance of the Muge Mesolithic shell middens and changes in settlement between the Boreal and Atlantic phases for central Portugal. Coastal ecosystems were altered due to diminution in upwelling and the occurrence of the 8.2 kyr cold event, with declining availability of marine resources, rapid sea level rise, and changes in coastal morphology. The result was that the previous coastal setting was no longer suitable for the hunter-gatherer-fishers causing a settlement shift to the new, large, and stable estuary of the Tagus Valley.

Mineralogical assemblages, geochemistry and fossil associations of Pleistocene–Holocene complex siliciclastic deposits from the Southwestern Doñana National Park (SW Spain): A palaeoenvironmental approach

On the basis of mineralogy, chemical and palaeontological data collected in a long core (93 m) three associations of facies are distinguished in the Late Pleistocene–Late Holocene evolution of the sedimentary infilling in nowadays Doñana National Park. From the lower, middle and upper associations of facies three sedimentological phases have been established. In the oldest phase (> 44 kyr BP), this area was occupied by supratidal, freshwater marshes located close to a brackish lagoon and inundated suddenly by brackish-marine inputs. The following phase (44–7 kyr BP) is characterized by the transition from supratidal to intertidal conditions, with the alternation of freshwater or brackish marshes situated very close or in the margin of the former lagoon and submitted to episodes of desiccation or tidal inundation. The last phase (7–3.0 cal kyr BP) comprised: a) a marine inundation during the maximum of the Flandrian transgression (∼ 7–6.5 cal kyr BP); and b) the progressive infilling of a brackish lagoon with marine connection and permanent fresh water inputs (6.5–3.5 cal kyr BP), partially enclosed by the Doñana spit. The phyllosilicate-rich, clayey–silty sequence of this latter infilling is interrupted by tsunami-like deposits at 4.2–3.6 cal kyr BP and 3.6–3.0 cal kyr BP. These high-energy events are characterized by textural (bimodal grain-size distribution, sorting decrease), mineralogical (crystallochemical changes in illites, increasing dolomite content) and geochemical changes (Ti anomaly), besides a sudden introduction of marine bivalves and microfauna and a strong decrease or the almost disappearance of the brackish ostracode assemblage. Ages of these deposits coincide with those indicated for other tsunamigenic layers detected in the southwestern Spanish coasts and some deep cores collected near the African–European plate boundary.

The sabkha sequence at Mussafah Channel (Abu Dhabi, United Arab Emirates): Facies stacking patterns, microbial-mediated dolomite and evaporite overprint

ABSTRACT The Mussafah Channel is a man-made canal cut perpendicular to the coastline, located to the southwest of the city of Abu Dhabi, United Arab Emirates, and is ideal for studying coastal depositional processes in an arid environment. The channel walls reveal a few meters of Pleistocene reworked dune deposits, unconformably overlain by Holocene carbonates and sabkha evaporites. The Holocene succession consists of intertidal to shallow subtidal sediments that vary significantly along depositional strike direction. Bladed gypsum crystals, gypsum rosettes, and nodular to highly contorted, discontinuous bands of classic sabkha anhydrite are present along the channel walls. Sedimentology, petrography, SEM, X-ray diffraction, and radiocarbon age-dating analyses of the sabkha sequence show the following profile from base to top: (1) non-bedded carbonate-rich sand: reworked aeolianite with an approximate (ca.) radiocarbon age in years (yrs) before present (BP) ca. 26,800 14C yrs BP; (2) cross-bedded to non-bedded carbonate-rich sand: aeolianite/reworked aeolianite (ca. 24,000–23,500 14C yrs BP); (3) crinkly-laminated stromatolitic bindstone: intertidal, low-energy microbial mat (ca. 6,600–6,200 14C yrs BP); (4) lower, discontinuous and in places reworked hardground: cemented channel-lag deposits (ca. 6,400 14C yrs BP); (5) peloid-skeletal packstone with rootlets or microbial-laminated peloid-skeletal packstone, laterally grading into fine- to coarse-grained, cross-bedded, cerithid-rich, bioclastic packstone, grainstone, and rudstone: lowermost intertidal to shallow subtidal, low-energy, mud-rich rooted and microbial-laminated lagoonal deposits and moderate- to high-energy, intertidal to shallow subtidal tidal-channel, tidal-delta, and tidal-bar deposits (ca. 6,200–5,200 14C yrs BP); (6) upper discontinuous and shingled hardground: cemented beach rock (ca. 5,700 14C yrs BP); (7) cross-bedded, bioclastic rudstone/grainstone, grading laterally into intervals displaying bladed gypsum crystals and nodular to enterolithic anhydrite: intertidal to shallow subtidal, high-energy longshore beach bar and beach spit deposits; overprinted by sabkha gypsum and anhydrite (ca. 5,000 14C yrs BP). Significant amounts of dolomite were found within the rooted and microbial-laminated mud-rich lagoonal carbonates, some of the tidal-channel/lagoonal deposits, the buried crinkly-laminated microbial mats, and within some of the Pleistocene carbonate-rich sands. The dolomite is very fine-crystalline and displays spherical morphologies as well as subhedral to euhedral dolomite rhombohedra. The formation of dolomite is interpreted to be related to dolomite-mediating microbial organisms which form the widespread microbial mat along the Abu Dhabi coastline. Microbial organisms are also present within the rooted and microbial-laminated lagoonal carbonates and, most probably, within all the other studied carbonates and the Pleistocene carbonate-rich sands. Biopolymers of microbial origin, referred to as Extracellular Polymeric Substances (EPS), are interpreted to play a key role in primary dolomite formation. The sabkha sequence at Mussafah Channel formed during the post-glacial Flandrian transgression, resulting in the reworking of the Pleistocene aeolian dunes and the deposition of intertidal to shallow subtidal carbonates. Recent find of whale bones within tidal-channel deposits overlying the microbial mat further document the initial Holocene transgression. During a subsequent slight sea-level fall (regression), these carbonates were overprinted by gypsum and anhydrite. The observed lateral and vertical facies variations reflect primary reservoir quality variations, an important aspect to be considered for geological facies and reservoir quality modeling.

Taxa de soerguimento atual do arquipélago de São Pedro e São Paulo, Oceano Atlântico Equatorial

O arquipélago de São Pedro e São Paulo situa-se no Oceano Atlântico Equatorial, no topo de uma elevação morfológica submarina de 90 km de comprimento, 25 km de largura e 3.800 m de altura, composta de rochas peridotíticas do manto, denominada Cadeia Peridotítica de São Pedro e São Paulo. A morfologia submarina é altamente acidentada com escarpas subverticais de centenas de metros de altura, sugerindo ocorrência de tectonismo recente, provavelmente ativo. O mapa de seppômen do arquipélago mostra duas plataformas de abrasão marinha, com altitude respectiva de 4~5 m e de 7~9 m. As plataformas são observadas nas três ilhas maiores nas mesmas faixas de altitude, indicando que não houve basculamento ou soerguimento diferencial entre as ilhas. Considerando a plataforma superior formada durante a Transgressão Flandriana e a plataforma inferior desenvolvida por erosão recente, a taxa média de soerguimento nos últimos 6 mil anos é calculada como 1.2~1.5 mm/ano. As datações 14C para os fósseis coralígenos da ilha Belmonte indicam a taxa de soerguimento nos últimos 6.600 anos como 1.5~1.8 mm/ano. Portanto uma taxa de 1.5 mm/ano é razoável para o soerguimento atual. Interpretando a cadeia peridotítica como um megamullion tectonicamente deformado, o soerguimento total seria 1500~3000 m e o início do tectonismo seria 1~2 Ma. Se a cadeia peridotítica é originada do manto oceânico subcrustal, o soerguimento total seria, aproximadamente, 9000 m e o início do tectonismo seria cerca de 6 Ma.

Fossil mollusc-faunas: Their bearing on the Holocene evolution of the Lower Central Plain of Bangkok (Thailand)

In this work, fossil molluscan assemblages are analyzed in order to reconstruct the evolution of the Northern Gulf of Thailand during the Holocene. The marine sediments (Bangkok Clay Formation) of the Lower Central Plain of Bangkok and the coastal plain of Phetchaburi were sampled at 16 localities, obtaining fossil shells and mangrove peat whose 14C ages range from 9000 to 2000 CYBP. A statistical treatment of abundance data returned four major groups, namely the Dendostrea rosacea association (intertidal mud), the Corbula fortisulcata– Mactra luzonica association (shallow infralittoral sandy mud), the Nuculana mauritiana– Timoclea scabra association (infralittoral sand spit) and the Timoclea scabra– Arcopagia pudica association (infralittoral mud). The data allowed both a stratigraphic correlation along two transects covering all of the Holocene basin and the creation of digitalized maps showing the presumable extension of the Thai paleogulf around the apex of Flandrian transgression event (about 5500 CYBP).

Ancient Coastlines in the Continental Shelf of the State of Ceará, Northeast Brazil: Evidence from Sediment Chemistry and Stable Isotopes

Continental shelf sediments from the state of Ceará, northeastern Brazil, have been studied to investigate meteoric diagenesis of marine sediments of previously defined ancient coastal lines. Major elements for 131 samples of carbonate sediments and C and O isotopes for 51 carapace samples of benthonic foraminifers of the Amphistegina radiata and Peneroplis planatus species were analyzed. Geochemical signatures of δ13C, δ18O, SiO2 (stoichiometrically calculated as quartz %), Sr and Mn, and XRD document the impact of meteoric diagenesis on relict sediments from current depths of 25-30 m, 45 m, and 80 m. Morphologies of the marine shelf at these depths, interpreted from previous bathymetric profiles, correspond to holocenic marine terraces. Despite a recent sedimentary cover, it was possible to confirm that these terraces possess relict detrital, biogenic, and continental material, that resulted from erosional reworking of ancient coastlines during the Flandrian transgression.

Principal component analysis (PCA) and mineral associations of litoraneous facies of continental shelf carbonates from northeastern Brazil

The distribution of mineral phases according to the provenance of carbonate and terrigenous facies of carbonate sediments from a large area of the continental shelf of northeast Brazil was investigated using a major element multivariate analysis approach. Heavy minerals such as ilmenite are restricted to the litoraneous facies of the continental shelf of the states of Paraíba and Pernambuco, and clay minerals are found in distal facies of the continental shelf of the State of Ceará. In the carbonate fraction, composed essentially by Mg-calcite and aragonite, there is co-variation between CaO/MgO and bathimetry in part of the studied continental shelf from depths between 15 and 20 m, apparently due to influence of the seawater temperature, degree of oxygenation and luminosity. The terrigenous facies are mainly composed of quartz, clay minerals, K-feldspars and micro-micaceous minerals, having Fe and Ti oxide and hydroxide minerals as major accessory phases. Major element behavior attests to the presence of arenaceous quartz-rich relict sediments in the 35, 60 and 80 m isobaths of the continental shelf of the state of Ceará which is here interpreted as a proxy of ancient coast lines during the Flandrian transgression.

Placer Deposits of Southern Tamil Nadu Coast, India

Exploration for placer deposits, especially for ilmenites, has been undertaken systematically in the southern coast of Tamil Nadu, India. On the basis of drainage network. Coastal landforms, lithology, and neotectonics, the study area has been grouped into five sectors: Mandapam, Valinokkam, Tuticorin, Manappad, and Kanyakumari. Ilmenites are abundant in Kanyakumari (Max. 53.39 wt%) and Tuticorin (Max. 20.88 wt%) sectors, negligible in Manappad (Max. 0.60 wt%) and Valinokkam (Max. 3.88 wt%) sectors and absent in the Mandapam sector. The abnormal enrichment of ilmenites in the Kanyakumari sector in the absence of any drainage network points to the possibility of a relict source. Literary and scientific evidence corroborates the existence of an Eastern Gondwana land called Lemuria, South of Kanyakumari which was later submerged in the Flandrian transgression. The association of other heavy minerals with ilmenites like overgrown and outgrown zircon supplements the idea of a longer stay of ilmenites in the depositional basin. Ilmenites from these fossil strandlines must have been reworked by the present day coastal processes and deposited in favorable bay-like NE-SW coastal configurations in Kanyakumari-Kuttankuli and Kallar-Vaippar regions under high energy wave conditions. The present study has disclosed the enrichment of ilmenites up to 1 m in depth in the above two zones which can be commercially exploited. The present study also calls for confirming part of the lost continent called Lemuria or Eastern Gondwana by systematic scientific investigations.