Complex Sedimentary System Research Articles

Characterization of Valley-Fill Alluvial Aquifers in Plutonic and Volcanic Semi-arid Andes Using Electromagnetic Methods: The Case of the Limarí Catchment (Chile)

Many areas of the world are facing sustained periods of water resource stress during which the enhanced exploitation of groundwater is key to maintaining irrigation and drinking water supplies. A good knowledge about groundwater resources is therefore essential to develop sustainable water management strategies. In this study, we aimed to characterize a mountainous watershed in the semi-arid Chilean Andes. The area of interest is distinguished by a high topographic gradient and narrow valleys filled with sedimentary deposits of various origins and surrounded by plutonic and volcano-sedimentary rocks. To characterize the hydrostratigraphy of this complex sedimentary system and to estimate the volume of groundwater stored, we implemented a multidisciplinary approach integrating geophysical data from transient electromagnetic sounding (TEM), hydrogeological, geological, geomorphological and groundwater quality information. The results indicate the presence of two aquifer layers in the majority of the investigated area: a superficial unconfined aquifer and a deeper confined (or semi confined) aquifer. We found that the width and depth of the sedimentary deposits increase with decreasing topography, while the proportion of fine material increases, in coherence with the sedimentation processes. Finally, we quantified the groundwater contribution of the different areas of the catchment and identified the main aquifer potential area in the pediplanes of the coastal mountain range (storing approximately 67% of the water available for extraction). The main contributions to the total uncertainties on the groundwater storage (ranging between 30 and 80% of the estimated volumes) are due to the propagation of the uncertainty on the thickness and porosity/specific yield of the modeled hydrostratigraphic layers. Due to the large spacing between TEM soundings and the limited number of stratigraphic bore logs in part of the studied area, the obtained characterization should be integrated with additional data for precise borehole sittings. Nevertheless, the implementation of TEM allowed to cover an extensive area and to reach large depth of exploration, so that it was possible to extract general information about the hydrostratigraphy of the different areas of the catchment.

Sedimentary facies analysis of Es3 in Jiangjiadian area of Linnan sag

Based on the investigation of the complex sedimentary system of Es3 in Jiangjiadian area of Linnan depression, the petrological characteristics, sedimentary facies types and characteristics of the upper, middle and lower sub sections of Es3 area are studied in depth and detail by combining the geological data of core, thin section and logging. The results show that Es3 in Jiangjiadian area is influenced by Xiakou fault. The lithic feldspar sandstone is relatively developed with low composition maturity. The gap filling is mainly clay minerals, kaolinite and Yimeng mixed layer are the main components. The sedimentary structure type is mainly bedding structure, and a few of them are developed in the stratification layer and biogenetic structure. The sedimentary facies is mainly delta facies and lake facies.

Seismic stratigraphy and deep-water sedimentary evolution of the southern Mozambique margin: Central Terrace and Mozambique Fracture Zone

Based upon new seismic reflection data, this study reveals the development of a complex sedimentary system on the lower-slope terrace off Maputo on the southern Mozambique margin. The deep-water sedimentary system clearly shows the interaction of downslope and alongslope processes. Downslope features include: a pronounced canyon, slope creep, submarine slides, and multi-stage mass-transport deposits. Alongslope features include: contourite drifts and sediment waves, erosional moats, valleys, erosive surfaces and a distinctive contourite terrace. We show an evolution through time as follows: (1) restricted marine sedimentation during the Early Cretaceous after the initial break-up, with slope progradational clinoforms and hemipelagite drape developed; (2) open marine sedimentation characterized by the onset of alongslope sedimentary processes during the Late Cretaceous and development of a contourite depositional system; (3) downslope gravity processes dominated sedimentation during the Paleocene-Eocene, including development of a canyon and submarine fan; and (4) an alongslope contourite depositional system was re-established on the lower slope in the Middle Miocene, while turbidites (from a northern source) covered the Mozambique Basin. The Mozambique Fracture Zone marks a distinct and steep slope seaward of the contourite terrace, and has significantly influenced both contourite and turbidite deposition. Our study provides new insights into the onset and evolution of bottom current control on margin sedimentation, the interaction of downslope and alongslope processes and how these processes have jointly sculpted this part of the southern Mozambique margin.

A review of sediment diversion in the Mississippi River Deltaic Plain

One of the proposed methods for restoring the disappearing Mississippi Delta is sediment diversion which uses channels and structures to divert water and sediment from the Mississippi and Atchafalaya Rivers into adjacent basins. This study presents a comprehensive review of geological and physical aspects of sediment dynamics in the Mississippi River Deltaic Plain (MRDP), with special reference to diversion studies over the past two decades. We synthesize these studies, present the current understanding of sediment diversions in the context of sediment dynamics, identify multiple key knowledge gaps, and make recommendations for future studies.To maximize net land building in the MRDP, management strategies should be focused on (a) enhancing river sediment delivery (both mud and sand), (b) increasing sediment retention in receiving basins and (c) minimizing erosion in bays and estuaries. Compared with extensive studies of land building, there have been relatively fewer studies of erosional processes. A heterogeneous coastal geological framework, cohesive sediment erodibility and subsidence together play complicated yet critical roles in future sediment dynamics in bays and estuaries of the MRDP. Sediment retention rates are highly sensitive to spatial and temporal scales, types of sediments and delivery season. Sediment diversions to seaward receiving basins provide more surge protection but tend to have lower sediment retention due to active coastal processes. Structures and devices that improve sediment retention, trap sediments, dissipate waves, and build living shorelines should be explored and cost-to-benefit analysis is needed. Long-term planning should consider more landward diversions, strategic community relocation, and nonlinear response of the complex sedimentary system of the MRDP.

Reservoir prediction of deep-water turbidite sandstones with seismic lithofacies control —A case study in the C block of lower Congo basin

Currently, conventional forecasting methods of well-to-seismic integration are unable to identify turbidite channel sandstones due to scarcity of well data in deepwater areas, small geophysical differences between sandstones and mudstones of turbidite channels and strong sandstones heterogeneity. The reservoir prediction of deep-water turbidite channels is still a difficult issue in deep-water research. On the basis of previous studies, we propose a new technology named “reservoir prediction of deep-water turbidite sandstones with seismic lithofacies control” in view of the characteristics of deep-water turbidite sandstones. This new technology improves the reservoir prediction of complex sedimentary systems after classifying seismic lithofacies and connecting lithofacies with rock-physics. Furthermore, it can accomplish the genetic classification statistics of rock-physics, improve conversion accuracy of seismic elastic parameters/reservoir parameters and achieve the quantitative reservoir prediction under the double control of seismic geomorphology and seismic lithofacies. The C block of Lower Congo Basin is characterized by few well data, complex lithology but high resolution-seismic. We use the technology to predict the reservoirs of this area and have achieved excellent results. This has great significance for the later exploration.

Relating Gestures and Speech: An analysis of students' conceptions about geological sedimentary processes

Advances in cognitive science and educational research indicate that a significant part of spatial cognition is facilitated by gesture (e.g. giving directions, or describing objects or landscape features). We aligned the analysis of gestures with conceptual metaphor theory to probe the use of mental image schemas as a source of concept representations for students' learning of sedimentary processes. A hermeneutical approach enabled us to access student meaning-making from students' verbal reports and gestures about four core geological ideas that involve sea-level change and sediment deposition. The study included 25 students from three US universities. Participants were enrolled in upper-level undergraduate courses on sedimentology and stratigraphy. We used semi-structured interviews for data collection. Our gesture coding focused on three types of gestures: deictic, iconic, and metaphoric. From analysis of video recorded interviews, we interpreted image schemas in gestures and verbal reports. Results suggested that students attempted to make more iconic and metaphoric gestures when dealing with abstract concepts, such as relative sea level, base level, and unconformities. Based on the analysis of gestures that recreated certain patterns including time, strata, and sea-level fluctuations, we reasoned that proper representational gestures may indicate completeness in conceptual understanding. We concluded that students rely on image schemas to develop ideas about complex sedimentary systems. Our research also supports the hypothesis that gestures provide an independent and non-linguistic indicator of image schemas that shape conceptual development, and also play a role in the construction and communication of complex spatial and temporal concepts in the geosciences.

Structure and evolution of a Messinian mixed carbonate-siliciclastic platform: the role of evaporites (Sorbas Basin, South-east Spain)

The Sorbas Member is a late Messinian complex sedimentary system that formed immediately following deposition of the Messinian evaporites in the Sorbas Basin (South-east Spain). This work describes the sequence architecture and facies organization of a continuous kilometre long, alluvial fan to open platform transect near the village of Cariatiz in the north-east of the basin. The post-evaporitic Cariatiz platform was a mixed carbonate-siliciclastic system composed of four intermediate-frequency, fifth-order depositional sequences (Depositional Sequences 1 to 4) arranged in an overall prograding trend. The intense fracturing and brecciation of these deposits is attributed to the deformation and dissolution of an evaporite body measuring several tens of metres in thickness. The four sequences display significant spatial–temporal variability in both architecture and facies distribution, with two main phases: (i) Depositional Sequences 1 and 2 are ooid and oobioclastic dominated, and show normal marine faunas; and (ii) Depositional Sequences 3 and 4 show a higher siliciclastic contribution and are microbialite dominated. These important changes are interpreted as modifications of the primary controlling factors. Following an initial 70 m drowning, possibly linked to increased oceanic input, Depositional Sequences 1 to 3 were controlled mainly by eustatic variations and inherited topography; their progradation destabilized the evaporite body near the end of the Depositional Sequence 2 period. During the second phase, Depositional Sequences 3 and 4 recorded a progressive restriction of the Sorbas Basin related to a 30 to 40 m fall in water level that was driven mainly by regional factors. These regional factors were dissolution and gravity-induced deformation of the evaporites and correlative evaporative fluid circulation associated with the contrasted arid/humid regional climate that, respectively, controlled sequence geometry and fluctuating water salinity which caused a microbialite bloom.

Using lithologic modeling techniques for aquifer characterization and groundwater flow modeling of the Sohag area, Egypt

Three dimensional lithologic modeling techniques have been used for detailed characterization and groundwater flow modeling of the Quaternary aquifer system of the Sohag area, Egypt. Well log data were used for building the lithologic model using RockWorks. A groundwater flow model, facilitated by MODFLOW 2000, was built using results of the lithologic model. The obtained lithologic model honored the well log data and revealed a complex sedimentary system, which is mainly composed of six lithologic categories: clay, clay and sand, fine sand, coarse sand, sand and gravel, and gravel. Inter-fingering and presence of lenses are the main characteristics of the sedimentary basin in the study area. A wide range of hydraulic conductivities is present, which vary spatially and control the groundwater flow. Heterogeneity of the aquifer system is spatially represented where different hydraulic conductivities are found in the different directions. Sandy layers tend to be connected. Hydraulic continuity is represented by inter-fingering and connection of sandy materials within the aquifer system.

Facies distribution and coral-microbialite reef development on a low-energy carbonate ramp (Chay Peninsula, Kimmeridgian, western France)

The Chay Peninsula (western France) succession corresponds to a Kimmeridgian shallow and low-energy ramp system that developed in the northeast of the Aquitaine Basin. The sedimentation shows a transition from a carbonate-dominated to a mixed carbonate–siliciclastic depositional environment that takes place at the base of a major, third-order sea-level transgression. Facies partitioning and coral-microbialite reef levels (i.e., reef windows) suggest higher-frequency (fourth-order) sea-level oscillations. Reef-growth phases (i.e., high-frequency reef windows) are interpreted to have been controlled by fifth-order sea-level oscillations. In the mixed siliciclastic–carbonate system, successive prograding units of shoreface sediments pass into thick marl–limestone alternations over a distance of tens of metres. Such remarkable short-distance lateral facies variations suggest a complex sedimentary system made of juxtaposed deposits that rapidly shift through time. Terrigenous fluxes, in modifying the light intensity and the nutrient level in the water column strongly controlled the facies distribution and notably the reef composition and growth. Identified coral genera suggest mixed photo-heterotrophic mode of nutrition and low-mesotrophic conditions in marine waters. For each reef-growth phase, nutrient increase favoured large amounts of microbialites to develop, forming a crust that entirely capped the coral reef surface. Thus, high-frequency fluctuations in nutrient input in tune with fifth- (or higher) order sea-level fluctuations controlled the reef development at a millennial scale. The Chay Peninsula reef distribution and development provide insight into understanding the response of reef communities under climatically-induced environmental changes.

Multiproxy Late Quaternary stratigraphy of the Nile deep-sea turbidite system — Towards a chronology of deep-sea terrigeneous systems

Understanding the recent formation of a sedimentary system such as a deep-sea turbidite system (DSTS) requires an accurate stratigraphic control on deposits. Due to the important terrigeneous input which disrupts the sedimentary record, DSTS is an environment where stratigraphic control is difficult to assess. Most of the time, traditional stratigraphic tools are not accurate enough. This has led to a rather limited number of studies concerning stratigraphy in DSTS. In this study, we examine several hemipelagic long piston cores collected from the Nile DSTS (eastern Mediterranean), in order to understand the recent evolution of the complex sedimentary system in this area. The first aim of this study is to show how to obtain a reliable timeframe in DSTS. Indeed, we provided a detailed ecostratigraphical scheme based on planktonic foraminiferal distribution, oxygen isotope records and lithostratigraphy (sapropels and tephra) of three cores where the sedimentation is least disturbed. We have identified 29 foraminiferal ecozones during the last 250,000 years BP, with an approximately 2000-year time resolution. The time span of each ecozone was constrained by the oxygen isotope record, 14C AMS radiometric data, tephrochronology and the sapropel chronology. These high-resolution ecostratigraphical time subdivisions have been applied in discontinuous mixed hemipelagic/turbiditic sequences of a levee record. This example shows how to date gravity events, formation and time periods of sedimentary accumulations.

Sediment texture, distribution and transport on the Ayeyarwady continental shelf, Andaman Sea

The Ayeyarwady continental shelf is a complex sedimentary system characterized by large sediment influx (> 360 million ton/yr), a wide shelf (> 170 km), a strong tidal regime (7 m maximum tidal range), and incised by the Martaban Canyon. Grain size distribution on the Ayeyarwady shelf reveals three distinct areas in terms of sediment texture (i) a near-shore mud belt in the Gulf of Martaban and adjacent inner shelf (ii) outer shelf relict sands and (iii) mixed sediments with varying proportions of relict sand and modern mud in the Martaban Canyon. The bulk of the terrigenous sediment discharged by the Ayeyarwady River is displaced eastwards by a combination of tidal currents and clockwise flowing SW monsoon current and deposited in the Gulf of Martaban resulting in shoaling of its water depths. Part of the sediment discharge reaches the deep Andaman Sea via the Martaban Canyon and the rest is transported westward into the Bay of Bengal by the counter-clockwise flowing NE monsoon currents.

Complex hydroseral vegetation succession and ‘dryland’ pollen signals: a case study from northwest Scotland

Pollen assemblages from sediment systems developed in response to changing sea level provide potentially valuable archives of local landscape dynamics in the coastal zone. Changes in wetland vegetation structure associated with the successional transition from saline to freshwater communities, and subsequent terrestrialization, however, will have marked effects on the palynological signal from surrounding dry land communities by altering the taphonomic properties of the pollen-recruiting system. We present data from one such system, a coastal wetland on the Coigach Peninsula in northwest Scotland, focusing here on reconstructing the hydroseral processes of wetland development, and how they affect the interpretation of the dry pollen signal. This contribution highlights the often-unacknowledged ambiguities inherent in reconstructing past environments from complex sedimentary systems, and outlines strategies for clarifying them.