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Alina Shchepetkina Murray K. Gingras John-Paul Zonneveld S. George Pemberton 《Estuaries and Coasts》2017,40(4):947-966
Fine-grained sediment deposition is often conceived to happen in still water conditions and to represent slow sedimentation rates. However, it has been increasingly noted that mud sedimentation commonly occurs under high-energy conditions. The macrotidal Petitcodiac River estuary is used as an example to investigate the significance of flocculation as an important process in the rapid removal of large amounts of sediments from suspension under turbulent flow conditions. A range of physical sedimentary structures was observed at the Petitcodiac River estuary intertidal flats and bars, including low-angle and horizontal planar lamination, current and climbing ripples, surficial fluid mud, soft-sediment deformation, microfaults, and mud rip-up clasts. Fluid mud within the study area contains considerable proportions of clay (21–67%) and contributes to the formation of creeping fluid-mud sheets and streams. Detailed examination of the naturally occurring clay flocs shows that they contain up to 77% of the entangled silt- and sand-sized grains. SEM and microscopic imaging of fluid mud reveal a substantial amount of bioclastic material within the flocs and dispersed among the sediments. These observations show that physicochemical and biological processes influence silt, plankton, and clay aggregation. Water samples and observations from the Petitcodiac River estuary confirm that flocs form in the water column and then settle to the tidal-channel floor and flanking intertidal flats. Laboratory experiments, using Petitcodiac sediment, show how the clay flocs have the potential to sweep the water of silt-sized suspended grains. Additionally, diatoms and their associated extracellular polymeric substance (EPS) sheaths might play a role in mineral aggregation and increased sediment cohesiveness. 相似文献
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遗迹化石在成因地层学中的意义--以加拿大阿尔伯塔省白垩系为例 总被引：2，自引：0，他引：2
遗迹化石代表沉积学和古生物学两方面的内容,是地层记录中潜在的环境指 示者．遗迹化石及其组合可有效地确定地层中各种不连续类型并解释其成因．在地层 意义解释方面,遗迹学的应用主要有：（１）利用受基底控制的遗迹相确定不连续面;（２） 通过仔细分析垂向软基底（准同生）遗迹化石序列获取环境变化的证据（与相序列可类比）． 在成因地层研究中,把受基底控制的遗迹相资料和遗迹化石序列的生态资料结合起来, 可极大地增强对多种地层界面辨认和解释的能力．当这一过程与常规的相分析和层序 地层研究结合起来时,将会成为一个强有力的解释地质记录的工具。 相似文献
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Significance of ichnofossils to genetic stratigraphy--Examples from the Cretaceous of Alberta, Canada 总被引：1，自引：0，他引：1
Trace fossils represent both sedimentological and paleontological entities, representing a unique blending of potential environmental indicators in the rock record. Trace fossils and trace fossil suites can be employed effectively to aid in the recognition of various discontinuity types and to assist in their genetic interpretation. Ichnology may be employed to resolve surfaces of stratigraphic significance in two main ways: 1) through the identification of discontinuities using substrate-controlled ichnofacies, and 2) through careful analysis of vertical softground (penecontemporaneous) ichnologic successions (analogous to facies successions). Ichnological analysis is a valuable tool in genetic stratigraphic studies. Integrating the data derived from substrate-controlled ichnofacies with paleoecological data from vertical ichnologic successions greatly enhances the recognition and interpretation of a wide variety of stratigraphic surfaces. When this is coupled with conventional facies analysis and sequence stratigraphy, a powerful approach to the interpretation of the rock record is generated. 相似文献
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An issue of concern for matched-field processing is the strong dependence between performance and precise knowledge about the environmental parameters. A robust matched-field processor based on minimax robust filtering methods was developed. Here, simulation methods are employed to evaluate the performance of the minimax robust method as well as other robust methods for a range-independent shallow water environment. The performance of the robust methods is compared with that of the nominal processor, that is, the processor based on a single set of environmental parameters thought to be closest to the actual. The matched-field processing performance is evaluated in terms of the peak-to-sidelobe ratio. The simulation results indicate that the robust methods provide significant performance improvements over the nominal processor in the presence of uncertainty in water column sound speed, channel depth, and sound speed in the bottom 相似文献
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This paper provides an overview of the history of ichnology from both Russian and international perspectives. However, the main purpose of the paper is to review how trace fossils can be used to discern the brackish-water sedimentary environments from their open-marine counterparts. A number of modern studies are presented, including: (1) Kouchibouguac Bay, New Brunswick, Canada; (2) Willapa Bay, Washington, USA; (3) Ogeechee River Estuary, Georgia, USA; and (4) Petitcodiac River estuary, New Brunswick, Canada. Cretaceous examples from the Western Canada Sedimentary Basin (i.e., McMurray Formation, AB, Canada and Gething Formation, British Columbia, Canada) are provided to test the models derived from the modern estuaries. 相似文献
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In fluvio-tidal settings, the sediment is dominantly derived from the river systems. However, the importance of landward tidal transport of sediment in tidally influenced sedimentary environments is difficult to assess, particularly in the rock record. This problem is addressed using two intervals within the Lower Cretaceous McMurray Formation, each representing a distinct inclined heterolithic stratification motif. The ichnological variation between the heterolithic intervals is analyzed to determine which lithosomes are associated with brackish-water (tidally influenced) colonization windows. From this, the relative fluvial influence responsible for the deposition of the fine and coarse members can be determined. Both of the inclined heterolithic stratification fabrics studied record the deposition of fluvio-tidal point bars wherein the heterolithic bedding represents variations in river discharge. The first fabric comprises inclined heterolithic stratification in which bioturbation only occurs in mudstone beds. This fabric indicates that deposition occurred in more proximal positions within a fluvio-tidal system (i.e. the outermost inner to middle estuary or distributary channels). In this example sand deposition is interpreted to represent high-energy, freshwater dune migration within a fluvial-dominated setting, whereas mud beds reflect brackish-water suspension deposition during times of low river discharge. The second fabric, which is interpreted to have developed in more distal depositional positions (i.e. the middle estuary or seaward of the turbidity maximum in deltas), consists of inclined heterolithic stratification with laminated mudstone and bioturbated sandstone. In these inclined heterolithic stratification successions the mudstone beds were deposited under the influence of freshwater and heightened sedimentation rates, whereas bioturbated sandstone was colonized under brackish-water conditions and in the presence of tidally facilitated sediment transport. In both examples, the bioturbated lithosomes are related to colonization windows that indicate the predominance at that time of marine or tidally influenced processes over fluvial processes. 相似文献
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Zaki A. Abdel-Fattah Murray K. Gingras S. George Pemberton 《Sedimentary Geology》2011,233(1-4):111-128
Unusually large biogenic sedimentary structures from the shallow quiescent-marine siliciclastics of the Upper Eocene Birket Qarun Formation in the Fayum area of Egypt display pronounced concretion formation around the trace fossils. The structures are massive, and vary morphologically, forming branched pillars (up to dm-scale), vertical (up to 180 cm height) amphora-like masses, and 3-D box-work “maze”. Bioturbation, mainly Thalassinoides attributable to the Glossifungites ichnofacies, mediated and modified the physical and chemical microenvironments influencing early diagenesis; i.e., burrows promote the precipitation of pervasive calcite-dominated cement. The inferred paragenesis, combined with the negative (light) carbon and oxygen stable-isotopic values of the bulk calcite (δ13CPDB from ?0.94 to ?4.98‰ and δ18OPDB from ?4.63 to ?7.22‰) and bulk dolomite (δ13CPDB from ?2.05 to ?8.23‰ and δ18OPDB from ?1.41 to ?11.20‰), imply that the pore-water carbon was derived directly from seawater and dissolution of metastable carbonate, which was mediated by bacterial decomposition of organic matter and mixing of meteoric ground water. Thereby, the carbonate cement precipitated mostly under eodiagenetic conditions near the sediment/water interface (<~3 m in depth). The distribution of these structures is confined to parasequence-bounding flooding surfaces (generally expressed as transgressive surfaces of erosion). Notably, sedimentological, ichnological and paragenetic data can be related to stratigraphic evolution such that geochemical and textural evidence is distinctly associated with (1) early cementation of the host sandstone during highstands of relative sea level, (2) the formation of firmgrounds during low relative sea level, (3) the development of a Glossifungites-demarcated discontinuity during initial relative sea-level rise, and (4) continued cementation with rising relative sea level. This was followed by burial diagenesis, evidence for which is derived from petrographic and isotopic data. 相似文献
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