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Stratigraphy and Sedimentation
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
Sediments accumulate within basins by aggradation, progradation and lateral accretion. Aggradation is the process of vertical filling, as in the flood basin of a river. Progradation is the filling from the margin, as in the case of an advancing delta front. Lateral accretion is caused by the process of accumulation against the margin of a channel, as in a river point bar (see Fig. 8.1). The vertical relationship between succeeding sedimentary units produced in this way may be either conformable or non-conformable. A conformable relationship may be either sharp or gradational. Two types of gradations are possible: a continuous gradation or an intercalated contact. A body of sand grading vertically up into a shale section through mixtures of sand and shale in various proportions, is an example of a continuous gradation. A sand body passing vertically up into a body of shale through an intermediate layer of closely spaced lenticles of sand and shale is an example of intercalation.
Net Ecosystem Carbon Balance of Coastal Wetland-Dominated Estuaries
Published in Lisamarie Windham-Myers, Stephen Crooks, Tiffany G. Troxler, A Blue Carbon Primer, 2018
Progradation is the result of bay infilling to a depth above MSL such that wetland plants can colonize, grow, and thereby effectively trap TSS from floodwaters. The rate of progradation is solely a function of the rate of bay infilling relative to SLR. Inadequate sediment inputs can reverse progradation, even in the absence of SLR (Mariotti and Fagherazzi 2013).
Tephrostratigraphic constraints on sedimentation and tectonism in the Whanganui Basin, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2020
Callum Rees, Julie Palmer, Alan Palmer
Influxes of conglomeratic and carbonaceous rich heterolithic facies within the basin succession are interpreted to be a feature of an alluvial and coastal plain adjacent to the paleo-axial range. The first influx of fluvial conglomerate occurs shortly before the Pakihikura Pumice (c. 1.6 Ma) within the upper Oroua catchment, whilst within the Rangitikei, there is a delay until around Toms Conglomerate (c. 0.6 Ma). We suggest gravels derived from uplifting basement in the position of the main axial range were entering the Whanganui Basin from the northeast. Sea level low stands being characterised by aggradation and progradation of broad fans of greywacke gravel forming an apron of sediment about the paleo-axial range front. Marine transgression is characterised by a warmer climate, reduction of erosion in headwater catchments and fluvial incision into and reworking of LST deposits. Landward migration of the coastal plain and fluvial distributary systems during rising sea level resulted in sedimentary infilling of channels and valleys. We suggest uplift in the main axial range occurred contemporaneously with the onset of volcanic activity at Mangakino caldera so that the first influxes of fluvial conglomerate and volcaniclastics occur in close proximity within the eastern Whanganui Basin succession.
Sedimentary processes, stratigraphic sequences and middens: the link between archaeology and geoheritage—a case study from the Quaternary of the Broome region, Western Australia
Published in Australian Journal of Earth Sciences, 2019
With the Canning Coast and Broome coastal region subject to a variable sea-level history, this has resulted in changes in coastal configuration and hence in sedimentation style. When the rising post-glacial Holocene sea reached the level of the present coast, sea level was 2 m higher, and it met a terrain of (semi-lithified) red sand dunes of the pindan and the Broome Sandstone. The sea invaded lowlands to form embayments, and erosionally attacked the red sand dunes and Broome Sandstone. The first result was spits and barriers developed along the headland of the rocky shores, and sand filling the embayments (derived from eroding red sand dunes, and from wave-abraded coastal shelly fauna). In time and with falling sea levels, the embayments began to fill with carbonate mud; the headlands of red sand dunes and Broome Sandstone accreted spits, beaches and dunes. The changes in the styles of sedimentation along the Canning Coast are shown in Figure 6. There were three stages in the history of the Canning Coast related to a falling sea level (Semeniuk, 2008): (1) when sea level reached its present position, an early phase of headland erosion, barrier formation for small embayments, and filling of these embayments with sand; (2) with falling sea level, filling of small embayments with mud; and (3) with a stabilised MSL in the present situation, local erosion and local progradation.
Paleo-environment and provenance in a lacustrine shallow-water delta-meandering river sedimentary system: insights from the Middle–Upper Jurassic formations of the Fukang Sag of Junggar Basin, NW China
Published in Australian Journal of Earth Sciences, 2019
L. Luo, X. Gao, X. Tan, J. Gluyas, J. Wang, X. Kong, J. Huang, H. Shao, F. Qu
The progradation, mouth bar and reverse rhythm, which are characteristics of a normal delta, were rarely observed in the shallow-water meandering river delta (Figures 12, 13, 15 and 16). The sandstone mainly consists of siltstone and fine sandstone (Figures 11–14) and the green-grey, brown and brownish-red mudstone were pervasive in the shallow-water meandering river delta facies (Figures 11–14 and 16). The granularity of sandstone in a shallow-water meandering river delta is generally less than in a normal delta, but oxide colours of mudstones are pervasive in shallow-water deltas. In shallow-water deltas sedimentary structures include parallel bedding, current bedding, cross-bedding and basal erosional scours. The shallow-water meandering river delta sedimentary succession has a large overall thickness but relatively thin single-layer sand bodies (1–15 m, mean 3 m) and relatively low sand–strata ratios (0.2–0.55), which are less than that of normal deltas (Figures 11–14). The meandering river facies are characterised by the thin, fine–medium-grained point bar sandstones and a lack of marsh deposits (Figures 15–17).