Small-amplitude lake-level fluctuations recorded in aggrading deltaic deposits of the Upper Pleistocene Thimi and Gokarna formations, Kathmandu Valley, Nepal

Small-amplitude lake-level fluctuations have been recognized from the aggrading delta-plain deposits in the lower parts of the Thimi and Gokarna formations, Kathmandu Valley, Nepal. The delta-plain deposits consist or gravelly sand beds of fluvial channel origin (coarse-sediment interval) and alternation of' fine to very line sand and sandy silt beds (line-sediment interval). Wave generated structures occur in the sand beds or the fine sediment intervals. The vertical and lateral facies changes suggest that the deposition or a set of coarse- and fine-sediment intervals associated with prograding delta front deposits was controlled by a lake-level rise and fall sequence superimposed on a long-term lake level rise trend. The aggradation of fluvial sediments occurred during a lake-level rise period with sufficient sediment supply to fill a newly created accommodation space on the delta plain. The observation or wave-generated structures in an overlying fine-sediment interval suggests that the delta plain was subsequently inundated due to further lake-level rise, exceeding the sedimentation rate. Subsequent delta progradation occurred during a lake-level stabilized phase after a lake level fall. The small-amplitude lake-level changes are thought to be attribute able to seasonal wet and dry cycles, as inferred based on the presence of peculiar aggrading delta successions, implying that lake-level fluctuations may have occurred over short time scales, and on the results of a previous palaeopalynological study in which a moist palacoclimate was inferred in the lower part of the Gokarna Formation in particular.

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Facies analysis of Sunakothi Formation, Kathmandu basin, Nepal and its significance

Journal of Nepal Geological Society ◽

10.3126/jngs.v47i1.23105 ◽

2014 ◽

Vol 47 (1) ◽

pp. 57-64

Author(s):

Mukunda Raj Paudel

Keyword(s):

Lake Level ◽

Facies Analysis ◽

Flood Plain ◽

Delta Front ◽

Gravel Beds ◽

Delta Plain ◽

Facies Associations ◽

Ripple Sand ◽

Lacustrine Delta ◽

Lacustrine Facies

This study decipher facies characteristic of Sunakothi Formation at southern part of Kathmandu Basin. Thick sandy and muddy sequence is found on an open lacustrine facies of the Kalimati Formation. Five facies associations have been recognized within the sandy and muddy facies. These are: (a) muddy rhythmites and silt and laminated to ripple sand bed of the prodeltaic origin (pd), (b) association of cross-stratification, rippledrift and parallel lamination in the lacustrine delta front origin (df), (c) muddy flood-plain and alteration of the fine and coarse sediments of delta-plain origin (dp), (d) sandy to silty rhythmites of the marginal shallow lacustrine origin above the delta-plain (ml), and (e) association of fluvial origin (fl ). Former three associations are interbeded by the thick gravel deposits, which is gravelly braided river origin. Transition from lacustrine to alluvial system is characterized by fluvial and deltaic system in the south. Sedimentology of the Sunakothi Formation indicates deposition during rapid lake level rise and also the thick channelized fluvial gravel beds within the sandy and muddy sequence indicate lake level fall. The cause could be climatic as well as activity of the basin margin tectonics. Sunakothi Formation is the southern counterpart of the Thimi-Gokarna Formations distributed in the northern part of the basin.

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Sedimentary system and coal seam distribution in the coal-bearing sequence stratigraphic framework in the Paleogene Meihe Formation (Meihe Basin, NE China)

10.21203/rs.3.rs-22238/v1 ◽

2020 ◽

Author(s):

Yueyue Bai ◽

Qingtian Lv ◽

Zhaojun Liu ◽

Pingchang Sun ◽

Rong Liu ◽

...

Keyword(s):

Coal Seam ◽

Accumulation Rate ◽

Mapping Method ◽

Sediment Supply ◽

Coal Seams ◽

Delta Front ◽

Contour Maps ◽

Delta Plain ◽

Fan Delta ◽

Wide Range

Abstract The Meihe Basin is one of the important Paleogene coal-bearing fault basins of northeastern China in the Dunhua-Mishan Fault Zone. The Lower Coal-bearing Member and the Upper Coal-bearing Member are the primary layers studied. Through field observation, core description and observation under microscope, fan delta facies and lake facies are observed as the main sedimentary facies of the coal-bearing layers, and subfacies of fan delta plain, fan delta front, shallow lake and swamp have also been recognized. Coal seams primarily accumulated in the subfacies of swamp and fan delta plain. The study on sequence stratigraphy is based on outcrop section, well-log analysis, core observation and geochemical analysis. From the Lower Coal-bearing Member to the Upper Coal-bearing Member, three third-order sequences have been recognized; the Lower Coal-bearing Member developed in Sequence I and the Upper Coal-bearing Member developed in Sequence III, both sequences have developed the lowstand systems tract (LST), the transgressive systems tract (TST) and the highstand systems tract (HST). Single-factor analysis and the multifactor comprehensive mapping method have been used to rebuild the lithofacies palaeogeography of each system tract in Sequence I and Sequence III. Through analysis of contour maps of total stratum thickness, sandstone thickness and sand content, as well as contour maps of thicknesses and numbers of layers of coal seams, the results indicate that the sedimentary environments and coal seam distributions are variable in different system tracts. Coal types accumulating in the swamp facies are primarily developed in the transgressive systems tract (TST) and the highstand systems tract (HST) of Sequence I with a wide range of continuous and large thicknesses and may be mined commercially. Both the balanced accommodation growth rate with peat accumulation rate and little or no influence from sediment supply and channel migration promote to form the stable coal accumulating environments.

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Outcrop analysis and facies model of an Upper Permian tidally influenced fluvio-deltaic system: Northern Sydney Basin, SE Australia

Geological Magazine ◽

10.1017/s0016756818000973 ◽

2019 ◽

Vol 156 (10) ◽

pp. 1715-1741 ◽

Cited By ~ 2

Author(s):

Jake Breckenridge ◽

Angelos G. Maravelis ◽

Octavian Catuneanu ◽

Kevin Ruming ◽

Erin Holmes ◽

...

Keyword(s):

Source Region ◽

Depositional Environments ◽

Sediment Supply ◽

Upper Permian ◽

Delta Front ◽

Sediment Grain Size ◽

Sequence Stratigraphic ◽

Delta Plain ◽

Facies Associations ◽

The Impact

AbstractAn integrated study of sedimentological, sequence-stratigraphic and palaeodispersal analysis was applied to the Upper-Permian clastic sedimentary succession in the Northern Sydney Basin, Australia. The succession is subdivided into fifteen facies and three facies associations. The facies associations are further subdivided into eight sub-facies associations. The sedimentary evolution involves progradation from delta-front to delta-plain to fluvial depositional environments, with a significant increase in sediment grain size across the unconformable contact that separates the deltaic from the overlying fluvial system. In contrast to the delta front that is wave/storm- and/or river-influenced, the delta plain is significantly affected by tides, with the impact of tidal currents decreasing up-sequence in the delta plain. The general lack of wave-influenced sedimentary structures suggests low wave energy in the delta plain. The abrupt termination of the tidal impact in the fluvial realm relates to the steep topographic gradients and high sediment supply, which accompanied the uplift of the New England Orogen. The sequence-stratigraphic framework includes highstand (deltaic forest and topset) and lowstand (fluvial topset) systems tracts, separated by a subaerial unconformity. In contrast to most of the mud-rich modern counterparts, this is an example of a sand-rich tidally influenced deltaic system, developed adjacent to the source region. This investigation presents a depositional model for tidal successions in regions of tectonic uplift and confinement.

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Delta formations associated with high-frequency (annual?) lake-level fluctuations: An example from the uppermost Pleistocene Gokarna Formation, Kathmandu Valley, Nepal

Himalayan Journal of Sciences ◽

10.3126/hjs.v2i4.925 ◽

2008 ◽

Vol 2 (4) ◽

pp. 242

Author(s):

T Sakai ◽

AP Gajurel ◽

H Tabata ◽

BN Upreti

Keyword(s):

High Frequency ◽

Lake Level ◽

Kathmandu Valley ◽

Lake Level Fluctuations

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Sequence Stratigraphy and Depositional Environment of the Zubair Formation in Rumaila Oilfields, Southern Iraq: Microfacies and Geochemistry

Iraqi Geological Journal ◽

10.46717/igj.54.2b.3ms-2021-08-23 ◽

2021 ◽

Vol 54 (2B) ◽

pp. 28-41

Author(s):

Hamid A. A. Alsultan

Keyword(s):

Sea Level ◽

Sequence Stratigraphy ◽

Gamma Ray ◽

Sediment Supply ◽

Delta Front ◽

Delta Plain ◽

Quartz Arenite ◽

Sandy Shale ◽

Sonic Logs ◽

Southern Iraq

In the Rumaila oilfields in southern Iraq, the Zubair Formation was deposited in a shallow environment as three main facies, delta plain, backshore, and delta front depositional conditions indicating a transition from delta front and delta plain to a highstand level due to the finning upward mode. The facies of the Zubair clasts show well-sorted quartz arenite sandstone, poorly sorted quartz arenite sandstone, clayey sandstone that has not been properly sorted, sandy shale, and shale lithofacies. The minor lithofacies were identified using well-logging methods (gamma ray, spontaneous potential and sonic logs) and petrography. The Zubair clasts are of transition environment that appears to be transported from freshwater and deposited in a marine environment forming many fourth-order cycles reflect sea level rise fluctuations and still-stand under tectonics developed the sequence stratigraphy. A misalignment between relative sea-level and sediment supply caused asymmetry sedimentary cycles. A shallower environment of shale-dominated rocks rich in organic matter and pyrite were exposed. The basinal shale of Ratawi at the Zubair bottom and the shallow carbonate of Shuaiba emplace on the Zubair represent the beginning of the delta build up (delta front and delta plain) to a highstand stage.

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