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1
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Coastal processes of Central Tamil Nadu, India: clues from grain size studies

100%
Angusamy N., Rajamanickam G. V.
Oceanologia
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2007
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tom 49
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nr 1
The sediments of the beaches along the central coast of Tamil Nadu from Pondicherry to Vedaranyam were studied for their textural variation. 108 sediment samples collected from the low-, mid-, and high-tidal zones, as well as the berms and dunes of different beach morpho-units were analysed. The study area was divided into three sectors (northern, central and southern) on the basis of prevailing energy conditions and oceanographic parameters. The poorly sorted, negatively skewed, coarser sediments of the northern sector are indicative of denudational processes taking place there. Medium-to-fine, moderately-to-well sorted, positivesymmetrically skewed sediments dominate the central sector, probably as a result of the influence of palaeo-sediments deposited by rivers from inland as well as by waves and currents from offshore. Fine, poorly sorted, positive-symmetrically skewed sediments dominate the southern sector, highlighting depositional processes. Linear Discriminant Function Analysis (LDF) of the samples indicates a shallow marine environment origin for all the three sectors. These results show that reworked sediments, submerged during the Holocene marine transgression, are being deposited on present-day beaches by waves, currents and rivers in the study area.
2
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Taphonomy of the fossil insects of the middle Eocene Kishenehn Formation

84%
Greenwalt D. E., Rose T. M., Siljestrom S. M., Goreva Y. S., Constenius K. N., Wingerath J. G.
Acta Palaeontologica Polonica
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2015
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tom 60
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nr 4
The lacustrine oil shales of the Coal Creek Member of the Kishenehn Formation in northwestern Montana comprise a relatively unstudied middle Eocene fossil insect locality. Herein, we detail the stratigraphic position of the fossiliferous unit, describe the insect fauna of the Coal Creek locality and document its bias towards very small but remarkably preserved insects. In addition, the depositional environment is examined and the mineral constituents of the laminations that comprise the varves of the Kishenehn oil shale are defined. Fifteen orders of insects have been recorded with the majority of all insects identified as aquatic with the families Chironomidae (Diptera) and Corixidae (Hemiptera) dominant. The presence of small aquatic insects, many of which are immature, the intact nature of >90% of the fossil insects and the presence of Daphnia ephippia, all indicate that the depositional environment was the shallow margin of a large freshwater lake. The fossil insects occur within fossilized microbial mat layers that comprise the bedding planes of the oil shale. Unlike the fossiliferous shales of the Florissant and Okanagan Highlands, the mats are not a product of diatomaceous algae nor are diatom frustules a component of the sediments or the varve structure. Instead, the varves are composed of very fine eolian siliciclastic silt grains overlaid with non-diatomaceous, possibly cyanobacteria-derived microbial mats which contain distinct traces of polyaromatic hydrocarbons. A distinct third layer composed of essentially pure calcite is present in the shale of some exposures and is presumably derived from the seasonal warming-induced precipitation of carbonate from the lake's waters. The Coal Creek locality presents a unique opportunity to study both very small middle Eocene insects not often preserved as compression fossils in most Konservat-Lagerstätte and the processes that led to their preservation.
3
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Depositional environment of sediments along the Southern coast of Tamil Nadu, India

84%
Angusamy N., Rajamanickam G. V.
Oceanologia
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2006
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tom 48
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nr 1
Grain size studies of sediments from beaches in the region from Mandapam to Kanyakumari, divided into 5 sectors, indicate that sediments are unimodal to polymodal in nature, coarse to fine grained, moderately to poorly sorted, and positively-negatively skewed in character. The inference to be drawn from these studies is that the variation in sedimentological parameters is governed by fluvial input, wave dynamics, and littoral transport of the sediments. Bivariant plots show that the Mandapam and Kanyakumari sectors can be classified as beach environments, whereas the Tuticorin and Valinokkam sectors come under the influence of riverine environments and the dune environment in the Manappad sector. The CM pattern of all five sectors shows a clustered distribution of sediments in the PQ and QR segments, indicating a graded mode of deposition. Visher diagrams depict a wave shadow environment for the Mandapam sector, whereas the Valinokkam, Tuticorin and Manappad sectors show double saltation populations characteristic of beaches, and the Kanyakumari sector is characterized by a more truncated population characteristic of a plunge zone, which is a high-energy environment.
4
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Upper Cambrian trilobite biostratigraphy and taphonomy at Kakeled on Kinnekulle, Vastergotland, Sweden

84%
Terfelt F.
Acta Palaeontologica Polonica
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2003
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tom 48
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nr 3
A section through the Upper Cambrian black shales and limestones at Kakeled on Kinnekulle, Västergötland, Sweden, extends from the lower–middle part of the Agnostus pisiformis Zone into the Peltura scarabaeoides Zone. Fossils are usually preserved only in the stinkstones, but in the A. pisiformis Zone trilobites can be found also in the shales. Lithologically, the stinkstones can be subdivided into primary coquinoid limestone, which include the majority of the fossils, and early diagenetically formed limestone. The orientation of cephala and pygidia of A. pisiformis were measured on four shale surfaces and one stinkstone surface. The majority of the shields were deposited with the convex side up and showed a preferred orientation, suggesting that their positions were affected by currents. Above the A. pisiformis Zone the section comprises the Olenus/Homagnostus obesus Zone (0.30 m), the upper part of the Parabolina spinulosa Zone (0.05 m), the Peltura minor Zone (1.15 m), and the Peltura scarabaeoides Zone (2.50 m). The Leptoplastus and Protopeltura praecursor zones are missing. The Olenus/H. obesus Zone is represented only by the O. gibbosus and O. wahlenbergi subzones, whereas the O. truncatus, O. attenuatus, O. dentatus, and O. scanicus subzones are missing.
5
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Priabonian, late Eocene chronostratigraphy, depositional environment, and paleosol-trace fossil associations, Pipestone Springs, southwest Montana, USA

67%
Hanneman D. L., Lofgren D., Hasiotis S. T., McIntosh W. C.
Acta Palaeontologica Polonica
|
2022
|
tom 67
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nr 1
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