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1

Depositional environment of sediments along the southern coast of Tamil Nadu, India

100%

Angusamy N. , Rajamanickam G. V.

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2006

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tom No. 48 (1)

87-102

EN

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.

2

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

88%

Angusamy N. , Rajamanickam G. V.

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tom No. 49 (1)

41-57

EN

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, positive-symmetrically 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.

3

Petrological and facies characteristics of bituminous coal seam No. 111 from the Libiąż layers in the region of Dąb near Chrzanów (USCB)

75%

Misiak J. , Misiak J.

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nr 4

4

Rozwój ryftu w późnym neoproterozoiku-wczesnym paleozoiku na lubelsko-podlaskim skłonie kratonu wschodnioeuropejskiego : analiza subsydencji i zapisu facjalnego

63%

Poprawa P. , Pacześna J.

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tom Vol. 50, nr 1

49-63

PL

Dla lubelsko-podlaskiego, górnoneoproterozoiczno-dolnopaleozoicznego basenu sedymentacyjnego przeprowadzono analizę subsydencji (backstripping) oraz analizę facjalną jego osadowego wypełnienia. Wydzielono cztery główne, częściowo współwystępujące, etapy tektonicznej ewolucji basenu, o odmiennych mechanizmach subsydencji: (1) późnoneoproterozoiczny ryft (faza subsydencji synryftowej w reżimie ekstensyjnym), (2) przejście od fazy syn- do postryftowej na przełomie późnego neoproterozoiku III i wczesnego kambru, (3) wczesnokambryjsko-środkowoordowicki pasywny brzeg kontynentalny (faza postryftowej subsydencji termicznej) oraz (4) późnoordowicko-późnosylurskie fleksuralne uginanie krawędzi Baltiki. Synryftowe wypełnienie basenu stanowią kontynentalne wylewy bazaltowe oraz kontynentalne zlepieńce i arkozy, obocznie zastępowane przez mułowce. Wykształcenie facjalne tych utworów dopuszcza synsedymentacyjną aktywność ekstensyjnych uskoków. Synryftowe depocentra rozwijały się zarówno wzdłuż obecnej strefy szwu transeuropejskiego, jak i wzdłuż SW przedłużenia aulakogenu Orsza-Wołyń. Efektem tych procesów było powstanie węzła potrójnego, którego porzuconym ramieniem jest druga z powyżej wymienionych stref. Przejście do fazy postryftowej subsydencji termicznej wyznaczają: stopniowo wygasająca subsydencja, równoczesna z morską transgresją, generalnym zmniejszaniem się frakcji materiału klastycznego i obocznym ujednoliceniem facjalnym oraz rozszerzaniem się zasięgu basenu. Przyjęto, że kambryjsko-środkowoordowicki pasywny brzeg kontynentalny był związany z domniemanym basenem (oceanem?) Tornquista, powstałym na SW od Baltiki w efekcie rozpadu super-kontynentu Rodinii. W takim ujęciu obecna pozycja kadomskiego orogenu na blokach małopolskim i górnośląskim w stosunku do kratonu wschodnioeuropejskiego nie jest reprezentatywna dla neoproterozoiku III i kambru. Ze względu na brak niepodważalnych dowodów na obecność synryftowych deformacji ekstensyjnych uznano, iż możliwa jest interpretacja wyników backstrippingu alternatywna względem modelu litosferycznej, basenotwórczej ekstensji. W alternatywnym modelu dla późnoneoproterozoiczno-środkowoordowickiego okresu rozwoju basenu jako przeważający mechanizm subsydencji basenu przyjęto termiczne studzenie litosfery, będące następstwem jej pasywnego przegrzania w czasie aktywności wulkanicznej w neoproterozoiku III. Model ten, choć dopuszczalny dla basenu lubelsko-podlaskiego, nie tłumaczy jednak rozwoju górnoneoproterozoicznych, kambryjskich i ordowickich basenów SW skłonu kratonu wschodnioeuropejskiego, genetycznie powiązanych z basenem tu omawianym. Począwszy od późnego ordowiku obserwowany jest systematyczny wzrost tempa subsydencji w czasie, które osiąga maksymalne wartości w późnym sylurze. Dla tego przedziału czasu obserwowany jest również silny wzrost subsydencji z NE ku SW, tj. ku skłonowi kratonu wschodnioeuropejskiego. Generalny rozwój subsydencji omawianego basenu w sylurze jest charakterystyczny dla procesu fleksuralnego uginania litosfery, w tym wypadku SW krawędzi Baltiki.

EN

For the Neoproterozoic to Lower Palaeozoic Lublin-Podlasie sedimentary basin 1-D subsidence analysis was conducted by means ofbackstripping. This was performed for 14 boreholes, representative for the basin, and additionally was compared with the results of similar analysis applied further to the NW, i.e. for the Baltic Basin. To constraint tectonic model for the basin the results of backstripping were related to facies architecture of the basin-fill. Four partially overlapping main tectonic phases of the basin development were identified: (I) the late Neoproterozoic syn-rift, extension-elated subsidence, (2) transition from synrift to postrift phase at the latemost Neoproterozoic III to earlymost Early Cambrian, (3) post-rift thermal subsidence of the passive continental margin during the late Early Cambrian to Middle Ordovician and (4) Late Ordovician to late Silurian flexural bending. The rifting phase was initiated with deposition of continental coarse-grained sediments and emplacement of continental basalt. Subsequently the syn-rift basin was filled with continental conglomerates and arkoses, laterally replaced by mudstones, with facies development possibly controlled by extensional fault block activity. This passed up-section into shallow marine claystones and mudstones. Development of syn-rift depocentres was roughly coeval along Peri-Tornquist zone and SW prolongation ofOrsha-Volhyn zone, leading to development of triple-point SW of analysed area, with the second of the above zones being an abounded arm. Passage to post-rift thermal subsidence of the passive continental margin is indicated by subsequently ceasing subsidence, coeval with marine transgression, fining of clastic sediments and relative facies unification, as well as expansion of depocentres. The passive margin is related here to a suspected Tornquist basin (ocean?), developed to the SW of Baltica as a result of break-up of the super-continent Rodinia. This requires an assumption, that recent position of a Cadomian orogen, recognised on Małopolska and Brunovistulicum, with respect to Baltica is not representative for the Neoproterozoic III and Cambrian. Lack of definite evidences for syn-rift extensional deformations leads to an alternative interpretation of the backstripping results. Instead oflithospheric, active extension, leading to development of the sedimentary basin, in the alternative model it was assumed that the Neoproterozoic to Middle Ordovician evolution of the Lublin-Podlasie basin was exclusively a result of thermal sag, related to cooling of litho sphere. This would be a consequence of passive heating of the system due to volcanic activity in the Neoproterozoic III. This alternative model, even if suitable for the Lublin-Podlasie basin, is not capable to explain the upper Neoproterozoic, Cambrian and Ordovician development of sedimentary basins at the SW slope of Baltica, which are genetically related to the analysed area. Any compromise between cooling after passive heating and cooling after active lithospheric extension, with different proportions between the both, is possible. Since the Late Ordovician gradual increase in subsidence rate in time is observed, which reaches maximum in the late Silurian (Pridoli). Overall pattern of the Silurian subsidence, both spatial and 1-D, is typical for a mechanism of flexural bending oflithosphere. A common development of Caledonian foredeep basins along e.g. some of Baltica and Eastern and Western Avalonia margins, coeval with Silurian flexural bending, enhances discussing such model for Lublin-Podlasie basin. Nevertheless, comparison of development of the analysed area with Holly Cross Mountains one during the Silurian does not support a simple foredeep model.

5

Depositional environment of sediments along the Southern coast of Tamil Nadu, India

63%

Angusamy N. , Rajamanickam G. V.

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tom 48

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nr 1

EN

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.