The GSSP for the base of the Lutetian Stage(early/middle Eocene boundary)is defined at 167.85 metres in the Gorrondatxe sea-cliff section(NW of Bilbao city,Basque Country,northern Spain;43°22'46.47"N,3&#...The GSSP for the base of the Lutetian Stage(early/middle Eocene boundary)is defined at 167.85 metres in the Gorrondatxe sea-cliff section(NW of Bilbao city,Basque Country,northern Spain;43°22'46.47"N,3°00'51.61"W).This dark marly level coincides with the lowest occurrence of the calcareous nannofossil Blackites inflatus(CP12a/b boundary),is in the middle of polarity Chron C21r,and has been interpreted as the maximumflooding surface of a depositional sequence that may be global in extent.The GSSP age is approximately 800 kyr(39 precession cycles)younger than the beginning of polarity Chron C21r,or~47.8 Ma in the GTS04 time scale.The proposal was approved by the International Subcommission on Paleogene Stratigraphy in February 2010,approved by the International Commission of Stratigraphy in January 2011,and ratified by the International Union of Geological Sciences in April 2011.展开更多
The uppermost part of the Upper Bathonian Sponge Limestone member, Patcham Formation, of the Jhura Dome of Kachchh Mainland is a thickening-and shallowing-upward succession topped by medium-to thick-bedded hummocky cr...The uppermost part of the Upper Bathonian Sponge Limestone member, Patcham Formation, of the Jhura Dome of Kachchh Mainland is a thickening-and shallowing-upward succession topped by medium-to thick-bedded hummocky cross-stratified grainstones deposited by storm waves. Occasionally, thin, commonly lenticular, intraclastic-bioclastic silty marl intercalations between the grainstones are highly bioturbated, in contrast to the grainstones, in which, for the most part, trace fossils occur scattered. Large exposures of bedding planes of the grainstones allow the detailed investigation of ichnological features, whereas the high density of traces in the soft marls precludes the identification of any ichnotaxa. Eighteen ichnotaxa have been recorded including Ophiomorpha, Thalassinoides, Taenidium, Gyrophyllites, Chondrites, Dactyloidites, Teichichnus, Bolonia, and Ancorichnus. Except for Ophiomorpha nodosa and Thalassinoides, which generally indicate moderate to high energy conditions and are the dwelling burrows of suspension-feeding to omnivorous crustaceans, the ichnotaxa represent a deposit-feeding behaviour of their producers and thus are characteristic of low-energy environments. The trace fossils form three ichnoassemblages characterized by(1) Ophiomorpha nodosa and Thalassinoides suevicus,(2)?Thalassinoides isp. A, Taenidium, and Bolonia lata,and(3) Ancorichnus. The dominance of traces of deposit-feeders in rocks indicative of high-energy events is counterintuitive and points to their non-contemporaneity. The sediments were deposited during brief highenergy events, whereas the trace fossils were produced when, after waning of storms low-energy conditions prevailed. This time-averaging is particularly pronounced in trace fossils that extend vertically downwards and may reach strata deposited under distinctly different conditions. Thus, environmental interpretations based on trace fossils should refer to colonisation surfaces rather than to the sediment surrounding the trace fossils. In the latter case, interpretations may be erroneous, especially when erosion subsequently destroyed sedimentary evidence of their original environment.展开更多
A spectacularly exposed slump is described from a 120-m-long road cut between the villages of Kanod and Deva in the northeastern Jaisalmer Basin of Rajasthan,India.The Upper Jurassic part of the sediments at the outcr...A spectacularly exposed slump is described from a 120-m-long road cut between the villages of Kanod and Deva in the northeastern Jaisalmer Basin of Rajasthan,India.The Upper Jurassic part of the sediments at the outcrop was formed in a near-shore setting and belongs to the Ludharwa Member of the Baisakhi Formation.The 3-m-thick unit shows a number of asymmetric folds and thrust faults leading to an imbrication of partly lithified sandstone beds.The deformation structures allow the reconstruction of a movement towards the northwest.This agrees well with the basin configuration that shows a deepening into this direction.Although the determination of a specific trigger mechanism is difficult for soft-sediment deformation structures,an earthquake caused by synsedimentary tectonics in the basin seems to be the most likely explanation.展开更多
基金Financial support was mainly provided by different projects of the Ministry of Science and Innovation of Spain,the Town Council of Getxo and the Basque Government.
文摘The GSSP for the base of the Lutetian Stage(early/middle Eocene boundary)is defined at 167.85 metres in the Gorrondatxe sea-cliff section(NW of Bilbao city,Basque Country,northern Spain;43°22'46.47"N,3°00'51.61"W).This dark marly level coincides with the lowest occurrence of the calcareous nannofossil Blackites inflatus(CP12a/b boundary),is in the middle of polarity Chron C21r,and has been interpreted as the maximumflooding surface of a depositional sequence that may be global in extent.The GSSP age is approximately 800 kyr(39 precession cycles)younger than the beginning of polarity Chron C21r,or~47.8 Ma in the GTS04 time scale.The proposal was approved by the International Subcommission on Paleogene Stratigraphy in February 2010,approved by the International Commission of Stratigraphy in January 2011,and ratified by the International Union of Geological Sciences in April 2011.
基金supported by the Jagiellonian University(DS funds)financial assistance for the fieldwork by DST(project EMR/ 2015/001574)financial support by the Alexander von Humboldt Foundation
文摘The uppermost part of the Upper Bathonian Sponge Limestone member, Patcham Formation, of the Jhura Dome of Kachchh Mainland is a thickening-and shallowing-upward succession topped by medium-to thick-bedded hummocky cross-stratified grainstones deposited by storm waves. Occasionally, thin, commonly lenticular, intraclastic-bioclastic silty marl intercalations between the grainstones are highly bioturbated, in contrast to the grainstones, in which, for the most part, trace fossils occur scattered. Large exposures of bedding planes of the grainstones allow the detailed investigation of ichnological features, whereas the high density of traces in the soft marls precludes the identification of any ichnotaxa. Eighteen ichnotaxa have been recorded including Ophiomorpha, Thalassinoides, Taenidium, Gyrophyllites, Chondrites, Dactyloidites, Teichichnus, Bolonia, and Ancorichnus. Except for Ophiomorpha nodosa and Thalassinoides, which generally indicate moderate to high energy conditions and are the dwelling burrows of suspension-feeding to omnivorous crustaceans, the ichnotaxa represent a deposit-feeding behaviour of their producers and thus are characteristic of low-energy environments. The trace fossils form three ichnoassemblages characterized by(1) Ophiomorpha nodosa and Thalassinoides suevicus,(2)?Thalassinoides isp. A, Taenidium, and Bolonia lata,and(3) Ancorichnus. The dominance of traces of deposit-feeders in rocks indicative of high-energy events is counterintuitive and points to their non-contemporaneity. The sediments were deposited during brief highenergy events, whereas the trace fossils were produced when, after waning of storms low-energy conditions prevailed. This time-averaging is particularly pronounced in trace fossils that extend vertically downwards and may reach strata deposited under distinctly different conditions. Thus, environmental interpretations based on trace fossils should refer to colonisation surfaces rather than to the sediment surrounding the trace fossils. In the latter case, interpretations may be erroneous, especially when erosion subsequently destroyed sedimentary evidence of their original environment.
基金supported by the Alexander von Humboldt Foundation, Germany [Matthias Alberti]the Department of Science and Technology, India [Dhirendra K.Pandey]the Jagiellonian University, Poland [Alfred Uchman]
文摘A spectacularly exposed slump is described from a 120-m-long road cut between the villages of Kanod and Deva in the northeastern Jaisalmer Basin of Rajasthan,India.The Upper Jurassic part of the sediments at the outcrop was formed in a near-shore setting and belongs to the Ludharwa Member of the Baisakhi Formation.The 3-m-thick unit shows a number of asymmetric folds and thrust faults leading to an imbrication of partly lithified sandstone beds.The deformation structures allow the reconstruction of a movement towards the northwest.This agrees well with the basin configuration that shows a deepening into this direction.Although the determination of a specific trigger mechanism is difficult for soft-sediment deformation structures,an earthquake caused by synsedimentary tectonics in the basin seems to be the most likely explanation.
