It is demonstrated here for the first time how Palaeoproterozoic stromatolites survived seismic disturbance of their substrate. The stromatolites under study could have been cyanobacteria or any other photo-autotrophi...It is demonstrated here for the first time how Palaeoproterozoic stromatolites survived seismic disturbance of their substrate. The stromatolites under study could have been cyanobacteria or any other photo-autotrophic microbes, which formed mats that covered a substrate of very fine-grained sandstones and mudstones of the Chaibasa Fm. in eastern India. The sediments represent a shelf environment. The local abundance of the stromatotites suggests that the tow-energy environment formed a suitable habitat. The common phases of tectonic quiescence were, however, occasionally interrupted by seismic shocks. These were sufficiently strong to deform the mat layers, the tower parts of which might already have been （semi-） consolidated. The mats became partly folded, partly faulted, and already consolidated parts of the stromatotite layers broke off. This can be deduced from the angular shapes of part of the broken-off fragments. It appears, however, that part of these fragments were stilt sufficiently soft to become rounded and deformed by rotting over the seafloor, probably under the influence of tidal currents. When come to rest, these fragments served as a new substrate for new generations of the microorganisms. These micro-organisms thus survived by continued growth on the reworked fragments and built up new stromatolites that may show an ‘angular disconformity＇ with the stromatotites of their substrate. It thus is shown that stromatotites have an adequate response to a sudden disturbance of their habitat, and that they survive earthquakes by colonization of broken-off fragments. We call the ‘healed＇ fragments ‘tombotiths＇ （tumbled stones）.展开更多
This discussion of a paper by Van Loon et al.（2016）, published in the Journal of Palaeogeography（2016, 5（4）, 381e390）, is aimed at illustrating that there are fundamental deficiencies, which include（1）incomple...This discussion of a paper by Van Loon et al.（2016）, published in the Journal of Palaeogeography（2016, 5（4）, 381e390）, is aimed at illustrating that there are fundamental deficiencies, which include（1）incomplete etymological reasoning for proposing a new genetic term ＂tomboliths＂ for stromatolitic bioclasts in the Palaeoproterozoic Chaibasa Formation, eastern India,（2） omission of empirical data in documenting depositional facies using sedimentological logs,（3） misapplication of the stratigraphic concept of ＂angular unconformity＂,（4） failure to consider the multifarious origins of earthquakes, and（5） a dated view on the basic tenets of process sedimentology and triggering mechanisms of liquefaction that are the basis for forming soft-sediment deformation structures（SSDS）. As a consequence, their conclusions are unconvincing.展开更多
Our contribution about a newly recognized sedimentological feature, which we called tombolith,has raised some comments on the etymology of the term, the assumed lack of field data, the usage of a term that has a speci...Our contribution about a newly recognized sedimentological feature, which we called tombolith,has raised some comments on the etymology of the term, the assumed lack of field data, the usage of a term that has a special meaning in stratigraphy, the origin of the seismic shocks that played a role, so-called basic tenets, the origin of soft-sediment deformation structures, and the role of liquefaction. We argue that most comments result from an insufficiently thorough reading of our text, whereas some other remarks concern aspects that we did not deal with. Finally, several remarks are based on outdated literature and from insufficient knowledge of the regional geology.展开更多
基金project was supported by the Foundation Dr Schurmannfonds,grants no.34/2006 and 57/2009,67/2010 and 82/2012the DST and the Department of Geology,Calcutta University for financial support and infrastructural support
文摘It is demonstrated here for the first time how Palaeoproterozoic stromatolites survived seismic disturbance of their substrate. The stromatolites under study could have been cyanobacteria or any other photo-autotrophic microbes, which formed mats that covered a substrate of very fine-grained sandstones and mudstones of the Chaibasa Fm. in eastern India. The sediments represent a shelf environment. The local abundance of the stromatotites suggests that the tow-energy environment formed a suitable habitat. The common phases of tectonic quiescence were, however, occasionally interrupted by seismic shocks. These were sufficiently strong to deform the mat layers, the tower parts of which might already have been （semi-） consolidated. The mats became partly folded, partly faulted, and already consolidated parts of the stromatotite layers broke off. This can be deduced from the angular shapes of part of the broken-off fragments. It appears, however, that part of these fragments were stilt sufficiently soft to become rounded and deformed by rotting over the seafloor, probably under the influence of tidal currents. When come to rest, these fragments served as a new substrate for new generations of the microorganisms. These micro-organisms thus survived by continued growth on the reworked fragments and built up new stromatolites that may show an ‘angular disconformity＇ with the stromatotites of their substrate. It thus is shown that stromatotites have an adequate response to a sudden disturbance of their habitat, and that they survive earthquakes by colonization of broken-off fragments. We call the ‘healed＇ fragments ‘tombotiths＇ （tumbled stones）.
文摘This discussion of a paper by Van Loon et al.（2016）, published in the Journal of Palaeogeography（2016, 5（4）, 381e390）, is aimed at illustrating that there are fundamental deficiencies, which include（1）incomplete etymological reasoning for proposing a new genetic term ＂tomboliths＂ for stromatolitic bioclasts in the Palaeoproterozoic Chaibasa Formation, eastern India,（2） omission of empirical data in documenting depositional facies using sedimentological logs,（3） misapplication of the stratigraphic concept of ＂angular unconformity＂,（4） failure to consider the multifarious origins of earthquakes, and（5） a dated view on the basic tenets of process sedimentology and triggering mechanisms of liquefaction that are the basis for forming soft-sediment deformation structures（SSDS）. As a consequence, their conclusions are unconvincing.
文摘Our contribution about a newly recognized sedimentological feature, which we called tombolith,has raised some comments on the etymology of the term, the assumed lack of field data, the usage of a term that has a special meaning in stratigraphy, the origin of the seismic shocks that played a role, so-called basic tenets, the origin of soft-sediment deformation structures, and the role of liquefaction. We argue that most comments result from an insufficiently thorough reading of our text, whereas some other remarks concern aspects that we did not deal with. Finally, several remarks are based on outdated literature and from insufficient knowledge of the regional geology.
