Dating impact craters: palaeogeographic versus isotopic and stratigraphic methods – a brief case study

2008 ◽  
Vol 145 (4) ◽  
pp. 586-590 ◽  
Author(s):  
MARTIN SCHMIEDER ◽  
ELMAR BUCHNER
Keyword(s):  
Middle Jurassic ◽  
Impact Craters ◽  
Late Triassic ◽  
Crater Formation ◽  
Impact Event ◽  
Multiple Impact

AbstractIsotopic and stratigraphic ages of the ~ 80 km diameter Puchezh-Katunki (Russia; 220 ± 10 to 167 ± 3 Ma) and the ~ 20 km diameter Obolon (Ukraine; 215 ± 25 to 169 ± 7 Ma) impact structures are associated with significant age uncertainties. As a case study, reconstructions of the palaeogeography at the time of crater formation (Late Triassic to Middle Jurassic) based on recent palaeogeographic maps help further to constrain impact ages. Palaeogeographic studies suggest that Puchezh-Katunki is older than 170 Ma and that Obolon is younger than 185 Ma. This also rules out that Obolon formed during a ~ 214 Ma Late Triassic multiple impact event as recently discussed.

Evidence for a late Triassic multiple impact event on Earth

Nature ◽  
10.1038/32397 ◽  
1998 ◽  
Vol 392 (6672) ◽  
pp. 171-173 ◽  
Author(s):  
John G. Spray ◽  
Simon P. Kelley ◽  
David B. Rowley
Keyword(s):  
Late Triassic ◽  
Impact Event ◽  
Multiple Impact

Provenance of Jurassic sedimentary rocks of south-central Quesnellia, British Columbia: implications for paleogeography

2004 ◽  
Vol 41 (1) ◽  
pp. 103-125 ◽  
Author(s):  
Nathan T Petersen ◽  
Paul L Smith ◽  
James K Mortensen ◽  
Robert A Creaser ◽  
Howard W Tipper
Keyword(s):  
Detrital Zircon ◽  
Middle Jurassic ◽  
Sedimentary Rocks ◽  
Source Area ◽  
Lower Jurassic ◽  
Early Jurassic ◽  
Late Triassic ◽  
Nd Isotopes ◽  
South Central ◽  
History Of

Jurassic sedimentary rocks of southern to central Quesnellia record the history of the Quesnellian magmatic arc and reflect increasing continental influence throughout the Jurassic history of the terrane. Standard petrographic point counts, geochemistry, Sm–Nd isotopes and detrital zircon geochronology, were employed to study provenance of rocks obtained from three areas of the terrane. Lower Jurassic sedimentary rocks, classified by inferred proximity to their source areas as proximal or proximal basin are derived from an arc source area. Sandstones of this age are immature. The rocks are geochemically and isotopically primitive. Detrital zircon populations, based on a limited number of analyses, have homogeneous Late Triassic or Early Jurassic ages, reflecting local derivation from Quesnellian arc sources. Middle Jurassic proximal and proximal basin sedimentary rocks show a trend toward more evolved mature sediments and evolved geochemical characteristics. The sandstones show a change to more mature grain components when compared with Lower Jurassic sedimentary rocks. There is a decrease in εNdT values of the sedimentary rocks and Proterozoic detrital zircon grains are present. This change is probably due to a combination of two factors: (1) pre-Middle Jurassic erosion of the Late Triassic – Early Jurassic arc of Quesnellia, making it a less dominant source, and (2) the increase in importance of the eastern parts of Quesnellia and the pericratonic terranes, such as Kootenay Terrane, both with characteristically more evolved isotopic values. Basin shale environments throughout the Jurassic show continental influence that is reflected in the evolved geochemistry and Sm–Nd isotopes of the sedimentary rocks. The data suggest southern Quesnellia received material from the North American continent throughout the Jurassic but that this continental influence was diluted by proximal arc sources in the rocks of proximal derivation. The presence of continent-derived material in the distal sedimentary rocks of this study suggests that southern Quesnellia is comparable to known pericratonic terranes.

scholarly journals Candidates for multiple impact craters: popigai and chicxulub as seen by EGM08, a global 5'×5' gravitational model

2010 ◽  
Vol 2 (1) ◽  
pp. 69-103 ◽  
Author(s):  
J. Klokočník ◽  
J. Kostelecký ◽  
I. Pešek ◽  
P. Novák ◽  
C. A. Wagner ◽  
...  
Keyword(s):  
High Spatial Resolution ◽  
Impact Craters ◽  
Stokes Parameters ◽  
Disturbing Potential ◽  
Gravitational Model ◽  
Secondary Crater ◽  
Complete Set ◽  
Multiple Impact ◽  
The Impact ◽  
Main Crater

Abstract. In 2008 the new Earth Gravitational Model (EGM08) was released. It contains a complete set of spherical harmonic coefficients of the Earth's gravitational potential (Stokes parameters) to degree 2190 and order 2159 that can be used for evaluation of various potential quantities with both the unprecedented accuracy and high spatial resolution. Two such quantities, the gravity anomaly and second-order radial derivative of the disturbing potential, were computed over selected areas with known impact craters. The displays of these derivatives for two such sites clearly show not only the strong circular-like features known to be associated with them but also other symmetrical structures which appear to make them multiple impact sites. At Popigai, Siberia, the secondary circular features fall in a line from the primary in the SE direction. At Chicxulub, Yucatán, there appears to be one secondary crater close to the primary in the NE direction, as well as possibly others in the vicinity of the main crater. Gravity information alone is not proof of the impact craters but it is useful in identifying candidate sites for further study, for future examination by geologists and geophysicists.

The provenance of Middle Jurassic sandstones in the Scotian Basin: petrographic evidence of passive margin tectonics 1This article is one of a series of papers published in this CJES Special Issue on the theme of Mesozoic–Cenozoic geology of the Scotian Basin. 2Geological Survey of Canada Contribution 20110319.

2012 ◽  
Vol 49 (12) ◽  
pp. 1463-1477 ◽  
Author(s):  
Gang Li ◽  
Georgia Pe-Piper ◽  
David J.W. Piper
Keyword(s):  
Early Cretaceous ◽  
Middle Jurassic ◽  
Mineral Chemistry ◽  
Passive Margin ◽  
Heavy Minerals ◽  
Late Triassic ◽  
Cape Breton Island ◽  
Grand Banks ◽  
Meguma Terrane ◽  
Geomorphological Evolution

The tectonic and geomorphological evolution of the Scotian margin and its hinterland is poorly known between Late Triassic rifting and the Early Cretaceous progradation of major deltas. This study determined sedimentary provenance of Middle Jurassic Mohican Formation sandstones from three wells using heavy minerals and mineral chemistry. Indicator minerals such as xenotime, altered ilmenite, and varietal types of garnet and tourmaline are similar to those in Hauterivian–Barremian sandstones in the western Scotian Basin, which are almost exclusively derived from the Meguma terrane. The wells adjacent to the Canso Ridge have more zircon and less ilmenite, indicating a greater contribution of polycyclic reworking, but with an ultimate source in the Meguma terrane. Zircon and ilmenite were likely derived in part from Carboniferous sandstones in eastern mainland Nova Scotia and Cape Breton Island. Any river drainage from the inboard terranes of the Appalachians either was diverted through the Fundy Basin or entered the easternmost Scotian Basin, where the Mohican Formation is 5.5 km thick, along the linear continuation of the southwest Grand Banks transform. Such sediment did not reach the Canso Ridge, suggesting that the Cobequid–Chedabucto fault zone in Orpheus graben was not a significant physiographic feature. This tectonically controlled paleogeography in the Middle Jurassic is quite different from that during active rifting in the Late Triassic – Early Jurassic. Middle Jurassic quiescence was followed in the Tithonian – Early Cretaceous by renewed tectonic uplift associated with rifting of Grand Banks from Iberia and Labrador from Greenland.

Dinosaur Architectural Adaptations for a Gymnosperm-Dominated World

2000 ◽  
Vol 6 ◽  
pp. 183-208
Author(s):  
David E. Fastovsky
Keyword(s):  
Late Cretaceous ◽  
Middle Jurassic ◽  
Vascular Plants ◽  
Late Triassic ◽  
Time Interval ◽  
Paraphyletic Group

The middle jurassic through Cretaceous was the heyday of gymnosperms. Gymnosperms—a paraphyletic group of seed-bearing, non-flowering vascular plants including conifers, ginkgos, seed ferns, cycads, and cycadeoids—comprised as much as 80% of global floras throughout this time interval. Even the much-heralded rise of angiosperms in the mid- to Late Cretaceous did little to shake the Mesozoic dominance among terrestrial floras of gymnosperms (in particular, conifers; see Tiffney, 1997). By the end of the Cretaceous, angiosperms comprised—depending upon whose estimate is being used—somewhere between 40 and 60% of the world's floras (Lidgard and Crane, 1988; Tiffney, 1997), leaving plenty of ecospace available for gymnosperms. The lower part of Figure 1, redrawn from Tiffney (1997), documents the flux of the major groups of plants throughout the Late Triassic-through-latest Cretaceous interval. The figure reaffirms that in the Mesozoic, gymnosperms were the floral force to be reckoned with.

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