o et al. determined the age and isotopic composition of granites in Sonora that would have been affected by this faulting. They determined that granites in the field area had uranium-lead zircon ages of 1763-1737 million years old and 1076 million years old, with isotopic compositions typical of rocks near Caborca, Mexico, on the southwest side of the fault, even though they were collected from the northeast side of the fault. This relationship was previously explained by 40 km of northward thrusting over the megashear, but Amato et al. used structural and stratigraphic relationships to show that the granites were not far-traveled, and that they must have been near their present location by 190 million years ago. These relationships are inconsistent with Late Jurassic megashear displacement and require either that no major strike-slip fault is present in Sonora or that strike-slip displacement occurred prior to Early Jurassic time.
Pleistocene megafloods in the northeast Pacific
C. Lopes and A.C. Mix, Departamento de Geologia Marinha, Laboratorio de Energia e Geologia, 2721-866 Amadora, Portugal. Pages 79-82.
Lopes and Mix show that anomalous amounts of fresh water entered the northeast Pacific Ocean from about 15,000 to 30,000 years ago. Some freshwater inputs can be linked to mega-floods from glacial lakes in land; other inputs may reflect deglacial water from massive ice sheets. These inputs (whatever the source of fresh water) were recorded in deep ocean sediments through microfossils (such as diatoms and foraminifera), and their study allows researchers to estimate past salinity variations for this particular area.
Exceptional preservation of marine diatoms in upper Albian amber
Vincent Girard et al., Universite Rennes 1, UMR CNRS 6118, Rennes, France. Pages 83-86.
Late Albian amber from Charente-Maritime (southwestern France) contains the first known marine diatoms prPage: 1 2 3 4 5 6 7 8 9 10 11 12 Related biology news :1
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