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High resolution 40 AR/ 39 AR chronostratigraphy of the Late Cretaceous El Gallo Formation, Baja California del Norte, Mexico
Author(s) -
Renne Paul R.,
Fulford Madeleine M.,
BusbySpera Cathy
Publication year - 1991
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/91gl00464
Subject(s) - geology , sanidine , cretaceous , chronostratigraphy , paleontology , magnetostratigraphy , mesozoic , alluvium , sedimentary rock , geochronology , stage (stratigraphy) , subsidence , radiometric dating , denudation , structural basin , tectonics , biotite , quartz
Laser probe 40 Ar/ 39 Ar analyses of individual sanidine grains from four tuffs in the alluvial Late Cretaceous (Campanian) El Gallo Formation yield statistically distinct mean dates ranging from 74.87±0.05 Ma to 73.59±0.09 Ma. The exceptional precision of these dates permits calculation of statistically significant sediment accumulation rates that are much higher than passive sediment loading would cause, implying rapid tectonically induced subsidence. The dates bracket tightly the age of important dinosaur and mammalian faunas previously reported from the El Gallo Formation. The dates support an age less than 73 Ma for the Campanian/Maastrichtian stage boundary, younger than indicated by several currently used time scales. Further application of the single grain 40 Ar/ 39 Ar technique may be expected to greatly benefit stratigraphic studies of Mesozoic sedimentary basins and contribute to calibration of biostratigraphic and magnetostratigraphic time scales.