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Calibration of the geological time scale is achieved by independent radioisotopic and astronomical dating, but these techniques yield discrepancies of approximately 1.0% or more, limiting our ability to reconstruct Earth history. To overcome this fundamental setback, we compared astronomical and 40Ar/39Ar ages of tephras in marine deposits in Morocco to calibrate the age of Fish Canyon sanidine, the most widely used standard in 40Ar/39Ar geochronology. This calibration results in a more precise older age of 28.201 +/- 0.046 million years ago (Ma) and reduces the 40Ar/39Ar method's absolute uncertainty from approximately 2.5 to 0.25%. In addition, this calibration provides tight constraints for the astronomical tuning of pre-Neogene successions, resulting in a mutually consistent age of approximately 65.95 Ma for the Cretaceous/Tertiary boundary.

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The Central Atlantic Magmatic Province (CAMP) is defined by tholeiitic basalts that crop out in once-contiguous parts of North America, Europe, Africa, and South America and is associated with the breakup of Pangea. 40Ar/39Ar and paleomagnetic data indicate that CAMP magmatism extended over an area of 2.5 million square kilometers in north and central Brazil, and the total aerial extent of the magmatism exceeded 7 million square kilometers in a few million years, with peak activity at 200 million years ago. The magmatism coincided closely in time with a major mass extinction at the Triassic-Jurassic boundary.

We review available data constraining the extent, volume, age and duration of all major Phanerozoic continental flood basalts (CFB or traps) and oceanic plateaus (OP), together forming the group of large igneous provinces (LIP), going from the smallest Columbia flood basalts at ∼16 Ma to the as yet ill-known remnants of a possible trap at ∼360 Ma in eastern Siberia. The 16 traps (CFB and OP) reviewed form a rather unimodal distribution with an initial modal volume of the order of 2.5 Mkm 3 . Most provinces agree with a rather simple first order model in which volcanism may have lasted of the order of 10 Ma, often resulting in continental break-up, but where most of the volume was erupted in about 1 Ma or sometimes less. This makes CFBs/OPs (LIPs) major geodynamic events, with fluxes exceeding the total output of present day hot spots and even possibly exceeding over short times the entire crustal production of mid-ocean ridges. The proposed correlation between trap ages and the ages of several geological events, including mass extinctions and oceanic anoxia, is found to have improved steadily as more data have become available, to the point that the list of trap ages may coincide with many major divisions in the geological time scale. The four largest mass extinctions in the last 260 Ma coincide to the best resolution available with four traps, making a causal connection between the two through some form of catastrophic climatic perturbations the most likely hypothesis. The time sequence of LIPs appears to have been random and there is no robust evidence for long time trends in the corresponding crustal production rate over the last 260 Ma.  2003 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS. All rights reserved. RésuméNous passons en revue l'ensemble des données qui permettent de contraindre l'étendue, le volume, l'âge et la durée de toutes les grandes provinces magmatiques basaltiques (en anglais LIP) d'âge Phanérozoïque, qu'il s'agisse des trapps ou plateaux basaltiques continentaux (en anglais CFB) ou des plateaux océaniques (OP), allant de la plus récente et plus petite (le plateau de Columbia âgé de ∼16 Ma) à l'une des plus anciennes, encore mal connue, située dans l'Est de la Sibérie et sans doute âgée de ∼360 Ma. Les 16 provinces passées en revue forment une distribution assez unimodale, avec des volumes initiaux de lave de l'ordre de 2,5 Mkm 3 . La plupart des provinces sont compatibles, au premier ordre, avec un modèle simple selon lequel le volcanisme a pu durer une dizaine de millions d'années et a en général conduit à une déchirure des continents et à l'ouverture d'un nouveau bassin océanique, mais où l'essentiel du volume des laves a été émis en environ 1 million d'années, parfois moins. Ceci fait des trapps (des LIP en général) des événements géodynamiques majeurs, avec des flux de matière ayant dépassé la production totale actuelle des points chauds et même, peut-être, pendant de brefs intervalles, la totalité de la production de croûte V.E. Courtillot, P.R. Renn...

Upper Triassic rocks in northwestern Argentina preserve the most complete record of dinosaurs before their rise to dominance in the Early Jurassic. Here, we describe a previously unidentified basal theropod, reassess its contemporary Eoraptor as a basal sauropodomorph, divide the faunal record of the Ischigualasto Formation with biozones, and bracket the formation with (40)Ar/(39)Ar ages. Some 230 million years ago in the Late Triassic (mid Carnian), the earliest dinosaurs were the dominant terrestrial carnivores and small herbivores in southwestern Pangaea. The extinction of nondinosaurian herbivores is sequential and is not linked to an increase in dinosaurian diversity, which weakens the predominant scenario for dinosaurian ascendancy as opportunistic replacement.