"Triassic-Jurassic 'Red Beds' of the Rocky Mountain Region": A Discussion

John B. Reeside
1929 The Journal of geology  
The conclusion drawn by Professor E. B. Branson in a recent paper on the "Red Beds" of the Rocky Mountain region that parts of these beds are marine is considered likely. The conclusion that there exists no basis for subdivision of the beds is not accepted, and a division of the Mesozoic part into Lower Triassic, Upper Triassic, and Jurassic units is advocated. The conclusion that no eolian deposits are present likewise is not accepted, and the interpretation of important parts of the Jurassic
more » ... ts of the Jurassic unit as eolian is advocated. Disagreement is expressed with much of Professor Branson's correlation table, and a substitute is offered. His paleographic map is considered invalid because based on erroneous correlations and interpretations of conditions. GENERAL STATEMENT Professor E. B. Branson's recent paper on the "Triassic-Jurassic 'Red Beds' of the Rocky Mountain Region"" bears upon specific and general problems of great interest. His observations are stated to cover nearly the whole region of occurrence of red beds of Mesozoic age, and his conclusions are far-reaching. Branson presents a map showing the distribution of red beds in the Rocky Mountain region3 and a table showing his age assignments and correlations of the included formations.4 He states, in summary,5 that no adequate basis is available for the separation of the lower from the upper red beds, that the vertebrate fossils known are of little value in correlation, that no appreciable part of the red-bed sequence from Permian to Jurassic is eolian in origin, and that various features of the red beds indicate a marine origin for the major part of them and a subaerial origin for other minor parts. He also presents a paleogeographic map of central North America in Upper Triassic time6 which shows an inland sea covering northwestern Texas, northern New Mexico and Arizona, eastern Nevada, southeastern Idaho, all of ' Published by permission of the director
doi:10.1086/623589 fatcat:pj35qozuhjawlobouf64rklwfa