Abstract

At 51 outcrops of the eolian Botucatú sandstone (Early Mesozoic) in Brazil and Uruguay the writers made 2892 measurements. A new instrument for making these measurements has been designed and constructed and is thought to provide accurate data more rapidly than present methods.

Two wind trends have been detected in the Botucatú sandstone. The southern outcrops indicate deposition by winds which blew mainly from the west or west-southwest; the northern outcrops indicate deposition by a prevailing wind blowing from the north or north-northeast.

Orientation of cross-bedding in the Botucatú sandstone suggests that most of this sand was deposited in the trade-wind belt, on the assumption that the wind belts have been a general feature throughout geological time. In some respects, the position of present-day high- and low-pressure areas in South America and vicinity are believed comparable to those existing in Triassic time. Early Mesozoic wind patterns and pressure belts, as determined from eolian cross-bedding dip directions, are in agreement with the paleomagnetic results reported by Creer.

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