MAGNETOSTRATIGRAPHY OF A MIDDLE JURASSIC RED-BED SEQUENCE FROM SOUTHERN MEXICO

Abstract

Palaeomagnetic results for 178 oriented samples from five sections (combined thickness of 75 M) of the red bed Tecomazuchil Formation, southern Mexico are reported. The formation has been assigned to the Bathonian(?)-Callovian, and the sections studies cover its uppermost portion. Alternating field (a.f.), thermal, combination of a.f. and thermal, and chemical demagnetizations were used to investigate the magnetic stability and vectorial directions of all samples. Most samples showed apparent stable behaviour with dominantly single or two-component magnetization. Reverse and intermediate polarity samples more often showed two- and multi-component remanences. Behaviour during demagnetization and rock-magnetic experiments indicate that the remanences reside in magnetite, haematite and goethite. The magnetostratigraphic results reveal a polarity pattern characterized by frequent polarity changes.