Abstract

Neogene sediments from La Portada and Bahia Inglesa formations located at Mejillones Peninsula and Caldera Port, northern Chile carry multicomponent magnetizations, which can lead to misidentification of the characteristic paleomagnetic vector and consequently, errors in chronostratigraphic and structural interpretation of the strata. Here we present a complete rock magnetic and paleomagnetic behavior study of Neogene sediments from La Portada and Bahia Inglesa formations. Isothermal remanent magnetization, thermal-magnetic susceptibility, magnetic hysteresis, and X-ray diffractometer experiments are combined with paleomagnetic, alternating field, and thermal demagnetization data to determine magnetization history. Remanent magnetizations generally comprises three components: a low blocking temperature (Tb) component, below 150 degrees C, close to the present-day field in direction, interpreted as a thermoviscous component; an intermediate Tb component, between 150 degrees C and 290 degrees C, overprinted by the low and the high Tb components, considered as the survival of the characteristic detrital magnetization; and a high Tb component, above 290 degrees C, thought to be of diagenetic origin. Detrital magnetite, titanomagnetite, and low titanium maghemite are identified as the main carrier of the magnetic remanence. Rock magnetic results of a minor group of samples at both locations detected the presence of a high-coercivity mineral, possibly hematite, interpreted to carry the high Tb component and to represent oxidation of minerals in postdepositional processes.