Characterization of distal turbidites in marine sedimentary sequences using magnetic mineral data and factor analysis of microfossils assemblages

Abstract

Results of a study of turbiditic deposits in a sequence of middle to late Holocene marine sediments from Alfonso Basin in the southern Gulf of California are presented. Turbidites are identified from analyses of core sections, X-ray images, texture and granulometry. Characterization of distal turbidites could be difficult, particularly for thin fine-grained deposits with little contrast in grain size, mineralogy and texture. We have here included analyses of microfossil and magnetic mineral data. Turbiditic currents transport material from various depths in the continental slope into the basin and it can be expected that turbiditic deposits are characterized by re-worked material, lack of microfossils or mixed assemblages with no content of paleoceanographic and paleoclimatic record. This may show in lack of internal coherence as quantified by factor analysis of microfossil assemblages. Turbidites in some cases may also show distinct magnetic properties as compared with those in the sediment sequence. In Alfonso Basin, turbidites show increased contents of detrital magnetic minerals volcanic-derived and transported from the basin slope. We identify twelve turbiditic layers through the sequence that present high magnetic susceptibility and low communalities from factor model to the microfossils data providing characterization of the turbidites.