Holocene laminated sediments from the southern Gulf of California: geochemical, mineral magnetic and microfossil study

• Published in: Journal of quaternary science Vol. 25; no. 6; pp. 989 - 1000
• Main Authors: Pérez-Cruz, Ligia, Urrutia-Fucugauchi, Jaime
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.09.2010
• Subjects: Basins; chemical composition; Coercive force; ENSO; Geochemistry; Gulf of California; Gulfs; Hysteresis; ITZC; Laminates; magnetic properties; Marine; marine laminated sediments; Mexico; Minerals; Radiolaria; radiolarians; Sediments; ISE, Mexico, Baja California, Alfonso Basin; AS, Atlantic, Intertropical Convergence Zone; ISE, Mexico, Baja California Sur, La Paz; ISE, Mexico, California Gulf
• ISSN: 0267-8179; 1099-1417; 1099-1417
• DOI: 10.1002/jqs.1386

Geochemical, magnetic mineral analyses and microfossils (radiolarians) are used to characterise a Holocene laminated sequence from the Alfonso Basin, northern Bay of La Paz, southern Gulf of California. In most cases, dark and light laminae show similar bulk chemical compositions and magnetic mineral properties. However, dark laminae contain relatively more terrigenous elements (Al, Si, Fe, K and Mg) supporting a pluvial origin related to the volcanic siliceous tuffs around the Bay of La Paz. In light laminae, calcium content is higher, representing biogenic input. The magnetic signal is dominated by low coercivity, fine‐grained low‐titanium titanomagnetites and magnetite. Hysteresis ratio parameters in domain state plots show that samples fall in the pseudo‐single domain field, indicating mixtures of single‐ and multi‐domain particles. Variations in hysteresis saturation magnetisation parameters for dark and light laminae reflect changes in relative mineral concentration. Results indicate a dominant volcanic source for magnetic minerals into the basin, associated with variable pluvial and/or aeolian transport. Low radiolarian abundance in dark laminae seems to be associated with larger penetration and longer residence time of oligotrophic subtropical waters into the bay that occurred during El Niño–Southern Oscillation (ENSO) events. Light laminae are the result of episodic pulses of high productivity. We suggest that dark/light laminae result from oceanographic and climatic cyclic processes, with main terrigenous input variation possibly associated with ENSO forcing of pluvial influx, and/or latitudinal migration of the Intertropical Convergence Zone. The laminated sequence of the Alfonso Basin formed a non‐annual depositional system, in contrast to the varved sediments characteristic of the central Gulf of California basins. Copyright © 2010 John Wiley & Sons, Ltd.