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

Abstract

Pérez-Cruz, L. and Urrutia-Fucugauchi, J. 2010. Holocene laminated sediments from the southern Gulf of California: geochemical, mineral magnetic and microfossil study.ABSTRACT: 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 Niñ o-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.

Hydrological changes and paleoproductivity in the Gulf of California during middle and late Holocene and their relationship with ITCZ and North American Monsoon variability

“…5b). Most of the Ca contained in the sediments of the core can be assigned to carbonates, most likely of marine origin (mainly coccolithofhorides and benthic foraminifera), as shown by earlier studies (Molina-Cruz et al, 2002;Douglas et al, 2007;Pérez-Cruz and Urrutia-Fucugauchi, 2010). It is compared the Ca concentrations from the core T-43 to CaCO3 values from the core NH01-15 (Gonzalez-Yajimovich et al, 2005, Fig.…”

“…These attributes-relatively high productivity and low oxygen content in the bottom waters-result in the formation of laminated sediments in the Alfonso Basin that represent non-annual depositional system (Molina-Cruz et al, 2002;Pérez-Cruz and Urrutia-Fucugauchi, 2010), in contrast to the varved sediments characteristic of central Gulf of California basins (e.g., Baumgartner et al, 1991;Pike and Kemp, 1997).…”

“…The Comondu Formation is composed of interbedded volcanic sandstones and conglomerates, rhyolitic ash-flow tuffs and andesitic lahars and lava flows (Nava-Sánchez et al, 1999). Thus, the study area receives aluminosilicates mostly from the volcanic siliceous tuffs surrounding the bay (Molina-Cruz et al, 2002;Pérez-Cruz and Urrutia-Fucugauchi, 2010). The mineralogy is characterized by quartz, magnetite, amphibole, pyroxene and an-rich feldspar (Gonzalez-Yajimovich, 2004), expected weathering materials of the surrounding siliceous tuffs.…”