GEOCHRONOLOGICAL STUDIES IN SANTA BARBARA BASIN: ⁵⁵Fe AS A UNIQUE TRACER FOR PARTICULATE SETTLING

Abstract

Sediments accumulate in the Santa Barbara Basin relatively rapidly: ,about 3-4 mm yr-' based on the analysis of varves. These deposits are ideal for studying the applicability of nuclear geochronological techniques in a natural situation. Studies of the depth distribution of several radionuclides, manmade 65Fe and naturally occurring "Pb and Th isotopes, in recent Santa l3arbara sediment layers permit an evaluation of the geochemical behavior of Fe, Pb, and Th in coastal waters and have established the usefulness of "Fe and ""Pb for dating coastial or near coastal sediments deposited during the last decade and halfcentury Gspectively.

From extreme rainfall to drought: 250 years of annually resolved sediment deposition in Santa Barbara Basin, California

“…1) indicates the distinctive changes in the sedimentary fabric of SBB cores created by the strong El Niño events of 1941, 1957, 1983, and 1997 upon which depths initial age assignments were based. These events (with an error of ±~2 year) were established through varve chronology (Soutar and Crill, 1977), radiometric dating ( 210 Pb) (Koide et al, 1972) and excess 55 Fe associated with atmospheric bomb fallout between 1962 and 65 (Krishnaswami et al, 1973). Schimmelmann et al (1992) used coreto-core correlation based on porosity and x-radiographs to position this radiometric chronology, generating dates for the gray layer at 1761 AD, the turbidite at 1811 AD, and the bioturbated Macoma event at 1841 AD.…”

Global Boundary Stratotype Section and Point (GSSP) for the Anthropocene Series: Where and how to look for potential candidates

“…The Santa Barbara Basin lies 100 km west of Los Angeles, USA (Figure 3), at depths of up to 590 m. Varves comprise dark terrigenous laminae derived from greater winter river runoff alternating with paler summer bloom laminae with diatoms (mainly Chaetoceros), planktonic foraminifera, radiolaria and silicoflagellates (Koide et al 1975, Field et al 2006, Barron et al 2015, reflecting seasonal NW winds that cause upwelling and increase biogenic productivity (Barron et al 2015). Varves have been dated using 210 Pb (Krishnaswami et al 1973, Koide et al 1975) and radiocarbon AMS . Before 1700 CE some drought years did not produce varves, with intermittent oxygenation events causing bioturbation, but from the 18 th century to the present the lamina have been shown to be consistently annual and without gaps .…”

“…The four in the Cenozoic that deal with stable isotope events (base Eocene, Quaternary, Calabrian and Holocene) and the iridium anomaly (base Paleocene) provide models for choosing markers for the base of the Anthropocene. [B&W] Key signals in marine cores from the Santa Barbara Basin, with a) Pu signal (Koide et al 1975), b) variations in sedimentation rates (Krishnaswami et al 1973), c) selected heavy metals (Schmidt and Reimers 1991) and d) planktonic foraminifera (Field et al 2006).…”

Comparison of two gravity coring devices for sedimentation rate measurement by 210Pb dating techniques

“…Sedimentation rate can be measured by counting the annual layers of varved sediments (Gross et al, 1963), palynological (pollen) methods (Bruland et al, 19754, independent dating of some anomaly (volcanic ash, landslides, glaciers, etc. ), radiometric dating of sediments, or other methods (Krishnaswami et al, 1973). Measurement of sedimentation rate by 210Pb dating technique is widely used for dating both marine and freshwater sediments.…”