Other
Scientific paper
Jul 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991gecoa..55.1875m&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 55, Issue 7, pp.1875-1895
Other
10
Scientific paper
Rare earth element (REE), major, and trace element analyses of 77 samples from the Mesozoic Franciscan Complex and Miocene Monterey Group of California (USA) indicate that magnitudes of the Ce anomaly (Ce/Ce*) and total REE abundances (SREE) in these rocks are controlled dominantly by (a) the amount of included metalliferous material, (b) the amount of direct terrigenous input, and (c) the overall burial rate. The relative importance of these individual processes varies across an ocean basin in such a way that REE relative fractionations and SREE correspond with its depositional environment. Our conclusions are supported by an extensive review of published REE data from various river, coastal, open-ocean, and ridge-influenced waters, as well as terrigenous, pelagic, and metalliferous sediment. The chert sequences record deposition in spreading ridge, open-ocean basin, and continental margin environments. The relative importance of metalliferous and terrigenous influences and the role of scavenging from seawater may be estimated from a sample's inferred depositional distance (km) from the spreading ridge, the major element chemistry, and the stratigraphie context. The Ce/Ce* values are low (~0.29) in the vicinity of spreading ridges and trend to successively higher (~ 1) values with decreasing metalliferous and increasing terrigenous influences. Other REE indicators ( REE, Lu n / La n , Eu / Eu *) also respond to metalliferous and terrigenous influences. Near the spreading ridge, chert REE appears determined by burial rate, while shale REE responds to metalliferous abundance. In open-ocean and continental margin environments, REE is controlled by sediment exposure time and therefore is related inversely to burial rate. REE data are consistent with the major elements Fe 2 O 3 , MnO, and Al 2 O 3 in reflecting the respective metalliferous and terrigenous sources. P 2 O 5 and CaO do not vary with Ce/Ce* in any environment, but CaO shows a weak negative correlation with REE. Trace element trends (e.g., V, Cr, Cu, Ge/Si, Rb, Sr, Y, Th, U) in general can similarly be accounted for in the context of depositional position relative to metalliferous and terrigenous inputs. REEs in chert appear less affected by post-depositional processes than either major or trace elements, indicating that REEs are better tools for paleoceanographic or tectonic reconstructions that are based on chert chemistry. This work complements recent efforts to elucidate the factors determining large-scale REE distributions in marine sediments and has direct bearing on previous attempts to use the Ce anomaly in older rocks and sediments as a recorder of secular variations and anoxic events in the overlying water column.
Buchholtz Ten Brink Marilyn R.
Gerlach David C.
Jones Llanwyn D.
Murray Richard W.
Price Russ III G.
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