Trace Elements in Marine Sediments from the Oxfordian (Late Jurassic):Implications for Seawater Chemistry, Erosional Processes, Changes inOceanic Circulation and More

摘要

The Oxfordian, first stage of the late Jurassic, is remarkably variable in terms of deposited sediments,geochemical tracers, and climate. The climate changed during the Middle Oxfordian from humid to arid with atemperature rise of more than five degrees. During this time, the ?13C reached maximum values. The positive excursion in?13C of carbonates from the Oxfordian (with an amplitude of more than 1‰) was reproduced in hemipelagic sections fromsoutheastern France. Analysis of major and trace elements of these carbonates were carried out by LA-ICP-MS in order toverify their application as palaeoproxies in conjunction with the changes mentioned in climate. As a novel approach 36elements were measured with regard to establish a complete and comprehensive analysis of the geochemical situation.Concentration peaks of P, Sr, Mn, Fe, Ba point to a more oligotrophic setting within the lower part of the sediment profilefrom southeastern France. Conversely, the positive ?13C excursion with ?13C values rising from 2 to 3 ‰ within theuppermost part of the profile coincide with more elevated concentrations of V, Fe, Mn, U arguing for an ocean-wideanoxia (Oceanic Anoxic Events OAE). High detrital input during this arid period is recorded by enhanced concentrationsof elements like Ti, Mn, Fe, Zr, Nb and W. This correlation of the ?13C excursion with trends in Ti, Nb, W as well as Mnand Fe contents reflects changes in the Oxfordian palaeooceanography and climate. During the late Oxfordian theenvironmental prerequisites were controlled by warm and arid conditions and an increased metal flux from the continentdue to the intensified chemical and physical weathering, erosion of rocks, as well as aeolian and fluvial transport to theoceans.