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

Abstract

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 a temperature rise of more than five degrees. During this time, the � 13 C reached maximum values. The positive excursion in � 13 C of carbonates from the Oxfordian (with an amplitude of more than 1‰) was reproduced in hemipelagic sections from southeastern France. Analysis of major and trace elements of these carbonates were carried out by LA-ICP-MS in order to verify their application as palaeoproxies in conjunction with the changes mentioned in climate. As a novel approach 36 elements 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 profile from southeastern France. Conversely, the positive � 13 C excursion with � 13 C values rising from 2 to 3 ‰ within the uppermost part of the profile coincide with more elevated concentrations of V, Fe, Mn, U arguing for an ocean-wide anoxia (Oceanic Anoxic Events OAE). High detrital input during this arid period is recorded by enhanced concentrations of elements like Ti, Mn, Fe, Zr, Nb and W. This correlation of the � 13 C excursion with trends in Ti, Nb, W as well as Mn and Fe contents reflects changes in the Oxfordian palaeooceanography and climate. During the late Oxfordian the environmental prerequisites were controlled by warm and arid conditions and an increased metal flux from the continent due to the intensified chemical and physical weathering, erosion of rocks, as well as aeolian and fluvial transport to the oceans.