Detailed record of the mid-Oxfordian (Late Jurassic) positive carbon-isotope excursion in two hemipelagic sections (France and Switzerland): A plate tectonic trigger?

Abstract

14 pagesInternational audienceThe Oxfordian (Late Jurassic) was a time of widespread change in Jurassic marine (carbonate) sedimentation patterns. A marked positive excursion in δ13C is dated as Middle Oxfordian in age. In this study we investigate if changes in carbonate sedimentation coincided with altered carbon cycling and climate. We use C-isotope records as a proxy for the evolution of the carbon cycle and compare δ13C-trends with the evolution of sedimentation in a segment of the opening Tethys seaway. One of the studied sections is located in the Subalpine basin of France (Trescléoux and Oze), the other in the Swiss Jura mountains (Liesberg). Carbon-isotope stratigraphy of carbonate carbon locates the peak values of the Middle Oxfordian positive excursion to the antecedens and parandieri subzones of the plicatilis and transversarium ammonite zones, respectively. Causes of the excursion remain enigmatic. The excursion seems not to coincide with a global oceanic anoxic event, but regionally enhanced organic carbon accumulation during the Early and early Middle Oxfordian may be the cause of the increase in δ13C. The excursion occurs during a time of progressive climate warming, and its peak values coincide with the first calcareous sediments recurring after a period of reduced carbonate accumulation in the Early and early Middle Oxfordian. The excursion is also time-equivalent to a major reorganisation of global ocean currents: the opening Atlantic and Tethys oceans combined with rising sea level led to the formation of an efficient circumglobal seaway.We conclude that this favoured the widespread recurrence of carbonate producers by providing new habitats. As a result, Ccarb burial increased, leading to a lower Corg/Ccarb burial rate and therefore to stabilisation and decrease in δ13C in the Middle Oxfordian. Thus, the mid-Oxfordian positive excursion in carbonate C-isotopes may reflect changes in the carbon cycle that were triggered by a copious reorganisation of the ocean current system caused by major plate tectonic movements

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

“…It belongs to the "Terre Noires" facies and consists of grey to black marls, which contain layers of carbonate nodules parallel to the bedding. These nodules are round to oval in shape, and about three to ten centimeters in diameter [1]. Up-section, nodules become more abundant.…”

“…The "Argovien" facies replaces the "Terre Noires" synchronously in the whole Subalpine basin, marking the top part of the Antecedens ammonite-subzone. Here another 94 samples were collected within 80 meters [1]. [77].…”

“…One of the most striking features of this time interval is the switch from dark and clayey or siliceous carbonate-poor sediments to light grey, carbonate-rich deposits. This peculiar switch, which is very distinct and obvious in the field, defines the boundary between "brown" and "white" Jurassic -reflecting the fundamental global changes the world was undergoing at that time [1]. The sudden and widespread changes in the marine carbonate sedimentation pattern, therefore, must be part of a response of the ocean-atmosphere-solid earth system to internal or external forces [see 1 and references therein].…”

“…However all the prior studies [1][2][3] lack the information about trace element contents in these sediments. For to this reason the following study was accomplished.…”

Evolution and Geological Significance of Larger Benthic Foraminifera

“…These changes were accompanied by modifications in the global carbon cycle as shown in the carbon isotope record (Louis-Schmid et al, 2007). They were triggered by the opening and/ or widening of the TethysAtlantic-Pacific seaway and a massive spread of shallow-marine carbonate production leading to higher P CO2 , and according to Louis-Schmid et al (2007) this increase in P CO2 may have triggered changes in the biological carbon pump and in organic carbon burial in the mid Oxfordian.…”