ABSTRACT Recently, a set of mercury (Hg) anomalies in Valanginian sediments recovered from European sections demonstrated that an important magmatic pulse occurred at the onset of the Weissert episode. In this study, we report the distribution of Hg contents near the onset of the Weissert episode from localities outside of Europe, in the proto–Atlantic Ocean (Blake Bahama and Cap Hatteras Basins, Deep Sea Drilling Project [DSDP] Holes 534A and 603B) and southern Tethys Ocean (Argo Abyssal Plain, Ocean Drilling Program [ODP] Hole 765C), in order to evaluate the global impact of volcanism during the Valanginian. In addition, we also reinvestigated the Orpierre and Angles sections of the Vocontian Basin at a very high time resolution, to examine the potential impact of regional volcanic activity during that time interval. The onset of the Weissert episode in the proto-Atlantic and in the southern Tethyan cores is marked by significant increases in Hg contents. The persistence of the Hg anomaly in Hg/total organic carbon and Hg/Al ratios suggests that Hg enrichments were not primarily controlled by runoff processes and/or redox conditions, but instead indicate an increase in volcanic activity. The Hg enrichments recorded from localities outside of Europe at different latitudes were correlated to those previously observed in European sections, thereby confirming the presence of a global Hg peak at the onset of the Weissert episode. This peak was probably related to the emplacement of the Paraná-Etendeka large igneous province, suggesting a key role for volcanic activity during the Valanginian global environmental perturbations. In coeval intervals in the Vocontian Basin, Hg records show abrupt and short-lived enrichments, which correspond in the sedimentary successions to a goethite-rich ocher-colored layer. Two regional processes could explain Hg deposition and sequestration in this region: increased Hg sequestration by organic matter production in an oxygen-depleted environment, and/or the presence of regional volcanic activity, which is also indicated by the occurrence of a distal volcanic ash layer.

Abstract Distal Aptian-Albian deep water channelled massive sands of the Vocontian Basin (SE France) are often associated with sand injections. The Bevons and Rosans areas in the Vocontian domain present probably the most spectacular outcrops showing complex networks of clastic sills and dykes injected into a thick marly/limy succession. Most injections are found in the channel banks, fed laterally from sandy channels. The sills are up to 10 metres thick in the vicinity of the connection with the channel feeder; they thin out and die into marls 2 or 3 kilometres away from it. Most dykes are injected from the sills rather from the channel itself: a few small dykes can be found under the channel fill. They are most abundant within a few hundred metres of the channel. Today, injections extending downwards from sills have up to 275 metres vertical extent, whereas injections extending upwards from sills never reach the contemporaneous palaeo-sea floor. Ptygmatic folding of the dykes by mechanical compaction indicates the amount of local post-injection compaction of shale and clearly shows that sand injection occurred prior to burial. Outcrop mapping shows that channel bank fracturing is contemporaneous with channel infilling. This is evidence of early syndepositional injection of the sandy material. Vocontian clastic injections provide good geometrical analogues to deep offshore clastic injectite networks and the opportunity to better understand genetic processes.

Abstract Oceanic Anoxic Event (OAE) 1b is well documented in western Tethys; however, records in Eurasia are still lacking. Here, we carried out high-resolution organic carbon isotope (δ 13 C org ), total organic carbon (TOC) content and mercury (Hg) concentration analysis of the lacustrine sediments from the Xiagou and Zhonggou formations in the Hanxiagou section of the Jiuquan Basin, NW China. The lacustrine δ 13 C org curve presents three stages of negative excursions above the basalt layer dated at 112.4 ± 0.3 Ma in the lowermost Zhonggou Formation. The three negative δ 13 C org excursions correspond well with the three sub-events (Kilian, Paquier and Leenhardt) of the OAE 1b in the Poggio le Guaine (central Italy), Vocontian Basin (SE France) and St Rosa Canyon (NE Mexico) sections, supporting the record of the terrestrial OAE 1b in the Jiuquan Basin. Five mercury enrichment intervals in Hg/TOC ratios were recognized, indicating that the pulsed volcanism from the Southern Kerguelen Plateau likely triggered OAE 1b. However, the decoupling between negative isotopic excursion shifts and mercury enrichments, signifying another carbon reservoir (with no link to mercury), probably contributed to the global carbon cycle perturbation during the OAE 1b period. Our results provide direct evidence to link OAE 1b and the terrestrial ecosystem in Eurasia.