Environmental Response to the Early Cretaceous Oceanic Anoxic Event 1d in the Eastern Tethyan: Paleoenvironmental Evidence from Southern Tibet

Key words: 
• Key words: Early Cretaceous /
• Oceanic Anoxic Events /
• paleoenvironment /
• eastern Tethys

Abstract: Abstract: [Objective] The Oceanic Anoxic Event 1d (OAE 1d), took place during the late Albian of the Early Cretaceous, represents a significant perturbation in the global carbon cycle associated with a greenhouse climate. Although extensive research has been conducted on the characteristics and origin of OAE 1d in the western Tethys and North Atlantic regions, the paleoenvironmental response to this event in the eastern Tethys remains poorly understood. [Methods] This study focuses on the Lower Cretaceous Lengqingre Formation at the Youxia section in Dingri (southern Tibet) within the eastern Tethyan domain. Here, an integrated approach of mineralogical, petrological, sedimentological, isotopic, and elemental geochemical analyses, was employed to evaluated the paleoenvironmental response to OAE 1d and its distinction from coeval global patterns compared to contemporaneous global records. [Results] (1) Both bulk carbonate and organic carbon isotope data confirm that the Youxia section records the OAE 1d excursion, supporting the global signal of this phenomenon. (2) Thin-section observations and terrigenous input proxies (e.g., Si/Al and Ti/Al ratios) indicate enhanced input of siliciclastic materials during OAE 1d, likely linked to accelerated hydrological cycling and intensified continental weathering related to coeval volcanic activity. (3) Corg/P ratios and framboidal pyrite characteristics reveal that the Youxia section was deposited under oxic to suboxic bottom-water conditions during OAE 1d, markedly different from the anoxic conditions observed in the western Tethys. This highlights the spatial heterogeneity in marine redox conditions during this event. (4) The absence of organic carbon-rich sediments at Youxia is attributed to a combination of oxic environmental conditions, intense terrigenous input, and dilution effects induced by rapid sedimentation rates. This suggests that organic carbon burial was suppressed by regional environmental controls in the Dingri region during OAE 1d. [Conclusion] The oxic-suboxic conditions and lack of organic-rich sediments in the eastern Tethys during OAE 1d underscore the regional heterogeneity in sedimentary and oceanographic responses to global Oceanic Anoxic Events. These findings provide critical insights into complexity of paleoenvironmental feedbacks during global Oceanic Anoxic Events.