Multiproxy Evidence of Oceanic Anoxic Event 1b in the South Atlantic: Insights from the Falkland Plateau

The Albian Oceanic Anoxic Event 1b (OAE 1b) is well documented in the western Tethys and North Atlantic, whereas its occurrence in the South Atlantic Ocean has only recently been investigated due to the scarcity of continuous Albian cores. This study integrates Total Organic Carbon (TOC), bulk carbonate carbon and oxygen isotopes (δ¹³C_carb and δ¹⁸O_carb), and calcareous nannofossils from the hemipelagic Albian succession of the Falkland Plateau (DSDP Hole 327A) to assess the record of OAE 1b in the South Atlantic. The Falkland Plateau is a key region for reconstructing Early Cretaceous oceanographic and climatic dynamics, particularly during the initial opening of the South Atlantic Ocean. The studied interval (Cores 25–14; 425.90–154.30 mbsf) comprises 42 samples dominated by nannofossil oozes and claystones. During deposition, Hole 327A was located at ~62°S, and benthic foraminiferal assemblages and paleobathymetric models indicate upper bathyal to outer neritic depositional depths. A total of 96 calcareous nannofossil species were identified, with species richness averaging 38 taxa and reaching a maximum of 63. Preservation is generally good, with slight dissolution and overgrowth. The Nutrient Index (NI) ranges from 0 to 93 with a mean of 43. Calcareous nannofossil biostratigraphy indicates a latest Aptian–Albian interval. The measured δ¹³C_carb values range from −10.09‰ to 3.54‰, δ¹⁸O_carb from −7.12‰ to 0.11‰, and TOC content from 0.04 to 4.59% (mean 0.80%). Two OAE 1b Kilian and Leenhardt levels were identified. The Kilian level occurs at 313.90–310.00 mbsf (Core 21), within the early Albian CC8a (equivalent to BC23), and is marked by a negative δ¹³C_carb excursion, NI fluctuations (29–79), and TOC values of 0.09–1.45%. The Leenhardt level occurs at 224.70–215.20 mbsf (Cores 17–18), within the early–middle Albian CC8b (equivalent to BC24), and is characterized by a negative δ¹³C_carb excursion, high NI values (72–93), and TOC contents of 0.60–1.03%. Both OAE 1b levels are associated with increased TOC, reduced oxygenation, and high abundances of eutrophic/mesotrophic calcareous nannofossil taxa. These features indicate enhanced primary productivity, likely driven by increased terrigenous nutrient input. The calcareous nannofossil response observed in the Falkland Plateau is consistent with patterns previously documented for OAE 1b in the North Atlantic and Tethys, supporting a broad regional response to this event in the Early Cretaceous oceans.