Paleoenvironmental changes during the late Albian oceanic anoxic event 1d: An example from the Capacho Formation, southwestern Venezuela

Abstract

The late Albian-early Cenomanian oceanic anoxic event 1d (OAE-1d; ~ 103 to 99.5 Ma) represents a global interval of enhanced organic carbon burial due to widespread oxygen deficiency in the water column and/or increased primary productivity. The biostratigraphy and geochemistry of organic-rich sediments in the La Grita Member (Capacho Formation) in southwestern Venezuela were studied to document the paleoenvironmental conditions that governed the deposition of this succession during OAE-1d. Carbon-isotope (δ 13 C carb and δ 13 C Corg ) chemostratigraphy and biostratigraphic constraints show that the La Grita Member spans the late Aptian period (Rotalipora appenninica Zone), and that OAE-1d is well recorded in this succession. A prominent increase in total organic carbon (TOC) values (up to 10%) is clearly recorded through the onset of OAE-1d, coinciding with a prominent change in

Geochemistry and palynology of the upper Albian at the Abu Gharadig Basin, southern Tethys: Constraints on the oceanic anoxic event 1d

“…Correlation to adjacent areas is in agreement with results from this study based on a positive carbon‐isotope anomaly and high organic matter content, from the northwestern Tethys (Bornemann et al, ; Bréhéret, , ; Coccioni, ), north, northwestern, and western Atlantic (Rodríguez‐Cuicas et al, ; Scott et al, ; Watkins et al, ; Wilson & Norris, ). Hofmann, Ricken, Schwark, and Leythaeuser () conducted their geochemical and isotopic study based on sites from the continental slope off N Africa and the abyssal plain.…”

“…Further studies confirmed the global distribution of the OAE 1d subevents; for instance, studies from the northwestern Tethys (in the Vocontian Basin, SE France, Bornemann et al, ; Bréhéret, ; Giorgioni et al, ; and in the Pialli Italian Apennines, Coccioni, ), the southern Tethys (in Tunisia, Ben Fadhel, Layeb, Hedfi, & Ben Youssef, ; Talbi, Lakhdar, Smati, Spiller, & Levey, ), the northwestern Atlantic (in Blake Nose Plateau, Watkins, Cooper, & Wilson, ; Wilson & Norris, ), the United States (Scott, Formolo, Rush, Owens, & Oboh‐Ikuenobe, ), and southwestern Venezuela (Rodríguez‐Cuicas, Montero‐Serrano, & Garbán, ). Generally, the OAE 1d is characterized by: (a) a low to moderate positive carbon excursion (0.5–2‰; Bornemann et al, ; Watkins et al, ; Wilson & Norris, ) and TOC contents (1–2 wt%; Bornemann et al, ; Bréhéret, , ; Rodríguez‐Cuicas et al, ); and (b) being a product of stratification collapse in the water column especially in the western tropical Atlantic (Wilson & Norris, ). However, recent studies indicated that OAE 1d was formed due to enhanced orbital forcing mechanisms that led to the development of unstable circulation patterns, which favored expanded deep‐water anoxia (Bornemann et al, ; Giorgioni et al, ).…”

“…This is in agreement with a study by Yao et al () from the eastern Tethys that indicated fluctuations of the monsoonal regime together with an unstable oceanic structure led to sensitivity of the oceanic carbon reservoir for orbital variabilities through the mid‐Cretaceous generally and the late Albian particularly. Rodríguez‐Cuicas et al () also showed that orbital forcing probably induced equatorial monsoonal activity during the OAE 1d in SW Venezuela. As a consequence, the triggering mechanism of the positive δ 13 C TOC excursion during the OAE 1d in the low‐latitude Abu Gharadig Basin refers generally to perturbation in the global carbon cycle; however, local factors, including changing terrestrial runoff or relative sea‐level and/or local productivity magnitudes and their consequences on stratification conditions, cannot be excluded.…”

“…These conditions of the sites in Hofmann et al () are in a good agreement with our low‐latitude OAE 1d in the Abu Gharadig Basin, southern Tethys. Further to the west of the Atlantic (western continental slope of Southern America), Rodríguez‐Cuicas et al () indicated that during the OAE 1d organic matter‐rich facies accumulated with δ 13 C TOC isotope values between −28 and −27‰ with moderate cyclic excursion and high TOC content (ca. 5–10 wt%).…”

“…In low‐latitude northern Africa, the current study is the first to focus and address in detail the OAE 1d subevent using multiple proxies. Various analyses have been carried out including palynological and palynofacies analysis to highlight and detect the position of OAE 1d and to reconstruct the corresponding paleoceanographic processes, that is, sedimentological and geochemical approaches (TOC/Rock‐Eval pyrolysis and isotopic analyses; Bornemann et al, ; Giorgioni et al, ; Rodríguez‐Cuicas et al, ; Scott et al, ).…”