Oceanic anoxic events and plankton evolution: Biotic response to tectonic forcing during the mid‐Cretaceous

Abstract

[1] Mid-Cretaceous (Barremian-Turonian) plankton preserved in deep-sea marl, organic-rich shale, and pelagic carbonate hold an important record of how the marine biosphere responded to short-and long-term changes in the ocean-climate system. Oceanic anoxic events (OAEs) were short-lived episodes of organic carbon burial that are distinguished by their widespread distribution as discrete beds of black shale and/or pronounced carbon isotopic excursions. OAE1a in the early Aptian ($120.5 Ma) and OAE2 at the Cenomanian/Turonian boundary ($93.5 Ma) were global in their distribution and associated with heightened marine productivity. OAE1b spans the Aptian/Albian boundary ($113-109 Ma) and represents a protracted interval of dysoxia with multiple discrete black shales across parts of Tethys (including Mexico), while OAE1d developed across eastern and western Tethys and in other locales during the latest Albian ($99.5 Ma). Mineralized plankton experienced accelerated rates of speciation and extinction at or near the major Cretaceous OAEs, and strontium isotopic evidence suggests a possible link to times of rapid oceanic plateau formation and/or increased rates of ridge crest volcanism. Elevated levels of trace metals in OAE1a and OAE2 strata suggest that marine productivity may have been facilitated by increased availability of dissolved iron. The association of plankton turnover and carbon isotopic excursions with each of the major OAEs, despite the variable geographic distribution of black shale accumulation, points to widespread changes in the ocean-climate system. Ocean crust production and hydrothermal activity increased in the late Aptian. Faster spreading rates [and/or increased ridge length] drove a long-term (Albian-early Turonian) rise in sea level and CO 2 -induced global warming. Changes in ocean circulation, water column stratification, and nutrient partitioning lead to a reorganization of plankton community structure and widespread carbonate (chalk) deposition during the Late Cretaceous. We conclude that there were important linkages between submarine volcanism, plankton evolution, and the cycling of carbon through the marine biosphere.

Demise of the northern Tethyan Urgonian carbonate platform and subsequent transition towards pelagic conditions: The sedimentary record of the Col de la Plaine Morte area, central Switzerland

“…The Late Early to Early Late Cretaceous witnessed a suite of recurrent oceanic anoxic episodes, which was unique for the entire Mesozoic and Cenozoic if one considers its frequency and multiple impact on the environment (e.g., Schlanger and Jenkyns, 1976;Arthur and Schlanger, 1979;Jenkyns, 1980;Leckie et al, 2002). The "mid"-Cretaceous anoxic episodes are an expression of major environmental change during this period, for which its manifestation was not limited to ocean basins, but extended also onto the adjacent shelves and continents (e.g., Schlager and Philip, 1990;Gröcke et al, 1999).…”

Speculative petroleum systems of the Punta del Este Basin (offshore Uruguay)

“…Black shales formed during the Early Aptian and AptianAlbian oceanic anoxic events (the so-called OAE1a and OAE1b, respectively; Leckie et al 2002) are widespread in the South Atlantic continental margin (Bray et al 1998, Davison 1999, Jungslager 1999, Van der Spuy 2003, Adekola et al 2012, Mello et al 2012. These world-class source rocks were drilled by several Deep Sea Drilling Program (DSDP) boreholes, such as DSDP 361 and DSDP 364 in Cape and Angola basins, respectively (Foresman 1978).…”

Marine palynology and environmental interpretation of the Lower Cretaceous (Barremian?–Aptian) rock units in the Koppeh-Dagh Basin, NE Iran

“…These oce anic anoxic events (OAEs) led to de po si tion of large amounts of or ganic mat ter in many parts of the world es pe cially in the Tethys Ba sin (Ar thur et al, 1990;Leckie et al, 2002;Baudin, 2005;Steuber et al, 2005;Ando et al, 2008;Föllmi, 2012). The Koppeh-Dagh sed i men tary ba sin, as part of the north ern Tethyan realm (Glen nie, 2000), stretches in an area cov er ing north east ern Iran, south ern Turkmenistan and north Af ghan i stan (Fig.…”