Mid-Cretaceous oceanic anoxic events in the Pacific Ocean revealed by carbon-isotope stratigraphy of the Calera Limestone, California, USA

Abstract

The paleoceanographic history of the Pacifi c Ocean during the mid-Cretaceous is poorly constrained due to the loss of much of the contemporaneous Pacifi c seafl oor to subduction and diffi culties in recovering chert-rich sediments by ocean drilling. Pelagic sediments that were originally deposited in the Pacifi c Ocean but that have been subsequently accreted during subduction potentially provide an alternative paleoceanographic archive. This study presents micropaleontological and carbon-isotope data from the Calera Limestone, part of the classic Franciscan Complex exposed in Permanente Quarry, central California, USA. In the three stratigraphic sections studied, pelagic limestones with low organic-carbon contents are the dominant lithology. However, two stratigraphic intervals are recognized that contain organic carbon, and these date to the early Aptian and late Albian-early Cenomanian. These time intervals correspond to two mid-Cretaceous oceanic anoxic events (OAEs): early Aptian OAE1a (equivalent to the "Selli level") and late Albian OAE1d (equivalent to the "Breistroffer event"). It is well established that both of these events were associated with signifi cant carbon-isotope excursions, which are also shown to exist in the Calera Limestone. The record of OAE1a from the Calera Limestone complements ocean drilling records by providing further evidence for variability in the sedimentary and stratigraphic record of this event. The carbon-isotope data from the late Albianearly Cenomanian provide the fi rst detailed chemobiostratigraphic record of this period for the Pacifi c Ocean, confi rming that environmental change occurred at this time in the Pacifi c, possibly related to OAE1d.

Biogeochemical sulfur cycling during Cretaceous oceanic anoxic events: A comparison of OAE1a and OAE2

“…Therefore, we cannot rule out option B presented by Robinson et al . []. However, the difference in the detailed chemostratigraphy has little impact on our interpretations that the section spans the pre‐OAE1a interval and most of the positive CIE (i.e., segments C1–C7 of Menegatti et al []) (Figure ).…”

“…The other places the negative δ 13 C excursion ~0.6 m below the organic‐rich chert layer [i.e., option B in Robinson et al . , ]. We have elected to display Figure a because our δ 13 C data do not show a negative δ 13 C excursion below the chert layer that was attributed to segment C3 in Figure b.…”

“…In Figure a, C1–C3, C7, and C8 refer to portions of the profile that we correlate with the δ 13 C carb segments of Menegatti et al [], which corresponds to the “option A” correlation of Robinson et al . []. The alternative correlation (option B) [ Robinson et al .…”

The Cogollo Group and the oceanic anoxic events 1a and 1b, Maracaibo basin, Venezuela

“…The early Aptian event (Selli event, OAE 1a) has its type locality in Italy, named "Livello Selli" (Coccioni et al 1989;Baudin et al 1998;Li et al 2008;Blättler et al 2011), and the event of early Albian (Paquier event, OAE 1b) was first recognized in the Vocontian basin in southeastern France (Bréhéret 1985(Bréhéret , 1994Herrle et al 2003). Both events are well represented by organic rich black shales in the Alpine-Mediterranean region and anthers regions of the world (Sliter 1989;Bralower et al 1993;Herrle et al 2003;Tsikos et al 2004;Robinson et al 2008;Hofmann et al 2008;Blättler et al 2011;Nuñez-Useche et al 2014).…”

“…These high total organic carbon (TOC) levels are the expression in the Maracaibo Basin sedimentary record of two oceanic anoxic events (OAEs): OAE 1a of the early Aptian (~ 120 Ma), represented by the Machiques Member, and the OAE 1b of the late Aptian (~ 113 Ma), represented by the Piché Member, both of them belong to the Apón Formation (Méndez et al 2008). These two bituminous intervals, whose correlative sections have been studied in many sedimentary basins in Europe, the Mediterranean sea, Florida (USA), Gulf of Mexico, the Pacific and the Atlantic oceans (Sliter 1989;Bralower et al 1993Bralower et al , 1994Jenkyns & Wilson 1999;Leckie et al 2002;Dumitrescu et al 2006;Hofmann et al 2008;Robinson et al 2008), represent two effective source rock levels. This implies a new configuration of the Cogollo Group and Río Negro Formation petroleum system.…”