Response and recovery of the Comanche carbonate platform surrounding multiple Cretaceous oceanic anoxic events, northern Gulf of Mexico

Abstract

a b s t r a c tThe ubiquity of carbonate platforms throughout the Cretaceous Period is recognized as a product of high eustatic sea-level and a distinct climatic optimum induced by rapid sea-floor spreading and elevated levels of atmospheric carbon-dioxide. Notably, a series of global oceanic anoxic events (OAEs) punctuate this time-interval and mark periods of significantly reduced free oxygen in the world's oceans. The best records of these events are often from one-dimensional shelf or basin sections where only abrupt shifts between oxygenated carbonates and anoxic shales are recorded. The Comanche Platform of central Texas provides a unique opportunity to study these events within a well-constrained stratigraphic framework in which their up-dip and down-dip sedimentologic effects can be observed and the recovery of the platform to equilibrium states can be timed and understood. Stable isotope data from whole cores in middle Hauterivian through lower Campanian mixed carbonate-siliciclastic strata are used to construct a 52-myr carbon isotope reference profile for the northern Gulf of Mexico. Correlation of this composite curve to numerous global reference profiles permits identification of several anoxic events and allows their impact on platform architecture and facies distribution to be documented. Oceanic anoxic events 1a, 1b, 1d, and 2 occurred immediately before, after, or during shale deposition in the Pine Island Member, Bexar Member, Del Rio Formation, and Eagle Ford Group, respectively. Oceanic anoxic event 3 corresponds to deposition of the Austin Chalk Group. Platform drowning on three occasions more closely coincided with globally recognized anoxic sub-events such as the Fallot, Albian-Cenomanian, and MidCenomanian events. This illustrates that the specific anoxic event most affecting a given carbonate platform varied globally as a function of regional oceanographic circumstances.Using chemo-and sequence-stratigraphic observations, a four-stage model is proposed to describe the changing facies patterns, fauna, sedimentation accumulation rates, platform architectures, and relative sea-level trends of transgressive-regressive composite sequences that developed in response to global carbon-cycle perturbations. The four phases of platform evolution include the equilibrium, crisis, anoxic, and recovery stages. The equilibrium stage is characterized by progradational shelf geometries and coralrudist phototrophic faunal assemblages. Similar phototrophic fauna typify the crisis stage; however, incipient biocalcification crises of this phase led to retrogradational shelf morphologies, transgressive facies patterns, and increased clay mineral proportions. Anoxic stages of the Comanche Platform were coincident with back-ground deposition of organic-rich shale on drowned shelves and heterotrophic fauna dominated by oysters or coccolithophorids. Eustatic peaks of this stage were of moderate amplitude (~30 m), yet relative sea-level rises were greatly enhanced by reduced sedimentation rates. In the recovery sta...

A revised chronostratigraphic framework for the Aptian of the Essaouira-Agadir Basin, a candidate type section for the NW African Atlantic Margin.

“…Tiskatine NC7A: The LAD of M. hoschulzii has been conventionally calibrated (Bralower et al, 1993; Ogg and Hinnov, 2012) to a position slightly above the base of the upper Aptian, at a level close to the base of the E. martini Zone (SMAS). This conventional calibration for the top NC7A appears depressed to more recent records from northwestern Europe (Jeremiah, 2000(Jeremiah, , 2001, the Gulf of Mexico (Phelps et al, 2015; Supplementary document) and this study at Tiskatine (EAB). Here at Tiskatine M. hoschulzii ranges up to the local "Hypacanthoplites" spp.…”

“…Its true LAD is more sporadic, with rare occurrences ranging up into the lowermost Albian of the North Sea (Jeremiah, 2001). Recent studies (Phelps et al, 2015;supplementary document) have shown a more extensive geographical distribution outside of the North Sea. At Tiskatine the acme of C. bosunensis is at bed MTTK 239 (Fig.…”

The Northern Gulf of Mexico During OAE2 and the Relationship Between Water Depth and Black Shale Development

“…Farther south, the Cenomanian‐Turonian Eagle Ford Shale of Texas is probably the best studied OAE2 interval in the Gulf of Mexico region (Corbett & Watkins, ; Corbett, Watkins, & Popspichal, ; Denne and Breyer, ; Denne et al, , ; Dodsworth, ; Donovan et al, ; Eldrett, Minisini, & Bergman, ; Eldrett et al, ; Frush & Eicher, ; Lowery & Leckie, ; Lowery et al, ; Lundquist, ; Pessagno, ; Phelps et al, ). Like in the Western Interior, the pre‐OAE2 sedimentary rocks of Texas are enriched in total organic carbon (TOC) up to ~9 wt % (Hentz & Ruppel, ) and contain proxy evidence for seafloor anoxia, including a lack of benthic foraminifera, absence of bioturbation, and enrichment in certain redox sensitive trace metals (e.g., Denne et al, ; Denne & Breyer, ; Donovan et al, ; Eldrett et al, , ; Lowery et al, ).…”

Mid-early late Albian foraminiferal assemblage from the El Abra Formation in the El Madroño locality, eastern Valles–San Luis Potosí Platform, Mexico: Paleoenvironmental and paleobiogeographical significance

“…Frizzell (1954, p. 76), reported that in Texas, C. texanus ranges upward from the Glen Rose Limestone of the Trinity Group into the progressively younger Walnut Clay, Comanche Peak Limestone, and Goodland Limestone of the Fredericksburg Group". Phelps et al (2015) indicated that this species ranges from the mid-to-upper Albian from west Texas. In Mexico, C. texanus has been reported by Scott and González-León (1991) (Figure 5a), which was defined by Vanderpool (1933) from the mid-Albian Comanchean "formation" in southern Oklahoma, later placed in the genus Buccicrenata by Loeblich and Tappan (1949).…”

“…Maync (1955a) recorded the species in the Lower Cretaceous (Guácharo limestone) of eastern Venezuela and prepared a detailed description. Dictyoconus walnutensis is widespread in the Gulf of Mexico region and has been regarded as a stratigraphic marker restricted to the mid-Albian (Douglass, 1960;Maync, 1955a;Bonet, 1956;Scott, 1990;Scott and González-León, 1991;Buitrón et al, 1995;Omaña and Alencaster, 2001;Monreal and Longoria, 1999;Fourcade et al, 1999;Waite et al, 2007); however, it could have ranged to the early late Albian (Phelps et al, 2015). In North Texas this species ranges to the top of Goodland Formation in which the basal upper Albian ammonite Dipoloceras cristatum occurs; so D. walnutensis ranges into basal upper Albian (written communication Scott, 2016).…”