Eocene–Oligocene Global Climate and Sea-Level Changes: St. Stephens Quarry, Alabama
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Eocene–Oligocene global climate and sea-level changes: St. Stephens Quarry, Alabama Kenneth G. Miller* James V. Browning Marie-Pierre Aubry Bridget S. Wade§ Miriam E. Katz† Andrew A. Kulpecz James D. Wright Department of Geological Sciences, Rutgers University, Piscataway, New Jersey 08854, USA ABSTRACT that ~0.4‰ of the increase at Oi1 time was est Oligocene marked the beginning of the ice- due to temperature. Maximum δ18O values house Earth, with large (i.e., near modern sized) We integrate upper Eocene–lower Oli- of Oi1 occur above the sequence boundary, ice sheets in Antarctica (e.g., Miller et al., 1991; gocene lithostratigraphic, magnetostrati- requiring that deposition resumed during the Zachos et al., 1992). However, considerable con- graphic, biostratigraphic, stable isotopic, lowest eustatic lowstand. A precursor δ18O troversy has surrounded the cause of the δ18O benthic foraminiferal faunal, downhole log, increase of 0.5‰ (33.8 Ma, mid-chron C13r) increase that culminated in Oi1, ranging from and sequence stratigraphic studies from the at SSQ correlates with a 0.5‰ increase in the early studies that attribute it entirely to a cooling Alabama St. Stephens Quarry (SSQ) core deep Pacifi c Ocean; the lack of evidence for a of deep-water (and hence, high-latitude surface hole, linking global ice volume, sea level, and sea-level change with the precursor suggests water) temperatures (Shackleton and Kennett, temperature changes through the greenhouse that this was primarily a cooling event, not 1975; Savin et al., 1975; Kennett and Shackleton, to icehouse transition of the Cenozoic. We an ice-volume event. Eocene–Oligocene shelf 1976), to a recent study that attributes the entire show that the SSQ succession is dissected by water temperatures of ~17–19 °C at SSQ are 1.5‰ δ18O increase observed in the deep Pacifi c hiatuses associated with sequence boundaries. similar to modern values for 100 m water to growth of ice sheets (Tripati et al., 2005). This Three previously reported sequence bound- depth in this region. Our study establishes latter interpretation requires: (1) ice storage that aries are well dated here: North Twistwood the relationships among ice volume, δ18O, is ~1.5 times that of modern ice sheets; (2) the Creek–Cocoa (35.4–35.9 Ma), Mint Spring– and sequences: a latest Eocene cooling event presence of large ice sheets in Antarctica and in Red Bluff (33.0 Ma), and Bucatunna-Chicka- was followed by an earliest Oligocene ice vol- the Northern Hemisphere; and (3) a global sea- sawhay (the mid-Oligocene fall, ca. 30.2 Ma). ume and cooling event that lowered sea level level (eustatic) fall of ~150 m. It is based on the In addition, we document three previously and formed a sequence boundary during the lack of a deep-sea Mg/Ca change associated with undetected or controversial sequences: mid- early stages of eustatic fall. the Oi1 δ18O increase (Lear et al., 2000), imply- Pachuta (33.9–35.0 Ma), Shubuta-Bump- ing little or no cooling. However, a dramatic nose (lowermost Oligocene, ca. 33.6 Ma), Keywords: Eocene-Oligocene, sea level, cli- drop in the calcite compensation depth occurred and Byram-Glendon (30.5–31.7 Ma). An mate, ice volume, Alabama, sequence stratigra- at this transition (Van Andel et al., 1975; Cox- ~0.9‰ δ18O increase in the SSQ core hole is phy, icehouse, greenhouse. all et al., 2005), and may have caused changes correlated to the global earliest Oligocene in carbonate ion activity that masked cooling in (Oi1) event using magnetobiostratigraphy; INTRODUCTION Mg/Ca records (Lear et al., 2004). this increase is associated with the Shubuta- There is ample evidence for a major global Bumpnose contact, an erosional surface, and The Eocene–Oligocene transition (ca. 35– cooling during the Eocene–Oligocene tran- a biofacies shift in the core hole, providing 33 Ma) was the most profound oceanographic sition. Paleontological evidence for cooling a fi rst-order correlation between ice growth and climatic change of the past 50 m.y. (e.g., includes the development of psychrospheric and a sequence boundary that indicates a Miller, 1992; Zachos et al., 2001). A global (cold-loving) ostracods (Benson, 1975), a sea-level fall. The δ18O increase is associ- earliest Oligocene (33.55 Ma) δ18O increase deep-sea benthic foraminiferal turnover (e.g., ated with a eustatic fall of ~55 m, indicating of 1.0‰–1.5‰ (Oi1 of Miller et al., 1991) Miller et al., 1992; Thomas, 1992), the loss of *[email protected] occurred throughout the Atlantic, Pacifi c, Indian, calcareous nannoplankton that thrived in early §Present address: Department of Geology and and Southern Oceans (Shackleton and Kennett, Paleogene warm, oligotrophic waters (Aubry, Geophysics, Texas A&M University, College Sta- 1975; Savin et al., 1975; Kennett and Shackle- 1992), regional evidence for cooling from pol- tion, Texas 77843, USA †Also at: Earth and Environmental Sciences, ton, 1976; Keigwin, 1980; Corliss et al., 1984; len (e.g., New Jersey; Owens et al., 1988), Rensselaer Polytechnic Institute, Troy, New York Miller et al., 1987; Zachos et al., 2001; Coxall mammalian turnover (e.g., England; Hooker et 12180, USA et al., 2005). Most studies agree that the earli- al., 2004), and microfossil assemblages (e.g., GSA Bulletin; January/February 2008; v. 120; no. 1/2; p. 34–53; doi: 10.1130/B26105.1; 9 fi gures; Data Repository Item 2007208. 34 For permission to copy, contact [email protected] © 2007 Geological Society of America Integrated sequence stratigraphy and the Eocene–Oligocene transition New Zealand; Nelson and Cook, 2001). Isoto- a major earliest Oligocene eustatic fall of ~55 m erous sections, and other complications due to pic evidence also indicates global cooling. The (Pekar et al., 2001; Miller et al., 2005a). Using nearshore infl uences. Linking deep-sea isotopes δ18 δ18 O increase in the deep Atlantic is typically the sea level/ Oseawater calibrations cited above, and sea-level records requires using magneto- 1.0‰ (e.g., Miller and Curry, 1982); the 1.5‰ this implies that ~0.5‰–0.6‰ of the deep-sea biostratigraphic correlations that have errors of δ18O increase at Ocean Drilling Program (ODP) δ18O increase was due to an increase in ice vol- 0.5–1.0 m.y. (e.g., Miller et al., 1990). Miller Site 1218 (deep Pacifi c; Coxall et al., 2005) ume and ~0.5‰–1.0‰ was due to a 2–4 °C et al. (1998) provided fi rst-order correlations implies that there was at least a 2 °C cooling in deep-water cooling. Sequence stratigraphic and between Miocene sequences and δ18O records at the deep Pacifi c. Comparisons of benthic fora- backstripping studies in New Jersey have docu- New Jersey continental slope Site 904, directly miniferal δ18O records and a latitudinal profi le mented that the mid-Oligocene eustatic lower- linking δ18O increases and sequence boundaries. of planktonic foraminiferal δ18O values show ing was ~50–60 m (Pekar et al., 2001; Miller et Such comparisons provide a prima facie link a shift in mean values of ~0.6‰ from the late al., 2005a), far less than the 160 m fall shown between ice volume and sequences, but such Eocene to the early Oligocene (Keigwin and by the Exxon curves. The absence of an earliest fi rst-order correlations for the Eocene and Oli- δ18 Corliss, 1986). This global change in Oseawater Oligocene event on the Exxon curve has been a gocene have been lacking until this study. is best explained by ice growth with a conse- source of discussion and debate for more than St. Stephens Quarry (SSQ) in Alabama has quent sea-level lowering of ~50–60 m (using 25 yr (Olsson et al., 1980). provided one of the global reference sections the δ18O/sea level calibrations of Fairbanks Until now, the data sets used to decipher ice- for the Eocene–Oligocene transition, yet the and Matthews [1978] and Pekar et al. [2002] volume changes across the Eocene–Oligocene basic relationships among sequences, sea level, of 0.11‰/10 m and 0.1‰/10 m, respectively). transition were derived from deep-sea locations temperature, and biotic events in this section Nevertheless, the precise amount of the δ18O largely drilled by the Deep Sea Drilling Proj- have been controversial. Pioneering sequence increase that is attributable to ice versus tem- ect and the ODP. In contrast, sea-level studies stratigraphic studies of the SSQ outcrop were perature remains debatable. of this interval have mostly examined seismic published as part of the Exxon sea-level curve Sea-level studies have established that a major profi les on continental margins (e.g., Vail et al., (Baum and Vail, 1988; Loutit et al., 1988; eustatic drop occurred in the earliest Oligocene. 1977) or marine sections on land (e.g., Vail et Fig. 1). SSQ outcrop studies have integrated Although the Exxon Production Research Com- al., 1987; Haq et al., 1987; Loutit et al., 1988; sequence stratigraphy with planktonic forami- pany (Exxon) sea-level curve shows no earli- Baum and Vail, 1988; Miller et al., 2005a). It niferal biostratigraphy (Mancini and Tew, 1991; est Oligocene change and a dramatic (160+ m) has proven diffi cult to obtain expanded and reli- Tew, 1992). Keigwin and Corliss (1986) identi- mid-Oligocene fall (Vail et al., 1977; Haq et al., able δ18O records for onshore marine sections fi ed a major (~1‰) δ18O increase in the low- 1987), studies in New Jersey have documented because of hiatuses, diagenesis, poorly fossilif- ermost Oligocene in the SSQ outcrop. ARCO Oil and Gas Company drilled a core hole at SSQ in 1987 that spanned the Eocene–Oligo- Baum and Vail (1988) This study Sequence Quant.