Climatic and environmental changes across the early Eocene climatic optimum at mid-Waipara River, Canterbury Basin, New Zealand

Abstract

The Cretaceous-Paleogene marine sedimentary succession exposed in the banks of the middle reaches of the Waipara River (referred to as mid-Waipara), north Canterbury, New Zealand, has been the subject of several high-profile studies of Paleogene paleoclimate over the past decade. It is one of relatively few sections globally where a multi-proxy approach is possible due to the good preservation of microfossils and organic biomarkers. The Eocene section is also well dated by magnetostratigraphy and biostratigraphy based on planktic foraminifera, calcareous nannofossils and dinoflagellate cysts (dinocysts). Here, we build on this previous work and undertake a comprehensive analysis of paleontological and geochemical indicators of climatic and environmental changes through the earlymiddle Eocene part of the section, with particular focus on the Early Eocene Climatic Optimum (EECO; 53.26-49.14 Ma). We correlate a 33.5 m-thick interval with the EECO, based on biostratigraphy, magnetostratigraphy, TEX86-paleothermometry and bulk carbonate δ 13 C. Our new sea-surface temperature (SST) record based on TEX86 agrees with a previous lower resolution record based on TEX86 and planktic foraminiferal δ 18 O and Mg/Ca ratios. The EECO interval in this section extends from the upper part of the New Zealand Waipawan Stage to the Mangaorapan/Heretaungan Stage boundary at 49.27 Ma. The EECO onset is not exposed, but the termination is well constrained by a fall in SST and shift to more positive δ 13 C values. Six negative carbon isotope excursions (CIEs) are recognised within the EECO and are tentatively correlated with CIEs J/K, M, O, Q, T and C22nH4 in the global δ 13 C compilation. The CIEs are associated with warmer SSTs, indicating that they represent hyperthermals. The BAYSPAR TEX86 calibration indicates SST increased by as much as12°C from the early Eocene (~55 Ma) to the EECO, where SST peaked at 35°C. SST gradually declined from mid EECO (~51 Ma) into the middle Eocene. The marked warming in the early EECO is associated with the highest abundance of warm-water taxa in calcareous nannofossil and dinocyst assemblages, the highest proportion of planktic foraminifera, and a coeval long-term shift to abundant angiosperm vegetation, primarily driven by a rise in Casuarinaceae. There is good agreement between TEX86 and marine microfossil-based proxies for temperature, providing confidence that both approaches are useful guides to past water temperature. Warm-water marine taxa are most abundant in P a g e 3 | 48 the EECO but are not dominant. Comparison of the abundance of nannofossil warm-water taxa between mid-Waipara and a low-latitude site on Shatsky Rise suggests the latitudinal temperature gradient between mid-and low-latitudes in the EECO was greater than the TEX86 proxy implies.There is no clear evidence for enhanced sedimentation rates associated with the EECO, in contrast to evidence from the nearby Mead Stream section. Superabundant Homotryblium, a euryhaline dinocyst, in the early and middle EECO suggests elevated salin...

Eocene (46–44 Ma) Onset of Australia‐Pacific Plate Motion in the Southwest Pacific Inferred From Stratigraphy in New Caledonia and New Zealand

“…Several early to middle Eocene sedimentary sections in New Zealand have been studied in detail over the last few decades. These include Mead Stream and Branch Stream in Marlborough (Dallanave et al, 2015; Hollis, Dickens, et al, 2005, Hollis, Field, et al, 2005; Slotnick et al, 2012, 2015; Strong et al, 1995), the mid‐Waipara River section of the north Canterbury Basin (Crouch et al, 2020; Dallanave et al, 2016; Hollis et al, 2009; Morgans et al, 2005), the Hampden Beach section of the south Canterbury Basin (Crouch & Brinkhuis, 2005; Morgans, 2009), and a number of exploration wells drilled offshore of eastern South Island in the Great South Basin (Cook et al, 1999) (Figures 1 and 8). Moreover, new magneto‐biostratigraphic data from South Island New Zealand have been published in recent years, putting some of the records into a precise temporal framework (Dallanave et al, 2015, 2016).…”

“…A common feature of these records is a long‐term (Myr‐scale) decrease in terrigenous supply straddling the New Zealand Porangan stage (i.e., mid‐Lutetian; Raine et al, 2015), approximately between 48–46 Ma and 43 Ma (Figure 8a). In Canterbury and Great South Basins, this manifests as a sedimentary hiatus (e.g., Takapu‐1A well and mid‐Waipara River; Cook et al, 1999; E. Crouch et al, 2020; Dallanave et al, 2016; McMillan & Wilson, 1997) or a condensed interval (Hampden Beach; Morgans, 2009). In Marlborough, it manifests as deposition of the Upper Limestone member of the Amuri Limestone, a unit that consists of ~75 m (at Mead Stream) of white micritic limestone virtually devoid of terrigenous content (Dallanave et al, 2015; Hollis, Dickens, et al, 2005, Hollis, Field, et al, 2005; Strong et al, 1995) (Figure 8a).…”

Maastrichtian-Rupelian paleoclimates in the southwest Pacific – a critical evaluation of biomarker paleothermometry and dinoflagellate cyst paleoecology at Ocean Drilling Program Site 1172

“…This is because of fundamental physiological restrictions in their individual tolerances (e.g., Reichgelt et al, 2018), whereas mean annual air temperature (MAAT) reconstructions from pollen assemblages are complicated because MAAT exerts much less control on the standing vegetation than seasonal temperature and hydrological extremes. Reconstructions of the warm Eocene primarily relied on organic geochemical proxies, notably TEX86 (Bijl et al, 2009;2013a;Cramwinckel et al, 2018;Crouch et al, 2020;Hollis et al, 2009;Sluijs et al, 2006;. These absolute SST estimates for the sw Pacific are closer to those from the equatorial Atlantic as they are to the deep-sea (Cramwinckel et al, 2018), which is surprising given that the South Pacific was presumably the dominant region of deep-water formation during the Eocene (Huber and Thomas, 2010;Thomas et al, 2003;2014).…”

Temperate Oligocene surface ocean conditions offshore Cape Adare, Ross Sea, Antarctica

“…The lowermost 60 m of the sediment record, below 352.5 mbsf, yield abundant and diverse dinocysts, that are common in Eocene Southern Ocean sediments (Bijl et al, 2013;Cramwinckel et al, 2020;Crouch et al, 2020)…”