Christopher J. Hollis

Multiple early Eocene hyperthermals: Their sedimentary expression on the New Zealand continental margin and in the deep sea

The Paleocene–Eocene thermal maximum (PETM) ca. 55.5 Ma was a geologically brief interval characterized by massive influx of isotopically light carbon, extreme changes in global climate, and profound variations in Earth system processes. An outstanding issue is whether it was an isolated event, or the most prominent example of a recurring phenomenon. Recent studies of condensed deep-sea sections support the latter, but this finding remains uncertain. Here we present and discuss lithologic and carbon isotope records across two lower Eocene outcrops on South Island, New Zealand. The PETM manifests as a marl-rich horizon with a significant negative carbon isotope excursion (CIE). Above, in sediment deposited between 54 and 53 Ma, are four horizons with similar though less pronounced expressions. Marl beds of all five horizons represent increased terrigenous sedimentation, presumably linked to an accelerated hydrological cycle. Five corresponding clay-rich horizons and CIEs are found in deep-sea records, although the lithologic variations represent carbonate dissolution rather than siliciclastic dilution. The presence of five intervals with similar systemic responses in different environments suggests a mechanism that repeatedly injected large masses of 13 C-depleted carbon during the early Eocene.

The Apectodinium acme and terrestrial discharge during the Paleocene–Eocene thermal maximum: new palynological, geochemical and calcareous nannoplankton observations at Tawanui, New Zealand

Manifestations of profound perturbations in biogeochemical systems during the Paleocene–Eocene thermal maximum (PETM) include a prominent global negative δ13C and a pronounced increase in the relative abundance of dinoflagellate cysts (dinocysts) assigned to the genus Apectodinium. While motile representatives of Apectodinium were most likely thermophilic and heterotrophic, the underlying causes of this dinoflagellate response are not well understood. Here we provide new insight by examining the palynology, chemistry and calcareous nannoplankton across the PETM in a continental slope section at Tawanui, New Zealand. Across the PETM, marked changes in the relative abundance of Apectodinium vary antithetically with significant changes in the δ13C of carbonate and organic matter. In general, the high relative abundance of Apectodinium relates to enhanced concentrations of dinocysts, signifying a ‘bloom’ of Apectodinium in surface waters during the PETM. Changes in Apectodinium and δ13C records correspond to variations in many other parameters, including a smaller negative shift in bulk carbonate δ13C than expected, increased terrestrial palynomorphs, elevated TOC and C/N ratios, lower carbonate contents, higher SiO2 and Al2O3 contents, and lower Si/Al ratios. All of these variations can be explained by an increase in delivery of terrigenous material to the continental margin. A peak in the relative abundance of Glaphyrocysta dinocysts at the onset of the PETM may indicate greater down slope transport of neritic material. Changes in calcareous nannoplankton abundances suggest increased nutrient availability in surface waters during the PETM. The combined results show that Apectodinium-dominated assemblages, global perturbations in carbon isotopes and enhanced terrigenous delivery closely correspond in time at Tawanui. A sudden and massive carbon injection to the ocean–atmosphere system may have enhanced weathering and increased terrigenous inputs to continental margins during the PETM. We further suggest that these inputs caused the Apectodinium acme by elevating primary productivity in marginal seas.

Tropical sea temperatures in the high-latitude South Pacific during the Eocene

Sea-surface temperature (SST) estimates of ~30 °C from planktic foraminifera and archaeal membrane lipids in bathyal sediments in the Canterbury Basin, New Zealand, support paleontological evidence for a warm subtropical to tropical climate in the early Eocene high-latitude (55°S) southwest Pacific. Such warm SSTs call into question previous estimates based on oxygen isotopes and present a major challenge to climate modelers. Even under hypergreenhouse conditions (2240 ppm CO2), modeled summer SSTs for the New Zealand region do not exceed 20 °C.

Brackish Foraminifera in New Zealand: A Taxonomic and Ecologic Review

Approximately one third (11 species) of the world obligate brackish foraminiferal taxa occur in New Zealands estuaries and upper reaches of enclosed harbours, inlets and lagoons. The previously confused local taxonomy of New Zealands obligate (11 species) and common facultative (9 species) brackish foraminifera is integrated with current overseas usage. Nineteen of the 20 brackish species in New Zealand have a world-wide distribution. All 20 species occur in northern New Zealand (lat 35?S) with a progressive decrease in diversity to 13 species in the south (lat 47?S). Cluster analysis based on the quantitative faunal counts of 68 samples from 5 study areas results in the recognition of nine brackish foraminiferal associations. Within brackish settings, salinity and secondly tidal exposure, are the two environmental factors having the strongest influence on foraminiferal distribution. With increasing salinity, brackish faunas increase in diversity, decrease in abundance of agglutinated taxa and increase in abundance of calcareous taxa. The associations exhibit the following general trend correlated with increasing salinity: a. Trochamminita (least saline); b. Haplophragmoides wilberti, Miliammina; c. Ammonia Miliammina; d. Elphidium excavatum, Ammonia Elphidium, Ammonia; e. Marginal Marine (most saline). Five associations are apparently restricted to the intertidal zone: a. Trochammina inflata (above mean high water); b. Trochamminita, Haplophragmoides wilberti (above mean sea level); c. Elphidium excavatum (predominantly mid-tidal); d. Ammonia Elphidium (between mean low and mean high water). Tidal current transport of foraminiferal tests produces mixed assemblages in the mouths and lower channels of New Zealand estuaries (diurnal microtidal and low mesotidal ranges).

Seismic stratigraphy and structural history of the Reinga Basin and its margins, southern Norfolk Ridge system

Abstract The Reinga Basin northwest of the North Island of New Zealand was initially formed by crustal extension in Cretaceous time. Gravity models suggest up to 35—40% crustal thinning. The seismic stratigraphy of the basin is continuous with that of the offshore western North Island, where reflectors are well constrained by oil exploration data. In the Reinga Basin, there are two Cretaceous sequences above an older Mesozoic basement. The lower sequence is apparently terrestrial and may include both pre‐rift and syn‐rift subsequences; the upper is a rift‐filling marine sequence. These are overlain by Paleocene and Eocene blanket sequences that were laid down during a period of relative tectonic quiescence consistent with cooling subsidence, continued submergence, a northeast‐facing continental shelf, and absence of a significant active plate boundary. A strong regional reflector, caused by a combined unconformity and Oligocene condensed sequence, separates the Paleogene and Neogene sequences. The Neogene...

Paleoecological insights into subduction zone earthquake occurrence, eastern North Island, New Zealand

Paleoecological investigations of three Holocene marginal-marine sedimentary sequences provide information on vertical tectonic deformation in a transect across the forearc basin adjacent to the Hikurangi subduction zone, New Zealand. The elevation of maximum postglacial sea level indicators at Te Paeroa Lagoon and Opoho is between 4 and 6 m below present mean sea level, indicating net subsidence since 7200 yr B.P. Opoutama is closer to the Hikurangi Trench and appears to lie near the edge of the zone of subsidence, as evidence for vertical movement there is equivocal. Some of the subsidence at Te Paeroa Lagoon and Opoho is likely to be a result of compaction. However, a component of subsidence probably happened coseismically in two events at ca. 7100 and 5550 yr B.P. Event signatures consist of tsunami deposits overlain by chaotically mixed, reworked sediment that appears to have filled rapidly created accommodation space at marine inlet sites 10 km apart. Large offshore earthquakes are suggested by the coincidence of tsunami inundation with sudden subsidence. Forward elastic-dislocation models indicate that the observed subsidence could be achieved in ∼M w 7.9 earthquakes on either the subduction interface or the Lachlan Fault, which would involve synchronous uplift of Mahia Peninsula. Combined rupture of the interface and the Lachlan Fault, either simultaneously in a ∼M w 8.1 earthquake, or consecutively, could explain larger amounts (>1.5 m) of coastal subsidence.

Foraminiferal, radiolarian, and dinoflagellate biostratigraphy of Late Cretaceous to Middle Eocene pelagic sediments (Muzzle Group), Mead Stream, Marlborough, New Zealand

Abstract Integrated biostratigraphic study of foraminifera, radiolarians, and dinoflagellates substantially improves age control of well‐exposed Late Cretaceous to late Middle Eocene (Haumurian‐Bortonian) Muzzle Group sediments at Mead Stream, inland Marlborough, New Zealand. The group, comprising 650 m of well‐bedded pelagic limestone, marl, and chert, consists of two formations: Mead Hill Formation (257 m) and Amuri Limestone (393 m). The latter includes five distinctive, informal units: Black Siltstone, Lower Limestone, Lower Marl, Upper Limestone, and Upper Marl. Muzzle Group is in fault contact with mid‐Cretaceous (Clarence Series) Split Rock Formation siltstones at its base, and is unconformably overlain by Oligocene (Landon Series) Weka Pass Limestone. The Cretaceous‐Tertiary (K‐T) boundary, within Mead Hill Formation, is marked by a distinct lithologic change from pale limestone to dark laminated mudstone grading up into a 23 m thick chert unit. Basal Paleocene biotas suggest a relatively complete...

Descent toward the Icehouse: Eocene sea surface cooling inferred from GDGT distributions

The TEX86 proxy, based on the distribution of marine isoprenoidal glycerol dialkyl glycerol tetraether lipids (GDGTs), is increasingly used to reconstruct sea surface temperature (SST) during the Eocene epoch (56.0–33.9 Ma). Here we compile published TEX86 records, critically reevaluate them in light of new understandings in TEX86 palaeothermometry, and supplement them with new data in order to evaluate long-term temperature trends in the Eocene. We investigate the effect of archaea other than marine Thaumarchaeota upon TEX86 values using the branched-to-isoprenoid tetraether index (BIT), the abundance of GDGT-0 relative to crenarchaeol (%GDGT-0), and the Methane Index (MI). We also introduce a new ratio, %GDGTRS, which may help identify Red Sea-type GDGT distributions in the geological record. Using the offset between TEX86H and TEX86L (ΔH-L) and the ratio between GDGT-2 and GDGT-3 ([2]/[3]), we evaluate different TEX86 calibrations and present the first integrated SST compilation for the Eocene (55 to 34 Ma). Although the available data are still sparse some geographic trends can now be resolved. In the high latitudes (>55°), there was substantial cooling during the Eocene (~6°C). Our compiled record also indicates tropical cooling of ~2.5°C during the same interval. Using an ensemble of climate model simulations that span the Eocene, our results indicate that only a small percentage (~10%) of the reconstructed temperature change can be ascribed to ocean gateway reorganization or paleogeographic change. Collectively, this indicates that atmospheric carbon dioxide (pCO2) was the likely driver of surface water cooling during the descent toward the icehouse.

Cretaceous demise of the Moa plate and strike-slip motion at the Gondwana margin

Radiolaria and paleomagnetic data from Deep Sea Drilling Project Sites 595 and 596 indicate that Early Cretaceous seafloor was formed at moderate to high latitudes in the Pacific. This inference requires a Cretaceous spreading ridge south of the Pacific-Phoenix Ridge and substantial dextral strike-slip motion at the Gondwana margin. The previously unrecognized southern oceanic plate, called here the Moa plate, was obliquely subducted beneath the Gondwana margin, and material accreted from it is now part of the Eastern province of New Zealand.

Latest Cretaceous to late Paleocene radiolarian biostratigraphy: A new zonation from the New Zealand region

The scarcity of records of Early Paleocene radiolarians has meant that while radiolarian biostratigraphy is firmly established as an important tool for correlation, there has been a long-standing gap between established zonations for the Cretaceous and from latest Paleocene to Recent. It has also led to considerable speculation over the level of faunal change across the Cretaceous/Tertiary (K/T) boundary. Consequently, the discovery of rich and diverse radiolarian assemblages in well-delineated K/T boundary sections within siliceous limestones of the Amuri Limestone Group in eastern Marlborough, New Zealand, is of great significance for biostratigraphy and K/T boundary research. This initial report is restricted to introducing a new latest Cretaceous to mid Late Paleocene zonation based on the radiolarian succession at four of these sections and a re-examination of faunas from coeval sediments at DSDP Site 208 (Lord Howe Rise). Three new Paleocene species are described:Amphisphaera aotea, Amphisphaera kina andStichomitra wero. Six new interval zones are defined by the first appearances of the nominate species. In ascending order these are:Lithomelissa? hoplites Foreman (Zone RK9, Cretaceous),Amphisphaera aotea n. sp. (Zone RP1, Paleocene),Amphisphaera kina n. sp. (RP2),Stichomitra granulata Petrushevskaya (RP3),Buryella foremanae Petrushevskaya (RP4) andBuryella tetradica (RP5). Good age control from foraminifera and calcareous nannofossils permits close correlation with established microfossil zonations. Where age control is less reliable, radiolarian events are used to substantially improve correlation between the sections. No evidence is found for mass extinction of radiolarians at the end of the Cretaceous. However, the K/T boundary does mark a change from nassellarian to spumellarian dominance, due to a sudden influx of actinommids, which effectively reduces the relative abundance of many Cretaceous survivors. An accompanying influx of diatoms in the basal Paleocene of Marlborough, together with evidence for an increase of total radiolarian abundance, suggests siliceous plankton productivity increased across the K/T boundary. Possible causes for this apparently localised phenomenon are briefly discussed.