Erica M. Crouch

Global dinoflagellate event associated with the late Paleocene thermal maximum

The late Paleocene thermal maximum, or LPTM (ca. 55 Ma), represents a geologically brief time interval (∼220 k.y.) characterized by profound global warming and associated environmental change. The LPTM is marked by a prominent negative carbon isotope excursion (CIE) interpreted to reflect a massive and abrupt input of 12 C-enriched carbon to the ocean-atmosphere reservoir, possibly as a result of catastrophic gas-hydrate release, on time scales equivalent to present-day rates of anthropogenic carbon input. The LPTM corresponds to important changes in the global distribution of biota, including mass extinction of marine benthic organisms. The dinoflagellate cyst record indicates that surface- dwelling marine plankton in marginal seas also underwent significant perturbations during the LPTM. We report on the dramatic response of representatives of the genus Apectodinium from two upper Paleocene–lower Eocene sections in the Southern (New Zealand) and Northern (Austria) Hemispheres, where the dinoflagellate records are directly correlated with the CIE, benthic foraminifera extinction event, and calcareous nannofossil zonation. The results indicate that the inception of Apectodinium -dominated assemblages appears to be synchronous on a global scale, and that the event is precisely coincident with the beginning of the LPTM. Apectodinium markedly declined in abundance near the end of the LPTM. This Apectodinium event may be associated with (1) exceptionally high global sea-surface temperatures and/or (2) a significant increase in marginal-marine surface-water productivity. Such a globally synchronous acme of dinoflagellate cysts is unprecedented within the dinoflagellate cyst fossil record.

Environmental precursors to rapid light carbon injection at the Palaeocene/Eocene boundary

The start of the Palaeocene/Eocene thermal maximum—a period of exceptional global warming about 55 million years ago—is marked by a prominent negative carbon isotope excursion that reflects a massive input of 13C-depleted (‘light’) carbon to the ocean–atmosphere system. It is often assumed that this carbon injection initiated the rapid increase in global surface temperatures and environmental change that characterize the climate perturbation, but the exact sequence of events remains uncertain. Here we present chemical and biotic records of environmental change across the Palaeocene/Eocene boundary from two sediment sections in New Jersey that have high sediment accumulation rates. We show that the onsets of environmental change (as recorded by the abundant occurrence (‘acme’) of the dinoflagellate cyst Apectodinium) and of surface-ocean warming (as evidenced by the palaeothermometer TEX86) preceded the light carbon injection by several thousand years. The onset of the Apectodinium acme also precedes the carbon isotope excursion in sections from the southwest Pacific Ocean and the North Sea, indicating that the early onset of environmental change was not confined to the New Jersey shelf. The lag of ∼3,000 years between the onset of warming in New Jersey shelf waters and the carbon isotope excursion is consistent with the hypothesis that bottom water warming caused the injection of 13C-depleted carbon by triggering the dissociation of submarine methane hydrates, but the cause of the early warming remains uncertain.

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.

Early Paleogene evolution of terrestrial climate in the SW Pacific, Southern New Zealand

[1] We present a long-term record of terrestrial climate change for the Early Paleogene of the Southern Hemisphere that complements previously reported marine temperature records. Using the MBT′-CBT proxy, based on the distribution of soil bacterial glycerol dialkyl glycerol tetraether lipids, we reconstructed mean annual air temperature (MAT) from the Middle Paleocene to Middle Eocene (62–42 Ma) for southern New Zealand. This record is consistent with temperature estimates derived from leaf fossils and palynology, as well as previously published MBT′-CBT records, which provides confidence in absolute temperature estimates. Our record indicates that through this interval, temperatures were typically 5°C warmer than those of today at such latitudes, with more pronounced warming during the Early Eocene Climate Optimum (EECO; ∼50 Ma) when MAT was ∼20°C. Moreover, the EECO MATs are similar to those determined for Antarctica, with a weak high-latitude terrestrial temperature gradient (∼5°C) developing by the Middle Eocene. We also document a short-lived cooling episode in the early Late Paleocene when MAT was comparable to present. This record corroborates the trends documented by sea surface temperature (SST) proxies, although absolute SSTs are up to 6°C warmer than MATs. Although the high-calibration error of the MBT′-CBT proxy dictates caution, the good match between our MAT results and modeled temperatures supports the suggestion that SST records suffer from a warm (summer?) bias, particularly during times of peak warming.

Correlation between the Paleocene-Eocene boundary and the Ilerdian at Campo, Spain

Abstract The Ilerdian is a well-established Tethyan marine stage, which corresponds to an important phase in the evolution of larger foraminifera not represented in the type-area of the classical Northwest-European stages. This biostratigraphic restudy of its parastratotype in the Campo Section (northeastern Spain) based on planktic foraminifera, calcareous nannofossils, dinoflagellate cysts and the distribution of the stable isotopes ∂13C and ∂18O is an attempt to correlate the Paleocene/Eocene boundary based on a characteristic carbon isotope excursion (CIE) marking the onset of the Initial Eocene Thermal Maximum (IETM) and the Ilerdian stage. The base of this ∂13C excursion has been chosen as the criterion for the recent proposal of the Global Stratotype Section and Point (GSSP) of the base of the Eocene (= base of the Ypresian) in the Dababiya Section (Egypt) to which an age of 54.9 Ma has been attributed. This level is also characterized by a marked extinction among the deep-water benthic foraminifera (Benthic Foraminifera Extinction Event, BFEE), a flood of representatives of the planktic foraminiferal genus Acarinina and the acme of dinoflagellate cysts of the genus Apectodinium. In the Campo Section, detailed biozonations (planktic foraminifera, calcareous nannofossils, dinoflagellate cysts) are recognized in the Lower and Middle Ilerdian. The correlation with the Ypresian stratotype is based on dinoflagellate cysts and calcareous nannofossils. The base of the Ilerdian is poor in planktic microfossils and its precise correlation with the redefined Paleocene/Eocene boundary remains uncertain.

A Revised Palaeocene (Teurian) Dinoflagellate Cyst Zonation from Eastern New Zealand

Organic-walled dinoflagellate cyst (dinocyst) assemblages are documented from Palaeocene (New Zealand Teurian Stage) sediments in five sections from eastern New Zealand: Tawanui, Angora Road, and Toi Flat-1 core in the East Coast Basin, the mid-Waipara River in the Canterbury Basin, and ODP Site 1121 on the eastern margin of Campbell Plateau. Based on dinocyst results from these sections, along with published earliest Palaeocene records from the East Coast, Canterbury, and Great South basins, a revised Palaeocene dinocyst zonation is proposed. The interval zones are labelled as New Zealand Dinocyst Palaeocene (NZDP), and the eight zones, NZDP1–NZDP8, encompass the entire Palaeocene extending from 66.04 to 55.96 Ma. Correlation of the NZDP zones with the International and New Zealand time scales is provided, and is based primarily on correlation with calcareous nannofossil biostratigraphy.

Late Eocene‐Oligocene Te Kuiti Group at Mount Roskill, Auckland, New Zealand

Abstract A 592 m deep water bore drilled at Mount Roskill in central Auckland, New Zealand, intersected products of the Auckland Volcanic Field (0–12 m), pumiceous sediments of the Tauranga Group (12–23 m), interbedded sandstone and mudstone of the Waitemata Group (23–475 m), and Te Kuiti Group sediments (475–592 m). This first record of Te Kuiti Group in the central Auckland area comprises erosionally truncated Glen Massey Formation beneath the Waitemata Group, a complete section through Mangakotuku Formation, and an incomplete Waikato Coal Measures section. Drilling stopped in Waikato Coal Measures, probably less than 30 m short of Paleozoic or Mesozoic basement. Vitrinite reflectance measurements indicate a lignite rank for coal fragments collected from the coal measures, and suggest a maximum burial depth of c. 800 m. Six Te Kuiti Group samples examined for palynomorphs and foraminifers gave ages ranging from Runangan to early Whaingaroan and show a transition from a predominantly terrestrial late Eoc...

An outcrop‐based study of the economically significant Late Cretaceous Rakopi Formation, northwest Nelson, Taranaki Basin, New Zealand

Abstract The Late Cretaceous Rakopi Formation (Pakawau Group) represents one of the most important petroleum source rock units and a potential reservoir unit in the highly prospective Taranaki Basin. This paper presents a predominantly outcrop‐based study of the sedimentology, petrography, stratigraphy, and depositional environment of the Rakopi Formation in the Paturau River and Pakawau areas of northwest Nelson, southern Taranaki Basin, together with some preliminary insights into the stratigraphie architecture of the Pakawau Group on a more basin‐wide scale. The Rakopi Formation is interpreted here as a terrestrial deposit, representing sedimentation in fluvial channels and their associated overbank and levee environments. However, the presence of dinoflagellates, glauconite, and elevated coal seam sulfur contents is evidence for periodic marine influence during deposition. This could be explained by a low‐gradient coastal plain paleogeography, crossed by a series of rivers and their associated floodplain deposits, episodically inundated by marine incursions during successive transgressions. A modern analogue setting from the present‐day Hauraki Graben, North Island, New Zealand, indicates that marine influence within coastal plain systems can extend several tens of kilometres inland. Given such a physiography, relatively small increases in relative sea level could potentially move the shoreline several kilometres or tens of kilometres farther inland, sufficient to introduce the type of marine influence on sedimentation that we suggest for the Rakopi Formation. The results from this study suggest a greater marine influence within the Rakopi Formation, northward into the greater Taranaki Basin, than has previously been recognised. This raises the possibility of both different reservoir facies as well as potentially a greater proportion of marine mudstones, which would have implications for both reservoir and trapping of hydrocarbons. In addition, marine‐influenced coaly rocks within the Rakopi Formation are expected to have greater petroleum generative potentials and to be more oil‐prone than their fully non‐marine counterparts.

Southern and Northern Hemisphere dinoflagellate cyst assemblage changes in association with the late Paleocene thermal maximum

When examining the dinoflagellate cyst (dinocyst) fossil record across the Paleocene–Eocene transition, it is apparent that representatives of one dinocyst genus, Apectodinium, show a dramatic response. This response has recently been highlighted by Bujak & Brinkhuis (1998), who compiled the distribution of the Apectodinium genus through the late Paleocene–early Eocene from available global dinocyst data. The first appearance of Apectodinium is in low latitude regions during the Selandian, and it subsequently migrates into mid and high latitudes during the late Paleocene in response to global warming. An eventual development of Apectodinium-dominated assemblages appears to have occurred throughout the world and is thought to be associated with the late Paleocene thermal maximum (LPTM). The best documented dinocyst successions of late Paleocene–early Eocene age come from marginal marine environments and from the Northern Hemisphere, in particular Northwest Europe (e.g. Heilmann-Clausen 1985; Powell et al. 1996), while corresponding detailed dinocyst information from the Southern Hemisphere remains limited. The appearance of Apectodinium-dominated dinocyst assemblages in Northwest Europe occurs within the NP9 Zone, and in close proximity to the latest Paleocene carbon isotope excursion (CIE) and benthic foraminiferal extinction event (BEE) (Bujak & Brinkhuis 1998). However, when the ‘Apectodinium Migration Model’ was published, first order calibration between the presence of Apectodinium-dominated assemblages and the latest Paleocene carbon and oxygen isotope excursions was not yet established. Therefore, two main objectives of our current study are to a) increase knowledge of dinocyst distributions from the Southern Hemisphere during the late Paleocene–early Eocene, and b) establish first order calibration between Apectodiniumdominated dinocyst assemblages and the isotope record. Consequently, we are focusing on New Zealand, which lies in a mid latitude S.H. position and contains a number of Paleocene–Eocene marine successions. One sequence in particular, the Tawanui Section, contains a ‘complete’ Paleocene–Eocene transition and a previous study has identified the BEE and CIE (Kaiho et al. 1996). The negative shift in the δC record has been recorded in both the bulk organic carbon (2.5‰) and the nC29 alkane (2.8‰), which is thought to be a useful tracer for terrestrial higher plants.