Search

Studies of early Paleogene climate suffer from the scarcity of well-dated sedimentary records from the southern Pacific Ocean, the largest ocean basin during this time. We present a new magnetostratigraphic record from marine sediments that outcrop along the mid-Waipara River, South Island, New Zealand. Fully oriented samples for paleomagnetic analyses were collected along 45 m of stratigraphic section, which encompasses magnetic polarity Chrons from C23n to C21n (~51.5-47 Ma). These results are integrated with foraminiferal, calcareous nannofossil, and dinoflagellate cyst (dinocyst) biostratigraphy from samples collected in three different expeditions along a total of ~80 m of section. Biostratigraphic data indicates relatively continuous sedimentation from the lower Waipawan to the upper Heretaungan New Zealand stages (i.e., lower Ypresian to lower Lutetian, 55.5 to 46 Ma). We provide the first magnetostratigraphically-calibrated age of 48.88 Ma for the base of the Heretaungan New Zealand stage (latest early Eocene). To improve the correlation of the climate record in this section with other Southern Ocean records, we reviewed the magnetostratigraphy of Ocean Drilling Program (ODP) Site 1172 (East Tasman Plateau) and Integrated Ocean Drilling Program (IODP) Site U1356 (Wilkes Land Margin, Antarctica). A paleomagnetic study of discrete samples could not confirm any reliable magnetic polarity reversals in the early Eocene at Site 1172. We use the robust magneto-biochronology of a succession of dinocyst bioevents that are common to mid-Waipara, Site 1172, and Site U1356 to assist correlation between the three records. A new integrated chronology offers new insights into the nature and completeness of the southern high-latitude climate histories derived from these sites.

The absolute position during the Cenozoic of northern Zealandia, a continent that lies more than 90% submerged in the southwest Pacific Ocean, is inferred from global plate motion models, because local paleomagnetic constraints are virtually absent. We present new paleolatitude constraints using paleomagnetic data from International Ocean Discovery Program Site U1507 on northern Zealandia and Site U1511 drilled in the adjacent Tasman Sea Basin. After correcting for inclination shallowing, five paleolatitude estimates provide a trajectory of northern Zealandia past position from the middle Eocene to the early Miocene, spanning geomagnetic polarity chrons C21n to C5Er (∼48–18 Ma). The paleolatitude estimates support previous works on global absolute plate motion where northern Zealandia migrated 6° northward between the early Oligocene and early Miocene, but with lower absolute paleolatitudes, particularly in the Bartonian and Priabonian (C18n–C13r). True polar wander (solid Earth rotation with respect to the spin axis), which only can be resolved using paleomagnetic data, may explain the discrepancy. This new paleomagnetic information anchors past latitudes of Zealandia to Earth's spin axis, with implications not only for global geodynamics, but also for addressing paleoceanographic and paleoclimate problems, which generally require precise paleolatitude placement of proxy data. Plain Language Summary: The ancient latitude (paleolatitude) of a tectonic plate can be determined from magnetism recorded in rocks (paleomagnetism). Earth's geomagnetic field, averaged over geological time, is symmetrical around Earth's spin axis. Hence, the direction of the remanent magnetization in rocks can provide the paleolatitude and orientation of a tectonic plate with respect to the geographic poles. Using marine sediments recovered during International Ocean Discovery Program Expedition 371, we present five paleolatitude estimates for northern Zealandia, a mostly submerged continent in the southwest Pacific encompassing New Zealand and New Caledonia. The reconstructed paleolatitudes span the time interval from 48 to 18 million years ago (middle Eocene to middle Miocene), and represent the first such estimates from northern Zealandia. Geodynamic models for Earth surface motion relative to the spin axis require several assumptions and do not accurately predict our results. Combined with data from other continents, a more precise reconstruction for Zealandia's past geography has implications for understanding various fossil records in this extensive region, including those important for past ocean circulation and climate models, and for the evolution of plants and animals. Key Points: We present five paleomagnetic‐based absolute paleolatitudes for northern Zealandia during the middle Eocene–early MiocenePaleolatitude estimates are based on paleomagnetic directions from two deep‐sea cores drilled in the Tasman SeaPrecise absolute paleolatitudes underpin accurate paleogeography, with implications for paleoclimate modeling [ABSTRACT FROM AUTHOR]

The Pacific plate circuit went through a complex reorganization during the early to middle Eocene, approximately coinciding with the onset of subduction along the western Pacific margin. However, the timing and dynamics of this change in the southwest Pacific and evolution of subduction beneath the Tonga‐Kermadec Arc are not fully resolved. We present magneto‐biostratigraphic data from an early to middle Eocene sedimentary section exposed in the Koumac‐Gomen area, New Caledonia, which is an emerged portion of the Norfolk Ridge. The 260 m‐thick succession contains a transition from pelagic micrite to terrigenous‐rich calciturbidite that is observed regionally in New Caledonia and which is interpreted to represent a shift from sedimentation on a stable submarine plateau to slope formation developed under a convergent tectonic regime. The stratigraphic contact between pelagic micrite and overlying calciturbidite is not exposed, but our magnetic polarity‐based chronology constrains the age of transition to 46–44 Ma, in agreement with the 45.3 Ma age recently obtained from the Noumea area in southern New Caledonia. We integrate records from New Caledonia with recent magnetostratigraphic data from South Island, New Zealand, where marked variations in terrigenous input occurred during the early and middle Eocene. Synchronous sedimentary changes in the southwest Pacific occurred at the same time as onset of rapid seafloor spreading south of Australia and New Zealand. We infer that the underlying cause of stratigraphic change was inception of slip at a new configuration of the Australia‐Pacific plate boundary, which evolved into the Tonga‐Kermadec subduction system. Plain language summary: New Caledonia and New Zealand expose sedimentary rocks that hold the key for understanding regional tectonic evolution. Using rock magnetism and micropaleontology, we determine the age of sedimentary records in New Caledonia. A change in sedimentation style indicates the onset of tectonic activity about 45 million years ago, which is the same time that significant changes in depositional style and rate are recorded by sediments in New Zealand, and changes in spreading rate are recorded by magnetic anomalies south of Australia and New Zealand. We interpret our evidence as recording inception of a new plate boundary in the southwest Pacific that ultimately resulted in development of the southwestern portion of the Pacific Ring of Fire. Key Points: We present a new integrated magneto‐biostratigraphic age model for Eocene sedimentary rocks in New CaledoniaThe regional onset of sediment gravity flows at ~46–44 Ma corresponds to the inception of rapid Australia‐Pacific plate motionNorthern Zealandia sedimentary change during the middle Eocene was likely related to initiation of the Tonga‐Kermadec subduction [ABSTRACT FROM AUTHOR]

The Rhenodanubian Flysch zone (RDF) is a Lower Cretaceous-lower Palaeocene turbidite succession extending for ~500 km from the Danube at Vienna to the Rhine Valley (Eastern Alps). It consists of calcareous and siliciclastic turbidite systems deposited in a trench abyssal plain. The age of deposition has been estimated through micropalaeontologic dating. However, palaeomagnetic studies constraining the age and the palaeolatitude of deposition of the RDF are still missing. Here, we present palaeomagnetic data from the Early Cretaceous Tristel and Rehbreingraben Formations of the RDF from two localities in the Bavarian Alps (Rehbrein Creek and Lainbach Valley, southern Germany), and from the stratigraphic equivalent of the Falknis Nappe (Liechtenstein). The quality of the palaeomagnetic signal has been assessed by either fold test (FT) or reversal test (RT). Sediments from the Falknis Nappe are characterized by a pervasive syntectonic magnetic overprint as tested by negative FT, and are thus excluded from the study. The sediments of the Rehbreingraben Formation at Rehbrein Creek, with positive RT, straddle magnetic polarity Chron M0r and the younger M'-1r' reverse event, with an age of ~ 127-123 Ma (late Barremian-early Aptian). At Lainbach Valley, no polarity reversals have been observed, but a positive FT gives confidence on the reliability of the data. The primary palaeomagnetic directions, after correction for inclination shallowing, allow to precisely constrain the depositional palaeolatitude of the Tristel and Rehbreingraben Formations around ~28°N. In a palaeogeographic reconstruction of the Alpine Tethys at the Barremian/Aptian boundary, the RDF is located on the western margin of the Briançonnais terrain, which was separated from the European continent by the narrow Valais Ocean. [ABSTRACT FROM AUTHOR]

We conducted an integrated magneto-biostratigraphic study of a 37 m-thick composite section exposed at two sites near Nouméa (New Caledonia). The section contains a transition from pelagic micrite to terrigenous-rich calciturbidites. This transition, observed regionally in coeval records of New Caledonia, marks a shift from pelagic sedimentation on a stable continental submarine plateau to turbidite deposition indicating development of a slope in a convergent tectonic regime. The studied section spans magnetic polarity Chrons C22r to C20r, calcareous nannofossil zones CNE5 to CNE10, and radiolarian zones RP9 to RP11 (49.5 to c. 44 Ma), and the micrite-turbidite transition occurred around 45.3 Ma (early middle Eocene). This transition could be the onshore correlative of a regional switch from tectonic extension to compression, which has been inferred from analysis of new seismic profiles acquired for the Tasman-northern Zealandia area, and that has been interpreted as precursor of the Tonga-Kermadec subduction initiation. [ABSTRACT FROM AUTHOR]

We present records of stable carbon and oxygen isotopes, CaCO3 content, and changes in calcareous nannofossil assemblages across an 81m thick section of upper Paleocene-lower Eocene marine sedimentary rocks now exposed along the Cicogna Stream in northeast Italy. The studied stratigraphic section represents sediment accumulation in a bathyal hemipelagic setting from approximately 57.5 to 52.2 Ma, a multi-million-year time interval characterized by perturbations in the global carbon cycle and changes in calcareous nannofossil assemblages. The bulk carbonate δ13C profile for the Cicogna section, once placed on a common timescale, resembles that at several other locations across the world, and includes both a long-term drop in δ13C and multiple short-term carbon isotope excursions (CIEs). This precise correlation of widely separated δ13C records in marine sequences results from temporal changes in the carbon composition of the exogenic carbon cycle. However, diagenesis has likely modified the δ13C record at Cicogna, an interpretation supported by variations in bulk carbonate δ18O, which do not conform to expectations for a primary signal. The record of CaCO3 content reflects a combination of carbonate dilution and dissolution, as also inferred at other sites. Our detailed documentation and statistical analysis of calcareous nannofossil assemblages show major differences before, during and after the Paleocene-Eocene Thermal Maximum. Other CIEs in our lower Paleogene section do not exhibit such a distinctive change; instead, these events are sometimes characterized by variations restricted to a limited number of taxa and transient shifts in the relative abundance of primary assemblage components. Both long-lasting and short-lived modifications to calcareous nannofossil assemblages preferentially affected nannoliths or holococcoliths such as Discoaster, Fasciculithus, Rhomboaster/Tribrachiatus, Sphenolithus and Zygrhablithus, which underwent distinct variations in abundance as well as permanent evolutionary changes in terms of appearances and disappearances. By contrast, placoliths such as Coccolithus and Toweius, which represent the main component of the assemblages, were characterized by a gradual decline in abundance over time. Comparisons of detailed nannofossil assemblage records at the Cicogna section and at ODP Site 1262 support the idea that variations in the relative and absolute abundances, even some minor changes, were globally synchronous. An obvious link is through climate forcing and carbon cycling, although the linkages between variations in calcareous nannoplankton, changes in δ13C records and oceanography will need additional work. [ABSTRACT FROM AUTHOR]

The Mead Stream section (South Island, New Zealand) consists of a 650-m-thick series of continuous, well-exposed strata deposited on a South Pacific continental slope from the Late Cretaceous to the middle Eocene. We examined the uppermost Paleocene--middle Eocene part of the section, which consists of ~360 m of limestone and marl, for detailed magnetic polarity stratigraphy and calcareous nannofossil and foraminifera biostratigraphy. Magneto-biostratigraphic data indicate that the section straddles magnetic polarity chrons from C24r to C18n, calcareous nannofossil zones from NP9a to NP17 (CNP11--CNE15, following a recently revised Paleogene zonation), and from the Waipawan to the Bortonian New Zealand stages (i.e., from the base of the Ypresian to the Bartonian international stages). The Mead Stream section thus encompasses 17 m.y. (56--39 Ma) of southwest Pacific Ocean history. The ages of calcareous nannofossil biohorizons are consistent with low- to midlatitude data from the literature, indicating that during the early--middle Eocene, the low- to midlatitude calcareous nannofossil domain extended at least to ~50°S-55°S in the South Pacific. Correlation of the magnetic polarity stratigraphy from the Mead Stream section with the geomagnetic polarity time scale allows us to derive sediment accumulation rates (SAR), which range between 8 and 44 m/m. Comparing the SAR with paleotemperature proxy records, we found that two intervals of increased SAR occurred during the early Eocene climatic optimum (52-50 Ma) and during the transient warming event peaking with the middle Eocene climatic optimum (40.5 Ma). This correlation indicates that, at Mead Stream, the climate evolution of the early--middle Eocene is recorded in a sedimentation pattern whereby, on a million year time scale, warmer climate promoted continental weathering, transportation, and accumulation of terrigenous sediments. [ABSTRACT FROM AUTHOR]

SUMMARY In the lowermost Eocene sedimentary record of Ocean Drilling Program Site 1262 (Leg 208, Walvis Ridge, South Atlantic Ocean), the presence of a ∼53-kyr-long normal polarity event has been recorded within the ∼2.55-Myr-long reverse polarity Chron C24r (∼53.3-55.9 Ma) and termed Palaeocene-Eocene magnetic reversal (PEMR). The origin of the PEMR has been speculatively related to a change in the Earth's rotation rate that was in turn influenced by an abrupt overturning of the ocean-atmosphere circulation that occurred during the Palaeocene-Eocene thermal maximum (PETM) at ∼55 Ma. Such provocative genesis for a magnetic-polarity reversal demands the PEMR to be confirmed (or refuted) in additional PETM sections. Here, we present detailed palaeomagnetic and rock-magnetic data from the Forada and Cicogna sections of the Belluno Basin in NE Italy, which contain an expanded and continuous record of the PETM termed clay marl unit (CMU). Our data indicate that these sediments were deposited during a continuous interval of reverse geomagnetic field polarity. We therefore conclude that no magnetic-polarity reversals occurred throughout the PETM. In addition, we studied the origin of the high degree of flattening affecting the characteristic magnetic component directions of the sediments, which we interpret as due to a combination of depositional inclination shallowing typical of detrital haematite, and post-depositional compaction of clays, particularly abundant in the carbonate-depleted CMU. [ABSTRACT FROM AUTHOR]

The early–middle Eocene was a time of complex reorganization in the kinematics of the Pacific plate circuit, related with the onset of the western Pacific subduction zone. As the geological history of the northwest Pacific active margin is relatively well known, the timing of the southwest Pacific evolution is still not fully resolved. Available seismic reflection data reveals the presence of widespread middle Eocene convergent deformation, reverse faulting, and uplift across the Tasman area and the Zealandia continent, east of Australia. This is the time when a major change occurred in the sedimentation pattern of marine sections exposed in New Caledonia and New Zealand, the only emerged portions of Zealandia. The Eocene sediment succession in New Caledonia is characterized by a shift from pelagic micrite deposited on a stable sub-marine plateau to high-energy, terrigenous-rich calciturbidite, indicating uplift and development of a slope. We present a new high-resolution paleo- and rock-magnetic study of a 260 m-thick section cropping out in the Koumac area of northern New Caledonia. The obtained robust magnetic polarity-based chronology pins in time the inception of the calciturbidite sedimentation at 45 Ma, in agreement to recent data from southern New Caledonia (1). These data are integrated with recent magnetostratigraphic data from the south island of New Zealand (2, 3). Here, coeval dramatic variations in the terrigenous input are related to opening of new basins capturing the drainage system, as result of newly activated regional tectonic. We put forward a tectonic frame, based on robust magnetic polarity age models and applicable to the whole northern Zealandia continent, where the eastward motion of the Pacific Plate results in a middle Eocene (46–45 Ma) regional reorganization. This is manifested by uplift and convergent deformation in the north (New Caledonia). To the south (New Zealand) the proximity of the Pacific-Australian rotational pole causes a more complex response, with opening of new basins accompanied by quick changes of variations of the sediment accumulation rates.1. Dallanave, E. et al. Magneto-biostratigraphic constraints of the Eocene micrite–calciturbidite transition in New Caledonia: tectonic implications. New Zeal. J. Geol. Geophys. 61, 145–163 (2018).2. Dallanave, E. et al. Constraining early to middle Eocene climate evolution of the southwest Pacific and Southern Ocean. Earth Planet. Sci. Lett. 433, 380–392 (2016).3. Dallanave, E. et al. Early to middle Eocene magneto-biochronology of the southwest Pacific Ocean and climate influence on sedimentation: Insights from the Mead Stream section, New Zealand. Geol. Soc. Am. Bull. 127, 643–660 (2015). [ABSTRACT FROM AUTHOR]

The Varignano section (Trento province, northern Italy) provides an exceptional opportunity for a direct correlation between shallow benthic (SB) zones and standard calcareous plankton zones at the Bartonian--Priabonian transition (middle--late Eocene). This transition has attracted great attention by biostratigraphers in the last decades in searching for a boundary stratotype section. The Alano di Piave section (NE Italy) is the leading candidate for the base Priabonian Global Stratotype Section and Point (GSSP). However, at Alano, larger foraminifera-bearing resedimented levels occur exclusively well below the critical interval. Conversely, the Varignano section, located ~80 km west of the Alano section, preserves several coarse bioclastic levels rich in larger foraminifera throughout the section. These levels are inter calated with basinal marlstones, crystal tuff layers, and an organic-rich interval. The Varignano section spans planktic forami niferal Zones E10 and E11 to lower E14, calcareous nannofossil Zones MNP16Bc to MNP18 and Chrons 18n to 17n.2n. The main calcareous plankton events recently proposed as primary base-Priabonian correlation tools, i.e., the last occurrence of the genus Morozovel loides and the Base common (= acme beginning) of Cribrocentrum erbae occur, respectively, within C17n.3n and C17n.2n. We correlate prominent crystal tuff layers exposed at Varignano with those outcropping at Alano, including the Tiziano bed, whose base has also been proposed as the GSSP level. The Varignano section spans the upper SB17 and the lower SB18 Zones, with the zonal boundary marked by the first occurrence of the genus Pellatispira. This event occurs in the lower part of Zones E13 and MNP17A within C18n, well below all the potential criteria to identify the GSSP that also includes Chron C17n.1n base. We point out that the usage of shallow-water biostratigraphers in placing the base of the Priabonian at the base of Zone SB19 is inconsistent with the proposed plankton events. [ABSTRACT FROM AUTHOR]