Denise K. Kulhanek

Ages and magnetic structures of the South China Sea constrained by deep tow magnetic surveys and IODP Expedition 349

Combined analyses of deep tow magnetic anomalies and International Ocean Discovery Program Expedition 349 cores show that initial seafloor spreading started around 33 Ma in the northeastern South China Sea (SCS), but varied slightly by 1-2 Myr along the northern continent-ocean boundary (COB). A southward ridge jump of approximate to 20 km occurred around 23.6 Ma in the East Subbasin; this timing also slightly varied along the ridge and was coeval to the onset of seafloor spreading in the Southwest Subbasin, which propagated for about 400 km southwestward from approximate to 23.6 to approximate to 21.5 Ma. The terminal age of seafloor spreading is approximate to 15 Ma in the East Subbasin and approximate to 16 Ma in the Southwest Subbasin. The full spreading rate in the East Subbasin varied largely from approximate to 20 to approximate to 80 km/Myr, but mostly decreased with time except for the period between approximate to 26.0 Ma and the ridge jump (approximate to 23.6 Ma), within which the rate was the fastest at approximate to 70 km/Myr on average. The spreading rates are not correlated, in most cases, to magnetic anomaly amplitudes that reflect basement magnetization contrasts. Shipboard magnetic measurements reveal at least one magnetic reversal in the top 100 m of basaltic layers, in addition to large vertical intensity variations. These complexities are caused by late-stage lava flows that are magnetized in a different polarity from the primary basaltic layer emplaced during the main phase of crustal accretion. Deep tow magnetic modeling also reveals this smearing in basement magnetizations by incorporating a contamination coefficient of 0.5, which partly alleviates the problem of assuming a magnetic blocking model of constant thickness and uniform magnetization. The primary contribution to magnetic anomalies of the SCS is not in the top 100 m of the igneous basement.

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.

First evidence of denitrification vis-à-vis monsoon in the Arabian Sea since Late Miocene

In the Arabian Sea, South Asian monsoon (SAM)-induced high surface water productivity coupled with poor ventilation of intermediate water results in strong denitrification within the oxygen minimum zone (OMZ). Despite the significance of denitrification in the Arabian Sea, we have no long-term record of its evolution spanning the past several million years. Here, we present the first record of denitrification evolution since Late Miocene (~10.2 Ma) in the Eastern Arabian Sea, where the SAM generates moderate surface water productivity, based on the samples retrieved during the International Ocean Discovery Program (IODP) Expedition 355. We find that (i) the SAM was persistently weaker from ~10.2 to 3.1 Ma; it did not intensify at ~8 Ma in contrast to a few previous studies, (ii) on tectonic timescale, both the SAM and the East Asian Monsoon (EAM) varied synchronously, (iii) the first evidence of denitrification and productivity/SAM intensification was at ~3.2–2.8 Ma that coincided with Mid-Pliocene Warm Period (MPWP), and (iv) the modern strength of the OMZ where denitrification is a permanent feature was attained at ~1.0 Ma.

Eocene nannofossil biostratigraphy of the mid-Waipara river section, Canterbury Basin, New Zealand: preliminary results

Samples collected from the middle reaches of the Waipara River, northern Canterbury Basin, New Zealand, provide a detailed record of calcareous nannofossil assemblages from lower Eocene to uppermost middle Eocene sediments of this southwestern Pacific, mid-paleolatitude region (~52°S). Biostratigraphic analysis indicates an almost complete section spanning nannofossil Zones NP10 to NP16 (Ypresian to Bartonian Stages), with a hiatus that encompasses all of NP15 (Lutetian Stage) and likely portions of upper NP14 and lower NP16. There is also evidence for an unconformity that includes part of upper NP10 and lower NP11, which is also found in other New Zealand sections. This paper documents the biostratigraphy and calcareous nannofossil assemblages of the mid-Waipara River section.