TY - JOUR
T1 - Testing for astronomical forcing of cycles and gamma ray signals in outer shelf/upper slope, mixed siliciclastic-carbonates
T2 - Upper Oligocene, New Zealand
AU - Read, J. Fred
AU - Li, Mingsong
AU - Hinnov, Linda A.
AU - Nelson, Campbell S.
AU - Hood, Steven
N1 - Funding Information:
We thank Fletcher Challenge Energy and Petrocorp Exploration Ltd. (now Shell) for providing gamma ray logs and access to the slabbed cores and company reports. Read especially thanks Rod Feller and David Waghorn for their help, along with Hugh Morgans for updates on the paleontologic age picks. Hood and Nelson thank the Ministry of Economic Development staff in the library and core store in Wellington, New Zealand. We thank Peter King for extremely helpful comments on an early version of the paper. We also thank Christian Zeeden, Mathieu Martinez and an anonymous reviewer, whose comments greatly improved the paper.
Publisher Copyright:
© 2020 Elsevier B.V.
Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.
PY - 2020/10/1
Y1 - 2020/10/1
N2 - We evaluate whether outer shelf/upper slope settings preserve a record of astronomical forcing using gamma ray logs from the upper Oligocene (upper Chattian) Tikorangi Formation, onshore Taranaki Basin, North Island, New Zealand. The formation is a siliciclastic‑carbonate succession deposited in outer neritic to upper bathyal depths at paleolatitudes of c. 45oS. Gamma ray and sonic logs calibrated to core indicate four lithofacies based on percent carbonate. These are calcareous siliciclastic mudrock (highest gamma ray values), highly calcareous siltstones (high gamma ray values), very fine to fine siliciclastic muddy packstones (intermediate gamma), and winnowed very fine to medium grain-dominated packstones and grainstones (low gamma). Detrended gamma ray logs were tuned using minimal tuning methods (405 kyr long eccentricity cycle or, where this was poorly developed, the ~100 kyr short eccentricity cycle) with sedimentation rates tested statistically against astronomical forcing. The tuned data show well developed long- and short-term eccentricity, obliquity, and a weak precessional forcing. Obliquity modulation is observed at the 1.2 Myr scale (one well) and 175 kyr scale (two wells). The floating time scale was tied to the absolute time scale via published biostratigraphy, the La2004 eccentricity solution, the Atlantic ODP site 1264 δ18O record, and the Mi-1 isotope event at c.23 Ma. Sea-level fluctuations typically were moderate (20 to 40 m) estimated from the δ18O record. The high gamma siliciclastic-prone units formed during warmer and wetter phases (and possibly slightly higher sea levels), whereas the cleaner carbonates with abundant inner-shelf-derived fine carbonate developed during cooler, drier phases (and possibly slightly lower sea levels). Gamma ray logs from outer shelf/upper slope settings provide valuable data sets for documenting the effects of astronomical forcing on the sedimentary record. The study supports climate models for New Zealand which predict generally increased precipitation with warming over the next 100 years. The study appears to be the first to record astronomical forcing in the Oligocene marine record of New Zealand.
AB - We evaluate whether outer shelf/upper slope settings preserve a record of astronomical forcing using gamma ray logs from the upper Oligocene (upper Chattian) Tikorangi Formation, onshore Taranaki Basin, North Island, New Zealand. The formation is a siliciclastic‑carbonate succession deposited in outer neritic to upper bathyal depths at paleolatitudes of c. 45oS. Gamma ray and sonic logs calibrated to core indicate four lithofacies based on percent carbonate. These are calcareous siliciclastic mudrock (highest gamma ray values), highly calcareous siltstones (high gamma ray values), very fine to fine siliciclastic muddy packstones (intermediate gamma), and winnowed very fine to medium grain-dominated packstones and grainstones (low gamma). Detrended gamma ray logs were tuned using minimal tuning methods (405 kyr long eccentricity cycle or, where this was poorly developed, the ~100 kyr short eccentricity cycle) with sedimentation rates tested statistically against astronomical forcing. The tuned data show well developed long- and short-term eccentricity, obliquity, and a weak precessional forcing. Obliquity modulation is observed at the 1.2 Myr scale (one well) and 175 kyr scale (two wells). The floating time scale was tied to the absolute time scale via published biostratigraphy, the La2004 eccentricity solution, the Atlantic ODP site 1264 δ18O record, and the Mi-1 isotope event at c.23 Ma. Sea-level fluctuations typically were moderate (20 to 40 m) estimated from the δ18O record. The high gamma siliciclastic-prone units formed during warmer and wetter phases (and possibly slightly higher sea levels), whereas the cleaner carbonates with abundant inner-shelf-derived fine carbonate developed during cooler, drier phases (and possibly slightly lower sea levels). Gamma ray logs from outer shelf/upper slope settings provide valuable data sets for documenting the effects of astronomical forcing on the sedimentary record. The study supports climate models for New Zealand which predict generally increased precipitation with warming over the next 100 years. The study appears to be the first to record astronomical forcing in the Oligocene marine record of New Zealand.
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U2 - 10.1016/j.palaeo.2020.109821
DO - 10.1016/j.palaeo.2020.109821
M3 - Article
AN - SCOPUS:85086911730
SN - 0031-0182
VL - 555
JO - Palaeogeography, Palaeoclimatology, Palaeoecology
JF - Palaeogeography, Palaeoclimatology, Palaeoecology
M1 - 109821
ER -
