Chronostratigraphic constraints for cryptochron C18n.1n-1 observed in Eocene sediments cored in the paleoequatorial Pacific on IODP Expedition 320

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doi: 10.1130/abs/2016AM-283335
Author(s): Acton, Gary; Evans, Helen; Ohneiser, Christian; Richter, Carl; Yamamoto, Yuhji; Yamazaki, Toshi
Author Affiliation(s): Primary:
Sam Houston State University, Department of Geography and Geology, Huntsville, TX, United States
International Ocean Discovery Program, United States
University of Otago, New Zealand
University of Louisiana at Lafayette, United States
Kochi University, Japan
University of Tokyo, Japan
Volume Title: Geological Society of America, 2016 annual meeting & exposition
Source: Abstracts with Programs - Geological Society of America, 48(7); Geological Society of America, 2016 annual meeting & exposition, Denver, CO, Sept. 25-28, 2016. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7592 CODEN: GAAPBC
Note: In English
Summary: Sediments from the paleoequatorial Pacific record the paleomagnetic field with high fidelity and contain cyclic variations in chemical and physical properties that can be astronomically tuned. In an effort to fill gaps from past coring and to construct complete stratigraphic sections spanning the Cenozoic, Integrated Ocean Drilling Program (IODP) Expeditions 320 and 321 cored sediments along a Pacific Equatorial Age Transect (PEAT). A total of 6,141 m of core was recovered from 23 holes cored at 8 Sites (Sites U1331 through U1338), providing stratigraphic constraints between sites through correlation of lithological, physical, magnetic, and chemical properties. In this study, we focus on using the extensive data set to document and to date a cryptochron (a geomagnetic event with a duration less than about 30 k.y.) that was observed in Chron C18n.1n. The cryptochron was observed at several sites, but was particularly well resolved in the magnetostratigraphy for Site U1333 (10.51655°N, 221.58072°E, 4853 m water depth), which contains a full sequence of Eocene magnetochrons from the base of Chron C20n into Chron 13n. Detailed progressive alternating field (AF) were conducted on discrete samples (7 cm3 cubes), U-channel samples (2 cm x 2 cm x 150 cm), and split-core sections, along with thermal demagnetization of select discrete samples. The cleaned paleomagnetic data were characterized by shallow inclinations, consistent with the sites being near the paleoequator, and by 180° alternations in declination downhole, reflecting magnetic polarity zones. The distinct geomagnetic excursion, referred to as Cryptochron C18n.1n-1, is observed as a full geomagnetic reversal of short duration and a relative paleointensity low. It occurs slightly above the stratigraphic mid-point of Magnetozone C18n.1n and can be well dated within the cyclostratigraphic framework developed for the PEAT sites. Given these attributes, Cryptochron C18n.1n-1 will be a useful new chronostratigraphic marker in the Geomagnetic Polarity Timescale.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Chronostratigraphy; East Pacific; Expedition 320; Expedition 321; Expeditions 320/321; Integrated Ocean Drilling Program; Marine sediments; North Pacific; Northeast Pacific; Pacific Ocean; Paleogeography; Sediments
Coordinates: N051844 N120405 W1261700 W1420942
N023028 N035000 W1175811 W1231222
Record ID: 2017022815
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States