Untangling inconsistent magnetic polarity records through an integrated rock magnetic analysis: A case study on Neogene sections in East Timor

Abstract

Inconsistent polarity patterns in sediments are a common problem in magnetostratigraphic and paleomagnetic research. Multiple magnetic mineral generations result in such remanence ''haystacks.'' Here we test whether end-member modeling of isothermal remanent magnetization acquisition curves as a basis for an integrated rock magnetic and microscopic analysis is capable of isolating original magnetic polarity patterns. Uppermost Miocene-Pliocene deep-marine siliciclastics and limestones in East Timor, originally sampled to constrain the uplift history of the young Timor orogeny, serve as case study. An apparently straightforward polarity record was obtained that, however, proved impossible to reconcile with the associated biostratigraphy. Our analysis distinguished two magnetic endmembers for each section, which result from various greigite suites and a detrital magnetite suite. The latter yields largely viscous remanence signals and is deemed unsuited. The greigite suites are late diagenetic in the Cailaco River section and early diagenetic, thus reliable, in the Viqueque Type section. By selecting reliable sample levels based on a quality index, a revised polarity pattern of the latter section is obtained: consistent with the biostratigraphy and unequivocally correlatable to the Geomagnetic Polarity Time Scale. Although the Cailaco River section lacks a reliable magnetostratigraphy, it does record a significant postremagnetization tectonic rotation. Our results shows that the application of well-designed rock magnetic research, based on the end-member model and integrated with microscopy and paleomagnetic data, can unravel complex and seemingly inconsistent polarity patterns. We recommend this approach to assess the veracity of the polarity of strata with complex magnetic mineralogy.

Resolving spatial heterogeneities in exhumation and surface uplift in Timor-Leste: Constraints on deformation processes in young orogens

“…This time constraint remains constant if beginning of shoaling is placed at 37 m instead of 163–177 m. Even if FO of Globorotalia tosaensis is truly at 197 m instead of 23 m, uplift is no earlier than 3.47 Ma. Additionally, age constraints from magnetostratigraphy in the Viqueque type section indicate that this uplift is confined between 3.35 and ~3 Ma [ Aben et al ., ]. Haig and McCartain [] used shallow water foraminifers in the lowest turbidite at 41 m to argue for island uplift, which is lower in the section than the foraminifera we find in the fine‐grained deposits (less likely to have undergone significant downslope transport) suggest.…”

“…Additionally, two specimens at 23 m are determined to be close to Globorotalia tosaensis . We favor placing the FO of Globorotalia tosaensis (and the corresponding 3.35 Ma marker) at 23 m instead of 197 m because Globorotalia tosaensis was found in a similar position near the base of the shale and turbidite sequence in the Cailaco basin and magnetostratigraphy from the same levels as our biostratigraphy in the Viqueque type section contains polarity reversals between 17 m and 197 m [ Aben et al ., ], but no polarity reversals are known between 3.47 and 3.35 Ma [ Cande and Kent , ; Lourens et al , ].…”

“…Samples up to the top of the Viqueque section contain Globigerina apertura, Globigerinoides obliquus , and Globigerinoides obliquus extremus, indicating the top of the section is older than 1.98 Ma [ Lourens et al , ; Wade et al , ]. Magnetostratigraphy in the Viqueque type section also indicates that the top of the section may be as old as 3 Ma [ Aben et al ., ].…”

Rock magnetic characterization of ferrimagnetic iron sulfides in gas hydrate-bearing marine sediments at Site C0008, Nankai Trough, Pacific Ocean, off-coast Japan

“…The most common feature in the analyzed samples is the occurrence for type 3 samples of high coercivity SD greigite (B c~6 0-65 mT) (Fig. 6e-h) (e.g., Aben et al 2014;Chang et al 2014). Only four analyzed type 3 specimens show SD pyrrhotite characterized by its typical kidney shape (Fig.…”

A Greigite-Based Magnetostratigraphic Time Frame for the Late Miocene to Recent DSDP Leg 42B Cores from the Black Sea

“…The preservation of greigite will therefore depend on the duration of the sediment in the pyritization-window. Since, the sedimentation rate determines the duration in which the material stays in the pyritizationwindow, it becomes an important factor in greigite preservation relative to pyrite formation (Kao et al, 2004;Aben et al, 2014). A balance between pyrite and greigite is clearly observed in rock-magnetic Types 2-5 (Figures 2, 3).…”