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SUMMARY We present high-resolution palaeomagnetic and rock magnetic results from 92 successive volcanic units on a 2 km tall Lima Limo (LL) section of the Oligocene Ethiopian flood basalts (OEFB). A total of 85 well-defined flow-mean characteristic remanent magnetization directions representing seven stable magnetic polarity zones with six transitional/excursional directions were determined. These results indicate the identification of four more polarity reversals than previous palaeomagnetic studies; the resulting magnetostratigraphy has, therefore, more polarity zonation. Comparison of this result with the most recently revised geomagnetic polarity time scale (GPTS, hereafter GPTS2016), by using available radiometric age data, could not find a unique correlation. Instead, it strongly suggests the recording of at least one very brief polarity chron or putative geomagnetic excursion. Our magnetostratigraphic interpretation infers that the relative timing between the OEFB eruptions and the Oi-2 global cooling estimated two possible scenarios: one where the lowermost reverse-polarity (R1) interval for the LL section is correlated to Chron C11r of GPTS2016, same as the interpretations of earlier studies, would make a causal linkage between the OEFB eruptions and the Oi-2 cooling less possible; and, the eruption timing estimated in another scenario correlating the R1 to Chron C12r might preserve the probability of its causal influence in the Oi-2 cooling. The resulting overall mean pole for the LL section of this study, 78.2° N in latitude and 213.0° E in longitude (A95 = 3.4°, N = 79), is closer to other co-eval palaeomagnetic poles from different regions and the reference pole of Africa. Our analysis of geomagnetic palaeosecular variation (PSV) shows that, compared to the Plio-Pleistocene, the Early Oligocene has higher degrees of PSV but its slightly weaker latitude dependence.

SUMMARY An active oroclinal bending is discovered in the Shan‐Thai Block to the south of the eastern Himalayan syntaxis. To investigate the evolution of the Simao Arc using palaeomagnetic techniques, the Middle Cretaceous red beds of the Nanxin Formation were sampled at the Zhengwan (22.8°N, 100.9°E) and Dadugang (22.4°N, 101.0°E) localities in the southern Simao Basin. Most of the studied samples revealed the presence of characteristic remnant magnetization with unblocking temperatures around 680 °C. A primary nature for this magnetization is interpreted on the basis of a positive fold and reversal test. Tilt‐corrected mean directions calculated for Zhengwan and Dadugang localities are characterized by large easterly deflected declination; D= 51.8°, I= 47.9°, ks= 45.0, α95= 6.9°, N= 11 and D= 64.1°, I= 48.1°, ks= 36.0, α95= 7.3°, N= 12, respectively. Steep inclination values at both these localities with respect to those expected are in the range previously reported from the Shan‐Thai Block, confirming their southward displacement by 6.2°± 1.7° as part of the Shan‐Thai Block. Combination of the present data (two localities) with those previously reported from Simao Basin (seven localities) reveals a positive palaeomagnetic oroclinal test, indicating that the present‐day arc‐like geometry of the Simao Basin was formed by oroclinal bending. Comparison with recent GPS and structural data suggest that formation of the Simao curvature started after the early Pliocene (after 4 Ma) and continuing until the present. Origin of the Simao Arc is ascribed to southwestward movement of the crustal material across the Ailao Shan‐Red River Fault (around the eastern Himalaya syntaxis), which was formed by westward movement of the decollement with progressive eastward deepening of the Lanping‐Simao Basin. Decoupling between the upper and the middle–lower crusts is a requisite condition for the arc formation on the continent.

A combined test and numerical study has been conducted for the failure analysis of unidirectional and woven composite laminated joints of an aircraft control rod. Joints with nine different geometries were tested under pin loading to evaluate the effects of the joint geometry on the failure load and mode. Nonlinear finite element analyses are performed with consideration of the contact and friction between the pin and the laminate. Failure was estimated on the characteristic curve using the Tsai-Wu and Yamada-Sun criteria. It was found that a finite element analysis based on the Tsai-Wu failure criterion with a friction coefficient of 0.1 most accurately predicts the failure load and mode of the joints.

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S U M M A R YPalaeointensity variation is investigated for an inferred time period spanning from 2.34 to 1.96 Ma. Twenty-nine consecutive lava flows are sampled along cliffs 350 m high generated by normal faulting on the Dobi section of Afar depression, Ethiopia. Magnetostratigraphy and K-Ar measurements indicate a lava sequence of R-N-R-N geomagnetic field polarities in ascending order; the lower normal polarity is identified as the Réunion Subchron. Reliability of palaeomagnetic data is ascertained through careful thermal demagnetization and by the reversal test. The Tsunakawa-Shaw method yielded 70 successful palaeointensity results from 24 lava flows and gave 11 acceptable mean palaeointensities. Reliability in palaeointensity data is ascertained by the similar values obtained by the IZZI-Thellier method and thus 11 reliable mean values are obtained from our combined results. After the older reverse polarity with the field intensity of 19.6 ± 7.8 µT, an extremely low palaeointensity period with an average of 6.4 µT is shown to occur prior to the Réunion Subchron. During the Réunion Subchron, the dipole field strength is shown to have returned to an average of 19.5 µT, followed by second extreme low of 3.6 µT and rejuvenation with 17.1 ± 5.3 µT in the younger reverse polarity. This 'W-shape' palaeointensity variation is characterized by occurrences of two extremely weak fields lower than 8 µT prior to and during the Réunion Subchron and a relatively weak timeaveraged field of approximately 15 µT. This feature is also found in sedimentary cores from the Ontong Java Plateau and the north Atlantic, indicative of a possibly global geomagnetic field phenomenon rather than a local effect on Ethiopia. Furthermore, we estimate a weak virtual axial dipole moment of 3.66 (±1.85) × 10 22 Am 2 during early stage of the Matuyama Chron (inferred time period of 2.34-1.96 Ma).

Paleomagnetic and rock magnetic investigations were performed on a 64-cm-thick section of nonmarine unconsolidated muddy sediment from the Gosan Formation on Jeju Island, Korea. This sediment was recently dated to have been deposited between 22 and 17 kyr BP calibrated, with a sedimentation rate of 13-25 cm/kyr, based on many radiocarbon ages. Interestingly, stepwise alternating field (AF) demagnetization revealed characteristic natural remanent magnetizations with anomalous directions, manifested by marked deviations from the direction of today's axial dipole field, for some separate depth levels. On the other hand, stepwise thermal (TH) demagnetization showed more complex behavior, resulting in the identification of multiple remanence components. For all TH-treated specimens, consistently two different components are predominant: a low-temperature component unblocked below 240-320 °C entirely having normal-polarity apparently within the secular variation range of the Brunhes Chron, and a high-temperature component with unblocking temperatures (Tubs) between 240-320 and 520-580 °C that have anomalous directions, concentrated in the ~ 13-34-cm-depth interval (~ 17-19 ka in inferred age) and possibly below ~ 53 cm depth (before ~ 20 ka). Rock magnetic results also infer the dominance of low-coercivity magnetic particles having ~ 300 and ~ 580 °C Curie temperature as remanence carriers, suggestive of (titano)maghemite and/ or Ti-rich titanomagnetite and magnetite (or Ti-poor titanomagnetite), respectively. A noteworthy finding is that AF demagnetizations in this study often lead to incomplete separation of the two remanence components possibly due to their strongly overlapping AF spectra. The unusual directions do not appear to result from self-reversal remanences. Then, one interpretation is that the low-temperature components are attributable to post-depositional chemical remanences, associated possibly with the later formation of the mineral phase having Tub ~ 300 °C, whereas the high-temperature components are of primary detrital origin that survived later chemical influence. Accordingly, the unusual directions might record geomagnetic instability within the ~ 17-22 ka period manifested by multiple excursional swings, partly associated with the Tianchi/Hilina Pali excursion. However, further work is needed to verify this interpretation and distinguish it from alternative explanations that invoke rock magnetic complexities as the cause of the unusual directions.

Information on the history of Earth's magnetic field is essential for understanding the geodynamo evolution, and variations in the intensity of the geomagnetic field in the past (paleointensity) are fundamentally important for constraining numerical geodynamo models. Despite a long history of research, there is still controversy about the long-term trend of time-averaged virtual (axial) dipole moment (V(A)DM): for example, the possibility of a stronger paleointensity during the Cretaceous Normal Superchron (