Kenneth Kodama

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Use of Anisotropy of Magnetic Susceptibility (Ams) Measurements for Orogenic Studies: Examples from the Betic Cordillera, Spain and Central Apennines, Italy

Application of anisotropy of magnetic susceptibility (AMS) fabrics to determine the kinematics of active tectonics: Examples from the Betic Cordillera, Spain and the northern Apennines, Italy

The anisotropy of magnetic susceptibility (AMS) technique provides an effective way to measure fa... more The anisotropy of magnetic susceptibility (AMS) technique provides an effective way to measure fabrics and in the process, interpret the kinematics of actively deforming orogens. We collected rock fabric data of alluvial fan sediments surrounding the Sierra Nevada massif, Spain, and a broader range of Cenozoic sediments and rocks across the northern Apennine foreland, Italy, to explore the deformation fabrics that contribute to the ongoing discussions of orogenic kinematics. Sierra Nevada is a regional massif in the hinterland of the Betic Cordillera. We recovered nearly identical kinematics regardless of specimen magnetic minerology, structural position, crustal depth, or time. The principal elongation axes are NE-SW in agreement with mineral lineations, regional GPS geodesy, and seismicity results. The axes trends are consistent with the convergence history of the Africa-Eurasia plate boundary. In Italy, we measured AMS fabrics of specimens collected along a NE-SW corridor spanning the transition from crustal shortening to extension in the northern Apennines. Samples have AMS fabrics compatible only with shortening in the Apennine wedge and have locked in penetrative contractional fabrics, even for those samples that were translated into the actively extending domain. In both regions we found that specimens have a low degree of anisotropy and oblate susceptibility ellipsoids that are consistent with tectonic deformation superposed on compaction fabrics. Collectively, these studies demonstrate the novel ways that AMS can be combined with structural, seismic, and GPS geodetic data to resolve orogenic kinematics in space and time. 1 Introduction A number of circum-Mediterranean orogens are associated with rapid slab rollback, resulting in paired compressional and extensional domains in the orogenic wedge of the retreating upper plate (Elter, 1975, Carminati

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Using Magnetic Methods to Assign Chronostratigraphy to Sedimentary Sequences II Posters

2015 AGU Fall Meeting, Dec 18, 2015

Reconciling independent chronologies of lake sediments in the Baza paleolake, Southern Spain

AGUFM, Dec 1, 2019

Ponencia presentada en: American Geophysical Union, Fall Meeting: San Francisco, USA, 9-13 decemb... more

Formation, northeastern Mexico of the shallow marine lower Cretaceous Cupido Global Milankovitch cycles recorded in rock magnetism

Palaeointensity of the 1.3 billion-yr-old Gardar basalts, southern Greenland revisited: no evidence for onset of inner core growth

Geophysical Journal International, Mar 8, 2019

The age of the inner core nucleation is a first-order problem in the thermal evolution of the Ear... more The age of the inner core nucleation is a first-order problem in the thermal evolution of the Earth that can be addressed with palaeomagnetism. We conducted a palaeointensity study on the 1.3 Ga Gardar basalts from southern Greenland to investigate previously reported high ancient geomagnetic field intensities. Biggin et al. used the earlier result to identify nucleation of Earth's solid inner core at 1.3 Ga. We collected 106 samples from 39 flows from the lavas of the Eriksfjord Formation, sampling 17 of the lower flows, 8 of the middle flows and 14 of the upper flows. Rock magnetic analyses, including magnetic hysteresis, first-order reversal curves and magnetic susceptibility versus temperature measurements, suggest that the predominate magnetic mineral in the lower basalts is low Ti titanomagnetite, whereas the middle and upper flows have varying amounts of hematite. The magnetic hysteresis data suggest that magnetic grains range from multidomain to single domain in character, with an apparent dominance of pseudo-single behaviour. Thellier-Thellier double heating experiments using the IZZI methodology yielded vector endpoint diagrams and Arai plots showing two components of magnetization, one up to approximately 450 • C and the higher temperature component typically from 450 • C up to 580 • C, but sometimes to as high as 680 • C. We attribute the lower temperature component, to partial overprinting by the nearby Ilimaussaq intrusion, and acquisition of viscous remanent magnetization. We use the Thellier autointerpreter assigning standard selection criteria vetted by cumulative distribution plots. This approach yields a palaeointensity of 6.5 ± 5.9 μT (1 SD) based on 27 samples from 13 flows and a nominal virtual dipole moment (VDM) of 1.72 × 10 22 Am 2. However, we cannot exclude the possibility of bias in this value related to chemical remanent magnetization (CRM) and multidomain effects. We isolate a conservative upper bound on palaeointensity as the highest palaeointensity result that is free of CRM effects. This yields a palaeointensity of ∼18 μT, and a VDM of ∼4.5 × 10 22 Am 2 , which is a field strength similar to many other Proterozoic values. Thus, our analysis of the Gardar basalts supports the conclusion of Smirnov et al. that there is no palaeointensity signature of inner core growth 1.3 billion yr ago.

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Rock magnetic cyclostratigraphy of the Doushantuo Formation, South China and its implications for the duration of the Shuram carbon isotope excursion

Precambrian Research, Feb 1, 2017

The Shuram excursion (SE), one of the largest-known negative carbon isotope anomalies, has been g... more The Shuram excursion (SE), one of the largest-known negative carbon isotope anomalies, has been globally observed in Ediacaran rocks. Precisely determining the duration of the SE is pivotal to understanding its controversial origin. Here, we present a detailed paleomagnetic, rock magnetic, cyclostratigraphic and carbon isotopic study of the SE in the Doushantuo Formation at the Dongdahe section in eastern Yunnan Province, South China. Although paleomagnetic results likely show a late Mesozoic remagnetization, careful mineralogic analyses indicate that the rock magnetic cyclostratigraphy carried by detrital pseudo-single domain (SD) or small multidomain (MD) titanomagnetite grains faithfully records orbitally-forced climate cycles in the Ediacaran. Multi-taper method (MTM) spectral analysis of magnetic susceptibility (MS) and anhysteretic remanent magnetization (ARM) series reveals significant spectral peaks at similar frequencies. Based on the ratios of their frequencies, these spectral peaks are assigned to a suite of Milankovitch cycles (long eccentricity, short eccentricity, obliquity and precession), yielding a sediment accumulation rate of 1.0 cm/kyr for the Doushantuo Formation. A 9.1 ± 1.0 Myr duration is indicated for the entire SE in South China. This result is in good agreement with independent estimates from North America and South Australia, thus supporting a primary origin for the SE. In combination with published geochronologic data, we suggest that the onset of the SE occurred at ca. 560 Ma, which provides a chronostratigraphic framework for evaluating the relationship between the SE and the evolution of metazoans in Ediacaran time.

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Magnetic and gravity evidence for a subsurface connection between the Palisades sill and the Ladentown basalts

Geological Society of America Bulletin, 1983

Total-field magnetic and gravity data were collected between the northwestern tip of the earliest... more Total-field magnetic and gravity data were collected between the northwestern tip of the earliest Jurassic age Palisades sill, near Mount Ivy, New York, and the Ladentown basalts, 1.3 km to the west, to determine if a subsurface connection exists between the two bodies. The magnetics measurements show a large, negative, total-field anomaly, suggesting that a subsurface body trends from the sill to the basalts. Gravity measurements also indicate that a dense subsurface body connects the flows and the sill. Two-dimensional magnetic modeling of the gravity and magnetic data suggest that the northern edge of a magnetic, dense slab cuts east-west across the field area. The base of the slab dips ∼ 10° to 15° to the south in the eastern part of the study area and is nearly horizontal in the western part. The existence of this connecting body suggests convincingly that the Ladentown basalts were formed by the eruption of Palisades magma onto the surface of the Newark Basin. The geometry of the body derived from the modeling may also indicate that the connecting body has been vertically offset 150 to 200 m from the Palisades sill to the east by a north-south-trending normal fault at the western tip of the Palisades sill. A fifth magnetics line trending east-west along the southern margin of the field area has a very small magnetic positive, suggesting that if an igneous connection exists between the Ladentown basalts and the New City Park magnetic anomaly, it is a minor feature.

Orbitally driven redox fluctuations during Cretaceous Oceanic Anoxic Event 2 (OAE2) revealed by a new magnetic proxy

Palaeogeography, Palaeoclimatology, Palaeoecology, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Using Anisotropy of Remanence to Decompact Sedimentary Strata for Basin Analysis and Cyclostratigraphic Studies: A New Technique

Resolving the Latemar Controversy: a new magnetostratigraphy at Rio Sacuz

High-Resolution Magnetostratigraphic and Rock Magnetic Cyclo-stratigraphic Study of the Eocene Arguis Formation, Spanish Pyrenees

In order to provide a high-resolution chronostratigraphic record, an 800 meter section of the Arg... more In order to provide a high-resolution chronostratigraphic record, an 800 meter section of the Arguis Formation, an Eocene marine flysch deposited in the Jaca Basin of the Spanish Pyrenees was sampled for magnetostratigraphy and rock magnetic cyclo-stratigraphy. Oriented cores were collected to refine a previously determined magnetostratigraphy. Their paleomagnetic analysis shows that the oldest 600 meters of the Arguis Formation spans chrons C18n.1n to C17n.2n or about two million years. For 300 m of the section 395 un- oriented hand samples were collected for rock magnetic cyclo-stratigraphy at a 75 cm sampling interval (about every 4 kyr) in order to resolve the precessional index. Anhysteretic remanent magnetization (ARM) was measured for each sample to construct a ferromagnetic mineral concentration time series. Spectral analysis of the ARM time series, calibrated by the magnetostratigraphically-determined chron boundaries, shows periodicities consistent with astronomical forcin...

Strain History of a Regional-Scale Decollement Fold, Northeast Mexico

Structural analysis of outcrop and anisotropy of magnetic susceptibility (AMS) data from the Sier... more Structural analysis of outcrop and anisotropy of magnetic susceptibility (AMS) data from the Sierra del Fraile anticlinorium (25°80'N / 100°30'W), Coahuila Marginal Folded Province, northeast Mexico, elucidates complex fold kinematics in an orogenic foreland. Sierra del Fraile is a regional-scale décollement fold, with a ~4.5 km clastic and carbonate section deformed above a ~3 km thick evaporite unit. Mesoscopic structures,

Shallowed vs. Concordant Paleomagnetic Inclinations in Asian red Beds: Tectonic Implications

Anomalously low paleomagnetic inclinations are often recorded in Asian red beds. Based on the ava... more Anomalously low paleomagnetic inclinations are often recorded in Asian red beds. Based on the available age control, most Tertiary sections show low inclinations while inclinations concordant with the paleomagnetic pole of Eurasia are generally recorded in Cretaceous red beds. This inclination pattern hinders tectonic interpretations but may also yield important constraints on the development of the Indo-Asia collisional system. To better constrain the reliability of the paleomagnetic record, we investigate the rock magnetic and petrologic signature in samples from 21 stratigraphic sections collected north of the Tibetan plateau. In addition to classic thermal demagnetization of NRM, IRM acquisition curves in fields up to 8 T were used to characterize magnetic mineralogy. Magnetite and hematite bearing samples can both be affected by inclination shallowing. AMS reveals a characteristic sedimentary fabric regardless of the degree of inclination shallowing. Separation of the paramagne...

Global Milankovitch Cycles Recorded by Rock Magnetism in the Shallow Marine Cretaceous Cupido Formation, NE Mexico (Invited)

A rock magnetic cyclo-stratigraphy was measured for the upper Barremian-lower Aptian Cupido Forma... more A rock magnetic cyclo-stratigraphy was measured for the upper Barremian-lower Aptian Cupido Formation of northeast Mexico. Anhysteretic remanent magnetization (ARM; 97 muT DC field, 100 mT peak AC field) was used to measure magnetic mineral concentration variations for the uppermost 150 m of the Cupido Fm (the `Cupidito'). The Cupido Fm is characterized by meter-scale, peritidal and subtidal carbonate cycles representative of inner and middle platform settings. Isothermal remanent magnetization (IRM) acquisition experiments and SEM examination suggest that micron-sized detrital magnetite derived from eolian dust carries the ARM signal. At the sampled sections (Potrero Garcia and Potrero Chico, 30 km apart), ARM records a synchronous 30-35 m oscillation with maxima coinciding with 4th-order sequence boundaries; this oscillation is superimposed by prominent higher-frequency variability. Tuning the 30-35 m oscillation to a 405-kyr periodicity (long eccentricity) focuses the higher...

Milankovitch Modulated Eocene Growth Strata From the Jaca Piggyback Basin, Spanish Pyrenees

New stratigraphic and rock magnetic data from the southern margin of the Jaca basin, Spanish Pyre... more New stratigraphic and rock magnetic data from the southern margin of the Jaca basin, Spanish Pyrenees, shows evidence of Eocene sedimentary cycles modulated by the climatic effects of Milankovitch orbital forcing. Tectonic processes simultaneously controlled larger-scale stratigraphic sequences and overall wedge-top basin development. Within the context of existing magnetostratigraphy, we described 1 km of marine basinal and prodeltaic rocks near Pico del Aguila, a large-scale synsedimentary fold, and collected samples every ~4krs for ~4myrs for lithologic and rock magnetic analysis. In magnetochrons C17r, C18n.1n, and C18n.1r (1.27myrs) anhysteretic remanent magnetization (ARM) variations occur with strong hierarchical bundling patterns suggestive of precession-scale cycles grouped into 100 kyr eccentricity cycles, and "super bundled" into 400 kyr eccentricity cycles. This pattern was exploited to construct an "eccentricity time scale" for the series producing a...

Assessing thermal effects on magnetic fabrics of sedimentary rocks: Results from synthetic and natural samples

Geophysical Research Letters, 2005

High‐resolution estimate for the depositional duration of the Triassic Latemar Platform: A new magnetostratigraphy and magnetic susceptibility cyclostratigraphy from basinal sediments at Rio Sacuz, Italy

Geochemistry, Geophysics, Geosystems, 2013

A new magnetostratigraphy and magnetic susceptibility cyclostratigraphy from Middle Triassic basi... more A new magnetostratigraphy and magnetic susceptibility cyclostratigraphy from Middle Triassic basinal sediments at Rio Sacuz, northern Italy, suggests a depositional duration of ~1 myr for most of the 670 m carbonate Latemar Platform, giving a high‐resolution estimate for the duration for the Latemar's deposition. The new magnetostratigraphy from Rio Sacuz clarifies the ambiguities in a previous magnetostratigraphic study of the Latemar caused by lightning strike remagnetizations. Our Rio Sacuz study was unaffected by lightning. Using thermal demagnetization, we show a Normal‐Reversed‐Normal‐Reversed sequence at the Latemar‐correlated locality of Rio Sacuz. With a polarity interval duration of ~0.25–0.5 myr for the Middle Triassic, this gives a depositional duration of ~1–2 myr. Rock magnetic experiments show that the magnetic carrier is magnetite, suggesting a primary, depositional‐age remanence. Measurement of magnetic susceptibility at 1 m intervals from Rio Sacuz reveals eigh...

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Exploring till bed kinematics using AMS magnetic fabrics and pebble fabrics: the Weedsport drumlin field, New York State, USA

Boreas, 2011

Gentoso, M. J., Evenson, E. B., Kodama, K. P., Iverson, N. R., Alley, R. B., Berti, C. & Kozlowsk... more Gentoso, M. J., Evenson, E. B., Kodama, K. P., Iverson, N. R., Alley, R. B., Berti, C. & Kozlowski, A. 2012 (January): Exploring till bed kinematics using AMS magnetic fabrics and pebble fabrics: the Weedsport drumlin field, New York State, USA. Boreas, Vol. 41, pp. 31–41. 10.1111/j.1502‐3885.2011.00221.x. ISSN 0300‐9483.Thick, relatively homogeneous basal tills exposed in the drumlins and flutes of the Weedsport drumlin and flute field in New York State exhibit anisotropy of magnetic susceptibility (AMS) and pebble fabrics that are consistently oriented parallel to the streamlined bedforms. The pebble fabrics and AMS fabrics are concordant. In this study, six drumlins and five flutes were sampled. Thermally induced, incremental reduction of isothermal remanent magnetization indicates that AMS is caused by primarily elongate maghaemite grains. The orientations of principal axes of maximum susceptibility (k1) are generally parallel to pebble long‐axis orientations, and tend to plunge...

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Rock-magnetic cyclostratigraphy for the Late Pliocene–Early Pleistocene Stirone section, Northern Apennine mountain front, Italy

Geological Society, London, Special Publications, 2012

Lithostratigraphic, magnetostratigraphic and rock-magnetic cyclostratigraphic data were combined ... more Lithostratigraphic, magnetostratigraphic and rock-magnetic cyclostratigraphic data were combined to create a high-resolution age model for 342 m of Late Pliocene–Middle Pleistocene marine deposits exposed in the Stirone River, northern Italy. Magnetostratigraphic analysis of 74 oriented samples at 21 stratigraphic horizons recognized five polarity zones between c. 3.0 and 1.0 Ma. Unoriented samples were collected every metre between 0 and 311 m and low-field magnetic susceptibility (χ) was measured for cyclostratigraphic analysis. The χ data series was tied to absolute time using the magnetostratigraphy and subjected to multi-taper method spectral analysis. The resultant power spectra revealed significant frequency peaks that are aligned with eccentricity, obliquity and precession Milankovitch orbital cycles. The χ data, correlated to the 41 ka obliquity and the 23 ka/19 ka precession cycles and anchored to a well-established biostratigraphic horizon, were used to create a high-reso...

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