Inconsistent magnetic polarities between greigite- and pyrrhotite/magnetite-bearing marine sediments from the Tsailiao-chi section, southwestern Taiwan

Horng, Chorng‐Shern; Torii, Masayuki; Shea, Kai-Shuan; Kao, Shuh‐Ji

doi:10.1016/s0012-821x(98)00239-8

Cited by 90 publications

(108 citation statements)

References 40 publications

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“…In the mudstone sequences, as indicated by the representative EJC section in Fig. 1b, widespread distribution of greigite has been reported in rocks for an area of 600-km 2 (Horng et al 1992(Horng et al , 1998Torii et al 1996). Coral reef limestones, overlying the mudstones, crop out on the local topographic highs that are closely linked to thrust faulting (Gong et al 1996).…”

Section: Geological Backgroundmentioning

confidence: 91%

“…Inland of southwestern Taiwan, authigenic greigite has been widely found in the PlioPleistocene marine sedimentary sequences (Horng et al 1992(Horng et al , 1998Torii et al 1996). It commonly occurs in fine-grained mudstones in contrast to magnetite that survives and predominates in the sandy strata.…”

Section: Implications Of Carbon-sulfur-iron Signatures For the Occurrmentioning

confidence: 99%

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Complicated Magnetic Mineral Assemblages in Marine Sediments Offshore of Southwestern Taiwan: Possible Influence of Methane Flux on the Early Diagenetic Process

Horng¹,

Chen²

2006

Terr. Atmos. Ocean. Sci.

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ABSTRACT1 Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan, ROC * Corresponding author address: Dr. Chorng-Shern Horng, Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan, ROC; E-mail: cshorng@earth.sinica.edu.twIn this paper, we present the results of down core variations in magnetic susceptibility and magnetic mineral composition of fifteen piston cores retrieved from the active continental margin offshore of southwestern Taiwan, where a wide distribution of bottom simulating reflectors (BSRs) related to gas hydrate layers has been detected. X-ray analysis on magnetic extracts from the cores indicates that detrital magnetite and authigenic greigite, in various proportions, are the dominant magnetic minerals in sediments. Non-magnetic, authigenic pyrite is generally associated with greigite, but it may co-exist with magnetite or may solely occur in sediments. Consequently, the sediment sequences of the fifteen piston cores have complicated magnetic mineral assemblages that result in various magnetic susceptibility profiles. For core segments containing detrital magnetite as the only magnetic mineral, values of magnetic susceptibility are moderate with small variations (8 -15 × 10 -6 SI), which can be regarded as the susceptibility backgrounds for the initially deposited sediments. However, high magnetic susceptibilities relative to the backgrounds were found in core segments where magnetic mineral is enriched in greigite. Magnetic susceptibilities lower than the backgrounds were found in segments where neither magnetite nor greigite were detected. The complicated occurrence of magnetic minerals reveals that their host sediments at different levels have suffered various degrees of early diagenetic process ranging from oxic to anoxic conditions. Due to very low sedimentary organic matter content in the study area, detrital magnetite persisted in sediments that were subjected to Terr. Atmos. Ocean. Sci., Vol. 17, No. 4, December 2006 1010 initially oxic (or sub-oxic) conditions. However, the sedimentary organic matter is apparently insufficient for providing reducing environments for the formation or enrichment of authigenic iron sulfides. Instead, we propose that gaseous methane derived from gas hydrates in deeper sedimentary layers should be the most likely source of extra organic matter. The different flux intensities of this gas either through slow diffusion or rapid venting resulted in various anoxic conditions, which caused the dissolution or survival of magnetite and the formation or enrichment of greigite and pyrite.

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Section: Geological Backgroundmentioning

confidence: 91%

Section: Implications Of Carbon-sulfur-iron Signatures For the Occurrmentioning

confidence: 99%

Complicated Magnetic Mineral Assemblages in Marine Sediments Offshore of Southwestern Taiwan: Possible Influence of Methane Flux on the Early Diagenetic Process

Horng¹,

Chen²

2006

Terr. Atmos. Ocean. Sci.

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“…Moreover, their occurrence depends also on the sediment grain size. Greigite occurs mainly in fine-grained sediments, whereas pyrrhotite is present in coarser grained sediments (Horng et al 1998). In the following paragraph, the differences in the magnetic mineralogy, i.e., greigite versus pyrrhotite, are not taken into account for understanding the distribution of the IS layers at Site C0008.…”

Section: Sf=5mentioning

confidence: 99%

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

Kars

Kodama

2015

Earth Planet Sp

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A high-resolution rock magnetic study was carried out in Integrated Ocean Drilling Program (IODP) Expedition 316 Hole C0008A located in the Megasplay Fault Zone of the Nankai Trough, SW offshore Japan, in order to document changes in magnetic properties throughout gas hydrate-bearing horizons. A total of 169 Pleistocene discrete samples were collected from~110 to 153 m core depth below sea floor (CSF), and their magnetic minerals concentration, grain size, composition, and rock magnetic parameters were estimated. Results showed the presence of iron oxides ((titano)-magnetite), iron sulfides (greigite and pyrrhotite), and their mixture, among which single-domain greigite is the most major magnetic mineral present in the samples. Two horizons containing ferrimagnetic iron sulfides (114.5-127.5 and 129.5-150 m CSF) covering almost the entire studied interval were identified, both associated with slight local pore water anomalies, suggesting occurrence of gas hydrates and anoxic conditions. These results are different from the neighboring Hole C0008C (215 m away from Hole C0008A) where four pore water anomalies and six iron sulfide-rich intervals were identified for the same time slice. Comparison of the lithology, physical properties, and geochemical data of the two boreholes at Site C0008 suggests that a combination of processes (e.g., availability of reactive iron, microbial activity) is responsible for such laterally varying distribution of the ferrimagnetic iron sulfides.

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“…The samples are from Pleistocene marine sediments of the Tsailiao-chi (TLC) section, southwestern Taiwan [Horng et al, 1998]. A total of four samples (TLC383.4A, 387.3C, 394.3B and 397.1B) were selected to elucidate the behavior of AC magnetic noise fields generated by the heater currents.…”

Section: Laboratory Tests For Spurious Magnetization and Comparison Omentioning

confidence: 99%

A new high‐precision furnace for paleomagnetic and paleointensity studies: Minimizing magnetic noise generated by heater currents inside traditional thermal demagnetizers

Zheng¹,

Zhao

Horng

2010

Geochem Geophys Geosyst

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[1] Although magnetic noise fields generated by heater currents in thermal demagnetizers have been noticed for a long time, no satisfactory tests have been conducted to quantify their effects. Toward this end, we have developed a new high-precision thermal demagnetizer that greatly reduces the magnetic noise field. We show the data quality generated by the new oven and the comparative results on several real samples that demonstrate the effects of the magnetic noise field due to heater currents. The properties of the spurious magnetization emanating from the heater currents critically depend on the decay rate of amplitude and its waveform of electric power which is delivered to oven coils at the end of the heating stage of thermal demagnetization. These results also illustrate the potential applications of this new instrument in paleomagnetism and paleointensity studies.

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Inconsistent magnetic polarities between greigite- and pyrrhotite/magnetite-bearing marine sediments from the Tsailiao-chi section, southwestern Taiwan

Cited by 90 publications

References 40 publications

Complicated Magnetic Mineral Assemblages in Marine Sediments Offshore of Southwestern Taiwan: Possible Influence of Methane Flux on the Early Diagenetic Process

Complicated Magnetic Mineral Assemblages in Marine Sediments Offshore of Southwestern Taiwan: Possible Influence of Methane Flux on the Early Diagenetic Process

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

A new high‐precision furnace for paleomagnetic and paleointensity studies: Minimizing magnetic noise generated by heater currents inside traditional thermal demagnetizers

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