GEOKEMIJA I MAGNETSKA ANALIZA STIJENA POVRŠINSKOGA SEDIMENTA RIJEKE LAMPENISU: POTRAGA ZA IZVOROM MAGNEZIJA U JEZERU TOWUTI, INDONEZIJA

Sediment from Lake Towuti has been extensively studied to reconstruct past climate and environmental changes. One of the remaining questions is the source of magnesium (Mg) and calcium (Ca) in the northern part of Lake Towuti. In this study, the source of high Mg and Ca content is examined by analysing surface sediment from the Lampenisu River (LR) and Mahalona River (MR) that merge before entering Lake Towuti. Twelve surface sediments from MR, LR, and the confluence of the two rivers (LMR) were subjected to geochemical (XRF), mineralogical (XRD), and rock magnetic (susceptibility and hysteresis parameter) analyses. The result shows that the Mg and Ca content in LR samples are higher than in MR samples. LR samples have a higher susceptibility and a lower frequency dependent susceptibility than MR samples. XRD analyses on extracted magnetic grains show the presence of minerals with a sodalite crystal structure, possibly valleyite in LR but not in MR samples. If valleyite indeed occurs in LR samples, it may contribute to their relatively high Ca content. At the same time, the high content of Mg in LR samples is likely due to the serpentinized peridotite rocks. LR is thereby considered to be the source of high Mg and Ca content in the northern portion of Lake Towuti. This study shows the importance of sediment-source identification in big lakes such as Lake Towuti, where the influx could come from several rivers around the lake.Sediment iz jezera Towuti opsežno je istraživan kako bi se rekonstruirale klimatske i okolišne promjene u prošlosti. Jedno od preostalih pitanja jest izvor magnezija (Mg) i kalcija (Ca) u sjevernome dijelu jezera Towuti. U ovome istraživanju izvor visokoga sadržaja Mg i Ca ispitan je analizama površinskoga sedimenta iz rijeke Lampenisu (LR) i rijeke Mahalona (MR) koje se spajaju prije ulaska u jezero Towuti. Dvanaest površinskih sedimenata iz MR, LR i ušća dviju rijeka (LMR) podvrgnuto je geokemijskoj (XRF), mineraloškoj (XRD) i magnetskoj analizi stijena (susceptibilnost i parametar histereze). Rezultat pokazuje da je sadržaj Mg i Ca u LR uzorcima veći nego u MR uzorcima. LR uzorci imaju veću susceptibilnost i manju susceptibilnost ovisnu o frekvenciji od MR uzoraka. XRD analize ekstrahiranih magnetskih zrnaca pokazale su prisutnost minerala s kristalnom strukturom sodalita, moguće valleyita u LR, ali ne i u MR uzorcima. Ako se valleyit doista pojavljuje u LR uzorcima, to može pridonijeti njihovu relativno visokom sadržaju Ca. Istodobno, visok sadržaj Mg u uzorcima LR vjerojatno je posljedica serpentiniziranih stijena peridotita. S obzirom na navedeno, LR se smatra izvorom visokoga sadržaja Mg i Ca u sjevernome dijelu jezera Towuti. Ovo istraživanje pokazalo je važnost identifikacije izvora sedimenta u velikim jezerima kao što je jezero Towuti, gdje donos materijala može dolaziti iz nekoliko rijeka oko samoga jezera

PEDOGENEZA LATERITNIH TALA I OBOGAĆIVANJE KRITIČNIH METALA: STUDIJA IZ JUGOISTOČNE SULAWESI, INDONEZIJA

Lateritic soil is a prospective source of metals termed critical or strategic metals due to their use in high-technology industries. Critical metals include rare earth elements (REEs). In this study, two profiles of lateritic outcrops from the Ni-producing area of Southeast Sulawesi in Indonesia were sampled for magnetic susceptibility as well µ-XRF analyses to identify how the concentration of critical metals changed during pedogenesis. The results show that there are three different patterns from the bottom layer up. The first pattern is enrichment experienced by Sc, La, Cr, and Ti. The second pattern is depletion experienced by Ni, Nd, and Ho. The third pattern is the localization of high concentration at a certain depth, as experienced by Co, Ce, and V. The concentration of certain critical metals correlates either positively or negatively with magnetic susceptibility, inferring that magnetic susceptibility might be used as a proxy indicator for critical metal concentration in lateritic soil.Lateritno tlo je potencijalni izvor metala koji se nazivaju kritični ili strateški metali zbog njihove upotrebe u industrijama visoke tehnologije. Kritični metali uključuju elemente rijetkih zemalja (REE). U ovom istraživanju uzorkovana su dva profila lateritnih izdanaka iz područja proizvodnje nikla u jugoistočnom Sulawesi u Indoneziji, s ciljem definiranja promjene koncentracija kritičnih metala tijekom pedogeneze korištenjem magnetne susceptibilnosti i μ-XRF analiza. Rezultati su ukazali na postojanje tri različita obrasca od donjeg sloja prema gore. Prvi obrazac predstavlja obogaćivanje Sc, La, Cr i Ti. Drugi obrazac predstavljen je sniženjem koncentracija Ni, Nd i Ho. Treći obrazac predstavlja lokalizaciju visokih koncentracija određenih metala na određenoj dubini, kao što su Co, Ce i V. Koncentracija nekih kritičnih metala korelira bilo pozitivno ili negativno s magnetnom susceptibilnosti, što upućuje na to da bi se magnetna susceptibilnost mogla koristiti kao indikator kritičnih koncentracija metala u lateritnom tlu

Karakterisasi Mineral Magnetik Sedimen Sungai Citarum Hilir Melalui Analisa Sifat Magnetik, Mineralogi serta Morfologi Magnetik

Sungai Citarum merupakan sungai utama yang ada di Provinsi Jawa Barat yang sangat penting bagi kehidupan sosial dan ekonomi. Di bagian hilir, Sungai Citarum ini banyak melewati daerah pemukiman padat penduduk, daerah industri, dan bahkan pesawahan. Oleh karena itu, perlu kajian mengenai kondisi Sungai Citarum salah satunya dengan mengidentifikasi parameter electrical conductivity (EC), total dissolve solid (TDS), pH dan suhu serta karakteristik mineral magnetik pada sedimen melalui analisis sifat magnetik, mineralogi dan morfologi magnetiknya. Pengukuran parameter EC, TDS, pH dan suhu dilakukan secara in situ pada sampel air Sungai Citarum, pengukuran sifat magnetik dilakukan pada sampel sedimen yang telah dipreprasi, sedangkan pengukuran mineralogi dan morfologi dilakukan pada sampel sedimen yang telah diekstraksi. Sifat magnetik sedimen diketahui dari nilai suseptibilitas magnetik dual frekuensi yang diukur menggunakan Bartington Magnetik Susceptibilitymeter, sedangkan mineralogi dan morfologi magnetik diketahui berdasarkan hasil pengukuran scanning electron microscope–energy disperdsive x-ray (SEM-EDS) dan x-ray diffractometer (XRD). Hasil pengukuran secara in situ pada sampel air menunjukkan bahwa rentang nilai EC, TDS, pH dan suhu berturut-turut adalah (200–4120) mS/cm, (100–2060) ppt, 7,34–9,22, dan (26,8–32,6) oC. Sedangkan, hasil pengukuran sifat magnetik menunjukkan bahwa sampel sedimen Sungai Citarum bagian hilir memiliki nilai suseptibilitas magnetik frekuensi rendah (cLF) dengan rentang (65,00–173,80) x 10-8 m3/kg, sedangkan rentang nilai suseptibilitas magnetik frekuensi tinggi (cHF) adalah (64,90–165,70) x 10-8 m3/kg. Dari kedua pengukuran cLF dan cHF diperoleh rentang nilai cFD (%) sebesar 0,15–4,66. Selanjutnya, hasil analisis morfologi dari citra SEM-EDS dan analisis mineralogi berdasarkan pengukuran XRD menunjukkan dominasi jenis mineral magnetik pada sampel sedimen adalah magnetit. Mineral magnetit ini memiliki morfologi berbentuk oktahedral sebagai representasi mineral magnetik alami dan ada pula yang berbentuk spherule sebagai representasi mineral magnetik karena adanya proses oksidasi akibat kehadiran material antropogenik pada sedimen Sungai Citarum bagian hilir

PRELIMINARNA PETROMAGNETSKA ISTRAŽIVANJA LAVA IZ 1849., 1926., 1963., 1968. I 1974. GODINE IZ VULKANA BATUR, BALI, INDONEZIJA: UVID U MAGMATSKI PROCES IZVORA I MAGNETSKU PRIRODU STIJENA

Geochemical and petrographic characterizations were carried out on five episodic effusive eruptions from Batur Volcano on the Island of Bali, Indonesia, and revealed that these lavas are basaltic to andesitic in composition. Various micro-textures were identified, reflecting pre-eruptive magmatic processes, magma mixing, and adiabatic decompression. Apart from XRF analyses, the five lava flows (L849, L926, L963, L968 and L974) were subjected to magnetic analyses in the form of magnetic susceptibility and magnetic hysteresis measurements. The presence of cyclicity in the magmatic process is suggested by the variation of micro-texture types, CaO content, and magnetic susceptibility values. Two possible models of this cyclicity are presented. In the first model, cyclicity is driven by the variation of influx from the lower magma chamber that affects the interaction of magma with the surrounding rocks. In the second model, cyclicity is affected by the appearance of a new magmatic vent, which causes intense interaction with surrounding rocks. This study infers that combined micro-texture, composition, and magnetic susceptibility analyses might provide insight into the cyclicity of lava episodes observed in active volcanos such as Batur.Geokemijska i petrografska istraživanja provedena na pet epizodnih efuzivnih erupcija iz vulkana Batur na otoku Baliju, Indonezija, otkrila su kako su te lave bazaltnoga do andezitskoga sastava. Prepoznate su različite mikroteksture odražavajući magmatske procese koji su prethodili erupcijama, kao i miješanje magme te adijabatska dekompresija. Načinjene su XRF analize, uz koje su pet tokova lave (L849, L926, L963, L968 i L974) također ispitani magnetskim analizama mjerenja magnetske susceptibilnosti i histereze. Na cikličnost magmatskoga procesa upućuju varijacije vrsta mikrotekstura, sadržaja CaO i vrijednosti magnetske susceptibilnosti. Prikazana su dva moguća modela navedene cikličnosti. U prvome modelu cikličnost je prouzročena varijacijom dotoka iz donje komore magme, što je utjecalo na njezino međudjelovanje s okolnim stijenama. U drugome modelu na cikličnost utječe pojava novoga magmatskog toka koji ima snažno međudjelovanje s okolnim stijenama. Studija upućuje na to da zajedničko korištenje analize mikrotekstura, sastava i magnetske susceptibilnosti može dati uvid u cikličnost epizoda istjecanja lave opaženih u aktivnim vulkanima kao što je Batur

Lithogenic and Anthropogenic Components in Surface Sediments from Lake Limboto as Shown by Magnetic Mineral Characteristics, Trace Metals, and REE Geochemistry

Lake Limboto is one of the major lakes in Sulawesi, Indonesia. It is currently undergoing serious degradation due to population pressure. As more residential areas have been established around the lake, the sedimentation rate has increased because of the contribution of anthropogenic particles. In this study, the lithogenic and anthropogenic components in surface sediments from 17 points in the lake were studied and identified using a combination of magnetic and geochemical analyses. The results showed that although the magnetic susceptibility values in R (residential) and NR (non-residential) areas were relatively similar, the values of saturation isothermal remanent magnetization (SIRM) as well as those of SIRM/χLF differed significantly, implying that the magnetic characteristics of the lithogenic component (in the NR area) differ from those of the anthropogenic component (in the R area). The discrepancy between the anthropogenic and lithogenic contributions was further supported by trace metals and rare earth element (REE) contents. Sediment samples in the R area contained higher levels of Mn, La, Pr, and Gd, while in the NR area they contained higher levels of Fe, Sc, Nd, and Ce. The magnetic susceptibility also correlated strongly with Fe, Cu, Zn, and Mn contents in the NR area. A similar correlation was not observed in the R area. The results above imply that a combination of magnetic and geochemical analyses can successfully differentiate lithogenic and anthropogenic components or contributions in lake sediments

Variations in the Concentration of Magnetic Minerals and Heavy Metals in Suspended Sediments from Citarum River and Its Tributaries, West Java, Indonesia

The Citarum River has a volcanic catchment area in West Java Province, and is one of the nationally strategic rivers in tropical Indonesia due to its roles in water supply and in power generation. The river is economically important, but it is also polluted by industrial, agricultural, and residential wastes. Suspended sediment samples were collected along a certain section of the Citarum River, starting in Balekambang through the area of Bandung Regency to the downstream village of Nanjung, where the river is dammed. Similar samples were also collected from seven tributaries of the Citarum River. Magnetic and heavy metal analyses show that unlike river sediments from a non-volcanic catchment area in temperate climates, magnetic susceptibility values tend to decrease downstream, showing that the magnetic minerals in the upstream area are mostly lithogenic in origin, containing more Fe-bearing minerals compared to those in tributary samples which are anthropogenic in origin. Anthropogenic pollution is also represented by the increase of Zn content along the river. The results suggest that applying magnetic methods for monitoring river pollution in the tropics or in the volcanic areas should be carefully analyzed and interpreted

A high-resolution, 60 kyr record of the relative geomagnetic field intensity from Lake Towuti, Indonesia

Past changes in the Earth\u27s magnetic field can be highlighted through reconstructions of magnetic paleointensity. Many magnetic field variation features are global, and can be used for the detailed correlation and dating of sedimentary records. On the other hand, sedimentary magnetic records also exhibit features on a regional, rather than a global scale. Therefore, the development of regional scale magnetic field reconstructions is necessary to optimize magnetic paleointensity dating. In this paper, a 60 thousand year (kyr) paleointensity record is presented, using the core TOW10-9B of Lake Towuti, located in the island of Sulawesi, Indonesia, as a part of the ongoing research towards understanding the Indonesian environmental history, and reconstructing a high-resolution regional magnetic record from dating the sediments. Located in the East Sulawesi Ophiolite Belt, the bedrock surrounding Lake Towuti consists of ultramafic rocks that render the lake sediments magnetically strong, creating challenges in the reconstruction of the paleointensity record. These sediment samples were subject to a series of magnetic measurements, followed by testing the obtained paleointensity records resulting from normalizing natural remanent magnetization (NRM) against different normalizing parameters. These paleointensity records were then compared to other regional, as well as global, records of magnetic paleointensity. The results show that for the magnetically strong Lake Towuti sediments, an anhysteretic remanent magnetization (ARM) is the best normalizer. A series of magnetic paleointensity excursions are observed during the last 60 kyr, including the Laschamp excursion at 40 kyr BP, that provide new information about the magnetic history and stratigraphy of the western tropical Pacific region. We conclude that the paleointensity record of Lake Towuti is reliable and in accordance with the high-quality regional and global trends