Quaternary nannoplankton in the Northeast Java Basin

In Indonesia, nannofosils are commonly used for age estimation on Miocene marine sediment, but they are rarely performed on Quaternary sediment. This paper introduces two nannofossil biozones, Martini (1971) and Backman et al. (2012) and the comparison between the two biozones. An uninterrupted interval of marine sediments was described and picked for quantitative nannoplankton analysis. The samples were taken from Ledok Formation to Lidah Formation in Pati Region, Northeast Java Basin. The samples were prepared by quick smear slides method and and analyzed by quantitative field of view method. Martini (1971) biozone can be used to subdivide the Late Miocene–Pleistocene sediments into 5 biozones, but Backman et al. (2012) can be used to classify the same sediments into 8 biozones. The biozone subdivision from Backman et al. (2012) is more detailed than that of Martini (1971) because an updated dating and biozone in the three new dating zone data.

DISTRIBUTION OF SUBSURFACE QUATERNARY SEDIMENT IN SOUTH BINTAN ISLAND WATERS AS A POTENTIAL HEAVY MINERAL PLACER OR RARE EARTH ELEMENT DEPOSIT BASED ON SEISMIC INTERPRETATION

Bintan Island is one of the areas traversed by the Southeast Asian granitoid belt which is known to have the potential for heavy mineral placer deposits. Due to the dwindling presence of heavy mineral placer deposits in land areas, it is necessary to look for the potential presence of heavy mineral placer deposits in water areas. Searching for placer heavy mineral deposits accomodation in these waters requires subsurface mapping.The method used in this subsurface mapping is a single channel seismic method with a total of 179 lines in the direction of northeast – southwest and west – east. The results of this seismic recording are then interpreted the boundaries of the seismic facies unit and distributed using the kriging method. Furthermore, the thickness calculates by using the assumption velocity 1600 m/s.Based on the facies unit boundaries that have been interpreted, the quaternary sediments that formed in the study area are divided into 2 types of units, namely: Unit 2 which is estimated to be fluvial – transitional sediment, and Unit 1 which is estimated to be transitional sediment – shallow sea. There is also a difference in thickness patterns in these two units, where unit 2 shows a pattern of sediment thickening that resembles a paleochannel trending northeast – southwest, while unit 1 is relatively uniform.From the results of this study, it can be said that the area that has potential for heavy mineral placer deposits is in the west - center of the southern waters of Bintan Island. Where the potential for heavy mineral placer deposits should be in the paleochannel deposits that are part of Unit 2.

Karakteristik Keteknikan Sedimen Kuarter Kaitannya dengan Potensi Bahaya Geologi di Kawasan DAS Cimanuk Bagian Hilir

ABSTRAKKabupaten Indramayu yang akan dikembangkan sebagai kawasan industri didominasi oleh endapan Kuarter yang terdiri atas endapan fluvial, dataran banjir, pematang pantai, dan delta. Daerah tersebut terletak pada area dekat sesar aktif, yakni segmen sesar Baribis-Subang dengan besaran magnitudo 6,5 Mw. Penelitian di wilayah DAS Cimanuk bagian hilir Kabupaten Indramayu, Provinsi Jawa Barat bertujuan untuk mengetahui karakteristik fisik dan mekanik serta kaitannya dengan potensi bahaya geologi yang bisa terjadi. Metode yang digunakan dalam penelitian ini adalah pengamatan 4 inti bor teknik dan pola kurva sondir (10 CPTu dan 13 CPT) serta analisis laboratorium yakni ukuran butir, hydrometer, batas-batas Atterberg, dan klasifikasi sedimen. Berdasarkan pengamatan inti bor, pola kurva sondir, dan analisis laboratorium, jenis sedimen yang berkembang di daerah penelitian adalah lempung, lanau, lanau pasiran, pasir lanauan dan pasir dengan karakteristik yang spesifik. Tingkat kepadatan sedimen pasir serta tingkat konsistensi sedimen lempung bagian utara penelitian menunjukkan karakteristik yang relatif lebih lepas dan lunak dibandingkan dengan bagian selatan. Berdasarkan karakteristik keteknikan menunjukkan bahwa nilai N-SPT < 10 atau CPT/CPTu < 6.000 kPa pada sedimen pasir dan pasiran berpotensi terhadap likuefaksi dan nilai N-SPT < 4 atau CPT/CPTu < 5.000 kPa pada sedimen lempung dan lanau berpotensi terhadap amblesan. Kata kunci: bahaya geologi, Cimanuk, sedimen kuarterABSTRACTAs a future industrial area, Indramayu Regency is dominated by Quaternary sediment of fluvial, flood plain, beach ridge and deltaic sediments. The area is close to active faults, The Baribis-Subang fault segment with 6.5 Mw. This research is conducted around the lower Cimanuk catchment of Indramayu. Its aims to determine mechanical and physical characteristics related to potential geological hazards. The methods used in this research are 4 core observation, cone penetration patterns (10 CPTu and 13 CPT) and laboratory analysis such as grain size, hydrometer, Atterberg limits and sediment classification. Based on its methods, sediments that develop at the research area are clay, silt, sandy silt, silty sand and sand with specific character. Level consistency and density of clay and sand at the northern area is relatively soft and loose than the southern one. Based on engineering characteristics, the results show that NSPT < 10 or CPT/CPTu < 6,000 kPa value of sandy and sand sediment are potential against liquefaction and N-SPT < 4 or CPT/CPTu < 5,000 kPa value of silt and clay sediment are potential against subsidence. Keywords: geological hazards, Cimanuk, quarternary sediment

Lithological and geomorphological indicators of glacial genesis in the upper Quaternary strata, Nadym River basin, Western Siberia

Analysing the genesis of Quaternary sediments is important for understanding the glaciation history and development of marine sediments in the northern part of Western Siberia. The problem is relevant since there is no consistent concept of the Quaternary sediment genesis in the north of Western Siberia. The formation of sediments is associated with marine, glacial and interglacial sedimentation conditions. The research objective is to identify the persistent features characterising the conditions of sedimentation and relief formation using the Nadym River basin as an example. The best method for studying this problem is a comprehensive analysis of the lithological, chronostratigraphic, petrographic and geomorphological studies of the Quaternary sediment upper strata. This study provides data from the analysis of the basic characteristics of quartz grains at the site. The rounding and morphology of the quartz grains provide evidence of possible glacial processing of some of the site strata. A petrographic study of selected boulder samples was performed. Some of them, by the shape and presence of striation, can be attributed to ice basins. The first use of a detailed digital elevation model applied to the study area made it possible to identify specific relief forms that could very likely be created during glaciations. Based on the analysis, we propose to consider the vast lake alluvial plains in the Nadym River basin as periglacial regions. This idea lays the lithological framework for understanding the reasons for the formation of the modern landscape structure. The materials and descriptions provided are of interest to researchers of Quaternary sediments, topography, vegetation and soil cover, particularly researchers engaged in revising the history of the natural environment development in the north of Western Siberia.

Sedimentological, Mineralogical and Geochemical Features of Late Quaternary Sediment Profiles from the Southern Tuscany Hg Mercury District (Italy): Evidence for the Presence of Pre-Industrial Mercury and Arsenic Concentrations

Southern Tuscany (Italy) is an important metallogenic district that hosts relevant S-polymetallic deposits that have intensely been exploited for centuries. Consequently, potential toxic elements, such as Hg and As, are widely distributed in the surrounding environment. In this paper, an extensive sedimentological, mineralogical and geochemical study of two Late Quaternary sediment profiles, partially outcropping along the coast of southern Tuscany (Ansedonia area), was carried out to evaluate the contents and mobility of Hg and As with the aims to contribute to the definition of the geochemical baseline of southern Tuscany before the human intervention and evaluate the potential dispersion of these harmful elements. The sedimentological, mineralogical and geochemical (major elements) features revealed that the studied profiles are mostly related to the local geological characteristics and the Quaternary geological history of the area. The concentrations and the normalized patterns of trace and rare earth elements highlighted the absence of any anthropogenic activity. This implies that the studied samples are to be regarded as good proxies for evaluating the geochemical baseline of southern Tuscany before the intense mining activity. The enrichment factors (EF) of most trace elements were indeed lower or close to 2, indicating a variability close to the average concentration of the Upper Continental Crust (UCC), while other elements slightly enriched, such as Pb, were in agreement with the natural baseline reported for southern Tuscany. Mercury and As displayed EF values >40 when compared to the average contents of UCC, although they decrease down to 4 when compared to the suggested baseline for southern Tuscany. The higher Hg and As contents detected in this study, inferred to natural sources, evidenced (i) the great natural variability occurring in largely mineralized areas and (ii) the importance of estimating reference environmental parameters in order to avoid misleading interpretations of the detected anomalies. Moreover, the results of leaching test on sediment samples denoted a relatively low mobility of Hg and As, suggesting that these elements are preferentially mobilized by transport of clastic sediments and such anomalies may be preserved for relatively long times in Quaternary sediments. However, leachable Hg (0.6–9.7 μg/L) and As (2.1–42.2 μg/L) concentrations are significantly high when compared to those of the Italian limit for groundwater (1 µg/L for Hg and 10 µg/L for As). Quaternary sediments from southern Tuscany could then be a potential, though natural, source of Hg and As to groundwater systems.