Sekuen Pengendapan Sedimen Miosen Tengah Kawasan Selat Madura

ABSTRACT Penelitian sekuen pengendapan sedimen telah dilakukan di kawasan Selat Madura.Daerah penelitian termasuk dalam Cekungan belakang busur Jawa Timur Utara. Penelitian difokuskan pada sedimen Miosen Tengah yang merupakan reservoar utama di cekungan ini. Tujuan dari penelitian ini adalah untuk mengetahui runtunan stratigrafi sikuen dan penyebaran system tract-nya yang selanjutnya diaplikasikan untuk mengetahui daerah yang potensial menjadi pemerangkap hidrokarbon. Berdasarkan hasil analisis stratigrafi sikuen dengan menggunakan 18 lintasan seismik dan 2 data sumuran, daerah penelitian terbagi menjadi lima runtunan pengendapan yaitu Sikuen Miosen Tengah – 1 (Sikuen MT – 1) yang terdiri dari Lowstand System Tract Miosen Tengah – 1 (LST MT – 1), Transgressive System Tract Miosen Tengah – 1 (TST MT -1) dan Highstand System Tract Miosen Tengah – 1 (HST MT – 1); Sikuen Miosen Tengah – 2 (Sikuen MT – 2) yang terdiri dari TST MT –2 dan HST MT – 2; Sikuen Miosen Tengah – 3 (Sikuen MT – 3) yang terdiri dari LST MT – 3, TST MT –3 HST MT – 3; Sikuen Miosen Tengah – 4 (Sikuen MT – 4) yang terdiri dari LST MT – 4, TST MT – 4 dan HST MT – 4; dan Sikuen Miosen Tengah – 5 (Sikuen MT – 5) yang terdiri dari TST MT – 5 dan HST MT – 5. Prospek pemerangkapan hidrokarbon di daerah penelitian dijumpai di beberapa bagian. Prospek pemerangkapan hidrokarbon pada endapan LST MT – 3 berupa perangkap antiklin. Prospek pemerangkapan hidrokarbon pada endapan LST MT – 4 yaitu perangkap struktur berupa antiklin dan perangkap stratigrafi berupa pembajian endapan LST MT – 4 sebagai reservoar pada tinggian Miosen Awal. Prospek pemerangkapan hidrokabon pada HST MT – 2 berupa perangkap antiklin. Prospek pemerangkapan hidrokarbon pada HST MT – 3 dan HST MT – 4 berupa perangkap antiklin di dua daerah dan pada endapan HST MT – 5 prospek pemerangkapan hidrokaron juga berupa struktur antiklin.

ODREĐIVANJE TEKSTURE I GEOKEMIJSKIH OBILJEŽJA ELEMENATA TALOŽINA MORSKOGA DNA UPORABOM MULTIVARIJANTNE ANALIZE, PODBAZEN SIMEULUE, INDONEZIJA

The Simeulue sub-basin is situated off north-western Sumatra between the outer arc and the mainlands. The sediment and geochemical element characteristics of basins are the important sedimentology variables to recognize the process of sediment deposition. However, the characteristics of the sediment and the geochemical elements in the Simeulue subbasin have not been well explained. This study aims to investigate the textural and geochemical elements characteristics of marine sediments and the distribution of these two variables to determine the sedimentary facies in the Simeulue sub-basin. Samples were taken from various depths in the sub-basin and collected during the 2017 Expedition of “Widya Nusantara” by using the “Baruna Jaya VIII” Research Vessel. The grain size trend analysis showed that the middle part of the basin was dominated by mud, while the edge of the basin near the island (mainland) was mostly dominated by coarser sediments. A geochemical element analysis was performed on each sample to observe the origin of the sediments. The results of these two analyses were subjected to multivariate statistics. This approach was selected because it is appropriate for determining the sedimentary facies and the depositional environments. Based on the multivariate analysis, the sedimentary facies in the Simeulue sub-basin was divided into five facies with similar sediment characteristics and depositional environments. These facies were deposited in the environment with low to medium energy.Podbazen Simeulue nalazi se uz sjeverozapadni rub Sumatre, između vanjskoga luka i kopna. Taložna i geokemijska obilježja bazena važne su sedimentološke varijable u prepoznavanju taložnih procesa. Te varijable u analiziranome prostoru do sada nisu bile dobro proučene. Stoga su istražene u ovome radu te je napravljena njihova razdioba kako bi se utvrdili taložni facijesi u tome podbazenu. Uzorci su uzeti na različitim dubinama tijekom ekspedicije „Widya Nusantara” 2017. godine, obavljene istraživačkim brodom Baruna Jaya VIII. Analiza trenda veličine zrna pokazala je kako u srednjemu dijelu bazena prevladava mulj, dok je na rubovima, u blizini kopna (otoka Sumatre) istaložen krupniji detritus. Geokemijska analiza načinjena je na svakome pojedinačnom uzorku s ciljem određivanja njegova podrijetla. Rezultati su naknadno analizirani multivarijantnom statistikom koja je odabrana kao najprimjereniji alat za određivanje taložnih facijesa i okoliša. Temeljem takve analize podbazen Simeulue podijeljen je u pet taložnih facijesa sa sličnim svojstvima taložina. Taložni okoliš bio je sličan, niskoenergijski do srednjoenergijski

KARAKTERISTIK ENDAPAN TSUNAMI KRAKATAU 1883 DI DAERAH TARAHAN, LAMPUNG

Our research location is situated at the south of Tarahan city, Lampung. This area has been drowned by tsunami waves that were generated by the eruption of Krakatau Volcano in 1883. This study is to understand the characteristics of the 1883 Krakatau tsunami deposit by observing the stratigraphic profile of 12 outcrops in the river overbanks and trenches, in 3 (three) transects. Laboratory analysis include grain size, microfauna (foraminifera and mollusk), and heavy mineral analysis. The identified tsunami deposit is a sand layer that mixed with shell and coral fragments. This sand layer is associated with pumice and volcanic ash layer, product of the 1883 Krakatau volcano eruption. The benthic foraminifera and mollusk content in the tsunami deposits show that the tsunami waves erode the sea floor sediments up to 30 to 40 meters depth. According to the outcrop observation and grain size analysis, there are four fining upward patterns can be observed in the tsunami deposit layer. This is indicates that at least four tsunami waves inundated the studied area. The vertical variation of heavy mineral shows the similar trend with the grain sizes. AbstrakLokasi penelitian terletak di sebelah selatan Kota Tarahan, Lampung merupakandaerah yang terkena dampak gelombang tsunami letusan Gunung Krakatau 1883. Penelitian inidilakukan untuk mengetahui karakteristik endapan tsunami Krakatau 1883 dengan mengamati profil stratigrafi pada dinding sungai dan parit uji pada 12 lokasi di 3 (tiga) transek. Analisis laboratorium meliputi analisis besar butir, mikrofauna (foraminifera dan moluska) dan mineral berat. Endapan tsunami yang teridentifikasi berupa lapisan pasir dengan pecahan cangkang dan fragmen karang. Lapisan pasir ini berasosiasi dengan lapisan abu vulkanik dan lapisan batuapung yang merupakan material hasil letusan Krakatau 1883. Kandungan foraminifera bentik dan moluska memperlihatkan bahwa gelombang tsunami menggerus dasar laut hingga kedalaman 30 - 40 m. Berdasarkan pengamatan singkapan dan analisis besar butir, terdapat empat pola perulangan struktur penghalusan besar butir ke arah atas dalam satu lapisan endapan tsunami. Hal itu menunjukkan bahwa kemungkinan ada empat gelombang tsunami yang terjadi pada saat itu. Hasil analisis mineral berat cenderung memperlihatkan pola perubahan komposisi ke arah atas mengikutiperubahan besar butir

HUBUNGAN VERTIKAL ANTARA KELIMPAHAN FORAMINIFERA DAN KARAKTERISTIK SEDIMEN INTI DI SELAT SUMBA, NUSA TENGGARA TIMUR

Data kelimpahan foraminifera dan karakteristik sedimen inti laut dalam digunakan sebagai proksi untuk merekonstruksi iklim, lingkungan, dan oseanografi di masa lalu. Penelitian ini menggunakan sebuah sampel sedimen inti laut dalam (ST-13) sepanjang 173 cm dari Selat Sumba, Nusa Tenggara Timur. Sampel sedimen tersebut diambil dengan menggunakan Kapal Riset Baruna Jaya VII pada saat Ekspedisi Widya Nusantara (E-WIN) tahun 2016. Sebanyak 22 subsampel sedimen diambil secara vertikal pada setiap interval delapan cm untuk analisa kelimpahan foraminifera, karakteristik fisik sedimen dan kandungan unsur kimianya. Tujuan dari penelitian ini adalah untuk mengetahui hubungan antara unsur biogenik (kelimpahan foraminifera) terhadap unsur anorganik (karakteristik fisik sedimen dan kandungan unsur kimia) melalui pengujian korelasi Pearson pada piranti lunak XLSTAT. Hasil analisis menunjukkan bahwa nilai korelasi yang tinggi antara kelimpahan foraminifera dengan nilai rata-rata, kemencengan, persentase pasir, Ca, dan Sr (-0,64, 0,72, 0,66, 0,71, dan 0,75). Sedangkan nilai korelasi yang lemah terjadi antara kelimpahan foraminifera terhadap pemilahan, kurtosis, Fe, Ti, dan K (-0,13, 0,43, -0,18, -0,43, dan -0,42). Nilai korelasi tersebut menunjukkan bahwa kelimpahan foraminifera mempengaruhi ukuran butir rata-rata, pergeseran distribusi kearah lebih kasar, persentase pasir, dan juga Ca dan Sr sebagai unsur dari cangkang foraminifera tersebut.Kata kunci: Kelimpahan foraminifera, karakteristik sedimen, korelasi Pearson, laut dalam, Selat SumbaData of foraminiferal abundance and deep sea core sediment characteristics are used as proxies to reconstruct climate, environment and oceanography in the past. A study was conducted on deep sea using a 173 cm length core sediment sample (ST-13) from the Sumba Strait, East Nusa Tenggara. This core was carried out from RV Baruna Jaya VIII during the Widya Nusantara (E-WIN) Expedition in 2016. The abundance of foraminifera, physical properties of sediment and chemical content were analyzed from 22 subsamples sediments at every eight cm intervals. The purpose of this study was to determine the relationship between biogenic elements (abundance of foraminifera) to organic elements (physical properties of sediment and chemical content) by Pearson’s correlation with XLSTAT software. The results showed that a strong correlation between foraminiferal abundance with mean, skewness, sand percentages, Ca, and Sr (-0.64, 0.72, 0.66, 0.71, and 0.75). Meanwhile, the weak correlation values occur between foraminiferal abundance and sorting, kurtosis, Fe, Ti, and K (-0.13, 0.43, -0.18, -0.43, and -0.42). It seems that foraminifera abundance affects the mean grain size, changes the distribution to more coarse, the percentage of sand, and also Ca and Sr as its from shell of the foraminifera.Keywords: Foraminifera abundance, sediment characteristics, Pearson’s correlation, deep sea sediment, Sumba Strait

DINAMIKA LINGKUNGAN PENGENDAPAN DELTA KALIGARANG, SEMARANG

Delta Kaligarang terletak di Utara Pesisir Semarang. Tujuan dari penelitian ini ialah untuk mengetahui dinamika lingkungan pengendapan yang terjadi di Delta Kaligarang, Semarang melalui analisis ukuran butir, material organik dan inorganik dari sembilan puluh contoh sampel. Hasil yang diperoleh menunjukkan adanya dua lingkungan pengendapan berdasarkan karakteristik sedimentologi (besar butir dan organik) yakni lingkungan energi relatif rendah (suspension load) dan lingkungan berarus turbulen (tidal). Selain itu, juga terdapat kenaikan nilai material organik dan inorganik, yang disertai adanya perubahan besar butir. Terlihat bahwa lapisan pada kedalaman 0-31 meter mengalami kenaikan nilai organik, seiring dengan besar butir yang berukuran silt. Hal tersebut berbeda dengan lapisan pada kedalaman 32-45 meter, di mana terdapat perselingan satuan batuan silt dan sand, serta nilai material organik turun.Kaligarang Delta is located in the North Semarang Coast. The objective of this research is to describe dynamic environmental changes in Kaligarang Delta based on grain size, organic and inorganic matters analyzes from ninety samples. The results indicated that two conditions occurred: low-energy-suspension-load environment and tidal (turbulent) environment. Furthermore, the increase of organic and inorganic matters coincides with the grain size distribution. At depth 0-31-meter, organic matter increased that coincident with silt grain size. At depth 32-45 meter the lithology shows interspersed of silt and sand

FASIES DAN LINGKUNGAN PENGENDAPAN BATUAN KARBONAT FORMASI PARIGI DI DAERAH PALIMANAN, CIREBON

ABSTRAK Batuan karbonat Formasi Parigi tersingkap baik di Komplek Kromong daerah Palimanan, Cirebon dimana studi fasies karbonat ini dilakukan.  Berdasarkan karakter fisik dan biota yang dikandungnya, batuan karbonat Komplek Kromong dapat dikelompokkan menjadi  7 fasies, yakni : (1) fasies boundstone, (2) fasies rudstone, (3) fasies cross bedded grainstone, (4) fasies foraminiferal packstone, (5) fasies algal-foram packstone,  (6) fasies floatstone, dan (7) fasies thin bedded wackestone-packstone. Fasies boundstone dapat dibagi menjadi 2 subfasies yaitu subfasies bafflestone dan subfasies framestone. Lingkungan pengendapan Formasi Parigi diperkirakan  diendapkan pada lingkungan reef front, reef crest, back reef, lagoon-surge chanel dan tidal flat-tidal chanel. Hasil analisis  fosil foraminifera besar menunjukkan  umur Formasi Parigi adalah Miosen Awal. Berdasarkan pada  pola lingkungan pengendapan Formasi Parigi diinterpretasikan terumbu bagian depan berada di sebelah timur laut, sedangkan terumbu bagian belakang di bagian baratdaya

DUBINA PROMJENE TERMOKLINA NA OTOKU SUMBA NA TEMELJU PLANKTONSKIH SKLOPOVA FORAMINIFERA I NJEGOVE IMPLIKACIJE NA EUTROFIKACIJU OD POSLJEDNJE DEGLACIJACIJE (~ 18 ka BP): PRELIMINARNA STUDIJA

Changes of the thermocline depth (DOT) at the Sumba Island offshore are not well-known compared to the DOT changes in the Timor Sea, the main exit passage of the Indonesian Through-flow (ITF). Planktonic foraminiferal assemblages in cores collected from the southwest Sumba offshore (ST08) and Sumba Strait (ST12, ST13, and ST14) were used as a tool to infer the DOT and paleoproductivity changes at the Sumba Island offshore. The DOT changes were indicated from the thermocline and mixed layer dwellers’ relative abundance while the paleoproductivity changes were indicated from the relative abundance of Neogloboquadrina dutertrei. This study suggests a contrast between the DOT pattern at the Sumba Island offshore and the DOT pattern in the Timor Sea during the Last Deglaciation–Holocene. The contrast DOT pattern indicated that the multi-millennial changes of the Australian-Indonesian monsoon (AIM) during the Last Deglaciation– Holocene were the main factors behind the DOT changes in this region while the effects of El Niño Southern Oscillation (ENSO) –like, Indian Ocean Dipole (IOD) –like, and ITF to DOT changes were minimal. Paleoproductivity enhancement at the Sumba Island offshore was not solely related to the monsoon-driven coastal upwelling intensification, which resulted in the DOT shoaling and eutrophic condition. The increase of nutrient availability in surface water due to river runoff increase and changes in the lifted water mass nature were also able to enhance productivity in this region.Područje ispitivanja nalazi se uz otok Sumba, a promjene dubine termokline (DOT) u ovoj regiji nisu dobro poznate u usporedbi s Timorskim morem. Zajednice planktonskih foraminifera korištene su za prepoznavanje DOT-a i promjene paleoproduktivnosti u jezgrama prikupljenim s jugozapadne Sumbe (ST08) i iz tjesnaca Sumba (ST12, ST13 i ST14). Ova studija sugerira da su tisućljetne promjene u režimu australsko-indonezijskoga monsuna (AIM) bile glavni čimbenik DOT promjena na jugozapadu Sumbe i tjesnaca Sumba nakon posljednje deglacijacije, što je stvorilo suprotne uvjete u odnosu na Timorsko more. Učinak poput južnih oscilacija El Niño (ENSO) i dipola Indijskoga oceana (IOD) sličnih DOT promjenama naznačen je samo oko kasnoga holocena, dok su promjene indonezijskoga protoka (ITF) utjecale samo na istočni tjesnac Sumba oko srednjega i kasnoga holocena. Produbljavanje termokline usko je povezano s poboljšanjem AIWM (AISM), El Niñom (La Niñom) i pozitivnim (negativnim) IOD-om. Poboljšanje paleoproduktivnosti nije bilo povezano samo s jačanjem DOT-a, već i s većom dostupnošću hranjivih sastojaka zbog povećanoga donosa slatke vode rijekama. Promjene u prirodi podignute vodene mase također su utjecale na promjene u paleoproduktivnosti

Palinologi Laut di Selat Sumba, Nusa Tenggara Timur

Penelitian ini merupakan bagian dari Ekspedisi Widya Nusantara 2016 yang bertujuan untuk merekonstruksi dinamika iklim dengan memperhatikan kondisi keanekaragaman morfologi polen, spora dan keanekaragaman flora sekitar perairan Selat Sumba pada Kala Holosen. Sedimen diambil menggunakan penginti gravitasi pada Kapal Riset Baruna Jaya VIII pada kedalaman kolom air 1283 m dengan panjang inti 243 cm. Kedalaman yang diamati yakni 0-102 cm dengan interval penyamplingan adalah 5 cm, sehingga diperoleh 22 sub-sampel. Jenis sedimen yang dominan adalah lanau sedangkan pasir hanya mendominasi bagian permukaan. Berdasarkan hasil analisis kuantitatif palinologi, lapisan dibagi menjadi empat zona dan untuk mengetahui umur dari tiap lapisan sedimen digunakan datum Foraminifera Globigerinella calida calida. Zona I dengan perkiraan umur  5662-7550 tahun yang lalu memiliki karakteristik, jenis Arboreal Pollen (AP) yang lebih dominan yakni Cupressaceae, sedangkan jenis spora yang dominan adalah Polypodiaceae dan Acrostichum aureum. Zona ini diintepretasikan beriklim panas dan basah, dengan nilai Pollen Marine Index (PMI) 100 dan indeks keanekaragaman adalah 0,35. Zona II berumur 4530-5662 tahun yang lalu dengan kehadiran Arboreal Pollen (AP) yang lebih dominan adalah Casuarinaceae dan spora Polypodiaceae, sehingga diintepretasikan iklimnya adalah panas dan basah, PMI = 105 dan Indeks keanekaragaman 1,56.  Zona III berumur  2265-4530 tahun terdapat Arboreal Pollen (AP) yakni Anonaceae 43,75 % dan Spora yakni Polypodiaceae 33 %, sehingga diintepretasikan beriklim panas dan basah, PMI= 118 serta Indeks keanekaragaman 2. Zona IV adalah lapisan paling muda berumur 2265-sekarang memiliki persentase Arboreal Pollen (AP) yang lebih dominan yakni Anonaceae sebanyak 44% dan adanya peningkatan kehadiran spora yakni taksa Acrostichum aureum sebanyak 41,2 %, PMI = 128,25 dan memiliki Indeks keanekaragaman 1. This research is part of Widya Nusantara Expedition 2016 aiming to reconstruct the dynamics of the climate by considering the condition of morphology of pollen, spore and the diversity of flora around the waters of the Sumba Strait in the time of Holocene. The sediment was taken using gravity corer on Research Vessel of Baruna Jaya VIII at a water column depth of 1283 m with a core length of 243 cm. The depth was observed at 0-102 cm and the sampling interval of 5 cm, so 22 sub-samples were obtained. The dominant type of sediment was silt and sand dominates on the surface. Foraminifera Globigerinella calida calida is used as a datum to determine relative age. Based on the results of the analysis, the layers are divided into four zones. Zone I with an estimated age of 5662-7550 years ago has a more dominant Arboreal Pollen (AP) type characteristic, namely Cupressaceae, while the dominant spores are Polypodiaceae and Acrostichum aureum. This zone is interpreted as a hot and wet climate, with a Pollen Marine Index (PMI) 100 and a diversity index of 0.35. Zone II was 4530-5662 years ago with the more dominant Arboreal Pollen (AP) presence being Casuarinaceae and Polypodiaceae spores, so the interpreted climate was hot and wet, PMI = 105 and the Diversity Index 1.56. Zone III aged 2265-4530 years. There are Arboreal Pollen (AP) i.e. Anonaceae 43.75% and Spores i.e. Polypodiaceae 33%, so it is interpreted as hot and wet climate, PMI = 118 and Diversity Index 2. Zone IV is the youngest layer of 2265 – now. It has the most dominant percentage of Arboreal Pollen (AP), Anonaceae as much as 44% and an increase in the presence of spores i.e. Acrostichum aureum taxes as much as 41.2%, PMI = 128.25 and has a Diversity Index of 1