Nanggulan Formation and Its Problem As a Basement in Kulonprogo Basin, Yogyakarta

Abstract

-Nanggulan Formation consists of the oldest clastic rock sequence exposed in Kulonprogo area, Yogyakarta. This paper discusses the position of Nanggulan Formation as a basement. The method used in this research is surface and subsurface investigations based on gravity surveys. The rock assemblage is exposed and distributed partly in the east flank of Kulonprogo Mountains with weak undulated morphology. The rock sequence is composed of sand to clay grain sizes such as sandstone, quartz sandstone, calcareous sandstone, claystone, fossiliferous claystone, calcareous claystone, siltstone, and coal seam intercalations. The total thickness of the sequence is less than 200 m. Based on the fossil and palynology investigations, previous investigators concluded the age of the rock was Eocene to Middle Miocene. The geological structures developed in the rocks are the lithological stratification, fractures, folding, and faulting. The subsurface interpretation based on gravity data revealed the rock was located under the andesite breccias with 2.44 g/cc density. The density of the rock sequence was 2.63 g/cc. The gravity interpretation shows a strong indication that Nanggulan Formation underlies the andesitic breccias presumably associated with Old Andesite Formation exposed in Kulonprogo Mountains. The limited distribution, the thickness, and the closed environmental deposition of Nanggulan Formation found in the present investigation raised problems on the position of the formation as the basement of Old Andesite Formation occurring in the Kulonprogo Mountain.

Kontrol Struktur Geologi Terhadap Kemunculan Formasi Nanggulan Di Daerah Kecamatan Naggulan Kabupaten Kulon Progo, Yogyakarta

“…Pada beberapa bagian Formasi Nanggulan, menunjukkan adanya pengaruh perlipatan dan pensesaran (Hartono and Sudradjat, 2017). Terdapat lipatan berupa sinklin dan antiklin serta sesar mendatar dextral.…”

Landslide Vulnerable Zones Based on Engineering Geological Assessment, Case Study: Wonotopo Area, Gebang District, Purworejo Regency, Central Java, Indonesia

“…The Nanggulan Formation consists of lignite insertion sandstones, claystone with limonite, marl, tuffaceous sandstone, Middle Eocene to Early Oligocene [4][5][6]. The Nanggulan Formation is overlain by Old Andesite Formation [6] or Kaligesing Formation and the Dukuh Formation [6].…”

“…The Kaligesing Formation is characterized by monomixed breccias, with andesite fragments, inserted by andesite sandstones and lava while the Dukuh Formation comprises polymixed breccias with andesite fragments, sandstones and limestones. The age of the formation is Late Oligocene-Early Miocene [4,6,7]. Above the Kaligesing-Dukuh Formation there are the Jonggrangan Formation and Sentolo Formation.…”

Hubungan Batu Gamping Formasi Sentolo dan Breksi Vulkanik Kulon Progo: Sebuah Koreksi Stratigrafi Studi Kasus di Daerah Wonotopo, Kecamatan Gebang, Kabupaten Purworejo, Jawa Tengah

“…Secara regional satuan litostratigrafi mulai dari yang tua ke muda terdiri dari Formasi Nanggulan, Formasi Kaligesing, Formasi Dukuh, Formasi Jonggrangan, Formasi Sentolo serta endapan gunung api Kuarter dan endapan aluvial. Menurut Hartono & Sudrajat (2017), Formasi Nanggulan merupakan formasi tertua di daerah Kulon Progo. Formasi tersebut diberi nama sebagai Nanggulan beds (Purnamaningsih dan Pringgoprawiro, 1981;Pringgoprawiro & Riyanto, 1987).…”

“…Formasi Nanggulan dicirikan oleh kehadiran batupasir bersisipan lignit, batulempung disertai konkresi limonit, napal, batupasir dan tufa. Berdasarkan kehadiran fosil-fosil foraminifera plangton, umur Formasi Nanggulan dapat ditentukan yaitu Eosen Tengah sampai Oligosen Awal (Hartono & Sudrajat, 2017). Menurut Van Bemmelen (1949), Suyanto & Roskamil (1975 dalam Hartono & Sudrajat (2017), serta Raharjo et.al.…”