Abstrak
Formasi Kabuh merupakan salah satu formasi yang cukup luas tersingkap di daerah Sangiran. Penelitian secara rinci mengenai Formasi Kabuh di Sangiran masih perlu dilakukan, terutama pada daerah yang belum pemah dilakukan pengukuran stratigrafi. Lokasi penelitian terletak pada daerah Jagan, Kec. Kalijambe, Kab. Sragen, Provinsi Jawa Tengah. Penelitian dilakukan pada dua jalur. Jalur pertama dimulai dari koordinat S 07°27’58,4”- E 110°5ri7,7”hingga S 07°27’58,9”- E 110°51’18,3”. Jalur kedua dimulai dari koordinat S 07° 27 59″- E 110° 51′ 04″ hingga S 07° 28’ 00″- E 110° 51′ 12”. Fokus penelitian pada Formasi Kabuh bagian paling bawah, yaitu dari kontak Formasi Pucangan dan Formasi Kabuh hingga lapisan tuf pertama. Metode yang digunakan adalah pengukuran stratigrafi dengan skala 1:10 dan arah arus purba. Formasi Kabuh paling bawah pada daerah Jagan terdiri dari 18 litofasies yang tersusun oleh batulempung hitam (Fsm), konglomerat karbonatan (Gt-Gh), batupasir karbonatan (Stl-Sh2-Sr2), batupasir silangsiur palung dengan ukuran sedang-kerikil (St2-St3-St4-St5-St6), batupasir silangsiur sejajar (Sp), batupasir gelembur arus- laminasi (Sri), batupasir halus berlapis (Shi), batulempung berlapis (Fm), batulanau tufan konvolut (FI), konglomerat bergadasi normal (Gmg), paleosoil (P), dan perlapisan tuf dengan sisipan lapilli-tuf (Pfa). Mekanisme pengendapan berupa arus traksi, saltasi, turbid, debris pseudoplastik dan suspensi. Secara vertikal arah arus purba mengalami perubahan relatif menuju tenggara (SE) hingga tenggara-timur (ESE) dan timur-timurlaut (NEE). Lingkungan pengendapan adalah delta lakustrin yang berubah menjadi sungai teranyam.
Kata kunci: Kabuh, Jagan, Sangiran, litofasies, arah arus purba, delta lakustrin, sungai teranyam
Sedimentation Proccess, Paleocurrent Direction, and Depositional Environment of the Lowest Part of Kabuh Formation in Jagan Area, Bukuran Village, Kalijambe District, Sragen Regency, Central Java Province
Abstract
Kabuh Formation is one of the formations are quite spacious exposed in the area of Sangiran. Details Researches on Kabuh Formations in Sangiran still needs to be done, especially in areas that stratigraphic measurements have not been done. The research location is situated in the area of Jagan, Kalijambe, Sragen, Central Java Province. The study was conducted on two lines. The first path starts from the coordinates S 0702 758,4 ”- E 11005117,7” until S 0702 758,9 ”- E 11005118,3”. The second track starts from the coordinates S 0702 759 ”- E 110051’04” until S 0702800 ”- E 1100 5112”. Kabuh Formation research focusing on the bottom, from the contact of Pucangan Formation until the first tuff on Kabuh Formation. The method is measuring lithostratigraphy with 1:10 scale and direction of the palaeo-current. Bottom of Kabuh Formation in Jagan area consists of 18 litofasies composed by black claystone (FSM), a calcareous conglomerate (Gt-Gh), calcareous sandstone (St1-SH2- Sr2), medium-gravel crossbedded sandstone (ST2 -St3-ST4-ST5-ST6), parallel crossbeddeded sandstone (Sp), layered claystone (Fm), konvolut tuffaceous siltstone (Fl), normally graded conglomerates (Gmg), paleosoil (P), and layering tuff with lapilli tuff (PFA). The mechanism of sedimentation is traction, saltation, turbidity, pseudoplastic debris current and suspensions. In the vertical direction of the current relatively changes southeast (SE) to the east-southeast (ESE) and the east-northeast (NEE). Delta lacustrine depositional environment is being turned into a braided river.
Keywords: Kabuh, Jagan, Sangiran. lithofacies, paleocurrent direction, lacustrine delta, braided river
Woro Sulistyo Wulandari1, Moch. Indra Novian2, Wartono Rahardjo2
(‘Mahasiswa Teknik Geologi UGM, 2Dosen Teknik Geologi UGM)
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