proses sedimentasi, arah arus purba, dan lingkungan

xvii
PROSES SEDIMENTASI, ARAH ARUS PURBA, DAN LINGKUNGAN PENGENDAPAN
FORMASI KABUH BAGIAN PALING BAWAH DI DAERAH JAGAN, DESA BUKURAN,
KECAMATAN KALIJAMBE, KABUPATEN SRAGEN, PROVINSI JAWA TENGAH.
Oleh: Woro Sulistyo Wulandari
NIM: 10/300872/TK/36678
Pembimbing : Moch. Indra Novian S.T., M.Eng. & Ir. Wartono Rahardjo
INTISARI
Formasi Kabuh merupakan salah satu formasi yang cukup luas tersingkap di daerah
Sangiran. Formasi ini dikenal dunia karena ditemukannya fosil fragmen manusia purba oleh
peneliti terdahulu. Penelitian secara rinci mengenai Formasi Kabuh di Sangiran masih perlu
dilakukan, terutama pada daerah yang belum pernah dilakukan pengukuran stratigrafi. Maksud
dari penelitian ini adalah melakukan pengukuran stratigrafi terukur secara rinci yang digunakan
untuk interpretasi lingkungan pengendapan. Lokasi penelitian terletak pada daerah Jagan, Desa
Bukuran, Kecamatan Kalijambe, Kabupaten Sragen, Jawa Tengah. Penelitian dilakukan pada dua
jalur. Jalur pertama dimulai dari koordinat S 07o27’58,4”- E 110o51’17,7” hingga S 07o27’58,9”E 110o51’18,3”. Jalur kedua dimulai dari koordinat S 070 27' 59"- E 1100 51' 04" hingga S 070
28' 00"- E 1100 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, analisis petrografi, komposisi butir,
dan arah arus purba. Hasil pengukuran stratigrafi menunjukkan Formasi Kabuh paling bawah
pada daerah Jagan terdiri dari 18 litofasies yang terdiri dari batulempung hitam (Fsm),
konglomerat karbonatan (Gt-Gh), batupasir karbonatan (St1-Sh2-Sr2), batupasir silangsiur
palung dengan ukuran sedang-kerikil (St2-St3-St4-St5-St6), batupasir silangsiur sejajar (Sp),
batupasir gelembur arus-laminasi (Sr1), batupasir halus berlapis (Sh1), batulempung berlapis
(Fm), batulanau tufan konvolut (Fl), konglomerat bergadasi normal (Gmg), paleosoil (P), dan
fasies perlapisan tuf dengan sisipan lapilli-tuf (Pfa). Mekanisme pengendapan berupa arus traksi,
saltasi, turbid, debris pseudoplastik dan suspensi. Batuan asal berupa batuan vulkanik primer
maupun sekunder, batuan beku asam, batuan beku basa, dan batuan karbonat. 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
xviii
THE SEDIMENTATION, PALEOCURRENT, AND ENVIRONMENT OF LOWERMOST
PART KABUH FORMATION AT JAGAN, BUKURAN VILLAGE, KALIJAMBE,
SRAGEN, CENTRAL JAVA PROVINCE
By: Woro Sulistyo Wulandari
10/300872/TK/36678
Advisor: Moch. Indra Novian, S.T., M.Eng. & Ir.Wartono Rahardjo
ABSTRACT
Kabuh Formation is one of the widely exposed sedimentary formation at Sangiran area.
Kabuh Formation is recognized by the world because of the hominid fossils have been found by
previous researchers. Detailed research is still important at this area, the area which has never
been excavated before. The purpose of this research is to measured section data and
interpretated the environment of Kabuh Formation. This research has been done at Jagan area,
Bukuran Village, Kalijambe, Sargen, Central Java. The measurement consists of two sections.
First section is from coordinate S 07o27’58,4”- E 110o51’17,7” until S 07o27’58,9”- E
110o51’18,3”. Second section is from coordinate S 070 27' 59"- E 1100 51' 04" until S 070 28'
00"- E 1100 51' 12”. The focus of this research is the lowermost part of Kabuh Formation, the
range of sections is from the contact of Kabuh and Pucangan Formation until Lower Tuff layer.
The methodes rmployed are stratigraphic measured section with 1:10 scale, petrographic
analysis, grain and mineral compositional analysis, grain morphology analysis, and
paleocurrent analysis. As result of stratigraphic measured section, 18 lithofacies was found at
Jagan area, which are: black clay (Fsm), calcareous conglomerate (Gt-Gh), calcareous
sandstone (St1-Sh2-Sr2), trough cross-bedded sandstone from fine sand to gravel (St2-St3-St4St5-St6), planar cross-bedded sandstone (Sp), ripple mark-laminated sandstone (Sr1), horizontal
bedded sandstone (Sh1), horizontal bedded clay (Fm), convolute laminated tuffaceous silstone
(Fl), normal gradded conglomerate (Gmg), ripple mark-laminated sandstone (Sr2), paleosoil
(P), and tuff with intercalation of lapilli-tuf (Pfa). The provenance consists of primary and
secondary volcaniclastic rocks, felsic igneous rocks, mafic igneous rocks, and carbonate rocks.
The mechanism of sedimentations are traction, saltation, turbidity current, pseudoplastic debris,
and suspension. There are vertical changing of paleocurrent direction. The dirrection is south
east (SE), then changed into east-south east (ESE) and north east-east (NEE). The sedimentation
of Lowermost part Kabuh Formation began with lacustrine delta to braided stream environment.
Key words: Kabuh, Jagan, Sangiran, Lithofacies, Paleocurrent, Lacustrine Delta, Braided stream