Geology of Sangiran

Sangiran is one of the villages in Kali Jambe sub-district, regency of Sragen, Central Java. It locates about 15 km north of Solo city. The name of Sangiran was chosen as a representative of those villages where within a single geological section we can find a succession of various human types.

Many scientists have undertaken an investigation on Sangiran. Firstly, van Es in 1931 published the geological map of Sangiran. Later, in 1976 to 1979 the Indonesia-Japan teamwork carried out an extensive research on Sangiran not only in geological aspects but also paleontological aspects (such as to carry out a number of excavations) and dating (see Suzuki 1985).

Geologically, the sediments of Sangiran area form the structure like a dome. Therefore, the area is commonly called as Sangiran dome (see Fig.1). There are four formations identified in this area, in ascending order: Puren (Upper Kalibeng), Sangiran (Pucangan), Bapang (Kabuh) and Poh Jajar (Notopuro) Formations (Itihara, 1985). Sartono (1975) assigned the Puren (Upper Kalibeng) Formation to Upper Pliocene, the Sangiran (Pucangan) Formation to Lower Pleistocene, the Bapang (Kabuh) and Poh Jajar (Notopuro) Formation to Middle Pleistocene.
The Puren (Upper Kalibeng) Formation is divided into four layers (old to young): bluish gray clay and silty clay (six thin tuff layers are recognized here), silt sand (Turitella beds), Balanus limestone, and clay and silt (Corbicula beds). The fission tract dating analysis, which is provided by Suzuki (1985) gave the result of lower part of this formation (Lower Tuff 1) is about 2.99 mya.

The Sangiran (Pucangan) Formation is divided into the basal Lower Lahar and the Black Clay as the main remaining part. The Lower lahar discordantly overlies the Puren (Kalibeng) Formation and consists of light gray unstratified andesitic tuff, fragments of tuff, pumice, calcareous nodules, mollusca and corals. The Black Clay includes bluish gray clay and silty clay containing intercalations of silt, sand, molluscan shell enclosure, foraminiferal sand, diatomite, peat and tuff. According to Itihara (1985), the Black Clay contains more than forty tuff layers. Among them only twelve tuff layers (T0 to T11) are useful for stratigraphical markers. Based on the fission tract dating analysis the age estimate of the middle part of Sangiran (Pucangan) Formation (T5) is about 1.51 mya and 1.16 mya for T10.

The Bapang (Kabuh) Formation consists mainly of clay, silt, sand, iron sand and gravel of fresh-water origin. But the lower part of this formation, so-called Grenzbank bed or zone, is coastal environment deposit and gradually change toward the top of formation to lacustrine and fluvial environment.

Grenzbank (means border bed) was introduced by von Koenigswald (1940) for calcareous bed whose thickness up to 1 m, marking the boundary between Sangiran (Pucangan) and Bapang (Kabuh) Formations. According to Sudijono (1985), the Grenzbank zone is a pebbly sand bed with one or more lenticular interbeds of hard calcareous sand and pebbles; often clay or silt intercalations are present. In some places around Sangiran the hard calcareous lenticular beds are found at two or more horizons. Based on petrographicaly analysis, He recognized that Grenzbank bed or zone consists of two different groups of lithology, namely the calclithite or terrigenous carbonate and calcareous conglomerate. The former particularly occupied the northern part and the later on the southern part of Sangiran area. Although the sedimentation environment of these groups are not clear but supposedly these groups were deposited in relatively high energy environment such as beach or stream.

In the Bapang Formation, three distinct tuff layers are frequently found, namely the Lower, Middle and Upper Tuff layers. Based on these three tuff layers, the Bapang (Kabuh) Formation is subdivided into four parts, namely the Lowermost, Lower part, Middle part and Upper part. In addition, there are also two other tuff layers called the Lowest Tuff and the Upper Middle Tuff layers. The former is pink and 10 to 60 cm thick. It occurs in the basal part, especially in the Grenzbank bed or zone, at a few places in the northwest Sangiran area (Itihara 1985).

The fission tract dating method has been applied to zircon grains from tuff and two tektite fragments found insitu in the middle part of Bapang (Kabuh) Formation; between Middle and Upper tuff layer. The result of analysis revealed that the age estimates of c 0.78 mya and 0.71 mya for two small fragments of tektite (Suzuki 1985). In addition, recent palaeomagnetic study suggests the age estimate of about 0.9 myr for the Grenzbank bed or zone as stated by Hyodo (1988).

The Poh Jajar (Notopuro) Formation discordantly overlies the Bapang (Kabuh) Formation and distributed in the hilly land surrounding the Sangiran dome. It consists of gravel, sand, silt and clay of fresh water origin. It also contains intercalation of lahar, pumice and tuff. Three markers beds are recognized, namely the Upper lahar, the Uppermost lahar and the Upper Pumice beds. Based on these three marker beds, the Poh Jajar (Notopuro) Formation is subdivided into the Lower, Middle and Upper parts. Based on the fission tract dating analysis the age estimate of the upper part of Pohjajar (Notopuro) Formation (Upper Pumice bed) is about 0.25 mya.

Vertebrate and hominid fossils
Sangiran (Pucangan) and Bapang (Kabuh) formation contain plenty of vertebrate fossils. According to Vos (1994) those vertebrate fossils are faunal member of (in ascending order) Satir (lower part of Sangiran/Pucangan fm), Cisaat (upper part of Sangiran/Pucangan fm), Trinil HK (Grenzbank zone) dan Kedung Brubus (lower part of Bapang/Kabuh fm). All of those faunal orders were assigned to Lower Plestocene.

Satir Fauna (2-1.5 mya) is characterized by Tetralophodon bumiajuensis, Hexaprotodon simplex, Geochelone and cervids. Cisaat fauna (1.2-1 mya): Stegodon trigonocephalus, Hexaprotodon sivalensis, cervids, bovids and possibly a felid and a suid. Trinil HK (Haupt-Knochen = main fossiliferous layer) (0.9 mya) and Kedung Brubus Fauna (0.8-0.7 mya) contain more varied genus and species than the previous faunas. Kedung Brubus Fauna bears a more mainland character then Trinil HK Fauna (Leinder,1985 & Vos, 1994).

Hominid fossils mainly come from the uppermost part of the Sangiran (Pucangan) Formation and the lower and middle part of Bapang (Kabuh) Formation, dated between at least 1.15 to 0.7 mya. In term of faunal terminology, hominid fossils of Sangiran area part of Trinil HK and Kedung Brubus Fauna and were assigned to the lower Pleistocene.

[18jan14St vbm]
@Kisaran ling pengen di Sangiran
~~ a long succession of depositional envi that range from ESTUARINE-PALUDAL (MARSHY) in the oldest H.erectus bearing levels, to RIVERINE in overlying deposits that contain more significant numbers of H.erectus remains [p.12]

@Puren fm ada marine mollusk
These are marine ls, siltstones, mudstones & muddy ss of the Puren fm. Association fauna include an abundance of marine mollusks (Andara sp) & rare fresh water forms such as Corbicula sp. These taxa suggest deposition in near-shore shallow-marine envi p.12]

Bandung, November 22, 2005.Sl
[30dec13Sn vbm] Puren formation is the oldest sediment (upper Pliocene) exposed (recovered) in Sangiran. It was deposited in a near-shore, shallow-marine environment (338:12). This formation contains no mammalian fossils but generally dominated by the abundance of marine mollusks and the scarcity of freshwater forms {JERSOPO]

The lithological trait of this formation in Sangiran consists of bluish grey clay, Turritela-bearing sand of shallow marine origin, Balanus limestone of coastal origin & Corbicula bearing clay and silt of brackish-water origin (Itihara 1994:125). At least 6 remarkable tufflayers are found mostly in bluish grey clay (inascending order): Lower Tuff 1-4; Middle Tuff and Upper Tuff (Yoshikawa & Suminto 1985:97).
338 [30dec13Sn vbm]
#Formasi batuan sedimen di Sangiran diendapkan mulai dr lingkungan estuarine-paludal (marshy) to riverine [p.12]
# H.erectus menghilang dr Sangiran pd late mid-Pleis yg kmd digantikan dg kemunculan methane plumes domed &a series of mud volcano
#Fm Puren mengandung abundance of marine mollusks (Anadara sp) & rare freshwater forms such as Corbicula sp. Berdasarka fauna tsb diperkirakan Fm Puren terbnt pd in a near-shore, shallow marine environment [p.12]
#Fm Sangiran tdd 2 members yi the basal Lower Lahar Unit & the overlying “black clay” (Watanabe & Kadar 1985; Bettis 2004). Black clya diendapakan di ling: shallow-marine, brackish-water, freshwater-lake & marsh envi. Thin, water-laid (dibnt di air) tuffs occur throughout the Sangiran Fm (Yoshikawa & Suminto 1985) [p.12]
#Perub ling pengendapan from quiet-water to fluvial envi menandakan bts ant Fm Sangiran & overlying Bapang fm (Watanabe & Kadar 1985; Larick 2001) [p.12-13]
#Fm Bapang mengandung 3 upward-fining cycles of fluvial conglo, sands, tuffaceous silts, reworked ash fall & a few air-fall tuffs (Fig.2) [p.13]
#Fm Pohjajar jg diendapkan di ling fluvial tp bedax dg Fm Bapang adl pd Fm Pohjajar mengandung higher proportion of fine-grained volcanic sediments. These occur as aerial tuffs, fluvially reworked ash fall & two lahar-formed diamictons: the Upper & Uppermost lahars [p.13]
#Di atas Fm Pohjajar terdpt high-level terrace fills on the modern landscape. These sediments are a fluvial ensemble [group]of alternating tuffaceous sandstone, conglo & fine-grained sediments that unconformably overlie the Pohjajar Fm & in many places cut into [inlay, menatah, insert, menyisip] the underlying Bapang & Sangiran Fm [p.13]
#Black clay dr Fm Sangiran mengandung terrestral vertebrate taxa well-adapted to marsly & lake-margin envi (Aimi & Aziz 1985). H.erectus fossils occur in the upper part of the black clay as one component in the fully terrestrial & endemic island-type fauna known as Cisaat (de Vos 1994; Larick 2001) [p.13]
#Fosil H.erectus banyak ditemukan di the lower & middle parts of the Bapang Fm hold the majority of the Dome’s H.erectus fossil & fosil hominin belum pernah ditemukan pd in the upper reaches of the Bapang or in any part of the Pohjajar Fm [p.13]
#[31-12-13Sl vbm] Lower Lahar & bg bwh black clay Fm Sangiran contain fossils of marine & brackish-water-dwelling organisms. The upper “black clay” has yielded fossils of terrestrial vertebrates such as Hexaprotodon simplex & various cervids that are well adapted to marshy conditions [p.14]
#The dome’s oldest H.erectus fossils occur in the upper 10m of the formation above Tuff 10 (Yoshikawa & Suminto 1985; Larick 2001) [p.14]
#Fm Bapang tdk selaras di atas Fm Sangiran => fluvial deposits of Bapang Fm unconformably overlie the Sangiran Fm. The contact is generally low-relief and the basal Bapang Fm contains common clasts ripped up from Sangiran Fm sediments & paleosols [p.14]
# GZ terdpt dibg bwh Fm Bapang ==> a distinctive, thin, iron-cemented conglo, the so called “GZ zone” ocurs at the base of Bapang Fm [p.14]
#Fm Bapang consists of a series ofupward-fining sedimentary cycles. Larick (2001) presented 5 such cycles ~~~ the framework has thus been refined to hold 3 cycles numbered in order of decreasing age (Fig 2). Each cycle consists of basal trough cross-bedded, tuffaceous pebbly coarse sandstone w/ lenses of pumiceous conglo deposited as bars & other channel deposites [p.14]
#Faunal remains in numerous bone beds are present in the coarse-grained portion of each cycle. The presence of more complete H.erectus cranial fossils in the younger sedimentary cycles corresponds to diminishing energy levels of the fluvial system through the Bapang Fm (Larik 2001). Fossils attributable to the Trinil (Hauptknochenschicht, H.K.; de Vos & Sondaar 1982) fauna are associated w/ cycle 1, while the Kedung-brubus fauna is associated w/ Cycles 2 & 3 [p.15]



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