#Fairly continuous outcrops are, however, found at 3 places (Fig.2; loc I-1, II & III-1) [p.12]
# The xbeng fm which is exposed in the Sangiran dome attains a total thickness of more than 126.5m.It probably corresponds to the Upper xbeng fm of Duyfjes (1936) extending from Trinil to Surabaya [p.17]
The xbeng fm in the Sangirandome is subdivided, in ascending order, into the following 4 members:
a] Bluish gray clay & silty clay. This member, more than 107m thick, is of marine origin. It consists mainly of bluish gray clay & silty clay with minor amounts of sandy clay, sandy silt, silty sand & sand. 6 thin tuff layers, namely Lower Tuff 1 (LT1), Lower Tuff 2 (LT2), Lower Tuff 3 (LT3), Lower Tuff 4 (LT4), Middle Tuff (MT) & Upper Tuff (UT) are recognized. Pyroclastic materials of tuffs are medium to coarse-grained crystal glass with subordinate amounts of heavy minerals.
These minerals are commonly scattered in 10 to 40cm zones except for LT1 layer, 7cm thick, at loc.I-1 & UT layer, 12cm thick, at loc.II. A silty sand bed & a sand bed, both of which contain molluscs: Turitella, Nassarius, Arca, Chione & foraminifera; Operculina etc. are recognized in this member. The former occurs about 2m above LT4 layer & the latter about 5m above MT layer. In general, sandy clay & sandy silt frequently contain molluscs such as Anomia, Ostrea, Arca, Chione, Turricula & Pleurotoma, whereas bluish gray clay & silty clay contain only a small number of Murex, Natica & Anomia.
b] Silty sand (=Turitella bed?). This member, 4.2 to 6.9m thick, is thought to have been deposited in shallow open marine condition. Molluscs such as Turitella, Marginella, Natica, Murex, Arca, Pecten, Ostrea, Chione & foraminifera such as Operculina are common.
c] Balanus ls. This member, 1 to 2.5m thick, consists of shell fragments of Balanus & molluscs. It is thought to have been deposited in coastal environment.
d] Clay & silt (=Corbicula bed?). This member (d), 0 to 10.1m thick, is mainly composed of dark bluish gray clay & silt & commonly contains molluscan shells of Corbicula. Two Corbicula beds, 0.3 to 1m thick, are recognized, one at the base & the other in the upper part. Small molluscs such as Aloides & Melanoides also abudantly occur in a dark bluish clayey part with the intecalations of diatomite at the top horizon (Fig.5; loc III-2). This member is thought to have been deposited in brackish water environment.
The above 4 members correspond to bluish gray (marine) clay, Turitella beds (argillaceous sand), Balanus ls & Corbicula bed of van Es (1931) respectively. Examination of these litho & bio-facies allows as assumption of gradually shallowing sedimentary basin. Since the Xbeng fm is discordantly overlain by the Lower Lahar, the full succession of the D member [Corbicula bed] can hardly be observed. At loc III-1 & III-2 near Pablengan (Figs2&5), the relationship between the Xbeng & Pucangan fm is, however, conformable because the D member, which concordantly underlies the Lower Lahar 0.7m thick, is well developed there.
#The representative geological columnar sections were made at 11 places, i.e. loc VIII at the irrigation canal near Cengklik (plate II-2), loc III-2 & III-3 near Pablengan, loc IV at the dam site (plate III-1), loc V-1, V-2, V-3, V-4 & V-6 at the Pb stream (plate IV-2), loc V-5 at the Pb site (plate IV-3), loc VI near Mb site (plate IV-1) & loc VII near Jagan (Fig.2). These columnar sections are shown in Figs.4&7 [p.17]
#The Pucangan fm has been divided into the basal Lower Lahar & the Black Clay as the main remaining part (van Es 1931; von Koenigswald 1940; Sartono 1961, 1970, 1975; Indonesia-Japan Joint Research team 1979)
# The Sangiran (Pucangan) formation has been divided in to the basal Lower Lahar and the Black Clay as the remaining part by some authors (Es 1931; Sartono 1961, 1970, 1975; Koenigswald 1940; Indonesia-Japan Joint Research Team, 1979).
# The Lower Lahar (lower volcanic breccias) discordantly overlies the Kalibeng formation in general. Conformable relationship between these two units is observed only near Pablengan (Fig 4). The thickness of the Lower Lahar varies from 0.7 m at loc.III-1 & III-2 near Pablengan to 46 m at irrigation canal near Cengklik (loc VIII). This lahar consists of light gray unstratified andesitic crystal tuff with rounded to subrounded fragments of pebble and cobble sizes, except for the aforesaid (tsb di atas) huge blocks. The fragments are mainly pyroxene andesite, hornblenda andesite & subordinate amounts of mudstone, sandstone, tuff, pumice, calcareous nodules, molluscs & coral (plate II-4). The number & size of the fragments generally decrease upwards.
#The stratigraphic gap ascribed to [disebabkan oleh] denudation of the Lower Lahar does not exceed 10.1m in thickness, because the Balanus ls played the role of resistant bed on account of its hardness
#The Black Clay, in places, abuts [berbatasan] the undulating surface [permukaan bergelombang] of the Lower Lahar, so that the relation between the two is regarded as mainly conformable & partially diastemic. The Black Clay is 111.3 m thick & mainly composed of bluish gray clay & silty clay containing intercalations of silt, sand, mollusks shell enclosure, foraminiferal sand, diatomite, peat & tuff (Fig 7). (3/12-10J lab mikropal) At weathered outcrops, the color of clay & silty clay changes from bluish gray to black. These clays frequently contain irregular porous nodules which resulted from the leaching out [pencucian keluar] of molluscs.
# (3/12-10J lab mikropal) The Black Clay contains more than 40 tuff layers. Among them T0, T1, T2, … T10 & T11 layers are good stratigraphic markers. Except for the T10 layers, 5 to 20 cm thick, other tuff layers are generally thin. These are gray to white & in places yellowish in color. In general, the tuffs are composed of medium to fine-grained volcanic glass, plagioclase & heavy minerals with minor amounts of quartz. Amphibole is the main component of heavy minerals occurring in these tuffs.
#The Black Clay is divided into the lower brackish and marine and upper lacustrine parts on its fossil content. The boundary between the lower & upper part is placed at the top of Shell 1 (S1) layer. Bluish gray clays & silty clays below T2 horison contain molluscs: Corbicula, Melanoides & Aloides. Diatomites & massive diatomecous clays at T2 horison yield marine diatoms: Actinocyclus, Coscinodiscus, Diploneis etc. Gray clays & silts between the top of T2 horison & the lower limit of S1 layer yield mollusks, Arca & foraminifera. S1 layer, 30 cm thick, is composed of yellowish gray silt. It contains mollusks: Arca, Paphia, Strombus, Dentalium & Melanoides. In the upper part, bluish gray clays, silty clays & silts yield abundant freshwater mollusks: Corbicula, Unio, Anodenta, Viviparus, Melanoides, Sulcospira, Brotia, Thiara etc.
[7des12St vbm] [p.19-20]
A tuffaceous & diatomaceus bed, about 0.8m thick, containing freshwater diatoms & molluscs: Navicula, Pinularia, Cymbella, Melanoides, Sulcospira & Viviparus, occurs at a horizon about 0.5m above T8 layer. Foraminiferal sand layers, 0.1 to 2.6m thick, are found at least 5 horizons. The horizons are between T6 & T7 layers, between T9 & T10 layers & between T11 layer & the base of the Kabuh fm. At these horizons fresh-water molluscs occur curiously in
association w/ foraminifera of deep marine facies.
The nature of preservation & association of these foraminifera, however, indicate that these fauna are allochthonous. In general, the foraminiferal sand layers are continuously distributed, but in
places disappear laterally.
Mammalian fossils occur at least 8 horizons above Shell 1 (S1) layer
(Fig.7). Hominid fossils, i.e. PIV, Pb, Pc & Pd (plate V), Pf, Ma, a skull cap & two mandible fragments come from the uppermost horizon of the Pucangan fm (Fig.7 & Fig.9 in separate sheet at back cover).
The first step of the sedimentation of the Pucangan fm begun w/ the flowing of a lahar into a brackish-water basin, as shown by facies similarity between the Corbicula bed of the Kalibeng fm & the bluish-gray silty clay above the Lower Lahar. In the Pucangan clay, the sedimentation was gradually changed from brackish-water & marine in the lower part to fresh-water in the upper part. Foraminiferal sand layers in the upper part of the Pucangan formation indicate
that the uplifted hinterland (daerah pedalaman, vicinity) of the basin was eroded to produce the allochthonous sediments. It is inferred that the basin began to be gradually constricted
[7des12St vbm] [p.20]
#The Kabuh fm, 5.8 to 58.6 m thick, is composed mainly of clay, silt, sand, iron sand & gravel of fresh-water origin. It also contains intercalations of conglomeratic sandstone know as Grenzbank & tuff.
#The Kabuh fm conformably overlies [melapisi, membebani]the Pucangan fm & in turn [pd giliranx] underlies [mendasari]discordantly the Notopuro fm. Grenzbank, lenticular calcareous conglomeratic sandstone layers of less than 2m thick, occurs only in the basal part, whereas tuff layers are frequently found in this formation. ~~~~ are respctively established in sequences of strata exposed near Bapang (Fig.2,4&9; S48 & S49; plate VI-5) & near triangulation stat T356 (183m asl) in the northwestern part of the area (Fig.2,4&9; S36)
#It is difficult to trace the tuff layers occur not only near Bapang (S48 & S49) but also near T356 (S36). In spite of their intermittent appearances, the MT layers at both localities are traceable & mutually [saling,satu sama lain] correlative. The three distinct tuff layers are called the LT, MT & UT layers. In addition, there are also two other tuff layers called the Lowest Tuff layer & the Upper Middle Tuff layer. In geological columnar sections (Fig.9), the horizon of the MT layer is shown as a horizontal line.
#The Lowest Tuff layer is pink & 10 to 60cm thick. It occurs in the basal part, esp in the GB zone, at a few places in the northwest Sangiran area. The LT layer is white & up to 100cm thick. At locality S48 near Bapang, it exists about 17m above the base of the Kabuh fm. It consists of fine-grained volcanic ash containing glass, plagioclase & quartz as light minerals & amphibole, opaque minerals & biotite as heavy minerals. The MT layer is yellowish white & up to 110cm thick. It’s most widely traceable. At locality S48 near Bapang, the MT layer, 50cm thick, occurs about 10m above the LT layer. It consists of tuffaceous sandy silt w/ thin intercalations of medium-grained sand. The tuffaceous part contains plagioclase & quartz as light minerals & amphibole, opaque minerals & pyroxene as heavy minerals. The upper MT layer, up to 60cm, consists of white volcanic ash. It occurs in the northwestern part of the area. The UT layer,up to 90cm thick, is pink & contains plagioclase, quartz, amphibole, opaque minerals & biotite. It’s easily traceable in the southern part of the Sangiran area. At locality S48, the UT layer is 60cm thick & occurs about 11m above the MT layer. It’s divided into the lower portion, 20cm thick, composed of tuff & the upper portion, 40cm thick, characterized by tuffaceous silt.
# The Kabuh fm is tentavively subdivided into 4 parts by the above descriebd three distinct tuff layers i.e. tye LT, MT & UT layers.
#The Lowermost part of the Kabuh fm ranges from the base of the formation up to the lower limit of the LT layer, varying in thickness from 4.2m to about 20m.