Dinoflagellate Cysts
an alternative Stratigraphic Tool
in marine Tertiary Strata in Indonesia
by Peter Morgenroth[1], A. Tjipto Rahardjo[2] and K. Anwar Maryunani[2]
E-mail address pmorgen@bdg centrin.net.id
Key words: Dinoflagellate cysts, Indonesia, Tertiary, zonation.
Abstract
Fossil dinoflagellate cysts, organic walled microplankton, are used as stratigraphic markers in various parts of the world, in marine sediments ranging from Lower Jurassic to recent.
These mikrofossils have often been proven to be a reliable alternative stratigraphic tool in sedimentary sequences where other microfossils, i. e. foraminifera and nannoplankton do not give satisfactory results.
In Indonesia to date only very little work has been done on fossil dinoflagellate cysts.
Recently, a team from the Department of Geology, Institut Teknologi Bandung has started investigations on 14 outcrops located on Java and which range in age from Middle Eocene to Middle Miocene.
Results are very encouraging: 12 outcrops contain abundant dinoflagellate cysts.
We have so far identified 88 different types.
Assemblages markedly change in time enabling us to establish a zonation based on these microfossils. To date we have established 7 zones. This zonation is based partly on locally occurring dinoflagellate types and partly on local ranges of types described from other areas. Dinoflagellate zonations, established in other parts of the world, cannot be readily applied.
Introduction
Dinoflagellates are unicellular planktonic organisms the majority of which live in marine waters, however less frequently they also occur in brackish and fresh water environments. They are classified among the algae and very abundant in recent seas. The majority of dinoflagellates ranges in size from about 20 to 100 micron. All dinoflagellates pass through a mobile stage during their life cycle using two flagella for propulsion.
Many modern dinoflagellates form during their life cycle a cyst, i. e. a layer of very resistant organic material around the protoplasm. The formation of a cyst may be triggered by various factors.
It is the cyst of a dinoflagellate that provides for its fossil record. The dinoflagellate itself is not preserved.
Dinoflagellate cysts are extracted from rocks by using acids (HCl, HF) which dissolve the rock, but do not attack the organic substance of the fossil cyst.
Undoubtful dinoflagellate cysts have been published from strata as old as Permian. However, cysts are rare till Lower Jurassic times. At about this time their occurrences become more regular and some stratigraphic marker species have been identified.
During the Middle Jurassic dinoflagellate cysts become abundant: Many cyst genera and species appear for the first time. From this time onwards a large variety of cysts is being observed -throughout the Upper Jurassic, the Cretaceous, Tertiary and recent.
Researchers, mainly from Europe, America and Australia, have studied the assemblages present in various geological provinces of the world.
It has been established, that many dinoflagellate cysts occur over large distances, some being worldwide, thus providing “ key-correlation “ markers in geographical provinces where the local dinoflagellate assemblages may differ considerably.
The stratigraphic value of dinoflagellate cysts had early been recognized by oil companies, which established detailed “in-house” stratigraphic systems based on dinoflagellate cysts and which are being used very successfully as a stratigraphic tool in hydrocarbon exploration/development.
Some time ago we realized that in Indonesia to date little work on dinoflagellate cysts has been done.
Some forms have been described from the Eocene of Nanggulan (Matsuoka, 1984), but we are not aware of any stratigraphic work been carried out.
At the ITB, we have formed a team with the task to systematically investigate the occurrences of dinoflagellate cysts in Indonesia and to determine whether this fossil group can be used for stratigraphic work in geological sections where the well established microfossils, viz. foraminifera and nannoplankton, do not give satisfactory results.
Applied Methods
We have tried to select for our study Tertiary outcrops on Java which have already been investigated and dated, based on foraminifera or nannoplankton, by other researchers.
We have then sampled those sections and tried to verify the datings by using planktonic foraminifera. For our research on the stratigraphic distribution of dinoflagellate cysts we have only used those sections where our results matched those of previous workers.
Several profiles, which contain rich dinoflagellate assemblages, have been excluded from this project as their exact stratigraphic position remains ambiguous.
In order to systematically identify the dinoflagellate cysts present in the various outcrops, all species found by us have been given a type number preceded by D.
For all sections investigated distribution charts have been prepared showing dinoflagellate distribution and frequency. Subsequently all data from the distribution charts has been compiled in a range chart and the dinoflagelate zonation has been established.
Finally, we have also prepared one or more single grain slides for most types with the aim to establish a reference/ type collection.
Work carried out and Results
To date we have visited and sampled several outcrops of Tertiary sediments located on the island of Java which are shown on figure 1.
Remark: This paper was published end of 2000. In the meantime we have concentrated our efforts on the Miocene on .Java and have recovered very rich microplankton assemblages from various sections. This enables us to establish a more detailed zonation in the Miocene.
1)Kalisonggo River, Nanggulan / Yogyakarta
To begin with, we took samples from the Eocene section exposed in the Kalisonggo river in Nanggulan near Yogyakarta, Central Java (fig. 2). This is the area from which dinoflagellate cysts have already been described (Matsuoka 1984) and considered by us as a good reference section to start stratigraphic investigations.
We have recovered many dinoflagellate cysts from this sequence, comprising 18 species. Some types are pictured on plate1.
The assemblage does not seem to vary within the exposure and we have therefore established one dinoflagellate zone, viz. D 30, for this interval (see fig.7).
We have recovered foraminifera from one sample only. The occurrence of Globorotalia (T) rohri indicates a Middle to ?Upper Eocene age (P12 - P14, possibly lower part of P15) for this dinoflagellate assemblage.
2) Kali Seputih, Nanggulan / Yogyakarta
We subsequently sampled some 50 meters of the youngest sequence of the Nanggulan Formation, which is exposed in the Kali Seputih creek, located less than 1 km to the southwest of the Kalisonggo section. The section outcrops directly below the Seputih village (fig. 2).
Here a sequence of claystones with thin sandstone intercalations is exposed. Plant remains and large foraminifera are common.
These beds are overlain (?unconformably) by marls belonging to the Seputih Formation. We have also collected samples from these marls.
The uppermost part of the Nanggulan Formation contains rich dinoflagellate assemblages comprising 21 different species. The assemblages can be readily separated from the assemblage typical for the Kalisonggo sequence, thus enabling us to establish a second dinoflagellate zone, viz. D 31, which overlies the D 30 zone.
This sequence was interpreted by Purnamaningsih & Pringgoprawiro (1981) to belong to the ?P15/16 - P17 foraminifera zones. Nannoplankton indicative for the NP19 - NP20 zones has also been reported from the section.
These results indicate an Upper Eocene to possibly Lowermost Oligocene age for the D 31 dinoflagellate zone (fig. 7).
From the Seputih marls we recovered 18 species.
A clear break in the dinoflagellate assemblages is present between the claystones, belonging to the upper part of the Nanggulan Formation, and the marls.
Unfortunately, at present the exact dating of the marls remains ambiguous. For the time being we have therefore refrained from using this dinoflagellate assemblage for stratigraphic purposes.
3) Batuasih Formation, Cilubang Bridge, Batuasih, some 15 km west of Sukabumi, West Java
Close to the village of Batuasih, sediments of Oligocene age outcrop which have already been studied in detail by various geologists and stratigraphers (fig. 3).
The section exposed in the river close to the Cilubang bridge has been dated by Kadar 1994 to belong to the CP 18 nannoplankton zone. The CP 18 is diagnostic for the upper part of the Lower Oligocene.
At the bridge, in 2 rivers, black shales with layers of phosphatic nodules outcrop.
We have closely sampled the outcrops, taking samples from both, shales and nodules.
Analysis of the shales shows that dinoflagellates occur, however that they are strongly affected by organic metamorphism.
To the contrary, analysis of the phosphatic nodules reveals well preserved dinoflagellate cysts (see plate 1).
We have identified 22 species.
The assemblage can easily be differentiated from the older D 31 zone, established in the upper part of the Nanggulan Formation. We have therefore established a third dinoflagellate zone, D 43, for the upper part of the Lower Oligocene (fig. 7).
Remark: For the time being, we are lacking samples from the lower part of the Lower Oligocene, viz. strata representing the planktonic foraminifera zones P18 - P19. Ranges of dinoflagellate cysts between the D31 and D43 zones remain still to be investigated.
4) Cibogo River, Padalarang, some 20 km NW of Bandung, Central Java
West of Padalarang the Cibogo River is flowing close to the main road Bandung, Punjak, Jakarta (fig. 4).
In the river a sequence of dark grey shales with some siltstone streaks is exposed.
In the sequence a fault occurs which separates Upper Oligocene beds from Lower Miocene beds.
Foraminifera investigated by us give safe evidence that the Oligocene beds belong to the P22 planktonic foraminifera zone. The following species co-occur: Globigerina sellii, G. binaensis, G. tripartita and Globoquadrina altispira.
The Miocene beds belong to the N5-N6 zones and are characterised by the occurrence of Globigerinita dissimilis, Globigerinoides subquadratus and Globorotalia peripheroronda. The N4 planktonic foraminifera zone is missing.
We have very closely sampled this section, recovered rich dinoflagellate assemblages, and have identified so far 38 different dinoflagellate cysts.
The Upper Oligocene sediments contain 29 different types. Some examples are shown on plate 2.
The assemblage present can readily be separated from the slightly older D43 assemblage typical for the Batuasih Formation.
We have therefore created a new dinoflagellate cyst zone, D59, for this interval (fig 7).
From the Lower Miocene beds we have identified 18 dinoflagellate cyst types.
In the section, a strong break has been observed between the Upper Oligocene and the Lower Miocene dinoflagellate assemblages.
For the dinoflagellate assemblage present in this Lower Miocene interval we have therefore established the D 44 zone (fig. 7).
5)Kali Gending River Section, Karangsambung, Central Java
The Kali Gending river is located some 4 km to the south of Karangsambung and some 20 km to the north of the town of Kebumen. The section sampled lies some 500 m up river from the junction of the Kali Gending with the Kali Luk Ulo main river, just beyond the village of Kali Gending (fig. 5).
In the river hard shales with intercalated sandstones occur. We have sampled the shaly intervals.
The presence of Globigerinoides sicanus indicates that the section belongs to the N8 - N9 foraminifera zones,which range from the uppermost part of the Lower Miocene into the lower part of the Middle Miocene.
Abundant silica cement affects the palynological preparations. However, we have been able to recover one rich dinoflagellate assemblage and recovered dinoflagellates from several other samples. A strong break is present between the older D 44 assemblage from the Cibogo river, Padalarang, and the assemblage found at Kali Gending: New types occur, several types characteristic for the D 44 zone are absent. We have therefore established the D 21 zone for this stratigraphic interval (fig. 7).
6)Cijarian River Section, Nyalindung, West Java
The section investigated is located close to the road Bogor - Pelabuhan Rata. Some 8 km to the east of Pelabuhan Ratu the road crosses the Cijarian river. Immediately to the east of the bridge, in the river bed, claystones with thin calcareous sandstone layers outcrop. The outcrop is well known for its rich mollusk fauna (fig. 6).
We have sampled both, claystones and calcareous sandstone beds and recovered from all samples very rich dinoflagellate assemblages.
Some types are pictured on plate 2.
Planktonic foraminifera investigated by us date the section as N12 - N13, e. g. upper part of Middle Miocene, based on the occurences of Globorotalia menardii, G. siakensis and Globigerinoides subquadratus.
The rich dinoflagellate assemblage from Cijarian can readily be differentiated from the D 21 zone established in Kali Gending.
For the Cijarian section we have therefore introduced the D103/ D106 range zone (fig. 7).
Remark: The sections discussed above have been used to establish our dinoflagellate zonation.
However, we have investigated additional profiles, which we have not included in this report for reasons given in the following chapter.
Additional Sections studied
- Kali Guwo, Jatirogo, Tuban, East Java
We have investigated a few samples which had originally been collected for dating by foraminifera. Foraminifera establish the presence zones N10 (Middle Miocene) and N16 (Upper Miocene).
From both intervals we have recovered dinoflagellate cysts.
However, at present we have too little sample material from these Miocene strata in order to be able to establish a reliable zonation.
- Kali Tlatah, Blora area, East Java
Principally the comments made for Kali Guwo apply also to this outcrop: We have recovered dinoflagellates from intervals dated to belong to the N17 zone (Upper Miocene) and N9 - N13 zones (Middle Miocene). Also for this Miocene interval we need additional samples to be able to establish a reliable zonation.
- Karangsambung Area
We have sampled three sections in this area, two profiles at Jatibungkus and one at Kali Sana, with the aim to get additional information on dinoflagellate cyst distribution in the Eocene/Oligocene.
In all three sections the same problem was encountered: Rich dinoflagellate cyst assemblages are present, however the dating of the samples with foraminifera remains problematic.
The dinoflagellate assemblages contain many dinoflagellate types, several of which are so far unique to the local profiles, i. e. have not been encountered in the type sections for our dinoflagellate zones introduced above.
At present we refrain from using these rich assemblages for stratigraphic purposes until the stratigraphic position of the profiles has been clarified.
Conclusions
The fact, that we have been able to isolate rich dinoflagellate cyst assemblages from most outcrops selected for this project, indicates that these microfossils are frequently occurring in marine -or marginally marine- Tertiary sediments in Indonesia.
Dinoflagellate assemblages show characteristic variations in time so that they can be readily used for stratigraphic purposes in Indonesia.
Problems have been encountered in two sections only: Weathering of the sediments is thought to have resulted in the destruction of the dinoflagellate cysts. Of course, this problem should not be expected to occur in subsurface sections, i. e. wells.
References
Kadar, A. P. (1994) On the age of the Rajamandala and Batuasih Formations, Central West Java, Indonesia, IGCP Congres , Ciangmai, Thailand.
Martodjojo, S. (1982) Evolusi Cekungan Bogor, Jawa Barat. Facultas Pasca Sarjana, Institut Teknologi Bandung, Indonesia.
Matsuoka, K. (1984) Some dinoflagellate cysts from the Nanggulan Formation in Central Java, Indonesia. Trans. Proc. Palaeont. Soc. Japan, N. S., No. 134, pp. 374-387, pls. 71-74.
Rubiyanto, K. & Harsolumakso, A. H. (1996) Studi nannoplankton pada Formasi Karangsambung dan Totogan di daerah Luk Ulo, Kebumen, Jawa Tengah. Buletin Geologi, Vol. 26, No.1, pp.13 - 43, InstitutTeknologi Bandung, Indonesia
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