Corresponding Author: Ratna
Husein
Email: [email protected]
INTRODUCTION
Sulawesi Island is a volcanic arc
extending from Sumatra, Java, and Nusa Tenggara continuously north to Sulawesi
and Halmahera, the Philippines, Japan, and other neighboring countries (Andini, 2019). This volcanic arc is a path of tectonic order as a
result of the subduction of one plate by another plate, as an implication of
Indonesia's location at the meeting point of three plates, namely the Eurasian
plate, the Pacific plate, and the Indo-Australian plate (Triana, 2017).
The age and depositional environment of volcanic rocks
can be analyzed to determine and predict pyroclastic lithofacies, which are
exposed in the research area consisting of pyroclastic flow deposits, namely
volcanic clastic lithic tuff (Ramadhani, 2021). Volcanic rocks such as lava facies, agglomerates,
and Parepare volcanic breccia have previously been studied as medial facies (Tania et al., 2020). Volcanic stratigraphy can provide an understanding of
volcanic succession for predictions, especially in reconstructing past
behavior. It is essential for identifying its relationship with volcanic
products and sedimentary basins where the volcanism occurred (Nugraheni, 2019).
This research was conducted to determine how the
biofacies are distributed vertically and the paleoenvironment of the Tanamailie
Parepare volcanic tuff. Determining volcanic biofacies is a grouping to
determine the vertical sequence of events so that volcano stratigraphy can
produce information and explain the geological history of volcanoes and be
understood as a geological order (Relindo, 2021).
Based on the background above,
this research aims to analyze the distribution characteristics of foraminifera
in the Parepare Tanmailie Pinrang volcanic tuff, South Sulawesi. The benefits
of this research are as an environmental assessment, namely as the distribution
of foraminifera in volcanic tuff, can be used as an indicator of environmental
conditions and changes in the past, assisting in environmental assessment and
geological studies, and as an ecological insight, namely this research can
provide valuable insight into the history of geology and processes that have
shaped the South Sulawesi region, contributing to the broader field of earth
sciences.
METHOD
This research
consists of several stages: literature review, field survey, laboratory
analysis, and interpretation. Field observations and measurable stratigraphic
measurements include identifying the characteristics of each rock layer in the
form of lithology, sedimentary structure, relationships between rock layers,
rock mineral content, fossil content, and geometry (upright and flat), taking
rock samples. The laboratory analysis carried out is micropaleontological
analysis to identify the characteristics of each type of fossil, age, and
depositional environment, which is then used for facies analysis, facies
associations, and depositional environment as well as the development of the
Parepare volcanic sediment deposit. Interpretation and reconstruction of basin
development are carried out using data collected and assisted by the results of
previous research such as regional geology, biostratigraphy, and the
relationship of rock outcrops and residual soil with other rocks or minerals in
the surroundings, as well as geological elements found in the field recorded
visually through the digital camera; the sample is then prepared for laboratory
analysis.
Surface data was
collected on the Measured Stratigraphic stretch, rock data collection, and
field descriptions. Samples were taken in layers representing the top, middle,
and bottom, which are considered to represent each thickness in the field. Rock
samples are also analyzed to determine the mineral content and chemical
composition.
The research
location is located in the Tanamailie area, Suppa District (Figure 1), Pinrang
Regency, and is astronomically located at 119ᵒ35'45" East Longitude
(East Longitude) and 4�0'45'' South Latitude (South Latitude). This area was
chosen because it is one of the best outcrops of Parepare volcanic tuff, where
the rocks can be measured stratigraphically and contains abundant fossils with
large fossil sizes. Suppose you cross via Parepare Beach to Tanjung Tanamailie
using a boat. In that case, the distance that can be covered is much shorter
compared to using the road. Link between Pinrang Regency and Pare-pare City.
This area is summarized in the Western Part of Pangkajene and Watampone Sheet
Map, South Sulawesi, scale 1:250,000, and the Earth Map of Indonesia, scale
1:50,000 published by the National Survey and Mapping Coordinating Agency ( Geology & Sukamto,
1982).
Figure 1. Map of research locations sources; Indonesian
Earth Map
Geomorphology
Parepare is one of the cities
that is developing towards the metropolitan capital in South Sulawesi, where
the city is bordered on the east by hills that extend from North to North West
as mountains through Pinrang, Parepare, Pangkajene, continuing to the western
part of Watampone. This mountain range is bordered to the east by the Walanae
Valley and the Walanae Terban as a ridge of mountain ranges that runs through
Pinrang to Watampone. The highest peak of the western mountains is 1694 meters
above sea level, and the average height is 1500 meters above sea level.
The distribution of the eastern
mountains is half the Parepare area, 22 km long, narrowing in the north and
widening 50 km to the south. Volcanic rocks dominate the rocks that make up
this area. In several places, some of it is composed of limestone in the form
of Kras, spreading on the eastern slopes, revealing the Kras topography. Some
of the hills between the Kras topography are composed of Pre-tertiary rocks,
found to the west, bordered by the Pangkajene plains, continuing towards the
wide Maros to the south.
The eastern part of the highest peak is 700 meters,
and the highest is 787 meters above sea level and extends relatively narrower
and lower; these mountains are composed of volcanic rock. To the north, it
narrows and becomes flatter, continues towards the south with a continuous height
of 20 km wide, and finally dips below the boundary between the Waianae Valley
and the Bone Plain. The Bone Plain extends to the northeast, occupying almost
the eastern third. In the middle of the mountains is the Waianae Valley as a
divider, extending from North to South, widening in the north to 35 km, and the
south, narrowing to only 10 km. In the middle of the Walanae Terban, the
Walanae River flows north-south, flanked by low hills as an alluvial plain that
continues north to Sengkang and extends around Lake Tempe.
Stratigraphy
The spread of volcanic rocks
covers the eastern part of Sidrap Regency and the northern part of Barru
Regency. It spreads to cover Parepare City to Pinrang Regency. This land
continues to the cape in front of or opposite the city of Pare-pare.
Pare-pare volcanic rocks
consist of breccia and volcanic conglomerate and lapilli tuff and fine-grained
tuff, some of which are found interbedded with lava and tuff sandstone composed
of trachyte and andesite; the tuff layer contains much biotite; Generally, the
wear is weak and some are crumbly, the color is grayish white to gray, some
layers appear to have a cross-layered structure and traces of vegetation. This
unit has a thickness of 500 m, is located on top of the Camba Formation rocks,
and is interpreted to be at the top of the Walanae Formation of Pliocene age,
from absolute method analysis of trachyte and tuff from northeastern Parepare
(Majene-Palopo et al.) (Nainggolan, 2021).
The regional stratigraphy of
the youngest sequence is spread around Parepare in the form of alluvium silt
deposits, sandy mud exposed along large rivers, lake deposits around Lake
Tempe's curve, and beach deposits consisting of gravel and clay along the coast.
Local beach deposits contain shell remains and coralline limestone (Qc).
Inserts of marine clay containing mollusks (Arca et al.) and iron peaks are
found around Lake Tempe. Rocks of Pleistocene age (unmapped) in the form of
exposed river steps in Sompoh Village, there are Archidiscodon celebensis as
ancient elephant bones found near the Walanae River (Nainggolan, 2021).
The Parepare Volcanic Unit with
the symbol (TPPV) Tertiary Pliocene Parepare consists of fine-grained volcanic
rock to lapilli. In several places, volcanic breccia contains lava inserts and
volcanic conglomerates. Petrographic analysis in the form of trachyte and
andesite, as well as tuffaceous sandstone. Fine volcanic rock outcrops as tuff
layers contain much biotite; generally wear weak and some crumbly; grayish
white to gray. Locally, criss-cross layers and plant remains are visible.
Part of the rock, this volcano in the eastern area,
consists mainly of Tertiary Pliocene Parepare Lava (Tppl), a trachyte structure
containing much biotite (Sukur,
2022). This unit, estimated to be
500 m thick, overlies the rocks of the Camba Formation and possibly intersects
with the upper part of the Walanae Formation. The age is Pliocene, based on
radiometric dating of trachyte and tuff from northeastern Parepare (Majene-Palopo
Sheet), which respectively gives 4.25 and 4.95 million years.
RESULTS
AND DISCUSSION
Deposition on marina or land sediments with volcanic
deposition is very different because the deposition rate is speedy and more
complex (Aritonang et
al., 2016). Agglomerate
facies are exposed in Parepare City and Lumpue Beach. The fragments and matrix
consist of trachytic monolithology. In the southern part, there are pumice
deposits. In the upper part, they are covered by lava flows and ignimbrite
deposits of various sizes of fume fragments (Bronto et al., 2014). Determining
the age and analysis of the pyroclastic facies is still a matter of discussion
because there are still differences of opinion regarding the age and
depositional environment (Noor, 2014). Based on the fragments' texture, structure, and
composition, the pyroclastic lithofacies consist of volcanic breccia facies and
tuff facies (Figure 2). In the upper part, the lava lithofacies are divided
into agglomerates in the Tonrangeng area, coherent lava, and autoclastic
breccia, which are exposed both on Lumpue beach and volcanic breccia exposed in
the Kupa area (Irfan et al.,
2015).
Figure 2. Outcrop of the measured stratigraphic location
of Tanamailie Pinrang
Facies Analysis Volcanic tufa exposed on Tanjung Tanamailie, fresh
grayish white, weathered brownish gray, consists of alternations between
relatively coarse and fine pyroclastic, carbonate in nature, the position of
rock layers is N118oE/8o.
The biostratigraphy is based on the zonation of planktonic foraminifera,
namely the initial appearance and final appearance of the characteristic
species found in each layer (Alyara,
2021). The results of the analysis
of the lower, middle, and upper layers, consisting of 4 continuous age periods
in harmony from the upper Middle Miocene to the Pliocene (Table 1), are
described as follows;
1.
The first layer is the lowest part of the measured
stratigraphy, consisting of alternating layers of fine tuff. The thickness of
each layer is between 150 cm - and 200 cm, the coarser-grained tuff layer is
between 10 cm and 150 cm, and the overall fine-grained tuff is thicker than the
coarser stuff.
In this layer, planktonic fossils are found, which
always appear in almost every layer, namely Globogerinoides sub quadratus
BRONNIMANN, Orbulina Bilobata (D'ORBIGNY), Globigerinoides immatures LEROY,
Globoquadrina altispira (CUSHMAN and JARVIS), Globigeroides trilobus (REUSS).
This zone is the oldest zone of
the lowest layer based on the Early Appearance of Globorotalia menardii
(D'ORBIGNY) to the Late Appearance of Globigerinoides sub quadratus BRONNIMANN,
which is characterized by Sphaeroidinellopsis subdevices - Globigerina Drury
Blow N13 zone, according to the Postuma age of the late Middle Miocene
(RAMADHAN, 2018 ).
The second layer is the lower
middle part of the measured stratigraphy consisting of alternating layers of
fine tuff, the thickness of each layer is between 50cm � 230cm, the coarser
grained tuff layers are between 20 cm � 150 cm each layer, the finer-grained
tuff is overall thicker rather than coarser grain tufa. In this layer, it is
located aligned above the lower middle layer; fossils found in this layer
include Globoquadrina dehiscence (CHAPMAN, PARR, COLLINS), Orbulina Bilobata
(D'ORBIGNY), Globigerinoides sacculifer (BRADY), Globigerinoides sub quadratus
BRONNIMANN, Globigerinoides immatures LEROY, Globoquadrina altispira (CUSHMAN
and JARVIS), Orbulina universal D'ORBIGNY.
This zone is the lower middle
part based on the Late Appearance of Globigerinoides sub quadratus BRONNIMANN
and the Late Appearance of Globoquadrina dehiscence (CHAPMAN, PARR, COLLINS),
which is characterized by Globigerina nepenthes - Globorotalia (T.) sickness to
Globorotalia (T.) continuous Blow zonation N14-N15, According to Postuma, the
age is Middle Miocene to Early Late Miocene.
2.
The third layer is the upper middle part of the
measured stratigraphy consisting of alternating layers of fine tuff, the
thickness of each layer is between 20cm � 70cm, the coarser grained tuff layers
are between 45 cm � 160 cm each layer, the finer-grained tuff is overall
thinner than tuff is coarser.
This layer is located in
harmony above the lower middle layer, the fossils found include Globorotalia
immatures LEROY, Globorotalia pseudomiocenica BOLLY and BERMUDEZ, Orbulina
universal D'ORBIGNY, Globorotalia menardii (D'ORBIGNY), Globoquadrina dehiscens
(CHAPMAN, PARR, COLLINS), Globorotalia Plesiotumida BLOW and BANNER, Orbulina
Bilobata (D'ORBIGNY), Globigerina praebulloides BLOW.
This zone is based on the Early
Appearance of Globorotalia pseudomiocenica BOLLI and the late emergence of
Globoquadrina dehiscence (CHAPMAN, PARR, COLLINS) to the Late Appearance of
Globorotalia Plesiotumida BLOW and BANNER, namely characterized by Globorotalia
(T.) acostaensis acostaensis - Globorotalia (G.) merotumida to Globorotalia (G.)
tumi-da plesiotumida � Sphaerodinellopsis subdehiscens paenedehiscens Blow zone
N16-N18, according to Postuma the age is late Miocene to early Pliocene.
The fourth layer is the top
part of the measured stratigraphy, consisting of alternating layers of fine
tuff; the thickness of each layer is between 30cm � and 100cm. The coarser-grained
tuff layer is between 10 cm and 110 cm, and the finer-grained tuff has a
thickness almost the same as the coarser tuff.
Figure 3. Tanamailie Stratigraphic Column
This layer is the top layer. The fossils found include Globorotalia
menardii (D'ORBIGNY), Orbulina Bilobata (D'ORBIGNY), Sphaerodinella subdevices
BLOW, Globorotalia myogenic PALMER, Globigerinita naparimaensis BRONNIMANN,
Globigerinoides sacculifer (BRADY), Orbulina universal D'ORBIGNY.
This zone is based on the Early and Late Appearance of the CUSHMAN and
JARVIS Globorotalia miocenica index fossil, which is characterized by
Globorotalia (G.) tumida � Sphaerodinellopsis subdehiscens paenedehiscens to
Sphaeroidinella dehiscens dehiscens - Globoquadrina altispira altispira Blow N18-N19
zoning, according to the Pliocene Postuma (Iskandar et al., n.d.).
The depositional environment is
characterized by abundant benthonic fossils (Figure 4). Textularilia sp Aphelis
Loeblich and Tappan and Nodosaria, interpreted as indicating a shallow marine
environment.
Figure 4. (Plate 1-5) Nodosaria ambigua and Nodosaria sp. (Plate
6-7)
Laevidentalina aphelis Loeblich and Tappan and Textularia
sp
CONCLUSION
Based on the
results of the description of the fossil content and the age interpretation of
the analysis results, which are represented by the lower layer and middle
layer, and the upper layer where measured stratigraphy was carried out from the
distribution of fossils, the age duration of N13-N19 or the last part of the
Middle Miocene to the Pliocene is obtained. Deposited in an outer neritic to
the inner neritic environment, based on abundant benthonic fossils found in
almost all layers, namely Nodosaria sp. and Textularia sp. The fossil analysis
provides an overview and shows that the volcanic tufa found in the Tanjung
Tanamailie area is the lower part of the Parepare volcanic stratigraphic
sequence.
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