The oldest exposed rock in the world, aged 439 – 360 million years ago (Silur – Devonian) located in Aduwey, Misool
© Hanang Samodra
"Archipelagic karst" in Raja Ampat area in Geosite Karst of Wayag
Earth was formed approximately 4.5 billion years ago. The exposed rocks in the Raja Ampat Geopark area, which make up the diversity value of the geological heritage, represent almost a tenth of the age of the Earth. These various types of rocks, ages, and environments of formation compose the complete geological history of the Raja Ampat area, which began hundreds of millions of years ago until now. The metamorphic rocks in Misool which originate from turbidite deposits, and are the oldest rocks exposed in Raja Ampat are 439-360 million years old (Silur-Devon). The Misool Basin is further filled by Mesozoic rocks such as shale, sandstone, and a small amount of limestone. Meanwhile, in the Batanta-Salawati realm in the northern part, it was 148 million years ago (Late Jurassic) due to expansion at the bottom of the Pacific Ocean.
This event caused the rise of ultramafic magma to the surface before finally congealing to form nickel-bearing ultramafic rocks in Waigeo and its surroundings. Sedimentation in the Tertiary Period in the south (Misool), in the middle (Batanta), and in the north (Waigeo) produces rock formations which are a collection of various types of sedimentary rock, volcanic rock, & limestone. The Eocene limestone outcrops in Misool & surrounding areas, as well as the Neogene limestone in West Waigeo (Gam, Kabui Bay) & in the vast Wayag Islands form a very significant karst landscape. Karst phenomena such as caves do not only occur on land, but also in the sea which is an extension. This place is a famous diving location. The east-west active fault that passes through the Raja Ampat area is the Sorong Fault. This left horizontal fault is an important geological structural component in the Geopark area, in addition to folding phenomena such as anticlines and synclines.
Physiology and Morphology
As an archipelago, the Raja Ampat area consists of hundreds of islands. The main islands in the Geopark area are Waigeo, Batanta, Salawati, and Misool. The height of these islands ranges from 0 m to 920 m asl. Waigeo is the highest island, where the peaks of the mountains reach a height of 920 m asl. Misool Island, which occupies the southern part of Raja Ampat, has a maximum height of 327 m asl. The high peaks (Mount Kupel, Mount Zadel) and the surrounding area (Mount Zaag) are occupied by karstified limestone.
Mayalibit Bay in Waigeo becomes a striking landscape when the long bay that stretches in a northwest-southeast direction seems to separate the island into 2 parts. By genesis, small islands in the interior of the bay are sea-stacks whose formation is influenced by geological structures (faults). This landscape segment is part of the Mayalibit Bay protected area. Gam Island and Kabui Bay in the south-west of Waigeo are islands and a group of small islands that show a karst landscape. The sea waters that separate each island have a depth of between 20 m (on the outskirts of the island) and 200 m (in open waters).
The northernmost part of Raja Ampat Regency is occupied by the Wayag Islands. To the northwest and northeast are Pulau Sayang and the Pacific Ocean, respectively, where the Federal Republic of Palau is located. The waters west of Wayag are included in the area of Central Halmahera Regency, North Maluku Province. The sea depth outside the Wayag Islands is on average less than 100 m.
The Wayag Archipelago (including Pulau Sayang) which is the outermost archipelago of Indonesia is a group of islands with a distinctive morphology. This northern group of islands (Wayag-Quoy-Uranie) has an archipelagic karst landscape. There are more than 100 limestone islands in this area, with varying sizes. Quoy Island east of Wayag Island is also often called Yin Island; while Uranie Island, east of Bag Island by the locals is called Mace Island. The islands that stick out from the seabed have a maximum height of 75 m above sea level, with steep edges
The Wayag-Quoy-Uranie archipelago forms a line with a northwest-southeast trend. This lineament is controlled by a northwest-southeast fault, which appears to be the main geological structure at Waigeo. Estuaries or steep walls on hills are also caused by geological structures, namely joints and faults. Shallow sea waters (less than 20 m) on Wayag Island are lined with limestone islands with towers forming a kind of lagoon. The bottom of the lagoon is overgrown with coral.
The various types of limestone hills on Wayag Island, ranging in shape from sinusoids to cones (conical), with a flat surface similar to a plateau, to towers characterize the outer karst phenomenon in this area. The diversity of hill forms is influenced mainly by geological structures, both fractures (joints) and faults (faults).
Various forms of limestone hills in the Wayag Islands which were initially influenced by the type of limestone lithology, stratigraphy, and geological structures (joints, faults).
© Hanang Samodra (2014).
From the lithological point of view, thick marl limestone which is softer and less resistant to dissolution tends to form a hemispherical hill with a curved peak. Limestone sequences, according to stratigraphy, are composed by alternating between easily soluble limestones and limestones that are more resistant to dissolution (coral limestones) which when karstified tend to form cones.
A hill or embankment with a flat top so that it gives a plateau-like appearance can be ascertained that the top is composed of limestone which is relatively soluble in type, such as marl limestone. The thick insertion of marl at the top of the hill also often triggers the formation of a hill with a horizontal peak. The rim of the plateau's hilltop is usually curved due to strong erosion and dissolution. The hillside with low horizontal peaks, which is on the beach and gives a terraced appearance, is interpreted as a step-beach landscape.
The faults and joints in the Wayag area are responsible for the origin of the various hills. Each protrusion is bounded by a vertical or nearly vertical wall, which is actually a fault plane or joint. The spread of the tower hills is so dense that there is almost no plain in between.
At Batanta, the rugged hills along the north coast have gentle slopes in the north and steep slopes in the south. Verstappen (1960) interpreted the rock formations as rock formations which in their development experienced a decline so that they were covered by the sea. The hills in central and western Batanta show karst topography. Dolina, uvala and polje color the limestone surface landscape, including several caves. The flow pattern in this karst segment tends to be below the ground surface.
Morphologically, Misool Island, which is located in the southernmost part of the Raja Ampat Regency, is divided into 3 geomorphological units, namely:
Uplifted coral reefs that form the shoreline were observed in the south-eastern part of Wayag Island. A similar phenomenon was seen on the islands of Mainsfield, Boo, Fam, Kofiau and Doif to the west of Batanta Island and Salawati Island.
Geopark areas reveal various types and ages of rocks, each of which is grouped into rock formations. Starting to become rocks and tectonic influences tell the geological history that began hundreds of millions of years ago until now.
These pre-Triassic rocks, or about 439 million-360 million years ago, were only exposed locally in the southwest part of Misool. This metamorphic rock unit that underlies the Mesozoic rocks is the oldest rock in the Raja Ampat Geopark area. Its thickness is thought to be more than 1,000 m (Rusmana et al, 1989).
This collection of rocks formed between 245 million and 65 million years was exposed at Waigeo, East Batanta, North Salawati and South Misool. In Waigeo the lithology is in the form of ultramafic rocks that are 148 million years old, and sedimentary rocks (Tanjungbomas Formation). In Batanta and Salawati there are sedimentary rocks and low grade metamorphic rocks (Waiyaar Formation, Tamrau Formation, Ofiolite Gag). While in Misool it is in the form of sedimentary rocks (Keskain Formation, Bogal Limestone and Napal Lios Members, Yefbi Shale, Demu Formation, Lelinta Shale, Facet Limestone, Fafanlap Formation). The thickness of all Mesozoic rocks is not less than 1,000 m.
The Tertiary rock group in Raja Ampat which was formed between 66.5 million to 2 million years ago is mainly in the form of sedimentary rock, limestone, and volcanic rock. In Waigeo, there are Lamlam Formation, Rumai Formation and Volcano Rock Members, Yeben Formation, and Puri Formation.
In Batanta and Salawati there are Faumai limestones, Sirga Formation, Batanta volcanic rocks, Kais limestones, Klasafet limestones, Dore volcanic rocks, Sagewin limestones, Yaripi Formation, Marchesa Formation, and Klasaman Formation. In North Salawati, the Neogene age 11-2 million years old were found locally, including the Yefman Breccia, which was initially influenced by the Sorong Fault system which trended west-southwest-east-northeast.
Meanwhile in Misool, limestone is mostly karstified (Daram sandstone, Zaag limestone, Napal Kasim, Openta limestone, and Atkari limestone). Tertiary rock thickness reaches thousands of meters.
is a simplest way to protect our Geological Heritage.
IUCN is developing a guideline for geoconservation in protected and conserved area.
IUCN mengembangkan sebua pedoman untuk geokonservasi di kawasan lindung dan dilestarikan.
RAJA AMPAT GEOTOURISM
The beauty of nature is the strength of the various locations in Raja Ampat, which are also worldwide. This eye-pleasing experience in these natural conditions will refresh your life.
With 2,713 islands, Raja Ampat has a unique landscape. Karst islands lie on the turquoise colored sea water, which will provide an unforgettable experience just by crossing them. We can stop at one of the islands, or maybe at the uplifted sand that appears only when the tide is low, to play on the soft white sand. If you want the beauty at once, we hike for a while until we arrive at the view point and witness the splendor for yourself.
Raja Ampat Stratigraphy (*JTL = Million Years Ago)
© Hanang Samodra