Fossils

Fossils are physical evidence of preexisting organisms, either plant or animal. The most common and apparent fossils are the preserved skeletal remains of animals. Other fossils, which are also evidence of past organisms, include leaf impressions, tracks and trails, burrows, droppings, and root casts.

Megalodon Tooth Fossil
Photo from The Bohol Chronicle

Fossilized tooth of Carcharocles megalodon, a huge shark that lived during the Miocene to Pliocene period, which lasted from around 15.9 to 2.6 million years ago, was accidentally found by quadrumvirate who went hiking. The fossilized tooth of one of the largest predators was found in an uphill road in Barangay Jandig in Maribojoc.

Analysis:

The discovered fossil only proves that the mainland Bohol was still underwater during the early Miocene. According to National Museum Bohol (2020), most fossils of the megalodon were determined to date back to the middle Miocene epoch to the Pliocene era, approximately 15.9 million to 2.6 million years ago.  Bohol became what we see on maps today because of the upliftment of the submerged portion of the island and the deposition of conglomerate at the town of Mabini and the extensive placing of the Maribojoc limestone.

Bohol’s Geological Evolution

Photo was taken last December 11, 2019, National Museum Bohol

The predator’s tooth was well-fossilized because of the abundance of sedimentary rocks in the locality, which significantly helps preserve the remains. This is also the second time to find such a fossil in the said locality. With the other Carcharocles megalodon fossils found from the different parts of the world, we can say that these fossils are considered index fossils. National Museum Bohol noted that only the teeth are found, especially here in the Philippines, because most of their skeleton, like other sharks, except for their teeth is made of not bone but cartilage

Weathering and Erosion; Rock Formation

        Weathering is related to the breaking down and loosening of rock or soil into smaller pieces, but the weathered pieces remain in place. Erosion is related to the movement of weathered (and sometimes non-weathered) pieces away from the source. Rock formations are usually the result of weathering and erosion sculpting the existing rock. The term rock formation can also refer to specific sedimentary strata or other rock units in stratigraphic and petrologic studies.

Bitoon Beach Rock Formations

Photo was taken last March 2, 2019, Anda, Bohol

Analysis:

Behind me is a rock formation that made Anda beaches famous go-to destination. The rock formation is formed after so many years of exposure to salt water. Salt also works to weather rock in a process called haloclasty. Saltwater seeps through the crevices and fissures of rocks on occasion. Salt crystals are left behind after seawater evaporates. The crystals put pressure on the rock as they develop, slowly splitting it apart. Haloclasty is linked to honeycomb weathering. Honeycomb weathering, as the name indicates, refers to rock formations with hundreds or even thousands of holes created by the development of salt crystals. In coastal locations, where sea sprays continuously push rocks to mix with salts, honeycomb weathering is frequent. Haloclasty is not just found in coastal areas. Weathering of the underlying rock can be aided by salt upwelling, a geologic process in which subterranean salt domes grow.

 

Plate Tectonics

        Tectonic plates are the divisions of the earth’s crusts that are in constant movement. The movement of these plates is made possible by the churning of magma (molten rock) found beneath the crust. At times one plate will collide with another, the result of which is that the heavier plate will move under the lighter one in what is known as subduction of plates. The process forces the underlying magma to the crust from where it emerges in violent eruptions. When the subduction and resultant eruptions happen in submerged sections of the crust over an extended period of geological time, it leads to the formation of island arcs.

Philippine Plate (https://bit.ly/3fyQfqg)

Analysis:

        The Philippine archipelago, composing 7,107 islands, is never an accident; thus, it was formed year after year as influenced by the movement of the Philippine plate. According to World Atlas (2018), the formation of the islands involved the movements of three plates which converged in the region, two of them being major plates (the Indo-Australian and Eurasian plates) and one minor plate (the Philippine Sea Plate). The Eurasian plate is made up of the continents of Asia and Europe and extends into the surrounding oceans and seas while the Indo-Australian plate is made up of the Indian subcontinent and the continent of Australia. The Philippine Sea Plate is the minor plate on which the islands of Taiwan, Indonesia, and the Philippines sit. The Philippine Plate is a tectonic plate comprising of oceanic lithosphere. Many of the thousands of islands which make up the Philippines are classified as island arcs which were formed as a result of subduction after the collision of the three plates (the Eurasian Plate, the Philippine Sea Plate, and the Indo-Australian Plate). The formation of the original island arcs is believed to have occurred millions of years ago at the southern part of the Philippine Sea Plate. The original island arcs are believed to have later collided with Sundaland forming a series of other islands in the archipelago. Sundaland (also called the Sundaic region) is a biogeographical region of Southeastern Asia corresponding to a larger landmass that was exposed throughout the last 2.6 million years during periods when sea levels were lower. It includes the Malay Peninsula on the Asian mainland, as well as the large islands of Borneo, Java, and Sumatra and their surrounding small islands.

Volcanoes and Earthquakes

        A volcano is an opening on the surface of a planet or moon that allows material warmer than its surroundings to escape from its interior. When this material escapes, it causes an eruption. Volcanoes often form a hill or mountain as layers of rock and ash build-up from repeated eruptions. Volcanoes are classified as active, dormant, or extinct.

Volcano Island Taal (https://go.nasa.gov/3xpejBV)

Analysis:

        Taal volcano is part of a chain of volcanoes along the island of Luzon, which were formed by two tectonic plates colliding, the Eurasian Plate and Philippine Mobile Plate over 500,000 years ago which resulted to subduction. Unlike other volcanoes found here in the Philippines and even worldwide, Taal volcano is a complex one. Instead of rising from the ground as a distinct, singular dome like its neighbor, Mayon, Taal consists of multiple stratovolcanoes, conical hills, and craters of all shapes and sizes. These features have grown together to form the 5-kilometer (3 mile) wide Volcano Island, one of the Philippines’ most volcanically active areas.  The island rises from the north-central side of Taal Lake, which in turn fills the much broader Taal caldera.

It is the second most active volcano in the Philippines with 35 historical eruptions. All recorded eruptions from Taal have stemmed from Volcano Island. Binintiang Malaki, the largest flank cone, is visible on the northwest side of the island at the end of an isthmus, which resulted from the volcanic eruption last 1707. In 1965, yet another violent phreatomagmatic volcano occurred on the island, which resulted in rock fragments, ashfall, and acid rain. Smaller explosions in the 1970s formed cones and craters that have since reshaped the elongated 1965 crater.

Earthquakes and volcanic activity is closely related to each other. In fact, earthquakes usually accompany a volcanic eruption. Similarly, unusual earthquakes can also lead to volcanic eruptions. This is because the main theory behind both these natural calamities lies in plate tectonics.

Mass Movement and Geologic Resources

        Mass movement, otherwise known as mass wasting, happens because tectonic processes have created uplift. Erosion, driven by gravity, is the inevitable response to that uplift, and various types of erosion, including mass movement, have created slopes in the uplifted regions.

https://binged.it/3rWmwwe

Analysis:

Mass movements were experienced during the 7.2 magnitude quake last 2013. Mountains became bald and many roads were blocked because of the different mass movements (rockfall and rock slide) brought by the earthquake. We can say that the slope stability of these areas influenced the event. The shaking during the earthquake weakened the body of rock or sediment. 

Riprap Wall
Photo was taken last February 17, 2019, Sikatuna, Bohol

Our province of Bohol has highways built on slope areas like Loboc, Balilihan, and more. These areas are protected by concrete riprap walls to prevent landslides that would harm motorists and bypassers. In the case of Loboc, the roots of the trees in manmade forest significantly mitigate the risk of mass movement in the area. 

References

NASA Earth Observatory (2014). Volcano island of Taal. Retrieved from https://go.nasa.gov/3xntVWt, August 5, 2021.

Philstar (2020). Sharks of Maribojoc: 2nd tooth fossil of megalodon found in Bohol. Retrieved from https://bit.ly/3fwMBwW, August 4, 2021.

The Bohol Chronicle (2020). 15-million-year-old Megalodon fossil tooth found by friends in Maribojoc. Retrieved from https://bit.ly/3CmMYEm, August 4, 2021.

World Atlas (2018). How were the islands in the Philippines formed? Retrieved from https://bit.ly/3lxUO7X, August 4, 2021.