The Bodjong Formation is a fossil locality renowned for its abundance of marine molluscs. The Bodjong is located in Indonesia, in the western region of the island of Java. The fossils from the formation represent organisms that thrived during the Pliocene epoch, at the end of the Tertiary period. The work done in Bodjong on mollusc stratigraphy has been used by many other paleontologists in comparing molluscan faunas across Southeast Asia. For instance, during the first quarter of the twentieth century, K. Martin developed a system for comparing molluscan fossils using guide species representing particular geologic ranges and stages. Because most species are limited in range, it is difficult to use standards of comparison over large areas. Consequently, the "Javan standard" is more effective than North American or Japanese standard faunas in comparing fossil collections of Southeast Asia. The island Borneo, which is located just north of Java, and the many other islands composing the Malay Archipelago (East Indies), presently share climates and topography similar to that of the Bodjong area. Thus, it is more likely that they would have shared more mollusc species with Bodjong than would European or East Asian localities (Shuto 289-290).
During the Pliocene, the area of the present Bodjong Formation was a marine environment. Around 4.1 million years ago, there was a regression of bottom waters -- a decrease in sea level that was accompanied by the cooling of surface waters. The expansion of Antarctic ice sheets during this time may have been responsible for the cooler water temperature. Accompanying this cooling of Javanese waters was a turnover in planktonic foraminiferal assemblages. In sediments 4.1 to 3.0 million years old, an increase in the abundance and frequency of organic carbon and benthic foraminifera deposited beneath the water surface was observed along with the cooled waters (Resig 426). Such an increase in carbon could be the result of the accumulation of detritus formed from the remains of dead organisms and species that were unable to survive in the cooler conditions. The abundance of decomposing matter would have provided more nutrients in the bottom layers of the ocean, allowing benthic foraminifera to thrive.
Geology of Western Java :
The map at right shows the surface geology of the western end of the island of Java. If you're not sure where Java is located, refer to the miniature map of Indonesia in the upper right corener of this page. (Java is colored red.)
The Bodjong Formation is found in the Pliocene strata near the westernmost end of the island, just south of the large coastal region of volcanic rock deposited by activity in the region around Mount Karang. Notice the large areas covered by volcanic deposits of the past two million years (labelled Quaternary Volcanic).
Click on the map for a larger view of the region (34K). Map adapted from Sandy, Atlas Indonesia, p.35.
Among the most abundant fossils found in the Bodjong Formation are those of molluscs. Molluscan shells fulfill the requirements needed for successful fossilization, which include having a wide geographic range, having hard body parts, and being buried relatively rapidly. Gastropod remains, which include the shells of marine snails, are found preserved because they are composed primarily of minerals that remain long after the organic substances forming the organism have decayed (Campbell, 1999). The mollusc fossils found in K. Martin's Indonesian studies that were used as guide species include: Turrtitella terebra bantamensis, Tritonalia bantamensis, Cantharus lulianus, Nassarius bodjongensis, Trigonostoma bantamense, Clavus malingpingensis, and Nucula bantamensis (Shuto 290). These species are primarily gastropods commonly found in shallow waters. Additional studies in Buton in South East Sulawesi, Indonesia, revealed additional fossils from deep water gastropods including the species Styliola subula, Cavolinia bituminata, Cavolinia mexicana, Cavolinia vendryesiana, and Diacria mbaensis (Janssen 179).
During the Pliocene, the Bodjong Formation in Indonesia was a deep-water marine environment. It is therefore likely that the mollusc remains found in the locality lived in deep-sea reef environments as opposed to a tide-pool or other shallow water environment. As the locality was a marine environment, the composition of the sediment and sand reflect the aquatic life that once inhabited the area. For instance, megaripple deposits consist largely of foraminiferal sand washed out from the Pliocene pelagic chalks and marls, mixed with some shallow-water bottom-dwelling organisms. Turritella sandstone is formed when long, slender and conical shells of the gastropod Turritella were laid in the ground in Java, in addition to Balanus limestone formed from barnacles, and Corbicula layers formed from the fossil remains of clams. These layers were found lying in the ground in ascending order as they were laid sequentially during the Pliocene (Roep 145).
Common Bodjong molluscs : The shells above come from the Bodjong Formation in western Java. From left to right: Nucula sp., Nassarius cf. macrocephala, and Turritella sp. Species of Nucula and Nassarius have been used as index fossils for Pliocene sediments across southeast Asia, while Turritella is a common and distinctive large fossil that may accumulate as Turritella sandstone.
Patterns of sedimentation provide evidence that slidings and currents may have resulted in channel fills and upliftings that are present in exposed oceanic sediment of the Bodjong area. Slidings result when such perturbations as rough ocean currents cause the sedimentation to be disturbed and loosened. The sediment from the upper levels then erodes and slides down, filling empty channels with sediment from above. In the Early Pliocene slope, the transformation of a slide into a channel fill where fossils could later be found was evident. Eroded channel sides from previously deposited cohesive sediment and irregular slide scars present evidence that the sedimentation and layers could have shifted in the area, resulting in levels that are not directly comparable to geologic layers in other regions. Ocean currents may have also played a major role in transporting biogenic materials from the initial sites of sedimentation and moving them to other areas. When studying the orientation and patterns of the sedimentation of fossils and biogenic materials, it is possible to make conclusions about the conditions of the ocean environment at the time of sedimentation. For instance, it is likely that swift currents would cause the fossils to be broken and therfore later found without a high degree of articulation (Roep 147-151).
Seismic and tectonic activity have since changed the sea level and elevation of the Bodjong area of Indonesia from that during the Pliocene. For instance, during the Pliocene, the layers that are currently above ground were one to two kilometers deeper. Quaternary contour currents may have been the cause of the shifting upward of the layers (Roep, 1996). Contour currents result from dense cold waters that flow around the bottom of the sea floor, causing erosion and rippling of the sediment. Just as ocean currents resulted in the disturbance of sedimentation, provoking slidings, the consistent disturbance of contour currents over long periods of time would be sufficient to alter and shift the layers of land. The movement and sliding of landmasses may have also been the cause of areas of sedimentation and materials being shifted. Recent volcanic activity among the Krakatau islands just west of Java provides evidence that the formation and shifting of landmasses during the Pliocene may have also been influenced by volcanic activity. For example, in 1930, the island Anak Krakatau was formed following an eruption, and since that time more than one meter of volcanic ash and ejecta has accumulated on the island (Whittaker, 1998). If such volcanic activity was capable of forming an entire new island from the destruction of a previous one, it is likely that volcanoes could have altered the sedimentation and orientation of landmasses about the Bodjong area.
Pliocene crabs : Though the Bodjong Formation is best-known for its many molluscs, there are also fossils of a few other invertebrates, including crabs. From left to right, these are Charybdis lucifera, Xantho (Lophoxanthus) scaberrimus, and Galene bispinosa. The images of Charybdis and Xantho are composite images, allowing you to view the dorsal (back) and ventral (belly) side of the same fossil crab.
Besides molluscs, smaller foraminifera are also abundant in the Bodjong formation (Boomgart, 1949). Foraminifera are protists that secrete a mineral shell, and these shells are often preserved in large numbers as fossils. There are a reported 292 species of smaller foraminifera described from 81 core samples of an exploration of 2000 m. depth in Java. Besides 166 previously known species, 30 new species of foraminifera were also reported. The Bodjong foram fauna, ranging from Miocene to Pliocene in age, represents a bathyal formation. Bathyal is defined as pertaining to the ocean bottom between the sublittoral and abyssal zones -- from depths of approximately 200 to 400 m. In the upper part, it has the character of a Globigerina-ooze, whereas in the lower part, a decrease in the fauna is observed. The continuous presence of pelagic, or open sea, species indicates a permanent open sea connection. The general character of the residues of the samples in the lower part points to unfavorable conditions, such as light and temperature, which affected the rate of sedimentation and fossilization (Boomgart, 1949).
In his study, Boomgaart applied the percentage method to measure the diversity of the smaller foraminifera. In 1934, before the exploration, the Bataafsche Petroleum Maatschappij drilled a well north of Bodjong to a depth of 2006 m. The available samples taken from the well ranged in depth from 217m to 2006m, and then were enumerated according to their depths in meters. In all, 81 samples of smaller foraminifera were selected for closer examination. With the percentage method, the diversity in percentage of the smaller foraminifera was determined for further analysis and study of the Formation. The percentage method is important in the study of Bodjong Formation, because it is also used to collect and analyze molluscs and corals. The percentage method has also been used in studying these kinds of fossils in other regions of the Indo-Pacific (Boomgaart, 1940).
During the study of Bodjong Formation, various ecological and environmental factors were considered when collecting data, and when using the results of the percentage method. For example, Norton and Natland studied ecological relations of temperature and depth. The influence of temperature was found to be more important in determining community preservation than was that of depth, contrary to previous statements by scientists Cushman, Natland, Kleinpell, and Glaessner. It is also argued that, regardless of the insufficient evidence available, the amount of light might influence the rate of sedimentation. Other factors that might have influenced the relative abundance of the character of the bottom-dwellers were salt and oxygen concentrations, pressure, associated fauna and flora, and character of the sea bottom. These factors might also be effective in influencing the abundance of mollusc and mollusc-like species in the region (Boomgaart, 1949).
Gastropods from Bodjong : The majority of large fossils from the Bodjong are marine gastropods, mostly deep-water species. Above from left to right, Babylonia sp., Bufonaria (3 shells of B. margaritula to the left and 2 of B. crumena to the right), and finally Tugurium (Haliphoebus) sp.
Much about the Pliocene ecology of the Bodjong area can be deduced from the study of fossils that have been found. The mollusc fossils found are mostly gastropods adapted to deep-water environments. Many of these molluscs had adapted their modes of reproduction to the ocean currents characteristic of their aquatic environments. The flow of water was effective for mollusc larvae to be dispersed thorough the water in large numbers. The reproductive success and fitness of the molluscs ensures their ability to thrive in this marine environment. Additionally, molluscs produce large numbers of larvae during each reproductive cycle, but because the larvae are prey to other organisms in the ocean, not all of them survive.
The dietary habits of molluscs also provide insight about the ecology of the Indonesian waters around western Java during the Pliocene. Some molluscs are carnivorous, and are secondary consumers in their aquatic ecosystems (Poutiers, 1995). These molluscs may be filter feeders, drawing in small organisms that float through the water. Therefore, in addition to molluscs, the waters around the Bodjong Formation must have also supported the zooplankton and other primary consumers and producers that were part of the food chains supporting these molluscs. Because especially small organisms like zooplankton and phytoplankton are not commonly fossilized, it is easy to overlook their presence during this time. However, the evidence from molluscs indicates that the deep-water environment of Indonesia during the Pliocene was rich with many small organisms.
Information regarding the mineral content and composition of Javanese waters during the Pliocene can also be gathered by analyzing the shells of molluscs. Mollusc shells are made primarily of calcium carbonate, with traces of strontium and other elements (Kim, 1999). In order for the mollusc's shell to be built, certain minerals must be present in the water. Therefore, calcium and other minerals and elements found within the shells of the molluscs must have been found in adequate quantities in the ocean waters around Indonesia in order for the molluscs to produce their shells.
Bodjong bivalves : Though gastropods are the most common mollusc shells found in the Bodjong, there are also many bivalves, including the ones pictured above. Bivalves can be easily distinguished from gastropods because they have two halves to their shell, often fitted with a hinge.
There is much evidence of marine life in Java from the fossils found in the Bodjong Formation. However, many other kinds of Pliocene fossils have also been discovered in the same area. Java was once connected with mainland Asia by a land bridge, but because of changes in sea level and because of tectonic activity, it became an island, trapping and isolating the animals there (Recer). The search for mammalian fossils has concentrated along a bend in the Solo River in Java, near the village of Trinil. In 1973, a hominid skullcap and two stone tools were found. In 1887, Eugene Dubois discovered a skullcap, a femur (thigh bone), and a molar (tooth) in the same area. This "Java or Solo man" was named Pithecanthropus erectus, which means "upright ape man". It is believed to belong to the species Homo erectus, now also known from China and eastern Africa.
Further excavations in the area around Bodjong revealed the fossilized remains of a dwarf Stegodon, found in July of 1992 by a team of the Geological Research and Development Center (GRDC). A Stegodon is a kind of saber-toothed elephant. The matrix from which this dwarf Stegodon was found also consisted of abundant shallow marine mollusks and a few volcanic components embedded in the coarse-grained cement. The environment of this particular limestone during the Pliocene was shallow open marine and was probably near a point where constant influxes from a river were common. The sandstone also included fragmentary remains of a small deer, rhinoceros, elephants, and Panthera tigris (a tiger).
The evidence of a high species richness indicates that the climate and resources of Java have changed throughout time to be able to support such diversity. Obviously, the marine environment during the Pliocene would have been unsuitable to the various mammals that lived in Java during the late Pliocene. However, the land and climate have changed throughout time, with each area of Java having particular topographic, vegetational, and climatic differences allowing the existence of different species. With each episode of change in a region, unique taxa of animals specially adapted to the particular conditions of that environment would have come to inhabit the area.
In considering the geological and ecological history of the Bodjong region, there is much evidence picturing it as a rich marine environment supporting a wide array of organisms during the Pliocene. This fossil locality in West Java, Indonesia has been the site of many excavations of molluscan fossils, allowing the Bodjong Formation to become a standard of comparison for other fossil localities in neighboring regions. Studies on the fossils and on the sedimentation of the area have allowed many inferences regarding the climate and geography of Bodjong during the Pliocene. Although seismic and volcanic activity have since changed the topography and climate of Bodjong, the land of western Java has consistently supported many different habitats and organisms, including a wide range of mammals and marine life. Excavations in the Bodjong Formation and in Java have been significant in providing greater fossil evidence characterizing the diverse organisms inhabiting this area of southeast Asia during the Pliocene.