Yahdi Zaim

Early Pleistocene 40Ar/39Ar ages for Bapang Formation hominins, Central Jawa, Indonesia

The Sangiran dome is the primary stratigraphic window for the Plio-Pleistocene deposits of the Solo basin of Central Jawa. The dome has yielded nearly 80 Homo erectus fossils, around 50 of which have known findspots. With a hornblende 40Ar/39Ar plateau age of 1.66 ± 0.04 mega-annum (Ma) reportedly associated with two fossils [Swisher, C.C., III, Curtis, G. H., Jacob, T., Getty, A. G., Suprijo, A. & Widiasmoro (1994) Science 263, 1118–1121), the dome offers evidence that early Homo dispersed to East Asia during the earliest Pleistocene. Unfortunately, the hornblende pumice was sampled at Jokotingkir Hill, a central locality with complex lithostratigraphic deformation and dubious specimen provenance. To address the antiquity of Sangiran H. erectus more systematically, we investigate the sedimentary framework and hornblende 40Ar/39Ar age for volcanic deposits in the southeast quadrant of the dome. In this sector, Bapang (Kabuh) sediments have their largest exposure, least deformation, and most complete tephrostratigraphy. At five locations, we identify a sequence of sedimentary cycles in which H. erectus fossils are associated with epiclastic pumice. From sampled pumice, eight hornblende separates produced 40Ar/39Ar plateau ages ranging from 1.51 ± 0.08 Ma at the Bapang/Sangiran Formation contact, to 1.02 ± 0.06 Ma, at a point above the hominin-bearing sequence. The chronological sequence of 40Ar/39Ar ages follows stratigraphic order across the southeast quadrant. An intermediate level yielding four nearly complete crania has an age of about 1.25 Ma.

Way out of Africa: Early Pleistocene paleoenvironments inhabited by Homo erectus in Sangiran, Java

A sequence of paleosols in the Solo Basin, Central Java, Indonesia, documents the local and regional environments present when Homo erectus spread through Southeast Asia during the early Pleistocene. The earliest human immigrants encountered a low-relief lake-margin landscape dominated by moist grasslands with open woodlands in the driest landscape positions. By 1.5 Ma, large streams filled the lake and the landscape became more riverine in nature, with riparian forests, savanna, and open woodland. Paleosol morphology and carbon isotope values of soil organic matter and pedogenic carbonates indicate a long-term shift toward regional drying or increased duration of the annual dry season through the early Pleistocene. This suggests that an annual dry season associated with monsoon conditions was an important aspect of the paleoclimate in which early humans spread from Africa to Southeast Asia.

New reconstruction and morphological description of a Homo erectus cranium: skull IX (Tjg-1993.05) from Sangiran, Central Java.

Skull IX (Tjg-1993.05) was unearthed from the upper stratigraphic zone (Bapang-AG levels) of the hominin-bearing sequence in Sangiran. This remarkably complete cranial specimen of Homo erectus from the early Pleistocene of Java preserves substantial portions of the vault and face. However, the distortion present in the original reconstruction has hampered detailed documentation of its morphological characteristics. We here report a new reconstruction of Skull IX that successfully recovers the original morphology and significantly differs from previous reconstructions. Detailed morphological description and the results of initial comparative analyses based on this new reconstruction are provided. The endocranial volume of Skull IX was measured as 870 cc using micro-CT data. The neurocranium of Skull IX is slightly smaller than the so far recorded smallest cranium from this zone, suggesting this individual was female. In most, but not all, aspects of the cranial vault form, details of the external surface structures, and facial morphology, Skull IX exhibits numerous similarities to the other Bapang-AG H. erectus specimens, indicating that it belonged to the Bapang-AG H. erectus population. Drawing on the expanded fossil sample of this chronoregional H. erectus group, we discuss their evolutionary status, degree of sexual dimorphism, and facial morphological variation in Afro-Asian earlier Homo specimens.

Lithostratigraphic Context for Kln-1993.05-SNJ, a Fossil Colobine Maxilla from Jokotingkir, Sangiran Dome

Jablonski and Tyler (1999) announced a new subspecies of colobine monkey based on a fossil partial maxilla from the Sangiran dome. The specimen is easily assigned to a living leaf monkey species—most extant Southeast Asian catarrhines differ only subspecifically from their Middle Pleistocene earliest local fossil ancestors. Yet Jablonski and Tyler (1999) reported an improbable provenance for the specimen; a mass-flow volcanic breccia generally considered late Pliocene in age. We show that the Lower Lahar was laid down amidst a range of paludal habitats and that its deposition predates the appearance of all-but-now extinct, water-tolerant mammals on emergent Java. No other catarrhine fossil has been ascribed to the Lower Lahar, not even hominins, which are the most gregarious members of the group. More probable provenance lies in the upper Sangiran or the lower Bapang formations. Either alternative would associate the specimen with other catarrhine fossils in more tenable Pleistocene environments. We also unravel errors and inconsistencies in the contextual report and in the discussion of dome geochronology. The various radiometric, paleomagnetic, and paleontologic studies cited show a discordance of about 300 Ka (thousand years) across the lithostratigraphic sequence. Plio-Pleistocene biogeographic hypotheses for Java must work with short and long chronologies.

Geological Evidence for the Earliest Appearance of Hominins in Indonesia

Until the end of Tertiary period (Pliocene), almost all Indonesian regions were still occupied by a marine environment. Tectonics and glacioeustatic changes took place during the Pleistocene to form the Indonesian Archipelago, including the emergent lands known as Sunda Land and the Sahul Shelf. The Sunda Land connected Asia mainland with the islands of Sumatra, Java and Kalimantan. It also acted as a land bridge and migration route for Homo erectus and vertebrate faunas from the Asia mainland to Java. In the Pleistocene, the sedimentations in Indonesian regions occurred mostly in non-marine environments: lakes and rivers (sometimes with marine influences) which are favorable for hominin and vertebrate occupations. The first arrival of vertebrate faunas from Asia to Indonesia through the Sunda Land at the end of the Late Pliocene and later on was followed by arrival of the early hominin – Homo erectus paleojavanicus (Meganthropus paleojavanicus) to Java in the Early Pleistocene (1.6–1.0 Ma). During the Middle to Late Pleistocene (1.0–0.125 Ma) there existed another hominin in Java as indicated by the presence of Homo erectus ngandongensis/soloensis. Recently, hominin fossils have also been discovered in eastern Indonesia, at Liang Bua, Flores island and are attributed to Homo floresiensis (orang pendek – pygmy people) dated as 12,000 BP or the end of Late Pleistocene probably coexistant with Homo sapiens. The very important site of hominin and vertebrate fossils in Indonesia and in Java is the Sangiran Dome. More than 152 fossils of Homo erectus in Indonesia are found in the Sangiran Dome, from Early Pleistocene deposits of the Sangiran Formation to Middle Pleistocene sediments of the Bapang Formation. These represent more than 77% of the total hominin specimens found in Java. The fossils represent an early human occupation since Sunda emerged from the Java Sea. Therefore, in the Quaternary, Java Island is the home for hominins in Southeast Asia. The human fossil Homo erectus and the vertebrate fossils found in Quaternary sediments in Java are very important for understanding human evolution in Indonesia and Southeast Asia and the initial expansion of hominins out of Africa.

Oligocene Shorebird Footprints, Kandi, Ombilin Basin, Sumatra

Recent fieldwork in the Ombilin Basin of west-central Sumatra resulted in the discovery of two distinct types of avian footprints, both referable to the ichnogenus Aquatilavipes. The footprints were discovered in the Oligocene Sawahlunto Formation in a creek side outcrop near the Kandi Ombilin Mine. Aquatilavipes wallacei is a small species of Aquatilavipes (∼ 19 mm wide; 27 mm long) with elongate third digits, wide total divarication angles (120–150°) and inwardly curved peripheral digits. Aquatilavipes ichnospecies A are also small traces (average 21 mm wide; 31 mm long) with elongate third digits and straight to slightly outwardly curved peripheral digits. These traces are similar in morphology to those of small modern shorebirds such as rails (Rallidae), sandpipers (Scolapacidae) or plovers (Charadriinae). The Sawahlunto traces occur in very fine-grained to fine-grained sandstone characterized by low-relief current ripples, many of which exhibit mud-draping. A low diversity invertebrate trace fossil assemblage consisting of Arenicolites, Diplocraterion, Planolites, Monocraterion, Skolithos and Coenobichnus co-occurs with the bird footprints. This succession is interpreted as intertidal sand flats. Probe and peck marks preserved on the same bedding planes as the bird footprints support the interpretation that these birds occupied the Kandi intertidal flats for foraging purposes.

Tsunami Evidence in South Coast Java, Case Study: Tsunami Deposit along South Coast of Cilacap

Cilacap Area is situated in coastal area of Southern Java and directly affected by tsunami hazard in 2006. This event was triggered by active subduction in Java Trench which active since long time ago. To detect tsunami and active tectonic in Southern Java, paleo-tsunami study is performed which is targeted paleo-tsunami deposit older than fifty years ago. During 2011 - 2016, 16 locations which suspected as paleo-tsunami location were visited and the test-pits were performed to obtain characteristic and stratigraphy of paleo-tsunami layers. Paleo-tsunami layer was identified by the presence of light-sand in the upper part of paleo-soil, liquefaction fine grain sandstone, and many rip-up clast of mudstone. The systematic samples were taken and analysis (micro-fauna, grainsize and dating analysis). Micro-fauna result shows that paleo-tsunami layer consist of benthonic foraminifera assemblages from different bathymetry and mixing in one layer. Moreover, grainsize shows random grain distribution which characterized as turbulence and strong wave deposit. Paleo-tsunami layers in Cilacap area are correlated using paleo-soil as marker. There are three paleo-tsunami layers and the distribution can be identified as PS-A, PS-B and PS-C. The samples which were taken in Glempang Pasir layer are being dated using Pb – Zn (Lead-Zinc) method. The result of Pb - Zn (Lead-Zinc) dating shows that PS-A was deposited in 139 years ago, PS-B in 21 years ago, and PS C in 10 years ago. This result indicates that PS -1 occurred in 1883 earthquake activity while PS B formed in 1982 earthquake and PS-C was formed by 2006 earthquake. For ongoing research, the older paleo-tsunami layers were determined in the Gua Nagaraja, close to Selok location and 6 layers of Paleo-tsunami suspect found which shown a similar characteristic with the layers from another location. The three layers deeper approximately have an older age than another location in Cilacap.

A Fossil Gourami (Teleostei, Anabantoidei) from Probable Eocene Deposits of the Ombilin Basin, Sumatra, Indonesia

ABSTRACT— Fossil fishes were first collected from deposits of the Sangkarewang Formation of the Ombilin Basin in Sumatra, Indonesia, in the 1870s, but a comprehensive study of these fishes was not published until almost 50 years later. New material from these deposits was collected in 2009, which included a small anabantoid fish. This fish is not conspecific with any of the material described previously and is here named as a new genus and species. A phylogenetic analysis indicates that the new anabantoid is closely related to Osphronemus among the taxa studied, and we place it in the family Osphronemidae. However, the new fish does not appear to belong to any of the named modern subfamilies, so we leave it incertae sedis in the family. Additionally, the osphronemid subfamilies are not recovered as a monophyletic group. The anabantoid named here and another previously described from the same locality are the only fossil anabantoids known. However, the age of the Sangkarewang Formation is not confirmed and has been variously attributed to Cretaceous, Palaeocene, Eocene, and Miocene, with Eocene being the presently favored estimate. Based on the presence of an anabantoid in these deposits, an Eocene age is reasonable and is not contradicted by the known fish fauna. http://zoobank.org/lsid:urn.lsid.zoobank.org:pub:53281C25-8E47-4C67-9952-A994B47F6656

A preliminary study of paleotsunami deposit along the south coast of East Java: Pacitan-Banyuwangi

Along the southern coast of East Java Indonesia, at a number of localities, it can be identified and attempted to assign the age of tsunami deposit. Laboratory analyses were conducted also to support this study such as Granulometry, Paleontology and radiometric dating analysis. The presence of tsunami 1994 deposit in the area of Pancer, Lampon, Prigi and Grajagan was found, as a result of 7.8 Magnitude Banyuwangi Earthquake. The radiometric dating analysis also identified some paleotsunami deposit of about 1921 and 1930 in the area of Prigi and Teleng. This paleotsunami is assumed to have a correlation with an earthquake in the south of Java at the same time. An outcrop in the Prigi and Teleng strongly convinced the fact of an earthquake generated tsunami in the south of Java in the year of about 1921 and 1930.