A review on paleoenvironment suitability for hominid fossils and other early vertebrate faunas: a case from Pucangan and Kabuh Formations, Central and East Java, Indonesia

The northern part of the East Java Basin has become a focus of research by earth scientists, among others, because of the existence of hominid fossils and remains of other vertebrate taxa within the Quaternary sedimentary sequence. Fossilbearing layers are found in the Kendeng Zone, mostly within the well-known Pucangan and Kabuh Formations, which are distributed from Central to East Java. However, not all formations contain vertebrate fossils as well as hominid elements. It is important to consider what factors may have influenced the concentration of vertebrate fossils in those formations. In this study, we describe sedimentary facies at three key field locations: Sangiran, Ngawi, and Mojokerto. Our study indicates that vertebrate remains and hominid fossils mainly accumulated in continental sediments associated with lacustrine and fluvial systems. In this regard, Sangiran and Ngawi B offer the greatest prospect for yielding hominid remains, owing to their unique paleoenvironmental and paleogeographical settings as a highland during the Early–Middle Pleistocene period. Certain parts of the Kabuh Formation in the Mojokerto region also hold high potential, especially those displaying evidence of continental deposition. INTRODUCTION The northern part of the East Java Basin (the area between 110°30' to 113° E and 6°22' and 7°41' S) has become a focus of considerable interest to earth scientists due to the existence of oil and gas resources, and a continuous sequence of sedimentary layers from Mid-Miocene to Pleistocene in age, some of which have yielded fossils of early hominids as well as a wide range of other vertebrate fossils which occur in certain Quaternary sediments. Based on physiographical expression, the northern part of the East Java Basin can be divided into four zones. From north to south, these are the North Java Sea Platform, Rembang, Randublatung Depression, and Kendeng. The Kendeng Zone is the most famous zone for paleontologists, since a number of hominid and other vertebrate fossil assemblages occur within this zone in the Pucangan and Kabuh Formations [1]. Furthermore, the Kendeng Zone can be divided into three sub-zones: West Kendeng (between Mt. Ungaran and Purwodadi), Middle Kendeng (between Purwodadi and Mt. Pandan), and East Kendeng (between Mt. Pandan and Mojokerto) (Figure 1). The Pleistocene lithological unit exposed at Pucangan hill 20 km north of Jombang (East Java) was named as “Pucangan” and Kabuh is the name of a village located about 7 km north of Ploso, in the Jombang region of East Java [3]. In the Sangiran area, hominid and other vertebrate fossils have mostly been correlated with the Pucangan and Kabuh Formations. In terms of their relative stratigraphical positions, the preceding formation is older than the later formation [4]. Along with Sangiran, Trinil is also well known as the site of hominid fossils and large vertebrate faunal assemblages. At Trinil, which is located about 8.5 km west of Ngawi (East Java), Dubois found the first pieces of the hominid fossil he named Pithecanthropus erectus, which is now known as Homo erectus [5]. SOR-LIFE