Towards an astronomical age model for the Lower to Middle Pleistocene hominin-bearing succession of the Sangiran Dome area on Java, Indonesia

Well-dated paleoanthropological sites are critical for studying hominin evolution and dispersal, especially when related to regional or global climate change. For the rich hominin fossil record of Africa, this has been facilitated by the development of high-resolution astronomically tuned age models. So far, such age models are lacking for the Pleistocene of SE Asia with its similarly rich fossil hominin record. This study aims to develop an astronomical age model for the classical Sangiran Dome area of central Java, using a semi-quantitative grain size record of the hominin-bearing Sangiran and Bapang Formations. Two initial age models were established based on two different sets of tie points and approaches (constant sedimentation rate and Bayesian age modelling). These models, which correspond to the paleoanthropological short and long chronologies for the arrival of Homo erectus on Java, were used to convert the grain size record into a time series for time series analysis. The preferred initial age model was then used as a starting point to correlate or tune the grain size record to the LR04 benthic δ18O isotope stack. This tuning was constrained by the sudden switch in grain size from obliquity to double obliquity related cycles; this switch can be linked to the onset of the Mid-Pleistocene Transition at ∼1.2 Ma marked by a similarly abrupt change in ice age history. Two slightly different astronomical age models are presented, while a one cycle hiatus at the base of the Grenzbank cannot be excluded. These age models are in better agreement with the short paleoanthropological chronology, arguing for a late arrival of H. erectus on Java. Finally, such astronomical age models, when finalized, will provide the accurate, precise, and high-resolution age control required to gain insight into the influence of both regional and global climate change on the Pleistocene paleoenvironment and potentially the hominin population of Java

Revised age and stratigraphy of the classic Homo erectus-bearing succession at Trinil (Java, Indonesia)

Obtaining accurate age control for fossils found on Java (Indonesia) has been and remains challenging due to geochronologic and stratigraphic uncertainties. In the 1890s, Dubois excavated numerous faunal fossils—including the first remains of Homo erectus—in sediments exposed along the Solo River at Trinil. Since then, various, and often contradictory age estimates have been proposed for the Trinil site and its fossils. However, the age of the fossil-bearing layers and the fossil assemblage remains inconclusive. This study constructs a chronostratigraphic framework for the Trinil site by documenting new stratigraphic sections and test pits, and by applying 40Ar/39Ar, paleomagnetic, and luminescence (pIRIR290) dating methods. Our study identifies two distinct, highly fossiliferous channel fills at the Trinil site. The stratigraphically lower Bone-Bearing Channel 1 (BBC-1) dates to 830–773 ka, while Bone-Bearing Channel 2 (BBC-2) is substantially younger with a maximum age of 450 ± 110 ka and an inferred minimum age of 430 ± 50 ka. Furthermore, significantly younger T2 terrace deposits are present at similar low elevations as BBC-1 and BBC-2. Our results demonstrate the presence of Early and Middle Pleistocene, and potentially even late Middle to Late Pleistocene fossiliferous sediments within the historical excavation area, suggesting that Dubois excavated fossils from at least three highly fossiliferous units with different ages. Moreover, evidence for reworking suggests that material found in the fossil-rich strata may originate from older deposits, introducing an additional source of temporal heterogeneity in the Trinil fossil assemblage. This challenges the current assumption that the Trinil H.K. fauna –which includes Homo erectus-is a homogeneous biostratigraphic unit. Furthermore, this scenario might explain why the Trinil skullcap collected by Dubois is tentatively grouped with Homo erectus fossils from Early Pleistocene sediments at Sangiran, while Trinil Femur I shares affinities with hominin fossils of Late Pleistocene age

Towards an astronomical age model for the Lower to Middle Pleistocene hominin-bearing succession of the Sangiran Dome area on Java, Indonesia

Well-dated paleoanthropological sites are critical for studying hominin evolution and dispersal, especially when related to regional or global climate change. For the rich hominin fossil record of Africa, this has been facilitated by the development of high-resolution astronomically tuned age models. So far, such age models are lacking for the Pleistocene of SE Asia with its similarly rich fossil hominin record. This study aims to develop an astronomical age model for the classical Sangiran Dome area of central Java, using a semi-quantitative grain size record of the hominin-bearing Sangiran and Bapang Formations. Two initial age models were established based on two different sets of tie points and approaches (constant sedimentation rate and Bayesian age modelling). These models, which correspond to the paleoanthropological short and long chronologies for the arrival of Homo erectus on Java, were used to convert the grain size record into a time series for time series analysis. The preferred initial age model was then used as a starting point to correlate or tune the grain size record to the LR04 benthic δ18O isotope stack. This tuning was constrained by the sudden switch in grain size from obliquity to double obliquity related cycles; this switch can be linked to the onset of the Mid-Pleistocene Transition at ∼1.2 Ma marked by a similarly abrupt change in ice age history. Two slightly different astronomical age models are presented, while a one cycle hiatus at the base of the Grenzbank cannot be excluded. These age models are in better agreement with the short paleoanthropological chronology, arguing for a late arrival of H. erectus on Java. Finally, such astronomical age models, when finalized, will provide the accurate, precise, and high-resolution age control required to gain insight into the influence of both regional and global climate change on the Pleistocene paleoenvironment and potentially the hominin population of Java

Towards an astronomical age model for the Lower to Middle Pleistocene hominin-bearing succession of the Sangiran Dome area on Java, Indonesia

Well-dated paleoanthropological sites are critical for studying hominin evolution and dispersal, especially when related to regional or global climate change. For the rich hominin fossil record of Africa, this has been facilitated by the development of high-resolution astronomically tuned age models. So far, such age models are lacking for the Pleistocene of SE Asia with its similarly rich fossil hominin record. This study aims to develop an astronomical age model for the classical Sangiran Dome area of central Java, using a semi-quantitative grain size record of the hominin-bearing Sangiran and Bapang Formations. Two initial age models were established based on two different sets of tie points and approaches (constant sedimentation rate and Bayesian age modelling). These models, which correspond to the paleoanthropological short and long chronologies for the arrival of Homo erectus on Java, were used to convert the grain size record into a time series for time series analysis. The preferred initial age model was then used as a starting point to correlate or tune the grain size record to the LR04 benthic δ18O isotope stack. This tuning was constrained by the sudden switch in grain size from obliquity to double obliquity related cycles; this switch can be linked to the onset of the Mid-Pleistocene Transition at ∼1.2 Ma marked by a similarly abrupt change in ice age history. Two slightly different astronomical age models are presented, while a one cycle hiatus at the base of the Grenzbank cannot be excluded. These age models are in better agreement with the short paleoanthropological chronology, arguing for a late arrival of H. erectus on Java. Finally, such astronomical age models, when finalized, will provide the accurate, precise, and high-resolution age control required to gain insight into the influence of both regional and global climate change on the Pleistocene paleoenvironment and potentially the hominin population of Java

The eastern Kendeng Hills (Java, Indonesia) and the hominin-bearing beds of Mojokerto, a re-interpretation

The eastern Kendeng Hills (Java, Indonesia) expose a 1000 m thick series that is used as a stratigraphic standard, representing the emergence of eastern Java from the sea. The fluvial top is rich in vertebrate fossils and yielded the Mojokerto (Perning) hominin skullcap, which is regarded as the earliest evidence of Homo erectus on Java, with age estimates ranging between 1.9 and 1.49 Ma. The series is commonly regarded as an uninterrupted record of coastal progradation. However, recent studies show that the emergence of eastern Java has been a complex process, under influence of tectonism, volcanism, sea-level fluctuations and fluvial dynamics, leaving a fragmented depositional record that varies from site to site. This is at odds with the prevailing stratigraphic practice of long-distance correlations and questions the existing interpretations of the eastern Kendeng reference sections. Here we present the results of a fieldwork-based re-interpretation of this key stratigraphic record, which we identified as the fill of a previously unrecognized Plio-Pleistocene embayment, surrounded by elongate uplift zones. Clinoform-bedded sandstones relate to a stage of explosive, high-silica volcanism, supplying large volumes of ash. The embayment fill is incised and covered by fluvial deposits, which we relate to the Middle Pleistocene Brantas. The fluvial strata have a cyclic build-up, probably representing sea-level controlled stages of aggradation and degradation. Based on a reconstruction of fluvial cycles, we provisionally link the conglomerate bed in which the Mojokerto Homo erectus was found to MIS14 (∼550ka). We infer that the published radiometric ages derive from reworked volcanic clasts that make up this incisive fluvial lag and are not representative for the age of deposition. Our study places the eastern Kendeng series in a new landscape context and changes our view of the timing of hominin migration to Java

The eastern Kendeng Hills (Java, Indonesia) and the hominin-bearing beds of Mojokerto, a re-interpretation

The eastern Kendeng Hills (Java, Indonesia) expose a 1000 m thick series that is used as a stratigraphic standard, representing the emergence of eastern Java from the sea. The fluvial top is rich in vertebrate fossils and yielded the Mojokerto (Perning) hominin skullcap, which is regarded as the earliest evidence of Homo erectus on Java, with age estimates ranging between 1.9 and 1.49 Ma. The series is commonly regarded as an uninterrupted record of coastal progradation. However, recent studies show that the emergence of eastern Java has been a complex process, under influence of tectonism, volcanism, sea-level fluctuations and fluvial dynamics, leaving a fragmented depositional record that varies from site to site. This is at odds with the prevailing stratigraphic practice of long-distance correlations and questions the existing interpretations of the eastern Kendeng reference sections. Here we present the results of a fieldwork-based re-interpretation of this key stratigraphic record, which we identified as the fill of a previously unrecognized Plio-Pleistocene embayment, surrounded by elongate uplift zones. Clinoform-bedded sandstones relate to a stage of explosive, high-silica volcanism, supplying large volumes of ash. The embayment fill is incised and covered by fluvial deposits, which we relate to the Middle Pleistocene Brantas. The fluvial strata have a cyclic build-up, probably representing sea-level controlled stages of aggradation and degradation. Based on a reconstruction of fluvial cycles, we provisionally link the conglomerate bed in which the Mojokerto Homo erectus was found to MIS14 (∼550ka). We infer that the published radiometric ages derive from reworked volcanic clasts that make up this incisive fluvial lag and are not representative for the age of deposition. Our study places the eastern Kendeng series in a new landscape context and changes our view of the timing of hominin migration to Java

The top of the Olduvai subchron in a high-resolution magnetostratigraphy from the West Turkana core WTK13, Hominin Sites and Paleolakes Drilling Project (HSPDP)

One of the major challenges in understanding the evolution of our own species is identifying the role climate change has played in the evolution of hominin species. To clarify the influence of climate, we need long and continuous high-resolution paleoclimate records, preferably obtained from hominin-bearing sediments, that are well-dated by tephro- and magnetostratigraphy and other methods. This is hindered, however, by the fact that fossil-bearing outcrop sediments are often discontinuous, and subject to weathering, which may lead to oxidation and remagnetization. To obtain fresh, unweathered sediments, the Hominin Sites and Paleolakes Drilling Project (HSPDP) collected a ~216-meter core (WTK13) in 2013 from Early Pleistocene Paleolake Lorenyang deposits in the western Turkana Basin (Kenya). Here, we present the magnetostratigraphy of the WTK13 core, providing a first age model for upcoming HSPDP paleoclimate and paleoenvrionmental studies on the core sediments. Rock magnetic analyses reveal the presence of iron sulfides carrying the remanent magnetizations. To recover polarity orientation from the near-equatorial WTK13 core drilled at 5°N, we developed and successfully applied two independent drill-core reorientation methods taking advantage of (1) the sedimentary fabric as expressed in the Anisotropy of Magnetic Susceptibility (AMS) and (2) the occurrence of a viscous component oriented in the present day field. The reoriented directions reveal a normal to reversed polarity reversal identified as the top of the Olduvai Subchron. From this excellent record, we find no evidence for the ‘Vrica Subchron’ previously reported in the area. We suggest that outcrop-based interpretations supporting the presence of the Vrica Subchron have been affected by the oxidation of iron sulfides initially present in the sediments -as evident in the core record- and by subsequent remagnetization. We discuss the implications of the observed geomagnetic record for human evolution studies.</p

Homo erectus at Trinil on Java used shells for tool production and engraving

The manufacture of geometric engravings is generally interpreted as indicative of modern cognition and behaviour. Key questions in the debate on the origin of such behaviour are whether this innovation is restricted to Homo sapiens, and whether it has a uniquely African origin. Here we report on a fossil freshwater shell assemblage from the Hauptknochenschicht ('main bone layer') of Trinil (Java, Indonesia), the type locality of Homo erectus discovered by Eugène Dubois in 1891 (refs 2 and 3). In the Dubois collection (in the Naturalis museum, Leiden, The Netherlands) we found evidence for freshwater shellfish consumption by hominins, one unambiguous shell tool, and a shell with a geometric engraving. We dated sediment contained in the shells with (40)Ar/(39)Ar and luminescence dating methods, obtaining a maximum age of 0.54 ± 0.10 million years and a minimum age of 0.43 ± 0.05 million years. This implies that the Trinil Hauptknochenschicht is younger than previously estimated. Together, our data indicate that the engraving was made by Homo erectus, and that it is considerably older than the oldest geometric engravings described so far. Although it is at present not possible to assess the function or meaning of the engraved shell, this discovery suggests that engraving abstract patterns was in the realm of Asian Homo erectus cognition and neuromotor control