Moderately diverse trace fossil assemblages occur in the Eocene Tambak Member of the Tanjung Formation, in the Asem Asem Basin on the southern coast of South Kalimantan. These assemblages are fundamental for establishing depositional models and paleoecological reconstructions for southern Kalimantan during the Eocene and contribute substantially to the otherwise poorly documented fossil record of birds in Island Southeast Asia. Extensive forest cover has precluded previous ichnological analyses in the study area. The traces discussed herein were discovered in newly exposed outcrops in the basal part of the Wahana Baratama coal mine, on the Kalimantan coast of the Java Sea. The Tambak assemblage includes both vertebrate and invertebrate trace fossils. Invertebrate traces observed in this study include Arenicolites, Cylindrichnus, Diplocraterion, Palaeophycus, Planolites, Psilonichnus, Siphonichnus, Skolithos, Thalassinoides, Taenidium, and Trichichnus. Vertebrate-derived trace fossils include nine avian footprint ichnogenera (Aquatilavipes, Archaeornithipus, Ardeipeda, Aviadactyla, cf. Avipeda, cf. Fuscinapeda, cf. Ludicharadripodiscus, and two unnamed forms). A variety of shallow, circular to cylindrical pits and horizontal, singular to paired horizontal grooves preserved in concave epirelief are interpreted as avian feeding and foraging traces. These traces likely represent the activities of small to medium-sized shorebirds and waterbirds like those of living sandpipers, plovers, cranes, egrets, and herons. The pits and grooves are interpreted as foraging traces and occur interspersed with both avian trackways and invertebrate traces. The trace fossils occur preferentially in heterolithic successions with lenticular to flaser bedding, herringbone ripple stratification, and common reactivation surfaces, indicating that the study interval was deposited in a tidally influenced setting. Avian trackways, desiccation cracks, and common rooting indicate that the succession was prone to both subaqueous inundation and periodic subaerial exposure. We infer that the Tambak mixed vertebrate-invertebrate trace fossil association occurred on channel-margin intertidal flats in a tide-influenced estuarine setting. The occurrence of a moderately diverse avian footprint and foraging trace assemblage in the Tambak Member of the Tanjung Formation illustrates that shorebirds and waterbirds have been using wetlands in what is now Kalimantan for their food resources since at least the late Eocene.
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RBINS Staff Publications 2024
The European Union Marine Strategy Framework Directive requires Member States to monitor and assess the health status of their marine habitats. Belgium put forward that the spatial extent and distribution of the major habitats (sandy mud to mud, muddy sands to sands and coarse-grained sediments), as well as that of gravel beds may only fluctuate within a margin that is limited to the accuracy of the current sediment distribution maps. Due to their ability to provide simultaneous bathymetry and backscatter strength (BS), reflecting seabed nature, multibeam echosounder systems (MBES) provide a time- and costefficient solution to anticipate on this legal obligation. However, as there is no formal quality level scale for the BS and consequently no level of reliability of the final decibel values, evaluating the BS quantitative capabilities to monitor habitat changes remains challenging. In a monitoring context, it is absolutely necessary to investigate to what extent the mean MBES-measured BS variation -from one cruise to another- actually represents a significant change in seabed properties and not only a change in the conditions of the water column (e.g., variation in near-bed suspensions, biological effects, increased occurrence of micro bubbles in the sea surface due to wind) at the time of the measurement. In order to evaluate the relative accuracy and the repeatability of MBES BS and to examine the external sources of variance in acoustic signatures, repeated measurements combining MBES with an Acoustic Doppler current Profiler (ADP) have been performed during tidal cycles on reference areas in the Belgian part of the North Sea. Currents and BS in the water column and vertical profiling of oceanographic parameters have been investigated allowing studying the influence of water column conditions on the BS. Measurements were conducted using two MBES systems to evaluate repeatability between echosounders. Ultimate goal is to arrive at seabed mapping and analyses protocols to obtain harmonized data products from a collaborative seabed mapping community.
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