AVIAN FORAGING ON AN INTERTIDAL MUDFLAT SUCCESSION, TANJUNG FORMATION, SOUTH KALIMANTAN, INDONESIA

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 trace fossil assemblages are fundamental for establishing depositional models and for paleoecological reconstructions of Eocene southern Kalimantan. Extensive forest cover has precluded previous ichnological analyses in the study area. The traces discussed herein were collected from newly discovered successions exposed in the basal part of the Wahana Baratam coal mine on the Kalimantan coast of the Java Sea.

This assemblage includes both vertebrate (avian) and invertebrate trace fossils. The Tambak invertebrate traces observed in this study include Cylindrichnus Diplocraterion, Palaeophycus, Planolites, Psilonichnus, Skolithos and Trichichnus. The avian footprints include at least four ichnospecies within two ichnogenera: Aquatailavipes and Ardeipeda sp. Several morphotypes assigned to Aquatailavipes occur and likely represent the activities of small to medium-sized shorebirds such as sand pipers or plovers. The single form of Ardeipedalikely reflects the foraging behaviour of a moderate to large-sized heron or egret. Inferred foraging traces include diminutive, shallow, circular to cylindrical pits and singular to paired horizontal grooves that occur interspersed with avian trackways and invertebrate traces.

These trace fossils occur preferentially in very fine- to fine-grained sandstone beds in a coarser grained interval between two coal seams. Lenticular to flaser bedding, herringbone ripple stratification and common reactivation surfaces indicate that the study interval represents a middle to upper intertidal flat succession, likely deposited on the margins of a tidally-influenced deltaic succession.