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Analyses of rock samples collected during recent fieldwork in the Ombilin Basin of west-central Sumatra, Indonesia yielded pollen data that constrain the age and depositional setting of associated plant macrofossil and vertebrate fossil-bearing units in the Sangkarewang and Sawahlunto formations. Articulated fish and plant fossils were recovered from bedding plane surfaces of fissile, laminated shales in the Sangkarewang Formation that are interpreted to have been deposited in an actively-subsiding, deep, anoxic lake. The overlying Talawi Member of the Sawahlunto Formation records stratigraphy consistent with deposition in a segue to marginal lacustrine marsh and poorly-drained paleosol settings. Interbedded carbonate mudstone / wackestone and lignitic claystone units in the basal Talawi Member preserve scattered, disarticulated fossils of fish, reptiles, an amphibian, and one mammal tooth. These beds grade into a heterolithic succession of fine-grained clastic rock, with coal interbeds likely deposited in a coastal alluvial setting. Marine influences in this interval are indicated by the nature of physical sedimentary structures in several zones, the presence of trace fossils such as Diplocraterion, Cylindrichnus and Teichichnus, and the occurrence of foraminiferal linings, dinocysts and other palynomorphs indicative of mangrove and back-mangrove settings. Palynological analysis indicates that the most probable age of the Sawahlunto Formation ranges from the middle to late Eocene, with a possible extension from the middle Eocene to the early Oligocene. 

Abstract Marine sedimentary rocks of the late Eocene Pagat Member of the Tanjung Formation in the Asem Asem Basin near Satui, Kalimantan, provide an important geological archive for understanding the paleontological evolution of southern Kalimantan (Indonesian Borneo) in the interval leading up the development of the Central Indo-Pacific marine biodiversity hotspot. In this paper, we describe a moderately diverse assemblage of marine invertebrates within a sedimentological and stratigraphical context. In the studied section, the Pagat Member of the Tanjung Formation records an interval of overall marine transgression and chronicles a transition from the marginal marine and continental siliciclastic succession in the underlying Tambak Member to the carbonate platform succession in the overlying Berai Formation. The lower part of the Pagat Member contains heterolithic interbedded siliciclastic sandstone and glauconitic shale, with thin bioclastic floatstone and bioclastic rudstone beds. This segues into a calcareous shale succession with common foraminiferal packstone/rudstone lenses interpreted as low-relief biostromes. A diverse trace fossil assemblage occurs primarily in a muddy/glauconitic sandstone, sandy mudstone, and bioclastic packstone/rudstone succession, constraining the depositional setting to a mid-ramp/mid to distal continental shelf setting below fair-weather wave base but above storm wave base. Each biostrome rests upon a storm-generated ravinement surface characterized by a low-diversityGlossifungitesorTrypanitestrace fossil assemblage. The erosional surfaces were colonized by organisms that preferred stable substrates, including larger benthic foraminifera, solitary corals, oysters, and serpulid annelid worms. The biostromes comprised islands of high marine biodiversity on the mud-dominated Pagat coastline. Together, the biostromes analyzed in this study contained 13 genera of symbiont-bearing larger benthic foraminifera, ~40 mollusk taxa, at least 5 brachyuran decapod genera, and 6 coral genera (Anthemiphyllia,Balanophyllia,Caryophyllia,Cycloseris,Trachyphyllia, andTrochocyathus), as well as a variety of bryozoans, serpulids, echinoids, and asterozoans. High foraminiferal and molluscan diversity, coupled with modest coral diversity, supports the hypothesis that the origin of the diverse tropical invertebrate faunas that characterize the modern Indo-Australian region may have occurred in the latest Eocene/earliest Oligocene. 

Premise of research. The Neogene collision of the Australian tectonic plate (Sahul) with Southeast Asia (Sunda) restructured the vegetation of both regions. The rarity of plant macrofossils from Sunda has limited the understanding of precollision vegetation and plants that migrated from Sunda to Sahul. Despite the importance of legumes in the living flora, no Malesian reproductive or pre-Neogene fossils of the Fabaceae are known.Methodology. We collected 47 plant macrofossils from the Tambak Member of the Tanjung Formation (middle-late Eocene) while surveying the Wahana Baratama coal mine near Satui, South Kalimantan, Indonesian Borneo. These fossils represent Southeast Asian forests before the Sahul-Sunda collision. We studied three isolated large (up to 72 mm in length) seeds from the upper Tambak Member, along with 43 fossil leaves and two palynological samples from the lower Tambak Member.Pivotal results. We describe the extinct legume Jantungspermum gunnellii gen. et sp. nov. The J. gunnellii seeds are flattened on one side, bilobed, and heart shaped with a long hilum (~60 mm) overlain on the suture, closely resembling Castanospermum, the Australian black bean tree. The leaves represent seven morphotypes, which include Fabaceae but are otherwise unidentifiable. One specimen preserves in situ cuticle. The palynoflora includes diverse ferns and palms, Typhaceae, Onagraceae, and forest taxa, including Podocarpaceae, Sapindaceae, and Fabaceae, indicating a largely freshwater coastal swamp environment in the lower Tambak Member.Conclusions. The Jantungspermum seeds are double the length of Castanospermum seeds, representing a closely related but extinct papilionoid taxon. The discovery suggests a Sundan precollision history, a much later Sunda-Sahul migration, and an eventual Asian extinction for the Castanospermum lineage, which today inhabits coastal rainforests of northern Australasia. The seeds represent the only known fossil relative of Castanospermum, the oldest legume fossils from Malesia, and one of the largest fossil angiosperm seeds. The new seeds, leaves, and palynomorphs provide a window into Eocene Malesian vegetation and rare macrofossil evidence of Sundan history for a living Australasian lineage. 

Abstract 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.