Palynology, taphonomy and geology of the early cretaceous Dinosaur Dreaming Fossil Site, Inverloch, Victoria, Australia

The recovery of vertebrate fossils from the Early Cretaceous Dinosaur Dreaming Fossil Site (DDFS), near Inverloch, Victoria, Australia, is restricted to an approximately 1 metre thick fluvial deposit, consisting of interbedded conglomerate and sandstone units that were deposited as part of a braided stream under high energy hyperconcentrated flow conditions. Palynological analyses of samples from this, at the time of deposition, high latitudinal site reveals a vegetation dominated by ferns, lycopods, gymnosperms and subordinate hepatics and mosses, indicative of microthermal (temperate to possible cool – temperate) settings. The palynology has also restricted the age of the site to 116.5 – 120 Ma (early to mid Late Aptian) in the upper part of the Cyclosporites hughesii Zone as defined by Partridge (2006). Comparison of the floral assemblage between sites affected and unaffected by periglacial structures has revealed only marginal differences, strongly suggesting little climatic variations during time of sediment deposition during this part of the Aptian. The DDFS lay at high latitudes in the Early Cretaceous, and there is evidence of climatic seasonality coupled with the time of onset of polar night conditions and the concomitant reduction in light availability observed in growth rings of arborescent taxa. Charcoal fragments attest to periodic wildfires brought about by the possible drying of the landscape. Homogenisation of cell walls in charcoal samples indicates that the fires occurred at temperatures ranging between 230°C to 340°C. Sedimentological evidence indicates that the skeletal elements accumulated in and around a lake environment prior to reworking. Bone modification and articulation patterns plus climatic settings support a subaerial exposure of skeletal material of several years. Partial sorting of light¬weight bone material is a result of hydraulic winnowing, most likely due to flooding resulting from heavy rain, prior to the reworking of the assemblage. The majority of bones were broken prior to mineralisation, implying trampling activity. However, only a few traces have been observed so far, suggesting that trampling occurred in sediments too fine grained to leave characteristic marks. Evidence of scavenging activity is restricted to marks on only a few bones. Disarticulated skeletal material was eventually reworked, transported and re-deposited following a high discharge hyperconcentrated flood event, with a short transport distance evidenced by the low degree of abrasion on outer bone surfaces. Weathering patterns of faunal elements do not show deterioration, which might be linked to cycles of freezing and thawing associated with periglacial environments. This is further corroborated by the flora which supports a microthermal (temperate to possible cool-temperate) setting.