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[dinosaur] Early Cretaceous dinosaur tracksite in England + dinosaur-bearing Griman Creek Formation in Australia




Ben Creisler
bcreisler@gmail.com



New papers:


Anthony P.Shillito & Neil S.Davies (2018)
Dinosaur-landscape interactions at a diverse Early Cretaceous tracksite (Lee Ness Sandstone, Ashdown Formation, southern England).
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
doi: https://doi.org/10.1016/j.palaeo.2018.11.018Â
https://www.sciencedirect.com/science/article/pii/S0031018218305522


Highlights

Dinosaur tracks represent an ecosystem with at least 7 different species.
Distribution of footprints on the original substrate controls new track emergence.
Gregarious behaviour may be responsible for patchy track distribution.
Variable detail observed in footprints attests to variable substrate conditions.
Dinosaurs acted as zoogeomorphic agents, trampling certain areas of the substrates.

Abstract

An assemblage of dinosaur footprints is reported from the Lower Cretaceous (Berriasian-Valanginian) Ashdown Formation of East Sussex, southern England. The ichnofauna is concentrated around a 2âm thick stratigraphic marker, the Lee Ness Sandstone, where recent cliff retreat has revealed 85 recognisable footprints attributable to 13 morphotypes, many of which bear high-fidelity skin impressions. The newly identified morphotypes mean that this tracksite hosts one of the most diverse dinosaur ichnoassemblages in the well-documented Mesozoic record of Britain; recording the activity of theropod, ornithopod, thyreophoran and possibly sauropod tracemakers. Most of the footprints were emplaced on a single floodplain mudstone horizon beneath a fluvial crevasse splay sandstone, where preservation was favoured by cohesive sediment and a prolonged interval of sedimentary stasis, during which trackways could be imparted. The sedimentological context of the trackways reveals evidence of interactions between dinosaurs and the riverine landscape that they inhabited; including the development of microtopographies around footprints, which impacted invertebrate burrowing activity, and evidence for dinosaur wading below the bankfull level of small meandering channels and oxbow lakes. Modern analogue suggests that the large dinosaurs may have played a significant role as zoogeomorphic engineers within the ancient floodplain setting, but the imperfect translation of sedimentary environment to sedimentary rock means that geological evidence for such is ambiguous.


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Phil R. Bell, Federico Fanti, Lachlan J. Hart, Luke A. Milan, Stephen J.Craven, Thomas Brougham & Elizabeth Smith (2018)
Revised geology, age, and vertebrate diversity of the dinosaur-bearing Griman Creek Formation (Cenomanian), Lightning Ridge, New South Wales, Australia.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)
doi: https://doi.org/10.1016/j.palaeo.2018.11.020Â
https://www.sciencedirect.com/science/article/pii/S0031018218305960


Highlights

The Griman Creek Formation is the only Mesozoic dinosaur-bearing unit in NSW (Australia).
New geological information provides evidence of a single 'local fauna'.
U/Pb dating yields a maximum age of ~100âMa; 10âMa younger than previously thought.
A faunal review reveals one of the most diverse Mesozoic Fauna in Australia.

Abstract

The mid-Cretaceous Griman Creek Formation (GCF), which crops out near the town of Lightning Ridge in the Surat Basin of north-central New South Wales, Australia, is noteworthy for its opalised vertebrate fauna. The fossil assemblage comprises remains of aspidorhynchid teleosts, lamniform chondrichthyans, dipnoans, chelid and possible meiolaniform turtles, leptocleidid-like and possible elasmosaurid plesiosaurians, anhanguerian pterosaurs, titanosauriform sauropods, megaraptoran theropods, ankylosaurians, several forms of non-iguanodontian and iguanodontian ornithopods, crocodylomorphs, enantiornithine birds, and stem and true monotremes, making it one of the most diverse mid-Cretaceous terrestrial vertebrate faunas in Australia. A detailed stratigraphic survey of twenty subterranean opal mines provides new information on the geology, age and palaeoenvironment of the main fossil-bearing beds. Vertebrate remains derive from the 'Finch Clay facies', laterally-extensive but discontinuous lenses of claystone that likely accumulated relatively rapidly in near-coastal but freshwater embayments (i.e. lagoonal conditions), and probably represent a single, roughly contemporaneous fauna. U-Pb age dating of detrital zircons extracted from a distinct layer of volcanogenic claystone immediately overlying one of the opalised fossil-bearing layers yields a maximum depositional age of 100.2â96.6âMa. These new dates confirm an early to mid-Cenomanian age for the fauna, rather than Albian, as has been reported previously. The GCF at Lightning Ridge is therefore equivalent to the middle part of the Winton Formation (Queensland) and several million years older than the sauropod-dominated fauna at Winton.

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