V031-0002
A New Look at the Lujiatun: Dinosaur Attrition in Burrows, not a Cretaceous Pompeii and not a Shoreline to the Jianshangou Lake

Monday, 14 December 2020
Poster
Elaine Chen1, Scott Angus MacLennan2, Sean Kinney3, Clara Chang3, Paul E Olsen3, Jingeng Sha4, Yanan Fang4, Jun Liu5 and Blair Schoene6, (1)Columbia University of New York, Palisades, NY, United States, (2)Princeton University, Princeton, NJ, United States, (3)Columbia University of New York, Earth and Environmental Science, NY, NY, United States, (4)State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Paleontology and Center for Excellence in Life and Paleoenvironment, Nanjing, China, (5)Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China, (6)Princeton University, Department of Geosciences, Princeton, NJ, United States
Abstract:
Famous for 3D Early Cretaceous dinosaurs and mammals, the Lujiatun Mb of the Yixian Fm (NE, China) has unresolved depositional, taphonomic and stratigraphic settings. LA-ICP-MS dating of zircons extracted from matrix of two Lujiatun blocks with articulated Psittacosaurus provide tests of competing hypotheses of taphonomy (catastrophic burial in pyroclastic flows or lahars vs attrition in burrows). Along with previously acquired CA-ID-TIMS ages[1], these data clarify the temporal relationship between the outcropping Lujiatun Mb and nearby lacustrine Jianshangou Mb with flattened, feathered dinosaurs.

We subjected Lujiatun zircons to LA-ICP-MS analysis, and the age spectrum shows that the Psittacosaurus matrix is neither pyroclastic flow[2] nor lahar[3], but a fluvial deposit with a large admixture of contemporaneous ash as suggested by Rogers et al[4]. Given the complete articulation of Psittacosaurus and most other dinosaurs and mammals, the simplest hypothesis for their burial is attrition in burrows[5], to be tested by granulometry.

CA-ID-TIMS zircon ages from the same outcrop1 (consistent with LA-ICP-MS) and a sequence of Lujiatun Mb (1 age) overlain by lava, overlain by Jianshangou Mb (2 ages) in the Huangbanjiagou core[6] have overlapping uncertainties at ~126 Ma, with possible total duration of ~160 Kyr, indicating very high deposition rates. In contrast, Chang et al.[7] argue that, given indistinguishable 40Ar/39Ar dates from outcropping Lujiatun and Jianshangou samples, the two units were deposited at the same time, as shore and lake facies. But the high accumulation rate indicated by CA-ID-TIMS ages, with their much lower uncertainties, show that the 40Ar/39Ar dates do not indicate contemporaneity. Rather, as shown by superposition, the simplest hypothesis is that there is one Lujiatun unit and one lava flow unit at both outcrop and core and that the Jianshangou was deposited after the Lujiatun.

[1] Kinney S+ 2016 IGC Abs 35 4626;

[2] Jiang B+ 2011 PPP 302 255;

[3] Wang X & Zhou Z 2003 in Chang M, The Jehol Biota 19;

[4] Rogers C+ 2015 PPP 427 89;

[5] Meng Q+ 2004 Nature 431 145;

[6] Wang Y+ 2016 PPP 464 110;

[7] Chang S+ 2017 PPP 487 399.

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