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First microfossil bonebed from Upper Triassic of Argentina

Ben Creisler

A recent paper:

Angel Praderio, Cecilia Apaldetti, Diego Abelín, Oscar Alcober and
Andrea Aguilar-Cameo (2015)
First Argentine microfossil bonebed from the Upper Triassic Marayes—El
Carrizal Basin, San Juan Province.
Palaios 30(10): 743-757
doi: 10.2110/palo.2014.055

The first Triassic microfossil bonebed found in Argentina is located
80 meters from the top of the Quebrada del Barro Formation in the
Marayes-El Carrizal Basin, in the province of San Juan. It consists of
specimens from at least 63 individuals from an anomalously high
concentration of fossils distributed laterally and vertically in a
meter-thick fine-grained deposit. Two new taxa from the genera
Sphenodontia and Eucynodontia had previously not been found in
Argentine Triassic quarries. The bonebed is preserved in a mudflow
deposit interbedded with calcic-Argillisols in the medial-distal zone
of a distributary fluvial system (DFS). The accumulation is
characterized by small-sized skeletal fragments (skulls, jaws and
vertebra; all less than 50 mm), low degree of articulation, variable
degrees of subaerial exposure, tooth marks, surface dissolution, and
an alkaline authigenic mineral suite. Detailed paleoenvironmental and
taphonomic characterization indicate that this accumulation underwent
three stages in its taphonomic history: (1) biogenic extrinsic
concentration; (2) local transportation and re-deposition by a mudflow
on a swampy floodplain; and (3) drying and pedogenesis. Additionally,
the deposit highlights biogenic activity as a way to concentrate a
paleofaunal assemblage that likely represents the original community,
and mudflow deposits from crevasse splays in DFS as a potential facies
for microfossil preservation.