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Vertebrate taphonomy of the Triassic Ischigualasto Formation of Argentina
From: Ben Creisler
A paper in the new JVP Memoir:
Carina E. Colombi, Raymond R. Rogers & Oscar A. Alcober (2013)
Vertebrate taphonomy of the Ischigualasto Formation.
Basal sauropodomorphs and the vertebrate fossil record of the
Ischigualasto Formation (Late Triassic: Carnian-Norian) of Argentina.
Journal of Vertebrate Paleontology Memoir 12: 31-50
Trends of preservation are established on the basis of 385 fossil
occurrences in the Ischigualasto Formation. The distribution and
preservational quality of vertebrate fossils are related to
sedimentary facies and stratigraphic position and follow trends in
basin evolution and paleoclimate. Fossils in the Ischigualasto
Formation are mainly concentrated along the margins of the basin.
Floodplain deposits preserve ca. 88% of fossils, which range from
unidentifiable fragments to articulated skeletons. The remaining
fossil occurrences (ca. 12%) come from coarser-grained fluvial channel
deposits and exhibit variable preservational quality, including some
well-preserved cynodont skulls. Fossils in the basal La Peña Member
(ca. 4% of occurrences) are generally highly weathered and
disarticulated with hematitic permineralization. The majority of
collected specimens (ca. 65% of occurrences) come from the overlying
Cancha de Bochas Member and range from isolated bones to articulated
skeletons. Calcite, rather than hematite, is the predominant agent of
permineralization. The succeeding Valle de la Luna Member (ca. 30% of
occurrences) preserves an association between vertebrate fossils and
plant remains. Fossil preservation suggests prolonged exposure prior
to burial under wetter conditions with superficial and penetrating
precipitation of hematite. The uppermost Quebrada de la Sal Member of
the Ischigualasto Formation is nearly barren of fossil remains.