Arroyo Seco de la Frazada (Middle Section) = La Huertita Fm nom. nov. (Pliocene of Argentina)

Where: Mendoza, Argentina (34.9° S, 68.5° W: paleocoordinates 35.0° S, 67.4° W)

• coordinate estimated from map

When: Montehermosan zone, La Huertita Formation, Pliocene (5.3 - 2.6 Ma)

• Forasiepi et al 2011: Aisol Fm Middle Section (SM).

•Vucetich et al. 2011: The fossil-bearing levels, the middle section of the Aisol Formation, have been considered no older than Huayquerian in age (late Miocene). The evolutionary stage of the new species suggests that the age of these sediments could be even younger, no older than early Pliocene and possibly up to late Pliocene.

•Garrido et al 2014: they redefine the stratigraphy here. The Middle section of Forasiepi et al 2011 corresponds to the La Huertita Fm now that's Pliocene in age.

•En suma, considerando los biocrones de los taxones representados en la Formación La Huertita, una edad Montehermosense para la unidad pareciera ajustarse con los registros. Su extensión en el Chapadmalalen- se podría considerarse de acuerdo a algunos roedores (Caviodon cuyano y el Ctenomyidae aff. Eucoelophorus).

• formation-level stratigraphic resolution

Environment/lithology: fluvial; condensed, gray, silty sandstone

• succession of fluvial epiclastic deposits that are arranged in a relationship of discrepancy (in the area of ​​the Valle Grande fault) over the levels of the Aisol Formation, being covered by erosive contact by the quaternary deposits corresponding to the “upper section” SS (sensu Forasiepi et al., 2011).
• The middle section (MS) is composed of fine-grained pebbly lithic sandstones, with good selection. The sandstones are friable and disposed in tabular banks, with low angle inclination (about 4o) to the east (Fig. 2). In the lower and middle parts of the MS, the sandstones include horizontal stratification with intercalation of very fine brownish-reddish mudstone levels, about 1 to 2 cm thick. Mud cracks are found occasionally in the mud- stones. In the one-third upper part, the sandstones are massive and the mudstone levels are thicker, about 15 cm (Fig. 2). At first sight, the mudstones provide a brownish-reddish appearance for the entire middle part of the profile. Fossil vertebrates are localized in the two- third lower parts of the section. Unlike the fossils of the LS, fossil material is well preserved, sometimes it is articulated, and lacks signals of transportation. The total thickness of the MS is approximately 8.50 m.

•Garrido, et al. 2014: The sediments of the La Formation Huertita offer at first sight an aspect similar to those of the Aisol Formation, mainly due to the reddish hues that these deposits share in large part. However, the detailed analysis of this sequence makes it possible to observe the existence of an important contrast in the lithological and facial constitution.

•In general, the La Huertita Formation has a broad domain of fine deposits (pelitic and psamitic) of floodplain (architectural element FF; table 2), which make up up to 85% of the succession (Figure 3 ). In this sense, the dominant facies corresponds to the levels of solid silty sandstones (Sm facies), a factor that gives the deposits a loessoid appearance. These sediments are highlighted by their compact and uniform character, pinkish gray (5R 8/2) and good granulometric selection. In some sectors there is a cyclical alternation of solid sand-silt deposits (Sm facies) and fine sandstones with convect stratification (Scl facies), which occurred in banks smaller than 30 cm thick. This last pattern suggests the periodic existence of heavily saturated earth in wate

Size class: macrofossils

Collection methods: Museo de Historia Natural de San Rafael, Mendoza, Argentina

Primary reference: A. M. Forasiepi, A. G. Martinelli, M. S. Fuente, S. Dieguez, and M. Bond. 2011. Paleontology and stratigraphy of the Aisol Formation (Neogene), San Rafael, Mendoza. Cenozoic Geology of the Central Andes of Argentina 135-154 [E. Vlachos/E. Vlachos]more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 189520: authorized by Evangelos Vlachos, entered by Evangelos Vlachos on 25.10.2017, edited by Grace Varnham and Miranta Kouvari

Creative Commons license: CC BY (attribution)

Taxonomic list

 Notoungulata - Hegetotheriidae
Pachyrukhinae indet.1 Kraglievich 1934 notoungulate
MHNSR-PV1085, MHNSR-PV1093, MHNSR-PV1136, MHNSR- PV1137, MHNSR-PV1138, MHNSR-PV1140, MHNSR-PV1171, MHNSR-PV1172, MHNSR- PV1180
Tremacyllus sp. Ameghino 1891 notoungulate
left dentary with p2-m2 and trigonid of m3 (MHNSR–PV1087; Fig. 8C) and a dentary with broken m2 (MHNSR-PV1061)
 Notoungulata - Mesotheriidae
Pseudotypotherium sp.1 Ameghino 1904 notoungulate
MHNSR-PV 1154. P. exiguum or P. subinsigne
 Rodentia - Caviidae
Caviidae indet.1 Gray 1821 caviomorph
Orthomyctera sp.1 Ameghino 1889 caviomorph
MHNSR-PV 1047 and MHNSR-PV 1112
Caviodon cuyano n. sp.2 Vucetich et al. 2011 caviomorph
MHNSR-PV 1101 (type)
Dolichotinae indet. mara
 Rodentia - Octodontidae
aff. Eucoelophorus sp.1 Ameghino 1909 caviomorph
 Rodentia - Abrocomidae
Abrocomidae indet. Miller and Gidley 1918 chinchilla rat
Protabrocoma sp.1 Kraglievich 1927 chinchilla rat
 Rodentia - Ctenomyidae
Ctenomyidae indet. Lesson 1842 caviomorph
 Cingulata - Dasypodidae
Dasypodidae indet.1 Gray 1821 armadillo
(MHNSR-PV 1135, MHNSR-PV 1094a, MHNSR-PV 1170, MHNSR-PV 1181
cf. Doellotatus sp.1 Bordas 1932 armadillo
 Xenarthra - Megatheriidae
Megatheriidae indet.1 Gray 1821 edentate
 Xenarthra - Glyptodontidae
Doedicurinae indet.1 Ameghino 1889 glyptodon
 Didelphimorphia - Didelphidae
Didelphidae indet.1 Gray 1821 opossum
cf. Philander opossum1 Linnaeus 1758 gray four-eyed opposum
Hesperocynus dolgopolae
Hesperocynus dolgopolae Reig 1958
single disarticulated skull with dentaries (MHNSR-PV1046)