Santa Cruz Formation Explained

Santa Cruz Formation
Period:	Miocene
Age:	Burdigalian-Langhian (Santacrucian-Friasian) ~
Type:	Geological formation
Prilithology:	Tuff, claystone, mudstone (Estancia La Costa Member) Claystone, mudstone, sandstone (Estancia La Angelina Member)
Subunits:	Estancia La Costa Member, Estancia La Angelina Member (coastal section)
Underlies:	Cerro Boleadoras Formation
Overlies:	Monte Léon Formation
Thickness:	Over 295 metres
Map:	Santa Cruz in Argentina (+Falkland hatched).svg
Country:	Argentina, Chile
Extent:	Austral Basin
Namedby:	Furque & Camacho
Year Ts:	1972
Location Ts:	near Lago Argentino

The Santa Cruz Formation is a geological formation in the Magallanes/Austral Basin in southern Patagonia in Argentina and adjacent areas of Chile. It dates to the late Early Miocene epoch, and is contemporaneous with the eponymous Santacrucian age of the SALMA timescale.^{[1] [2]} The Santa Cruz Formation is known for its abundance of vertebrate fossils, including South American native ungulates (astrapotheres, litopterns, notoungulates),^[3] as well as rodents, xenarthrans (armadillos, sloths, anteaters), and metatherians.

The formation extends from the Andes to the Atlantic coast. In its coastal section it is divided into two members, the lower, fossil rich Estancia La Costa Member, which consists predominately of tuffaceous deposits and fine grained mudrock, and the upper fossil-poor Estancia La Angelina Member, which consists of sedimentary rock, primarily mudrock, and sandstone. The environment of deposition was mostly fluvial, with the lowermost part of the Estancia La Costa Member being transitional between fluvial and marine conditions. The environment of the Estancia La Costa Member is thought to have been relatively warm and humid, but likely became somewhat cooler and drier towards the end of the sequence.

Stratigraphy

The Santa Cruz Formation is exposed in isolated outcrops across the Magallanes/Austral Basin extending from the Atlantic coast to the Andes, especially along the Santa Cruz River, as well as along the southern coastline of Santa Cruz Province.^[4] While primarily located in Argentina, small outcrops are also found in Chile.^[5] The base of the formation is defined by a marine regression event transitioning from the marine environment of the underlying Monte Léon Formation, which formed when large areas of Patagonia were submerged as a part of the Patagoniense Transgression.

The main source of sediment input to the basin was from the Andean orogeny to the west. The formation reaches a maximum thickness of over 295 meters, though the total thickness of the formation is strongly controlled by subsequent erosion and the 295 meters likely does not represent a complete sequence. The formation primarily consists of floodplain deposits. The lower parts of the formation have an abundance of tuffs and tuffaceous sediments. These likely originated from distant eruptions that were transported into the basin by aerial fallout, wind and/or river transport. The formation likely spans an approximately 3 million year interval in the late Early Miocene around 18 to 15.2 million years ago, during the Burdigalian and Langhian stages.

Paleoenvironment

The environment of the Santa Cruz Formation is thought to have been relatively warm and humid, including a mix of open savanna, gallery forests and semi-deciduous forests. Permanent bodies of water such as lakes, ponds and streams are likely to have been present.^[6]

Paleoflora

Name	Species	Locality	Material	Notes	Image
Nothofagus^[7]	Indeterminate	Rincón del Buque, Punta Sur	Leaves, wood
Araucaria	Indeterminate	Punta Sur	Twig	Morphologically similar to A. marensii from the Eocene of Antarctica
Lauraceae	Indeterminate	Punta Sur	Wood	Assigned to form genus Laurinoxylon
Myrceugenia	M. chubutense	Punta Sur	Wood	A member of the family Myrtaceae
Eucryphiaceoxylon	E. eucryphioides	Punta Sur	Wood	Wood probably belonging to the genus Eucryphia
Faboideae	Indeterminate	Punta Sur	Wood	Possible affinities to Sophora (Fabaceae)
Doroteoxylon	D. vicenti-perezii	Punta Sur	Wood	Wood with affinities to the subfamily Caesalpinioideae
Akanioxylon^[8]	A. santacrucensis	Punta Sur	Wood
Chloridoideae	Indeterminate		Phytoliths	Grass
Panicoideae
Danthonioideae
Pooideae

Paleofauna

Invertebrates

Name	Species	Material	Notes	Image
Crassostrea^[9]	C. orbignyi	Numerous individuals in large beds at the base of the formation	A marine true oyster
Diplodon^[10]	D. cf. colhuapiensis		A freshwater bivalve belonging to Hyriidae
Stephadiscus^[11]	Indeterminate		A terrestrial gastropod belonging to Charopidae
Gastrocopta^[12]	G.patagonica
?Scolodonta	Indeterminate
Punctum	P. patagonicum
Zilchogyra	Z. miocenica		A terrestrial gastropod belonging to Charopidae
Patagocharopa	P. enigmatica		A terrestrial gastropod of uncertain affinities, possibly a member of Charopidae
Porifera	Unspecified	Spicules	Freshwater sponge
Bacillariophyceae	Unspecified	Frustules	Freshwater diatoms
Chrysophyceae	Unspecified		Freshwater algae

Amphibians

Name	Species	Locality	Material	Notes	Image
Calyptocephalella^[13]	C. cf. canqueli	Estancia La Costa, Rinconada de los López	Skull and jaw fragments	A calyptocephalellid frog
Neobatrachia	Indeterminate	Estancia La Costa	Skull fragments and presacral vertebrate	A frog originally assigned to "Leptodactylidae", but requires further investigation

Birds

Name	Species	Locality	Material	Notes	Image
Anisolornis	A. excavatus			A bird of uncertain affinities, authors have varyingly suggested affinities to trumpeters or limpkins
Ankonetta	A. larriestrai		Partial tarsometatarsus	A basal member of Anatidae
Badiostes	B. patagonicus			A member of the family Falconidae
Brontornis	B. burmeisteri			Controversial taxonomic position, either considered a terror bird or an anserimorph
Dryornis^[14] ^[15]	D. pampeanusD. hatcheri		Two partial left humerus	A New World vulture.
Eutelornis	E. patagonicus E. australis		Limb fragments	A member of Anseriformes, relationships of the species to each other or to other Ansiferiformes is uncertain
Liptornis	L. hesternus			A member of Anhingidae
Macranhinga	Indeterminate			A member of Anhingidae
Miocariama^[16]	M. santacrucensis		Partial cranium and tibiotarsi fragments	A seriema
Nothurinae	2 Indeterminate species			Tinamou
Opisthodactylus	O. patagonicus		Limb, vertebra and skull fragments	A member of Rheidae
Patagornis	P. marshi			A terror bird
Phorusrhacos^[17]	P. longissimus		Partial skulls	A terror bird
Protibis	P. cnemialis		distal end of tibiotarsus	Potentially a spoonbill
Psilopterus	P. lemoinei P. bachmanni			A terror bird
Thegornis	T. musculosus T. debilis			A member of the family Falconidae
Archaeopsophia^[18]	A. aoni			A member of the family Psophiidae (trumpeters)
Chehuenia	C. facongrandei			A roller
Kaikenia	K. mourerchauvirea			An anatid belonging to the subfamily Tadorninae
Peioa	P. australis			A member of Anseriformes.

Reptiles

Name	Species	Locality	Material	Notes	Image
Pristidactylus^[19]	Indeterminate	La Cueva	Fragmentary jaw bones	Originally assigned to the dubious genus "Erichosaurus"
Pleurodonta
Tupinambis		Monte León	Fragmentary dentaries and maxilla	A teiid lizard
Colubridae		Cerro Observatorio	Partial trunk vertebrae	A snake

Mammals

Meridiungulates

Litopterns

Name	Species	Locality	Material	Notes	Image
Adianthus^[22]	A. bucatus			An adianthid litoptern
Anisolophus^[23]	A. australisA. floweri			A proterotheriid litoptern
Diadiaphorus^[24] ^[25]	D. majusculusD. sanctaecrucis D. sp.			A proterotheriid litoptern
Tetramerorhinus^[26]	T. cingulatumT. fleaglei T. mixtum T. lucarius T. prosistens T. sp.	Estancia La Costa Member		A proterotheriid litoptern
Theosodon^[27]	T. fontanaeT. garretorum T. gracilis T. karaikensis T. lydekkeri T. patagonicum	Estancia La Costa Member		A macraucheniid litoptern
Thoatherium	T. minisculumT. sp.	Estancia La Costa Member		A proterotheriid litoptern

Notoungulates

Name	Species	Locality	Material	Notes	Image
Adinotherium^[28] ^[29] ^[30] ^[31] ^[32]	A. ovinumA. robustum A. sp.			A toxodontid notoungulate
Cochilius^[33]	C. sp.			An interatheriid notoungulate
Hegetotherium^[34]	H. mirabileH. sp.			A hegetotheriid notoungulate
Homalodotherium	H. cunninghami			A homalodotheriid notoungulate
Interatherium^[35]	I. anguliferumI. brevifrons I. dentatum I. interruptum I. robustum I. rodens I. supernum			An interatheriid notoungulate
Neoicochilus	N. undulatus			An interatheriid notoungulate
Nesodon	N. imbricatus			A toxodontid notoungulate
Notohippus^[36]	N. toxodontoides			A notohippid notoungulate
Pachyrukhos	P. moyani			A hegetotheriid notoungulate
Patriarchus^[37]	P. palmidens			An interatheriid notoungulate
Protypotherium^[38]	P. attenuatumP. australe P. praerutilum P. sp.			An interatheriid notoungulate

Xenarthrans

Pilosa

Name	Species	Locality	Material	Notes	Image
Analcimorphus^[39] ^[40]	A. giganteusA. inversus	Estancia La Costa Member		A basal megatherioid sloth
Analcitherium^[41]	A. antarcticum	Estancia La Costa Member		A scelidotheriid sloth
Eucholoeops^[42]	E. frontoE. ingens E. litoralis E. titans	Estancia La Costa Member		A megalonychid ground sloth
Hapalops	H. longiceps H. elongatus H. indifferens H. angustipalatus H. platycephalus H. ponderosus H. rectangularis			A ground sloth belonging to Megatherioidea
Hyperleptus	Indeterminate			A megatherioid ground sloth of uncertain affinities
Megalonychotherium	M. atavus			A megalonychid ground sloth
Mylodontidae	Indeterminate
Nematherium	N. angulatum
Pelecyodon	P. cristatus			A ground sloth
Planops	P. magnus			A megatheriid ground sloth
Protamandua^[43]	P. rothi			An anteater
Prepotherium	P. potensP. filholi			A ground sloth
	Indeterminate			A ground sloth
Schismotherium^[44] ^[45]	S. fractum			A ground sloth
Xyophorus	X. atlanticusX. latirostris			A nothrotheriid ground sloth

Cingulata

Name	Species	Locality	Material	Notes	Image
Anantiosodon^[46]	A. rarus			An armadillo
cf. Asterostemma	cf. A. depressa			A glyptodont
Cochlops	C. muricatus			A glyptodont
Eucinepeltus	E. petesatus			A glyptodont
Metopotoxus	M. laevatus			A glyptodont
Parutaetus	P. sp.			An armadillo
Peltephilus	P. ferox P. giganteus P. nanus P. pumilus P. strepens			A horned armadillo
Proeutatus	P. carinatusP. deleo P. lagena P. oenophorus P. robustus			An armadillo
Propalaehoplophorus	P. australis P. incisivus P. minus			A glyptodont
Prozaedyus	P. exilis P. proximus			An armadillo
Stenotatus	S. patagonicus			An armadillo
Stegotherium	S. tauberi S. tessellatum			An armadillo
Vetelia^[47]	V. puncta			An armadillo

Metatherians

Name	Species	Locality	Material	Notes	Image
Abderites	A. meridionalis			A member of Abderitidae (Paucituberculata)
Acdestis	A. owenii A. lemairei			A member of Palaeothentidae (Paucituberculata)
Acrocyon^[48]	A. sectorius			A borhyaenid sparassodont
Acyon	A. tricuspidatus			A hathliacynid sparassodont
Arctodictis	A. munizi			A borhyaenid sparassodont
Borhyaena	B. tuberata			A borhyaenid sparassodont
Cladosictis	C. patagonia			A sparassodont
Lycopsis	L. torresi			A sparassodont
Microbiotherium ^[49]	M. acicula M. patagonicum M. gallegosense M. tehuelchum			A member of Microbiotheriidae (Microbiotheria)
Palaeothentes	P. aratae P. minutus P. intermedius P. lemoinei P. pascuali			A member of Palaeothentidae (Paucituberculata)
Perathereutes	P. pungens			A hathliacynid sparassodont
Phonocdromus	P. gracilis			A member of Pichipilidae (Paucituberculata)
Prothylacinus	P. patagonicus			A sparassodont
Pseudonotictis	P. pusillus			A hathliacynid sparassodont
Sipalocyon	S. gracilis S. obusta			A hathliacynid sparassodont
Stilotherium	S. dissimile			A member of Caenolestidae (Paucituberculata)

Rodents

Name	Species	Locality	Material	Notes	Image
Acarechimys	A. minutusA. minutissmus A. constans A. gracilis			A member of Octodontoidea
Acaremys^[50]	A. murinus A. messor			A member of Acaremyidae (Octodontoidea)
Adelphomys	A. candidus			A member of Octodontoidea
Dudumus	Indeterminate, potentially new species			A member of Octodontoidea
Eocardia	E. montana "E". excavata "E". fissa			A member of Cavioidea
Neoreomys	N. australis			A member of Cavioidea
Perimys	P. erutus P. onustus P. incavatus			A member of Chinchilloidea
Phanomys	P. mixtus P. vetulus			A member of Cavioidea
Pliolagostomus	P. notatus			A member of Chinchilloidea
Prolagostomus	P. pusilllus			A member of Chinchilloidea
Prospaniomys	Indeterminate, potentially new species			A member of Octodontoidea
Pseudoacaremys	P. kramarzi			A member of the family Acaremyidae (Octodontoidea)
Schistomys	S. erro			A member of Cavioidea
Sciamys	S. principalis S. varians S. latidens			A member of the family Acaremyidae (Octodontoidea)
Scleromys	S. angustus			A member of Chinchilloidea
Spaniomys	S. riparius S. regularis			A member of Octodontoidea
Steiromys	S. dentatus S. duplicatus			A member of Erethizontoidea

Primates

Name	Species	Locality	Material	Notes	Image
Homunculus^[51] ^[52] ^[53]	H. patagonicus, H. vizcainoi			A New World monkey
Killikaike^[54]	K. blakei			A New World monkey, some authors regard the taxon as a synonym of Homunculus patagonicus, while others regard them as distinct.

Meridiolestida

!Name!Species!Locality!Material!Notes!Image

Necrolestes^[55]

N. patagonicus

Skull and postcranial remains

A mole-like meridiolestidan, youngest known member of the group

Notes and References

1. Book: Matheos . Sergio D. . Sedimentology and paleoenvironment of the Santa Cruz Formation . 2012-10-11 . Early Miocene Paleobiology in Patagonia . 59–82 . Vizcaíno . Sergio F. . 1 . Cambridge University Press . 10.1017/cbo9780511667381.005 . 978-0-511-66738-1 . 2022-11-06 . Raigemborn . M. Sol . Kay . Richard F. . Bargo . M. Susana.
2. Cuitiño . José I. . Vizcaíno . Sergio F. . Bargo . M. Susana . Aramendía . Inés . 2019-05-31 . Sedimentology and fossil vertebrates of the Santa Cruz Formation (early Miocene) in Lago Posadas, southwestern Patagonia, Argentina . . en . 46 . 2 . 383–420 . 10.5027/andgeoV46n2-3128 . 0718-7106 . free. 11336/96343 . free .
3. Book: Cassini . Guillermo H. . Paleobiology of Santacrucian native ungulates (Meridiungulata: Astrapotheria, Litopterna and Notoungulata) . 2012 . Early Miocene Paleobiology in Patagonia: High-Latitude Paleocommunities of the Santa Cruz Formation . 243–286 . Bargo . M. Susana . Cambridge . Cambridge University Press . 978-0-521-19461-7. Cerdeño . Esperanza . Villafañe . Amalia L. . Muñoz . Nahuel A. . Kay . Richard F. . Vizcaíno . Sergio F..
4. Cuitiño . José I. . Sol Raigemborn . M. . Susana Bargo . M. . Vizcaíno . Sergio F. . Muñoz . Nahuel A. . Kohn . Matthew J. . Kay . Richard F. . 2021-04-07 . Insights on the controls on floodplain-dominated fluvial successions: a perspective from the Early–Middle Miocene Santa Cruz Formation in Río Chalía (Patagonia, Argentina) . Journal of the Geological Society . 178 . 4 . 10.1144/jgs2020-188 . 2021JGSoc.178..188C . 233779691 . 0016-7649.
5. Raúl Ugalde, Enrique Bostelmann, Karina E. Buldrini, and José Luis Oyarzún Lithofacies, architecture, and depositional environments of the Santa Cruz Formation in Chilean Patagonia (2015) XIV Congreso Geológico Chileno
6. Kay . Richard F. . Vizcaíno . Sergio F. . Bargo . M. Susana . Spradley . Jackson P. . Cuitiño . José I. . August 2021 . Paleoenvironments and paleoecology of the Santa Cruz Formation (early-middle Miocene) along the Río Santa Cruz, Patagonia (Argentina) . Journal of South American Earth Sciences . en . 109 . 103296 . 10.1016/j.jsames.2021.103296. 233693434 . free . 2021JSAES.10903296K .
7. Book: Brea . Mariana . Fossil plant studies from late Early Miocene of the Santa Cruz Formation: paleoecology and paleoclimatology at the passive margin of Patagonia, Argentina . 2012 . Early Miocene Paleobiology in Patagonia: High-Latitude Paleocommunities of the Santa Cruz Formation . 104–128 . Bargo . M. Susana . Cambridge . Cambridge University Press . 10.1017/cbo9780511667381.008 . 978-0-521-19461-7. Zucol . Alejandro F. . Iglesias . Ari . Kay . Richard F. . Vizcaíno . Sergio F..
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