T.I.E.S. Neogene Basin Evolution in the Atuel basin, Sosneado Region, Mendoza, Argentina Laura Giambiagi J. Brian Mahoney Kris Benusa Olivia Iverson Dave Kimbrough Conicet University of Wisconsin University of Wisconsin University of Wisconsin- San Diego State University Mendoza, Argentina Eau Claire, WI Eau Claire, WI Eau Claire, WI San Diego, CA Argentina

Abstract Stratigraphic successions in the southern Atuel basin record progressive orogenic exhumation and basin subsidence in the Miocene retroarc foreland basin related to the structural evolution of the Malargüe fold and thrust belt, northwest of Malargüe, W E

Argentina (~35°S). Miocene strata in the eastern Atuel basin include thin- to medium bedded lithic arenite of the Agua de la Blanco Creek La Manga Creek Cuchilla de la Tristeza Range Meson thrust Middle J + K Sosneado thrust Piedra Fm. unconformably overlying tilted strata of the Cretaceous Malargüe Group. The basal contact of the Agua de la Piedra 2.0 RD LF AP is an angular unconformity with the underlying Malargüe Group. These successive angular unconformities show progressive AP AP 1.0 deformation of synorogenic retroarc foreland basin strata in response to movement on the Malargüe fold and thrust belt. EF 0.0 Upper K + Paleogene Agua de la Piedra El Meson thrust Analysis of the Agua de la Piedra Formation constrains the depositional setting and provenance of these synorogenic strata. El Sosneado thrust The base of the Agua de la Piedra Fm. (>550 m) is a parallel-bedded coarse pebble-boulder conglomerate; this begins a cyclic -1.0 Upper J + K -2.0 succession of four fining upward sequences grading from a basal lenticular cobble-boulder conglomerate into well-stratified PA+TE CH

Depth (km) Upper Cretaceous coarse lithic arenite and overlying siltstone. Abundant structures (channel fills, basal scour marks, parallel and trough-cross -3.0 stratification) indicate fluvial and alluvial fan deposition in the retroarc foreland basin. -4.0 -5.0 0 2 4 km Clast counts reveal episodic variations in clastic input. The first clast count collected 200 m from the base of the section W shows abundant rhyolite detritus derived from the Permian-Triassic Choiyoi Group of the Frontal Cordillera. The second count E collected 275 m from the base of the section shows an increase in sandstone and limestone clasts distinguished by ammonite fossils, characteristic of the Jurassic Tordillo Formation. Giambiagi et. al. (2008) inferred the maximum age for the Agua de la 40 39 Piedra Fm. is ~13 Ma based on Ar/ Ar ages on conglomerate boulders. Clast data coincides with the exposure of both the Left: Cross section of the Atuel basin region. CH: Basement Rock; EF: El Freno Formation; PA+TE: Puesto Araya and Tres Esquinas Formations; Middle J+K: M. Jurassic-Cretaceous; Upper J+K: U. Jurassic-Cretaceous; Frontal Cordillera and Jurassic strata of the Neuquén basin at this time. Data from two detrital zircon samples indicate sediment Upper K + Paleogene: Upper Cretaceous to Paleocene; AP: Agua de la Piedra Formation; LF: Loma Fiera Formation; RD: Rio Diamante Formation. Middle Left: Google Earth image of regional structure. Note El Meson derived from both the Permian-Triassic Choiyoi Group of the Cordillera Frontal and populations of Paleozoic and Mesozoic and El Sosneado thrust faults duplicating Agua de la Piedra Fm. Middle Right: Google earth image of stratigraphic section. Yellow markers denote different stations throughout the section.Right: Photograph of measured grains presumably derived from the Neuquén basin. Syndepositional grains were not recognized, implying a lack of volcanism stratigraphic section. Color change indicates stratigraphic units. during deposition of the Agua de la Piedra Fm.

Purpose Detrital Zircon Geochronology The south-central Andes are characterized by latitudinal stratigraphic variations that reflect changes in the rate and pattern of orogenic exhumation. Detailed analyses, including conglomerate clast counts, detrital zircon studies, and zircon Hf isotopic analyses, Sosneado Region, Atuel Basin Stratigraphy constrain the timing and pattern of an eastward propagating fold and thrust system that has influenced Andean deformation since 7 5 early Miocene time. The primary objective of this investigation is to assess the influence of variations in subduction geometry 18 550 Choiyoi Jura-Cretaceous island arc intrusion Late K- Jura- PZ/MZ sediment along the Andean margin on basin development and evolution. 16 Choiyoi 6 Early T Cretaceous (Cord. Principal) 4 14 Choiyoi R 5 R R e e l e a l

12 l a t a i t t v i i r

v 3 v e

500 r e r

4 e e e e p b 10 p b p b r m o r r m o m o u b Famatinian u b u b a N a N a b 8 3 N b b Andean Geologic History Famatinian i l i

2 i i l l t i i y t

Pampean t y Above: Conglomerate channels in bold relief The base of the Agua de la Piedra Fm. 6 Pampean Grenville y against finer-grained overbank deposits. (~350 m) 450 2 Famatinian is a parallel-bedded coarse pebble- 4 Grenville Pampean 1 1 01JBM11 boulder conglomerate; this begins a 2

cyclic succession of four fining 0 0 0 upward sequences grading from a 0 500 1000 1500 2000 2500 3000 0 200 400 600 800 1000 1200 0 100 200 300 400 500 600 400 1JBM11 1JBM11 1JBM11 basal lenticular cobble-boulder conglomerate into well-stratified 350 coarse lithic arenite and overlying siltstone. Abundant structures (channel fills, basal scour marks, parallel and 7 6 6 Late K- Jura-Cretaceous Jura-Cretaceous Early T arc plutons trough-cross stratification) indicate 6 J-K sediment 5 arc plutons 300 fluvial and alluvial fan deposition in 5 Choiyoi Late K-Early Choiyoi 5 R R R e e the retroarc foreland basin. 4 e 4 T arc PZ/MZ sediment l l l a a a t t t i i Mendoza, Choiyoi i v v v volcanics r

r (Cord. Principal) r e 4 e e e e Argentina e

Meters Clast Count 2 p p p b b b r r r m m m o 3 3 o o u u b u b 250 b a a N a N 3 N b b 02JBM11 Famatinian b

Famatinian i i i l l l Famatinian i i i t t t y y 2 y 2 Above: Base of conlgomerate channel. Note 2 Pampean Grenville Pampean coarse grained lag deposit, basal scour marks, 1 and graded bedding (~250 m) 200 1 Grenville 1

0 0 0 Clast Count 1 0 500 1000 1500 2000 2500 3000 0 200 400 600 800 1000 1200 0 100 200 300 400 500 600 02JBM11 original 02JBM11 original 02JBM11 original 150

GONDWANA The Upper Malargüe Group consists of

A continental red beds as well as fine-grained La Serena R 30ºS E 30ºS L

L I

D sedimentary rocks derived from a playa lake CHILENIA R F 100 O Las Peñas P R C basin R O E origin that was Upper Cretaceous to Paleocene I N R N Salagasta T P C Region A

I P L in age. The contact between the Upper A San Juan C

L O

C R INTERPRETATION O D Malargüe Group and the Agua de la Piedra R I L D L

I E L CUYANIA 50 L R Formation is marked by an angular * The stratigraphic section measured represents a braided fluvial system within a retroarc foreland basin E A Mendoza

R

A

C U Y O unconformity. Santiago B A S I N 34ºS 34ºS * Conglomerate clast counts in the lower section reveal a large population of rhyolite detritus, probably derived from Choiyoi Group exposures in the Cordillera Principal. Parallel bedded S a n R a f a e l Very Very r a n g e Silt Fine Medium Coarse Pebble 71ºW 68ºW Fine Coarse Cross bedded 100 Km * Clast counts in the upper section document an influx of sedimentary clasts, indicating renewed uplift Choiyoi Group outcrops Above: Pebble conglomerate with well developed clast imbrication (~200 m) Channels of the Cordillera Principal A. Digital elevation map of South America. Red circle denotes location of Mendoza, Argentina. B. Left map shows earthquake Scours occurrences along western South America. Larger circles indicate a higher magnitude earthquake. Right map shows the depth to * Significant changes in detrital zircon populations between samples suggest major provenance shifts, the subducting slab beneath western South America. C. Map of the morphostructural belts that characterize the south-central probably indicative of episodic unroofing of progressively deeper levels of the Cordillera Principal during Andes. From east-west they are the Cordillera Coastal, the Cordillera Principal, the Cordillera Frontal, and the Precordillera. progressive eastward propogation of the thrust system within the Malargüe fold and thrust belt. Further east are basement uplifts of the Sierra Pampeanas. D. Location map of the Atuel basin at ~35oS latitude.

Malargüe Fold-thrust Belt Andean Neogene Basin Stratigraphy A Before 15 Ma Molles Fm. Clast Count 1 AGE Western Eastern Sector Sector Rhyolite Cobble Pleistocene Sandstone Cobble Limestone Pebble Basalt Pebble Acknowledgements

Alumbre fault El Freno fault La Manga fault No Andesite Pebble deposition Basin 1 Foreland Volcanic Sandstone Pebble I would like to acknowledge the T.I.E.S. – Argentina program for affording me the 15-11 Ma Agua de la Piedra Fm. B Chert Pebble

Holocene opportunity to research the Andes mountain range, and the Hostel Alamo for providing Rhyolite Pebble warmth and unexcelled hospitality. I would like to thank Todd Lau and Samantha Taylor for HIATUS Siltstone Pebble Paleogene Sandstone Pebble assistance in preparing samples for zircon dating. Finally, I would like to thank the Arizona La Manga Tuff Pebble Laserchron Center for their collaboration and outstanding expertise. inverted fault Eroded

0 10 20 30 40 50 60 Late

10.5-9 Ma Compression C La Manga Loma Fiera Fm. Meson

bypass fault fault Early

Cretaceous Clast Count 2

Above: Brandon Wick and Greg Valitchka measuring Limestone Cobble

Regional Late Ssubsidence the stratigraphic section. Top right: Clast count 1 9 - 8 Ma La Manga Basalt Cobble D Sosneado References bypass fault Rhyolite Cobble fault taken from approximately 200m from the bottom of the stratigraphic section shows a large amount of rhyolite Sandstone Cobble Giambiagi, L. B., Bechis, F., Garcia, V. and Clark, A., 2008, Temporal and spatial relationship clasts, followed by andesitic and sandstone clasts. Limestone Pebble 1 between thick- and thin-skinned deformation in the Malargüe fold thrust belt, southern Central Andes:

Middle Basalt Pebble Sag Bottom right: Clast count 2 taken from Tectonophysics (in press).

phanse Jurassic approximately 250m shows a significant decrease in Andesite Pebble Alumbre fault Arroyo Blanco Sosneado rhyolite clasts, and a distinct increase in sandstone and Chert Pebble Giambiagi, L. B., Mescua, J., Bechis, F., Martinez, A., Folguera, A., 2011, Pre-Andean deformation of 8 - 1 Ma fault fault Rhyolite Pebble

E Early limestone clasts. the Precordillera southern sector, southern Central Andes: Geosphere (in press). Sandstone Pebble Tuff Pebble *Above units

phase correspond with Late Synrift 0 5 10 15 20 25 30 35 40 Triassic stratigraphic 10 km ? column on right ?

Left: Diagram of fold-thrust belt development within the Malargüe fold and thrust belt in last 15 Ma. Note progressive eastward development of thrust system, with sequential motion through the Alumbre, El Freno, La Manga and El Sosneado faults. Right: Stratigraphic section within the Atuel basin(Giambiagi et al., 2008).