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Neotectonic basin and landscape evolution in the Eastern Cordillera of NW Argentina, Humahuaca Basin (~24°S)

October 2013
Basin Research 25(5)

October 2013
25(5)

DOI:10.1111/bre.12016

Authors:

Heiko Pingel

Universität Potsdam

Manfred R Strecker

Universität Potsdam

R. N. Alonso

National University of Salta

Intermontane basins are important repositories for sediment storage, documenting the tectonic, climatic, and sedimentary evolution of orogens in time and space. The Quebrada de Humahuaca in the Southern Central Andes of NW Argentina is an ideal setting to study the evolution of an intermontane depositional environment, which is located within a very narrow section of the Eastern Cordillera between 23-24°S. Ongoing shortening, associated surface uplift and progressive aridification, due to orographic barrier uplift, have helped accommodate and retain a variety of late Miocene to Quaternary sedimentary deposits in the Humahuaca basin. These deposits record the transition from an originally open foreland to an intermontane basin depositional environment. Here, we present new U-Pb zircon ages of intercalated volcanic ashes and paleocurrent data, suggesting that prior to ~4.3 Ma, the Qda. de Humahuaca was an integral part of a contiguous foreland basin, whose fluvial network was subsequently decoupled from the foreland due to basement-block uplifts in the course of an eastward-migrating deformation front. Subsequently, the basin experienced at least three cycles of hydrologic isolation and filling followed by headward erosion, renewed fluvial connectivity and erosion, respectively. The ultimate basin-filling episode between ~800 ka and

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Neotectonic basin and landscape evolution in the

Eastern Cordillera of NW Argentina, Humahuaca

Basin (~24°S)

Heiko Pingel,*Manfred R. Strecker,*Ricardo N. Alonso†and Axel K. Schmitt‡

*DFG Leibniz Center for Surface Process and Climate Studies, Institut f €

ur Erd- und Umweltwissenschaften,

Universit €

at Potsdam, Potsdam, Germany

†Departamento de Geolog

ıa, Universidad Nacional de Salta, Salta, Argentina

‡Department of Earth and Space Sciences, UC Los Angeles, Los Angeles, CA, USA

ABSTRACT

The intermontane Quebrada de Humahuaca Basin (Humahuaca Basin) in the Eastern Cordillera of

the southern Central Andes of NW Argentina (23°–24°S) records the evolution of a formerly contig-

uous foreland-basin setting to an intermontane depositional environment during the late stages of

Cenozoic Andean mountain building. This basin has been and continues to be subject to shortening

and surface uplift, which has resulted in the establishment of an orographic barrier for easterly

sourced moisture-bearing winds along its eastern margin, followed by leeward aridiﬁcation. We pres-

ent new U–Pb zircon ages and palaeocurrent reconstructions suggesting that from at least 6 Ma until

4.2 Ma, the Humahuaca Basin was an integral part of a largely contiguous depositional system that

became progressively decoupled from the foreland as deformation migrated eastward. The Humahu-

aca Basin experienced multiple cycles of severed hydrological conditions and subsequent re-captured

drainage, ﬂuvial connectivity with the foreland and sediment evacuation. Depositional and structural

relationships among faults, regional unconformities and deformed landforms reveal a general pattern

of intrabasin deformation that appears to be associated with different cycles of alluviation and basin

excavation in which deformation is focused on basin-internal structures during or subsequent to

phases of large-scale sediment removal.

INTRODUCTION

To understand the spatiotemporal evolution of tectoni-

cally active range fronts in mountain belts, it is essen-

tial to unravel the relationships between styles and

rates of tectonic deformation, surface uplift, and the

distribution of precipitation and surface processes that

reﬂect relief and local climatic conditions. This evolu-

tion may be partially recorded by the sedimentary

deposits preserved in intermontane basins in the

peripheral sectors of an orogen, in the compartmental-

ized basins within broken forelands, or farther away in

adjacent foreland basins.

Sediment accumulation within contiguous foreland

basins is predominantly determined by the ﬂexural

response of the crust to the topographic load from an

adjacent fold-and-thrust belt and from the sediments

derived from the orogen (e.g. Beaumont, 1981; De-

Celles & Giles, 1996). As a fundamental characteristic

of foreland basins, protracted deformation and coeval

deposition progressively extend into the previously

undeformed, distal foreland regions, with the orogenic

deformation front and associated sedimentary facies

patterns advancing in a systematic spatiotemporal pat-

tern (e.g. DeCelles & Giles, 1996). In contrast, broken

foreland basins may develop in regions where shorten-

ing is accommodated along reactivated high-angle struc-

tures inherited from former tectonic regimes (Jordan &

Allmendinger, 1986; Jordan & Alonso, 1987), often

leading to highly diachronous and spatially disparate

basement uplifts (reviewed in Strecker et al., 2011).

Isolated range uplifts promote much more subdued

ﬂexural subsidence with accommodation space that is

limited to the margins of the individual ranges (Strec-

ker et al., 2011). If these tectonic characteristics are

paired with arid climate conditions, headwater basins

can become isolated from the downstream ﬂuvial net-

work, leading to sediment accumulation between uplift-

ing ranges (Meyer et al., 1998; Sobel et al., 2003;

Hilley & Strecker, 2005). Over geological timescales, an

array of isolated to variably connected and laterally

restricted depocentres may develop, forming a land-

scape similar to the partially coalesced basins observed

in Cenozoic orogenic plateaus and their ﬂanks, such as

the southern part of the Andean Altiplano-Puna Plateau

or the Tibetan Plateau and the adjacent Qilian Shan in

Asia (Meyer et al., 1998; Sobel et al., 2003; Alonso

et al., 2006; Strecker et al., 2009).

Correspondence: Heiko Pingel, Institut fu

¨r Erd- und Umwelt-

wissenschaften, Universita

¨t Potsdam, Karl Liebnecht-Str. 24,

D-14476 Potsdam-Golm, Germany E-mail: heiko.pingel@geo.

uni-potsdam.de

554

Basin Research (2013) 25,554–573, doi: 10.1111/bre.12016

EAGE

The dynamics of basin hydrology in these environ-

ments may depend on a type of competition between

uplift of downstream ranges, which favours fragmentation

of the ﬂuvial network, and headward incision, which pro-

motes the persistence or re-integration of rivers draining

the periphery of these orogens (Sobel et al., 2003; Hilley

& Strecker, 2005; Garcia-Castellanos, 2007). As a result,

changes in climatic conditions or tectonic rates may cause

these marginal basins along the ﬂanks of an orogenic pla-

teau to transition between conditions in which ﬂuvial con-

nectivity is promoted or basins are hydrologically isolated

from their downstream watersheds. These alternations in

the ﬂuvial network are expected to inﬂuence the rate and

tempo of sediment removal from the interior of the oro-

gen to the unrestricted parts of foreland basins.

The Andean broken foreland areas of the northern

Sierras Pampeanas, the Santa Barbara System and parts

of the Eastern Cordillera of NW Argentina (Fig. 1)

illustrate the complex morphology resulting from tec-

tonic uplift, basin formation and basin excavation along

the eastern ﬂanks of the orogenic Altiplano-Puna Pla-

teau. While ﬁeld studies in this region show that rivers

connecting intermontane basins with the foreland are

often interrupted due to spatial and temporal changes

in deformation, climate and the erodibility of exposed

bedrock (e.g. Hilley & Strecker, 2005), predicting the

combinations of driving factors responsible for alternat-

ing states of basin isolation and ﬂuvial connectivity is

still difﬁcult. Deposits preserved in the intermontane

basins are often deformed, faulted and frequently show

syntectonic growth as a result of initial foreland frag-

mentation and out-of-sequence deformation, demon-

strating clear tectonic inﬂuence on basin sedimentation

(for a summary see Strecker et al., 2011; Hilley et al.,

2005). Moreover, regional unconformities show that

large volumes of sediment have been rapidly removed

from these basins once they have been re-captured

(Hilley & Strecker, 2005; Strecker et al., 2009). These

superposed processes raise an interesting and as yet

unexplored possible feedback between the re-integration

of these intermontane basins with the foreland through

ﬂuvial connectivity and renewed faulting within the

orogenic realm following the removal of sedimentary

loads. While these relationships among tectonics,

sedimentation and erosion have been suspected to exist

in many intermontane basins of the NW Argentine

Andes (Strecker et al., 1989, 2009; Hilley & Strecker,

2005; Alonso et al., 2006), the timescales for individual

ﬁlling and excavation cycles have remained poorly con-

strained.

A rich record of frequently intercalated volcanic ashes

in the sediments of the southern Humahuaca Basin of

NW Argentina (~23.5°S, Fig. 1) provides the requisite

chronology to quantify temporal associations among tec-

tonics, climate and sedimentation on the scale of a single

intermontane basin. In our study, we present new chrono-

stratigraphic (

206

Pb/

238

U zircon and AMS

C), struc-

tural and sedimentological data for various preserved

conglomeratic basin ﬁlls within the Humahuaca Basin and

document that (a) the transition between a largely contin-

uous foreland depositional environment and a subsequent

fault-bounded intermontane basin is related to more pro-

nounced surface uplifts to the east after ~4.2 Ma; (b) the

intermontane basin stage has been characterized by multi-

ple cycles of basin ﬁlling and subsequent sediment

removal; and, although speculative, (c) out-of-sequence

reactivation of faults within the basin may be closely

linked with sediment evacuation.

REGIONAL AND GEOLOGICAL SETTING

The Humahuaca Basin (Jujuy Province) is the northern-

most intermontane sedimentary basin in an array of

reverse-fault bounded basins within the Eastern Cordil-

lera of NW Argentina along the eastern Puna Plateau

margin, the southern extension of the Bolivian Altiplano

(Fig. 1). The Humahuaca Basin is surrounded by high-

elevation mountain ranges exceeding 5,000 m a.s.l. that

consist of smaller reverse and thrust fault-bounded

blocks. The Sierra Alta separates the basin from the inter-

nally drained and arid Puna Plateau to the west, while the

Tilcara ranges constitute the boundary with the humid

foreland depositional system to the east. At present, the

Humahuaca Basin is connected to the foreland via a nar-

row, fault-bounded bedrock gorge to the south, through

which the Rıo Grande exits the basin (Figs 2 and 9).

Here, the course of the Rıo Grande ﬁrstly follows and

then obliquely crosses the trace of the west-dipping

reverse fault that bounds the southern sector of the Til-

cara ranges.

Basement blocks constitute the basin-bounding ranges

that have been uplifted along north to north–northeast

striking, bivergent thrust and reverse-fault systems

(Rodrıguez-Fernandez et al., 1999; Kley et al., 2005;

Fig. 2). At the latitude of the Humahuaca Basin, the east-

ern margin of the neighbouring Altiplano-Puna Plateau

records a middle Eocene to Oligocene deformation his-

tory, inﬂuenced by pre-existing crustal heterogeneities

and structures that were reactivated during Cenozoic

compression (Coutand et al., 2001, 2006; Deeken et al.,

2006; Hongn et al., 2007; Insel et al., 2012). Between 10

and 8 Ma, the eastern plateau margin apparently attained

sufﬁcient elevation and relief to intercept moisture-bear-

ing easterly winds; this topography constituted a major

orographic barrier to atmospheric circulation on a hemi-

spheric scale, resulting in the aridiﬁcation of the orogen

interior and the establishment of humid conditions on the

eastern ﬂanks (Allmendinger et al., 1997; Kleinert &

Strecker, 2001; Starck & Anzotegui, 2001; Strecker et al.,

2007; Uba et al., 2007; Carrapa et al., 2008; Mulch et al.,

2010; Vezzoli et al., 2012). During the Mio-Pliocene,

deformation migrated into the present-day Eastern Cor-

dillera, where the formerly contiguous foreland basin was

partitioned by regional range uplifts. This deformation is

spatially disparate, highly diachronous (reviewed in

Basin & landscape evolution in the E Cordillera

Strecker et al., 2007, 2009) and ongoing (Bevis & Isacks,

1984; Cahill et al., 1992; USGS/NEIC PDE-catalogue).

The basement rocks exposed along the ﬂanks of the

Humahuaca Basin comprise tightly folded late Protero-

zoic to early Palaeozoic low-grade metasediments of the

Puncoviscana Formation (Turner, 1960; Omarini, 1983).

These units are unconformably overlain by Cambro-

Ordovician sandstones and quartzites of the Meson and

Santa Victoria groups (Moya, 1988; Sanchez & Salﬁty,

1999; Ace~nolaza, 2003). An angular unconformity sepa-

rates these sediments from the late Cretaceous to

Palaeogene Salta Group related to the Cretaceous Sal-

ta Rift (Salﬁty, 1982; Galliski & Viramonte, 1988; Mar-

quillas et al., 2005). The most prominent strata of these

sequences exposed in the southern Humahuaca Basin are

continental red beds of the Pirgua Subgroup, white sand-

stones and yellow-coloured marine carbonates of the

Lecho Formation and the stromatolitic Yacoraite Forma-

tion (Balbuena Subgroup), respectively, and ﬂuvial

deposits of the Lumbrera Formation (Santa Barbara Sub-

group). For detailed reviews, see Marquillas et al. (2005)

and Sanchez & Marquillas (2010).

These lithologies are typically overlain by early Ceno-

zoic foreland sediments such as the Quebrada de los Col-

orados Formation (middle Eocene–Oligocene), the

deposits of the Oran Group (Miocene–Pliocene) or equiv-

alent strata (Gebhard et al., 1974; Russo & Serraiotto,

1978; Dıaz & Malizzia, 1983; Vergani & Starck, 1989;

Coutand et al., 2001) in the Puna and present-day

foreland regions to the east of the study area. However,

these sediments have mostly been removed in the highly

exhumed Eastern Cordillera (Jordan & Alonso, 1987;

Kley et al., 2005). A regional exception to this general

pattern is a ca. 6-km thick succession of middle Eocene to

Pliocene foreland and intermontane basin deposits in the

Cianzo Basin of the Eastern Cordillera, 20 km east of the

town of Humahuaca (details in Siks & Horton, 2011).

Strata overlying the Salta Group in the Humahuaca Basin

largely consist of weakly consolidated, mainly

conglomeratic deposits that reﬂect a complex history of

deposition, erosion and deformation that spans the late

Miocene and Quaternary.

Three major units have previously been described:

the Maimara Formation (Salﬁty et al., 1984), the Uquıa

Formation (Castellanos, 1950; Marshall et al., 1982;

Walther et al., 1998) and thick conglomeratic ﬁlls of

Quaternary age (Tchilinguirian & Pereyra, 2001;

Robinson et al., 2005; Strecker et al., 2007; Sancho

et al., 2008). In the following sections, we will reﬁne

this stratigraphic framework for the southern part of

the Humahuaca Basin and focus our attention on its

distinct volcanic ash-bearing conglomerates and sand-

stones that document sustained deposition, deformation

and erosion in the basin, and which provide excellent

stratigraphic markers to assess the late Cenozoic basin

evolution.

METHODS

We used stratigraphic and structural analysis, together

with detailed geological mapping of exposed units

(Fig. 3), regional unconformities, sediment provenance,

lateral facies pinch-outs and lithological contacts to docu-

ment the tectono-sedimentary history of the southern

Humahuaca Basin. A similar approach is used in an

ongoing chronostratigraphic study of the northern Huma-

huaca Basin (Streit et al., 2012).

Fig. 1. Topography and east-draining river network of the

South Central Andes in NW Argentina and S Bolivia based on

SRTM-GTOPO30. Structural information is taken from Sobel

et al. (2003), Mortimer et al. (2007), Hain et al. (2011), Mulch

et al. (2010), Uba et al. (2007), Allmendinger & Zapata (2000),

Kley et al. (1997) and Carrapa et al. (2006). Dashed lines delin-

eate morphotectonic domains. Letters relate to major intermon-

tane basins in NW Argentina discussed in the text: H, Quebrada

de Humahuaca; T, Quebrada del Toro; L, Lerma Basin; C,

Calchaquı Basin; SM, Santa Marıa Basin; CA, El Cajon-Campo

Arenal Basin; F, Bolson de Fiambala Basin. Black box indicates

location of Fig. 2.

556

H. Pingel et al.

Despite apparent similarities between the various sy-

norogenic lithologies, spatiotemporal changes in the

sediment sources result in distinct differences among

the conglomeratic ﬁll units in the Humahuaca Basin.

We characterized the compositional differences of the

ﬁlls by counting at least 100 clasts from within a 0.25-

grid in key stratigraphic units. To deduce sediment

provenance and transport directions for ancient river

systems, we measured ~1,600 imbricated clasts at 33

localities. Where possible, we measured the orientation

of at least 50 clasts per site, applied corrections for

structural dip and displayed them in unidirectional rose

diagrams using OSXStereonet software (by N. Cardozo

& R. Allmendinger).

(a)

(b)

Fig. 2. (a) Simpliﬁed geology of the Humahuaca Basin and surroundings and (b) geological cross section after Rodrıguez-Fernandez

et al. (1999) and own data. Black box indicates the area mapped in detail (Fig. 3a).

Basin & landscape evolution in the E Cordillera

(a) (b)

(c)

Fig. 3. (a) Geological map of the central study area between Tilcara and Purmamarca in the southern Humahuaca Basin. Triangles

represent U–Pb zircon sample locations (see Table S1) and thick black lines show the position of measured stratigraphic sections from

Fig. 6. Map is rotated anti-clockwise by 20°. (b) Simpliﬁed late Cenozoic chronostratigraphy of the study area. Unless otherwise

indicated, values represent averaged U–Pb zircon ages from this study.

a40

Ar/

Ar-biotite (Strecker et al., 2007);

OSL-quartz

(Robinson et al., 2005; Sancho et al., 2008);

AMS14C (this study). (c) Subsurface interpretations of severely deformed strata. Shown

are pseudo-fault-plane solutions calculated from fault-kinematic indicators documenting thrust kinematics during the Pliocene. Pv,

Puncoviscana Fm; Sa, Salta Group; M, Maimara Fm; T, Tilcara Fm; Q, Quaternary gravels.

558

H. Pingel et al.

To provide a chronological base for different tectonic

and sedimentological events, we dated 12 volcanic ash

deposits interbedded in the Mio-Pleistocene basin strata

using U–Pb zircon geochronology. Samples were

crushed, sieved and treated with standard heavy-liquid

and magnetic separation techniques to isolate zircon

crystals. About 30 crystals per sample were handpicked,

mounted in epoxy, polished and cleaned, and then

gold-coated for microprobe analysis. Crystals free of

inclusions, or cracks were selected for U–Pb analysis

using the CAMECA IMS 1270 ion microprobe at the

University of California in Los Angeles, following pro-

tocols described in Schmitt et al. (2003) and Grove

et al. (2003). The

206

Pb/

238

U ages have been corrected

for common Pb and initial disequilibrium. The uncer-

tainties in U–Pb ages, estimated from the reproducibil-

ity of standard AS3 zircons (1,099.1 Ma; Paces &

Miller, 1993), were 2.2% and 2.7% (1 standard devia-

tion) for the analytical sessions in July 2009 and June

2010, respectively.

RESULTS

U–Pb zircon geochronology

Most analysed samples show complex zircon age distribu-

tions. This could be due to protracted pre-eruptive crystal

residences (e.g. Schmitt et al., 2003), or post-eruptive

reworking in which case mixing and contamination with

detrital crystals during emplacement would lead to the

presence of multiple age populations. We therefore sys-

tematically omitted older ages from our calculations of an

average zircon crystallization age. The statistically uni-

form younger age population was then used as an approxi-

mation for the depositional age, while acknowledging that

this is likely to overestimate the eruption age because of

pre-eruptive zircon crystallization (e.g. by ~0.1 Ma for

the large-volume Atana ignimbrite; Schmitt et al., 2001).

Most samples yielded consistent

206

Pb/

238

U ages for the

majority of crystals, as indicated by near-unity values for

the mean square of weighted deviates (MSWDs), suggest-

ing only minor reworking. In some cases, however, only a

small percentage of crystals deﬁned a coherent young

population; in these cases, we have interpreted the

206

Pb/

238

U zircon age as the maximum age for deposition.

Results are shown in Figs 3–5, and summarized in Table

S1.

Late Miocene to Pleistocene stratigraphy

Maimara Formation

The ochre to yellow beds of the Maimara Formation

unconformably overlie the older lithologies exposed in

the basin, including the Proterozoic Puncoviscana For-

mation. The Maimara Formation generally comprises

arkosic sandstones and interbedded cobble conglomer-

ates, and is at least 250-m thick (Fig. 6). The matrix-

(a) (b) (c)

(d) (e) (f)

Fig. 4.

207

Pb/

206

Pb vs.

238

206

Pb zircon data for Maimara samples, uncorrected for common Pb and regression lines with a ﬁxed

y-axis intercept corresponding to common Pb (

207

Pb/

206

Pb =0.83). Concordia segment (ages in Ma) is plotted for initial disequilib-

rium D

230

Th/

238

U=0.2 and D

231

Pa/

235

U=3. Number of analyses excluded from regression is given in parentheses.

Basin & landscape evolution in the E Cordillera

to clast-supported conglomerates are composed of well-

rounded pebbles and cobbles, and occasionally boul-

ders, mainly from Proterozoic (23.5% P

) and Palaeo-

zoic (64.5% P

) sources (Puncoviscana Fm. & Meson

Group). This unit also contains clasts of limestones

and sandstones from the Cretaceous to Palaeogene Salta

Group (12% C

) and a minor proportion of lithic-rich,

late Miocene to Pliocene ignimbrites with the nearest

known exposures conﬁned to the Puna Plateau to the

west (e.g. Riller et al., 2001).

The most complete section is exposed in the Quebrada

de Maimara, west of the town of Maimara (Figs 3 and 6),

where the succession has been thrust eastward over Plio-

cene conglomerates. Fossil-rich clay beds and siltstones

dominate the basal 50 m of this section and contain

freshwater ostracods (Limnocythere sp.; Fig. 8b) and intact

calcic encrustations of charophyte oogonia. The following

200-m thick sequence of interbedded sandstones and

conglomerates is intercalated with at least seven volcanic

ash layers.

About 75 m of faulted strata of the Maimara Formation

is also exposed at Incahuasi, located about 10 km south of

the Quebrada de Maimara. This section unconformably

overlies palaeo-relief developed in the Proterozoic to Pal-

aeozoic basement and comprises several metre-thick

banks of moderately consolidated ﬁne-grained arkosic

sandstones that are frequently intercalated with rhyolitic

ash layers, debris-ﬂow deposits and conglomeratic

channel ﬁlls (Fig. 6). Further exposures of the Maimara

Formation exist east of the town of Tilcara, along the Rıo

Huasamayo, where the Maimara

´Formation has been

thrust over late Pleistocene conglomerates (e.g. Salﬁty

et al., 1984; Marrett et al., 1994; Fig. 8a).

The presence of ignimbrite clasts sourced in the Puna

supports the notion of an eastward ﬂuvial transport across

the present-day Sierra Alta, the major mountain range

that now constitutes the eastern margin of the Altiplano-

Puna Plateau west of the basin. The notion of a western

provenance is in agreement with our palaeocurrent esti-

mates that demonstrate an east–southeast-directed palae-

o-drainage system at that time (Fig. 7). We therefore

conclude that the former ﬂuvial network must have

drained eastward across both ranges that now delimit the

basin.

Our U–Pb zircon ages from various volcanic ashes

(08HUM03; 08HUM05; 08HUM07; 09HUM12;

10HUM02; 10HUM21; 10HUM23; Figs 4 and 6; Table

S1) constrain that this depositional setting existed at least

between 5.92 0.12 Ma (MSWD =1.4; n=14) and

4.18 0.11 Ma (MSWD =0.68; n=10).

Tilcara Formation

In the southern Humahuaca Basin, the Maimara Forma-

tion is overlain by a series of metre-thick interbedded

conglomerate, fanglomerate and sandstone beds, at least

250-m thick, which also contain volcanic ash layers. The

transition to subsequent lithologies is always character-

ized by a pronounced regional unconformity, rendering

all measurements of total sediment thickness minimum

estimates (Figs 8c, d). In contrast to the Maimara Forma-

tion, the poorly consolidated strata comprise well-

rounded and well-imbricated pebble- to boulder-sized

clasts with only a minor quantity of Salta Group clasts,

(a)

(b)

(c)

(d)

Fig. 5.

207

Pb/

206

Pb vs.

238

206

Pb zircon data for Tilcara and

Quaternary gravel samples, uncorrected for common Pb and

regression lines with a ﬁxed y-axis intercept corresponding to

common Pb (

207

Pb/

206

Pb =0.83). See caption of Fig. 4 for addi-

tional information.

560

H. Pingel et al.

but no ignimbrites (27.5% P

; 71% P

; 1.5% C

Carbonate cementation of conglomerates occurs in metre-

thick beds. The nearly ﬁlled pore spaces, within such

beds, suggest advanced pedogenic K-horizon formation

(e.g. Gile et al., 1966; Machette, 1985), a common feature

associated with conglomerate deposits in the semi-arid

environments of the southern Central Andes (e.g. Strec-

ker et al., 1989). Clast-imbrication measurements record

a change to a southerly direction of sediment transport

(Figs 6 and 7). While on average, this change demon-

strates a rotation of ca. 20°towards the south (Fig. 7),

palaeocurrent directions measured along continuous sec-

tions reﬂect a dramatic reorganization of the ﬂuvial system

by more than 90°(Fig. 6).

Two ashes sampled in the lower part of the section

(08HUM01 and 08HUM08) yielded overlapping U–Pb

zircon ages of 3.66 0.20 (MSWD =1.6; n=6) and

3.52 0.08 Ma (MSWD =0.44; n=8; Fig. 5; Table

S1). Because these age determinations are statistically

indistinguishable, we consider them to represent the same

ash horizon. A second ash layer from the upper section

(09HUM05) yielded a signiﬁcantly younger

206

Pb/

238

zircon age of 2.50 0.10 Ma (MSWD =1.4; n=9;

Fig. 5; Table S1).

Previous stratigraphic and palaeontological studies

have shown that in the northern Humahuaca Basin, strata

of the Maimara Formation are overlain by the fossil-bear-

ing ﬂuvial Uquıa Formation. This unit comprises mud

and sandstones with occasional conglomeratic beds and

interbedded volcanic ash horizons (Castellanos, 1950;

Reguero et al., 2007). Clast counts for the Uquıa Forma-

tion at a limited number of outcrops reveal ~10% Prote-

rozoic rocks (Puncoviscana Fm.) and ~90% Palaeozoic

rocks (Meson Group). Age determinations of a basal vol-

canic ash from the Uquıa Formation (3.54 0.04 Ma;

Marshall et al., 1982) and from within the upper third of

the section (zircon ﬁssion-track age ~2.5 Ma; Walther

et al., 1998) are in good agreement with our chronology

of the Tilcara Formation. Furthermore, palaeomagnetic

results from the Uquıa Formation (Marshall et al., 1982)

imply that its uppermost strata may be as young as

~1.5 Ma. As the topmost section of the Tilcara Formation

is not preserved, we are unable to determine an upper

depositional age limit. However, we infer that the timing

of deposition was similar in both sub-basins. We consider

this assumption to be valid because (a) we do not ﬁnd any

evidence of other deposits between 2.5 and >1 Ma in the

southern Humahuaca Basin, and (b) the oldest

Quaternary sediments that cover both formations uni-

formly may be as old as ~1 Ma. It is therefore quite possi-

ble that the (unpreserved) top of the Tilcara Formation in

the southern basin is temporally equivalent to the ~1.5-

Myr old top of the Uquıa Formation to the north.

Although chronostratigraphic investigations in the

northern Humahuaca Basin are still ongoing (Streit et al.

2012), we have sufﬁcient evidence for lithological differ-

ences between the corresponding Plio-Pleistocene depos-

its in the two sub-basins to establish a new lithological

unit in the southern basin: the Tilcara Formation. Our

radiometric ages show that deposition of this unit took

place between ~4.2 and 2.5 Ma and by correlation may

have lasted until approximately 1.5 Ma.

Landslide deposits

We identiﬁed multiple voluminous landslide deposits

south of Maimara village that unconformably cover older

units along the eastern basin margin (Fig. 3a). These

deposits predominantly consist of Palaeozoic and Creta-

ceous to Eocene rocks, and overlie previously exhumed

Palaeozoic rocks that dip steeply westward. Multiple, per-

vasively shattered rock sheets with no stratigraphic con-

text are located 60 m above the valley ﬂoor and appear to

be sourced in the eastern basin-bounding range. In places,

the landslide deposits have been subsequently covered by

sub-horizontally bedded conglomerates of Pleistocene

age. The depositional age of the landslide deposits can,

therefore, be only crudely constrained to be older than the

Pleistocene conglomerates.

Fig. 6. Measured stratigraphic sections located near Incahuasi

and in the Quebrada de Maimara. Detailed locations are given in

Fig. 3a.

Basin & landscape evolution in the E Cordillera

To the west of the Rıo Grande and north of Incahuasi

(Fig. 3a), a voluminous Quaternary landslide deposit that

extends for approximately 3.5 km to the north has been

preserved covering an erosional palaeo-landscape in the

previously deposited and folded units. The deposit com-

prises two distinct source lithologies: (a) basal conglomer-

ates whose clast composition, size and general appearance

match the conglomeratic sections of the Maimara Forma-

tion; and (b) Proterozoic basement, found only in the

upper section of the landslide. In both parts, the rocks are

heavily sheared and fractured, with the degree of

cataclasis increasing with depth, culminating at the bot-

tom where underlying undifferentiated sediments have

been injected upward into the fully disintegrated rocks.

The contact between the two units comprising the land-

slide deposit is very sharp and resembles a thrust fault

identical to the relationships that can be observed along

the present-day basin-bounding Sierra Alta to the west.

The landslide deposit is covered by ash-bearing fanglom-

erates that have been dated to ~1 Ma (see section below),

which were subsequently tilted by faulting.

Quaternary gravels

The youngest deposits in the southern Humahuaca Basin

constitute thick gravel ﬁlls covering palaeotopography in

the previously deformed and eroded units. Two lithologi-

cal units can be distinguished on the basis of clast compo-

sitions. The ﬁrst unit comprises dark grey to black

fanglomerates that were derived exclusively from source

regions to the west. These sediments consist predomi-

nantly of angular to subangular clasts of the Puncoviscana

Formation, together with less abundant clasts from the

Meson and Salta groups. We thus interpret these strata to

be proximal alluvial-fan deposits sourced from the Sierra

Alta. At several locations corresponding to more distal

sectors of the inferred alluvial fans, the fanglomerates in-

terﬁnger with well-stratiﬁed layers of pebble conglomer-

ates, graded sands and unconsolidated silty clay. The

layers are characterized by lateral, east–west-oriented

pinch-outs. By analogy with the present-day depositional

environment of the Rıo Grande and from the geometry of

the pinch-outs, we infer that the former ﬂuvial system

also drained southward. The youngest zircons from a tra-

chy-dacitic ash deposit in the upper part of a deformed

succession 2 km north–west of Incahuasi yielded mid-

Pleistocene ages (1.06 0.10 Ma; n=2; 08HUM11;

Fig. 5; Table S1), which we infer to represent a maxi-

mum depositional age.

The second unit in the Quaternary gravels comprises

a group of grey alluvial-fan deposits and ﬂuvial conglom-

erates (Fig. 8e) that are widely distributed within the

Humahuaca Basin, its tributary valleys and in the basin

outlet region to the north of Volcan village (Figs 2 and

9). These gravels typically consist of approximately

equal proportions of Proterozoic and Palaeozoic clasts

with minor contributions from Cretaceous lithologies,

representing the present-day exposure of rock types in

the surrounding source areas. The oldest conglomeratic

ﬁll in this unit forms an abandoned geomorphic surface

to the east of the town of Tilcara, which is up to 400 m

above the present-day baselevel and has an

Ar/

Ar-

biotite age of ~800 ka, taken from a volcanic ash layer in

the lower third of the section (Strecker et al., 2007).

Other investigators have further differentiated these

gravels and document at least one additional, separate ﬁll

unit at lower elevations, corresponding to a third basin-

ﬁlling episode between 93.8 7.9 and 65 4ka

(Tchilinguirian & Pereyra, 2001; Robinson et al., 2005;

Sancho et al., 2008). In the south of Tilcara, this younger

ﬁll unit has been episodically downcut during the last

~65 ka, which has resulted in ﬂuvial terrace surfaces at

successively lower elevations (Fig. 8f). In the tributary

Quebrada de Purmamarca in the south–west of the study

area, even younger deposits, up to 250-m thick, constitute

massive basin ﬁlls that have been dated 47.6 2.8 ka

(OSL, Robinson et al., 2005) and, although at the limit of

the dating method, at 49.55 1.7 ka BP (23°40.9′S, 65°

34.5′W; AMS

C this study).

Structures

Three east-vergent, basement-involved fault systems

deﬁne the structural framework of the Humahuaca Basin:

(a) the basin-bounding Purmamarca Thrust Fault to the

west; (b) a set of thrust-and-reverse faults within the Til-

cara ranges to the east; and (c) the Tumbaya Fault in the

basin centre, close to the Rıo Grande (Fig. 9).

The Purmamarca Thrust Fault juxtaposes Proterozoic

basement of the Sierra Alta over Meso-Cenozoic sedi-

ments along the western basin margin and has developed

a characteristic deformation pattern in the overthrust

lithologies, involving steep eastward dips, or overturned

strata. Moreover, multiple splays have developed from

that fault extending into the basin, offsetting the Cenozoic

strata (Figs 2 and 3). The Sierra Alta belongs to a set of

subparallel basement ranges that have been uplifted along

bivergent thrust and reverse faults. Apatite ﬁssion track

Fig. 7. Palaeoﬂow directions in the Humahuaca Basin derived from clast-imbrications measured in late Miocene to Pleistocene basin

strata. Directions are presented on unidirectional rose diagrams for each site. Panels (a), (b) and (c) show the development of the

ﬂuvial network in the Maimara, Tilcara and Quaternary gravel formations respectively. Panel (b) also shows data from the Uquıa

Formation in the northern Humahuaca Basin. A combination of all clast imbrications for each unit is given in panel (d) highlighting a

signiﬁcant change in transport directions after 4.2 Ma associated with changes in the topographic boundary conditions. Palaeoﬂow

directions in the Quaternary gravels are biased by a lack of properly distributed sample sites; locations are mainly along the eastern

margins of the basin, thus more prone to reﬂect westerly drainages. Results of provenance analyses are shown in histogram plots

depicting mean clast compositions of conglomeratic units.

562

H. Pingel et al.

(a) (b)

Basin & landscape evolution in the E Cordillera

(a)

(b) (c)

(e)(d)

(f)

Fig. 8. (a) Thrust fault near Tilcara along the Rıo Huasamayo, juxtaposing late Miocene Maimara deposits against Quaternary

gravels. Arrows and dashed lines indicate the vertical displacement (up to 20 m) of a formerly contiguous terrace surface. (b) SEM

image of Limnocythere sp. from the lower beds of the Maimara Formation. (c) Deformed bedding-parallel erosion surfaces in the Til-

cara Formation preserved below Quaternary landslide deposits. Tectono-sedimentary relationships suggest an episode of river incision

and excavation prior to deformation. (d) Another example of the marked regional unconformity between the Tilcara Formation and

Quaternary gravels. (e) Thick conglomeratic ﬁll unit (Quaternary gravels) near the town of Tumbaya. (f) Panoramic view towards the

east showing well developed geomorphic surfaces along the western ﬂanks of the Tilcara ranges at successively lower elevation.

564

H. Pingel et al.

thermal modelling suggests that exhumation of the east-

ernmost ranges constituting the Sierra Alta began

between 15 and 10 Ma (Deeken et al., 2004).

Present-day elevations of the eastern basin-bounding

Tilcara ranges are attributed to shortening, crustal thick-

ening and block rotation along multiple major east-verg-

ing thrust faults located within the range (Rodrıguez-

Fernandez et al., 1999; Fig. 2). Because fault activity

was mainly restricted to areas east of the Humahuaca

Basin, the Proterozoic basement and overlying Palaeozo-

ic to Mesozoic strata along the western ﬂanks of the

range were affected by westward tilting of this basement

block.

At Molle Punco, near Tumbaya (Figs 2 and 9), Prote-

rozoic rocks of the Puncoviscana Formation are thrust

over the Palaeozoic successions of the Meson Group along

the Tumbaya Fault. The Tumbaya Fault can be traced

into the northern Humahuaca Basin, intersecting the

course of the Rıo Grande repeatedly. In the southern Hu-

mahuaca Basin, this fault is responsible for an uplifted

central range (Fig. 3a) that causes the narrowing of the

basin. The surface expression of the fault and associated

basement exposure gradually decrease northward, but the

fault location can still be inferred from west-dipping

Cenozoic basin strata in its hanging wall.

The sedimentary strata and landforms in the southern

Humahuaca Basin attest to protracted deformation during

the Plio-Pleistocene (see section below and Fig. 3c). The

deformation includes thrusting of Precambrian to

Mesozoic rocks over the conglomerates of the Maimara

Formation along the Purmamarca Thrust Fault and asso-

ciated folding, and the subsequent tilting of late Miocene

to Pleistocene basin sediments in the hanging wall of the

Tumbaya Fault until after 1 Ma.

Shortening within the basin was further accommodated

by a number of mesoscale structures, mostly affecting the

Maimara and Tilcara formations. Tight to open folding

and the development of generally east-vergent and shal-

low-dipping thrust systems led to multiple stacked repeti-

tions of the Miocene-Pliocene strata within the basin

(Fig. 3). These thrusts are often associated with the

development of drag folds, and shortening is in places

accommodated by antithetic west-vergent faults. This

pronounced Plio-Pleistocene strain accommodation in the

southern Humahuaca Basin is mainly observed in the west

of the Rıo Grande between the Purmamarca and

Tumbaya faults.

Fig. 10. Schematic cross section (~250 km) of the Andean margin in NW Argentina at ~23.5°S showing times of pronounced Ceno-

zoic deformation. (1) Letcher (2007); (2) Deeken et al. (2005); (3) A. Deeken personal communication (2012); (4) Deeken et al. (2004);

(5) Siks & Horton (2011); (6) Reynolds et al. (1994, 2000).

Fig. 9. Simpliﬁed structural map of the location and strike of

major fault systems responsible for the basin geometry. Indicated

are (a) the Purmamarca Thrust Fault, (b) the Tilcara Thrust

System and (c) the central Tumbaya Fault. Solid thick white line

represents the watershed between the internally drained Puna

Plateau and the presently externally drained Eastern Cordillera;

dashed lines delineate the Humahuaca Basin and adjacent sub-

basins (Tres Cruces and Cianzo basins); also shown is the

location of the Zapla anticline east of San Salvador de Jujuy.

Basin & landscape evolution in the E Cordillera

Tectono-sedimentary relationships and

deformation of basin sediments

The Maimara Formation rests unconformably on

deformed sandstones of the Palaeogene Lumbrera Forma-

tion (upper Salta Group) and Proterozoic to Palaeozoic

basement rocks. This unconformity and onlap relation-

ships between the Maimara Formation and the underly-

ing, irregularly shaped basement surface suggests

deposition on palaeotopography that was sculpted into

these rocks prior to ~6 Ma. To date, no evidence has been

observed supporting an unconformable relationship

between the Maimara Formation and the intermontane

Tilcara Formation. The Tilcara Formation is always cut

by a marked regional unconformity that in many places

has been subsequently altered and obscured by continued

deformation, erosion and deposition. Lateral correlation

with the Uquıa Formation in the northern Humahuaca

Basin suggests that deformation following the initial inci-

sion occurred after ~1.5 Ma. Near the Tumbaya Fault at

Incahuasi (Figs 3a and 9), this deformed unconformity

resembles ﬂuvial erosion surfaces sculpted into the

Tilcara Formation that are tilted at ~20–30°W, parallel to

bedding (Fig. 8c). These unconformable relationships

and the vestiges of an erosional palaeotopography in the

Tertiary sedimentary rocks are well preserved under a

>1.06 0.1 Ma conglomeratic ﬁll unit that dips 10°–

15°W. Basal remnants of this earlier ﬁll unit have a depo-

sitional age of about 0.8 Ma.

A subsequent conglomerate unit (~94–65 ka at Tilcara

and <50 ka near Purmamarca) ﬁlled palaeotopography,

covering the channel of the former trunk stream, which is

now being re-excavated. This >200-m thick ﬁll unit ter-

minates in a smooth terrace surface that is connected with

the mountain fronts. At Purmamarca, these gravels are

generally not affected by fault displacement or other

deformation. Near Tilcara, however, a prominent thrust

fault close to the eastern margin of the basin (Fig. 8a)

juxtaposes the Maimara Formation with young

terrace-forming sections of the Quaternary strata (Salﬁty

et al., 1984; Marrett et al., 1994). Here, deformation

resulted in vertical offsets between 15 and 20 m, which

translates into an average vertical displacement rate of

0.27 0.04 mm/a during the last 65 kyr. Horizontal

displacements of ~40 m (Sancho et al., 2008) suggest

shortening rates of 0.62 0.04 mm/a. Although these

rates are only approximations, they emphasize the impor-

tance of protracted tectonic activity in the Humahuaca

Basin within the interior of the orogen, which is compati-

ble with the characteristics of regional shallow crustal

seismicity (e.g. Bevis & Isacks, 1984; Cahill et al., 1992).

It is noteworthy that this youngest deformation followed a

major phase of gradual basin evacuation.

DISCUSSION

Foreland basin fragmentation and orographic

barrier development

Crustal deformation corresponding to the region of the

present-day interior of the Puna Plateau initiated in

Eocene to Oligocene time (e.g. Kraemer et al., 1999; Car-

rapa et al., 2005; Deeken et al., 2006; Hongn et al., 2007;

Letcher, 2007; Fig. 10). While individual ranges were

uplifted, thick synorogenic strata buried the region that

now constitutes the Eastern Cordillera and adjacent

regions to the east (Reynolds et al., 2001; Deeken et al.,

2006; DelPapa et al., in review). Today, these sediments

are only rarely preserved in the uplifted Eastern Cordil-

lera and the south-eastern ﬂanks of the present-day Puna

Plateau (Jordan & Alonso, 1987; Bossi et al., 2001; Cout-

and et al., 2001; Kley et al., 2005; Mortimer et al., 2007)

and none appear to have been retained in the southern

Humahuaca Basin. A regional exception is a ca. 6-km

thick succession of middle Eocene to Pliocene foreland

and intermontane basin deposits in the Cianzo Basin

(Fig. 9), about 20 km east of the town of Humahuaca,

where deformation and severed drainage conditions have

been documented at ca. 10 Ma (Siks & Horton, 2011).

Similarly, the Tres Cruces Basin in the Puna (Fig. 9) to

the west has retained thick Cenozoic deposits (e.g. Boll &

Hernandez, 1986; Coutand et al., 2001). In both cases,

major reverse faults enclosing the basins have helped to

preserve the Cenozoic sedimentary record. These regional

relationships support the notion of widely distributed

early Tertiary sediments in the area of the Eastern Cordil-

lera and regions farther east. Their general absence in

these high-elevation sectors of the orogen thus suggests

their removal during regional exhumation in the realm of

the Eastern Cordillera at about 15–10 Ma (Deeken et al.,

2004, 2006; Coutand et al., 2006; Siks & Horton, 2011).

The earliest synorogenic strata recognized in the south-

ern Humahuaca Basin belong to the Maimara Formation

and were deposited on a palaeotopography of exposed

Proterozoic and Palaeozoic basement. Deposition of Mai-

mara sediments after a prolonged period of exhumation

and deformation along the former orogenic ﬂanks clearly

documents that by ca. 6 Ma (and possibly some time

(a)

(b)

Fig. 11. Conceptual model of foreland-basin fragmentation. (a)

The Maimara Formation is deposited into an exposed basement

palaeotopography in a largely continuous depositional system

since ca. 6 Ma. (b) Surface uplifts to the east led to re-routing of

the ﬂuvial network and deposition of the Tilcara Formation into

an intermontane basin after 4.2 Ma.

566

H. Pingel et al.

earlier), new topographic conditions had evolved that

would have promoted sedimentation in the study area.

Our palaeocurrent and provenance data including ignim-

brite clasts from currently isolated areas in the Puna inte-

rior and clasts from the Eastern Cordillera document that

these sediments were sourced from the west. As the

Humahuaca Basin and the Puna are not connected any-

more, this observation conﬁrms that thrusting in the

Sierra Alta had not completely interrupted eastward-

draining rivers at about 6 Ma and that the ﬁnal disruption

of the ﬂuvial network must have occurred later.

We do not record any sedimentary evidence for uplift

of the Tilcara ranges at the time when the Maimara For-

mation was deposited. This suggests that the Humahuaca

Basin was part of an unrestricted foreland, and that sur-

face uplift of the eastern ranges started later, coupled with

the deposition of the Tilcara Formation. Alternatively,

one could envision a scenario with an eastward-directed

antecedent ﬂuvial network that may have traversed the

uplifting Tilcara ranges and transported sediment

towards the regions farther east. In both settings, more

pronounced surface uplift in Plio-Pleistocene time would

have ultimately forced the full establishment of intermon-

tane basin conditions and the formation of an efﬁcient

drainage divide, with rivers routing sediments towards

the south. Although not documented in this study, a lat-

eral correlation between the Maimara Formation and the

upper sections of the Oran Group east of the ranges can-

not be excluded. Sediments of the Oran Group may yield

additional information to further elaborate these interpre-

tations in future.

Nevertheless, Oran Group sediments exposed in the

Zapla anticline to the south-east of the Tilcara ranges

(Fig. 9), record a major pulse in deformation prior to

5 Ma (Reynolds et al., 1994, 2000; reviewed in Kley &

Monaldi, 2002). This is consistent with our palaeocurrent

data from the Tilcara Formation that record a distinct

early Pliocene changeover of ﬂuvial transport towards a

north–south-oriented drainage system, which is also doc-

umented in the Uquıa Formation of the central and

northern Humahuaca Basin (Fig. 7). Based on the cur-

rently available data, we conclude that full intermontane

basin conditions were achieved during the deposition of

the Tilcara Formation, but that an antecedent drainage

system traversing a proto-Tilcara range may have existed

prior to that (Fig. 11).

Palaeo-environmental evidence from the Miocene-Pli-

ocene palaeontological and sedimentary record prior to

pronounced uplift indicates that climatic conditions dur-

ing that time were relatively humid. While the Uquıa

Formation is well known for its fossil assemblage indicat-

ing subtropical to tropical warm, humid conditions

(Alonso et al., 2006; Reguero et al., 2007; Reguero &

Candela, 2008), ostracods analysed in this study addition-

ally attest to the existence of permanent freshwater bodies

in the lower Maimara Formation, clearly indicating that

topography and relief conditions must have been sub-

dued. Calcic rhizoconcretions and nodules in the upper

section of the Maimara Formation indicate regional wet–

dry seasonality, a characteristic, which is maintained in

the overlying Tilcara and Uquıa formations. In stark con-

trast are the more arid conditions and the efﬁcient oro-

graphic barrier to the east observed in the Humahuaca

Basin today. Stratigraphic relationships and inferred pal-

aeoclimatic indicators suggest that aridiﬁcation may be a

relatively young phenomenon, related to the uplift of the

Tilcara ranges.

The timing of tectonic uplift and associated aridiﬁca-

tion appears to have been diachronous and basin-speciﬁc

throughout the southern Central Andes, and determined

by the individual behaviour of the basin-bounding faults.

Although such environmental shifts are a hallmark of vir-

tually all intermontane basins along the eastern ﬂank of

the Puna Plateau and generally took place during the Plio-

cene (Bossi et al., 2001; Kleinert & Strecker, 2001; Starck

& Anzotegui, 2001; Coutand et al., 2006; Hain et al.,

2011), our observations demonstrate that in the Humahu-

aca Basin, the change to drier conditions probably

occurred as late as Plio-Pleistocene time.

Basin -fill evolution and deformation in the

Humahuaca Basin

The abrupt change in palaeoﬂow directions during the

deposition of the Tilcara Formation at ~4.2 Ma and the

associated facies change from distal to rather proximal

sources (upward coarsening; Figs 3 and 6) record the tec-

tonically induced reorganization of east-ﬂowing river net-

works that formerly traversed the Tilcara ranges

(Fig. 11). By analogy with neighbouring intermontane

basins (e.g. the Toro and Lerma basins), the strata of the

Tilcara Formation are interpreted as heralding the attain-

ment of an intermontane basin stage. At that time, deposi-

tion in the Humahuaca Basin must have taken place

under conditions of restricted ﬂuvial connectivity with

the foreland; otherwise, the deposition of over 250 m of

sediment within the basin may not have been possible.

Others have suggested that protracted internal drain-

age (e.g. Sobel et al., 2003) or restricted external drainage

(e.g. Hilley & Strecker, 2005) appear to be related to the

combined effects of high uplift rates, exposure of resistant

rocks and aridity. In this context, the following mecha-

nisms for basin aggradation between 4.2 and ~1.5 Ma

may be envisioned: (1) increased surface-uplift rates in

the Tilcara ranges, associated with activity along a reverse

fault that obliquely crosses the outlet region, and/or

exposure of more resistant rock types reducing the ﬂuvial

transport efﬁciency within the basin; and (2) a change in

global and/or regional climatic conditions towards

increased aridity, reduced runoff and transport capacity.

Reduced runoff by increased aridity appears unlikely

given the record of humid palaeoclimatic conditions.

Moreover, the Tilcara Formation belongs to a group of

spatially widespread Miocene-Pliocene conglomerates in

NW Argentina commonly known as Punaschotter (Penck,

1920). These deposits are more likely related to individual

Basin & landscape evolution in the E Cordillera

range uplifts, because their diachronous deposition in var-

ious intermontane basins and foreland regions excludes a

coeval sedimentary response to regional climate change

(McPherson, 2008; Schoenbohm et al., 2008). As glacia-

tion in the Central Andes has not been documented prior

to 3.5 Ma (Clapperton, 1979) and subsequent glaciations

have been minor due to limited moisture availability

(Haselton et al., 2002), it seems also unlikely that the style

and deposition of the Tilcara conglomerates in the Hu-

mahuaca Basin results from glacial erosion at high eleva-

tion. Therefore, although a global trend towards colder

and drier climates since mid-Miocene (e.g., Zachos et al.,

2001) may have favoured basin isolation, it is unlikely to

have initiated basin ﬁlling here at 4.2 Ma. We therefore

favour the ﬁrst scenario as the most likely mechanism for

initializing partial hydrological isolation of the Humahu-

aca Basin, which is consistent with the inferred tectonic

forcing and severing of the ﬂuvial system. The transition

towards coarser grain sizes with the onset of deposition of

the Tilcara Formation is thus best explained by erosion of

more proximal sources in the uplifting Sierra Alta and

Tilcara ranges.

Based on the depositional age estimates from the Tilcara

and Uquıa formations (i.e. ~4.2–1.5 Ma) and the uncon-

formably overlying Quaternary gravel (<1.06 0.10 Ma),

it appears that ﬂuvial connectivity with the foreland must

have been re-established in the intervening time period.

Although our data are currently insufﬁcient to resolve the

processes that led to basin excavation, incision rates at the

valley outlet must have been sufﬁcient to preserve external

drainage, and sufﬁcient transport capacity must have

existed to allow sediment from upstream to bypass the

basin while large volumes of sediment were removed.

These processes, however, do not necessarily imply more

availability of moisture in the Humahuaca Basin itself, but

may instead represent efﬁcient headward erosion at the

location of the valley outlet, where current precipitation

rates abruptly decline upstream towards the Humahuaca

Basin (Strecker et al., 2007).

Although later surface processes have often altered

the unconformity in the Tilcara Formation, preserved

vestiges of deformed erosion surfaces suggest that ﬂu-

vial incision predated an episode of deformation in the

basin. These events were followed by a prolonged

phase of restricted hydrological connectivity with the

foreland associated with basin ﬁlling of up to 400-m

thick ﬂuvial and alluvial gravel between >1.06 and

<0.8 Ma. Whether this ﬁlling episode was linked to

tectonically induced basin isolation farther downstream,

regional uplift of the Tilcara ranges or the result of

climatic forcing remains uncertain. It is, however, con-

ceivable that the ongoing surface uplift of the Tilcara

ranges exceeded a regional threshold elevation to form

an efﬁcient orographic barrier to cause basin-wide

semi-arid conditions (i.e. reduced runoff and transport

capacities) as observed today.

These 400-m thick gravels were largely removed from

the basin during basin excavation, followed by the

deposition of a second major ﬁll, which reached a thick-

ness of approximately 250 m between at least about 94

and 65 ka in the Humahuaca Basin (Robinson et al.,

2005; Sancho et al., 2008) and until after ~50 ka in the

tributary Quebrada de Purmamarca (this study). This ﬁll

unit and all previous deposits now form the substrate for

gravel-covered pediments and multiple ﬂuvial terraces

that have been sculpted into these deposits. These terrace

systems were formed at successively lower elevations

(Fig. 8f), indicating renewed incision that may record

recent reductions in channel gradients and/or changes in

local baselevel with respect to the Andean foreland. These

periods of sediment removal are episodic and have

occurred some time between 65 and 50 ka and the present

day. Faulting that has affected these deposits is an expres-

sion of renewed deformation within the basin during, or

shortly after an episode of extensive basin excavation in

the Pleistocene (Fig. 8a).

Although the last basin-ﬁll episode in the Humahuaca

Basin coincides to some extent with more humid phases

documented in the Altiplano-Puna Plateau (e.g. Bobst

et al., 2001; Placzek et al., 2006), a direct correlation can-

not be observed. Due to limited age control on the youn-

ger Quaternary deposits and landforms in the

Humahuaca Basin, we cannot entirely exclude such a pos-

sible correlation. However, aggradation during humid

phases requires that sediment generation from hillslopes

must increase with precipitation more rapidly than the

increase in the transport capacity of rivers that would

result from enhanced discharge in rivers during this time.

Interestingly, our observations point towards a sys-

tematic behaviour among erosion, deposition and tec-

tonic processes in the Humahuaca Basin, an intriguing

relationship that can also be found in other intermon-

tane basins of the NW Argentine Andes (Strecker

et al., 1989; Hilley & Strecker, 2005). According to

these observations, basin-internal/out-of-sequence

deformation occurs during or following episodes of

enhanced basin excavation. This is documented at least

three times in the stratigraphic record of the southern

Humahuaca Basin. First, after ~1.5 Ma, the Tilcara

Formation was partly removed from the basin followed

by major out-of-sequence thrusting along the basin-

internal Tumbaya Fault. Here, deformation ceased

prior to 1 Ma, which is documented by the onlap of

~1-Myr old gravels. Second, deformed remnants of

these gravels, which lack evidence of syntectonic depo-

sition, might also indicate that deformation occurred in

association with the removal of the strata. Third,

renewed, but locally limited deformation of young river

terraces near Tilcara is observed right after the removal

of the youngest Quaternary gravels. Although this phe-

nomenon and the associated mechanisms will require

more detailed studies in the future, it is conceivable

that the removal of basin ﬁlls and the resulting reduc-

tion in lithostatic stresses on formerly locked thrust

and reverse faults could ultimately result in the reacti-

vation of these faults.

568

H. Pingel et al.

Regional context of foreland fragmentation

and basin-fill evolution

Many intermontane basins along the Puna margin record

the partial or complete loss of ﬂuvial connectivity with the

foreland through the presence of thick conglomeratic ﬁlls

(Strecker et al., 2007). Periodic reconnection to the fore-

land is documented by marked ﬂuvial incision and excava-

tion of these basin ﬁlls, reﬂected in distinct regional

unconformities and complex onlap relationships. Virtu-

ally all basins in the northern Sierras Pampeanas, the

Santa Barbara System and the Eastern Cordillera of

north-western Argentina exhibit similar, but diachronous,

patterns of basin-ﬁll and erosion throughout their history

(reviewed in Strecker et al., 2007, 2009). The unifying

characteristic in the history of these basins is that follow-

ing the reorganization of ﬂuvial systems by surface uplift,

the establishment of orographic barriers results in pro-

gressive aridiﬁcation, interrupted drainages and reduced

ﬂuvial transport capacity (Sobel et al., 2003). While the

basins in the arid interior of the orogen (the Puna Plateau)

have maintained internal drainage systems, resulting in

thick sediment accumulations (Alonso et al., 1991; Van-

dervoort et al., 1995), the intermontane basins along the

eastern ﬂank have alternated between restricted external

and transient internal drainages, and fully integrated ﬂu-

vial systems connected with the foreland.

At present, virtually all of the intermontane basins to

the east of the Puna are hydrologically connected to the

foreland, often via narrow, deeply incised bedrock gorges

(Fig. 1). For example, the Toro Basin at 24.5°S was cut

off from the foreland between 8 and 6 Ma and has subse-

quently experienced at least two cycles of basin ﬁlling and

excavation (Marrett & Strecker, 2000; Hilley & Strecker,

2005). Similarly, between 5.2 and 2.4 Ma, the uplift of an

orographic barrier to the east of the present-day Calc-

haquı Valley at ~25.5°S caused aridiﬁcation associated

with deposition of the conglomeratic San Felipe Forma-

tion, which was subsequently incised, deformed and

ﬁnally overlain by another conglomeratic gravel after

2.4 Ma (Coutand et al., 2006). After renewed sediment

removal, a subsequent gravel unit with complex onlap

relationships was deposited that once formed a continu-

ous surface of coalesced alluvial fans and river gravel.

River superposition, incision and removal of most of the

gravels in the lower Calchaquı Basin document the ongo-

ing erosion of this unit (Coutand et al., 2006; Strecker

et al., 2007). The Santa Marıa Basin at ~26.5°S is a result

of foreland compartmentalization related to basement

uplift to the east that occurred after 6 Ma (Kleinert &

Strecker, 2001; Bossi et al., 2001;Sobel & Strecker, 2003),

which was followed by aridiﬁcation, severed ﬂuvial con-

nection to the foreland, deformation, erosion and ﬁnally,

the deposition of thick conglomerates after 2.9 Ma (Strec-

ker et al., 1989). These units were subsequently incised,

as documented by successively lower pediments and ﬂu-

vial terraces. Further examples of this type of basin devel-

opment are provided by the El Cajon and Fiambala

basins, at 27°S and 27.5°S, respectively (Mortimer et al.,

2007; Carrapa et al., 2008), emphasizing the similarities

between the processes and depositional facies that control

the evolution of intermontane basins within this environ-

ment.

We suggest that the tectono-sedimentary history of the

Humahuaca Basin and other intermontane basins in NW

Argentina can be best explained through a threshold pro-

cess described in Sobel et al. (2003), in which active uplift

of downstream topographic barriers steepens the channels

that traverse these ranges, while aggradation upstream

must keep pace with the associated uplift of the channel.

As rates of rock uplift increase relative to the transport

efﬁciency (related to precipitation) and bedrock erodibil-

ity, internal drainage is favoured. Conversely, low rates of

rock uplift in the downstream basement ranges, a high

level of erodibility of exposed rock types and pronounced

rainfall gradients all promote incision, headward erosion

and basin capture. All of these processes ultimately con-

tribute to sustaining ﬂuvial connectivity with the fore-

land. This, however, is only possible if the narrow outlets

of the arid basins are in close proximity to steep rainfall

and run-off gradients or if the structural setting is condu-

cive to funnelling moist air into the orogen interior during

protracted moist episodes. In turn, this condition would

increase precipitation, run-off and erosion, which would

ultimately help to achieve or re-establish external drain-

age conditions. Indeed, on the basis of our chronology,

observations and interpretations, we are able to show that

the intermontane Humahuaca Basin is the result of pro-

gressive rock uplift and associated surface processes in the

Eastern Cordillera that commenced at 15–10 Ma and sub-

sequently led to deposition of the Maimara Formation at

about 6 Ma. The largely continuous depositional system

ﬁnally became dismembered after 4.2 Ma when topogra-

phy of the Tilcara ranges deﬂected the ﬂuvial network

into rang-parallel drainage. Until about 1.5 Ma, the basin

was characterized by restricted ﬂuvial conditions most

likely related to ongoing regional uplifts. Afterwards, the

basin was rapidly excavated and internally deformed. The

ensuing regional palaeotopography in the basin was sub-

sequently reﬁlled between >1.06 and <0.8 Ma. The rea-

son for the initial excavation is not known, but this could

have been related to headward erosion and ﬂuvial connec-

tivity, followed by re-established hydrological isolation.

The resulting basin ﬁll, then, was largely removed,

deformed and replaced by a younger ﬁll that periodically

has been excavated some time after ~65 and 50 ka. Exca-

vation, again, seems to have been accompanied by basin-

internal deformation, recorded by offset ﬂuvial terraces

near Tilcara, while currently the basin is aggrading (Riv-

elli & Flores, 2009).

SUMMARY AND CONCLUSIONS

In this study, we have combined new provenance and

palaeocurrent data from the sedimentary record of the

Basin & landscape evolution in the E Cordillera

intermontane Humahuaca Basin of the Eastern Cordillera

of the southern Central Andes with 12 new

206

Pb/

238

zircon age estimates from intercalated volcanic ash depos-

its to assess its spatiotemporal evolution. This enabled us

to improve our understanding of the neotectonic basin

and landscape evolution of an intermontane setting in the

immediate vicinity of the intra-orogenic Puna Plateau, the

world’s second largest plateau, and an important barrier

to atmospheric circulation and surface-process regimes.

We suggest that the coupled tectonic, erosion and sedi-

mentary processes and associated landscape development

in the Humahuaca Basin reﬂect an environment whose

evolution is relevant for the assessment of intermontane

basins worldwide, including the North American Lara-

mide province, and the Tien Shan and Qilian Shan base-

ment uplifts in Asia. From our analysis, we draw the

following conclusions:

(1) In comparison with the previously developed chro-

nostratigraphy for the Humahuaca Basin, our new

U–Pb zircon dates extend the lower boundary of

the Maimara Formation into late Miocene, older

than 5.92 0.12 Ma, conﬁrms existing ages from

the northern basin, and reveals Quaternary ﬁlls as

old as ~1 Ma.

(2) On the basis of provenance, lithology and spatial

distribution, we introduced a new stratigraphic

unit, the Tilcara Formation, in the southern

Humahuaca Basin that is apparently coeval with

the radiometrically and palaeontologically con-

strained Uquıa Formation from the central and

northern sectors of the basin. The Tilcara Forma-

tion highlights the different depositional environ-

ments and source areas between the southern and

northern parts of the basin.

(3) The sedimentary units in the Humahuaca Basin

record a transition between a partially segmented

foreland basin and a fault-bounded intermontane

basin in the course of surface uplift to the east.

This resulted in a change in ﬂuvial connectivity

and the re-arrangement of the formerly eastward-

draining river network into an axial, south-directed

drainage after ~4.2 Ma.

(4) Repeated hydrological disconnection from the fore-

land due to tectonism and ensuing aridiﬁcation in

the lee of rising topography repeatedly resulted in

restricted ﬂuvial connectivity and possibly transient

ﬂuvial isolation and accumulation of at least three

basin-ﬁll units during Plio-Pleistocene times. After

episodic re-capture, these ﬁlls were partially evacu-

ated by ﬂuvial incision. This is similar to other inter-

montane basins along the eastern ﬂank of the Puna

where surface uplift resulted in the tectonic defeat

of ﬂuvial networks, hydrological isolation and basin

aggradation, until renewed river incision exceeded

rock uplift at tectonically active basin outlets.

(5) We furthermore observed that major deformation

events in the Humahuaca Basin apparently fol-

lowed a phase of enhanced removal of basin-ﬁll

units, a scenario that has been observed in other

intermontane basins of NW Argentina. We

speculate that this behaviour is related to the

reduction in lithostatic stresses acting on subsur-

face structures during major phases of basin

excavation.

ACKNOWLEDGEMENTS

Strecker, Alonso and Pingel acknowledge funding by the

DFG-Leibniz Center for Earth Surface Process and Cli-

mate Studies (DFG grant STR 373/19-19) and funds

provided by DFG grant STR373/32-1. Schmitt acknowl-

edges the use of the ion microprobe facility at UCLA, in

part supported by a grant from the Instrumentation and

Facilities Program, Division of Earth Sciences, U.S.

National Science Foundation. We are grateful for con-

structive reviews by F. Schlunegger, F. Davila, J. Kley

and editorial support from P. van der Beek.

SUPPORTING INFORMATION

Additional Supporting Information may be found in the

online version of this article:

Table S1. Summary of U–Pb zircon analytical data of

volcanic ash samples in the Humahuaca Basin using

CAMECA IMS 1270 ion microprobe at UCLA.

REFERENCES

ACEN

˜OLAZA, G.F. (2003) The Cambrian System in Northwest-

ern Argentina: stratigraphical and palaeontological frame-

work. Geol. Acta,1(1), 23–39.

ALLMENDINGER, R.W. & ZAPATA, T. (2000) The footwall ramp

of the Subandean decollement, northernmost Argentina, from

extended correlation of seismic reﬂection data. Tectonophysics,

321(1), 37–55.

ALLMENDINGER, R.W., JORDAN, T.E., KAY, S.M. & ISACKS, B.L.

(1997) The evolution of the Altiplano-Puna Plateau of the

Central Andes. Annu. Rev. Earth Planet. Sci.,25(1), 139–174.

ALONSO, R.N., JORDAN, T.E., TABBUTT, K.T. & VANDERVOORT,

D.S. (1991) Giant evaporite belts of the Neogene central An-

des. Geology,19(4), 401–404.

ALONSO, R.N., BOOKHAGEN, B., CARRAPA, B., COUTAND, I., HAS-

CHKE, M., HILLEY, G.E., SCHOENBOHM, L., SOBEL, E.R.,

STRECKER, M.R., TRAUTH, M.H. & VILLANUEVA, A. (2006)

Tectonics, climate, and landscape evolution of the Southern

Central Andes: The Argentine Puna Plateau and adjacent

regions between 22 and 30°S. In: The Andes,22 (Ed. by O.

Oncken, G. Chong, G. Franz, P. Giese, H.-J. G€otze, V. A.

Ramos, M.R. Strecker & P. Wigger), pp. 265–283. Frontiers

in Earth Sciences, Springer, Berlin, Heidelberg.

BEAUMONT, C. (1981) Foreland basins. Geophys. J. Roy. Astron.

Soc.,65(2), 291–329.

570

H. Pingel et al.

BEVIS,M.&ISACKS, B.L. (1984) Hypocentral trend surface anal-

ysis: probing the geometry of Benioff Zones. J. Geophys. Res.,

89 (B7), 6153–6170.

BOBST, A.L., LOWENSTEIN, T.K., JORDAN, T.E., GODFREY, L.V.,

KU, T.L. & LUO, S. (2001) A 106ka paleoclimate record from

drill core of the Salar de Atacama, northern Chile. Palaeogeo-

graphy, Palaeoclimatology, Palaeoecology,173, 21–42.

BOLL,A.&HERNA

´NDEZ, R.M. (1986) Interpretacion estructural

del area Tres Cruces. Bol. Inf. Pet.,7,2–14.

BOSSI, G., GEORGIEFF, S., GAVRILOFF, I., IBAN

˜EZ,L.&MURU-

AGA, C. (2001) Cenozoic evolution of the intramontane Santa

Marıa Basin, Pampean Ranges, northwestern Argentina. J. S.

Am. Earth Sci.,14(7), 725–734.

CAHILL, T., ISACKS, B.L., WHITMAN, D., CHATELAIN, J.L.,

PEREZ,A.&MING CHIU, J. (1992) Seismicity and tectonics in

Jujuy Province, northwestern Argentina. Tectonics,11(5), 944

–959.

CARRAPA, B., ADELMANN, D., HILLEY, G.E., MORTIMER, E., SO-

BEL, E.R. & STRECKER, M.R. (2005) Oligocene range uplift

and development of plateau morphology in the southern

central Andes. Tectonics,24, TC4011, doi:10.1029/

2004TC001762

CARRAPA, B., STRECKER, M.R. & SOBEL, E.R. (2006) Cenozoic

orogenic growth in the Central Andes: evidence from sedi-

mentary rock provenance and apatite ﬁssion track thermo-

chronology in the Fiambala Basin, southernmost Puna

Plateau margin (NW Argentina). Earth Planet. Sci. Lett.,247

(1–2), 82–100.

CARRAPA, B., HAUER, J., SCHOENBOHM, L., STRECKER, M.R.,

SCHMITT, A.K., VILLANUEVA,A.&SOSA GOMEZ, J. (2008)

Dynamics of deformation and sedimentation in the northern

Sierras Pampeanas: an integrated study of the Neogene Fiam-

bala basin, NW Argentina. Geol. Soc. Am. Bull.,120(11–12),

1518–1543.

CASTELLANOS, A. (1950) El Uquiense, Sedimentos Neogenos de

Uquıa (Senador Perez) en la Provincia de Jujuy (Argentina).

Facultad de Ciencias Matematicas Fısicas y Quımicas y Natu-

rales de la Universidad Nacional del Litoral, 36, Serie Tecnic-

o Cientıﬁco, 55 p., Rosario.

CLAPPERTON, C.M. (1979) Glaciation in Bolivia before

3.27 Myr. Nature,277(5695), 375–377.

COUTAND, I., COBBOLD, P.R., de URREIZTIETA,M.,GAUTIER,P.,

CHAUVIN, A., GAPAIS,D.,ROSSELLO,E.A.&LO

´PEZ-GAMUND,

O. (2001) Style and history of Andean deformation, Puna Pla-

teau, Northwestern Argentina Tectonics,20(2), 210–234.

COUTAND, I., CARRAPA, B., DEEKEN, A., SCHMITT, A.K., SOBEL,

E.R. & STRECKER, M.R. (2006) Propagation of orographic bar-

riers along an active range front: insights from sandstone

petrography and detrital apatite ﬁssion-track thermochronol-

ogy in the intramontane Angastaco Basin, NW Argentina

Basin Res.,18(1), 1–26.

DECELLES, P.G. & GILES, K.A. (1996) Foreland basin systems.

Basin Res.,8(2), 105–123.

DEEKEN, A., SOBEL, E.R., HASCHKE,M.&RILLER, U. (2004)

Age of initiation and growth pattern of the Puna Plateau,

NW-Argentina, constrained by AFT thermochronology. 19th

Colloquium on Latin American Geosciences. Terra Nostra, Pots-

dam, Germany, Abstract Volume, 05(1), 39.

DEEKEN, A., SOBEL, E.R., HASCHKE,M.&RILLER, U. (2005)

Age of initiation and growth pattern of the Puna plateau,

NW-Argentina, constrained by AFT thermochtonology. 19th

Colloquium on Latin American Geosciences, GeoForschungs-

Zentrum Potsdam, Potsdam, Germany, 18–20 April.

DEEKEN, A., SOBEL, E.R., COUTAND, I., HASCHKE, M., RILLER,

U. & STRECKER, M.R. (2006) Development of the Southern

Eastern Cordillera, NW Argentina, constrained by apatite ﬁs-

sion track thermochronology: from Early Cretaceous exten-

sion to Middle Miocene shortening. Tectonics,25, TC6003,

doi: 10.1029/2005TC001894

DEL PAPA, C.E., HONGN, F.D., POWELL, J., DOCAMPO, M.,

STRECKER, M.R., PETRINOVIC, I.A., SCHMITT, A.K. & PER-

EYRA, R. (in review) Middle Eocene-Oligocene broken fore-

land evolution in the Andean Valle Calchaqui, NW

Argentina: insights from stratigraphic, structural, and prove-

nance studies. Unpublished Manuscript.

DıAZ, J.I. & MALIZZIA, D.C. (1983) Estudio Geologico y sedi-

mentologico del Terciario Superior del Valle Calchaquı. Uni-

versidad Nacional de Tucuman, Facultad de Ciencias Naturales,

Boletın Sedimentologico,2(1), 8–28.

GARCIA-CASTELLANOS, D. & (2007) The role of climate during

high plateau formation. Insights from numerical experiments.

Earth Planet. Sci. Lett.,257, 372–390.

GALLISKI,M.&VIRAMONTE, J.G. (1988) The Cretaceous paleor-

ift in Northwestern Argentina: a petrologic approach. J. S.

Am. Earth Sci.,1(4), 329–342.

GEBHARD, J., GUIDICE,A.&GASCON, J. (1974) Geologıa de la co-

marca entre el Rıo Juramento y Arroyo Las Tortugas, Provin-

cias de Salta y Jujuy, Republica Argentina. Revista de la

Asociacion Geologica Argentina,29(3), 359–375.

GILE, L.H., PETERSON, F.F. & GROSSMAN, R.B. (1966) Morpho-

logical and genetic sequences of carbonate accumulation in

desert soils. Soil Sci.,101(5), 347–360.

GROVE, M., JACOBSON, C.E., BARTH, A.P. & VUCIC, A. (2003)

Temporal and spatial trends of Late Cretaceous - early Ter-

tiary underplating Pelona and related schist beneath southern

California and southwestern Arizona. Geol. Soc. Am. Spec.

Pap.,374, 381–406.

HAIN, M., STRECKER, M.R., BOOKHAGEN, B., ALONSO, R.N., PIN-

GEL,H.&SCHMITT, A.K. (2011) Neogene to Quaternary bro-

ken-foreland formation and sedimentation dynamics in the

Andes of NW Argentina (25°S). Tectonics,30, TC2006,

doi:10.1029/2010TC002703

HASELTON, K., HILLEY, G.E. & STRECKER, M.R. (2002a) Aver-

age Pleistocene climatic patterns in the southern Central An-

des: controls on mountain glaciation and paleoclimate

implications. J. Geol.,110(2), 211–226.

HILLEY, G.E. & STRECKER, M.R. (2005) Processes of oscillatory

basin ﬁlling and excavation in a tectonically active orogen.

Quebrada del Toro Basin, NW Argentina. Geol. Soc. Am.

Bull.,117(7–8), 887–901.

HILLEY, G.E., BLISNIUK, P.M. & STRECKER, M.R. (2005)

Mechanics and erosion of basement-cored uplift provinces.

J. Geophys. Res.,110 (B12), B12409, doi:10.1029/

2005JB003704

HONGN, F.D., DELPAPA, C., POWELL, J., PETRINOVIC, I., MON,

R. & DERACO, V. (2007) Middle Eocene deformation and sedi-

mentation in the Puna-Eastern Cordillera transition (23°-

26°S): control by pre-existing heterogeneities on the pattern

of initial Andean shortening. Geology,35 (3), 271–274.

GARCIA-CASTELLANOS, D. (2007) The role of climate during

high plateau formation. Insights from numerical experiments.

Earth Planet Sci. Lett.,257, 372–390. doi:10.1016/j.epsl.

2007.02.039

INSEL, N., GROVE, M., HASCHKE, M., BARNES, J.B., SCHMITT,

A.K. & STRECKER, M.R. (2012) Paleozoic to early Cenozoic

cooling and exhumation of the basement underlying the east-

Basin & landscape evolution in the E Cordillera

ern Puna plateau margin prior to plateau growth. Tectonics,

31, TC6006. doi:10.1029/2012TC003168

JORDAN, T.E. & ALLMENDINGER, R.W. (1986) The Sierras Pam-

peanas of Argentina: a modern analogue of Rocky Mountain

foreland deformation. Am. J. Sci.,286 , 737–764.

JORDAN, T.E. & ALONSO, R.N. (1987) Cenozoic stratigraphy and

basin tectonics of the Andes Mountains, 20-28°S lat. AAPG

Bull.,71 (1), 49–64.

KLEINERT,K.&STRECKER, M.R. (2001) Climate change in

response to orographic barrier uplift: paleosol and stable isotope

evidence from the Late Neogene Santa Marıa Basin, Northwes-

tern Argentina. Geol. Soc. Am. Bull.,113(6), 728–742.

KLEY,J.&MONALDI, C. (2002) Tectonic inversion in the Santa

Barbara System of the central Andean foreland thrust belt,

northwestern Argentina. Tectonics,21, 1061, doi:10.1029/

2002TC902003.

KLEY, J., M€uLLER, J., TAWACKOLI, S., JACOBSHAGEN,V.&MA-

NUTSOGLI, U. (1997) Pre-Andean and Andean-age deforma-

tion in the Eastern Cordillera of southern Bolivia. J. S. Am.

Earth Sci.,10(1), 1–19.

KLEY, J., ROSSELLO, E.A., MONALDI, C.R. & HABIGHORST,B.

(2005) Seismic and ﬁeld evidence for selective inversion of

Cretaceous normal faults, Salta Rift, Northwestern Argen-

tina. Tectonophysics,399(1–4), 155–172.

KRAEMER, B., ADELMANN, D., ALTEN,M.&SCHNURR, W. (1999)

Incorporation of the Paleogene foreland into the Neogene

Puna plateau: the Salar de Antofalla area, NW Argentina. J.

S. Am. Earth Sci.,12(2), 157–182.

LETCHER, A.J. (2007) Deformation history of the Susques basin

(~23°S, 66°W), Puna Plateau, NW Argentina: new constraints

by apatite (U-Th)/He thermochronology and

Ar/

Ar geo-

chronology, and implications for plateau formation in the cen-

tral Andes. MSc Thesis, Stanford University, USA.

MACHETTE, M.N. (1985) Calcic soils of the southwestern United

States. In: Soils and Quaternary Geology of the Southwestern

United States,203 (Ed. by D.L. Weide & M.L. Faber), pp. 1–

21. Geol. Soc. Am. Special Paper, Denver, CO.

MARQUILLAS, R.A., DELPAPA,C.&SABINO, I.F. (2005)

Sedimentary aspects and paleoenvironmental evolution of a

rift basin: salta Group (Cretaceous-Paleogene), northwestern

Argentina. Int. J. Earth Sci. (Geol.Rundsch.),94 (1), 94–113.

MARRETT, R.A. & STRECKER, M.R. (2000) Response of intracon-

tinental deformation in the Central Andes to Late Cenozoic

reorganization of South American plate motions. Tectonics,19

(3), 452–467.

MARRETT, R.A., ALLMENDINGER, R.W., ALONSO, R.N. & DRAKE,

R.E. (1994) Late Cenozoic tectonic evolution of the Puna Pla-

teau and adjacent foreland, Northwestern Argentine Andes.

J. S. Am. Earth Sci.,7(2), 179–207.

MARSHALL, L.G., BUTLER, R.F., DRAKE, R.E. & CURTIS, G.H.

(1982) Geochronology of Type Uquian (Late Cenozoic) Land

Mammal Age. Argent. Sci.,216(4549), 986–989.

MCPHERSON, H.M. (2008) Climate and tectonic controls on sedi-

mentation and deformation in the Fiambala Basin of the

southern Puna Plateau, Northwest Argentina. MSc Thesis,

Ohio State University, USA.

MEYER, B., TAPPONNIER, P., BOURJOT, L., METIVIER, F., GAUDE-

MER, Y., PELTZER, G., SHUNMIN,G.&ZHITAI, C. (1998) Crus-

tal thickening in Gansu-Qinghai, lithospheric mantle

subduction, and oblique, strike-slip controlled growth of the

Tibet plateau. Geophys. J. Int.,135(1), 1–47.

MORTIMER,E.,CARRAPA,B.,COUTAND,I.,SCHOENBOHM,L.,SO-

BEL, E.R., SOSA GOMEZ,J.&STRECK ER, M.R. (2007) Fragmenta-

tion of a foreland basin in response to out-of-sequence basement

uplifts and structural reactivation: El Cajon-Campo del Arenal

Basin, NW Argentina. Geol. Soc. Am. Bull.,119(5–6), 637–653.

MOYA, M.C. (1988) Lower Ordovician in the southern part of

the argentine Eastern Cordillera. In: The Southern Central An-

des,17, (Ed. by H. Bahlburg, C. Breitkreuz & P. Giese), pp.

55–69. Frontiers in Earth Sciences, Springer Berlin Heidel-

berg.

MULCH, A., UBA, C.E., STRECKER, M.R., SCHOENBERG,R.&

CHAMBERLAIN, C.P. (2010) Late Miocene climate variability

and surface elevation in the Central Andes. Earth Planet. Sci.

Lett.,290(1–2), 173–182.

OMARINI, R. (1983) Caracterizacion Litologica, Diferencion y

Genesis de la Formacion Puncoviscana Entre el Valle de Lerma y

la Faja Eruptiva de la Puna. Unpublished thesis, Universidad

Nacional de Salta, Argentina.

PACES, J.B. & MILLER, J.D. (1993) Precise U-Pb ages of Duluth

Complex and related maﬁc intrusions, northeastern Minne-

sota: geochronological insights into physical, petrogenetic,

paleomagnetic and tectonomagnetic processes associated with

the 1.1 Ga mid-continent rift system. J. Geophys. Res.,98,

13997–14013.

PENCK, W. (1920) Der Südrand der Puna de Atacama (NW-Ar-

gentinien): Ein Beitrag zur Kenntnis des Andinen

Gebirgstypus und der Frage der Gebirgsbildung. Abhandlun-

gen der S€achsischen Akademie der Wissenchaften,1,3–420.

PLACZEK, C., QUADE,J.&PATCHETT, P.J. (2006) Geochronology

and stratigraphy of late Pleistocene lake cycles on the southern

Bolivian Altiplano: implications for causes of tropical climate

change. Geol. Soc. Am. Bull.,118(5–6), 515–532.

REGUERO, M.A. & CANDELA, A.M. (2008) Bioestratigrafıa de las

secuencias neogenas tardıas de la Quebrada de Humahuaca,

Provincia de Jujuy. Implicancias paleoambientales y paleobio-

geograﬁcas. Relatorio del XVII Congreso Geologico Argentino,

1, 286–296.

REGUERO, M.A., CANDELA, A.M. & ALONSO, R.N. (2007) Bio-

chronology and biostratigraphy of the Uquıa Formation (Plio-

cene-Early Pleistocene, NW Argentina) and its signiﬁcance in

the Great American Biotic Interchange. J. S. Am. Earth Sci.,

23(1), 1–16.

REYNOLDS, J.H., IDLEMAN, B. D., HERNA

´NDEZ,R.M.&NAESER,

C. W. (1994) Preliminary chronostratigraphic constraints on

Neogene tectonic activity in the Eastern Cordillera and Santa

Barbara System, Salta Province, NW Argentina. GSA

Abstracts,26 (7), A–503.

REYNOLDS,J.,GALLI,C.,HERNA

´NDEZ,R.,IDLEMAN,B.,KOTILA,

J., HILLIARD,R.&NAESER, C. (2000) Middle Miocene tectonic

development of the transition zone, Salta Province, northwest

Argentina: magnetic stratigraphy from the Metan Subgroup,

Sierra de Gonzalez. Geol. Soc. Am. Bull.,112(11), 1736–1751.

REYNOLDS, J., HERNA

´NDEZ, R.M., GALLI, C.I. & IDLEMAN,

B.D. (2001) Magnetostratigraphy of the Quebrada La Por-

celana section, Sierra de Ramos, Salta Province, Argentina:

age limits for the Neogene Oran Group and uplift of the

southern Sierras Subandinas. J. S. Am. Earth Sci.,14(7),

681–692.

RILLER, U., PETRINOVIC, I., RAMELOW, J., STRECKER,M.&

ONCKEN, O. (2001) Late Cenozoic tectonism, collapse caldera

and plateau formation in the central Andes. EPSL,188(3–4),

299–311.

RIVELLI,F.R.&FLORES, E.M. (2009) Proteccio

´ndema

´rgenes en

el rı

´o grande, tramo las quebradas trancas - Tilcara. Cuarto

Simposio Regional sobre Hidrı

´ulica de Rı

´os, Salta, Argentina. 4p.

572

H. Pingel et al.

ROBINSON, R.A.J., SPENCER, J.Q.G., STRECKER, M.R., RICHTER,

A. & ALONSO, R.N. (2005) Luminescence dating of alluvial

fans in intramontane basins of NW Argentina. In: Alluvial

Fans: Geomorphology, Sedimentology, Dynamics,251 (Ed. by

A. Harvey, A. Mather & M. Stokes) pp. 153–168, Geol. Soc.

London Special Pub.

RODRI

´GUEZ-FERNA

´NDEZ, L.R., HEREDIA,N.,SEGGIARO,R.E.&

GONZA

´LEZ, M. (1999) Estructura andina de la Cordillera

Oriental en el area de la Quebrada de Humahuaca, Provincia

de Jujuy, NO de Argentina. Trabajos de Geologıa,21,321–332.

RUSSO,A.&SERRAIOTTO, A. (1978) Contribucion al conocimien-

to de la estratigrafıa Terciaria en el Noroeste Argentino. Actas

del VII Congreso Geologico Argentino,1, 715–730.

SALFITY, J.A. (1982) Evolucion paleogeograﬁca del Grupo Salta

(Cretacieo-Eogenico), Argentina. Actas del V Congreso Latino-

american Geologıa,1,11–26.

SALFITY, J.A., BRANDA

´N, E.M., MONALDI, C.R. & GALLARDO,

E.F. (1984) Tectonica compresiva Cuaternaria en la Cordil-

lera Oriental Argentina latitud de Tilcara (Jujuy). Actas del

IX Congreso Geologico Argentino,2, 427–434.

´NCHEZ, M.C. & MARQUILLAS, R.A. (2010) Facies y ambientes

del grupo Salta (cretacico-paleogeno) en Tumbaya, Quebrada

de Humahuaca, provincia de Jujuy. Revista de la Asociacion

Geologica Argentina,67(3), 383–391.

´NCHEZ,M.&SALFITY, J.A. (1999) La cuenca Cambrica del

Grupo Meson en el Noroeste Argentino: desarrollo

estratigraﬁco y paleogeograﬁco. Actas del Geologica Hispanica,

34(2–3), 123–139.

SANCHO,C.,PENA,J.L.,RIVELLI,F.,RHODES,E.&MUNOZ,A.

(2008) Geomorphological evolution of the Tilcara alluvial fan (Ju-

juy Province, NW Argentina): tectonic implications and paleoen-

vironmental considerations. J. S. Am. Earth Sci.,26(1), 68–77.

SCHMITT, A.K., de SILVA, S.L., TRUMBULL, R.B. & EMMER-

MANN, R. (2001) Magma evolution in the Purico ignimbrite

complex, N. Chile: evidence for zoning of a dacitic magma by

injection of rhyolitic melts following maﬁc recharge. Contrib.

Mineral. Petrol.,140, 680–700.

SCHMITT, A.K., GROVE, M., HARRISON, T.M., LOVERA, O.,

HULEN,J.&WALTERS, M. (2003) The Geysers-Cobb Moun-

tain magma system, California (Part 1): U-Pb zircon ages of

volcanic rocks, conditions of crystallization and magma resi-

dence times. Geochim. Cosmochim. Ac.,67(18), 3423–3442.

SCHOENBOHM, L., CARRAPA, B., BYWATER, S., MCPHERSON,H.&

PRATT, J. (2008) Climatic and tectonic controls on deposition

of the Punaschotter conglomerate in Neogene marginal basins

of the Puna Plateau (NW Argentina): evidence from zircon

U-Pb geochronology. AGU Fall Meeting Abstracts, T41C–04,

2008, San Francisco, USA.

SIKS, B.C. & HORTON, B.K. (2011) Growth and fragmentation

of the Andean foreland basin during eastward advance of

fold-thrust deformation, Puna plateau and Eastern Cordillera,

northern Argentina. Tectonics,30, TC6017, doi:10.1029/

2011TC002944

SOBEL, E.R. & STRECKER, M.R. (2003) Uplift, exhumation and

precipitation: tectonic and climatic control of Late Cenozoic

landscape evolution in the northern Sierras Pampeanas,

Argentina. Basin Res.,15(4), 431–451.

SOBEL, E.R., HILLEY, G.E. & STRECKER, M.R. (2003) Formation

of internally drained contractional basins by aridity-limited

bedrock incision. J. Geophys. Res.,108 (B7), 2344, doi:10.

1029/2002JB001883

STARCK,D.&ANZoTEGUI, L. (2001) The late Miocene climatic

change - persistence of a climatic signal through the orogenic

stratigraphic record in northwestern Argentina. J. S. Am.

Earth Sci.,14(7), 763–774.

STRECKER, M.R., CERVENY, P., BLOOM,A.&MALIZIA, D. (1989)

Late Cenozoic tectonism and landscape development in the

foreland of the Andes: Northern Sierras Pampeanas (26–28°

S), Argentina. Tectonics,8(3), 517–534.

STRECKER, M.R., ALONSO, R.N., BOOKHAGEN, B., CARRAPA, B.,

HILLEY, G.E., SOBEL, E.R. & TRAUTH, M.H. (2007) Tectonics

and climate of the Southern Central Andes. Annu. Rev. Earth

Planet. Sci.,35(1), 747–787.

STRECKER, M.R., ALONSO, R.N., BOOKHAGEN, B., CARRAPA, B.,

COUTAND, I., HAIN, M., HILLEY, G.E., MORTIMER, E., SCHO-

ENBOHM,L.&SOBEL, E.R. (2009) Does the topographic distri-

bution of the Central Andean Puna Plateau result from

climatic or geodynamic processes? Geology,37(7), 643–646.

STRECKER, M.R., HILLEY, G.E., BOOKHAGEN,B.&SOBEL, E.R.

(2011) Structural, geomorphic, and depositional characteris-

tics of contiguous and broken foreland basins: examples from

the eastern ﬂanks of the central Andes in Bolivia and NW

Argentina. In: Tectonics of Sedimentary Basins: Recent

Advances (Ed. by C. Busby & A. Azor), John Wiley & Sons,

Ltd, Chichester, UK. doi: 10.1002/9781444347166.ch25

STREIT, R.L., BURBANK, D.W., STRECKER, M.R. & ALONSO,

R.N. (2012) Neogene-quaternary tectonics, sedimentation,

and erosion of the Quebrada de Humahuaca and Casa Grande

Basin, Intermontane Basins on the margin of the Puna Plateau

(23-24˚S). In: NW Argentina, AGU Fall Meeting, December

2012, San Francisco, USA.

TCHILINGUIRIAN,P.&PEREYRA, F.X. (2001) Geomorfologıa del

sector Salinas Grandes-Quebrada de Humahuaca, provincia de

Jujuy. Revista de la Asociacion Geologica Argentina,56,3–15.

TURNER, J.C.M. (1960) Estratigrafıa de la Sierra de Santa Victo-

ria y adyacencias. Bol. Acad. Nac. de Ciencias Cordoba,41(2),

163–196.

UBA, C.E., STRECKER, M.R. & SCHMITT, A.K. (2007)

Increased sediment accumulation rates and climatic forcing

in the central Andes during the late Miocene. Geology,35

(11), 979–982.

VANDERVOORT, D.S., JORDAN, T.E., ZEITLER, P.K. & ALONSO,

R.N. (1995) Chronology of internal drainage development

and uplift, southern Puna plateau, Argentine Central Andes.

Geology,23(2), 145–148.

VERGANI,G.&STARCK, D. (1989) Aspectos Estructurales del

Valle de Lerma al Sur de la Ciudad de Salta. Boletın Inform.

Petrol.,20,(2–9). Buenos Aires

VEZZOLI, L., ACOCELLA, V., OMARINI,R.&MAZZUOLI, R. (2012)

Miocene sedimentation, volcanism and deformation in the

Eastern Cordillera (24°30′S, NW Argentina): tracking the

evolution of the foreland basin of the Central Andes. Basin

Res.,24(6), 637–663.

WALTHER, A., ORGEIRA, M., REGUERO, M., VERZI, D., VILAS, J.,

ALONSO, R.N., GALLADO, E., KELLY,S.&JORDAN, T.E.

(1998) Estudio Paleomagnetico, Paleontologico y Radimetrico

de la Formacion Uquıa (Plio-Pleistoceno) en Esquina Blanca

(Jujuy). Actas del X Congreso Latinoamericano de Geologıa y

VI Congreso Nacional de Geologıa Economica,1, 77.

ZACHOS, J., PAGANI, M., SLOAN, L., THOMAS,E.&BILLUPS,K.

(2001) Trends, rhythms, and aberrations in global climate

65 Ma to present. Science,292(5517), 686–693.

Manuscript received 26 June 2012; In revised form 26

November 2012; Manuscript accepted 07 December 2012.

Basin & landscape evolution in the E Cordillera

Milankovitch-paced erosion in the southern Central Andes

Article

Full-text available

Jan 2023

It has long been hypothesized that climate can modify both the pattern and magnitude of erosion in mountainous landscapes, thereby controlling morphology, rates of deformation, and potentially modulating global carbon and nutrient cycles through weathering feedbacks. Although conceptually appealing, geologic evidence for a direct climatic control on erosion has remained ambiguous owing to a lack of high-resolution, long-term terrestrial records and suitable field sites. Here we provide direct terrestrial field evidence for long-term synchrony between erosion rates and Milankovitch-driven, 400-kyr eccentricity cycles using a Plio-Pleistocene cosmogenic radionuclide paleo-erosion rate record from the southern Central Andes. The observed climate-erosion coupling across multiple orbital cycles, when combined with results from the intermediate complexity climate model CLIMBER-2, are consistent with the hypothesis that relatively modest fluctuations in precipitation can cause synchronous and nonlinear responses in erosion rates as landscapes adjust to ever-evolving hydrologic boundary conditions imposed by oscillating climate regimes.

Cenozoic Exhumation and Deformation of the Intermontane Pastos Chicos Basin in the Southern Central Andes: Implications for the Tectonic Evolution of the Andean Plateau (Puna) and the Eastern Cordillera Between 23° and 24°S, NW Argentina

Article

Full-text available

Feb 2023
TECTONICS

The Andean Plateau of north‐western Argentina (Puna) at a mean elevation of ca. 4.2 km constitutes the southern continuation of the Altiplano; it is a compressional basin‐and‐range province comprising fault‐bounded, high‐elevation mountain ranges and largely internally drained basins with often thick sedimentary and volcaniclastic fill. Growing sedimentological and structural evidence supports the notion that the north‐western Argentine Andes between 22° and 26°S developed from an initial extensive broken‐foreland system that extended across the present‐day eastern Andean flank during the early to middle Eocene. However, compelling evidence of the tectonic history of this region is still missing. Here, we present new apatite fission track and zircon (U–Th)/He thermochronological data and U–Pb zircon ages from intercalated volcanic ash deposits from the Pastos Chicos Basin (23.5°S, 66.5°W) to constrain basin formation and the timing of major crustal deformation in the northern Puna. Inverse thermal modeling of the thermochronological data provides further temporal constraints on the late Cenozoic cooling history of the crust in this region and, by inference, on the timing of upper‐crustal shortening, range uplift, and basin formation in the northern sector of the present‐day Puna Plateau. Specifically, we argue for plateau‐wide distributed deformation in the Eocene between 23° and 24°S, followed by spatially disparate and diachronous deformation (Oligocene to Pliocene).

Structural Inheritance in the Eastern Cordillera, NW Argentina: Low‐Temperature Thermochronology of the Cianzo Basin

Article

Full-text available

Jun 2024
TECTONICS

The present‐day deformation style of the Eastern Cordillera in NW Argentina is strongly influenced by the inversion of pre‐existing Paleozoic and Mesozoic structures. In particular, the extensional faults and lithological contrasts resulting from the Cretaceous–Paleogene Salta Rift phase form heterogeneities that were preferentially reactivated during the Andean orogeny. Constraining the timing and characteristics of reactivation is a key to understanding the interplay between tectonics and inherited crustal anisotropies. In this study, we combine structural and sedimentological field data with a low‐temperature thermochronology data set from the area surrounding the fault‐bounded Cianzo basin. The southeastern boundary is formed by the inverted Hornocal fault, which was the basin‐bounding normal fault of the Lomas de Olmedo sub‐basin (Salta Rift basin). Lacustrine deposits of the Yacoraite Formation overspill on the footwall of this fault and mark tectonic quiescence during the post‐rift phase of the Salta Rift. Apatite (U‐Th‐Sm)/He and fission track ages in the Hornocal fault hanging wall show an onset of rapid cooling interpreted to be concomitant with fault inversion between the latest Oligocene and middle Miocene (∼24–15 Ma). Low‐temperature thermochronology data also constrain the timing of major folding in the eastern limb of the Cianzo syncline to pre‐10 Ma, whereas the western limb started tilting post‐10 Ma. Characterization of exhumation patterns related to fault activity surrounding the Cianzo basin emphasizes the influence of the pre‐existing structural framework on deformation in fold‐and‐thrust belts.

Sand pipes as potential indicators of seismicity in the Casa Grande Formation, Northwestern Argentina

Article

Full-text available

Apr 2024

Soft-sediment deformation structures (SSDS) develop when sediment, temporarily in a fluid-viscous state, deforms, resulting in the alteration of the original sedimentary structures (Lowe, 1975; Allen, 1982; Owen, 1987; Owen and Moretti, 2011). Deformation can occur rapidly, near the surface, during or after deposition (Allen, 1977; Allen, 1982). The main mechanisms through which a saturated granular material, initially in a solid state, transitions into a fluid-viscous state capable of mobilizing and dragging particles are referred to as liquefaction and fluidization (Lowe, 1975; Allen, 1982). The resulting structures by these processes include convolute bedding, load structures, clastic dikes, disturbed bedding, water escape structures, sand pipes and dish-and-pillar structures (Lowe, 1975; Owen, 1987; Rodríguez-Pascua et al., 2000; Jolly and Lonergan, 2002; Hurst et al., 2003; Schillizzi et al., 2010; Berra and Felletti, 2011; Sánchez et al., 2013). These structures are typically confined within discrete sedimentary layers, bounded by unaltered strata (Lowe, 1975; Hurst et al., 2003). The mechanisms that induce liquefaction and fluidization processes can be 'external' (allogenic) triggers, such as earthquakes, or 'internal' (autogenic) triggers, such as water waves, rapid sediment deposition, or groundwater movements (Allen and Banks, 1972; Obermeier, 1996; Owen and Moretti, 2011). The characteristics of the SSDS and their context provides insights into the mechanisms that initiated the processes associated with their formation. Furthermore, the stratigraphic distribution of these structures enables the identification of time intervals with recurring or non-recurring triggering agents. In the Casa Grande Formation (middle Eocene; Eastern Cordillera, Jujuy, Argentina), a suite of sedimentary structures has been described at different scales, interpreted as responses to contemporaneous tectonic deformation processes along with sedimentation. Among these structures, some have been recognized as products of sediment liquefaction and fluidization processes, as well as progressive folding of the substrate (Montero López et al., 2018). This lithostratigraphic unit, characterized by red to reddish-brown siltstones and sandstones, crops out along the Casa Grande valley, bounded to the east by the Sierra de Mal Paso and to the west by the Espinazo del Diablo in the northern sector of the Argentine Eastern Cordillera and its transition to the Puna region (Fig. 1). An intraformational unconformity (Figs. 1c, 2), led to propose a new subdivision into: Casa Grande I and Casa Grande II sequences (Montero López et al., 2018). The aim of this contribution is to present a comprehensive description and interpretation of specific discordant structures identified as sand pipes, within the Casa Grande II sequence (Figs. 3, 4). Additionally, we aim to discuss potential geological processes and factors that may have led to their formation. The sand pipes occur within two sand beds and are characterized by a vertical or subvertical disposition that cross-cut the depositional bedding. They exhibit an inverted funnel geometry in side view and tabular in plan view and are notable for their dimensions, which span from 0.72 to 2.10 m at each analyzed level, exhibiting consistent lateral distribution (Figs. 4, 5). The internal material of the structures is the same as that of the host rock, and based on their characteristics, two distinct zones can be identified (Figs. 5, 6, 7): a) central zone: corresponds to the internal part of the structures, characterized by medium-sized sands exhibiting a massive structure and, b) marginal zone: outer layer composed of finely laminated sandy material and, in some cases areas with finer material, displaying either a distinct vertical lamination or minor disturbances with folding features (Fig. 6). Considering the characteristics of the structures, the mechanism responsible for their formation are interpreted as liquefaction and fluidization. Similar attributes observed in other deposits are interpreted as the consequence of forceful upward water fluidization and dewatering from underlying induced by overpressurization (e.g., Chan et al., 2019; Espinoza et al., 2020). The fluid injection occurs as pressurized water is discharged from the lower layers, fluidizing the sediments and the area around them, in multiple points, along its upward path (Draganits et al., 2003; Wheatley et al., 2016; Chan et al., 2019; Fig. 8a). The development of a central and marginal zone is interpreted as a result of a flow velocity gradient during the injection (Ross et al., 2011, 2014; Fig. 8b). The presence of a marginal zone is consistent with shear between the fluidized flow and the surrounding sediment (Deynoux et al., 1990; Draganits and Janda, 2003; Draganits et al., 2003; Chan et al., 2019) which induced grain alignment parallel with the direction of the flow; on the other hand, the central zone is massive which is consistent with high flow velocities (Fig. 8c). Among the potential triggers for these processes a seismic event is interpreted following the criteria proposed by Owen and Moretti (2011). These criteria include vertical repetition, lateral continuity, morphology comparable with structures formed by recent earthquakes and the geological context (i.e., proximity to faults).

Did Changes in Seasonality and Fire Frequency Cause C4 Grass Expansion in South America? Investigations from N.W. Argentina Using Geochemical Proxies for Climate and Vegetation Change.

Thesis

Full-text available

Apr 2021

Adit Ghosh

The impact of climate change on vegetation dynamics and fire regimes has been the subject of much interest in determining how anthropogenic climate change might alter ecological communities. Here, I study the C4 grassland expansion during the late Miocene-Pliocene epoch in N.W. Argentina from paleosols from three terrestrial sedimentary basins- Palo Pintado, La Viña and Río Iruya. I hypothesize that increased seasonality associated with the strengthening of the South American Summer Monsoon drove the spread of C4 grasses and increased fire frequency, leading to a positive feedback between increased C4 cover and fire regimes. We test this hypothesis using multiproxy analysis using novel biomarkers (i.e. polycyclic aromatic hydrocarbons) as a proxy for fire frequency and vegetation type, carbon isotopic analysis of bulk organic matter as a proxy for C4 vegetation and bulk elemental geochemical analysis of paleosols as a proxy of mean annual precipitation and temperature. We observe the appearance of ~50% C4 cover in La Viña and Río Iruya prior to the Miocene-Pliocene boundary. Precipitation appears to play an important role in the spread of C4 cover in both La Viña with decreasing precipitation resulting in the greater spread of C4 cover. We do not observe a significant change in fire regimes during this spread in C4 vegetation at La Viña and Río Iruya. We establish that the lack C4-fire feedback is either due to the lack of high enough C4 cover, or the absence of this feedback mechanism in late Miocene-Pliocene South America. However, we observe trends in gymnosperm proliferation with changes in fire regimes, with one proxy showing a decrease in gymnosperm proliferation with increasing fire frequency and two proxies showing an increase in gymnosperm proliferation with decreasing fire frequency.

Landscape response to tectonic deformation and cyclic climate change since ca. 800 ka in the southern Central Andes

Preprint

Full-text available

Apr 2024

Theory suggests that the response time of alluvial channel long-profiles to perturbations in climate is related to the magnitude of the forcing and the length of the system. Shorter systems may record a higher frequency of forcing compared to longer systems. Empirical field evidence that system length plays a role in the climate periodicity preserved within the sedimentary record is, however, sparse. The Toro Basin in the Eastern Cordillera of NW Argentina provides an opportunity to test these theoretical relationships as this single source-to-sink system contains a range of sediment deposits, located at varying distances from the source. A suite of eight alluvial fan deposits is preserved along the western flanks of the Sierra de Pascha. Farther downstream, a flight of cut-and-fill terraces have been linked to eccentricity-driven (100-kyr) climate cycles since ca. 500 ka. We applied cosmogenic radionuclide (10Be) exposure dating to the fan surfaces to explore (1) how channel responses to external perturbations may or may not propagate downstream, and (2) the differences in landscape response to forcing frequency as a function of channel length. We identified two generations of fan surfaces: the first (G1) records surface activity and abandonment between ca. 800 and 500 ka and the second (G2) within the last 100 kyr. G1 fans record a prolonged phase of net incision, which has been recognised throughout the Central Andes, and was likely triggered by enhanced 100-kyr global glacial cycles following the Mid-Pleistocene Transition. Relative fan surface stability followed, while 100-kyr cut-and-fill cycles occurred downstream, suggesting a disconnect in behaviour between the two channel reaches. G2 fans record higher frequency climate forcing, possibly the result of precessional forcing of climate (ca. 21/40-kyr timescales). The lack of a high-frequency signal farther downstream provides field support for theoretical predictions of a filtering of high-frequency climate forcing with increasing channel length. We show that multiple climate periodicities can be preserved within the sedimentary record of a single basin. Differences in the timing of alluvial fan and fluvial terrace development in the Toro Basin appears to be associated with how channel length affects fluvial response times to climate forcing as well as local controls on net incision, such as tectonic deformation.

The Late Miocene mammals from the Humahuaca Basin (northwestern Argentina) provide new evidence on the initial stages of the Great American Biotic Interchange

Article

Full-text available

Sep 2023

We describe new Upper Miocene mammalian specimens from the Maimara Formation (Late Miocene to Early Pliocene) exposed at Humahuaca Basin (23°–24°S), northwestern Argentina (NWA), and analyse their taxonomy and relevance for our understanding of the initial stages of the Great American Biotic Interchange (GABI). The stratigraphical and geochronological control of the studied specimens indicates a time window of c. 6.6–5.8 Ma. These data are crucial for establishing the oldest records of the Holarctic immigrants of the GABI. The first record of cricetid rodents from the Maimara Formation is reported. Moreover, with an age of c. 6 Ma it is the first appearance datum (FAD) of these rodents in South America. The age of the procyonid Cyonasua recorded in this unit is estimated between c. 6.6 and c. 6.4 Ma. The record of procyonids and cricetids in the same continuous sedimentary sequence suggests that the time interval between the dispersion of both groups into the continent during GABI was c. 1 myr. Of the autochthonous mammals from the Maimara Formation, the first records of litopterns, chlamyphorid and mylodontine xenarthrans, and caviomorph rodents (including new species Pithanotomys? solisae and Palaeocavia humahuaquense) are described. FADs of immigrant and autochthonous mammals in NWA suggest a major faunal turnover during GABI at the Messinian, probably linked to global climatic changes and the tectonic activity that affected the Humahuaca Basin at that time. Hypsodonty, a dominant feature among Maimaran mammals, may be related to a landscape strongly influenced by the Andean uplift.

Paleoenviromental evolution of the Cenozoic foreland basin to intermontane basins in the Eastern Cordillera, North-Western Argentina

Article

Sep 2023
J S AM EARTH SCI

Application of TOPSIS model in active tectonic prioritization: Madeira watershed, South America

Article

Full-text available

Jul 2023
J S AM EARTH SCI

The Andes orogenic belt is one of the most tectonically active zones located between the convergent margins of the South American plate and the Pacific plate. From the dissected western belt to the expanded alluvial plain of Amazon basin, the Madeira watershed bears recent tectonic imprints. The tectonic signature is well documented by the spatial and linear characteristics of the five sub watersheds along with the Madeira trunk river and channels. The level of tectonic activeness has been assessed on the sub watersheds of the Madeira River, which is one of the main right-hand tributaries of the Amazon River. On the five defined sub-watersheds and the main channel watershed of Madeira, several morphometric indices, viz., asymmetry factor (AF), tilt angle (β), sinuosity index (SI), channel concavity (ɵ), elongation ratio (Re), circularity ratio (Rc), transverse topographic symmetry factor (T) and basin shape index (Bs), have been used. To rank the watersheds based on tectonic activity, we applied the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) The active tectonics was also tested by a comparative study of linear indicators as Hack profiles, longitudinal profiles and segment-wise stream gradient index (SL) of watersheds 2 (rank 1) and 3 (rank 6). The results reveal that the most tectonically active watershed 2 is located in a high seismic magnitude zone with several deep earthquake epicenters. The least tectonically active watershed 6 is located in a low seismic zone.

Seismotectonics of the thick-skinned Santa Bárbara System in northwestern Argentina: implications for regional crustal rheology and structure

Preprint

Full-text available

Jun 2023

The Andean foreland is divided into morphotectonic provinces characterized by diverse deformation styles and seismogenic behavior partially stemming from distinct geological histories that preceded the current phase of subduction. The transition between the high Andes and the eastern foreland is exposed to numerous natural hazards and contains critical economic infrastructure, yet we know relatively little about regional active tectonics due to few geophysical investigations. Here we use waveforms collected during a 15-month-long seismic network deployment in the Santa Bárbara System (SBS) of northwest Argentina following the 2015 Mw 5.7 El Galpón earthquake to determine the distribution and magnitude of local earthquakes, obtain a regional 1D seismic velocity model, and improve our overall understanding of SBS neotectonics. Of the nearly 1200 recorded earthquakes, ~700 occurred in the crust with half of the moment release associated with events deeper than 25 km. The depth extent of seismicity supports the notion that the SBS upper and middle crust are homogeneous and that the lower crust is composed of granulites. These conditions likely formed during Paleozoic mountain building and Salta Rift-related Cretaceous magmatism, which dehydrated the crust. We find no clear indications that a shallow, low-angle detachment fault inferred to have been active during Cretaceous rifting exerts a strong control on modern deformation in contrast to the active décollement beneath the adjacent fold-and-thrust belt of the Subandes to the north. It remains unclear how active, inverted normal faults in the SBS shallow crust connect to the deeper zones of seismicity.

Foreland basins

Article

Jan 1981

C. Beaumont

Estudio Paleomagnético, Paleontolõgico y Radimétrico de la Formaciõn Uquía (Plio-Pleistoceno) en Esquina Blanca (Jujuy)

Article

Jan 1998

Tectónica compresiva Cuaternaria en la Cordillera Oriental Argentina latitud de Tilcara (Jujuy)

Article

Jan 1984

Interpretación estructural del área Tres Cruces

Article

Jan 1986

Geomorphology of the salinas grandes-quebrada de humahuaca area, Jujuy province

Article

Jan 2001

Geomorphology of the Salinas Grandes-Quebrada de Humahuaca area, Jujuy Province. Landforms in the area between Salinas Grandes and Quebrada de Humahuaca (23°-24°S and 65°-66°W), Jujuy Province, are related to fluvial process and, to a lesser extent, also to mass wasting and aeolian process. In higher zones, above 4500 m, moraines and other glacigenic features, such as moraines, glacial valleys and cryogenic structures are also evident. The relationships between regional geomorphological evolution, the tectonic environment and the dynamic evolution of the latter were a particular focus of study, likewise the impact of regional climatic oscillations on geomorphological development. The climatic and structural conditions show a great variation for which reason, the area is particularly interesting for examining their interrelationships in the process of landscape evolution.

Facies and environments of the salta group (Cretaceous-paleogene) in Tumbaya, quebrada de humahuaca, jujuy province

Article

Nov 2010

The red deposits of Salta Group (Cretaceous-Paleogene) which outcrops in the quebrada de Tumbaya, right margin of Quebrada de Humahuaca (province of Jujuy), they are characterized by facies that differs from the typical ones in their places of the Salta Group basin. They are proximal facies, characterized by arid and semi-arid conditions whose accumulation advanced on the N-NW side of the Salto-Jujuy high structure. Salta Group is separated from the underlying Cambrian Meson Group by an erosive discordance. An angular discordance at the top of the Group separates it from the superposed Quaternary deposits. In Tumbaya, the two main units of Salta Group, the synrift and post-rift, are represented. The research and study of sedimentary facies allowed to identify and to characterize the three Subgroups (Pirgua, Balbuena and Santa Bárbara) and to differentiate their formations. The Pirgua Subgroup consists of eolian sandstones; it is not possible to differentiate its three formation units, therefore it is mentioned as Pirgua Formation. The Balbuena Subgroup is subdivided into two formations, Lecho and Yacoraite Formations. The Lecho Formation is characterized by sheet floods facies and the Yacoraite Formation displays transitional, continental and marine litoral-sublitoral carbonatic environmental conditions influenced by tidal currents and storms. The three formations of Santa Barbara Subgroup are present: (Mealla, Maíz Gordo and Lumbrera), which represent a fining-upward fluvial succession with development of multiple paleosoils; there have also been identified sheet floods and floodplain facies.

Contribución al conocimiento de la estratigrafía terciaria en el noroeste argentino

Article

Jan 1979

Estudio geológico y sedimentológico del Terciario superior del Valle Calchaquí

Article

Jan 1983

Evolución paleogeográfica del Grupo Salta (Cretácico-Eogénico), Argentina

Article

Jan 1982

José A Salfity

Estratigrafía de la Sierra de Santa Victoria y adyacencias

Article

Jan 1960

J.C.M. Turner

Neotectonic basin and landscape evolution in the Eastern Cordillera of NW Argentina, Humahuaca Basin (~24°S)

Abstract

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