Miocene forebulge development previous to broken foreland partitioning in the southern Central Andes, west‐central Argentina

Abstract

In the distal region of the modern flat‐slab segment in the southern Central Andes, an unusual stack of middle Miocene paleosols together with regional upwarping and normal faulting indicate episodic aggradation and condensed sedimentation contemporaneous with the principal stage of foreland basin development associated with foreland flexure farther to the west. These features are consistent with development of a forebulge zone during the early stages of a proposed asymmetric foreland basin system. Sedimentary thickness farther east and far from the Cordilleran tectonic loads suggests accommodation and preservation driven by “nonisostatic” dynamic subsidence. Regional overlapping relationships and basin modeling suggest that the Modern broken foreland (present Sierras Pampeanas) can be interpreted as a reactivation of a formerly partitioned broad forebulge.

Tectonic Models for the Evolution of Sedimentary Basins

“…Thus, forebulges buried under basin sediments are either a relic of former stages when the tectonic load was more distant from the foreland or active forebulges subdued below sea level by other subsidence mechanisms. This later interpretation is consistent with the notion by Dávila et al (2007) that dynamic loading sourced in the mantle produced additional subsidence of the sub-Andean peripheral bulge allowing it to be overlain by later sediments. In addition to static loads, dynamic loading underneath the basin (e.g., viscous mantle corner flow above a subducting plate; Catuneanu et al, 1997) may cause long-wavelength subsidence and forebulge sediment overflow.…”

Dynamic uplift during slab flattening

“…5b). High-gradient fluvial beds developed on top of the paleosols (Dávila et al, 2007), consistent with a relief increase, and direct evidence of the steeper topographic gradients. Today, both sedimentary sequences are found between 0.4 and 1 km above sea level (Fig.…”

“…(2000) and Kaban et al (2003) also consider the full lithospheric structure, but make different assumptions about oceans and continents than TDL. paleosols that were originally deposited near sea level (Dávila et al, 2007) on the Pampean surface, and can be seen today at over 1 km above sea level. We point out that slab density contrasts and mantle viscosity structures were not adjusted to best fit the amplitudes.…”

The Los Llantenes Formation in the Precordillera of Jagüe (La Rioja Province) and the recognition of a rifting stage in the early evolution of the late Paleozoic basins in western Argentina.

“…Los rasgos descritos son distintivos de cuencas extensionales que tienden a generar una fuerte compartimentación del registro estratigráfico, expresado en frecuentes cambios litológicos, cierta diacronía de las facies y hasta discontinuidad areal del registro (e.g., López Gamundí y Astini, 2004), características todas que permiten diferenciarlo de un marco tectónico de cuenca de antepaís (Tabla 1). El gran espesor de la unidad permitiría, asimismo, descartar una extensión asociada con flexión dentro de la zona de domamiento periférico en un contexto de antepaís (e.g., Dávila et al, 2007).…”