Basin Research - Volume 24, Issue 3, 2012

Important aspects of the Andean foreland basin in Argentina remain poorly constrained, such as the effect of deformation on deposition, in which foreland basin depozones Cenozoic sedimentary units were deposited, how sediment sources and drainages evolved in response to tectonics, and the thickness of sediment accumulation. Zircon U‐Pb geochronological data from Eocene–Pliocene sedimentary strata in the Eastern Cordillera of northwestern Argentina (Pucará–Angastaco and La Viña areas) provide an Eocene (ca. 38 Ma) maximum depositional age for the Quebrada de los Colorados Formation. Sedimentological and provenance data reveal a basin history that is best explained within the context of an evolving foreland basin system affected by inherited palaeotopography. The Quebrada de los Colorados Formation represents deposition in the distal to proximal foredeep depozone. Development of an angular unconformity at ca. 14 Ma and the coarse‐grained, proximal character of the overlying Angastaco Formation (lower to upper Miocene) suggest deposition in a wedge‐top depozone. Axial drainage during deposition of the Palo Pintado Formation (upper Miocene) suggests a fluvial‐lacustrine intramontane setting. By ca. 4 Ma, during deposition of the San Felipe Formation, the Angastaco area had become structurally isolated by the uplift of the Sierra de los Colorados Range to the east. Overall, the Eastern Cordillera sedimentary record is consistent with a continuous foreland basin system that migrated through the region from late Eocene through middle Miocene time. By middle Miocene time, the region lay within the topographically complex wedge‐top depozone, influenced by thick‐skinned deformation and re‐activation of Cretaceous rift structures. The association of the Eocene Quebrada del los Colorados Formation with a foredeep depozone implies that more distal foreland deposits should be represented by pre‐Eocene strata (Santa Barbara Subgroup) within the region.

The details of how narrow, orogen‐parallel ocean basins are filled with sediment by large axial submarine channels is important to understand because these depositional systems commonly form in through‐like basins in various tectonic settings. The Magallanes foreland basin is an excellent location to study an orogen‐parallel deep‐marine system. Conglomerate lenses of the Upper Cretaceous Cerro Toro Formation have been previously interpreted to represent the fill of a single submarine channel (4–8 km wide, >100 km long) that funneled coarse detritus southward along the basin axis. This interpretation was based on lithologic correlations. New U/Pb dating of zircons from volcanic ashes and sandstones, coupled with strontium isotope stratigraphy, refine the controls on depositional ages and provenance. Results demonstrate that north‐south oriented conglomerate lenses are contemporaneous within error limits (ca. 84–82 Ma) supporting that they represent parts of an axial channel belt. Channel deposits 20 km west of the axial location are 87–82 Ma in age. These channels are partly contemporaneous with the ones within the axial channel belt, making it likely that they represent feeders to the axial channel system. The northern Cerro Toro Formation spans a Turonian to Campanian interval (ca. 90–82 Ma) whereas the formation top, 70 km to the south, is as young as ca. 76 Ma. Kolmogorov–Smirnoff statistical analysis on detrital zircon age distributions shows that the northern uppermost Cerro Toro Formation yields a statistically different age distribution than other samples from the same formation but shows no difference relative to the overlying Tres Pasos Formation. These results suggest the partly coeval deposition of both formations. Integration of previously acquired geochronologic and stratigraphic data with new data show a pronounced southward younging pattern in all four marine formations in the Magallanes Basin. Highly diachronous infilling may be an important depositional pattern for narrow, orogen‐parallel ocean basins.

Three‐dimensional (3D) modelling allows observation of geological features that may not be evident by classical two‐dimensional approaches. This is particularly important in the Pico del Águila anticline (Central External Sierras, Southern Pyrenees, Spain), a structure characterized by important geometrical variability in 3D. The Pico del Águila is a N–S‐trending fold, transverse to the E–W‐trending South‐Pyrenean thrust front, with well‐exposed growth strata that record the evolution of the structure and the influence of the South‐Pyrenean thrust front. Fold kinematics is complex and not precisely quantified. It is characterized by multiple folding mechanisms acting simultaneously in a heterogeneous stratigraphic sequence. To better understand the fold's structural evolution, 3D reconstruction and geomechanical restoration of the structure were performed. The restoration takes into account rock mechanical properties without assuming a specific kinematic model. Our work suggests that the growth of the structure was characterized by variable uplift/sedimentation rates through time and between fold limbs. The restoration also reveals that a combination of multiple folding mechanisms operated simultaneously in different units and structural domains during anti‐clinal growth. This has major implications in the understanding of detachment folds with associated growth strata, as such structures are described in many settings as potential traps for hydrocarbons and natural resources.

The Late Messinian fill of the Nijar Basin (Betic Cordillera, southeastern Spain) mainly consists of clastic deposits of the Feos Formation that at basin margins rest unconformably above the primary evaporites of the Yesares Formation, the local equivalent of the Mediterranean Lower Gypsum. The Feos Fm. records the upward transition towards non‐marine environments before the abrupt return to fully marine conditions at the base of the Pliocene. The Feos Fm. is clearly two‐phase, with ‘lower’ and ‘upper’ members, which exhibit substantial differences in terms of facies, thickness, depositional trends and cyclical organization. These members record two distinct sedimentary and tectonic stages of Nijar Basin infilling. A high‐resolution, physical‐stratigraphic framework is proposed based on key beds and stratigraphic cyclicity and patterns that differ largely from those of most previously published studies. The predominant influence on stratigraphic cyclicity is interpreted to be precessionally driven climate changes, allowing their correlation to the Late Messinian astronomically calibrated chronostratigraphic framework. Detailed correlations suggest a phase of enhanced tectonic activity, possibly related to the Serrata‐Carboneras strike‐slip fault zone, during the first stage (‘lower’ member), resulting in a strongly articulated topography with structural lows and highs controlling sediment thickness and facies variation. Tectonic activity decreased during the second stage (‘upper’ member), which is characterized by (1) a progressively dampened and homogenized, (2) overall relative base‐level rise and (3) gradual establishment of hypohaline environments. Facies characteristics, overall stacking patterns and depositional trends of the Feos Fm. are analogous with uppermost Messinian successions of the Northern Apennines, Piedmont Basin and Calabria. Despite minor differences related to the local geodynamic setting, these basins experienced a common Late Messinian history that supports the development of a single, large Mediterranean water body characterized by high‐frequency, climatically‐driven changes in sediment flux and base‐level.

This study undertakes a multi‐disciplinary approach (sedimentology, carbon isotopes, magnetic susceptibility and thickness distribution) to improve understanding of a major Palaeozoic carbonate platform, the Frasnian platform of Belgium. These combined techniques are used to reconstruct the platform history, which evolved in two main steps. During the first phase, the basin was strongly influenced by faulting, producing notable thickness and facies variations, with open ocean conditions, with good water circulation and no/or limited barrier reef. The second phase of platform development was less influenced by differential subsidence, as indicated by homogeneous facies distribution. However, this platform developed under restricted waters, with low circulation which is likely related to the development of a barrier reef.

To decipher the thermal structure of the sedimentary veneer in southern Israel, new values of thermal conductivity and porosity as well as of the radiogenic heat budget are provided. Thermal conductivity is measured for lithotypes and scaled up for geological formations. The new data are higher than most of the previously measured values, in particular for sandstones and siltstones, whose mean values are 5.0 and 2.9 W m⁻¹ K⁻¹. Mean values of the most abundant lithotypes, which are dolomites and limestones, are on the order of 4.1 and 2.7 W m⁻¹ K⁻¹, respectively. The total radiogenic heat production of the sedimentary cover varies slightly over southern Israel, due to variable lithology and total sediment thickness, yielding a maximum heat flow on the order of 4 mW m⁻² where the sedimentary section is thickest (ca. 7 km). A temperature prognosis was made by calculating temperature profiles to the top of the crystalline basement at five well locations applying the new thermal‐conductivity data set and three scenarios of surface heat flow (50, 55 and 60 mW m⁻²). The calculated temperatures best match with measured drillstem‐test temperatures by using heat‐flow values close to the upper bound of range. Surface heat flow on the order of 55–60 mW m⁻² is supported by a reevaluation of an existing temperature log and the application of thermal conductivity from this study. The temperature prediction for southern Israel shows values of 100–120°C at 3500–4500 m depth, indicating a geothermal potential that can be used for heating as well as electricity production.