Salar Basin Research Articles

Evidence for high-elevation salar recharge and interbasin groundwater flow in the Western Cordillera of the Peruvian Andes

Abstract. Improving our understanding of hydrogeological processes on the western flank of the central Andes is critical to communities living in this arid region. Groundwater emerging as springs at low elevations provides water for drinking, agriculture, and baseflow. However, the high-elevation sources of recharge and groundwater flow paths that convey groundwater to lower elevations where the springs emerge remain poorly quantified in the volcanic mountain terrain of southern Peru. In this study, we identified recharge zones and groundwater flow paths supporting springs east of the city of Arequipa and the potential for recharge within the high-elevation closed-basin Lagunas Salinas salar. We used general chemistry and isotopic tracers (δ18O, δ2H, and 3H) in springs, surface waters (rivers and the salar), and precipitation (rain and snow) sampled from March 2019 through February 2020 to investigate these processes. We obtained monthly samples from six springs, bimonthly samples from four rivers, and various samples from high-elevation springs during the dry season. The monthly isotopic composition of spring water was invariable seasonally in this study and compared to published values from a decade prior, suggesting that the source of recharge and groundwater flow paths that support spring flow is relatively stable with time. The chemistry of springs in the low-elevations and mid-elevations (2500 to 2900 m a.s.l.) point towards a mix of recharge from the salar basin (4300 m a.s.l.) and mountain-block recharge (MBR) in or above a queñuales forest ecosystem at ∼4000 m a.s.l. on the adjacent Pichu Pichu volcano. Springs that clustered along the Río Andamayo, including those at 2900 m a.s.l., had higher chloride concentrations, indicating higher proportions of interbasin groundwater flow from the salar basin likely facilitated by a high degree of faulting along the Río Andamayo valley compared to springs further away from that fault network. A separate groundwater flow path was identified by higher sulfate concentrations (and lower Cl-/SO4-2 ratios) within the Pichu Pichu volcanic mountain range separating the city from the salar. We conclude that the salar basin is not a hydrologic dead end. Instead, it is a local topographic low where surface runoff during the wet season, groundwater from springs, and subsurface groundwater flow paths from the surrounding mountains converge in the basin, and some mixture of this water supports groundwater flow out of the salar basin via interbasin groundwater flow. In this arid location, high-elevation forests and the closed-basin salar are important sources of recharge supporting low-elevation springs. These features should be carefully managed to prevent impacts on the down-valley water quality and quantity.

Detrital sources and sediment delivery to the early post-rift (Albian-Cenomanian) Newfoundland Basin east of the Grand Banks: results from ODP Leg 210

Abstract The young narrow arm of the Atlantic Ocean that separated Newfoundland from Iberia in the Albian–Cenomanian accumulated a thick succession of muddy gravity flow deposits that were recovered by drilling at Ocean Drilling Program Site 1276 off the Grand Banks of Newfoundland. The sediment thickness and sand content are somewhat surprising given the number of contemporaneous shelf and slope basins that would have acted as traps for detritus shed from the Newfoundland margin. A set of individual studies was undertaken to trace the source of this detritus and to test hypotheses that the material might have been derived, in part, from the east (Iberia), the north (Flemish Cap and northern rift extensions), and/or from various sources to the west (Grand Banks, Interior Newfoundland, Avalon Uplift). By synthesizing seismic data, paleocurrent data from gravity flow deposits, sediment composition (sand detrital modes, clay mineralogy) and detrital mica ages we conclude that the likely source of the Albian–Cenomanian sediment was the Avalon Uplift, situated in the southern Grand Banks. Key pieces of evidence that lead us to this result are: thinning of the sediment package towards the north and thickening towards the southwest, the paleocurrent directions apparently suggesting a southwesterly source, the low proportion of potassium feldspar in the sandstones, and the lack of palygorskite in the shales as compared to Iberian-sourced successions. The apparent inconsistency of detrital mica ages from these deposits, suggesting an Iberian (Hercynian) source with age 270–340 Ma, is attributed to the localization of rifting along a Paleozoic continental suture zone, the Hercynian Front. This tectonic front separates distinctly different geologic units (domains) on the conjugate margins. Such a suture would have generated a significant peripheral foreland basin across the now-submerged shelf regions of Newfoundland allowing transfer of sediment from the Iberian to the Newfoundland domains. Upon Mesozoic rifting and uplift, these mica-bearing sediments from the foreland basin succession could have been reworked and shed eastward into the nascent Atlantic Ocean basin at ODP Site 1276. Alternatively, Hercynian metamorphism and deformation might have extended onto what is now the southeastern Grand Banks, so that young detrital micas could have been derived directly from the Avalon Uplift. Results from this work are relevant to an assessment of sandstone distribution in parts of the Salar Basin and the expected diagenetic overprint for sandy reservoir facies.

IS THERE A VIABLE PETROLEUM SYSTEM IN THE CARSON AND SALAR BASINS, OFFSHORE NEWFOUNDLAND?

The Carson Basin on the eastern Grand Banks of Newfoundland has been penetrated by four wells ‐ Bonnition H‐32, Osprey H‐84, Skua E‐41 and St. George J‐55 ‐ which were drilled along its western margin. The adjacent deeper‐water Salar Basin to the east remains undrilled with the exception of ODP holes 1276A and 1277. The Carson Basin wells contain a thick Mesozoic and Cenozoic sedimentary section which includes reservoirs and seals; but source rocks, such as those present in the adjacent Jeanne d'Arc Basin, have not been found. To assess the petroleum system, well samples were collected to provide Rock Eval and vitrinite reflectance data, and analysed biostratigraphically to obtain ages and depositional environments. These analyses indicate that a Late Jurassic source rock, similar to the Egret Member (of the Rankin Formation) of the Jeanne d'Arc Basin, may be present in the deeper‐water, distal parts of the Carson and Salar Basins; this is based on a regional palaeotectonic reconstruction, together with gravity and magnetic data, including sea‐floor spreading magnetic anomalies. We interpret the absence of the Egret Member in the four wells to reflect the wells' locations rather than the Member's absence from the two basins.An integrated 4D model of the Carson Basin was built from biostratigraphy and seismic surfaces, to which an Egret‐like source rock was added. The modelling showed that significant volumes of hydrocarbons could have been generated, mostly during the main Late Cretaceous drifting event in the area. Hence, significant volumes of hydrocarbons could be present in the Carson and Salar Basins, mainly in stratigraphic traps in Early Cretaceous clastic reservoirs.

Extensional tectonics in convergent margin basins: An example from the Salar de Atacama, Chilean Andes

The Salar de Atacama basin of northern Chile preserves stratigraphic evidence for the evolution of the Andean cycle. It has evolved from a non-arc-related rift, through back-arc and inter-arc stages, to a Neogene fore-arc basin. Accumulation of the sedimentary succession was mainly due to extensional faulting. Important but short-duration contractional episodes do link to known fast-order plate-margin changes, but their stratigraphic effect appears to be restricted to uplift/erosion rather than creation of significant flexural subsidence. The Salar de Atacama basin originated as part of a regional rift system during Permian time and contains 2 km of Permo-Triassic continental detritus and volcanic rocks. The area remained above depositional base level throughout Late Triassic to Late Cretaceous time. Syn-rift continental red beds were deposited to a thickness of at least 2 km on a parallel rift segment in the Domeyko area to the west. Continued Triassic-Jurassic extension in the Domeyko basin resulted in a classic continental to marine transition, with deposition of a 2 km+ Jurassic mixed carbonate/clastic sequence. In latest Cretaceous-Eocene time, the Salar basin was an arc-related basin and accommo-dated some 4 km+ of continental detritus (Purilactis Group) due to back-arc extension, sediment being derived from the Domeyko Cordillera and arc rocks to the west. Late Eocene right-lateral strike-slip faulting and associated restraining bend uplift were driven by a high rate of oblique convergence between the Farallon and South American plates. This deformation complicated the stratigraphy of the Purilactis Group and inverted the western basin margin, which formed the dominant provenance area for a 2-km-thick Oligocene continental basin-fill component (Paciencia Group).The Oligocene basin was an extensional to trans-tensional basin. The Miocene-Holocene Salar basin is a continental fore-arc basin. This latest segment of the basin fill comprises pyroclastic and continental sedimentary rocks thrust over Quaternary gravels in many places. The Cordillera de la Sal is an intrabasinal uplift, initiated as a thin-skinned contractional feature. Thus, the superposed basin-fill components represent responses to distinctly different geodynamic settings.

From Foreland Rift to Forearc Basin: Tectono-Thermal Controls on Subsidence and Stratigraphic Development in the Mesozoic-Recent Salar de Atacama Basin, Chilean Andes

The Salar de Atacama and westerly adjacent Domeyko basins originated as Permian foreland rifts, containing some 2 km of Triassic synrift red beds. Continued extension and volcanic are establishment resulted in deposition of important Jurassic marine source rocks in the Domeyko basin. Rift basin subsidence was controlled by extension, followed by thermal sagging. Middle Cretaceous contraction (opening of the south Atlantic) inverted the Domeyko back-arc basin as a thrustbelt. To the east, the Salar basin subsequently accommodated 4 km of Late Cretaceous-Palaeocene continental detritus. Accommodation space reflected the interplay between limited flexural loading and thermal effects related to a 150 km eastward jump of the Andean volcanic arc to the margin of the arc-related, foreland-style basin. Late Eocene transpression (high rate of oblique convergence between the Farallon and South American plates) inverted the western basin margin, sourcing a 2 km thick Oligocene intra-arc basin-fill component. Accommodation space was controlled by thermal sagging associated with a further 100 km eastward arc jump. The Salar de Atacama basin thus provides a model for the evolution of complex, mixed origin basins associated with a migrating volcanic arc and varying crustal stress regime. The complex interplay between variable tectonic style and thermal processes inmore » controlling subsidence and resultant stratigraphic development is not yet adequately constrained. However, simple, single stage tectono-sedimentary models commonly used in play definition may not be appropriate in complex, arc-related basin settings.« less

Upper Triassic—Lower Jurassic salt basin southeast of the Grand Banks

A grid of multichannel seismic reflection (MCS) profiles has been used to delineate and map a large, apparently tectonically controlled basin and associated diapiric province beneath the continental slope and rise southeast of the Grand Banks of Newfoundland. The depocenter, for which we propose the name Salar basin, is defined both landward and seaward by pronounced hinges in acoustic basement. It is approximately 400 km long, 35–70 km wide, and covers an area of approximately 20,000 km 2. The southern end of the basin is marked by the intersection of the Southeast Newfoundland Ridge with the South Bank High on the Grand Banks, and the northern end is bounded by the southwestern margin of Flemish Cap. The Salar basin generally parallels the much smaller Carson basin, which lies beneath the Grand Banks immediately to the west, and it merges with this basin north of 45°22′N. Based upon correlation with contiguous deposits sampled by drilling in the Carson basin, we infer piercements filling the Salar basin to be mobilized Late Triassic-Early Jurassic evaporites, probably predominantly halite. A consequent early Mesozoic age for the Salar basin implies a multi-stage rifting history for the Newfoundland Basin, as has been documented for the adjacent Grand Banks. Initial extension, which probably formed the Salar basin's bounding basement hinge zones, occurred in Late Triassic—Early Jurassic time, and was associated with rifting of North America from Africa and extension in western Europe. The presence of early Mesozoic evaporites in a basin southeast of the Grand Banks suggests development of a significant, but shallow and restricted, seaway between the Grand Banks and the Iberian peninsula, probably connected northward with coeval salt provinces of northwestern Europe. A second rift phase related to separation of Iberia and the Grand Banks affected the Grand Banks and Salar basin in Late Jurassic to Early Cretaceous time, after a period of epeirogenic subsidence during the Early and Middle Jurassic. Uplift associated with this extension led to the development of the widespread “U” (Avalon) unconformity across the Grand Banks, the Salar basin and the Newfoundland Basin out to the J-Anomaly and may have induced the first halokinesis in the Salar basin. The second rift phase culminated in the initiation of seafloor spreading in mid-Early Cretaceous (Aptian) time at a location now marked by the J-Anomaly.