The Tacoma Desert: Facts and Features BY adiabatic The Tacoma Desert forms one of the major hyper-arid deserts of the world and it is known to be the driest place on Earth. The extreme aridity of the climate and unusual mineralogy of the resoling In the Tacoma region is of considerable interest because of Its value as an analogue to the Martian surface. The sedimentary succession In the Tacoma Desert records deposition under an arid to semiarid climate from the late Jurassic (1 mama) to the present day (Hartley, 2005).
Comparison with other long-lived deserts such as the Iamb, Sahara and Australia deserts suggests that the Tacoma s also the oldest extant desert. Arid environments account for 30% of the global land surface, a figure that is increasing annually owing to desertification (Hartley, 2002). The present day location of the Tacoma Desert within the dry subtropical climate belt is the principal cause of aridity (Fig. 1). This extreme aridity has resulted in a number of usual and unique features.
These include the very low rates of erosion and accumulation of a range of unusual salts, including percolates, ideates, and nitrates in the soils as well as the more common halite, gypsum and anhydrite (Clarke, 2005). To understand the history of aridity In the Tacoma Desert and Its relevance to arid zone morphogenesis, resoling formation, and supervene normalization, It Is vital to approach this subject from a whole resoling perspective. Knowing about these approaches Is critical for effective mineral exploration In the area because it hosts many of the world’s most significant porphyry copper-gold ore deposits (e. . Schismatic, the largest open pit copper mine in the world). Sedimentation of the Tacoma Desert Miocene to Pliocene sedimentary rocks in northern Chile occur within two fault- mounded basins, the Central Depression (including an eastward extension, the Calm basin) and the Predawn Depression (Fig. 2) (Hartley and Chon, 2002). The north-trending Central Depression extends throughout northern Chile Into Southern Peru and It Is separated from the Coastal Cordillera to the west by the Tacoma fault zone. Coastal Cordillera is characterized by high relief on all scales and active faulting along the Tacoma Fault.
This high relief contrasts with the smooth, directed surfaces further inland. There are a series of transgression’s faults within the eastern margin that separate he depression from the Periodical. The Predawn Depression consists of a series of endorphin basins developed between the eastern, thrust-bounded margin of the Periodical and the Miocene to Holocene volcanic arc of the High Andes (Hartley and Chon, 2002). Sedimentation was continuous throughout the Miocene to the present In the Predawn Depression. From the Oligocene to early Miocene, fluvial, alluvial-fan and playa-lake sediments were deposited under a semiarid climate.
History of Aridity mostly terrestrial sediments of the region (Clarke, 2005). Table 1 shows the most elevate Occidentalizing and strategically data. Stereographic Units Age Lethality Depositional environment Unnamed units in Salary De Tacoma Pliocene- Holocene Evaporates and classics Evaporative lakes (such as Salary De Tacoma) Hilarious and Solaced evaporates Polio-Pleistocene Anhydrite, halite, gypsum Continental playa lake San Pedro Group Oligocene- Middle Miocene Mudstone, gypsum, anhydrite, halite Continental evaporative lake Practices Formation Late Cretaceous- Pliocene Conglomerate, mudstone, indicates volcanic, gypsum, halite.
Westerly derived alluvial fans feeding into playa lakes Quavered Monarchs Formation Early Cretaceous Siltstone, sandstones, limestone, gypsum, halite casts. Coastal saline lagoons Coracles Group Early Jurassic Limestone, sandstone, calcareous and bituminous shale, anhydrite, gypsum. Marine to evaporative marginal marine. Pan De Azure Formation Late Triassic Felsitic prophylactics, sandstone, limestone, gypsum. Fluvial overlain by marine sediments Chaffinch Formation Late Triassic Conglomerates, felsitic-intermediate volcanic, limestone, sandstone, halite casts.
Alluvial fan Table 1 . Sedimentary history of aridity in the Tacoma Desert, showing representative therapeutic units. Modified from original table by Clarke, 2005. Aridity in the Tacoma Desert region has persisted for the past 200 Ma according to three paleographer reasons (Clarke, 2005). The first one states that the Tacoma region has been approximately at the same platitudes during this period of time. Secondly, the South American continent has maintained the same north-south orientation and thirdly, the region has always been near the western margin of the continent.
Tacoma Desert Climate present day, which suggests that the present-day controls on climate may extend into he late Jurassic (Hartley, 2005). The present day hipper-aridity in the Tacoma Desert region is induced primarily by subtropical anticyclone atmospheric subsidence. This is reinforced by the presence of the upwelling, north-flowing, cold Humboldt Current along the west coast of South America, which prevents precipitation in the coastal regions. A further controlling factor is the rain shadow effect of the Andean Cordillera, which prevents humid air from reaching the Pacific coastline.
The continentally effect, occurs where rain- bearing trade winds cannot penetrate continental interiors and there’s a westward ointment-wide decrease in rainfall across South America, is also considered another cause for aridity. Tectonic Landforms The peddling, either as a bare rock surface or associated with its alluvial spread termed the Tacoma Gravels, is preserved as a high terrace above the rivers and is a single surface throughout the southern desert. Bedrock faulting has displaced the depositional surface of the Tacoma Gravels in many places, particularly along the margins of the longitudinal depressions.
The faulting reflected in the alluvium is principally longitudinal (approximately N-S) in trend. The majority of such structures are the surface expression of hidden bedrock faulting along or near the major structures that were originally responsible for the basin and range topography (Mortimer, 1973). All faults are apparently high angle normal or reverse, but the nature of the faulting is difficult to determine because of the alluvial mantle. The Tacoma Fault is a reputed strike-slip fault of continental dimensions that crosses the ROI Salads inland from Central (Mortimer, 1973).
Even though the Tacoma Fault has apparently not significantly displaced topographic elements in the outworn desert, it has been a zone of preferred erosion. Conclusion The Tacoma contains the longest continuous record of sedimentation under an arid to semiarid climate and it’s the driest place on Earth. The principal causes of aridity in western South America for the last 150 Ma, in the Tacoma Desert region, have been location within the southern hemisphere trade wind belt, atmospheric subsidence, the continentally effect and the presence of ancestral Humboldt Current.