An assessment of stratigraphic completeness in climate-sensitive closed-basin lake sediments; Salar de Atacama, Chile

• Published in: Journal of Sedimentary Research Vol. 73; no. 1; pp. 91 - 104
• Main Authors: Lowenstein, Tim K, Hein, Matthew C, Bobst, Andrew L, Jordan, Teresa E, Ku, Teh-Lung, Luo, Shangde
• Format: Journal Article
• Language: English; Japanese
• Published: Society of Economic Paleontologists and Mineralogists 01.01.2003; Society for Sedimentary Geology
• Subjects: Atacama Desert; Cenozoic; Chile; climate change; cores; Holocene; lacustrine environment; lake sediments; lithostratigraphy; paleoclimatology; Quaternary; Quaternary geology; reconstruction; Salar de Atacama; Salar fault system; sedimentation; sedimentation rates; sediments; South America; Chile, Atacama
• ISSN: 1527-1404; 1938-3681
• DOI: 10.1306/061002730091

Dated subsurface cores, 40 m, 100 m, and 200 m in length, from the Salar de Atacama, Chile, record changes in climate and tectonics over the past 325 ka. These cores were used to assess completeness of the stratigraphic record and how that record was influenced by faulting and climate change. The same basic facies, efflorescent halite crust and cement (subaerial halite), and chevron halite (saline lake) occur in each core. The dominant facies is efflorescent halite formed in a subaerial environment like that in the Atacama basin today. Thick, well-preserved efflorescent crusts in the Salar de Atacama cores illustrate that major sediment aggradation occurred in subaerial environments by growth of efflorescent halite from evaporation of ground-water brines. Similar pedogenically formed evaporites may be preserved in the geologic record. The N-S trending Salar Fault System has downdropped the eastern block of the Salar de Atacama (core 2002) relative to the western block (cores 2005 and 2031). Relative faulting rates over the past 60 ka were determined from stratigraphic offset and uranium-series ages from core 2005. Major faulting along the Salar Fault System occurred between 16.5 and 5.4 ka, with offset of 26.5 m and faulting rates of 2.4 m/kyr. Aggradation of efflorescent halite crusts on the downdropped eastern block served to smooth out topographic variations created by faulting. Although stratigraphic units in core 2002 shifted down >30 m over the past 60 ka, the thickness and sedimentary features are similar for all but one equivalent stratigraphic unit in all three cores. Faulting along the Salar Fault System, despite significant offset, did not alter the basic stratigraphic record. Temporal completeness of the stratigraphic record, within the limits of the age dates and their errors of greater than (plus sign underlined) 3 ka, was examined qualitatively by comparing long-term sedimentation rates (0.6-0.9 m/kyr) and shorter-term sedimentation rates (0.3-3.6 m/kyr). The similarity of sedimentation rates on the 10 kyr scale and the longer 100 to 300 kyr scale suggests temporal completeness of Salar de Atacama sediments, at least at the 10 kyr scale. Although hiatuses, long periods of subaerial exposure, and dissolution of evaporites may have occurred, the main climate fluctuations at Salar de Atacama over the last 100 ka are recorded in all three sub-surface cores. Paleoclimate records obtained from such cores are therefore representative of basin-wide climate change and are valid for regional paleoclimate reconstructions.