Miocene Gypcretes from the Calama Basin, northern Chile
- 1 March 1998
- journal article
- research article
- Published by Wiley in Sedimentology
- Vol. 45 (2) , 351-364
- https://doi.org/10.1046/j.1365-3091.1998.0166e.x
Abstract
Gypcretes of Miocene age are preserved beneath a 9·53 ± 0·36 Ma ignimbrite along the eastern margin of the Oligo‐Pleistocene Calama Basin, northern Chile. They are restricted to a single stratigraphic horizon developed within laterally extensive (>35 km) coalesced alluvial fan deposits, developed along the margin of an endorheic basin. Two types of gypcrete are recognized. Type 1 comprises almost completely gypsum‐cemented sandstones containing alabastrine nodules and columns, sub‐vertical and horizontal veins of fibrous gypsum and ‘v‐shaped’ cracks infilled by clastic material, and are interpreted as surface weathered gypsic crusts. Type 2 gypcretes are composed of massive, reddened poikilitic and mesocrystalline gypsum (up to 80% of the rock) with isolated bedding‐parallel, clast‐rich lenses (200 × 30 cm) and sub‐vertical veins of fibrous gypsum. The massive texture resembles that of well developed B horizons in Quaternary alluvial desert soils. The crystal forms suggest an origin as a subsurface gypsic crust formed by a combination of hydromorphic (poikilitic) and illuvial (mesocrystalline) processes with the fibrous gypsum veins suggestive of periodic surface exposure.Gypcrete horizons are up to 25 m thick and composed of both gypcrete types. They represent superimposed phases of surface and subsurface gypcrete development. Quaternary gypcretes are developed in arid climatic regimes, but are not considered to develop under hyper‐arid climates. An arid climate is considered to have prevailed in the study area up to 9·5 Ma after which a change to hyper‐aridity favoured gypcrete preservation.Keywords
This publication has 18 references indexed in Scilit:
- Upper Cenozoic volcanism and tectonism in the Andes of northern ChilePublished by Elsevier ,2003
- Stages and rate of the gravel shattering process by salts in desert Reg soilsGeoderma, 1993
- Desert GeomorphologyPublished by Taylor & Francis ,1993
- Soil-catena development with time in a hot desert, southern Israel—field data and salt distributionJournal of Arid Environments, 1991
- Evolution of Quaternary duricrusts in Karinga Creek drainage system, Central Australian groundwater discharge zoneAustralian Journal of Earth Sciences, 1991
- The central Australian groundwater discharge zone: Evolution of associated calcrete and gypcrete depositsAustralian Journal of Earth Sciences, 1988
- The evolution of holocene reg (gravelly) soils in desertsCATENA, 1986
- Sheet-flow-dominated gravel fans of the non-marine middle Cenozoic Simmler Formation, central CaliforniaSedimentary Geology, 1984
- Sheetfloods, sheetwash, sheetflow, or ... ?Earth-Science Reviews, 1982
- Geology and origin of the Chilean nitrate depositsPublished by US Geological Survey ,1981