ABSTRACT: Fossil tufa deposits at Miette Hot Springs, Jasper National Park, Canada.

CGRG Bibliography of Canadian Geomorphology
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Abstract

Modern hot springs and fossil tufa deposits are found in Sulphur Creek Valley at Miette Hot Springs. The calcareous fossil tufa, up to 7m thick and extending nearly 500m along the west side of the valley, precipitated from waters that issued from a line of perched springs located ~30m above the valley floor. Interpretation of stable oxygen isotopes and the calcified biota suggests that the fossil springs were thermal, issuing waters at 40-50°C. C14 dating of bone material from the tufa deposits indicates that they formed ~3,800 years ago. The fossil tufa formed on an unstable slope and was disrupted by landslides and rockfalls during and after growth. Many tufa morphotypes are present, including domal tufa around the spring orifices; flat-banded tufa that formed on horizontal or gently inclined surfaces; wedge-shaped tufa generated by progressive filling of small basins or rimpools; roll-over and vertical tufa formed by precipitation at slope breaks or on steeply inclined surfaces; and hummocky bedded tufa that developed by encrustation of bryophyte colonies growing in spring water splash zones. The tufa morphotypes embrace a variety of facies. Four are primary, microbially mediated facies: Porous Laminar Tufa consists of alternating thick (0.5-2.5cm) porous laminae and thin (maximum 0.7cm) dense laminae bounded by swaly planes; Dense Laminar Tufa contains alternating light and dark laminae of comparable thickness (0.5-1.5cm) bounded by relatively flat planes; Streamer Tufa is composed of thin (0.1-0.5cm) wavy laminae whose upper surfaces have streamer textures defined by sinuous filamentous patterns oriented parallel to the bedding; and Crenulated Tufa is highly porous and comprised of paper-thin, non-conformable, crenulated sheets. Inorganic precipitation led to the formation of Sheet Tufa, a sheet-like crystalline crust composed of coarse spar calcite crystals aligned perpendicular to the sheet plane, and a Tufa Breccia/Conglomerate which developed where calcite precipitated as a cement between lithoclasts emplaced by rockfalls. Some components were preserved by calcareous encrustation/replacement of macrophytes. Calcified bryophyte colonies (~60 x 30 cm) are scattered throughout the tufa. Locally, the cellular walls and structures of tree branches were replaced by calcite, generating mineralized wood. Massive Tufa, which is a dense, featureless facies, and Granular Tufa, which looks like a grainstone on a macroscopic level, have undergone extensive diagenetic alteration.

Bibliography of Canadian Geomorphology