Cyclic development of large, complex, calcite dendrite crystals in the Clinton travertine, Interior British Columbia, Canada

Bands of large (up to 4 cm long) three-dimensional crystallographic dendrites form the terrace fronts in an old travertine mound exposed near Clinton, British Columbia. The dendrites, with their long axes perpendicular to the terrace front, are characterized by numerous levels of branching. Each branch is formed of multitudes of skeletal rhombs, four- and six(?)-sided bipyramidal crystals, or prismatic hexagonal crystals that are precisely aligned along crystallographic precepts. Although individual branches are formed of one type of suberystal, neighbouring branches may be formed of different subcrystal types. Highly supersaturated waters that were generated by rapid CO2 degassing of the spring water during its turbulent flow over the steep terrace fronts probably drove dendrite precipitation. The presence of growth lines indicates that growth was episodic. Type I growth lines probably fanned annually in response to seasonal climate changes whereas Type II growth lines, which formed less frequently, may reflect changes in the flow velocity and/or flow patterns of the spring waters. Early diagenetic modification of the dendrites involved crystal face enlargement, cements formed of trigonal prisms or needle-fiber crystals, microbial infestation that mediated substrate dissolution, and/or deposition of denital calcite crystals that formed in the water column. Much of the diagenetic modification may have taken place during the periods when the dendrites had temporarily stopped growing. The dendrites in the Clinton travertine are an excellent example of complex, episodic calcite crystal growth that was extensively modified by early diagenctic processes in a surface environment. The same spring waters from which the dendrites were precipitated mediated much of the early diagenesis. (c) 2007 Elsevier B.V. All rights reserved.