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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 1005

Last Page: 1005

Title: Holocene Tepees and Stromatolites from Southern Australia and Their Paleohydrologic Significance: ABSTRACT

Author(s): John Warren

Article Type: Meeting abstract


Along the southern coastline of South Australia, coastal salinas were created by the stabilization of the late Pleistocene-Holocene sea approximately 6,000 y.b.p. In these isolated seepage depressions stromatolites (millimeter laminated), algal tufas, tepees, and other fenestral crusts and mounds constitute a marginal aragonite facies. The fenestral limestone crusts 10 to 30 cm thick) are underlain by a highly porous, open boxwork limestone.

During late winter and spring the water table is high in the calcreted, Pleistocene calcarenite dunes which surround and underlie the salinas. Consequently the hydraulic gradient between the dune and the salina is steep; meteoric-influenced ground water seeps into the salina margin. Waters driven by this ground water head seep into the boxwork beneath the crusts and are confined by this crust aquitard. The pressure causes the crust to expand and become slightly concave. During the late summer and autumn, the dune water table and associated hydraulic gradient are lower by the processes of evapotranspiration. Concentration of the salina waters and lowering of the salina water level causes a lowering of the


crust. This lowering is coincident with passive and neomorphic precipitation of aragonite on and within the crust. The alternate lifting and falling of the crust in conjunction with aragonite deposition during the falling stage cause a seasonal increment in crust size. As the crust is laterally confined by the calcreted dunes, overthrusting of the crust occurs and tepees are formed.

Millimeter layered indurated stromatolites, growing millimeter laminated algal mats and poorly laminated algal tufas (including Conophyton-like tufas) all form in this schizohaline zone. The breaking of the crust along megapolygonal overthrust zones creates zones of pressured ground water upwelling that commonly control the three-dimensional distribution of stromatolites and tufas. In some marginal zones of Marion Lake stromatolites are only found atop tepee crests. All finely laminated stromatolites probably grew up to the ambient water level.

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