POOL MERINGUE: A NEW SPELEOTHEM FROM CARLSBAD CAVERNS OF POSSIBLE BIOLOGIC ORIGIN

Pool meringue is a newly defined calcite speleothem from Carlsbad Caverns, NM, that forms subaqueously coating the bottom of cave pools. It usually coats previously formed calcite pool crust but can form as the initial pool lining. We have identified two distinct forms of pool meringue but intermediate forms also occur. The main form is characterized by having a wispy, peaked form reminiscent of the surface of a lemon meringue pie. Individual peaks are less than 1 cm high and 1 to 1.5 cm in diameter. In some cases, they occur as more elongate forms 1 cm high and 5-10 cm long. This form occurs in shallow pools, usually less than 10 cm deep, that show little evidence of active flow during formation. In one pool, 703-09 pool meringue grades upward into webulite, a web-like form that forms coating and connecting pool fingers.

The surface of typical pool crust is covered with distinct crystal faces; pool meringue, in contrast, has a smooth surface. In the microscope, pool meringue appears as simple overgrowths on pool crust calcite. Webulite also occurs as overgrowths, in this case on pool fingers, despite its obvious draping morphology. The distinction between pool crust/pool finger and meringue/webulite is very difficult to see in thin section although hand samples show a faint color change marking the transition.

A less common form of pool meringue is narrower and forms elongate ridges 1 cm high by 0.2 cm wide. Individual ridges extend parallel to flow directions for 10 cm or more with < 1 cm between ridges. Pools containing this more ridged form show greater evidence of active flow including rimstone dams and flowstone above and/or below the pool. This form is also different in the microscope: instead of clear calcite there is a core of clotted micrite that is coated with elongate crystals, perhaps of aragonite.

The external morphology of both forms of pool meringue contrasts with typical pool crust and suggests a biologic origin. The connection with webulite, thought to be calcified slime, supports this model. In addition, the micritic core of the elongate form may represent former microbial communities.