Otto Bornemann, Reinhard Fischbeck
One of these Quaternary channels runs across the salt dome; locally, the channel cuts the cap rock down to the rock salt. The Stassfurt potash seam cuts across at the bottom of this channel under Quaternary sediments. The extent of leaching and the stages of transformation of the potash seam were explored by six boreholes sited perpendicular to the strike. The potassium minerals of the potash seam had been completely dissolved down to 90-130 m beneath the salt surface. The cavities formed by leaching were filled with sand and clay material from the overlying sediments. Only at about 170 m below the top of the salt dome was the potash seam, encountered in the form of carnallite, unaffected by water from the overlying sediments.
Between 90 and 170 m below the top of the salt dome, the potash seam was encountered in different stages of transformation. The sequence from bottom to top was as follows: unchanged carnallitic rock, followed by a zone of kainitic rock, ending with a potash-free halitic rock containing clastic material from the overlying sediments.
Diagenesis of the clastic Elsterian sediments interbedded in the rock salt blocked further migration of solutions into the potash seam. No evidence has been found for further subrosion of the potash seam since the Elsterian (i.e., the last 300,000 years).
AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.