EVOLUTION OF SALT DIAPIR TOPOGRAPHY AND KARST MORPHOLOGY DURING LAST GLACIAL CYCLE (PERSIAN GULF, IRAN)

Spectacular cave systems and exokarst forms were studied on three salt diapirs (Hormoz Island, Larak Island and Namakdan diapir on Qeshm Island). They represent mature stage of salt karst with great variety of exo- and endokarst forms (caves, sinkholes, blind valleys, shafts, karrens). Evolution of caves (with length up to 6.5 km) is closely connected to sea level oscillation during last glacial and Holocene.

Radiocarbon and U/Th dating of corrals and oysters taken from marine terraces on both salt diapirs was used to: 1) calculate the uplift rate along transect across salt diapirs, 2) describe the evolution of Holocene and Pleistocene marine terraces and valleys which represent erosion base for cave systems. Radiocarbon dating of wooden twigs buried in the abandoned cave levels and OSL dating of quartz grains from sediments were used to deduce the evolution of caves in the past.

Caves and large blind valleys started to develop in last glacial after sea left predominant part of diapirs. Due to uplift of salt diapirs (up to 7 mm/y depending on position on transect) the cave levels were lifted into higher altitude and hence preserved from Holocene sea transgression. Streams draining salt diapir incised about 30 m below recent sea level into dry bottom of Persian Gulf at the last glacial maximum.

About 9 kyr BP rapid sea transgression reached margin of diapirs. Diapirs were partly eroded by sea abrasion and Holocene marine terrace deposition started. Between 9 and 6 ka BP the marine transgression (about 14 mm/y) outstripped the uplift rate of diapirs. Paragenesis with caves completely filled by sediments is typical for this stage. Accessible cave passages are younger than 4-6 kyr BP.