The awareness of the importance of subaerial exposure in the diagenesis of limestones has led to the recognition of a variety of subaerial phenomena in carbonate sequences such as vadose cements and calcrete crusts. Other such phenomena include paleokarsts, of which there are surprisingly few detailed descriptions.
One problem in recognizing paleokarst is to differentiate it from both Holocene and ancient interstratal (or subadjacent) karst. This is a post-burial effect which can create subsurface karstic surfaces along unconformities or bedding surfaces. The unconformity between the Lower and Upper Carboniferous in South Wales displays karstic features which have formed interstratally and have overprinted and were controlled by the original erosional relief along the unconformity. Interstratal karst can be differentiated from true paleokarstic surfaces by simple stratigraphic criteria.
Paleokarsts are common in the Mississippian limestones of Britain, and three types can be recognized in the shelf sequences in South Wales. First, there are large clay-filled hollows interpreted as solution dolines; second, there are mammillated karstic surfaces overlain by paleosols and calcrete crusts with abundant alveolar fabrics (rootlet tubules), interpreted as a type of deckenkarren analogous to Holocene South African Makondo karsts. Third, there are unusual paleokarstic zones consisting of bands of rubbly limestones containing large, irregular fluted blocks surrounded by clay-filled solution pipes and fissures and analogous to Holocene Kavornossen karren, Puerto Rico.
The paleokarsts provide information on the paleoclimate, paleohydrology, and the vegetation cover existing at the time of their formation and are useful paleoenvironmental indicators. They are the raw material for paleogeomorphology and obviously can provide excellent sites for hydrocarbon accumulation.