Calcarenite

The morphology of collapse dolines varies according to their maturity and effectiveness of the removal of collapsed material. In addition, the variable balance between various geomorphic processes due to local geologic, hydrologic and climatic settings results in a diverse morphology of collapse dolines and dynamics of their morphogenesis. A single generalised proposed sequence of collapse dolines morphogenesis has therefore limited value and more detailed study is needed in terrains which differ in terms of geology, hydrology and/or climate. There is a particularly well exposed karst in Stockyard Gully National Park in the southwestern coastal part of Western Australia, formed in Quaternary aeolianites, consisting of a dense field of collapse dolines up to 100 m in diameter and on average 10 m deep. Extensive field work combined with available data of local rock stratigraphy and a comparison to collapse dolines worldwide revealed that the principal processes of collapse doline formation in Stockyard Gully National Park are similar to processes responsible for collapse doline formation worldwide (i.e., collapses above underground chambers and removal of the collapsed material). However, rock characteristics in the area influence their morphometry due to the mechanical weakness of aeolianite compared to well-cemented limestones, and a surface calcrete layer with stronger mechanical resistance than underlying aeolianite. Consequently, we propose a new 4-stage multiphase breakdown sequence of collapse doline morphogenesis in aeolianites, divided into cave dome, calcrete caprock dome, young collapse doline, and mature collapse doline. Calcrete caprock dome is stabilised by the uppermost well cemented calcrete and represents a distinctive phase just before the final breakdown to form an actual collapse doline.

In syngenetic karst speleogenesis and lithogenesis are concurrent: caves and karst features are forming at the same time as the loose sediment is being cemented into a soft, porous rock. “Eogenetic karst” and “soft-rock karst” are closely related terms for features developed in soft, poorly-consolidated limestones.
The distinctive features of syngenetic karst are: shallow horizontal cave systems; a general lack of directed conduits (low irregular chambers occur instead); clustering of caves at the margins of topographic highs or along the coast; paleosoil horizons; vertical solution pipes which locally form dense fields; extensive breakdown and subsidence to form collapse-dominated cave systems; a variety of surface and subsurface breccias and locally large collapse dolines and cenotes; and limited surface sculpturing (karren).
These features are best developed in host sediments that have well developed primary matrix permeability and limited secondary cementation (and hence limited mechanical strength), for example dune calcarenites. Certain hydrological environments also assist: invading swamp waters or mixing at a well-developed watertable; or, near the coast, mixing at the top and bottom of a freshwater lens floating on salt water. Where these factors are absent the karst forms tend to be more akin to those of classical hard-rock or telogenetic karst.