EVOLUTION OF QUATERNARY DURICRUSTS IN KARINGA CREEK DRAINAGE SYSTEM, CENTRAL AUSTRALIAN GROUNDWATER DISCHARGE ZONE, 1991,
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Arakel Av,

Quaternary calcrete, silcrete and gypcrete duricrusts in Karinga Creek drainage system, central Australia, contain abundant late-stage diagnetic features. These indicate repeated episodes of dissolution, precipitation and mobilization of duricrust components in the landscape, following the initial development of the duricrust mantle. 'Mature' duricrust profiles incorporate assemblages of diagnostic textural features and fabrics that clearly indicate the extent of karstification during the past 27 000 years. Diagenetic features in the duricrusts permit recognition of the stages involved in vadose modifications of compositional, textural and morphological features and, hence, assessment of the impact of karst dissolution, precipitation and mobilization of duricrust components under prevailing environmental conditions. At landscape level, the continued development of secondary porosity-permeability zones in topographically elevated areas, and maintenance of effective topographic gradients for soil creep are considered essential for redistribution of duricrust components and lateral and vertical extension of karst features within the Quaternary duricrust mantle. Although developing over a comparatively short span of time, late-stage modification of the Quaternary duricrusts has important implications for evolution of Quaternary landscapes and distribution of groundwater discharge-recharge patterns. Accordingly, differential dissolution and reprecipitation within the duricrust profiles have progressively given way to development of karst solution pipes and cavities, with the latter now acting as effective conduits for recharge of local aquifers in the region

A MIDDLE PROTEROZOIC PALEOKARST UNCONFORMITY AND ASSOCIATED SEDIMENTARY-ROCKS, ELU BASIN, NORTHWEST CANADA, 1991,
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Pelechaty S. M. , James N. P. , Kerans C. , Grotzinger J. P. ,

A major palaeokarst erosion surface is developed within the middle Proterozoic Elu Basin, northwestern Canada. This palaeokarst is named the sub-Kanuyak unconformity and truncates the Parry Bay Formation, a sequence of shallow-marine dolostones that were deposited within a north-facing carbonate platform under a semi-arid climate. The sub-Kanuyak unconformity exhibits up to 90 m of local relief, and also formed under semi-arid conditions when Parry Bay dolostones were subaerially exposed during a relative sea-level drop of about 180 m. Caves and various karren developed within the meteoric vadose and phreatic zones. Their geometry, size and orientation were largely controlled by northwest- and northeast-trending antecedent joints, bedding, and lithology. Near-surface caves later collapsed forming valleys, and intervening towers or walls, and plains. Minor terra rossa formed on top of highs. Karstification was most pronounced in southern parts of Bathurst Inlet but decreased northward, probably reflecting varying lengths of exposure time along a north-dipping slope. The Kanuyak Formation is up to 65 m thick, and partially covers the underlying palaeokarst. It consists of six lithofacies: (i) breccia formed during collapse of caves, as reworked collapse breccia and regolith; (ii) conglomerate representing gravel-dominated braided-fluvial deposits; (iii) sandstone deposited as braided-fluvial and storm-dominated lacustrine deposits; (iv) interbedded sandstone, siltstone and mudstone of sheet flood origin; (v) dolostones formed from dolocretes and quiet-water lacustrine deposits; and (vi) red-beds representing intertidal-marine mudflat deposits. Rivers flowed toward the northwest and northeast within karst valleys and caves; lakes were also situated within valleys; marine mudflat sediments completely cover the palaeokarst to the north. A regional correlation of the sub-Kanuyak unconformity with the intra-Greenhorn Lakes disconformity within the Coppermine homocline suggests that similar styles of karstification occurred over an extensive region. The Elu Basin palaeokarst, however, was developed more landward, and was exposed for a longer period of time than the Coppermine homocline palaeokarst

THE OCCURRENCE AND EFFECT OF SULFATE REDUCTION AND SULFIDE OXIDATION ON COASTAL LIMESTONE DISSOLUTION IN YUCATAN CENOTES, 1993,
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Stoessell R. K. , Moore Y. H. , Coke J. G. ,

Dissolution of carbonate minerals in the coastal halocline is taking place in the karst terrain along the northeastern coast of the Yucatan Peninsula. The dissolution is being accelerated in cenotes (sinkholes) where sulfate reduction and oxidation of the produced sulfide is occurring. Hydrogen-sulfide concentrations ranged from 0.06 to 4 mmolal within the halocline in two sinkholes. Relative to concentrations expected by conservative mixing, fluids with high hydrogen-sulfide concentrations were correlated with low sulfate concentrations, high alkalinities, low pH values, and heavy sulfur isotope values for sulfate. Hydrogen-sulfide concentrations were less than those predicted from sulfate reduction, calculated from deficiencies in measured sulfate concentrations, indicating mobility and loss of aqueous sulfide. Fluids with low hydrogen-sulfide concentrations were correlated with very high calcium concentrations, high strontium and sulfate concentrations, slightly elevated alkalinities, low pH values, and sea-water sulfur isotope values for sulfate. Gypsum dissolution is supported by the sulfur isotopes as the major process producing high sulfate concentrations. However, oxidation of aqueous sulfide to sulfuric acid, resulting in carbonate-mineral dissolution is needed to explain the calcium concentrations, low pH values, and only slightly elevated alkalinities. The halocline may trap hydrogen sulfide that has been stripped from the underlying anoxic salt water. The halocline can act as a stable, physical boundary, holding some of the hydrogen sulfide until it is oxidized back to sulfuric acid through interaction with the overlying, oxygenated fresh water or through the activity of sulfide-oxidizing bacteria

Synsedimentary collapse of portions of the lower Blomidon Formation (Late Triassic), Fundy rift basin, Nova Scotia, 1995,
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Ackermann Rv, Schlische Pw, Olsen Pe,

A chaotic mudstone unit within the lower Blomidon Formation (Late Triassic) has been traced for 35 km in the Mesozoic Fundy rift basin of Nova Scotia. This unit is characterized by highly disrupted bedding that is commonly cut by small (<0.5 m) domino-style synsedimentary normal faults, downward movement of material, geopetal structures, variable thickness, and an irregular, partially faulted contact with the overlying unit. The chaotic unit is locally overlain by a fluvial sandstone, which is overlain conformably by mudstone. Although the thickness of the sandstone is highly variable, the overlying mudstone unit exhibits only gentle regional dip. The sandstone unit exhibits numerous soft-sediment deformation features, including dewatering structures, convoluted bedding, kink bands, and convergent fault fans. The frequency and intensity of these features increase dramatically above low points at the base of the sandstone unit. These stratigraphic relations suggest buried interstratal karst, the subsurface dissolution of evaporites bounded by insoluble sediments. We infer that the chaotic unit was formed by subsidence and collapse resulting from the dissolution of an evaporite bed or evaporite-rich unit by groundwater, producing dewatering and synsedimentary deformation structures in the overlying sandstone unit, which infilled surface depressions resulting from collapse. In coeval Moroccan rift basins, facies similar to the Blomidon Formation are associated with halite and gypsum beds. The regional extent of the chaotic unit indicates a marked period of desiccation of a playa lake of the appropriate water chemistry. The sedimentary features described here may be useful for inferring the former existence of evaporites or evaporite-rich units in predominantly elastic terrestrial environments

Quaternary environmental change in the western desert of Egypt: evidence from cave speleothems, spring tufas and playa sediments, 2003,
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Brook G. A. , Embabi N. S. , Ashour M. M. Et Al.

Eolianites and Karst Development in the Mayan Riviera, Mexico, 2011,
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Kelley Kristin N. , Mylroie John E. , Mylroie Joan R. , Moore Christopher M. , Collins Laura R. , Ersek Lica, Lascu Ioan, Roth Monica J. , Moore Paul J. , Passion Rex, Shaw Charles

Coastal Quintana Roo, Mexico, including islands such as Cozumel and Isla Mujeres, contains numerous ridges of Quaternary eolian calcarenite in two packages, one Pleistocene and one Holocene. The Pleistocene eolianites are recognizable in the field by well-developed terra rossa paleosol and micritic crust on the surface, containing a fossil epikarst. The foreset beds of these eolianites commonly dip below modern sea level, and fossilized plant root structures are abundant. The Holocene
eolianites lack a well-developed epikarst, and have a calcernite protosol on their surfaces. The degree of cementation, and the grain composition, are not reliable indicators of the age of Quaternary eolianites.

The Pleistocene eolianites have been previously described (e.g. Ward, 1997) as exclusively regressive-phase eolianites, formed by the regression during the oxygen isotope substages (OIS) 5a and 5c. However, certain eolianites, such as those at Playa Copal, contain flank margin caves, dissolution chambers that form by sea water/fresh water mixing in the fresh-water lens. For such mixing dissolution to occur, the eolianite must already be present. As the flank margin caves are found at elevations of 2-6 m above current sea level, the caves must have developed during the last interglacial sea-level highstand, and the eolianites could not have formed on the regression from that or younger highstands. Therefore the eolianites must be transgressive-phase
eolianites developed at the beginning of the last interglacial sea-level highstand, or either transgressive- or regressive-phase eolianites from a previous sea-level highstand that occurred earlier in the Pleistocene. There is no field evidence of oxygen isotope substage 5c or 5a eolianites as suggested by Ward (1997).

Most coastal outcrops show classic regressive–phase Pleistocene eolianites as illustrated by complex and well-developed terra rossa paleosols and epikarst, and dense arrays of fossilized plant roots. However, in addition to flank margin caves, other evidence of transgressive-phase eolianites includes notches in eolianites on the west side of Cozumel, with subtidal marine facies onlapping the notches. The absence of a paleosol between those two units indicates that the eolianite is a transgressive-phase deposit from the last interglacial. All Holocene eolianites are, by definition, transgressive-phase units.

VARIATIONS IN EVAPORITE KARST IN THE HOLBROOK BASIN, ARIZONA, 2013,
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Neal J. T. , Johnson K. S. , Lindberg P.

At least six distinct forms of evaporite karst occur in the Holbrook Basin―depending considerably on overburden and/or bedrock type. Early Permian evaporites in the 300-m-thick Corduroy Member of the Schnebly Hill Formation include halite, sylvite, and anhydrite at depths of 215-250 m. Karst features result from collapse of overlying Permian and Triassic strata into underlying salt-dissolution cavities. Evaporite karst occurs primarily along the 100+ km-long dissolution front on the southwestern edge of the basin, and is characterized by numerous sinkholes and depressions generally coincident with the axis of the Holbrook Anticline―in reality a dissolution-collapse monocline. “The Sinks” comprise ~ 300 individual sinks up to 200 m across and 50 m deep, the main karst features along the dissolution front. Westerly along the dissolution front, fewer discrete sinkholes occur, and several breccia pipes are believed to be forming. Numerous pull-apart fissures, graben-sinks, sinkholes, and broad collapse depressions also occur.A newly recognized subsidence/collapse area of some 16 km2 occurs in the western part of the basin, northward from the extension of the Holbrook “anticline.” The Chimney Canyon area is some 12 km east of McCauley Sinks, a postulated breccia pipe exemplified in, and possibly manifested in at least four other closed depressions. Interferometric Synthetic Aperture Radar (InSAR) data of one depression shows active subsidence of ~4 cm/yr.Karst formation is ongoing, as shown by repeated drainage of Dry and Twin Lakes into newly opened fissures and sinkholes. These two playa lakes were enlarged and modified in recent years into evaporation 2impoundments for effluent discharge from a nearby pulp mill. Four major drainage events occurred within these playa reservoirs during the past 45 years, collectively losing more than 1.23 x107 m3 (10,000 acre-feet) of water and playa sediment. Drainage occurs through piping into bedrock joints in Triassic Moenkopi Formation (sandstone) in the bottom and along the margins of these playas. Effluent discharge has been discontinued into these playas, although recurring precipitation can fill the basins.