Inland Sabkha Research Articles

Implications of diapir-derived detritus and gypsic paleosols in Lower Triassic strata near the Castle Valley salt wall, Paradox Basin, Utah

Gypsum-bearing growth strata and sedimentary facies of the Moenkopi Formation on the crest and NE flank of the Castle Valley salt wall in the Paradox Basin record salt rise, evaporite exposure, and salt-withdrawal subsidence during the Early Triassic. Detrital gypsum and dolomite clasts derived from the middle Pennsylvanian Paradox Formation were deposited in strata within a few kilometers of the salt wall and indicate that salt rise rates roughly balanced sediment accumulation, resulting in long-term exposure of mobile evaporite. Deposition took place primarily in flood-basin or inland sabkha settings that alternated between shallow subaqueous and subaerial conditions in a hyperarid climate. Matrix-supported and clast-supported conglomerates with gypsum fragments represent debris-flow deposits and reworked debris-flow deposits, respectively, interbedded with flood-basin sandstone and siltstone during development of diapiric topography. Mudstone-rich flood-basin deposits with numerous stage I to III gypsic paleosols capped by eolian gypsum sand sheets accumulated during waning salt-withdrawal subsidence. Association of detrital gypsum, eolian gypsum, and gypsic paleosols suggests that the salt wall provided a common source for gypsum in the surrounding strata. This study documents a previously unrecognized salt weld with associated growth strata containing diapir-derived detritus and gypsic palesols that can be used to interpret halokinesis.

Impact of basin evolution, depositional environment, pore water evolution and diagenesis on reservoir-quality of Lower Paleozoic Haima Supergroup sandstones, Sultanate of Oman

ABSTRACTSandstones of the Early Paleozoic Miqrat Formation and Barik Sandstone Member (Haima Supergroup) are the most prolific gas/condensate containing units in the northern part of the Interior Oman Sedimentary Basin (IOSB). The reservoir-quality of these sandstones, buried to depths exceeding 5 km, is critically related to the depositional environment, burial-related diagenetic reactions, the timing of liquid hydrocarbon charge and the replacement of liquid hydrocarbon by gas/condensate.The depositional environment of the sandstones controls the net-sand distribution which results in poorer reservoir properties northwards parallel to the axis of the Ghaba Salt Basin. The sandy delta deposits of the Barik Sandstone Member have a complex diagenetic history, with early dolomite cementation, followed by compaction, chlorite formation, hydrocarbon charge, quartz and anhydrite precipitation and the formation of pore-filling and pore-lining bitumen. In the Miqrat Formation sandstone, which is comprised of inland sabkha deposits, similar authigenic minerals occur, but with higher abundances of dolomite and anhydrite, and less quartz cement. The deduced pore water evolution from deposition to recent, in both the Miqrat Formation and the Barik Sandstone Member, reflects an early addition of saline continental waters and hydrocarbon-burial related mineral reactions with the likely influx of lower-saline waters during the obduction of the Oman Mountains.Four structural provinces are recognized in the IOSB based on regional differences in the subsidence/uplift history: the Eastern Flank, the Ghaba and Fahud Salt Basins and the Mabrouk-Makarem High. In the Fahud Salt Basin, biodegradation of an early oil charge during Late Paleozoic uplift resulted in reservoir-quality degradation by bitumen clogging of the pore space. On the Eastern Flank and the Mabrouk-Makarem High, however, the early oil bypassed the area. In contrast, post-Carboniferous liquid hydrocarbons were trapped in the Mabrouk-Makarem High, whereas on the Eastern Flank surface water infiltration and loss of hydrocarbons or biodegradation to pore occluding bitumen occurred. In the Ghaba Salt Basin, post-Carboniferous hydrocarbon charge induced a redox reaction to form porosity/permeability preserving chlorite in the reservoirs. The liquid hydrocarbons were replaced since the obduction of the Oman Mountains by gas/condensate which prevented the deep parts (>5,000 m) of the Ghaba Salt Basin from pore occluding pyrobitumen and thus deterioration of the reservoir quality.

Geomorphological and sedimentological characteristics of coastal and inland sabkhas, Southern Kuwait

Sabkha deposits in the southern sector of Kuwait occur as scattered, irregular, and closed lowland areas of different sizes. On the basis of their field occurrence, and geographic setting two distinct types of sabkhas are recognized, coastal and inland. The coastal sabkhas extend along the elongated depression in Al-Jailaiaha and Al-Khiran areas. The inland sabkhas are formed in the irregular slopes in the western side of the desert area in Al-Maqwa, Urafjan, and Al-Gurain areas. Formation of sabkhas is related to pre-existing morphological features such as depressions and gentle slopes, and is distributed in the study area in different geomorphological zones. Both coastal and inland sabkhas are subjected to mobile sand invasion under the action of the northwesterly prevailing wind. Texturally, both groups of sabkhas may be classified within the gravelly to slightly gravelly muddy sand class. Their sediments are mostly unimodal with a modal class of medium sand, poorly sorted, nearly symmetrical and mesokurtic. The surface features of quartz grains show the mechanical and chemical action on their surfaces. Mineralogically, coastal and inland sabkhas are mainly composed of quartz, feldspars, gypsum and rock fragments, which are mostly of carbonate type. Skeletal fragments and oolites are present in the coastal sabkhas and are absent in the inland sabkhas. Based on the heavy-mineral suites, most of sabkha sediments are thought to be derived from Al-Dibdibbah deposits, which were derived from the Arabian Shield igneous and metamorphic rocks by wadi A1-Rimmah-Al-Batin valley system.

Chemical and isotopic methods for confirming the roles of wadis in regional groundwater recharge in a regional arid environment: a case study in Al Ain, UAE

AbstractIn arid environments groundwater may represent the most important source of water for sustaining life. The timing and nature of precipitation may induce infiltration and recharge on a small scale. The Al Ain region, UAE was chosen and from 1996 to 1997 studies were conducted to illustrate spatial distribution of recharge for groundwater by using chemical and isotopic methods. According to the field survey, UAE can be hydrogeologically classified into five parts: mountain area, wadis, sand dunes, inland sabkhas and coastal sabkhas, respectively. In this report, we studied a typical wadi, Wadi Mieshiq area. Upstream of the wadi, it was found that the groundwaters were characterized by low salinity. Stable isotopes of groundwaters in the wadi were lighter than those of the stream waters in the mountain area, since stream water was affected by evaporation before it infiltrated into the ground. The isotopes of recharged water into the wadi must have isotopically light values. From the results above, groundwater along the wadi was mainly derived from not only water from the mountain area but also infiltrated water during the flood period. Wadis are an important recharge region for groundwater. Copyright © 2001 John Wiley & Sons, Ltd.

Desertification in the Eastern Province of Saudi Arabia

The problem of land degradation in the Eastern Province of Saudi Arabia is not a new phenomenon, but during the last decade it has grown to be a serious threat to the delicate desert ecosystems, and also to the urban and industrial areas, due to an increase in sand movement. The area under investigation is situated on the Gulf coast north of Jubail and is approximately 20 km in width centered along the coastline. The total area is almost 1000 km2. Eight vegetation types were classified according to the dominant and co-dominant species. A comparative study of the vegetation in a fenced, non-grazed area and in an open grazed area showed that the impact of grazing and recreational activities have largely reduced the value of the rangelands. The reduction in species diversity and density leads to an increase in wind and sand dynamics. Exposed roots, giant ripples, changes in the extension of inland sabkhas and new active dunes could be observed in many parts of the study area. It could be proved that most inland sabkhas in the area are pure deflational features with considerable dynamic due to the reduction in vegetation cover during the recent years. The monitoring of vegetation density was carried out during helicopter flights with the help of GPS and a video camera. Image processing on a personal computer allowed accurate calculations of vegetation density. Observations on active dune fields in the area showed that the size of the dune fields almost doubled in 15 months. Tests in small enclosures showed that there is a potential for natural recovery even in severely damaged areas. In just one year without grazing and with average precipitation there is a significant difference in vegetation cover. Strict grazing management and camping regulations are required to prevent further degradation and allow the recovery of damaged ecosystems. Community involvement and education is necessary for the development of an understanding of regulations and the need for preservation.

Three-Dimensional Modeling of an Aeolian Dune/Interdune System: Applications to Hydrocarbon Production

The Al Liwa region of the northeast Rub Al Khali, United Arab Emirates, comprises compound crescentic draa and subcircular inland sabkhas that are flanked to their north by a sand sea of smaller dunes extending almost to the coast of the Arabian Gulf. This controlled the supply of sand from the north and influenced water-table positions within interdune areas. The draa, up to 170 m high, comprise both fine and coarse sands with a strong carbonate component, and are migrating very slowly to the south-southeast. The evaporite-encrusted interdune sabkhas often are underlain by foreset dune sands that also indicate transport to the south-southeast. The northern fringe of smaller dunes migrates southward more rapidly than the draa, but their northern supply of sand now has been cut off by flooding of the Gulf, initiating the deflation of coastal areas down to the water table. A deep-penetrating radar survey, coupled with large-scale trenching, provides a three-dimensional model of dune/interdune systems. This fieldwork aids a clearer understanding of dune/interdune heterogeneities and interconnectedness, which in turn is providing more realistic reservoir models for interwell simulation studies within the Permian Rotliegende gas fields of northwest Europe.

Sedimentology of a Proterozoic erg: the Venkatpur Sandstone, Pranhita‐Godavari Valley, south India

ABSTRACTReappraisal of the Late Proterozoic Venkatpur Sandstone indicates that the bulk of the sandstone is aeolian in origin. Aeolian stratification types, namely (i) inverse graded translatent strata, (ii) adhesion laminae, (iii) grainflow strata and (iv) grainfall strata, are present throughout the outcrop belt. Nine facies have been identified that represent both aeolian and related aqueous environments within a well‐developed erg. Cosets of large cross‐beds at the Bellampalli section in the NW of the study area record dune fields in the interior of the sand sea. To the SE, at the Godavari River and Ramgundam sections, a progressive increase in the relative proportion of the flat‐bedded to cross‐bedded facies and intercalated non‐aeolian facies delineates the transition from the dune‐field to sand‐sheet environment. An alternating sequence of aeolian and marine sediments at Laknavaram, in the extreme SE, marks the termination of the sand sea. Palaeocurrent data suggest that the NW‐SE trend of the sections represents a transect across the sand sea in a direction normal to the resultant primary palaeowind direction.Abundant horizontally stratified units in the Vankatpur Sandstone do not always represent the interdune sediments. On the basis of the thickness and geometry of the units, nature of bounding surfaces and associated facies sequence, the facies is variously interpreted to represent interdune, inland sabkha, sand sheet and coastal sand flat deposits.

Marginal Erg Facies: A Trial Approach toward a Descriptive Classification

During the late 1970s and early 1980s, sedimentologists began recognizing the margins of eolian sand seas as separate, components which differed from interior sand seas in geometry, extent, and facies. Stratigraphers have now observed these differences in eolian rocks. Erg margins may be grouped in five ways: (1) by associations with extradunal environments-coastal plain, lacustrine, periglacial, marine (tidal flat, coastal sabkha, beach, and lagoon), and arid alluvial (alluvial fan, fluvial, playa, inland sabkha); (2) by allocyclic controls-eustasy, plate tectonism, and climate; (3) by autocyclic controls-local tectonism, topography, vegetation, hydrology, structure, sediment source and supply, and wind regime; (4) by geographic position-upwind, downwind, and along-wind margins; and (5) by sedimentary facies-texture and architecture. In contrast with erg interiors, erg margins are characterized by smaller, less complex dune-forms related to thinner sand accumulation; elementary dune architecture; more vegetation and bioturbation; high occurrence of sand sheet, zibar, and serir facies; expansive, low-relief interdunes with widely distributed dunes; and a greater proportion of interbedded extradunal deposits. Some of the published studies on ancient eolian systems have identified erg margin facies that have been influences by marine and arid alluvial processes. Few reports have described lacustrine-eolian and periglacial-eolian interactions. This study is an attempt tomore » organize known features of modern and ancient erg margins into a scheme based on erg margin controls.« less

The Triassic — early Jurassic succession in the northern North Sea: megasequence stratigraphy and intra-Triassic tectonics

Abstract The occurrence of Triassic to early Jurassic mudstone and sandstone sequences in the northern North Sea basin, and their possible significance in terms of basinal subsidence pattern is reviewed. The latest phase (Scythian) in a period of crustal stretching is illustrated from the Horda Platform where block rotation has been accompanied by infilling (> 2000 m) of alluvial deposits in a series of N-S oriented, asymmetric sub-basins. The ‘post-rift’ succession is subdivided into three megasequences which, in their broad areal development over most of the northern North Sea basin, contrast with the rift-infill sequences. The late Scythian-Ladinian megasequence (PR1) documents an early phase of widespread, fine-grained, floodbasin deposition which was interrupted by prograding, sandy sheetflood lobes (Teist Fm). The latter were derived from marginal alluvial fan bajadas along the Norwegian hinterland and from certain segments of the East Shetland uplands. This phase of infilling culminated with basinwide, sand deposition (Lomvi Fm) from amalgamated fans and braided river systems. Although classified as ‘post-rift’, megasequence PR1 does show some ‘growth’ along the older rift lineaments. The Carnian-early Rhaetian megasequence (PR2) records retrogradation of the earlier sandy systems towards the basin margins (lower Lunde Fm) followed by renewed establishment of extensive lacustrine and coastal floodbasin conditions (middle Lunde Fm.). Low-lying tracts within the northerly floodbasins allowed influx of brackish lagoonal waters from a sea to the north. The sequence culminates with repeated progradation of extensive sandy alluvial plains (lower and middle parts of upper Lunde Fm). The early Rhaetian-Sinemurian megasequence (PR3) also records retrogradation of the earlier sandy fluvial systems (middle to upper parts of upper Lunde Formation), followed by the development of extensive, fine-grained floodbasins and occasional brackish-marine lagoons (uppermost Lunde Fm.) into which isolated sandy streams and fan deltas prograded from both East Shetland and Norwegian margins. Subseqeunt progradation of streams and fan systems eventually allowed the development of northward, through-flowing, axial river systems (Statfjord Fm). There are clear signs of more active intra-basinal tectonics during this third stage in the basin’s post-rift history, with latest Triassic-earliest Jurassic depocentres tending broadly to occupy the sites of the future Viking and Sogn Grabens. In the central North Sea the three-fold megasequence development cannot easily be recognized, though broadly time-equivalent units can be identified. The earliest phase was dominated by inland floodbasin deposition (Smith Bank Fm.) but this was replaced towards the Norwegian hinterland by, at first, lacustrine/lagoonal and inland sabkha deposition, and later, by sandy alluvial fan development (Skagerrak Fm.). The second phase was dominated by sandy alluvial deposition in the northern and eastern reaches but became muddy floodbasin-dominated farther west. The latest phase is only fragmentarily preserved and therefore poorly recognized because of major mid-Jurassic erosion over much of the central North Sea. Where preserved it tends to be sandy, especially in the Norwegian sector. The pattern of initial retreat of sandy fluvial systems followed by extensive, fine-grained floodbasin development, subsequent progradation of sandy alluvium and eventual development of axial, through-flowing river systems appears to have been characteristic of each of the 3 post-rift intervals (particularly of the first and third, but also, albeit more crudely, of the second) and is interpreted in terms of an increasing then decreasing rate of relative base-level rise. This, in turn, is argued to have been caused largely by increasing then decreasing basinal subsidence rates. Intra-Triassic tectonics are reflected in (a) early Triassic rifting, (b) three distinct phases of post-rift subsidence and (c) clear signs of differential fault movement and sediment growth along certain intra-basinal lineaments, particularly in the third post-rift interval.

The Sherwood Sandstone Group (Triassic) of the Wessex Basin, southern England

Data from released wells indicate that the subdivision of the Sherwood Sandstone Group into the Budleigh Salterton Pebble Beds and the Otter Sandstone Formation is equally applicable in both the outcrop and subcrop of the Group in the Wessex Basin. The Sherwood Sandstone Group was deposited largely from braided streams but an inland sabkha may have occupied the depocentre during deposition of the lower parts of the Otter Sandstone Formation. The Budleigh Salterton Pebble Beds may have been removed from parts of the Wessex Basin by erosion prior to deposition of the Otter Sandstone Formation.

Desert sedimentary environments, present and past—A summary

Tropical deserts develop where the potential rate of evaporation exceeds that of precipitation, where rainfall is too low or spasmodic to support vegetation. These usually occur in the trade-wind belts north and south of the equator and in the rain shadow of mountain ranges. About half the area of deserts comprise outcrop subject to erosion and deflation. The rest consists of sediments of fluvial (wadi), lacustrine (salina), paralic (coastal sabkha) and aeolian origin, and of evaporites. Ephemeral streams deposit sands and gravels over basin-margin alluvial fans, and over desert plains where sub-surface cementation commonly takes place. Evaporation of basin-centre temporary lakes results in a crust of halite (inland sabkha). Fluvial sands are an important source of dune sand; the finer fractions are removed from the desert in suspension to become loess and the coarser grain remain as a deflation lag. The axes of sand dunes are transverse to moderate winds and parallel to strong winds. Giant forms of the latter dune type were prevalent during the last ice age, and in coastal areas carbonate-cemented dune sands extend below present sea level; this suggests a causal relationship between polar glaciations and strong desert winds. Desert fluvial sediments rarely reach the sea, so the warm and clear coastal waters are ideal for the manufacture of organic carbonates. Longshore currents sweep them into offshore bars behind which evaporitic lagoonal conditions develop. The lagoons become sabkhas as they are infilled with algally bound marine and wind-blown sediment. Although there are desert sequences as old as about 2000 Ma, they seem to have occurred only sporadically during the earth's history. It seems likely that their occurrence was controlled by the past size of continents, their location relative to the equator, by the freedom of circulation of global oceanic water and by the presence of ice caps. The Permo-Triassic was a time of extensive evaporite deposition and dune activity. By implication, other known occurrences of evaporites may be marginal to wadi and dune sequences that have yet to be identified.

Aspects of the diagenesis of the Sherwood Sandstones of the Wessex Basin and their influence on reservoir characteristics

Summary The Sherwood Sandstone Group sandstones of the Wessex Basin are important potential reservoirs for both hydrocarbons and geothermal brines. Analyses of conglomerate, sandstone and siltstone samples from outcrop and deep boreholes indicate a complex diagenetic history that has had important positive and negative effects on the reservoir properties. Over most of the basin, early diagenesis (eodiagenesis) is dominated by calcrete development but, towards the basin centre, non-ferroan dolomite associated with early evaporitic sulphate cements that appear to have been deposited in an inland sabkha or playa environment are important. Later diagenesis (mesodiagenesis) is characterized by selective framework grain dissolution of feldspars, and anhydrite cementation and subsequent dissolution—processes that have locally yielded significant secondary porosity. However, in some cases this secondary porosity has been destroyed by the precipitation of late manganiferous ferroan calcite and ferroan dolomite. Quartz cements are locally important. Rocks near the present-day outcrop have been affected by weathering processes (telodiagenesis) that have resulted in decalcification, and the precipitation of kaolinite, illite and iron hydroxides. The key factors determining the permeability of the sandstones are the original grain size and degree of sorting, the precipitation and subsequent removal of anhydrite, and the extent of early and late carbonate cementation, framework grain dissolution and overgrowth.

Sedimentologic Controls on Production in Giant Eolian Reservoirs in Western U.S. Overthrust: ABSTRACT

The Jurassic Nugget Sandstone is a 1500-ft (457-m) thick eolian reservoir that produces prolifically throughout the Wyoming Overthrust belt. Nugget fields exhibit exceptional, but predictable reservoir anisotropy. Based on detailed core, log, and production analyses, this study documents Nugget reservoir behavior as a strongly layered system with preferred directional permeability. Anschutz Ranch East and Painter Reservoir fields contain numerous fieldwise vertical permeability barriers that are interpreted as amalgamated inland sabkhas (interdunes) associated with significant diastems. The inland sabkhas contain internal erosion surfaces and abundant eolian ripples, and they are commonly disturbed by burrowing or salt growth. Carbonate and silicate cements render the inland sabkha deposits tight, creating vertical permeability barriers (K/sub v/ less than or equal to 0.001 md). Strongly preferred directional permeability parallels dune strike. Dune orientations determined from dipmeter logs and oriented cores relate directly to production rates and premature breakthrough of injected fluids. Preferred permeability along the predominant dune axis can be 5-50 times greater than permeability across dune cross-bedding. Detailed well data documenting dune orientation and diastems should be used early in field development to determine appropriate spacing and the well pattern. By incorporating these concepts into a reservoir management plan, eolian reservoirs can be moremore » efficiently exploited.« less

SOME HOLOCENE GEOMORPHOLOGICAL AND SEDIMENTOLOGICAL OBSERVATIONS FROM OMAN AND THEIR PALAEOGEOLOGICAL IMPLICATIONS

Observed exhumed Pleistocene river channel conglomerates now standing as ridges, and inland sabkha sedimentological structural phenomena from Oman, are discussed. Their significance as tools in the interpretation of similar palaeogeological environments is considered. Correlation with similar channel fills elsewhere in Arabia and Iran indicates aggradation as having occurred between 35,000–7,000 yrs BP and suggests that this was principally by sustained flow during pluvial phases accompanying the last global glaciation, (at least in this part of the Middle East). Elevations of the now inverted channels above their deflated desert surroundings are used for calculating deflation rates, and reservoir porosity‐permeability characteristics of similar ancient deposits are considered. Additional and new data on halite crust structures from the Umm‐as‐Samim inland sabkha are presented mainly in photographs backed by factual data which are commented upon; sabkha formation probably commenced about 4,500 yrs BP. The preservation of similar origin halite deposits in the stratigraphic record is briefly discussed.This note is intended to augment data on desert environments that appear to have either had passing mention, or simply recording without assessment of their significance as tools or indicators in the interpretation of similar palaeogeological environments. It is the hope that the observations recorded here will stimulate further work on these and other Holocene phenomena in the region concerned and also elsewhere, together with dissemination of results, so that implications to various aspects of applied geology can be better evaluated and understood.

Isotope hydrology of inland sabkhas in the Bardawil area, Sinai

The changes in stable isotope composition of inland sabkhas can throw light on the hydrologic mechanisms which operate in these systems. Inflow waters were found to be of meteoric origin. Immediately after local rain, water drains from surrounding sand dunes onto the top of the salt crust, dissolving it. Further inflow of waters keeps the sabkhas inundated for weeks, but the different sabkhas were found to be open to varying degrees to the inflow of groundwaters and to outflow of brines into bottom sediments.

Description and Mode of Formation of the Supratidal Evaporite Facies in Northern Sinai Coastal Plain

ABSTRACT In the Northern Sinai coastal plain, to the south of the Bardawil lagoon, two types of sabkhas occur: coastal sabkhas or salt flats connected at present to the lagoon and flooded occasionally by lagoon water, and inland sabkhas cut off from the lagoon by sand dunes. At present lagoon beach sabkhas are under the influence of lagoon waters. The evaporitic minerals forming in them depend mainly on the hydrography of the lagoon and especially along the shoreline reaches of the lagoon. Inland sabkhas on the other hand are presently under the influence of groundwater discharging to them after rainy periods, which redissolves part of the evaporitic minerals (halite) precipitated in earlier evaporitic cycles. In sabkhas in which carbonate sediments are in contact with brines, arid zone suprat dal diagenesis takes place, thus causing the formation of diagenetic dolomite. In other sabkhas only gypsum and halite occur. It is concluded that the evaporitic facies developed in the different sabkhas depend primarily on the salinity of the lagoon water, the type of host sediment in the sabkha, and the extent of flushing of the sabkha by groundwater.