Evaporite Basin Research Articles

Geomorphology and Quaternary geology of the Dakhla Oasis Region, Egypt

Dakhla Oasis (25.5°N, 29°E) occupies a structurally localized depression at 90–140 m above sea level, ∼1200 km 2 in area, below a 300 m escarpment bordering the Libyan Plateau, Western Desert of Egypt. Semi-arid intervals of the Quaternary period generated eight sedimentary formations, separated by erosion during hyper-arid intervals. Sediments comprise three generations of colluvial/fluvial fanglomerates, two generations of tabular spring-laid clastic and chemical sediments, two generations of mound springs and basinal sediments. of fluvio-lacustrine, evaporitic, pluvio-aeolian and aeolian origins. Discussion of these sediments is organized according to geomorphic region, from north to south, plateau, scarp and piedmont, lowland and cuesta plain. Chronological evidence is restricted to many radiocarbon dates of Holocene cultural material associated with playa sediments (9−4.5 ka), a Th U isochron age of ∼62.0 ±7.6 ka for basinal evaporites, and two Th U ages of ∼176 and ∼170 ka for a boulder of derived travertine. The regional Quaternary sequence is reconstructed from stratigraphic and geomorphic relationships of the sediments and erosion surfaces. It is broadly similar to sequences earlier reconstructed in the topographically similar Kharga Oasis region 150 km to the east, and Kurkur Oasis, 400 km to the south-southeast. Speculations on chronology and driving mechanism are offered in conclusion.

The combined application of organic sulphur and isotope geochemistry to asses multiple sources of palaeobiochemicals with identical carbon skeletons

Five immature sediments from a Messinian evaporitic basin, representing one evaporitic cycle, were studied using molecular organic sulphur and isotope geochemistry. It is shown that a specific carbon skeleton which is present in different “modes of occurrence” (“free” hydrocarbon, alkylthiophene, alkylthiolane, alkyldithiane, alkylthiane, and sulphur-bound in macromolecules) may have different biosynthetic precursors which are possibly derived from different biota. It is demonstrated that the mode of occurrence and the carbon isotopic composition of a sedimentary lipid can be used to “reconstruct” its biochemical precursor. This novel approach of recognition of the suite of palaeobiochemicals present during the time of deposition allows for identification of the biological sources with an unprecedented specificity.

Discussion on sequence stratigraphy of carbonate–evaporite basins: models and application to the Upper Permian (Zechstein) of northeast England and adjoining North Sea

I. G. Goodall , G. M. Harwood , A. C. Kendall & T. McKie write: In his recent reappraisal of the stratigraphy of the English Zechstein, Tucker (1991) presents an elegant model of the evolution and stratigraphical relationships of the various formations in this section. However, some aspects of the interpretation deserve further discussion; namely the duration and relative completences of the sequences, the relationships of the Trow Point Bed (and underlying megabreccia-slide) and the Edlington Formation within the alternative stratigraphy, and the relative contributions of climatic and eustatic controls on evaporate mineralogies and sequence development. Duration and completeness of sequences . The 5 Ma timespan of the Zechstein ( Menning et al. 1988 ) falls within the periodicity range of third order ‘eustatic’ cycles (1–10Ma), implying that the sequences described by Tucker are high frequency fourth order sequences ( sensu Mitchum & Van Wagoner 1991 ). Given a period of 0.1–0.2 Ma for fourth order cycles it is evident that the seven sequences identified by Tucker do not represent all the potential eustatic cycles during Zechstein deposition. The stratigraphical record is likely to be most complete during the third order sea-level rise i.e. within the more carbonate-dominated lower Zechstein, where Tucker’s sequence model is most applicable. In contrast, the upper part of the Zechstein section must have been largely deposited during a third order sea-level fall. It is within this more evaporite-dominated section (sequences 5, 6 and 7) that the record of the ‘hidden/missing’ fourth order eustatic cycles lie. This interval may contain the

Recognition of paleobiochemicals by a combined molecular sulfur and isotope geochemical approach.

Study of organic matter in immature sediments from a Messinian evaporitic basin shows that consideration of structures, modes of occurrence, and carbon isotopic compositions of free and sulfur-bound carbon skeletons allow identification of biochemical precursors. Detailed information concerning biotic communities present during deposition of sediments can be retrieved in this way. Moreover, unprecedented biochemicals were recognized; these extend the horizon of biomarker geochemistry.

A new look at the structural geology of the southern side of the Central and Eastern High Atlas mountains

We give a general description of two evaporite basins discovered, one under, and the other south of the Lower Jurassic carbonate platform which fringes the Atlas Gulf in the south. The larger of these basins lies in the triangle Tazzouguert, Aoufouss, Tarda. The smaller, whose extent is difficult to determine (it being considerably deformed and partially covered over by the southward sliding of the Liassic carbonate platform), lies north of Tinerhir and Ifer. Marl and evaporite Middle Liassic deposits from this smaller basin form a tectonic window in the massive limestones of the Liassic carbonate platform at Tisgui (Todrha gorges). This window clearly shows that the zone in question was affected by southward sliding. To the East of Tazzouguert going towards Bouanane the carbonate platform backs directly onto the African craton.

3-D seismic and horizontal wells

The Rainbow evaporite basin, centered on latitude 58°N and longitude 119°W, is situated approximately 900 km from Calgary in the remote northwest corner of Alberta, Canada. It is approximately 30 × 30 km in areal extent with a relatively uneventful surface topography which is covered by muskeg and stunted coniferous forest. The climate is continental with severe winters (temperatures dip to −50° C or lower).

Sequence stratigraphy of carbonate-evaporite basins: models and application to the Upper Permian (Zechstein) of northeast England and adjoining North Sea

The successions of carbonate-evaporite basins, which are periodically cut off from the world ocean, are considered in terms of their sequence stratigraphy. Two basin types are distinguished: those where incomplete drawdown takes place and those showing complete drawdown and wholesale basin desiccation. It is argued that, following relative sea-level falls, sequences begin with the evaporites, precipitated as marginal lowstand gypsum wedges in the first basin type and as lowstand basin-centre halite fills in the second. The evaporites pass up into carbonate sediments which are mainly deposited on shallow-water platforms around the basin during transgressive and highstand systems tracts. The concepts and models developed are applied to the Zechstein (Upper Permian) strata of northeast England and adjoining North Sea. Seven sequences are proposed, with some containing thin parasequences. The sequence approach to carbonate—evaporite basins, which considers both basin margin and basin centre facies, gives a more encompassing perspective of sedimentation than the traditional cycle concept, with its emphasis on the basin centre.

AN ISOLATED CARBONATE BANK IN THE ZECHSTEIN MAIN DOLOMITE BASIN, WESTERN POLAND

Isolated carbonate banks in starved basins are very attractive targets for hydrocarbon prospecting. In the Zechstein (Late Permian) Main Dolomite (Ca2) Basin of Western Poland, six such banks or isolated platforms have been penetrated by wells, and gas and/or oil has been found in all of them. The largest is the Chartów Platform. which lies a few tens of kilometres from the edge of the carbonate shelf and shows well‐defined facies zonation, Three shallowing‐upward cycles may be distinguished in the bank‐edge sands, while the central (lagoonal) region and lower slope show a single deepening‐upward sequence. Local rapid subsidence, usually balanced by the rate of deposition, is inferred for the edge of the Chartów Platform: this subsidence was not balanced in other zones. The driving force for increased local subsidence may have been related to subtle block movements, and the break‐up of the P21 (Werra) evaporite platform. The rate of increased subsidence fluctuated: pulses of relatively rapid subsidence disturb the sequence, which was controlled by sea‐level fluctuations. Differential subsidence and sea‐level changes are common during the evolution of evaporite basins, and isolated platforms similar to the Chartów structure may be common in other evaporite basins, where isolated banks are located between the central and marginal areas.

Trans-Aravalli Vindhyan Evaporites under the Semi-desertic plains of Western India - Significance of Depositional Features

Abstract A large evaporite basin of upper Proterozoic and early Cambrian age exists in the sub-surface of western part of India, now represented by the semi-desertic plains of Punjab-Haryana-Rajasthan and extending beyond the Salt Range of Pakistan. This has come to light in recent years by intensive exploratory drilling. Under a thick blanket of Quaternary sediments (305-330 m) of southwest Punjab (Faridkot and Ferozepur districts) and north-west Haryana (Sirsa district), in contiguity with Sriganganagar district of Rajasthan, there occurs in the sub-surface huge thickness of sedimentary rocks, essentially sub-horizontal in disposition. Part of this sedimentary sequence consists of halite and associated evaporites (polyhalite, anhydrite, limestone and dolomite), attaining a cumulative thickness of over 600 mat Hansera in Rajasthan. Synthesis of available data suggests that the present evaporite sequence constitutes a marginal facies of a larger evaporite basin existing to the west.

Dolomitizing Seas in Evaporitic Basins: A Model for Pervasive Dolomitization of Upper Miocene Reefal Carbonates in the Western Mediterranean

Petrographic, stratigraphic, and stable-isotopic data from a dolomitized upper Miocene reef complex on Mallorca, Spain, coupled with the presence of extensive Messinian subtidal evaporite deposits throughout the western Mediterranean suggests that Messinian evaporitic brines were responsible for dolomitization. Thermodynamic reaction-path modeling was undertaken to more rigorously and quantitatively demonstrate the dolomitizing potential of this evaporitic system. These calculations provide maximum amounts of dissolution or precipitation (moles/L) to maintain a specified fluid-rock equilibrium. Significant amounts of dolomite can be created when brines ar concentrated by evaporation prior to reaction with calcite. Heavy stable isotopes of Mallorcan dolomites are consistent with an evaporitic origin; however, lighter stable isotopes do not preclude this model. Calculations show that mixing evolved brines with unaltered seawater or continental waters produces a suite of fluids with much greater dolomitization potential than seawater and oxygen-isotope signatures approaching those of seawater. This evaporitic-basin model serves as one hypothesis for the many dolomitized upper Miocene reef complexes around the western Mediterranean, and may be applicable to many older Phanerozoic carbonates associated with basinal evaporites.

Structure, Stratigraphy, and Climate of the Mesozoic Chignecto Subbasin, Bay of Fundy, Canada

The Chignecto subbasin is one of three Triassic/Jurassic subbasins in the Bay of Fundy rift system of southeastern Canada. Although no wells have been drilled in the subbasin, offshore seismic data and onshore outcrop data show that the basin contains typical rift structures and stratigraphy. The Chignecto subbasin is an asymmetric rift basin bounded on the west by a series of gently to moderately dipping normal faults. The seismic data show that the total heave on these boundary faults locally exceeds 10 km. Most strata within the basin dip gently to the west toward the boundary faults. Field data show that a divergent wrench fault zone composed of numerous strike-slip, oblique-slip, and normal faults bounds the Chignecto subbasin on the south. The normal faults bounding the basin on the west and the divergent wrench fault zone on the south are reactivated Paleozoic compressional structures. Major stratigraphic features in the Chignecto subbasin include an unconformity that subdivides the basin strata into pre- and syn-rift sequences and an asymmetric arrangement of sedimentary and seismic facies and corresponding lithologies. The Triassic/Jurassic syn-rift strata within the basin thicken toward the western boundary faults. Coarser-grained strata of alluvial-fan and fluvial origin interfinger with finer-grained stratamore » of fluvial and lacustrine origin near the boundary faults. Eolian deposits and evaporites in adjacent Mesozoic rift basins indicate an arid climate for the Late Triassic/Early Jurassic. Large-amplitude reflections observed within the western half of the basin probably represent high-velocity evaporites or carbonates deposited within the deepest part of the Chignecto subbasin.« less

Tectonic and Climate Changes Expressed as Sedimentary Cycles and Stratigraphic Sequences of the Paleogene Lake Uinta System, Central Rocky Mountains, Utah and Colorado

Lake Uinta strata record both long- and short-term changes in climate and tectonic regime. Late Paleocene to late Eocene deposits are characterized by evaporite units (including halite and bicarbonate salts) and organically derived carbonate with extreme positive {delta}{sup 13}C and slightly negative {delta}{sup 18}O values that serve as evidence the lake was the center of a closed hydrologic system. Large reconfigurations of the lake system were tectonically induced and gave rise to relatively thick, lithologically distinct stratigraphic sequences. Simultaneous climate changes initiated very rapid lake level expansions and contractions as well as shifts in lake-water alkalinity and salinity (or chemistry) which resulted in the development of small- to large-scale sedimentary and stratigraphic cycles. Maastrichtian to earliest Eocene phases formed in local depressions (piggy back basins) on the thrust sheets, and in the incipient Uinta basin. Lake system reached its greatest aerial and volumetric extent in the middle and late Eocene and was centered in the foreland formed in front of high-angle reverse faults that bounded the rising Laramide structural blocks. At this time chemical precipitates, including basin centered carbonate and evaporite facies, formed during episodes of tectonically induced subsidence at the center of the clastic sediment-starved basin. Some fault-bounded marginsmore » of the Uinta basin are marked by synorogenic coarse debris that extends from the mountain front to the clastic sediment-starved lake. Tectonically induced stratigraphic sequences of the Lake Uinta system express environments for several million years whereas climatic cycles reflect much shorter episodes and very rapidly changing conditions.« less

Jurassic evaporitic deposits in Southern Tunisia: a climatically and tectonically controlled sedimentation

Jurassic evaporites in Southern Tunisia are Upper Lias to Bajocian in age and correspond to two lithologic units (Mestaoua and Krachoua Formations). Each of them represents a major sedimentary sequence corresponding to subaqueous evaporite basin, sabkha and shallow marine platform environments of deposition. Rapid lateral and vertical changes in facies and thickness, especially within Upper Lias evaporites (Mestaoua Formation) is related to an E-W normal fault. The latter generates a down faulted graben (Tataouine subsiding basin) bordered by two uplifted horsts (Tebaga mole and Libyan Craaton). Evaporites occured preferentially in the Tataouine basin which has acted as an evaporitic depocenter. Favourable climate conditions (arid period), together with tectonic framework, induced and strongly controlled this sedimentation. Eustatic fluctuations are responsible for transgressive episodes at the base of major sequences and are factors controlling evaporitic sedimentation.

Brine evolution and mineral deposition in hydrologically open evaporite basins

Brine evolution and mineral deposition in hydrologically open evaporite basins

Similarities in the Dolomitization of Upper Miocene Reef Complexes in Mallorca and the Las Negras Area, Spain: Possible Evidence for a Mediterranean Dolomitizing Event during the Messinian

Reef complexes in the Las Negras area and the island of Mallorca, over 600 km to the northeast, contain dolomite with remarkably similar stratigraphic distribution and petrographic characteristics. In both reef complexes dolomite occurs as 5-50 {mu}m euhedral cements and microcrystalline replacement of red-algal fragments and muds. In addition, anhedral, moldic-zoned dolomite cements (5-20 {mu}m) are abundant in the youngest reefs of both areas. All inter-reefal erosional surfaces are cross-cut by dolomite cements. Distribution of dolomite within the reefal sequences is controlled by (1) proximity to the youngest reef margin. Dolomite abundances decrease from 100% to 0% over a 10 km transect into the platform interior in Mallorca. Stratigraphic and petrographic timing support a dolomitization event following exposure of the reefs, during initial deposition of the onlapping Messinian sequence in Mallorca, and before Pliocene deposition in Las Negras. In both areas, dolomitization took place as a Messinian transgression covered the reefs. Evidence for multiple dolomitization events has not been found. Mallorcan dolomites have heavy stable isotopes suggesting saline dolomitizing fluids. One hypothesis for dolomitization invokes brines associated with the deposition of extensive Messinian basinal evaporites. An early Messinian evaporitic lowstand could concentrate marine brines, and with the ensuing transgression bringmore » them in contact with CaCo{sub 3} platforms, dolomitizing them. The similar styles and timing of dolomitization in these two distinct and distant reef settings suggest that dolomitization of late Miocene reefs around the western Mediterranean may have been genetically related to the Messinian salinity crisis.« less

Seismic facies of the Permian section of the Barents Shelf: analysis and interpretation

The Palaeozoic succession of the Barents Shelf has been investigated with data from only a few wells. However, a considerable amount of high-quality seismic data complements the sporadic well control, permitting an extensive seismic study of the three major intervals distinguished in the Permian section. The lowermost Interval I consists of an evaporitic sequence. Both vertical and horizontal gradations of the seismic facies are recognized and interpreted in terms of basin evolution. In the centre of the basin, a lower unit characterized by high-amplitude parallel reflections grades upwards to a mounded reflection-free upper unit. The mounds are interpreted as salt pillows overlying a lower unit with lithology dominated by anhydrite. A rather thick evaporite interval in basinal setting passes laterally to a mixed carbonaceous-anhydritic section on the margins and basinal highs. The thickness distribution and the areal extent of the seismic facies provide information on the configuration of the evaporite basin, on syn-sedimentary tectonism and on evaporite diagenesis. As a result of renewed transgression, the overlying Interval II was deposited in open-marine conditions on a shallow shelf. Belts and patches of seismic mounds, interpreted as carbonate build-ups, are widely spread on the basinal highs and on the basin margins. Depositional environments are inferred from the distribution of build-ups. During the progressive drowning of the shelf, a back-stepping belt of seismic mounds were deposited on the southern basin margin. This transgressive episode, which constitutes Interval III, culminated in the generalized deposition of deep-water facies.

Evaporite, carbonate, and siliciclastic transitions in the Jurassic sequences of southeastern Tunisia

Evaporite, carbonate and siliciclastic transitions occur within the Jurassic deposits of southeastern Tunisia. These facies are grouped into four major transgressive-regressive sequences corresponding to various environments of deposition. The latter include sabkha, subaqueous evaporite basin, carbonate tidal flats to shallow marine platform, bioherms and mixed siliciclastic ramp. Rapid lateral and vertical variations in thicknesses and facies are controlled by tectonic, climatic and eustatic factors. East-west and NW-SE fault systems generated a down-faulted graben (Tataouine basin) bordered by two uplifted horsts (Tebaga Mole and Libyan Craton) and have acted as an evaporite depocenter or as a siliciclastic trap. Eustatic-related transgressions occurring during Late Lias, Bajocian, Early/Middle Callovian, and probable Upper Callovian-Oxfordian have led to opening and/or deepening of the marine basin accompanied by carbonate sedimentation rapidly replacing evaporite or siliciclastic deposition. This Jurassic example not only confirms that tectonics and, to a lesser extent, climate largely controlled evaporite, carbonate, and siliciclastic transitions; it also demonstrates that sea-level changes may be another factor controlling such transitions in these ancient deposits.

Halite depositional facies in a solar salt pond: A key to interpreting physical energy and water depth in ancient deposits?

Subaqueous deposits of aragonite, gypsum, and halite are accumulating in shallow solar salt ponds constructed in the Pekelmeer, a sea-level salina on Bonaire, Netherlands Antilles. Several halite facies are deposited in the crystallizer ponds in response to difference in water depth and wave energy. Cumulate halite, which originates as floating rafts, is present only along the protected, upwind margins of ponds where low-energy conditions foster their formation and preservation. Cornet crystals with peculiar mushroom- and mortarboard-shaped caps precipitate in centimetre-deep brine sheets within a couple of metres of the upwind or low-energy margins. Downwind from these margins, cornet and chevron halite precipitate on the pond floors in water depths ranging from a few centimetres to {approximately} 60 cm. Halite pisoids with radial-concentric structure are precipitated in the swash zone along downwind high-energy shorelines where they form pebbly beaches. This study suggests that primary halite facies are energy and/or depth dependent and that some primary features, if preserved in ancient halite deposits, can be used to infer physical energy conditions, subenvironments such as low- to high-energy shorelines, and extremely shallow water depths in ancient evaporite basins.

Diagenesis and Porosity Development Associated with Major Sea Level Fluctuations, Upper Permian, Jameson Land, East Greenland: ABSTRACT

The Upper Permian of Jameson Land includes two major carbonate sequences, represented by the Karstryggen and Wegener Halvoe formations. The initial Karstryggen transgression led to the development of a shallow marine platform with structurally controlled evaporite basins (salinas) separated by stromatolitic, peloidal, or micritic carbonate depositional areas. The Wegener Havloe sequence reflects more rapid and extensive transgression with the deposition of three subcycles of fully marine, platform, or biohermal carbonates containing minor evaporites near the basin margins. Bioherms (bryozoan-brachiopod-marine cement mounds) show > 100 m of relief, indicating that large relative sea level changes were involved. Both the Karstryggen and Wgener Havloe cycles were terminated by major regressions, which led to karstic and/or fluvial incision of the underlying sequences. Not surprisingly, carbonate and evaporite diagenesis was greatly affected by these regional or eustatic sea level fluctuations. Evaporites dissolved or were replaced by calcite and celestite under the influence of meteoric waters. Limestones show collapse brecciation, grain leaching, soil development, and characteristic vadose and phreatic cements. Most significantly meteoric flushing led to massive dissolution of botryoidal marine cements (aragonite and probable high-Mg calcite) within biohermal facies on the Wegener Peninsula. This early porosity resurrection led to the preservation of porous biohermmore » core zones until hydrocarbon migration. Only late (posthydrocarbon), probably hydrothermal fluid flow led to cementation of the bioherm cores while expelling most of the reservoired hydrocarbons. If the sea level changes affecting the Greenlandic Permian are eustatic, then this study may provide significant clues to porosity development throughout the largely unexplored northern Zechstein basin.« less

Depositional and Diagenetic History of a Pennsylvanian Algal-Mound Complex: Bug and Papoose Canyon Fields, Paradox Basin, Utah and Colorado (1)

During the Middle Pennsylvanian (Desmoinesian), the Paradox basin was an enclosed, evaporitic basin consisting of a deep trough with a shallow shelf rimming its south and west side. During Desert Creek deposition, at least two large phylloid algal-mound complexes flourished on or at the edge of the shelf. One complex is now delineated by Aneth field and the other is partly delineated by Bug and Papoose Canyon fields. In the Bug-Papoose Canyon algal-mound complex of southeastern Utah and southwestern Colorado, carbonate mud mounds grew by accumulation of platy algal fragments, by baffling and trapping of fine sediment by the algae, and by precipitation of botryoidal aragonite cement between fragments. Extensive diagenesis of the accumulations began with syndepositional precipitation of botryoidal cement, inferred to have been aragonite, on phylloid algal plates, creating a topographically prominent, rigid framework containing abundant pore space. Brecciation during compaction created more pores. Parts of voids were subsequently filled by internal sediment and by calcite and gypsum cements. Finally, the algal-mound accumulations were extensively dolomitized and their porosity increased by dissolution. The relationship of these algal mounds to the Desert Creek shelf edge suggests that delineation of the shelf edge holds the promise of further discoveries of algal mounds as it is traced to the west and east of Bug and Papoose Canyon fields.