Interdune Environments Research Articles

Diagenetic characteristics of the Jurassic Navajo Sandstone in the Covenant oil field, central Utah thrust belt

The Jurassic Navajo Sandstone core in the Covenant field includes eolian dune interbedded with carbonate playa lake and fluvial interdune facies. Dune facies samples are bleached but not depleted in iron; bleached dune facies outcrop samples are depleted in iron. Bleached dune facies in the core samples contains ferroan dolomite, quartz overgrowths that do not completely fill pore spaces, grain-coating and pore-filling illite, coarse-grained gray hematite, kaolinite, and trace pyrite. Reddish brown interdune facies are typically very fine-grained sandstone and siltstone and contain dolomite and ferroan dolomite cement, illite pore-filling, and very fine-grained, red hematite. Diagenetic mineralogy and chemical compositions overlap the mineralogy and compositions of outcrop samples. The carbon and oxygen isotopic composition of dolomite in interdune facies and adjacent dune facies is derived from groundwater discharge modified by evaporation in a playa lake interdune environment, not from interaction with hydrocarbons. The iron in bleached dune facies is incorporated in coarse-grained hematite, ferroan dolomite, and trace pyrite. The bleached diagenetic mineral association of ferroan dolomite-hematite-pyrite with is metastable relative to more reducing conditions produced by petroleum. The reservoir temperature of 188F (87C) is too high for bacterial sulfate reduction and too low for geologically significant thermochemical sulfate reduction accounting for the association of abundant in produced water and trace pyrite in the core.

Evidence for Pleistocene wet aeolian dune and interdune accumulation, S. Pedro da Maceda, north‐west Portugal

AbstractOutcrops and cored/counter‐flushed boreholes in the coastal area between Espinho and Aveiro (north‐west Portugal) were investigated to reconstruct the changing patterns of sedimentation during the Late Pleistocene–Holocene. To obtain a common comparison basis, the grain‐size data from outcrop and borehole samples were analysed. The outcrops and the cored parts of the boreholes were dated by radiocarbon and optically stimulated luminescence. The results show that, on top of pebble‐rich beds of fluvial origin, a wet aeolian dune and interdune environment was active during the later part of the Pleistocene, turning to dry aeolian at the transition to the Holocene. The data indicate also that aeolian accumulation was controlled by vegetation changes (climate) and groundwater table fluctuations. During the Holocene, a podzol formed on the Pleistocene dunes and extensive vegetation precluded major aeolian accumulations. Remobilization of sand started again because of human deforestation and – last but not least – the Little Ice Age.

Feature: The sedimentary signature of deserts and their response to environmental change

Desert sedimentary systems comprise a variety of related sub‐environments including aeolian dunes, intervening interdunes, sandsheets, salt flats, playa lakes, ephemeral fluvial systems and alluvial fans. These are highly sensitive, and undergo subtle but systematic morphological and sedimentary adjustments in response to externally‐imposed environmental change. This article presents a dynamic model explaining how desert successions – particularly aeolian dune and interdune environments – are determined both by intrinsic sedimentary behaviour, such as dune migration, and by the imposition of externally‐forced changes such as climate change.

Implications to Exploration of Porosity Relationships and Paragenetic Sequences, Jurassic Navajo (Nugget) Sandstone, Utah and Southwestern Wyoming: ABSTRACT

We have studied in outcrop and in the subsurface the reservoir characteristics and diagenesis of the Early Jurassic, eolian, Navajo (Nugget) Sandstone in Utah and southwestern Wyoming. Principal topics include: texture, framework constituents, intergranular and intragranular cements, matrix, directional porosity, porosity types, and hydraulic conductivity. Present characteristics of the sandstone are related to variations in dune and interdune environments, fluctuating ground-water chemistry, and postdepositional environments. Diagenesis, in which an open-system diagenetic model is considered, superimposes and is influenced by these variations and events. The sandstone was deposited principally in dune and interdune settings. Surface and/or near-surface cementation, mostly by grain overgrowth and calcite from ground-water solutions, consolidated the sediment. Thereafter, the succession was uplifted, eroded, and buried by Middle Jurassic formations. During the Late Jurassic through Eocene, the sandstone was affected by compressional folding and thrust faulting in central and northern Utah and southwestern Wyoming. During the Tertiary, extensional deformation occurred. Petrographic criteria in thin sections indicate that secondary leached porosity generally is common to dominant in surface, near-surface, and possibly in deep subsurface sequences. Variations in porosity and volume of cements with depth exist and are correlative in all areas studied. Porosity changes with depth, as well as the volume of cements, are the result of downward-decreasing surface leaching of intergranular and intragranular cements, creation of secondary porosity, effects of initial stratification types, and facies changes. Compaction of the sandstone due to mechanical rearrangement of detrital grains and intergranular pressure solution played little or no role in modification of porosity or hydraulic conductivity. Likely, they account for not more than 5% of the porosity reduction. Greatest porosity reduction (16%) was by cementation. Present mean total porosity is 19%, ranging from 3 to 35%. End_of_Article - Last_Page 952------------

Depositional Environments and Regional Stratigraphy of Jurassic Norphlet Formation in South Alabama: ABSTRACT

In the western Gulf coastal plain area the Norphlet Formation is typically characterized by nonmarine and red bed lithofacies. In south Alabama, the Norphlet consists of an updip conglomerate, a basal shale, red beds overlying the shale, and an upper quartzose sandstone, the Denkman Member. The Norphlet unconformably overlies either salt, anhydrite, red beds, or Paleozoic rocks. The Smackover Formation overlies the Norphlet with a sharp contact over most of south Alabama, except in parts of Mobile County where the contact is gradational. The conglomeratic lithofacies is discontinuous in areal extent, and is present in cores from Escambia, Monroe, and Wilcox Counties. It consists of red and gray sandstone, conglomerate, and conglomeratic sandstone. The shale lithofacies also appears to be discontinuous in areal extent, and is present in cores from Escambia County. It consists of mostly black shale, with some brown and red shale. The red bed lithofacies was penetrated in wells in Escambia and Clarke Counties. It consists of red, brown, and gray, very fine to coarse-grained sublitharenite and subarkose, with an average composition of 64% quartz, 13% feldspar, 8% rock fragments, and 10% matrix. It is characterized by low-angle planar cross-beds and discontinuous laminae, along with interbedded silt and coarse sand. The qu rtzose lithofacies (or Denkman Member) is present in cores from Mobile, Baldwin, Escambia, Clarke, Choctaw, and Washington Counties. It attains a thickness of from 400 to over 700 ft (122 to over 213 m) in parts of Choctaw, Washington, and Mobile Counties, and thins to the northeast and east (Clarke, Monroe, Conecuh, and Escambia Counties) where Norphlet red beds and conglomerates predominate. The quartzose lithofacies consists of gray and brown, very fine to medium-grained subarkose with an average composition of 76% quartz, 12% feldspar, 3% rock fragments, and 2% matrix. It is characterized mainly by low to high-angle planar cross-beds, and also contains slump structures, wavy discontinuous laminae, and massive intervals. Norphlet deposition in south Alabama occurred in an arid climate. The lower shale probably was deposited in lagoons or mud flats left from a retreating hypersaline sea which had deposited the Louann salt. Accompanying the retreat of this sea were climatic and/or tectonic changes which resulted in clastics being shed from exposed paleo-highs. Initial clastic deposition occurred in alluvial-braided stream environments which are represented by sediments of the conglomeratic and red bed lithofacies. These sediments were reworked into downdip areas and deposited in desert dune and inter-dune environments. A transgression near the end of Norphlet time resulted in reworking of underlying sediments and deposition in intertidal environments. These deposits may be partial landward equivalents o seaward Smackover carbonates. Dune, interdune, and intertidal environments are represented by the quartzose lithofacies or Denkman Member. Basement paleo-highs not only were a source of sediments but also controlled Norphlet deposition in that the formation thins or is absent over them. The Norphlet Formation is an important reservoir in south Alabama. Stratigraphic relations indicate that lower Smackover Formation carbonate mudstone provide the petroleum source rocks. Reservoirs are facies selective, occurring mainly in Norphlet intertidal, eolian, and braided-stream deposits. Traps are due to a combination of favorable stratigraphic, structural, and diagenetic development. End_of_Article - Last_Page 1690------------