Algal Packstone Research Articles

Bio-lithofacies and diagenesis in the early-middle oligocene of Abu Dhabi, United Arab Emirates

The Early to Middle Oligocene is missing throughout much of the Arabian Peninsula. Only in the Oman Mountains and related linear NW-SE trending mountains are these sediments found. In the United Arab Emirates shallow water carbonates of the Asmari Formation (Early to Middle Oligocene) range from 435–481 m (1427–1578 ft), cropping out at the Jabal Hafit area near Al Ain. Detailed measured sections, sampling and thin section analysis show these carbonates comprise seven distinct facies: 1) Nummulitic Packstone, 2) Foraminiferal Wackestone/Packstone (non-Nummulitic forams), 3) Echinoderm/Red Algal Packstone, 4) Coral Framestone, 5) Peloidal Packstone, 6) Mudstone/Wackestone, and 7) Dolomite. Diagenetic events which have affected the Oligocene section include early cementation, formation of micrite envelopes, inversion of original aragonite and high Mg-calcite fabrics (i.e., biogenic tests and early marine cements) to low Mg-calcite, leaching of tests, dolomitization, stylolitization and fracturing, late diagenetic coarse calcite spar cementation, emplacement of bitumen within stylolitic seams and finally, hematite and pyrite staining. A depositional model has been proposed based on the fossil and lithofacies assemblages which suggests that a deep, outer shelf, quiet water lagoon supplies peloids to the back-reef, reef and fore-reef facies as well as the shallow open marine facies of the inner shelf. A short-lived sea level low is believed to have occurred, where continental waters manifested their presence in rare chertification and partial to complete dolomitization of some samples.

Carbonate Bank Sedimentation in a Volcaniclastic Arc Setting: Lower Carboniferous Limestones of the Eastern Klamath Terrane, California

ABSTRACT Carboniferous volcaniclastic-arc deposits of the eastern Klamath terrane, California, include Late Visean/Namurian limestone lenses that formed as small carbonate banks. The limestone lenses, within the Bragdon and Baird formations, reach 17 m in thickness and 1.2 km in length. Slope deposits consist of argillaceous spiculitic wackestone, and bank-edge deposits include ooid grainstone, Striatifera packstone, argillaceous phylloid algal packstone, and argillaceous skeletal packstone. Bank-interior deposits include skeletal wackestone/packstone and argillaceous sandy mudstone. The limestone lenses overlie proximal deltaic deposits of thick-bedded volcaniclastic sandstone and conglomerate. Carbonate banks developed on delta lobes during intervals of minimal clastic sedimentation, ossibly related to sea-level rise and volcanic quiescence. The carbonate banks were short-lived depositional systems, and they were covered by prograding deposits of younger volcaniclastic sands.

Early Permian (Middle-Late Wolfcampian) phylloid algal/Tubiphytes bioherms and associated facies along the margin of the Orogrande Basin, Hueco Mountains, west Texas

Middle-Late Wolfcampian phylloid algal/Tubiphytes biohermal complexes have been found exposed in western outliers of the Hueco Mountains of far west Texas. Paleogeographically, the bioherms are located along the fault-controlled shelf margin between the Late Paleozoic Diablo Platform and Orogrande Basin. Although Virgilian and Early Wolfcampian phylloid algal mounds are well-known from the Hueco and Sacramento Mountains, outcropping Middle-Late Wolfcampian bioherms have not been described previously from the Orogrande Basin area.The biohermal complexes are exposed in three large outliers that lie about 3 miles west of the main Hueco Mountains and extend for about 12 miles in a north-south direction. The shelf margin complexes are in the Hueco Canyon Formation and correlate to well-bedded shelf facies in the main Hueco Mountains based on fusulinid biostratigraphy.The phylloid algal/Tubiphytes shelf margin bioherms contain an upward shallowing facies succession, which consists of, in ascending order: (1) phylloid algal wackestone-bafflestone, (2) phylloid algal bafflestone-packstone, (3) phylloid algal-fusulinid bafflestone-packstone, and (4) Tubiphytes boundstones and Tubiphytes-fusulinid-phylloid algal packstones and grainstones. Unlike some previously described Wolfcampian phylloid algal buildups, the phylloid algal mound facies in these buildups contain only rare calcisponges, heliosponges, and marine radial fibrous cements. On the crest of the southern outlier there occurs a rather different type of bioherm, which contains nodular boundstones that are composed of encrusting red algae and bryozoans, and in which calcisponges are common. That bioherm is thought to be slightly younger in age than the phylloid algal/Tubiphytes bioherms, and it might also have been formed in a deeper-water setting.Bordering the phylloid algal/Tubiphytes bioherms on the seaward side are overlapping tongues and channels of lithoclastic-skeletal debris and skeletal grainstones and packstones. Some of these forereef units extend seaward into slope facies, which consist of dark-gray cherty limestones that generally lack skeletal fossils, but contain a rich ichnofossil assemblage in the shallower upper slope beds. Backreef facies consist mainly of skeletal-peloidal packstones and wackstones.The Hueco Mountains outlier exposures are significant because: (1) they establish the presence of a Middle-Late Wolfcampian shelf margin with distinct topographic relief in the southern Orogrande Basin, and (2) they provide an easily accessible field laboratory to study Middle-Late Wolfcampian shelf-to-basin facies relationships and shelf margin bioherms. Middle-Late Wolfcampian shelf margin bioherms are of particular interest because they represent an important transitional stage in the evolutionary history of Late Paleozoic reef communities, and because they form important petroleum reservoirs just to the east in the Delaware and Midland Basins.

Rival Producing Trends in Burke County, North Dakota

The Rival beds are a shallowing-upward limestone to evaporite sequence in Burke County, North Dakota. Rival oil production in this part of the basin occurs from shoreline carbonates and pod-shaped algal banks which developed basinward of shorelines. Shoreline carbonates are predominantly grainstones which produce in Rival and Foothills fields. Porosity is intergranular and vuggy. The updip trap facies in these shoreline trends is anhydrite. Occluding cements are anhydrite, baroque dolomite, and prismatic calcite spar. Cumulative oil production is over 13 million bbl in the Rival field, where good porosity, permeability, and an effective trap are present. Algal bank sediments are productive in Black Slough, Tioga, and North Tioga fields. Peloidal, skeletal, and algal packstones and grainstones in these fields contain intergranular, moldic, and vuggy porosity. Occluding cements are fibrous calcite, prismatic calcite spar, and baroque dolomite. Impermeable mudstones and wackestone surround the algal banks and constitute the trap facies. Rival oil production from the Tioga fields along the Nesson anticline is over 14 million bbl. Rival potential exists for both shoreline and algal bank plays in the southern and western portions of Burke County, where depositional trends cross well-defined paleostructural features.

Palo Pinto (Missourian) Algal Limestone Buildups as Hydrocarbon Reservoirs, Conley Field, Hardeman County, Texas: ABSTRACT

Mississippian and Pennsylvanian carbonates are important hydrocarbon reservoirs in the Hardeman basin of north Texas. The basin axis extends northeast-southwest, and stratigraphy at Conley field indicates that the area was structurally high during both the Mississippian and Pennsylvanian. The Palo Pinto Formation at Conley field is composed mainly of platy algal packstones with subordinate fossiliferous shales. The algal limestones thicken over the crest of the ancient structural high, where the low lime-mud content and the abundance of platy algae indicate that the depositional environment for the Palo Pinto was shallow (less than 100 ft in depth) and current-swept marine in character. Local thickening of the Palo Pinto can be explained as growth of platy algal bafflestones which nucleated on the crests of paleostructural highs. The shales indicate periodic inundation accompanied by renewed terrigenous clastic influx. The highest parts of the carbonate buildups were altered by freshwater diagenesis during episodic periods of emergence. Dissolution of metastable allochems led to the formation of moldic porosity. Subsequently, during burial diagenesis, occlusion of pore space by calcspar cements, neomorphism, pressure solution, and some replacements occurred. The best porosity and permeability occur in packstone and grainstone facies, indicating that the reservoir mainly is controlled bymore » depositional processes and only altered to an extent by diagenesis. Fracture porosity is not a major factor in this reservoir.« less

Depositional and Diagenetic Controls on Reservoir Development in a Pennsylvanian Phylloid Algal Buildup: ABSTRACT

Reinecke field is one of a series of fields in the Horseshoe atoll (Midland basin, west Texas) that produce from Pennsylvanian phylloid algal buildups. Examination of cores from the Reinecke field indicates that porosity in the field is controlled largely by two factors: (1) leaching of biotic constituents and matrix; and (2) dolomitization. These two factors have led to development of a complex reservoir. Six major rock types have been identified from the field. These are in order of abundance: (1) medium-crystalline, ferroan dolomite, (2) echinoderm-foram wackestone, (3) echinoderm-fusulinid packstone-grainstone, (4) phylloid algal-bryozoan-foram packstone, (5) coarsely crystalline, high-porosity, ferroan dolomite, and (6) shale. Reservoir porosity and permeability are controlled by the distribution of rock types. In the southern end of the field, two areas of differing character occur: one in which the rocks are more than 80% dolomite and a second in which the rocks consist of interbedded dolomite and fossiliferous lime wackestone to grainstone. Most of the oil from the field is produced from these two areas. A third reservoir type that rims the northern half of End_Page 115------------------------------ the field consists largely of echinoderm-fusulinid packstone and grainstone interbedded with phylloid algal packstone. The remainder of the field has very little data available. Production from the northern half of the field is generally low. Laterally continuous, high-porosity dolomites appear to be present throughout the field. These dolomites can transmit large volumes of fluid and are responsible for a water breakthrough problem in the field. As a result of complex variations in depositional and diagenetic facies, the reservoir is a laterally and vertically heterogeneous rock body with complex production problems. End_of_Article - Last_Page 116------------

Dolomitization by Spray-zone Brine Seepage, San Andres, Colombia

ABSTRACT Dolomitization of Pleistocene carbonates on San Andres Island has occurred as a result of brine seepage in the spray zone. Brines have formed by supratidal evaporation of surf spray and sea water trapped in splash pools on a rocky coast line where the solutions percolated downward through metastable algal packstone. The formation of evaporites and dolomite is terminated when brines are diluted by meteoric water. The dolomitized algal limestone grades laterally into unaltered algal limestone exhibiting typical cementation by sparry calcite. The algal limestone is accreted to the weathered surface of a cliff-forming limestone of Miocene age.