Algal Banks Research Articles

Stable Isotope Analysis of Antipatharian Diets from the Northwestern Gulf of Mexico

Antipatharians, or black corals, form a key component of the benthic fauna found throughout the Gulf of Mexico (GOM). In the northwestern GOM, they are a common member of the communities found on the natural relic coral—algal banks known as the South Texas Banks as well as on artificial reefs. They are known to provide important habitat for many ecologically and economically important species in the area but are relatively understudied. Here we present a study on their trophic ecology using stable isotope analysis of carbon and nitrogen from 2 species, Antipathes atlantica and Stichopathes luetkeni from a mesophotic artificial reef in close proximity to the South Texas Banks. We observed that a large proportion of the 2 coral’s diets was composed of detrital matter, likely driven by the continuous disturbance of the benthos by high velocity benthic currents common to the region that support a persistent nepheloid layer below 30 m. Both species also show a reliance on different members of the planktonic community, with A. atlantica consuming more micro and mesozooplankton compared to S. luetkeni. Comparative analysis between soft tissue and skeletal material also indicates that A. atlantica may change its diet on a seasonal basis, while S. luetkeni appears to rely on detrital matter consistently. This study represents the first assessment of the diets of these organisms and provides valuable insight on the trophic ecology of 2 common antipatharian corals in the GOM on natural and artificial reef ecosystems.

Revisiting the 'bank of microscopic forms' in macroalgal-dominated ecosystems.

Theoretical ecological models, such as succession and facilitation, were defined in terrestrial habitats, and subsequently applied to marine and freshwater habitats in intertidal and then subtidal realms. One such model is the soil seed bank, defined as all viable seeds (or fruits) found near the soil surface that facilitate community restoration/recovery. "Banks of microscopic forms" have been hypothesized in aquatic habitats and recent work from aquaculture has highlighted dormancy in algal life cycle stages. To reinvigorate the discussions about these algal banks, we discuss differences in life cycles, dispersal, and summarize research on banks of macroalgal stages in aquatic ecosystems that may be easier to explore with modern advances in molecular technology. With focus on seminal work in global kelp forest ecosystems, we present a pilot study in northern California as proof of concept that Nereocystis luetkeana and Alaria marginata stages can be detected within kelp forests in the biofilm of rocks and bedrock using targeted primers long after zoospore release. Considering the increased interest in algae as an economic resource, [blue] carbon sink, and as ecosystem engineers, the potential for "banking" macroalgal forms could be a mechanism of resilience and recovery in aquatic populations that have complex life cycles and environmental cues for reproduction. Molecular barcoding is becoming an important tool for identifying banks of macroalgal forms in marine communities. Understanding banks of macroalgal stages, especially in deforested habitats with intense disturbance and grazer pressure, will allow researchers and marine resource managers to facilitate this natural process in recovery of the aquatic system.

Modeling temporal variations of Gracilaria Greville and Hypnea J.V. Lamouroux (Rhodophyta) assemblages on a midlittoral reef platform at Piedade Beach, Pernambuco State, Brazil

The diversity of algal banks composed of species out the genera Gracilaria Greville and Hypnea J.V. Lamouroux have been impacted by commercial exploitation and coastal eutrophication. The present study sought to construct dynamic models based on algal physiology to simulate seasonal variations in the biomasses of Gracilaria and Hypnea an intertidal reef at Piedade Beach in Jaboatao dos Guararapes, Pernambuco State, Brazil. Five 20 × 20 cm plots in a reef pool on a midlittoral reef platform were randomly sampled during April, June, August, October, and December/2009 and in January and March/2010. Water temperature, pH, irradiance, oxygen and salinity levels as well as the concentrations of ammonia, nitrate and phosphate were measured at the sampling site. Forcing functions were employed in the model to represent abiotic factors, and algal decay was simulated with a dispersal function. Algal growth was modeled using a logistic function and was found to be sensitive to temperature and salinity. Maximum absorption rates of ammonia and phosphate were higher in Hypnea than in Gracilaria, indicating that the former takes up nutrients more efficiently at higher concentrations. Gracilaria biomass peaked at approximately 120 g (dry weight m-2) in March/2010 and was significantly lower in August/2009; Hypnea biomasses, on the other hand, did not show any significant variations among the different months, indicating that resource competition may influence the productivity of these algae.

The hunt for Cummingsella (Carboniferous, Chlorophyta)

Until recently Cummingsella was only known by two rare and puzzling species, erected on very limited material. The genus was therefore considered as representing a very uncommon and puzzling form that played no role in carbonate sedimentation. Recent studies of Viséan carbonates in the American Midcontinent have disclosed a prolific Cummingsella flora that indicates the proximity of an algal bank. Cummingsella can therefore be considered locally abundant, cosmopolitan (Europe, Australia, North America), ranging in age from the Tournaisian to the Namurian (Serpukhovian).

Structural variation in the brown alga Sargassum cymosum and its effects on associated amphipod assemblages.

The presence of diverse biological substrates adds complexity to coastal landscapes and increases the number of ecological niches that can be used by the mobile epifauna. Studies on the influence of structural complexity have focused mainly on algal host species, but there is little information about the influence of intraspecific structural variation on the associated mobile epifauna. In this work, we examined whether intraspecific variation in the brown alga Sargassum cymosum influenced the structure of amphipod assemblages on two shores with different wave exposure. At least 15 fronds were randomly sampled at Fortaleza and Perequê-Mirim beaches, on the Atlantic coast of São Paulo state, southeastern Brazil, and 12 variables were measured for each alga. The amphipods were identified and counted. The greatest structural variation in S. cymosum occurred within shores, whereas the differences between shores were mainly related to algal size. These characteristics influenced amphipod assemblages differently on each shore, with the greatest effects being associated with variables related to morphological complexity, such as holdfast size, the number and size of branches, and the extent of cover by sessile colonial animals. These findings show that monospecific algal banks are not homogeneous, and that morphological differences and interactions with other biological substrates can influence the mobile epifaunal assemblages.

Rhodalgal-bryomol temperate carbonates from the Apulian shelf (Southeastern Italy), relict and modern deposits on a current dominated shelf

Mound-shaped algal banks and associated bioclastic deposits have been investigated on the Apulian shelf, SE Italy, off Capo d’Otranto and Santa Maria di Leuca within a bathymetric range of 53–60m water depth. The bioclastic deposits form different sand-gravel skeletal assemblages; each one characterised by different associations and occurrence of prevailing organisms in relation to substratum types. These deposits lie on a lee shore and form rhodalgal and bryomol relict-modern deposits which originate from the banks’ erosion by means of bottom currents and storms. These play a significant role in reworking bottom preventing colonization by a sessile stabilizing bottom community, and mobile deposits prevent large encrustations. Sediments are thus characterised by a variable taphonomical preservation state and time-averaging as shown by the occurrence of abraded bryozoan growth forms. The banks, sub-circular in shape, display a maximum diameter of 70 m and 1–2m relief. Their position on the shelf coincides with the present day 50 m isobath and it is assumed to correspond to a paleoshore such as that which formed in the Holocene during the transgression following the last ice age. Living counterparts of these banks occur today north of the study area at 10–30 m water depth.

Carbonate Mound Reservoirs in the Paradox Formation: An Outcrop Analogue along the San Juan River, Southeastern Utah: ABSTRACT

Abstract Carbonate-mound reservoirs within the Pennsylvanian (Desmoinesian) Paradox Formation are major producers of oil and gas in the Paradox Basin of Utah, Colorado, and Arizona. Outcrops of the Paradox Formation along the San Juan River of southeastern Utah provide small-scale analogues of reservoir heterogeneity, flow barriers and baffles, depositional facies, and geometry. These characteristics can be used in reservoir-simulation models for secondary/tertiary recovery of oil from small fields in the basin. Morphologically, algal buildups within the Ismay zone of the Paradox Formation consist of large, northwest-trending algal banks separated by interbank troughs or channels. Smaller secondary algal mounds and intermounds define the upper surfaces of the algal banks. Cyclic sedimentation is recorded by four dominant facies recognized in a single, shoaling-upward sequence: (1) substrate carbonate, (2) phylloid algal, (3) intermound, and (4) skeletal capping. An outcrop locality in the Wild Horse Canyon area displaying these and additional facies was selected for detailed study. Along the walls of Wild Horse Canyon, depositional facies characteristic of a typical algal bank transition laterally from a shallow shelf phylloid-algal mound, to bank-margin reef wall, to an off-mound detrital wedge and fan bounded at the top by a flooding surface. The phylloid-algal facies generally exhibits a textural succession composed, from base to top, of rudstone and cementstone, packstone, bafflestone, and skeletal grainstone. Algal plates, brachiopods, bryozoans, and rugose corals are commonly found in the mound complex. The reef wall, deposited in a higher-energy setting, is composed of rudstone, lumpstone, and cementstone textures. The detrital wedge/fan consists of transported algal-plate material and skeletal debris in interbedded grainstone, wackestone, and mudstone textures with open-marine fossils. Within the mound complex is an intermound trough, interpreted to be a tidal channel, through which material was transported to the detrital fan. Similar algal buildups constitute the primary reservoir facies in most small oil and gas fields in the basin to the east. Understanding facies relationships observed at outcrop enhances prediction capabilities when these same facies and relationships are observed in the subsurface. For example, the presence of reef-wall facies in subsurface core might serve as a proximity indicator for a prospective drilling target. Similarly, extent of porosity and permeability development and distribution in buildup-associated facies (intermound and interbank troughs, reef wall, detrital wedges, and fans) would control flow paths and flow barriers, thereby impacting sweep efficiency in secondary/tertiary recovery programs. The nature of stratigraphic boundaries, vertical facies successions, lateral facies relationships, and facies characteristics within the outcropping buildup complex provide the keys to understanding distribution and behavior of algal-buildup reservoirs in the subsurface.

Salt Dome Growth, Thrust Fault Growth, and Syndeformational Stratigraphy, La Popa Basin Northern Mexico: ABSTRACT

ABSTRACT Surface expression of two salt domes and a thrust fault in the La Popa basin of Northern Mexico near Monterrey, Nuevo Leon suggest a complex history of interrelated salt tectonics, Late Cretaceous clastic and carbonate sedimentation, and thrust fault growth. Detailed stratigraphic analysis of clastic sediments and shallow marine carbonates of the Difunta Group (Campanian and Maestrichtian) near the two salt domes indicate that delta front sandstones thin and pinch out towards the salt domes. Successively higher sandstones lap higher and farther onto the domes and probably covered the domes completely during Late Cretaceous time, though present day erosion precludes the certainty of complete coverage. During high sea level stands, algal and rudistid carbonate banks formed on the flanks of the domes and may also have covered the domes completely. Facies irregularities in the enclosing sedimentary rocks clearly indicate that the salt domes were active during Late Cretaceous time. Though hidden under the allochthonous block of the La Popa fault, a major northwest-southeast trending thrust fault, the presence of a third dome is implied by the occurrence of evaporites on the fault plane and by the presence of similar, though smaller, faults associated with the two exposed domes. The La Papa fault may be thought of as an out-of-the-syncline, southwest verging thrust fault with the overthrust block acting as a trap door for evaporites derived from the salt dome. The largest carbonate bank in the basin, the 250-meter (800-foot) thick La Popa Limestone Lentil, occurs only on the upthrown side of this fault. The downthrown side is comprised of an unusually thick [approximately 4.600-meter (15,000-foot)] sequence of clastic rocks with an atypically high sand/shale ratio. This combination indicates that, during high sea level stands, carbonate banks grew on shoal areas that were present on the overthrust side of the fault. During low sea level stands, deltaic and shallow marine clastic sedimentation became concentrated in low areas associated with the down thrown side of the fault.

Macroalgal-sediment nutrient interactions and their importance to macroalgal nutrition in a eutrophic estuary

The potential for algal banks to influence water quality and sediment nutrient flux was examined through laboratory experiments and in situ monitoring of algal banks. Loose macroalgal banks displayed seasonal changes in tissue nutrient concentrations suggesting a strong dependence on water column nutrients. These banks fail to generate conditions suitable to sediment nutrient release. Dense banks generated low oxygen conditions in the inter-algal water (0–1 mg l −1), corresponding to zones of high, and relatively stable, phosphate and ammonium concentrations (up to 96 μg l −1 PO 4P and 166 μg l −1 NH 4N). Laboratory experiments confirmed that macroalgal banks can generate reducing conditions at the sediment surface, regardless of the aeration regime, through the decomposition of macroalgal tissue. Platinum electrode potentials as low as −200 mV were recorded in the inter-algal water. In such banks, redox-dependent sediment nutrient release and anaerobic accumulation of nitrogen accounted for inter-algal nutrient concentrations of over 60 μg l −1 phosphate and 800 μg l −1 ammonium. The generation of reducing conditions in inter-algal water required 7 days of still conditions and so this mechanism of nutrient generation is unlikely to be important in winter, when strong winds frequently shift the algal banks. It is suggested that in summer this mechanism may provide a source of nutrients to dense algal banks, supplementing reserves stored in winter.

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.

Aneth Oil Field, Giant Carbonate Stratigraphic Trap, Paradox Basin, Utah, U.S.A.

The Aneth oil field (approximately 400 million bbl original primary reserves) occurs within an isolated southeast-northwest-trending Pennsylvanian (Desmoinesian) algal carbonate bank buildup located approximately 25 mi (40 km) basinward of the main carbonate shelf of the Paradox basin in Utah. Desmoinesian deposition was strongly cyclic, with as many as 30 main evaporite-carbonate cycles recognized. The Aneth algal bank is part of the Desert Creek cycle, which is the first cycle above that of the most widespread salt-bearing cycle. The Desert Creek carbonate facies grades basinward to increasingly prevalent evaporite facies, dominated by thick salt beds in the basin center. Within the isolated algal-mound facies, the Desert Creek cycle is characterized by a vertical succession that includes (1) basal black, organic-rich, dolomitic, silty shale, (2) overlying dark chalky, finely crystalline dolomite, which grades upward into (3) the main carbonate mound facies, dominated by accumulations of calcareous, leafy green algae with associated brachiopods, fusulinids, small foraminifera, ostracodes, and rare corals. Mound buildups are overlain by a relatively thin, black, organic-rich shale unit, the basal bed of the succeeding mound-bearing Ismay cycle. This unit thickens markedly on the flanks of the Desert Creek and other mound buildup. Interrelated depositional processes of these variousmore » sedimentary facies have resulted in a close association between source rock, large reservoir, and seal at Aneth, and contributed significantly toward the large size of the Aneth accumulation.« less

Comparison of Paleogene Paleogeography: Southern Coast Ranges and Western Transverse Ranges

The paleogene stratigraphic sequence exposed in the southwestern San Rafael Mountains at the southern terminus of the Coast Ranges, consists of up to 850 m (2,800 ft) of the marine limestone, sandstone, and mudstone that lies with a unique depositional contact upon Franciscan Complex rocks. Lithofacies identified represent four sedimentary environments: (1) foreslope talus deposits of a neritic algal bank (Sierra Blanca limestone), (2) bathyal basin plain and outer submarine fan deposits (Juncal/Anita Formation and Cozy Dell Shale), (3) suprafan lobe deposits of a bathyal submarine fan (lower Mitilija Sandstone), and (4) sublittoral shelf deposits (upper Matilija Sandstone). Similarities between paleogene rocks in the southwest San Rafael mountains and the western Santa Ynez Mountains of the Transverse Ranges, approximately 60 km (40 mi) to the west, suggest deposition in a similar paleogeographic setting. Paleomagnetic data suggests post-Paleogene clockwise rotations of the western Transverse Ranges of 90{degree}+. Counterclockwise rotation of the western Transverse Ranges by this amount aligns the similar depositional sequences of the western Transverse Ranges with the northwest-trending Paleogene forearc basin of the southern Coast Ranges and eliminates the necessity for an east-west-oriented Paleogene basin at the site of the present western Transverse Ranges.

Stratigraphy of the Wakarusa Limestone Member of the Bern Formation (Wabaunsee Group, Virgilian Stage, Upper Pennsylvanian) of East-Central Kansas

The Wakarusa Limestone Member of the Bern Formation crops out as a prominent east-facing escarpment in a northeast-trending belt across eastcentral Kansas. The limestone is light gray, hard, and fossiliferous. Horn corals are abundant locally. In Greenwood County a small, 18-foot thick algal bank has been identified. The member is interpreted to have been deposited under normal open-marine conditions in the shallow, warm Kansas Sea. The Wakarusa is the upper limestone member of the Bern Formation (Wabaunsee Group, Virgilian Stage, Pennsylvanian System). The Wakarusa crops out in a narrow band across east-central Kansas. The unit was named by J. W. Beede in 1898 for exposures along Wakarusa Creek just south of Auburn in southwestern Shawnee County. One of the best exposures now is along 170 just west of Topeka near the center of section 31, T. 11 S., R. 15 E. (Plate 1). The outcrop band extends diagonally south-southwest from Brown County in the north to Chautauqua County in the south. The best exposures are south of the Kansas River Valley. Because the Wakarusa is a prominent bench-forming limestone across most of the outcrop belt in eastern Kansas, it has received more-than-normal attention from surface mappers and stratigraphers. Following the initial work of Beede (1898), Condra (1927) extended his work south from Nebraska to include the Wakarusa. R. C. Moore followed with a series of reports on the Pennsylvanian in eastern Kansas, which included the Wakarusa (1936, 1937, 1948, 1949, and 1964). The unit has been mentioned in many other publications, theses, and dissertations. There are, however, three theses of particular importance (Owen, 1959; Ross, 1960; and Myers, 1968) and one short publication (Myers and Robbins, 1968). Many of the field guides in eastern Kansas also include a stop or two at an outcrop of the Wakarusa Limestone Member and adjacent beds. This short paper is intended to give This content downloaded from 157.55.39.203 on Sat, 27 Aug 2016 06:13:52 UTC All use subject to http://about.jstor.org/terms 68 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCE

Geologic Characterization of Caddo Limestone Reservoir, Curry Unit, Stephens County, North-Central Texas: ABSTRACT

Three classic carbonate models (carbonate bank, oolitic shoal, and tidal flat) are applied to interpret the depositional environments and diagenesis of the Caddo limestone (Middle Pennsylvanian). The study area is located in west-central Stephens County, approximately 4 mi southwest of Breckenridge, Texas. Phylloid algal mounds developed on a lower Caddo ramp, along the transition of the Concho platform and Fort Worth basin. Within the area defined as the Curry unit, phylloid algal mounds and intermound facies aggraded to sea level. This led to the development of an areally restricted carbonate bank. Some phylloid algal buildups underwent subaerial exposure, and fresh water leached unstable carbonate minerals, creating minor secondary porosity (<10%). An oolitic shoal (0-9.2 m thick) overlies and partially intergrades with the phylloid algal bank. Ooids were deposited along the margin of the preexisting bank, whereas fine-grained oolitic and peloidal packstone were deposited on the bank. The bank margin oolite exhibits oomoldic porosity in excess of 15%. The uppermost 6.1-24.4 m of the Caddo represents intertidal deposition. Sediment, primarily algal remains and carbonate mud, was deposited on a preexisting surface of ooids and peloids. Fenestral fabric. rhizoliths, brecciated zones, and small-scale channels are common features. A wide variety of poremore » types are present in the intertidal zone; intraskeletal, framework, biomoldic, and vuggy pores are most important. Throughout this zone, porosity exceeds 10% and permeability averages 12 md. The Curry unit has produced approximately 28 million bbl of oil (primary and secondary) from the upper Caddo. Depositional environments and diagenesis of the Caddo are complex. A greater understanding of these complexities may enable geoscientists to evaluate remaining future potential within the Caddo and in other similar carbonate accumulations.« less

Platy Algal Banks: Modern and Ancient: ABSTRACT

Platy Algal Banks: Modern and Ancient: ABSTRACT

Development and Distribution of Rival Reservoirs in Central Williston Basin, Western North Dakota: ABSTRACT

The Mississippian Rival (Nesson) beds in the central Williston basin, North Dakota, are a limestone to evaporite regressive sequence. Progradation of the depositional system produced several distinct shallowing-upward genetic units. Cyclicity in Rival beds was produced by periodic fluctuations in sea level. Rival oil reservoirs are porous and permeable packstones and grainstones. The dominant allochems in these reservoir rocks are peloids and skeletal and algal fragments. These sediments were deposited along carbonate shorelines and within algal banks that developed basinward of shorelines. The trapping mechanism along shorelines is a lithofacies change from limestone to anhydride. Algal banks are locally productive along paleostructural trends where bathymetric shallowing produced shoals dominated by the Codiacean alga Ortonella. Algal banks are flanked by impermeable carbonate mudstones and wackestones deposited in interbank and protected shelf environments. Two distinct Rival bank trends occur in the central basin: a northwest-southeast trend in McKenzie and Williams Counties, North Dakota, parallel with the Cedar Creek anticline, and a northeast-southwest trend along the Nesson anticline and the northeast flank of the basin, parallel with the Weldon-Brockton fault trend.

Carbonate Facies and Stratigraphic Framework of Middle Magdalena (Middle Pennsylvanian), Hueco Mountains, West Texas: ABSTRACT

The middle Magdalena of the Hueco Mountains, west Texas, is best exposed in the vicinity of Pow Wow Canyon, particularly along the western scarp of the range. It can be divided into two major depositional sequences, the lowermost of which consists predominantly of alternating bank, interbank, and shoal deposits of Atokan age. These banks are low-relief accumulations of Donezella, with coeval slackwater skeletal wackestones and interbedded deposits of foraminiferal sands. A prominent zone of intertonguing Chaetetes biostromes punctuates the middle part of this sequence. The Desmoinesian sequence begins as a series of rubbly limestones in association with abundant silicified plant remains and is interpreted as a set of paleosols. These are overlain by argillaceous, low-diversity wackestones and packstones of lagoonal origin, followed by carbonates of more open-marine circulation with abundant corals and other stenotypic fossils. In turn, these deposits are succeeded by a sequence of phylloid algal banks that increase in resistance upward to where they represent strata of the upper Magdalena. At this locality, however, the upper Magdalena is very thin because it is truncated by the pre-Hueco unconformity which, so prominent at the head of the canyon, can now be traced to the western scarp. These deposits aremore » directly analogous to subsurface reservoir facies of the same age on the opposite side of the Diablo uplift in the Permian basin and thus provide an opportunity to generate reservoir models based on extensive outcrop exposure.« less

Producing Characteristics and Depositional Environments of Lower Pennsylvanian Reservoirs, Parkway-Empire South Area, Eddy County, New Mexico

The Parkway-Empire area, on the Northwest shelf of the Permian basin about 15 mi (24 km) northeast of Carlsbad, New Mexico, produces gas from stratigraphic traps within four Lower Pennsylvanian zones: lower and middle Morrow sandstones, Atoka sandstones, and Strawn limestones. The lower Morrow sandstones, which occur at about 11,400 ft (3,470 m), are interpreted to be a prograding fluvial-deltaic sequence of channels and point bars with a northwest source. They trend toward the southeast, generally normal to the Morrowan paleoslope. The lower Morrow sands are separated from the middle Morrow sandstones by a widespread, dark-gray, organic lagoonal shale. In southeastern New Mexico, middle Morrow sandstones are a transgressive series of marine beaches and bars deposited along the northeast-trending ancient shoreline. Stratigraphic traps are created in the lower and middle Morrow sandstones by variations in cementation and depositional patterns. Productive Atoka sandstones occur at approximately 10,700 ft (3,260 m) and appear to be a series of prograding barri r bars deposited along the northeast-trending shoreline. Strawn limestones produce from a series of small, low-relief algal banks developed along northeast depositional strike. The Strawn limestones occur between 10,250 and 10,500 ft (3,120 and 3,200 m). The area is economically attractive. Payout of a typical well occurs in 1.2 years with a rate of return of 78.1%. Pennsylvanian completions in this area have typical ultimate recoveries of approximately 1.5 bcf (42 × 106 m3) of gas and 22,000 bbl (3.5 × 106 L) of condensate. The stacked nature of the reservoirs causes a success rate of 85.2% for this area. The high success rate, good production, and attractive economics make this area of the Morrow trend an important exploration target.

Upper Pennsylvanian Marine Algal Banks of Kansas: Comparison and Implications: ABSTRACT

Marine algal banks (mounds or buildups) present in the Shawnee Group (Upper Pennsylvanian) crop out in eastern Kansas. The youngest of about 20 banks known to occur in the section differ in shape and size but, in general, cause a local increase in thickness that is compensated by a decrease in thickness of the overlying shale. The phylloid algae, Eugonophyllum and Epimastopora, trapped and bound the carbonate mud in a role similar to the modern sea grass, Thalassia, in Florida Bay. The soft mudbanks created barriers to water circulation and fauna distribution. The Shawnee banks decrease in size, contain less algae and more micrite, and are more difficult to define with decreasing age. The Plattsmouth bank formed instantaneously by building on the normal lithology over a large area; the Ervine Creek bank started locally and spread laterally so it is funnel shaped; the Hartford bank is diffuse with the algae occurring in small curls instead of larger, flat blades. All three banks are capped with a layer of osagite/pellets/fusulinids. The Plattsmouth bank is topped with a crust of algal(?) material, and the Ervine Creek bank shows evidence of solution features, indicating possible subaerial exposure. Interpretation of the sequence is that the elongated banks were formed in shallow, warm water parallel to shore in a regressive environment until smothered by an influx of fine clastic material. Differences in size, shape, algae type and quantity, and postdepositional alterations result from subtle differences in setting and timing of development. End_of_Article - Last_Page 1318------------

Lower Pennsylvanian Reservoirs of Parkway-Empire South Field Area, Eddy County, New Mexico: ABSTRACT

The Parkway-Empire area is located on the Northwest shelf in central Eddy County, approximately 15 mi (24 km) northeast of Carlsbad, New Mexico. This area produces oil and gas from the lower and middle Morrow sandstones, Atoka sandstones, and Strawn limestones. Oil is also produced from the Queen and Seven Rivers sandstones, and the Grayburg, San Andres, and Wolfcamp dolomites. All of these zones are productive from stratigraphic traps. The lower Morrow sandstones occur at a depth of about 11,400 ft (3,474 m). They are interpreted to be a prograding fluvial-deltaic sequence of channels and point bars sourced from the northwest. They trend toward the southeast, normal to depositional strike. The lower Morrow sandstones are separated from the middle Morrow sandstones by a widespread, dark gray, organic, lagoonal shale. In the Parkway area, the middle Morrow sandstones are thought to be a transgressive series of marine beaches and submarine bars which trend toward the northeast, parallel to depositional strike. Stratigraphic traps are created in the lower and middle Morrow sandstones by variations in cementation and depositional patterns. Productive Atoka sandstones occur at a depth of approximately 10,700 ft (3,261 m). These sands are thought to be a series of prograding beaches with a northeast trend. Strawn limestones produce from a series of small, low-relief algal banks developed along depositional strike to the northeast. The Strawn limestone is about 300 ft (91 m) thick and occurs between 10,250 and 10,500 ft (3,124 and 3,200 m). End_Page 116------------------------------ Wells in this area have typical ultimate recoveries of between 1.0 and 3.0 bcf of gas. The combination of stacked reservoirs and good production makes this area of the Morrow trend especially attractive. End_of_Article - Last_Page 117------------