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NARROW
GeoRef Subject
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all geography including DSDP/ODP Sites and Legs
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Canada
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Alberta
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Red Deer River valley (1)
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fossils
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microfossils (5)
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Robert Travis Clarke (1937–2024): a tribute to one of the pillars of AASP-TPS
Abstract: An integrated palynological and sedimentological study of Wilcox/Carrizo outcrops in and near Tahitian Village, Bastrop County, Texas, has led to a reevaluation of their chronostratigraphic significance and depositional environments. Strata at the well-known Pine Forest Golf Course and nearby Red Bluff outcrops, together with lesser-known outcrops in the vicinity, are important for source-to-sink linkages with coeval downdip Wilcox Group strata in the deep-water Gulf of Mexico (GOM). This updip succession is fragmentary, with erosional breaks between lithologic units. It represents nearshore shallow-marine to coastal environments throughout, with widespread evidence of tidal influence. Shallow-marine trace fossils are present, and although these are generally sporadic in sandstones, the Calvert Bluff Formation includes extensive Ophiomorpha galleries. Sabinetown Formation parasequences are mostly mud-dominated tidalites with locally common marine trace fossils in more arenaceous intervals. A bioturbated siltstone immediately above the Sabinetown Formation yielded the first Texas record of common to abundant Apectodinium, an acme potentially indicating the Paleocene–Eocene Thermal Maximum (PETM), and thereby providing a correlation with PETM intervals in GOM wells. At all locations, the base of the Carrizo Formation is a marine Glossifungites surface. Siltstone rip-up clasts draped on sigmoidal cross-beds and robust Ophiomorpha indicate the Carrizo Formation probably represents a tidal delta, not fluvial channels.
Abstract Palynofloral assemblages associated with strata of the McMurray Formation, Wabiskaw Member, and Clearwater Formation can be placed into a classification scheme based primarily on dinocyst content. Although most of the palynofloral assemblages are dominated by terrestrially derived pollen and spores, the dinocysts can be used to characterize fresh water through a marine continuum in which to place these diverse paleoenvironments. Freshwater and slightly brackish paleoenvironments are most characteristic of the McMurray Formation, whereas stressed, shoreface, and nearshore paleoenvironments are most characteristic of the Wabiskaw Member and Clearwater Formation strata. Dinocyst assemblages from the McMurray Formation are characterized by the freshwater algae Hurlandsia rugara and rare Holmewoodinium sp., with varying abundances of Nyktericysta spp. group dinocysts. The relative abundance and diversity of these Nyktericysta spp. dinocysts can be correlated with increased brackish influence. Locally within the McMurray Formation, the presence of Vesperopsis spp. may indicate significant brackish influence.Within the overlying Wabiskaw Member and Clearwater Formation, dinocyst assemblages are indicative of the southward-transgressing Clearwater Sea. Assemblages may be dominated by species of Circulodinium (C. deflandrei and C. brevispinosum), Odontochitina operculata, Oligosphaeridium spp., Palaeoperidinium cretaceum plus a host of accessory taxa indicative of stressed paleoenvironments, including several new undescribed species. Significantly, the distribution and nature of the palynofloral assemblages do not validate the historic threefold division of the McMurray Formation into lower, middle, and uppermembers, nor do the palynofloral assemblages reflect a gradual upward increase in marine influence. Instead, the palynofloral assemblages indicate much more regionally diverse paleoenvironments, with brackish influence recognized throughout.
A tribute to Douglas James Nichols, Palynologist, 1942–2010
Front Matter
A Tribute to Garry Davis Jones
Abstract On May 6, 2004, the world of applied paleontology dimmed with the premature death of Garry D. Jones at the age of 51. Garry was a dynamo in oil industry biostratigraphy, moving it forward even during the difficult economic times of the 1990s. Garry received a Bachelor’s degree from Catawba College in North Carolina in 1974. He went on to study benthic foraminiferal ecology with Charlie Ross, receiving a Masters of Science degree from Western Washington University in 1977. Garry then returned to the East Coast, completing a Ph.D. under Fred Swain at the University of Delaware. Garry’s dissertation “Foraminiferal Paleontology and Geology of Lower Claibornian Rocks, Inner Coastal Plain, North Carolina” formed the basis of North Carolina Geological Survey Bulletin 8, published in 1983. In 1981 Garry joined UNOCAL as a research biostratigrapher in Brea, California. At UNOCAL he was an active participant in the Woods Hole Oceanographic Institution’s Integrated Ceno-zoic Biostratigraphy program and also the University of South Carolina’s Gulf of Mexico Foraminiferal Morphometrics and Isotope project. It was at Brea that Garry worked on North Sea data and published on a paleoecological model of late Paleocene agglutinated foraminifera using the paleo-slope transect approach. Using microfossils to solve geologic problems would be a continuing theme in Garry’s work. He wrote and coauthored many UNOCAL technical memoranda over the course of his career. In 1992 Garry moved to Lafayette, Louisiana, and plunged into Gulf Coast biostratigraphy with both feet. Garry built a strong network of experienced workers to quickly come up to speed on the massive knowledge base of the Gulf Coast Cenozoic. Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 1–2.
Abstract The papers presented in this SEPM Special Publication are the result of the successful SEPM Research Conference of the same name held on the campus of Rice University in Houston, Texas, during the days of March 6–11, 2005. Dr. Garry D. Jones originated the idea of a problem focused microfossil conference and he was the primary driving force during the conferences early planning until his untimely passing in May of 2004. At that time a group of Garry’s colleagues carried forward his wishes for the conference through to its successful completion. More than 150 participants from 20 countries registered for the conference, and over 90 oral and poster sessions were given during the three formal days of the conference. In addition, 22 corporate and institutional sponsors donated over US $35,000 to ensure the success of this event. After expenses the remaining funds were passed on to SEPM, and a scholarship was established in Garry’s memory to support students conducting micropaleontological research and is administered by the North American Micropaleontology Society (NAMS). During the course of the conference, five invited speakers initiated the two-and-a-half days technical sessions. These included: John Anderson (Rice University), Mike Simmons (Neftex, UK), Ernest Mancini (University of Alabama), Henk Brinkhuis (University of Utrecht) and James Ogg (Purdue University). The topics of the scientific sessions themselves covered the entire realm of micropaleontology of the Phanerozoic from all corners of the globe. On the Tuesday evening of the conference, the Plenary Dinner was held in the science exhibits hall of the Houston Museum of Natural Science. Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 5–6.
Abstract Fuzzy c-means clustering (FCM) is an exploratory data-analysis method that identifies groups of samples with similar compositions. In spite of FCM being well established in the field of pattern recognition, to date it has had little application in biostratigraphy. In contrast to the hard clustering methods commonly used in biostratigraphy, FCM has the advantage that it can accommodate mixtures and/or gradations between clusters. This is an important feature for biostratigraphical data analysis because such data sets often include samples that are transitional between two or more “pure” faunal or floral assemblages. As an evaluation of FCM we used it to resolve Jurassic miospore and pollen biofacies from the Pentland, Fulmar, and Heather formations from two closely spaced wells in the Hawkins Field, Central North Sea, UK. These data were chosen because they contain a flora for which there is substantial paleoecological literature and, as such, would provide a suitable evaluation of the application of the FCM method to industrial biostratigraphical data. The results demonstrated that FCM could extract floral associations that were relatable to stratigraphy and sea-level changes. Fuzzy c-means produced a five-cluster (i.e., five assemblages) solution. We named each assemblage after the taxon that was dominant in the assemblage. The Cyathidites assemblage is stratigraphically distinct and restricted entirely to the nonmarine Pentland Formation. The remaining four assemblages (Perinopollenites elatoides, Lycopodiumsporites, Cerebropollenites mesozoicus , and Callialasporites) are ecologically distinct and occur primarily in the Fulmar and Heather formations. The P. elatoides assemblage is representative of lowstand regression. The C. mesozoicus assemblage is indicative of warmer, drier, possibly semiarid or seasonally arid climatic conditions. The Lycopodiumsporites assemblage is transitional between cooler, wetter to warmer, drier climatic conditions with the floral dominance of P. elatoides being replaced by C. mesozoicus . The Callialasporites assemblage is interpreted as representing warm, wet seasonal climatic conditions, possibly a back-mangrove biotope, with its maximum development occurring slightly above the maximum flooding surface. Ultimately, this succession of curves was used as a proxy for sea-level changes in the study area, enabling the recognition of maximum flooding surfaces, genetic sequences, and parasequences that improved inter-well correlation. Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 9–20.
Abstract Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 21–27. Biostratigraphy is making a significant contribution to value creation and realization when planning and drilling hydrocarbon development wells. Biosteering production wells provides the support to enable operators to drill more ambitious and technically challenging wells with increased levels of confidence. Precise biostratigraphic and lithostratigraphic control whilst drilling increases safety, saves money, and greatly increases the long-term potential of production wells at relatively small cost. Following the completion of four exploration and appraisal wells, the Kristin Field is currently under development utilizing twelve either highly deviated or horizontal production wells that are technically challenging and expensive to drill. Biostratigraphy, and in particular micropaleontology, is helping with both of these issues by providing quantitative real-time wellsite stratigraphic support, increasing confidence in the placement of casing shoes, by ensuring that wells are landed at the correct stratigraphic level with the correct hole angle, and by negating the necessity for costly lookahead vertical seismic profiles (VSPs). Depth of burial and thermal maturity precludes the use of palynology through most of the Kristin Mesozoic well sections. Micropaleontology has therefore been utilized as a stand-alone tool for stratigraphic calibration of the Upper Cretaceous Intra Lange Sands, the Lower Cretaceous “Albian Shale”, and the Middle Jurassic Melke Formation, all of which are critical in terms of drilling operations on the field.
Biostratigraphy Breaking Paradigms: Dating the Mirador Formation in the Llanos Basin of Colombia
Abstract Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 29–40. The two major oil fields in Colombia discovered in the last fifty years are the Caño Limón and Cusiana fields. Caño Limón is located in the eastern region of the unfolded Llanos of Colombia, and Cusiana is located in the leading thrust sheet of the Llanos Foothills. Paleogene strata in both areas were part of a large foreland basin active since the latest Cretaceous. In both cases the main reservoir is a quartz arenite unit, informally called the Mirador formation, that has always been assumed to extend as a continuous Eocene sandstone layer from the Llanos Foothills into the Llanos Basin. However, recent palynological data suggested that this unit is diachronous across the Llanos and Llanos Foothills. Here, we dated 44 sections in the Llanos Basin and Llanos Foothills using a new zonation that is proposed for the region. Biostratigraphic results constrain the age of the Mirador Formation in the Llanos Foothills as early to middle Eocene with no evidence of a biostratigraphic gap with underlying early Eocene strata. In most of the Llanos Basin, including Caño Limón, the quartz arenite unit has an Oligocene age and rests unconformably upon Upper Cretaceous or Paleocene strata. Additionally, there are areas in the Llanos Basin where mudstone, not sandstone, is the dominant facies overlying the unconformity, suggesting that the basal sandstone in the Llanos Basin is not a laterally continuous body of rock. The absence of lower to middle Eocene quartz arenite beds in most of the Llanos Basin can be explained either by bypass or accumulation and subsequent erosion. These results imply a new paleogeography for the time of accumulation of Eocene and Oligocene reservoir units, a different model for basin evolution, and a different fluid-migration history to explain how the Caño Limón and Cusiana oil fields were filled.
Assemblage-Based Biozonations: A Key Tool in the Detection of Reworked Calcareous Nannofossils
Abstract Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 41–55. Determining the age of oil-well cuttings samples with microfossils is problematic in wells with a significant amount of reworked fossils. In addition, caving is a common problem in cuttings and a species’ base cannot be used with any confidence. If an age-group plot indicates that some of the fossil markers are older than the overall assemblage would suggest, then a biostratigraphic zonation that utilizes assemblage events (e.g., downhole increases, dominance shifts, and morphologic shifts) is needed to correctly determine the age of the sediment. This is especially true if the age of the reworked fossils is only slightly older than the age of the indigenous assemblage. A well from the slope of the Gulf of Mexico sampled 1500 m of Pleistocene section with numerous reworked Pliocene specimens. Utilizing a zonation scheme with 18 horizons based on nine last occurrences and 23 assemblage changes, nine events were identified. Twelve species were interpreted to be reworked. In an example from the upper Pliocene of the Gulf of Mexico, a well was noted to contain a large number of reworked nannofossils from the lower Pliocene and upper Miocene. Many of these reworked species have their extinction points within nannofossil zone NN16 (basal upper Pliocene) or NN15 (uppermost lower Pliocene). A high-resolution, assemblage-based zonation scheme of the Pliocene was used, which utilizes 26 species to define 23 separate horizons. Five upper Pliocene events were identified using the species assemblage changes and highest occurrences. Eighteen species were interpreted as being reworked. A third example is a well from the Gulf of Mexico that contained rare but consistent occurrences of upper Eocene calcareous nannofossils in what was believed to be an Oligocene section. The zonation scheme used to subdivide the section utilizes 28 species to define 27 events within the Oligocene and uppermost upper Eocene. The species were divided into four age groups, which, along with the species’ assemblage changes and highest occurrences, were used to identify 11 events within the Oligocene to uppermost Eocene. Fourteen species were determined to be reworked in the section.
Calculating Calcareous Nannofossil Absolute Abundances and Uncertainties for Paleoceanographic Studies
Abstract Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 57–66. The random settling technique (RST) and the spiking method (SM) are two independent methods that have been combined and used by several authors to calculate absolute abundance of calcareous nannofossils. Both methods usually did not give similar results, and this leads to the question of which one gives a better estimate of nannofossil absolute abundances. In this study, the RST and SM were used to calculate the nannofossil absolute abundances of middle Eocene sediment samples from ODP Leg 171B. Our analyses show similar and reproducible results for both methods. A collector’s curve was used to determine that at least six fields of view are needed to get a good representation of all the taxa present in the samples used for this study. The results of a χ 2 test showed that the distribution of the nannofossils on the cover slip is uniform with random variation, and the error analyses showed that the SM has greater uncertainties than the RST because of error associated with the diameter of microbeads used for spiking.
Abstract Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 67–82. Solar energy (light) is essential for organisms that host algal symbionts. Hence, growth of these organisms is restricted to the photic zone. Among the larger benthic foraminifers, large rotaliids show changes in their test shapes when depth increases, becoming thinner and flatter in deeper environments. This morphological variability is shown clearly in the genus Amphistegina . In oligotrophic waters from the Indo-Pacific region, test shape can be mathematically expressed by the function Z o = 2.592 T/D -2.293 , where Z o represents depth and T/D is the thickness-to-diameter ratio. Amphistegina test-shape distribution is strongly correlated with light extinction with depth. Light penetration depends on water transparency, which diminishes as biological productivity increases. Thus, Z o must be corrected for mesotrophic environments where light penetration is more limited. In mesotrophic conditions, Amphistegina test shape can be expressed mathematically as Z m = 1.037 T/D -2.293 whereas in oligotrophic–mesotrophic transitional situations the equation is Z om = 2.046 T/D -2.293 . Z o Z m and Z om can be used as quantitative bathymetric indicators. In the Latium–Abruzzi and Menorca carbonate platforms, paleodepths inferred from Z m and Z om , respectively, are highly consistent with those obtained from the distribution of the red-algae associations. Thus, paleobathymetric models for both carbonate platforms have been constructed using Amphistegina T/D values as main indicators, supported by information from red algae and other biota. According to the inferred paleobathymetry, in the Latium–Abruzzi platform the inner ramp went from shoreline down to 10 m depth, the middle ramp from 10 m down to 35 m depth, and finally, the outer ramp corresponds to depths greater than 35 m. The Menorca platform paleobathymetric reconstruction indicates an inner ramp from 0 m down to 20 m depth, a middle ramp from 20 m down to 40 m, a ramp slope from 40 m down to 80 m, and, finally, an outer ramp no deeper than 100 m. Bathymetric ranges in the Menorca platform, deeper than those from the Latium–Abruzzi ramp, are consistent with greater light penetration. The Amphistegina T/D index can also be used as a sediment-transport indicator. In the Menorca platform, sediment transport from the inner ramp down to the middle ramp, and even down to the lower ramp slope, are indicated by thick, ex situ Amphistegina specimens in relatively deep environments. The distribution of red algae and the co-occurrence of shallow organisms such as epiphytic foraminifers and fragments of hermatypic corals (Porites) confirm downslope transport and the role of the inner-ramp factory as an important sediment source.
Abstract Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2008 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 83–92. Beds of benthic macro-vegetation are important in shallow-water, carbonate-producing regimes. Seagrass blades baffle currents, leading to deposition of fine sediment, and grass root systems effectively bind the sediment, preventing erosion. Seagrass and benthic macroalgae are substrates for a variety of epibionts, including foraminifera. Due to their higher preservation potential, foraminifera can be used as proxies in studies of ancient vegetation-bed environments. In this actualistic study, we investigated the potential of using foraminifera to reconstruct the taxonomic composition and density of the vegetation, water depth, and a range of other environmental variables. At each of the six localities selected, vegetation densities were recorded in 50 cm x 50 cm grids located at 10 m intervals along transects. A sediment sample from the top 1 cm of the seafloor was taken at each station, and samples of each of the major genera of vegetation algae, seagrass, and macroalgae were collected at each locality. In the laboratory, vegetation was examined, and relatively large foraminifers were picked from the 2.0–0.5 mm sediment fractions. Total foraminiferal density was recorded as the number of individuals per plant and per gram of sediment picked. Dead foraminifers were categorized by taphonomic condition: pristine, good, altered, and extremely altered. Sorites and Planorbulina are the dominant large foraminifers living on the preferred substrates, Thalassia and Halimeda , in proportions that vary according to locality. However, sediment assemblages are dominated by Archaias, Cyclorbiculina , and Valvulina , with very few live individuals. In vegetation beds dominated by seagrasses, foraminiferal density in the sediment appears to reflect the standing Thalassia density to a degree, but maximum test density occurs in moderately dense seagrass beds. The most reliable proxy for the presence and density of seagrass beds is the relatively high quality of test preservation as assessed by the quality of preservation index (QPI), the percent of live, pristine, and good tests in an assemblage. Medium- to high-density seagrass beds consistently rank in the range of 70–85%, whereas sparse beds are much lower. In addition, processes of alteration, such as abrasion versus encrustation and cementation, are promising areas for further study. These preliminary results indicate strongly that taphonomic state and mode of alteration should be included in future carbonate-platform foraminiferal studies
Abstract Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 95–109. Abundant and accurate paleontologic ages and dates help to refine the magnitude and scale of structural and sedimentary events. They are critical in understanding the geologic history of Pennsylvanian and Permian strata of southeastern Arizona, southern New Mexico, and west Texas, U.S.A. A well-established fusulinacean zonation in these intervals is one of several well-studied fossil zonations used for successful petroleum exploration in this area. The results have led to the timing of movements of large structural blocks and show the progressive, but not uniform, movements on different blocks at different times caused by reactions to stages in the Marathon–Ouachita orogeny to the south and east. Superimposed on this structural history are the patterns of Pennsylvanian and Permian cyclic deposits resulting from repeated sea-level fluctuations thought to be mainly of glacioeustatic origin. The magnitude of these sea-level fluctuations, and the lateral extent of each transgression onto various structures, can be used as a gauge in determining the height of various structures at different times. Inasmuch as the Pennsylvanian and Permian sea levels are well dated by fossils, it is possible to identify each sea-level fluctuation and to compare it to a “standard” cratonic sea-level curve on the more stable parts of the craton. Paleontologically well-dated structural movements and the timing and magnitude of sea-level fluctuations help identify various types of petroleum reservoirs. They include lowstand-wedge carbonate reefal buildups in lower slope to basinal settings, multiple thin sheetlike porous deposits on platform crests, karsted platform-edge facies, and coarse shelf carbonate debris reworked into porous platform slope and basin deposits. In addition a variety of other shelf-margin features, including variously large-sized slide blocks (many more than 5 km on a side) of shallow shelf carbonates were displaced by faulting or gravity sliding during the Pennsylvanian and/or Permian into basinal settings.
Micropaleontology and Paleoenvironments of Saudi Arabian Upper Permian Carbonates and Reservoirs
Abstract Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 111–126. Foraminiferal and calcareous algal biofacies of the Upper Permian to Lower Triassic carbonates provide important guides to the depositional paleoenvironment of these important gas-reservoir carbonates of the Khuff Formation in Saudi Arabia. Thin-section analysis has revealed smaller foraminifera that have been variously considered as useful for subdividing the Permian section, despite the absence of the conventional fusulinid species. The Permian–Triassic boundary lies within the Formation, and is defined by locally significant biostratigraphic evidence. Because all species are extinct, paleoenvironmental interpretation is based on the vertical stacking arrangement of various biofacies based on the principle of anticipated paleobathymetric tiering, assisted by the application of morphogroup characteristics. This approach is linked to biological expectations of carbonate secreting organisms associated with successive transgression-linked retrogradational facies movement and regression-linked progradational facies movement, in conjunction with various carbonate textures. Foraminiferal and calcareous algal biocomponents have been used to determine subtle paleoenvironmental variations, both vertically and horizontally, in the subsurface. Paleoenvironmental factors are here suggested to include those that are based on the paleogeography, in terms of seawater temperature, solar incidence, prevailing wind direction, and proximity to land. Eustatic and autocyclic paleobathymetric variations would be expected to cause higher-frequency paleoecological changes in salinity, turbidity, wave energy, and carbonate productivity rates. The following biofacies have been established: Spirorbis–ostracod–gastropod; gastropod–brachiopod–ostracod; ostracod– Mizzia-Gymnocodium; Agathammina–Hemigordius; Agathammina–Hemigordius–Globivalvulina; Nankinella–Staffella; bryozoa; and Pachyphloia–Protonodosaria . The reservoirs here considered display subtle paleoenvironmental variations of an extensive, generally shallow marine, carbonate platform that ranged from intertidal to depths within intrashelf basins that probably rarely exceeded storm wave base. Paleoenvironments ranged from intertidal, shallow to deep subtidal, and shallow shoals. In addition, certain localities display sufficiently diverse events that there is the potential for refined interwell correlation as well as their use for biosteering development wells. Morphogroups have been used to assist in paleoenvironmental interpretation.
Using Jurassic Micropaleontology to Determine Saudi Arabian Carbonate Paleoenvironments
Abstract Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 127–152. Depositional and potential reservoir layers in the Jurassic carbonates of Saudi Arabia cannot necessarily be recognized by core description or wireline log interpretation alone. Recent studies based on thin-section micropaleontology of closely spaced core samples have led to elucidation of such layers in heterogeneous reservoir carbonates, based on the vertical tiering of various paleoenvironmentally sensitive biocomponents. When integrated with core descriptions, such biofacies and their lateral variations provide a powerful tool for optimal reservoir development. The biofacies guide sequence-based frameworks towards three-dimensional lithofacies and reservoir facies distribution models, with the added power of facies prediction away from drilled locations. The 13 carbonate reservoirs in the Jurassic Shaqra Group of Saudi Arabia are developed in seven formations, of which the Arab Formation hosts the world’s largest onshore reservoir. The lithostratigraphic succession is composed of the Lower Jurassic Marrat Formation, the Middle Jurassic Dhruma and Tuwaiq Mountain formations, and the Upper Jurassic Hanifa, Jubaila, and Arab formations, which terminate with a succession of interbedded carbonates and evaporites of which the final thick evaporite is termed the Hith Formation. The Marrat Formation, of Toarcian age, hosts the Marrat Reservoir. The Dhruma Formation, of Bajocian–Bathonian age, hosts the Faridah, Sharar, and Lower Fadhili reservoirs. The Tuwaiq Mountain Formation hosts the Upper Fadhili and Hadriya reservoirs, and is of Callovian age. The Oxfordian Hanifa Formation hosts the Hanifa reservoir, which is overlain by the Jubaila and Arab formations, of Kimmeridgian age, and together host the Arab Reservoir. The Hith Formation is of probable Tithonian age and hosts the Rimthan and Manifa reservoirs. An ascending order of tiered deep- to shallow-marine foraminiferal assemblages has been determined for each formation and applied to distinguish both long-term and high-frequency paleobathymetric variations. Micropaleontology has regained its importance in such industrial applications, and has significantly outgrown its traditional, but equally important, chronostratigraphic use. Because age-significant foraminiferal species are rare in the Shaqra Group, micropaleontological biofacies and their paleoenvironmental aspects are of especial importance. In addition to the intrareservoir applications, recent studies are focusing on the application of biofacies for regional studies and delimitation of potential reservoir targets in frontier areas. Using this technique for the Hanifa Formation, a regional lithofacies trend map has been deduced, which is currently assisting seismic program planning for exploration activities.
Abstract The Mesozoic, mid-Cretaceous (Barremian to Cenomanian) deposits of southern Croatia comprise a succession of shallow tropical-water, inner-platform deposits that formed on a Bahama-type isolated Adriatic carbonate platform in the Dinarides. This succession is dominated by benthic foraminifers and dasycladalean algae, and is exposed in a nearly continuous outcrop section on the islands and along the coast of southern Croatia. It has been studied in terms of sedimentary facies, paleoecology, and biostratigraphy. The present study documents that several species of benthic foraminifers (cuneolinids, orbitolinids, alveolinids) and dasycladalean algae (Salpingoporella) have exceptional age-diagnostic value for mid-Cretaceous biostratigraphy. These are abundant, and they have a widespread distribution and a restricted stratigraphic range. They evolved rapidly and became extinct suddenly. The mid-Cretaceous benthic associations, including a total of 106 species and 57 genera of benthic foraminifers and 48 species and 20 genera of dasycladalean algae, were analyzed to establish the principal diversity patterns at (sub)stage level of resolution. The Early Aptian marked the foraminiferal diversity maximum, whereas significant diversity drops are recorded in the Late Aptian and Early Cenomanian. The foraminiferal distribution within the oligotrophic habitats of the platform interior was controlled primarily by relative sea-level oscillations, variations in oceanic circulation rate, and nutrient availability in surface waters. There is a positive correlation between episodes of increased diversification and the regional relative sea-level rises, whereas regressive episodes resulted in reduction of oligotrophic habitats and decreased species richness. The dasycladaleans were the most diversified during the tidal-flat-dominated Barremian, and from that peak diversity decreased through the Early Aptian. A significant diversity drop occurred in the Late Aptian, and it was contemporaneous with the maximum abundance of Salpingoporella dinarica . The mid-Cretaceous dasycladaleans never fully recovered from the Early Aptian platform deepening event, and their post-Aptian diversity pattern implies dependence on factors other than relative sea level and associated changes in habitats. Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 153–170.
Abstract Cyanobacteria and/or bacteria are a major part of the biomass, although their recognition as significant constituents of the sedimentary record has largely b overlooked in rocks other than Precambrian and Paleozoic stromatolites. Their extremely small size has been one of the major obstacles in the recognition of such constituents, which can be observed properly only at high-resolution SEM imaging. Here we present evidence of accumulation of cyanobacterial “microspheroids” as predominant components of sediments of the Cenomanian–Turonian deposits in the “Sierra de Parras”, northeastern Mexico, during an interval of predominantly dysoxic to anoxic conditions. The stratigraphic section includes a sequence of limestones and marls with well-defined rhythms at the decimeter to millimeter scale. This facies shows internal structures that are arranged in nearly even-parallel “varve-like” dual laminae less than 3 mm thick. A few scattered planktonic foraminifera and radiolaria occur in the dark laminae, while the light laminae are composed almost entirely of microspheroids. Total carbonate (CaCO 3 ) content varies from 43.0% to 78.3%, and TOC is relatively high, between 0.3% and 3.6% (consistently higher than 1.6%), suggesting an environment favorable for preservation of organic matter. Inorganic-element concentrations (Mo, V, Cr) suggest that the sequence at Parras accumulated in a dysoxic to anoxic environment in which microbial communities were predominant, as also revealed by petrographic and SEM analyses. Microfacies reveal that compositional differences in the laminae are associated with varying abundance of cyanobacterial “microspheroids”. The distinctive laminae are the result of recurring cycles of calcareous cyanobacteria blooms, which remained dominant throughout the sedimentary sequence. Organic-carbon-rich black shales and limestones of the Parras region further document unique paleoceanographic situations during the early Late Cretaceous, when strong intermittent dysoxic or anoxic bottom conditions developed at the site of the Parras deposits and were associated with rhythmical production of cyanobacteria. Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 171–186.
Abstract The Late Cretaceous pathways of ocean circulation differ fundamentally from modern oceanographic settings and were constrained primarily by the paleogeographic continental constellation of the past. We have conducted a detailed biogeographic analysis of the global distribution of 25 of the most common genera of Late Cretaceous (Santonian–Maastrichtian) larger foraminifera from tropical and subtropical latitudes. We have established a global data base for Late Cretaceous larger symbiont-bearing foraminifera to compare the extent of biogeographic provinces, to analyze distributional patterns of genera and patterns of biodiversity, and to examine geological factors regulating shifts and pathways in the evolution of diversity through time. The analysis of distributional patterns in Cretaceous larger foraminifera (Santonian/Maastrichtian) exhibits prominent biogeographic patterns that reveal extents over regional, superregional, and circumtropical levels. The spatial patterns that emerge from these studies are used to highlight some of the environmental variables exerting control over the biogeographic distribution of larger foraminifera in time and space. The biogeographic patterns observed are strongly constrained by a complex and intriguing mixture of geological history, physical oceanography, and protistan biology. The latitudinal ranges of individual genera may provide clues to infer sea-surface temperature (SST) ranges and the heat transfer regulated by the major ocean current regimes. The longitudinal range of taxa is applied as a measure for dispersal capabilities as controlled by the prevailing currents and SST patterns. The biogeographic data compiled also allowed us to assess diversity patterns among assemblages of larger foraminifera from different localities in the Late Cretaceous oceans and to identify hotspots of diversity. Presence–absence patterns and distributional extents of key taxa suggest the existence of four major biogeographic provinces: the Caribbean, the “European” Tethys, the North African Tethys, and the Indo-Asiatic provinces. The biogeographic provinces appear to be constrained mainly by the “circumglobal” Cretaceous current-system dynamics and the prevailing temperature gradient at the ocean surface. The biogeographic pattern of generic diversity of Late Cretaceous larger foraminifera correlates with the size and extent of shallow-water shelf and reefal areas present in the Cretaceous oceans. The Late Cretaceous hotspot of larger foraminiferal diversity is centered in shallow-water areas of the European Tethys, the largest reef and shelf region at this time. Geologic Problem Solving with Microfossils: A Volume in Honor of Garry D. Jones SEPM Special Publication No. 93, Copyright © 2009 SEPM (Society for Sedimentary Geology), ISBN 978-1-56576-137-7, p. 187–232.