Stratigraphic Zones Research Articles

Absence of a Medieval Climate Anomaly, Little Ice Age and twentieth century warming in Skarvsnes, Lützow Holm Bay, East Antarctica

AbstractPalaeoclimate changes, such as the Medieval Climate Anomaly and the Little Ice Age, are well-defined in the Northern Hemisphere during the past 2000 years. In contrast, these anomalies appear to be either absent, or less well-defined, in high-latitude regions of the Southern Hemisphere. Here, we inferred environmental changes during the past two millennia from proxies in a sediment core from Mago Ike, an East Antarctic lake in Skarvsnes (Lützow Holm Bay). Variations in lake primary production were inferred from fossil pigments, sedimentological and geochemical proxies and combined with absolute diatom counts to infer past diatom productivity and community changes. Three distinct stratigraphic zones were recognized, resulting from a shift from marine to lacustrine conditions with a clear transition zone in between. The presence of open-water marine diatoms indicates a coastal zone seasonally free of sea ice between c. 2120–1500 cal yr bp. Subsequently, the lake became isolated from the ocean due to isostatic uplift. Freshwater conditions were established from c. 1120 cal yr bp onwards after which the proxies are considered highly sensitive to temperature changes. There is no evidence for a Medieval Climate Anomaly, Little Ice Age or twentieth century warming in our lake sediment record suggesting that studies that have imposed Northern Hemisphere climate anomalies onto Southern Hemisphere palaeoclimate records should be treated with caution.

Water Distribution in the Montney Tight Gas Play of the Western Canadian Sedimentary Basin: Significance for Resource Evaluation

SummaryWater distribution in unconventional gas reservoirs is a key parameter that influences many aspects of resource exploitation including selecting geographic areas for multiwell development programs, identifying target zones for horizontal wells, calculating reserves, estimating permeability, and understanding variability in gas and water production. Insights on water distribution in the Montney tight gas play of northeast British Columbia and northwest Alberta were gained by integrating reliable water-saturation measurements from full-diameter core samples with other core, well-log, and geologic data. Water distribution in the studied Montney section was found to be related to stratigraphic architecture and rock fabric (defined by degree of bioturbation), and is interpreted to have been influenced by the displacement efficiency of mobile formation water updip through tight Montney siltstones during hydrocarbon charging. Low-gradient clinoform units with few shaly zones in the Lower Montney section enabled efficient water displacement and led to water contents at or close to irreducible water saturation. Higher-gradient clinoform units with greater facies variation and common shaly zones in the Upper Montney allowed less-efficient water displacement, and significant volumes of mobile water were retained in parts of the section. Water saturation varies widely and directly influences gas effective permeability. A simple method for determining gas effective permeability from well logs was developed on the basis of empirical relationships derived from the core and log data set. Gas-effective permeability logs generated by this method help to identify target zones with superior reservoir quality for exploitation by use of horizontal multistage-fracturing technology. A Pickett plot with gas-effective-permeability lines was found to be a useful tool for a log-based comparison of Montney rock quality by stratigraphic zone or geographic area. This work shows that understanding water distribution and its influence on gas effective permeability leads to the improved delineation of "sweet spots" for resource development in unconventional gas plays.

Modelling site formation dynamics: geoarchaeological, chronometric and statistical approaches to a stratified rockshelter sequence, Polynesia

Formation processes and chronology are central to many archaeological endeavours, and accuracy in the latter is dependent on control of the former. Here we consider how to integrate geoarchaeological and chronometric evidence to better understand the formational history, along with the timing and duration of cultural activities, at a regionally significant site in the southern Cook Islands (Polynesia) which dates from ∼12th century AD. Initially we model natural and cultural processes of deposition using geoarchaeological evidence. The results are integrated with 21 radiocarbon dates, including nine new AMS results on identified medium and short-lived materials. Sample outliers are identified manually and statistically and a Bayesian analysis helps to refine age estimates for the site's 12 stratigraphic zones. The timing and rate of sediment accumulation is further considered through an age–depth model. Finally, the chronology developed from these combined approaches is used to address three key processes: 1) initial site use, potentially relevant to human colonisation of this Polynesian island and archipelago; 2) on-site activities and patterns of resource use; and 3) major marine deposition events which disrupted cultural activities and may have palaeoclimatological significance. The approach developed here potentially has utility elsewhere, particularly where human activities are recurrent and of limited duration.

Chronostratigraphy of the sedimentary record of Limnopolar Lake, Byers Peninsula, Livingston Island, Antarctica

AbstractThe chronostratigraphy of the sedimentary record of Limnopolar Lake, located on Byers Peninsula (Livingston Island, South Shetland Islands, Maritime Antarctica), is described based on radionuclides and radiocarbon age dating. The oldest moss macrofossil age was 6700±50 yrbp(7510±80 cal yrbp) from which the age/depth model estimates a basal age for the sedimentary record ofc.8300 cal yrbp, suggesting an earlier deglaciation of Byers Peninsula than reported in previous studies. Lithological units and other stratigraphic zones are described throughout the sediment core, showing different mineralogical composition and a fine alternation of clays and silty clays and moss layers ofDrepanocladus longifolius.Based on magnetic susceptibility analyses, a number of probable primary and reworked tephra layers were identified, seven of them confirmed by SEM observations, and most of them in agreement with the regional tephrachronology stratigraphy for the north-west Antarctic Peninsula. Sedimentation rates showed no significant changes during the last 5000 years with the exception of an abrupt event that took place around 5400 cal yrbp, which implied the sedimentation ofc.30 cm of clays in a very short time, probably related to a period of glacial re-advance that caused abrupt changes in geomorphological processes in the catchment.

Anomalous molybdenum isotope trends in Upper Pennsylvanian euxinic facies: Significance for use of δ98Mo as a global marine redox proxy

The use of molybdenum isotope data (δ98Mo) from organic-rich shales to draw inferences concerning marine paleoredox conditions at a global scale is predicated upon the assumptions of (1) a residence time of Mo in seawater much greater than the ocean mixing time, and (2) quantitative removal of Mo from a strongly euxinic ([H2S]aq>11μM) water column to the sediment, thus preserving the seawater δ98Mo signature. In this study we analyze Mo isotopic variation in the Hushpuckney Shale, a 73-cm-thick unit representing the late transgressive to early regressive stages of a glacio-eustatic cyclothem (Swope Formation) deposited in the Late Pennsylvanian Midcontinent Sea (LPMS) of North America. The Hushpuckney can be subdivided into four stratigraphic zones of distinctive geochemical character. Zones I and III, which accumulated under weakly euxinic conditions, acquired relatively high δ98Mo values (+0.9 to +1.1‰), whereas Zone II, which accumulated under intensely euxinic conditions, acquired lower δ98Mo values (~+0.6‰). Zone IV, which accumulated under suboxic conditions in the water column, acquired the heaviest δ98Mo values (+1.1 to +1.8‰). These results contrast with the pattern of redox — δ98Mo covariation in modern marine environments, in which the heaviest δ98Mo values are found in the most intensely euxinic facies.We evaluate three different hypotheses to account for the Mo isotopic patterns of the Hushpuckney Shale. One hypothesis, seawater–freshwater mixing, is rejected owing to isotopic mass balance considerations. A second hypothesis is a local control on δ98Mo by water-column redox cycling of Mn, with particulate Mn-oxyhydroxides adsorbing isotopically light Mo and transferring it to the sediment, a process that was most active during deposition of Zone II. The significance of this scenario is that euxinic black shales may not reliably record global seawater δ98Mo in areas where a Mn-particulate shuttle is operative. A third hypothesis is based on rapid secular variation of the Mo isotope composition of Late Pennsylvanian global seawater. In order to account for δ98Mo trends within the Hushpuckney Shale, seawater δ98Mo must have varied by ~1.2‰ at a ~100-kyr timescale, which would have been possible only if the residence time of Mo in Late Pennsylvanian seawater was <100kyr. Although both the second and third hypotheses are viable based on the present limited δ98Mo dataset, we discuss how each model might be tested through additional Mo isotope data.

A 1000-yr record of environmental change in NE China indicated by diatom assemblages from maar lake Erlongwan

Past environmental changes based on diatom relative abundances have been inferred from the maar Lake Erlongwan in northeast China. The limnology of Lake Erlongwan is affected by the strongly seasonal regional climate. The composition of diatom assemblages, in turn, responds to changes in the seasonal duration of ice cover in winter, water-column turnover in spring and autumn, and thermal stratification in summer. Statistical analysis of the sedimentary diatom assemblages reveals three significant stratigraphic zones over the past 1000yr. The highest abundance of the planktonic species Discostella species occurs between AD 1050 and 1400 and suggests an annual ice-free period of long duration and well-developed summer stratification of the water column. This planktonic diatom peak between ca. AD 1150 and 1200 suggests that this period was the warmest over the past 1000yr. The interval between AD 1400 and 1800 is marked by a decline in planktonic diatoms and suggests shorter duration of the ice-free season, weaker water stratification and possibly generally cold conditions. After AD 1800 relative abundances of planktonic diatoms, including Puncticulata praetermissa and Asterionella formosa, increase again, which indicates lengthening of the duration of the annual ice-free period and a stronger overturn of the water column. All these data imply that the pattern of the seasons is different between the MWP and the 20th century.

Marlim Field: Mature-Field Optimization

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 139376, ’Marlim Field: An Optimization Study on a Mature Field,’ by Dirceu Bampi, Petrobras, and Odair Jose Costa, Halliburton, prepared for the 2010 SPE Latin American &amp; Caribbean Petroleum Engineering Conference, Lima, Peru, 1-3 December. The paper has not been peer reviewed. Giant fields provide a significant portion of the total hydrocarbon production in Brazil. Most of these fields are in advanced exploitation stages. A drainage-optimization study was performed on the Marlim field, a giant and mature field in the Brazilian Campos basin. Reservoir-flow simulations were used to optimize the methodology and increase the recoverable-oil volume by accelerating the oil production. As a result, new-well proposals became more economically attractive. Introduction The Marlim field, discovered in 1985, is in the northeastern part of the Campos basin in water depths between 600 and 1200 m. Reservoir depths are 2500 to 2750 m, with temperatures between 65 and 72°C. Marlim is part of a large complex of reservoirs including the Marlim Sul and Marlim Leste fields. The original oil in place is 1.012×109 std m3, and the maximum permeable thickness is 125 m. The reservoir is unconsolidated sand-stone with an average net-/gross-thick-ness ratio of 86%, average porosity of 30%, and permeability of 1 to 10 dar-cies. The petrophysical analysis indicated original water saturation of 15%, saturation pressure of 265 kgf/cm2, and residual-oil saturation of 23%. The oil at reservoir conditions has a viscosity of 4–8 cp and gravity of 18–25°API. The reservoir is divided into five stratigraphic zones. Every zone is in hydraulic communication, although, in some areas, the communication is somewhat constrained. The reservoir has small aquifers underlying the oil, and solution-gas drive is the main production mechanism. The reservoir is undergoing a secondary-recovery process by use of seawater injection. Production startup occurred in March 1991, and water injection began in September 1994. Peak production occurred in April 2002 with 9.79×104 m3/d. Oil production averaged 4.48×104 m3/d, with water cut of 54% in April 2010. The cumulative oil production surpassed 3.18×108 m3 in April 2010, representing 32% recovery. The field contains more than 200 wells, with 125 in operation and a producer/injector ratio of 1.85. The current reservoir-exploitation stage, with oil-production decline and a significant increase in water production, presents serious challenges in maintaining extraction cost at acceptable levels. To accelerate field oil production and increase the recoverable volume, this simulation-optimization study considered drilling 16 new producing wells and attempted to identify targets for future sidetracks from these new wells.

A Huge Caseid Pelycosaur from North-Western Sardinia and Its Bearing on European Permian Stratigraphy and Palaeobiogeography

Skeletal remains, some loose on the surface and others still embedded, have been recovered from the uppermost part of an outcrop of the Permian Cala del Vino Formation located near Torre del Porticciolo (Alghero, Nurra, NW Sardinia). Taphonomic analysis suggests that all the elements pertain to a single individual; ongoing studies indicate the fossil represents a large caseid close (or referable) to Cotylorhynchus; otherwise restricted to a narrow geographic and stratigraphic zone of the central USA. The new finding, the first of a caseid in Italy and one of few in Europe, enlarges the known distribution of the family and provides a significant and key chronostratigraphic constraint for the continental succession of this area and, in turn, helps establish a stratigraphic framework for the Permian units cropping out in Italy and southern France.

New reconstruction and morphological description of a Homo erectus cranium: Skull IX (Tjg-1993.05) from Sangiran, Central Java

Skull IX (Tjg-1993.05) was unearthed from the upper stratigraphic zone (Bapang-AG levels) of the hominin-bearing sequence in Sangiran. This remarkably complete cranial specimen of Homo erectus from the early Pleistocene of Java preserves substantial portions of the vault and face. However, the distortion present in the original reconstruction has hampered detailed documentation of its morphological characteristics. We here report a new reconstruction of Skull IX that successfully recovers the original morphology and significantly differs from previous reconstructions. Detailed morphological description and the results of initial comparative analyses based on this new reconstruction are provided. The endocranial volume of Skull IX was measured as 870 cc using micro-CT data. The neurocranium of Skull IX is slightly smaller than the so far recorded smallest cranium from this zone, suggesting this individual was female. In most, but not all, aspects of the cranial vault form, details of the external surface structures, and facial morphology, Skull IX exhibits numerous similarities to the other Bapang-AG H. erectus specimens, indicating that it belonged to the Bapang-AG H. erectus population. Drawing on the expanded fossil sample of this chronoregional H. erectus group, we discuss their evolutionary status, degree of sexual dimorphism, and facial morphological variation in Afro-Asian earlier Homo specimens.

Generalized methods and solvers for noise removal from piecewise constant signals. I. Background theory

Removing noise from piecewise constant (PWC) signals is a challenging signal processing problem arising in many practical contexts. For example, in exploration geosciences, noisy drill hole records need to be separated into stratigraphic zones, and in biophysics, jumps between molecular dwell states have to be extracted from noisy fluorescence microscopy signals. Many PWC denoising methods exist, including total variation regularization, mean shift clustering, stepwise jump placement, running medians, convex clustering shrinkage and bilateral filtering; conventional linear signal processing methods are fundamentally unsuited. This paper (part I, the first of two) shows that most of these methods are associated with a special case of a generalized functional, minimized to achieve PWC denoising. The minimizer can be obtained by diverse solver algorithms, including stepwise jump placement, convex programming, finite differences, iterated running medians, least angle regression, regularization path following and coordinate descent. In the second paper, part II, we introduce novel PWC denoising methods, and comparisons between these methods performed on synthetic and real signals, showing that the new understanding of the problem gained in part I leads to new methods that have a useful role to play.

Eagle Ford shale reservoir properties from digital rock physics

Joel D. Walls and Steven W. Sinclair report on a workflow for analysis of cores samples from two wells in a shale reservoir focused primarily on the relationship between porosity and permeability in the stratigraphic zone of interest.

Environmental variability in Lake Naivasha, Kenya, over the last two centuries

Lake Naivasha, Kenya, is one of a number of freshwater lakes in the East African Rift System. Since the beginning of the twentieth century, it has experienced greater anthropogenic influence as a result of increasingly intensive farming of coffee, tea, flowers, and other horticultural crops within its catchment. The water-level history of Lake Naivasha over the past 200 years was derived from a combination of instrumental records and sediment data. In this study, we analysed diatoms in a lake sediment core to infer past lacustrine conductivity and total phosphorus concentrations. We also measured total nitrogen and carbon concentrations in the sediments. Core chronology was established by 210Pb dating and covered a ~186-year history of natural (climatic) and human-induced environmental changes. Three stratigraphic zones in the core were identified using diatom assemblages. There was a change from littoral/epiphytic diatoms such as Gomphonema gracile and Cymbella muelleri, which occurred during a prolonged dry period from ca. 1820 to 1896 AD, through a transition period, to the present planktonic Aulacoseira sp. that favors nutrient-rich waters. This marked change in the diatom assemblage was caused by climate change, and later a strong anthropogenic overprint on the lake system. Increases in sediment accumulation rates since 1928, from 0.01 to 0.08 g cm−2 year−1 correlate with an increase in diatom-inferred total phosphorus concentrations since the beginning of the twentieth century. The increase in phosphorus accumulation suggests increasing eutrophication of freshwater Lake Naivasha. This study identified two major periods in the lake’s history: (1) the period from 1820 to 1950 AD, during which the lake was affected mainly by natural climate variations, and (2) the period since 1950, during which the effects of anthropogenic activity overprinted those of natural climate variation.

Small Foundation Displacements along Horizontal Strata Reflect River-Stage History

A four-year record (2002–2005) of river stages and very small displacements measured deep in the foundation soil of the interstate bridge at Vicksburg, Mississippi, explains movements that were detected within the bridge. Most foundation-soil displacements occurred within a horizontal zone about 6 ft (2 m) thick in Tertiary strata at elevation −62 ft (−19 m) relative to mean sea level. The stratigraphic zone of weakness consists of stiff, CH clay and subordinate thin beds of fine sand. The zone owes much of its vulnerability to prehistoric landsliding. Lesser movements, however, have extended along the same horizon into the bluff and ground not previously affected by the landslide. During the study interval, displacement events within the bridge foundation soil ranged up to about 0.1 in. (0.3 cm) and lasted a few days or less, coinciding with relatively rapid drops of the river to low levels. This coincidence seems to result from a lag in the response of groundwater pressure to dropping river level, as well as from vulnerability at a time of rapid drawdown.

Exploring former subglacial Hodgson Lake, Antarctica. Paper II: palaeolimnology

Direct exploration of subglacial lakes buried deep under the Antarctic Ice Sheet has yet to be achieved. However, at retreating margins of the ice sheet, there are a number of locations where former subglacial lakes are emerging from under the ice but remain perennially ice covered. One of these lakes, Hodgson Lake (72°00.549′S, 068°27.708′W) has emerged from under more than 297–465m of glacial ice during the last few thousand years. This paper presents data from a multidisciplinary investigation of the palaeolimnology of this lake through a study of a 3.8m sediment core extracted at a depth of 93.4m below the ice surface. The core was dated using a combination of radiocarbon, optically stimulated luminescence, and relative palaeomagnetic intensity dating incorporated into a chronological model. Stratigraphic analyses included magnetic susceptibility, clast provenance, organic content, carbonate composition, siliceous microfossils, isotope and biogeochemical markers. Based on the chronological model we provisionally assign a well-defined magnetic polarity reversal event at ca 165cm in the lake sediments to the Mono Lake excursion (ca 30–34ka), whilst OSL measurements suggest that material incorporated into the basal sediments might date to 93±9ka. Four stratigraphic zones (A–D) were identified in the sedimentological data. The chronological model suggests that zones A–C were deposited between Marine Isotope Stages 5–2 and zone A during Stage 1, the Holocene. The palaeolimnological record tracks changes in the subglacial depositional environment linked principally to changing glacier dynamics and mass transport and indirectly to climate change. The sediment composition in zones A–C consists of fine-grained sediments together with sands, gravels and small clasts. There is no evidence of overriding glaciers being in contact with the bed reworking the stratigraphy or removing this sediment. This suggests that the lake existed in a subglacial cavity beneath overriding LGM ice. In zone D there is a transition to finer grained sediments characteristic of lower energy delivery coupled with a minor increase in the organic content attributed either to increases in allochthonous organic material being delivered from the deglaciating catchment, a minor increase in within-lake production or to an analytical artefact associated with an increase in the clay fraction. Evidence of biological activity is sparse. Total organic carbon varies from 0.2 to 0.6%, and cannot be unequivocally linked to in situ biological activity as comparisons of δ13C and C/N values with local reference data suggest that much of it is derived from the incorporation of carbon in catchment soils and gravels and possibly old CO2 in meteoric ice. We use the data from this study to provide guidelines for the study of deep continental subglacial lakes including establishing sediment geochronologies, determining the extent to which subglacial sediments might provide a record of glaciological and environmental change and a brief review of methods to use in the search for life.

Fossil plankton depth zones

Varied evidence from the known depth correlated distribution of benthic shelly facies communities in the Ordovician and Silurian clearly shows that graptolite taxonomic diversity increased from the nearshore regions to the shelf margin regions, as well as into the deeper portions of epicontinental basinal areas. We then consider a method for determining the depth distribution of individual graptolite taxa. This method depends on correlating the first appearance of graptolite taxa as one departs from shoreline in terms of the underlying benthos, arrayed in benthic assemblages. The first appearance departing from shoreline corresponds with the upper depth limits of each taxon in terms of the underlying depth indicated by the underlying, associated benthos. The depth of maximum abundance for each taxon should correspond to that point in the increasing relative abundance of that taxon where relative increase in abundance ceases. The lower depth limit of each taxon should correspond to that point on the relative abundance curve where increase in total relative abundance ceases. Using information about the stratigraphic ages indicated by the graptolite faunas, zone-by-zone, combined with that provided by the communities present within the associated and formerly underlying benthic assemblages should provide a more refined stratigraphic zonation than that obtained without combining both.

Biostratigraphy and paleoecology of the Oligo-Miocene succession in Fars and Khuzestan areas (Zagros Basin, SW Iran)

Paleontological and biostratigraphical studies on carbonate platform succession from southwest Iran documented a great diversity of shallow-water benthic foraminifera during the Oligocene–Miocene. Larger foraminifera are the main means for the stratigraphic zonation of carbonate sediments. The distributions of larger benthic foraminifera in two outcrop sections (Abolhayat and Lali) in the Zagros Basin, Iran, are used to determine the age of the Asmari Formation. Four assemblage zones have been recognized by distribution of the larger benthic foraminifera in the study areas. Assemblage 3 (Aquitanian age) and 4 (Burdigalian age) have not been recognized in the Abolhayat section (Fars area), due to sea-level fall. The end Chattian sea-level fall restricted marine deposition in the Abolhayat section and Asmari Formation replaced laterally by the Gachsaran Formation. This suggests that the Miocene part of the formation as recognized in the Lali section (Khuzestan area) of the Zagros foreland basin is not present in the Abolhayat outcrop. The distribution of the Oligocene larger benthic foraminifera indicates that shallow marine carbonate sediments of the Asmari Formation at the study areas have been deposited in the photic zone of tropical to subtropical oceans. Based on analysis of larger benthic foraminiferal assemblages and microfacies features, three major depositional environments are identified. These include inner shelf, middle shelf and outer shelf. The inner shelf facies is characterized by wackestone–packstone, dominated by various taxa of imperforate foraminifera. The middle shelf is represented by packstone–grainstone to floatstone with a diverse assemblage of larger foraminifera with perforate wall. Basinwards is dominated by argillaceous wackestone characterized by planktonic foraminifera and large and flat nummulitidae and lepidocyclinidae. Planktonic foraminifera wackestone is the dominant facies in the outer shelf.

Re-examination of the Zone I Material from Tamar Hat (Algeria): Zooarchaeological and Technofunctional Analyses

New analyses of faunal and lithic remains from stratigraphic Zone I (the top 15 layers) of the Iberomaurusian site of Tamar Hat, provide new data for understanding the function of this site and various activities carried out there. The occupation of Tamar Hat Zone I occurred in a prevailing mountainous environment which especially favoured game such as Barbary sheep. Zooarchaeological study of mammal remains revealed behaviours and technical processes which are related to hunting activity and the various stages of processing and butchering these animals. In addition, a technofunctional analysis of the backed bladelets indicates impact damage typical of the kind produced on projectile points used in hunting. Strong similarities in techniques and behaviours were observed in all of the occupation phases of Zone I.

Characterization and 3D reservoir modelling of fluvial sandstones of the Williams Fork Formation, Rulison Field, Piceance Basin, Colorado, USA

This study describes the stratigraphic characteristics and distribution of fluvial deposits of the Upper Cretaceous Williams Fork Formation in a portion of Rulison Field and addresses 3D geologic modelling of reservoir sand bodies and their associated connectivity. Fluvial deposits include isolated and stacked point-bar deposits, crevasse splays and overbank (floodplain) mudrock. Within the Williams Fork Formation, the distribution and connectivity of fluvial sandstones significantly impact reservoir productivity and ultimate recovery. The reservoir sandstones are primarily fluvial point-bar deposits interbedded with shales and coals. Because of the lenticular geometry and limited lateral extent of the reservoir sandstones (common apparent widths of ∼500–1000 ft; ∼150–300 m), relatively high well densities (e.g. 10 acre (660 ft; 200 m) spacing) are often required to deplete the reservoir. Heterogeneity of these fluvial deposits includes larger scale stratigraphic variability associated with vertical stacking patterns and structural heterogeneities associated with faults that exhibit lateral and reverse offsets. The discontinuous character of the fluvial sandstones and lack of distinct marker beds in the middle and upper parts of the Williams Fork Formation make correlation between wells tenuous, even at a 10 acre well spacing. Some intervals of thicker and amalgamated sandstones within the middle and upper Williams Fork Formation can be correlated across greater distances. To aid correlation and for 3D reservoir modelling, vertical lithology proportion curves were used to estimate stratigraphic trends and define the stratigraphic zonation within the reservoir interval. Object-based and indicator-based modelling methods have been applied to the same data and results from the models were compared. Results from the 3D modelling indicate that sandstone connectivity increases with net-to-gross ratio and, at lower net-to-gross ratios (<30%), differences exist in the cumulative volume of connected sandstone bodies between the indicator- and object-based lithology models. Therefore, the types of lithology-modelling methods used for lower net-to-gross ratio reservoir intervals are important.

2007 CUSHMAN AWARD WINNER: CITATION FOR LOUISETTE ZANINETTI

The 2007 Joseph A. Cushman Award for “Outstanding Achievement in Foraminiferal Research” is presented to a very fine lady scientist, Louisette Zaninetti, in recognition of her lifetime contribution to foraminiferal research. Almost the entire academic career of Louisette Zaninetti is connected with Geneva. This is where she obtained a diploma in Natural Sciences in 1962 and where six years later she defended her Ph.D. thesis on the Triassic foraminifera from the Almtal (Austria), under the direction of Professor Paul Bronnimann. After a short postdoc period in Perth (Australia), she returned to Geneva and worked as Lecturer at the university. In 1974, she was appointed Assistant Professor, and then in 1983, Professeur Extraordinaire in the Departments of Animal Biology and Geology and Paleontology. In 1980, however, she took a year off and worked as micropaleontological adviser for Pacific Energy and Minerals, Golden, Colorado. During this period, Louisette managed to publish her first major publication “Les Foraminiferes du Trias,” largely based on her Ph.D. thesis. This was a seminal work in a field that had been largely neglected and, remarkably, “not thought to exist” by some! It was published as a monograph in the Rivista Italiana di Paleontologia in 1976, and in it, not only did she recognize the stratigraphic potential of these Triassic foraminifera but also, together with colleagues, laid the foundations of a workable stratigraphic zonation. On the way, she had to resolve numerous and formidable systematic problems which previously had discouraged many from using foraminifera as …

Provenance of Albian sandstones in the São Luís–Grajaú Basin (northern Brazil) from evidence of Pb–Pb zircon ages, mineral chemistry of tourmaline and palaeocurrent data

Provenance of Albian sandstones in the southern margin of the São Luís–Grajaú Basin, northern Brazil, is documented for the first time. Palaeocurrent patterns, mineral chemistry of tourmaline and 207Pb/ 206Pb zircon dating, were used to define potential source areas for these deposits. The studied quartz-sandstones were sourced from different areas, discriminated essentially by palaeocurrent patterns and provenance-sensitive heavy mineral indices that suggest changes in provenance. Based on palaeocurrent patterns and RuZi, the studied sedimentary succession was subdivided into four heavy mineral zones, generically named A, B, C and D, in ascending stratigraphic order. Chemical analysis of tourmaline indicates provenance from metasedimentary rocks as metapelites and metapsammites, with lesser amounts of granites, pegmatites and aplites. 207Pb/ 206Pb ages from detrital zircon reveal a direct fingerprint of Archean and Proterozoic terrains in the source. Three major zircon populations were defined: Archean (3103–2545 Ma), Paleoproterozoic (2460–1684 Ma) and Neoproterozoic (993–505 Ma). Small groups of Mesoproterozoic (1570–1006 Ma) and Paleozoic (535–441 Ma) grains are also present. The potential source terrains for these stratigraphic zones were deduced on the basis of the overlap of probability density of zircon ages from the studied quartz-sandstones, with U–Pb and Pb–Pb zircon data from the basement of the São Luis–Grajaú Basin that includes the Amazonian and São Luís cratons, Araguaia and Gurupi belts, Borborema Province and Parnaiba Basin. The sediments of the Zone A were supplied from the São Luís Craton and Gurupi Belt and from the northwestern portion of the Borborema Province. The main source areas for the Zones B, C and D were the eastern portion of the Amazonian Craton and Araguaia Belt, and the Borborema Province. Zircons with ages of ca. 1000 Ma were attributed to the Cariris Velho Event, widely recognized in Borborema Province. The predominance of zircon and tourmaline grains with high textural maturity supports a strong contribution from sedimentary and metasedimentary rocks form Parnaiba Basin and Araguaia Belt, respectively. A more specific evaluation of these source regions is not yet possible due to the limited number of detrital zircon ages from these regions, mainly from the Parnaiba Basin. However this Paleozoic basin was one of the most important source of sediment for the Albian sandstones in the São Luís–Grajaú Basin.