Nonmarine Systems Research Articles

Depositional architecture of early rift non-marine systems and implications for reservoir development: Oligocene to Miocene Al Wajh Formation, Midyan Basin of Red Sea, Saudi Arabia

Exhumed early rift alluvial fan and braided fluvial fan systems are rare and consequently understanding facies distribution, stratal architecture, reservoir connectivity, and controls on stratigraphic development of these systems is quite difficult. The outcrops of early Oligocene to early Miocene Al Wajh Formation in the Red Sea region of Saudi Arabia provide an opportunity to investigate the depositional architecture and reservoir potential of an early rift alluvial to fluvial system. Eleven lithofacies (F1-F11) and four facies associations (alluvial fan facies association (FA1), braided fluvial fan facies association (FA2), floodplain facies association (FA3) and delta front facies association (FA4)) are identified in four subbasins (Maqna 1–2, Sukk and Ifal), suggesting deposition in an alluvial-braided fluvial fan system. FA1 (36–100%) and FA4 (9–13%) have higher relative proportion and widely distributed in the northern subbasins (Sukk and Ifal subbasins) while the relative proportion of FA2 (50–82%) and FA3 (18%) increases towards southern subbasins (Maqna-1 and Maqna-2 subbasins). Distribution of facies associations, relative reduction in the clast diameter, and general southward paleoflow direction suggest that the northern subbasins (Sukk and Ifal) represent the proximal settings and southern subbasins represent medial (Maqna-1 subbasin) and distal settings (Maqna-2 subbasin) of a large alluvial-braided fluvial fan environment. Stratal architecture of proximal conglomeratic channel deposits highlight that despite reasonable thickness and spatial connectivity (several meters), these deposits may have marginal reservoir quality because of poor sorting and high matrix content. Sandstone beds occurring in medial settings have a higher potential to act as hydrocarbon reservoirs by displaying excellent reservoir properties on the account of their significant thickness (up to few meters), coarse grain sizes, better sorting, considerable spatial connectivity (10s of meters) and lower proportion of interbedded mudstone.

Stratigraphic paleobiology

Abstract Stratigraphic paleobiology uses a modern understanding of the construction of the stratigraphic record—from beds to depositional sequences to sedimentary basins—to interpret patterns and guide sampling strategies in the fossil record. Over the past 25 years, its principles have been established primarily through forward numerical modeling, originally in shallow-marine systems and more recently in nonmarine systems. Predictions of these models have been tested through outcrop-scale and basin-scale field studies, which have also revealed new insights. At multi-basin and global scales, understanding the joint development of the biotic and sedimentary records has come largely from macrostratigraphy, the analysis of gap-bound packages of sedimentary rock. Here, we present recent advances in six major areas of stratigraphic paleobiology, including critical tests in the Po Plain of Italy, mass extinctions and recoveries, contrasts of shallow-marine and nonmarine systems, the interrelationships of habitats and stratigraphic architecture, large-scale stratigraphic architecture, and the assembly of regional ecosystems. We highlight the potential for future research that applies stratigraphic paleobiological concepts to studies of climate change, geochemistry, phylogenetics, and the large-scale structure of the fossil record. We conclude with the need for more stratigraphic thinking in paleobiology.

Dating lacustrine carbonate strata with detrital zircon U-Pb geochronology

Abstract Carbonate lacustrine strata in nonmarine systems hold great potential for refining depositional ages through U-Pb dating of detrital zircons. The low clastic sediment flux in carbonate depositional environments may increase the relative proportion of zircons deposited by volcanic air fall, potentially increasing the chances of observing detrital ages near the true depositional age. We present U-Pb geochronology of detrital zircons from lacustrine carbonate strata that provides proof of concept for the effectiveness of both acid-digestion recovery and resolving depositional ages of nonmarine strata. Samples were collected from Early Cretaceous foreland basin fluvial sandstone and lacustrine carbonate in southwestern Montana (USA). Late Aptian–early Albian (ca. 115–110 Ma) maximum depositional ages young upsection and agree with biostratigraphic ages. Lacustrine carbonate is an important component in many types of tectonic basins, and application of detrital zircon U-Pb geochronology holds considerable potential for dating critical chemical and climatic events recorded in their stratigraphy. It could also reveal new information for the persistent question about whether the stratigraphic record is dominated by longer periods of background fine-grained sedimentation versus short-duration coarse-grained events. In tectonically active basins, lacustrine carbonates may be valuable for dating the beginning of tectonic subsidence, especially during periods of finer-grained deposition dominated by mudrocks and carbonates.

Lacustrine carbonate platforms: Facies, cycles, and tectonosedimentary models for the presalt Lagoa Feia Group (Lower Cretaceous), Campos Basin, Brazil

Studies of lacustrine carbonate rocks in continental rifts have received huge interest in recent years because of their great economic value in the South Atlantic. However, most existing facies and tectonosedimentary models for carbonate platforms are based on marine carbonate systems, whereas models for nonmarine systems are scarce. The main aim of this paper is to establish such models and to further our understanding of the hydrocarbon-bearing late synrift Lower Cretaceous carbonate successions of the Campos Basin, Brazil. This paper is based on a proximal to distal industrial data set of three-dimensional (3-D) seismic, cores, and well logs from the Coqueiros Formation (Coquina), southern Campos Basin. The dominant carbonate facies in the Coqueiros Formation are mollusk-rich grainstones, rudstones, and floatstones, which form the main reservoir facies. The 3-D seismic interpretations show an oblique extensional rift system, characterized by a series of grabens, half grabens, accommodation zones, and horsts oriented northeast–southwest to north–northeast-south–southwest. Three tectonic domains are recognized based on structural style, stretching factors, and subsidence rates as well as facies and different types of lacustrine carbonate platforms. Proximal rift margin areas are characterized by a series of half grabens with footwall and hanging-wall dip slopes of shallow lacustrine carbonates and fluviodeltaic mixed carbonate and siliciclastic deposits in marginal, hanging-wall basins. Central areas are carbonate rich with platforms established over horst blocks surrounded by deeper-water carbonate facies. Distal areas have the highest amount of stretching and subsidence and accumulate the thickest carbonate successions over a template of buried horsts and grabens. The entire carbonate succession underlies a thick layer of Aptian salt, which forms the seal to this prolific hydrocarbon system.

Global Patterns of Extinction Risk in Marine and Non-marine Systems

Despite increasing concern over the effects of human activities on marine ecosystems, extinction in the sea remains scarce: 19-24 out of a total of >850 recorded extinctions implies a 9-fold lower marine extinction rate compared to non-marine systems. The extent of threats faced by marine systems, and their resilience to them, receive considerable attention, but the detectability of marine extinctions is less well understood. Before its extinction or threat status is recorded, a species must be both taxonomically described and then formally assessed; lower rates of either process for marine species could thus impact patterns of extinction risk, especially as species missing from taxonomic inventories may often be more vulnerable than described species. We combine data on taxonomic description with conservation assessments from the International Union for Conservation of Nature (IUCN) to test these possibilities across almost all marine and non-marine eukaryotes. We find that the 9-fold lower rate of recorded extinctions and 4-fold lower rate of ongoing extinction risk across marine species can be explained in part by differences in the proportion of species assessed by the IUCN (3% cf. 4% of non-marine species). Furthermore, once taxonomic knowledge and conservation assessments pass a threshold level, differences in extinction risk between marine and non-marine groups largely disappear. Indeed, across the best-studied taxonomic groups, there is no difference between marine and non-marine systems, with on average between 20% and 25% of species being threatened with extinction, regardless of realm.

Genetically Related Incised Valleys and Deltas: Sequence and Modern Analogue Modeling From the Nonmarine Santa Barbara Coalfield, Late Pliocene, Italy

Abstract The morphodynamics of coeval incised valleys and deltas are relatively well understood in marine-paralic environments, but not in the nonmarine, lacustrine counterparts. Here, we analyze the morphology and depositional and sequence architecture of a small-scale valley to deltaic complex preserved in a late Pliocene intermontane coalfield in the Northern Apennines, Italy. Outcrop exposures are integrated with 160+ well logs in an area of less than 1.5 km2. The main goal of this study is to demonstrate that spatially restricted yet fully preserved nonmarine systems are well suited for depositional, sequence, and modern analogue modelling, and deserve more attention in the literature. In this study, outcrop and borehole data are merged into isopach maps, highlighting the sedimentary response to a discrete cycle of lake-level retreat and re-expansion. Falling-stage and lowstand phases were characterized by incision of a meandering valley onto a previous highstand shelf, and by the avulsive progradation of an attached, shelf-edge delta. The supply-dominated character of the depositional system along with the limited wave fetch favored in this phase the preservation of the maximum regressive surface across the entire incised-valley to deltaic transect. The following lake-level re-expansion involved estuarine valley back-filling, and the transition from river-dominated to wave-dominated deltaic deposition. Enhanced wave ravinement and associated shoreline-independent prodelta forestepping promoted the development of a transgressive shelf-break bypass. These results are compared with reference sequence and accommodation models, as well as with two modern Ethiopian lakes undergoing acute forced regression. The similar scale and morphology of modern stranded highstand shelves and shelf-edge deltas provide a parallel for assessing the original topographic gradients and depositional dynamics of the late Pliocene case study. Modern and ancient analogues also shed light on the amplification of climate records in endorheic lakes, on the potentially strong avulsive character of falling-stage deltas, and on the sedimentary response to short-lived lacustrine fluctuations in rapidly subsiding basins.

Influence of environmental variables in the efficiency of phage therapy in aquaculture.

Aquaculture facilities worldwide continue to experience significant economic losses because of disease caused by pathogenic bacteria, including multidrug-resistant strains. This scenario drives the search for alternative methods to inactivate pathogenic bacteria. Phage therapy is currently considered as a viable alternative to antibiotics for inactivation of bacterial pathogens in aquaculture systems. While phage therapy appears to represent a useful and flexible tool for microbiological decontamination of aquaculture effluents, the effect of physical and chemical properties of culture waters on the efficiency of this technology has never been reported. The present study aimed to evaluate the effect of physical and chemical properties of aquaculture waters (e.g. pH, temperature, salinity and organic matter content) on the efficiency of phage therapy under controlled experimental conditions in order to provide a basis for the selection of the most suitable protocol for subsequent experiments. A bioluminescent genetically transformed Escherichia coli was selected as a model microorganism to monitor real-time phage therapy kinetics through the measurement of bioluminescence, thus avoiding the laborious and time-consuming conventional method of counting colony-forming units (CFU). For all experiments, a bacterial concentration of ≈ 105 CFU ml−1 and a phage concentration of ≈ 106–8 plaque forming unit ml−1 were used. Phage survival was not significantly affected by the natural variability of pH (6.5–7.4), temperature (10–25°C), salinity (0–30 g NaCl l−1) and organic matter concentration of aquaculture waters in a temperate climate. Nonetheless, the efficiency of phage therapy was mostly affected by the variation of salinity and organic matter content. As the effectiveness of phage therapy increases with water salt content, this approach appears to be a suitable choice for marine aquaculture systems. The success of phage therapy may also be enhanced in non-marine systems through the addition of salt, whenever this option is feasible and does not affect the survival of aquatic species being cultured.

Secondary foundation species as drivers of trophic and functional diversity: evidence from a tree–epiphyte system

Facilitation cascades arise where primary foundation species facilitate secondary (dependent) foundation species, and collectively, they increase habitat complexity and quality to enhance biodiversity. Whether such phenomena occur in nonmarine systems and if secondary foundation species enhance food web structure (e.g., support novel feeding guilds) and ecosystem function (e.g., provide nursery for juveniles) remain unclear. Here we report on field experiments designed to test whether trees improve epiphyte survival and epiphytes secondarily increase the number and diversity of adult and juvenile invertebrates in a potential live oak-Tillandsia usneoides (Spanish moss) facilitation cascade. Our results reveal that trees reduce physical stress to facilitate Tillandsia, which, in turn, reduces desiccation and predation stress to facilitate invertebrates. In experimental removals, invertebrate total density, juvenile density, species richness and H' diversity were 16, 60, 1.7, and 1.5 times higher, and feeding guild richness and H' were 5 and 11 times greater in Tillandsia-colonized relative to Tillandsia-removal limb plots. Tillandsia enhanced communities similarly in a survey across the southeastern United States. These findings reveal that a facilitation cascade organizes this widespread terrestrial assemblage and expand the role of secondary foundation species as drivers of trophic structure and ecosystem function. We conceptualize the relationship between foundation species' structural attributes and associated species abundance and composition in a Foundation Species-Biodiversity (FSB) model. Importantly, the FSB predicts that, where secondary foundation species form expansive and functionally distinct structures that increase habitat availability and complexity within primary foundation species, they generate and maintain hot spots of biodiversity and trophic interactions.

Stable Isotopes Reveal Widespread Anaerobic Methane Oxidation Across Latitude and Peatland Type

Peatlands are an important source of the atmospheric greenhouse gas methane (CH4). Although CH4 cycling and fluxes have been quantified for many northern peatlands, imprecision in process-based approaches to predicting CH4 emissions suggests that our understanding of underlying processes is incomplete. Microbial anaerobic oxidation of CH4 (AOM) is an important CH4 sink in marine sediments, but AOM has only recently been identified in a few nonmarine systems. We used (13)C isotope tracers and followed the fate of (13)C into CO2 and peat in order to study the geographic extent, relative importance, and biogeochemistry of AOM in 15 North American peatlands spanning a ∼1500 km latitudinal transect that varied in hydrology, vegetation, and soil chemistry. For the first time, we demonstrate that AOM is a widespread and quantitatively important process across many peatland types and that anabolic microbial assimilation of CH4-C occurs. However, AOM rate is not predicted by CH4 production rates and the primary mechanism of C assimilation remains uncertain. AOM rates are higher in fen than bog sites, suggesting electron acceptor constraints on AOM. Nevertheless, AOM rates were not correlated with porewater ion concentrations or stimulated following additions of nitrate, sulfate, or ferric iron, suggesting that an unidentified electron acceptor(s) must drive AOM in peatlands. Globally, we estimate that AOM could consume a large proportion of CH4 produced annually (1.6-49 Tg) and thereby constrain emissions and greenhouse gas forcing.

Increased continental weathering flux during orbital-scale sea-level highstands: Evidence from Nd and O isotope trends in Middle Pennsylvanian cyclic carbonates

Despite the common occurrence of orbital-scale (104–105yr) sedimentary cycles in a wide range of Proterozoic through Neogene marine and non-marine depositional systems, understanding the effects and phase relationships of orbital-scale climate drivers on time-equivalent marine and non-marine deposits is difficult mainly due to correlation limitations between the geographically isolated deposition settings. Results from this study assess the relationships between orbital-scale continental weathering flux and glacial–interglacial marine cycles using Nd isotopes (from whole rock limestones) and δ18O values (from conodont apatite) from Middle Pennsylvanian cyclic marine carbonates in the U.S. Southwest.Conodont δ18O trends from 2 of 4 sampled glacial–interglacial carbonate cycles support previous interpretations that observed water-depth changes were controlled by glacio-eustasy (30–50m magnitudes) combined with <1° seawater temperature changes. Two additional sampled cycles show initially increasing, then decreasing δ18O trends. Based on these results, we suggest that δ18O better defines a eustatic sea-level curve, rather than a facies-derived curve.εNd trends in 5 of 8 sampled cycles are higher during regressive intervals (early glacial phase) and lower during sea-level highstands (interglacial phase), supporting the hypothesis that increases in precipitation and/or air temperatures during interglacial intervals result in increased continental weathering rates and/or increased flux of weathered solutes to the Middle Pennsylvanian marine basin. This hypothesis is in contrast to traditional sequence stratigraphic interpretations (increased siliciclastic shedding into marine basins during falling sea level/lowstands) and suggests that climatically-controlled precipitation and/or air temperature fluctuations influenced continental weathering flux more than sea level-controlled shoreline or baseline position in this paleotropical location. These results highlight the use of combined εNd and δ18O analyses as a tool for evaluating the response of marine and coeval non-marine systems to orbital-scale climate changes, particularly in deep-time depositional systems.

Anaerobic oxidation of methane: an underappreciated aspect of methane cycling in peatland ecosystems?

Abstract. Despite a large body of literature on microbial anaerobic oxidation of methane (AOM) in marine sediments and saline waters and its importance to the global methane (CH4) cycle, until recently little work has addressed the potential occurrence and importance of AOM in non-marine systems. This is particularly true for peatlands, which represent both a massive sink for atmospheric CO2 and a significant source of atmospheric CH4. Our knowledge of this process in peatlands is inherently limited by the methods used to study CH4 dynamics in soil and sediment and the assumption that there are no anaerobic sinks for CH4 in these systems. Studies suggest that AOM is CH4-limited and difficult to detect in potential CH4 production assays against a background of CH4 production. In situ rates also might be elusive due to background rates of aerobic CH4 oxidation and the difficulty in separating net and gross process rates. Conclusive evidence for the electron acceptor in this process has not been presented. Nitrate and sulfate are both plausible and favorable electron acceptors, as seen in other systems, but there exist theoretical issues related to the availability of these ions in peatlands and only circumstantial evidence suggests that these pathways are important. Iron cycling is important in many wetland systems, but recent evidence does not support the notion of CH4 oxidation via dissimilatory Fe(III) reduction or a CH4 oxidizing archaea in consortium with an Fe(III) reducer. Calculations based on published rates demonstrate that AOM might be a significant and underappreciated constraint on the global CH4 cycle, although much about the process is unknown, in vitro rates may not relate well to in situ rates, and projections based on those rates are fraught with uncertainty. We suggest electron transfer mechanisms, C flow and pathways, and quantifying in situ peatland AOM rates as the highest priority topics for future research.

Mesozoic Tectonics and Sedimentation of the Giant Polyphase Nonmarine Intraplate Ordos Basin, Western North China Block

The Mesozoic Ordos Basin is a large intracontinental basin that is characterized by a thick, undeformed stratigraphic succession over a wide region that is bounded by deformed polyphase orogenic belts on all margins. Structural and stratigraphic studies document a diverse history of Late Palaeozoic through Cretaceous shortening, extension and strike‐slip on the northern and western basin margins, and a longer‐lived contractile setting in the southern part of the basin. In response to these structural episodes, associated basins formed within, or adjacent to, the marginal mountain belts and were filled by a variety of nonmarine depositional processes. Synchronously, subsidence across the whole of the Ordos block resulted in a large, integrated basin, also filled by nonmarine systems, that spanned across distinct structural domains. These stratigraphic and structural characteristics are interpreted to suggest that mechanical contrasts between the basin interior and the marginal mountain belts fundamentally control the timing, distribution and styles of deformation and basin formation on the margins of the Ordos block. This mechanical contrast between the Ordos Basin and its margins encouraged the repeated, polyphase deformation on its margins, whereas the vast area of the Ordos block continued to subside uniformly. These characteristics are typical of many large basin systems found on relatively recently assembled continents, like southern Eurasia. Examples that may be similar in many respects to the Ordos Basin include other collisional successor basins of China, such as the Tarim, Junggar and Sichuan basins.

Nonmarine sequence stratigraphy: Updip expression of sequence boundaries and systems tracts in a high-resolution framework, Cenomanian Dunvegan Formation, Alberta foreland basin, Canada

Ten allomembers, labeled J-A, have been mapped in the deltaic Dunvegan Formation using 2340 wells and 63 outcrop sections. Each allomember spans about 200 k.y., is bounded by regional transgressive surfaces, and consists of 3-10 component shingles, apparently of autogenic origin. Allomembers H-E are discussed in this article. Their internal stacking patterns and bounding surfaces permit interpretation as depositional sequences. Sequences H-F have a sigmoidal-prismatic geometry, downlap to the southeast, and thin northwest onto the coastal plain. No differential thickening exists toward the orogen in the southwest. In contrast, sequence E thickens markedly toward the northwest. The tabular geometry of sequences H-F suggests accommodation was controlled by sea level change, whereas the wedge geometry of sequence E suggests significant tectonic tilting. Subaerial unconformities that bound valleys and extend onto adjacent interfluve paleosols can be traced 120-330 km updip into outcrop. The base of each sequence is characterized by shoreline backstep of 80-150 km. Transgressive and highstand shingles in each sequence comprise marine deltaic deposits that pass landward into coastal plain strata. Falling-stage shingles offlap seaward with little or no nonmarine equivalents updip, whereas lowstand shingles show renewed coastal onlap. In outcrop, three nonmarine systems tracts are recognized: (1) A channel-dominated, low-accommodation systems tract fills valleys up to 35 m deep and is equivalent to the early transgressive systems tract. (Begin page 1968) (2) A lacustrine-dominated, high-accommodation systems tract comprises mudstone enclosing ribbon channel sandstones, blankets interfluves, and forms the bulk of each sequence. It is equivalent to late transgressive and early highstand systems tracts. (3) A paleosol-dominated, low-accommodation systems tract occupies the upper part of each sequence and is capped by the sequence boundary. It is equivalent to the late highstand systems tract. Sequence-bounding interfluve paleosols represent tens of thousands of years of pedogenesis related to slow aggradation, followed by fluvial entrenchment and clastic bypass, and represent the late highstand, falling-stage, lowstand, and early transgressive systems tracts. Coastal plain deposits record only part (perhaps

Sulfate Minerals in Evaporite Deposits

Evaporite deposits preserve a wealth of information on Earth’s past surface conditions. The deposits are sensitive indicators of depositional environment and climate, recorded in a wide variety of mechanically and chemically produced sedimentary structures and fabrics. Unique to evaporite deposits is the record they carry of the hydrochemistry of surface waters, including seawater. Sulfate minerals are important components in understanding the hydrochemistry of ancient surface waters. Sedimentological aspects of evaporite deposits were compiled by Melvin (1991). In the compilation, sedimentology specific to Ca-bearing sulfates was described by Warren (1991); Lowenstein and Hardie (1985), Handford (1991), and Smoot and Lowenstein (1991) discussed the sedimentology of evaporites in general. These general principles can be applied specifically to the sulfate minerals in evaporite deposits. Sedimentological aspects of sulfate minerals in evaporite deposits are not discussed here. For this information, the reader is referred to the above references. Hardie et al. (1985) and Spencer and Lowenstein (1988) discussed the petrography of evaporites and the interpretation of fabrics of evaporite minerals. Examples of petrographic aspects of sulfate minerals in evaporites are presented here along with references specific to the sulfate minerals. For a more complete understanding of these aspects the reader is referred to the above references. The major focus of this chapter is on the chemical aspects of the common sulfate minerals that occur in evaporite deposits. The discussion begins with an explanation of the concept of chemical divides and the determination of evaporation paths, and the evolution of brines in accordance with mineral solubility and the composition of dilute inflow waters. Determination of the precipitation pathways of the more soluble salts is more complex. Examples of sulfate-mineral assemblages in evaporation systems, calculated via thermochemical modelling, are given for both marine and non-marine systems. The mineralogy of evaporite deposits is …

Dormancy in Invertebrates

The ability to survive in a dormant state is a widespread, yet unevenly distributed feature among invertebrates. Organisms belonging to classes and phyla that include fresh-water or terrestrial representatives are more likely to possess a dormant stage than those in groups that are exclusively marine. Moreover, within taxa where has evolved, it is more common among fresh-water and terrestrial species than in marine species. This correlation between and habitat across 29 free-living invertebrate phyla raises the question of cause and effect. Are dormant stages more commnon in fresh-water and terrestrial habitats because there is greater selection for in those environments, or is a prerequisite for the successful invasion of non-marine systems? The mechanism of varies among species and ranges from a specialized diapausing embryo to a quiescent adult. Dormancy has most likely arisen multiple times in invertebrate life histories, both within and between phyla. Although may facilitate the invasion of fresh-water and terrestrial habitats, it is not always a requirement: many non-marine species do not exhibit dormancy. Additional key words: diapause, quiescence, life history, fresh-water, marine All natural environments vary, and organisms may occasionally experience conditions that are limiting for growth, survival, or reproduction. The form and nature of this variability differ among habitats, however, and this has led to the evolution of a wide array of life histories (reviewed by Roff 1992; Stearns 1992). For example, some species are iteroparous and offset the negative effects of temporal variation with long-lived adults that reproduce multiple times (Murphy 1968; Goodman 1984). Alternatively, other organisms avoid deleterious environmental conditions with reliable migration (Dingle 1978; Levin et al. 1984; Wiener & Tuljapurkar 1994). However, many species without either of these traits persist in variable environments. Often, these taxa inhabit relatively isolated, transient systems that can support life only for a fraction of the year (e.g., arctic tundra, deserts, temporary ponds). When organisms cannot migrate away from declining environmental conditions, and active adults cannot survive, the only viable option is persistence through dormancy. Dormancy has evolved in numerous bacterial, fungal, protist, plant, and animal species, but is completely unknown in many groups. Although all forms result a Present address: Illinois Natural History Survey, Champaign, IL 61820, USA. Voice: 217-244-2139. Fax: 217333-6294. E-mail: caceres@mail.inhs.uiuc.edu in some type of metabolic and/or developmental depression, the term dormancy actually encompasses a wide range of physiological states (see Hand 1991). Therefore, the form and duration of the dormant state vary widely among taxa. Whereas some species remain dormant only as long as conditions are unfavorable, others remain dormant for time periods much longer than the unfavorable environmental conditions, in :some cases for a century or more (Harper & White 1974; Henis 1987; Hairston et al. 1995; Caiceres 1997). ]Dormancy that extends beyond the duration of the environmental hardship introduces potential costs and benefits. When is not terminated upon the return of favorable conditions, there is the potential cost of lost reproduction. However, when the dormant prcpagules from a single cohort continue to introduce recruits into the active population for several years, populations of short-lived adults can sample different environments much in the same way as a long-lived iteroparous species (Seger & Brockmann 1987). Thus, overlapping generations are established in populations that might otherwise consist of discrete cohorts (Templeton & Levin 1979). ]In theory, the evolution of prolonged should be an alternative to either iteroparity or dispersal (Venable & Lawlor 1980; Levin et al. 1984; Rees 1994). In fact, these alternative life histories have been found in some natural systems. Rees (1993), in This content downloaded from 157.55.39.127 on Wed, 29 Jun 2016 04:32:53 UTC All use subject to http://about.jstor.org/terms

Marine and nonmarine systems tracts in fourth-order sequences in the Early-Middle Cenomanian, Dunvegan Alloformation, northeastern British Columbia, Canada

Abstract The Early to Middle Cenomanian Dunvegan Alloformation is a 3rd-order clastic sequence that was deposited on the western margin of the Alberta foreland basin. The alloformation, comprising ten allomembers (A-J) has been mapped over 33 000 km 2 using 1500 well logs and 40 outcrops. Regional flooding surfaces are used to define allomembers because they are more reliably identified in well logs than are Exxon-type unconformities (although in many instances unconformities and flooding surfaces are coplanar). The Dunvegan records episodic deltaic progradation from NW to SE along the axis of the foreland basin. This paper focuses on an 800 km 2 study area in NE British Columbia where both shallow marine and coastal plain strata are exposed in the valleys of the Peace and Beatton rivers. Marine strata comprise sandier-upward successions that grade from platy mudstone through cm-scale interbeds of wave rippled fine sandstone to dm-scale beds of HCS, commonly including large gutter casts. Successions may be capped by SCS and cross-bedded, fine-grained sandstone, sometimes with a rooted top. The succession of facies suggests a strongly wave-influenced deltaic shoreline. Gutter casts are consistently orientated shore-normal and appear to have been formed by oscillatory wave scour during storms. Sandstone distribution varies between successive progradational packages (‘shingles’) in allomember J, suggesting that delta switching was an important control on depositional cyclicity. Coastal plain deposits include small-scale (few metres) coarsening-upward successions of carbonaceous mudstone, siltstone and fine sandstone interpreted as lake and bay-fill deposits. Decimetre scale sharp-based sandstones may represent crevasse splays whereas lenticular, rippled and crossbedded sandstones were probably deposited in distributary channels. Rooted palaeosols are abundant. Both coastal plain and marine strata are locally replaced by erosive-based bodies of cross-bedded sandstone up to 25 m thick and 0.5–3 km wide, interpreted as incised valley fills underlain by type 1 sequence boundaries. Additional evidence of relative sea-level fall is provided by regressive surfaces of marine erosion beneath sharp-based shoreface sandstones. If attached to highstand deposits, these sandstones are assigned to the falling stage systems tract, whereas detached sandstones are assigned to the lowstand systems tract. During the early part of the transgressive systems tract, sedimentation was confined to incised valleys but later, interfluves were buried by sediments that locally contain dense Thalassinoides burrow systems, Teredolites and well-developed mud drapes, suggestive of brackish, tidally-influenced conditions. Overlying coastal plain strata lack evidence of marine influence and are attributed to the highstand systems tract.

Assimilatory sulfur metabolism in marine microorganisms: characteristics and regulation of sulfate transport in Pseudomonas halodurans and Alteromonas luteo-violaceus.

Sulfate transport capacity was not regulated by cysteine, methionine, or glutathione in Pseudomonas halodurans, but growth on sulfate or thiosulfate suppressed transport. Subsequent sulfur starvation of cultures grown on all sulfur sources except glutathione stimulated uptake. Only methionine failed to regulate sulfate transport in Alteromonas luteo-violaceus, and sulfur starvation of all cultures enhanced transport capacity. During sulfur starvation of sulfate-grown cultures of both bacteria, the increase in transport capacity was mirrored by a decrease in the low-molecular-weight organic sulfur pool. Little metabolism of endogenous inorganic sulfate occurred. Cysteine was probably the major regulatory compound in A. luteo-violaceus, but an intermediate in sulfate reduction, between sulfate and cysteine, controlled sulfate transport in P. halodurans. Kinetic characteristics of sulfate transport in the marine bacteria were similar to those of previously reported nonmarine systems in spite of significant regulatory differences. Sulfate and thiosulfate uptake in P. halodurans responded identically to inhibitors, were coordinately regulated by growth on various sulfur compounds and sulfur starvation, and were mutually competitive inhibitors of transport, suggesting that they were transported by the same mechanism. The affinity of P. halodurans for thiosulfate was much greater than for sulfate.