Marine Invasions Research Articles

Pleistocene palynostratigraphy in the St. Lawrence Valley and middle Estuary

The litho-biostratigraphic framework of the upper middle and upper Quaternary units of the St. Lawrence basin results from the interplay of ice advance/retreat, isostatic depression/rebound, fluvial processes and climatic changes. Each main climatic cycle is characterized by a sedimentary sequence representative of the associated changing depositional environments. The climatic significance of the units is assessed with reference to the pollen content, and the evolving trend of the inferred vegetation. Five assemblages are defined: (1) the mixed woods assemblage related to temperate deciduous forests, (2) the boreal forest subdivided into a balsam fir (A. balsamea) dominated assemblage, a pine (P. banksiana or P. divaricata) dominated assemblage, and a spruce dominated assemblage (Picea mariana), (3) the forest tundra (subarctic zone), (4) the shrub tundra with subarctic plants, and (5) the herb tundra (arctic zone). Three marine invasions, older than Late Wisconsinan, record a progressive vegetal recolonization: a pre-Illinoian marine episode, the post-Illinoian marine invasion of Guettard Sea (6–5 transition), and the Cartier Sea invasion (substage 5b?). Three types of lake inundated the lowlands: (1) lake systems associated with interstadial or interglacial fluvial drainage, (2) deglacial lakes, with a gradual vegetal recolonization, (3) pre-glacial lakes, whose pollen indicates boreal forest replacement by forest tundra and herb tundra.

Continental break up and the distribution of fishes of Western Gondwana during the Early Cretaceous

Many Early Cretaceous fishes were endemic to western Gondwana, making their fossils potentially useful tools in biogeographic reconstruction. These occur in a variety of tectonic settings; for example, in rift basins of the East Brazilian Rift System (EBRIS) and corresponding sites in western Africa, in non-rift basins within the EBRIS region, and in interior localities far removed from this area in both Africa and Brazil. Furthermore these occurrences span much of the Early Cretaceous and include syn-rift and post-rift (transitional and marine) deposits. Development of a permanent equatorial seaway in the late Aptian is identified as a crucial event in the biogeographical history of western Gondwana, but several earlier tectonic events are recognized that could have played an important role in pre-drift intercontinental speciation. Different patterns of distribution are noted among non-marine fishes, some taxa occurring within areas of rifting while others are more widespread. The earliest Cretaceous marine fishes in NE Brazil are late Aptian and early Albian endemic circum-Gondwanan taxa. Their arrival coincides with the formation of the equatorial seaway but they occur in strata that were deposited under conditions of anoxia and abnormally high salinity. A more widespread marine invasion (probably from Caribbean Tethys) occurred in the middle and late Albian as oxygen and salinity levels were normalized and surface water exchange began in the equatorial Atlantic.

Detecting invasions of marine organisms: kamptozoan case histories

Detecting marine invasions can be challenging, especially for lesser-known taxa, and requires (a) thorough field surveys of the region of interest for members of the taxon, (b) systematic analyses to identify all species found, (c) literature searches for the worldwide distribution of these species and for previous records of the taxon in this region, and (d) application of rigorous criteria to assess whether each species found is native or introduced. We carried out these steps in order to detect and document kamptozoan (entoproct) invasions on the American mid-Atlantic coast. We report on the occurrence of two colonial kamptozoans (Barentsia benedeni, Loxosomatoides laevis) in Chesapeake Bay (Maryland and Virginia, USA). On the American Atlantic coast, B. benedeni had previously only been reported from Massachusetts, although this species has a worldwide distribution in bays and harbors. The genus Loxosomatoides had not previously been reported from North America and L. laevis was known only from India. Since the genus Loxosomatoides was very poorly characterized, we briefly review all four of its species, which differ only slightly from each other. We have also synonymized L. japonicum with L. laevis. We did not find any of the kamptozoan species previously recorded in surveys of Chesapeake Bay and the American Atlantic coast. This is the first detailed consideration of anthropogenic influences on kamptozoan distributions, and we emphasize that most kamptozoan species are cryptogenic pending further investigation.

Geochemical constraints on marine invasion and provenance change related to the opening of the Japan Sea: an example from the Lower Miocene shales in the Hoda section, Shimane Peninsula, SW Japan

Geochemical changes related to the opening of the Japan Sea are described in the Miocene shale sequence across the boundary of the nonmarine Koura and the marine Josoji formations in southwest Japan. Typical shales of the Koura Formation were derived from source material of acid to intermediate compositions. The Josoji Formation consists of black shales and is more homogeneous in composition than the Koura Formation, with gradual change from intermediate to basic source rock compositions. CIA values [chemical index of alteration; ratio of (Al to Al+Ca+Na+K)×100] for the upper Koura and Josoji formations show higher values (70–80) than those of the underlying lower and middle Koura Formation (40–60). This indicates that highly weathered detritus was supplied to the basin after transgression of the Japan Sea. Both Koura and Josoji shales are depleted in Nb compared with the average composition of cratonic shales, suggesting a volcanic arc signature. Total organic carbon and nitrogen contents increase gradually upward in the two formations, while total sulfur contents show oscillatory change. This relationship suggests a signal of fluctuating sea water invasion into the sedimentary basin during the deposition of the upper units of the Koura Formation (probably between 20–23 Ma) and a regression dominated by fluvial conditions for the lower Josoji Formation.

Non‐indigenous species as stressors in estuarine and marine communities: Assessing invasion impacts and interactions

Invasions by non‐indigenous species (NIS) are recognized as important stressors of many communities throughout the world. Here, we evaluated available data on the role of NIS in marine and estuarine communities and their interactions with other anthropogenic stressors, using an intensive analysis of the Chesapeake Bay region as a case study. First, we reviewed the reported ecological impacts of 196 species that occur in tidal waters of the bay, including species that are known invaders as well as some that are cryptogenic (i.e., of uncertain origin). Second, we compared the impacts reported in and out of the bay region for the same 54 species of plants and fish from this group that regularly occur in the regionÂ's tidal waters. Third, we assessed the evidence for interaction in the distribution or performance of these 54 plant and fish species within the bay and other stressors. Of the 196 known and possible NIS, 39 (20%) were thought to have some significant impact on a resident population, community, habitat, or process within the bay region. However, quantitative data on impacts were found for only 12 of the 39, representing 31% of this group and 6% of all 196 species surveyed. The patterns of reported impacts in the bay for plants and fish were nearly identical: 29% were reported to have significant impacts, but quantitative impact data existed for only 7% (4/54) of these species. In contrast, 74% of the same species were reported to have significant impacts outside of the bay, and some quantitative impact data were found for 44% (24 /54) of them. Although it appears that 20% of the plant and fish species in our analysis may have significant impacts in the bay region based upon impacts measured elsewhere, we suggest that studies outside the region cannot reliably predict such impacts. We surmise that quantitative impact measures for individual bays or estuaries generally exist for <5% of the NIS present, and many of these measures are not particularly informative. Despite the increasing knowledge of marine invasions at many sites, it is evident that we understand little about the full extent and variety of the impacts they create singly and cumulatively. Given the multiple anthropogenic stressors that overlap with NIS in estuaries, we predict NIS‐stressor interactions play an important role in the pattern and impact of invasions.

Siempre algún día (review)

288 Arizona Journal of Hispanic Cultural Studies War propaganda films in Mexico, simultaneously addressing each government's distinct goals. Four other essays, on the banana enclave in Colombia, the copper mines in Chile, the U.S. imposition of marriage and divorce law in Puerto Rico, and the Sandino rebellion, all show the ambiguous outcomes of U.S. corporate and military expansion in Latin America. While men and women used U.S. gender prescriptions favoring the nuclear family to achieve their own goals in the Chilean and Puerto Rican cases, residents of the banana enclave were not homogenized by the United Fruit Company: they developed multiple connections with the outside world and retained a dynamic local culture. The marine invasion of Nicaragua both provoked a nationalist response and won many local adherents. Both the marines and Sandino's followers appropriated local styles of violence, and the regional war actually expanded the reach ofthe Nicaraguan state. The revolt was not purely nationalist , nor was the invasion simply an external imposition. Two concluding essays by Emily Rosenberg and William Roseberry applaud the collection's successful use of cultural analysis, and integration of cultural and materialist approaches, respectively. A final visual essay by Maria del Carmen Suescun Pozas examines the meanings of eleven images by U.S. and Latin American artists that focus on imperialist themes. One ofthe collection's larger messages is that Latin Americans were not passive victims ofthe U.S. imperial enterprise, and U.S. actors needed to adapt their goals to local social and political conditions. Likewise , U.S involvement often provoked tacit and open resistance, as well as unintended consequences. Furthermore, the essays illuminate the gender and racial constructs developed by both U.S. and Latin American actors, and show how these ideas were part and parcel of the post-colonial encounter in the Americas. In short, imperialism is about much more than political and economic domination, and imperial control is always partial and contradictory. While pointing to important limitations in traditional political and economic approaches, as a group, the essays also raise a new set of questions. While cultural approaches point to the multiplicity of "encounters" between the U.S. and Latin America, how do we square the diversity of local interactions with the fact the U.S. was and is an imperial force in Latin America, and that this presence does have systemic properties? Moreover, how can theoretical discussions of U.S. generated representations of Latin America take into account how Latin Americans interpreted these discourses and images? In short, by deconstructing the discourses of imperialism , modernization, international relations , and so on, can we replace them with more adequate theories, or simply produce individual stories? For the most part, these excellent and at times brimant essays do not respond to these questions. However, readers of this volume will no doubt thank the authors for opening up this set of problems, and look forward to the further development of these important debates. Joel P. Stillerman The University of Arizona Siempre algún dÃ-a Tusquets Editores, 1998 Por Justo Vila Justo Vila (Badajoz, 1954) nace en el seno de una familia de jornaleros que se vio obligada a emigrar a las cuencas mineras de Arizona Journal of Hispanic Cultural Studies 289 Asturias para encontrar trabajo. De regreso a Extremadura, Vila compaginó sus estudios con trabajos como jornalero, albañil, educador, etc. Miembro fundador de la SEGUEF (Sociedad de Estudios de la Guerra Civil y el Franquismo), ha publicado varios libros de historia y la novela La agonÃ-a del buho chico (1994). En Siempre algún dÃ-a, Vila recrea el perÃ-odo histórico de una gran parte del siglo XIX y principios del XX a través de la crónica de una familia de Artobas. Este pequeño pueblo de la provincia de Badajoz se convierte en sujeto paciente de las leyes de desamortización implementadas poi el gobierno central de Madrid, y, a su vez, es testigo de los avances tecnológicos que comienzan a llegar de Europa a la penÃ-nsula. La trama argumentai de Siempre algún dÃ-a relata los avalares de una familia de Artobas a través de cinco...

Global Invasions of Marine and Estuarine Habitats by Non-Indigenous Species: Mechanisms, Extent, and Consequences

SYNOPSIS. Non-indigenous species (NIS) are increasingly conspicuous in marine and estuarine habitats throughout the world, as the number, variety, and effects of these species continue to accrue. Most of these NIS invasions result from anthropogenic dispersal. Although the relative importance of different dispersal mechanisms varies both spatially and temporally, the global movement of ballast water by ships appears to be the largest single vector for NIS transfer today, and many recent invasions have resulted from this transfer. The rate of new invasions may have increased in recent decades, perhaps due to changes in ballast water transport. Estuaries have been especially common sites of invasions, accumulating from tens to hundreds of NIS per estuary that include most major taxonomic and trophic groups. We now know of approximately 400 NIS along the Pacific, Atlantic and Gulf coasts of the U.S., and hundreds of marine and estuarine NIS are reported from other regions of the world. Although available information about invasions is limited to a few regions and underestimates the actual number of NIS invasions, there are apparent differences in the frequency of NIS among sites. Mechanisms responsible for observed patterns among sites likely include variation in supply of NIS, and perhaps variation in properties of recipient or donor communities, but the role of these mechanisms has not been tested. Although our present knowledge about the extent, patterns and mechanisms of marine invasions is still in its infancy, it is clear that NIS are a significant force of change in marine and especially estuarine communities globally. Taxonomically diverse NIS are having significant effects on many, if not most, estuaries that fundamentally alter population, community, and ecosystems processes. The impacts of most NIS remain unknown, and the predictability of their direct and indirect effects remains uncertain. Nonetheless, based upon the documented extent of NIS invasions and scope of then* effects, studies of marine communities that do not include NIS are increasingly incomplete.

How Does Immigration Influence Local Adaptation? A Reexamination of a Familiar Paradigm

How Does Immigration Influence Local Adaptation? A Reexamination of a Familiar Paradigm

Pattern, process, and prediction in marine invasion ecology

Invasions frequently continue long after dispersal corridors have been well established. Six interrelated processes (changes in donor regions, new donor regions, changes in recipient region, invasion windows, stochastic inoculation events, and dispersal vector changes) are examined to explain this phenomenon. The combination of these processes makes it difficult to forge a list of species from potential donor regions that will never become successful invaders and, by extension, to thus define the characteristics of species that have failed to invade. Predictions relative to which species will invade and when they will invade can be improved by more detailed attention to these six categories of interrelated processes that mediate invasion success.

Late Stage 5 Glacio-isostatic Sea in the St. Lawrence Valley, Canada and United States

Although post-glacial marine sediments of late Wisconsinan and early Holocene age are common in eastern Canada and the northeastern United States, remnants of older Pleistocene marine sediments are scarce. A fossiliferous marine clay that predates the classical Wisconsinan was recently discovered in the St. Lawrence Valley. A dominantly estuarine environment is inferred from the geochemistry of the shells (δ18O = −7.1) and from benthic foraminifer and ostracode assemblages. The clay indicates a marine invasion (Cartier Sea) shallower and probably shorter than that during the upper late Wisconsinan Champlain Sea episode (12,000–9,500 yr B.P.). The pollen content shows that regional vegetation during the marine episode began as open tundra, then became aBetulaandAlnus crispaforest, reached a climatic optimum withQuercus, Corylus,andAbies,and concluded as aPinus/Piceaboreal forest. A corrected infrared stimulated luminescence age of 98,000 ± 9000 yr is compatible with the epimerization ratio of shells. The Cartier Sea resulted from a post-glacial glacio-isostatic marine invasion in the St. Lawrence lowlands. It probably occurred during late stage 5 and is tentatively assigned to the transition of oxygen isotope substages 5b/5a. This marine episode dates to stage 5 of the preceding continental glacier which extended to middle latitudes in NE America.

The Jurassic succession in west-central Argentina: stratal patterns, sequences and paleogeographic evolution

Abstract Jurassic rocks in west-central Argentina are predominantly marine and marginal-marine siliciclastics, associated with prominent but volumetrically subordinate carbonates and evaporites. Facies developments were ruled by paleogeographic persistence within the southern-infratropical latitude belt (within 40–50°S) and by siliciclastic derivation from the Patagonian hinterland to the southwest. Minor volcanic and volcaniclastic supply arrived from the west, out of a magmatic belt related to Circum-Pacific convergence. Timing of the main marine-flooding events and general correspondence with the high-rank stratal packaging recorded in western North America, suggest that global eustasy was also a factor in controlling the local stratigraphic record. Early Jurassic sedimentation occurred within a series of semi-isolated depocentres linked to fault-bounded Triassic troughs. The Sinemurian-Toarcian deposits record depocentre expansion and coalescence. These trends were coeval with progressively more widespread marine invasions from the northwest and west, leading to an elongate marine seaway which connected central Patagonia with the Pacific domain. During the Aalenian-Bajocian the region was subject to a more subdued tectonism and the foreland side of the basin became fringed by an extensive clastic embankment. Bathonian and Early Callovian were times when coarse clastics prograded into the basin, while the marine embayment shrank as a result of stepwise forced regressions. During Late Callovian to Oxfordian globally rising sea-level, the depocentre witnessed the appearance of cosmopolitan invertebrates and a stratal pattern of basin widening and depositional underbalance, that promoted cratonward onlap and inception of widespread carbonate deposition. Ooidal-coralline carbonate development was terminated after a relatively sudden (Messinian-style) event that desiccated a large tract of the Andean basin, and favored massive precipitation of anhydrite. In the course of the Kimmeridgian the evaporite basin was largely flooded by siliciclastics and turned into a broad and featureless mudflat-salina complex, linked to a widespread erg and to an ephemeral drainage system. By the Tithonian, at a period of peak oceanic stand, marine connection was reinstated and recorded as the most widespread Jurassic transgression across the Neuquen-Aconcagua embayment. Shelfal deposition consisted of molluscs and ooid-dominated carbonate terraces that grew in pulses tuned to eustatic fluctuations. Like in other prolific petroleum provinces around the world the Tithonian basinal strata involve widespread euxinic deposits featuring unusually high organic content.

Séquence de la transition Illinoien–Sangamonien : forage IAC-91 de l'île aux Coudres, estuaire moyen du Saint-Laurent, Québec

A series of Pleistocene deposits extending over 155 m below sea level was drilled at Aux Coudres Island, in the middle St. Lawrence Estuary, Quebec. The series, which basis is unknown, is divided into two sedimentary units: the lower Baie-Saint-Paul Glacial Complex facies (−155 to −125 m), which is correlated with the Illinoian (isotopic stage 6), and a stratified sequence referred to as the île aux Coudres Formation. The latter is subdivided into four zones: a very compact lower clay (−125 to −102 m), rhythmites with Paleozoic schist debris (−102 to −71 m), and prodeltaic silts and deltaic sandy silts with brackish water benthic foraminifera (−71 to −2 m). The spore and pollen content indicates a schrub tundra followed by an afforestation sequence of a boreal forest that changes to an Abies forest and then to an interglacial mixed forest with Betula, Jugions, Carpinus or Ostrya, Carya, and, at the top, Betula, Tsuga, Quercus, and Ulmus. The accumulation of the sediments of the Île aux Coudres Formation required approximately 3500 years, beginning with a deep marine environment (about 300 m) followed by shallowing waters during the subsequent glacioisostatic rebound phase of the regression. The sedimentation is assigned to a main postglacial marine invasion, referred to as the Guettard Sea, which occurred prior to two regional glacial episodes and was partly contemporaneous with Bell Sea invasion in the Hudson Bay lowlands. A major postglacial sedimentary influx in the Atlantic Ocean, during the Illinoian-Sangamonian transition and at the beginning of the Sangamonian (transition 6–5 and early substage 5e) is inferred from this marine event.

CAT-scan in marine stratigraphy: a quantitative approach

Computed axial tomography (CAT-scan) gives a pseudo-3D representation of sedimentary cores. Sediments may be described and numerically processed from digitized high resolution images. A 150 m long borehole was drilled and sampled at Île-aux-Coudres, middle estuary of the St. Lawrence, Québec, and analysed by a tomodensitometer (CAT-scanner). This borehole represents mainly the Illinoian-Sangamonian transition series (isotopic stage 5e, 130-80 kyr B.P.) of a post-glacial glacioisostatic marine invasion and the subsequent regressive prodelta. Four representative samples, 900 mm long, were chosen for analysis from a transition zone between glacial and prodeltaic sediments. They have been described from tomographic longitudinal and transversal sections, from CT number series, and also from classical analysis such as grain size, organic matter and carbonates. CT numbers reflect sedimentary characteristics and are closely linked to grain size and to organic matter. Carbonates are only weakly correlated, probably because of its low concentration. Bed thickness and numerical processing of CT number series are used to characterize lamina, and allow for depicting sub-annual, annual and longer periodicities. Clay facies, fine and thick rhythmites, and isolated diamicton beds were identified. From bottom to top, the first sample contains homogeneous clay rhythmites, typical of a distal environment; the second is composed of diamictons and thin, alternating light-dark annual lamina sets; in the third sample, annual light-dark rhythmites are slightly thicker and display subtle semi-annual cyclicities; in the fourth sample, annual rhythmites are several centimetres in thickness and contain preserved sub-annual events, of possible seasonal cyclicity. This succession of facies and associated stratal periodicities may be typical of transgressive sedimentation in a basin such as the St. Lawrence estuary during the transition from glacial to non-glacial conditions.

Un patrimoine paysager à protéger : les dunes littorales de Merlimont et de Berck (Pas-de-Calais)

The coastal dunes of Merlimont and Berck (Pas-de-Calais, France) : an outstanding landscape to protect. The earliest coastal dunes, between the Canche and Authie estuaries, formed probably at the end of the sedimentary development of the «Plaine maritime picarde», around 2300-2100 BP (Subatlantic), after the last marine invasion which took place 2500-2370 years ago. Briquet's researches on historical development of the Merlimont and Berck coastal dunes are recalled. Since the last World War, the western dune system has changed significantly. The height of the coastal foredune has increased from a few meters to more than 15 m. At the same time, the rate of coastline retreat was 1 m per year at least. Both phenomena are related to the regional marine and aeolian dynamics. The foredune evolution with blowouts, gaps and rear sand-sheets (called «pourrières» in Picardy) implies massive sand supply from the beach. On the contrary, «caoudeyres» (deep blowouts) and parabolic dunes which form at the rear of the foredune by deflation scouring and progressive dune translation develop with a very low rate of beach sand supply.

Végétation et fluctuations climatiques postglaciaires sur la côte septentrionale gaspésienne, Québec

The postglacial (ca. 13 000 BP) vegetational and climatic history is reconstructed from the pollen analytical study of the sediments of two lakes located in coastal northern Gaspé Peninsula. J'Arrive Lake (altitude: 56 m) was submerged by the Goldthwait Sea until about 11 400 BP. Euloge Lake, 83 m in altitude and less than 1 km from the shore, escaped the marine invasion. Before 10 400 BP, the vegetation, very scarce at first, evolved to a herb tundra that lasted for over a millenium. A cold climatic oscillation correlative with the Younger Dryas is identified at both sites between 10 700 and 10 400 BP, during this herb tundra phase. After 10 400 BP, dwarf birch and willows colonized the sites, leading to a shrub tundra. The afforestation of the area began only around 9300 BP, with the late arrival of spruce and aspen. This phase was interrupted at 8650 BP by the upsurge of green alder, in response to another cold oscillation. Since 7250 BP, the present forested landscape finally developed in three steps, characterized by (i) a high diversity of forest species until 2500 BP, (ii) a loss of diversity until 1000 BP that favoured spruce and balsam fir, and (iii) an increase of heliophilous trees, shrubs, and herbs. These reconstructions contribute to the late-glacial palaeogeography of Eastern North America through the unravelling of conditions close to the retreating ice.

Late Quaternary marginal marine deposits and palaeoenvironments from northeastern Buenos Aires Province, Argentina: A review

The late Quaternary marginal marine deposits along eastern Argentina (Southwestern Atlantic) are reviewed according to our present knowledge. In the northeastern coastal area of Buenos Aires Province they have been assigned to a series of transgressions and regressions ranging from the late Pliocene to the late Quaternary. The most widely accepted model is Frenguelli's (1957) classical chronostratigraphical scheme of: ‘Belgranense’, late Pleistocene marine sediments at 3–6 m above m.s.l. and ca. 26,000−>35,000 14C years BP, the ‘Querandinense’, Pleistocene-Holocene estuarine sediments below or at present m.s.l., and the most extensive ‘Platense’, mid-Holocene marine deposits at 4.5−2 m above m.s.l. dated at ca. 8000-1340 14C years BP. The restricted ‘Belgranense’ deposits, recorded in Samborombon Bay, in Magdalena at ca. 32,000 BP, near Mar Chiquita at ca. 24,900 and 30,500 BP and southwards in Bahía Blanca at ca. 26,000–35,500 BP, may belong to an interstadial (González et al., 1986). The molluscan composition suggests a marine invasion of the area but not a typical interglacial cycle characterized by euhaline and warm water elements. However, the oxygen isotope record argues against an interstadial during the interval 34−27 ka and the chronological control for these deposits is very poor, suggesting that they most probably have been elevated neotectonically. The Pleistocene-Holocene ‘Querandinense’ deposits, extensively distributed along the Bonaerensian coastal plain and continental shelf (ca. 11,000 14C years BP), with very low faunal diversity, abundance of freshwater ostracods and absence of the warm water molluscs characteristic of the Holocene ridges, indicate low salinity and cool water conditions. Further dating and isotope analysis of these deposits are required for a better understanding of the chronology of climatic events by the end of the Pleistocene in this area and to establish whether or not they could correspond to the Younger Dryas event of the northern hemisphere. ‘Platense’ littoral ridges formed between ca. 7600 and 2500 BP extend in several subparallel rows from ca. 34° S to ca. 39° S. They formed either as beaches or possibly as sublittoral bars in Samborombon Bay, where they reach 120 km long, 10–30 m wide and up to 5 m thick at 4.5–5 m above m.s.l., or in the supratidal and intertidal zones in Mar Chiquita at 2–4 m above m.s.l. Molluscs and ostracods suggest a brackish marine to marine brackish environment of lower salinity than the modern Atlantic littoral. During the mid-Holocene, the oceanic waters were mixing with large amounts of Antarctic ice melting in the South Atlantic (Isla, 1990) probably reducing salinity along the Bonaerensian littoral. The oldest littoral ridges accumulated during the Hypsithermal and in the Punta Indio area, their different geometry and alignment, greatest age, highest diversity and warmer affinity of the molluscan fauna suggest a short interval of reversal of the atmospheric circulation pattern. Further research is necessary for a better understanding of the chronology of the marine late Quaternary deposits, coastal evolution and climatic changes in this area.

Miocene palaeogeography of the Mizunami group of the Tono region, central Japan

The Miocene Mizunami Group developed in three basins, the Kani, Mizunami and Iwamura basins of the Tono region, central Honshu, Japan. The Miocene palaeogeography of the Tono region is reconstructed on the basis of data obtained during the last ten years. Six palaeogeographic maps (I-a, b, II-a, b, c and III) covering the time period from 20 to 15 Ma ago show the palaeoenvironmental conditions at each developmental stage: I-a, volcanic activity in a small lake in the Kani Basin; I-b, two lakes in the Kani and Mizunami basins; II-a, marine invasion of the Iwamura and Mizunami basins and persistence of a lake in the Kani Basin; II-b and c, continued spread of the sea in the two basins and disappearance of a lake in the Kani Basin in stage II-c; III, rapid subsidence and formation of a wider and deeper sea. A palaeogeographic map of southwest Japan at ca. 16 Ma is also presented to show the geological setting of the Mizunami Group. The Mizunami Sea was a quasi-cratomic basin in the Tono region which was connected to the Pacific Ocean throughout the Miocene.

Les environnements sédimentaires du bas Sénégal après les barrages de Diama et de Manantali

During the last decades, in the estuarine part of the Senegal river, noticeable hydrological changes occurred.Downstream, from Gandiol to the mouth, these changes may be related to the inlet migration as well as pronounced marine invasions during the drought of 1972–1982 but mainly to the recent coming into operation of Diama retention dam. Upstream, from Diama to Saint-Louis, low salinity waters, due to floodgate opening, seem to generate sedimentary disturbance and faunal scarcity. In the Diama reservoir, the disappearence of polyhaline species has not been truly compensated by freshwater species settling owing to the remanent salinity and the extreme instability of this environnement.

Marine invasion processes: interactions between native and introduced marsh snails

We test two hypotheses to explain the success of a biological invader in marshes on the Pacific coast of North America. The first hypothesis focuses on the competitive superiority of an invading species over native species; the second hypothesis focuses on the absence of ecological equivalents in the aboriginal biota, such that no competitive interactions are necessary to facilitate successful invasion. As a model system we experimentally manipulated the introduced pulmonate snail Ovatella myosotis and the native prosobranch snails Assiminea californica and Littorina subrotundata. Manipulations included pair-wise enclosures to determine of Ovatella depressed the growth of the native;species; pair-wise associations to determine whether or not snails demonstrated negative or positive clustering; removal experiments to see if native snails invaded regions occupied by Ovatella, and reciprocal transplants on a vertical gradient to determine the physiological breath of the target species. In addition to monitoring population abundances of all three species seasonally, dietary overlap of these gastropods was also examined. No evidence of competitive superiority by Ovatella was found. Ovatella possesses the physiological capacities to exist in a semiterrestrial environment and is therefore able to take advantage of resources unavailable to native gastropods. We conclude that the successful establishment of this Atlantic snail in the Pacific Northwest did not arise at the expense of native species.

Lagoon and Tidal Flat Sedimentation of the Upper Devonian Nisku Formation in Southern Alberta

Since 1985, 26 oil pools containing 64 million bbl of oil in place have been discovered in the Nisku Formation in southern Alberta. The thoroughly dolomitized Nisku Formation varies from 20 to 30 m thick in southern Alberta and northern Montana. It overlies anhydrites and shaly carbonates of the Southesk or Duperow formations and underlies anhydrites of the Stettler or Potlatch formation. Burrowed, nodular-bedded skeletal wackestone, deposited over a shallow marine shelf, forms the basal Nisku Formation. These strata are succedded diachronously and unconformably by several tidal-flat and lagoon facies that include (1) southeast-thinning washover fans of cross-bedded peloidal grainstone; (2) laminated mudstone to current-bedded peloidal and intraclastic grainstone sourced within the lagoon; (3) stromatolitic mudstones; (4) laminated anhydrite beds precipitated during salina episodes; (5) Amphipora and brachiopod wackestones and thrombolites containing Renalcis, serpulids, and ostracoes, marking a brief marine invasion; and (6) brackish or freshwater shale and mudstone containing fragmented lycopod leaves and antiarch fish remains. These sediments are overlain by cross-bedded, peloidal, and calcisiltite grainstone and stromatolitic mudstone deposited in tidal channels and over shoals. All facies have been subjected to periodic subareal exposure which has produced leaching, solution collapse brecciation, teepee structures, and nodular-mosaic and void-filling anhydrite.more » Permeable reservoirs exist where leached, dolomitized tidal flat and lagoon sediments contain intercrystalline and pelmoldic porosity and little anhydrite cement.« less