A multiproxy palaeoecological record of Holocene lake sediments from the Rio Tapajós, eastern Amazonia

Two sediment cores up to 42 m in length were raised from the wide, deep, section of the lower Tapajós River, Amazonia, referred to as Lago Tapajós. These cores reveal a history of subtle environmental change that began with the formation of Lago Tapajós as sea level rose about 11,000 years ago. The sediments of the lake were deposited fairly quickly—at a rate of ca. 4 m per millennium and are uniformly fine grained, with low organic content. The fossil pollen record derived from these sediments reveals that forest surrounded this site throughout the Holocene. The largest change in the core took place between ca. 5500 and 4200 cal. years BP and reflects a transition from coarser to finer sediments. Coincident with the change in sediment is a slight transition in the pollen spectra with an increase in Poaceae abundance at the expense of the pioneer tree Cecropia cecropia. A tentative explanation is offered in which increased human activity, possibly spurred by climatic change, resulted in the formation of some local grasslands. However, despite the apparent actions of humans, there is no indication of basin-wide transformation of landscapes in this record. The Holocene persistence of forest as the dominant landscape matrix around Lago Tapajós is supported by low δ¹³C values and by the constant geochemistry and mineralogy of the lake sediments.     

Growth forms and palaeoenvironmental interpretation of stromatoporoids in a Middle Devonian reef, southern Morocco (west Sahara)

Growth forms of well-preserved stromatoporoids, including genera Actinostroma, Stachyodes, and Stromatopora, are described for the first time from the Devonian Sabkhat Lafayrina reef complex of southern Morocco (west Sahara), one of the best exposed Middle-Devonian stromatoporoid-dominated fossil reefs. Three facies types representing the well illuminated fore-reef, reef-core and transition to back-reef facies display the distribution and growth of stromatoporoids in a high latitude setting at 40–50° south of the palaeoequator. Stromatoporoids are largely in growth position and reflect the well-preserved reef architecture. Although outcrops are low topography, the reef's prominent profile is indicated by presence of spur and groove form and a clearly defined reef margin. Stromatoporoids are mostly laminar and domical forms, with little evidence of ragged margins, and indicate normal turbulence shallow waters, with low sediment deposition.     

Plio-Pleistocene climatic change in the Turkana Basin (East Africa): evidence from large mammal faunas

We investigated palaeoclimatic change in the Turkana Basin during the Pliocene climatic shift toward increased aridity in Africa. We analyzed the palaeoecology of this area using mammal faunas as environmental indicators. Twenty Plio-Pleistocene fossil assemblages and a comparative dataset of 16 modern localities covering a wide range of climatic and ecological conditions across Africa were analyzed. We constructed community profiles using taxonomic variables which reflect ecological information. Principal component analysis and bivariate correlation were used to study changes in the community structure of these mammalian faunas and to draw palaeoenvironmental inferences. Subsequently, least-squares regressions yielded climatic estimates (annual rainfall and drought length) for the studied period. An additional set of 8 modern faunas was used to validate these regression models. The climatic estimates showed a drying trend throughout the sequence. The biomes in the Turkana Basin changed from semi-evergreen rain forest to deciduous woodland and savanna during the middle-late Pliocene. This was the most important climatic shift detected in our study. Evidence suggests a continuous presence of savannas from 2.5 million years ago onwards. This pattern of climatic change is consistent with isotopic evidence on global climate, and with independently derived regional palaeoenvironmental evidence (i.e., micromammals, palaeovegetation, soil carbonates and palaeosols).     

Impact of disturbance on the Holocene development of a temperate peatland (Southern Québec)

A temperate peatland located in the St. Lawrence lowlands (Southern Québec) was studied in order to specify the past influence of natural and anthropogenic disturbances on its postglacial development. Seven profiles were analysed for pollen, macroremains, microfossils, macro- and microcharcoal, and loss-on-ignition. Fire incidence was important between 9300 and 8200 cal b.p. and during the last 300 years. The Early Holocene fires were contemporaneous with local waterlogged conditions, which prevented the destruction of peat. In contrast, the effects of the recent fires were enhanced by surface dryness resulting from the creation of at least six successive ditch networks over the entire peatland. The modification of the local hydrology and the regular occurrence of fire induced profound vegetation changes. The bryophytic carpet notably regressed in favour of a shrubby coverage, dominated by Chamaedaphne calyculata, Aronia melanocarpa and Betula populifolia. The results obtained suggest that rehabilitation of such an ecosystem is realistic, although relatively urgent in order to preserve the relict populations of endangered species, such as Woodwardia virginica and Dendroica palmarum. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The occurrence and preservation of ammonites in the Blue Lias Formation (lower Jurassic) of Devon and Dorset, England and their palaeoecological, sedimentological and diagenetic significance

More than two thirds of beds in the lowest Jurassic, Blue Lias Formation lack ammonites, which are commonly preserved in irregular or planar-bedded, bioturbated limestones, very rarely in laminated limestones and almost never in laminated black shales. Ammonites are preserved in 3D in nodular and planar-bedded limestones and at any orientation to bedding. Co-occurrence with macrobenthos and absence from beds without benthos suggest that Blue Lias ammonites were nektobenthonic. Scour structures and imbrication of ammonites in the Best Bed imply presence of traction currents. Lack of epifauna on large cephalopod shells (and other fossils) implies rapid deposition in event beds. Blue Lias deposition was episodic, not slow and continuous as the fine grain size implies. Undistorted trace fossils, uncrushed ammonites and stable isotope values all suggest early cementation of limestone beds from pore waters of a similar composition to contemporary Jurassic sea water. A clear diagenetic trend exists, with limestones having least, and laminated black shales most, modified stable isotope values. Contrast between trace fossil fills and host sediment demonstrates that Blue Lias rhythms are primary, but limestone beds have been diagenetically cemented.     

Long-term retrospection on mangrove development using sediment cores and pollen analysis: A review

Mangroves are biogenic systems that accumulate sedimentary sequences, where cores can provide records of mangrove species variation in distribution with past climate change and sea-level change. Fossil evidence used for palaeoecological reconstruction is based on organic remains that preserve identifying features so that they can be identified to generic levels at least. This includes macrofossils such as fruit, flowers, wood or leaves, or microfossils particularly pollen. Anaerobic conditions in mangrove sediment allow the long-term preservation of these fossil records. Fossil pollen from core samples is concentrated for microscopic examination by use of standard chemical treatments, but refinements of these are necessary for the peculiarities of mangrove peat. Pollen diagrams are expressed in concentrations, or more usefully in mangrove environments as proportions relative to others, as this has been shown to demonstrate the depositional environment actually underneath the mangrove forest. Radiocarbon dating of sedimentary sequences is used to date palaeoecological successions shown by fossil sequences, or long-term sedimentation rates. Sediment accretion in the last 50–200 years can been analysed better using Cs¹³⁷ and Pb²¹⁰ analyses. From pollen and macrofossils mostly recovered from stratigraphic cores of sedimentary rock and more recent sediment, the evolution and dispersal of mangroves through geological time has been reconstructed. While reconstruction of actual temperatures in these earlier records is associative to the fossil types present, it is apparent that mangroves have always been tropical species, extending to higher latitudes only during global warm periods. Many sedimentary records show mangroves deeper than the present lower limit of mangrove growth at mean sea-level. These indicate sea-level rising over time, and mangroves keeping pace with rising sea-level. Stratigraphic dating shows accretion rates of 1 mm a⁻¹ for low island locations, and up to 1.5 mm a⁻¹ in high islands/continental margins. Sedimentary records can also show die-off of mangroves with more rapid sea-level rise and replacement by open water during rising sea-level, landward retreat of mangrove zones, or replacement of mangroves by freshwater forest with sedimentary infill. The causes of mangrove community changes identified in the palaeoecological record can only be inferred by comparison with ecological studies in the modern environment, the link between the two that may be possible through long-term mangrove monitoring being poorly established.     

The remarkable Middle Pliocene non-marine mollusc record from Ceresole d’Alba, Piedmont, north-west Italy: Biochronology, palaeobiogeography and palaeoecology supported by fossil plants

A noteworthy, well-preserved non-marine mollusc fauna has been recorded from Middle Pliocene silty sediments at Ceresole d’Alba (Piedmont, NW Italy), a site described by F. Sacco in the 19th century. The fauna is characterised by rich assemblages of terrestrial and aquatic taxa showing a high degree of species diversity and the dominance of archaic land prosobranchs and pulmonates. A high rate of extinct taxa (at least 50%) and a good percentage of endemics are recognised. Many species are restricted to the Middle Pliocene and for some species, a Mio-Pliocene central-western European origin is noticed. The palaeoecological features of two distinct assemblages show dominant hygrophilous and thermophilous forest elements in the first one and prevailing freshwater taxa, testifying an environment of swamps or small water bodies, in the latter. A direct record of ancient vegetation has been provided by fruit and seed assemblages recovered from an organic layer and from two leaf assemblages sampled in the overlaying laminated muds. The fruit and seed assemblages clearly represent the record of a few azonal plant communities growing very close to the deposition site. On the ground of the ecological preferences of the modern plant analogues, both leaf and fruit assemblages indicate swamp communities poor in arboreal species. The percentage of extinct plant species is surely higher than 29% (nine species out of 31), and most probably close to 48% (15 species out of 31). The plant assemblages provide limited climatic indications, whereas warm-temperate and humid climate conditions are pointed out on the basis of modern preferences of several mollusc taxa. These climatic indications agree with those obtained from rich plant assemblages of neighbouring Pliocene sites. A correlation of the recorded palaeofauna and palaeoflora with the faunistic and floristic assemblages from the Middle Pliocene sediments of one of the most important non-marine palaeontological sites in the Piedmont Basin, the Villafranchian type-succession at Villafranca d’Asti (RDB quarry), is inferred.     

Charcoal analysis, a method to study vegetation and climate of the Holocene: The case of Lago di Pergusa (Sicily, Italy)

The direct comparison between microcharcoal and pollen data from the Holocene sediment core of Lago di Pergusa (central Sicily, Italy) led us to investigate the linkages between fire, vegetation, and climate in the Mediterranean Basin. The role of human populations in shaping the environment of the last millennia was closely examined as well. Pollen and charcoal were extracted using a standard pollen methodology and both identified from the same pollen slides. At Lago di Pergusa the importance of fire in maintaining and favouring a Mediterranean vegetation, a basic concept in ecology, seems to be inconsistent, as important fires took place in the open environments with xeric vegetation at the beginning of the Holocene well before the expansion of evergreen vegetation. On the contrary some big fires seem to have happened in the period (around 8000 years BP) in which the greatest wetness, the thickest forest canopy, and the most important expansion of submontane vegetation of the record are found. A probable explanation of this phenomenon can be found in the precipitation regime, in the increased available biomass and in the resulting increase in combustible material, indicating also that the highest humidity achieved in central Sicily during the Holocene was not strong enough to prevent fires. During this period drops in arboreal pollen concentration match in minima in the charcoal curves. Fires were practically absent during the Neolithic and Eneolithic periods and not responsible for the general trend towards aridification identified in the pollen record, at times in which prehistoric populations are generally believed to have caused forest clearance by burning. Important and frequent burnings are documented for the Bronze and Iron Ages and probably not all of them were fires of living trees, but burning of wood for producing metals, cooking or heating. The occurrence of a fire around 3700 years BP temporarily caused a minor decrease of arboreal pollen concentration. In the open landscapes of the two last millennia an almost continuous sign of regional burnings is recognized, confirming the historical evidence of an intense land use in central Sicily at least since Roman times.     

‘Cambrian’ demosponges in the Ordovician of Morocco: Insights into the early evolutionary history of sponges

Cambrian spicular sponge faunas are dominated by a distinctive assemblage of demosponges and hexactinellids that are known from Burgess shale-type faunas worldwide. Most of these are previously unknown outside the Lower-Middle Cambrian (and perhaps Tremadoc) and have no obvious close relatives in later sequences. This paper describes examples of Choia sp., Pirania auraeum sp. nov. and Hamptonia christi sp. nov. from the Arenig of Morocco, associated with isolated hexactinellid spicules. A summary of the stratigraphic ranges of the major Cambrian sponge lineages is provided. These indicate an environmental contrast in the Lower Palaeozoic evolution of hexactinellids and non-lithistid demosponges, with demosponges probably undergoing cryptic diversification in nearshore environments during the Upper Ordovician.     

Gigantoproductid and allied productid brachiopods from the “Calcaires à Productus” (late Viséan-Serpukhovian; Montagne Noire,southern France): Taxonomy and palaeobiogeographical position in the Palaeotethys

The “Calcaires à Productus” or “Calcaires à Productus giganteus” on the southern slope of the Montagne Noire (Hérault, France) consist of numerous isolated olistolitic limestone blocks, generally transported by gravitational flows into siliciclastic basinal deposits. The present paper is the first systematic monographic study of gigantoproductids, semiplanids, and some other large-sized productid brachiopods from the upper Viséan to Serpukhovian strata of the Montagne Noire. Gigantoproductids are represented by abundant Datangia semiglobosa and Kansuella spp.; a single Globosoproductus specimen is described. The semiplanids are represented by Latiproductus aff. latissimus, L. latissimus complicatus and L. edelburgensis, and the linoproductids by Balakhonia aff. kokdscharensis. The Montagne Noire productid faunas are found in very different facies including shell beds and microbial mounds. They are most abundant in assemblages from agitated, shallow water environments with a firm substrate where rugose corals are rare or absent. The palaeobiogeographical relations to the other regions in the western Palaeotethys are often limited to taxa with an almost cosmopolitan character. Worth noting is the absence of Gigantoproductus sensu stricto in the Montagne Noire. This genus, and other brachiopod taxa, migrated probably during the late Serpukhovian into southern France. On a larger scale, the presence of Kansuella indicates faunal exchanges with the eastern Palaeotethys (South China) via a westward migration path along North China, the Central Asian Orogenic Belt and south-eastern Laurussia. The studied taxa, even at the genus level, did not migrate into North America even if the Alleghanian Isthmus was still open.