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L'Arbreda Cave is one of the southernmost of the Reclau Caves (Serinya, Girona, northeastern Iberian Peninsula), located between the west margin of the Pla d'Usall and the Serinyadell river, at an altitude of about 211 m a.s.l. The Pla d'Usall forms part of the Banyoles-Besald Basin, which is bounded by Eocene and Neogene reliefs. It is filled with sediments of Plio-Pleistocene age. The cave is a shelter formed by travertine cascades with a degree of karstification, and contains sedimentary deposits ranging from the end of the Middle Pleistocene to the Early Holocene, thus constituting an important archaeo-palaeontological record for an understanding of the prehistoric occupation of northeastern Iberia. It is one of the most complete and best-dated terrestrial sequences in Iberia from the Mousterian to the Early Holocene period. In this paper we present a palaeoenvironmental and palaeoclimatic reconstruction of the sequence based on non-flying small mammals (insectivores and rodents) and pollen analyses. The environmental and climatic results, together with the absolute dating of the sequence and direct comparison with NorthGRIP delta O-18 and the sea-surface temperatures (SST) of the Alboran Sea, allow us to identify various climatic periods within our sequence: a cold period between interstadials 12 and 10 in Level I, probably interstadial 10 in Level H-2 the Last Glacial Maximum (LGM) in Levels C and B, the Bolling-Allered interstadial (B/A) in Level A, and the Preboreal/Boreal (Pr/B) in the Terra Rossa Level We want to thank the editor Dr. Paul Hesse and the three reviewers (Prof. Gloria Cuenca-Bescos and two anonymous) for their comments that improve the final version of the manuscript. This paper is part of the projects HAR2013-48784-C3-2-P, CGL2012-38358 and 2014-SGR900. Excavations ara funded by "Conselleria de Cultura Generalitat de Catalunya". J.M. Lopez-Garcia is a beneficiary of a Beatriu de Pinos postdoctoral fellowship (2011BP-A200001) from the Generalitat de Catalunya, a grant co-funded by the European Union through the Marie Curie Actions of the 7th Framework Program for R + D

The Nihewan Basin in North China contains the densest concentration of early Pleistocene Paleolithic sites outside Africa. This paper introduces a new archaeological site complex at Madigou (MDG) that was systematically excavated from 2011 to 2014 in the northeastern part of the Nihewan Basin. The site contains fossils and well-preserved stone artefacts in fluvio-lacustrine sediments. Our magnetostratigraphic results situate the MDG sedimentary sequence in the early Brunhes normal chron and the late Matuyama reverse chron, including the Jaramillo normal subchron. The MDG artifact layers are positioned within the pre-Jaramillo Matuyama chron, with an estimated age of ca. 1.2 Ma, close to the onset of Mid-Pleistocene climate transition. The MDG core and flake technology includes bipolar flaking of siliceous dolomite cobbles, and freehand flaking of chert and brecciated chert block fragments. Mammalian fauna and pollen compositions indicate that the MDG hominins lived in an open habitat varying from lightly-wooded grassland to an ecosystem dominated by sparse steppe near the shore of the Nihewan paleolake. Our combined results in the fields of archaeology, paleontology, palynology and magnetochronology suggest that innovations in technological behavior may correlate with adaptations to high environmental variability during the start of Mid-Pleistocene climate transition.

Proximal alluvial sediments represent a useful sedimentary archive to reconstruct the tectono-climatic history of continental rift basins. However, poor dating of coarse fluvial successions usually prevents high-resolution distinction of tectonic and climatic processes, and thus good determination of process rates. This paper presents a dating study of Plio-Pleistocene Kalavryta river system during the early history of the Corinth Rift (northern Peloponnese, Greece) based on magnetostratigraphy and palynology. This river system developed across several active normal fault blocks that are now uplifted along the southern rift margin. The detailed sedimentary record constrains alluvial architectures from the proximal basin to the river outlet where small deltas built into a shallow lake. In four magnetostratigraphy sections the correlation to the reference scale relies on the identification of the Gauss/Matuyama magnetic reversal and biostratigraphic elements. The river system developed between about 3.6 to 1.8 Ma, with sediment accumulation rates (SARs) ranging from 0.40 to 0.75 mm yr−1. SAR is lower in the alluvial fans than in the deltaic system, and higher at the centre of the normal fault depocentres than at the fault tip. By comparison with worldwide Cenozoic SARs, our values are higher but lie in the same range as those determined in coarse alluvial foreland basins. Moreover, in the context of overfilled intra-mountainous rift basins, these rates are minimum values and can be used as a proxy for accommodation rate. Therefore, early rift stratal wedges and growth synclines attest high sedimentation rates and also high rates of tectonic processes. Finally, in the distal river system, floral compositions and changes of vegetation deduced from palynological data are coherent with alternating fluvio-deltaic and shallow lacustrine deposits, which are linked to relative base level variations. Dry/cool climate is preferentially recorded during periods of low lake level, while the warm/moist climate is mainly recorded in prodelta deposits during periods of high lake level. This correlation suggests that, despite the dominant control of active faulting, climate is a key control of syn-rift stratigraphic architectures.

International audience; Understanding the formation of the Qilian Shan in the NE Tibetan Plateau provides insights into the growth mechanisms of the northern portion of the plateau through time. The onset time of exhumation in the Qilian Shan is still debated. The Qinghai Nan Shan subrange, located in the southeastern Qilian Shan, is cut by the Yellow River that forms Longyang Gorge, providing a good vertical profile for thermochronological investigation of exhumation. In this paper, we reconstruct the cooling and exhumation history of the Eastern Qinghai Nan Shan using apatite fission-track(AFT) and apatite (Usingle bondTh)/He(AHe) thermochronological dating on basement rocks. The fission-track data display a marked age-elevation trend from Early Cretaceous (114–122 Ma) ages at the bottom of the canyon to Early-Middle Jurassic ages (165–180 Ma) at the top. Mean (Usingle bondTh)/He ages are mainly Early Cretaceous (97–128 Ma) with one Eocene outlier (42 Ma). Combined with fission track lengths, Dpar values and thermal modeling results, these data indicate that the study area resided above the closure temperature of AFT and AHe until Early Cretaceous. Rapid cooling occurred during the Early Cretaceous and early Cenozoic likely driven by the Lhasa and Indian blocks collision with the southern margin of the Asian continent. Nonetheless, since then exhumation was limited to less than a few kilometers in the study area. Combined with regional geological studies, the thermochronological analysis demonstrates that, since the Mesozoic, intense exhumation occurred simultaneously along the northern and southern margins of the Qilian Shan. Hence, we suggest that the geomorphic framework of the northeast margin of the Tibetan Plateau was established during the Early Cretaceous-early Cenozoic.

Analyses of stratigraphic sequences within the paleocanyons of the Hualapai Plateau, Arizona, are important because these deposits offer the only evidence for the Paleogene-Neogene geological history of the Grand Canyon area. In this paper, we focus on the origins and paleoenvironmental significance of the West Water Formation, located within the Milkweed and West Water paleocanyons on the Hualapai Plateau. We propose that the supposed “limestone unit” of the West Water Formation at and near its type section is not a limestone; rather, it is a 21 m-thick valley calcrete, overprinted by a ~ 1–2 m-thick pedogenic calcrete, and subsequently dolomitized in its upper-to-middle sections, with a superimposed 4 m-thick red paleosol. We also propose that this unit is not coeval in age or origin with the Long Point limestone on the Coconino Plateau, and that the presence of a complex calcrete-dolocrete-paleosol alters previous interpretations associated with this unit. Evidence for a calcrete-paleosol origin, beyond the West Water Formation's lack of fossils, includes: its predominantly micritic calcite-palygorskite composition; its textures characteristic of valley and pedogenic calcrete deposits (as exhibited by thin section, SEM, and TEM analyses); and its association with a relatively thick overlying red paleosol that also contains abundant palygorskite. Stable carbon and oxygen isotope values from carbonate cements are also within the range expected of a near-surface calcrete. Carbonate minerals within the calcrete-dolocrete were precipitated at or near the water table in a valley setting due to evaporation and/or CO 2 degassing in a semi-arid to arid environment of deposition. High 87 Sr/ 86 Sr values within the calcrete were inherited from groundwater infiltrating through Music Mountain Formation arkosic sediments, which were derived from a Precambrian source terrane to the south and southwest. No absolute ages exist for the Music Mountain Formation and West Water Formation in the Milkweed and West Water paleocanyons; these sediments could range in age from the Late Cretaceous to the latest Eocene-earliest Oligocene, and may record the Eocene-Oligocene Transition in the Grand Canyon area.

This paper provides a high-resolution temperature reconstruction for the last Millennium from Lake Atnsjøen, SE Norway (61°52′31″N, 10°10′37″E). The sedimentary record reveals strong influence of the large-scale global climate patterns on the local climate in southern part of Eastern Norway. We reconstructed mean July air temperature using Chironomidae-based transfer function and fossil Chironomidae assemblages. The reconstruction was supported by a selection of climate-sensitive geochemical and paleoecological sedimentary proxies of terrestrial and aquatic origin, including Cladocera, pollen and macrofossils. Presented results revealed that summer temperatures were 1–2 °C warmer than the mean Millennial temperatures during the 11th, 13th, 15th and 20th centuries and 1–2 °C lower during the 12th, 14th, 17th–18th centuries. A persistent cold period, the Little Ice Age (LIA), occurred between 1550 and 1800 CE, was interrupted by a short warming at 1650 CE. The recognized regional climate fluctuations during the last Millennium affected the lake and its catchment, of which the strongest impact was caused by the LIA cooling. During the LIA the catchment vegetation was impacted by climate deterioration and the lake productivity reached its lowest level during the last Millennium. The current temperature reconstruction is in agreement with a previous continental scale temperature reconstruction for Europe. From obtained results it emerges that during the LIA the climate of western Scandinavia has been dictated by the atmospheric patterns originating from the North Atlantic. peerReviewed

Evaluating and understanding bio-environmental relationships at different spatial and temporal scales is important for accurately assessing marine productivity in relation to oceanographic conditions in changing Arctic ecosystems. In this paper, we compare four different bio-environmental datasets, in order to shed new light on the complex marine ecosystem of the Baffin Bay-Labrador Sea region, as well as the historical links between environmental changes and the ecosystem. Satellite dataset was used to describe the regional distribution of chlorophyll a, sea ice concentration (SIC), sea surface temperature (SST) and sea surface salinity (SSS). Chlorophyll a data were also analysed together with shrimp assessment dataset to examine the relationship between marine pelagic productivity and bottom feeders off the Greenland coast. A microfossil dataset (diatom valves) from 57 surface sediment stations was used to describe diatom concentration and diversity across the study region. It was also used in combination with satellite data from the same sites to analyse species-environment relationships and develop a diatom-based transfer function for reconstructing past changes in SIC, SST and SSS. Subsequently, we applied the diatom transfer function on three short sediment cores from off SW and W Greenland spanning the last few centuries. A monitoring dataset of sea ice observations and instrumental measurements of water temperature and salinity, together with atmospheric data (air temperature and wind conditions) from Greenland, were used to develop a more complete picture of 20th and 21st century changes in ocean-climate conditions. Our comparative analyses show clear spatial distribution patterns of marine phytoplankton and identify key ecological groups linked to oceanic conditions. In addition, we find a significant correlation between the different trophic levels, culminating in a ‘productivity boom’ in 2001 CE. On a longer temporal scale, the transfer function reconstructions reveal a good correlation with the satellite, monitoring and observational trends, as well as a consistent, long-term decrease in sea ice linked to ocean-climate variability.

This paper is not subject to U.S. copyright. The definitive version was published in Palaeogeography, Palaeoclimatology, Palaeoecology 451 (2016): 73-83, doi:10.1016/j.palaeo.2016.03.018.

Glacial sediment is an important paleoclimatological and paleoenvironmental archive. In the Mediterranean region most of the Quaternary glaciers were hosted in carbonate mountains. Diagenetical processes in carbonate sediments tend to impact preservation of glacial features and complicate the establishment of accurate chronologies. This paper presents a sedimentological study of a paleoglacier hosted in the carbonate Velebit Mountain, Croatia. Three carbonate tills were studied in order to evaluate their depositional environments and the diagenetical processes that affect them. The tills were selected from lateral moraines of different glacial stages of the paleoglacier and they are interpreted as lodgement and melt-out tills. Diagenetical processes such as cementation, dissolution and increase in organic content were enhanced by the percolation of water through the sediment and the propagation of rootlets. This research demonstrates the importance of understanding the diagenetical processes affecting carbonate tills after their sedimentation. Studies like this are an essential research stage prior to conducting geochronological and paleoclimatological interpretations based on paleoglaciers in carbonate regions.

Volcanic islands are unique contexts to analyze the controls on calcrete development in settings with varied relief, climate and vegetation, and lacking carbonate host rocks. This paper discusses the formation of Quaternary calcrete profiles in Gran Canaria volcanic Island, under direct influence of the SAL (Saharian Air Layer). Calcrete profiles are multi-storey and composed of prismatic, massive, laminar, pisolithic, ooid-bearing, sandy mudstones with rhizoliths and brecciated horizons. Host rocks include basalts, siliceous mudstones, volcanic sands and gravels and bioclastic-rich sands. Carbonate is mostly calcite but some dolomite occurs in massive horizons. The main microfabrics include laminated micrite, fine crystalline dolomite, desiccated micrite, micrite-clay groundmass, oriented Mg-rich clays, peloids, spherulites and coated grains. δ13C varies from −3.26 to −9.18‰ VPDB and δ18O from +0.86 to −3.24‰ VPDB. The 87Sr/86Sr ratios are between 0.707504 and 0.708860, indicating that calcium was mostly supplied from the CaCO3-rich aeolian dust coming from the Sahara Desert. Calcrete profiles are mostly pedogenic with roots and microorganisms enabling carbonate precipitation within the soils. The correlation trend of δ13C and δ18O points to a climate control on precipitation, with the heavier isotope values in the horizons containing dolomite. Sedimentation rates interplayed with calcrete formation processes and erosion to outline the profiles/horizons. Amalgamated laminar horizons formed when the rate of calcrete formation was higher than sedimentation and erosion, whereas areas or periods with relatively higher sedimentation allowed the separation of calcrete horizons. The direction of the winds supplying aeolian dust, and the varied relief, vegetation and climate favored better development of calcretes in the relatively arid and lowland areas of the eastern side of the island. Our study shows that calcretes contain the record of the paleoenvironmental controls that operated in volcanic islands with no previous carbonate substrates.

This paper presents pollen analyses and radiocarbon dating on Crocuta coprolites from Las Ventanas (LV) and Carihuela (Car) Caves in southern Spain (Granada), with the aim of reconstructing the environmental conditions of these hominin sites. The LV coprolites are radiocarbon dated from c. 37,890 to 6980 cal yr BP, and the Car coprolites from c. 31,063 to 7861 cal yr BP. Overall, the palaeoecological scenario inferred from both coprolite series display similar patterns, with Pinus, Poaceae, and Artemisia as dominant during the full Pleistocene, and an important contribution of Quercus in the most recently dated coprolite samples. While the palynology is consistent with results of former investigations on the past environments in the region as obtained from other deposits (peat bogs, cave infills), the Late Glacial and Holocene chronology of several coprolites in both sites is in conflict with the generally accepted timing of extinction of Crocuta in western Europe. A discussion on the taphonomical processes and potential sources of carbon contamination of the radiocarbon samples is provided. The correlation between pollen from coprolites and from sedimentary records, and the paucity of the fossil bone record suggests nevertheless, that a late survival of Crocuta in southern Spain should not be categorically discarded.

The Last Interglacial Period (LIP) is often regarded as a good analogue for potential climatic conditions under predicted global warming scenarios. Despite this, there is still debate over the nature, duration and frequency of climatic changes during this period. One particularly contentious issue has been the apparent evidence of climatic instability identified in many marine cores but seemingly lacking from many terrestrial archives, especially within the Arctic, a key region for global climate change research. In this paper, geochemical records from Lake El'gygytgyn, north-eastern Russia, are used to infer past climatic changes during the LIP from within the high Arctic. With a sampling resolution of ~ 20–~ 90 years, these records offer the potential for detailed, high-resolution palaeoclimate reconstruction. This study shows that the LIP commenced in central Chukotka ~ 129 thousand years ago (ka), with the warmest climatic conditions occurring between ~ 128 and 127 ka before being interrupted by a short-lived cold reversal. Mild climatic conditions then persisted until ~ 122 ka when a marked reduction in the sedimentation rate suggests a decrease in precipitation. A further climatic deterioration at ~ 118 ka marks the return to glacial conditions. This study highlights the value of incorporating several geochemical proxies when inferring past climatic conditions, thus providing the potential to identify signals related to environmental change within the catchment. We also demonstrate the importance of considering how changes in sedimentation rate influence proxy records, in order to develop robust palaeoenvironmental reconstructions.

In this paper we present a paleoceanographic reconstruction of the southwestern South Atlantic for the past 13 kyr based on faunal and isotopic analysis of planktonic foraminifera from a high-resolution core retrieved at the South Brazil Bight continental slope. Our record indicates that oceanographic changes in the southwestern South Atlantic during the onset of the Holocene were comparable in strength to those that occurred during the Younger Dryas. Full interglacial conditions started abruptly after 8.2 kyr BP with a sharp change in faunal composition and surface hydrography (SST and SSS). Part of the observed events may be explained in terms of changes in thermohaline circulation while the other part suggests a dominant role of winds. Our data indicate that during the Early Holocene upwelling was significantly strengthened in the South Brazil Bight promoting high productivity and preventing the establishment of the typically interglacial menardiiform species. In general terms, oceanographic changes recorded by core KF02 occurred in synchrony with Antarctica's climate.

This paper is not subject to U.S. copyright. The definitive version was published in Palaeogeography, Palaeoclimatology, Palaeoecology 469 (2017): 159-160, doi:10.1016/j.palaeo.2016.11.028.

article i nfo This paper presents an updated, extensive review of glacier fluctuations during the past 1000 years in the extratropical Andes of South America between ca. 17° and 55°S. Given the variety of environmental conditions and evidence available for glacier fluctuations across this wide latitudinal range, regional accounts are given for the Desert Andes (∼17°-31°S), the Andes of central Chile and Argentina (31°-36°S), and the North (36°-45°S) and South (45°-55°S) Patagonian Andes. The techniques, dating limitations, and interpretations of the glacier records along this transect are also discussed. Information on glacier fluctuations in the Desert Andes is limited to the 20th century. Documentation on past glacier variations is more abundant in the Central Chilean-Argentinean Andes, but the number of chronologies dealing with glacier fluctuations prior to the 1900s is also limited. Most records indicate that glaciers were generally more extensive prior to the 20th century, with dates of maximum expansion ranging from the 16th to the 19th centuries. The number and extent of glaciers increase significantly in the Patagonian region, where the evidence available for dating glacier variations during the past centuries is more abundant and the dating control for glacier events is generally better than in the northern parts of the study area. For some Patagonian glaciers, maximum Little Ice Age (LIA) or post-LIA advances have been precisely dated by dendro- geomorphological determinations or in situ measurements. However, for most sites, the evidence available is still preliminary and there is considerable variability in the extent and timing of events related to the maximum LIA expansion identified in most areas between the 16th and 19th centuries. Evidence is starting to appear at a growing number of sites for glacier advances during the first half of the past millennium. These events were generally less extensive than the LIA maximum pulses. Despite the occurrence of several post- LIA readvances over the past 100-110 years, most areas in the Andes of extratropical South America have experienced a general pattern of glacier recession and significant ice mass losses. The differences in the glacier histories observed at local and regional scales probably reflect the inherent limitations associated with the glacier records and/or the dating techniques used in each case together with the varying dominance of precipitation, temperature and other climatic and non-climatic factors on glacier mass balance and glacier dynamics. These differences indicate that the late Holocene glacier history of southern South America is more complex than commonly assumed. The evidence discussed in this study highlights not only the immense potential for glaciological studies of this region but also a significant need for an increased number of detailed, well-dated records of glacier fluctuations.

South-central Chile is one of the most geodynamically active areas in the world, characterized by frequent volcanic eruptions and numerous earthquakes, which are both recorded in lake sediments. In Lago Icalma (39°S), long piston and short gravity coring, as well as 3.5 kHz high-resolution seismic profiling, have been carried out in order to study the Holocene sedimentary infill of the lake, with a special focus on earthquake-triggered deposits. Macroscopic description of sediment cores and detailed grain-size analyses allow us to identify four types of seismically-induced deposits, or “seismites”: slump deposits, chaotic deposits, turbidites s.s. and homogenites. Homogenites are characterized by the occurrence of three distinct units on grain-size profiles (i.e., a coarse base, a thick homogeneous unit topped by a thin layer of very fine sediment) and by the typical distribution of the grain-size parameters in a skewness–sorting diagram, while turbidites s.s. are characterized by a continuous fining-upward trend. Radiocarbon, 210Pb dating, and tephrochronology allow us to demonstrate that the regional seismotectonic activity was probably very high between 2200 and 3000 cal years BP as well as between 7000 and 8000 cal years BP and that none of the historically documented earthquakes has triggered a seismite in Lago Icalma. The most recent seismite recognized in the sediments of Lago Icalma is a slump deposit dated at 1100 ± 100 AD, i.e., older than the period covered by historical records. The remarkable record of seismites between 2200 and 3000 cal years BP is probably influenced by a major eruption of Sollipulli volcano at 3000 cal years BP, which has rejuvenated the stock of terrigenous particles available for erosion, by depositing a thick layer of pumices all over the watershed of Lago Icalma and by clearing the vegetation covering the volcanic ash soils. This paper demonstrates that the record of seismically-triggered deposits in lake sediments is not only controlled by the intensity of the triggering earthquake and the occurrence of unstable sediment along the lake slopes but also by the presence of particles available for erosion/remobilisation in the watershed.

This paper examines the interdependence among the different forcing factors in the evolution of the Traba coastal wetland (Galicia, NW Spain) based on lithofacies and diatom analyses of three cores reaching the basement. According to radiocarbon data, the wetland originated 5700 cal yr BP, a time when similar systems on the Atlantic coast of the Iberian Peninsula were formed. Diatom assemblage data allow the estimation of the sea level position at 5700 cal yr BP at least 7 m below present-day mean sea level. Attenuation of the sea-level rise at that time was a major driving mechanism that permitted the establishment of an incipient beach–dune complex, causing water-logging in the Traba basin. However, the location of this incipient wetland on a basement high, which prevented an open connection to the sea, made topographic inheritance the main forcing factor in the subsequent evolution of the wetland. Thus, Traba was never a coastal lagoon system, as it has sometimes been defined. The maximum permeability of the beach–dune complex enclosing the wetland was recorded after its origin until 2900 cal yr BP, when increased stormy conditions affected the Galician shelf waters. Since then, the evolution of the wetland has been mainly controlled by more local factors, especially the continental sediment supply. Changes in land use in the basin have accelerated the infilling of the water body since the 19th century. This rapid infilling makes the whole system more prone to total encroachment in the short term, rather than to sea drowning. Palaeoenvironmental analyses showing the main trends in the long-term evolution of coastal wetlands can be of key importance in any management decisions aimed at preserving these kinds of sensitive coastal environments. Ministerio de Ciencia y Tecnología; REN2000-0468 Ministerio de Ciencia y Tecnología; CGL2004-0048BTE

Earlier workers have established sea level curves for the Ashgillian–Llandovery sequence on Anticosti Island, Quebec, Canada, based on sedimentology and on brachiopod and reef communities. The complete Anticosti sequence has been collected for conodonts to provide a database of over 77 600 conodonts derived from 272 samples through the 800–1100 m sequence. This paper uses a statistical analysis of the database to establish the pattern of conodont communities and their interpreted water depths. This allows the establishment of a eustatic sea level curve for the sequence. This curve is in general agreement with those of the earlier workers, but is more detailed and better constrained stratigraphically given the large sampling program. The curve reflects more oscillating sea level changes for the whole sequence than those constructed earlier, and different water depths for certain intervals from those established earlier. The curve is valuable given that the Anticosti sequence is one of the most complete in the world for this interval, and its divergence from global eustatic curves for this interval is noted.

This paper uses a multi-proxy approach involving pollen, plant macrofossils, speleothem isotopes, and alluvial history of streams to reconstruct the history of prairie expansion and contraction along the prairie-forest border of southeastern Minnesota, USA. Early Holocene forests were replaced by prairie along this border, but eastward expansion of prairie stalled for 2000 yr when the prairie-forest ecotone stabilized. Prairie invaded the area from the west 8000^9000 yr B.P., but mesic forest remained less than 100 km to the east until about 6000 yr B.P. Changes in N 13 C values in speleothem calcite, that reflect the rise of C4 grasses, correlate well with the presence of C4 grass species identified in the plant macrofossil record. Periods of large floods correlate with speleothem evidence of dry summers, increased cool-season precipitation (both resulting in less plant cover to absorb moisture), and change to prairie vegetation. fl 2002 Elsevier Science B.V. All rights reserved.

Two types of laminated sediments are compared in this paper: the Kimmeridgian bituminous laminites of Orbagnoux (French Southern Jura Mountains) and the present-day ‘kopara’ of the French Polynesia atolls or Kiritimati (Christmas) Island from the Pacific Ocean. The kopara is made of laminated sediments, several tens of centimetres thick, that cover the floors of most shallow ( 3 -rich laminae. The top few centimetres host a succession of bacterial populations, from aerobic to strictly anoxic. Most carbonate grains are precipitated in situ, due to bacterial activity (s.l.). The Kimmeridgian bituminous laminae of Orbagnoux are partly made of flat stromatolites that show many similarities with the kopara. This analogy allows us to refine the interpretation of the Southern Jura platform where laminated, organic matter-rich, carbonates were deposited in many places.