Palaeoenvironmental Reconstruction Research Articles

Barnacle-rich facies as a tool for palaeoenvironmental reconstructions

Palaeoenvironmental data are fundamental in determining the manifold impacts of climate change. This paper argues that sessile barnacles are an excellent palaeoenvironmental proxy: they are present in nearly all nearshore environments, and their shell consists of diagenetically stable low-magnesium calcite and grows fast enough to record short-term variations. To demonstrate their utility, specimens from several Western Mediterranean Pliocene and Pleistocene barnacle-rich deposits are analysed herein, using for the first time a combination of sedimentology, taphonomy, stable isotope geochemistry and detailed comparisons with modern counterparts. Within shelf carbonate systems, barnacle diversity is highest in the shallow, nearshore waters and decreases moving offshore, thus providing a good proxy for the reconstruction of water depth and distance from the coastline. Barnacle taphonomy is also informative. Well-preserved complete specimens are characteristic of protected areas, whereas less well-preserved specimens occur in high-energy areas. The presence/absence of opercular plates is also particularly relevant for evaluating hydrodynamic conditions. As regards the C and O stable isotope ratios, due to the porous and coarse-grained nature of the deposits in which barnacle remains are usually found, the shells are often exposed to meteoric water percolation during diagenesis. Among the analysed specimens, only those collected from fine-grained deposits display no evidence of alteration and have isotopic ratios in line with those of their modern counterparts. These fossils display intra-shell variations that in modern barnacles have been related to short-term environmental changes (e.g., seasonal cycles). These results demonstrate that barnacles can always be useful for detailed palaeoenvironmental reconstructions based on skeletal assemblages. Furthermore, with further research aimed at gathering more data and assessing potentially interfering signals, they could become useful proxies for palaeoseasonality.

The trace fossil Thalassinoides paradoxicus Kennedy, 1967 revisited from its type locality (Albian-Cenomanian chalk, SE England)

The trace fossil Thalassinoides includes ichnospecies that have been recognised for a long time and widely used in the interpretation of depositional systems. Despite its broad occurrence, the ichnotaxonomic status of this important ichnogenus is far from being unmistakable, which in turn hampers its application in palaeoenvironmental reconstructions. One of the most common ichnospecies is Thalassinoides paradoxicus, originally described from the Paradoxica Bed of the Lower Chalk in the Hunstanton Cliff in SE England. To demarcate this characteristic form from similar ichnospecies, T. paradoxicus is reexamined and described from its type locality. It is characterised by an ‘irregular, very extensive horizontal burrow network, occurring at several levels, connected by vertical shafts’ (Kennedy), but its morphological variability also includes a range of significant architectural elements as well as burrow portions with a laminated wall, scratches and pellets. A series of colonisation events along omission surfaces can be reconstructed based on the occurrence of several burrow generations. T. paradoxicus is an important constituent of shallow-marine environments and subtle variations in morphology may help to constrain facies interpretations. Based on modern analogues and finds of body fossils within their burrows, decapod crustaceans (foremost callianassid shrimp) are known producers of T. paradoxicus from the Mesozoic onwards, whereas older records can be attributed to other malacostracans but also trilobites.

Multi-method characterization of the recent sediment from the Dibi subsidence lake in the tropical Adamawa region (central Cameroon): Implications for the palaeoenvironmental reconstruction

The evolution and functioning of various tropical ecosystems is poorly understood due to a lack of quantitative techniques to characterize the physicochemical composition of soils and sediment. Here, a detailed multi-method study of lithological changes is provided from a core taken from the silted-up Dibi subsidence lake (central Cameroon). To unravel the provenance of sediment, mineral constituents, and organic matter sources, an array of tools are applied including a spectrophotometer, a laser particle sizer, Rock-Eval pyrolysis, X-ray diffractometer (XRD), a portable X-ray fluorescence (XRF) spectrometry, and an inductively coupled plasma-atomic emission spectroscopy (ICP-AES) instruments. The studied core consists of light-colored deposits at the base (Unit 1) overlain by dark humic deposits (Unit 2). The sediment is very well graded (grading index Sd < 0.35Ф), indicative of bottom suspended to rolling transport. Unit 1 is characterized by relatively low values of total organic carbon (TOC: 2%–5%) whereas the dark Unit 2 has high contents of TOC (10%–33%). The core shows a high oxygen index (OI) value (average = 207 mg carbon dioxide (CO2)/g TOC) and a low hydrogen index (HI) value (average = 107 mg hydrocarbon (HC)/g TOC). This indicates highly altered organic matter (OM), likely from decomposed terrestrial plants. The chlorophyll-α fingerprint (peak around 675 nm) also reveals an autochtonous primary production of organic matter. The mineralogical assemblage of Unit 2 comprises kaolinite, quartz, feldspars, montmorillonite, ilmenite, siderite, gibbsite, rutile, and anatase whereas that of Unit 1 is similar but differs with the presence of illite and the absence of gibbsite. The high titanium dioxide (TiO2) and zirconium (Zr) contents confirm that the source rocks also are comprised of granites, and gneiss without volcanic rocks, such as basalts and trachytes. The source rocks have been intensively weathered using some parameters such as ln(Al2O3/Na2O), K2O/Rb, K/Al, and weathering indices, where Al2O3 denotes aluminum oxide, Na2O denotes sodium oxide, K2O denotes potassium oxide, Rb denotes rubidium, K denotes potassium, and Al denotes aluminum. The enrichment factors (EF) of redox-sensitive trace elements and their relation with TOC, the negative values of manganese/iron ratio (Mn∗) associated to three elemental ratios (cupper/zinc (Cu/Zn), thorium/uranium (Th/U), and vanadium/chromium (V/Cr)) attest to the predominance of sub-oxic to anoxic bottom waters in Dibi lake during sediment deposition. The data also show low primary productivity at the base of the core, followed by an increase towards the top, linked to the intensification of weathering and facilitated by humid climatic conditions, usually increase terrestrial input and palaeoproductivity. The petrological data show a generally warm and humid palaeoclimate. This climatic variation has contributed to the large spread of the savannah and disappearance of the forest. This study sheds light on the late Pleistocene to Holocene palaeoenvironment evolution of the Adamawa region which could be integrated into the context of the Pleistocene to Present regional evolution of the tropical palaeoenvironment.

Palaeoenvironmental reconstruction of a lower to middle Permian terrestrial composite succession from the Catalan Pyrenees: Implications for the evolution of tetrapod ecosystems in equatorial Pangaea

Tetrapod diversity in Permian terrestrial ecosystems of southwestern Europe is poorly recorded by bone specimens, but it is better represented by an important tetrapod ichnological record that is relevant to our understanding of vertebrate communities in equatorial Pangaea. Herein, two tetrapod ichnoassociations from three new ichnosites, within Cisuralian and Guadalupian volcanosedimentary terrestrial successions (the Lower Red Unit and the Upper Red Unit deposits) of the Castellar de n'Hug sub-basin (Catalan Pyrenees, NE Iberian Peninsula) are presented. Tetrapod ichnology in combination with stratigraphic and facies analyses permit a characterisation of these ecosystems. The sedimentary deposits show an evolution from fluvial meandering systems to playa-lake floodplains, denoting increased aridification and seasonality under a monsoonal regime. The ichnofossil record shows how tetrapod assemblages shifted from a prevalence of non-amniotes and eureptiles to a dominance of therapsids, eureptiles and parareptiles. The reported ichnotaxa are distributed in two ichnoassociations. The first preserves Batrachichnus, Dromopus, Hyloidichnus, Characichnos and an indeterminate tetrapod morphotype, whereas the second is defined by the presence of Dromopus, Hyloidichnus, Brontopus antecursor and Pachypes. The stratigraphically older ichnoassociation, preserved in volcaniclastic and fluvial deposits, presents features of the early Erpetopus biochron, whereas the stratigraphically younger one, preserved in playa-lake deposits, is constrained to the Brontopus sub-biochron. Biostratigraphic and magnetostratigraphic data suggest a late Cisuralian to middle Guadalupian age for the whole succession. The ichnoassemblage highlights a palaeobiogeographical connection between the Pyrenean Basin and other peri-Tethyan basins, which allows us to expand our knowledge about the palaeoecology and palaeobiodiversity of the Cisuralian to Guadalupian terrestrial ecosystems.

Simulating carbon accumulation and loss in the central Congo peatlands.

Peatlands of the central Congo Basin have accumulated carbon over millennia. They currently store some 29 billion tonnes of carbon in peat. However, our understanding of the controls on peat carbon accumulation and loss and the vulnerability of this stored carbon to climate change is in its infancy. Here we present a new model of tropical peatland development, DigiBog_Congo, that we use to simulate peat carbon accumulation and loss in a rain-fed interfluvial peatland that began forming ~20,000 calendar years Before Present (cal. yr BP, where 'present' is 1950 CE). Overall, the simulated age-depth curve is in good agreement with palaeoenvironmental reconstructions derived from a peat core at the same location as our model simulation. We find two key controls on long-term peat accumulation: water at the peat surface (surface wetness) and the very slow anoxic decay of recalcitrant material. Our main simulation shows that between the Late Glacial and early Holocene there were several multidecadal periods where net peat and carbon gain alternated with net loss. Later, a climatic dry phase beginning ~5200 cal. yr BP caused the peatland to become a long-term carbon source from ~3975 to 900 cal. yr BP. Peat as old as ~7000 cal. yr BP was decomposed before the peatland's surface became wetter again, suggesting that changes in rainfall alone were sufficient to cause a catastrophic loss of peat carbon lasting thousands of years. During this time, 6.4 m of the column of peat was lost, resulting in 57% of the simulated carbon stock being released. Our study provides an approach to understanding the future impact of climate change and potential land-use change on this vulnerable store of carbon.

Late Permian to early Middle Triassic palaeoenvironmental reconstructions of the High Atlas, Morocco: Geodynamic and climate implications in the intertropical western Peri-Tethyan domain

This study characterizes the depositional environment and climate evolution from the late Permian to the early Middle Triassic, based on detailed sedimentological and palaeosol analysis. Sequence stratigraphy and palaeoenvironmental reconstructions were used to define the Permian-Triassic (P-T) evolution of the High Atlas basins as well as to make a comparison with European basins.The late Permian in Morocco is dominated by distal fluvial fan environment, under arid to semi-arid paleoclimate conditions. Above the P-T unconformity (BS1), the Lower Triassic deposits, record a similar climate evolution from arid to subhumid conditions. In the Argana Basin, the Early Triassic starts by an aeolian deflation lag, followed by stacked debris flow lobes and sheetflood ephemeral alluvial fan deposits, showing immature to locally mature calcretes. The Marrakech High Atlas basins are further characterized by well-developed aeolian dunes in alluvial fan environment. These arid environments evolve through time from proximal to distal deposits, as a retrogradational trend, until well-developed floodplain or lacustrine deposits under semi-arid to subhumid climate (maximum flooding surface, MFS). From MFS, the evolution from distal to proximal environments, testified the progradational trend which is capped by a newly defined angular unconformity (BS2). Above this tectonically induced BS2, the sedimentary section, dated as Anisian is characterized by palaeoenvironments that include meandering river fluvial packages deposited in a semi-arid floodplain.Basin configuration, border fault direction, palaeoenvironments and palaeocurrents recorded in the Argana Basin confirm an independent system, separate from the Marrakech High Atlas (MHA) area during the Triassic. Above BS1, remnant topographies resulted in discrete catchment and discrete drainage systems are evidenced by palaeocurrent and palaeowind measurements controlled by border faults. Palaeoenvironment reconstructions show that the MHA was made up of numerous independent basins during the Early Triassic and the remnant topographies are progressively infilled until BS2. After the BS2, the palaeo-drainage became axial and basins were probably connected in the MHA. Above the P-T unconformity, a common climate evolution is observed in Morocco during the Lower Triassic until BS2, which could correspond to the European Hardegsen unconformity. The sedimentation record shows a similar change in climate and geodynamics to that recorded from both Europe and Morocco.

δ13Corg perturbations preserved by the interglacial Datangpo Formation in South China with implications for stratigraphic correlation and carbon cycle

Palaeoclimatic and palaeoenvironmental reconstructions of the Cryogenian Period have attracted attention in relation to the debated “Snowball Earth” hypothesis and the early evolution of metazoan life. The carbon cycle and redox conditions of the Sturtian-Marinoan non-glacial interval have been subjected to much controversy in the past decades because of the difficulty of the lack of a high-resolution stratigraphic correlation scheme. As one of the typical Sturtian-Marinoan interglacial deposits, the Datangpo Formation was widely distributed in South China with shales continuously deposited. The previous zircon dating data of the Datangpo Formation provide important ages for global constrain of the Sturtian-Marinoan non-glacial interval. Here we present a high-resolution straitigraphic study of the organic carbon isotopes, of the Datangpo Formation from a drill core section in northern Guizhou Province. Based on measured episodic δ13Corg perturbations, three positive shifts and three negative excursions are identified. A δ13Corg-based chemostratigraphic correlation scheme is proposed herein that works well for the Datangpo Formation regionally. Meanwhile, the δ13Corg vertical gradients changed dynamically throughout the formation. This discovery implies that a significant ocean circulation overturn might have occurred in the upper Datangpo Formation, coinciding with the potential oxygenation.

Coastal response to Holocene Sea-level change: A case study from Singapore

The deceleration of early to mid-Holocene (10–7 cal. ka BP) relative sea-level rise (RSLR) played a key role in transforming coastal systems from estuaries to deltas. Palaeoenvironmental reconstruction of coastal evolution provide case studies that can help project the response of modern coastal systems to future RSLR. The response of deltas to future RSLR is particularly important to South, Southeast and East Asia which collectively contain 71% of the global coastal population living below 10 m in elevation and 75% of the global coastal floodplain population. However, few Holocene studies of equatorial delta systems exist.Here, we investigate the early to mid-Holocene coastal response to decelerating rates of RSLR through paleoenvironmental reconstruction of the Kallang River Basin, Singapore. We produce a multi-proxy (sedimentology, stable carbon isotope, XRF elemental ratios) record from sediment core MSBH01B to compare with the Holocene relative sea-level record for Singapore. We identify different phases of coastal response through the interplay between accommodation space (A) driven predominantly by RSLR and sedimentation rate (S).In the early Holocene rapid RSLR coupled with low sedimentation rates (A/S = 5.1 ± 0.3) led to mangrove disappearance in the Kallang River Basin coastal area within ∼300 years (9.5–9.2 cal. ka BP). Estuarine sediments were deposited from 9.2 to 8.8 cal. ka BP during continued high rates of RSLR coupled with highest sedimentation rates (A/S = 3.1 ± 0.8) as the coastline retreated. Prodelta sediments were deposited from 8.8 to 8.2 cal. ka BP during decreasing rate of RSLR and high sedimentation rates (A/S = 4.6 ± 5.2). Delta front sediments were deposited during this delta initiation phase from 8.2 to 7.6 cal. ka BP as during a period of low and consistent RSLR and sedimentation rates (A/S = 1.7 ± 0.2). Finally, a prograding delta started forming from 7.6 to 7.2 cal. ka BP during lowest rates of RSLR and sedimentation rates (A/S = 1.7 ± 0.2). Our record provides a case study of possible responses of modern delta systems under a spectrum of predicted sea-level rise scenarios and accompanying sedimentation rates. This study provides an estimated threshold A/S value of 1.7 for coastal retreat to inform policy and mitigation/adaptation measures for Singapore and a simple methodology to obtain local threshold values of other equatorial cities built on floodplain and/or delta systems.

Modern pollen- and phytolith-vegetation relationships at a wetland in northeastern South Africa

In palaeoenvironmental reconstructions, few studies have focused on comparing the presence of pollen and phytoliths in surface sediments to the local vegetation. Notwithstanding inherent differential pollen and phytolith preservation, production, and dispersal, which affect their recovery and interpretation in sediment archives, there remains a need to explore modern pollen-vegetation, phytolith-vegetation and pollen-phytolith relationships to improve palaeoenvironmental reconstructions. We carried out palynological and phytolith analysis on six surface sediment samples linked to the botanical survey of five vegetation survey plots at Gustav Klingbiel Nature Reserve, Mpumalanga province in northeastern South Africa, to understand the relationships between the modern pollen and phytolith assemblages in the surface sediments and the contemporary vegetation of the study area. Correspondence Analysis (CA) was undertaken to examine the fingerprint of the local vegetation in the modern pollen-phytolith assemblage and evaluate whether the phytolith and pollen assemblages were tracking each other. CA illustrated that pollen and phytolith proxies are not tracking the same primary vegetation signals; modern pollen assemblages best represent the components of forest and wetland vegetation. In contrast, modern phytolith assemblages best represent grassland vegetation. Our study shows that differential pollen and phytolith preservation, production and dispersal significantly affect sediment records more than anticipated, thus combining multi-proxies (e.g., phytoliths, pollen) provides a more accurate basis for the interpretation of fossil spectra in palaeoenvironmental reconstructions.

Palaeoenvironmental reconstruction of Loch Duart (NW Scotland, UK) since the Last Glacial Maximum: implications from a multiproxy approach

ABSTRACTA sediment core from the salt marsh fringing Loch Duart, NW Scotland, UK, containing Lateglacial to Holocene sediments, was analysed using a multi‐element geochemical approach to elucidate the relative sea level (RSL) and palaeoenvironmental changes associated with the deglaciation of the British and Irish Ice Sheet. Elemental and isotopic measurements of rhenium, osmium, carbon and nitrogen, X‐ray fluorescence scanning, radiocarbon dating, and foraminiferal analysis produced a suite of data that complements the existing biostratigraphic framework. This suite of bio‐, litho‐ and chemostratigraphic analyses permits discussion of RSL changes that reflect the interplay between post‐glacial eustatic rise and glacio‐isostatic adjustment. The osmium‐isotope (187Os/188Os) data, coupled with a new age–depth model, depict an RSL fall between 16.8 and 14.1 ka cal bp at an average rate of 2 mm a−1. Falling RSL culminates in basin isolation and is followed by subsequent marine inundation from 11.6 ka cal bp. This RSL record preserves the local interaction between glacial isostatic adjustment and glacio‐eustatic sea‐level change, a relationship that is reflected in the sediment's 187Os/188Os signature. This is the first known application of the osmium isotope system in an isolation basin that is shown to be a viable proxy for RSL change, a technique that could be applied to glacially influenced isolation basins globally.

Taxonomy and palaeoecology of the fossil anamorphic fungus Mycoenterolobium eccentricum (R.K. Kar) G. Worobiec, n. comb.

Microremains of fungi from Neogene deposits from the Gray Fossil Site (Tennessee, United States) and the Bełchatów Lignite Mine (Poland), similar to the enigmatic fossil-species Kutchiathyrites eccentricus R.K. Kar, 1979, were reconsidered as representatives of the modern mitosporic genus Mycoenterolobium Goos, 1970. A new combination, Mycoenterolobium eccentricum (R.K. Kar) G. Worobiec, n. comb., is proposed. The geographical and stratigraphical range and ecology of the fossil and modern Mycoenterolobium species are discussed. Investigated remains of Mycoenterolobium eccentricum (R.K. Kar) G. Worobiec, n. comb. document the first fossil record of this fungus from both Northern America and Europe, while the Bełchatów mine represents the northernmost known fossil and modern occurrence of the Mycoenterolobium genus. Both modern and fossil species of Mycoenterolobium seem to prefer warm (tropical to warm temperate), usually humid climates. They are associated with plant debris (mainly wood) decaying in a damp or aquatic environment. Mycoenterolobium eccentricum (R.K. Kar) G. Worobiec, n. comb. is suggested to be used as a non-pollen palynomorph proxy for palaeoclimatic and palaeoenvironmental reconstructions.

Biomarker proxies for reconstructing Quaternary climate and environmental change

ABSTRACTTo reconstruct past environmental changes, a range of indirect or proxy approaches can be applied to Quaternary archives. Here, we review the complementary and novel insights that have been provided by the analysis of chemical fossils (biomarkers). Biomarkers have a biological source that can be highly specific (e.g. produced by a small group of organisms) or more general. We show that biomarkers are able to quantify key climate variables (particularly water and air temperature) and can provide qualitative evidence for changes in hydrology, vegetation, human–environment interactions and biogeochemical cycling. In many settings, biomarker proxies provide the opportunity to simultaneously reconstruct multiple climate or environmental variables, alongside complementary and long‐established approaches to palaeoenvironmental reconstruction. Multi‐proxy studies have provided rich sets of data to explore both the drivers and impacts of palaeoenvironmental change. As new biomarker proxies continue to be developed and refined, there is further potential to answer emerging questions for Quaternary science and environmental change.

Large-scale culturing of Neogloboquadrina pachyderma, its growth in, and tolerance of, variable environmental conditions.

The planktic foraminifera Neogloboquadrina pachyderma is a calcifying marine protist and the dominant planktic foraminifera species in the polar oceans, making it a key species in marine polar ecosystems. The calcium carbonate shells of foraminifera are widely used in palaeoclimate studies because their chemical composition reflects the seawater conditions in which they grow. This species provides unique proxy data for past surface ocean hydrography, which can provide valuable insight to future climate scenarios. However, little is known about the response of N. pachyderma to variable and changing environmental conditions. Here, we present observations from large-scale culturing experiments where temperature, salinity and carbonate chemistry were altered independently. We observed overall low mortality, calcification of new chambers and addition of secondary calcite crust in all our treatments. In-culture asexual reproduction events also allowed us to monitor the variable growth of N. pachyderma's offspring. Several specimens had extended periods of dormancy or inactivity after which they recovered. These observations suggest that N. pachyderma can tolerate, adapt to and calcify within a wide range of environmental conditions. This has implications for the species-level response to ocean warming and acidification, for future studies aiming to culture N. pachyderma and use in palaeoenvironmental reconstruction.

From land to sea: provenance, composition, and preservation of organic matter in a marine sediment record from the North‐East Greenland shelf spanning the Younger Dryas–Holocene

The organic matter content of marine sediments is often used to infer past changes in ocean conditions. However, the organic carbon pool preserved in coastal sediments is a complex mixture derived from different sources and may not reflect in situ processes. In this study, we combine taxonomic identification of reworked palynomorphs with pyrolysis organic geochemistry and reflected‐light organic petrographic microscopy to investigate the provenance, composition and preservation of organic matter in a marine sediment core retrieved from the NE Greenland shelf. Our study reveals continuous yet variable input of land‐derived organic carbon to the marine environment throughout the late Younger Dryas–Holocene, with the highest input of inert carbon in the late Younger Dryas. Although the sediments contain some recent marine palynomorphs, there is no other evidence of fresh marine organic carbon. In contrast, our results indicate that these shelf sediments represent a significant sink of recycled organic carbon. The results of pyrolysis geochemistry revealed that ~90% of the total organic carbon in the sediments is inert. The organic petrography analyses revealed that &gt;70–84% of the organic carbon in the sediment core is terrigenous. Reworked dinoflagellate cysts showed a continuous provenance of Cretaceous land‐derived material, most likely from the nearby Clavering Island. Our study points to the importance of constraining the organic matter origin, composition and preservation in marine sediments to achieve more accurate palaeoenvironmental reconstructions based on organic proxies.

Geoarchaeological investigation of a prehistoric tell in a coastal environment: the lowest levels at Kirrha (Plain of Delphi, Phocis, Greece)

Located downstream of the deltaic plain of Delphi and close to the present-day coastline, the tell of Kirrha is the largest Bronze Age site (Middle to Late Helladic I) in Phocis (Greece), covering an area of around 6 ha. The deepest, and therefore oldest, archaeological levels of the tell have never been reached. A multidisciplinary investigation combining geophysics (ARP and ERT surveys), coring, sedimentological and geochemical analysis (grain-size, CaCO3 content, magnetic susceptibility), observation of the microfaunal remains and radiocarbon dating provided for the first-time capital information about the internal structure of the tell of Kirrha as well as the date of the earliest occupation phase. The results indicate a thickness of occupation layers ranging from 7 to 9 m (until 2 m b.s.l.). While some archaeological indicators found in the cores (such as very isolated pottery fragments) suggest a probable Neolithic occupation, the radiocarbon dating results presented here indicate a first occupation at the very beginning of the Bronze Age (Early Helladic II). Palaeoenvironmental reconstruction reveals that the first inhabitants of Kirrha settled in a coastal-marsh-type environment that was being filled in by fine-grained alluvial deposits from the Pleistos and Hylaithos rivers. Geophysical surveys also revealed that parts of the tell have been eroded by a palaeochannel or buried under alluvial sediments.

The internal structure of a debris-covered glacier on Mars revealed by gully incision

Viscous flow features (VFFs) in Mars' mid latitudes are analogous to debris-covered glaciers on Earth. They have complex, often curvilinear patterns on their surfaces, which probably record histories of ice flow. As is the case for glaciers on Earth, patterns on the surfaces of VFFs are likely to reflect complexities in their subsurface structure. Until now, orbital observations of VFF-internal structures have remained elusive. We present observations of internal structures within a small, kilometer-scale VFF in the Nereidum Montes region of Mars' southern mid latitudes, using images from the Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) instruments on Mars Reconnaissance Orbiter. The VFF-internal structures are revealed by a gully incision, which extends from the VFF headwall to its terminus and intersects curvilinear undulations and a crevasse field on the VFF surface. Near to the VFF terminus, the curvilinear VFF-surface undulations connect to the VFF-internal layers, which are inclined and extend down to the VFF's deep interior, and possibly all the way to the bed. Similar structures are common near to the termini of glaciers on Earth; they form under ice flow compression where ice thins and slows approaching the ice margin, and ice flow is forced up towards the surface. We performed 3D ice flow modeling which supports this analogy, revealing that the inclined VFF-internal structures, and associated curvilinear structures on the VFF surface, are located in a zone of strong ice flow compression where ice flow deviates upwards away from the bed. The inclined VFF-internal structures we observe could represent up-warped VFF-internal layering transported up to the surface from the VFF's deep interior, or thrust structures representing debris transport pathways between the VFF's bed and its surface. Our observations raise numerous considerations for future surface missions targeting Mars' mid-latitude subsurface ice deposits. Inclined layers formed under flow compression could reduce the requirement for high-cost, high-risk deep drilling to address high-priority science questions. They could allow futures missions to (a) access ice age sequences for palaeoenvironmental reconstruction via shallow sampling along transects of ice surfaces where layers of progressively older age outcrop, and/or (b) access samples of ice/lithics transported to shallow/surface positions from environments of astrobiological interest at/near glacier beds. However, our observations also raise considerations for potential drilling hazards associated with structural complexities and potential dust/debris layers within subsurface ice deposits on Mars. They highlight the importance of characterizing VFF-surface structures, and their relationships to VFF-internal structure and ice flow histories ahead of ice access missions to Mars.

A High Arctic inner shelf–fjord system from the Last Glacial Maximum to the present: Bessel Fjord and southwest Dove Bugt, northeastern Greenland

Abstract. The Greenland Ice Sheet (GrIS) responds rapidly to the present climate; therefore, its response to the predicted future warming is of concern. To learn more about the impact of future climatic warming on the ice sheet, decoding its behavior during past periods of warmer than present climate is important. However, due to the scarcity of marine studies reconstructing ice sheet conditions on the Northeast Greenland shelf and adjacent fjords, the timing of the deglaciation over marine regions and its connection to forcing factors remain poorly constrained. This includes data collected in fjords that encompass the Holocene thermal maximum (HTM), a period in which the climate was warmer than it is at present. This paper aims to use new bathymetric data and the analysis of sediment gravity cores to enhance our understanding of ice dynamics of the GrIS in a fjord and inner shelf environment as well as give insight into the timing of deglaciation and provide a palaeoenvironmental reconstruction of southwestern Dove Bugt and Bessel Fjord since the Last Glacial Maximum (LGM). North–south-oriented glacial lineations and the absence of pronounced moraines in southwest Dove Bugt, an inner continental shelf embayment (trough), suggest the southwards and offshore flow of Storstrømmen, the southern branch of the Northeast Greenland Ice Stream (NEGIS). Sedimentological data suggest that an ice body, theorized to be the NEGIS, may have retreated from the region slightly before ∼ 11.4 cal ka BP. The seabed morphology of Bessel Fjord, a fjord terminating in southern Dove Bugt, includes numerous basins separated by thresholds. The position of basin thresholds, which include some recessional moraines, suggest that the GrIS had undergone multiple halts or readvances during deglaciation, likely during one of the cold events identified in the Greenland Summit temperature records. A minimum age of 7.1 cal ka BP is proposed for the retreat of ice through the fjord to or west of its present-day position in the Bessel Fjord catchment area. This suggests that the GrIS retreated from the marine realm in Early Holocene, around the onset of the HTM in this region, a period when the mean July temperature was at least 2–3 ∘C higher than at present and remained at or west of this onshore position for the remainder of the Holocene. The transition from predominantly mud to muddy sand layers in a mid-fjord core at ∼ 4 cal ka BP may be the result of increased sediment input from nearby and growing ice caps. This shift may suggest that in the Late Holocene (Meghalayan), a period characterized by a temperature drop to modern values, ice caps in Bessel Fjord probably fluctuated with greater sensitivity to climatic conditions than the northeastern sector of the GrIS.

Importance and role of neotaphonomic collections: the example of microvertebrate and experimental collection management

ABSTRACT The development of taphonomy has improved our knowledge of site formation and palaeoenvironmental reconstructions. It has also stimulated many neotaphonomic analyses that bring clues to some of the alterations and modifications processes of fossilisation and accumulations. This article aims to show that such neotaphonomic analyses and experiments, by generating a lot of valuable material and associate data, need to be integrated into official collections for future preservation. We will focus here upon two examples of neotaphonomic collections: 1 owl pellet microvertebrate collections and 2 collections resulting from experimental work (simulation and monitoring). We detail some problems for incorporating such new type of materials in Museums and some requirements for their curation. In the era of open science, there is a need to improve the management and curation of such unconventional collections to incorporate them into future classical comparative research, training and education as well as exhibitions.

Pliocene volcanic terrain of the South Caucasus as a missing link in Eurasian palaeobiogeography: Dating and palaeoenvironments of vertebrate assemblages of the Jradzor locality, Armenia

Cenozoic faunal exchanges between Europe, Asia, Africa and America played a key role in shaping modern-day Eurasian ecosystems with dispersal pathways controlled by the dynamics of natural palaeogeographic barriers (e.g., deserts, isthmuses, large water bodies, etc.). The South Caucasus is a mountainous region between Asia and Europe, which served as an important dispersal route during the late Cenozoic for the intercontinental exchanges of diverse terrestrial vertebrates. The Pliocene geology of this region is dominated by volcanic and volcaniclastic deposits that are generally not favourable for fossil preservation. However, a few rich fossil vertebrate faunas do occur although they lack comprehensive palaeoenvironmental and age constraints. In this paper, we present an integrated study of the stratigraphy and palaeontology of the Jradzor section located in the Gegham volcanic province of Armenia, to improve knowledge of late Cenozoic dispersal pathways. The 57-m-thick succession comprises 19 fossiliferous horizons with at least 48 identified vertebrate taxa (excluding birds). The palaeoenvironmental reconstruction suggests that the succession was deposited within a short-lived dammed lake that was subject to pyroclastic density flows, and later evolved into soil catenas. Taphonomic observations indicate that pyroclastic flows caused a high mortality of small-size vertebrates in most fossiliferous horizons, while a catastrophic lahar buried the large vertebrate fauna. Multiproxy dating places the studied section between 4.3 and ∼ 3.03 Ma and the mammalian fauna correlates to the MN15. Comparison with similar age localities from across the region shows that Jradzor comprises the most continuous Pliocene succession with the highest number of fossil taxa and fills the MN15 interregional gap. The rich fossil vertebrate faunas have Asian and primarily European affinities. Findings show that the South Caucasus was a significant dispersal route for terrestrial vertebrates between Europe, Asia and Africa, and is of crucial importance for understanding Eurasian palaeogeography.

Sea-level change and human occupation over 6000 years on Areoso Island (Ría de Arousa, NW Iberian Peninsula)

Coastal areas are extremely sensitive to variations in environmental conditions. The interaction of marine and continental processes causes a high degree of dynamism, generating depositional formations of great value for palaeoenvironmental reconstruction. This paper focuses on two pedostratigraphic deposits located under the current beach, in close proximity to archaeological tumuli located on Areoso Island (Ría de Arousa, NW Iberian Peninsula). Employing a geoarchaeological approach, sea-level rise, environmental conditions and human occupation over a 6000-year period are interpreted. The results of granulometric and mineralogical data, elemental composition and stratigraphic features, help to identify three successive environments: continental (rock weathering, soil formation and erosion); a transition to a coastal environment; and the establishment of full coastal conditions. The geomorphological evolution of the last 6.0 kyr BP has been controlled by climate, sea-level rise and human activity. The continental facies shows evidence of low sea-level up to 4.8 kyr BP and the first evidence of coastal processes after 3.2 kyr BP. These pedostratigraphic deposits located in an open coastal system improve the Holocene sea-level rise curve in the NW Iberian Peninsula and help to understand the context in which the most important archaeological structures on the island (the tumuli) began to be eroded.