Paleoenvironmental Interpretations Research Articles

Holocene to present-day coastal landscapes of Bar al Hikman (Oman): Neolithic waypoints on the shores of the Arabian Sea

Dramatic climatic and environmental changes over the last 12,000 years have significantly impacted Arabian coastal stratigraphy and human populations. The Bar Al Hikman peninsula (BAH), the largest low-lying area (1000 km2) along the Arabian Sea coast of Oman is a monsoon storm-dominated carbonate-evaporite system, where late Neolithic artifacts suggest human presence from at least 5.75–5.05 ka before the present (BP). Despite its archaeological significance at the crossroads of important Neolithic coastal sites in Dhofar, Masirah, and Ja'alan coast, paleoenvironmental interpretation, timing, and expression of relative sea level (RSL) changes in this coastal area remain poorly understood. Fortunately, the extensive size and arid climate of the area have preserved carbonate-dominated Mid-Late Holocene coastal geomorphologies exceptionally well, making this area an excellent geological archive to study past coastal environments, thereby understanding how environmental changes at BAH influenced Neolithic human mobility and settlement patterns. This study reconstructs the paleoenvironment of BAH over the last 12,000 years using a combination of field and remote sensing techniques, including satellite imagery, digital elevation models, bathymetric data, GIA modeling, and Sea Level Index Points to trace RSL history. The Holocene transgression began flooding the extensive continental shelf offshore BAH around 10 ka BP, progressively separating Masirah from the mainland through channel formation between 9.5 and 8.0 ka BP. It then inundated the present-day BAH peninsula around 7.7 ka BP, reaching a highstand of 2.5–3.2 m above present sea level by 6.0 ka BP (Mid-Holocene Highstand; MHHS), before gradually declining to the current level. Human presence documented at BAH (5.75–5.05 ka BP) coincides with the end of the mid-Holocene highstand, and the onset of the regression. This relative sea level history is contemporaneous to the aridification of Arabia, a period of transition from mangrove-dominated intertidal settings to coral reef and carbonate coastal barriers. The disappearance of mangrove-like gastropods around 5.4 cal ka BP and the subsequent appearance of significant coral fragments in the sediment indicates a critical change in terms of environmental settings with less nutrients and a warmer sea surface temperature). Comparing the findings at BAH to well-established nearby Neolithic sites on Masirah Island, the scarcity of prehistoric remains at BAH suggests that during the Mid-Holocene Highstand (MHHS), the small, rocky, paleo-low-lying islands at BAH may have served as waypoints and shelters between Masirah and the mainland.

Taphonomy and taphofacies of the bioclastic accumulations of Baía Formosa Paleolagoon (Quaternary), Rio de Janeiro state, Brazil

The study of taphofacies is extremely relevant in Paleontology as it provides support for paleoenvironmental interpretation by associating the preservation state of fossil content with sedimentological and stratigraphic characteristics. Despite its importance, there are few analyses of taphofacies in bioclastic accumulations of invertebrates in Brazilian sedimentary basins or Quaternary sedimentary accumulations. Therefore, this article aims to identify taphofacies in Holocene bioclastic accumulations distributed along the coastal plains of Armação de Búzios, Rio de Janeiro State, Brazil. After qualitative observations and taphonomic analysis of material from two outcrops located in the Canal Marina Porto Búzios, three distinct taphofacies were identified. Taphofacies 1 was interpreted as a beach environment related to strandlines; taphofacies 2 was interpreted as a shallow lagoon environment; and taphofacies 3 was interpreted as a lagoon margin. The taphofacies identified in this study are related to the maximum Holocene transgression, which occurred in the region about 6000 years BP, and the subsequent marine regression. This study presents relevant and unprecedented data, enabling a better understanding of the coastal evolution of Armação dos Búzios and Cabo Frio.

How old are the Mojave topographic dunes? The implications of new luminescence dating analyses from the Cady Mountains, Mojave Desert, southwest USA

The aeolian landforms of the Mojave Desert in the SW USA have been studied in detail over the last three decades, particularly in terms of their relationship to the region's topography and Pleistocene climate / sediment supply histories, as well as wider developments, such as the aeolian “sediment state” concept. In this context, the evolution of the Mojave River and its associated palaeolakes is thought to have been a key control on long-term sediment supply to aeolian systems, and luminescence dating chronologies for a range of (resulting) aeolian landforms have been related to these hydrological changes. Here we argue that at least some of these aeolian chronologies need to be re-assessed.We focus on luminescence chronologies for aeolian landforms within and marginal to the Cady Mountains, a mountain block adjacent to the Mojave River and palaeolake Manix, east of Barstow, California. We demonstrate that quartz in this locale exhibits several malign luminescence properties, and that low temperature K-feldspar infrared stimulated luminescence (IRSL) consistently exhibits high anomalous fading rates. Both contribute to age underestimation. We address these issues via post-infrared IRSL (pIRIR) and post-isothermal post-IR (pIt-IR) analyses of K-feldspars. The resulting ages span the last ~120 ka and imply phases of aeolian activity of a substantially greater antiquity than previously inferred. Notably, at one well-studied site – the Soldier Mountain sand ramp – the new ages suggest a landform dating not to Marine Isotope Stage (MIS) 1 or 2, as previously suggested, but more likely to MIS 5. The Cady Mountain record indicates that the only period of the last glacial cycle lacking evidence for aeolian sedimentation is ~40–9 ka, broadly consistent with expectations of increased regional humidity. These results also suggest that site topographic context may influence the age structure of aeolian deposits. In this instance, sand ramps consistently represent the oldest type of deposit (range ~ 40–120 ka), while early-mid Holocene dune accumulation is associated with sandsheets and valley-fill sands. Based on these findings, we argue that there is a need to critically re-assess the existing regional luminescence age database, and that there is potential to significantly revise our understanding of the region's aeolian system responses, and associated paleoenvironmental interpretations.

Advancing the automated foraminifera fossil identification through scanning electron microscopy image classification: A convolutional neural network approach

Abstract Handling more than thousand fossil foraminifera data is very challenging, especially for old-way identification. Determining morpho-taxonomy by conventional microscopic observation is very time-consuming and can lead to innacuracy identification. We are certain that the process could be advanced through big data analysis using a machine learning approach. Foraminifera fossils have already become a common standard for biostratigraphic proxies and paleoenvironmental interpretation. Therefore, the objective of this study was to develop an automated identification method using Convolutional Neural Networks (CNN). We used standardized Scanning Electron Microscopy (SEM) images of foraminifera acquired from various open-source databases for image classification. The analysis was conducted using Python programming language in Google Colaboratory. The image dataset is categorized based on its genus (n: 138) and divided into training and test/validation data for accuracy simulation (total image: 1833; data training: 1387; test/validation: 237/237). The best-fit accuracy values of the training-data and testing-data were between 97-86%:73-77%, with parameters including epoch number ranging up to 40, learning rates of 0.05, and a batch size of 64. These values indicate good prospects for foraminifera SEM Image taxonomic classification, demonstrating a noteworthy level of identification accuracy (63%). The outcomes of this study offer a new method for further effective automated morpho-taxonomic identification of foraminifera fossils using other conventional optic microscopy.

Enigmatic vertebrate swimming trace fossils from the Wapiti Formation, Alberta, Canada, and their implications for paleoenvironmental reconstruction

Vertebrate ichnofossil research, when compared with invertebrate ichnological analyses, tends to put greater emphasis on identifying the trace makers rather than associating the trace fossils with animal behaviors to interpret local paleoenvironmental conditions. In 2011, several sandstone blocks bearing unusual deformational structures were collected from the Wapiti Formation exposed near Red Willow Falls, Alberta, Canada. The sandstone blocks were analyzed for their sedimentary characteristics and the morphology of the enigmatic structures in order to identify their origins and their significance for paleoenvironmental interpretation. The deformational features are interpreted to be the swim tracks of small vertebrates attempting to escape a flash flood event. The sedimentology of the sandstone suggests a rapid increase in water flow in an overbank setting, and the orientation of the traces indicate that the trace maker was initially moving against, and then moving perpendicular to, the current. This is likely the first case of a trace fossil exhibiting clear association between vertebrates and flash flood events. As such, these traces provide an excellent example of the utility of vertebrate trace fossils for assessing organism response to changing environmental conditions, thus facilitating interpretation of local geological events.

Ocean bottom-water oxygenation across the Late Miocene–Early Pliocene biogenic bloom

The Late Miocene–Early Pliocene biogenic bloom (ca. 9–3.5 millions of years ago, My) represents a period of globally heightened marine biological productivity. Paleoenvironmental studies across this interval show alternating phases of low-oxygen eutrophic and well-oxygenated oligotrophic conditions. Here, we focus on the bottom water oxygenation changes during the biogenic bloom to assess the validity of the enhanced Benthic Foraminifera Oxygen Index (EBFOI). The index was calculated for three ocean drilling sites: Ocean Drilling Program Site 1085 (southeast Atlantic), and International Ocean Discovery Program sites U1506 (southwest Pacific) and U1488 (equatorial Pacific). The quantitative study of benthic foraminiferal assemblages from Site 1488 allowed us to infer the paleoenvironmental evolution across the biogenic bloom. At this site, we document a shift from stable oxygen concentrations and seasonal input of phytodetritus (8.7–4.3 My) to short-term fluctuations between low oxygen eutrophic conditions and well-oxygenated oligotrophic conditions (4.3–3.0 My). The EBFOI calculated at sites 1085 and U1506 was cross-referenced with the published paleoenvironmental conditions. While the EBFOI proves to be a valuable tool to infer paleoenvironmental changes at the seafloor, it has limitations, as evidenced by comparisons with paleoenvironmental interpretations of Site U1488, where it does not consistently align with inferred oxygen conditions.

Tooth wear analyses track niche partitioning at Gerakarou, a 1.8 Ma old site from Greece

The climatic instability of the Early Pleistocene induced regional paleoenvironmental changes, which impacted faunal composition and dynamics. It coincides with the Homo dispersal out of Africa. The role played by the Eastern Balkans in this dispersal is at the heart of current scientific debates. The rich fossil assemblage of Gerakarou-1 (2–1.8 Ma; northern Greece) can provide important insight into the environmental conditions of that time and area. In this study, we provide insights into the dietary habits of the herbivore guild of Gerakarou-1 at both short and long-term scales based on two complementary dental proxies, mesowear and microwear textures applied on 70 specimens and we infer the local paleoecology and paleoenvironment. As diet varies between and among populations within the same species, we conduct a population-level study, including a reference dataset of 144 extant individuals belonging to six populations of ruminants with well-known ecology. As we aim to contribute to the collective effort of the community to improve the mesowear methodology, we propose and discuss here the benefits of an alternative, quantitative Geometric Morphometric approach. We show that the occlusal relief, as calculated in the classical mesowear approach, is a variable of little relevance and that the quantitative approach allows better discrimination between dietary categories. By proposing for the first time a multi-scale and multi-proxies study of the entire herbivore guild at Gerakarou-1, we nuance and clarify the paleoecology and niche-partitioning of the ungulates from this site and improve past paleoenvironmental interpretations.

Tracking the past: Isotopic paleoecology (δ13C, δ18O) of the Late Pleistocene megafauna from northeast of South America

Fossils from natural tanks can contribute to the paleoenvironmental interpretation of the Brazilian Intertropical Region (BIR), an important study area for the Quaternary in South America. In this paper we present results of δ13C and δ18O for Eremotherium laurillardi (δ13C = −4.6 ‰, δ18O = 33.0 ‰), Toxodon platensis (δ13C = −3.8 ‰, δ18O = 35.5 ‰), and Notiomastodon platensis (δ13C = −2.9 ‰, δ18O = 31.6 ‰) from Zabelê tank, compared to other localities, suggesting that these taxa had a mixed-feeder diet with a higher consumption of C4 plants (pi > 60%), living in a transition zone between woodland savannah and open savannah. The Zabelê tank, northeastern Brazil, presents Optically Stimulated Luminescence ages ranging from 41.2 to 30.4 ky (Lujanian Stage/Age; Late Pleistocene). The origin of the fossiliferous layer through debris flow suggests short periods of intense rainfall under drier climatic conditions. Compared to other locations in the BIR, Zabelê documented a drier climate (δ18O = 31.6–33.4 ‰), which preceded the last glacial maximum. These new isotopic data to OSL ages associated with previous data from the BIR contribute to the understanding of the paleoecology and paleoenvironment dynamics of South America.

Transmission characteristics and the factors influencing stable oxygen isotopes in precipitation, soil water, and drip water in Remi Cave, Western Hunan, China

Understanding the modern transport processes of δ18O between different waters in cave systems can provide a basis for the paleoenvironmental interpretation of records of stalagmite δ18O. We conducted monthly in-situ monitoring of local precipitation, soil water at three different soil depths, five drip water sites and environmental parameters in Remi cave, Western Hunan Province, Central China, from December 2020 to January 2024. During the monitoring period, due to differences in geological structure and ventilation effect at different locations within the cave, cave air temperature and relative humidity gradually remained constant from the cave entrance to the deep parts of the cave. On intra-annual timescales, precipitation δ18Op were depleted in the wet season and enriched in the dry season, which were mainly controlled by changes in moisture sources, upstream convective activity, and rainout effects. With the increasing thickness of the soil layer above the cave, soil water δ18Osoil gradually became negative and leveled off, possibly because shallow soil water responded sensitively to local year-round precipitation, accompanied by surface evaporation. While, deep soil water with more negative δ18O, may be mainly replenished by heavy precipitation during the wet season, but the effect of water retained in the soil from preceding years couldn’t be excluded and would be needed to verify by conducting more monitoring studies on the variation of δ18Osoil covering the long period. The mean δ18O values of drip water at sites D1 and D2 near the cave entrance were heavier than that of shallow soil water and precipitation, possibly due to evaporation from the thin overlying soil layer, together with ventilation effect. There were seasonal variations of δ18Od values at site D5 in the deep parts of the cave, which may be associated with the seasonal variation of drip rate at this site. Due to the smoothing effect of soil layer and epikarst zone, there were no seasonality in δ18Od values at sites D3 and D4, in the middle and deep parts of the cave. The mean δ18Od at these two sites were lighter than amount-weighted annual mean δ18Op, and close to the deep δ18Osoil and the wet-season amount-weighted mean δ18Op values. This suggests that the thick soil layer overlying the cave raises the precipitation threshold, causing these sites to be mainly recharged by heavy rainfall in the wet season. Therefore, the δ18O of stalagmites growing under these drip sites may mainly inherit the wet-season δ18Op signal. The short monitoring period of this study (three years) and the lack of modern calcite δ18O data, mean that caution is need in interpreting stalagmite δ18O on a timescale longer than that of this study.

Organic geochemistry of the middle Paleozoic Ora Formation in Iraq: Implications for source rock assessment and hydrocarbon potentiality

The Ora Formation (late Devonian–early Carboniferous) is thought to be a potential source rocks for the Paleozoic petroleum system of Iraq. The source potential from the Ora Formation is evaluated for the first time ever in this study from western and northern Iraq which integrates data from organic geochemistry including Total Organic Carbon (TOC) analysis, HAWK pyrolysis, gas chromatography (GC), and gas chromatography mass spectrometry (GC-MS) and mineralogical X-ray diffraction and scanning electron microscopy. The shale and muddy carbonate succession within the Ora Formation from surface section in northernmost Iraq and subsurface section from two wells (Akkas-1 and Akkas −3) from western Iraq have been employed to assess the source rock potentiality, thermal maturity, kerogen type, organic content, and depositional environment. In addition to organic geochemical analyses, mineralogical XRD and SEM-EDS were used to support the paleoenvironmental interpretation of the Ora Formation. The results from TOC and HAWK analyses reveal that the Ora Formation ranges from poor to good as a source rock. However, the HAWK data suggests that the surface samples from northernmost Iraq are highly mature, highly weathered, or both. Kerogen analysis revealed that the Ora Formation contains immature type III and mixed II-III kerogens. Low TOC values were attributed to factors such as significant clastic input, weathering effects, and the prevailing oxic environment during deposition. The presence of detrital influx of quartz and feldspars, along with the occurrence of illite and kaolinite clay minerals, suggest a detrital input with weathering influence under hot arid and warm humid conditions. Biomarker analysis of the light hydrocarbons using GC and GC-MS revealed that these light hydrocarbons were generated from marine planktonic algae sources, possibly with some contributions from terrestrial and/or microbially reworked organic matter. These high mature light hydrocarbons in subsurface section were originated from anoxic marine shale source rocks. They were most likely from the Cambro-Ordovician Khabour Formation and were contaminated from another source.

Abrupt cooling of cold seasons at the middle-late Holocene transition revealed by alkenone records from North China

In saline lakes, the paleoenvironmental interpretation of long-chain alkenones (LCAs) is difficult due to the inputs of Isochrysidales Group 2i, which are ice-related bloomers. Here, we perform detailed analysis of LCAs and long-chain alkenoates in sediment cores from Lake Daihai in north China. During the late Holocene, alkenone-inferred temperatures and the Group 2i species abundance indicate a long-term warming trend in cold seasons (winter and early spring), possibly driven by regional insolation and by atmospheric CO2 concentrations. Notably, our records indicate cold climate conditions during the period of 4.3–3.0 cal ka BP, possibly linked to the abrupt expansion of Arctic winter sea ice in a given of low insolation and atmospheric CO2 concentration conditions. The abrupt cooling may have led to the collapse of the East Aian Summer Monsoon (EASM) and the deterioration of the ecosystems in northern China during the middle to late Holocene transition, and thus likely accounted for the nearly synchronous Chinese Neolithic cultural collapses.

The Last Glacial Maximum climate at Boomplaas Cave, South Africa

With a rich sequence of floral and faunal remains spanning the past >65,000 years, Boomplaas Cave is among the more important paleoenvironmental archives from South Africa's southern Cape. However, over the last several decades, its paleoenvironmental records have been the subject of conflicting interpretations, fueling uncertainty over fundamental aspects of Quaternary climate change in the region. Most significantly, researchers have variably interpreted the fossil plant and animal assemblages dating to the Last Glacial Maximum (LGM) as indicating harsh and arid or humid and productive conditions. This review critically examines the paleoenvironmental evidence from Boomplaas Cave, focusing on its LGM deposits and how they relate to the contentious problem of moisture availability through time. We show that interpretations of aridity during the LGM either (i) lack robust ecological links between the evidence and the paleoenvironmental interpretation, or (ii) are based on spurious patterns arising from sampling effects. In contrast, interpretations of relatively humid conditions during the LGM are grounded in present-day ecological observations and are consistent with both local and regional paleoenvironmental datasets. Overall, the evidence strongly supports the characterization of the LGM as a time of relatively humid conditions, with the transition to the Holocene characterized by increasing aridity. Several lines of evidence from Boomplaas Cave further suggest that this phase of increased humidity was associated with a dominance of winter rainfall, in contrast to the aseasonal rainfall regime that characterizes the southern Cape today.

New insights into endolithic palaeocommunity development in mobile hard substrate using CT imaging of bioeroded clasts from the Pliocene (Almería, SE Spain).

Bioeroded carbonate clasts from a Pliocene shallow-marine succession of Almería (SE Spain, Betic Cordillera) were analysed with computed tomography (CT). This revealed the detailed 3D architecture of bioerosion structures hidden within and allowed for their ichnotaxonomic identification (14 ichnospecies of 5 ichnogenera) and quantification. Borings are produced by worms, mostly polychaetes and sipunculids dominated, followed by bivalves and lastly by sponges. The crosscutting relationship between the borings and their preservation characteristics points to a complex colonization history of the clasts with repeated bioerosive episodes interrupted by physical disturbances, including overturning and abrasion of the clasts followed by their recolonization. Our findings facilitated paleoenvironmental interpretation and can be compared to analogous modern-day ecological succession. The sharp dominance of worm borings - early successional species - may be related to frequent, periodic, physical disturbance that possibly prevented the cobble-dwelling macroboring community from being overtaken by sponges - late successional taxa. CT, hand sample and petrographic observations detected, aside from borings, other irregularly shaped pores which are interpreted to be generated by diagenetic processes including dolomitization, silicification and dissolution, representing an intraparticle moldic and moldic enlarged porosity. Boring porosity crosscutting the diagenetically altered grains suggests the later occurrence of bioerosion processes. Irregular shapes ranging from roughly spherical, elongate sub-polyhedral to amoeboid resemble morphologies produced by modern sponges. Moldic pores possibly acted as primary domiciles for boring sponges, which infested, altered and enlarged pre-existing pores as they grew (as happens in the modern), providing an example of how biological and non-biological processes interacted and together influenced endolithic palaeocommunity development.

Late Miocene to Early Pliocene benthic foraminifera from the Tasman Sea (International Ocean Discovery Program Site U1506)

Abstract. Modern and fossil benthic foraminifera have been widely documented from New Zealand, but detailed studies of material collected from drilling expeditions in the Tasman Sea are scarcer. This study aims to provide an updated taxonomic study for the Late Miocene–Early Pliocene benthic foraminifera in the Tasman Sea, with a specific focus on the paleoceanographic phenomenon known as the Biogenic Bloom. To achieve these goals, we analysed 66 samples from International Ocean Discovery Program (IODP) Site U1506 located in the Tasman Sea and identified a total of 98 taxa. Benthic foraminifera exhibit good preservation, allowing for accurate taxonomic identification. The resulting dataset serves as a reliable and precise framework for the identification and classification of the common deep-water benthic foraminifera in the region. The paleobathymetric analysis based on depth-dependent species indicates deposition at lower bathyal depths. Additionally, the quantitative analysis of the benthic foraminiferal assemblages allowed us to explore their response to the Biogenic Bloom at Site U1506. The paleoenvironmental analysis, focused on the Early Pliocene part of the Biogenic Bloom, points to high-productivity conditions driven by phytoplankton blooms and intensified vertical mixing of the ocean waters. These results provide valuable insights into the paleoceanographic events in the Tasman Sea, particularly the Biogenic Bloom, highlighting the significance of benthic foraminifera as reliable proxies for deciphering paleoenvironmental conditions. The taxonomic identifications and paleoenvironmental interpretations presented herein will aid in future paleoceanographic studies and facilitate comparisons with other deep-sea regions.

Pleistocene record of mammals and pollen from Mexico (Las Tazas, Valsequillo, Puebla) and their paleoenvironmental interpretation

Pleistocene record of mammals and pollen from Mexico (Las Tazas, Valsequillo, Puebla) and their paleoenvironmental interpretation

A new methodology for foraminifera extraction from cemented calcareous shelf sediments

Choosing the most conservative technique to extract unequivocally identifiable foraminiferal tests is crucial to avoid biases in sedimentary sequence dating and paleoenvironmental interpretations. However, for problematic samples containing heavily encrusted specimens, the concentration and isolation of microfossils might be challenging. In this work, we analyzed Early-Middle Pleistocene samples from the International Ocean Discovery Program (IODP) Site U1460, located on the southwestern Australian shelf platform, characterized by extensive early marine diagenesis. At this site, foraminiferal preservation varies between the glacial and interglacial phases. In particular, tests are highly encrusted in samples representing sea-level lowstands of glacials while exhibiting better preservation in samples corresponding to interglacials. As the application of previously established, very conservative preparation techniques (e.g., sieving technique, soaking in H2O2 solution and gentle sonication) did not produce satisfactory results, it was necessary to set up a new procedure for foraminifera isolation specifically for the cautious cleaning of cemented benthic and planktic foraminiferal tests. This new methodology combines the use of a freeze-dryer with repeated soakings in highly-diluted H2O2 solution to disaggregate the material. To evaluate the efficiency of our technique objectively, we considered the improvements obtained with our procedure on the worst-preserved samples of our record (corresponding to glacials) and the best-preserved (associated with interglacials). Despite being more time-consuming than other preparation techniques, this newly developed procedure produces excellent results in samples exhibiting a high level of encrustation for reliable quantitative studies and isotope analysis on foraminiferal assemblages. Our new methodology is highly conservative and thus preserving even delicate taxa.

Putting the dead to work: A new method to assess the autochthony of marine Ostracoda death assemblages

Sedimentary and paleontological records can be powerful means of reconstructing ecological and physical environmental changes, by using a variety of records extending proxies to extend chronologies beyond the reach of instrumental or manual records. Ostracods are often used as paleoenvironmental proxies. Estimating the population age structure could be a useful tool for assessing the influence of some environmental parameters on death assemblages and for determining the autochthoneity or allochthoneity of the species that make up the thanatocoenosis. In the literature, several methods based on population age structure have been proposed to distinguish autochthonous and allochthonous components of life/death ostracod assemblages.The Adult:Juveniles ratio analysis of a rich and well-preserved ostracod assemblage from one site in the circalittoral zone of Pontine Archipelago, in the central-eastern Tyrrhenian Sea, is presented. The new Specific Population Stage Index (SPS) is proposed, built upon the measurements of all growth stages in the assemblage. The population structure using the new SPS Index on three different grain sizes is tested against a list of putative in situ and transported ostracod specimens. The analysis on the small grain size (maximum heigth >63 µm) proved the most effective in describing the putative life ostracod assemblage, whereas in the largest grain size (maximum height >180 µm) the young instars of the smaller species are under-represented. This includes species generally under-represented in the fossil record of the Mediterranean, probably due to sample processing bias and not to the rarity of the species itself. Assessing the autochthoneity of modern/fossil assemblages has great potential for acquiring baseline information on ecosystems before the onset of human activities, making this an extremely powerful approach essential to evaluating anthropogenic impacts. This approach seeks to identify the in situ life assemblages within an ostracod population to ensure that paleoenvironmental interpretations are not biased by transported allochthonous elements.

ECOLOGY OF NON–MARINE OSTRACODA FROM LA FE RESERVOIR (EL RETIRO, ANTIOQUIA) AND THEIR POTENTIAL APPLICATION IN PALEOENVIRONMENTAL STUDIES

Littoral macrophytes from La Fe Reservoir (El Retiro, Antioquia) were sampled for ostracods during June and September 2008. This allowed the identification of four genera and six species of ostracods belonging to the Cyprididae and Candonidae families, where Chlamydotheca and Cypridopsis were found to be the dominant genera. Chlamydotheca unispinosa was the most abundant species in the assemblage. Furthermore, the environmental variables such as temperature, electrical conductivity, dissolved oxygen, and pH were also measured to establish their relation to ostracod taxa, using Canonical Correspondence Analysis (CCA). Results confirm the cosmopolitan character of Cypridopsis vidua and evidence the importance of plant substrate on the occurrence and distribution of the Cyprididae family. The possible application of the recorded ostracod assemblage in paleoenvironmental interpretations is discussed.

First dinosaur tracks found in the Mulichinco Formation (Lower Cretaceous), Neuquén Basin, Argentina: Paleoenvironmental implications

This study focuses on the analysis of the first dinosaur tracks discovered in the Mulichinco Formation, Neuquén Basin, Argentina. The deposition of this unit occurred during the early Valanginian, Early Cretaceous, making it the oldest known record of dinosaur tracks for that period in the basin. The aim of this study is to provide a paleoenvironmental interpretation of the area and potential trackmakers based on the morphology of the tracks and the facies analysis of the depositional system. The depositional system evolved from a moderately sinuous fluvial system in the lower interval to a braid distal plain system with the development of bodies of water without marine influence, culminating in an estuary with marine influence in the upper interval. The paleoenvironmental conditions during the deposition of the unit were favourable for the presence and interaction of diversity large continental vertebrates. The track-bearing surfaces in the lower interval suggest that the organisms exploited the temporary gaps created between channel migration and floodplain formation as areas for transit or water sources. In the middle interval, the abundant presence of traces fossils of invertebrates and symmetrical ripples suggest a more stable depositional system where fluctuations in the water column were common. The co-occurrence of various track-makers and remains of large vertebrates described in the Mulichinco Formation is unusual among track sites at the basin. Overall, this study provides new insights into the Early Cretaceous paleoenvironmental conditions of the Neuquén Basin and the diversity of large vertebrates that inhabited the region during this time.

Aquatic invertebrate mandibles and sclerotized remains in Quaternary lake sediments

Subfossil remains of aquatic invertebrates found in lacustrine sediments are useful paleoenvironmental indicators. Strongly scleroticized chitinous body parts from the exoskeleton or exuviae from invertebrates are often the most resistant to degradation during syn- and post-depositional processes. Invertebrate mandibles and body parts that superficially resemble mandibles, such as claw-like appendages and pygopodia, are frequently found in sieved Quaternary lacustrine, palustrine, and deltaic sediments. Guides, catalogs and atlases have been published that are well suited for the identification of subfossil remains for several invertebrate groups, such as chironomids, cladocerans, and ostracods, among others. However, aquatic invertebrate remains of several ecologically important invertebrate groups continue to be underused in paleoenvironmental studies, in part, because there are few visual keys or other documentation sources (e.g. descriptions, catalogs or atlases) that increase awareness and facilitate identification. Here we present sets of digital photomicrographs of pre-identified aquatic invertebrate specimens collected from streams, lakes and ponds that have been chemically cleared to preserve structures that are observed in subfossil remains in sieved sediment samples, commonly the > 100 μm size fractions. In addition, we present examples of these structures from Quaternary lake-sediment samples and cite the dispersed literature that demonstrate that these remains are preserved and remain identifiable in the fossil record. We document mandibles from several taxonomic groups that include Crustacea: Amphipoda, Isopoda, Ostracoda, and Notostraca; and Insecta orders: Coleoptera, Diptera, Ephemeroptera, Hemiptera, Odonata, Lepidoptera, Megaloptera, Plecoptera, and Trichoptera. The compilation of microphotographs also includes pygopodia and claw appendages of Plecoptera and Trichoptera, with additional images of other common invertebrate mouthpart and head remains. We describe several types of fossilizing structures that are, to our knowledge, not previously described in the paleoecological literature (e.g. mandibles of amphipods or plecopterans) but also show that some structures are considerably more variable than expected based on available descriptions, such as the mandibles of Ephemeroptera or Trichoptera, and that these can potentially be separated into different morphotypes useful for identification of subfossil material. We also discuss the potential of analyzing and interpreting the additional remains together with the remains of more commonly analyzed invertebrate groups (e.g. Chironomidae) to contribute to paleoenvironmental interpretations, which will allow assessments of functional groups (e.g. predators, shredders, grazers) or habitat types (e.g. littoral, profundal or lotic environments) that aquatic invertebrate remains originate from.