“…A total of 93 sediment samples were analyzed for ostracod abundance and diversity. The material recovered was well preserved, with a small proportion of broken and reworked valves, that is, shells were not opaque, without evidence of dissolution, abrasion or overgrowths (Holmes, 2001; Keatings et al, 2007). The percentage of carapaces in the assemblages was less than 1%.…”
South American paleoreconstructions are of global interest because it is the only landmass extending from the tropics to the southern high latitudes and intersecting the entire southern westerly wind belt. In this context, endorheic environments, as Lake Cari-Laufquen Grande (LCLG; 41º35'S, 69º25'W) are excellent sites for paleoenvironmental studies, since they react rapidly to changes in the precipitation/evaporation ratio. In this study, the limnological conditions prevailing during the last 3000 years have been inferred based on a multiproxy analysis of the sedimentary sequence of LCLG (water depth 4 m, core length 505 cm). Today, this is one of the few lakes in Northern Patagonia, providing a unique paleoclimatic and paleoecological lacustrine record. The ostracod assemblages, along with sedimentological, petrophysical and geochemical data, show hydrological changes in Cari-Lauquen Grande basin during the studied period. Our results indicate the continuous presence of a saline to brackish lake. However, changes in ostracod assemblages and sedimentological features reveal variations in the relative salinity of the system. The lake paleosalinity was estimated based on ostracod salinity optima, using a calibration dataset of 29 species and 72 different environments. Intervals of high salinity (24-26 g L-1) were dominated by L. rionegroensis (morph.I) and organic-poor sediments. Periods of lower salinity (14-20 g L-1) favored the occurrence of oligo-mesohaline taxa, such as R. whatleyi, L. rionegroensis (morph.III), Cypridopsis sp., L. patagonica and I. ramirezi. The sediments further display higher values of both TOC and magnetic susceptibility. These salinity changes are interpreted as water level variations, associated in turn to cold-wet and warm-dry periods in northern Patagonia. Our results provide new insights into the late-Holocene environmental history of the region, characterized by a paucity of records. In addition, the ostracod paleoecology modeled using a WA approach allowed quantitative inferences of salinity changes, highlighting their potential in Quaternary paleoclimate research.
“…A total of 93 sediment samples were analyzed for ostracod abundance and diversity. The material recovered was well preserved, with a small proportion of broken and reworked valves, that is, shells were not opaque, without evidence of dissolution, abrasion or overgrowths (Holmes, 2001; Keatings et al, 2007). The percentage of carapaces in the assemblages was less than 1%.…”
South American paleoreconstructions are of global interest because it is the only landmass extending from the tropics to the southern high latitudes and intersecting the entire southern westerly wind belt. In this context, endorheic environments, as Lake Cari-Laufquen Grande (LCLG; 41º35'S, 69º25'W) are excellent sites for paleoenvironmental studies, since they react rapidly to changes in the precipitation/evaporation ratio. In this study, the limnological conditions prevailing during the last 3000 years have been inferred based on a multiproxy analysis of the sedimentary sequence of LCLG (water depth 4 m, core length 505 cm). Today, this is one of the few lakes in Northern Patagonia, providing a unique paleoclimatic and paleoecological lacustrine record. The ostracod assemblages, along with sedimentological, petrophysical and geochemical data, show hydrological changes in Cari-Lauquen Grande basin during the studied period. Our results indicate the continuous presence of a saline to brackish lake. However, changes in ostracod assemblages and sedimentological features reveal variations in the relative salinity of the system. The lake paleosalinity was estimated based on ostracod salinity optima, using a calibration dataset of 29 species and 72 different environments. Intervals of high salinity (24-26 g L-1) were dominated by L. rionegroensis (morph.I) and organic-poor sediments. Periods of lower salinity (14-20 g L-1) favored the occurrence of oligo-mesohaline taxa, such as R. whatleyi, L. rionegroensis (morph.III), Cypridopsis sp., L. patagonica and I. ramirezi. The sediments further display higher values of both TOC and magnetic susceptibility. These salinity changes are interpreted as water level variations, associated in turn to cold-wet and warm-dry periods in northern Patagonia. Our results provide new insights into the late-Holocene environmental history of the region, characterized by a paucity of records. In addition, the ostracod paleoecology modeled using a WA approach allowed quantitative inferences of salinity changes, highlighting their potential in Quaternary paleoclimate research.
“…The material, well preserved with <5% of the valves broken, and the presence of both adults and juveniles of different molt stages, suggests that reworking and size sorting did not occur and that the shells were accumulated in situ. Therefore, it may be considered that the ostracod assemblages represent an autochthonous biocoenoses, reflecting the environmental conditions of the sampling site (Holmes, 2001; Keatings et al, 2007; Cusminsky et al, 2011). Figure 5 (color online) Bioproxies (% relative abundance) determined for the El Toro Lake sediment core.…”
The limnological conditions during the past 700 yr were reconstructed based on multiproxy analysis of a short sedimentary sequence from El Toro Lake (~40°S, 70°W). Mineralogical and geochemical features, as well as ostracods and chironomids, record hydrologic changes in the El Toro Lake basin. The ostracod Limnocythere rionegroensis var. 1, a reliable indicator of high salinity, and Eucypris fontana, a euryhaline species with preferences for moderate-salinity waters, are studied as paleolimnological proxies. The chironomid fauna indicates less saline conditions in the mid-twentieth century. These salinity changes are interpreted in terms of negative–positive hydrologic balance. High lake level and low salinity between AD 1500 and 1700 match with the wetter and colder climate during the second pulse of the Little Ice Age in northern Patagonia. High-salinity conditions occurred during the late nineteenth century, corresponding to the driest period during the past 400 yr in northeastern Patagonia. An increase in the precipitation around the middle of the twentieth century, in contrast to the records from the Chilean side of the mountains, correlates with a positive phase of the Southern Annular Mode. This is associated, in turn, with a strengthening, poleward shift of the midlatitude westerlies, possibly enhancing easterly moist air flows into central-north Patagonia.
“…Az együttesben számos juvenilis egyedet figyeltünk meg, ami az asszociáció autochton jellegét bizonyítja (RUIZ et al 2003). Nagyon kevés a kettős teknőjű példány, ami nem túl gyors üledékképződésre utal (HOLMES 2001).…”
Section: öSszehalmozott Molluszkákat Tartalmazó Finomszemű Homokunclassified
“…A juvenilis egyedek jelenléte itt is igazolta az együttes autochton jellegét (RUIZ et al 2003). Az ostracoda teknőknek csak kisebb hányada volt kettős teknő, ami nem túl gyors sebességű üledékképződésre utal (HOLMES 2001).…”
Section: öSszehalmozott Molluszkákat Tartalmazó Finomszemű Homokunclassified
The 'Northern Imbricate Zone' along the northern edge of the Eastern Mecsek Mts, SW Hungary, are a complicated, narrow, uplifted band of basement, partly covered by Neogene sediments. The area is heavily deformed, with young, post-Miocene tectonic movements. Pannonian (Upper Miocene) lacustrine sediments are most widely distributed around the village of Nagymányok. Through their investigation it is possible to reveal the Late Miocene and subsequent evolution history. The present study concentrates on the temporary outcrops of Lake Pannon deposits created in 2015 south of Nagymányok, accompanied with fossil collection from the individual strata. This ~120 m thick sedimentary successsion is atypical compared to other parts of the Mecsek Mts, with relatively fine-grained, fossil-rich clays to fine sands above the thin (<3 m), gravelly base sands of local provenance. The fauna is dominated by bivalves; however, gastropods, ostracods and fish and plant remains have also been found. The base sands belong to the Prosodacnomya dainellii-P. vutskitsi mollusc biozones, the finer sediments to the Congeria rhomboidea biozone. Through the joint interpretation of the litho-and biofacies the sedimentary environments and the age of deposition of the sediments were identified, while the evolution of the wider surroundings was delineated by adding the tectonic observations, borehole data and seismic sections to the previous information. Lacustrine sedimentation first started only in the northern foreland of the mountains, accummulating offshore marls, claymarls and silts (Szák Claymarl Fm). The time of flooding is unknown in the trough directly at the foot of the mountains due to the lack of wells and palaeontological data; the wide platform north of it became flooded no sooner than 8.9 Ma based on mollusc data. This was followed by the fine sands to clays of the Alpine-Carpathian delta system (Újfalu Fm), approx. 7.3 Ma ago, as indicated by molluscs belonging to the Prosodacnomya dainellii and P. vutskitsi littoral biozones. As no clinoforms are present on seismic profiles, the northern foreland must have been a shallow underwater high at that time. The Northern Imbricate Zone in the mountains were dryland during most of the Late Miocene. Sedimentation started here approximately coevally with the arrival of the delta system at the foot of the mountains. Flooding ensued on a dissected topography. The delta sediments with dominantly sublittoral fauna above the thin littoral base sands indicate rapid transgression. Late Miocene sedimentation was accompanied by small-scale movements of strike-slip character. More important tectonic deformations followed afterwards: strike-slip to north-vergent reverse displacements happened along the northern master fault of the Mecsek and roughly parallel planes.
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