Late Holocene Sediments Research Articles

Rare earth element geochemistry of sediments from the southern Okinawa Trough since 3 ka: Implications for river-sea processes and sediment source

Abstract The sediment sources in the southern Okinawa trough (SOT) are still controversial and few studies have focused on the effects of transport processes on the elemental composition of initial terrigenous materials. Here we present rare earth element (REE) and trace element data on siliciclastic sediments from 14C age-dated Core S3, which was collected from the SOT, to provide reliable evidence for illustrating the modified effects of marine environments on terrigenous sediments deposited at different stages and exposing changes in sediment source over the past 3 ka. Compared with bulk sediments, the siliciclastic sediments in S3 have more variable REE fractionation parameters and lower middle REE (MREE) contents. Our REE data indicate that during river-sea processes, MREE-enriched fractions such as Fe–Mn oxides and carbonate were added to the original terrigenous sediments before deposition, weakening the degree of REE fractionation in the initial sediments; thus, care should be taken when using REE data from bulk samples to decipher source changes. The temporal changes in sediment source in S3 can be broadly identified based on the REE fractionation parameters of the residual fractions, and the results are largely consistent with the findings obtained by heavy mineral examinations. Units 1 and 3 are dominated by reworked shelf sediments of Changjiang origin,while the proportion of Taiwan-derived sediment is notably higher in Units 2 and 4. The sediment flux of Taiwan origin in the SOT was much smaller than previously thought. Huanghe-derived sediments and volcanic materials did not contribute significantly to the late Holocene sedimentation in the SOT. The large variations in sediment sources in S3 were possibly caused by changes in transport patterns driven by time-dependent changes in oceanic currents.

Late-Holocene sedimentation and sodium carbonate deposition in hypersaline, alkaline Nasikie Engida, southern Kenya Rift Valley

Continental rift systems are often characterized by geothermal activity and associated discharge of hot groundwater, which can substantially impact the water, solute and sediment budgets of rift-valley lakes. Hot-spring inflow can result in complex lake hydro- and geochemistry, but also buffers against the desiccation of closed-basin lakes in dry climate regimes. Consequently, hydrothermally fed lakes can potentially provide continuous sedimentary records from regions where other types of paleoenvironmental archives are lacking. This is illustrated by Nasikie Engida, a shallow hypersaline and alkaline (soda) lake in the semiarid Rift Valley of southern Kenya. Here, inflow of hot-spring water has maintained a shallow but permanent water body and continuous deposition of sediments through past climate episodes when many other lakes in the eastern (Gregory) branch of the East African Rift System stood dry. We present the first data on late-Holocene sedimentation in this remarkable lacustrine system, typified by authigenic nahcolite [NaH(CO3)] formation during part of its recorded history. Our data include measurements of bulk-sediment and mineralogical composition, clastic-mineral grain size and magnetic susceptibility. Analytical issues related to the large amount of salts within the sediments, both as crystals and in solution in the pore water, are discussed. We also present exploratory time series of the stable-isotope composition of bulk organic matter and authigenic nahcolite. Core lithostratigraphy and preliminary radiocarbon dating indicate that Nasikie Engida has accumulated finely laminated sediments continuously since ca. 2850 cal year BP, which is remarkable given its current maximum depth of only 1.6 m. Synsedimentary nahcolite appears abruptly ~ 2260 cal year BP and since then has been deposited regularly, in the form of distinct pure layers up to several cm thick. Its formation has been enabled by high pCO2, supplied principally from geothermal sources, accumulating in a high-density brine. Although Nasikie Engida has likely been saline over the entire time span covered by the studied sediment sequence, variation in nahcolite deposition and bulk-sediment composition suggests multi-decadal to centennial oscillations in water-column stability and stream inflow driven by variation in climatic moisture balance. Further analyses of this paleoenvironmental archive may thus produce the first continuous climate-proxy record from a vast dry region of equatorial East Africa. Moreover, Nasikie Engida’s extraordinary setting makes it a unique modern analogue for the interpretation of ancient nahcolite-bearing salt-lake deposits.

The Traces and Chronology of the Strong Historical Earthquakes on Cape Zyuk, East Crimea

The results of studying the geological and archaeological traces of the strong earthquakes on Cape Zyuk where the ancient settlement existed from the turn of the 6th to the 5th centuries B.C. to the first-third–middle of the 6th century A.D. are presented. The detailed knowledge gained on this monument allowed us to compile the timeline of the strong earthquakes for the past 2500 years. The detection of the seismotectonic deformation of the Late Holocene sediments indicates that the rupture of the source of a strong earthquake at Cape Zyuk extended to the surface. The dating of this event is constrained by the upper age of the second half of the 4th century B.C. to the beginning of the third century B.C. The previous event is dated to before the turn of the 6th–5th centuries B.C. Besides these events, there were presumably another four earthquakes in 63 B.C., before the second half of the 4th century B.C., in the first third to the mid-6th century A.D., and in the 18th century. Presumably Cape Zyuk was struck by four or five strong earthquakes during the past 2500 years. The lack of information about the earthquakes between the 6th and 18th centuries, i.e., during more than a 1000-year period, can probably be related to both the long period of quiescence between seismic activations and to the incompleteness of the collected data.

Palynomorphs from Late Holocene sediments of the eutrophic Lake Manyas, NW Anatolia

Lake Manyas is one of the twelve “Ramsar Sites” in Turkey designated as “Wetlands of International Importance.” The wildlife and ecological richness of the lake has been the subject of several studies for many years; however, no detailed palynological study has been reported from the area. A rich and diverse assemblage of palynomorphs from sediment samples of the lake were studied to investigate how micro-flora and -fauna in and around the lake were reflected in the deposits during the Late Holocene. Palynomorphs were grouped into four categories; arboreal taxa (AP) made up 30,7%, non-arboreal taxa (NAP) 9,6%, aquatic and marshland plants 26,8% and zoological remains 32,8% of the total of 1463 particles. Apart from AP and NAP taxa, pollen of shoreline plants i.e. reeds, sedges and grasses growing around the lowland areas of the lake; spores of cryptogams, liverworts, and bryophyte-peat moss; free-floating or rooted angiosperms; zygospores of green algae; plant-like algae and cyanobacteria; and ubiquitous protozoans living along the shores of the lake on wet ground are grouped under aquatic and wetland plants and organisms. A total of 37 morphological types of zoological remains were described and identified. Three palynological zones (PZ) were delineated based on absolute abundance and percentages of the taxa; PZ I ca 1690–1790 AD, PZ II to ca1790–1890 AD, and PZ III to ca 1890–1998 AD. The turnover of the zones was discussed by inferring to anthropogenic influences and climatic changes.

Refining the late-Holocene coastline and delta development of the northern Yangtze River delta: Combining historical archives and OSL dating

Historical documents provide a general chronological overview of the environmental evolution of the Yangtze River delta (YRD) during the last ca. 2000 years; however, absolute dating of the region’s late Holocene sediment is relatively rare. Optically stimulated luminescence (OSL) dating has been increasingly applied to the age determination of Holocene deposits in deltaic environments. In this study, three 23–27 m long drill cores running from south to north were collected from the Qihai plain of the northern YRD in order to reconstruct the history of this region’s formation since the late Holocene. A total of 24 samples from the three cores were subjected to OSL dating using coarse silt-sized (45–63 μm) quartz. The OSL ages range from approximately 190–3490 a revealing that the age of the delta front and delta plain facies in the coring sites are younger than 500 a while the sediments in the underlying prodelta facies are older than 2000 a. On the basis of the large age gap between the two set of deposits, we suspect that the coring sites remained submerged from 2000 to 500 years ago. As the central core has older and coarser sandy deposits than the neighbouring cores, we infer that the central core was located on a sandy mouth bar, while other cores sat within distributary channels within the estuary. The OSL ages are consistent with both the chronology implied by historical documents and other stratigraphic records in the area. This study enhances the chronological framework of land formation and delta evolution in the Qihai plain area of the YRD and thereby consolidates the conclusions derived from the application of a single technique alone.

A hidden species becoming visible: biogeography and ecology of Rhynchotalona latens (Cladocera, Anomopoda, Chydoridae)

A long hidden chydorid (Chydoridae, Cladocera) taxon, first found as fossil specimens and recently redefined as Rhynchotalona latens (Sarmaja-Korjonen et al., Hydrobiologia 436: 165–169, 2000) is investigated for its biogeography and ecology. Late Holocene sediment sequence from Lake Sylvilampi, NE Finnish Lapland, and R. latens spatial distribution in relation to limno-climatic attributes in Finland were examined. Principal component analyses of fossil cladoceran communities showed that R. latens is mostly affiliated with Alonella excisa–Alonopsis elongata–Alonella nana species pool. Generalized linear modeling of R. latens responses to limno-climatic variation indicated that it prefers acidic, mesotrophic, humic and shallow lakes with organic sediments in NE Lapland and has a north boreal-subarctic climatic affiliation. At the northern end of its geographical distribution (NE Lapland), it reproduces with abundant gamogenesis under environmental stress. The specialized taxon is a benthic detritivore and scraper and has a Holarctic northern–alpine distribution. It is a glacial relict associated with modern analogs of periglacial aquatic environments, and it occurs in semi-aquatic wetlands, lush lake littorals and clear and cold waters. Examination of chydorids as bioindicators, especially those with restricted niches, allow us to understand biodiversity responses of lake littorals under changing limno-climatic regimes.

Neotectonics and related crustal deformation along Carbyn thrust fault, South Andaman, India: implications of the frontal surface faulting and propagation of tectonic activity towards Andaman trench

Paleoseismic investigations have been carried out across an ~ 10-m-high scarp along the Carbyn thrust fault, that marks the structural contact between the overriding Ophiolite suite of the Cretaceous age and under riding Andaman Flysch group (Oligocene) in the outer-arc setting of the Northern segment of Sunda-Andaman subduction zone. The Carbyn thrust fault is one of the important concomitant faults in the accretionary prism of the Andaman subduction zone and the surface trace marks a N-S trending thrust fault with Easterly dip which extends for a length of about 30 km in the Eastern half of South Andaman, starting from Carbyn area up to Chidiyatapu (Southernmost tip of the South Andaman) through Kodiyaghat and Burmanallah areas. The thrust has emplaced dismembered Cretaceous Ophiolite slices over Oligocene siliciclastic turbidites (Andaman Flysch) almost in a N-S trending linear zone of deformation. The 10-m-high scarp expressed at the interface between Ophiolite suite and Andaman Flysch group borders the topographic front of Ophiolite suite and breaks the Quaternary and late Holocene succession almost up to a length of 3.7 km from Carbyn to Burmanallah area, registers the youngest surface deformation along the thrust. The scarp is abrupt and sharp trending in N-S direction shows variations in displacement along the strike and has preserved its initial geometry without erosion. Trench exposure and Georadar survey across the scarp at Carbyn area reveals a very low angle thrust fault that cuts the bedrock surface (Ultramafics of Ophiolite Suite) rocks against the young alluvial surface deposited by Prothrapur Nallah and Carbyn creek at Carbyn area. The thrust fault shows flattening of the fault geometry around 16° at the base of the trench and dips 8–10° at near surface. The expression of the scarp at the frontal position of Ophiolite Suite and verging towards the West displacing late Holocene sediments reflects advancing of thrusting and propagation of tectonic activity towards Andaman trench.

Late Weichselian to Holocene history of the Baltic Sea as reflected in ostracod assemblages

The study presents the first description and analysis of ostracod records from three sites cored in different parts of the Baltic Sea during the IODP Expedition 347, Baltic Sea Paleoenvironment. Our data present the first high‐resolution ostracod records from the Late Weichselian and Holocene sediments collected across the Baltic Sea Basin. Using published data on modern ostracod species ecology of the Baltic Sea, we were able to provide ostracod‐based palaeoreconstructions of the history of the region. The stratigraphical framework for the sites is based on radiocarbon‐based age models. The three studied sites reveal different ostracod assemblage successions that reflect environmental changes in the study area. Site M0060, located in the Kattegat area, contains the oldest ostracod assemblages that document a marine environment with very high sedimentation rates during the most recent deglaciation. Between ~13 000 and 7500 cal. a BP a modern‐like near‐shore environment developed. Site M0059 in the southwestern Baltic Sea, Little Belt area, contains assemblages reflecting the transition from a freshwater lake to the brackish Littorina Sea between ~7500 and 7300 cal. a BP. Site M0063 is the deepest location in the central Baltic, Landsort Deep, and yielded very limited ostracod data, but comparison with our organic carbon data allowed us to distinguish the Yoldia Sea, Ancylus Lake and Littorina Sea intervals. The ostracod record correlates well with the organic carbon record with alternation between periods of hypoxia and periods of low oxygen that still supported ostracods.

Middle to late Holocene sedimentation dynamics and paleoclimatic conditions in the Lake Ulaan basin, southern Mongolia

This study presents a reconstruction of the middle to late Holocene sedimentation dynamics and paleoclimatic implications in Lake Ulaan, southern Mongolia for the first time. The dynamics is inferred from weathering intensity, Accelerator Mass Spectrophotometry (AMS) radiocarbon dating and estimated sedimentation rates. Result shows that a higher sedimentation rate of 4.6 cm.kyr‑¹ between 2.7 and 6.0 cal kyr BP and a lower sedimentation rate of 1.6-1.8 cm.kyr‑1 after 2.7-3.2 cal kyr BP are associated with a climatic shift from humid in the middle Holocene to arid in the late Holocene within the Lake Ulaan basin. This result from the Lake Ulaan basin in southern Mongolia correlates with the middle and late Holocene climatic records reconstructed from other lakes in Mongolia and Central Asia. Further investigation of lacustrine sedimentary sequences and more age data from Lake Ulaan are still needed to constrain better the Holocene sedimentation history in southern Mongolia and Central Asia.

Mid and Late Holocene flooding reconstruction based on fluvial archives of the East Carpathian rivers

This paper focused on the analysis of the interpretation potential given by fluvial archives, in order to decipher the Mid- to Late Holocene sedimentary history. The database discussed here refers to 65 dated ages (mostly radiocarbon), mappings of the most representative floodplain reaches of Suceava, Moldova and Siret rivers, and 23 outcrops analysed in floodplain deposits (river banks or gravel pits). The study results concentrated on (a) describing the regional features of Eastern Carpathian floodplains, (b) the floodplain morphology and its correlation with the structure of fluvial deposits and (c) identifying the paleoevents of fluvial activity on a centennial timescale. In this way, we were able to identify a general pattern of the dynamic geomorphology history for the rivers situated eastward of the Carpathians, which resulted from combining the Mid- to Late Holocene sedimentation phases, the avulsion and lateral migration processes that occurred during high fluvial activity intervals and the morphological adjustment of the rivers channels, from braiding to wandering and sinuously–meandering. The chronological overlay of the events revealed that the time intervals with the most extensive fluvial processes on the rivers draining the Eastern Carpathians occurred (in years before present) during 6200, 5300, 4100–4080, 3600, 2300–2200 (Iron Age), 1300 (Migrations Period), 950–970 (Medieval Climate Anomaly), 750–520 BP (Little Ice Age)and that these intervals generally overlap the high precipitation palaeoclimatic episodes documented in Romania. The fluvial activity of the rivers during the Mid- to Late Holocene has been compared as well with several records of paleo–climates variability over the geographical area of Romania. The result showed that many flooding episodes were coincident with the wet and cold intervals which were also identified in the variation of the other proxydata, especially after 4.7 kcal BP.

Comparison of elemental concentration in near-surface late Holocene sediments and precipitation regimes of the Yucatán Peninsula (Mexico): a preliminary study

Paleoclimate research in the Yucatán Peninsula of Mexico has mainly involved fossil pollen preserved in sedimentary archives whilst geochemistry has received limited attention. In this study, we compared concentrations of K, Ti, Fe, Ca and Sr in 35 near-surface late Holocene sediments collected from different permanent and seasonal water bodies across the peninsula with mean annual precipitation of 600-1600 mm in order to explore the relationship between concentrations of inorganic elements and precipitation. The calcareous provenance has a diluting effect and sediments have less K, Ti and Fe (associated with clastics) and more Ca and Sr (associated with carbonate and evaporite) compared to the Upper Continental Crust. Individual elements and ratios of K/Ca, Ti/Ca and Fe/Ca in samples with minimal clastics did not show any relationship with precipitation. Average values of elemental ratios in sediments with more clastics increase as the mean annual precipitation increases. However, the sampling protocol and presence of most of the sampled water bodies being in a single precipitation cluster (i.e. 1200-1400 mm/year) did not allow a complete evaluation of the potential correlation between precipitation and elemental ratios. Considering that the concentration of Ti is low in sediments of the limestone-rich Yucatán Peninsula and Fe is mobile in anoxic depositional environments, the K/Ca ratio can be used as a preliminary proxy to evaluate precipitation in sedimentary records.

The late Pleistocene – Holocene paleoclimate reconstruction in the Adamawa plateau (Central Cameroon) inferred from the geochemistry and mineralogy of the Lake Fonjak sediments

In the aim of improving the understanding of paleoclimate variations in the transitional zone between the sahelian and sub-equatorial rainforest belts, paleoclimate conditions of the Adamawa plateau were reconstructed from geochemical and mineralogical records coupled with radiocarbon dating of lacustrine sediments since 13,339 cal yr BP. The Lake Fonjak depositional sequence displays eight lithofacies made up of: light greenish grey clayey mud; black clayey mud mostly composed of volcanic ash; light grey silty clayey mud; dark grey sandy layer with coarse rounded fragments of volcanic rocks; light grey silty mud; dark grey silty mud; light grey silty mud; dark grey silty mud with few rootlets, and an herbaceous peat. In this depositional sequence, organic matter contents range from 9% to 59%. A correlation between the age-depth model and lithofacies of this depositional sequence suggests Late Pleistocene sediments at the base and Late Holocene sediments at the top. These Holocene sediments exhibit in XRD data various minerals assemblages with relative contents varying from 15% to 42% for quartz; 19%–37% for kaolinite; 12%–37% for micas; 5%–18% for serpentine; 1%–9% for feldspars; 5%–7% for gibbsite and 11% for olivine. As far as detrital minerals are concerned, they are: quartz, orthoclase, siderite, vivianite, hornblende, plagioclase and opaque minerals. Major element abundances in decreasing order in these sediments are as follow: silicium, aluminium, iron and titanium. The highest content of SiO2, Fe2O3, MnO, CaO, Na2O and K2O are recorded within either the volcanic ash layer or its overlapped lithofacies; whereas, P2O5, MgO, TiO2 and Al2O3 exhibit their highest values at the top of the sequence. Trace elements vary little in these sediments, except for Co which rises abruptly within the volcanic ash layer. However, Ni, Co, Cr and Cu are twice to three times enriched with respect to average shale composition; whereas V and U are depleted. REE show complex behavior, alternatively increasing and decreasing, except for Ce; and Eu with positive anomaly. The geochemical classification of these sediments ranges them within Fe-shales with few litharenite. They were deposited under dysoxic to suboxic conditions, except around 4200 cal yr BP and around 2500 cal yr BP where these conditions were anoxic. The Lake Fonjak sediments derive from highly weathered mafic rocks probably andesite as suggested by PIA: 95.32–99.10%, CIA: 86.46–97.45%, CIW: 95.70–99.12% and La/Sc vs. Co/Th diagram. This sedimentation took place within three paleoclimate phases: 13,339–4400 cal yr BP; 4400–2400 cal yr BP; and 2400 cal yr BP to present. This paleoclimate was predominantly humid and marked either by the slowdown of rainfall and an intensification of the dry season, or by the reinforcement of rainfalls.

Controls on organic matter distribution in oxygen minimum zone sediments from the continental slope off western India

Abstract The causes of organic-rich sediments in contact with the perennial oxygen minimum zone (OMZ) on the continental slope off western India have been debated extensively, largely in relation to two main controlling factors: high productivity in the water column and enhanced preservation due to oxygen deficiency in bottom waters. In order to better understand the causes for organic-richness in sediments, three sediment cores recovered from the upper OMZ (UOMZ) at 500 m, middle OMZ (MOMZ) at 812 m and lower OMZ (LOMZ) at 1168 m water depths from the continental slope off Ratnagiri (west coast of India) were investigated for their organic matter (OM) and their stable isotopic (δ13C and δ15N), geochemical and rock magnetic parameters. The bottom water dissolved oxygen (DO) concentrations were 0.4 μM, 5.8 μM and 25 μM at UOMZ, MOMZ and LOMZ core locations respectively. Maximum age of the sediments recorded in these cores was 4500 yrs BP. Sedimentation rates in the upper sections of the UOMZ and MOMZ cores were lower (5 to 7 cm/kyr) than that in the LOMZ core (20 cm/kyr). Organic carbon (Corg) content was highest (upto 7.9%) in the UOMZ core than in other cores (upto 4.9%). Enriched δ13Corg values (−18.6 to −16.8‰) in the MOMZ core were indicative of reworked organic matter in the lower section. The δ15N values ranged from 4 to 7.4‰, however, with lower values for the reworked sediments at MOMZ site. The parameters representing productivity and redox conditions increased towards core top in all the cores, whereas terrigenous parameters decreased towards core top in the MOMZ and LOMZ cores. Despite the MOMZ core was always in OMZ in the lower section, very low Corg content coinciding with high terrigenous and reworked OM were deposited in the sediments prior to 1700 years BP. Rock magnetic properties indicate that the degree of diagenetic conditions varied in different sections of the cores and also among the cores within OMZ. Authigenic magnetite and authigenic uranium occurred in the lower sections of UOMZ and LOMZ cores and, authigenic magnetite in the upper sections of MOMZ core. These results suggest that productivity played an important role in organic-richness of the sediments and bottom water oxygen concentration has little effect on the preservation of OM. Besides, sedimentation rates, reworked organic matter, and topography at the core site indeed contribute on the distribution of organic matter in the Late Holocene sediments.

Late Holocene paleoceanography in the Chukchi and Beaufort Seas, Arctic Ocean, based on benthic foraminifera and ostracodes

Calcareous microfossil assemblages in late Holocene sediments from the western Arctic continental shelf provide an important baseline for evaluating the impacts of today’s changing Arctic oceanography. This study compares 14C-dated late Holocene microfaunal assemblages of sediment cores SWERUS-L2-2-PC1, 2-MC4 and 2-KL1 (57 mwd), which record the last 4200 years in the Herald Canyon (Chukchi Sea shelf), and HLY1302-JPC-32, GGC-30, MC-29 (60 mwd), which record the last 3000 years in the Beaufort Sea shelf off the coast of Canada. Foraminiferal and ostracode assemblages are typical of Arctic continental shelf environments with annual sea-ice cover and show relatively small changes in terms of variability of dominant species. Important microfaunal changes in the Beaufort site include a spike in Spiroplectammina biformis coinciding with a decrease in Cassidulina reniforme in the last few centuries suggesting an increase of Pacific Water influence and decreased sea-ice. There is low-amplitude centennial-scale variability in proportions of benthic foraminiferal species, such as C. reniforme. In addition to these species, Cassidulina teretis s.l., Elphidium excavatum clavatum and Stainforthia feylingi are also common at this site. At the Herald Canyon site in the last few centuries, C. reniforme peaks around 150 years BP and then decreases while Spiroplectammina earlandi spikes and Acanthocythereis dunelmensis decreases also suggesting an increase in Pacific Water influence and decreased sea-ice at this site. This site also includes Buccella spp. and Elphidium excavatum clavatum. Differences in benthic foraminifera and ostracode species dominance between the two sites may be due to a greater influence of Pacific Water in the Chukchi shelf, compared to the more distal Beaufort shelf, which is also affected by the Beaufort Gyre and the Mackenzie River.

GEOMORPHIC EVOLUTION OF THE PALAMARI BAY (NORTHEASTERN SKYROS ISLAND) DURING LATE HOLOCENE

Palamari bay is loceted on the northeastern coast of Skyros island (Sporades islands, Aegean sea). The area is of fundamental archaeological interest because of a prehistoric archaeological site, located at the northern part of the bay. In order to investigate the geomorphic evolution of the broader area a detailed geomorphological mapping of the coastal and submarine area of the bay at a scale 1:5000 was carried out. Additionally the stratigraphy of the late Holocene sediments was studied and micropaleontological and palynological study of collected samples from the deposits of the coastal alluvial plain as well as radiocarbon dating of selected layers rich in organic material were done. The main morphological features of the coastal zone are two beachrock formations with the first one extending along the coastline reaching a depth of-1.70 m and the second one occupying the southern part of the bay lying between -1.90 and -2.90 m below sea level. Microfaunal and palynological analysis of collected samples identified two main sedimentary sequences. The uppermost sedimentary unit represents a terrestrial depositional environment dominated by aeolian wellsorted sands and fluvial sediments. The underlying sequence showed a lagoonal depositional environment, implying a protected lagoon connected to the sea, which was periodically supplied with fresh water. This lagoon existed between 3700 years BP and 700 years BP as radiocarbon dating showed. The existence of this lagoon after that period is possible.

Geochemistry of Marmara Lake sediments - Implications for Holocene environmental changes in Western Turkey

Beginning from the Early Holocene marked environmental changes have been revealed by a multi-proxy study of two radiocarbon-dated sediment cores from Lake Marmara. Both cores are composed of fine clastic sediments deposited over the last 1845 years. The core taken from the western depocentre supplementary consists of a 20 cm thick interval which represents a time period of 10.28 to 8.28ka yrBP. A desiccation event caused 6435 year hiatus in the sedimentary record. The lake was established again at 1.85ka yrBP. After a transitional humid phase at the beginning of the Late Holocene, overall arid conditions were continuously effective.Especially the difference between the geochemical composition of Early and Late Holocene sediments indicates distinctive environmental conditions. Respective humid phases took place in between 10.28 and 8.28ka yrBP (Early Holocene) and 1.85 to 1.72ka yrBP (Late Holocene). The Early Holocene phase is characterized by higher fluvial activity controlled by the humid climate and active tectonics. Right after the Middle Holocene droughts, a short-termed tendency to relatively fresh and oxic conditions prevailed. However, the small surface area of the lake and its shallow conditions caused fast variations of hydrology, oxidation level, salinity and organic productivity during the last 1850 years. We suggest that a combination of the instability of the Eastern Mediterranean climate and local conditions is the main control on the changing paleo-environment during the study period.

Paleo-ENSO revisited: Ecuadorian Lake Pallcacocha does not reveal a conclusive El Niño signal

Information about decadal to millennial variability of El Nino Southern Oscillation (ENSO) is fundamental for the assessment of ENSO responses to natural and anthropogenic forcings. Despite a growing number of ENSO reconstructions, the overall picture of Holocene ENSO variability is inconsistent. Here, we revisit the iconic Holocene ENSO sediment record of Lake Pallcacocha, Ecuador (Rodbell et al., 1999). We asked: (i) How coherent are the records of clastic layers (flood layers) in the sediments of Lake Pallcacocha and adjacent Lake Fondococha? (ii) What are the synoptic-scale atmospheric conditions that lead to intense precipitation and, potentially, to alluvial activity promoting the deposition of clastic layers in these lakes? (iii) Is intense precipitation in this area associated with El Nino, or not? We analyzed clastic layers in Late-Holocene sediments from multiple cores in Lakes Pallcacocha and Fondococha from Cajas National Park, southern Ecuadorian Andes. Additionally, we investigated precipitation data from 13 nearby meteorological stations to test if intense precipitation (percentiles P0.95, P0.99, P0.995) is predominantly related to El Nino conditions or not (based on 15 different ENSO indices). Our results show that the absolute flood frequencies (clastic layers per 100 years) differ substantially from lake to lake. This indicates that the frequency of clastic layers reflects different sensitivities (thresholds of precipitation) of the catchments to alluvial activity. 210Pb ages suggest that neither the 1982/83 nor the 1997/98 very strong El Ninos produced clastic layers comparable to those found in the late Holocene. Daily precipitation records from meteorological stations close to Lake Pallcacocha including a high-altitude station from the western slope of the Andes did not show unusually high precipitation during the super El Nino 2015/16. We further find that intense precipitation in this area occurs at roughly equal probability under El Nino, La Nina and neutral conditions. Although the spectral properties of the late Holocene clastic layers in Lake Pallcacocha fall into the typical ENSO frequency band, we do not find evidence in the recent sediments and the meteorological data that would support a diagnostic link between alluvial activity in Lake Pallcacocha and strong El Nino events. Our data do not support the idea that the (late) Holocene flood record of Lake Pallcacocha is a conclusive paleo-El Nino record

Maximum flood area during MIS 1 in the Almenara marshland (Western Mediterranean): Benthic foraminifera and sedimentary record

The sedimentological and micropaleontological analysis of three mechanical cores in the marshland of Almenara (Valencian Community, Spain) has allowed the reconstruction of the Holocene evolution of this wetland. The cold and dry 8.2-ka event might be represented in Almenara by a massive carbonate precipitation bed, upon which mid- and late-Holocene sediments were subsequently deposited. The direct influence of sea-level changes has been recorded in the two cores (S-4 and S-5) located near the marsh barrier, at 400–450 m from the current coastline. The maximum flood area during MIS 1 (last 11,600 years) is represented in these cores by sediments indicative of different littoral subenvironments (shoreface, foreshore, backshore). These sediments contain typically littoral marine foraminiferal species such as Ammonia beccarii, Rosalina globularis, Asterigerinata mamilla, Adelosina longirostra, Cibicidoides lobatulus, Elphidium macellum, and Bolivina pseudoplicata. The base of these littoral sedimentary materials has been dated as 5480 and 5580 cal. yr BP. At this moment, the inner area (core S-7) was occupied by a restricted oligohaline marsh subject to water-table fluctuations and with scarce individuals of brackish water foraminifera, such as Ammonia tepida, Haynesina germanica, or Cribroelphidium excavatum, that in more recent times (since at least 1700 cal. yr BP) gradually evolved to a palustrine area.

First evidence of a lake at Ancient Phaistos (Messara Plain, South-Central Crete, Greece): Reconstructing paleoenvironments and differentiating the roles of human land-use and paleoclimate from Minoan to Roman times

Phaistos was one of the most important Minoan palaces in Crete and previous studies have addressed its relationship with the paleo-seashore position during historical times. Here, we reconstruct the environmental evolution of Phaistos from Early Minoan to Roman times. Study of two stratigraphic sections and nine boreholes drilled in the westernmost part of the Messara Plain has revealed the stratigraphy of the Mid- to Late-Holocene sediments. Laboratory analyses comprise granulometry, magnetic susceptibility measurements and identification of mollusks, diatoms and pollen grains. Eighteen radiocarbon dates provide a robust chronostratigraphy. In addition, a geophysical survey (electric resistivity tomography (ERT) method) was conducted to reveal the sub-surface morphology in the coring area. The results reveal that a freshwater lake existed from ca. 2100–2000 BC to ca. 1200–1100 BC, which subsequently became swampland until ca. 700 BC. A lake retreat is identified at ca. 1200–1000 BC and can be interpreted as resulting from the 3.2 cal kyr BP rapid climate change (RCC) dry event, observed elsewhere in the Eastern Mediterranean. Subsequently, from the 7th to the 5th century BC, there was the input of detrital material and fluvial dynamics prevailed until at least Roman times. The origin of the lake and its disappearance are discussed in the context of regional climate change and local tectonic activity, without excluding possible human influences. We also reconstruct the vegetation history for the period from the Late Minoan to the Early Archaic period. Pollen analysis reveals a Mediterranean maquis landscape dominated by Olea, together with hygrophilous vegetation, and highlights a clear transition from limnic to swampy environmental conditions around 1100 BC. The pollen sequence is also important for assessing the impact of the 3.2 cal. kyr BP RCC event and for assessing the possibility of an abrupt discontinuity in human activity around Phaistos after the demise of the Minoan Civilization.

Eemian and post-Eemian fluvial dynamics in the Lesser Caucasus

Mountain regions such as the Lesser Caucasus are a focus of ongoing environmental changes. To understand their future evolution, information about their former geomorphic and environmental dynamics is required. The former fluvial dynamics derived from fluvial sediment archives can offer such insights. However, the fluvial dynamics of the Lesser Caucasus since the Eemian interglacial have not been systematically investigated so far. Thus, we have studied late Pleistocene and Holocene sediments of several rivers originating from the central Lesser Caucasus. The studied rivers show a mostly coherent record of fluvial dynamics: Minor aggradation occurred during early Marine Isotope Stage (MIS) 5, incision during late MIS 5 or early MIS 4, intensive silty aggradation at least during late MIS 3, incision during early MIS 2, coarse-grained aggradation probably during some millenia until ca. 19 ka, and aggradation ca. 14-13 ka. Following incision around the Pleistocene/Holocene transition, aggradation resumed around 6.0, 3.4 – 2.0 and 0.5 – 0.15 cal. ka BP. Generally, periods of aggradation, incision and stability could be linked with regional climatic or anthropogenic influences on regional landscape stability and water availability. The fluvial dynamics of the central Lesser Caucasus mostly differed even between neighbouring regions, and only in cases of significant hemispheric climatic fluctuations as around 20 ka, during the Pleistocene/Holocene transition or the Little Ice Age, were similar over-regional fluvial patterns observed. This demonstrates the individual character of river systems especially in mountain regions such as the southern Caucasus with strong geoecological gradients. Thus, to understand the former landscape dynamics of mountain landscapes, investigations of fluvial sediment archives on a regional to sub-regional scale are necessary.