Recent Sediments Research Articles

Biogeochemical features of the formation of Holocene sediments in Lake Dukhovoe (Eastern Baikalia)

A 6-meter core of Holocene sediments from Lake Dukhovoe was studied. As shown by the radiocarbon dating of lacustrine sediments, Lake Dukhovoe was formed in the Early Holocene (10 cal ka BP). The upper 180 cm of sediment is represented by sapropel, and the boundary of lake sediments is at 293 cm. This is an early stage of lake evolution, devoid of biogenic sedimentation. The microbiological studies of the sediment were carried out, which showed a high total number of heterotrophic bacteria in the upper (0–15 cm) and deeper (110–180 cm) sapropel intervals. Mineral bottom sediments (180–293 cm) are characterized by the presence of groups of phosphorus-reducing and ferromanganese bacteria. The contents of Na, Mg, Al, Si, Al, Ca, Fe, Mn, Zr and Cr in sapropel are within the average concentrations for the earth’s crust, and U and Mo exceed them.

Особенности экологического состава планктонных и бентосных фораминифер в поверхностных осадках Татарского пролива (Японское море)

he fauna of planktonic and benthic foraminifera of the Tatar Strait in the surface layer of sediments from cores sampled during the cruise LV85 on the R/V «Akademik Lavrentiev» in May 2019 has been studied. The benthic foraminifera assemblages, consisting of living and dead shells, correspond in their ecological appearance to the modern cold-water oceanographic conditions of the studied area. Among planktonic foraminifera, along with the dominant subarctic form Neogloboquadrina pachyderma dex., there are single tropical and subtropical species (Globorotalia inflatа, Globigerinoides ruber and Neogloboquadrina dutertrei). The authors believe that the above warm-water forms entered the Tatar Strait from the southwestern part of the Sea of Japan with the warm waters of the Tsushima Current. Fossil finds of warm-water fauna in Pleistocene and Holocene sediments play an important role in deciphering the geological record in the northern part of the Sea of Japan. Their presence in sedimentary sections makes it possible to trace the northward migration of the warm current and assess the extent of its influence on coastal ecosystems in the past.

Reconstruction of the Late Quaternary climate of Oka Plateau (East Sayan) based on sedimentary record from high-mountain freshwater lake

We present the results of a comprehensive study of Holocene sediments from high-mountain Lake Sagan-Nur located in East Sayan. The lake is freshwater and has glacial origin. The sediments have been studied by X-ray diffractometry (XRD), IR spectroscopy, laser grain-size analysis, X-ray fluorescence analysis, AMS (14С) and 210Pb dating. The mineral composition of lake bottom sediments is dominated by phyllosilicates, quartz and feldspars. The method of mathematical modeling of their complex XRD profiles was used for correct identification of layered silicates. It has been established that the structural characteristics and quantitative ratios of these minerals change in response to climate changes in the region. The study of sediments composition and, especially, the precision mineralogical-crystallochemical analysis of layered silicates allowed us to reconstruct the climatic conditions of sedimentation.

Changes in the Provenance of the Holocene Deposits of the Oga and Tsivolki Bays (Novaya Zemlya Archipelago) according to Sr, Nd, and Pb Isotope Data

Changes in the Provenance of the Holocene Deposits of the Oga and Tsivolki Bays (Novaya Zemlya Archipelago) according to Sr, Nd, and Pb Isotope Data

The Middle to Late Holocene in the Agro Pontino and the Fondi basin (Lazio, Italy): A palaeogeographical overview

The Agro Pontino, a vast plain located south of Rome (southern Lazio, Italy), has served as a valuable resource for central Italian palaeogeographical, vegetational and archaeological studies for decades. This paper reviews the regional development of the Agro Pontino and adjacent Fondi basin from the Würmian (Marine Isotope Stages 2–5d) until the end of the protohistoric, with an emphasis on the period around the Early Bronze Age (EBA) date of the Avellino eruption. Following postglacial relative sea level rise, a dissected Pleistocene landscape drowned and was filled with lagoonal, fluvial, alluvial, lacustrine and marsh deposits. In the Agro Pontino, two lakes emerged divided by an alluvial fan. The unique regionally preserved stack of Middle to Late Holocene sediments, including multiple macroscopically visible tephra layers within a depositional environment, allowed for a detailed regional palaeogeographical, tephrochronological and vegetational reconstruction. This study presents the latest palaeogeographical findings from the Agro Pontino and the Fondi basin for the Middle Holocene and the EBA, for which tephra identification and dating forms the solid basis. It contributes to the reconstruction of the Pontine plain and the Fondi basin during this period and furthers our palaeoenvironmental knowledge of the conditions for human subsistence in this region during the later phase of the EBA, around the time of the Avellino eruption (c. 1900 calBC).

Catagenetic trends in composition and structure parameters of asphaltenes

Сatagenetic transformations of asphaltenes of organic matter (OM) from recent sediments and fossil rocks were studied on rocks sampled from different sedimentary basins (Timan-Pechora, Mezen, West Siberian, Kuznetsk, Aldan-Maya and Middle Amur) of Russia. Changes in the elemental composition of asphaltenes were analyzed with the Veselovsky’s model of the formation of major groups of fossil fuels using cO parameter (cO = (O/8 – N)/(C/3)) as compared with the total carbon based on elemental analysis. Just as the Van-Krevelen diagram, the plot built in C–cO coordinates for OM of various genetic forms demonstrates a significant difference in the asphaltenes composition evolution during catagenesis. At the same time, the cO parameter has notably increased in asphaltenes of both types of OM. Structural transformations of asphaltenes during catagenesis were identified in the course of high-resolution NMR (nuclear magnetic resonance) spectroscopy. The research results comprise data on carbon distributions in the aromatic and aliphatic groups in the investigated asphaltenes of different type OM of sediments and rocks at different stages of lithogenesis. A correlation between the asphaltene composition and structural parameters depending on thermocatalytic transformations is revealed. The asphaltenes of terrestrial organic matter are distinguished by higher cO values and different carbon yields of aromatics (higher) and aliphatics (lower) throughout the catagenesis phase. The highly transformed marine OM is marked by surge condensation of aromatic rings in asphaltenes, which makes them similar to asphaltenes of the terrestrial type OM.

Fossil insectivorous mammals (Eulipotyphla) of the southern Pre-Urals (Bashkortostan, Russia)

Seven species of red-toothed shrews (Sorex araneus, Sorex isodon, Sorex tundrensis, Sorex caecutiens, Sorex minutus, Sorex minutissimus, Neomys fodiens), white-toothed shrews (Crocidura sp.), moles (Talpa sp.) and hedgehogs (Erinaceus sp.) were found in Late Pleistocene and Holocene deposits of the southern part of the western slope of the Ural Mountains. In the Late Pleistocene and Early Holocene deposits, the red-toothed shrews were dominated by S. tundrensis. This species disappeared from the area by the Late Holocene, when S. araneus became the predominant species. Smaller mandibular sizes have been registered for S. araneus in the Middle and Late Holocene, as compared to the sizes of older samples. The morphometric criteria have been established for a species differential diagnosis of the Late Pleistocene – Early Holocene mandibular samples of S. araneus and S. tundrensis, found in local deposits of the southern Pre-Urals area studied.

Rapid subsidence in the Kathmandu Valley recorded using Sentinel-1 InSAR

ABSTRACT Urban subsidence poses significant challenges for rapidly developing cities. Published InSAR data reveal Kathmandu as a prime example, demonstrating an alarming rate of subsidence during rapid urban expansion. To monitor the spatiotemporal evolution of recent subsidence, we use Sentinel-1 Synthetic Aperture Radar (SAR) data and the LiCSBAS open-source processing package. Vertical surface motion maps from 2015 to present reveal many localized zones with high subsidence rates (>100 mm year−1), while the mountains that surround the valley have experienced slight surface uplift of ~5 mm year−1. The highest subsidence rate is ~200 mm year−1 and occurs in the centre of the Kathmandu metropolitan area. The distribution of subsidence in the valley matches with areas of the Pliocene to recent sediment up to 500 m thick. The deep aquifer compaction is likely to be the main driver of subsidence in the Kathmandu Valley. Time-series data show a dominant linear subsidence signal with weak sinusoidal signal peaks associated with groundwater recharge of shallow aquifers during the monsoon season. Subsidence rates decrease in proximity to the main river channels, likely driven by the seasonal recharge into the distal floodplain. The distribution of subsidence in the Kathmandu Valley has significant implications for future flood risk and infrastructure in the city.

Опыт определения копромаркеров в отложениях археологических памятников (по материалам стоянки Сельунгур, Южный Кыргызстан)

Introduction. The article discusses the results of a study of ash layers from Holocene deposits at the Selungur (Surungur) Cave. Goals. So, the work attempts a practical evaluation of a method of identifying coprostanols in archaeological sediments. The investigation of Holocene deposits of the site was carried out in 2018 and 2021 field seasons. The study identifies a total of 7 Holocene layers that represent the typical ‘fumier’ facies of cave and rock shelter deposits connected to pastoralism and animal husbandry practices, and built up of stratified layers of burnt herbivore dung. The sequence contains a record of multiple earthquakes that disturbed the sediments and effected in water escape structures, plastic deformations, and faults. Nevertheless, the stratigraphy remains easily readable. Unfortunately, archaeological and paleofaunistic materials were never found but a series of ash-containing interlayers suggests that the cave was repeatedly visited by ancient humans. Materials. In the ash deposits, our micro charcoal analysis has identified areas of concentration of burnt dungs which was used for fire. Series of samples were taken throughout the section of Holocene deposits for gas mass spectrometry analysis. The research efforts have also included the analysis of modern dung from herbivores inhabiting the area, such as cows, sheep, goats, horses and donkeys, for the latter obtained data to serve as a reference collection. Results. Unfortunately, layer 7 of the Selungur Cave proved characterized by poor preservation of fire products, while layers 6–1 yielded somewhat rich data. The obtained results make it possible to identify coprosterols and determine that equine dung was used in layers 6-2 as a fuel, and goat dung — in the first layer. The most widespread distribution of equines in this region occurred during the existence of Dayuan (Parkan) state, in the third century BC and later in the Middle Ages. Most likely, during these periods the mountain corridor comprising the Selungur Cave could have been used as a pass of the Silk Road that connected the Fergana and Alay valleys. The accumulation of the upper layer, in our opinion, is associated with the modern era.

Geologic Map of the Bedford 30- x 60-minute Quadrangle, Indiana

The Geologic Map of the Bedford 30- x 60-minute Quadrangle shows the Mississippian and lower Pennsylvanian bedrock units and the overlying Pleistocene and Holocene deposits distributed over eight counties. The mapped area includes five physiographic divisions of the Southern Hills and Lowlands Region in south-central Indiana. Bedrock units and unconsolidated deposits were characterized by outcrop field observations, and new and archived borehole data. Bedrock data was consolidated into a single mapping database, which was then processed using gridding and contouring tools in ArcGIS Pro, resulting in rock formation contact lines, mappable at 1:100,000 scale. Additional information used to delineate contacts for unconsolidated deposits was based upon Indiana Department of Natural Resources water well database and soils data from the Soil Survey Geographic (SSURGO) database. Light detection and ranging (LiDAR) digital elevation models were also used to identify landforms and refine contacts between surficial units. The mapped bedrock units, from east to west, range in age from the Borden Group (lower Mississippian) to the Raccoon Creek Group (Lower Pennsylvanian) with the strike oriented generally from northwest to southeast. Quaternary deposits are found in river and stream valleys and filling the Wabash and Scottsburg lowlands with glacial deposits. Quaternary sediments were mostly deposited during the last two major advances of the Laurentide Ice Sheet into south-central Indiana. Brief summaries of all mapped bedrock units and unconsolidated deposits are listed on the map sheet, with more detailed descriptions in the accompanying pamphlet. Bedrock survey drill hole data points are also displayed on the map with corresponding links to expanded drill hole information for each of the survey drill holes listed in the pamphlet. In addition to the map and pamphlet, a composite spatial data set that conforms to the standardized database schema known as GeMS (Geologic Map Schema) is also available for download from this site. Both ESRI-licensed geodatabase and open shapefile versions of the spatial data set are available for download. Metadata records associated with each element within the spatial data set contain detailed descriptions of their purpose, constituent entities, and attributes. This geologic map was funded in part through the STATEMAP program supported by the U.S. Geological Survey under Cooperative Agreement No. G21AC10646.

Holocene Depositional History of Low-Lying Reef-Rim Carbonate Islets of Fakarava Atoll, Northwest Tuamotu, Central South Pacific

Assumptions about the fate of low-lying coral reef islands (atolls) facing global warming are poorly constrained, due to insufficient information on their depositional history. Based on the U/Th dating of 48 coral clasts, the chronostratigraphic analysis of excavated sections through rim islets (motu) at the windward and leeward sides of Fakarava Atoll (Tuamotu, French Polynesia) reveal that the deposition of coral detritus started approximately 2000 years ago. Most of these deposits lie on conglomerate pavements or reef flat surfaces, and are about 4500 to 3000 years old. The islet expansion at the windward sites seems to have operated coevally across the reef rim, from the ocean-facing shore lagoonwards. Meanwhile, well-developed, continuous, elongated, vegetated islets mostly occur along the windward, northeast to southeast coast, and isolated islets, vegetated or not, associated with the dense networks of conglomerates, are common on the leeward, partly submerged, western rim. Islet accretion on the windward rim sides is believed to have been mainly triggered by winter storms and occasional cyclonic events, whilst the leeward atoll parts were most likely shaped by distant-source swells from mid to high latitudes. The projections of the accelerated sea level rise in the future suggest that the long-term islet stability at Fakarava could be altered because the islets have accreted under the conditions of the falling sea level.

North Atlantic forcing of Indian Winter Monsoon intensification: Evidence from Holocene sediments from the tropical Indian Ocean Island of Sri Lanka

The teleconnection between the Asian monsoon system and North Atlantic forcing is an enduring prospect of the Earth’s climate. During the Holocene interstadial, the Indian summer monsoon showed asynchronous weakening links to ice rafting events documented in the North Atlantic region. However, the sensitivity of the Indian Winter Monsoon in response to North Atlantic cold spells is unclear due to a lack of compelling evidence. This study aims to extract the deglacial Indian Winter Monsoon signals using lithogenic tracers in coastal sediments and explore its association with the North Atlantic cooling episodes. A 5.1 m sediment core was retrieved from Pottuvil Lagoon in the southeastern coast of Sri Lanka, and the concentrations of K, Rb, Mg, Al, and Ti in 101 sub-sections were analysed using ICP-MS. The core- chronology was established by Bacon 2.2 age-depth modelling based on calibrated AMS 14C dates. The monsoon signal was reconstructed using element proxies and compared with the drift ice indices from the North Atlantic deep-sea sediments. Results revealed distinct phases of intense monsoon activity at 2553–2984 years BP, 3899–5021 years BP, and 5244–5507 years BP intervals with intermittent weak phases during 2253–2553, 2984–3899, and 5021–5244 years BP. The episodes of the intensified Indian Winter Monsoon coincided with Bond Events 2, 3, and 4, showing a strong coherence with the North Atlantic’s deglacial climate. Thus, on a millennial scale, North-Atlantic cooling has triggered intense winter monsoon conditions over the tropical Indian Ocean region from the mid to late Holocene. In comparison with regional monsoon archives, the Pottuvil winter monsoon record exhibits an anti-phase association with the Indian Summer Monsoon during Holocene ice-rafted debris events. The geochemical approach executed in this study could provide new insight into the millennial-scale pacing of the winter counterpart of the Indian monsoon links to climate extremes of high northern latitudes.

Precious Metals in the Holocene Sediments of the Chukchi Sea

Abstract ––We studied the distribution of gold, silver, and platinum group elements (Pd, Pt, Rh, Ir, and Ru) in two bottom sediment cores of the southern Chukchi Sea. It is shown that the Holocene pelite–silty sediments with an age of up to 4.0 ka BP are significantly enriched in these elements, except for Ru and Rh, relative to their clarkes. Native silver minerals were found in all samples by probe microanalysis, whereas gold minerals were revealed only in the surface layer of the sediment core closest to the Chukchi Sea coast. Multicomponent statistical analysis of the chemical composition and grain size of the sediments and the content of organic matter in them has led to the conclusion about the accumulation of clastogenic and chemogenic forms of precious metals. The abnormally high content of gold (0.3 ppm) in the recent sediments near the Chukchi Peninsula coast might be due to its additional removal from the continent as a result of the placer mining there.

Mineralogy of Recent Sediments of Al-Teeb River Basin-East Missan Governorate, Southeastern Iraq

This research aims to define the mineralogical composition of recent sediments that were deposited around the Al-Teeb River basin in the east Missan Governorate and try to determine the provenance or the source of these sediments. The study area represents the southeastern edge of the Mesopotamian Plain and is part of it. 15 samples were collected from eight stations of recent sediment that was deposited around the Al-Teeb River; two field works are covered (December 2019 and August 2021). Mineralogical study of the sediment after separating the light and heavy minerals by heavy liquid Bromoform in order to determine the mineralogical composition of the studied samples by using the petrographic microscope the light mineral fraction composed (95.5%) of the total mineralogy. The light components of these sediments consist mainly of quartz about 25.31%, feldspars (potash and plagioclase feldspar) about 9.53%, sedimentary rock fragments (carbonate rock fragments up to 33.39%, chert rock fragments 7.65%, evaporates fragments, 7.31%), (igneous rock fragments, and metamorphic rock fragments about 6.94%). The major component of the heavy minerals residue is opaque minerals with a range of 36.76% and non-opaque minerals with a range of 63.24%. The non-opaque minerals are mainly of chlorite 7.42%, pyroxenes composed of both orthopyroxene and clinopyroxene 6.37%, amphiboles composed of hornblende, glaucophane, and tremolite 7.02%, (mica: biotite and muscovite) 9.81%, zircon 7.54%, tourmaline 5.1%, epidote group 5.91%, rutile 4.5%, kyanite 2.2%. The sediments have two types of stability: moderately stable and ultra-stable. The mineralogical composition shows that the major sources of these sediments are; the river terraces and flood plain of the river in the Mesopotamian Plain, another source of these sediments is the aeolian deposits that separated from sand dune fields in the studied area, and outcrops of ancient sedimentary formations in the southeastern of Iraq as specified by the incidence of the carbonate rock fragments.

Cryptotephra preserved in Lake Suigetsu (SG14 core) reveals the eruption timing and distribution of ash fall from Japanese volcanoes during the Late-glacial to early Holocene

Long sedimentary successions extracted for palaeoclimate research regularly preserve volcanic ash (tephra) fall from explosive eruptions and are increasingly used to elucidate the timing and scale of past events. This study investigates the non-visible tephra (cryptotephra) layers preserved in the annually laminated and intensively 14C dated sediments of Lake Suigetsu (SG14 core), Japan. The cryptotephra investigations reported here focus on the Late-glacial to early Holocene sediments that were deposited between two visible tephra layers, the Ulleungdo (U)-Oki (10.2 ka) and the Sambe ‘Sakate’ (19.6 ka), and consequently span an interval of abrupt climate change making any newly identified cryptotephra layers invaluable chrono-stratigraphic markers. Using major and trace element volcanic glass compositions the cryptotephra are used to assign provenance to chrono-stratigraphically relevant eruption units. Five new cryptotephra layers are identified within this time interval. Three cryptotephra layers are from Kyushu volcanoes (SG14-1337 and SG14-1554 [Sakurajima]; and SG14-1806 [Kirishima]), all of which offer important chronological constraints on archaeological (Jomon) cultural transitions in southern Japan during the last termination. Another cryptotephra (SG14-1579), is assigned to activity on Niijima Island providing the first known distal occurrence and age of the eruption. Finally, the SG14-1798 cryptotephra precisely dated at 16,619 ± 74 IntCal20 yrs BP (2σ) is linked to Asama (As) volcano and more precisely the later phases of the As-YKU eruption. This discovery greatly expands the distribution of ash fall from this multi-phased eruption at Asama volcano, which affected an area in the region of 120,000 km2. Refining the timing of the eruption and the distribution of As-YKU ash fall is important as it offers an excellent chrono- and climato-stratigraphic marker suitable for assessing spatial variability in environmental response to past climate change during the termination of the last glacial.

Foraminifera in the Holocene sediments at the shallow sea from Phu Loc (Thua Thien Hue) to Hoi An (Quang Nam) (0÷60 m of water depth)

The shallow sea (0÷60 m of water depth) from Phu Loc (Thua Thien Hue) to Hoi An (Quang Nam) belongs to the internal shelf in Central Vietnam. This is quite a good geological structure for the land-sea interaction study, especially during the Holocene. Therefore, it is necessary to study the geological history of the area during the Holocene period. Foraminifera is the subject of geological studies to solve the environmental problems of sedimentary, stratigraphic, and paleogeography. However, at present, the research documents on Foraminifera in the sediments in Vietnam in general as well as in the research area in particular are still very modest. This paper presents research results of Foraminifera fauna in Holocene sediments from Phu Loc (Thua Thien Hue) to Hoi An (Quang Nam) (0÷60 m of water depth). 93 species, belonging to 48 genera, 28 families and 5 suborders Foraminifera have been identified based on the analysis of 59 available samples. Miliolina Delage et Hérouard, 1896 has 06 families, 18 genera and 40 species; Rotaliina Delage et Hérouard, 1896 has 12 families, 15 genera and 29 species; Textulariina Delage et Hérouard, 1896 has 03 families, 05 genera and 07 species; Lagenina Delage et Hérouard, 1896 has 03 families, 04 genera and 07 species; Globigerinina Delage et Hérouard, 1896 has 04 families, 06 genera and 10 species. The quality of the benthonic Foraminifers is dominant, clearly showing the geological environment of the shallow sea near shore, where the hydrodynamic regime is high and the salt concentration is not stable.

Impact of Natural and Anthropogenic Factors on Late Holocene Sedimentation in the Chukchi Sea

Impact of Natural and Anthropogenic Factors on Late Holocene Sedimentation in the Chukchi Sea

Application of mid-infrared spectroscopy for the quantitative and qualitative analysis of organic matter in Holocene sediment records

The organic matter composition of lake sediments influences important in-lake biogeochemical processes and stores information on environmental changes. Extracting this information is notoriously difficult because of the complexity of the organic matter matrix, which routinely imposes trade-offs between high temporal and analytical detail in the selection of methods of analysis. Here, we demonstrate the potential of diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) for achieving both of these objectives using untreated bulk samples from two Holocene lake-sediment cores from central Sweden. We develop quantitative models for sediment total organic carbon (TOC) with the same predictive abilities as models based on samples diluted with KBr and qualitatively characterize the organic matter using a spectra processing-pipeline combined with principal component analysis. In the qualitative analysis we identified four organic matter sub-fractions and the interpretation of these is supported and further advanced with molecular data from pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Within these organic fractions, compound groups such as aromatics, lignin, aliphatics, proteins and polysaccharides were identified by means of DRIFTS and the analyses and processes outlined here enables rapid and detailed quantitative and qualitative analysis of sediment organic matter. The DRIFTS approach can be used as stand-alone method for OM characterization with high temporal resolution in Holocene sediment records. It may also function as a screening process for more specific analyses of sample subsets, such as when coupled with pyrolysis-GC/MS to further tease apart the OM composition, identify sources and determine degradation status.

Recent increase in sediment dry matter, carbon, and phosphorus accumulation in small boreal lakes with clayey catchments

This study estimated the mass accumulation rates of sediment (MAR), carbon (CMAR), and phosphorus (PMAR) in small Finnish lakes with agricultural clayey catchments over a 25-year period (1986–2011) and compared these with the conditions before major agricultural land use. Twenty-two lakes were cored for recent and reference (pre-disturbance) sediments. The recent sediment section was selected based on the 1986 137Cs fallout peak (TOP), whereas the pre-disturbance section (REF) was selected immediately below the first signs of human-induced erosion. The 50-cm reference section was dated with 14C at both ends. The mass accumulation rates were estimated based on dating, weighing, and chemical analysis for both sediment sections. Furthermore, sediment-penetrating echo soundings were used to estimate the amount of sediment in the whole lake basins. These data were used to examine area-specific loading from clay-rich catchments. The average whole-basin pre-disturbance MAR, PMAR, and CMAR were 62 g m−2 a−1, 0.06 g m−2 a−1, and 4.7 g m−2 a−1, respectively. The corresponding recent rates were 11, 13, and 8-fold (693 g m−2 a−1, 0.79 g m−2 a−1, and 37 g m−2 a−1). In the recent conditions, sediments were generally more minerogenic and MAR, PMAR, and CMAR were higher in lakes with more arable fields in their catchments. Average area-specific suspended sediment load from the catchment for the region (∼39% clayey soils) was approximately 69–137 kg ha−1 a−1 in the undisturbed state and 767–1534 kg ha−1 a−1 in recent conditions based on 100–50% retention. The results demonstrate that the increases in sediment, nutrient, and organic matter accumulation due to agriculture can be several fold over undisturbed state.

Impact of aerobic reworking of biomass on steroid and hopanoid biomarker parameters recording ecological conditions and thermal maturity

Steranes and hopanes are the biomarkers of eukaryotic sterols and bacterial hopanols. Extracted from sedimentary rock, they are widely used to assess burial temperatures and palaeoecological conditions. The relative proportion of steranes and hopanes is commonly applied as a measure of the flux of eukaryotic versus bacterial biomass into sediments, and the relative abundances of C27, C28 and C29 steranes are proxies for shifts in eukaryote ecology. In Recent sediments, intact sterols provide additional information about particular eukaryotic origins. However, biological lipid distributions are not always recorded faithfully in sediments. Based on observations on modern algae and plants, and on 558 million year old fossil macroalgae from the Ediacaran of the White Sea, we suggest that these biomarker proxies can be severely altered by aerobic microbial reworking, to the extent that a complete loss of primary ecological information may occur. Network analysis on the biomarker data suggests that oxic degradation also affects isomer and homolog distributions of saturated and aromatic steroids, hopanes, cheilanthanes and n-alkanes, generating anomalies in apparent thermal maturity indicators and other proxies. In our dataset, between Ediacaran macroalgae that experienced the least and the most oxic degradation, the absolute concentration of biomarkers decreases 80-fold, and at the same time the proportion of steranes over hopanes decreases by a factor of 82, while the proportion of C29 steranes among total steranes decreases from 91% to 47%. Such redox dependent offsets may explain the recurrently erratic behaviour of numerous biomarker parameters. While these results impart constraints on the interpretation of biomarker distributions, they do provide a tool for evaluating the effects of oxygen exposure and microbial degradation on organic matter preservation in recent and ancient environments and may point towards a solution for the correction of such effects.