Stratigraphic Signature Research Articles

The Neapolitan Yellow Tuff record in the Gaeta Gulf (Eastern Tyrrhenian margin, Southern Italy)

Abstract. The Neapolitan Yellow Tuff caldera-forming eruption (ca. 15 kyr) is a large event that occurred at Phlegrean Fields during the Late Glacial–Holocene time span. The eruptive products represent a widespread isochronous marker that links the marine and terrestrial stratigraphic record of the central Mediterranean and Northern Europe sequences. In this research, we describe the stratigraphic signature of the NYT deposits in the Late Glacial–Holocene shelf sequence of the Gulf of Gaeta (northern Campania region, southern Tyrrhenian Sea) throughout the seismo-stratigraphic interpretation of a grid of high and very high-resolution Chirp seismic profiles. The seismo-stratigraphic data allowed to individuate in the Upper Pleistocene–Holocene stratigraphic architecture a continental shelf characterized by an offlap prograding succession followed by a very thick transgressive onlapping unit, and by an upper highstand unit mainly characterized by undulations probably linked to gas-prone sediment. The NYT reflector observed was parallel and with a high amplitude. It was continuously detected from the shelf to the slope within transgressive deposits. On the inner shelf, its continuity was interrupted by shallow gas pockets. The NYT depths ranges from 2 m b.s.f. on the slope to 38 m b.s.f. on the continental shelf. The NYT event appeared to have played a key role in controlling the stratigraphic architecture of the studied area during the last transgression, acting as a trigger for the formation of the aggradational sedimentary successions fed by pyroclastic and volcaniclastic deposits.

Chaotic behavior of geophysical logs for stratigraphic hiatuses: A case study from Upper Assam Shelf, India

We propose a novel fractal analysis-assisted approach for stratigraphic characterization to understand the in-situ subsurface geology of hydrocarbon reservoirs. By employing correlation dimension and multifractal detrended fluctuation analysis, we quantify the self-similarity and long-range dependencies in the geophysical logs, reflecting the unique sedimentation processes inherent in the stratigraphic formations of the Bhogpara oil field in the Upper Assam basin. The fractal properties of the logs associated with various stratigraphic units are used to establish a fractal-based stratigraphic signature. The hierarchy of the studied formations, based on the correlation dimension ranging from 1.98 to 1.13, is follows as: Girujan > Tipam > Barail > Kopili > Prang > Narpuh > Lakadong-Therria. Furthermore, the spectrum width values, was found to range from 0.70 to 2.04, reflecting the spatial correlation, geological complexity, and heterogeneity inherent in each formation as: Kopili > Prang > Narpuh > Barail > Girujan > Tipam > Lakadong-Therria. This method identifies common fractal patterns between wellbores and aids in determining the spatial continuity of stratigraphic units. Our approach effectively detects lateral variations in subsurface formations, linking well log fractality with depositional patterns through various transitional environments, such as lacustrine to shallow marine to fluvial, in presence of different fluids. The petroliferous formation exhibits lowest fractal dimension and weak multifractality. The research utilizes fractal analysis to improve stratigraphic correlation, enhancing subsurface characterization and reservoir delineation, particularly in complex geological environments, and enhancing reliability.

Tectonic and sedimentary evolution of the Northern Cameroon Cretaceous rift basins: A study of the Babouri-Figuil and Mayo Oulo-Lere basins

The Babouri-Figuil and Mayo Oulo-Lere basins located in Northern Cameroon are small elongated sedimentary asymmetric half-grabens associated with the development of the West and Central African Rift System (WCARS). The evolution of these basins began during the Precambrian pre-rift period and continued through the Late Jurassic - Early Cretaceous periods, although details of their development remain unclear. The aim of this study is to understand the evolution and development of the border faults and their control on syn-rift geometry, accommodation space, and the resulting stratigraphic architecture. Using a combination of multiples surface and subsurface well logs data, we demonstrate the relationship and evolution of various stages of rifting and the associated sedimentary architecture. The basin is composed of an alluvial to lacustrine succession that developed during its tectonic evolution. A 3-stage tectonic model is proposed for the evolution of the basin that uses fault propagation analysis to describe the sedimentary architecture and evolution of basin geometry. The three stages of the model are the early rift, rift climax, and late rift; here, the early rifting phase is marked by the reactivation of faults in the Lower Cretaceous. The rift climax phase resulted in the interconnection of small segmented border faults leading to the high rate of activation of major border faults and to the development of the half graben structure of the basins. The late rift stage is marked by a decrease in border fault activity and accommodation. Sediment distribution and the facies architecture are controlled by tectonic subsidence created throughout the rifting phases. The stratigraphic signature of the Babouri-Figuil and Mayo Oulo-Lere basins are punctuated by the lacustrine water transgression-regression cycles, and controlled by the balance between the rate of sediment supply and tectonic accommodation. The progressive change between overfilled to starved sedimentary architecture is illustrated by this stratigraphic succession. Additional age assessment and sub-surface data in future work could help confirm the structures identified on the surface.

Mitochondrial genomes of Pleistocene megafauna retrieved from recent sediment layers of two Siberian lakes

Ancient environmental DNA (aeDNA) from lake sediments has yielded remarkable insights for the reconstruction of past ecosystems, including suggestions of late survival of extinct species. However, translocation and lateral inflow of DNA in sediments can potentially distort the stratigraphic signal of the DNA. Using three different approaches on two short lake sediment cores of the Yamal peninsula, West Siberia, with ages spanning only the past hundreds of years, we detect DNA and identified mitochondrial genomes of multiple mammoth and woolly rhinoceros individuals—both species that have been extinct for thousands of years on the mainland. The occurrence of clearly identifiable aeDNA of extinct Pleistocene megafauna (e.g. >400 K reads in one core) throughout these two short subsurface cores, along with specificities of sedimentology and dating, confirm that processes acting on regional scales, such as extensive permafrost thawing, can influence the aeDNA record and should be accounted for in aeDNA paleoecology.

Mitochondrial genomes of Pleistocene megafauna retrieved from recent sediment layers of two Siberian lakes.

Ancient environmental DNA (aeDNA) from lake sediments has yielded remarkable insights for the reconstruction of past ecosystems, including suggestions of late survival of extinct species. However, translocation and lateral inflow of DNA in sediments can potentially distort the stratigraphic signal of the DNA. Using three different approaches on two short lake sediment cores of the Yamal peninsula, West Siberia, with ages spanning only the past hundreds of years, we detect DNA and identified mitochondrial genomes of multiple mammoth and woolly rhinoceros individuals-both species that have been extinct for thousands of years on the mainland. The occurrence of clearly identifiable aeDNA of extinct Pleistocene megafauna (e.g. >400 K reads in one core) throughout these two short subsurface cores, along with specificities of sedimentology and dating, confirm that processes acting on regional scales, such as extensive permafrost thawing, can influence the aeDNA record and should be accounted for in aeDNA paleoecology.

Stratigraphic evidence of relative sea level changes produced by megathrust earthquakes in the Jalisco subduction zone, Mexico. The signature of the 1995 Colima-Jalisco earthquake (Mw 8) as a modern analogue

Geological evidence of megathrust earthquakes along the Mexican Pacific coast relies predominantly on tsunami deposits. Records of coseismic relative sea-level changes are scarce even though such evidence can complement and constrain tsunami records, providing information to reconstruct past earthquake rupture dimensions to improve the earthquake hazard assessment of the region. This paper provides the first diatom-based quantitative reconstruction of coastal subsidence along the Mexican subduction zone through the analysis of coastal wetland sediments. We use the stratigraphic signature of the 1995 Colima-Jalisco earthquake (Mw 8.0) as this earthquake is instrumentally well-constrained, allowing us to evaluate our findings and establish approaches to investigate earlier earthquakes. Deposits beneath the wetland Estero Potrero Grande reveal a stratigraphic sequence, < 28 cm beneath the wetland surface, that resembles a signature of rapid submergence. This sequence consists of a horizontal bed of silt with highly humified organic matter abruptly overlain by a horizontal bed of grey silt. The abrupt stratigraphic contact between the two units extends across >1 km of the wetland. Using 14C ages and 137Cs chronohorizons to build an age-depth model, we estimate the age range (1985–2003 CE) and mean age (1995 CE) of this abrupt stratigraphic contact, coincident with the year of the earthquake. Three elemental log-ratios (S/Zn, Br/Zn and Ca/Zn) indicate an abrupt increase of salinity across the stratigraphic contact, which we interpret as marsh submergence recording coseismic coastal subsidence, reflected as relative sea-level rise. Fossil diatom assemblages confirm this trend, and through quantitative approaches we estimate its magnitude (−0.06 ± 0.08 m and − 0.11 ± 0.23 m), which is comparable with coastal subsidence measured by geodetic instruments. Our records reveal a millimetric spike of sand, which we interpret as a signature of the tsunami that accompanied this great earthquake. These findings demonstrate that coastal wetland sediments from the Mexican Pacific coast can record tectonic induced relative sea-level changes. This approach can allow us to better understand the long-term spatial and temporal behavior of this subduction zone.

Secondary controls on the stratigraphic signature of the carbon isotope excursion marking the Paleocene-Eocene thermal maximum at Ocean Drilling Program Site 1135

The negative carbon isotope excursion (CIE) associated with an ancient global warming event referred to as the Paleocene Eocene thermal maximum (PETM, ca. 56 Ma) is commonly observed to have a smaller magnitude in marine records than in terrestrial records. This disparity has been attributed to secondary mechanisms that either attenuate or amplify the CIE magnitude in marine and terrestrial records, respectively. Here we investigate the effects of carbonate diagenesis and sediment mixing on the stratigraphic signature of the CIE in a PETM record recovered at Ocean Drilling Program (ODP) Site 1135 in the southern Indian Ocean. Comparison of parallel planktic foraminifer δ13C records constructed with two different analytical techniques – conventional gas source mass spectrometry (GSMS) measurements of individual whole shells versus in-situ microanalyses on subdomains inside individual foraminifer shells using secondary ion mass spectrometry (SIMS) – shows that both the δ13CGSMS and δ13CSIMS records capture the CIE. However, the δ13CSIMS records yield excursion magnitudes (acarininids = 5.3‰, morozovellids = 3.9‰) that are ~1.6‰ larger than in the whole-shell δ13CGSMS records. Patterns of intrashell δ13C variation delineated by the in-situ SIMS microanalyses indicate that the smaller CIE magnitude registered by δ13CGSMS records is chiefly due to incorporation of diagenetic calcite overgrowths by GSMS analyses of whole foraminifer shells. We also find that many foraminifer shells are infilled with fine-fraction carbonate (nannofossils) and posit that incorporation of non-CIE nannofossils into these infillings further bias whole-shell GSMS δ13C measurements toward more positive values over the CIE interval. We propose that 5.3‰ is the best estimate of the CIE in this deep-sea record, a near match to the average CIE magnitude published for terrestrial PETM records.

Geological features of the Special Nature Reserve of Montalbano Jonico Badlands (Basilicata, Southern Italy)

ABSTRACT A geological, geomorphological and geo-touristic map, at 1:5000 scale, has been produced for the most representative area of the regional ‘Special Nature Reserve of Montalbano Jonico Badlands’, with the aim to represent the scientific and landscape features which allowed the establishment of the Reserve. The area is located in the Province of Matera (Basilicata), on the southwestern sector of the Apennines Quaternary foredeep, in Southern Italy. The map highlights stratigraphic signatures of international interest and badland landscapes, imprinted on a clayey marine succession straddling the Early-Middle Pleistocene boundary. This stratigraphic interval can be considered as an international reference section for global paleoclimatic signatures during Marine Oxygen Isotopic Stages 20–18 and for the base of the Middle Pleistocene Subseries/Subepoch. With the goal to disseminate these knowledges, to improve future research and to promote sustainable geo-tourism, the map allows visitors to enjoy the scientific features and scenery of the Reserve.

Anthropogenic atmospheric deposition caused the nutrient and toxic metal enrichment of the enclosed lakes in North China

Anthropogenic emissions have resulted in increases in the atmospheric fluxes of both nutrient and toxic elements. However, the long-term geochemical impacts on lake sediments of deposition activities have not been clearly clarified. We selected two small enclosed lakes in northern China—Gonghai, strongly influenced by anthropogenic activities, and Yueliang lake, relatively weakly influenced by anthropogenic activities—to reconstruct historical trends of atmospheric deposition on the geochemistry of the recent sediments. The results showed an abrupt rise in the nutrient levels in Gonghai and the enrichment of toxic metal elements from 1950 (the Anthropocene) onwards. While, at Yueliang lake, the rise on TN was from 1990 onwards. These consequences are attributable to the aggravation of anthropogenic atmospheric deposition in N, P and toxic metals, from fertilizer consumption, mining and coal combustion. The intensity of anthropogenic deposition is considerable, which leave a significant stratigraphic signal of the Anthropocene in lake sediments.

Morphodynamic Preservation of Fluvial Channel Belts

The fluvial sedimentary record is largely composed of deposits from relatively common flow events, rather than more catastrophic scour-and-fill events. At the scales of bedforms, such deposits are preserved within the stratigraphic record because they rapidly accumulate within, and are protected by, morphodynamic topographic depressions that occur naturally in the fluvial system as a result of feedbacks between flow, sediment transport, and topography. Examples include the preservation of ripples in front of dunes, dunes in front of bars, and bars within channels. Here, we used 3D seismic data that images preserved channel belts to test the hypothesis that alluvial-ridge basins, morphodynamic depressions formed between raised channel beds due to decreasing sedimentation rates away from channels in alluvial settings, are a source of topography driving channel-belt-scale preservation. Using the 3D seismic data, we measured the stratigraphic positions of channel belts, as well as their lengths, widths, sinuosities, and centerline orientations in the 3D seismic dataset. Results are consistent with well-preserved channel belts steered by alluvial-ridge-basin topography. Further, the thickness of the channel-belt interval exceeds the relief of any one alluvial-ridge basin, suggesting the volume records the filling of multiple alluvial-ridge basins and that the process is common. Characterizing the stratigraphic signature of alluvial-ridge basins is necessary for understanding contrasting fluvial architectures where external forcings prevented their formation.

The San Francisco Estuary, USA as a reference section for the Anthropocene series

A San Francisco Estuary core was analysed at high resolution to assess its component stratigraphic signatures of the Anthropocene in the form of non-native species, Hg, spheroidal carbonaceous particles, δ13Corg, δ15N, radiogenic materials, and heavy metals. Time series analysis of the core using Ti data provides a chronology to depth 167 cm into the 1960s. Below this, to depth 230 cm, the lowermost part of the core may extend to the 1950s or potentially a little earlier. The earliest anthropogenic marker recorded in the core is the excursion in Hg (beginning at 190 cm) which may denote the early 1960s and is the closest stratigraphic marker in the core to the proposed mid-20th century timing for the onset of the Anthropocene. Biostratigraphical signatures of non-native species arriving in the 1970s–1980s are widespread key markers and are significant tools for the correlation of Anthropocene deposits across the estuary. The absence of signals that indicate pre-1950s deposits precludes the use of the core to mark the Holocene–Anthropocene boundary. However, the core provides an important reference section to demonstrate the palaeontological distinctiveness of Anthropocene series deposits.

Straits and seaways: end members within the continuous spectrum of the dynamic connection between basins

Abstract Straits and seaways are fundamental connectors of oceans, seas and more rarely lakes. They are ubiquitous in the modern geography and should be common in ancient landscapes. We compare their characteristics to improve our understanding of these features, with the aim to define better their geological use. We review geomorphological, oceanographic, geological and depositional characteristics based on well-documented modern and ancient examples, with a stronger focus on the rock record. ‘Strait’ and ‘seaway’ are differentiated by their spatial and temporal scale. This influences the type and persistence of oceanographic circulation and sediment distribution. Straits are individual depositional systems, with predictable bedform and facies changes along the sediment transport pathway, whereas seaways are larger and longer-lived physiographic domains, composed of numerous depositional systems. Therefore, their stratigraphic signature in the rock record should be significantly different. We conclude that straits and seaways are end members of a continuum, giving rise to the occurrence of intermediate cases with transitional characteristics. The distinctive geological usage of the terms ‘strait’ and ‘seaway’, even without sharp boundaries between end members, may be helpful for predicting their occurrence, stratigraphy, palaeogeography, biota distribution and potential distribution of reservoirs and seals for fossil resources and CO 2 storage.

The Ernesto Cave, northern Italy, as a candidate auxiliary reference section for the definition of the Anthropocene series

Annually laminated stalagmites ER77 and ER78 from Grotta di Ernesto provide an accurate annual record of environmental and anthropogenic signals for the last ~200 years. Two major transitions are recorded in the stalagmites. The first coincides with the year 1840 CE, when a change from porous and impurity-rich-laminae to clean, translucent laminae occurs. This is accompanied by a steady increase in the growth rate, a decrease in fluorescence and a sharp increase in δ13C values. These changes concur with the end of the Little Ice Age. The second transition takes place around the year 1960 CE and corresponds with an increase in both annual growth rate and sulfur concentration in stalagmite ER78 at 4.2 mm from the top, and with the deflection point in the 14C activity curve in stalagmite ER77 at 4.8 mm from the top. This latter is the stratigraphic signal proposed as the primary guide for the definition of the Anthropocene series. The following shift toward depleted δ34S–SO4 in stalagmite ER78 suggests that industrial pollution is a major source of sulfur. The interpretation of atmospheric signals (S, δ34S, 14C) in the stalagmites is affected by attenuation and time lags and the environmental signals are influenced by soil and ecosystem processes, while other anthropogenic signals (δ15N, 239Pu) are not recorded. For these reasons, the stalagmite record is here proposed as an auxiliary (reference) section rather than a global standard. In summary, Grotta di Ernesto contains one of the best stalagmite records documenting the Anthropocene, and one of only two stalagmite records where the S peak has been measured at high resolution.

Assessing the validity of proposed paleo-tsunami deposits in Sweden

Until recently, the offshore effects of modern tsunamis were unknown. It is only within the past fifteen years that studies have started to examine the sedimentologic and stratigraphic signatures of modern tsunamis in the marine environment. Claims of paleo-tsunami deposits in Sweden, however, predate any knowledge of the offshore effects of tsunamis by more than ten years. These claims are based on lacustrine sediment sequences that would have been at outer shelf water depths during the proposed tsunamis. While numerous claims of paleo-tsunami deposits exist in Sweden, relatively few of these claims are reported in the peer-reviewed literature.The current study re-examines proposed paleo-tsunamis from Stockholm, Iggesund, and northern Uppland and points out a lack of critical geographical, stratigraphical, and chronological data. Additionally, consideration of the Holocene stratigraphy of these locations in the context of what is now known about the effects of tsunamis in the offshore environment indicates that there is currently no credible evidence of paleo-tsunamis in Sweden.

Changing provenance and stratigraphic signatures across the Triassic–Jurassic boundary in eastern Spitsbergen and the subsurface Barents Sea

Changing provenance and stratigraphic signatures across the Triassic–Jurassic boundary in eastern Spitsbergen and the subsurface Barents Sea

A quantitative depositional model of a large distributive fluvial system (Megafan) with terminal aeolian interaction: The Upper Jurassic Guará DFS in southwestern Gondwana

ABSTRACT Recent studies have shown that distributive fluvial systems are the dominant fluvial forms in modern continental sedimentary basins, thus composing a large part of the stratigraphic record. This study provides a basin-scale architectural analysis of the Guará Formation, from the Upper Jurassic record of southwestern Gondwana, and attempts to compare the formation's depositional model to those developed for distributive fluvial system (DFS) successions. This time interval is significant because it was a period of intense tectonic activity related to the Paraná–Etendeka plume and the Gondwana breakup. Quantitative analyses were performed on stratigraphic sections at 17 locations (exposing a total of 720 m of stratigraphy) located in southern Brazil and northern Uruguay, from a larger dataset of 64 locations (comprising a total of 1070 m of stratigraphy). Four facies associations were identified: perennial fluvial channel fills, ephemeral fluvial channel fills, floodplain deposits, and aeolian deposits, indicating a dryland climate. Spatial trends were analyzed along a downstream-oriented transect (NNE–SSW) across the system. Grain size, channel-body thickness, number of stories, and bar thickness decrease downstream, indicating a reduction in channel depth, flow capacity, and channelization of the fluvial system, interpreted to be associated with downstream-increasing bifurcation, infiltration, and evapotranspiration. Based on spatial trends and distribution of facies associations, the deposits are interpreted to have been accumulated from a large DFS which can be divided into four zones, from proximal to distal: Zone 1, dominated by perennial fluvial channels; Zone 2, a mixture of perennial and ephemeral channels; Zones 3 and 4, deposits situated externally of the fluvial channel belts dominated by aeolian and floodplain deposits prevailing in each zone, respectively. The Guará Formation likely records the stratigraphic signature of the largest distributive fluvial systems reconstructed from both modern and ancient datasets, and one of the first where fluvio–aeolian interaction is quantified. The Guará Formation DFS model presented herein is key to understanding paleoenvironmental, paleoclimatic, and geotectonic changes related to Gondwanan fragmentation.

Airborne ultra-wideband radar sounding over the shear margins and along flow lines at the onset region of the Northeast Greenland Ice Stream

Abstract. We present a high-resolution airborne radar data set (EGRIP-NOR-2018) for the onset region of the Northeast Greenland Ice Stream (NEGIS). The radar data were acquired in May 2018 with the Alfred Wegener Institute's multichannel ultra-wideband (UWB) radar mounted on the Polar 6 aircraft. Radar profiles cover an area of ∼24 000 km2 and extend over the well-defined shear margins of the NEGIS. The survey area is centered at the location of the drill site of the East Greenland Ice-Core Project (EastGRIP), and several radar lines intersect at this location. The survey layout was designed to (i) map the stratigraphic signature of the shear margins with radar profiles aligned perpendicular to ice flow, (ii) trace the radar stratigraphy along several flow lines, and (iii) provide spatial coverage of ice thickness and basal properties. While we are able to resolve radar reflections in the deep stratigraphy, we cannot fully resolve the steeply inclined reflections at the tightly folded shear margins in the lower part of the ice column. The NEGIS is causing the most significant discrepancies between numerically modeled and observed ice surface velocities. Given the high likelihood of future climate and ocean warming, this extensive data set of new high-resolution radar data in combination with the EastGRIP ice core will be a key contribution to understand the past and future dynamics of the NEGIS. The EGRIP-NOR-2018 radar data products can be obtained from the PANGAEA data publisher (https://doi.pangaea.de/10.1594/PANGAEA.928569; Franke et al., 2021a).

Neon isotopic signature applied to detrital provenance assignment in foreland basins

Cosmogenic noble gas isotope 21Ne in terrestrial rocks has been used primarily to determine timing and rates of the Earth's surface evolution. Here we explore the ability of detrital 21Ne as a provenance tracer, considering that Ne isotopes produced in source rocks could be preserved in minerals over geological time and might be predominant in total Ne inventory of sediments sunk in basins. This ability is predicated on potential source terranes of a given stratigraphic section with distinct neon isotopic signatures. Here we analyze neon isotopes of a well-dated Miocene–Pleistocene sedimentary archives in Kuqa foreland basin of southern Tianshan. The data suggest that the neon isotopic signature, which is expressed as εNe and defined in this work as the excess 21Ne/20Ne-ratio relative to atmospheric ratio, is stratigraphically sensitive to changes in local source terranes. This result is compatible with U/Pb provenance analysis and also supported by evidences from sandstone petrography and heavy mineral analysis. Influence of other non-source related 21Ne components in sedimentary archives on sensitivity of εNe has proven to be negligible. Furthermore, the integrated stratigraphic signatures of neon isotope and U/Pb age permit the detection of differential erosion in drainage basin, by which the tectonic or climatic effects on geomorphic evolution could be deciphered.

Timelapse of the geomorphologic and stratigraphic evolution of a Late Cretaceous deep-sea fan, northern Santos basin, Brazil

Deep-sea fans are the terminal sinks of clastic sediment, nutrients and pollutants produced in continental landmasses. They are also major targets for oil and gas on continental margins. Several recent studies have applied seismic geomorphology to delineate deep-sea fans, however, most of them describe a relatively short period of the geologic time, disfavoring the observation of long-term geomorphologic changes and the resulting depositional architecture. We analyzed the geomorphologic evolution and architecture of the Maastrichtian, deeply buried, Maricá deep-sea fan in northern Santos Basin, offshore SE Brazil. Using three-dimensional seismic data and logs from three wells, we mapped five horizons (stratal slices), including fan base, fan top and three internal horizons. The examination of lobes and channel networks on each horizon resulted in a timelapse that capture major geomorphologic transformations of the deep-sea fan from inception to abandonment. The Maricá deep-sea fan is a sand-rich system deposited directly onto the irregular topography of the Maricá mass-transport deposit, and its geometry is also influenced by structural highs uplifted by active halokinesis. Six lobes were mapped, which present variable growing patterns and associated stratigraphic signatures indicative of aggradation, progradation, retrogradation, and lateral switching. Four types of channel morphology were identified (straight, sinuous, meandering, and braided-like). Channel length and sinuosity tend to increase with time in the whole fan and within individual lobes. Amplitude maps and well-log motifs suggest that sandy sediments occur mainly as channel-fill deposits and that different channel morphologies produce contrasting stratigraphic architectures and reservoir heterogeneities. Our results show that channel network and sand-body architecture evolve in a predictive fashion mostly controlled by fan aggradation. However, the interaction with the underlying topography causes morphologic changes at the lobe and depositional element scale that often deviate from the overall trend and affect sand distribution across the fan surface.

Stratigraphic signature of the Perito Moreno ice-dammings during the Little Ice Age (southern Patagonia, Argentina)

The spectacular water outburst occurring semi-periodically when the ice-dam formed by the external front of the Perito Moreno glacier collapses, is one of the most attracting events in the UNESCO ‘Parque Nacional Los Glaciares’ of southern Patagonia. These occurrences have been documented since 1936. Instead, evidence of previous events has been only indirectly provided by dendrochronology analysis. Here we show for the first time radiocarbon-dated sediment cores collected within a small inlet of Brazo Sur, that is, the southern arm of Lago Argentino that record ice-dammings in the Little Ice Age, at 324–266 cal yrs BP, as measured on a vegetal fragment sampled at ca. 14 cm from the top of a core. A common characteristic of the three sediment cores is the abrupt change in the stratigraphic record found at variable depths of 14–18 cm from the top of the cores. This change is marked by a hiatus spanning ca. 3200 years, separating planar-laminated sediments below from an alternation of erosional and depositional events above it, indicating recurring high-energy conditions generated by the emptying of the lake basin. In addition, we observed significant changes in the abundance of environmental indicators as testate amoebae below and above the hiatus. These well-preserved stratigraphic records highlight the key role of glaciolacustine deposits in reconstructing the glacial dynamics and palaeoclimate evolution of a glaciated region.