Paleogene–Quaternary Polyfacies Sedimentary System of the Southern Nansen Basin

Groundwater data from the natural analogue site Ruprechtov have been evaluated with special emphasis on the uranium behaviour in the so-called uranium-rich clay/lignite horizon. In this horizon in-situ Eh-values in the range of −160 to −280 mV seem to be determined by the SO42−/HS− couple. Under these conditions U(IV) is expected to be the preferential redox state in solution. However, on-site measurements in groundwater from the clay/lignite horizon show only a fraction of about 20% occurring in the reduced state U(IV). Thermodynamic calculations reveal that the high CO2 partial pressure in the clay/lignite horizon can stabilise hexavalent uranium, which explains the occurrence of U(VI). The calculations also indicate that the low uranium concentrations in the range between 0.2 and 2.1μg/l are controlled by amorphous UO2 and/or the U(IV) phosphate mineral ningyoite. This confirms the findings from previous work that the uranium (IV) mineral phases are long-term stable under the reducing conditions in the clay/lignite horizon without any signatures for uranium mobilisation. It supports the current knowledge of the geological development of the site and is also another important indication for the long-term stability of the sedimentary system itself, namely of the reducing geochemical conditions in the near-surface (30m to 60 m deep) clay/lignite horizon. Further work with respect to the impact of changes in redox conditions on the uranium speciation is on the way.

Download Full-text

The Sedimentary Facies and Evolution Characteristics of the Middle and Deep Strata in the Nanpu No. 3 Structural Area

Frontiers in Earth Science ◽

10.3389/feart.2021.703070 ◽

2021 ◽

Vol 9 ◽

Author(s):

Hui Zhang ◽

Zhiqin Lan ◽

Xiaoyan Li ◽

Xinglong Huang

Keyword(s):

Shallow Lake ◽

Oil And Gas ◽

Sedimentary Facies ◽

Seismic Profile ◽

Tectonic Activity ◽

Lake Basin ◽

Braided River ◽

Break Zone ◽

Sedimentary System ◽

Deep Strata

In this study, due to the inconsistencies in the understanding of the sedimentary types in the second section of the Dongying Formation (Ed2) and the third section of the Shahejie Formation (Es3) in the middle and deep strata of Nanpu No. 3 structural area, the depositional characteristics of the deep braided river delta, fan delta, deep-water slump turbidite fan, and coastal and shallow lake in the Nanpu No. 3 structural area were examined in-depth. The investigations were begun based on the descriptions and observations of core samples obtained from eight cored wells in the study area, in combination with seismic, well logging, and rock ore data. The results revealed that the sources of the material in the study area originated from the Shaleitian salient in the southwest direction. It was determined that the fan deltas and the shallow lake sedimentary system had developed during the SQ1 sequence and SQ2 sequence periods. The braided river deltas and the shallow lake and turbidite sedimentary system with multi-stage superposition had developed during the SQ3 to SQ7 sequence periods, and their distribution range had been controlled by the structural background of the gentle slope zone of the lake basin. On that basis, a sequence deposition filling model controlled by a slope break zone in the middle and deep strata of the Nanpu No. 3 structural area was established in this study starting from the typical seismic profile, in which such factors as the tectonic activity characteristics, lake basin boundary shape, water depths, and so on, were comprehensively considered. The goal of this research investigation was to provide beneficial information for oil and gas explorations in similar areas.

Download Full-text

Protracted northward drifting of South China during the assembly of Gondwana: Constraints from the spatial-temporal provenance comparison of Neoproterozoic−Cambrian strata

Geological Society of America Bulletin ◽

10.1130/b35791.1 ◽

2021 ◽

Author(s):

Qiong Chen ◽

Guochun Zhao ◽

Min Sun

Keyword(s):

South China ◽

Detrital Zircons ◽

Northern Margin ◽

Northern India ◽

Geological Evolution ◽

System 2 ◽

Sedimentary System ◽

Provenance Variations ◽

Late Neoproterozoic ◽

T Values

Neoproterozoic to Paleozoic sedimentation shows systematic temporal-spatial variations within South China, which must be considered in reconstructing geological evolution of South China in response to global plate reorganization from the breakup of Rodinia to the assembly of Gondwana. We use >1000 new U-Pb and Hf isotopic data for detrital zircons from Neoproterozoic−Cambrian strata across the western (i.e., Longmenshan) and eastern (i.e., Wuyishan) margins of South China, coupled with compiled stratigraphic and magmatic information, to constrain change in provenance through time. First-order conclusions are as follows: (1) detrital zircons from the Neoproterozoic strata of the two margins were mainly sourced from the Panxi-Hannan arc and the Jiangnan orogen, signaling a rough self-sufficient sedimentary system; (2) newly identified Cambrian molasse-like sediments in the western margin, in which abundant detrital zircons are 550−500 Ma old with positive εHf(t) values, were mainly derived from the 580−500 Ma Cadomian arc belt along the Iran-Turkey margin; and (3) the Cambrian sediments in the eastern margin document more increased contributions from the Grenvillian-age provinces most possibly in Australia. Such spatial-temporal provenance variations signal the northward drifting of South China, from a position connecting with Iran-Turkey and northern India to that approaching Australia during the late Neoproterozoic−Cambrian period. We highlight that the activity of oblique oceanic-continental convergence accreted Asian terranes onto the northern margin of Gondwana, hence contributing to the ultimate Gondwana architecture under global plate reorganization.

Download Full-text

Hydro-climatic fluctuations and their impact on Lake Abhe environments (Ethiopia & Djibouti): a lesson from the past 10,000 years

10.5194/egusphere-egu21-4634 ◽

2021 ◽

Author(s):

Carlo Mologni ◽

Laurent Bruxelles ◽

Fabien Arnaud ◽

Pierre Sabatier ◽

Anne-Lise Develle ◽

...

Keyword(s):

East African ◽

Climatic Fluctuations ◽

Climatic Oscillations ◽

Sedimentary Records ◽

Hydrological Changes ◽

Precession Cycle ◽

Afar Region ◽

Geomorphic Features ◽

Sedimentary System ◽

The Impact

Throughout the last 14 ka, tropical Africa experienced significant hydrological changes that were mainly driven by the orbital precession cycle, which controls the intensity of the African monsoon. Recent studies conducted in lake and deltaic sedimentary records suggest that long-term monsoon humid oscillations (African Humid Period / AHP ~14 &#8211; ~6 ka) were punctuated by centennial-scale episodes of hyperaridity. However, the abrupt or gradual aridification modalities since the end of the AHP and the modalities of the centennial-scale episodes, as well as their impacts on past and current environments are still debated.The Lake Abhe basin in the Central Afar region (Ethiopia & Djibouti) is the endorheic receptacle of freshwater originating in the Ethiopian Highlands, and represents a hydro-sedimentary system sensitive to hydro-climatic changes in East Africa. Today it is characterized by residual lakes (Gamari and Afambo lakes) and a hyper-arid climate, while during the AHP, the Abhe basin was occupied by a Mega-lake and by humid environmental conditions. Holocene climatic disruptions drastically changed the landscapes and ways of life along this basin.&#160;&#160;The aim of this study is to describe, interpret and estimate the impact of hydro-climatic oscillations on the evolution of Lake Abhe&#8217;s littoral lacustrine environments and palaeolandscapes since the AHP from different viewpoints.Indeed, this research combines paleoclimatological and geomorphological studies based on a new set of 14C ages on two lacustrine cores and on several morpho-sedimentary outcrops spanning the Early to Late Holocene. Our results allow us to: a) refine the temporal occurrence and the hydrological modalities of the AHP including short-term arid episodes linked to Younger Dryas and 8.2 ka North Atlantic events; b) recognise some paleo-shoreline geomorphic features linked to lake level fluctuations, as well as the development littoral pedological horizons and the activation/shutdown of the perilacustrine fluvial network during humid and arid events; c) track these changes until the present day, and discuss their evolution scenario in the near future.Comparing with other regional climatic records, we show how Lake Abhe basin was highly reactive to East African monsoonal regimes, and how current hydrological changes could impact its environments.&#160; &#160;&#160;&#160;&#160;

Download Full-text

Spatial variation in provenance signal: identifying complex sand sourcing within a Carboniferous basin using multiproxy provenance analysis.

Journal of the Geological Society ◽

10.1144/jgs2021-045 ◽

2021 ◽

pp. jgs2021-045

Author(s):

B. Anders ◽

S. Tyrrell ◽

D. Chew ◽

C. Mark ◽

G. O'Sullivan ◽

...

Keyword(s):

Spatial Variation ◽

Drainage System ◽

Provenance Analysis ◽

Rock Composition ◽

Content Type ◽

Metasedimentary Rocks ◽

Sedimentary System ◽

Supplementary Material ◽

Sandstone Formation ◽

Proterozoic Basement

Multiple factors (e.g. source rock composition, climate, nature/scale of sedimentary system) influence the volume and composition of sediment delivered to basins. Fluctuations in these parameters produce cryptic source signals which can vary within the same sedimentary system. Bespoke multi-proxy provenance approaches, targeted at minerals of variable stability, allow for an assessment of natural biasing (recycling) and intra-basinal spatial variations.Provenance of fluvial/deltaic sandstones (Mullaghmore Sandstone Formation) in the NW Carboniferous Basin, Ireland, has been constrained using zircon and apatite U-Pb geochronology, trace elements in apatite and Pb-in-K-feldspar analysis. Zircon U-Pb grain populations are consistent with feldspar data, suggesting Proterozoic basement highs offshore Ireland and Scotland were the main contributor with minor supply from Archean-Palaeoproterozoic rocks of Greenland/NW Scotland and Caledonian-aged rocks. However, apatite data shows a much larger proportion of Caledonian-aged grains of metamorphic origin, suggesting significant sediment was recycled from Neopropterozoic metasedimentary rocks. The spatial variation in provenance indicates that, at onset of clastic input, sediment was being routed to the basin through a complex drainage system, comprising of several discrete hinterland catchments, rather than supply from a single, large interconnected sedimentary system. Such complexities can only be identified with the careful application of a bespoke multi-proxy provenance approach.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5536691

Download Full-text