Provenance Of Clastic Sediments Research Articles

Zircon U-Pb ages and provenance characteristics of the Zhiluo Formation sandstones and the formation background of the uranium deposit in Huangling area, Ordos Basin, China

The newly discovered medium-scale Huangling uranium deposit is located in the Shuanlong area of the southeast Ordos Basin. This paper presents the systematic geochemical and zircon U-Pb studies on the Zhiluo Formation sandstones in the Huanling area. The data obtained play an important role in deducing the provenance and tectonic setting of the source rocks. The results show that the lower part of the Zhiluo Formation is mainly composed of felsic sedimentary rocks. The source rocks originated from a continental island arc environment in terms of tectonic setting. U-Pb ages of detrital zircons obtained can be roughly divided into three groups: 170–500 Ma, 1600–2050 Ma, and 2100–2650 Ma. Based on the characteristics of trace elements and rare earth elements (REE) and the zircon U-Pb dating results, it is considered that the Cryptozoic Edo provenance of the Zhiluo Formation mainly includes magmatic rocks (such as granodioritic intrusions) and metamorphic rocks (such as gneiss and granulite) in the orogenic belts on the northern margin of the North China Plate and in the Alxa Block. Based on sedimentological and petrological results, it can be concluded that the provenance of clastic sediments in the Zhiluo Formation was in north-south direction. The preconcentration of uranium is relatively low in the Lower Zhiluo Formation in the Huangling area. Meanwhile, the paleocurrent system in the sedimentary period is inconsistent with the ore-bearing flow field in the mineralization period, which restricts the formation of large-scale and super-large-scale uranium deposits and ore zones in the southeast Ordos Basin. The understanding of provenance directions will provide crucial references for the Jurassic prototype recovery and paleo-geomorphology of the Ordos Basin and the prediction of potential uranium reservoirs of the basin.©2021 China Geology Editorial Office.

Geochemical and palynological analysis of Faiyum Lake sediments, Egypt: Implications for holocene paleoclimate

During most of the Holocene, the Faiyum Depression in Middle Egypt was connected to the Nile River and contained an extensive freshwater lake. Geochemical analysis of a lacustrine sediment core (Qaru-9) from the depression provides evidence of changes in Nile sediment discharge related to changes in Ethiopian African Monsoon (EAM) precipitation, and allows us to reconstruct changes in Nile River runoff, vegetation and erosion in both the near and far catchment. Major and trace elements reveal significant changes in clastic sediment provenance, with sources oscillating between (i) a Blue/Atbara Nile fluvial contribution during the African Humid Period (AHP) and in the late Holocene (i.e. c. 10–7.5 & c.4–0 ka cal BP, respectively), (ii) a White Nile contribution between c. 7.5–4 ka cal BP with aeolian contributions and carbonate deposits occurring during local arid and wetter conditions, respectively. We also use geochemical data to assign variations in the paleowater properties of the Faiyum Lake (i.e. redox condition, paleosalinity and paleoproductivity) throughout the Holocene. Changes in pollen and algal remains in early to mid Holocene sediments confirm a deep freshwater lake prior to c. 10–8 ka cal BP but diminishing water levels after this period. The Faiyum Lake was a deep freshwater lake between 10 & 6 ka cal BP with fluctuating lake levels between 6–4 ka cal BP and during the late Holocene. In the later period, an abrupt drop in lake level occurred followed by increasing salinity as hydrological modifications occurred.

Detrital graphite particles in the Cryogenian Nantuo Formation of South China: Implications for sedimentary provenance and tectonic history

The tectonic history of the Yangtze block of South China prior to the Ediacaran Period has been a matter of debate. In particular, the tectonic history of the Shennongjia terrane in the central-northern margin of the Yangtze block is poorly understood, and the tectonic relationship between the Shennongjia terrane and the Huangling massif (exposed in the Huangling anticline) is unclear. Previous researchers have reported U-Pb dates of detrital zircons and Nd isotopic compositions of clastic rocks from Cryogenian successions in the Shennongjia terrane to identify ancient crustal remnants and the provenance of clastic sediments, and to constrain the age and crustal evolution of the Yangtze block. Here, we describe abundant graphite discs from silty mudstone of the Cryogenian Nantuo Formation in the Shennongjia area of the Yangtze block. These graphite discs are opaque, ∼23–171 μm in size, and highly reflective. Most are abraded or rounded, although some show hexagonal crystalline morphology. Their Raman spectra are distinct from those of indigenous carbonaceous material (CM) in the sedimentary matrix from the Nantuo Formation at the same locality. Raman CM geothermometric analysis indicates that graphite discs experienced a maximum metamorphic temperature of nearly 600 °C, which is inconsistent with the relatively low metamorphic grade of the host rock. These observations indicate that the graphite discs are of detrital origin, most likely derived from high-grade metamorphic rocks in the basement of the Yangtze block (e.g., the Archean-Paleoproterozoic Kongling terrain in the core of the Huangling anticline), consistent with the hypothesis that the Shennongjia region was a part of Yangtze block by the end of the Cryogenian Period.

20,000 years of Nile River dynamics and environmental changes in the Nile catchment area as inferred from Nile upper continental slope sediments

Multi-proxy analysis of two marine sediment cores (MS27PT and MD04-2726) from the Nile continental slope provides evidence of changes in Nile sediment discharge related to changes in Ethiopian African Monsoon (EAM) precipitation, and allows us to reconstruct changes in Nile River runoff, vegetation and erosion in the Nile headwaters. Sediment element composition and neodymium isotopic composition reveal significant changes in clastic sediment provenance, with sources oscillating between a Saharan aeolian contribution during the Last Glacial Maximum/deglacial transition and during the Late Holocene, and a Blue/Atbara Nile fluvial contribution during the African Humid Period (AHP). This study provides a new understanding of past environmental changes. Between 14.6 and 14.13 ka there was a major input of sediments from the Ethiopian Highlands, consistent with a stronger EAM at that time. Climate in the Nile basin was wetter between 14.8 and 8.4 ka, with a corresponding increase in Blue Nile water and sediment discharge via the main Nile into the Eastern Mediterranean. The gradual climatic transition from the AHP to the present-day dry climate was reflected in a decrease in Blue Nile sediment deposition and flood discharge between 8.4 and 3.7 ka, with aridity at a maximum between 3.7 and 2.6 ka. The onset of drier conditions in the Blue Nile basin seems to have begun before the 8.2 ka cooling event in the North Atlantic. We speculate that the climatic change from the wet AHP to the dry late Holocene may have been a result of a break in the low latitude dynamic equilibrium between climate, vegetation and erosion, which may in turn have affected the climate in higher latitudes. Reduced Nile flow may also have had an impact on Levantine Intermediate Water originating in the Eastern Mediterranean through an increase in intermediate water formation.

The De Long Islands: A missing link in unraveling the Paleozoic paleogeography of the Arctic

The vast Laptev and East Siberian shelves in the eastern Russian Arctic, largely covered by a shallow sea and buried beneath sea ice for 9months of the year, remain one of the least studied parts of continental crust of the Earth and represent a big unknown when performing pre-Cenozoic reconstructions of the Arctic. The De Long Islands provide an important window into the geology of this area and are a key for understanding the Early Paleozoic history of the Amerasian Arctic. Four of them (Jeannette, Henrietta, Bennett and Zhokhov islands) were studied using structural data, petrographic and geochemical analyses and U–Pb zircon age dating to offer the following new constraints for the Early Paleozoic paleogeography of the Arctic realm. The basement beneath the De Long Islands is of Late Neoproterozoic to earliest Cambrian age, about 670–535Ma. In the Early Paleozoic, the De Long Islands were located along the broad Timanian margin of Baltica, with a clastic sediment provenance from the Timanian, Grenville–Sveconorwegian, and Baltic Shield domains. The Cambro-Ordovician volcaniclastic successions on Jeannette and Henrietta islands formed part of a continental volcanic arc with a corresponding back-arc basin located to the south (in present co-ordinates). On the continent-ward side of the back-arc basin, shallow marine shelf clastic and carbonate rocks were deposited, which are exposed today on Bennett Island in the south-west of the archipelago (in modern coordinates). The De Long Islands together with other continental blocks, such as Severnaya Zemlya, Arctic Alaska–Chukotka, and the Alexander Terrane, formed the contiguous active continental margin of Baltica during the Early Paleozoic. Today however, these terranes are spread out over a distance of 5000km across the Arctic and eastern Pacific margins due to the subsequent opening of a series of Late Paleozoic, Mesozoic and Cenozoic oceanic basins.

Detrital zircon ages and provenance of the Upper Paleozoic successions of Kotel’ny Island (New Siberian Islands archipelago)

Plate-tectonic models for the Paleozoic evolution of the Arctic are numerous and diverse. Our detrital zircon provenance study of Upper Paleozoic sandstones from Kotel’ny Island (New Siberian Island archipelago) provides new data on the provenance of clastic sediments and crustal affinity of the New Siberian Islands. Upper Devonian−Lower Carboniferous deposits yield detrital zircon populations that are consistent with the age of magmatic and metamorphic rocks within the Grenvillian-Sveconorwegian, Timanian, and Caledonian orogenic belts, but not with the Siberian craton. The Kolmogorov-Smirnov test reveals a strong similarity between detrital zircon populations within Devonian−Permian clastics of the New Siberian Islands, Wrangel Island (and possibly Chukotka), and the Severnaya Zemlya Archipelago. These results suggest that the New Siberian Islands, along with Wrangel Island and the Severnaya Zemlya Archipelago, were located along the northern margin of Laurentia-Baltica in the Late Devonian−Mississippian and possibly made up a single tectonic block. Detrital zircon populations from the Permian clastics record a dramatic shift to a Uralian provenance. The data and results presented here provide vital information to aid Paleozoic tectonic reconstructions of the Arctic region prior to opening of the Mesozoic oceanic basins.

Implications of Franciscan Complex graywacke geochemistry for sediment transport, provenance determination, burial‐exposure duration, and fluid exchange with cosubducted metabasites

AbstractInterpretation of graywacke provenance has long been used to evaluate the record of tectonic process in orogenic belts. Our geochemical data from graywackes of the Franciscan subduction complex, California, show that the connection between sedimentary record and geologic processes may be more complex than previously believed. Trace elements and Nd‐Sr‐Pb isotopes of Franciscan graywackes indicate two sources types. One group lacking negative Eu anomaly (Eu/Eu* > 0.9), shows slightly concave‐up heavy rare earth elements, arc‐like trace element patterns, and western Pacific island arc‐like Pb isotopes, reflecting derivation from older accreted oceanic‐arc terranes in the Sierra Nevada‐Klamath Mountains. The other group displays small negative Eu anomalies, with trace element patterns resembling post‐Archean Australian shale and Pb isotopes similar to Jurassic‐Cretaceous Sierran batholith. There is no systematic separation of these two groups by depositional ages. Thus, geochemistry of the graywackes may partly reflect variation in location of sediment delivery systems, rather than solely reflecting evolution of the neighboring arc. Variation of Nd‐Sr isotopes with stratigraphic‐age for the graywackes mimics the trends of the coeval Great Valley Group clastic‐rocks, suggesting that (1) they share the same sediment sources, (2) there are no “exotic” sediment sources that fed the Franciscan trench, and (3) burial‐exposure cycles for Franciscan clastic rocks were comparatively brief. Comparison of Franciscan graywacke and metabasite geochemistry corroborates earlier conclusions that metabasites had little or no chemical exchange with fluids from cosubducted graywacke. Detrital zircon age populations, major element chemistry, and detrital framework modes, when compared to our data suggest that the former three parameters underrepresent the mafic component of clastic sediment provenance.

Precambrian crustal evolution of the Yangtze Block tracked by detrital zircons from Neoproterozoic sedimentary rocks

Integrated U–Pb dating, Hf-isotope and trace-element analysis of detrital zircons from the Fanjingshan and Xiajiang sediments in the southeastern part of the Yangtze Block has been used to identify ancient crustal remnants and the provenance of clastic sediments, and to provide an overview of crustal evolution in the now-covered parts of the Yangtze Block. The zircon dating indicates that the Fanjingshan Group, which previously was regarded as 870 Ma old, actually was deposited in a ∼800 Ma rift basin similar to other contemporaneous basins in the Yangtze Block; the regional unconformity separating the Fanjingshan Group from the overlying Xiajing Group is dated to 800–740 Ma. Differences in clast compositions and the trace-element and Hf-isotope signatures of zircons between the Fanjingshan Group and the Xiajiang Group suggest changes in the source areas within the Yangtze Block. The combined ages and Hf-isotope data for each group show different histories of crustal evolution in their source areas. In the Yangtze Block, a previously unrecognized source (∼4.3 Ga) is suggested by the Hf model ages of the oldest zircons. Both recycling of ancient crustal materials and minor addition of juvenile material took place in the time intervals 2.5–2.4 Ga, 2.0–1.7 Ga and 0.85–0.8 Ga. The most important generation of juvenile crust appears to have occurred at 1.6–1.4 Ga in the source area of the Fanjingshan Group, and at 0.95–0.85 Ga and 0.78–0.74 Ga in the source area of the Xiajiang Group. This is the first documentation of early Mesoproterozoic (1.6–1.4 Ga) juvenile crust in South China.

Geochemical Identification of Clastic Sediment Provenance from Known Sources of Similar Geology: The Cretaceous Scotian Basin, Canada

Abstract This study tests the effectiveness of a geochemical approach in identifying provenance in a basin where different sources do not show strongly contrasting geology. Petrological studies indicate that at least three distinct rivers, draining reactivated horsts of the Appalachian orogen, supplied sediment to the Lower Cretaceous deltaic sandstones and mudrocks in the offshore Scotian Basin. Ninety-five samples mostly from conventional core were analyzed for 44 major and trace elements. The data were first screened for variability unrelated to provenance, including changes in elemental abundance due to weathering and diagenesis, and the effects of grain size and sorting on element variation. The effect of hydraulic sorting was distinguished from the effects of concentration of ultrastable heavy minerals from polycyclic sources. Multivariate statistical analysis by principal-component analysis (PCA) was used to test the hypothesis of three discrete sources suggested by the petrologic model. Major-element PCA on sandstones discriminated the sources, but results from trace-element PCA required further investigation using element biplots to understand their significance. Only a few elements were found to be diagnostic of different sources, namely K, Rb, Sr, U, Th, Nb, and Ti, with the latter two of value only for sandstones. All of these are elements that are abundant in the granites of the Appalachians. Most published geochemical discrimination diagrams did a poor job of distinguishing the three petrographically recognized sources. In other basins with quite different hinterland geology, other elements are known to be of value in discriminating provenance. Thus it is unlikely that a globally applicable set of elemental discriminants can identify terrigenous sediment sources. Rather, systematic investigation is needed that evaluates processes such as diagenesis and sorting and then tests geographic and stratigraphic variability in bulk geochemistry, informed by at least semiquantitative petrographic data.

40Ar / 39Ar geochronology and provenance of detrital K-feldspars, Ordovician, Upper Mississippi Valley

The Upper Ordovician strata of the Upper Mississippi Valley contain numerous thin, shale layers. Eighteen of these shale layers were previously thought to be altered volcanic ash beds, known as K-bentonites. Radioisotopic geochronology of six of the multiple shale-bed-partings throughout the Upper Ordovician indicate a non-volcanic origin and provide clues for clastic sediment provenance and dispersal, and depositional environments on epeiric seas. The shale-bed-partings occur throughout the Tippicanoe I supersequence; all but one are within carbonate units. One hundred thirty-six 40Ar / 39Ar Single Crystal Laser Fusion analyses of K-feldspar derived from these beds yield apparent ages that range from 754 Ma to 3.1 Ga. The age distributions of the K-feldspars show distinctive populations when the data are plotted according to their stratigraphic position. Samples from the Glenwood Shale and Platteville Group show an age distribution clustering around 850 Ma and 1.0 Ga respectively. Shale samples from four beds within the Galena Group show an age distribution expanding from 754 Ma to 3.1 Ga. The Glenwood and Platteville clusters correspond with the ages of nearby basement rock and Cambrian–Ordovician sandstones, while the shale-bed-partings of the Galena are interpreted to have been sourced from a broader region. These differences suggest that the Glenwood and Platteville samples were sourced from local rocks, whereas the Galena shale samples correspond with flooding of the local region area and connection to a new and complex source region. These shale-bed-partings can be interpreted in two ways: as pulses of terreginous material entering the system and overwhelming carbonate deposition, or as background sediment, accumulating during pauses in carbonate deposition. While the older Glenwood and Platteville samples can be interpreted in either way, the samples from the Galena are better interpreted as condensed background sediment.

The Brabant Massif as part of Armorica/Gondwana: UPb isotopic evidence from detrital zircons

UPb isotopic ratios of zircons are used as time-dependent geochemical tracers for the formation of the zircons and for the sum of processes and their intensities effective for the disturbance of the UPb systems during the history of the zircons. By comparison detrital zircons can thus serve as indicators for the provenance of clastic sediments. The UPb systematics of 57 carefully selected fractions of detrital zircons from four Cambrian sandstones of the Ardennes and the Brabant Massif have been investigated. According to the UPb data features of color and shape of these zircons are suited for distinguishing to major groups: 1. (1) colourless, mainly rounded, subordinately subhedral or euhedral zircons which are characterized by U contents below 300 ppm and by apparent 207Pb/ 235U ages between 0.53 Ga and 1.65 Ga. 2. (2) reddish, generally subrounded to very well rounded zircons with U contents from 240 ppm to more than 800 ppm and apparent 207Pb/ 235U ages between 1.75 Ga and 2.4 Ga. From the group of colourless zircons only one fraction yields concordant UPb data and documents a Cadomian/PanAfrican crystal growth at 545 Ma. UPb data of the other colourless zircons arrange in a fan-shaped area in the Concordia diagram below Concordia and from 530 Ma to 600 Ma. Zircons with such UPb characteristics are well-known from Central and Southern Europe. They suggest a strong Cadomian/Pan-African influence. The reddish zircons are dominantly derived from Archean to Early Proterozoic crystalline rocks. Based on these results and on comparison with U-Pb data of other detrital zircons the Ardennes and the Brabant Massif must be regarded to be coherent to the Gondwana continental plate before the Caledonian orogeny.