Source Terrain Research Articles

Fluvial Facies Architecture and Sequence Stratigraphy of the Tertiary Duchesne River Formation, Uinta Basin, Utah, U.S.A.

Continental sequence stratigraphy in upstream fluvial environments can be complex due to the interplay of source tectonics, local and global climate change, and topography. The Tertiary Duchesne River Formation, Utah, U.S.A., represents the last stage of intermontane basin fill in the Uinta Basin. It is surrounded by sediment source mountain ranges of the Uinta Mountains to the north and the Sevier Fold-Thrust Belt (FTB) to the west. Excellent basin-scale exposure of the Duchesne River Formation allows the vertical and lateral characterization of facies architectures in the upstream environments. The four members of the Duchesne River Formation are distinctive lithological units. The lower three members comprise a typical upward-fining unconformity-bounded fluvial sequence from the basal coarse-grained unit into the overlying fine-grained units. The fourth uppermost coarse-grained member records the onset of another upward-fining cycle. The sequence stratigraphy of these unconformity-bounded upward-fining cycle(s) was primarily tectonics-driven due to uplift of the Uinta Mountains. The Duchesne River Formation records a distinct change in fluvial–lacustrine styles between the western and eastern part of the basin, demonstrating the variable allogenic controls of tectonic subsidence and discharge related to the local climate and source-terrain input within the basin. Specifically, the western degradational fluvial system with a high net-sandstone-to-gross-thickness ratio of the basal member was controlled by high discharge due to a wet climate and two source-terrain inputs (i.e., Uinta Mountains and Sevier Fold-Thrust Belt), whereas the eastern aggradational fluvial system with a low net-sandstone-to-gross-thickness ratio was controlled by low discharge due to a dry climate and single source terrain input (i.e., Uinta Mountains). The development of local lacustrine environments on the alluvial plain of the third member, present in the western Uinta Basin, was controlled by differential tectonic subsidence in the basin. The Duchesne River Formation preserves a valuable example of an upstream fluvial sequence, and demonstrates how internal facies architectures at the basin scale were dictated by allogenic controls.

Deposition of the Upper Rewa Sandstone Formation of Proterozoic Rewa Group of the Vindhyan Basin, M.P., India: A Reappraisal

Abstract The Upper Rewa Sandstone Formation of the Rewa Group in the Vindhyan basin is composed mainly of medium to very fine grained, iron pigmented arenaceous rocks variously interpreted as fluvial, marine or continental deposits. The Upper Rewa Sandstone Formation consists of channelized, laterally shifting sand bodies comprising 1-2 m thick fining upward (FU) sharply/erosionally based cycles. Each shoaling bar cycle is characterized by presence of large scale planar and trough cross-bedding, horizontal bedding showing primary parting lineation, wave and current ripples, herringbone cross-bedding and tidal bundles with double mud-drapes and indicates marine environment of deposition and rule out the possibility of continental sedimentation. However, channelized nature of sand bodies composed of shoaling bar cycles with signatures of wave modification and exposure in the lower part of the succession and well developed horizontally bedded lithofacies showing primary parting lineation and well sorted character of sandstones in the upper part of the succession may imply deposition under subtidal to intertidal setting in estuarine to bordering beach environments. The palaeocurrent study shows polymodal to bimodal and unimodal palaeocurrent patterns. The dominant polymodal palaeocurrent patterns with temporal trends directed towards NW, N and SW also corroborate marine origin and sediment dispersal under combined action of wave and currents. Petrographically, sandstone is quartzarenite and consists of mostly monocrystalline quartz, feldspar, mica, rock-fragments and heavy minerals such as hypersthene, zircon, hornblende, tourmaline, rutile, augite, kyanite and andalusite indicating sediment contribution from mixed sedimentary/metamorphic and igneous source terrain. Qm-F-Lt and Qt- F-Lt plots reveal that the Upper Rewa Sandstone Formation shows continental block province with stable craton (C) and in uplifted basement (B) where C>B.

High-resolution numerical modeling of mesoscale island wakes and sensitivity to static topographic relief data

Abstract. Recent decades have witnessed a drastic increase in the fidelity of numerical weather prediction (NWP) modeling. Currently, both research-grade and operational NWP models regularly perform simulations with horizontal grid spacings as fine as 1 km. This migration towards higher resolution potentially improves NWP model solutions by increasing the resolvability of mesoscale processes and reducing dependency on empirical physics parameterizations. However, at the same time, the accuracy of high-resolution simulations, particularly in the atmospheric boundary layer (ABL), is also sensitive to orographic forcing which can have significant variability on the same spatial scale as, or smaller than, NWP model grids. Despite this sensitivity, many high-resolution atmospheric simulations do not consider uncertainty with respect to selection of static terrain height data set. In this paper, we use the Weather Research and Forecasting (WRF) model to simulate realistic cases of lower tropospheric flow over and downstream of mountainous islands using the default global 30 s United States Geographic Survey terrain height data set (GTOPO30), the Shuttle Radar Topography Mission (SRTM), and the Global Multi-resolution Terrain Elevation Data set (GMTED2010) terrain height data sets. While the differences between the SRTM-based and GMTED2010-based simulations are extremely small, the GTOPO30-based simulations differ significantly. Our results demonstrate cases where the differences between the source terrain data sets are significant enough to produce entirely different orographic wake mechanics, such as vortex shedding vs. no vortex shedding. These results are also compared to MODIS visible satellite imagery and ASCAT near-surface wind retrievals. Collectively, these results highlight the importance of utilizing accurate static orographic boundary conditions when running high-resolution mesoscale models.

Parallel, Realistic and Controllable Terrain Synthesis

AbstractThe challenge in terrain synthesis for virtual environments is to provide a combination of precise user control over landscape form, with interactive response and visually realistic results.We present a system that builds on parallel pixel‐based texture synthesis to enable interactive creation of an output terrain from a database of heightfield exemplars. We also provide modelers with control over height and surrounding slope by means of constraint points and curves; a paint‐by‐numbers interface for specifying the local character of terrain; coherence controls that allow localization of changes to the synthesized terrain; and copy‐paste functionality to directly transplant terrain regions.Together these contributions provide a level of realism that, based on user experiments, is indistinguishable from real source terrains; user control sufficient for precise placement of a variety of landforms, such as cliffs, ravines and mesas; and synthesis times of 165ms for a 10242 terrain grid.

Sandstone petrology and geochemistry of the Oligocene–Early Miocene Panjgur Formation, Makran accretionary wedge, southwest Pakistan: Implications for provenance, weathering and tectonic setting

The Oligocene–Early Miocene Panjgur Formation is comprised of submarine fan and abyssal plain turbidites deposited within the Makran subduction complex. Sandstones of the formation are litharenite to feldspathic litharenite. Petrographic data indicates a quartzose-recycled provenance dominated by plutonic and metamorphic fragments. Major elements concentrations reveal a moderate level of mineralogical maturity and high values of Chemical Proxy of Alteration (CPA; 88.29) coupled with a high Th/U ratio (9.37), which reveals intense weathering in the source area. The Zr, Nb, Y, and Th concentrations are comparable to upper continental crust (UCC) values and trends in Th/Cr, Th/Co, and Cr/Zr ratios support contribution from a felsic source. However, enrichment in Ni and Cr, reinforced by trends in Ni/Co, Cr/V, V/Ni and Y/Ni ratios, reveals mixing of the felsic source with mafic/ultramafic source terrains. Tectonic discrimination plots suggest continental arc to active continental margin setting. This study supports the Katawaz-delta-Panjgur submarine fan model and upholds the initial southward transport of predominantly felsic detritus from the Himalayan orogenic belt controlled by the Chaman–Ornach Nal transform fault system. This study further adds that the Bela–Muslimbagh ophiolites, associated mélanges and the West Pakistan Fold–Thrust Belt, from the east, and the Chagai–Raskoh volcanic arc, from the west, were also concurrently shedding mafic/ultramafic detritus to the basin, and that the depositional system in the Makran region turned westward, roughly parallel to the present active margin of the Makran accretionary wedge.

Provenance and paleoweathering reconstruction of the Mesoproterozoic Hongshuizhuang Formation (1.4 Ga), northern North China

This is the first study presenting major and trace elemental data from the Mesoproterozoic Hongshuizhuang Formation shales in Yanshan basin, North China, in order to reconstruct its provenance and chemical weathering history. The shales are strongly depleted in Na2O and Sr and enriched in Y and transition metal elements relative to upper continental crust. Low Zr concentrations and various discriminant plots (e.g., Th/Sc–Zr/Sc and Al2O3–TiO2–Zr) indicate insignificant mineral sorting or recycling of these shales. The rocks show light rare earth element (REE) enrichment (La/YbCN = 3.99–6.92), flat heavy REE, and significantly negative Eu anomalies (Euan = 0.57–0.68) in chondrite-normalized REE patterns, similar to post-Archean Australian average shales. The fairly uniform REE patterns and trace element ratios indicate that the Hongshuizhuang Formation shales were derived from a felsic source area with granodiorite as the dominant contributor. Mixing calculations suggest a mixture of 30 % granite porphyry, 5 % basalt, and 65 % granodiorite as the possible source of the shales, also supporting that granodiorite was the predominant source. Intense chemical weathering of the source terrain is indicated by high values of the premetasomatized chemical index of alteration, plagioclase index of alteration, Rb/Sr, a strong positive correlation between TiO2 and Al2O3, depletion of CaO, Na2O, and Sr, and mineral compositions. Such strong chemical weathering suggests a warm and wet paleoclimate, perhaps due to high atmospheric CO2 and CH4 concentrations, and a near-equatorial location of the North China Craton in the Columbia supercontinent at 1.4 Ga.

Petro-chemistry and diagenesis of sandstones of Patherwa Formation, Son Valley, India

The sandstone of Patherwa Formation, (Semri Group) is constituted by quartz, feldspar, micas, rock fragments and heavy minerals. Abrupt changes in the grain size are recorded and sandstone is grouped as fine–grained (FGS), medium–grained (MGS), coarse–grained (CGS) and very coarse–grained (VCGS). The field and petrographic divisions are equally reflected in their chemistry. CGS shows highest SiO2 content (mean 86.59 wt%) followed by MGS (mean 80.78 wt%), VCGS (mean 76.51 wt%) and FGS (mean 75.21 wt%). SREE content is highest in FGS (180.51 ppm) and lowest in CGS (129.64 ppm). VCGS possesses anomalously high SREE values (2070.62 ppm). Range of weathering indices including CIA, CIW, PIA and ICV indicates moderate to strong chemical weathering in the provenance. Large range of variation in weathering indices suggests that physical weathering facilitated chemical weathering, under subtropical humid climate. Mechanical compaction led the rearrangement of grains forming point and long contacts while diagenesis dissolved mobile grains which made sandstone highly quartzose. The progressive compaction getting initiated at the sediment–water interface continued till deep burial in a rapidly subsiding basin. Geochemical provenance modelling suggests production of detritus from a predominately granite–gneissic terrain bearing some mafic rocks. Palaeocurrent data indicates sediment supply from two source terrains, i.e. BGC and Bijawar. Synthesis of petrochemical attributes and diagenesis history, assigns a tectonically active setting where generation of positive relief and its desecration was taking place in quick tandem. The most likely such setting is tectonic uplift due to continental collision.

Geochemistry of the Eocene Jijuntun Formation oil shale in the Fushun Basin, northeast China: Implications for source-area weathering, provenance and tectonic setting

Within the fault-bound Fushun Basin of northeastern China, the Eocene Jijuntun Formation hosts extensive deposits of thick lacustrine oil shale. Systematic sampling and geochemical analysis of these deposits has revealed that the parent rocks of the oil shale underwent moderate chemical weathering; and that its mineralogy and trace and rare earth element geochemistry were mainly controlled by parent rock composition, with no synsedimentary changes in the source terrain. Based on source rock and tectonic setting discrimination diagrams, we concluded that the parent rocks of the oil shale were mostly basalts of the Paleogene Laohutai Formation. These basalts originated in a continental back arc environment and contain abundant nutrient elements such as Fe, P, Ni, Cu and Zn, all of which are essential for the growth of aquatic photoautotrophs in lakes. Continuous, high primary productivity in the Jinjuntun lacustrine depocentre, combined with a stable tectonic setting and underfilled sedimentary environment, were key factors in the genesis of its oil shale.

Sevier belt exhumation in central Utah constrained from complex zircon (U-Th)/He data sets: Radiation damage and He inheritance effects on partially reset detrital zircons

Research Article| March 01, 2015 Sevier belt exhumation in central Utah constrained from complex zircon (U-Th)/He data sets: Radiation damage and He inheritance effects on partially reset detrital zircons William R. Guenthner; William R. Guenthner 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA †Current address: Department of Geology, University of Illinois, Urbana-Champaign, Champaign, Illinois 61820, USA; wrg@illinois.edu. Search for other works by this author on: GSW Google Scholar Peter W. Reiners; Peter W. Reiners 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar Peter G. DeCelles; Peter G. DeCelles 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar Jerry Kendall Jerry Kendall 2ExxonMobil Exploration Company, Houston, Texas 77060, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2015) 127 (3-4): 323–348. https://doi.org/10.1130/B31032.1 Article history received: 10 Nov 2013 rev-recd: 25 Apr 2014 accepted: 29 Jul 2014 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation William R. Guenthner, Peter W. Reiners, Peter G. DeCelles, Jerry Kendall; Sevier belt exhumation in central Utah constrained from complex zircon (U-Th)/He data sets: Radiation damage and He inheritance effects on partially reset detrital zircons. GSA Bulletin 2015;; 127 (3-4): 323–348. doi: https://doi.org/10.1130/B31032.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Thermochronologic dates of partially reset detrital grains are often difficult to interpret because of the potential for variation in inherited predepositional dates and kinetic behaviors of grains from diverse source terrains. In this study, we present several examples of complex detrital zircon (U-Th)/He date distributions from sedimentary rocks that have been heated to temperatures in or near the zircon He partial retention zone, leading to several types of date-eU correlations caused by variations in predepositional inherited age and radiation-damage–induced He diffusion kinetics. These examples are from three subvertical transects in mountain ranges in central Utah: the Wasatch Range near Provo, Utah, the Oquirrh Mountains, and the Stansbury Mountains. Each range lies in the hanging wall of one of three major thrust sheets that compose part of the Charleston-Nebo salient, a segment of the Cretaceous Sevier fold-and-thrust belt. Zircon grains from two of these transects (the Stansbury and Oquirrh Mountains) show large date variations that can be at least partially understood with a radiation-damage–based model for He diffusion in zircon. We combine the output from this model with a new approach for understanding partially reset data sets that relies upon the concept of an “inheritance envelope.” The transect from the Wasatch Range is relatively simple and does not require an inheritance-based interpretation. We document a pulse of 5 km of exhumation in this range at ca. 100 Ma. Time-temperature (t-T) constraints from inheritance envelopes in the Oquirrh Mountains transect suggest a pulse of exhumation beginning at either 110 or 100 Ma. Finally, for the Stansbury transect, the inheritance envelope approach yields inconclusive results; some aspects of the model generate inheritance envelopes that match the measured data set, whereas others do not. Despite their complexity, the t-T histories for these nonideal data sets represent some of the only in situ constraints on the timing of Cretaceous exhumation of Sevier-style deformation in the U.S. Cordillera. In the case of the Oquirrh and Wasatch Range data sets, these direct measurements of thrust sheet t-T histories offer some insight into the evolution of the Sevier fold-and-thrust belt of central Utah. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Late Cretaceous Conglomerates of the Qahlah Formation, north Oman

Abstract Conglomerate sequences over 700 m thick were deposited subsequent to ophiolite emplacement during Late Cretaceous time in north Oman. The conglomerates were deposited by streams draining the allochthonous ophiolite and Hawasina complex after their obduction onto autochthonous Mesozoic and older Oman shelf sequences and subsequent uplift. The conglomerates belong to the Qahlah Formation of Late Cretaceous age, which is sandwiched between the Semail Ophiolite/Hawasina complex and Maastrichtian–Palaeogene carbonate rocks. The siliciclastics of the Qahlah Formation are the first sediments deposited over the obducted oceanic crust sequence of ophiolite and Hawasina lithologies. In five locations studied in north Oman, the thickness of the formation varies from 140 m to over 700 m and comprises interbedded conglomerate, sandstone and siltstone. The sediments were deposited in isolated segmented depressions each characterized by its source terrain depending on lithologies exposed in the source area. Lithofacies associations, clast sorting and grain roundness suggest deposition in stream-dominated alluvial fans. Clasts in the conglomerates range from subangular to subrounded pebbles to boulders with both grain and matrix (sandstone) support. Cross-bedded fining-upwards sequences in channelized conglomerate and sandstone suggest deposition by high-energy flows in the proximal to distal reaches of alluvial fans. High proportions of chert and ophiolite fragments in the conglomerates suggest rapid erosion of obducted oceanic crust. The presence of Loftusia -bearing carbonate beds and bivalve-bearing conglomerate beds in different sections indicates occasional interruption of alluvial deposition by marine transgressions.

Provenance discrimination and Source-to-Sink studies from a dryland fluvial regime: An example from Kachchh, western India

Tracing the sediment delivery from its source terrain to its ultimate sink envisage multiple factors that play a vital role in understanding present day erosional engine. To accomplish this, it is significant to distinguish the variable end-members contributing to the basin. The findings from the study of dryland coastal fluvial regime in Kachchh (Western India), which is one of the end members contributing to the Gulf of Kachchh coast (partial sink) and finally to the Arabian Sea (ultimate sink) have been presented here. Multi-proxy sediment provenance proxies such as grain-size, clay minerals, geochemistry and magnetic minerals have been employed to evaluate the provenance discriminating characteristics of the Kachchh dryland fluvial system and factors influencing them. The results of different proxies indicate that the provenance signatures of uplands are quite characteristic with magnetic susceptibility (χ) values of <2010−7 m3 kg−1 and smectite (S)/kaolinite (K) ratio between 0.26 and 0.49. The middle reaches show marked increase in magnetic mineral concentration with χ values (14010−7 m3 kg−1) and S/K ratio (4.92), while the estuarine tract shows χ values (8010−7m3 kg−1), S/K ratio (1.90) and, characteristic heavy minerals (i.e. mica minerals), probably reflect the interplay between land and sea oscillations. Major sources of sediments within catchment scale were identified, viz., upland sedimentary rocks (Juran and Bhuj Formation sandstone-shale) and middle reaches volcanic (Deccan Trap Formation basalt) rocks. The present study draw cautions in provenance of sediment discrimination in areas influenced by Deccan basalt that has the overwhelming sediment delivery and a comparatively subdued effects of other provenance signatures. The studied proxies of mineralogy of clays, magnetic minerals and geochemistry of heavy and major elements serve as the potential for fingerprint of sediment source regions and hence behold a strong position in source to sink studies globally.

Microfacies analysis of deep-water breccia clasts: a tool for interpreting shallow- vs. deep-ramp Paleogene sedimentation in Cephalonia and Zakynthos (Ionian Islands, Greece)

The tectono-sedimentary evolution of the western Pre-Apulian zone of the Hellenides is investigated through comparison of the microfacies of clasts from breccia beds within gravity-flow successions of Zakynthos with those of the carbonate ramp of the westernmost part of Cephalonia. After the demise of a Late Cretaceous rimmed platform, the Paleogene successions of the Ionian Islands represent different facies patterns of a carbonate ramp. In western Cephalonia (Lixouri peninsula), different successions suggest the existence of five juxtaposed tectono-sedimentary sectors, remnants of a larger carbonate ramp. In Zakynthos, six distinct sectors with different toe of slope-proximal basin stratigraphic successions were recognized, all affected by a Paleocene-Lower Eocene hiatus, which can be grouped into two tectono-sedimentary units. Through the analysis of successions of the Lixouri peninsula and breccia clasts from Zakynthos, 24 age-constrained and spatially related Upper Cretaceous–Oligocene microfacies types were recognized, illustrating a variety of sedimentary environments. These microfacies were allocated to five different stages in the evolution of a tectono-sedimentary model from down-faulting, through backstepping, uplift and dismantling, to fault-controlled subsidence and finally complete drowning. Various microfacies of the clasts can be correlated to the stratigraphic record of the Lixouri peninsula, whereas others are absent there. Thus an inferred adjacent source terrain, now tectonically obliterated, was likely located west of the present-day Ionian Islands.

Detrital and igneous zircon ages for supracrustal rocks of the Kyrgyz Tianshan and palaeogeographic implications

We report detrital zircon ages for Precambrian and early Palaeozoic metasediments from the Tianshan orogen in Kyrgyzstan, an important component of the Central Asian Orogenic Belt and compare these with published ages from the Chinese Tianshan and the Tarim craton. These data provide information on possible source terrains and suggest that Precambrian basement is widespread in the Tianshan and may, at least in part, represent continental fragments rifted off the Tarim craton during the early history of the Central Asian Orogenic Belt. Distinct differences in the Precambrian zircon age distribution between the North and Middle Tianshan of Kyrgyzstan support earlier ideas that these two terranes had different crustal histories prior to their amalgamation in the early Palaeozoic. We envisage an archipelago-type scenario for the Palaeo-Asian Ocean south of the Siberian craton in the late Neoproterozoic to early Palaeozoic in which numerous island arcs and Precambrian crustal fragments derived from Tarim drifted northwards (in present coordinates) and were amalgamated and tectonically stacked together during several ocean closure and accretion–collision events. This is surprisingly similar to what has been envisaged for the evolution of Indonesia where Mesozoic rifting of fragments from the Australian margin was followed by Cretaceous collisions and Cenozoic collision of Australia with the SE Asian margin. In both Central Asia and Indonesia continental crust has arrived in the region in multiple episodes and has been fragmented and juxtaposed by subduction-related processes. Continental growth during this process was minimal.

Contrasting geochemical cycling of hafnium and neodymium in the central Baltic Sea

The central Baltic Sea is a marginal brackish basin which comprises anoxic bottom waters and is surrounded by geological source terrains with a wide variety of compositions and ages. This allows the investigation of water mass mixing using radiogenic isotope compositions of Nd and Hf as well as their geochemical cycling across varying redox conditions in the water column. In this study, we present the distribution of Nd and Hf concentrations and their isotopic compositions for 6 depth profiles and 3 surface water sites obtained during a cruise in the central Baltic Sea onboard the RV Oceania as a part of the international GEOTRACES program.The results obtained indicate that Nd isotopes effectively trace the mixing between more radiogenic saline waters from the south and unradiogenic fresh waters from the north, which helps to understand the reliability of Nd isotopes as water mass tracer in the open ocean. In surface waters, Nd shows higher concentrations and less radiogenic isotope compositions at the northern stations, which are progressively diluted and become more radiogenic to the south, consistent with the counterclockwise circulation pattern of central Baltic Sea surface waters. In contrast to the variable Nd concentrations, Hf shows much less variability. At the Gotland Deep station, the Nd concentrations of the euxinic waters are higher by a factor >10 than those of the overlying oxygen-depleted waters, whereas Hf only shows small concentration variations. This indicates faster removal of Hf from the water column than Nd. Moreover, the dissolved Hf isotope signatures document great variability but no consistent mixing trends. Our explanation is that Hf has a lower residence time than Nd, and also that the Hf isotope signatures of the sources are highly heterogeneous, which is attributed to their differing magmatic and tectonic histories as well as incongruent post-glacial weathering around the central Baltic Sea.

Mobility and Transport of Nd Isotopes in the Vadose Zone During Weathering of Granitic Till in a Boreal Forest

There is a broad correlation between the eNd values for rivers (including both the water and the particulate material it carries) and the age of the source terrain. This paper presents Nd isotope distribution data for soil, soil water, groundwater, and stream water samples gathered in a small catchment in northern Sweden. The results show that the release of Nd and Sm from boreal forests into streams and, eventually, into the oceans is more complicated than previously realized. The weathering of till causes changes in both the Nd isotopic composition and Sm/Nd ratios. Both the Sm/Nd ratio and eNd were higher in strongly weathered soils horizons than in less weathered till, since minerals with high Sm/Nd ratios were, on average, more resistant to weathering than those with low Sm/Nd ratios. In contrast to the situation for the main minerals and the major elements, the weathering of rare earth elements (REE) was not restricted to the E-horizon: the measured REE concentrations continued to increase with depth in the C-horizon. In addition, REE released by weathering in the upper parts of the soil profile were partly secondarily retained at deeper levels. Therefore, the dissolved Nd released by weathering in the upper soil horizons was trapped and did not enter the groundwater directly. Rather, the Nd in the groundwater largely originated from weathering within the groundwater zone. However, this was not the only source of Nd in the stream water. The Nd isotope composition and Sm/Nd ratio were determined by the mixing between of Nd and Sm in the groundwater and REE-carrying organic material washed out of the soil profile. The groundwater close to the stream reaches the upper soil horizons during high discharge events such as snowmelts, and organic matter carrying Nd and Sm is washed out of the soils and thus released into the stream. Therefore, the Nd exported from catchment is derived from both the weathering within the groundwater zone, and the organic matter washed out from the soil. If longer timescales with more advanced weathering stages in the groundwater zone are considered, it cannot be ruled out that there will be a shift towards more radiogenic values in the exported Nd. Recorded shifts in the Nd isotopic composition in the ocean may thus not only reflect changed source regions, but also the weathering history of the same source region.

Stratigraphy and depositional environments of the Mamfe Formation and its implication on the tectonosedimentary evolution of the Ikom-Mamfe Embayment, West Africa

AbstractA 42 m thick outcropping portion of the Mamfe Formation is subdivided into Manyu (31 m thick) and Kesham (11m thick) Members on the basis of textural, mineralogical and structural differences. The Manyu Member (Albian) consists of folded and indurated, medium to coarse grained arkosic sandstones and thickly laminated organic-rich shales deposited in a lacustrine environment. The Kesham Member (Cenomanian) consists of subarkoses intercalated with massive green shale and mudstone deposited in a fluvial environment. The change in depositional environment was tectonically controlled. The mid Cretaceous paleogeography of the embayment was governed by the NE-SW trending “Ikom ridge” which prevented marine incursion from adjacent the Benue Sea. Evaporites found within the basin were precipitated from ocean water that was periodically spilled by strong tides and storms across the ridge into the embayment. The filling-up of the embayment to base level in the Cenomanian resulted in a shift in the depositional center downstream to adjoining lower Benue Trough. Similarity in heavy mineral composition and maturity of the Cenomanian sandstones with recent clastics in the embayment indicates their derivation from the same source terrain and relatively stable tectonic and climatic conditions at the source area since the Cenomanian time.

Petrography and geochemistry of Eocene sandstones from eastern Pontides (NE TURKEY): Implications for source area weathering, provenance and tectonic setting

Subaerial weathering level, source area and tectonic environments were interpreted by using petrographic and geochemical characteristics of Eocene age sandstones found in the eastern Pontides. The thickness of Eocene age clastic rocks in the eastern Pontides ranges from 195 to 400 m. Mineralogical components of sandstones were mainly quartz, feldspar, rock fragments, and opaque and accessory minerals. Depending on their matrix and mineralogical content, Eocene age sandstones are identified as arkosic arenite-lithic arenite and feldspathic wacke-lithic wacke. CIA (Chemical Index of Alteration) values observed in the Eocene age sandstones (43–55) suggest that the source terrain of the sandstones was not affected by intense chemical weathering. Low CIW/CIA (Chemical Index of Weathering/Chemical Index of Alteration) values of the sandstones studied here suggest only slightly decomposed material and having undergone little transport until final deposition. Zr/Hf, Th/Sc, La/Sc and CIA ratios are low and demonstrate a mafic source; on the other hand, high LREE/HREE ratios and a slightly negative Eu anomaly indicate a subordinate fclsic source. Modal mineralogical and SiO2/Al2O3 and K2O/Na2O and Th, Zr, Co, Sc of Eocene age sandstone contents indicate that they are probably magmatic arc originated and deposited in the back arc basin.

Geochemistry of Mesoproterozoic sedimentary rocks of upper Vindhyan Group, southeastern Rajasthan and implications for weathering history, composition and tectonic setting of continental crust in the northern part of Indian shield

The upper Vindhyan succession of southeastern Rajasthan is divisible into Kaimur, Rewa and Bhander Groups. The major and trace element (including rare earth elements) data of the upper Vindhyan shales and sandstones are investigated to determine the weathering history, composition, and tectonic setting of Mesoproterozoic continental crust. CIA (chemical index of alteration) values, A–CN–K plot (A=Al2O3, CN=CaO*+Na2O, K=K2O) and depletion in U, Na2O, CaO, Sr and Ba suggest that the source area experienced moderate to high degree of chemical weathering under warm and humid conditions. Provenance modeling indicates that the Kaimur sandstones are best modeled with a mixture having 40% granitic gneiss, 20% Tonalite–Trondhjemite–Granodiorite (TTG), 20% mafic enclaves and 20% Berach Granite of the Banded Gneissic Complex (BGC). A mixture of 60% granitic gneiss, 20% mafic enclaves and 20% Berach Granite of the BGC can model the Rewa and Bhander Groups. It is suggested that the upper Vindhyan sedimentation commenced at the time of Delhi–Sausar orogeny at about 1100–1000Ma. The orogenic movements uplifted the parts of old continental crust in the BGC terrain creating positive areas, which exposed older crustal blocks containing TTG as important component. The debris of Kaimur sandstone probably derived from these uplifted blocks. As indicated by Palaeocurrent data, the Rewa and Bhander formations were derived from Bundelkhand Granitic Gneiss Complex (BGGC) occurring to the north of the basin and/or the Chotanagpur Granitic Gneiss Complex (CGGC) of eastern Indian shield. The derivation of Lower and upper groups of Vindhyan succession from different source terrains of identical composition suggests that at the time of Vindhyan sedimentation, the BGC of Rajasthan, the BGGC of Central India and the CGGC of eastern India had similar lithological composition. This implies that well before the origin of the Vindhyan basin these discrete terrains evolved as a single unit that existed as a Mesoarchaean nucleus in the northern part of the Indian shield.

Shipping Uphill: The Morris Canal

The design and construction of New Jersey’s Morris Canal had to overcome three major obstacles: the lack of an immediately obvious water source, the rugged and mountainous terrain, and financing.

Geochemistry and detrital modes of Proterozoic sedimentary rocks, Bayana Basin, north Delhi fold belt: implications for provenance and source-area weathering

Bayana Basin, sited along the eastern margin of the north Delhi fold belt of the Aravalli Craton, contains an ∼3000 m-thick sequence comprising one volcanic and seven sedimentary formations of the Delhi Supergroup. The sedimentary units are the Nithar, Jogipura, Badalgarh, Bayana, Damdama, Kushalgarh, and Weir formations in order of decreasing age. Petrographic study of the sandstones as well as major and trace elements (including rare earth elements) and bulk-rock analyses of the shales and sandstones allow the determination of their provenance, source-rock weathering, and basinal tectonic setting. The sandstones are quartz rich and were derived mainly from exhumed granitoids typical of a craton interior. Geochemical patterns of the sandstones and shales are similar. However, trace element abundances are low in sandstones, probably due to quartz dilution. The coarser clastic Damdama and Weir sandstones, which occur at higher stratigraphic levels, have strikingly low trace element concentrations compared with the underlying Bayana and Badalgarh sandstones. All samples show uniform LREE-enriched patterns with negative Eu-anomalies (Eu/Eu* = 0.16–0.23) and are similar to those of post-Archaean Australian shales (PAAS). However, the (La/Yb) n ratios (averages 11–18) of all the sedimentary units are higher than those of PAAS, except for the Bayana Sandstone, which has low values (average 6.77). The chemical index of alteration (70–78) and the plagioclase index of alteration (87–97) values and the A–CN–K diagram suggest moderate to intense weathering of the source area. The provenance analyses indicate that basin sedimentation was discontinuous. It received input from a terrain comprising granitoids, mafic rocks, sedimentary sequences, and tonalite-trondhjemite-granodiorite (TTG) suites. The Nithar and Badalgarh sandstones received input from a source consisting predominantly of granitoids. The succeeding Damdama and Weir sandstones received debris from granitoids and TTG in different proportions. The Kushalgarh shale was possibly derived from a source consisting granites and mafic rocks with a TTG component. The pre-existing sedimentary formations also contributed intermittently during the different phases of sedimentation. Bulk-rock geochemical data suggest Mesoarchaean gneisses and late Archaean granites of BGC/BGGC (Banded Gneissic Complex/Bundelkhand Granitic Gneiss Complex) basement as possible source terrains. These data indicate deposition in a continental rift setting. The coeval formation of many rift-related Proterozoic sedimentary basins in the BGC/BGGC terrain suggests that the North Indian Craton underwent major intracratonic extension during Proterozoic time, probably triggering the break up of Earth's first supercontinent.