scholarly journals The Paleoproterozoic Francevillian succession of Gabon and the Lomagundi-Jatuli event

Geology ◽  
2020 ◽  
Vol 48 (11) ◽  
pp. 1099-1104 ◽  
Author(s):  
Karen Bakakas Mayika ◽  
Mathieu Moussavou ◽  
Anthony R. Prave ◽  
Aivo Lepland ◽  
Michel Mbina ◽  
...  
Keyword(s):  
Dissolved Inorganic Carbon ◽  
Isotope Effects ◽  
A Priori ◽  
Shallow Marine ◽  
C Cycle ◽  
Storm Wave ◽  
Isotope Profile ◽  
Marine Realm ◽  
Facies Change ◽  
Marine Facies

Abstract The Paleoproterozoic Francevillian succession of Gabon has figured prominently in concepts about Earth’s early oxygenation and genesis of a large positive excursion in carbon-isotope values, the Lomagundi-Jatuli event (LJE). Here we present a detailed study of a 139-m-long core of Francevillian rocks marked by carbonate δ13C (δ13Ccarb) values of 5‰–9‰ that decline upsection to near 0‰, a trend inferred by many workers as a fingerprint of the LJE and its termination. However, we show that the shift in δ13Ccarb values coincides with a facies change: shallow-marine facies are marked by the strongly positive values, whereas deeper-marine facies (below storm wave base) are at ∼0‰. The most circumspect interpretation of such facies dependence of δ13Ccarb is that shallow-marine settings record the isotope effects of local physical and biochemical processes driving the ambient dissolved inorganic carbon (DIC) pool to heavier values, and the lighter values (∼0‰) in deeper-water facies track the DIC of the open-marine realm where δ13C was largely unaffected by fractionations occurring in shallow-water settings. Further, a transgressing redoxcline created conditions for precipitation of Mn-bearing minerals and chemotrophic microbial biota, including methane cycling communities evident by organic δ13C (δ13Corg) values of −47‰ and Δδcarb-org values as high as 46‰. Thus, the Francevillian C-isotope profile reflects basin-specific conditions and is not a priori an indicator of global C-cycle disturbances nor of the termination of the LJE.

Nummulites Fayumensis N. Sp. and Nummulites Tenuissimus N. Sp. from Munquar El-rayan, Fayum, Egypt

2018 ◽  
Vol 48 (1) ◽  
pp. 17-28 ◽  
Author(s):  
Safia Al Menoufy ◽  
Mohamed Boukhary
Keyword(s):  
New Species ◽  
Foraminiferal Assemblage ◽  
Shallow Marine ◽  
Marine Facies ◽  
Benthic Foraminiferal Assemblage ◽  
Insight Into ◽  
Important Site

Abstract Nummulites fayumensis n. sp. and Nummulites tenuissimus n. sp. are described from the Munqar El-Rayan Section, Fayum, Egypt. Nummulites tenuissimus belongs to the N. partschi group, while N. fayumensis belongs to the N. gizehensis group, based on diameter and protoconch sizes, septal shape and granulations. Both new species are of Lutetian age, assigned to SBZ14/15, and encountered in shallow-marine facies. Wadi El-Rayan is an important site for vertebrate fossils in Egypt and the abundant larger benthic foraminiferal assemblage provides insight into paleoenvironmental parameters associated with the deposition of Eocene-age rock units of the Munqar El-Rayan Section.

High resolution linkage of channel-coastal plain and shallow marine facies belts, Desert Member to Lower Castlegate Sandstone stratigraphic interval, Book Cliffs, Utah-Colorado, USA

2019 ◽  
Vol 131 (9-10) ◽  
pp. 1643-1672 ◽  
Author(s):  
Simon A.J. Pattison
Keyword(s):  
Coastal Plain ◽  
Sediment Supply ◽  
Data Set ◽  
Shallow Marine ◽  
Book Cliffs ◽  
Marine Facies ◽  
Sequence Boundaries ◽  
Allogenic Processes ◽  
Stacking Patterns ◽  
Order Sequence

AbstractThe Campanian Desert Member and Lower Castlegate Sandstone in the Book Cliffs of east-central Utah to western Colorado, USA, has served as a foundational data set in the development of sequence stratigraphy. Contrary to previous work, no third-order sequence boundaries are recognized. These were originally thought to partition the neighboring coastal plain and shallow marine facies belts into separate systems tracts, unlinked in time or space. In contrast, adjoining channel-coastal plain and shallow marine facies belts are genetically-, temporally-, and spatially-related. Evidence includes the (i) synchronous, strongly progradational stacking patterns within each facies belt, (ii) gradational and conformable transitions between adjoining facies belts, accentuated by the ubiquity of flat-topped, rooted foreshore sandstones passing upwards into carbonaceous-rich-mudstone-dominated coastal plain, (iii) parasequence-scale interfingering of coastal plain-channel and foreshore-shoreface deposits, with channels, white caps and coals embedded within stacked shoreface parasequences, (iv) regional correlation of coals and flooding surfaces, and (v) near orthogonal paleocurrent relationship between channels and shorelines. Terminal channels incise into proximal foreshore-shoreface sandstones in most Desert-Castlegate parasequences. Incisions are generally confined to the parasequence in which the channels are nested, rarely cutting deeper. These shoreface-incised channels are cut and filled at a parasequence-scale, and are bounded above by the same flooding surface that caps each foreshore-shoreface package. The ubiquity of ascending regressive shoreface trajectories and near absence of descending regressive trajectories that intersect depositional slope argues against any significant sea level fall. Increased rates of sediment supply, driven by autogenic and/or allogenic processes, likely generated the strongly progradational Desert-Castlegate great tongue of sandstone.

Tectonic and climatic controls on a Mesozoic forearc basin succession, Alexander Island, Antarctica

2002 ◽  
Vol 139 (3) ◽  
pp. 313-330 ◽  
Author(s):  
GARY J. NICHOLS ◽  
DAVID J. CANTRILL
Keyword(s):  
Facies Analysis ◽  
Fossil Plants ◽  
Forearc Basin ◽  
Gradual Reduction ◽  
Shallow Marine ◽  
Continental Deposits ◽  
Deformation Event ◽  
Marine Facies ◽  
Land Deformation ◽  
The Antarctic

The Cretaceous Fossil Bluff Group on Alexander Island, on the west side of the Antarctic Peninsula, contains a remarkably complete record of the evolution of a forearc basin. The latest (Aptian–Albian) stages in the basin history are recorded in a well-exposed succession at the southern end of the island, where a series of nunataks provide exposure of over a thousand metres of shallow marine and continental deposits. An abrupt facies shift from upper shoreface marine facies to braided fluvial deposits is interpreted as the record of regional uplift in the volcanic arc. This event coincides with the Palmer Land deformation event which may be related to a mid-Cretaceous mantle plume. A gradual reduction in depositional gradient and a return to shallow marine conditions towards the top of the exposed section is interpreted as a consequence of erosion of the arc and subsidence within the basin. Palaeocurrent data and facies distributions indicate that the continental deposits formed a fan-shaped wedge at least 30 km in diameter in the southern part of the forearc basin. Fossil plants indicate that the palaeoclimate was warm and humid throughout the period of deposition. Mapping and facies analysis of the upper part of the Fossil Bluff Group in southern Alexander Island has resulted in a revision of the stratigraphic terminology for the area. The Triton Point Member, formerly part of the Neptune Glacier Formation, has been raised to formation status and two members (the Citadel Bastion Member and the Coal Nunatak Member) and a Bed (the Upper Coal Nunatak Sandstone Bed) are defined here within the formation.

scholarly journals Marine Regression and Palaeoenvironments During the Holocene in the Richardson River Basin, District of Mackenzie, N.W.T.

2007 ◽  
Vol 38 (2) ◽  
pp. 185-192
Author(s):  
Daniel E. Kerr
Keyword(s):  
River Basin ◽  
Marine Sediments ◽  
Late Quaternary ◽  
Intertidal Environment ◽  
River Bank ◽  
Shallow Marine ◽  
Isostatic Uplift ◽  
River Basin District ◽  
Marine Facies ◽  
The Many

ABSTRACT A detailed stratigraphie analysis was carried out on a river-bank section of late Quaternary marine sediments in the Richardson River Basin, N.W.T. The sedimentary sequence represents a gradual shallowing of the sea in an estuarine environment, from a relatively shallow marine faciès to an intertidal environment. The withdrawal of the sea from the Richardson River Basin began prior to 10,300 years BP. Isostatic uplift caused the gradual regression of the sea to its present-day level. The marine sediments yielded 26 ostracode and 14 foraminifer species. Faunal evidence is indicative of brackish-water marginal marine conditions resulting from the dilution of nearshore marine waters by freshwater discharge from the many streams and rivers draining the basin of the Richardson River.

scholarly journals Reconstruction of Thermal Conditions in the Subboreal Inferred from Isotopic Studies of Groundwater and Calcareous Tufa from the Spring Mire Cupola in Wardzyń (Central Poland)

Water ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 1945 ◽  
Author(s):  
Tomasz Gruszczyński ◽  
Jerzy Małecki ◽  
Anastasiia Romanova ◽  
Maciej Ziułkiewicz
Keyword(s):  
Stable Isotopes ◽  
Environmental Changes ◽  
Dissolved Inorganic Carbon ◽  
A Priori ◽  
Thermal Conditions ◽  
Climate Conditions ◽  
Calcareous Tufa ◽  
Isotopic Studies ◽  
Living Organisms ◽  
Cool Climate

Studies with application of stable isotopes of oxygen and carbon have been performed on calcareous tufa, groundwater and dissolved inorganic carbon (DIC) from the spring mire cupola in Wardzyń. This study was focused on the verification of the a priori hypothesis that the analysed calcareous tufa is a chemical deposit and on the attempt to supplement an earlier scenario of environmental changes in the Subboreal with oscillations of water temperature. The constructed model of chemical and isotope balance, and δ13C determinations in DIC, allowed for calculating ratios of stable isotopes of carbon in particular speciations and in gaseous CO2. The obtained results coupled with δ13C values in calcite indicate that this mineral precipitated from the solution chemically (without the contribution of living organisms). Additionally, it was possible to reconstruct the temperature range at which the calcareous tufa was formed. The reconstructed scenario of changes in the thermal conditions was refined based on δ18O determinations in groundwater and calcite. Accordingly, the oldest calcareous tufa, with an age of about 5500 cal years BP, was formed in cool climate conditions (with average annual temperatures by about 3 °C lower than presently). The formation of younger series of the calcareous tufa took place between 4400–2900 cal years BP and represents a much warmer period with two distinct cooler episodes at 3900 and 3000 cal years BP, respectively. The course of the obtained temperature curves correlates well with the GISP2 curve and curves obtained for other sites in Northern, and Central Europe.

Middle–Upper Cambrian Trilobites of the Genus Nganasanella Rosova, 1963 and Their Stratigraphic Significance

2021 ◽  
Vol 62 (07) ◽  
pp. 746-764
Author(s):  
A.L. Makarova
Keyword(s):  
Siberian Platform ◽  
Type Species ◽  
Lower Boundary ◽  
River Section ◽  
Shallow Marine ◽  
Upper Cambrian ◽  
Regional Stage ◽  
Stratigraphic Position ◽  
Marine Facies ◽  
Stratigraphic Chart

Abstract —This paper presents a revision for the genus Nganasanella Rosova, 1963, first described in the stratotype of the Kulyumbean Regional Stage of the Kulyumbe River section (northwest of the Siberian Platform). This section is typical of the upper Cambrian sediments of the Kotuy–Igarka facies region, formed in a shallow marine shelf. As shown by the study, the genus comprises seven species. The species N. nganasanensis Rosova, 1963 (type species), N. tavgaensis Rosova, 1963, N. glabella (Kobayashi), 1943, N. granulosa Rosova et Makarova, 2009, and N. vernacula Rosova et Makarova, 2009 are found in the Siberian Platform. The species N. australica sp. nov. occurs in northeastern Australia. The species N. trisulcatus (Ergaliev), 1980 is widespread in southern Kazakhstan. Some species (N. granulosa and N. vernacula) are found in open marine facies sediments along with the cosmopolitan agnostid species Glyptagnostus reticulatus (Angelin), 1851, serving as a marker of the lower boundary of upper Cambrian strata in the International Chronostratigraphic Chart and the General Stratigraphic Chart of Russia. The species N. trisulcatus and N. australica are found slightly above Glyptagnostus reticulatus. Representatives of the genus Nganasanella are a link between strata of different facies containing different trilobite associations. Their stratigraphic position can serve as an argument for the correlation of the Kulyumbean Regional Stage with units containing Glyptagnostus reticulatus, i.e., the Omnian and Idamean regional stages, the lower parts of the Kutugunian Horizon and the Sakian Regional Stage, and the Paibian Stage of the International Chronostratigraphic Chart.

Carbon Cycle

2006 ◽  
Author(s):  
Thomas S. Bianchi
Keyword(s):  
Dissolved Inorganic Carbon ◽  
Global Climate ◽  
Food Resource ◽  
Carbonate Reservoir ◽  
Reduced Form ◽  
Short Term ◽  
C Cycle ◽  
Ecosystem Level ◽  
Short And Long Term ◽  
Life On Earth

Carbon is the key element of life on Earth and exists in more than a million compounds (Holmén, 2000; Berner, 2004). The unique covalent long-chained and aromatic carbon compounds form the basis of organic chemistry and the “roadmap” for understanding life from the cellular to the ecosystem level. The oxidation states of C atoms range from +IV to −IV; methane (CH4) is the most reduced form of C (−IV), with CO2 and other carbonate forms existing in the most oxidized state (+IV). The major reservoirs of C are stored in the Earth’s crust, with much of it as inorganic carbonate and the remaining as organic C (e.g., kerogen) (figure 13.1; Sundquist, 1993). The global C cycle can be divided into short- and long-term cycles based on the vast differences in the turnover times of different C pools (Berner, 2004). The carbonate reservoir can be divided into two primary subreservoirs: (1) dissolved inorganic carbon (DIC) in the ocean (H2CO3, HCO3−, and CO32−), and (2) solid carbonate minerals [CaCO3, CaMg(CO3)2, and FeCO3] (Holmén, 2000). While the global C cycle is quite complex, it is perhaps the best understood of all the bioactive element cycles. In fact, there have been numerous review papers on this cycle (e.g., Keeling, 1973; Degens et al., 1984; Siegenthaler and Sarmiento, 1993; Sundquist, 1993; Schimel et al., 1995; Holmén, 2000). Much of the interest in the global C cycle in recent years stems from linkages with environmental issues concerning carbon-based greenhouse gases (e.g., CO2 and CH4) and their role in global climate change (Dickinson and Cicerone, 1986). As described in chapter 8, short-term controls on the C cycle are largely a function of the uptake of inorganic C by autotrophs to fuel fixation in photosynthesis, and the utilization of organic carbon as a food resource by heterotrophs recycling inorganic C back into the system. This short-term cycle, which allows for the transfer of C between the lithosphere, hydrosphere, biosphere, and atmosphere over periods of days to thousands of years, is relatively short in comparison to the more than 4 billion year age of the Earth.

Sign in / Sign up

Export Citation Format

Share Document