News Release

New GSA Bulletin articles published ahead of print in November

Peer-Reviewed Publication

Geological Society of America

Boulder, Colo., USA: The Geological Society of America regularly publishes articles online ahead of print. GSA Bulletin topics studied this month include the nature and dynamics of China and Tibet; major reorganization of the Snake River modulated by passage of the Yellowstone Hotspot; and Weddell Sea Embayment ice streams, Antarctica. You can find these articles at


Devonian to Triassic tectonic evolution and basin transition in the East Kunlun−Qaidam area, northern Tibetan Plateau: Constraints from stratigraphy and detrital zircon U−Pb geochronology
Jiaopeng Sun; Yunpeng Dong; Licheng Ma; Shiyue Chen; Wan Jiang
Abstract: The late Paleozoic to Triassic was an important interval for the East Kunlun−Qaidam area, northern Tibet, as it witnessed prolonged subduction of the South Kunlun Ocean, a major branch of the Paleo-Tethys Ocean whose closure led to the formation of Pangea. However, the geologic history of this stage is poorly constrained due to the paucity of tectonothermal signatures preserved during a magmatic lull. This article presents a set of new provenance data incorporating stratigraphic correlation, sandstone petrology, and zircon U−Pb dating to depict changes in provenance that record multiple stages of topographic and tectonic transition in the East Kunlun−Qaidam area over time in response to the evolution of the South Kunlun Ocean. Devonian intra-arc rifting is recorded by bimodal volcanism and rapid alluvial-lacustrine sedimentation in the North Qaidam Ultra High/High Pressure Belt, whose sources include the Olongbuluke Terrane and southern North Qaidam Ultra High/High Pressure Belt. Southward transgression submerged the East Kunlun−Qaidam area during the Carboniferous prior to the rapid uplift of the Kunlun arc, which changed the provenance during the Early Permian. This shift in provenance for the western Olongbuluke Terrane and thick carbonate deposition throughout the North Qaidam Ultra High/High Pressure Belt in the late Early Carboniferous indicate that the North Qaidam Ultra High/High Pressure Belt should have been inundated, terminating an ∼95 m.y. erosion history. The closure of the South Kunlun Ocean in the late Triassic generated a retroarc foreland along the Zongwulong Tectonic Belt, which is represented by the development of a deep-water, northward-tapering flysch deposystem that was supplied by the widely elevated Kunlun−Qaidam−Olongbuluke Terrane highland. This new scenario allows us to evaluate current models concerning the assembly of northern Tibet and the tectonic evolution of the Paleo-Tethys Ocean.
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Transition from slab roll-back to slab break-off in the central Apennines, Italy: Constraints from the stratigraphic and thermochronologic record
Maria Giuditta Fellin; Malwina San Jose; Claudio Faccenna; Sean D. Willett; Domenico Cosentino ...
Abstract: Stratigraphic and thermochronologic data are used to study the processes that shaped the topography of the central Apennines of Italy. These are part of a major, active mountain belt in the center of the Mediterranean area, where several subduction zones control a complex topography. The Apennines were shaped by contraction at the front of the accretionary wedge overlying the subducting Adria microplate followed by extension at the wedge rear in response to eastward slab roll-back. In the central Apennines, intermontane extensional basins on the western flank rise eastward toward the summit. We contribute with new data consisting of 28 (U-Th-Sm)/He and 10 fission track ages on apatites to resolve a complex pattern of thermal histories in time and space, which we interpret as reflecting the transitional state of the orogen, undergoing a two-phase evolution related to initial slab retreat, followed by slab detachment. Along the Tyrrhenian coast, we document cooling from depths ≥3−4 km occurring between 8 and 5 Ma and related to the opening of marine extensional basins. Post−5 Ma, a broader region of the central Apennines exhibits cooling from variable depths, between <2 km in most areas and ≥3−4 km in the northeast, and with different onset times: at ca. 4 Ma in the west, at ca. 2.5 Ma in the center and northeast, and at ca. 1 Ma in the southeast. Between 5 and 2.5 Ma, exhumation is associated with modest topographic growth during the late stages of thrusting. Since 2.5 Ma, exhumation has concurred with the opening of intermontane basins in the west and in the east, with regional topographic growth and erosion, that we interpret to be associated with the locally detaching slab.
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Recalibrating the Devonian time scale: A new method for integrating radioisotopic and astrochronologic ages in a Bayesian framework
Claire O. Harrigan; Mark D. Schmitz; D. Jeffrey Over; Robin B. Trayler; Vladimir I. Davydov
Abstract: The numerous biotic, climatic, and tectonic events of the Devonian cannot be correlated and investigated without a well-calibrated time scale. Here, we updated the calibration of the Devonian time scale using a Bayesian age-depth model that incorporates radioisotopic ages and astrochronology durations. We used existing radioisotopic ages collected and harmonized in the last two geologic time scale compilations, as well as new U-Pb zircon ages from Emsian {Hercules I K-bentonite, Wetteldorf, Germany: 394.290 ± 0.097(0.21)[0.47] Ma} and Eifelian K-bentonites {Tioga B and Tioga F K-bentonites, Fayette, New York, USA: 390.82 ± 0.18(0.26)[0.48] Ma and 390.14 ± 0.14(0.23)[0.47] Ma, respectively}. We anchored floating astrochronology stage durations on radioisotopic ages and chained astrochronologic constraints and uncertainty together to extrapolate conditioning age likelihoods up or down the geologic time scale, which is a new method for integrating astrochronology into age-depth modeling. The modeling results in similar ages and durations for Devonian stages regardless of starting biostratigraphic scaling assumptions. We produced a set of rescaled biostratigraphic zonations, and a new numerical calibration of Devonian stage boundary ages with robust uncertainty estimates, which allow us to evaluate future targets for Devonian time scale research. These methods are broadly applicable for time scale work and provide a template for an integrated stratigraphic approach to time scale modeling.
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The protoliths of central Himalayan eclogites
Guibin Zhang; Jiaxing Wang; A. Alexander G. Webb; Lifei Zhang; Shuaiqi Liu ...
Abstract: Eclogites represent the highest pressure conditions yet observed from rocks thrust to the surface in the central Himalaya. A detailed investigation of the protolith nature of these eclogites is needed to better understand pre-Himalayan geological history. Retrogressed eclogites were collected from Thongmön (Dingri County) and Riwu (Dinggye County), central Himalaya, China. We investigated the bulk rock major and trace elements, Sr-Nd isotopes, zircon geochronology, and Hf-O isotopes. These retrogressed eclogites experienced five stages of metamorphic evolution from prograde amphibolite-facies to peak eclogite-facies, and high pressure granulites-facies, granulites-facies then final amphibolite-facies overprinting during exhumation. Geochemically, they are subalkaline basalts with high FeO contents and a tholeiitic affinity; trace elements show similarities with enriched mid-ocean ridge basalts. Bulk rocks have a wide range of εNd(t) values from −0.24 to +7.08, and an unusually wide range of initial 87Sr/86Sr ratios of 0.705961−0.821182. Zircon relict magmatic cores from both Thongmön and Riwu eclogites yield a consistent protolith age of ca. 1850 Ma, with enriched heavy rare earth element patterns and significant negative Eu anomalies. These relict cores have oxygen isotopes signatures of δ18O = 5.8−8.1‰, εHf(t) values of −4.85 to +9.59, and two-stage model ages (TDM2) of 1.91−2.81 Ga. Metamorphic overgrowth zircons yield much younger ages of ca. 14 Ma. Integration of all of the above data suggests that the protolith of these central Himalayan retrogressed eclogites might be Proterozoic continental flood basalts of the North Indian Plate, generated under a post-collisional extension setting during the assembly of the Columbia Supercontinent. Occurrence of both Neoproterozoic−early Paleozoic rocks and ca. 1.85 Ga rocks in the regional crystalline rocks may reflect either unrecognized sub-horizontal Main Central Thrust exposure(s) or exhumation of a deeply cut part of the Greater Himalayan Crystalline complex. In combination with previous reports of Late Cretaceous, Neoproterozoic, and similar but younger Paleoproterozoic protolith, it is clear that the central Himalayan eclogites originate from multiple sources of protolith.
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Detrital geochronology and lithologic signatures of Weddell Sea Embayment ice streams, Antarctica—Implications for subglacial geology and ice sheet history
Liana M. Agrios; Kathy J. Licht; Trevor Williams; Sidney R. Hemming; Lauren Welch ...
Abstract: Tills from moraines adjacent to major ice streams of the Weddell Sea Embayment contain distinct detrital zircon (n = 5304) and K-bearing mineral age populations (n = 323) that, when combined with pebble composition data, can be used to better understand Antarctica’s subglacial geology and ice sheet history. Till representing the Institute, Foundation, Academy, Recovery and Slessor Ice Streams each have distinct detrital zircon age populations. Detrital Ar-Ar ages are mostly younger than zircon ages, and distinctive populations include 270−300 Ma (Institute), 170−190 Ma (Foundation), and 1200−1400 Ma (Recovery), which are not easily explained by known outcrops. Pebble fractions of the Foundation and Academy tills are most diverse with up to >40% exotic erratics. The southern side of the Recovery Glacier has fossiliferous limestone erratics. Mixing models created using a nonlinear squares curve-fitting approach were developed to evaluate contributors of zircons to Foundation Ice Stream till. These model results and pebble lithology data both indicate that unexposed (subglacial) bedrock is mixed with exposed rocks to produce the observed till. Notably, the model required limited local Patuxent Formation input to the Foundation till’s zircon population. Our data suggest that sandstones underlie the Foundation Ice Stream and Recovery Glacier troughs, which has a bearing on basal ice flow conditions and results in geological controls on ice stream location. This geo- and thermo-chronological characterization of the ice streams will enable ice-rafted debris in Weddell Sea marine sediments to be traced back to its sources and interpreted in terms of ice stream dynamics.
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Magmatism and related metamorphism as a response to mountain-root collapse of the Dabie orogen: Constraints from geochronology and petrogeochemistry of metadiorites
Yang Yang; Yi-Can Liu; Yang Li; C. Groppo; F. Rolfo
Abstract: Post-collisional mountain-root collapse and subsequent massive partial melting occurred in the high-temperature (HT) ultrahigh-pressure (UHP) metamorphic terrane of the North Dabie complex zone (NDZ), central China. The NDZ was deeply subducted in the Triassic, producing widespread migmatites and various magmatic intrusions in the Cretaceous. Post-collisional metadiorites with distinctive large K-feldspar augen porphyroblasts, locally reported but rarely exposed in the NDZ, underwent a complex evolutional history. In this contribution, integrated studies including field investigation, petrographic observation and mineral analysis, zircon U-Pb geochronological and Hf isotopic analyses, and whole-rock elemental and Sr-Nd-Pb isotopic analyses of the metadiorites were carried out. Our results provide new constraints on the mountain-root collapse in the Dabie orogen. The metadiorites are enriched in large ion lithophile elements and light rare earth elements, whereas they are depleted in high field strength elements and heavy rare earth elements with significant Ba positive anomalies, a composition consistent with the lower continental crust. All the studied samples have moderately enriched initial 87Sr/86Sr ratios (0.707582−0.708099), low εNd(t) values (−15.3 to −20.4), and low initial Pb isotopic ratios (16.0978−16.8452, 15.3167−15.4544, and 37.1778−37.8397 for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, respectively). However, they have highly negative εHf(t) values and Paleoproterozoic two-stage Hf model ages, which are only partially consistent with data from the associated UHP metamorphic rocks. Such features suggest the metadiorites resulted from a magma produced by mixing of Triassic UHP mafic lithologies and minor amounts of mantle-derived materials. Zircon morphological analysis and U-Pb sensitive high-resolution ion microprobe dating combined with conventional thermobarometry indicate that these upwelling melts crystallized at pressure-temperature (P-T) conditions of 5.4−5.7 kbar and 750−768 °C at ca. 130 Ma and subsequently suffered HT metamorphism at ca. 125 Ma. We conclude that the metadiorites’ precursors were derived from partial melting of the Triassic subducted Neoproterozoic mafic lower-crustal rocks, with addition of minor amounts of mantle-derived materials in the Early Cretaceous, in response to mountain-root collapse of the orogen. Based on petrographic textures and mineral compositions, it is moreover inferred that formation of the distinctive K-feldspar porphyroblasts is likely related to a two-stage process, i.e., crystallization derived from biotite breakdown after the formation of the metadiorite at T = 640−703 °C and P < 4.5 kbar and coarsening related to shear deformation.
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Major reorganization of the Snake River modulated by passage of the Yellowstone Hotspot
Lydia M. Staisch; Jim E. O’Connor; Charles M. Cannon; Chris Holm-Denoma; Paul K. Link ...
Abstract: The details and mechanisms for Neogene river reorganization in the U.S. Pacific Northwest and northern Rocky Mountains have been debated for over a century with key implications for how tectonic and volcanic systems modulate topographic development. To evaluate paleo-drainage networks, we produced an expansive data set and provenance analysis of detrital zircon U-Pb ages from Miocene to Pleistocene fluvial strata along proposed proto-Snake and Columbia River pathways. Statistical comparisons of Miocene-Pliocene detrital zircon spectra do not support previously hypothesized drainage routes of the Snake River. We use detrital zircon unmixing models to test prior Snake River routes against a newly hypothesized route, in which the Snake River circumnavigated the northern Rocky Mountains and entered the Columbia Basin from the northeast prior to incision of Hells Canyon. Our proposed ancestral Snake River route best matches detrital zircon age spectra throughout the region. Furthermore, this northerly Snake River route satisfies and provides context for shifts in the sedimentology and fish faunal assemblages of the western Snake River Plain and Columbia Basin through Miocene−Pliocene time. We posit that eastward migration of the Yellowstone Hotspot and its effect on thermally induced buoyancy and topographic uplift, coupled with volcanic densification of the eastern Snake River Plain lithosphere, are the primary mechanisms for drainage reorganization and that the eastern and western Snake River Plain were isolated from one another until the early Pliocene. Following this basin integration, the substantial increase in drainage area to the western Snake River Plain likely overtopped a bedrock threshold that previously contained Lake Idaho, which led to incision of Hells Canyon and establishment of the modern Snake and Columbia River drainage network.
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Apatite fingerprints on the magmatic-hydrothermal evolution of the Daheishan giant porphyry Mo deposit, NE China
Pan Qu; Wubin Yang; Hecai Niu; Ningbo Li; Dan Wu
Abstract: Porphyry deposits are the main source for global Cu and Mo production. The generation of hydrous silicate magmas and subsequent separation of volatile-rich magmatic fluids with hydrothermal alteration are significant processes leading to the formation of porphyry deposits. However, a specific understanding of these processes has been limited by a lack of direct mineralogical records in the evolving magmatic-hydrothermal system. In this paper, we present an integrated textural and geochemical investigation on apatite from the giant Daheishan porphyry Mo deposit in NE China, illustrating that apatite can be a potential recorder of the magmatic-hydrothermal evolution of porphyry systems. Apatite from the ore-forming porphyry displays distinctive core-rim textures, with melt inclusions in the resorption cores (Type-A1) and co-existing of melt and fluid inclusions in the euhedral rims (Type-A2), indicating a magmatic-hydrothermal origin of apatite. This is also supported by both chemical and isotopic compositions obtained by in situ analyses using laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) and LA-multi collector-ICP-MS. The late Type-A2 apatite is relatively enriched in incompatible elements, such as rare earth elements (REE) and Th, but slightly depleted in fluid-mobile elements such as Na and S, compared to the early Type-A1 apatite. Relatively homogeneous (87Sr/86Sr)i ratios (0.70436−0.70504) of the Type-A1 and Type-A2 apatites indicate that they were formed in a relatively closed system without detectable contamination. Meanwhile, some apatite in the wall rock (biotite granodiorite) shows characteristics of secondary altered textures, resulting from the intensive alteration by hydrothermal fluids exsolved from the porphyry system. Apatite trapped in mineral phenocrysts of the wall rock is usually unaltered (Type-B1 apatite), with clear oscillatory growth zones in cathodoluminescence (CL) images. In contrast, the intergranular apatite is commonly altered (Type-B2 apatite), with chaotic zoning in CL images, abundant micro-fractures and secondary fluid inclusions. Compositionally, the Type-B2 apatite shows notable tetrad REE patterns, relatively lower light-REE and S contents, and elevated 147Sm/144Nd ratios compared to the Type-B1 apatite. LA-ICP-MS U-Pb dating yields a lower intercept age of 171.4 ± 2.3 Ma for Type-B2, which is consistent with the age of 171.5 ± 2.4 Ma for Type-A2, but is notably younger than the Type-B1 apatite (175.5 ± 1.3 Ma). It is suggested that the Type-B2 apatite has been significantly reset by hydrothermal fluids exsolved from the porphyry system. Therefore, we conclude that the textures and geochemistry of apatite in porphyry systems can be used as a potential proxy for recording fluid exsolution and hydrothermal alteration processes.
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Rapid eruption of the Emeishan continental flood basalts: New paleomagnetic and geochronologic constraints
Yingchao Xu; Liandi Zheng; Zhenyu Yang; Ya-Bo Tong; Bin Wang ...
Abstract: The duration of the eruption of the Emeishan large igneous province is hotly debated. We conducted a magnetostratigraphic and geochronological study of the core area of the large igneous province in the Binchuan area of Yunnan Province, southwestern China, in order to constrain the duration of the eruption. The results of detailed thermal demagnetization experiments revealed two remanent magnetic components from the volcanic rocks of 11 composite sections. A low-temperature component separated below 300 °C is interpreted as a recent viscous remanence. Additionally, reliable characteristic remanent magnetizations were revealed above 400 °C, with unblocking temperatures up to 580−680 °C, which passed the fold test and record three magnetozones. Zircons from the felsic ignimbrites exposed in the final stage of the mafic volcanism are dated to 258.2 ± 0.7 Ma (n = 15; mean square of weighted deviates = 1.3) by sensitive high-resolution ion microprobe. Stratigraphic and magnetostratigraphic correlations of the Emeishan basalts in the Binchuan sections indicate that the eruption of the mafic rocks of the Emeishan large igneous province can be clearly divided into early (reverse polarity subzone), middle (normal polarity subzone), and late (reverse polarity subzone) stages, with a total duration of less than 1.7 m.y. (260.8−259.1 Ma). However, by combining this chronology with previously reported conodont biostratigraphic results from locations around the Emeishan large igneous province, and comparing the dominant normal-reverse polarity sequence in the Emeishan large igneous province with the geomagnetic polarity time scale, we obtain a much shorter duration of the main eruptive stage of <0.8 m.y. (260.4−259.6 Ma). About three quarters of the basalts of the Emeishan large igneous province record have a normal polarity and erupted within 0.4 m.y., while the other quarter, mainly distributed in the central zone, shows a reverse polarity and much shorter duration. Given the short duration of the eruption, gas volatiles would have been released into the atmosphere at high rates, which might provide a causal link between the rapid eruption and the end-Guadalupian mass extinction. Before the mantle plume eruption, localized eruptions probably occurred. After eruption of the mafic Emeishan flood basalts, an acid volcanic eruption occurred in the early Wuchiapingian, which was sporadically distributed in the Emeishan large igneous province.
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Constraining the timing of Arabia-Eurasia collision in the Zagros orogen by sandstone provenance (Neyriz, Iran)
Parisa Gholami Zadeh; Xiumian Hu; Eduardo Garzanti; Mohammad Hossein Adabi
Abstract: The Zagros orogen, formed by the collision of the Arabian and Eurasian continental margins, represents one of the largest and richest oil and gas provinces in the world. The Zagros fold-thrust belt records collision and convergence along the Neotethys suture zone. By coupling field observations, sandstone modal analysis, U-Pb zircon dating, and Hf isotopic data from the Upper Cretaceous to Pliocene sedimentary succession of the Neyriz region, this paper documents several major provenance changes that allow us to propose a refined scenario for the Zagros orogeny. An ophiolitic complex dated by detrital-zircon U-Pb geochronology as ca. 95 Ma provided detritus to Upper Cretaceous-Paleocene strata deposited along the northeastern margin of the Arabian lower plate (ophiolite provenance). Yet, on the southwestern margin of the Eurasian upper plate, upper Paleocene-lower Eocene strata indicate provenance from Mesozoic magmatic rocks yielding zircons dated as ca. 240 Ma and 170 Ma as well as the recycling of clastic rocks. Since the early Miocene, the sedimentary basin located on the Arabian plate received both ophiolitic detritus and magmatic-arc, recycled clastic, and axial-belt metamorphic detritus from Eurasia. U-Pb ages of detrital zircons reflect polyphase magmatism at 170 Ma, 95 Ma, and 40 Ma on the Eurasian active margin. Our results indicate that progressive accretion, uplift, and exhumation of the Zagros orogen was well under way by the beginning of the Miocene in the Neyriz region. Literature data from adjacent regions suggest that the Arabia/Eurasia collision may have occurred diachronously and later in the Kermanshah and Lurestan areas to the north.
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Age, material source, and formation mechanism of bedding-parallel calcite beef veins: Case from the mature Eocene lacustrine shales in the Biyang Sag, Nanxiang Basin, China
Ao Su; Paul D. Bons; Honghan Chen; Yue-xing Feng; Jian-xin Zhao ...
Abstract: The mechanisms leading to the formation of bedding-parallel calcite beef veins have been widely debated, with discussions centered on timing or burial depth of vein generation, source of the vein material, driving forces for vein initiation and widening, and growth direction and mechanism. To address these issues, a comprehensive study of drill core samples containing beef veins in the mature Eocene lacustrine Hetaoyuan Formation in the Biyang Sag, Nanxiang Basin, China was undertaken through a combination of microstructural observation, isotopic geochronological, geochemical, and fluid inclusion analyses, as well as basin modeling. X-ray diffraction and total organic carbon content analyses indicate that most of the beef veins accumulated in calcite-rich laminated shales with high organic matter contents. These beef veins yielded an absolute laser ablation−multi-collector−inductively coupled plasma−mass spectrometry U-Pb age of ca. 41.02 ± 0.44 Ma, which corresponds to a burial depth of 500−800 m. Such a shallow burial depth suggests that the full compaction and consolidation of sediments would not yet have been achieved, which is compatible with the following observations: (1) plastic deformation of shale laminae adjacent to the veins, and (2) a beef vein formation temperature of ∼59 °C derived from fluid-inclusion microthermometry. The radio-isotopic age of the beef veins is ∼1−3 m.y. younger than the stratigraphic age of the host rock (ca. 43.1 Ma) but earlier than the model-derived timing of oil generation (ca. 35.8 Ma) and tectonic extrusion (ca. 23.0−13.0 Ma). The beef vein formation predated bacterial sulfate reduction, as evidenced by crosscutting relationships with carbonate concretions, pyrite framboids, and apatite pellets. A two-stage formation model for these beef veins is proposed. When burial depth of laminated shales rich in organic matter and calcite reaches the methanogenic zone, overpressure triggered by biogenetic gas generation results in horizontal hydrofracturing, initiating cracks that act as gas expulsion pathways. Once all the generated gas has migrated, the opened fractures close again due to overburden load. The materials fed by pressure solution of host-rock calcite fractions then mobilized into the unhealed horizontal fractures by diffusion. Subsequently, by a force of crystallization, antitaxial, displacive growth of calcite fibers commenced, contemporaneous with fracture dilation, eventually leading to the formation of bedding-parallel beef veins.
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Linking sediment supply variations and tectonic evolution in deep time, source-to-sink systems—The Triassic Greater Barents Sea Basin
Albina Gilmullina; Tore Grane Klausen; Anthony George Doré; Valentina Marzia Rossi; Anna Suslova ...
Abstract: Triassic strata in the Greater Barents Sea Basin are important records of geodynamic activity in the surrounding catchments and sediment transport in the Arctic basins. This study is the first attempt to investigate the evolution of these source areas through time. Our analysis of sediment budgets from subsurface data in the Greater Barents Sea Basin and application of the BQART approach to estimate catchment properties shows that (1) during the Lower Triassic, sediment supply was at its peak in the basin and comparable to that of the biggest modern-day river systems, which are supplied by tectonically active orogens; (2) the Middle Triassic sediment load was significantly lower but still comparable to that of the top 10 largest modern rivers; (3) during the Upper Triassic, sediment load increased again in the Carnian; and (4) there is a large mismatch (70%) between the modeled and estimated sediment load of the Carnian. These results are consistent with the Triassic Greater Barents Sea Basin succession being deposited under the influence of the largest volcanic event ever at the Permian-Triassic boundary (Siberian Traps) and concurrent with the climatic changes of the Carnian Pluvial Event and the final stages of the Northern Ural orogeny. They also provide a better understanding of geodynamic impacts on sedimentary systems and improve our knowledge of continental-scale sediment transport. Finally, the study demonstrates bypass of sediment from the Ural Mountains and West Siberia into the adjacent Arctic Sverdrup, Chukotka, and Alaska Basins in Late Carnian and Late Norian time.
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Effects of sea-level variation and sedimentary noise variation on the development of biogenic reefs since the Pliocene among the Xisha Islands, South China Sea
Ke Zhao; Xuebin Du; Jixin Jia; Xinong Xie; Fang Hao ...
Abstract: Carbonate strata are a vital and favorable reservoir for global oil and gas exploration, and carbonate sedimentary systems record ancient oceanic and paleoclimatic conditions, including paleoenvironmental variations throughout geologic periods. Carbonate platforms are widely distributed among the Xisha Islands in the South China Sea and contain large amounts of oil and gas resources. Biogenic reefs are the dominant parts of the carbonate platforms in the Xisha Islands; however, research on the factors that control and affect biogenic reef development is lacking. In this study, a core from well XK-1, which is located on Yongxing Island in the Xisha Islands, a sedimentary noise model, and time-series analyses were used to determine the effects of sea-level fluctuations from 5.3 Ma to present. The results show that coral reefs in the Xisha Islands are sensitive to eustatic fluctuations and that a decrease in sea level essentially corresponds to an increase in sedimentation rate. Indexes of the East Asian monsoon and other environmental indexes show that the Pleistocene and Holocene were suitable for coral growth; however, the trends shown by these indexes and the sea-level variation indicate that the future growth of coral reefs will be at a disadvantage. Research on the controlling factors of biogenic reefs is of significance for understanding reef growth, performing global reef comparisons, and encouraging the future protection of coral reefs.
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