Revised Maximum Depositional Age for the Ediacaran Browns Hole Formation: Implications for Western Laurentia Neoproterozoic Stratigraphy

Abstract Constraining the depositional age of Neoproterozoic stratigraphy in the North American Cordilleran margin informs global connections of major climatic and tectonic events in deep time. Making these correlations is challenging due to a paucity of existing geochronological data and adequate material for absolute age control in key stratigraphic sequences. The late Ediacaran Browns Hole Formation in the Brigham Group of northern Utah, USA, provides a key chronological benchmark on Neoproterozoic stratigraphy. This unit locally comprises <140 m of volcaniclastic rocks with interbedded mafic-volcanic flows that lie within a 3500 m thick package of strata preserving the Cryogenian, Ediacaran, and the lowermost Cambrian history of this area. Prior efforts to constrain the age of the Browns Hole Formation yielded uncertain and conflicting results. Here, we report new laser-ablation-inductively-coupled-mass-spectrometry U-Pb geochronologic data from detrital apatite grains to refine the maximum depositional age of the volcanic member of the Browns Hole Formation to 613±12 Ma (2σ). Apatite crystals are euhedral and pristine and define a single date population, indicating they are likely proximally sourced. These data place new constraints on the timing and tempo of deposition of underlying and overlying units. Owing to unresolved interpretations for the age of underlying Cryogenian stratigraphy, our new date brackets two potential Brigham Group accumulation rate scenarios for ~1400 m of preserved strata: ~38 mm/kyr over ~37 Myr or ~64 mm/kyr over ~22 Myr. These results suggest that the origins of regional unconformities at the base of the Inkom Formation, previously attributed to either the Marinoan or Gaskiers global glaciation events, should be revisited. Our paired sedimentological and geochronology data inform the timing of rift-related magmatism and sedimentation near the western margin of Laurentia.

Download Full-text

Juxtaposition of diverse, subduction-related tectonic blocks with contrasting metamorphic features and ages in the Paleoproterozoic Aketashitage orogen, NW China: Implications for Precambrian orogeny

Geological Society of America Bulletin ◽

10.1130/b35766.1 ◽

2020 ◽

Author(s):

Qian W.L. Zhang ◽

Jia-Hui Liu ◽

Zhen M.G. Li ◽

Meng-Yan Shi ◽

Yi-Chao Chen ◽

...

Keyword(s):

Mass Spectrometry ◽

Inductively Coupled Plasma ◽

Subduction Zones ◽

Plate Tectonics ◽

Secondary Ion Mass Spectrometry ◽

Orogenic Belt ◽

Early Precambrian ◽

Inductively Coupled ◽

The North ◽

Depositional Age

The comprehensive investigation of orogenic-related litho-structural assemblages, metamorphism, and geochronology in early Precambrian orogens can help us better understand the features of plate tectonics in early Earth. The Paleoproterozoic Aketashitage orogenic belt is located at a key position in northwestern China and connects the North China craton, Tarim craton, Altaids orogen, and Tethys orogen. Garnet-bearing mafic and paragneissic granulite occur as interlayers or blocks preserved within paragneissic matrix, and two to three generations of metamorphic mineral assemblages were identified. Geothermobarometry and pseudosection modeling yielded clockwise metamorphic P-T paths passing from 7.5‒8.6 kbar/575‒715 °C (M1) through 7.4‒12.2 kbar/715‒895 °C (M2) and finally to 5.2‒7.3 kbar/710‒800 °C (M3) for the mafic and paragneissic granulite as well as amphibolite, which is indicative of metamorphic features of subduction/collision zones. Peak metamorphic P-T conditions of all the samples lie in the medium P/T facies series, suggesting that the thermal gradient (∼20‒31 °C/km) of this Paleoproterozoic orogenic belt was obviously higher than most of the Phanerozoic subduction zones. Secondary ion mass spectrometry (SIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb dating of zircon and monazite yielded metamorphic ages of ca. 1.98−1.96 Ga in the eastern part of the orogen, ca. 1.86−1.85 Ga in the western part, and a maximum depositional age of ca. 2.06 Ga for paragneiss. Compared with previous studies, the Aketashitage orogen is composed of unordered juxtaposition of diverse, subduction-related tectono-metamorphic blocks with different protoliths, metamorphic grades, and ages preserved within the paragneissic matrix deposited in the Paleoproterozoic, which is highly similar to Phanerozoic mélange. A Paleoproterozoic subduction-metamorphic-exhumation-accretionary process was deciphered, similar to that found in accretionary/orogenic wedge in Phanerozoic orogens. The juxtaposition of diverse, subduction-related tectonic blocks with contrasting ages and metamorphic features can serve as a marker of early Precambrian orogens and plate tectonics.

Download Full-text

Paleoproterozoic crustal history of the southwestern Grenville Province: evidence from Nd isotopic mapping

Canadian Journal of Earth Sciences ◽

10.1139/e95-040 ◽

1995 ◽

Vol 32 (4) ◽

pp. 472-485 ◽

Cited By ~ 20

Author(s):

C. Holmden ◽

A. P. Dickin

Keyword(s):

Crustal Material ◽

Grenville Province ◽

Detrital Zircon Geochronology ◽

Bay Area ◽

The North ◽

History Of ◽

Depositional Age ◽

Central Gneiss Belt ◽

Superior Craton ◽

Common Association

Nd isotopic mapping in the North Bay area of the Central Gneiss Belt, southwestern Grenville Province, has revealed the precise trend of a TDM model age line developed between the uplifted southern margin of the Archean Superior craton (TDM = 2.7 Ga) and a Paleoproterozoic allochthon (TDM = 1.9 Ga). Separating these two crustal blocks is a narrow zone of gneisses with intermediate TDM ages. These transitional gneisses are interpreted to reflect a remnant fault or ductile shear zone, of uncertain age, along which crustal material from both blocks mechanically mixed during their juxtaposition. Accordingly, the nature of the TDM line in the North Bay area is interpreted to be tectonic. In the Temiscaming area, widespread exposures of mature metasedimentary gneisses are shown by their TDM ages to be dominantly of Paleoproterozoic provenance. These results are consistent with the existing detrital zircon geochronology, inferring a maximum depositional age of ~1.7 Ga. The anorogenic chemistry of the North Bay orthogneiss and mixed calc-alkaline–alkaline chemistry of the Temiscaming gneisses suggest a connection between Paleoproterozoic anorogenic magmatism and synsedimentary quartzite deposition, which is a common association in 1.9–1.6 Ga accretionary orogens of southern Laurentia. The relatively close correspondence between widespread 1.9 Ga TDM ages and U–Pb crystallization ages as old as 1.74 Ga implies that rocks of the Central Gneiss Belt were originally the juvenile products of Paleoproterozoic orogenesis.

Download Full-text

Discussion of the reply by R.L. Romer and U. Kroner on “Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf” 1Appears in Canadian Journal of Earth Sciences, 49(6): 775–780, 10.1139/e2012-006.

Canadian Journal of Earth Sciences ◽

10.1139/e2012-049 ◽

2012 ◽

Vol 49 (11) ◽

pp. 1372-1377

Author(s):

David I. Schofield ◽

John W.F. Waldron ◽

Chris E. White ◽

Sandra M. Barr

Keyword(s):

Inductively Coupled Plasma ◽

Sedimentary Rocks ◽

Sediment Provenance ◽

Inductively Coupled ◽

Geochemical Signature ◽

North Wales ◽

Plasma Mass Spectrometry ◽

History Of ◽

Spectrometry Technique ◽

Depositional Age

In their article ‘Reply to the discussion by J.W.F. Waldron and C.E. White on “Geochemical signature of Ordovician Mn-rich sedimentary rocks on the Avalonian shelf”’, R.L. Romer and U. Kroner reinterpret geochronological data presented by J.W.F. Waldron, D.I. Schofield, C.E. White, and S.M. Barr to imply an Ordovician, not a Cambrian, depositional age for the succession of the Harlech Dome, North Wales, and Meguma Supergroup, Nova Scotia. However, an extensive history of biostratigraphic and geological survey data refutes this interpretation and shows that the rocks are unequivocally Cambrian. Waldron et al. used the U–Pb zircon laser-ablation – multicollector – inductively coupled plasma – mass spectrometry technique primarily to provide information on sediment provenance and not depositional age. Investigation of anomalously young 206Pb/238U ages showed evidence of Pb loss. These data provide little constraint on depositional age and cannot be used to infer that the Harlech Grits Group is Ordovician.

Download Full-text

Diagenetic and Epigenetic Mineralizing Events in the Kalahari Copperbelt, Botswana: Evidence from Re-Os Sulfide Dating and U-Th-Pb Xenotime Geochronology

Economic Geology ◽

10.5382/econgeo.4809 ◽

2021 ◽

Author(s):

Wesley S. Hall ◽

Holly J. Stein ◽

Andrew R.C. Kylander-Clark ◽

Murray W. Hitzman ◽

Yvette D. Kuiper ◽

...

Keyword(s):

Inductively Coupled Plasma ◽

Wall Rock ◽

Rock Fragment ◽

Northern Margin ◽

Inductively Coupled ◽

Central African Copperbelt ◽

Plasma Mass Spectrometry ◽

History Of ◽

Depositional Age ◽

Host Rocks

Abstract The ages of sedimentation and copper-silver mineralization in the late Meso- to Neoproterozoic Kalahari Copperbelt in Botswana, an economically significant copper province, have previously been poorly constrained within a ~600 m.y. period that spans the Neoproterozoic from the assembly and breakup of Rodinia to the assembly of Gondwana. Rhenium-osmium geochronology of molybdenite and copper sulfide minerals and U-Th-Pb laser ablation split-stream inductively coupled plasma-mass spectrometry (LASS ICP-MS) analysis of xenotime grains are utilized to provide absolute and relative age data on the host rocks and mineralizing events within the Ghanzi Ridge region of the Kalahari Copperbelt. The data reveal a prolonged history of events, which is partially comparable with depositional and mineralizing events in the neighboring Central African Copperbelt. Abundant disseminated molybdenite is located within a shale layer near the base of the Proterozoic D’Kar Formation at the Northeast Mango Two deposit. Unusual molybdenite textures suggest organic matter may have been a precursor. Two molybdenite separates from a small calcite-molybdenite stringer in a wall-rock fragment that is enclosed within an epigenetic quartz-calcite-chalcopyrite vein with ill-defined and mismatched margins yielded Re-Os ages of 981 ± 3 and 981 ± 7 Ma. These ages indicate an early hydrothermal mineralizing event in the basin. A xenotime inclusion intergrown with molybdenite and chalcopyrite within the epigenetic vein yielded a younger U-Th-Pb age of 538 ± 8 Ma, suggesting two mineralizing events are preserved in a complex 6-cm-wide vein. Based on vein texture and alteration, the ages represent an ~981 Ma calcite-molybdenite mineralization event overprinted by an ~538 Ma quartz-chalcopyrite-molybdenite mineralization event, perhaps during reopening of the vein. Re-Os and U-Th-Pb geochronology were utilized at the Zone 6 deposit on minerals associated with a hydrothermal quartz-calcite-chalcocite-idaite-bornite vein. Several authigenic xenotime grains that occur along the margin of the vein yielded three concordant U-Th-Pb ages that indicate xenotime growth at ~950 to 925 Ma while other xenotime grains in a similar position yielded mostly discordant data, suggesting disturbance of the isotopic system in the xenotime grains. A coprecipitated chalcocite-idaite mixture within the hydrothermal vein produced an Re-Os age of 549.0 ± 11.2 Ma. Re-Os analysis obtained from a coprecipitated molybdenite-bornite mixture at the Northeast Fold deposit yielded an age of 515.9 ± 2 Ma. Together, the earliest Neoproterozoic Re-Os molybdenite and U-Th-Pb xenotime ages provide both a minimum depositional age constraint for the lowermost D’Kar Formation and clear evidence that diagenetic hydrothermal mineralizing events took place within the Ghanzi basin. The timing of this mineralizing event corresponds with a poorly documented regional thermal event that affected the northern margin of the Kalahari craton during the final stages of the assembly of Rodinia at ~980 Ma. The lower to middle Ghanzi Group of the Kalahari Copperbelt is at least 100 m.y. older than the host rocks within the neighboring Central African Copperbelt, which are associated with the breakup of Rodinia. The latest Neoproterozoic to Cambrian Re-Os and U-Th-Pb ages indicate that hydrothermal copper-silver mineralizing events occurred during the Pan-African (~600–480 Ma) fold-thrust evolution of the Ghanzi-Chobe zone and were broadly synchronous with widespread epigenetic hydrothermal copper-cobalt mineralizing events in the adjacent Central African Copperbelt.

Download Full-text

Ras al Khaimah: further archaeological discoveries

Antiquity ◽

10.1017/s0003598x00150070 ◽

1976 ◽

Vol 50 (200) ◽

pp. 216-222

Author(s):

Beatrice De Cardi

Keyword(s):

United Arab Emirates ◽

The State ◽

Focused Attention ◽

North East ◽

The North ◽

History Of ◽

The City

Ras a1 Khaimah is the most northerly of the seven states comprising the United Arab Emirates and its Ruler, H. H. Sheikh Saqr bin Mohammad al-Qasimi, is keenly interested in the history of the state and its people. Survey carried out there jointly with Dr D. B. Doe in 1968 had focused attention on the site of JuIfar which lies just north of the present town of Ras a1 Khaimah (de Cardi, 1971, 230-2). Julfar was in existence in Abbasid times and its importance as an entrep6t during the sixteenth and seventeenth centuries-the Portuguese Period-is reflected by the quantity and variety of imported wares to be found among the ruins of the city. Most of the sites discovered during the survey dated from that period but a group of cairns near Ghalilah and some long gabled graves in the Shimal area to the north-east of the date-groves behind Ras a1 Khaimah (map, FIG. I) clearly represented a more distant past.

Download Full-text

Sequencing Analysis and Phylogenetic Tree of HPV Isolated from Breast Cancer Patients at Thi-Qar Province/Iraq

10.32792/utq/utjsci/vol7/2/10 ◽

2020 ◽

pp. 37-40

Keyword(s):

Nucleotide Sequence ◽

Phylogenetic Tree ◽

Evolutionary Relationship ◽

Nucleotide Sequencing ◽

Sequencing Analysis ◽

Breast Cancer Patients ◽

The North ◽

Formalin Fixed Paraffin ◽

Formalin Fixed Paraffin Embedded ◽

History Of

Genetic variety examination has demonstrated fundamental to the understanding of the epidemiological and developmental history of Papillomavirus (HPV), for the development of accurate diagnostic tests and for efficient vaccine design. The HPV nucleotide diversity has been investigated widely among high-risk HPV types. To make the nucleotide sequence of HPV and do the virus database in Thi-Qar province, and compare sequences of our isolates with previously described isolates from around the world and then draw its phylogenetic tree, this study done. A total of 6 breast formalin-fixed paraffin-embedded (FFPE) of the female patients were included in the study, divided as 4 FFPE malignant tumor and 2 FFPE of benign tumor. The PCR technique was implemented to detect the presence of HPV in breast tissue, and the real-time PCR used to determinant HPV genotypes, then determined a complete nucleotide sequence of HPV of L1 capsid gene, and draw its phylogenetic tree. The nucleotide sequencing finding detects a number of substitution mutation (SNPs) in (L1) gene, which have not been designated before, were identified once in this study population, and revealed that the HPV16 strains have the evolutionary relationship with the South African race, while, the HPV33 and HPV6 showing the evolutionary association with the North American and East Asian race, respectively.

Download Full-text

North American Association for the Study of Religion (NAASR)

Bulletin for the Study of Religion ◽

10.1558/bsor.v44i2.27304 ◽

2015 ◽

Vol 44 (2) ◽

pp. 29-30

Author(s):

Matt Sheedy

Keyword(s):

North American ◽

American Association ◽

The North ◽

History Of

I interviewed Russell McCutcheon back in March 2015, about his new role as president of the North American Association for the Study of Religion (NAASR), asking him about the history of the organization, goals for his tenure, and developments for NAASR’s upcoming conference in Atlanta in November 2015.

Download Full-text