scholarly journals High-resolution isotope stratigraphy of the Lower Ordovician St. George Group of western Newfoundland, Canada: implications for global correlation

2009 ◽  
Vol 46 (6) ◽  
pp. 403-423 ◽  
Author(s):  
Karem Azmy ◽  
Denis Lavoie
Keyword(s):  
High Resolution ◽  
Sea Level ◽  
Sea Level Changes ◽  
Global Correlation ◽  
Lower Ordovician ◽  
Isotope Stratigraphy ◽  
Platform Carbonates ◽  
The Baltic ◽  
Marine Platform ◽  
Bottom To Top

The Lower Ordovician St. George Group of western Newfoundland consists mainly of shallow-marine-platform carbonates (∼500 m thick). It is formed, from bottom to top, of the Watts Bight, Boat Harbour, Catoche, and Aguathuna formations. The top boundary of the group is marked by the regional St. George Unconformity. Outcrops and a few cores from western Newfoundland were sampled at high resolution and the extracted micritic materials were investigated for their petrographic and geochemical criteria to evaluate their degree of preservation. The δ13C and δ18O values of well-preserved micrite microsamples range from –4.2‰ to 0‰ (VPDB) and from –11.3‰ to –2.9‰ (VPDB), respectively. The δ13Ccarb profile of the St. George Group carbonates reveals several negative shifts, which vary between ∼2‰ and 3‰ and are generally associated with unconformities–disconformities or thin shale interbeds, thus reflecting the effect of or link with significant sea-level changes. The St. George Unconformity is associated with a negative δ13Ccarb shift (∼2‰) on the profile and correlated with major lowstand (around the end of Arenig) on the local sea-level reconstruction and also on those from the Baltic region and central Australia, thus suggesting that the St. George Group Unconformity might have likely had an eustatic component that contributed to the development–enhancement of the paleomargin. Other similar δ13Ccarb shifts have been recorded on the St. George profile, but it is hard to evaluate their global extension due to the low resolution of the documented global Lower Ordovician (Tremadoc – middle Arenig) δ13Ccarb profile.

Arenigian (Early Ordovician) sea-level history and the response of conodont communities, western Newfoundland

2004 ◽  
Vol 41 (7) ◽  
pp. 843-865 ◽  
Author(s):  
Shunxin Zhang ◽  
Christopher R Barnes
Keyword(s):  
Sea Level ◽  
Environmental Gradient ◽  
Sea Level Change ◽  
Level Curve ◽  
Sea Level Changes ◽  
Baltic Region ◽  
Level Change ◽  
Lower Ordovician ◽  
Central Australia ◽  
The Baltic

Four cluster analyses were performed, which recognized 17 conodont communities in the Arenigian (Lower Ordovician) of western Newfoundland. The analyses include 69 598 identifiable conodont specimens recovered from 153 conodont-bearing samples from four stratigraphical sections representing the environmental settings of the platform, upper proximal slope, lower proximal slope, and distal slope. The distribution of conodont communities along the platform to slope environmental gradient shows that sea-level changes simultaneously affected the development and replacement of the conodont communities in the different facies. The pattern of change in conodont communities allows an interpretation of sea-level change that is correlated precisely into the detailed graptolite biozonation. A gradual transgression lasted most of Tetragraptus approximatus Zone time, which was followed by a brief regression; a transgression–regression cycle occurred in the T. akzharensis Zone time; a major transgression caused a highstand during the entire Pendeograptus fruticosus Zone time, which was followed by a major regression in the early Didymograptus bifidus Zone time; Isograptus victoriae lunatus Zone time included repetitive oscillations of sea level; a severe regression in the earliest I. i. victoriae Zone time was represented by the St. George unconformity on the platform and the Bed 12 megaconglomerate on the slope, reaching the lowest sea level during the I. i. maximus Zone time. The Arenigian sea-level curve developed by this study only partly agrees with that from the Baltic region and central Australia based on trilobite communities.

scholarly journals Upper Arenig trilobite biostratigraphy and sea-level changes at Lynna River near Volkhov, Russia

2003 ◽  
Vol 50 ◽  
pp. 105-114
Author(s):  
T. Hansen ◽  
A.T. Nielsen
Keyword(s):  
Shallow Water ◽  
Sea Level Rise ◽  
Sea Level ◽  
Abundance Ratio ◽  
Basal Part ◽  
Sea Level Changes ◽  
Faunal Turnover ◽  
Lower Ordovician ◽  
Water Conditions ◽  
Tentative Interpretation

Over 5000 trilobites have been collected from Lower Ordovician rocks exposed at the Lynna River in the Volkhov region, east of St. Petersburg, Russia. Bed-by-bed sampling has been carried out through the upper part of Volkhov Formation (top of Jeltiaki Member and the entire Frizy Member), the Lynna Formation and the basal part of the Obukhovo Formation. This interval, which is 7.5 metres thick, correlates with the upper part of the Arenig Series, and presumably even ranges into the very base of the Llanvirn. A preliminary biostratigraphical investigation of top Jeltiaki Member (BIIβ), Frizy Member (BIIγ) and basal Lynna Formation (BIIIα) reveals a rather continuous faunal turnover lacking sharp boundaries, and the biostratigraphical zonation (BIIβ–BIIIα) is primarily defined by the index trilobite taxa. The trilobite ranges are generally in agreement with the pattern described by Schmidt in 1907. The abundance ratio between Asaphus and the ptychopygids seems to be related to changes in relative sea level with Asaphus preferring the most shallow water conditions. A tentative interpretation of sea-level changes suggests an initial drowning at the base of BIIγ, immediately followed by a lowstand that in turn was succeeded by a moderate sea-level rise and then a significant fall. The last marks the BIIγ/BIIIα boundary. Correlation with sections in Scandinavia suggests that the basal part of BIIγ is strongly condensed.

Isotope stratigraphy ( 87 Sr / 86 Sr , 13 C ) and depositional sequences of the Aruma Formation, Saudi Arabia: Implications to eustatic sea‐level changes

2020 ◽  
Vol 55 (12) ◽  
pp. 7594-7612
Author(s):  
Sherif Farouk ◽  
Khaled Al‐Kahtany ◽  
Sreepat Jain ◽  
Fayez Ahmad ◽  
Abdelbaset El‐Sorogy
Keyword(s):  
Saudi Arabia ◽  
Sea Level ◽  
Sea Level Changes ◽  
Depositional Sequences ◽  
Aruma Formation ◽  
Isotope Stratigraphy

High-resolution Stratigraphy of Holocene Lagoon Terraces of Southern Brazil

2015 ◽  
Vol 83 (1) ◽  
pp. 52-65 ◽  
Author(s):  
Natália B. dos Santos ◽  
Ernesto L.C. Lavina ◽  
Paulo S.G. Paim
Keyword(s):  
High Resolution ◽  
Sea Level ◽  
Radiometric Dating ◽  
Sea Level Changes ◽  
Relative Sea Level ◽  
Base Level ◽  
Depositional Processes ◽  
Close Relationship ◽  
Northern Portion ◽  
Depositional Architecture

AbstractThe northern portion of the coastal plain of the Rio Grande do Sul State (southernmost Brazil) comprises an outer sandy barrier that protects a complex lagoon system formed during the Holocene. The terraces of three different lagoons (Gentil, Malvas and Pinguela) formed along their margins record the depositional processes and the relative base level changes over the past 5000 yr. Therefore, our main objective was to characterize and quantify base level fluctuations from the study of these terraces, to correlate them to sea-level changes and to describe the depositional architecture related to the distinct sea-level stages (high-resolution sequence stratigraphy). Satellite images, topographic and GPR profiles, auger holes and radiometric dating were used. The main results indicate a close relationship between relative base level and relative sea-level changes, a stillstand period just after the last transgressive maximum (4840–4650 cal yr BP) and a subsequent overall relative sea-level fall of about 3 m. Both a normal (highstand systems tract) and a forced regression (falling-stage systems tract) controlled the geological record preserved in the terraces. The highstand (older terrace) is characterized by agradational bedding, whereas the falling stage comprises three progradational sets (terraces) bounded by erosive surfaces related to smaller-scale sea-level drops.

The Silurian Mulde Event and a scenario for secundo–secundo events

2002 ◽  
Vol 93 (2) ◽  
pp. 135-154 ◽  
Author(s):  
Lennart Jeppsson ◽  
Mikael Calner
Keyword(s):  
High Resolution ◽  
Sea Level ◽  
Greenhouse Effect ◽  
Sedimentary Facies ◽  
Sea Level Changes ◽  
Secondary Result ◽  
Sedimentary Succession ◽  
Detailed Record ◽  
Quaternary Glaciations ◽  
Oceanic Model

ABSTRACTGraphic correlation using graptolites and conodonts provides a high-resolution timescale for correlating from coastal to deep oceanic sections and, thereby, also a detailed record of the sequence of changes during the Mulde Secundo-Secundo Event. That interval includes sedimentary facies otherwise unknown in older Wenlock to early Ludlow strata on Gotland. The identified sequence of changes includes a detailed record of, in order: two extinctions (Datum points 1 and 1·5); widespread deposition of carbon-rich sediments extensive enough to cause a δ13C increase of c. 4.8‰, the onset, maximum and end of a sea-level fall and rise of at least 16 m during 30 kyr; a third extinction (Datum 2); a disaster fauna; and a slow faunal recovery. Thus, a secondary result of the event was a weakened greenhouse effect triggering a glaciation: the Gannarve Glaciation (new term). The order of changes proves that regression did not cause the extinctions. Faunal and sea-level changes, as well as the sedimentary succession, fit well with predictions based on an oceanic model. Extinctions were primarily caused by a severe drop in primary planktonic productivity, causing starvation among planktonic larvae in non-coastal settings. The Grötlingbo Bentonite (new term), the thickest in the Wenlock of Gotland, was deposited across the basin shortly after Datum 2. Temporal resolution is high enough to permit some comparison with Quaternary glaciations.

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