Age Controls on the Tanqua and Laingsburg Deep-Water Systems: New Insights on the Evolution and Sedimentary Fill of the Karoo Basin, South Africa

Fildani, Andrea; Drinkwater, Nicholas; Weislogel, Amy L.; McHargue, T.; Hodgson, David M.; Flint, Stephen S.

doi:10.2110/jsr.2007.088

Cited by 81 publications

(80 citation statements)

References 31 publications

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“…15). (Fildani et al, 2007;20.75°E). The magnetostratigraphy and corresponding ages, therefore, support an age range of ca.…”

Section: Magnetostratigraphymentioning

confidence: 98%

“…U-Pb ages published from the Ecca Group yield maximum depositional ages ranging from ca. 274-250 Ma (Fildani et al, 2007;Fildani et al, 2009;McKay et al, 2016;McKay et al, 2015). The younger ages in this range are problematic in that they require the PTB to be placed within the middle Ecca Group, as opposed to the biostratigraphically-supported placement in the overlying terrestrial fluvio-lacustrine strata of the Beaufort Group (Figs.…”

Section: Geologic Backgroundmentioning

confidence: 99%

“…Some authors have explained this apparent age inversion by applying a diachronous sedimentation model across the Karoo Basin, where the submarine fans of the Ecca Group in the southwest are considered correlative with the terrestrial Permian-Triassic sections located farther east (Fildani et al, 2007;Fildani et al, 2009). However, this interpretation is not supported by recent regional mapping that shows continuity of the marine Ecca Group for over 500 km across the basin, with a series of interfingering submarine fan deposits, all overlain by eastward prograding deltaic deposits (Flint et al, 2017).…”

Section: Geologic Backgroundmentioning

confidence: 99%

“…2), and we interpret this as mainly resulting from the contrasting interpretations of complicated U-Pb datasets. (Fildani et al, 2007;Fildani et al, 2009;McKay et al, 2016;McKay et al, 2015). The former age calculations were based on the single youngest grain (Fildani et al, 2007;Fildani et al, 2009) or sub-population of youngest grains (McKay et al, 2016;McKay et al, 2015), whereas our analysis was based on the weighted mean 206 Pb/ 238 U age of all isolated Permian grains (< 280 Ma) that met the specified quality criteria (section 3.3).…”

Section: Shrimp U-pb Geochronologymentioning

confidence: 99%

“…274-250 Ma age range for deposition of the underlying Ecca Group, and therefore a Triassic age for the Beaufort Group ( Fig. 2) (Fildani et al, 2007;Fildani et al, 2009;McKay et al, 2016;McKay et al, 2015). This depositional age assignment requires that the PTB be placed within the upper Skoorsteenberg Formation of the Ecca Group, ~2000 m below the biostratigraphically constrained PTB in the upper Beaufort Group (Fig.…”

Section: Introductionmentioning

confidence: 99%

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Refining the chronostratigraphy of the Karoo Basin, South Africa: magnetostratigraphic constraints support an early Permian age for the Ecca Group

Belica¹,

Tohver²,

Poyatos‐Moré

et al. 2017

Geophysical Journal International

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Summary:The Beaufort Group of the Karoo Basin, South Africa provides an important chrono-and biostratigraphic record of vertebrate turnovers that have been attributed to the End-Permian mass extinction events at ca. 252 Ma and ca. 260 Ma. However, an unresolved controversy exists over the age of the Beaufort Group due to a large dataset of published U-Pb SHRIMP zircon results that indicate a ca. 274-250 Ma age range for deposition of the underlying Ecca Group. This age range requires the application of a highly diachronous sedimentation model to the Karoo Basin stratigraphy and is not supported by published paleontologic and palynologic data. This study tested the strength of these U-Pb isotopic datasets using a magnetostratigraphic approach. Here we present a composite ~1500 m section through a large part of the Ecca Group from the Tanqua depocentre, located in the southwestern segment of the Karoo Basin. After the removal of two normal polarity overprints, a likely primary magnetic signal was isolated at temperatures above 450°C. This section is restricted to a reverse polarity, indicating that it formed during the Kiaman Reverse Superchron (ca. 318-265 Ma), a distinctive magnetostratigraphic marker for Early−Middle Permian rocks. The Ecca Group has a corresponding paleomagnetic pole at 40.8°S, 77.4°E (A95 = 5.5°). UPb SHRIMP ages on zircons are presented here for comparison with prior isotopic studies of the Ecca Group. A weighted mean U-Pb age of 269.5 ± 1.2 Ma was determined from a volcanic ash bed located in the uppermost Tierberg Formation sampled from the OR1 research core. The age is interpreted here as a minimum constraint due to a proposed Pb-loss event that has likely influenced a number of published results. A comparison with the Geomagnetic Polarity Time Scale as well as published U-Pb TIMS ages from the overlying Beaufort Group supports a ca. 290-265 Ma age for deposition of the Ecca Group.

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“…15). (Fildani et al, 2007;20.75°E). The magnetostratigraphy and corresponding ages, therefore, support an age range of ca.…”

Section: Magnetostratigraphymentioning

confidence: 98%

Section: Geologic Backgroundmentioning

confidence: 99%

Section: Geologic Backgroundmentioning

confidence: 99%

Section: Shrimp U-pb Geochronologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Refining the chronostratigraphy of the Karoo Basin, South Africa: magnetostratigraphic constraints support an early Permian age for the Ecca Group

Belica¹,

Tohver²,

Poyatos‐Moré

et al. 2017

Geophysical Journal International

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Magnetostratigraphic constraints on the age of the lower Beaufort Group, western Karoo basin, South Africa, and a critical analysis of existing U‐Pb geochronological data

Tohver

Lanci

Wilson

et al. 2015

Geochem Geophys Geosyst

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We studied three partially overlapping sections with a composite thickness of ∼600 m in the upper Permian fluvial siltstones and fine‐grained sandstones of the Abrahamskraal Formation, the basal unit of the Beaufort Group, in the Karoo Basin of Western Cape Province, South Africa. Paleomagnetic analysis reveals three components of Natural Remanent Magnetization (NRM). Heating to ∼180°C removes a remanent magnetization parallel to the present‐day field, which is interpreted as a viscous overprint. An intermediate unblocking temperature component is removed by heating to 450°C; this direction is always of normal polarity and is identical to a regional overprint imparted during the Early Jurassic emplacement of the Karoo Large Igneous Province. A high‐temperature component isolated above 450°C is of dual polarity and is interpreted as primary on the basis of a positive reversals test. The virtual geomagnetic pole position for the Abrahamskraal Formation computed from the average high‐temperature characteristic remanent magnetization direction is in agreement with the late Permian directions for stable Gondwana and with previous results from the lowermost Abrahamskraal Formation and Waterford Formation at the Ouberg Pass section. The predominantly normal polarity of this magnetization is in agreement with either a middle‐late Lopingian age (ca. 254–256 Ma) or a late Guadalupian age (ca. 262 Ma) according to the global geomagnetic polarity time scale. We integrate these new results with existing magnetostratigraphic, biostratigraphic, and geochronological results from the Karoo Basin, with particular emphasis on the controversy over zircon age data reported from the underlying Ecca Group.

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Deep Borehole Lithostratigraphy and Basin Structure of the Southern Karoo Basin Re-Visited

Linol

Chere

Muedi

et al. 2016

Origin and Evolution of the Cape Mountains and Karoo Basin

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Age Controls on the Tanqua and Laingsburg Deep-Water Systems: New Insights on the Evolution and Sedimentary Fill of the Karoo Basin, South Africa

Cited by 81 publications

References 31 publications

Refining the chronostratigraphy of the Karoo Basin, South Africa: magnetostratigraphic constraints support an early Permian age for the Ecca Group

Refining the chronostratigraphy of the Karoo Basin, South Africa: magnetostratigraphic constraints support an early Permian age for the Ecca Group

Magnetostratigraphic constraints on the age of the lower Beaufort Group, western Karoo basin, South Africa, and a critical analysis of existing U‐Pb geochronological data

Deep Borehole Lithostratigraphy and Basin Structure of the Southern Karoo Basin Re-Visited

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