Late Silurian and Early Devonian biostratigraphy in the Hill End Trough and the Limekilns area, New South Wales

Packham, Gordon; Percival, Ian G.; Rickards, R. B.; Wright, Anthony J

doi:10.1080/03115510108619106

Cited by 9 publications

(7 citation statements)

References 14 publications

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“…Deep-water conditions continued in overlying units including deposition of mudstone and turbidites of the Early Devonian Cunningham Formation (Figure 4b). The Hill End Trough succession contains few age specific fossils but the base of the succession is considered as no older than late Ludlow (Packham et al 2001). These relationships are consistent with extensional development of the Hill End Trough in the Late Silurian during deposition of the Anson Formation and Dungeree Volcanics.…”

Section: Hill End Trough and Adjoining Highssupporting

confidence: 56%

Plate-driven extension and convergence along the East Gondwana active margin: Late Silurian–Middle Devonian tectonics of the Lachlan Fold Belt, southeastern Australia

Fergusson¹

2011

Australian Journal of Earth Sciences

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The Lachlan Fold Belt of southeastern Australia developed along the Panthalassan margin of East Gondwana. Major silicic igneous activity and active tectonics with extensional, strike-slip and contractional deformation have been related to a continental backarc setting with a convergent margin to the east. In the Early Silurian (Benambran Orogeny), tectonic development was controlled by one or more subduction zones involved in collision and accretion of the Ordovician Macquarie Arc. Thermal instability in the Late Silurian to Middle Devonian interval was promoted by the presence of one or more shallow subducted slabs in the upper mantle and resulted in widespread silicic igneous activity. Extension dominated the Late Silurian in New South Wales and parts of eastern Victoria and led to formation of several sedimentary basins. Alternating episodes of contraction and extension, along with dispersed strike-slip faulting particularly in eastern Victoria, occurred in the Early Devonian culminating in the Middle Devonian contractional Tabberabberan Orogeny. Contractional deformation in modern systems, such as the central Andes, is driven by advance of the overriding plate, with highest strain developed at locations distant from plate edges. In the Ordovician to Early Devonian, it is inferred that East Gondwana was advancing towards Panthalassa. Extensional activity in the Lachlan backarc, although minor in comparison to backarc basins in the western Pacific Ocean, was driven by limited but continuous rollback of the subduction hinge. Alternation of contraction and extension reflects the delicate balance between plate motions with rollback being overtaken by advance of the upper plate intermittently in the Early to Middle Devonian resulting in contractional deformation in an otherwise dominantly extensional regime. A modern system that shows comparable behaviour is East Asia where rollback is considered responsible for widespread sedimentary basin development and basin inversion reflects advance of blocks driven by compression related to the Indian collision.

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Section: Hill End Trough and Adjoining Highssupporting

confidence: 56%

Plate-driven extension and convergence along the East Gondwana active margin: Late Silurian–Middle Devonian tectonics of the Lachlan Fold Belt, southeastern Australia

Fergusson¹

2011

Australian Journal of Earth Sciences

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“…Deep-water conditions continued in overlying units including deposition of mudstone and turbidites of the Lower Devonian Cunningham Formation (Figure 4b). The Hill End Trough succession contains few age-specific fossils but the base of the succession is considered as no older than late Ludlow (Packham et al 2001). These relationships are consistent with extensional development of the Hill End Trough in the Late Silurian during deposition of the Anson Formation and Dungeree Volcanics.…”

Section: Hill End Trough and Adjoining Highsmentioning

confidence: 57%

Plate-driven extension and convergence along the East Gondwana active margin: Late Silurian–Middle Devonian tectonics of the Lachlan Fold Belt, southeastern Australia

Fergusson

2010

Australian Journal of Earth Sciences

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“…In the Cowra Trough, the Bulls Camp Volcanics (sample GA1594761) are of earliest Lochkovian age, as the unit is conformably underlain by a terminal Silurian graptolite assemblage, and overlain by rocks containing middle-Lochkovian conodonts (Pogson and Watkins 1998). In the Hill End Trough, a middle Lochkovian age is indicated for the lower Turondale Formation (sample GA1528019; Jagodzinski and Black 1999), because the upper part of the unit incorporates 'detrital' conodonts of late Lochkovian age in allochthonous limestone blocks (Packham et al 2001). Overlying the Turondale Formation is the Merrions Formation, with three samples from its type-section (samples GA1528025, GA1528027, and GA1530245; Jagodzinski and Black 1999) each assigned an early Pragian age, based on the presence of Pragian index fossils in overlying sedimentary strata (Packham et al 2001).…”

Section: Sample Descriptionsmentioning

confidence: 99%

“…In the Hill End Trough, a middle Lochkovian age is indicated for the lower Turondale Formation (sample GA1528019; Jagodzinski and Black 1999), because the upper part of the unit incorporates 'detrital' conodonts of late Lochkovian age in allochthonous limestone blocks (Packham et al 2001). Overlying the Turondale Formation is the Merrions Formation, with three samples from its type-section (samples GA1528025, GA1528027, and GA1530245; Jagodzinski and Black 1999) each assigned an early Pragian age, based on the presence of Pragian index fossils in overlying sedimentary strata (Packham et al 2001). Although Bodorkos et al (2012Bodorkos et al ( , 2017 summarised these CA-TIMS and SHRIMP dates in abstract form, the underlying analytical data are presented here for the first time.…”

Section: Sample Descriptionsmentioning

confidence: 99%

Examination of SHRIMP U-Pb zircon geochronology accuracy from samples dated by both SHRIMP and CA-TIMS

Magee

Bodorkos

Crowley

et al. 2022

Preprint

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Abstract. Estimations of the reproducibility of U-Pb ages from SHRIMP instruments are based on data from studies nearly two decades old. Since that time, refinement of analytical procedures and manufacturing and installation improvements may have reduced the fundamental uncertainties of SHRIMP U-Pb analysis. This paper investigates 35 SHRIMP-TIMS double-dated “real-world” geologic samples from a variety of igneous rock types to better understand both geological and analytical sources of disagreement between the two dating methods. Geoscience Australia’s (GA) use of high-precision chemical abrasion thermal ionization mass spectrometry (CA-TIMS) for chronostratigraphy in Australian sedimentary basins has produced a substantial selection of precisely dated zircons, which we can use to cross-correlate the SHRIMP and CA-TIMS ages throughout the Phanerozoic. Thirty-two of the 35 ages were reported with external SHRIMP uncertainties less than 1 % (95 % confidence), below previous estimates of the reproducibility limits of the SHRIMP. Six of eight cases where the CA-TIMS age was outside the SHRIMP uncertainty envelope were in samples where the reported SHRIMP age had a sub-0.66 % uncertainty, suggesting that SHRIMP analyses of untreated zircon which report smaller uncertainties are probably overoptimistic. The mean age-offset between SHRIMP and TIMS is 0.097 %, but the distribution is bimodal. Geological explanations for SHRIMP-CA-TIMS age discrepancies are uncovered by considering intrusive and extrusive age results separately. All but one sample where the SHRIMP age is more than 0.25 % older are volcanic. This offset could be explained by the better single-grain age-resolution of TIMS, allowing identification and exclusion of antecrysts from the eruptive population, while SHRIMP does not have a sufficient single-grain precision to deconvolve these populations – leading to an apparent older SHRIMP age. In contrast, SHRIMP ages from plutonic rocks- particularly plutonic rocks from the early Paleozoic- are typically younger than the CA-TIMS ages from the same samples, most likely reflecting Pb loss from non-chemically-abraded SHRIMP zircons, while chemical abrasion of zircons prior to TIMS analysis destroyed or corrected these areas of Pb loss.

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Late Silurian and Early Devonian biostratigraphy in the Hill End Trough and the Limekilns area, New South Wales

Cited by 9 publications

References 14 publications

Plate-driven extension and convergence along the East Gondwana active margin: Late Silurian–Middle Devonian tectonics of the Lachlan Fold Belt, southeastern Australia

Plate-driven extension and convergence along the East Gondwana active margin: Late Silurian–Middle Devonian tectonics of the Lachlan Fold Belt, southeastern Australia

Plate-driven extension and convergence along the East Gondwana active margin: Late Silurian–Middle Devonian tectonics of the Lachlan Fold Belt, southeastern Australia

Examination of SHRIMP U-Pb zircon geochronology accuracy from samples dated by both SHRIMP and CA-TIMS

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