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Link to original content: https://pubmed.ncbi.nlm.nih.gov/38552008
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. 2024 Mar 29;10(13):eadl3452.
doi: 10.1126/sciadv.adl3452. Epub 2024 Mar 29.

Tectonic trigger to the first major extinction of the Phanerozoic: The early Cambrian Sinsk event

Paul M Myrow  1 , John W Goodge  2   3 , Glenn A Brock  4 , Marissa J Betts  5 , Tae-Yoon S Park  6   7 , Nigel C Hughes  8 , Robert R Gaines  9
Affiliations

Tectonic trigger to the first major extinction of the Phanerozoic: The early Cambrian Sinsk event

Paul M Myrow et al. Sci Adv. .

Abstract

The Cambrian explosion, one of the most consequential biological revolutions in Earth history, occurred in two phases separated by the Sinsk event, the first major extinction of the Phanerozoic. Trilobite fossil data show that Series 2 strata in the Ross Orogen, Antarctica, and Delamerian Orogen, Australia, record nearly identical and synchronous tectono-sedimentary shifts marking the Sinsk event. These resulted from an abrupt pulse of contractional supracrustal deformation on both continents during the Pararaia janeae trilobite Zone. The Sinsk event extinction was triggered by initial Ross/Delamerian supracrustal contraction along the edge of Gondwana, which caused a cascading series of geodynamic, paleoenvironmental, and biotic changes, including (i) loss of shallow marine carbonate habitats along the Gondwanan margin; (ii) tectonic transformation to extensional tectonics within the Gondwanan interior; (iii) extrusion of the Kalkarindji large igneous province; (iv) release of large volumes of volcanic gasses; and (v) rapid climatic change, including incursions of marine anoxic waters and collapse of shallow marine ecosystems.

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Figures

Fig. 1.
Fig. 1.. Tectonic setting of the Neoproterozoic and Cambrian systems in East Antarctica and Australia.
Locations of Kangaroo Island (KI) and Nimrod Glacier area of the central Transantarctic Mountains (CTM) shown with black stars; similar geologic relations occur in the Shackleton Range (SR), shown by a white star. Early Paleozoic trench migrated oceanward between Cambrian (1, solid line) and Devonian time (2, dashed line). ARC, Adelaide Rift Complex; FP, Fleurieu Peninsula; LFB, Lachlan Fold Belt; NVL, northern Victoria Land; PM, Pensacola Mountains; Tas, Tasmania. Reconstruction modeled from GPlates (88) and alignment of geophysical anomalies (89), with mid-Cambrian equator from Scotese (90). Inferred eastern edge of Precambrian cratons (purple dashed line) from Goodge and Finn (91) in Antarctica and Tasman Line (TL) in Australia. Distribution of sedimentary units after Foden et al. (19), Goodge (15), and Cox et al. (92). Extent of Ross and Delamerian orogens shown by horizontal ruling (15, 93). Inferred Neoproterozoic rift-margin faults from Preiss (30) and Goodge (15). West-dipping early Paleozoic marginal subduction zone (blue barbed line) was sinistral-oblique in middle Cambrian time [line 1; (60)]; by late Cambrian, convergence was geometrically more complicated (line 2), including multiple arcs and back-arcs [see (10) and (94)]. Dashed line separates two convergent margin domains—to the south in East Antarctica dominated by Andean-type continental-margin magmatic arc, and to the north from northern Victoria Land into Australia dominated by accretionary supra-subduction zone volcanism and marginal-basin development.
Fig. 2.
Fig. 2.. Stratigraphic comparison of Cambrian Series 2, Stage 4 strata on Kangaroo Island and central Transantarctic Mountains.
Inset shows location of sections in the restored continents (Fig. 1) and in Delamerian and Ross orogens. Stratigraphic units described in Results. The sections record five stages, from platform buildup through tectonic response to post-tectonic subsidence, although relative thicknesses and lithotypes vary. SS, sandstone; Sh, shale; Slst, siltstone; FS, fine sandstone; Carb, carbonate; Cgl, conglomerate.
Fig. 3.
Fig. 3.. Trilobites recovered from the Holyoake Formation (82°13.185′S, 160°16.122′E).
(A and B) Estaingia bilobata; CMCIP 88140 and CMCIP 88142, respectively. (C and D) Meniscuchus cf. M. menetus; CMCIP 88138 and CMCIP 96988, respectively. (E and F) Pagetides (Discomesites) sp.; CMCIP 88139 and CMCIP 96989, respectively.
Fig. 4.
Fig. 4.. Time correlation diagram comparing Cambrian events in central Ross and Delamerian orogens.
Timescale shows series and stages, and Atdabanian and Botoman trilobite divisions for comparison. Schematic stratigraphic columns show primary depositional relations between biostratigraphically designated units (16, 17, 31, 32, 36), and colored bars denote time span of key events constrained by geochronological data (–21, 44, 45). Note similar successions of archaeocyathid reefal carbonate, to black shale, and shallow-water sandstone, all down-cut and overlain by carbonate-clast conglomerate. Orogenic magmatism occurred through this period, but punctuated termination of carbonate deposition, shoaling, and overlap by prograding alluvial fanglomerate marks onset of supracrustal deformation in both areas. Syn- to post-orogenic cooling of micas and slates in metasedimentary lithologies mark metamorphism associated with structural shortening and thickening. Fm, Formation; Ls, Limestone.
Fig. 5.
Fig. 5.. Model depicting sedimentary and structural evolution of central Ross Orogen during Cambrian late Series 2.
(A) Reef and shoal deposition phase, dominated by carbonate buildup (Shackleton Limestone) over older siliciclastic strata. Undifferentiated basement includes metamorphic rocks and Neoproterozoic Beardmore Group. Outboard subduction operated at this time (14). S.L., sea level. (B) Initial thrusting phase, in which inland basement was uplifted and eroded, and marine platform underwent initial tectonically induced subsidence, resulting in deepening and development of a capping phosphatic hardground (heavy brown line). (C) Ongoing oceanward thrust displacement led to further crustal loading and deposition of a clastic shoaling succession, including nodular shale (Holyoake Formation) and shallow-marine sandstone (Starshot Formation). Subaerial alluvial-fan deposits sourced from inland thrust sheets were dominated by basement debris. (D) Mature thrust propagation phase, in which forward-propagating thrusts cut into Shackleton Limestone, producing carbonate-clast debris containing archaeocyathid fossils. Ongoing erosion, transport, and alluvial deposition led to accumulation of coarse alluvial-fan deposits (Douglas Conglomerate). Narrow vertical rectangle in (D) corresponds to stratigraphic section in Fig. 2. Primary field relations, sedimentation patterns, faunal occurrences, and geochronological constraints provided by earlier studies (16, 17, 23, 95).
Fig. 6.
Fig. 6.. Time diagram for the Cambrian, showing the oldest and youngest possible age of the Sinsk event and the Stage 3 to 4 boundary (black arrows with radiometric dates).
The base of Stage 4 and the P. janeae Zone is younger than 514.45 ± 0.36 Ma; the date of 511.87 ± 0.14 from the middle to upper P. janeae Zone is the upper limit for both the Sinsk and the supracrustal deformation event described herein. Dated units from the Kalkarindji LIP in Australia are shown as gray squares with error bars. Two ages from both the Kalkarindji dikes/volcanics and Antrim basalt represent minimum and maximum ages. The time span during which tectonic shortening occurred along the Ross-Delamerian margin of Antarctica and Australia, and during which the Sinsk event took place, is shown as a horizontal gray band. Sources of age data cited in Discussion.
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