Provenance of Ediacaran (Sinian) sediments in the Helanshan area, North China Craton: Constraints from U–Pb geochronology and Hf isotopes of detrital zircons

Significance Erosion below the Great Unconformity has been interpreted as a global phenomenon associated with Snowball Earth. Geological relationships and thermochronologic data provide evidence that the bulk of erosion below the Great Unconformity in Colorado occurred prior to Cryogenian glaciation. We suggest that there are multiple, regionally diachronous Great Unconformities that are tectonic in origin.

Diachronous

Snowball Earth

10.1073/pnas.1913131117

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Citations (72)

Composite and diachronous stratigraphic surfaces in low-gradient, transitional settings: The J-3 “unconformity” and the Curtis Formation, east-central Utah, U.S.A.

Journal of Sedimentary Research (2019)

Valentin Zuchuat Ivar Midtkandal Miquel Poyatos‐Moré Sigrid Da Costa Hannah L. Brooks

ABSTRACT Unconformities, by definition, correspond to erosional or nondepositional surfaces, which separate older strata below, from younger rocks above, encapsulating significant time gaps. However, recent studies have highlighted the composite nature of some unconformities, as well as their heterochronous and diachronous character, which challenge the use of such a definition in a four-dimensional dynamic environment. The J-3 Unconformity, separating the Middle Jurassic Entrada Sandstone from the Upper Jurassic Curtis Formation (and laterally equivalent units) in east-central Utah (USA), is laterally variable, generated by either erosion-related processes such as eolian deflation, and water-induced erosion, or by deformational processes. The J-3 Unconformity is a composite surface, formed by numerous processes that interacted and overlapped spatially and temporally. This study therefore demonstrates the heterochronous, diachronous, and non-unique nature of this surface interpreted as unconformity, where one process can be represented by varying expressions in the stratigraphic record, and conversely many processes may result in the same stratigraphic expression.

Diachronous

Geologic time scale

10.2110/jsr.2019.56

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Citations (17)

The Proterozoic Qinggouzi microfossil assemblage and its biostratigraphic constraints on the Great Unconformity in northeastern North China Craton

Precambrian Research (2023)

Wentao Zheng Qing Tang Shuhai Xiao Ke Pang Junyao Kang

Diachronous

10.1016/j.precamres.2023.107130

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Citations (3)