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Abstract: Gamma-ray (GR) logging and detrital zircon geochronology provide new constraints on changing provenance in the southern Hailar Basin of northeastern China. The basement of this region is characterized by low GR values of 70–90 API. This is overlain by a rift-fill sequence, the GR values of which exhibit a broad range in its lower part (70–160 API), but a more restricted range (80–110 API) in its upper part. Post-rift sediments dominate the basin fill, and are characterized by higher GR values of 120–160 API. Detrital zircon samples from the lower rift sequence and post-rift sediments share similar age distributions, with a single dominant age population of 150–110Ma. Samples from the upper rift sequence exhibit a bimodal age distribution with peaks at 180–150Ma and 360–300Ma. The synchronous changes in zircon age populations and GR values in the strata suggest changing sedimentary source characteristics, thus revealing a rapid shift from active rifting to post-rift thermal sagging of the Hailar Basin in the Early Cretaceous. The basal rift-fill deposits are interpreted to have been mainly derived from erosion of local highs internal to the basin itself, although acidic air-fall ash from the extensive late Mesozoic volcanism in the Great Xing''an Range probably also contributed. Post-rift sediments are dominated by materials shed from the Great Xing''an Range magmatic belt. [Copyright &y& Elsevier]

Abstract: This study uses new seismic reflection profiles and exploratory well data to analyze the structural characteristics and evolution of the Sanjiang Basin in eastern Heilongjiang, NE China. The basin sequence was divided into six stratigraphic units, representing discrete Middle-Upper Jurassic, Lower Cretaceous, Upper Cretaceous, Eocene–Oligocene, Miocene and Quaternary phases of development. The Sanjiang Basin initiated as a passive marginal rift flank to the southern Mongol–Okhotsk Ocean during the Middle Jurassic, and primary basin growth was terminated by orogenic deformation related to the Mongol–Okhotsk suture to the north and the accretion of the Nadanhada terrane to the east. Middle-Upper Jurassic strata are controlled by half-graben structures active during this phase of basin growth, and are limited largely to the west Suibin sub-basin. The wider basin experienced renewed rifting and large-scale sag caused by back arc extension along the Eurasian continental margin in the Early Cretaceous, terminating during the Late Cretaceous in a phase of intense compression at the contemporary Andean-type continental margin. This produced a series of thrust-folds through the Lower and Upper Cretaceous successions, and led to the development of a regional-scale erosional unconformity. Minor subsequent Cenozoic extension is attributed to back-arc extension along the West Pacific continental margin, with Eocene–Oligocene, Miocene, and Quaternary deposits unconformably overlying the Mesozoic sequences in half-graben and extensional fault-demarcated depocenters, most prominently in the east Qianjin sub-basin. [Copyright &y& Elsevier]