Abstract Geochemical data from South China Sea sedimentary rocks show the effects of both source composition and depositional environments. This enables us to link tectonic trends with erosion in the Pearl River region since c. 32 Ma. In particular, a shift in the geochemistry appears to signal a response to a well-recorded regional tectonic event at c. 23–25 Ma, probably corresponding to a jump in the seafloor spreading axis from the west to the SW within the South China Sea. This may correlate with the uplift of the West Yunnan Plateau and possibly also the eastern Tibetan Plateau. Clay mineralogy, sand–mud ratio, and major and rare earth element concentrations, also varied in response to the environment in the drainage areas of the palaeo-Pearl River. By comparing data from the modern sources and the sedimentary record from the northern South China Sea, especially the erosion–transportation–deposition patterns, three groups of index minerals (Ati, GZi, ZTR), as well as rare earth elements can be recognized. These are used to characterize the Pearl River from the east to the west, representing three different parent rock sources. The evolution of the palaeo-Pearl River can be tracked by variations of heavy minerals and key elements that are indicative of provenance.

Abstract The greater South China Sea (SCS) Basin is composed of basins of different generations and styles. These polyhistory basins formed in complicated geologic settings and evolved through different tectonic regimes. Based on a classical basin classification scheme and data from previous studies, we summarize the evolution of tectonic environments of the SCS in the Mesozoic-Cenozoic into a Late Triassic-middle Eocene divergent-convergent cycle and a late Eocene-present divergent-convergent cycle. The two cycles are in turn composed of four evolutionary phases, which are (1) Late Triassic-Middle Jurassic divergent continental margin setting, (2) Late Jurassic-middle Eocene convergent intracontinentalsetting, (3) late Eocene-Miocene divergent continental margin setting, and (4) Pliocene present convergent continental margin setting. We identify temporal sequence and spatialdistribution of major polyhistory basins in the SCS associated with the four basin evolutionary phases in the two tectonic cycles. Each basin corresponds to a specific pressure, space, and temperature, and overprinting of the basin caused changes in pressure, space, and temperature with time. Unraveling this complex and dynamic nature of the polyhistory basins can be instrumental in assessing the hydrocarbon potential and exploration risk in the SCS.

Abstract The physical packaging into unconformity-bounded units of the upper Oligocene and lower Miocene neritic strata in southeastern Australia is chronologically consistent with third-order putative global sequences and glaciations. Foraminiferal biofacies data show both recurrence and progression. Species used as proxies for inner-neritic and outer-neritic environments display recurring fluctuations in close harmony with stratal packaging. In contrast to this recurrence or cycling, biofacies cluster groups are strongly sequential or “progressive” at the third-order, 10 6 -year scale, with very little overlap between the successional assemblages named Angahook, Jan Juc-1, Jan Juc-2, and Puebla. The Angahook–Jan Juc-1 and Jan Juc-2–Puebla biofacies boundaries, implying some turnover in communities, fall respectively at sequence boundaries Ru4–Ch1 and Ch4–Aq1 and glacioeustatic perturbations OCi-1 and MAi-1 (= Mi1), but the Jan Juc-1–Jan Juc-2 boundary within the Jan Juc Formation falls close to the flooding surface of sequence TB1.2. These third-order patterns of recurrence and sequential change were largely sustained at higher frequencies in the study of an interval approaching a glacial within the Jan Juc-1. Samples at the centimeter scale (about 2–4 cm spacing) over one meter of alternating soft and hard (lithified) layers yield four biofacies groups mainly on abundance variations of individual species and species groups. The clusters are cleanly separated superpositionally (thus, strongly successional), reflecting environmental cycles at 10 4 -year scale, perhaps in the Milankovitch band of 41,000 years. Shallower-water species dominate clusters B and D from hard layers, whereas deeper-water species are more abundant in clusters A and C from soft layers. The differences suggest paleodepth change of 50–70 m, with maxima in the soft layers and minima at the tops of hard layers. The high abundance of infauna and a stronger mixing between shallower-water and deeper-water species indicates an oxygen-poor environment coupled with bioturbation. Similarities between faunas of third-order and Milankovitch scales include: (i) coincidence of biofacies with lithofacies or lithostratigraphy is due largely to abundance variations of the prominent species, (ii) recurring biofacies signals of sea-level change are chronologically consistent with other published proxies of glacioeustasy, and (iii) clustered assemblages of benthic foraminifera are distinct and strongly successional.

Abstract: The neritic stratigraphic record in southern Australia sorts into four cycles or sequences which resemble global second-order cycles based on sequence stratigraphy. The record is highly incomplete at the second order, due especially to a 9 my gap in the middle Eocene and poor and restricted records of the early Oligocene and the late Miocene series, and at the third order where hiatuses become more apparent as stratigraphy advances. Correlations and age determinations are based mostly on micropalaeontology and are limited by the neritic facies, the extratropical situation and the lack of a local or regional geomagnetic pattern. In this composite regional succession, we have had to proceed from regional stages based only loosely on fossils, to biostratigraphic ranges and formal zones (of planktonic foraminifera), to faunal associations based on transgressions and regressions, so that we are but a short step from a revision of the regional stages in terms of sequence biostratigraphy. This geochrono- logical scaffolding is important not only to the neritic realm itself, but to the neritic-oceanic link and ODP drilling in one direction and to the terrestrial environmental and paleobiological realm in the other. The Cenozoic record of global climatic deterioration has temporary reversals punctuated by four sharp coolings (“chills”) in the early middle Eocene, earliest Oligocene, middle Miocene and late Pliocene, and they too are chronologically consistent with the regional neritic record. In the oldest cycle, the sediments are marginal marine siliciclastics with several very brief transgressions with marine microfaunas and rare macrofossils but no limestones. Extratropical carbonates begin abruptly in the late middle Eocene series at the base of the second cycle and the Wilson Bluff transgression, which is the Khirthar Restoration of the Indo-Pacific region. At the same time there develops a distinction between warmer and cooler intermediate watermasses in the Indian Ocean, and the Leeuwin Current is born. These events are responses to accelerated Australia/Antarctica separation from 43- 42 Ma. The third-order components of this cycle are marked by marine transgressions; they are consistent in number and timing with the putative late Eocene global pattern. The third cycle is the Miocene oscillation which begins in late Oligocene time and peaks in sea level and warming at the Miocene climatic optimum in early middle Miocene time. As shown in a correlation chart, the extratropical “cool-water carbonates” are mostly in the second and third cycles, although there are carbonates in the extensive marine horizons of the Pliocene reversal. The Eocene-Miocene neritic carbonate record comprises third-order sequences, seen most clearly as marine transgressions. The transgressions can be related to third-order glaciations and eustatic cycles in plausible if not always compelling correlations. Horizons of warming, upwelling, and siliceous facies complete a framework of an outstanding extratropical, neritic carbonate record.