The well-known Pleuronectia badensisFontannes, 1882 (currently classified as Cristatopecten cristatus badense) is declared as a n omen protectumagainst the older synonym Pecten burdigalensis var. ...polonica Pusch, 1837 considered a nomen oblitum. It ranges from the early to the late Miocene (Burdigalian–Messinian) of the NE Atlantic and Mediterranean. In the Central Paratethys it appeared in the early Miocene (Karpatian, correlating with the latest Burdigalian) and became extinct in the middle Miocene (Late Badenian, correlating with the early Serravallian). In Poland – the northernmost part of Central Paratethys – the occurrence of this taxon is limited to the late Early Badenian (late Langhian).
Analyses of the biogeochemical branched and isoprenoid tetraether (BIT) index and elemental geochemistry from Well XK1 provide insight into the development of the Xisha Islands carbonate platform in ...the South China Sea (SCS) since the Early Miocene. BIT is the ratio of branched glycerol dialkyl glycerol tetraethers (bGDGTs) to isoprenoid glycerol dialkyl glycerol tetraethers (iGDGTs), which are derived from meteoric and marine environments respectively. BIT serves as a novel proxy for tracking sea-level changes.
The BIT curve of Well XK1 is characterized by “low–high–low–high” alternating stages, indicating the superposition of sea-level changes on carbonate platform evolution in the SCS. Following the rapid expansion of the SCS in the early stages of the Early Miocene, biogenic reefs began to form, and BIT oscillated intensely. The SCS started to regress after its initial expansion during the Middle Miocene, at which time global sea level was also falling significantly. The combination of both tectonic activity and eustatic variation has resulted in the deposition of strata with reef-beach facies, which are characterized by high BIT values. Relative sea level reached its lowest point in the late stages of the Middle Miocene (~11.6Ma). Subsequent sea-level rise between the Late Miocene and Pliocene induced a negative shift in BIT, and lagoonal facies formed under optimal warm marine conditions. Periodic exposure caused the reefs of the Xisha Islands to suffer from erosion during the Pleistocene, which is consistent with a second elevation in the BIT index. However, modern trends show increasing regional water depths again.
Major and trace element curves (Na, Si, P, B, Ga, Mo, Zn), as well as the associated ratios (Na2O/K2O, Na2O/SiO2, B/Ga, Ti/Sr, Zr/Sr, Al/Sr, Th/U), accurately record sea-level variations. Several significant discontinuities correlate with sea-level shifts, and provide important details about the geomorphology, sedimentation patterns, and diagenesis types on the SCS carbonate platform. The agreement between organic and inorganic geochemical data demonstrates that our reconstructions of SCS sea-level changes and modes of carbonate platform development are robust.
Our findings also demonstrate that carbonate evolution in the Xisha Islands was shaped by relative sea-level changes, implying that sea level fluctuations in the SCS were controlled by global eustatic factors in addition to regional tectonic subsidence.
•A combination of novel biogeochemistry and classical elemental geochemistry proxies is applied to geological studies.•A long-term sea level variation of the South China Sea is well developed.•Carbonate platform evolution model of Xisha Islands is proposed.
Sea surface temperatures (SST) have been identified as a main controlling factor on larger benthic foraminifera (LBF) living in tropical to sub-tropical shallow-water carbonate and mixed ...siliciclastic‑carbonate platforms. Changes in SST, along with those in ocean acidification and nutrient content recorded in the global oceans throughout their history will not only continue but also be amplified in the future at an unprecedented rate of change possibly reaching levels found in the geological record. This study focuses on the Oligocene (mean SST 8 °C higher than present) and the Miocene (SST 5–8 °C higher than present) epochs which were characterized by a higher richness in porcelaneous LBF (pLBF) than today. A systematic re-assessment and comprehensive literature survey of stratigraphic ranges and palaeogeographic distribution in the Western Tethyan (Mediterranean) and Indo-Pacific regions are used to evaluate the impact of changes in SST, seawater pCO2 and pH on the biodiversity of the Oligocene–Miocene pLBF Alveolinella, Austrotrillina, Borelis, Bullalveolina, Flosculinella, and Praebullalveolina. Two peaks in species richness were identified during the Aquitanian and Langhian–Serravallian. These peaks occurred when SST was ∼29 °C, with pCO2 of ∼400 ppm and pH > 7.8. These values are comparable to those of today. The minima in species richness recorded in the Rupelian–early Chattian, in the Burdigalian and from the Tortonian onward can be correlated to the detrimental effects of both minimum (< 26 °C) and maximum (> 31 °C) SST thresholds. High pCO2 (> 600 ppm) values, which are limited to the Rupelian–early Chattian, are also detrimental to species richness. Seawater pH higher than 7.7 did not negatively affect species richness. These historical trends have serious implications for the future diversity of pLBFs with the increasing likely scenario of rising SST and pCO2 and lowering of pH values in the near future. These developments can potentially lead to diversity decrease and even extinction of pLBFs. However, the resilience of present-day pLBF species to rising SST and pCO2 levels is underpinned by the evolutionary histories of their fossil counterparts during climate variations, albeit at much different rates of change.
•The Aquitanian and Langhian–Serravallian peaks in richness occurred when SST c. 29 °C.•Detrimental effects of high pCO2 (> 600 ppm) in the Rupelian–early Chattian.•Detrimental effects of high tropical SST (> 31 °C) during the beginning of MCO.•Detrimental effects of low tropical SST (< 26 °C) in the Tortonian.•Sea-level highstands affected diversification of Oligocene–Miocene pLBF.
We reconstructed the orbital-scale variability of deep-water mass properties in the equatorial Indian Ocean during the late early to late Miocene (17.9 to 8.2 Ma) using benthic foraminiferal oxygen ...(δ18O) and carbon (δ13C) isotope records, in combination with X-ray fluorescence scanner elemental records at International Ocean Discovery Program (IODP) Site U1443. These records suggest that hyperthermal-like features (negative excursions in δ18O and δ13C coupled to suboxic and acidic conditions in the deep ocean) developed at eccentricity maxima during the Miocene Climatic Optimum (MCO; 16.9 to 14.7 Ma) on an almost ice-free Earth. Elevated Mn and U concentrations indicate that bottom and pore waters in the Indian Ocean became progressively suboxic during the later phase of the MCO. A fundamental change in deep-water circulation occurred after the expansion of the East Antarctic Ice Sheet during the Middle Miocene Climatic Transition (MMCT; 14.7 to ~13.8 Ma). Stepwise increases in δ18O at ~13.8 and ~13.1 Ma concurred with dampening of deep-water δ18O and δ13C variability, as Antarctic ice cover expanded and became more stable. A marked improvement in deep-water oxygenation after ~13.5 Ma coincided with the end of the last δ13C maximum of the Monterey Excursion. Carbonate dissolution in the equatorial Indian Ocean intensified and prolonged episodes of reduced carbonate deposition during the Carbonate Crash interval (~12.6 to 8.6 Ma) were not restricted to eccentricity maxima as during the MCO. Rising Mn and U concentrations after ~9 Ma indicate decreased oxygenation of bottom and pore waters, associated with the onset of the Biogenic Bloom in the Indian Ocean.
•10-Myr Indian Ocean Miocene record of deep water oxygenation/carbonate preservation.•Warming at Miocene Climatic Optimum onset synchronous in Pacific and Indian Oceans.•Miocene Climatic Optimum hyperthermals coupled to acidic and suboxic deep waters.•Marked improvement in Indian Ocean deep water oxygenation after ~13.5 Ma.
Environmental conditions in one of Earth's most densely populated regions, East Asia, are dominated by the monsoon. While Quaternary monsoon variability is reasonably well understood, pre-Quaternary ...monsoon variability and dynamics remain enigmatic. In particular, little is known about potential relationships between northern hemispheric monsoon response and major Cenozoic changes in Antarctic ice cover. Here we document long-term East Asian summer monsoon (EASM) intensification through the Late Miocene–Pliocene (∼8.2 to 2.6 Ma), and attribute this to progressive Antarctic glaciation. Our new high-resolution magnetic records of long-term EASM intensification come from the Late Miocene–Pliocene Red Clay sequence on the Chinese Loess Plateau; we identify underlying mechanisms using a numerical climate-model simulation of EASM response to an idealized stepwise increase in Antarctic ice volume. We infer that progressive Antarctic glaciation caused intensification of the cross-equatorial pressure gradient between an atmospheric high-pressure cell over Australia and a low-pressure cell over mid-latitude East Asia, as well as intensification of the cross-equatorial sea-surface temperature (SST) gradient. These combined atmospheric and oceanic adjustments led to EASM intensification. Our findings offer a new and more global perspective on the controls behind long-term Asian monsoon evolution.
•Improved magnetochronology for the Shilou Red Clay on the Chinese Loess Plateau.•New magnetic records of the Late Miocene–Pliocene East Asian Summer monsoon.•East Asian Summer monsoon intensity increases progressively from ∼8 to 2.6 Ma.•Asian monsoon intensification is attributed to increased Antarctic glaciation.
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