Continental red beds, widely formed at various geologic timescales, are sedimentary rocks and sediments with red as the main color. Geoscientists have analyzed the geomorphology, paleomagnetism, paleoenvironments, paleontology, energy, and minerals in continental red beds. Despite the agreement that fine-grained hematite is closely related to the color of continental red beds, controversies and problems still exist regarding the micro-mechanism of their formation. As a review, this paper details the composition and color properties of pigmentation in red beds, analyzes the existence and distribution of authigenic hematite, and summarizes the iron sources and the formation of hematite. In addition, we introduce the fading phenomenon observed in continental red beds, including three types of secondary reduction zones: reduction spots, reduction strips, and reduction areas. Lastly, this paper summarizes the evolution of color in continental red beds, emphasizes the relationship between authigenic hematite and the diagenetic environment, and proposes possible research directions for future red bed-related issues.

The Pearl River Delta (PRD, China) has undergone complex geological development within a multi-island faulted basin, shaped by the interplay of regional tectonic movements, Quaternary sea-level fluctuations, and fluvial-marine interactions. Despite a great number of studies on the Holocene sedimentary sequences and spatial differences of lithofacies and environments, scant attention has been paid to the overarching human influence on deltaic evolution and coastline modifications since the Neolithic epoch. To further elucidate the spatial variation in Holocene sedimentation and its underlying basement topography shaped during the Last Glacial Maximum (LGM), we compiled a comprehensive dataset incorporating borehole data from over 2800 cores (the maximum depth can reach 92.5 m) within the PRD. Subsequently, high-resolution isobath maps of Quaternary deltaic deposits were generated, offering unprecedented insights into sediment distribution. This dataset facilitated a nuanced reconstruction of pre-Holocene topography, revealing a zone characterized by elongated, deep-incised valleys governed by NW-SE fault orientations. Further, we delineated coastline shifts since the period of maximum Holocene transgression (~7000 years BP), contributing to an enhanced understanding of the formation and evolutionary patterns of the delta and river network oscillations. Our findings illuminate an increasing anthropogenic impact on the rate of fluvial sedimentation and land growth, particularly accentuated over the last two millennia, favoring deltaic accretion.

Sedimentary facies color is an important paleoclimate indicator, but may be unreliable in thick continental red beds. The Danxia Formation is the landscape strata of the Danxia basin, and its color fluctuates between reddish-brown and reddish-purple vertically. This study examined the ferric oxides characteristics, distribution, and mineral composition of the Danxia Formation using a variety of analytical techniques, including optical microscopy, high-resolution scanning electron microscopy, electron probe microanalysis, X-ray diffraction, and micro-Raman spectroscopy. The results indicate that the reddish-brown mineral is composed primarily of fine hematite with traces of goethite, while the reddish-purple mineral consists solely of fine hematite. These hematites exhibit a particle size range of submicron to micron and display various morphologies, including spherical, flake, and fibrous forms. Goethite particles are needle-shaped and often form star-shaped aggregates containing twins. Whole rock geochemical analysis reveals a strong positive correlation between iron and iron group elements, as well as phosphorus and rare earth elements. The findings suggest that the reddening of the Danxia Formation occurs during diagenesis, with fine hematite forming as a result of the alteration of iron-bearing detrital grains. In addition, vertical color variations in Danxia Formation are not attributable to the paleoclimate records, but rather the result of the differentiation of sediment sources. This study provides a novel viewpoint for examining the coloration of thick continental red beds in other regions.

The Pearl River Delta (PRD) has undergone complex geological development within a multi-island faulted basin, shaped by the interplay of regional tectonic movements, Quaternary sea-level fluctuations, and fluvial-marine interactions. Despite a great number of studies on the Holocene sedimentary sequences and spatial difference of lithofacies and environments, scant attention has been paid to the overarching human influence on deltaic evolution and coastline modifications since the Neolithic epoch. To further elucidate the spatial variation in Holocene sedimentation and its underlying basement topography shaped during the Last Glacial Maximum (LGM), we compiled a comprehensive dataset incorporating borehole data from over 2,800 cores within the PRD. Subsequently, high-resolution isobath maps of Quaternary deltaic deposits were generated, offering unprecedented insights into sediment distribution. This dataset facilitated a nuanced reconstruction of pre-Holocene topography, revealing a zone characterized by elongated, deep-incised valleys governed by NW-SE fault orientations. Further, we delineated coastline shifts since the period of maximum marine transgression (~7000 years BP), contributing to an enhanced understanding of the formation and evolutionary patterns of the delta and the river network oscillations. Our findings illuminate increasing anthropogenic impact on the rate of fluvial sedimentation and land growth, particularly accentuated over the last two millennia, favoring deltaic accretion. The current study has considerable implications for understanding the dynamic interplay between land-sea interactions and anthropogenic activities in shaping the delta, and stands to significantly inform land and resource management strategies, as well as future urban planning within the delta's bay areas.

Southeast Asia’s biodiversity refugia, shaped by Neogene–Quaternary climatic shifts and the Tibetan Plateau uplift, preserve relict lineages like Exbucklandia (Hamamelidaceae). Once widespread across ancient continents, this genus now survives in Asian montane forests, offering insights into angiosperm diversification. Chloroplast haplotypes formed three clades—Clade I (E. tricuspis), Clade II (E. populnea), and Clade III (E. tonkinensis)—with E. longipetala haplotypes nested within II/III. Nuclear microsatellites (SSRs) identified two ancestral gene pools: E. populnea and E. tricuspis showed predominant ancestry in Pool A, while E. tonkinensis and E. longipetala were primarily assigned to Pool B. All taxa exhibited localized genetic admixture, particularly in sympatric zones. Divergence dating traced the genus’ origin to tropical Asia, with northward colonization of subtropical China ~7 Ma yielding E. populnea and E. tonkinensis. Quaternary Glacial Cycles triggered southward expansions, chloroplast capture, and localized hybridization. Morphological, nuclear, and plastid molecular evidence supports reclassifying E. longipetala as E. populnea × E. tonkinensis hybrids lacking genetic cohesion and E. tricuspis as a distinct species with a mixed nuclear composition. This study highlights how paleoclimate-driven gene flow shaped the phylogeography of relict taxa in Southeast Asia and the urgency of habitat restoration to conserve Exbucklandia.