Journal of Palaeogeography最新文献

The coastal plain of Laizhou Bay in Bohai Sea is a transitional area of land–sea interaction. Sediments in this area can bear significant information of sea-level fluctuation, climate change, as well as regional geological setting. Here, in this study, new sporopollen data from three boreholes (GK138, GK111 and GK95) in the coastal plain of Laizhou Bay, Bohai Sea were investigated, and the pollen spectrum since the late middle Pleistocene was established as six sporopollen assemblage zones (I–VI), i.e., Pinus–Quercus–Artemisia, Gramineae–Artemisia–Chenopodiaceae, Picea–Pinus–Quercus–Artemisia, Picea–Pinus–Betula–Gramineae–Artemisia, Picea–Pinus–Cupressaceae–Chenopodiaceae and Pinus–Quercus–Gramineae–Artemisia–Chenopodiaceae. Combining with existing sedimentary successions and detailed radiocarbon dating results of the sediments from the three boreholes, paleovegetation and climatic evolution since the late middle Pleistocene were reconstructed. The findings revealed that climatic changes in this area since the late middle Pleistocene were characterized by alternating cold-arid and warm-humid conditions, which were well correlated with marine isotopic stages (MIS). The present study offers specific insight into the climatic dynamics in the North China Plain since the late middle Pleistocene and provides evidence of a clear link among the palynoflora in the area, the glacial–interglacial period climate-driven sea-level changes, and the marine δ¹⁸O records.

Studying the grain-size dependent compositional variability in modern river sediments provides a key to decipher the information stored in the sedimentary archive and reconstruct the evolution of the Earth's surface in the past. Bedload sand along the Xigaze cross section of the Yarlung Tsangpo (upper Brahmaputra River) ranges in mean grain size from 0.72 Φ to 3.21 Φ, is moderately to poorly sorted and slightly platykurtic to moderately leptokurtic with sub-angular to sub-spherical grains. Litho-feldspatho-quartzose to feldspatho-litho-quartzose sand (Q 43%–65%; F 13%–44%; L 11%–28%) contains 3.4%–14.4% heavy minerals including amphibole (64%–89%), epidote (4%–11%), chloritoid (0–10%), and clinopyroxene (2%–6%). The marked textural and compositional variability observed across the Xigaze transect of the Yarlung Tsangpo mainstem is controlled by both fluvial and aeolian processes, including repeated reworking by westerly and glacial winds, as well as by local contributions from northern and southern tributaries draining the Lhasa Block and the Himalayan Belt, respectively. The modern sedimentary case here will shed new light on interpreting paleogeography and provenance.

Representatives of the subfamily Lonsdaleiinae Chapman, 1893 are common in the Mississippian of the western Palaeotethys. A general analysis of the origin, distribution and evolution of that subfamily has been undertaken. The most probable hypothesis for the origin of the genus Lonsdaleia McCoy, 1849 is to acquire colonialism via the genus Axophyllum Milne Edwards and Haime, 1851. Actinocyathus d’Orbigny, 1849 would be a descendant of Lonsdaleia by increasing integration in the colonies. The first occurrences of Lonsdaleia have been recorded in the lower Visean from northern Britain and northern Tianshan Mountains of northwestern China, but the diversification and migration to the whole Palaeotethys only happened in the late Visean. Three hypotheses are proposed on that matter. The Serpukhovian was also a period of migrations and diversification for these genera. Both Lonsdaleia and Actinocyathus have been recorded in Bashkirian refuges, the Sverdrup Basin in northern Laurasia and the Tindouf Basin in northern Africa, respectively. The division of the western Palaeotethys into six subprovinces based on the distribution of corals is proposed.

Postmiogypsinella intermedia Sirel and Gedik, 2011 is reported for the first time from the shallow-marine limestones of the upper Chattian Qom Formation, Central Iran. This miogypsinid species has so far only been recorded from the upper Oligocene of Malatya (type locality) and Sivas (Central Anatolia) in eastern Turkey and from the upper Oligocene of the Prebetic Domain, SE Spain. The new record from Central Iran, paleobiogeographically located at the Eurasian margin of the Tethyan Seaway between the Western and Eastern Tethys realms, indicates that the paleogeographic distribution of this species has to be extended eastwards as far as Central Iran. This observation is not unexpected, since miogypsinid foraminifers with eccentric embryonic–nepionic apparatus (e.g., Miogypsinella, Miogypsinoides, Miogypsina) are usually widely distributed. The accompanying larger benthic foraminifera, including Miogypsinoides complanatus (Schlumberger), Miogypsinoides formosensis Yabe and Hanzawa, Spiroclypeus margaritatus (Schlumberger), Operculina complanata (Defrance), and Risananeiza pustulosa Boukhary et al., indicate the late Chattian age (corresponding to SBZ 23 Biozone). Postmiogypsinella intermedia is indicative of a shallow-marine middle ramp environment with oligotrophic conditions and inhabited the relatively deeper part of the photic zone.

Protolepidodendralean lycopsids are characteristic of morphologically complex leaves. Most taxa of this group are herbaceous and widely distributed in global Devonian sediments, with exceptions of a few members, such as Frenguellia eximia from the Lower Carboniferous of Argentina. In this study, we focus on the morphology of Frenguellia eximia and emend its generic and specific diagnoses, based on new materials from the Upper Devonian Hongguleleng Formation of West Junggar, Xinjiang Uygur Autonomous Region, Northwest China, within the fossil-bearing bed palynologically dated as a latest Famennian age. This is the first finding of Frenguellia eximia out of Gondwana. Frenguellia eximia bears planate leaf with three upward pairs of lateral tips, isomorphic sporophyll to the leaf, and elongated, oval sporangium. Leaf morphology of the members of the Order Protolepidodendrales is summarized and classified into lateral-tip and distal-tip types. Lateral-tip type leaf consists of an obvious main body and several paired lateral tips, whereas distal-tip type leaf shows a petiole and a distal lamina with several planate or three-dimensional segments. Two leaf types probably indicate two independent evolutionary routes of microphylls evolving from simple leaf of pre-lycopsids during the Devonian period. The new occurrence of Frenguellia eximia further shows paleophytogeographical similarities between West Junggar and northwestern Gondwana.

Tectonic activity and sediment supply have significantly affected the rifted basin fillings and hydrocarbon accumulations. The Huanghekou Sag in the southeastern Bohai Bay Basin is a hydrocarbon rich sag and was bounded by the Bonan Uplift to the north in the Paleogene, which strongly affected sediment disribution and hydrocarbon accumulation in this region. The sediment supply mechanism of the Paleogene parent rocks in this area has not been revealed yet. Therefore, the Huanghekou Sag is a natural laboratory to reveal the relationship between the tectonic activties and hydrcoarbon accumulations in a rifted basin. In this study, the tectonic evolution characteristics of the Bonan Uplift in different geological periods are revealed during the main fault depression periods. Then, the direction of the provenance and distribution of the depositional system of the Bonan Uplift are analyzed based on the sedimentary system and mineralogy analysis. Finally, the sediment supply in the Bonan Uplift in different geological periods has been systematically studied. The results indicated that sediment supply is the dominant factor of hydrocarbon accumulation in the Paleogene in the Huanghekou Sag. During the Paleocene-Middle Eocene, extensive denudation occurred in the Bonan Uplift, sediments were mainly sourced from the Bonan Uplift in the northern margin of the Huanghekou Sag. During the Late Eocene to Early Oligocene, the Bonan Uplift had a large angle rotation and subsidence due to the strong rifting of the Bozhong Sag in the north, and the sand supply capacity was seriously reduced. Due to the different sediment supply in different geological periods, high quality reservoir and cap conditions were formed in the Paleogene in the central and northern parts of the Huanghekou Sag, which is conducive to the accumulation and preservation of oil and gas.

Many aspects of the Late Ordovician Mass Extinction (LOME) aftermath and recovery have been puzzling due to heterogeneities in tempo and triggering mechanisms. Benthic fossil groups, which are the most severely affected by oxidative stress, offer the best opportunities for understanding both biological and ecological recovery after the LOME. In recent studies, deep-water sponge assemblages (which may have had high physiological tolerance to oxygen deviations) have been reported widely across South China in the immediate aftermath of the extinction interval. In order to further explore the lateral and temporal distributions of sponges, and ecological effects of benthic recovery during this critical interval, this study presents new Llandovery sponge assemblages recovered from two sections in Hunan Province, South China, accompanied by geochemical analyses. The sponge communities are preserved by pyritic spicule replacements and shows a relatively deep-water affinity (estimated around 60–150 m in depth) comparable to several previously reported assemblages in South China, and consistent with the observed graptolite ecology. Geochemical analysis of total organic carbon (TOC) and major and trace element composition in both sections show similar trends, indicating a shift in redox state of the bottom-water from persistent anoxia or intermittent euxinia in the earliest Rhuddanian, becoming oxygenated in the early Aeronian. Based on the present study and previous biological and geochemical data from South China, the distribution of early Silurian sponge assemblages in South China demonstrates a gradual expansion towards deeper regions when ocean redox conditions ameliorated. This study confirms the continuity of the end-Ordovician sponge faunas and taxa, both laterally across South China, and temporally through the early Silurian. The pioneering colonization of sponges in low-oxygen environments after the LOME may have set the stage for the subsequent recovery of other benthic organisms.

Celadonite and glauconite are comparable in terms of physical, chemical and mineralogical characteristics. Formation of both these minerals requires slightly oxygen-depleted conditions in a semi-confined micro-environment, facilitating the uptake of Fe into the structure. Although glauconite is ubiquitous in marine deposits, celadonite forms in both marine and non-marine environments, more commonly by altering intermediate to mafic rocks. A review of data across the geological column shows that both these minerals are more common in the Mesozoic and Cenozoic, which may be related to extensive volcanism. The composition of celadonite and glauconite is highly variable and is controlled by the availability of cations within the pore water micro-environment. The major element composition of celadonite overlaps with that of evolved to highly evolved glauconite to a large extent. Existing data and representative samples of celadonite and glauconite reveal subtle differences in X-ray diffraction parameters and Fourier transform infrared (FTIR) spectra. Celadonite shows sharper basal and hkl reflections than glauconite. It characteristically exhibits distinct 11 $\overline{1}$–021, 003–022, 023 and 130–13 $\overline{1}$, and 060 reflections at less than 1.51 Å, indicating a better-ordered crystallographic structure than glauconite. The FTIR spectra of celadonite and glauconite show similar absorption bands although Si–O bending, Si–O stretching and OH–stretching bands are sharper and well resolved in celadonite than that of glauconite. For palaeoenvironmental interpretations, it is, therefore, necessary to examine the subtle differences in X-ray diffraction parameters and FTIR spectra to confirm the identification of these two minerals. The composition of celadonite relates closely to the host rock and depositional environment. The celadonite associated with mafic rock shows relatively high Fe, Mg and low Al contents. In contrast, those associated with felsic to intermediate composition rocks show slightly higher contents of Al and lower content of Fe, Mg. The mineral chemistry of celadonite varies from marine to continental settings. Marine celadonite contains higher Fe, Mg and lesser Al than their non-marine counterpart. Celadonite with relatively higher Al may show slightly lower interlayer K than Fe and Mg-rich celadonite for charge balancing.

The Early Permian bauxite in the Sichuan Basin is an important part of karst-type bauxite deposits in South China Block and its provenance is poorly understood. Here we present results of mineralogy, whole-rock geochemistry, detrital zircon U–Pb ages and trace element compositions of the bauxitic claystone from the Lower Permian Dazhuyuan Formation and those of the siltstone from the underlying Lower Silurian Hanjiadian Formation in Huayingshan region, Sichuan Basin, South China Block to constrain the provenance of the bauxitic claystone. Detrital zircons from bauxitic claystone and siltstone have similar age spectra, and the ages of bauxitic claystone are classified into five groups of 2600–2200 Ma, 1800–1600 Ma, 1200–900 Ma, 900–650 Ma, and 650–400 Ma respectively. Those of the siltstone are classified into four groups of 2600–2200 Ma, 1200–900 Ma, 900–650 Ma, and 650–400 Ma respectively. We propose that the bauxitic claystone in the study region has mixed sources: the siltstone of the Lower Silurian Hanjiadian Formation probably constitutes the dominant source, and the Late Paleoproterozoic magmatic rocks along the western margin of the Yangtze Block are probably the secondary source. Moreover, the source materials of the Hanjiadian Formation siltstone are mainly sourced from Grenville-aged magmatic rocks in the Cathaysia Block and Neoproterozoic magmatic rocks in the Jiangnan orogen, with minor contributions from the underlying clastic sediments in the Cathaysia Block and Pan-African magmatic rocks in the orogen in eastern Gondwana.