Pub Date : 2024-09-30DOI: 10.1016/j.palaeo.2024.112526
Hao Yun , Xingliang Zhang , Joachim Reitner
Well-preserved, distinctive columnar microbialites were discovered in the Wirrealpa Limestone (Stage 4, Series 2 of Cambrian) of South Australia. However, further studies are still required to unveil the microstructure and formation process of these microbialites. A microbial buildup from the Wirrealpa Limestone examined herein suggests that the microbialitic columns are composed of densely-distributed, polymorphic, and patched fabrics produced by microbes. These fabrics are inter-framed by packstone sediments that characterized by calcareous metazoan skeletons and cerebroid ooids. The patched fabrics can be categorized into three types: 1) laminated ‘patches’, 2) homogeneous microsparitic ‘patches’ (mesoclots), and 3) cemented ‘patches’ containing tightly-packed chancelloriid sclerites. There are two preservational conditions of chancelloriid sclerites. After death of the chancelloriid individuals (belonging to Chancelloria and rare Allonnia) that dwelled among or near the microbial reef, abundant sclerites were exfoliated, transported, and concentrated. Then, some of them were cemented by microbial communities, forming the third type ‘patches’, while others were accumulated in the packstones within reefal cavities and inter-framework space along with many skeletal fragments from trilobites and mollusks. Thus, this lower Cambrian thrombolite-stromatolite complex was formed within an ecosystem lacking archaeocyaths but dominated by microbes (reef builders) and chancelloriids (reef dwellers).
{"title":"Microstructure and chancelloriid sclerites within a microbial buildup of the Wirrealpa Limestone (Cambrian Stage 4), South Australia","authors":"Hao Yun , Xingliang Zhang , Joachim Reitner","doi":"10.1016/j.palaeo.2024.112526","DOIUrl":"10.1016/j.palaeo.2024.112526","url":null,"abstract":"<div><div>Well-preserved, distinctive columnar microbialites were discovered in the Wirrealpa Limestone (Stage 4, Series 2 of Cambrian) of South Australia. However, further studies are still required to unveil the microstructure and formation process of these microbialites. A microbial buildup from the Wirrealpa Limestone examined herein suggests that the microbialitic columns are composed of densely-distributed, polymorphic, and patched fabrics produced by microbes. These fabrics are inter-framed by packstone sediments that characterized by calcareous metazoan skeletons and cerebroid ooids. The patched fabrics can be categorized into three types: 1) laminated ‘patches’, 2) homogeneous microsparitic ‘patches’ (mesoclots), and 3) cemented ‘patches’ containing tightly-packed chancelloriid sclerites. There are two preservational conditions of chancelloriid sclerites. After death of the chancelloriid individuals (belonging to <em>Chancelloria</em> and rare <em>Allonnia</em>) that dwelled among or near the microbial reef, abundant sclerites were exfoliated, transported, and concentrated. Then, some of them were cemented by microbial communities, forming the third type ‘patches’, while others were accumulated in the packstones within reefal cavities and inter-framework space along with many skeletal fragments from trilobites and mollusks. Thus, this lower Cambrian thrombolite-stromatolite complex was formed within an ecosystem lacking archaeocyaths but dominated by microbes (reef builders) and chancelloriids (reef dwellers).</div></div>","PeriodicalId":19928,"journal":{"name":"Palaeogeography, Palaeoclimatology, Palaeoecology","volume":"655 ","pages":"Article 112526"},"PeriodicalIF":2.6,"publicationDate":"2024-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142416824","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-30DOI: 10.1016/j.palaeo.2024.112525
Gaojie Li , Guoqing Xia , Changjun Ji , Michael Wagreich , James G. Ogg , Haisheng Yi
A composite eastern Tethyan oxygen and carbon isotope curve reveals major climate changes through the Late Jurassic. Despite significantly lower values and different amplitudes in scale, the δ18O data from whole-rock carbonates present fluctuant temperature results similar with well-studied composite δ18O curves of diagenetically-screened biogenic calcites, and are possibly acceptable as a paleotemperature proxy. The paleoclimate trends imply a cool global Callovian-Oxfordian transition, a mid-Oxfordian warming, a late Oxfordian cooling, a turbulent Kimmeridgian climate, a warm earliest Tithonian and rapid early Tithonian cooling event. The climate shift from the earliest Tithonian warmth to the middle early Tithonian cool climate was up to 8 °C decrease in some regions. These paleoclimate changes are greatly consistent with the eustatic sea-level changes, biological evolutions and paleoatmospheric CO2 reconstructions, and are recorded by coeval carbon isotope perturbations relating to the organic carbon accumulations in marine sediments. Coupled δ18O and δ13C chemostratigraphy evidence that higher temperatures lead to more rapid continental weathering, increased nutrient-rich runoff into the oceans, and intensified marine productivity, resulting in increased organic‑carbon burial and more positive δ13C values in limestones. The decrease in primary productivity and burial rates during cooling periods is, in turn, commonly accompanied by low δ13C values.
{"title":"Late Jurassic paleoenvironmental reconstruction based on stable oxygen isotopes in bulk carbonates from the Qiangtang Basin, eastern Tethys","authors":"Gaojie Li , Guoqing Xia , Changjun Ji , Michael Wagreich , James G. Ogg , Haisheng Yi","doi":"10.1016/j.palaeo.2024.112525","DOIUrl":"10.1016/j.palaeo.2024.112525","url":null,"abstract":"<div><div>A composite eastern Tethyan oxygen and carbon isotope curve reveals major climate changes through the Late Jurassic. Despite significantly lower values and different amplitudes in scale, the δ<sup>18</sup>O data from whole-rock carbonates present fluctuant temperature results similar with well-studied composite δ<sup>18</sup>O curves of diagenetically-screened biogenic calcites, and are possibly acceptable as a paleotemperature proxy. The paleoclimate trends imply a cool global Callovian-Oxfordian transition, a mid-Oxfordian warming, a late Oxfordian cooling, a turbulent Kimmeridgian climate, a warm earliest Tithonian and rapid early Tithonian cooling event. The climate shift from the earliest Tithonian warmth to the middle early Tithonian cool climate was up to 8 °C decrease in some regions. These paleoclimate changes are greatly consistent with the eustatic sea-level changes, biological evolutions and paleoatmospheric CO<sub>2</sub> reconstructions, and are recorded by coeval carbon isotope perturbations relating to the organic carbon accumulations in marine sediments. Coupled δ<sup>18</sup>O and δ<sup>13</sup>C chemostratigraphy evidence that higher temperatures lead to more rapid continental weathering, increased nutrient-rich runoff into the oceans, and intensified marine productivity, resulting in increased organic‑carbon burial and more positive δ<sup>13</sup>C values in limestones. The decrease in primary productivity and burial rates during cooling periods is, in turn, commonly accompanied by low δ<sup>13</sup>C values.</div></div>","PeriodicalId":19928,"journal":{"name":"Palaeogeography, Palaeoclimatology, Palaeoecology","volume":"655 ","pages":"Article 112525"},"PeriodicalIF":2.6,"publicationDate":"2024-09-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142416822","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-29DOI: 10.1016/j.palaeo.2024.112521
Xinwei Chen , Hanlin Chen , Xiubin Lin , Xiaogan Cheng , Chao Chen , Johannes Rembe , Hao Zou
Understanding the late Cenozoic temporal and spatial development of northeastern Pamir and the west Kunlun Mountains (WKMs) is critical for our knowledge of intracontinental orogeny in Central Asia. In this study, sedimentary analyses and anisotropy of magnetic fabrics (AMF) studies were conducted in four sections along the foreland of the northeastern Pamir and the WKMs. Combined with the results of previous researches, our AMF and sedimentological results reveal a shift in paleocurrent directions from variable azimuths in the Kelizuoyi Formation to northward-directed azimuths in the upper strata in the Kekeya, Keliyang and Keyikejia sections, suggesting a gradually northward migration of the WKMs and its foreland basin. Since the early Miocene, the prevailing drainage systems in the Aertashi and Paojianggou sections have been mainly controlled by the northeastern Pamir and the drainage systems in the Kekeya, Keliyang and Keyikejia sections were controlled by the uplift of the WKMs. The constant paleocurrent and regional strain directions in the Paojianggou section support a pre-existing arcuate Pamir since the early Miocene. Under these circumstances, the evolution of late Cenozoic sediment succession and the characteristics of the AMF in the Paojianggou section were mainly controlled by crustal thickening and exhumation of the Pamir.
{"title":"Late Cenozoic deformation of the northeastern Pamir and the west Kunlun Mountains: Insights from anisotropy of magnetic fabrics and sedimentary analysis","authors":"Xinwei Chen , Hanlin Chen , Xiubin Lin , Xiaogan Cheng , Chao Chen , Johannes Rembe , Hao Zou","doi":"10.1016/j.palaeo.2024.112521","DOIUrl":"10.1016/j.palaeo.2024.112521","url":null,"abstract":"<div><div>Understanding the late Cenozoic temporal and spatial development of northeastern Pamir and the west Kunlun Mountains (WKMs) is critical for our knowledge of intracontinental orogeny in Central Asia. In this study, sedimentary analyses and anisotropy of magnetic fabrics (AMF) studies were conducted in four sections along the foreland of the northeastern Pamir and the WKMs. Combined with the results of previous researches, our AMF and sedimentological results reveal a shift in paleocurrent directions from variable azimuths in the Kelizuoyi Formation to northward-directed azimuths in the upper strata in the Kekeya, Keliyang and Keyikejia sections, suggesting a gradually northward migration of the WKMs and its foreland basin. Since the early Miocene, the prevailing drainage systems in the Aertashi and Paojianggou sections have been mainly controlled by the northeastern Pamir and the drainage systems in the Kekeya, Keliyang and Keyikejia sections were controlled by the uplift of the WKMs. The constant paleocurrent and regional strain directions in the Paojianggou section support a pre-existing arcuate Pamir since the early Miocene. Under these circumstances, the evolution of late Cenozoic sediment succession and the characteristics of the AMF in the Paojianggou section were mainly controlled by crustal thickening and exhumation of the Pamir.</div></div>","PeriodicalId":19928,"journal":{"name":"Palaeogeography, Palaeoclimatology, Palaeoecology","volume":"655 ","pages":"Article 112521"},"PeriodicalIF":2.6,"publicationDate":"2024-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142359697","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-27DOI: 10.1016/j.palaeo.2024.112522
Salma Aboutofail, Hamid Slimani
Palynological research, carried out in the Paleocene–Eocene transition of the Sekada section, Tangier Unit (western External Rif, northwestern Morocco), revealed the presence of a palynological content composed essentially of dinoflagellate cysts (dinocysts), phytoclasts and amorphous organic matter (AOM). Their qualitative and quantitative analyses allowed a detailed biostratigraphic interpretation, a reconstruction of the paleoenvironment and paleoclimate and identification of the Paleocene–Eocene Thermal Maximum (PETM) interval in the Sekada section.
Thanetian and Ypresian ages, previously assigned respectively to the grey-brown marls and the marly limestones in the studied section are here revised based on several marker dinocyst events. Acmes of the subtropical dinocyst Apectodinium spp. (in particular, Apectodinium homomorphum), recorded along the analyzed interval, represent a response to the global warming of the PETM, and therefore support the assignment of this interval to the Paleocene–Eocene transition.
Quantitative analyses of the main constituents of kerogen (dinocysts, phtoclasts, AOM) and selected dinocyst groups, which are previously considered in the literature as environmental markers, generally suggest a proximal (coastal eutrophic) depositional environment. Furthermore, quantitative fluctuations in the heterotrophic dinocyst Apectodinium and open marine autotrophic dinocysts versus total dinocysts, and in phytoclasts, AOM and palynomorphs versus total kerogen appear to be controlled by fluctuations in terrestrial inputs, which are most likely related to climate changes.
{"title":"The Paleocene–Eocene Thermal Maximum (PETM) interval in the southwestern Mediterranean Tethys at Morocco: New data from a high-resolution study of dinoflagellate cysts and palynofacies in the Rif Chain","authors":"Salma Aboutofail, Hamid Slimani","doi":"10.1016/j.palaeo.2024.112522","DOIUrl":"10.1016/j.palaeo.2024.112522","url":null,"abstract":"<div><div>Palynological research, carried out in the Paleocene–Eocene transition of the Sekada section, Tangier Unit (western External Rif, northwestern Morocco), revealed the presence of a palynological content composed essentially of dinoflagellate cysts (dinocysts), phytoclasts and amorphous organic matter (AOM). Their qualitative and quantitative analyses allowed a detailed biostratigraphic interpretation, a reconstruction of the paleoenvironment and paleoclimate and identification of the Paleocene–Eocene Thermal Maximum (PETM) interval in the Sekada section.</div><div>Thanetian and Ypresian ages, previously assigned respectively to the grey-brown marls and the marly limestones in the studied section are here revised based on several marker dinocyst events. Acmes of the subtropical dinocyst <em>Apectodinium</em> spp. (in particular, <em>Apectodinium homomorphum</em>), recorded along the analyzed interval, represent a response to the global warming of the PETM, and therefore support the assignment of this interval to the Paleocene–Eocene transition.</div><div>Quantitative analyses of the main constituents of kerogen (dinocysts, phtoclasts, AOM) and selected dinocyst groups, which are previously considered in the literature as environmental markers, generally suggest a proximal (coastal eutrophic) depositional environment. Furthermore, quantitative fluctuations in the heterotrophic dinocyst <em>Apectodinium</em> and open marine autotrophic dinocysts versus total dinocysts, and in phytoclasts, AOM and palynomorphs versus total kerogen appear to be controlled by fluctuations in terrestrial inputs, which are most likely related to climate changes.</div></div>","PeriodicalId":19928,"journal":{"name":"Palaeogeography, Palaeoclimatology, Palaeoecology","volume":"655 ","pages":"Article 112522"},"PeriodicalIF":2.6,"publicationDate":"2024-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142359696","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-27DOI: 10.1016/j.palaeo.2024.112524
Olmo Miguez-Salas , Francisco J. Rodríguez-Tovar , Javier Dorador , Brian J. Bett , Miros S.J. Charidemou , Jennifer M. Durden
Ichnological research has generally assumed that abyssal plains are dominated by quiescent, homogenous environmental conditions. Thus, deep-sea trace fossil assemblage changes have been usually linked to significant spatial and temporal environmental variations. Here, we conducted a comparative ichnological analysis between a small abyssal hill (50 m elevation) and the surrounding abyssal plain; this modest bathymetric variation is known to generate substantial environmental heterogeneity for the benthic fauna community of the Porcupine Abyssal Plain (c. 4850 m depth), Northeast Atlantic. Based on X-ray data from a 5 × 5 core grid emplaced in two box cores, we compared hill and plain bioturbational sedimentary structures, including trace fossil assemblages (e.g., ichnotaxonomy) and biodeformational structures (e.g., mixed-layer depth). We observed that topographically-enhanced near-bottom currents over the hill likely produce significant changes in depositional dynamics and sediment properties (e.g., grain size, organic matter content and degradation), and control specificities of bioturbational sedimentary structures (e.g., trace fossils, mixed layer attributes such as thickness, mottled background, discrete traces). Palaeoichnological data suggested that the abyssal plain had experienced consistent conditions during the last thousands of years while the abyssal hill recorded improving environmental conditions for the trace maker community. Our results highlight the complexity of the deep-sea environment, demonstrating that small changes in bioturbated sedimentary assemblages appear even within the same box core (m-scale), and that substantial changes can occur due to environmental heterogeneity (e.g., subtle topographic variations) at the local scale (km-scale). Considering the vast global extent of abyssal hill terrain, we suggest that their influence on the bioturbational sedimentary record may be significantly under-appreciated and require more attention in palaeoenvironmental reconstructions.
{"title":"Small topographical variations controlling trace maker community: Combining palaeo- and neoichnological data at the Porcupine Abyssal Plain","authors":"Olmo Miguez-Salas , Francisco J. Rodríguez-Tovar , Javier Dorador , Brian J. Bett , Miros S.J. Charidemou , Jennifer M. Durden","doi":"10.1016/j.palaeo.2024.112524","DOIUrl":"10.1016/j.palaeo.2024.112524","url":null,"abstract":"<div><div>Ichnological research has generally assumed that abyssal plains are dominated by quiescent, homogenous environmental conditions. Thus, deep-sea trace fossil assemblage changes have been usually linked to significant spatial and temporal environmental variations. Here, we conducted a comparative ichnological analysis between a small abyssal hill (50 m elevation) and the surrounding abyssal plain; this modest bathymetric variation is known to generate substantial environmental heterogeneity for the benthic fauna community of the Porcupine Abyssal Plain (c. 4850 m depth), Northeast Atlantic. Based on X-ray data from a 5 × 5 core grid emplaced in two box cores, we compared hill and plain bioturbational sedimentary structures, including trace fossil assemblages (e.g., ichnotaxonomy) and biodeformational structures (e.g., mixed-layer depth). We observed that topographically-enhanced near-bottom currents over the hill likely produce significant changes in depositional dynamics and sediment properties (e.g., grain size, organic matter content and degradation), and control specificities of bioturbational sedimentary structures (e.g., trace fossils, mixed layer attributes such as thickness, mottled background, discrete traces). Palaeoichnological data suggested that the abyssal plain had experienced consistent conditions during the last thousands of years while the abyssal hill recorded improving environmental conditions for the trace maker community. Our results highlight the complexity of the deep-sea environment, demonstrating that small changes in bioturbated sedimentary assemblages appear even within the same box core (m-scale), and that substantial changes can occur due to environmental heterogeneity (e.g., subtle topographic variations) at the local scale (km-scale). Considering the vast global extent of abyssal hill terrain, we suggest that their influence on the bioturbational sedimentary record may be significantly under-appreciated and require more attention in palaeoenvironmental reconstructions.</div></div>","PeriodicalId":19928,"journal":{"name":"Palaeogeography, Palaeoclimatology, Palaeoecology","volume":"655 ","pages":"Article 112524"},"PeriodicalIF":2.6,"publicationDate":"2024-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142416850","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-26DOI: 10.1016/j.palaeo.2024.112514
Kaiyu Cao , Lin Chen , Yongxiu Lu , Yao Zhang , Mengjing Li , Duo Wu , Yilong Wang , Liang Chen , Xiaonan Zhang , Rui Yang , Youliang Huang , Aifeng Zhou
The ecological evolution of lakes and their watersheds and the driving mechanisms are a key topic in paleoenvironmental research. However, the relative impacts of human activities and climate change on lake ecosystems since the last deglaciation remain unclear. We conducted a high-resolution study of the chain length distribution and concentration of n-alkanes in a sediment core from Lake Qilu in SW China, to reveal the ecological changes and their controlling factors since 14.6 cal kyr BP. Based on studies of modern samples, short-chain, medium-chain, and long-chain n-alkanes are associated with bacteria/algae, aquatic plants, and terrestrial plants, respectively. Combining the ACL17–33, Paq, and Σn-alkane indices, we found that both aquatic and terrestrial plants proliferated at Lake Qilu from 14.6 to 6 cal kyr BP, which was associated with a relatively warm and wet climate and dynamic strong winds. During the interval from 6 to 2 cal kyr BP, aquatic plants flourished, accompanied by a rapid surge in the regional productivity, primarily due to human activities. After 2 cal kyr BP, anthropogenic eutrophication was the primary cause of the increase in bacteria and algae populations. These results suggest that, before 6 cal kyr BP, climatic factors dominated the n-alkanes distribution; whereas after 6 cal kyr BP, human activities became the primary factor controlling the n-alkanes and ecological changes in Lake Qilu.
湖泊及其流域的生态演变及其驱动机制是古环境研究的一个重要课题。然而，自上一次冰期以来，人类活动和气候变化对湖泊生态系统的相对影响仍不清楚。我们对中国西南部齐鲁湖沉积物岩芯中的正构烷烃链长分布和浓度进行了高分辨率研究，以揭示自 14.6 cal kyr BP 以来的生态变化及其控制因素。根据对现代样本的研究，短链、中链和长链正构烷烃分别与细菌/藻类、水生植物和陆生植物有关。结合ACL17-33、Paq和Σn-烷烃指数，我们发现在14.6-6 cal kyr BP期间，齐鲁湖的水生植物和陆生植物都大量繁殖，这与相对温暖湿润的气候和动态强风有关。在公元前 6 千年至公元前 2 千年期间，水生植物蓬勃发展，伴随着区域生产力的迅速飙升，这主要是由于人类活动造成的。公元前 2 千年后，人为富营养化是细菌和藻类数量增加的主要原因。这些结果表明，在公元前 6 千年之前，气候因素主导着正构烷烃的分布；而在公元前 6 千年之后，人类活动成为控制齐鲁湖正构烷烃和生态变化的主要因素。
{"title":"Natural and anthropogenic forcing of ecological and environmental changes at Lake Qilu, SW China, since the last deglaciation","authors":"Kaiyu Cao , Lin Chen , Yongxiu Lu , Yao Zhang , Mengjing Li , Duo Wu , Yilong Wang , Liang Chen , Xiaonan Zhang , Rui Yang , Youliang Huang , Aifeng Zhou","doi":"10.1016/j.palaeo.2024.112514","DOIUrl":"10.1016/j.palaeo.2024.112514","url":null,"abstract":"<div><div>The ecological evolution of lakes and their watersheds and the driving mechanisms are a key topic in paleoenvironmental research. However, the relative impacts of human activities and climate change on lake ecosystems since the last deglaciation remain unclear. We conducted a high-resolution study of the chain length distribution and concentration of <em>n</em>-alkanes in a sediment core from Lake Qilu in SW China, to reveal the ecological changes and their controlling factors since 14.6 cal kyr BP. Based on studies of modern samples, short-chain, medium-chain, and long-chain <em>n</em>-alkanes are associated with bacteria/algae, aquatic plants, and terrestrial plants, respectively. Combining the ACL<sub>17–33</sub>, Paq, and Σ<em>n</em>-alkane indices, we found that both aquatic and terrestrial plants proliferated at Lake Qilu from 14.6 to 6 cal kyr BP, which was associated with a relatively warm and wet climate and dynamic strong winds. During the interval from 6 to 2 cal kyr BP, aquatic plants flourished, accompanied by a rapid surge in the regional productivity, primarily due to human activities. After 2 cal kyr BP, anthropogenic eutrophication was the primary cause of the increase in bacteria and algae populations. These results suggest that, before 6 cal kyr BP, climatic factors dominated the <em>n</em>-alkanes distribution; whereas after 6 cal kyr BP, human activities became the primary factor controlling the <em>n</em>-alkanes and ecological changes in Lake Qilu.</div></div>","PeriodicalId":19928,"journal":{"name":"Palaeogeography, Palaeoclimatology, Palaeoecology","volume":"655 ","pages":"Article 112514"},"PeriodicalIF":2.6,"publicationDate":"2024-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142416166","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-26DOI: 10.1016/j.palaeo.2024.112518
Caroline A.E. Strömberg , Beverly Z. Saylor , Russell K. Engelman , Angeline M. Catena , Daniel I. Hembree , Federico Anaya , Darin A. Croft
Miocene ecosystem change in the Central Andes is not well understood because of a dearth of well-dated fossil sites from the region. The late Middle Miocene (∼13–12 Ma) Quebrada Honda Basin (QHB) in southern Bolivia (22° S) helps fill this gap and provide vital insights into Neotropical paleoenvironments. The site is among the best-characterized Middle Miocene terrestrial vertebrate sites of South America and has a robust temporal, spatial, and lithostratigraphic framework for analyzing its sedimentary facies, fossils, and paleoenvironment. Here, we present new plant silica (phytolith) assemblage data from the QHB as well as new analyses of QHB faunal data. Phytolith assemblage data indicate two broad vegetation types: one suggestive of more open habitats (≥ 60% presumably open-habitat grasses) and the other of more closed habitats (typically dominated by potential bamboos and other forest indicators). Compositional overlap suggests that these vegetation types represent distinct plant communities within a broader biome that lacks an exact modern analog among studied Neotropical vegetation; however, it was likely akin to modern Neotropical semi-deciduous/dry forest to wooded savanna. No clear temporal or spatial trends in phytolith composition are evident in the QHB, and the same is broadly true for QHB vertebrates based on analyses of 872 identified specimens. Abundances of some mammals (certain rodents, armadillos, turtles, and the notoungulate Hemihegetotherium) vary slightly among well-sampled local areas and stratigraphic intervals, paralleling phytolith assemblage data suggesting local heterogeneity. The new floral and faunal data, combined with previous studies of paleosols, ichnofossils, ectothermic vertebrates, and mammal ecological diversity of the QHB, point to a mosaic landscape in lowland subtropical to tropical conditions that did not change substantially during the preserved interval. These results add critically to our understanding of Neotropical landscape evolution, suggesting that the QHB had not undergone substantial uplift, counter to recent reconstructions of Andean orogeny in the Eastern Cordillera.
{"title":"The flora, fauna, and paleoenvironment of the late Middle Miocene Quebrada Honda Basin, Bolivia (Eastern Cordillera, Central Andes)","authors":"Caroline A.E. Strömberg , Beverly Z. Saylor , Russell K. Engelman , Angeline M. Catena , Daniel I. Hembree , Federico Anaya , Darin A. Croft","doi":"10.1016/j.palaeo.2024.112518","DOIUrl":"10.1016/j.palaeo.2024.112518","url":null,"abstract":"<div><div>Miocene ecosystem change in the Central Andes is not well understood because of a dearth of well-dated fossil sites from the region. The late Middle Miocene (∼13–12 Ma) Quebrada Honda Basin (QHB) in southern Bolivia (22° S) helps fill this gap and provide vital insights into Neotropical paleoenvironments. The site is among the best-characterized Middle Miocene terrestrial vertebrate sites of South America and has a robust temporal, spatial, and lithostratigraphic framework for analyzing its sedimentary facies, fossils, and paleoenvironment. Here, we present new plant silica (phytolith) assemblage data from the QHB as well as new analyses of QHB faunal data. Phytolith assemblage data indicate two broad vegetation types: one suggestive of more open habitats (≥ 60% presumably open-habitat grasses) and the other of more closed habitats (typically dominated by potential bamboos and other forest indicators). Compositional overlap suggests that these vegetation types represent distinct plant communities within a broader biome that lacks an exact modern analog among studied Neotropical vegetation; however, it was likely akin to modern Neotropical semi-deciduous/dry forest to wooded savanna. No clear temporal or spatial trends in phytolith composition are evident in the QHB, and the same is broadly true for QHB vertebrates based on analyses of 872 identified specimens. Abundances of some mammals (certain rodents, armadillos, turtles, and the notoungulate <em>Hemihegetotherium</em>) vary slightly among well-sampled local areas and stratigraphic intervals, paralleling phytolith assemblage data suggesting local heterogeneity. The new floral and faunal data, combined with previous studies of paleosols, ichnofossils, ectothermic vertebrates, and mammal ecological diversity of the QHB, point to a mosaic landscape in lowland subtropical to tropical conditions that did not change substantially during the preserved interval. These results add critically to our understanding of Neotropical landscape evolution, suggesting that the QHB had not undergone substantial uplift, counter to recent reconstructions of Andean orogeny in the Eastern Cordillera.</div></div>","PeriodicalId":19928,"journal":{"name":"Palaeogeography, Palaeoclimatology, Palaeoecology","volume":"656 ","pages":"Article 112518"},"PeriodicalIF":2.6,"publicationDate":"2024-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142571897","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-25DOI: 10.1016/j.palaeo.2024.112519
Vlatko Brčić , Viktória Baranyi , Bosiljka Glumac , Marko Špelić , Ladislav Fuček , Duje Kukoč , Krešimir Petrinjak , Ivan Mišur , Marko Budić , Damir Palenik , Nikola Belić , Ana Kamenski , Jasmina Martinčević Lazar , Sanja Šuica , Anita Grizelj , Irena Ciglenečki , Jelena Dautović
Early Jurassic (late Pliensbachian–early Toarcian) Large Igneous Province (LIP) magmatism affected the entire ocean-atmosphere system culminating in a cascade of paleoenvironmental perturbations known as the Jenkyns Event which globally impacted marine, transitional and terrestrial paleoenvironments. Carbonate platforms at low latitudes in the Western Tethys realm drowned or shifted to non-skeletal production during the early Toarcian due to sea level rise, global warming, and ocean acidification. Unlike deep-marine deposits, shallow-marine carbonates present a challenge in defining global geochemical signals due to common diagenetic modifications. An integrated dataset including δ13Ccarb and δ18Ocarb, TOC, biomicrofacies, SEM, XRD, and palynological study of two stratigraphic successions in the Plitvice Lakes region, Bjelopolje (BJ) and Plitvice Spring (PS), in Croatia, provides an overview of the paleoenvironmental evolution and lateral facies changes in a peritidal setting during the Early Jurassic on the Adriatic Carbonate Platform (AdCP). The investigated stratigraphic succession starts with upper Pliensbachian, peloid-ooid-bioclastic grainstones alternating with fenestral and massive mudstones overlain by lower Toarcian, lagoonal, bioturbated, “spotted” limestones with horizons indicative of short-lived subaerial emergence during the early Toarcian. A negative excursion in δ13Ccarb, foraminifer assemblages, and the predominance of Classopollis pollen within the “spotted” limestones marks the stratigraphic position of the Jenkyns Event. Global-scale events (sea level variation, climate change, C-cycle perturbation, anoxia) operated simultaneously with local to regional synsedimentary tectonics and eustatic movements that preserved the AdCP carbonate factory from collapse or drowning but resulted in pronounced facies differentiation on the shallow-marine carbonate platforms.
{"title":"Impact of the Jenkyns Event on shallow-marine carbonates and coeval emerged paleoenvironments: the Plitvice Lakes region, Croatia","authors":"Vlatko Brčić , Viktória Baranyi , Bosiljka Glumac , Marko Špelić , Ladislav Fuček , Duje Kukoč , Krešimir Petrinjak , Ivan Mišur , Marko Budić , Damir Palenik , Nikola Belić , Ana Kamenski , Jasmina Martinčević Lazar , Sanja Šuica , Anita Grizelj , Irena Ciglenečki , Jelena Dautović","doi":"10.1016/j.palaeo.2024.112519","DOIUrl":"10.1016/j.palaeo.2024.112519","url":null,"abstract":"<div><div>Early Jurassic (late Pliensbachian–early Toarcian) Large Igneous Province (LIP) magmatism affected the entire ocean-atmosphere system culminating in a cascade of paleoenvironmental perturbations known as the Jenkyns Event which globally impacted marine, transitional and terrestrial paleoenvironments. Carbonate platforms at low latitudes in the Western Tethys realm drowned or shifted to non-skeletal production during the early Toarcian due to sea level rise, global warming, and ocean acidification. Unlike deep-marine deposits, shallow-marine carbonates present a challenge in defining global geochemical signals due to common diagenetic modifications. An integrated dataset including δ<sup>13</sup>C<sub>carb</sub> and δ<sup>18</sup>O<sub>carb</sub>, TOC, biomicrofacies, SEM, XRD, and palynological study of two stratigraphic successions in the Plitvice Lakes region, Bjelopolje (BJ) and Plitvice Spring (PS), in Croatia, provides an overview of the paleoenvironmental evolution and lateral facies changes in a peritidal setting during the Early Jurassic on the Adriatic Carbonate Platform (AdCP). The investigated stratigraphic succession starts with upper Pliensbachian, peloid-ooid-bioclastic grainstones alternating with fenestral and massive mudstones overlain by lower Toarcian, lagoonal, bioturbated, “spotted” limestones with horizons indicative of short-lived subaerial emergence during the early Toarcian. A negative excursion in δ<sup>13</sup>C<sub>carb</sub>, foraminifer assemblages, and the predominance of <em>Classopollis</em> pollen within the “spotted” limestones marks the stratigraphic position of the Jenkyns Event. Global-scale events (sea level variation, climate change, C-cycle perturbation, anoxia) operated simultaneously with local to regional synsedimentary tectonics and eustatic movements that preserved the AdCP carbonate factory from collapse or drowning but resulted in pronounced facies differentiation on the shallow-marine carbonate platforms.</div></div>","PeriodicalId":19928,"journal":{"name":"Palaeogeography, Palaeoclimatology, Palaeoecology","volume":"655 ","pages":"Article 112519"},"PeriodicalIF":2.6,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142416165","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-25DOI: 10.1016/j.palaeo.2024.112515
Elisabeth Teca Oliva , Elisabeth Michel , Giuseppe Siani , Xavier Crosta , Carina B. Lange , Consuelo Martínez Fontaine , Paola Cárdenas
The Southern Ocean is a key region for climate changes, notably for deep ocean–atmosphere CO2 exchange, linked to the upwelling of deep waters, south to the Polar Front, that is driven through Southern Hemisphere Westerly Winds and Antarctic Circumpolar Current positions and intensities. Previous studies using a range of different proxies have proposed the latitudinal migration of the Antarctic Circumpolar Current and Southern Westerly Winds in the Southeast Pacific since the Last Glacial Maximum, but with conflicting results. We present a paleoceanographic reconstruction from the Last Glacial period to the Late Holocene based on diatom and foraminiferal assemblages from the marine sediment core MD07-3081, retrieved from the Southeast Pacific at 49° S, proximal (∼100 km) offshore the south coast of Chile. During the Last Glacial, the presence of polar diatoms is not observed, suggesting that the Polar Front did not approach 49° S. During the deglaciation, an increase of Chaetoceros spp. spores is observed together with the opportunistic planktonic foraminifer Globigerinita glutinata, which indicates a greater nutrient availability, linked to the influence of the Southern Ocean upwelling. The presence of Neogloboquadrina incompta, a subtropical species, during two periods of the deglaciation (15.2 ka and 12.3–11.5 ka) is associated with a southward shift of the Subtropical Front linked to a reduction of the South Pacific split jet. During the deglaciation to the Early Holocene transition, the increase of open ocean diatoms thriving both north and south of the Subantarctic Zone indicates a greater influence of the Antarctic Circumpolar Current, possibly displaced ∼3° south of its current position at 46° S. In the Late Holocene, the increase of subtropical-temperate species, e.g. Fragilariopsis doliolus, is indicative of a greater influence of warm waters coming from the Peru–Chile Countercurrent. This study of the diatom and foraminiferal assemblages provide new insights into the paleoceanography of the SE Pacific since the Last Glacial Maximum and the role of the Southern Ocean during this climate transition.
{"title":"Paleoceanography of the Southeast Pacific since the late glacial from diatom and foraminiferal assemblages","authors":"Elisabeth Teca Oliva , Elisabeth Michel , Giuseppe Siani , Xavier Crosta , Carina B. Lange , Consuelo Martínez Fontaine , Paola Cárdenas","doi":"10.1016/j.palaeo.2024.112515","DOIUrl":"10.1016/j.palaeo.2024.112515","url":null,"abstract":"<div><div>The Southern Ocean is a key region for climate changes, notably for deep ocean–atmosphere CO<sub>2</sub> exchange, linked to the upwelling of deep waters, south to the Polar Front, that is driven through Southern Hemisphere Westerly Winds and Antarctic Circumpolar Current positions and intensities. Previous studies using a range of different proxies have proposed the latitudinal migration of the Antarctic Circumpolar Current and Southern Westerly Winds in the Southeast Pacific since the Last Glacial Maximum, but with conflicting results. We present a paleoceanographic reconstruction from the Last Glacial period to the Late Holocene based on diatom and foraminiferal assemblages from the marine sediment core MD07-3081, retrieved from the Southeast Pacific at 49° S, proximal (∼100 km) offshore the south coast of Chile. During the Last Glacial, the presence of polar diatoms is not observed, suggesting that the Polar Front did not approach 49° S. During the deglaciation, an increase of <em>Chaetoceros</em> spp. spores is observed together with the opportunistic planktonic foraminifer <em>Globigerinita glutinata</em>, which indicates a greater nutrient availability, linked to the influence of the Southern Ocean upwelling. The presence of <em>Neogloboquadrina incompta</em>, a subtropical species, during two periods of the deglaciation (15.2 ka and 12.3–11.5 ka) is associated with a southward shift of the Subtropical Front linked to a reduction of the South Pacific split jet. During the deglaciation to the Early Holocene transition, the increase of open ocean diatoms thriving both north and south of the Subantarctic Zone indicates a greater influence of the Antarctic Circumpolar Current, possibly displaced ∼3° south of its current position at 46° S. In the Late Holocene, the increase of subtropical-temperate species, e.g. <em>Fragilariopsis doliolus,</em> is indicative of a greater influence of warm waters coming from the Peru–Chile Countercurrent. This study of the diatom and foraminiferal assemblages provide new insights into the paleoceanography of the SE Pacific since the Last Glacial Maximum and the role of the Southern Ocean during this climate transition.</div></div>","PeriodicalId":19928,"journal":{"name":"Palaeogeography, Palaeoclimatology, Palaeoecology","volume":"655 ","pages":"Article 112515"},"PeriodicalIF":2.6,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142359699","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-24DOI: 10.1016/j.palaeo.2024.112520
Sunhwa Bang , Youngsook Huh
This study presents the first continuous carbonate boron isotope (δ11Bcarb) record from Middle Ordovician carbonate rocks, focusing on the Taebaek section in Korea. The δ11Bcarb values analyzed from the Makgol, Jigunsan, and Duwibong formations range between 7.5 ‰ and 17.8 ‰, falling within the published Paleozoic range. Samples exhibit minimal diagenetic alteration, as evidenced by weak correlations between isotopic factors and elemental ratios (δ11Bcarb, δ13Ccarb, δ15Nbulk, B/Ca, Mn/Sr, and Na/Ca) as well as mineralogical observations used to select unaltered micrite portions. Using the δ11Bcarb data, we reconstruct pH levels (8.4 to 9.1) which suggest that this shallow shelf environment acted as a CO2 sink during the Middle Darriwilian, despite periods of acidification coinciding with sea level rise and expansion of anoxic zones. Weakening of the basin's CO2 uptake capacity via reduced CaCO3 precipitation and photosynthesis accompanied these oceanographic changes. Our findings provide new insights into the dynamics of CO2 accumulation and pH in Middle Ordovician shallow marine settings in relation to sea level fluctuations. This work lays the foundation for further research into ocean chemistry and carbon cycle perturbations during this important period in Earth's history.
{"title":"Reconstructing CO2 uptake capacity and pH dynamics in the Middle Ordovician Taebaeksan Basin, Korea","authors":"Sunhwa Bang , Youngsook Huh","doi":"10.1016/j.palaeo.2024.112520","DOIUrl":"10.1016/j.palaeo.2024.112520","url":null,"abstract":"<div><div>This study presents the first continuous carbonate boron isotope (δ<sup>11</sup>B<sub>carb</sub>) record from Middle Ordovician carbonate rocks, focusing on the Taebaek section in Korea. The δ<sup>11</sup>B<sub>carb</sub> values analyzed from the Makgol, Jigunsan, and Duwibong formations range between 7.5 ‰ and 17.8 ‰, falling within the published Paleozoic range. Samples exhibit minimal diagenetic alteration, as evidenced by weak correlations between isotopic factors and elemental ratios (δ<sup>11</sup>B<sub>carb</sub>, δ<sup>13</sup>C<sub>carb</sub>, δ<sup>15</sup>N<sub>bulk</sub>, B/Ca, Mn/Sr, and Na/Ca) as well as mineralogical observations used to select unaltered micrite portions. Using the δ<sup>11</sup>B<sub>carb</sub> data, we reconstruct pH levels (8.4 to 9.1) which suggest that this shallow shelf environment acted as a CO<sub>2</sub> sink during the Middle Darriwilian, despite periods of acidification coinciding with sea level rise and expansion of anoxic zones. Weakening of the basin's CO<sub>2</sub> uptake capacity via reduced CaCO<sub>3</sub> precipitation and photosynthesis accompanied these oceanographic changes. Our findings provide new insights into the dynamics of CO<sub>2</sub> accumulation and pH in Middle Ordovician shallow marine settings in relation to sea level fluctuations. This work lays the foundation for further research into ocean chemistry and carbon cycle perturbations during this important period in Earth's history.</div></div>","PeriodicalId":19928,"journal":{"name":"Palaeogeography, Palaeoclimatology, Palaeoecology","volume":"655 ","pages":"Article 112520"},"PeriodicalIF":2.6,"publicationDate":"2024-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142359270","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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