Mercury Isotope Geochemistry in Ediacaran Cap Carbonates and Cretaceous Oceanic Red Beds

Cretaceous oceanic red beds (CORBs): Different time scales and models of origin

The Cretaceous is an important period in which many geological events occurred, especially the OAEs (oceanic anoxic events) which are characterized by black shale, and the oxic process characterized by CORBs (Cretaceous oceanic red beds). In this paper, the causative mechanism behind the formation of black shale and the oceanic red beds are described in detail. This may explain how the oceanic environment changed from anoxic to oxic in the Cretaceous period. It is suggested that these two different events happened because of the same cause. On the one hand, the large-scale magma activities in Cretaceous caused the concentration of CO2, the release of the inner energy of the earth, superficial change in the ocean-land, and finally, the increase of atmospheric temperature. These changes implied the same tendency as the oceanic water temperature show, and caused the decrease in O2 concentration in the Cretaceous ocean, and finally resulted in the occurrence of the OAEs. On the other hand, violent and frequent volcanic eruptions in the Cretaceous produced plenty of Fe-enriched lava on the seafloor. When the seawater reacted with the lava, the element Fe became dissolved in seawater. Iron, which could help phytoplankton grow rapidly, is a micronutrient essential to the synthesis of enzymes required for photosynthesis in the oceanic environment. Phytoplankton, which grows in much of the oceans around the world, can consume carbon dioxide in the air and the ocean. Meanwhile, an equal quantity of oxygen can be produced by the phytoplankton during its growth. Finally, the oxic environment characterized by red sediment rich in Fe3+ appeared. The anoxic and oxic conditions in the Cretaceous ocean were caused by volcanic activities, but they stemmed from different causative mechanisms. The former was based on physical and chemical processes, while the latter involved more complicated bio-oceanic-geochemical processes.

During the Late Cretaceous, Earth's climate oscillated between warm and cool states, and global oceans changed between anoxic and oxic conditions, resulting in black/gray shales and oceanic red beds (ORBs) deposition, respectively. To understand such climate/ocean dynamics, this study investigated bulk Hg and Hg isotopes, as well as Fe3+/Fe2+ in Upper Cretaceous sediments deposited in southern Tibet and the North Atlantic. In both areas, black/gray shales show much higher Hg concentrations than ORBs, indicating enhanced Hg flux to global oceans during time of black/gray shale deposition. Black/gray shales show lower Fe3+/Fe2+ and positive Δ199Hg, suggesting a significant input of Hg into the anoxic/dysoxic ocean via atmospheric deposition. The isotope values are consistent with a volcanic source for this excess Hg. ORBs show high Fe3+/Fe2+ and negative shifts of Δ199Hg, suggesting that the dominant source of Hg into the oxic oceans was via terrestrial runoff. This study suggests that volcanism was an important driver of the climate/ocean dynamics during the Late Cretaceous.

Abstract: Cretaceous oceanic red beds (CORBs) represented by red shales and marls, were deposited during the Cretaceous and early Paleocene, predominantly in the Tethyan realm, in lower slope and abyssal basin environments. Detailed studies of CORBs are rare; therefore, we compiled CORBs data from deep sea ocean drilling cores and outcrops of Cretaceous rocks subaerially exposed in southern Europe, northwestern Germany, Asia and New Zealand. In the Tethyan realm, CORBs mainly consist of reddish or pink shales, limestones and marlstones. By contrast, marlstones and chalks are rare in deep‐ocean drilling cores. Upper Cretaceous marine sediments in cores from the Atlantic Ocean are predominantly various shades of brown, reddish brown, yellowish brown and pale brown in color. A few red, pink, yellow and orange Cretaceous sediments are also present. The commonest age of CORBs is early Campanian to Maastrichtian, with the onset mostly of oxic deposition often after Oceanic Anoxic Events (OAEs), during the early Aptian, late Albian‐early Turonian and Campanian. This suggests an indicated and previously not recognized relationship between OAEs, black shales deposition and CORBs. CORBs even though globally distributed, are most common in the North Atlantic and Tethyan realms, in low to mid latitudes of the northern hemisphere; in the South Atlantic and Indian Ocean in the mid to high latitudes of the southern hemisphere; and are less frequent in the central Pacific Ocean. Their widespread occurrence during the late Cretaceous might have been the result of establishing a connection for deep oceanic current circulation between the Pacific and the evolving connection between South and North Atlantic and changes in oceanic basins ventilation.

CORBs are described from a north–south transect from the passive European margin with the Helvetic–Ultrahelvetic shelf and continental slope through the Alpine Tethys, including the Rhenodanubian Flysch Zone into the southern, tectonically active margin of the Austro-Alpine microplate, including the Northern Calcareous Alps. In the Helvetic (shelf) and Ultrahelvetic (slope) part of the European margin, the proportion of CORBs in the Upper Cretaceous successions increases significantly with increasing water depth and increasing pelagic character. In the Ultrahelvetic units of Upper Austria (Rehkogelgraben, Buchberg), CORBs define a continuous red interval from the Lower Turonian to the Lower Campanian. The onset of CORB deposition in the Ultrahelvetic Zone corresponds to a major change in paleoceanographic conditions from anoxic during the Late Cenomanian OAE 2 to highly oxic during the Early to Middle Turonian. In the Rhenodanubian Flysch, hemipelagic red and green shales alternate with turbiditic siltstones and minor sandstones in the Upper Aptian–Lower Cenomanian Lower Varicolored Marls, the Coniacian–Lower Campanian Seisenburg Formation, and the uppermost Campanian Perneck Formation. CORBs in the Rhenodanubian Flysch are controlled mainly by tectonic events and sea-level changes, and occur during times of transgressions, low clastic input, and low turbidite frequencies. In the Austro-Alpine Northern Calcareous Alps, CORBs occur from the Santonian onwards in the upper parts of transgressive sequences of the Gosau Group, e.g., in the Tiefenbach and the Dalsenalm sections. In areas where clastic input was low, CORB deposition continued up into the Maastrichtian. Based on these data a peak of oceanic red beds is inferred for the middle Santonian–Early Campanian time interval. Prerequisites for CORB sedimentation are low clastic input, low sedimentation rates, and increasing paleo–water depth. CORBs can be classified as a variation of three end members: clayey CORBs, consisting mainly of terrigenous clay minerals; calcareous CORBs, mainly pelagic limestones; and siliceous CORBs, consisting mainly of biogenic SiO2.

Oceanic red beds, preserving primary depositional remanent magnetization, play a key role in reconstructing the Tethyan paleogeography. However, partial remagnetization caused by chemical processes could be pervasive in these rocks, leading to flawed reconstructions, and thus, differentiating secondary and primary remanences is important. In this paper, we conduct multiple X‐ray diffraction, petrographic, diffuse reflectance spectroscopy, and rock magnetic analyses on the Upper Cretaceous oceanic red beds (CORBs) from the Cailangba section in the Gyangze region of the Tethyan Himalaya. Our results reveal that the CORBs contain coarse‐grained detrital hematite with a narrow coercivity distribution, as well as fine‐grained authigenic hematite with a broad coercivity distribution. The coarse‐grained population is mainly composed of >400 nm hematite grains and unblocks close to the Néel temperature (675°C), consistent with a detrital origin. In contrast, the fine‐grained population is mainly composed of <30−400 nm hematite grains and progressively unblocks below 650°C, consistent with a chemical (authigenic) origin. In addition to these two populations of hematite, a small amount of goethite, unblocking below 120°C, is detected. Due to the distinct unblocking temperature spectra of these two populations of hematite, isolating the primary detrital remanence of the coarse‐grained hematite from the chemical remanence of the fine‐grained hematite in the CORBs through high‐resolution thermal demagnetization treatment is feasible. This study lends confidence to the paleomagnetic studies of these oceanic red beds in Tethyan paleogeographic reconstructions.

New biostratigraphic data from the Cretaceous Bolinxiala Formation in Zanda, southwestern Tibet of China, and their paleogeographic and paleoceanographic implications

The Cretaceous oceanic red beds (CORBs) and their implications for “oceanic oxic events” have been widely studied by geologists globally. In southern Tibet, CORBs are extensively distributed within the Upper Cretaceous strata of the northern Tethyan Himalaya (NTH). A well-exposed, CORB-bearing, mixed carbonate–shale sequence is found in the Zhangguo section of Rilang Township, Gyangze County. The Chuangde Formation in this section is characterized by well-preserved CORBs, which include reddish shale, limestone, marlstone, and interbedded siltstone. These CORBs are stratigraphically overlain by the Jiabula/Gyabula Formation (predominantly shale) and underlain by the Zongzhuo Formation (“mélange”). However, the precise age, depositional environments, and regional/global correlations of these CORBs, as well as their implications for synchronous versus diachronous oceanic oxic events, remain to be fully understood. In this study, a comprehensive analysis of foraminiferal biostratigraphy and microfacies is conducted for the CORB-bearing Chuangde Formation and the upper Jiabula (Gyabula) Formation in the Zhangguo section. Five planktic foraminiferal biozones including Dicarinella asymetrica, Globotruncanita elevata, Contusotruncana plummerae, Radotruncana calcarata, and Globotruncanella havanensis are identified through detailed biostratigraphic analysis, confirming a Campanian age for the Chuangde Formation and its CORBs. These findings are broadly correlated with typical Upper Cretaceous CORBs in pelagic–hemipelagic settings across the NTH in southern Tibet. Nine microfacies and four facies associations are identified within the Upper Cretaceous strata of Gyangze and adjacent areas through field and petrographic analyses. Notably, it is indicated that planktic foraminiferal packstone/grainstone CORBs were deposited in outer shelf to upper slope environments, while radiolarian chert CORBs are inferred to have formed in deep-water, basinal settings below the carbonate compensation depth (CCD).

The Cretaceous oceanic red beds (CORBs) and their implications for “oceanic oxic events” have been widely studied by geologists globally. In southern Tibet, CORBs are extensively distributed within the Upper Cretaceous strata of the northern Tethyan Himalaya (NTH). A well-exposed, CORB-bearing, mixed carbonate-shale sequence is found in the Zhangguo section of Rilang Township, Gyangze County. The Chuangde Formation in this section is characterized by well-preserved CORBs, which include reddish shale, limestone, marlstone, and interbedded siltstone. These CORBs are stratigraphically overlain by the Jiabula/Gyabula Formation (predominantly shale) and underlain by the Zongzhuo Formation (“mélange”). However, the precise age, depositional environments, and regional/global correlations of these CORBs, as well as their implications for synchronous versus diachronous oceanic oxic events, remain to be fully understood. In this study, a comprehensive analysis of foraminiferal biostratigraphy and microfacies is conducted for the CORB-bearing Chuangde Formation and the upper Jiabula (Gyabula) Formation in the Zhangguo section. Five planktic foraminiferal biozones including Dicarinella asymetrica, Globotruncanita elevata, Contusotruncana plummerae, Radotruncana calcarata, and Globotruncanella havanensis are identified through detailed biostratigraphic analysis, confirming a Campanian age for the Chuangde Formation and its CORBs. These findings are broadly correlated with typical Upper Cretaceous CORBs in pelagic-hemipelagic settings across the NTH in southern Tibet. Nine microfacies and four facies associations are identified within the Upper Cretaceous strata of Gyangze and adjacent areas through field and petrographic analyses. Notably, it is indicated that planktic foraminiferal packstone/grainstone CORBs were deposited in outer shelf to upper slope environments, while radiolarian chert CORBs are inferred to have formed in deep-water, basinal settings below the carbonate compensation depth (CCD).

The “Cretaceous oceanic red beds (CORBs)” associated with “oceanic oxic events” have become a hot topic for geologists from around the world. In southern Tibet, the CORBs are widely distributed in the Upper Cretaceous of the northern Tethys Himalayas, but they have never been reported from the southern Tethyan Himalaya (Tibet, China). A mixed Upper Cretaceous carbonate‐shale succession is well exposed in the Gyabukeqing section of Guru town, Yadong County, southern Tibet, which tectonically belongs to the southern Tethyan Himalaya. These sedimentary strata constitute the transition from the Gangbacunkou Formation shale towards the Zongshan Formation limestone through the Jiubao Formation alternations of marl and shale. The Gangbacunkou Formation is characterized by grey‐greenish shales occasionally interspersed with laminated marls, followed by the Jiubao Formation composed of marls with interbeds of shales, which is overlain by the limestones of the Zongshan Formation. A 5‐m‐thick purplish marl bed was found from the lower Jiubao Formation in the Gyabukeqing section, and these reddish marls are assignable to shallow marine red beds. Detailed foraminifer biostratigraphy established five planktic foraminifer zones: Dicarinella covcavata, D. asymetrica, Globotruncanita elevata, G. ventricosa, and Radotruncana calcarata throughout the entire Upper Cretaceous succession in the Gyabukeqing section. The reddish marl beds are constrained as middle Campanian in age as they are calibrated to the middle part of the foraminifer Radotruncana calcarata Zone. As a comparison, the typical CORBs of pelagic–hemipelagic settings are also documented from the Upper Cretaceous of the northern Tethys Himalayas in southern Tibet. A total of 10 microfacies were recognized from the entire sequence of the Upper Cretaceous outer shelf‐slope settings in the Yadong area, southern Tibet. The Yadong red marl beds represent the sedimentation of the foraminiferal biomicrite/foraminiferal wackestone and mudstone/mudrock microfacies, pointing to a shallow marine continental shelf margin setting. Global biostratigraphic correlations indicate that the Yadong red marl beds are coeval with the typical CORBs of the Gyangze and Kangmar documented from the northern Tethys Himalayas in this study or reported previously from the same region as well as elsewhere in the world. The Yadong red beds also are comparable in lithology and biostratigraphy with the shallow marine red beds documented from Europe, and they all may represent the contemporaneous deposition of the CORBs in shallow shelf. These shallow marine CORBs share similar depositional mechanisms: undergoing a phase of iron and manganese enrichment in seawater due to injection of deep sea anoxic water to shallow shelf, followed by oxidization in shallow settings or being oxidized during diagenetic process or a response to the oxygenation of coeval CORBs in deep seas.

Discovery of radiolaria from Upper Cretaceous Oceanic Red Beds in Daba, Kangmar and its paleogeographic implication

Research Article| October 01, 2008 Nd isotopic excursion across Cretaceous ocean anoxic event 2 (Cenomanian-Turonian) in the tropical North Atlantic Kenneth G. MacLeod; Kenneth G. MacLeod * 11Department of Geological Sciences, University of Missouri, Columbia, Missouri 65211, USA *E-mail: macleodk@missouri.edu. Search for other works by this author on: GSW Google Scholar Ellen E. Martin; Ellen E. Martin 22Department of Geological Sciences, University of Florida, Gainesville, Florida 32611, USA Search for other works by this author on: GSW Google Scholar Susanna W. Blair Susanna W. Blair 22Department of Geological Sciences, University of Florida, Gainesville, Florida 32611, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Kenneth G. MacLeod * 11Department of Geological Sciences, University of Missouri, Columbia, Missouri 65211, USA Ellen E. Martin 22Department of Geological Sciences, University of Florida, Gainesville, Florida 32611, USA Susanna W. Blair 22Department of Geological Sciences, University of Florida, Gainesville, Florida 32611, USA *E-mail: macleodk@missouri.edu. Publisher: Geological Society of America Received: 30 Mar 2008 Revision Received: 10 Jul 2008 Accepted: 16 Jul 2008 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2008 Geological Society of America Geology (2008) 36 (10): 811–814. https://doi.org/10.1130/G24999A.1 Article history Received: 30 Mar 2008 Revision Received: 10 Jul 2008 Accepted: 16 Jul 2008 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Kenneth G. MacLeod, Ellen E. Martin, Susanna W. Blair; Nd isotopic excursion across Cretaceous ocean anoxic event 2 (Cenomanian-Turonian) in the tropical North Atlantic. Geology 2008;; 36 (10): 811–814. doi: https://doi.org/10.1130/G24999A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Late Cretaceous fish debris from Demerara Rise exhibits a dramatic positive excursion of 8 ϵNd units during ocean anoxic event 2 (OAE2) that is superimposed on extremely low ϵNd(t) values (−14 to −16.5) observed throughout the rest of the studied interval. The OAE2 ϵNd excursion is the largest yet documented in marine sediments, and the majority of the shift is estimated to have occurred over <20 k.y. Low background ϵNd values on Demerara Rise are explained as the Nd isotopic signature of the South American craton, whereas eruptions of the Caribbean large igneous province or enhanced mixing of intermediate waters in the North Atlantic could have caused the excursion. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Lithofacies, microfacies and depositional environments of Upper Cretaceous Oceanic red beds (Chuangde Formation) in southern Tibet

Earth system changes during the cooling greenhouse phase of the Late Cretaceous: Coniacian-Santonian OAE3 subevents and fundamental variations in organic carbon deposition

Cretaceous Oceanic Red Beds (CORBs) represent important archives of paleoceanographic and paleoclimatic conditions during Earth&amp;#8217;s greenhouse intervals. In this study, we focus on Upper Aptian and Upper Albian CORBs from the Trento Plateau (Southern Alps, NE Italy), integrating geochemical (ICP-OES, ICP-MS), rare earth element (REE), and thermomagnetic analyses to elucidate local and global factors controlling their deposition. Aptian CORBs exhibit higher and more variable oxygenation, favoring hematite formation and enrichment in light rare earth elements (LREEs), whereas Albian CORBs reflect slightly lower O2 levels and greater climatic stability. The absence of redox-sensitive elements such as Mo and Cr confirms that anoxia was not a limiting factor in either interval. Thermomagnetic data reveal incomplete magnetite oxidation in both Aptian and Albian samples, indicative of reduced oxygen availability during deposition. These depositional differences are linked to local tectonic subsidence of the Trento Plateau, which influenced sedimentation rates, as well as global climatic shifts following major Oceanic Anoxic Events (OAEs). Our multi-proxy approach highlights that, despite contrasting oxygenation histories, both intervals maintained sufficiently oxic bottom waters&amp;#8212;whether through higher dissolved O2 or lower sedimentation rates&amp;#8212;to enable the formation of CORBs. Our findings advance the understanding of mid-Cretaceous paleoceanography, demonstrating that CORBs can form under varying yet consistently oxic conditions, shaped by the interplay of tectonics, sediment supply, and climate feedbacks.&amp;#160;