Origin of Cretaceous Oceanic Red Beds from the Vispi Quarry Section, Central Italy: Visible Reflectance and Inorganic Geochemistry
Published:January 01, 2009
Xiumian Hu, Wenbin Cheng, Junfeng Ji, 2009. "Origin of Cretaceous Oceanic Red Beds from the Vispi Quarry Section, Central Italy: Visible Reflectance and Inorganic Geochemistry", Cretaceous Oceanic Red Beds: Stratigraphy, Composition, Origins, and Paleoceanographic and Paleoclimatic Significance, Xiumian Hu, Chengshan Wang, Robert W. Scott, Michael Wagreich, Luba Jansa
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A major change in oceanic sedimentation from Uppermost Cenomanian organic-carbon-enriched black shales (Bonarelli Level) to predominantly Lower Turonian oceanic red beds occurred in the Tethys. This paper presents high-resolution inorganic geochemical and mineralogical data on the transitional interval from the Scaglia Bianca to the Scaglia Rossa above the Bonarelli Level of the Vispi Quarry section, Umbria-Marche basin, Italy. Limestones from the Vispi Quarry section have very low Al2O3 concentrations (0.19–1.14 wt%) indicating low input of terrigenous detritus. Elements characterizing lithogenic input, such as Ti, K, Mg, Rb, and Zr, are of similar concentration in both the white limestone and the red/pink limestone and correlate positively with Al2O3, pointing to a homogeneous source area. The sources of terrigenous detrital input did not change throughout the transition from the Scaglia Bianica to the Scaglia Rossa. Geochemical data show that the red limestones were deposited under more oxic conditions, close to the sediment-water interface, as opposed to the white limestones in the Vispi Quarry section. This is supported by: (1) high Fe2O3 values (0.22% in average) and high Fe3+/ TFe ratio (0.58); (2) low values of relative enrichment factor (EF) of redox-sensitive elements U, V, Cr, Co, and Ni in the red limestones, with ratios of Ni/Co <2.5, V/Cr <1.2, V/(V+Ni) < 0.6, Fe3+/TFe > 0.45; and (3) a strongly negative 6Ce anomaly (0.28–0.42). The positive correlation between the peak height of hematite in the diffuse reflectance spectrophotometry (DRS) diagram and redness values (R2 = 0.98) indicates that hematite is responsible for the color of the limestones in the Vispi Quarry section. The DRS data confirm that the red color of the Scaglia Rossa limestones is the result of low concentration (~ 0.1 wt%) of finely dispersed hematite. SiO2(excess) P, and Ba productivity proxies show that there is no significant difference in depositional conditions and paleoproductivity levels between red limestone and white limestone. An increase in dissolved oxygen in bottom waters is the most probable cause of the origin of the red color. We suggest that intensification of bottom circulation with waters having higher content of dissolved oxygen may have resulted in significant oxidation of bottom sediments.
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Cretaceous Oceanic Red Beds: Stratigraphy, Composition, Origins, and Paleoceanographic and Paleoclimatic Significance
The occurrence of marine red beds has been known for at least 140 years, since Stúr (1860) and Gümbel (1861) first described them from the Púchov beds in the Carpathians and the Nierental beds in the Eastern Alps. A few biostratigraphic and sedimentological studies followed, particularly in European countries. However, detailed investigations on paleoceanographic and paleoclimatic implications related to Cretaceous marine red beds were initiated by Prof. Chengshan Wang, Dr. Xiumian Hu, and their colleagues. This collection of papers resulted from two collaborative research projects funded in part by UNESCO/IUGS International Geosciences Project IGCP 463 and IGCP 494. The IGCP 463 “Upper Cretaceous Oceanic Red Beds: Response to Ocean/Climate Global Change” (2002-2006) was led by Prof. Chengshan Wang (China University of Geosciences, Beijing, China), Prof. Massimo Sarti (Universitá Politecnica delle Marche, Italy), Dr. Robert Scott (University of Tulsa and Precision Stratigraphy Associates, USA), and Prof. Luba Jansa (Dalhousie University, Canada). The objective of IGCP 463 was to study major paleoceanographic phenomena recorded by sedimentary sequences in the world oceans. Cretaceous deposition changed several times from widespread organic-carbon-enriched shales that indicate a dysoxic to anoxic deep ocean environment, to mostly reddish clays and marls deposited in an oxic marine environment during the Late Cretaceous.