Repeated enrichment of trace metals and organic carbon on an Eocene high-energy shelf caused by anoxia and reworking
| Autor: | Simon W. Poulton, Olaf G. Podlaha, S. van den Boorn, Sadat Kolonic, Hans-Juergen Brumsack, Christian März, Bernhard Schnetger, M. Al-Alaween, S. Aqleh, Thomas Wagner |
|---|---|
| Rok vydání: | 2016 |
| Předmět: |
chemistry.chemical_classification
Total organic carbon 010504 meteorology & atmospheric sciences Phosphorus chemistry.chemical_element Mineralogy Geology 010502 geochemistry & geophysics 01 natural sciences Sedimentary depositional environment chemistry Source rock Environmental chemistry Marl Organic matter Trace metal Oil shale 0105 earth and related environmental sciences |
| Zdroj: | Geology. 44:1011-1014 |
| ISSN: | 1943-2682 0091-7613 |
| Popis: | Petroleum source rocks are strongly enriched in organic carbon (OC), and their trace metal (TM) contents often reach low-grade ore levels. The mechanisms leading to these coenrichments are important for understanding how extreme environmental conditions support the formation of natural resources. We therefore studied organic-rich Eocene marls and limestones (oil shale) from the central Jordan Amzaq-Hazra subbasin, part of a Cretaceous–Paleogene shelf system along the southern Neo-Tethys margin. Geochemical analyses on two cores show highly dynamic depositional conditions, consistent with sedimentological and micropaleontological observations. Maximum and average contents, respectively, in OC (~26 and ~10 wt%), sulfur (~7 and ~2.4 wt%), phosphorus (~10 and ~2 wt%), molybdenum (>400 and ~130 ppm), chromium (>500 and ~350 ppm), vanadium (>1600 and ~550 ppm) and zinc (>3800 and ~900 ppm) are exceptional, in particular without any indication of hydrothermal or epigenetic processes. We propose a combination of two processes: physical reworking of OC- and metal-rich 30 material from locally exposed Cretaceous–Paleogene sediments (as supported by reworked nannofossils), and high marine productivity fueled by chemical remobilization of nutrients and metals on land that sustained anoxic-sulfidic conditions. Burial of high-quality organic matter (hydrogen index 600–700 mgHC/gOC) was related to strongly reducing conditions, punctuated by only short-lived oxygenation events, and to excess H2S, promoting organic matter sulfurization. These processes likely caused the OC and TM coenrichments in a high-energy shallow-marine setting that contradicts common models for black shale formation, but may explain similar geochemical patterns in other black shales. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|