Variations in primary aragonite, calcite, and clay in fine-grained calcareous rhythmites of Cambrian to Jurassic age - an environmental archive?
Munnecke A, Westphal H (2005)
Publication Language: English
Publication Type: Journal article, Original article
Publication year: 2005
Journal
Book Volume: 51
Pages Range: 592-607
Journal Issue: 1
URI: http://link.springer.com/article/10.1007/s10347-005-0053-x
DOI: 10.1007/s10347-005-0053-x
Abstract
Limestone-marl alternations represent a common type of fine-grained calcareous rhythmites during the entire Phanerozoic. Their diagenetic overprint, however, obliterates their value for palaeoenvironmental interpretations. The original mineralogical composition of the carbonate fraction (aragonite, high-Mg calcite, low-Mg calcite) would potentially yield important information on palaeoenvironmental conditions: for example shallow-water carbonate factories are usually characterised by extensive aragonite production, whereas pelagic carbonate production is dominated by calcitic organisms. Therefore, a reconstruction of the pre-diagenetic mineralogical composition of limestone-marl precursors would be desirable.
A particularly conspicuous attribute of fine-grained calcareous rhythmites is the intercalation of two rock types that have undergone two entirely different diagenetic pathways (“differential diagenesis”). As indicated by earlier petrography work, in the interlayers selective aragonite dissolution has taken place, and the dissolved aragonite provided the cement for the limestones. Primary aragonite usually is not preserved in diagenetically mature fine-grained limestones. However, in a recently published paper a method is proposed to quantify the primary mineralogical composition of the precursor sediments of a fine-grained calcareous rhythmite. Here we apply this method to several published data sets from sections of Cambrian to Jurassic age. We try to answer the following questions: Where does the aragonite come from, especially during times of “calcite seas”? What is the impact of the enhanced pelagic carbonate production since the Late Jurassic on the formation of limestone-marl alternations? How much dissolved aragonite is lost to sea water during early marine burial diagenesis, i.e. how closed is the diagenetic system? As demonstrated for the five examples shown here, the new method for reconstructing primary mineralogy potentially provides insight into ancient depositional environments, surface productivity, and ocean chemistry.
Authors with CRIS profile
Involved external institutions
Germany (DE)How to cite
APA:
Munnecke, A., & Westphal, H. (2005). Variations in primary aragonite, calcite, and clay in fine-grained calcareous rhythmites of Cambrian to Jurassic age - an environmental archive? Facies, 51(1), 592-607. https://dx.doi.org/10.1007/s10347-005-0053-x
MLA:
Munnecke, Axel, and Hildegard Westphal. "Variations in primary aragonite, calcite, and clay in fine-grained calcareous rhythmites of Cambrian to Jurassic age - an environmental archive?" Facies 51.1 (2005): 592-607.
BibTeX: Download