--> --> For Volcanic Ash to be the Key to Organic Rich Rock Formation, the Implications are Dramatic; but are they Probable?

AAPG Rocky Mountain Section Meeting

Datapages, Inc.Print this page

For Volcanic Ash to be the Key to Organic Rich Rock Formation, the Implications are Dramatic; but are they Probable?


Zimmerle (1983) and Parker (2017) concluded that all organically enriched rocks are the result of volcanogenic input; direct ash fall and redeposition of ash fall minerals. Cin-Ty A. Lee et al. (2018) wrote that volcanic ash was a driver of carbon burial in the Cretaceous. Frebourg et al. (2016) examined outcrops of the Boquillas-Eagle Ford and concluded that the cyclicity of organic enrichment, and those nutrients causing organic enrichment were from volcanic ash fall. Sonnenfeld et al. (2016) found “hundreds” of layers of volcanic ash in the organically enriched Niobrara Formation. For ash to be the key to organic enrichment (1) a connection must exist between OAEs and voluminous ash fall and, (2) altered ash must largely be un-quantified in sedimentary rocks. Ross et al. (2005) observed “the near-ubiquitous occurrence of mafic volcaniclastic deposits as an integral component in large igneous provinces.” Rocky Mountain Section – AAPG: 2019 Annual Meeting 44 “Mafic volcaniclastics make up a significant fraction of large igneous province eruptive volume”. “The volcaniclastics in flood basalts may be the major missing link between flood basalts and extinctions.” (Ukstins Peate et al., 2015). The complexity of diagenetic alteration can be appreciated in this description of a tuff from the Eocene Green River Shale. “The Mahogany marker tuff consists of authigenic sodium feldspar, analcime, quartz, ankerite, dolomite, potassium, feldspar, calcite with lesser amounts of siderite, hematite, pyrite, undifferentiated clays, pyrrhotite, biotite, marcasite, and locally dawsonite. (Mason, Glenn, 1983). Volcanogenic rocks “hidden” in plain sight include quartz sand and mud (Smyth et al., 2003), chert (Wadia, 2007; Chatellier, 2015), bauxite deposits (Isphording et al., 1995), hematite in red beds (Kruiver et al., 2000), and chamosite in oolitic iron ore (Ulf Sturesson, 1992). Jurassic uranium ore is leached from ash (Falkowski et al. 1979) as is Eocene uranium in Gulf Coast sediments (Hall, S. et al., 2013). Trona (NaCO3) of the Green River Shale and in Turkey is an evaporative mineral from ash fall alteration (Turkey -- Helvaci, C., 2010). Volcanogenic rocks are part of OAEs and their alteration minerals are much more diverse than just bentonites and tonsteins.