Petrology of Lower Cretaceous carbonate mud mounds (Albian, N. Spain): insights into organomineralic deposits of the geological record

Abstract

The process of organomineralization is increasingly well understood with respect to modern carbonate sediments accumulating adjacent to tropical reef atolls and reef caves. Mineralization related to non-living organic substrates results in autochthonous micrite production (`automicrites').`Automicrites' are the main constructive element of Lower Cretaceous (Albian) carbonate mud mounds in northern Spain. These slope mud mounds occur within transgressive and early highstand system tracts encompassing several macrobenthic ecological zones. They are clearly separated from the biocalcifying carbonate factory (Urgonian carbonate platforms), in both space and time. Within these build-ups, most`automicrites' were initially indurated and accreted to form a medium-relief growth framework.`Automicrites' have a uniform, presumably high-Mg-calcite precursor mineralogy. They show an inorganic stable-isotope signature ( ¶ 13 C around +3á3&) within the range of early marine cements, and skeletal compounds lacking major vital effects. Epi¯uorescence microscopy shows that they have facies-speci®c¯uorescence, which is similar to skeletal compounds of Acanthochaetetes, but clearly different from allomicritic sediment and cements, which are mostly nonuorescent. The EDTA-soluble intracrystalline organic fraction (SIOF) of Albian automicrites shows an amino acid spectrum that is similar to shallow subsurface samples from their modern counterparts. Gel electrophoresis of the SIOF demonstrates an exclusively acidic character, and a mean molecular size range between 20 and 30 kDa. Experiments in vitro (inhibition tests) indicate that the SIOF has a signi®cant Ca 2+ -binding capacity. Fluorescence and chemical characteristics of SIOF point to a main substance class, such as humic and fulvic acids, compounds that form from pristine organic matter during early diagenesis. Biomarker analyses provide evidence for the crucial role of biodegradation by heterotrophic microorganisms, but no biomarker for cyanobacteria has been found. Primary sources of organic material should have been manifold, including major contributions by metazoans such as sponges. It is concluded that many carbonate mud mounds are essentially organomineralic in origin and that the resulting fabric of polygenetic muds (`polymuds') may represent ancestral metazoan reef ecosystems, which possibly originated during the Neoproterozoic.

Successive stages of calcitization and silicification of Cenomanian spicule-bearing turbidites based on microfacies analysis, Polish Outer Carpathians

“…4B, C). Such calcitization of si li ceous sponges con cur rently with sil ica dis so lu tion is a known phe nom e non, doc u mented mainly from mod ern and an cient shal low-wa ter en vi ronments, in clud ing spiculitic car bon ate mud-mounds and reefs (Froget, 1976;Land, 1976;Wiedenmayer, 1980;Reitner and Keupp, 1991;Reitner, 1993;Hammes, 1995;Reitner et al, 1995;Warnke, 1995;Pisera, 1997;Neuweiler et al, 1999;Kauffman et al, 2000). The dis so lu tion of the opal ine sil ica of spicules and their re place ment by cal cium car bon ate may have oc curred both within the liv ing sponge, and dur ing its de cay in the weakly ce mented ma te rial, a few centi metres thick, as so ci ated with bac te rial mats (Hartman, 1979;Pratt et al, 1986;Bavestrello et al, 1996).…”

Carbonate mounds: From paradox to World Heritage

“…Devuyst and Lees (2001) found at the base of several buildups in Ireland grumous, clotted and/or peloidal carbonate muds, they consider as a precursor to the formation of Waulsortian polymuds. Neuweiler et al (1999) concluded that many mud mounds were essentially organomineralic in origin, i.e. formed by mineralization in close association with non-living organic substrates.…”

Defining organominerals: Comment on ‘Defining biominerals and organominerals: Direct and indirect indicators of life’ by Perry et al. (2007, Sedimentary Geology, 201, 157–179)

“…Thereafter, examples of organominerals and organomineralization processes have been documented, and the former papers cited, in mainstream scientific literature, beginning with our own work on carbonate organomineral formation in modern and recent microbialites and ooids (Défarge et al, 1996;Reitner et al, 1997;Arp et al, 1999;Trichet et al, 2001;Arp et al, 2003;Gautret et al, 2004;Gautret and Trichet, 2005), ancient microbialite analogues (Camoin et al, 1999;Tribovillard et al, 1999Tribovillard et al, , 2000, mud mounds (Neuweiler et al, 1999), encrusting sponge cements (Russo et al, 2006), housing tubes of worms (Fischer et al, 2000), coral EPS (Reitner, 2005), decaying sponge tissues (Delecat et al, 2001), and during laboratory experiments with microbialite-, ooid-and meteorite-extracted organic matter (Reitner, 2004). Organominerals and organomineralization processes have also been brought up in a discussion, involving one of us, about the origin of lower Paleozoic carbonate mud (Pratt, 2001;Arp et al, 2002).…”