The Significance of Hiatus Beds in Shallow-Water Mudstones: An Example from the Middle Jurassic of Switzerland

Abstract

Limestone beds formed in nearly carbonate-free shallow-water mudstones by discontinuous sedimentation and erosion are called hiatus beds. Anaerobic oxidation of organic matter by microbes provided excess alkalinity, inducing carbonate precipitation. A multiphase history of such beds is documented from the Swiss Jurassic by several cementation and dissolution phases. Four cement types occur: micrite as earliest cement (␦ 13 C Ϫ10 to Ϫ20‰), stellate calcite between micrite-cemented parts (␦ 13 C Ϫ5 to Ϫ10‰), fibrous calcite cement in dissolution cavities (␦ 13 C Ͻ Ϫ30‰), and blocky calcite in remaining pores (␦ 13 C Ϫ5‰). Except for the late blocky cement, all cements contain pyrite, indicating carbonate precipitation within the sulfate reduction zone. After early cementation by micrite, the beds moved relatively upwards into a shallower geochemical zone and some even to the seafloor because of erosion. Cavities formed during reburial by dissolution in the upper part of the sulfate reduction zone and in the upper part of the methanogenic zone. Strongly reduced sedimentation rates provided the requisite stable geochemical conditions for at least several thousands of years, which permitted precipitation and dissolution of carbonate by biochemical processes and diffusion. This happened on short-lived swells caused by differential subsidence and rotation along listric faults when basement structures became reactivated during the extensional stress regime from opening of the Tethys. During the Jurassic and Cretaceous breakup of Pangea the shelf area increased, and differential subsidence on these newly formed shelves was the main factor responsible for the observed postPaleozoic maximum in hiatus beds and hiatus concretions.

Mass occurrence of benthic coccoid cyanobacteria and their role in the production of Neoarchean carbonates of South Africa

“…This indicates that the calcification occurred within the biodiagenetic zone of bacterial oxidation (e.g. Mazzullo, 2000;Wetzel and Allia, 2000), perhaps with some contribution from the bacterial sulphate reduction processes.…”

Storm-influenced deposition and cyclicity in a shallow-marine mudstone succession - example from the Middle Jurassic ore-bearing clays of the Polish Jura (southern Poland)

“…It is likely that the hi a tus ho ri zons from the Silesian-Cra cow area could be linked with intrabasinal swells, where the sed i men ta tion rate was lower and the ero sion more in ten sive than in the in ter ven ing lows. The as so ci a tion of hi a tus con cre tions with short-lived bot tom el e va tions, form ing due to the syndepositional tec ton ics, was re ported by Wetzel and Allia (2000) from the Mid dle Ju ras sic of Swit zer land. Dif fer en ti a tion of the sea-floor into swells and de pres sions, re sult ing from salt move ments and syndepositional faults, is a phe nom e non known from the epicontinental ba sin of Po land (e.g., Dadlez, 1994;Feldman-Olszewska, 1997).…”

Origin and paleoecology of Middle Jurassic hiatus concretions from Poland

“…As was previously pointed out by Kennedy and Klinger (1972), the history of formation of hiatus concretions may be very complex, consisting of several repeated episodes of exhumation and burial. The occurrence of hiatus concretions in the rock sequences may be related either to sealevel changes (see Voigt 1968;Hesselbo and Palmer 1992) or differential basin subsidence (Wetzel and Allia 2000). They are also an effect of carbonate precipitation in the 'calcite seas' prevailing during Early Paleozoic and Mesozoic times (see Palmer and Wilson 2004).…”

“…They are also an effect of carbonate precipitation in the 'calcite seas' prevailing during Early Paleozoic and Mesozoic times (see Palmer and Wilson 2004). Indeed, the majority of hiatus concretions occur in Ordovician (Wilson 1985), Devonian (Baird 1976(Baird , 1981, Jurassic (e.g., Hallam 1969;Kaźmierczak 1974;Baird and Fürsich 1975;Hesselbo and Palmer 1992;Wetzel and Allia 2000;Majewski 2000;Zatoń et al 2006;Reolid et al 2010a) and Cretaceous (Kennedy and Klinger 1972;Kennedy et al 1977) deposits. Although most hiatus concretions described from the fossil record (see above) are calcitic, some have a different mineralogy.…”