Late Devonian sea-level changes, catastrophic events, and mass extinctions

Abstract

Late Devonian history is explained through event stratigraphy comprising a sequence of 18 sea-level changes, catastrophic events, and mass extinctions. Generally rising sea level during the initial Frasnian Stage, beginning with the Taghanic onlap and ending with a sea-level fall and major mass extinction, was interrupted by several exceptionally rapid, very high rises of sea level. These rises may be related to a series of comet showers, as suggested by the coincidence of the Alamo Impact in Nevada and the older Amönau Event in Germany with two of the sea-level rises. The subcritical, off-platform marine Alamo Impact is demonstrated to have produced greatly different effects in deep water from those previously recorded on the carbonate platform.The series of comet showers, most notably those around the Frasnian-Famennian boundary, evidenced by microtektites in widely separated regions, not only produced the late Frasnian mass extinction, but also induced global cooling. This cooling resulted in Southern Hemisphere glaciation. Generally falling sea level during the later Famennian Stage was interrupted by several warmer, interglacial episodes, evidenced by glacio-eustatic rises. Another, less severe mass extinction occurred during an abrupt sea-level fall near the end of the Famennian. This glacio-eustatic fall is interpreted to have resulted from a severe, terminal glacial episode.Interpretation of Late Devonian history suggests that impacts and comet showers coincided with sea-level rises, whereas mass extinctions occurred during, not at the start of, sea-level falls.

The Devonian/Carboniferous boundary in the Holy Cross Mountains (Poland)

“…In both ar eas, the same biostratigraphic in ter vals are char ac ter ized by the same lithofacies and fau nal as sem blages. The si mul ta neous ap pearance of sim i lar de pos its was caused by com mon fac tors, linked with global sea level fluc tu a tions, re sult ing from glaciations on the south ern hemi sphere (see Sandberg et al, 2002;Caputo et al, 2008;Isaacson et al, 2008).…”

“…This phe nom e non was linked with a large-scale gla cial ep i sode in the south ern hemi sphere, causing rel a tively rapid sea level fall (Streel et al, 2000;Sandberg et al, 2002;Caputo et al, 2008;Isaacson et al, 2008;Kalvoda et al, 2013;Kumpan et al, 2013).…”

Upper Kellwasser carbon isotope excursion pre-dates the F–F boundary in the Upper Devonian Lennard Shelf carbonate system, Canning Basin, Western Australia

“…Today, over 350 km of Middle to Late Devonian carbonates are exposed in the northern part of the basin and have been subjected to decades of stratigraphic, paleontological, and geochemical research (Guppy et al, 1958b;Playford and Lowry, 1966;Druce, 1976;Playford, 1980;Becker and House, 1997;George et al, 1997;Stephens and Sumner, 2003;Nothdurft et al, 2004;Playford et al, 2009;and others). During the interval of time most relevant to this study, namely the Late Frasnian and Early Famennian, the reefal platform and slope system exhibited progradational growth morphology and experienced episodic collapse events that transported large amounts of material down-slope (Playford, 1980;Sandberg et al, 2002;Playton, 2008;Playford et al, 2009). An abrupt fall in sea level coincident with the F-F boundary resulted in the sub-aerial exposure and erosion of platform-top facies while sedimentation continued uninterrupted on the slope and in the basin.…”

“…These horizons are characterized by significant faunal turnover, positive carbon isotope excursions (average amplitude of about +3‰), and the deposition of black shales and bituminous limestones (e.g. McGhee, 1996), and are thought to reflect widespread anoxic conditions (Feist, 1985;Buggisch, 1991;Wendt and Belka, 1991;Hallam and Wignall, 1999) during pulses of sea level transgression (Johnson et al, 1985;Sandberg et al, 1988;Buggisch, 1991;Sandberg et al, 2002).…”

On the sensitivity of the Devonian climate to continental configuration, vegetation cover and insolation

“…During the late Famennian, Earth's climate cooled 30 again (Brezinski et al, 2009;Joachimski et al, 2009), with some studies even indicating glaciations (Caputo, 1985;Caputo et al, 2008;Brezinski et al, 2008Brezinski et al, , 2009. Whether this is accompanied by a sea-level transgression linked to the development of ocean anoxic conditions (Johnson et al, 1985;Bond and Wignall, 2008) or a sea-level drop (Sandberg et al, 2002;Haq Age [Ma] 18 O values from conodont apatite from Joachimski et al (2009), but using a different NBS120c standard for calibration (Lécuyer et al, 2003). Note the inverted scale on the y axis since an increase in δ 18 O translates in a temperature decrease.…”