Physical characteristics of tephra layers in the deep sea realm: the Campanian Ignimbrite eruption

Abstract

Tephra deposits in the deep sea can survive undisturbed for long periods of time and, on regional scales, tend to be much better preserved than their subaerial counterparts. In this study, grain size distributions and thicknesses of tephra deposits from the Campanian Ignimbrite (CI) eruption (39 000 yr BP; magnitude c. 7.7) preserved in thirty-three deep sea cores are analysed to infer key eruption parameters. Distal deep sea tephra thickness data show an exponential decrease with distance from source. Such trends are difficult to identify in distal subaerial data owing to reworking and limited exposure. We find that tephra grain size distributions are much less affected by depositional environment than thickness, with trends that are consistent across distal subaerial, lacustrine and deep sea environments. The CI layer exhibits bimodal grain size distributions to distances of c. 1000 km, after which it becomes unimodal. Such trends can be related to different mechanisms of tephra transport in the atmosphere, whereby at proximal to medial distances the Plinian and co-ignimbrite phases produce distinct plumes. Within 150 and 900 km from source, Plinian tephra constitutes 40 + 5% of the deposit volume. Beyond this region where coarse particles are deposited, the plumes merge and fines derived largely from co-ignimbrite elutriation are spread in the atmosphere at velocities greater than the settling velocities of the particles.

A chemostratigraphic study of the Campanian Ignimbrite eruption (Campi Flegrei, Italy): Insights on magma chamber withdrawal and deposit accumulation as revealed by compositionally zoned stratigraphic and facies framework

“…It was accompanied by a huge volcano-tectonic collapse, giving birth to the Campi Flegrei caldera (CFc; Rosi and Sbrana, 1987;Perrotta et al, 2006;Scarpati et al, 2013). The CI plinian eruption emplaced a large volume of pyroclastic fall and pyroclastic density current products, which resulted in a very complex sequence in proximal, medial and distal outcrops [e.g., Barberi et al (1978);Di Girolamo et al (1984); Rosi and Sbrana (1987);Fisher et al (1993); Scarpati (1994, 2003); Orsi et al (1996); Rosi et al (1996Rosi et al ( , 1999; Cappelletti et al (2003); Perrotta et al (2006); Fedele et al (2008); Perrotta (2012, 2016); Engwell et al (2014); Scarpati et al (2015aScarpati et al ( , 2015b; Sparice (2015)]. …”

Construction of volcanic records from marine sediment cores: A review and case study (Montserrat, West Indies)

“…Such processes may be particularly relevant within active volcanic arc environments, where water depths are shallower than in ocean basins and where complex topography may develop. For example, tephra fallout deposits from the Campanian Ignimbrite, in the Mediterranean Sea, suggests tephra thickness varies according to the surrounding bathymetry (Engwell et al, 2014), and because submarine flows are commonly channelized in depressions, fallout tephras are more likely to survive erosion when they are emplaced on bathymetric highs. In less dynamic environments tephra fallout deposits in marine sediments are commonly normally-graded as they reflect the different sinking velocities of the different eruptive particles through the water column until they reach the ocean floor (Manville and Wilson, 2004).…”

Late Pleistocene-Holocene volcanic activity in northern Victoria Land recorded in Ross Sea (Antarctica) marine sediments

“…Given that tephra horizons are regionally better preserved in marine environments than in subaerial ones (Engwell et al 2014), we decided to analyse in detail tephra layers in marine cores recovered during the last 30 years by Italian Antarctic Research Program (PNRA). We report here the results of tephrostratigraphic and geochemical studies on eight tephra beds identified in marine sediment sequences from Ross Sea gravity cores.…”