Derek Rust

Holocene tectonic uplift patterns in northeastern Sicily: evidence from marine notches in coastal outcrops

Abstract Marine notches are groove-like features formed in rocky coastal outcrops in relation to past sea levels, and are widely used as indicators of rates and patterns of tectonic activity. Examination of uplifted notches in the complex plate boundary setting of northeast Sicily reveals the need for considerable care in their interpretation. Present notch-forming processes are dominated by carbonate dissolution, aided by microbial activity, as waves surge and recede at the base of the cliffs, and produce notches approximately 0.5xa0m above present biological mean sea level (i.e. above an organic constructional rim of coralline algae, used to define sea level). At sea level, dissolution is restricted through saturation and the bedrock protected by the outbuilding algal rim. This assemblage varies in response to fetch exposure and uplift rate, typically producing a complex band of uplifted notch features exposed above sea level. Correlations (based on height) of the shallow and discontinuous notch indentations within this band are unreliable. However, the upper margin of the band, marked by the roof of the uppermost notch, is a prominent and laterally persistent feature easily recognised as the boundary between subaerial and marine processes. We propose that this is an approximately coeval datum formed when post glacial sea-level rise decelerated in the mid Holocene to match the rate of tectonic uplift, a notion strengthened by the available dates of about 5xa0ka for this feature. Subsequent uplift outpaced later sea-level rise, taking the notches above sea level. This proposed datum varies in height from about 2xa0m at Capo Milazzo (on the north coast) to about 5xa0m on the east coast bordered by the Messina fault system. The height differential is consistent with the respective elevations of nearby marine terraces dating from the last interglacial at about 125xa0ka, but also exhibits shorter term variations suggesting Holocene increases in activity rates on more localised structures affecting the localities involved. Regionally, northeast Sicily is characterised by long term differential uplift rather than behaving as a coherent block. The highest uplift rate, probably exceeding 2xa0mmxa0a −1 (calculated using the sea-level curve from Fairbanks, R.G., 1989. A 17000-year glacio-eustatic sea level record; influence of glacial melting rates on the Younger Dryas event and deep-ocean circulation. Nature 342, 637–642 ), is suggested for a notch locality on the upthrown side of the Malta Escarpment. Rates of about 2xa0mmxa0a −1 are indicated by the 5xa0m notch at localities bordered by the Messina fault system, and a rate close to 1xa0mmxa0a −1 is suggested for the (undated) 2xa0m notch at Capo Milazzo.

Flank instability on Mount Etna: Radon, radar interferometry, and geodetic data from the southwestern boundary of the unstable sector

[1]xa0Understanding Etnean flank instability is hampered by uncertainties over its western boundary. Accordingly, we combine soil radon emission, interferometric synthetic aperture radar (InSAR), and electronic distance measurement (EDM) data to study the Ragalna fault system (RFS) on the SW flank of the volcano. Valuable synergy developed between our differing techniques, producing consistent results and serving as a model for other studies of partly obscured active faults. The RFS, limited in its surface expression, is revealed as a complex interlinked structure ∼14 km long that extends from the edifice base toward the area of summit rifting, possibly linking northeastward to the Pernicana fault system (PFS) to define the unstable sector. Short-term deformation rates on the RFS from InSAR data reach ∼7 mm yr−1 in the satellite line of sight on the upslope segment and ∼5 mm yr−1 on the prominent central segment. Combining this with EDM data confirms the central segment of the RFS as a dextral transtensive structure, with strike-slip and dip-slip components of ∼3.4 and ∼3.7 mm yr−1, respectively. We measured thoron (220Rn, half-life 56 s) as well as radon, and probably because of its limited diffusion range, this appears to be a more sensitive but previously unexploited isotope for pinpointing active near-surface faults. Contrasting activity of the PFS and RFS reinforces proposals that the instability they bound is divided into at least three subsectors by intervening faults, while, in section, fault-associated basal detachments also form a nested pattern. Complex temporal and spatial movement interactions are expected between these structural components of the unstable sector.

Holocene sea-level change in Sicily and its implications for tectonic models: new data from the Taormina area, northeast Sicily

The northeast coast of Sicily shows emergent marine features that have been uplifting during the Holocene along the footwalls of two major regional fault systems, the Malta Escarpment and Messina fault system. Previously, uplift rates were interpreted as up to about 1.8 mm/mm a−1. New dates on shelly remains, collected close to sea-level, from the Taormina area north of Mount Etna, and amended sea-level curves, are used to show that uplift over the past 6000 years has been proceeding at a slower rate of about 1.4 mm a−1. However, over a longer time period, from the Tyrrhenian Oxygen Isotope Stage 5.5 (about 125 ka) to the present day, the uplift rate has been yet slower, at about 1 mm a−1. Northeast Sicily lies in a complex plate boundary region whereas, in contrast, the rest of Sicily appears to have been stable throughout the later Quaternary. Further comparisons show that the French Mediterranean coast [Lambeck, Bard (2000) Earth Planet. Sci. Lett., 175, 202–222] is a region of crustal stability, where movement is dominated by subsidence of the outer portion of the proglacial forebulge of the last glaciation. There the coastline has been progressively submerged during the Holocene, and sea level has never been higher than at present. Northeastern Sicily uplift is therefore more likely controlled by plate processes that mask most of the effects of glacio-hydro-isostatic adjustment.

Postglacial fault movement and palaeoseismicity in western Scotland: a reappraisal of the Kinloch Hourn fault, Kintail

The Kinloch Hourn fault is the most prominent of a number of suspectedpostglacial faults in the western Scottish Highlands. These faults areinterpreted to have been reactivated by repeated large (M > 6)palaeoseismic events following deglaciation 10,000–13,000 years ago.Based on inferred deflections of drainage courses, previous studies of thefault have estimated 160 ± 40 m cumulative left-lateral displacementalong a 14 km long active segment during postglacial times. Reportedsoft-sediment deformation phenomena imply that activity on the KinlochHourn fault has persisted into the late Holocene, with the most recentmovement having been associated with a magnitude 5.5–6.0 surface-faultingevent between 3500 and 2400 years ago. The marked contrast betweensuch palaeoseismic activity and the present-day seismic quiescence ofwestern Scotland has stimulated this critical reappraisal of the KinlochHourn fault.This paper reassesses the key lines of evidence for postglacial fault activityand palaeoseismicty on the Kinloch Hourn fault, combining the analysis of1:15,000-scale air photos, field-based geomorphic mapping andpalaeoenvironmental investigations. Our reappraisal of inferred drainagedeflections across the fault contends that previous reports of significant(102 m) left-lateral slip on the fault during the Holocene arespurious. Instead, incidences of Holocene channel abandonment along thefault line are non-synchronous and probably reflect non-tectonic drainagechanges. The timing of soft-sediment deformation in the vicinity of the faultis revised to an early Holocene date (8990–8580 calendar years BP), whichis in accord with both the palaeoenvironmental history of the site andconsistent with published ages of earthquake-induced liquefactionphenomena documented elsewhere in western Scotland. An alleged recent(post-2400 radiocarbon years BP) ground rupture on the fault isquestioned in the light of uncertainty about both the nature of the faultedsoil deposit and the late Holocene age attributed to it.The study concludes that there is no convincing evidence for postglacialsurface rupture on the Kinloch Hourn fault and speculates that the casefor significant (101–102 m) postglacial movement on otherfaults in western Scotland may be similarly `unproven.