Showing papers by "Malcolm B. Hart published in 2013"

Timing, origin and emplacement dynamics of mass flows offshore of SE Montserrat in the last 110 ka: Implications for landslide and tsunami hazards, eruption history, and volcanic island evolution

Abstract: [1] Mass flows on volcanic islands generated by volcanic lava dome collapse and by larger-volume flank collapse can be highly dangerous locally and may generate tsunamis that threaten a wider area. It is therefore important to understand their frequency, emplacement dynamics, and relationship to volcanic eruption cycles. The best record of mass flow on volcanic islands may be found offshore, where most material is deposited and where intervening hemipelagic sediment aids dating. Here we analyze what is arguably the most comprehensive sediment core data set collected offshore from a volcanic island. The cores are located southeast of Montserrat, on which the Soufriere Hills volcano has been erupting since 1995. The cores provide a record of mass flow events during the last 110 thousand years. Older mass flow deposits differ significantly from those generated by the repeated lava dome collapses observed since 1995. The oldest mass flow deposit originated through collapse of the basaltic South Soufriere Hills at 103–110 ka, some 20–30 ka after eruptions formed this volcanic center. A ~1.8 km3 blocky debris avalanche deposit that extends from a chute in the island shelf records a particularly deep-seated failure. It likely formed from a collapse of almost equal amounts of volcanic edifice and coeval carbonate shelf, emplacing a mixed bioclastic-andesitic turbidite in a complex series of stages. This study illustrates how volcanic island growth and collapse involved extensive, large-volume submarine mass flows with highly variable composition. Runout turbidites indicate that mass flows are emplaced either in multiple stages or as single events.

Marine geoconservation in the United Kingdom

Abstract: Although the conservation of geological and geomorphological features is a well-established practice in the UK, the conservation of such features in the marine environment has been largely ignored until recently. The provisions made for conserving biodiversity in The Marine and Coastal Access Act 2009 and Marine (Scotland) Act 2010 provide for the conservation of geological and geomorphological features, whilst similar provisions are currently going through the Northern Ireland Assembly in the Northern Ireland Marine Bill. The importance of such features within the marine environment, their interactions with biological features and processes and their value in complimenting terrestrial features, particularly in relation to our understanding of events during the Quaternary, are explored. Opportunities for the conservation of these features under the Marine and Coastal Access Act 2009 are reviewed in particular, as are a range of methodologies for their identification. The use of stakeholder groups in the selection and inclusion of these features in English inshore and offshore, and Welsh offshore areas are discussed. Some of the challenges that emerged during this process are highlighted, in particular that of communicating an understanding of the significance, value and vulnerability of geological and geomorphological features. The development of coastal access in England and Wales provides opportunities for improving public understanding of geology and geomorphology in the marine environment through its promotion and interpretation on the coast. This and other initiatives that raise awareness of these features may provide future support for their inclusion in any future revision of Marine Conservation Zones.

Proliferation of Oberhauserellidae During the Recovery Following the Late Triassic Extinction: Paleoecological Implications

Abstract: A paleoecological study of benthic foraminifera through the lower Hettangian in the Doniford Bay section (west Somerset, U.K.) is presented. The sudden and brief appearance of Oberhauserellidae in the aftermath of the Late Triassic extinction is defined as a proxy for environmental perturbations indicating severe biotic stress conditions. Oberhauserellidae, associated with the genus Reinholdella are distinguished from other species by a high abundance, low diversity, high dominance and an abnormally small size. This suite of characters mimics an opportunistic behavior where these r-strategists and grazer feeders maximize their full ecological potential at a time of low-oxygen conditions on the sea-floor and a high food supply: both of which appear to be the main triggers of this paleoecological change. The disappearance of these opportunistic benthic foraminifera coincides with the appearance of infaunal, low-oxygen-tolerant generalists, and the restoration of stable environmental conditions (e.g., well-stratified water mass and oligotrophic conditions), characterizing the initial stages of recovery following the Late Triassic extinction event.

The Cretaceous/Paleogene Boundary Events in the Gulf Coast: Comparisons between Alabama and Texas

Abstract: Following identification of the Chicxulub crater on the Yucatan Peninsula, the Cretaceous/Paleogene (K/Pg) boundary sections in the Gulf Coastal Plain were recognised as being of international significance. In the period 2009–2012, M. B. Hart and co-workers have investigated a number of successions in the Brazos River area, Falls County, Texas, and reported on their sedimentology, micropaleontology and geochronology. Comparable sections in Alabama have received relatively little attention in recent years and this is now being addressed. Sections on Highway 263 near Braggs, Mussel Creek and Moscow Landing appear to have been deposited in shallower-water environments as compared to those in Texas. The Braggs section, which is often regarded as the ‘type’ section by workers in the area, is—in fact—rather atypical. Above a sharp erosive surface at the top of the Prairie Bluff Chalk Formation (in a mudstone facies), the majority of the overlying strata are concordant with few signs of hiatuses at lithological boundaries. Many of the carbonate-rich beds within the mudstones of the Clayton Formation (Pine Barren Member) of the Lower Paleocene appear to be diagenetic in origin. In the Mussel Creek succession, which is relatively close to the Braggs section, there are numerous hiatuses detected, many of which show complex bioturbation. Above the almost flat, but bioturbated, top of the Prairie Bluff Chalk Formation is a thin, complex succession of sandstones, clay-stones, eroded blocks of the Prairie Bluff Chalk Formation and prominent fragments of charcoal. This complex series of ‘events’ is followed by a carbonate-rich bed with broken shell fragments and phosphatic clasts, including ammonite fragments, above which is a series of Paleocene mudstones and carbonate-rich beds comparable to those recorded in the Braggs section. The Moscow Landing succession, exposed on the west bank of the Tombigbee River, is located approximately 135 km west-northwest of the Braggs area. In this succession the Prairie Bluff Chalk Formation (in a more carbonate-rich facies) is overlain by a brown, coarse, spherule-bearing sandstone that is associated with a small number of widely-spaced, internally complex, channels before—in turn—being overlain by a succession of mudstones and carbonate-rich beds. We identify two regionally important events in these three locations. The top-Prairie Bluff Chalk Formation surface is smooth, but undulating, and appears to be the result of regional erosion at the time of the Chicxulub impact. Between this surface and the local base of Zone P1a, the Clayton (Basal) Sands contain an admixture of sediments, re-worked clasts of the underlying Prairie Bluff Chalk Formation, re-worked macrofossils, re-worked microfossils and (in the west of Alabama) re-deposited spherules. We have been able to piece together the sequence of events in all these sections and linked our preliminary interpretations to both the now-buried Miller’s Ferry sections and the Brazos River area.

Statoliths: neglected microfossils

Abstract: In the Callovian mudstones associated with the Christian Malford Lagerstatte (Wilby et al. , 2008), exceptionally large numbers of statoliths have been found in normally prepared (White Spirit method of Brasier, 1980) micropalaeontology residues. Statoliths, like the otoliths in teleost fishes, are aragonitic ‘stones’ found in the stato-acoustic organs (statocysts) of squid. While statoliths are relatively well known in the biological literature (Lipinski, 1986, 1997; Hanlon & Messenger, 1996) they remain almost undescribed in the field of micropalaeontology. Otoliths are the stato-acoustic organs of bony (teleost) fish and can be well preserved as fossils (Frost, 1924, 1926; Rundle, 1967; Stinton & Torrens, 1968; Lowenstein, 1971; Patterson et al. , 1993; Patterson, 1998, 1999; Hart et al. , 2006, 2009). In some of these accounts of Jurassic otoliths there are a number of illustrations …

A critical evaluation of the Paleocene-Eocene Thermal Maximum: an example of things to come?

Abstract: The Paleocene–Eocene Thermal Maximum (PETM), arguably the most dramatic hyperthermal event recorded to date, occurred approximately 55 million years ago (Ma). During this event thousands of petagrams of carbon were released into the atmosphere and hydrosphere affecting the climate, ocean chemistry and marine and terrestrial ecosystems. With a duration of approximately 100,000 years (though possibly as long as 170,000 years) and global temperature increases of between 48°C, terrestrial and marine faunal turnover occurred including mammalian dispersal, rapid evolutionary and ecological change and transient diversification. The PETM, therefore, offers a valuable insight into shifts in the climate regime and the resultant marine and biotic response that may be relevant to future anthropogenically induced climate change. The mechanisms for delivery of isotopically light carbon into the atmosphere and hydrosphere remain a hotly debated topic. Here we discuss numerous possible sources of carbon and the mechanisms responsible for their release.