Single Catastrophic Event Research Articles

A giant landslide on the north flank of Tenerife, Canary Islands

The extent of mass wasting along the north flank of Tenerife has been mapped using swath bathymetry, GLORIA side‐scan sonar, and 3.5‐kHz echo sounder data. The marine surveys show that, north of Tenerife, a giant landslide is exposed over an area of 5500 km2 of the seafloor, more than twice the surface area of the island. The landslide truncates an older ridge and valley topography that is associated with the shield building basalts on Tenerife. We interpret the ridge and valley topography as the result of subaerial erosion. The landslide is estimated to have a length of 100 km, a width of up to 80 km, and a volume of about 1000 km3. It extends onshore into the Orotava and Icod valleys which have been interpreted as of landslide origin. K‐Ar dating of basaltic flows in the steep headwall of Orotava suggests an age of formation for the valley is younger than 0.78 Ma and may even be younger than 0.27 Ma. The Icod valley is located immediately to the north of the most recent volcano on Tenerife, Las Cañadas, and has been associated with the collapse of its caldera, between 1.2 and 0.2 Ma. A young age for the landslide is supported by the 3.5‐kHz echo sounder data which show that the landslide is draped by a thin (< 10 m) layer of younger sediment. The landslide did not form, however, during a single catastrophic event but represents the amalgamation of a number of separate landslides. The occurrence of the ridge and valley topography in water depths of up to 2.5 km suggests that the shield‐building basalts have subsided by at least this amount since they formed, 3.3–8.0 Ma. We speculate that this subsidence is caused by some form of stress relaxation that occurs in the underlying lithosphere. The giant landslide imaged in our sonar data is associated with the late stages in the development of the most recent volcano on Tenerife, Las Canadas, which only began at about 1.8 Ma. Thus landsliding may be a particular feature of the time soon after emplacement when because of incomplete isostatic adjustment, oceanic volcanoes have their greatest elevations above sea‐level and therefore are most susceptible to slope failure.

A Catastrophic Death Assemblage of a New Species of Cormorant and Other Seabirds from the Late Pliocene of Florida

ABSTRACT A new late Pliocene (upper Pinecrest beds, 2.4–2.0 Ma) fossil locality in Florida has produced thousands of bones and 137 whole and partial skeletons of a new species of cormorant, Phalacrocorax filyawi, that is related phylogenetically to Recent taxa currently restricted to the eastern north Pacific. Evidence from the bones and the stratigraphy of the site indicate that the cormorants died in a single catastrophic event, perhaps a red tide. At least eight other taxa of seabirds and shorebirds also were recovered from the site and include two new species of gull, Larus perpetuus and L. lacus, described herein. The depositional environment reflected by this fauna is a coastal lagoon and beach or shoreline habitat that rarely is preserved in the fossil record of Florida. The fossil cormorant and other seabirds from the Pliocene support molluscan evidence that the Florida Gulf Coast was characterized then by cold-water up welling and a highly productive marine system. Marine cormorants in the eastern Pacific may have extended into the Gulf of Mexico in the early Pliocene during submergence of the Panamanian Isthmus, but became extinct in this region by the end of the Pliocene.

A Catastrophic Death Assemblage and Paleoclimatic Implications of Pliocene Seabirds of Florida

A deposit of fossil seabirds from the late Pliocene of Florida includes more than 130 skeletons of an extinct cormorant that is related phylogenetically to Recent species currently restricted to the eastern north Pacific. Evidence suggests the birds died in a single catastrophic event, perhaps a red tide. The fossil cormorant, along with other extinct seabirds and marine mammals, supports molluscan evidence for cold-water upwelling along the Florida Gulf Coast during the Pliocene. A decline in species richness of marine vertebrates throughout the Pliocene of Florida coincides with cessation of upwelling after emergences of the Panamanian Land Bridge.

The Role of Transients in Weather Regimes and Transitions

Transition of weather regimes is examined in a highly simplified model. Two completely distinct internal methods of transition are identified. The first is a synoptically triggered large-scale instability, while the second is an energy inconsistency between the large-scale and synoptic scales that does not allow the two scales to equilibrate. In the atmosphere, the first case appears as a sudden propagation and damping (or vice versa) of the large-scale pattern with no obvious warning, while the second is consistent with the synoptician's description of a regime being disrupted by a single catastrophic event such as explosive cyclogenesis. The first method is always fast (on a synoptic time scale), while the second does not have to be, though often is. By examining what causes the regimes to fail, one can better understand the role of the transients during all phases of weather regimes.

The K-T boundary and contiguous strata in western Canada: interactions between paleoenvironments and palynological assemblages

A detailed palynological study of samples from 12 localities in western Canada indicates that, through the K-T boundary interval, a series of changes occurred within plant communities and that these changes are overprinted by variations related to latitudinal and climatic differences. Distinctive palynofloras are present below the boundary, in the boundary claystone and above the boundary. Time must be represented in the change from one palynoflora to another, and therefore between their host sediments, as each palynoflora represents a reproductively mature plant community. Boundary claystone floras are closely linked to those of the latest Maastrichtian and so predate the extinction event. Following the extinctions, opportunistic floras characterized by one or two dominant species were established. The dominant opportunistic taxa vary geographically and generally reflect abundances established in latest Maastrichtian floras. There is strong evidence to suggest that the K-T event coincides with a period of increased wetness over most of western North America, which locally results in organic-rich sediments underlying the boundary claystone. This suggests that changes noted at and contiguous to the boundary were not solely owing to a single catastrophic event but, at least in part, resulted from a longer term alteration in the complex series of factors controlling plant community development.

Larval ecology, life history strategies, and patterns of extinction and survivorship among Ordovician trilobites

Differences in the larval ecology of Ordovician trilobites directly influenced the outcome of the Ashgill extinction (latest Ordovician) and indirectly governed the pattern of evolution in post-Ordovician trilobites. Larval ecology also affected survivorship patterns within the Ordovician, particularly between the Llandeilo and the Caradoc stages. All taxa with pelagic adults became extinct by the end of the Ordovician. Similarly, trilobites with entirely planktonic larvae had all but disappeared by the end of the Ordovician. Although suffering a significant loss in diversity, taxa with benthic larvae provided the ancestral stock for the majority of post-Ordovician lineages. Trilobites with a two-stage protaspid period (single planktonic followed by benthic larvae) suffered least during the Ashgill extinction, giving rise to approximately 23% of the new genera appearing in the early Silurian.Patterns of extinction/survivorship among trilobite taxa with different developmental strategies indicate that the so-called Ashgill extinction was most likely the result of a composite phenomenon, including environmental perturbations, ecosystem breakdown and biogeographic restriction, and was not the consequence of a single catastrophic event (e.g., bolide collision). Indeed, our results are consistent with extinction models which invoke periodic global cooling and sea level regression associated with glaciation. Taxa with planktonic larvae first suffered a marked decline in diversity between the Llandeilo and the Caradoc (end of Middle Ordovician), coincident with the onset of the Ordovician-Silurian glaciation. During this time interval, the paleogeographic ranges of most surviving genera with solely planktonic larvae were severely constricted to lower latitude paleobiogeographic provinces. During the Ashgill (Rawtheyan to Hirnantian), climatic and sea level fluctuations were most extreme because of continued and more extensive glaciation. At this time, when extinctions were particularly severe, there was also a significant effect upon the survivorship of taxa with benthic larvae.Our results indicate that the proportion of the life cycle spent in the water column, dependent upon a planktonic food source, was a critical factor in the survivorship of trilobite taxa during Middle to Late Ordovician time. Consequently, differences in life history patterns predisposed individual taxa to survival or extinction.

The carbon-isotope shift at the Permian/Triassic boundary in the southern Alps is gradual

Carbon isotope ratios in marine carbonate rocks have been shown to shift at some of the time boundaries associated with extinction events; for example, Cretaceous/Tertiary1 and Ordovician/ Silurian2. The Permian/Triassic boundary, the greatest extinction event of the Phanerozoic3, is also marked by a large δ13C depletion4,5. New carbon isotope results from sections in the southern Alps show that this depletion did not actually represent a single event, but was a complex change that spanned perhaps a million years during the late Permian and early Triassic. These results suggest that the Permian/Triassic (P/Tr) extinction may have been in part gradual and in part 'stepwise'6,7, but was not in any case a single catastrophic event.

Depositional features of March 1982 Mount St Helens sediment flows

On 19 March 1982, 2 yr after initial eruption, Mount St Helens erupted explosively, resulting in the deposition of new sediment flows in the Toutle River drainages (Fig. 1). We conducted field observations of these flows during the period 29 March–5 April 1982. By this time, the rivers, rapidly re-establishing pre-eruption channel levels, had down-cut through the new flows, allowing us to examine the internal structure of the flows before they could be extensively modified by reconstruction projects. The flows were characterized by a distinct three unit sequence. A basal massive to graded layer (unit 1) consists of large clasts in grain to grain contact. It is overlain by a distinctly finer-grained stratified unit (unit 2) of similar thickness. The top unit (unit 3) contains very large matrix-supported clasts and transported log debris (Fig. 2). This sequence has not previously been documented where its origin could clearly be ascribed to a single catastrophic depositional event. The sequence provides a useful model for interpreting similar deposits in the rock record.

Fluctuations in the evolution of Palaeozoic intertebrates

Summary The problem of interpreting faunal fluctuations is reviewed and it is stressed that numerical abundance cannot be assessed, and morphological diversity only by comparing taxa or the subjective views of specialists. Comparisons at generic and higher taxon levels are made for the more common Palaeozoic fossil groups for appearance of new and extinction of old stocks. The striking diversification (and often appearance) of many groups with calcareoushard parts during the Ordovician is stressed and related to evidence for particularly widespread shallow seas at that time. In detail, groups do not show precise time agreement in their later evolutionary ‘bursts’, but significant periods seem to be during the early and mid-Devonian and the early Carboniferous, but these are at taxon grades lower than the Ordovician diversification. For extinctions it is often possible to separate intrataxal, presumably competitive, extinctions during the rapid rise of a group, from extinctions which appear to affect unrelated stocks. Significant periods for the latter are around the mid- and late Devonian and the mid- and late Carboniferous. These extinctions occur pari passu , rather than as single catastrophic events. Possible long-continued palaeogeographical causes are considered.

A Study of Small Business Failure: Smith & Griggs of Waterbury

Historians have recorded some of the more spectacular failures in American business, but the subject of business failure in itself has not been intensively studied. To lay the groundwork for such a study, the experience of individual firms should be examined in detail and attention should be directed to small as well as large business units. The history of Smith & Griggs provides an example of “discontinuance” which came about not as a result of a single catastrophic event but by a process of long-time attrition involving every phase of the company's operations.