The Hulopoe Gravel,Lanai, Hawaii: New Sedimentological Data and their Bearing on the “Giant Wave” (Mega-Tsunami) Emplacement Hypothesis

—Recognition that many oceanic islands are shaped by giant landslides has highlighted claims that the Hulopoe Gravel on south Lanai, Hawaii, was deposited by giant waves (mega-tsunami) generated by such a landslide. This interpretation is controversial. Resolution of the controversy has global implications because mass wasting of oceanic islands has been a common process for as long as hot spot volcanism has affected the ocean basins. Thus, if mega-tsunami are attendant upon the mass wasting process, their effect on earth surface processes should be discernible for much of geological time and may be comparable to that resulting from bolide impacts that form astroblemes.¶Detailed facies analysis of the pebble, cobble and boulder gravels that form the Hulopoe Gravel type section shows that the gravels are composed predominantly of basalt clasts with appreciable amounts of limestone clasts in 8 of the 14 beds present. Deposition was not continuous: eight disconformities are recognized in the 9.2 m type section, three of which are associated with truncated paleosols. The Hulopoe Gravel was not deposited by a single tsunami at 105 ka, as has been proposed. One bed is clearly an alluvial deposit. The origins of others are unclear but the facies data do not exclude tsunami as one of the processes that deposited individual beds within the Hulopoe Gravel, either above or below sea level.     

Predictive Modeling of the Evolution of Fault Structure: 3-D Modeling and Coupled Geomechanical/Flow Simulation

Reconstruction of geological structures has the potential to provide additional insight into the effect of the depositional history on the current-day geomechanical and hydro-geologic state. Accurate modeling of the reconstruction process is, however, complex, necessitating advanced procedures for the prediction of fault formation and evolution within fully coupled geomechanical, fluid flow and temperature fields. In this paper, a 3-D computational approach is presented that is able to forward model complex structural evolution with multiple intersecting faults that exhibit large relative movement within a coupled geomechanical/flow environment. The approach adopts the Lagrangian method, complemented by robust and efficient automated adaptive meshing techniques, an elasto-plastic constitutive model based on critical state concepts, and global energy dissipation regularized by inclusion of fracture energy in the equations governing state variable evolution. The proposed model is validated by comparison of 2-D plane strain and 3-D thin-slice predictions of a bench-scale experiment, and then applied to two conceptual coupled geomechanical/fluid flow field-scale benchmarks.     

Seasonal Variation in the Covering ­Behaviour of the Echinoid Paracentrotus lividus (Lamarck)

Abstract. Covering behaviour is displayed by several regular echinoid species but its functional significance has yet to be quantified. Some of the most popular theories have interpreted this behaviour as an adaptive response to avoid over-exposure to light and/or as an anti-predator strategy. Since both predation pressure and light intensity may be seasonal as well as diurnal in nature, the aim of the present study was to quantitatively examine, in situ , the potential seasonality of covering behaviour in the purple sea urchin, Paracentrotus lividus (Lamarck). Data were collected over a one-year period at Lough Hyne, Co. Cork in Ireland. A peak in covering activity was observed over the summer months. Predator density and light intensity (sunlight hours) were also shown to vary seasonally at Lough Hyne. Covering behaviour in P. lividus , as in other echinoids, may be a response to a number of simultaneously interacting factors. At Lough Hyne, however, light intensity and covering item availability appear to be particularly important factors.     

Modelling microseismicity of a producing reservoir from coupled fluid‐flow and geomechanical simulation

In this paper, we investigate production induced microseismicity based on modelling material failure from coupled fluid‐flow and geomechanical simulation. The model is a graben style reservoir characterized by two normal faults subdividing a sandstone reservoir into three compartments. The results are analysed in terms of spatial and temporal variations in distribution of material failure. We observe that material failure and hence potentially microseismicity is sensitive to not only fault movement but also fluid movement across faults. For sealing faults, failure is confined to the volume in and around the well compartment, with shear failure localized along the boundaries of the compartment and shear‐enhanced compaction failure widespread throughout the reservoir compartment. For non‐sealing faults, failure is observed within and surrounding all three reservoir compartments as well as a significant distribution located near the surface of the overburden. All shear‐enhanced compaction failures are localized within the reservoir compartments. Fault movement leads to an increase in shear‐enhanced compaction events within the reservoir as well as shear events located within the side‐burden adjacent to the fault. We also evaluate the associated moment tensor mechanisms to estimate the pseudo scalar seismic moment of failure based on the assumption that failure is not aseismic. The shear‐enhanced compaction events display a relatively normal and tight pseudo scalar seismic moment distribution centred about 10⁶ Pa, whereas the shear events have pseudo scalar seismic moments that vary over three orders of magnitude. Overall, the results from the study indicate that it may be possible to identify compartment boundaries based on the results of microseismic monitoring.     

Quantifying Spatial Patterns of Intertidal Biodiversity: Is Movement Important?

Abstract.  Small-scale patterns of low-, mid- and high-shore intertidal species density, richness and abundance were systematically examined to assess the potential influence of 'mobility' on spatial community dynamics and diversity. Mobile taxa outnumbered sessile species by approximately 2:1, whereas sessile individuals were over 12 times as numerous as mobile ones over the entire study site. Patterns of density, richness and abundance differed with shore level and substratum. The results also highlighted the importance of clearly distinguishing between species density and species richness when examining spatially quantitative data. The rank order of habitats from highest to lowest species density was not the same when analysed in order of species richness. The potential for the mobile proportion of assemblages to influence small-scale diversity assessment through movement was greater at mid- and high-shore zones because the ratio of mobile species was higher and abundance (relative to the lower shore) was low. These observations might reflect the relative influence of the land–sea gradient of immersion on diversity and mobility in intertidal communities. The influence of mobile organisms on marine ecosystem function may be significant because small-scale patterns of movement are known to positively influence biodiversity. High richness paired with low abundance, however, may result in underestimating the functional role of mobile intertidal species.     

New information on the giant Devonian lobe-finned fish Edenopteron from the New South Wales south coast

Abstract

Edenopteron, with a lower jaw some 48?cm long, and total length perhaps exceeding 3 m, is the largest Devonian lobe-fin known from semi-articulated remains. New material described from the type locality (Boyds Tower, south of Eden) includes three slightly smaller articulated skulls and jaws, and additional bones of the shoulder girdle. Another articulated skull roof, shoulder girdle and palate is described from a second locality (Hegarty Bay), about 10?km south of Boyds Tower. Both localities represent the upper part of the Worange Point Formation, of late Famennian age (uppermost Upper Devonian). The new morphological evidence supports a close relationship to the tristichopterids Mandageria and Cabonnichthys, from the slightly older (Frasnian, Upper Devonian) fossil fish assemblage at Canowindra, New South Wales. Features of the shoulder girdle (supracleithrum, anocleithrum) suggest that Edenopteron is more closely related to Mandageria than Cabonnichthys. Eight characters are used to define a tristichopterid subfamily Mandageriinae, to which Notorhizodon from the Middle Devonian of Antarctica is also referred. The Mandageriinae is endemic to East Gondwana (Australia–Antarctica). In combination with possibly the most primitive tristichopterid, Marsdenichthys from the Frasnian of Victoria, these distributions implicate East Gondwana as a likely place of origin for the entire group. This relates to the major but unresolved question of a possible Gondwana origin for all the land vertebrates (tetrapods).

• An endemic Gondwanan sub-group (Mandageriinae) of the Devonian fishes closest to land animals (tetrapodomorph tristichopterids) is confirmed.

• Retention of primitive features (e.g. accessory vomers) points to an earlier origin of the Mandageriinae in East Gondwana, consistent with the Victorian occurrence of another primitive tristichopterid (Marsdenichthys).

• Edenopteron is confirmed from a second south coast fossil site, and new characters indicate its closest relative is Mandageria from Canowindra, NSW.

• Congruent evidence of older Gondwanan occurrences in other groups (basal tetrapodomorphs, rhizodontids, canowindrids), and previously dismissed trace fossil evidence (Grampians trackways), implicate South China and East Gondwana as the likely place of origin for all land vertebrates.

     

Gosses bluff — diapir,crypto‐volcanic structure or astrobleme?∗

Gosses Bluff, west of Alice Springs, Northern Territory, comprises a roughly circular rim of steeply dipping sandstone, locally overturned with downward facing folds, surrounding a topographically lower core of steeply dipping faulted sandstone, shale, and limestone. Abundant shattercones occur both in outcrop and to depths of 1,000 m. The structure lies on an’ anticlinal trend‐Structural, gravity, seismic and drill hole data indicate that the structure continues to some depth. Shattercones also occur outside the rim of Gosses Bluff. At a nearby prominence, Mt Pyroclast, they occur with peculiar breccias and devitrified glassy rocks, some of which may be of volcanic or impact fusion origin.

Gosses Bluff has previously been regarded as a diapir caused by salt intrusion. The evidence now available suggests that it is a crypto‐explosion structure, resulting either from deep‐seated explosive volcanic activity, or from meteorite impact, probably at some time during the Mesozoic Era.