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The Mackenzie Trough provides a high resolution signal for paleoceanography as a result of high sedimentation rates at the mouth of the Mackenzie River. Three cores were collected along a transect covering a depth range of 58–671 m and the time period of the last 11 500 cal BP. Prior to the last ~10 000 cal BP, the distal core is characterized by laminated sediment and a foraminiferal fauna of Arctic Bottom Water calcareous species and abundant planktic foraminifera suggesting little freshwater runoff and (or) perennial sea-ice cover. This occurs at a similar time as laminated sediments from the west of this site, which have been suggested to be part of the Lake Agassiz flood outburst and (or) cold period. If this outburst occurred, the very positive oxygen isotope values from our core (PC3; >+3.0 ppm) indicate that it did not flow through the Mackenzie Trough. After 9000 cal BP, the faunas in the three cores differ because of timing and different water depths. However, it is possible to see a progression of cold saline water prior to 10 000 cal BP, with a freshening of surface water after 10 000 cal BP where tintinnids (brackish water ciliates) occur with incursions of deep water Arctic calcareous species to ~3000 years BP. A sequence of mixed faunas appears as sea ice returns, at least periodically in the last 3000 cal BP; but (in core PC2 only) a return to more sea ice is recorded by both foraminifera and dinocysts in the last few hundred years. La fosse du Mackenzie fournit un signal à haute résolution pour la paléocéanographie en raison des taux élevés de sédimentation à l’embouchure de la rivière Mackenzie. Trois carottes ont été prélevées le long d’un transect couvrant une plage de profondeurs de 58 à 671 m; la période de temps couvre les derniers 11 500 années calendaires avant le présent (années cal. BP). Avant les derniers ~10 000 années cal. BP, la carotte distale est caractérisée par des sédiments laminés et une faune de foraminifères d’espèce calcaire des eaux du fond de la mer Arctique et les nombreux planctons foraminifères suggèrent peu d’écoulement d’eau douce et (ou) un couvert permanent de glace de mer. Cela se produit en même temps qu’une déposition de sédiments laminés à l’ouest de ce site; ces sédiments feraient partie du débordement de l’inondation et (ou) de la période froide du lac Agassiz. Si ce débordement a eu lieu, les valeurs très positives de l’isotope de l’oxygène de notre carotte (PC3; >+3,0 ppm) indiquent qu’il ne s’est pas écoulé à travers la fosse du Mackenzie. Après 9000 années cal. BP, les faunes dans les trois carottes diffèrent en raison des moments de déposition et des profondeurs d’eau différentes. Il est toutefois possible de voir une progression de l’eau froide saline avant 10 000 années cal BP. Après 10 000 années cal. BP, on note un adoucissement de l’eau de surface; en effet, des tintinnides (un cilié planctonique d’eau saumâtre) se retrouvent mélangés à des espèces calcaires d’eau profonde de l’Arctique jusqu’à ~3000 années BP. Une séquence mixte de faunes apparaît au retour de la glace de mer, du moins périodiquement, au cours des dernières 3000 années cal. BP. Cependant, un retour à plus de glace de mer est enregistré dans les foraminifères et les dinokystes au cours des quelques dernières centaines d’années (seulement dans la carotte PC2). [ABSTRACT FROM AUTHOR]

Megathrust earthquakes in western North America may be preceded by a precursor phase several years prior to megathrust, induced earthquakes. For example, on 27 March 1964, a 9.2 magnitude (on the Richter scale) earthquake occurred on the coast of Alaska. Changes in foraminifera and diatom assemblages at Girdwood Flats, Alaska, provide evidence of a precursor to this earthquake, thereby detailing a previously unknown sequence of events. We describe further evidence of precursor phases from marshes in Turnagain Arm, Alaska, United States, and farther south in Netarts Bay, Oregon, United States; this is the first time that two widely spaced locations have been examined for earthquake-related precursor stages. The Alaska earthquake offers the possibility to compare a modern sequence (A.D. 1964) of events with the geologic record. The Netarts Bay marsh has experienced no modern earthquake that could be used for comparison, but the nature of megathrust zones implies that the modern and ancient events should be physically similar. New cores examined from Turnagain Arm include both the 1964 earthquake and an event identified and dated at 1800 yr B.P. Prior to the 1964 event, the foraminifera and thecamoebian assemblages changed from a forest phase to a mildly brackish stage; this sequence was dated as being 15 yr or less in length, using Pb210 and Cs137 dating techniques. The event at 1800 yr B.P. was also associated with a similar precursor stage, indicating a small subsidence prior to the megathrust earthquake-related subsidence event. In Netarts Bay a new core was taken at a previously cored site to make use of carbon-14 dates and the assurance that at least four events were known to have occurred over the past 3000 yr. The new core contains four transitions, each identified by a mineralic deposit, often sharply bounded below and gradationally overlain by marsh peat. Transition in this context refers to the section of core analyzed, ∼15 cm above and below each of the four sand layers. Foraminiferal assemblage analyses indicate that these units represented a high marsh prequake phase followed by a lower marsh precursor stage, the earthquake-related deposition (sand layer), and then a rebound back into postquake marsh deposits. Sand deposits with either no or few foraminifera are inferred as tsunami/ earthquake-related deposition stages. These transitions in two Widely separated geographic areas (Alaska and Oregon) indicate that similar mechanisms operate for large megathrust earthquakes at subduction zones from Alaska to northern California in the Cascadia Subduction Zone, thus implying that precursor events also occur and can be detected by foraminiferal zonation all along this area. In a recent article (Dragert et al., 2001), scientists from the west coast suggested that "slow" or "silent" earthquakes they measured with continuous geographical positioning systems might be indicators of megathrust earthquakes. The transitions we document may be the prehistoric representations of these "silent" quakes. Foraminiferal evidence may help by allowing, more accurate positioning of seismometers along the west coast of North America and thereby lead to more precise and timely earthquake prediction methods. [ABSTRACT FROM AUTHOR]

Studies assemblages of agglutinated foraminifera from the Carboniferous coal-bearing strata of the Sydney basin, Cape Breton Island, Nova Scotia. Seat earths beneath several coal seams containing assemblages dominated by Trochamina; Coal-seam split and coarse siltstone containing assemblages dominated by Ammobaculites and Ammotium; Analysis of foraminiferal biofacies.

Presents a reply to comments on a paper on records of prehistoric hurricanes on the South Carolina Coast based on micropaleontological and sedimentological evidence. Inconsistent use of calcareous layers; Methods of detecting hurricanes.