Water resurge into newly excavated impact craters causes both erosion and conspicuous graded deposits in those cases where the water is deep enough to overrun the elevated crater rim. We compare published information on resurge deposits from mainly the Lockne, Tvären, and Chesapeake Bay structures with new results from low-velocity impact experiments and numerical simulations. Notwithstanding the limitations of each of the analytical methods (observation, experiment, and simulation), we can visualize the resurge process for various initial impact-target configurations, for which one single method would have been insufficient. The focus is on the ways in which variations in impact angle and target water depth affect water-cavity collapse, the initiation and continuation of the resurge, its transformation into a central water plume, and subsequent antiresurge, as well as tsunami generation. We show that (1) the resurge at oblique impacts, as well as impacts into a target with a varied water depth, becomes strongly asymmetrical, which greatly influences the development of the central water plume and sediment deposition; (2) the resurge may cause a central peak–like debris cumulate at the location of the collapsing central water plume; (3) at relatively deep target waters, the resurge proper is eventually prevented from reaching the crater center by the force of the antiresurge; (4) the antiresurge is separated into an upper and a lower component; (5) the resurge from the deep-water side at an impact into water of varied depth may overcome the resurge from the shallow-water side and push it back out of the crater; and (6) contrary to rim-wave tsunamis, a collapse-wave tsunami requires deeper relative water depth than that of Lockne, the crater-forming impact event with the currently deepest known target water depth.

Modern ecologic models for conodonts were extrapolated principally from experience with North American shallow-water subequatorial faunas. Further evidence can be derived from the calcareous lower part of the Swedish Ordovician. This succession among other things offers uniformity of facies, as well as long-ranging conodont genera. Paleomagnetic data indicate deposition at 60°S, i.e., relatively cool climate and fluctuations in air and shallow-water temperatures. The succession might represent a subantarctic shallow-water carbonate platform. Another interpretation favors depth of 100 to 500 m. The relative frequencies of long-ranging conodont genera were plotted against facies data. All data indicate complexity of interaction of depth, temperature, and current dependent factors that influenced the distribution of conodont genera, in particular during a regressive phase about the Arenigian-Llanvirnian transition. Microzarkodina, Periodon , and Protopanderodus had extended frequency minima during the regression. Paroistodus was abundant before the regression, then apparently disappeared from Europe. In a section at Skövde, formed perhaps in particularly deep water, Baltoniodus has a minimum and Drepanoistodus a maximum that might correspond to the peak of regression, but elsewhere the conditions are either ambiguous or reversed. At least Protopanderodus and Periodon probably were not epibenthic, since they occur with shelly fauna in carbonates as well as with graptolites in dark mudstones and with radiolarians in ophiolite-associated cherts (in Scotland). The importance of sorting by differential transport is stressed throughout the study.

Conodonts are phosphatic, denticulated structures in the average size range from 0.1 to 1 mm. They grew by the centrifugal accretion of lamellae. Conodonts are a homogeneous group. Basic interpretations must apply to all kinds of conodonts. Internal and outer morphologic features indicate that they were skeletal elements designed to lend a certain limited rigidity to an organ in which the maximation of surface area was an advantage. Conodonts show evidence of muscle insertion. It is suggested that the muscles operated a tentacle apparatus. Platform and hibbardelliform (trichonodelliform) elements were probably located sagittally on opposite sides of the mouth; if, as a consideration of all known evidence seems to indicate, the conodonts were located close to, but not within, the mouth, this suggests that the mouth was surrounded by a lophophore-like organ. It is suggested that conodonts belonged to planktonic, wormlike lophophorates, with phosphatic lophophore supports. If this is true, they would not be closely related to any living group.

In Europe, a Lower Ordovician conodont zonation can be established for the calcareous, partially condensed succession of the Baltic Shield. Sporadic conodont occurrences in the graptolitic shale facies can be correlated with this zonation. The Tremadocian to Llanvirnian Series are dealt with, and eleven conodont zones are established in these series. From below, these are the zones of Cordylodus angulatus, Paltodus deltifer (both Tremadocian), Paroistodus proteus, Prioniodus elegans, P. evae (corresponding to the Arenigian extensus Zone), Baltoniodus triangularis, B. navis, Paroistodus originalis, Microzarkodina parva (corresponding to the main part of the Arenigian hirundo Zone), and Amorphognathus variabilis (top of hirundo Zone, Llanvirnian bifidus Zone). For handling the material, some new taxa have had to be described. The taxonomy is based on multielement species, where such can be established. The multielement species are defined on morphologic and statistical criteria, as well as on the pattern of evolution. The taxonomic approach allows a more "natural" classification on the suprageneric level than the form-taxonomy previously used for this material. An evolutionary pattern is discernible for the drepnodids (each species containing drepanodiform and oistodiform elements) and the prioniodids (species containing prioniodiform elements, branched compound elements with symmetry transition, and oistodiform elements). On a suggestion from Professor O. H. Walliser, elements belonging to multielement species are distinguished by adding the ending "-form" to the name of the genus they would have been brought to in a purely formal taxonomy. The word formed in this way is an adjective. The following new taxa are named: Drepanoistodus gen. nov., Paroistodus , gen. nov., Protopanderodus , gen. nov., Stolodus , gen. nov., Baltoniodus , gen. nov., Microzarkodina , gen. nov., Microzarkodina parva n. sp., M. ozarkodella n. sp. The following genera are redefined: Oistodus, Scandodus, Scolopodus, Drepanodus, Paltodus, Prioniodus, Gothodus.