Point Assemblage Research Articles

Paleoproterozoic arc and ophiolitic rocks on the northwest-margin of the Trans-Hudson Orogen, Saskatchewan, Canada: their contribution to a revised tectonic framework for the orogen

A new lithotectonic framework for the northwestern Reindeer Zone of the Trans-Hudson Orogen divides rocks into five northwest- to north-dipping volcano-sedimentary assemblages: (1) at the structural base, the 1.92–1.87 Ga largely sedimentary Levesque Bay Assemblage (partly equivalent to former ‘MacLean Lake gneisses’), which lies within the confines of the Kisseynew Domain and is tectonically imbricated with metasedimentary rocks of the <1.85 Ga McLennan and Burntwood groups; (2) the turbiditic Duck Lake Assemblage, also located along the northern edge of the Kisseynew Domain; it contains detrital zircons ranging in age between 1.92 and 1.87 Ga; (3) the ?1.92 Ga mafic–ultramafic volcano-plutonic Lawrence Point Assemblage of the La Ronge Domain; (4) the ≥1.88 Ga felsic to intermediate volcano-plutonic Reed Lake Assemblage of the La Ronge Domain; and (5) the turbiditic Milton Island Assemblage of the Rottenstone Domain, which contains detrital zircons ranging in age between 2.83 and 1.86 Ga. The assemblages are intruded by a variety of 1.91–1.78 Ga mafic to felsic plutons. The Lawrence Point Assemblage is interpreted as a dismembered supra-subduction zone ophiolite. High-MgO refractory harzburgite (‘Group 1’ ultramafic rocks), at the structural base of the assemblage, is geochemically identical to the upper mantle section of selected supra-subduction zone ophiolites and mantle tectonites. Chromite and olivine compositions of the ‘Group 1’ ultramafic rocks are also comparable to those of ophiolitic harzburgite and mantle tectonite. Mafic metavolcanic rocks of the assemblage are classified as subalkaline tholeiitic basalts. Their trace element patterns and Hf, Ta, Th, Y, Nb, and La element ratios resemble those of modern back-arc basin basalts. The Reed Lake Assemblage represents a subduction-generated arc complex that was built on top of the Lawrence Point Assemblage; its mafic metavolcanic rocks are subalkaline basalts, with calc-alkaline trends, and elevated Th and Ce concentrations and negative Nb anomalies. Feldspar porphyry dykes intruding the Lawrence Point and Duck Lake assemblages constrain timing of Lawrence Point ophiolite emplacement onto the Duck Lake Assemblage to 1.86–1.84 Ga. The trace element geochemistry of the dykes suggests continued arc volcanism after ophiolite emplacement. Mafic metavolcanic rocks of the Levesque Bay Assemblage are geochemically similar to those of the Lawrence Point Assemblage. Other ultramafic rocks (peridotite to pyroxenite) are abundant in the Lawrence Point Assemblage, but have similar geochemistry to small ultramafic bodies intruding the Reed Lake, Duck Lake and Levesque Bay Assemblages. They represent a separate, later phase (?1.86 Ga) of ultramafic plutonism, which post-dates ophiolite emplacement. Timing of Lawrence Point ophiolite emplacement (between 1.86 and 1.84 Ga) and geochemistry of later felsic and mafic/ultramafic volcanism suggest that the Lawrence Point ophiolite and overlying Reed Lake arc assemblage were not accreted to the Hearne Craton prior to 1.86 Ga, but were first accreted to the Flin Flon–Glennie Complex after 1.86 Ga.

Modular construction of early Ediacaran complex life forms.

Newly discovered, exceptionally preserved, soft-bodied fossils near Spaniard's Bay in eastern Newfoundland exhibit features not previously described from Ediacaran (terminal Neoproterozoic) fossils. All of the Spaniard's Bay taxa were composed of similar architectural elements-centimeter-scale frondlets exhibiting three orders of fracticality in branching. Frondlets were combined as modules atop semi-rigid organic skeletons to form a wide array of larger constructions, including frondose and plumose structures. This architecture and construction define the "rangeomorphs," a biological clade that dominated the Mistaken Point assemblage (575 to 560 million years ago) but does not appear to be ancestral to any Phanerozoic or modern organisms.

A Reconsideration of Stone Point Assemblages

A Reconsideration of Stone Point Assemblages

Paleoecology of the oldest known animal communities: Ediacaran assemblages at Mistaken Point, Newfoundland

Ediacaran fossils at Mistaken Point, southeastern Newfoundland (terminal Neoproterozoic; 565–575 Ma) represent the oldest known animal communities. In contrast to most Phanerozoic fossil assemblages, in which postmortem transportation, bioturbation, and the accumulation of hardparts obscure community relationships, all fossils in the Mistaken Point assemblages were sessile, soft-bodied organisms that show no evidence of mobility in life or transportation after death. Mistaken Point assemblages are spectacularly preserved on large bedding planes as in situ census populations of hundreds to thousands of fossils, recording the living soft-bodied benthic community at the moment it was smothered by volcanic ash. This unique preservation style allows ecological tests routinely conducted in modern communities (e.g., species richness, abundance, “biomass,” diversity, and evenness, as well as statistical tests of nearest-neighbor interactions) to be applied to the fossil communities. Observed patterns of community variability are consistent with the theory that Mistaken Point fossil surfaces are “snapshots” recording different stages of ecological succession, progressing from communities of low-level feeders (e.g., pectinates and spindles) to frond-dominated communities with complex tiering and spatial structure. The presence of diverse slope communities at Mistaken Point suggests that the deep sea was colonized rapidly during the evolution of complex organisms. Species richness, abundance, and diversity values, as well as levels of intraspecific interaction, all fall within the typical range observed in modern slope communities. These structural similarities imply that ecological processes present in Ediacaran communities at Mistaken Point were strikingly similar to the processes that operate in modern deep-sea animal communities.

Projectile Point Typology and Chronology in the North Central Sierra Nevada

Despite years of concerted research, no well substantiated projectile point chronology for the western slope of the central Sierra Nevada has been established. Several reasons for this have been identified, including a lack of datable contexts, stratigraphic mixing, and excessive morphological variability resulting from material constraints and regular tool resharpening. Existing projectile point typologies, while accommodating the full range of morphological variation, have proven cumbersome due to large numbers of distinct types and sub-types. Further, chronological control has relied on inferences drawn from other regions, with little local support for inferred point sequences. To address these problems, the following study employs a large assemblage of projectile points from three stratified archaeological sites in the American River watershed. Projectile points are segregated using two common measurements—neck width and proximal shoulder angle. The newly defined types are then compared to regional stratigraphic patterns, revealing a consistent sequence of dart and arrow point types spanning the middle through late Holocene.

Radiocarbon dates for bifacial points atScotch Creek 1, Northern Territory

Scotch Creek 1 is situated on a tributary of the Adelaide River, on seasonally inundated coastal plains lying between Darwin and the western Arnhem Land escarpment. Apart from earthen mounds it is one of the few stratified open sites in this region to have been excavated (see Smith and Brockwell 1994). Intercalated with floodplain sediments the site contains a rich assemblage of bifacial points, debris associated with point manufacture, and organic remains such as eggshell and bone.

Geology and geochemistry of the Burnthill Granite and related W – Sn – Mo – F mineral deposits, central New Brunswick

Several significant W – Sn – Mo – F-bearing hydrothermal mineral deposits occur in the Miramichi Highlands of central New Brunswick. These deposits are spatially and temporally related to a group of five subcircular, undeformed, high-level, posttectonic granite plutons (Burnthill, Dungarvon, Rocky Brook, Sisters Brook, Trout Brook) of Middle Devonian age. The largest of the plutons is the Burnthill Granite (area = 180 km2), which comprises a texturally variable, polyphase intrusion composed of biotite monzogranites and alkali feldspar granites (International Union of Geological Sciences (IUGS) classification); apatite and zircon are the ubiquitous accessory minerals. Field and petrographic data indicate that the Burnthill Granite and two small (&lt; 7 km2) adjacent intrusions (Buttermilk Brook and Burnthill Mine granites), located 1 km from the southeast contact of the main intrusion, are genetically related and are epizonal in character. Classic epizonal features include sharp, discordant intrusive contacts with the host metasediments; a narrow contact metamorphic aureole with local zones of intense hydrothermal alteration and mineralization; an isotropic internal fabric; evidence of multiple intrusion; and the presence of porphyries.Geochemically the pluton is composed of mildly peraluminous, high-silica granites (SiO2 &gt; 74 wt. %), with low abundances of TiO2, MgO, CaO, P2O5, Sr, Ba, and Eu, and high concentrations of Y, Nb, Sn, Cs, Ta, W, Th, and U; high FeO/MgO ratios and Na2O + K2O contents are typical. Covariation among many of the major and trace elements within the volumetrically important phases of the Burnthill Granite can be explained by the process of fractional crystallization, and has resulted in an enrichment of those elements of economic interest (viz., Sn and W) in the more evolved granites. However, the anomalous behaviour of certain elements in these most evolved phases requires the operation of an additional process; this was most likely aqueous phase saturation followed by fluid separation, a process whose activity is corroborated by field and petrographic evidence (e.g., the development of miarolitic cavities and myrmekite). Normative Ab–Or–Q–An contents for the Burnthill Granite have a mean compostion of Ab31Or28Q38An3. This average value is almost identical to that of the piercing point assemblage in the "haplogranodiorite" system with 3 % normative anorthite, and is consistent with crystallization under water-saturated conditions at about 1 kbar (100 MPa) and 730–800 °C.Structural and petrochemical data demonstrate that the W – Sn – Mo – F-bearing mineral deposits were deposited in fracture and fault systems that developed after crystallization was completed, from hydrothermal fluids that were compositionally similar (high concentrations of F, Na, K, Sn, W) to the more evolved silicate melt phases of the Burnthill Granite. In addition to generating the wolframite–cassiterite–fluorite mineral deposits that occur in both endo- and exo-granitic settings, these fluids produced zones of intense, fracture-controlled, aluminosilicate alteration (viz., K-feldspathization, albitization, greisenization, and topaz alteration) that envelop the zones of mineralization.

The Williamson Site and the Late Archaic Eldorado Phase in Eastern Kansas

The Williamson site is a Late Archaic El Dorado phase occupation located along Eagle Creek, a tributary of the Neosho River in east-central Kansas. Artifacts, features and faunal remains indicate that the Late Archaic deposits represent a series of seasonally occupied residential extractive camps focused on the resources available in the vicinity of Eagle Creek and the Neosho River ca. 3500-3600 radiocarbon years B.P. Other El Dorado phase components in eastern Kansas include larger occupations on alluvial terraces, smaller camps located on tributary streams, and upland burial mounds. These sites are characterized by projectile point assemblages including lanceolate, notched, and stemmed forms. El Dorado phase subsistence patterns were focused on prairie and riparian woodland resources. Mortuary data suggest the presence of differentiated social status within El Dorado phase society. The El Dorado phase adaptation can be viewed as a western variant of a broader Late Archaic tradition. Other expressions of this tradition include Late Archaic manifestations in eastern Kansas and the Nebo Hill and Sedalia phases located to the east along the Missouri River drainage.

Paleontologic and Sedimentologic Character of Corell's Point Faunal Assemblage (Upper Devonian: Famennian), Southwestern New York State: ABSTRACT

The Corell's Point faunal assemblage of the lower Gowanda Shale Member, Canadaway Formation, represents a series of burrowed zones yielding biocoenoses of benthos, taphocoenoses of nektos, and wood fragments. Marine-transported animals and plants are generally pyritized, but many endemic organisms are not. The faunal assemblage occurs at various levels in the Gowanda Shale, and may recur in adjacent stratigraphic units. The Corell's Point faunal assemblage and associated pyrite nodules apparently formed in a starved shelf setting, influenced by sporadic influxes of sediment, possibly by distal turbidites. Cephalopods were added to the Corell's Point assemblage by postmortem pelagic drift; their attendant epizoans probably detached and gave rise to small, locally abundant auloporid mounds. Some organisms may have been rafted in attached to algal mats; these mats possibly carried ammonoids, nautiloids, wood fragments, pelmatozoans, bivalves, gastropods, and fishes, producing infrequent dense associations of these organisms. Mild bioturbation of surface muds was effected by Zoophycos and infaunal mollusks. Winnowing of fine muds by organisms may account for the consistent silty texture of sediment associated with the Corell's Point faunal assemblages; underlying and overlying strata are generally fine-grained with discrete siltstone beds. Zoophycos and other lebensspuren, plants, and some cephalopods are encountered in sections of the Gowanda Shale lacking the Corell's Point faunal assemblage. These shales and siltstones exhibit relatively little evidence of fauna-induced sediment mixing. End_of_Article - Last_Page 1164------------

Breakage Patterns of Central Illinois Woodland Projectile Points

In most projectile point assemblages, it is common to find a large proportion of broken specimens. Assuming most broken specimens were broken prior to deposition in the archaeological record, three possible factors correlating with breaks are examined: (1) blade proportions, (2) major functional category, (3) haft morphology. Hypotheses for the role of each factor are framed and tested on a group of specimens from central Illinois. Use category appears to be the major factor in blade breakage, although total extent of breakage is also related to haft morphology.

Flake Tools Stratified Below Paleo-Indian Artifacts

In northwest Missouri, Lithic stage flake tools struck from prepared cores have been excavated underlying a Paleo-Indian fluted point assemblage. These assemblages were in two different loesses of the last glaciation. Thermoluminescent analysis of stone tools dates the Paleo-Indian occupations at 8690 +/- 1000 B.C. and 12,855 +/- 1500 B.C.; the Lithic stage occupations must be older than 13,000 B.C. on the basis of geologic correlation, lithic analysis, and cultural stratigraphy.

The Scoggin Site: a Study in Mckean Typology

The Scoggin Site, an Early Middle Period Bison kill in south-central Wyoming, yielded two distinct stylized projectile point varieties from the one bone layer present. This single component affords optimum opportunity to study the two varieties of points in one context. The technology for the projectile point assemblage is described, and literature concerning the deep side-notched Early Middle Period or Archaic age points from the Northwestern Plains and the northern Great Basin is discussed.In order to discover if the deep side-notched projectile points from Scoggin (reminiscent of much later projectile point types) were indeed part of the McKean classification, their dimensions were compared to those of the indented base McKean lanceolate projectile points from the same site. The measurements overlap or can be otherwise explained for both lanceolate and side-notched forms. The Statistical Package for the Social Sciences (SPSS) was used to demonstrate that the two types of points are quite homogeneous.The question as to why the points differ stylistically has several possible answers. For example, the two types may represent interacting but identifiable ethnic groups, or the numerical superiority of the side-notched point may reflect hafting superiority. At any rate, the deep side-notched point is an integral part of the Early Middle Period and can be classified as McKean.

Significance of Variability in Archaic Point Assemblages

The analysis of a sample of Archaic points from , private collections led the author to question the effectiveness of traditional tool typologies to explain morphological variability. Causes of variations are discussed; time, space and functional specialization are estimated to contribute only part of the total variation. A systems model relating point manufacture and use to hunting strategies is presented. Chipping and retouching techniques are defined as elements of the system variety. Technical choices constitute the mechanisms maintaining the system in a state of equilibrium; technological change results from the introduction of new sets of techniques. The nature of the choices and the range of variations tolerated within the system are deduced from the analysis of the sample. The analysis relies on a recently developed method of recording morphological characteristics. More extensive methods of testing the model are briefly described.

多重有向連続体理論序説 : 一般化された連続体力学理論における director frame の多重化について

This paper tries to construct the theory of multi-directed continuum mechanics, by multiplying the director frame based on the thought of generalized continua. The multi-directed continuum corresponds to the medium which has many degrees of freedom for the deformation of every material particle. Mathematically it is considered as an assemblage of material points which have a macro director polyad (i.e. frame) and n micro director polyads. And actually, one of such continua will be the continuous model of discrete or heterogeneous media (e.g. reticulated framestructures, prismatic shells, layered media, and composit materials). Independently of dimension the basic equations are formulated by Hamilton's principle (§4), after defining the geometrical relations (§2) and the strain measures (§3). In section 5 some different expressions of them are concidered for comparison. Therefore by varying values of indices, they can form the theories of one, two and three dimension respectively, and fundamentally imply the concepts in many published works of the generalized continuum mechanics. Section 6 is a review of the concept of directors and gives the outline of an ideal multi-directed continuum model for actual media by analogy. Then it is noted that the deformation of a macro polyad space which includes micro polyads, is constrained homogeneously.

A Bone Needle From a Midland Site

Investigation of a western Texas campsite containing an apparently discrete assemblage of Midland points and other tools has yielded part of a tiny bone needle.

The Barnes Site: A Fluted Point Assemblage from the Great Lakes Region

AbstractA collection from a small Late Wisconsin site is described. This assemblage exhibits a distinctive coreworking technique and a distinctive variety of fluted points. It is dated on geological grounds to between 11,000 B.C. and 9000 B.C. at a time when spruce stands were probably becoming established in the area. The contrasts between this assemblage and others described from Northeastern North America suggest a number of hypotheses not testable with the available data.

I. On homogeneous division of space

1. The homogeneous division of any volume of space means the dividing of it into equal and similar parts, or cells, as I shall call them, all sameways oriented. If we take any point in the interior of one cell or on its boundary, and corresponding points of all the other cells, these points form a homogeneous assemblage of single points, according to Bravais’ admirable and important definition. The general problem of the homogeneous partition of space may be stated thus.