Geomorphology

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Department
Archaeology
Course
AR246
Professor
Jonathan Haxell
Semester
Winter

Description
STUDY NOTES:AR246 Dr. Haxell Examination Date: Wed 16/3:30PM/University Stadium SECTION # 2: Geo-archaeology:Archaeology and the Physical Environment Geo-archaeology:Application of the techniques of the Earth Sciences Earth Sciences: Sciences related to earths physical spheres -Eg. Sciences of the lithosphere, hydrosphere, atmosphere, cryosphere, biosphere •Petrology: Study of rocks & minerals (study of the lithosphere) -minerals (geological equivalent of elements) -geologically produces solids – unique chemical composition -exhibit distinct physical properties – crystal shape, colour, hardness -rocks – combinations of some minerals -Types or rocks/minerals can only occur where ingredients are present -Depends on formation process -Igneous minerals/rocks – produced by volcanic activity -Sedimentary rocks/minerals – generated by depositional event (grand canyon) -Metamporphic minerals/rocks – modified – temperature or pressure of deep burial -marble (produced by limestone) -Explains source of regolith GOAL: -identify and classify minerals/rocks -geo-archaeology is limited to identifications -Methods: ○Eg. Physical mineralogy -identification of minerals based on physical properties: -macroscopic/microscopic study – interactions with matter/energy ○Petrography -Thin section analysis of rocks/minerals -minerals identified by; shape, colour, cleavage, fluorescence & pleochroism ○Chemical analysis: -characterization of rocks/minerals by chemical composition -chemical assay, diffraction of crystallography ○Lithology: study of lithics (rocks) -distribution of rock types -created in UK. - William Stratus Smith: By identification of exposed outcrops •Articulation with Archaeology: -identifies origins of lithic/ceramic artefacts -Unique structure/composition – illustrates raw material source (origin of material) -Explains foundations of earths geomorphology -Lithosphere is origin of the “regolith” -regolith – broken up material covering bedrock: -ie. Unconsolidated rock/sediments/soils -required for life on earth -provides context for archaeological deposits: -covers and preserves them. (spatial relationships) •Sedimentology: The study of the regolith -Sediments: Broken up particles of various size -extremely small – silt (dust from the movement glaciers) and colloid (chemical reaction) particles -Come from: -parental rock (lithosphere) -Organic material (biosphere) -Chemical water – acid water (dissolves limestone) -Volcanic activity – ash/lava -cosmic material – comets -Why are sediments imp? -represent matrix for archaeological deposits -Interpretation of matrix data allows reconstruction of: -Paleoenvironment (past environments) -Paleoecology (environmental interactions) -Site Ecology (formation processes/taphonomy) -Methods: -identify: Source of sediment/conditions of production -Generation – how did that sediment come to be -Transformational History – life history of the sediment since deposition -cultural modification – what transformations were a product of human activity -identify its: lithic components -petrological techniques: Physical mineralogy, petrographic analysis, chemical analysis -in residual sediments (those deposited adjacent to their source) -in derived sediments (product of transport mechanisms) -chemical components: -identified by traditional chemical assays – phosphate testing -trace element analysis (identifying source by chemical signature) -spectroscopy: If invested with energy – materials return to normal state emitting radiation (electro-magnetic radiation) -Instrumental NeutronActivationAnalysis (INAA): When irradiate with neutrons – all elements emit radiation -organic components -identified by macro-microscopic analysis of plant & animal fossils -Peat – accumulation of incompletely decayed plant remains -subaqueous sediment (underwater) -Foraminifera: single cell, moveable animals -Ostracods: microscopic shell fish (leave their shells behind) -Diatoms: Plant populations •Identifying Sediment Transport Mechanism: -different mechanisms produce unique characteristics: ○Eg. Gravity: caves produce clastic (broken rock) deposits -angular shattered rock -unsorted ○Colluvial Deposits: water-driven, slope erosion events -run-off over time -may be unsorted -single event (landslide) -produces thick unsorted layer: diamicton ○Aeolian deposits: Wind transported -very fine particles – little surface wear -sailing rocks: Rains, produces a slick surface, the wind comes down and defeats friction between the surface and the rock -Highly sorted ○Glacial transport -generates deposit of considerable size/variation -due to grinding effect of the glacier ○Riverine Deposits: -two classes -Fluvial: in river deposits -Alluvial: deposited by rivers -highly sorted by water velocity ○Coastal Deposits: -Marine -Lacustrine: lake derived -sorted by water velocity and often graded -Required variables: ○Sediment texture: measurement of particle size on scales -Qualitative scale – Wentorth (ordinal): boulder, cobble, gravel, sand -Logarithmic scale – Krumbein phi-scale with vertical line going through it -designed to have smaller number ○Particle shape: measures of sphericity – proportional dimensions -highly spherical – most proportional (like a sphere) -low spherical – longer or rectangular in shape -roundness – smoothness of surface -Imp. For reconstructing source conditions: Eg. Frost cracks. ○Particle orientation: Identifies direction of current – water/wind derived deposits ○Patterns of particle of sorting: Identifies comparative energy of transport mechanism -high-energy currents – transport all particle size -lower-energy currents – carry only small particles ○Sediment Structure: (bedding) -illustrate changes in condition with time -Horizontal bedding – distinct vertical variation: -Graded bedding – decreasing particle size, caused by decreasing energy movement -Cross bedding – non horizontal within strata -illustrates direction of current -cross-laminated: stacked up in the direction of the current SIDENOTE: Data collection Strategies: ○use geological sieves: graded sieves – mesh lining in each, the mesh getting smaller & smaller on the way down ○sediment cores: tubes pressed down into the soft sediment ○Kubiena boxes: 5 Sided box pressed into the wall of the unit ○Particle sorting: Imp. To identify the relationship btwn particles •Reconstruct of depositional Environment: -Depends on observations about sediment source/transport -Source environmental conditions -Transport Processes -Mesoscale environment: -Eg. Cryogenic sediments – suggest periglacial conditions -Aeolian deposits – imply cold environments (Seds.Are loose, no plants to keep in place) -Colluvial effect – Suggest treeless slopes (Diamicton – landslides) -Microscale environment: -implied by traits of transport -Eg. Wind/water speed direction deduced -Changes in depositional environment – Identified by sediment structure (ie. Bedding) -produces varves – seasonal biological sediment: -Dark in summer – descending biological material from upper level -Light in winter – Calcareous (calcium carbonate) deposits -Relative dating of events •Pedology: Soil Science – Result of modification of sediment through time by mechanical (weathering)/chemical (acid rain) effects produced by climate (wind, rain, frost)/biota -Soil vs. Sediments: -Sediment deposits result from a bounded event (beginning/end) -Soils form in/on sediments (on-going process) -Implications for Archaeology: -Soil development implies passage of time -Cannot be interpreted stratigraphically -Pedology – involves study of two related processes -Digaenesis – lithification of soil to sedentary rocks -Pedogenesis – generation of soils -surface down: colonification of sediment by organic population, releases chemical compounds at surface, then transported down through sediments by water and modifies subsurface material. -Produces soil column. -O-horizon: decaying organic matter (roots) -A-horizon: mixed organic/sediments (topsoil) -E-horizon: Leeched (elevated) -doesn't always develop -B-horizon: Illuvated – received from E-horizon (subsoil) -K-horizon: Inorganic salts/carbonates -doesn't always develop -C-horizon: unmodified parent material -R-horizon: Bedrock -Pedrogenesis: Soil development depends on a # of variables ○Climate: Moisture/temperature influence nature of soils that develop -Eg. Desert environments: Seds. Weathered by sun/wind -support few plant populations: Nothing to anchor seds exposed to repeated transport/deposition -Temperate Environment: Grassland & Deciduous forests -roots hold sediments in place which permit soil development -discarded vegetation: generates deepA-horizon -rainfall draws organic material down: well developed B-horizon -Cold northern climate: Boreal
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