| 제 4 장. Sedimentary Structures | ||||||||||||||||||||
|
1. Stratification
① bedding and lamination(few millimeter thick) ② Cross-stratification ③ Irregular stratification - sliding(slumping)-folding - convolute, load structure escape - bioturbation - burrow, roots |
|
2. Bedding Plane Structure
A. Tool mark B. Scour mark C. Bed form - ripple, sand wave, dune, antidune D. Biogenic mark E. etc : grading coarsening-upward fining-upward massive
- Ripple migration and cross-bedding - Flaser bedding - wave bedding - lenticular bedding ───────→ mud content increase ───────→
┌ Physical (inorganic) └ Biogenic (organic)
┌ primary (pre-lithification) └ secondary (chemical) |
|
3. Physical structure(inorganic)
1) Bedding structure
① horizontal bedding : lake, beach, deep marine - parallel, continuous rather uniform, monotonous
ⓐ rhythmites thin, repetitious sequence(cyclic) - texture, composition 의 교호 * seasonal charge (varve) - glacial lake * beach bed - uprush and backwash (grain size, composition)
ⓑ upper flow plane bed or flat bed (no movement of sediment) fluvial - braided, alluvial fans, glacial outwash →sand, gravel horizontal bedding for a few meter scale.
② Bedforms and their internal stratification
ⓐ current - generated structure (lower flow regime) * foreset stratification : influenced by sediment texture, velocity, bed shear stress. by depth ratio → angular contact (increasing depth, increasing suspension load) → tangential → concave * plan view ――――――――――― increasing flow strength ――――――――→ linear → undulatory → cuspate → rhomboid(planed off) → flat bed
* trough cross-bedding ← lenticular & trough shaped sets의 측방 이동 누적에 의해 형성. * tabular cross-bedding ← linear bedforms의 수평적 이동 누적에 의해 형성 ◎ Reactivation surface : interruption in migration or erosional surface. caused by flow rates, tidal stage, tidal current direction
* Climbing ripple cross-stratification : 다량의 부유 퇴적물 유입 (ripple in drift): 측방 이동 + 상향 누적 (ripple in phase: 주로 상향 누적 by rapid sediment input)
* Hummocky cross-stratification low-angle and gently undulation cross-stratification (dip : 3～6°) wavelength : ～ a few meters height : up to 30～40cm (보통 수 centimeter) caused by storm waves on shelf
ⓑ current - generated structures (upper flow regime) * upper plane bed * antidune - stream, tidal inlet, gentle-sloping beach (line-crested) → low preservation (뒤따르는 waning flow에 의해 대개 상쇄되어 보존 가능성은 낮음)
ⓒ wave - generated structures wave ripples : symmetrical (peak-crest, round-trough) - wave ripple crest - straight/slightly sinuous with common bifurcations - wave ripple - chevronlike cross-stratification controlled by wave size, grain size, wave period, depth of water * ripple index (R.I.) : ripple length/height * ripple symmetry index (R.S.I.) : length of horizontal projection of (R.S.I.) ( 2.5 〈 current ripple ) ( 2.5 〉 wave ripple ) (R.I.) ( 0～4 wave ripple ) ( 15〈 current ripple )
ⓓ other bedding type ① flaser and lenticular bedding : tidal, streams, intertidal beach altermating of energy 또는 sand mud availability ┌ flaser : thin mud + sand - 비교적 high energy └ lenticular : discontinuous sand lens - 비교적 low energy ② wavy bedding : continuous mud (undulating) ③ graded bedding (inverse drading) : a few centimeters - distribution grading - no fine in lower part - coarse-tail grading - all size but grading in only coarse part * by turbidy currents, shallow water, intertidal - sudden decrease of competence flooding (waning) 또는 hurricanes에 의해 형성 가능 ④ imbrication and internal fabric * preferred orientation by gravitational field with current flow : gravel, fossils on bedding surface *imbrication : overlapping arrangement → dip current 지시 : long axes parallel to flow normal to flow : rolling of clasts in bed load * parting lineation : thin sandstone → flow parallel to lineation
2) Bedding plane structure
(1) Bottom mark (sole mark) : 퇴적층 층리면 하부에 imprint로서 보존, 상하 퇴적층은 조직이 상이함 : by current and gravity ⓐ flute or flute cast - by current (sediment accumulation : rapid high turbulent flow) up turbidite에서 많이 산출 indicator of current direction and paleoslope ⓑ scour mark(transverse) - ridgelike transverse to paleocurrent direction - a few cm in scale ⓒ flute rill mark : long, narrow scour(anastomosing shape) parallel to current direction (tidal flat에서 형성) ⓓ longitudinal furrows and ridges : straight, long, spaced closed ridge and furrows ⓔ tool mark : by downcurrent transport of pebbles, shells, twigs, branches, fishbone * Groove cast (striation cast) : linear 긁힘(물체에 의해 파인 흔적) * Brush marks * Skip casts * Chevron marks * Prod marks * Bounce marks
(2) Surface marks : all not related to current a few millimeter ～ a centimeter in scale ① current generation features * current crescents (obstacle mark) : 장애물 주위에 생기는 구조 (stream, foreshore beach, tidal flat 환경) * sand shadows : aeolian setting 의 current crescents ( low preservation ) * rill marks : small, bifurcation dendritic erosional feature ( low preservation )
② climate - related features * raindrop impressions : mud or muddy sand surface (a few millimeter) - arid, semiarid. (not always symmetric <by falling oblique rain>: ripple-like) * mud cracks : polygonal, V-shaped-supratidal, floodplain, playalake, sabkhas.
③ 기타 * swash marks : up-backwash on foreshore area (Figure 3-35) : extensive, concave seaward - diagnostic indicator of shoreline(기울기에 따라 간격 달라짐) * adhesion ripple : wind blowing sand over a wet substrate. (eolian 환경)(3-36) * pit and mound structure : volcano - shaped or pitlike by water/gas escaping * crystal impression : ice, halite, gypsum, pyrite in tidal flats, sabkhas, lagoons
3) Penecontemporaneous deformation structure
(1) Load structure by mass of overlying sediment unit (coarse sand over mud) * Load cast : flute caster 유사 but not distinct linear alignment, no regular display * Flame structure : mud intruding the overlying coarse unit
(2) Ball and pillow structure : elliptical or pillow-shaped (pseudo-nodule) by slumping or downslope sliding(?) (liquefaction of the mud and mobilization of mud) a few centimeter ～ 1 meter
(3) Dish structure : discountinuous, concave-upward laminations in sandstones * dish and pillar - water escape structure dewatering → columns or pillars of massive sands. (upward flow of water)
(4) Convolute bedding : complex folding in mud or fine sand, remarkable continuity of individual bed in convolute unit (slump structure 와 혼동 - due to gravity only, soft sediment faulting 와 함께 발생) → (liquefaction, turbidite 층에서 많이 산출)
(5) Slump structure : rapid sedimentation + slope instability complicated, toothpaste-type folding w/ overturned folds and faults from glacial, point bar, dune, delta, tidal flats turbidite
(6) injection structure : a few cm ~ several m sandstone sill - concordant ┐ by liquefaction + loading sandstone dike - discordant ┘ (jnjection from mostly below, some above) |
down stream|
4. Biogenic Structure
: 퇴적환경의 주요정보 제공 ( intrabasinal structucture → epifaunal(in faunal)) ichnology trace fossil(lebenspurren) bioturbation ← sediment reworking by organism (1) Boring & Burrows 1) Boring : penetrating of a hard substrate(shell, rock : carbonate) for food protection (3-43) fungi, algal, sponges, worms, gastropods, bivalves, echinoids indicate ┌ ancient shoreline in beach rock ├ marine substrate └ framework of reefs 2) Burrows :┌ shelter, locus for feeding, dwelling, escape (3-44, 45) └ single, vertical tube ┐ u-shape burrows ┘
(2) Tracks, trails, resting traces - epifaunal 1) tracks : vertebrates, arthropod (3-46) 2) trail : gastropod in low-energy : tide flat, lagoon, shallow shelf, deep ocean n(3-47) 3) resting trace : somewhat like mold starfish 4) feeding, escaping, grazing, dwelling structures
(3) fecal pellets - gastropod, bivalves, echinoids, holothurians, polychaete, arthropod, fish fine sand ~ pebble size. avoid shape (sand ~ mostly) occurs in terrigenous, carbonate low energy : lagoonal, estuarine, lake, tidal flat, shallow marine - flaser, lenticular bedding을 형성키도 함 |
|
5. Late diagenetic or Chemical structure
1) Mineral segregation → concretion, nodule, septaria, geodes, sand crystals. * concretion, nodule : amorphous mass of various mineral composition radial, concentric ~ up to several m 특정 층준에 형성 - chert, iron oxide, pyrite, calcite, gypsum, others 핵 - fossils(insects, plants, fish) 기원 - microgeochemical 환경 from tissue decay * septarian structure : shrinking mass → mineral precipitation(calcite, quartz 가 흔함) - solution → crack, pocket을 유발 in carbonate rocks →tepee(calcite에 물의유입 또는 결정화 작용, 의해 “∧” 모양으로 부풀어오른 구조 - groundwater → ion을 공급 - geode
2) Solution structures - Pressure - soultion at carbonates(evaporite, quartz arenites) Stylolite : marble 에 흔함 : insoluble concentration on the stylolitic surface
3) Coloration → Fe-Oxide 에 의한 Color change (FeS2, Fe2O3, FeO) → liesgang banding
4) Diapiric structure - salt, mud |
|
제1장. 퇴적물 및 퇴적암의 일반적인 성질 |
