402-pp2 - UNIVERSITY OF SOUTH ALABAMA GY 402 Sedimentary...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: UNIVERSITY OF SOUTH ALABAMA GY 402: Sedimentary Petrology Lecture 2: Grain size and Descriptive Parameters Last time... Origin of sediment Siliciclastic (reworked stuff) Volcaniclastic (primary deposition) Carbonate (in situ mostly biogenic) Chemical (evaporite/hydrothermal) Organic (coals) Meandering Rivers Delta Mobile Estuaries Barrier Islands Beaches 15 km NASA Landsat image Today's Agenda A) Basic sediment grain size B) Ternary plots C) Interpreting grain size data D) Grain size parameters Grain size There are several different schemes: 1) US Army Corp of Engineers (mesh size) 2) Soil scientists 3) Academic geologists (metric) From: Lewis, D.W., 1984. Practical Sedimentology.van Nostrand Reinhold, New York, 229p. Udden-Wentworth grain size (Wentworth, 1922) Gravel: (>2.00 mm) Sand: (0.063 mm 2.00 mm) Silt: (0.004 mm 0.063mm) Clay: (< 0.004mm) 229p. From: Lewis, D.W., 1984. Practical Sedimentology.van Nostrand Reinhold, New York, 229p . Phi (M) grain size M = -log2d 229p. From: Lewis, D.W., 1984. Practical Sedimentology.van Nostrand Reinhold, New York, 229p . Phi (M) grain size M = -log2d 16 mm = -4M 4 mm = -2M 2 mm = -1M 1mm = 0M 500 :m = +1M 250 :m = +2 M 125 :m = +3 M 62.5 :m = +4 M 4 :m = +8 M Grain size classification (simplified) Grain size classification With grain size data, you have 4 variables that you need to be able to visualize. Graphically, this is not easy as we only have 2 dimensions to work with. The solution..... Grain size classification With grain size data, you have 4 variables that you need to be able to visualize. Graphically, this is not easy as we only have 2 dimensions to work with. The solution..... Ternary plots. Sand-Silt-Clay Scheme 1 Folk (1954) Symbol Index C-clay; Z-silt; M-mud; S-sand; sC-sandy clay; sM-sandy mud; sZ- sandy silt; cS-clayey sand; mS-muddy sand; zS-silty sand Sand-Silt-Clay Scheme 2 Sheppard (1954) Symbol Index C-clay; Z-silt; S-sand; sC-sandy clay; zS-silty sand; sZ- sandy silt; zC- silty clay cS-clayey sand; szc-sand-silt-clay; cZ-clayey silt Gravel-Silt-Fines Scheme Folk (1954) Symbol Index M-mud; G-gravel; S-sand; sM sandy mud; mS-muddy sand; (g)M-slightly gravelly mud; (g)S-slightly gravelly sand; (g)sM-slightly gravelly sandy mud; (g)mS-slightly gravelly muddy sand; gM-gravelly mud; gms-gravelly muddy sand; gS-gravelly sand; mG-muddy gravel; MsG-muddy sandy gravel; sG sandy gravel Plotting data Folk (1954) Example data point: Sand: 46%; Clay 25%; Silt: 29% Step 1: Plot sand (46%) Step 2: Plot clay (25%) Step 3: Confirm silt (29%) Plotting data Folk (1954) Example data point: Sand: 46%; Clay 25%; Silt: 29% 46% Step 1: Plot sand (46%) Step 2: Plot clay (25%) Step 3: Confirm silt (29%) Plotting data Folk (1954) Example data point: Sand: 46%; Clay 25%; Silt: 29% Step 1: Plot sand (46%) Step 2: Plot clay (25%) Step 3: Confirm silt (29%) 25% Plotting data Folk (1954) 30% Example data point: Sand: 46%; Clay 25%; Silt: 29% Step 1: Plot sand (46%) Step 2: Plot clay (25%) Step 3: Confirm silt (29%) Plotting data Folk (1954) 30% Example data point: Sand: 46%; Clay 25%; Silt: 29% 46% Step 1: Plot sand (46%) Step 2: Plot clay (25%) Step 3: Confirm silt (29%) Your sample is sandy mud (sM) 25% w t% retained per sieve 10.00 20.00 30.00 40.00 50.00 60.00 0.00 gravel vc sand c sand m sand grain size f sand vf sand coarse silt fine silt clay Grain Size Histograms: Case Study 1 Grain Size Histograms: Case Study 1 w t% retained per sieve 60.00 50.00 40.00 30.00 20.00 10.00 0.00 gravel vc sand f sand vf sand m sand c sand coarse silt fine silt clay grain size Fine grained sediment. Depositional energy ___________ ? Grain Size Histograms: Case Study 2 60.00 45.00 40.00 50.00 35.00 40.00 30.00 25.00 30.00 20.00 20.00 15.00 10.00 10.00 5.00 0.00 0.00 gravel gravel f sand vc sand vc sand vf sand c sand c sand m sand coarse silt fine silt clay w t% retained per sieve w t% retained per sieve grain grain size Grain Size Histograms: Case Study 2 45.00 40.00 35.00 30.00 25.00 20.00 15.00 10.00 5.00 0.00 gravel vc sand vf sand m sand c sand f sand coarse silt fine silt clay w t% retained per sieve grain size Moderately sorted sediment. Depositional energy ________ ? Grain Size Histograms: Case Study 3 w t% retained per sieve 40.00 35.00 30.00 25.00 20.00 15.00 10.00 5.00 0.00 gravel vc sand vf sand m sand c sand f sand coarse silt fine silt clay grain size Grain Size Histograms: Case Study 3 w t% retained per sieve 40.00 35.00 30.00 25.00 20.00 15.00 10.00 5.00 0.00 gravel vc sand vf sand m sand c sand f sand coarse silt fine silt clay grain size Bimodal sediment. Depositional energy ___________ ? Grain Size Histograms: Case Study 3 w t% retained per sieve 40.00 35.00 30.00 25.00 20.00 15.00 10.00 5.00 0.00 gravel vc sand vf sand m sand c sand f sand coarse silt fine silt clay grain size Bimodal sediment. Depositional energy ___________ ? Depositional environment: ____________________? Descriptive parameters Source: Blatt, Middleton and Murray (1980) Descriptive parameters Source: Blatt, Middleton and Murray (1980) Descriptive parameters Medium = 50 Source: Blatt, Middleton and Murray (1980) Descriptive parameters Mean (average) = 16 + 50 + 84 3 Source: Blatt, Middleton and Murray (1980) Blatt, Descriptive parameters Blatt, Source: Blatt , Middleton and Murray (1980) Sorting = 84 - 16 + 95 - 5 4 6.6 Descriptive parameters Mode = the most frequent particle size Source: Blatt, Middleton and Murray (1980) Descriptive parameters Skewness: 16 + 84 +2 50 + 16 + 84 +2 50 2(84 - 16) 2(95 - 5) Positive (fine) skewness Symmetrical Negative (coarse) skewness Descriptive parameters Kurtosis (curve peakedness) = 95 - 5 2.44(75 - 25) Platykurtic Mesokurtic Leptokurtic Other descriptive parameters Roundness Particle shape Other descriptive parameters Roundness Particle shape Both of these can be quantitatively measured but what a pain in the ass! Much better to use qualitative methods. Qualitative (Powers, 1953) Quantitative (Folk, 1980) Roundness (comparison of determination techniques) Roundness Figure 14: Grain Sphericity: Composite Sample 4 60 50 Pe rce ntage 40 30 20 10 0 0.15 0.20 0.30 0.40 0.60 0.85 Roundness Scale (Powers, 1953) Modal A Modal B Bulk Descriptive parameters (simple visual comparisons) Sampling Techniques Unconsolidated (soft) sediment (grab, coring, hand sampling) Lithified sedimentary rock (hammer, drill, saw) Upcoming Stuff Homework Writing Assignment 1 (Paper structure): Due Thursday 2) Read Grain Size Lab Manual (online) Thursday: No Lecture Municipal Park walk (grain size assignment prep) meet me at the amphitheatre at 11:15 AM This Weekend Get your samples! Next Tuesday: Sedimentary Rock Classification ...
View Full Document

This note was uploaded on 02/05/2012 for the course GLY 402 taught by Professor Staff during the Fall '11 term at S. Alabama.

Ask a homework question - tutors are online