Dr Mohamed Yousef (Geology Dept., Faculty of Science, Ain Shams University) 9/30/2025 1 GEO 3151 Structural, Field Geology and Surveying For Third Level Students – Oil and Gas Chemistry Program Dr. Mohamed Yousef Ain Shams University Course Assessment • Final written (theoretical) exam – 40 marks • Mid-Term Exam – 10 • Semester work – 20 marks • Oral exam – 10 marks • Practical exam – 20 marks 1 2 Dr Mohamed Yousef (Geology Dept., Faculty of Science, Ain Shams University) 9/30/2025 2 Textbook Davis, G. H., Reynolds, S. J., and Kluth, C., 2012, Structural Geology of Rocks and Regions, Hoboken, Wiley. Criteria for Determining Top and Bottom of Beds Lecture 1 3 4 Dr Mohamed Yousef (Geology Dept., Faculty of Science, Ain Shams University) 9/30/2025 3 Learning Objectives • Understand why 'way-up' criteria matter • Recognize physical, structural, paleontological, and igneous indicators • Apply these criteria to field examples Why It Matters • Determines stratigraphic younging direction • Critical for mapping and fold interpretation • Essential in basin analysis & petroleum geology 5 6 Dr Mohamed Yousef (Geology Dept., Faculty of Science, Ain Shams University) 9/30/2025 4 Categories of Criteria • Physical • Paleontological • Igneous 7 8 Dr Mohamed Yousef (Geology Dept., Faculty of Science, Ain Shams University) 9/30/2025 5 Tracing & Correlation • Compare deformed beds with nearby undeformed sequences • Helps determine original 'upright' orientation Scours, Channels, Conglomerates • Channels: concave-up base → top above • Conglomerates: clasts often derived from underlying rocks • Solution surfaces: irregular at tops of beds 9 10 Dr Mohamed Yousef (Geology Dept., Faculty of Science, Ain Shams University) 9/30/2025 6 Graded Bedding • Coarse → fine upward sequence = top direction • Distinguish from current sorting or imbrication Cross-Bedding • Concave-up foresets point to top • Truncation of laminae = most reliable indicator 11 12 Dr Mohamed Yousef (Geology Dept., Faculty of Science, Ain Shams University) 9/30/2025 7 Mud Cracks & Ripple Marks • Mud cracks taper downward • Ripple crests are sharper; troughs smoother Sole & Tool Marks • Flute casts: bulbous end = upstream, taper = downstream, top above • Groove & tool marks cut into finer bed below → show younging direction 13 14 Dr Mohamed Yousef (Geology Dept., Faculty of Science, Ain Shams University) 9/30/2025 8 Pebble Dents & Dewatering • Pebble impressions: bulged side down, indented side up • Dewatering pillars: vertical escape structures indicating upward Cleavage vs Bedding • In upright beds → cleavage steeper than bedding • In overturned limbs → cleavage-bedding relation reversed • Curved cleavage usually bows toward stratigraphic top 15 16 Dr Mohamed Yousef (Geology Dept., Faculty of Science, Ain Shams University) 9/30/2025 9 Paleontological Indicators • • Fossils and biological structures provide facing criteria • • Especially useful in carbonate strata • • Often supplement physical indicators in clastic successions Geopetal Fabric • Fossil cavities (e.g., brachiopods, gastropods) partially filled with sediment • Remaining voids filled later with cement • Indicates original ‘up’ direction 17 18 Dr Mohamed Yousef (Geology Dept., Faculty of Science, Ain Shams University) 9/30/2025 10 Bryozoa & Brachiopods • Bryozoa encrust fossil shells on their upper surfaces • Crania-like brachiopods: convex valve points upward • Provide reliable top indicators in carbonates Pelecypods as Indicators • Rudists stand upright with free valve at top • Disarticulated shells often convex side up due to currents • Encrustation or borings indicate upper surfaces 19 20 Dr Mohamed Yousef (Geology Dept., Faculty of Science, Ain Shams University) 9/30/2025 11 Other Fossil Indicators • Worm trails: ridges/grooves left on bedding surfaces • Gastropods (vermetids): feeding tubes point upward • Corals: solitary narrow end down, colonial calyx upward • Echinoids: flat side down, convex side up Igneous Indicators • Tops of lava flows more vesicular • Branching tubules: branch down, join upward • Contact metamorphism below flows, not above 21 22 Dr Mohamed Yousef (Geology Dept., Faculty of Science, Ain Shams University) 9/30/2025 12 Pillow Lavas • Upper surfaces: convex and smooth • Bottoms: cusped, indenting underlying pillows • More vesicular near tops • Columnar jointing common at top • Heat alteration beneath but not above flow 23