GEOS 1004 Lecture Notes - Lecture 16: Geologic Time Scale, Cross-Bedding, Graded Bedding
Document Summary
Lecture 16: sedimentary rocks ii and geologic time. Sedimentary features: stratigraphy: sedimentary layers (bedding) are laid down oldest on the bottom, youngest on the top (superposition), and are normally close to horizontal. Original horizontality - rocks were originally horizontal, which can be seen. Cross cutting relationships - younger rocks or structures cut across layers. Superposition, horizontality, and cross-cutting relationships define relative time in rock sections. today. Look-up items: define "superposition", "original horizontality", and "cross cutting relationships. " 2)cross bedding: layering within layers, geometry of layers; indicate type (streams, wind) and direction of transport: graded bedding= layers sorted by grainsize; denote flood events. Ripples, cracks, fossils, etc. indicative of water type (e. g. fresh or marine, water depth, current velocity, climate, etc. ) They enable reconstruction of depositional environments (e. g. useful for climate studies), creating predictable framework for how layers change spatially (e. g. useful for finding coal, oil, etc.
