Reading: Boggs Chapter 10 (and a little from Ch. 9)
The main topics for today were: (1) The Beach to Shelf Transition, and (2) Siliciclastic Continental Shelves.
First a discussion on how to distinguish between marine and nonmarine environments based on the study of ancient deposits in the stratigraphic record. There are some key features that can be found in sediments which provide clear evidence for deposition in either marine or nonmarine environments. What are they (we listed them in class)? Be sure to know some examples of these.
1. Beach to Shelf Transition. Boggs Figures 9.21, 9.24, 9.25: show transition in environments and vertical succession that we would see in stratigraphy.
2. Continental Shelves. (a) Tide-dominated and (b) Storm-dominated. Definitions of each, relative importance worldwide. Figures in handout, and text Figures 10.1-10.3 and 11.3. Note difference between broad interior (epicontinental) seaways and relatively narrow continental-margin shelfs.
(a) Tide-dominated. How they work, types of seafloor features (ridges and bedforms), style of deposition.
(b) Storm-dominated. What they look like, how they work, importance of fair weather vs. storm wave base, coastal set-up and return flow, role in transporting and depositing sand on continental shelves. Figures in handout, text Figures 10.5-10.7. We discussed the processes and deposits of large shelf storm events. A nice example of an ancient storm-dominated shelf sequence: the Upper Jurassic of Alberta (see handout). Note the gradual stratigraphic transition from turbidites to shelf storm deposits, implications for shelf dynamics, and reconstructed paleogeography.
Reading: Boggs Chapter 12
Today we introduce stratigraphy as the study of age and physical relationships in sedimentary deposits: the vertical and lateral arangement of strata, their age, distribution, rates of deposition, record of changing environments and events through time, and tectonic and sea-level controls on sedimentation.
Organizing Strata into: laminae, beds, and lithofacies (Boggs Fig. 12.1).
Contacts are: gradational, sharp, and unconformities (see below).
Stratigraphic Architecture is a term used to describe the vertical and lateral arrangement of different sedimentary facies in a depositional basin. We sketched a facies panel and discussed its significance.
Gaps in the stratigraphic record: "stratigraphy is more gap than record". Nice examples from the Grand Canyon (see handout). Less than 10% of Paleozoic time is represented by deposits in the Gr. Canyon section.
Four types of unconformities: (a) paraconformity; (b) disconformity; (c) angular unconformity; (d) nonconformity. We sketched and discussed how they form, differences in their erosional and tectonic significance, and examples of each. See text figures and class handout, nice examples from the Grand Canyon.
implications for shelf dynamics, and reconstructed paleogeography.
We looked at some Field Photos at the end of class. Thanks to Marli Miller for beautiful photos!