Estimating scales of environmental signals and stratigraphic preservation Liz Hajek – Penn State University

Estimating scales of environmental signals and stratigraphic preservation Goals: – Develop an innate sense of “how big is big” or “how fast is fast” in different sedimentary settings – Think critically about the fidelity of the stratigraphic record and sampling/measurement scales – Estimate stratigraphic scales that are likely to preserve climate, tectonic, land-use or eustatic signals in different settings Adaptable for students at any level

Estimating scales of environmental signals and stratigraphic preservation Penn State Advanced Stratigraphy coarse goal: Students learn to pose a stratigraphic question, determine the appropriate methods of data collection, analyze and communicate the results, and evaluate uncertainty. Activities support coarse goal by providing: – Baseline literacy with rates and scales of geological processes – Introduction to and practice with key concepts

Estimating scales of environmental signals and stratigraphic preservation Activities: – Rates and Scales “cheat sheet” – Estimate river-response timescales using measurements from Google Earth – Estimate allogenic/mass-balance/compensation timescale for a fluvial basin fill

Estimating scales of environmental signals and stratigraphic preservation Activities: – Rates and Scales “cheat sheet” – Estimate river-response timescales using measurements from Google Earth – Estimate allogenic/mass-balance/compensation timescale for a fluvial basin fill

Estimating scales of environmental signals and stratigraphic preservation Activity – introduction – Rates and Scales “cheat sheet” Over the coarse of a semester, students develop a reference list of examples of characteristic scales and rates of geologic processes Key processes: subsidence, eustasy, sediment yield, etc. Goals: 1)Develop a “reasonableness” filter for relevant processes 2)Grapple with inherent uncertainty in stratigraphic estimation, quantification, and interpretation

Rates and Scales Reference Sheet Crib sheet for your reference How big is big? How fast is fast? What’s typical? Characteristic and extreme rates and scales of processes and systems relevant to stratigraphy Example locations/systems for each scale Format: a few pages of organized notes or tables – think of something you’d want to print and have on your bulletin board or in the back of your field book What to include: any time we talk about rates and scales during class, you should find examples for your reference sheet Example: we’ve gone through subsidence and eustasy. You should note: - typical rates and scales (length and time) for different tectonic setting - typical rates and scales (length and time) for sea-level drivers

Match the plots with tectonic setting -Foreland basin -Passive margin -Forearc basin -Pull-apart basin (strike-slip) -Intracratonic basin Figures from Xie and Heller, 2009, GSA Bulletin A B C D E

Match the plots with tectonic setting -Foreland basin -Passive margin -Forearc basin -Pull-apart basin (strike-slip) -Intracratonic basin Figures from Xie and Heller, 2009, GSA Bulletin Intracratonic Foreland Passive margin Forearc Pull-apart

Miller et al., 2005, Science Sedimentation Groundwater/lake storage Thermal expansion Ice sheets Continental collision Sea-floor spreading

Miller et al., 2005, Science

Summerfield and Hulton, 1994, JGR Rank the following rivers by denudation rate (small to large). Where do you guess they fit on the plot? Colorado Mississippi Ganges Nile Danube Amazon Lena

Summerfield and Hulton, 1994, JGR

Rank the following rivers by denudation rate (small to large). Where do you guess they fit on the plot? Colorado Mississippi Ganges Nile Danube Amazon Lena

Channel gradient Modal elevation Annual runoff Temperature Relief ratio Local relief Runoff variability Precipitation Summerfield and Hulton, 1994, JGR

Estimating scales of environmental signals and stratigraphic preservation Activity – summary – Rates and Scales “cheat sheet” Goals: 1)Develop a “reasonableness” filter for relevant processes 2)Grapple with inherent uncertainty in stratigraphic estimation, quantification, and interpretation – Discussion opportunities: Broad range of processes – biological, chemical, too! Sampling and Sadler effect Variability within groups, but driving variables & processes are apparent

Estimating scales of environmental signals and stratigraphic preservation Activity – summary – Estimate river-response timescales using measurements from Google Earth Goals: 1)Understand how alluvial river scale and sediment load influences response time to external forcing 2)Grapple with inherent uncertainty in stratigraphic estimation, quantification, and interpretation

Estimating scales of environmental signals and stratigraphic preservation Activity – summary – Estimate river-response timescales using measurements from Google Earth

Estimating scales of environmental signals and stratigraphic preservation Estimate river-response timescales using measurements from Google Earth – Castelltort and Van Den Driessche (2003); Paola et al., 1992, Basin Research; Armitage et al., 2011, Nature Geosci

Estimating scales of environmental signals and stratigraphic preservation Estimate river-response timescales using measurements from Google Earth – Timescale of alluvial response is primarily a function of river length and “diffusivity” (i.e., sediment flux) Response time River length Diffusivity Sediment flux Mean slope Width Length, width, and slope  Google Earth Sed. flux  Milliman and Syvistki, 1992, Jour of Geol & Hovius, 1998, SEPM Sp.Pub. 59

Estimating scales of environmental signals and stratigraphic preservation Estimate river-response timescales using measurements from Google Earth – Exercise is scalable – for a low-risk activity, give students data directly from Hovius paper and have them calculate and compare – Example:

Estimating scales of environmental signals and stratigraphic preservation Estimate river-response timescales using measurements from Google Earth – Timescale of alluvial response is primarily a function of river length and “diffusivity” (i.e., sediment flux) – Big rivers with small Qst have LONG response times (hundreds of thousands of years+) – Estimates will differ from Castelltort and Van Den Driessche (especially with Milliman and Syvitski Qst). – Ask students to compare and think about why (measurement errors, etc.)

Estimating scales of environmental signals and stratigraphic preservation Activity – summary – Estimate river-response timescales using measurements from Google Earth Goals: 1)Understand how alluvial river scale and sediment load influences response time to external forcing 2)Grapple with inherent uncertainty in stratigraphic estimation, quantification, and interpretation – Discussion opportunities: If precise estimates are difficult TODAY, where we can see, measure, and monitor systems, consider uncertainty in ancient reconstructions (order-of-magnitude = fine, factor of two = great!) Despite challenges, useful estimates are possible! Design stratigraphic studies accordingly

Estimating scales of environmental signals and stratigraphic preservation Activities: – Rates and Scales “cheat sheet” – Estimate river-response timescales using measurements from Google Earth – Estimate allogenic/mass-balance/compensation timescale for a fluvial basin fill Connecting lessons – Example: Deposits of what type of river would be likely record glacial eustatic changes?