Society of Independent Professional
Earth Scientists

 Click here for the 2026 S.I.P.E.S. Dues Form - please use this form to update your contact information as well

Click here to pay your dues online

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Next Event:

March 26, 2026

Our Presenter:

Ned Sterne

"A palinspastic restoration of Colorado – up to 209 kilometers of horizontal shortening by multiple orogenies?"

All attendees MUST RSVP!

Please RSVP by 11:30 a.m. on March 23

Click here to RSVP

When: Thursday, March 26, 2026, 11:30 a.m. - 1:30 p.m.

Where: Wynkoop Brewery - 1634 18th Street, Denver, CO 80202

Cost Structure:

• Members $25 (Presentation & Meal)
• Non-members $30 (Presentation & Meal)
• Walk-ins will no longer be allowed due to an issue with the Wynkoop.  Please pre-purchase a lunch to attend.  Sorry for the inconvenience!

Please feel free to share this information with any friends and colleagues who might be interested!

Mask requirements voluntary for vaccinated attendees.

Abstract:

For a 2017 field trip hosted by the Denver area geologic study groups, several of us including Bob Raynolds, Jim Granath and Steve Cumella built a restorable cross section following Interstate 70 (I-70) across Colorado using a variety of constraints. Key among these were low-temperature thermochronologic data to establish an end-Cretaceous datum for the top of the restoration, and magnetotelluric data defining an undulating mid-crustal interface adopted as the decollement for the bottom of the restoration. The restoration revealed 77 km (48 mi) of horizontal shortening within the Proterozoic upper crust built the basement uplifts of Colorado.

After the 2017 trip, we revised the section in light of additional seismic and magnetotelluric processing, recognition the Sawatch Uplift was carried on a major east-directed blind thrust, and the realization our original interpretation had not addressed gravity data. A review of the gravity literature showed numerous batholiths in the upper crust of the I-70 corridor, that if present showed our interpretation was wrong.

To address this, FastGrav freeware developed by Aaron Price was used to model the gravity response along the magnetotelluric transect used to fix the mid-crustal decollement in the I-70 section. This preliminary model showed the observed Bouguer gravity could be closely matched by thickening the lower-density upper crust at the expense of the higher-density lower crust across the central part of Colorado.  In other words, the gravity modeling showed our interpretation of the I-70 section was permissible.  While this result was gratifying, it indicated gravity data could be used to constrain depths to the mid-crustal interface and decollement not just in the I-70 corridor, but across all of Colorado - our work had only just begun.

With the expert guidance of Bill Pearson using GMSYS software and helpful advice from Craig Jones (CU Boulder) and Ben Drenth (USGS), FastGrav gravity models were constructed every 0.25 degrees latitude across Colorado. The models incorporated seismic tomography defining both depth to the Moho and density variations in the mantle, with a regional Dakota surface compiled by Steve Cumella to add shallow shale-dominated, low-density polygons across basins. Observed Bouguer gravity was matched by varying depths to the mid-crust interface. Prior seismic tomography studies had shown the Colorado Rockies were “rootless” meaning the Moho beneath Colorado was flat and its high topography was not compensated by an Airy root at the Moho. Our modeling showed thickening the upper crust above a thinned lower crust created an Airy root at the mid-crust interface that with coincident lower densities in the mantle supports Colorado’s high elevations.

The mid-crust decollement defined by the gravity models was combined with surface thrust trends to build geologic cross sections spaced every 0.25 degrees latitude across Colorado. Palinspastic restorations of the Proterozoic upper crust along each of the sections were made using Halliburton’s LithoTect software.  Unlike our original I-70 interpretation that showed the restored upper crust thickening from 15 km in the east to 30 km in the west, the restorations showed a uniform restored Proterozoic upper crust thickness of approximately 12.5 km, which became an important interpretive guide.  Batholiths were assigned the same density as the rest of the upper crust and shown to thicken the upper crust beneath the Colorado Mineral Belt and in the San Juan Volcanic Field. Deformation of the upper crust reflects multiple orogenic cycles including Proterozoic assembly of the North America craton followed by significant thrust events during the Ancestral Rocky Mountain and Laramide orogenies. The restored sections were used to construct palinspastic maps of Colorado showing between 88 and 209 km (55-130 mi) of horizontal shortening has built the basement uplifts of Colorado.
 

Bio:

Ned Sterne received a B.A. in geology from Harvard in 1979 having finished a solo undergraduate honors thesis on the Indus-Tsangpo Suture Zone of Ladakh, northern India.  He completed an M.A. in geology in 1981 at Dartmouth resulting in the discovery of natural ammonium illites associated with exhalative Pb-Zn-Ag ore deposits in northern Alaska.  He did Rocky Mountain and international petroleum exploration from 1981 to 2015. Since retiring in 2015, he has been studying the geology of Colorado.  Ongoing projects include showing how stacked triangle zones have built the thrusted basement uplifts of Colorado, the palinspastic restoration of a cross section following I-70 across Colorado, a palinspastic map restoration of Colorado based on gravity modeling, and illustrating how deformation of the Rocky Mountain Erosion Surface has rerouted rivers across Colorado and parts of neighboring states since the Laramide orogeny. In 2022, he served as president of the Colorado Scientific Society.

WHAT IS SIPES?

The Society of Independent Professional Earth Scientists (SIPES) is the only national organization designed exclusively for the independent or consulting professional earth scientist. Members include geologists, engineers, geophysicists, geochemists, and other earth scientists. 

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Our Mission

To be the pre-eminent organization for furthering the professional business interests of independent practitioners of earth sciences. 

• Professional Competence

• Professional Business Ethics

• Presenting a favorable, credible and effective image of Society



Local Events:

Monthly Meetings

Meetings for 2026 will be held at the

Wynkoop Brewery

1634 18th Street

Denver, CO 80202