Massanutten Synclinorium Virtual field trip via GigaPan

Massanutten Synclinorium Virtual Field Trip via GigaPan

There are a bunch of GigaPan images hosted on this page, gathered here to supplement a Field Studies in Geology course to examine these sites in the northern Shenandoah Valley, Massanutten Range, and Fort Valley of Virginia (all part of the Massanutten Synclinorium).

Stop 1: Conococheague Formation exposed at Mulberry Run

Easternmost portion of the south-facing outcrop:

Petri dish full of ooids, the spherical building blocks of oolitic limestone:

Samples of stromatolites from other sites, similar to those in the Conococheage Formation:

(Credit Ariel Anbar)

Two views of Shark Bay, western Australia, a place in the modern world where stromatolites are thriving; geologists infer the depositional setting of the Conococheague Formation would have been similar:

(Credit Ariel Anbar)

(Credit Ariel Anbar)

Q: What is the “take home message” regarding our interpretation of the depositional conditions that prevailed during the deposition of the Conococheague Formation and related Cambrian carbonates?

Stop 2: Tumbling Run (New Market, Lincolnshire, & Edinburg Formations)

The uppermost end of the outcrop (stratigraphically, the lowest/oldest layers): the contact between the New Market and overlying Lincolnshire:

In Tumbling Run itself, Ca and CO3 ions (dissolved from local source rocks such as those displayed in the outcrop) reprecipitate to form fresh deposits of travertine, like this:

Q: What is the overall story recorded by the outcrops at Tumbling Run? (Hint: it changes from bottom/older to top/younger.)

“Stop” 3: Lower Martinsburg Formation on Route 11

Limy shale of the Martinsburg Formation exposed at the intersection of Funk Road and Route 11. This is stratigraphically higher than the Tumbling Run site’s uppermost strata:

Stop 4: Upper Martinsburg Formation on Millner Road:

Very steeply dipping strata of graywacke and shale (lacking any calcite), exhibiting graded bedding due to deposition by turbidity currents:

Graded bed from the Martinsburg Formation as seen in hand sample:

Outcrop showing bedding/cleavage relationships in Martinsburg Formation:

A sample of graded bedding from the Martinsburg Formation, shown in two orientations, as well as before and after cutting into four pieces:

Q: Which of the two previous GigaPans is shown “right side up?” Which is “up side down?” Why?

Stop 5: Massanutten Formation at Passage Creek

Outcrop #1 adjacent to Fort Valley Road, in the George Washington National Forest:

A hand sample of Massanutten Formation quartz sandstone:

Outcrop #2 adjacent to Fort Valley Road, in the George Washington National Forest:

Outcrop #3, up the hill from outcrops #1 and #2:

The overall regional structure (the Massanutten Synclinorium) is hinted at by these two outcrops in Passage Creek:

On the east side of the syncline, the strata dip to the west:

On the west side of the syncline, the strata dip to the east:

Q: What way (what direction) was the current flowing when these strata were deposited (from left to right, or right to left)? What structure tells you this? Explain.

Two views of Buzzard Rocks, the cliffs above and to the east of the outcrop we visit:

Trace fossils in the Massanutten Sandstone: A comparison between a “raw” GigaPan and annotations showing the trace fossils:

Stop 6: Helderberg Group limestones exposed on Fort Valley Road:

These strata overlie the Massanutten Formation, and show prominent cleavage due to post-depositional tectonic squeezing during the Alleghanian Orogeny:

A slab of the Keyser Limestone, one of the layers within the Helderberg Group (explore it for copious fossils!):

Q: Taken together, what do the Massanutten Formation and Helderberg Group have to say about depositional conditions during the Silurian and early Devonian? How does this relate to what we saw in the Martinsburg Formation? Explain.

Stop 7: Mahantango Formation

Black shale outcrop at the intersection of Fort Valley Road and Ramsey Road.

Mahantango Formation showing trace fossils (orange-colored tubes), Fort Valley Road:

Mahantango Formation, showing carbonate nodules:

Mahantango Formation showing intersection of bedding and cleavage, with both body fossils and trace fossils, exposed near Trinity Church:

Mahantango Formation sample showing a large straight nautiloid fossil:

Mahantango Formation outcrop showing Zoophycos trace fossils:

Another Mahantango Formation outcrop showing Zoophycos trace fossils:

Mahantango Formation sample showing a nice example of the Zoophycos trace fossil:

Mahantango Formation sample showing a shell-rich horizon:

Q: How do the strata of the Mahantango Formation relate to the presence or absence of mountain-building during the late Devonian? How does this relate to what we saw in the Massanutten Formation and Helderberg Group? Explain.

Stop 8: Veach Gap, to see deformation induced by Alleghanian mountain-building

Four views of the anticlines exposed at Veach Gap (all are folds within the Massanutten Sandstone):

Here’s an anticline developed in Needmore Formation shale, further south in the Fort Valley. Note the prominent cleavage “fan” superimposed on the sedimentary layering:

Q: How do these structures relate temporally to the strata they overprint? Explain.

Q: What can you infer about the tectonic location of the Alleghanian Orogen based on these structures, relative to the locations of the Taconian and Acadian Orogenies before it?

Thanks for exploring these images!