GSA North Central Section meeting in Madison, WI: 5/2015

Just prior to graduation I submitted an abstract entitled, “Interpretation of a Paleo-Inlet’s Depositional History: A Ground Penetrating Radar Investigation, Grand Island, MI.” I presented this research using power point as a medium.  A previous analysis of a 50MHZ Ground Penetrating Radar (GPR) subsurface profile of the entire Grand Island Tombolo revealed a depositional feature displaying channel fill reflection patterns near the center of the tombolo and beneath the modern strandplain.

100MHZ GPR profile of paleo-inlet
Common radar stratigraphic terms

This author hypothesized that this feature could be a Paleo-inlet which existed prior the deposition of the modern strandplain and formation of the tombolo.  A higher resolution (100MHZ) GPR profile of this feature was collected to allow for a more detailed analysis.  The content presented in Madison displays evidence pointing to the existence of channel like conditions in the proposed paleo-inlet through the use of radar stratigraphic analysis.

Paleo-inlet facies (B1-4) were identified using radar stratigraphic analysis.  The facies are bounded by the modern strandplain above (A) and prograding sand spits below (C).
Paleo-inlet facies (B1-4) were identified using radar stratigraphic analysis. The facies are bounded by the modern strandplain above (A) and prograding sand spits below (C).

A paleo-geographic reconstruction of the Grand Island Tombolo was created based on the authors understanding of lake level chronology, regional geology, and and applied radar stratigraphy.  This reconstruction is meant to provide a base illustration which I hope will foster future discussion, decomposition of current hypothesis, and construction of new hypothesis.

During the Nippising high stand a cuspate foreland is present sub aerially and a straight exists between the East and West bedrock lobes.
During the Nippising high stand a cuspate foreland is present sub aerially and a straight exists between the East and West bedrock lobes.
Longshore  drift moves sediment through the straight until it reaches a lower energy regime by the cuspate foreland.   Two separate sand spits develop. The larger spit progrades north and east away from the cuspate foreland.   The second smaller spit progrades north and west away from the eastern bedrock lobe of Grand island.
Longshore drift moves sediment through the straight until it reaches a lower energy regime by the cuspate foreland.
Two separate sand spits develop.
The larger spit progrades north and east away from the cuspate foreland.
The second smaller spit progrades north and west away from the eastern bedrock lobe of Grand island.
The sand spits do not merge in the middle. Strong northeast storm winds open sequential inlets allowing sediments to move south through the sand spits and be deposited on the lee side. Complex channel fill patterns are deposited in the inlet during calm weather.
The sand spits do not merge in the middle.
Strong northeast storm winds open sequential inlets allowing sediments to move south through the sand spits and be deposited on the lee side.
Complex channel fill patterns are deposited in the inlet during calm weather.
Eventually a tombolo is formed as sediment fully chokes the lee side of the inlet.   A modern strand plain progrades north into Trout Bay forming the sequence of dune ridges observed on the tombolo today.
Eventually a tombolo is formed as sediment fully chokes the lee side of the inlet.
A modern strand plain progrades north into Trout Bay forming the sequence of dune ridges observed on the tombolo today.

My full PowerPoint presentation can be accessed below.  Enjoy!

“Interpretation of a Paleo-Inlet’s Depositional History: A Ground Penetrating Radar Investigation, Grand Island, MI.”

My research partner and co-author, Sean Morrison, is currently working on a paper regarding this topic in addition to studying as a master’s student at University of Waterloo in Canada under the direction of John Johnston.  Future research by this author will be released on this blog.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s