[Aztlan] Dating of beach ridges

[David Hixson]

I look forward to Bruce's response to E.P.'s question.  Bruce and I corresponded regarding the older fossilized beach ridges many months ago, and I greatly appreciated his comments.

For those who would like a visual reference for these beach ridges, go to <<http://maps.google.com/maps>> or Google Earth, and type in "Celestun".  If you zoom in and out of the satellite imagery, panning north and south of the modern town, you will see that the peninsula of Celestun is essentially a linear conglomeration of late holocene beach ridges.  These are in fact still being built (and eroded) today, as currents whip around the NW tip of the Yucatan Peninsula, depositing sands further south along the west coast.  Isla Arena (the small sandy peninsula just south of Celestun) is another example.

Archaeological surveys of the coastal beach ridges have regularly commented that they can be as young as 1000 to 3000 years ago (see Eaton 1978;  Andrews 1983)

However, if you type in "Sinkeuel" into the Google Maps or Google Earth search engine, you will see the much older fossilized beach ridges a few kilometers west / southwest of rancho Sinkeuel.  In this particular imagery, they appear as lines of taller forest in the seasonally inundated western Maya wetlands, roughly paralleling the curve of the NW coast.  These fossilized beach ridges (called "tzekeles" in some of the literature) were likely formed when sea levels were much higher.  Using SRTM (Shuttle Radar Topography Mission) data, I have estimated that the sea level would have needed to be over 4 meters above pmsl (present mean sea level) in order for these formations to have occurred.  The last time this could have happened was during the last interglacial period 129,000 - 120,000 years ago.  This would be in line with similar inland beach ridges documented in Florida (see the last few paragraphs of
 <<http://disc.sci.gsfc.nasa.gov/geomorphology/GEO_6/GEO_PLATE_C-14.shtml>>).

-Dave

P.S. If you are already looking in this area, turn your browser to 20.669358 degrees latitude, -90.282429 degrees longitude.  You'll see the glare and shadow from my van parked in the middle of the seasonal wetlands, at the intersection of two rough trails.

__________________________________________________
David Hixson
Ph.D. Candidate
Tulane Anthropology
chunchucmil at yahoo.com




----- Original Message ----
From: E.P. Grondine <epgrondine at yahoo.com>
To: aztlan at lists.famsi.org
Sent: Monday, September 21, 2009 7:11:25 PM
Subject: [Aztlan] Dating of beach ridges

Gracias, Bruce - 

"Topping this pile are even younger "beach ridges" of calcareous sand dating to only 3,000 years ago."

How was the date for these "beach ridges" determined? Any kind of precise dating? Any deeper marine organisms found in the deposits? Previous analysis of depostional mechanisms?

E.P. Grondine
Man and Impact in the Americas