Thursday, April 13, 2006

Cartography: Paleogeogrpahic Maps of North America

Blogged at the CCA weblog on Tuesday is a link to a fantastic project undertaken by Dr. Ron Blakey.The maps created by Dr. Blakey represent time slices of the geologic transformations, via plate tectonics, to the core of ancient North America, "Laurentia". The time slice maps are taken at 5-10 million year intervals over the past 550 million years. (PerryGeo has created a fantastic animated gif of these maps!)

The projects website contains 40 of the most representative time slices. From these maps you can witness how the physiography of Laurentia has changed through geologic history. Mountains rise, rifts open, deserts form, and lakes deepen as the earth's tectonic plates subside and become reborn.

Of particular interest to me is the time slice of Late Triassic (210Ma).

Eastern Pennsylvania sits contently just above the Triassic equator. Africa has recently slammed into the East Coast forming the super continent of Pangaea. This collision, the Appalachian orogeny, is reminiscent of the modern collision of India and Asia. The mountains formed on the East Coast may have been as grand as the Himalayas. But by 250 Ma, Africa and Laurentia have been sent on their way. A rift basin develops as the two continents drift in opposing directions.

Along the Eastern Seaboard of the
US, this Triassic basin (geologic history) widened and deepened as huge blocks of the earth dropped due to tensional stress. Lakes formed within many of these half graben basins. Some of these lakes would rival the Great Lakes and Caspian Sea.

Eastern Pennsylvania, erosion from the massive mountains to the West was transported in to this basin. Large chunks of rock and sandy sediment were moved by water and gravity to form mud chocked braided streams and gravely sand bars on the margin of the newly formed lake. As the basin deepens, the lake goes through cycles of drainage and enclosure. These cycles change the depth and depositional regime of the basin lake. Some times shallow, the lake deposits are sandy and exposed to air and the critters that roam the area. At other times, and in other areas of the lake, it is incredibly deep and deprived of oxygen. Thin chemical laminea are deposited in these areas. As the mountains eroded and the subsiding resigned the basin in-filled and shallowed again. In the hot and dry region above the equator, the deposits on the lake margin formed a playa like environment. The muddy shoreline cracked and split as it was wetted and then baked by the sun.

For the next few million years, the lake shallowed and the mountains eroded. As pressure was release, the Earth thrust magma into near surface chambers and lava outflows. Into the Cretaceous and Tertiary periods of the past 150 million years, the regal mountains which once supplied the Triassic lake with sediment are eroded to reflections of their former selves. The sediments of the
Piedmont and Coastal Plain are now the home of the highest peaks.

Since I am no geologist, understand that this description may be a bit fictitious, but it is the way I like to see it.

Head on over to the CAA blog to read some more, or to read another rendition of the geologic history of Laurentia, based on these maps, check out the BLDGBLOG.

(Pictures are credited to Dr. Ron Blakey. Fantastic work!)

Tuesday, April 11, 2006

Science Blog: Remote Sensing for Mayan Ruins

From a story recently covered at the Science Blog. Researchers from NASA and the University of New Hampshire in Durham have discovered a number of previously unknown Mayan temple ruins in a densely forested region around San Bartolo, Guatemala. The team employed the use of NASA's Airborne Synthetic Aperture Radar (AIRSAR) to remotely sense the jungle floor. Flown from 8km above the relative topography, AIRSAR's long wavelength allows it to penetrate the jungle canopy and collect data that has escaped other methods.

The research team noticed a "fingerprint" in vegetation growth patterns that indicated the possible presence of a Mayan ruin. On field checking, it was quickly learned that the fingerprint is the result of differential moisture and vegetation growth due to the limestone building materials used by the Mayans.

The remote sensing segment of this project is combined with a detailed climactic study which leads the researchers to conclude that the Mayan civilization may have crumbled due to a series of disruptive climactic events. A better understanding of these cataclysmic processes and their impact on societies will help inform modern nations on how to avoid such pitfalls.

The AIRSAR system was developed in 1988 by the Jet Propulsion laboratory at the California Institute of Technology. The AIRSAR missions covering South America were flown in March 2004. Other archaeological applications of the AIRSAR technology include extensive work at Angkor, Cambodia [also, a great PDF], temples in Nakhorn Ratchasima province, Thailand, 19th century plantations in Georgia, and a study in Tikal, Guatemala to be presented at this years Computer Applications and Quantitative Methods in Archaeology Conference.

GeoPriv - Geographic Location Privacy Protocol

With location specific information and services becoming widely available, the privacy and restriction of these data becomes very important. GeoPriv is a transfer protocol (in development) aimed at authorizing the delivery of and rendering location specific information.

The basics of this protocol, as I understand it, is an authorization system built from a rule set (policy) which is composed of Conditions, Actions, and Transformations. This policy is stored as an XML document or in a relational database on the location server. The Condition segment of this policy is a set of expressions that are based on certain variables, such as requester identification, server information, and external variables derived from the location itself. These expressions are interpreted as TRUE or FALSE and the Action of PERMIT is granted if the conditions are met. Lastly, the Transformation is an algorithm with defines the resolution at which locational information will be delivered. The transformation combines the union of the permissions to define the requesters level of accuracy. These transformations, as well as the entire policy is intended to be extensible for specific application use.

It appears that the implementation of this protocol could be useful in displaying location sensitive archaeological sites. As I mentioned in a previous post, archaeological site location is highly guarded by both the state government and the archaeologists who investigate them. The fear of looting and disturbance is often cited as the reason for such secrecy. Although, I understand these concerns, I also feel that in a time when archaeologists justify our existence with the preservation of "the Publics'" heritage, we need to loosen our death grip on where sites are so the publics can feel the same senses of place that we do. All rants aside, the GeoPriv protocol, with the use of locational transformations could be a useful tool in disseminating resolution adjusted information on site locations based on conditional rules.

I admit, I only have a general understanding of the specifics of this protocol, so please investigate it a bit (they also have a list-serv) and let me know what you think.