Posted by: Johan Normark | March 29, 2009

The Chicxulub fracture zone and the Spanish Colonial border

During the 2008 season the Cochuah Regional Archaeological Survey (CRAS) project surveyed what was a border area during the Colonial period (1544-1821), the early Mexican independence (1821-1847) and the Caste War and its aftermath (1847-1901). From the indigenous perspective, this border appears to have been fluid, but less so for the Spaniards or at least for their political system that was tied to the agricultural and sociopolitical strategies they brought over from Europe. My hypothesis is that this situation was partly affected by the Chicxulub fracture zone, created from an asteroid impact 65 million years ago. I argue that karstic features within the Chicxulub fracture zone were important attractors in the Prehispanic settlement expansions during droughts and there is compelling evidence that these locations were not settled during the Colonial droughts. All the karstic features within the fracture zone were not formed by the effects from this impact, but at least the deeper features, such as cenotes (sinkholes with water) may have their origin in the morphology caused by the impact. There are also karstic features outside the fracture zone but they are less frequent within the research area.

The Chicxulub fracture zone and the Spanish colonial border in 1680

The Chicxulub fracture zone and the Spanish colonial border in 1680

Settlement near karstic features, apart from cenotes, is without exception Prehispanic and not Colonial. The result of this year’s survey shows the importance of the fracture zone for the Spanish politics and its transparent nature for the indigenous population (in both Prehispanic and Colonial times). This has implications for the palaeoclimatic models since they partly work from how climate affect people today rather than taking into account past sociopolitical and economic changes that have created the contemporary situation.

Cenotes are available within the extensive Chicxulub fracture zone. The cenotes are partly formed by subsidence of the limestone that was formed on top of the impacted older bedrock. The extent of this fracture zone is still debated. Originally it was argued to have a radius of 90 km, counting from the center near the port of Chicxulub. This is the 5-km-wide band called the ring of cenotes. The ring of cenotes is permeable and affects the flow of groundwater and hydrogeologically it isolates Merida from the rest of the peninsula. This fact should also be taken into consideration since Richardson Gill uses Merida’s meteorological record from the 20th century in order to describe how droughts affect society. Areas outside Merida had access to more groundwater due to the fracture zone and hence were less affected by decreased rain (even if water levels decreased in cenotes).

Researchers have detected three other rings caused by the Chicxulub impact and the outer edge of the outer ring has a radius of roughly 170 +- 25 km. However, this is not a homogenous ring since to the west we have the Ticul fault zone that reduces the extent of the fracture zone in this area. The fracture zone extends further away to the southeast (into the Cochuah region), and possibly even more to the east. The concentric Holbox fracture zone has been suggested to be part of the greater Chicxulub fracture zone as well and this area is more than 170 km from the center of the impact. This fault zone in the Yalahau region has cenotes and wetlands.

Map of the Cochuah region after the 2008 field season

Map of the Cochuah region after the 2008 field season

The border of the Chicxulub fracture zone (the fourth ring) cuts through the Cochuah region in between the two largest known Prehispanic sites (Ichmul to the north and Yo’okop to the south). The area within the fracture zone is the area the Spaniards controlled. If we overlay the greatest extent of the proposed fourth ring (170 km from the center) with that of Farriss’ proposed colonial border (in 1680) we see that they partially overlap in the Cochuah region. The two kinds of borders are roughly 10 km apart and neither one of them were or are clearly delimited. However, the proposed extension of 170 km does not include the cenote at Sacalaca and the large rejolladas at Chakal Ja’as and San Pablo. These karstic features are, however, within the radius proposed by Sharpton and others (1993): 145-195 km from the port of Chicxulub. The distribution of caves in the region partly follows the concentric rings of the fracture zone. Yo’aktun, the cenote at Sacalaca, Santa Cruz and Xtojil are in line. The southernmost alignment known in the region is between San Salvador, Abuelos, and Gruta de Alux. These are also aligned with the Colonial border in 1680. If these caves form the edge of the fracture zone than only Santa Rosa and Sak Chikin are truly outside the fracture zone.

In any case, the Colonial extension beyond the 170-km limit in the eastern peninsula can partially be explained by the need of a coastal control. In the interior of the peninsula, there seems to be little extension of the early Colonial border beyond the fourth ring. The fracture zone formed the border of Spanish control but it was possible for the indigenous population to move across the border during the Colonial period droughts, something pointed out by Farris. In the Cochuah region, the area south and east of the fracture zone lacked permanent water but had better agricultural opportunities due to deeper soils. This area lacks larger Colonial and Spanish derived settlement, but as the survey in 2008 shows it has several Prehispanic sites despite its lack of permanent water sources. The density of Prehispanic settlement on both sides is more or less the same.

As of yet, no cenotes have been encountered south of the fracture zone within the CRAS area (that is if we extend the fracture zone another 10 km). The Prehispanic inhabitants in the southern part of the Cochuah region used a seasonal aguada at Yo’okop and perhaps haltuns and chultuns at other sites. Two chultuns are located 250 and 600 m from the large well at Sisal. No mounds were directly associated with the chultuns in this year’s survey, with the exception of Chumkatzin. Apart from these possible water reservoirs, there are few known water sources for the inhabitants south of the fracture zone.

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