ps418

Just wanted to pass along a brief description of a paper I read today:

Buck, B.J., and G.H. Mack. 1995. Latest Cretaceous (Maastrichtian) aridity indicated by paleosols in the McRae Formation, south-central New Mexico. Cretaceous Research 16(5): 599-572.

The McRae Formation in south-central New Mexico is about 420m thick, and consists of two members, the Jose Creek and the Hall Lake. The formation is of Cretaceous age, based upon the included dinosaur fauna. The formation is rich in paleosols (at least 26), many of which contain in situ tree trunks.

14 paleosols, from 45-150m thick, are recognized in the Jose Creek Member. These are classified as <a href="http://www.fao.org/waicent/faoinfo/agricult/agl/agll/prosoil/horglos.htm#argic" target="_blank">argillisols</a>. These display well-developed soil horizonation (A-E-Bt-Bc-C), and soil structures such as blocky peds and clay cutans. Downward bifurcating, downward-tapering root traces are abundant, some of which are silicified (root petrifactions).

Several of these paleosols are blanketed by ash-fall tuffs burying tree stumps up to 1.7m! in diameter, with preerved large roots penetrating and cross-cutting the underlying palesol horizons (see fig. 5).

12 paleosols are recognized in the overlying Hall Lake Member, from 70-450cm thick. These are classified as <a href="http://www.fao.org/waicent/faoinfo/agricult/agl/agll/prosoil/calc.htm" target="_blank">calcisols</a> and <a href="http://soils.ag.uidaho.edu/soilorders/vertisol/" target="_blank">vertic</a> calcisols. Soil horizons and soil structures are well-developed, and at least one paleosol includes a "massive, well-indurated bed of pedogenic calcrete up to 4m thick," which indicates a very advanced stage of calcisol development. Calcisols are diagnostic of semi-arid environments.


Patrick

MOJO-JOJO

Er...do I need to know this for the quiz tomorrow? <img src="confused.gif" border="0">