Tertiary vegetation, climate, and altitude of the Rio Grande depression, New Mexico–Colorado

Abstract

Late Eocene to middle Oligocene floras from the area of the present Rio Grande depression represent a time sequence from the upper part of mixed subtropical forest (Bernalillo flora), to an ecotone between broadleaved sclerophyll and mixed conifer forest (Red Rock Ranch flora), to subalpine conifer forest (Hillsboro and Hermosa floras). The implied difference in mean annual temperature of ~ 11°C suggests that altitude increased 2,000 m in 6–8 my. Construction of the Datil-Mogollon volcanic pile, averaging about 1,200 to 1,500 m thick, is thought to be largely responsible for the forest zonation, but regional doming accompanying volcanism may also be involved. The Oligocene subalpine conifer forests now occur in the piñon-juniper belt 900 and 1,200 m below the present subalpine zone, consistent with the subsidence that formed the Rio Grande rift beginning in the late Oligocene/early Miocene and continuing to the present. Later epeirogenic uplift of ~ 1200 m is implied by fossil plants in the Galisteo (~ 40 my bp), Creede (~ 27 my bp) and Tesuque (~ 14 my bp) Formations that border, or are in the rift.

Diachronous episodes of Cenozoic erosion in southwestern North America and their relationship to surface uplift, paleoclimate, paleodrainage, and paleoaltimetry

“…Early studies using the NLR technique were simple qualitative comparisons (e.g., MacGinitie, 1953MacGinitie, , 1966MacGinitie, , 1969, whereas later NLR analyses used the modern global lapse rate (Axelrod, 1968(Axelrod, , 1997Axelrod and Bailey, 1976). NLR analyses typically yield low paleoelevation estimates (~300 m for ca.…”

The Late Cenozoic uplift - climate change paradox

“…The most commonly used measure of paleoaltitude is through the analysis of floras, although this has only been used in a few regions (for the southern Rocky Mountains: MacGinitie 1953; Axelrod and Bailey 1976;Meyer 1986;Chase 1992, 1994;Wolfe 1992b;Gregory and McIntosh 1996;Wolfe et al 1997;for Tibet: Hsu 1978;Xu 1981;Powell 1986;Spicer et al 2001; for Japan: Momohara 1994; for the Andes: Wijninga 1996aWijninga , 1996b. The use of fossil plant assemblages has been criticized because the localities where the fossils occur may represent special environments in upland areas, such as valley plains where sediment occurred.…”

“…This method of interpretation of paleoclimate from fossil leaf assemblages assumes that genera and species may have adapted to different conditions, but that the physiologic response remains constant (Chaloner and Creber 1990). Axelrod and Bailey (1976) presented a detailed discussion of the methodology involved in interpreting paleoaltitude from the paleotemperatures indicated by the fossil flora. Meyer (1986) made a new estimate of the original elevation of the Oligocene Florissant site in Colorado (Fig.…”

History and causes of post-Laramide relief in the Rocky Mountain orogenic plateau

“…This latter view is supported by paleoelevation estimates derived from leaf margin analyses, which suggest no net change since Eocene time (Gregory and Chase, 1992;1994). Additional paleoelevation proxies based on geochemical, stratigraphic, paleobarometric, and other paleobotanical methods have yielded varying results, both for and against each interpretation (Axelrod and Bailey, 1976;Wolfe et al, 1998;Sahagian et al, 2002;Poulson and John, 2003;Hay et al, 1989). As a result, the history of regional elevation change remains unresolved (cf.…”