Aeolian Geomorphic Response to Climate Change: An Example from the Estancia Valley, Central New Mexico, USA

Abstract

Three generations of Holocene aeolian activity are preserved along the axis of the Estancia Valley, central New Mexico, USA. The transition from large dome dunes to parabolic dunes to loess reflects differences in sedimentation and environments. controlled by climate change. The aeolian landscape developed on the final lacustrine plain of a complex series of freshwater pluvial lakes that occupied the valley from ca. 24,000 BP to ca. 10,500 BP, during the maximum development and subsequent deglacial phases of the Laurentide glacier. Climate change associated with the disappearance of the final pluvial lake initiated dome dune formation. The dome dunes are characterised by low-angle tabular cross-laminations and tabular ungraded fine-medium beds. The internal structures indicate that limited sediment availability controlled dome dune formation. Development was initiated and sustained by prevailing westerly winds, consistent in direction, but marked by gustiness. Accumulation was episodic, punctuated by periods of stability with weak mollisol development. Charcoal from one mollisol dates to ca. 8,500 BP. After this time, the dome dunes attained their greatest relief and were capped by a thick, cemented gypsiferous soil. A series of at least five stacked, weak mollisols lapped on to the flanks of the dome dunes, ca. 4.660 BP.|Overlying the stacked soils and dome dunes is a second generation of parabolic dunes with associated deflation basins. These dunes developed under westerly winds varying in intensity. Spatial limitation of dune migration contributed to sediment retention, forcing dunes to increase in height and allowing stacking of successive generations of landforms. Parabolic dunes originating along the eastern margin of Laguna del Perro climbed from the playa floor and overrode the dome dunes. Sediment movement by traction and saltation was hindered, slowing transportation rates, enhancing retention, and resulting in rapid accumulation. Sediment supply was limited by the presence of ephemeral standing water in the playa. Deflation of the marginal areas was further limited by periodic rainfall events, allowing diagenetic overgrowths that stabilised the original gypsiferous lacustrine plain. Depositional episodes were transitory in the dune field, not associated with marked climate change, and were separated by periods of stability.|Modern aeolian activity involves the deposition of loess. Loess is also reworked by sheetwash, as well as in playa marginal areas of the larger parabolic dunes. Under modern climate conditions, aeolian sedimentation in the Estancia Valley is marked by very limited sand supply, almost exclusively locally derived, and high rates of retention. The discontinuous vegetation cover provides localised zones for trapping of fine suspended gypsite, allowing loess accumulation. Loess accumulates in sites preferential for vegetation development, such as inactive trough blowouts and hollows between adjacent dunes.