Depositional histories of vegetation and rainfall intensity in Sierra Madre Oriental Mountains (northeast Mexico) since the late Last Glacial

Abstract : An evaporite enriched sediment archive from the dry Sandia Basin located in the water-stressed western foothills of the Sierra Madre Oriental Mountains (northeast Mexico) was studied to reconstruct depositional histories of vegetation and rainfall intensity in orbital to millennial-scales over the last ~32.5 cal ka. Surrounding vegetation had more C3 plants during the late last glacial and deglaciation and the expansion of more drought tolerant C4 plants occurred only after ~5 cal ka BP. Clastic minerals were sourced from different lithologies within the watershed and their abundances helped to infer runoff dynamics and hence the rainfall intensities. Deposition of more mixed-layer clay represented wetter intervals over the late last glacial and deglaciation. Transportation of clastics from the nearby lithology during these wetter intervals suggested that high-intensity rainfall events were less frequent. Response to the Heinrich stadials (H3, H2 and early H1) was mainly similar (drier) and erosion in the watershed remained less-than-average. Transportation of more quartz-rich sediments from distal lithologies during the late Bølling-Allerød (B/A) interstadial and between ~6.2 and 4 cal ka BP with a depositional hiatus between ~12.7 and 6.2 cal ka BP represented the intervals of more frequent high-intensity rainfall events, possibly related to short-lived storms. We hypothesize that the Gulf of Mexico sea surface temperature was a principal forcing. Total annual precipitation in this region decreased but the frequency of short-lived storms increased during the warmer Atlantic Multidecadal Oscillation (AMO) states. Warmer conditions also led to deposition of more gypsum. Our observation, however, needs further evaluation under the modern-day greenhouse warming scenario.