HR: 0800h
AN: PP31A-1506    [Abstracts]
TI: Long period variability of a High Resolution Hydraulic Balance Proxy for Southern California and Northwestern Mexico: A 50 ka-long Sediment Record from Laguna Salada Basin, Baja California, Mexico
AU: * Aco-Palestina, A
EM: abelaco@cicese.mx
AF: Departamento de Geologia, CICESE, km 107 Carretera Tijuana-Ensenada, Ensenada, BC 22860 Mexico
AU: Contreras, J
EM: juanc@cicese.mx
AF: Departamento de Geologia, CICESE, km 107 Carretera Tijuana-Ensenada, Ensenada, BC 22860 Mexico
AU: Martin-Barajas, A
EM: amartin@cicese.mx
AF: Departamento de Geologia, CICESE, km 107 Carretera Tijuana-Ensenada, Ensenada, BC 22860 Mexico
AU: Hergeura, J C
EM: herguera@cicese.mx
AF: Division de Oceanologia, CICESE, km 107 Carretera Tijuana-Ensenada, Ensenada, BC 22860 Mexico
AU: Rendon-Marquez, G
EM: grendon@cicese.mx
AF: Departamento de Geologia, CICESE, km 107 Carretera Tijuana-Ensenada, Ensenada, BC 22860 Mexico
AB: The Salton Trough region of southern California and the Mexicali valley in northwestern Mexico are areas of rapid subsidence due to extension along the San Andreas-Imperial fault system and are being filled by clastic sediments transported by the Colorado River. The relatively high sedimentation rates of these basins have a high potential to preserve high-resolution climatic information. With this goal in mind, we drilled a 42 m-long core in the center of the Laguna Salada, a lacustrine basin located west of the Mexicali valley and to the south of the Salton Trough. Two ¹⁴C dates from plant remnants indicate sedimentation rates are in the order of 1mm/yr; based on this we estimate the age of the bottom of the core close to 50 Ka. This high sedimentation rate could in principle allow us to reconstruct the climatic variability of this hyperarid region on timescales ranging from centennial and millennial periodicities up to Milankovitch forcing. Here we present data on the first-order changes introduced by the later longer periods. Sedimentary facies in the core were identified based on color, granulometry, mineralogical composition and primary structures such as laminations, dissecation cracks, and bioturbation. Additionally, we obtained reflectivity of sediments every 5 mm to 1 cm, depending on the scale of primary structures. The recovered stratigraphy consists of three sedimentary successions. The lower part of the core is characterized by an alternation of mud and silt laminae of varying thickness between 5mm-1cm, probably deposited during stage 3. This ancient paleolake was dominated by sub-aqueous conditions with a permanent water table year-round. Good preservation of laminae suggests seasonal bottom anoxia. During the last glacial maximum, moisture conditions changed drastically. Laminations are replaced by finely stratified sand and further upsection by repetitive packages 50cm-thick composed of fine sand, brown mud, greenish silt and mud, and mud, caped with dissecation cracks and laminated gypsum. These sediments were deposited in a continental sabka environment with intermittent freshwater input, as evidenced by the clear dissecation cycles. Transition to the Holocene climate is characterized by deposition of well-classified sand with textural properties very similar to that of modern eolian dunes. This is indicative of extreme hyper-arid conditions. The Holocene, on the other hand is marked by a return to periodic wet and dry conditions. Present high rates of local precipitation during El Ni¤o years and periodic infillings by occasional discharges from the Colorado river are balanced by high evaporation rates that lead to intermittent diseccation of the lake and yield a characteristic alternation of laminated mud, fine sand, and evaporitic deposits.
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4910 Astronomical forcing
DE: 4914 Continental climate records
DE: 8164 Stresses: crust and lithosphere
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005