Search Results

You are looking at 1 - 2 of 2 items for :

  • Author or Editor: David M Schultz x
  • Earth Interactions x
  • All content x
Clear All Modify Search
David M. Schultz, Timothy M. DelSole, Robert M. Rauber, and Walter A. Robinson
Full access
Marcello Gugliotta, Jonathan G. Fairman Jr., David M. Schultz, and Stephen S. Flint

Abstract

The Lajas Formation in the Neuquén Basin, Argentina, consists of a succession of mainly deltaic deposits. In the Middle Jurassic (170 million years ago), the basin was in western Gondwana roughly at the same paleolatitude as its present location (32°–40°S). Decimeter-scale, interbedded, coarser-grained and finer-grained beds in channelized and nonchannelized deltaic deposits have been interpreted as a product of variability in river discharge. The coarser-grained sandstone beds have erosional bases and contain mudstone clasts; internal cross bedding is commonly directed paleoseawards. These beds are interpreted as deposition during river-flood conditions. In contrast, the finer-grained beds are composed of interlaminated sandstone and mudstone, deposited during interflood periods. Bidirectional ripples and millimeter-scale sand–mud laminae suggest the influence of tides. This sedimentological evidence raises the question of whether these cycles represent annual variability in fluvial input. To answer this question, a simulation using the Fast Ocean Atmosphere Model for the Middle Jurassic was run to equilibrium. The model shows that the paleoclimate of the Neuquén Basin was characterized by a strong seasonal cycle, with a wet winter and a dry summer. Model runs suggest that February mean temperatures were 28°C with 4-mm precipitation (±4 mm standard deviation) per month, whereas August mean temperatures were 8°C with 34-mm precipitation (±17 mm standard deviation) per month. The strong seasonal cycles in the simulation, representing 24% of the variance in the precipitation time series, suggest that the sedimentological cycles represent annual variations. The simulation also suggests a Middle Jurassic climate where increased seasonality of precipitation occurred farther poleward than previously thought.

Full access