Print this pagePaleodischarge and Sediment Budget Analysis of the Late Cretaceous Torrivio Sandstone, San Juan Basin, New Mexico, U.S.A.
Abstract
We present the first estimate of paleodischarge and sediment budget analysis of the Late Cretaceous, fluvial Torrivio Sandstone in the San Juan Basin, New Mexico, which is interpreted to feed the Upper Turonian Gallup delta. This outcrop-based study documents the size and scale of trunk channels within the Torrivio, which helps to establish the size and scale of the drainage basin and the source-to-sink mass balance of a linked stratigraphic system. A trunk river is represented by thickest preserved channel storey contained within an incised valley. The search for the trunk river was spread over a linear outcrop length of about 70 km with 42 measured sections. A high resolution photomosaic and 3 measured sections helped in mapping the dimensions of the trunk river and included estimations of bankfull channel depth, width and grain size. These have been used in the calculation of depositional slope, flow velocity, and water and sediment discharge. The estimated average bankfull channel depth is approximately 10 m, the bankfull channel width ranges from 75 m to 120 m, the paleo-depositional slope is of the order of 10-4, and the mean flow velocity is approximately 1.3 m/s. The bankfull channel dimensions, estimated using established empirical relationships between bedform height and channel depth, and channel depth and width, result in underestimation of channel depth (4.5 m to 7.5 m) and overestimation of channel width (130 m to 330 m). The bankfull water discharge ranges from about 1000 m3/s to 1800 m3/s, with a mean value of about 1500 m3/s. The drainage area in this study, estimated using power law relationship between discharge and drainage area, ranges from about 34,000 km2 to 70,000 km2. The drainage area estimated from previously published paleotectonic reconstruction is about 65,000 km2, which falls within the range of above values. Mean annual sediment discharge for corresponding bankfull channel dimensions ranges from 1.7 x 106 m3 to 2.8 x 106 m3 with mean at 2.3 x 106 m3.
High frequency Milankovitch-scale parasequences have been documented in the Gallup Sandstone. The mean annual sediment discharge, when projected over this high frequency time-period, provides possible limits to the total sediment that could have been transported to the depositional sink through the Torrivio trunk channel, thus facilitating a mass balance study using the published paleogeographic reconstructions of the Gallup deltaic sink.
AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018