CHARACTERIZING THE PHANEROZOIC STRATIGRAPHIC ARCHITECTURE OF SOUTH AMERICA USING SLOSS-TYPE SEQUENCES

Sequences are defined as discrete packages of sedimentary rock bounded by interregional erosional surfaces. They are the ideal stratal units for regional stratigraphic study, but few continent-wide studies have been published. We present a new continental-scale study of the six, Sloss-type sequences across South America and southern Central America, with emphasis on stratigraphic architecture.

Details of the sediments across South America, including offshore shelf regions, were compiled using available publications, seismic data, and well records. RockWorks 17 software was used to track sequence boundaries, lithologic data, and locations. A three-dimensional lithology model, isopach maps, and basal sequence lithology maps were created for each of the six sequences.

Results show that siliciclastics dominated deposition in the earliest three sequences (Sauk, Tippecanoe, and Kaskaskia). However, their areal extent was primarily limited to selected basins in western and central South America. The volume of siliciclastics deposited within the Sauk, Tippecanoe, and Kaskaskia sequences showed a steady increase from 1.02 to 1.75 to 3.07 million km³, respectively. The latter three sequences (Absaroka, Zuni, and Tejas) show a more diverse mix of carbonates and siliciclastics and a progressive increase in both areal extent and sediment volume, with a peak total of over 32.9 million km³ of sediment deposited in the Tejas sequence. Siliciclastic deposition within the Absaroka sequence totaled 4.19 million km³, increased in the Zuni to 18.8 million km³, and rose to 28.0 million km³ in the Tejas. The Tejas sequence alone contains 44.1% of all sandstone and 52.1% of all shale deposited across South America.

Carbonate deposition reflected a similar pattern in the latter sequences with 1.17 million km³ deposited in the Absaroka, 1.89 million km³ in the Zuni, and 3.98 million km³ in the Tejas. The relative amount of carbonate deposition increased sharply in the Absaroka (16.3% of the total carbonate deposition), continued through the Zuni (26.3% of the total), and peaked in the Tejas (55.4% of the total). In fact, the latter three sequences contain 98.0% of all carbonate rock deposited across South America. Isopach maps show much of the Zuni and Tejas sequences were deposited adjacent to the Andes Mountains and offshore.