Abstract

This is the first of two articles which describe the sedimentation, facies, and interpreted geologic history of the late Precambrian Hazel Formation of West Texas. This paper summarizes the late Precambrian Hazel Formation of West Texas as an alluvial fan system; the second provides a facies and depositional model; and reinterpretation of the stratigraphic relationship between the Hazel and Allamoore Formations.

The Hazel Formation is a Precambrian arid-region alluvial- fan system. Sediment was shed northward from the highlands that consisted of granitic rocks on the south, fronted by deformed interbedded volcanic and carbonate rocks on the north. Subsequent intense folding of the southern parts of the Hazel Formation produced a structurally complex terrain.

The Hazel Formation consists of three principal facies that are: (1) proximal, chiefly limestone clast conglomerate; (2) mid-fan, alternating limestone clast conglomerate and arkosic sandstone; and (3) distal, dominantly very finegrained arkosic sandstone. The proximal facies consists of thick, massive, poorly sorted boulder and cobble conglomerate and thin horizontally bedded granule-bearing sandstone. Toward the north and vertically it grades abruptly into alternating conglomerate and sandstone of the mid-fan. Locally, basal proximal conglomerate and immediately adjacent mid-fan sandstone are interbedded with carbonate rocks like those of the Allamoore Formation. The distal facies is composed chiefly of very fine- grained sandstone; fine-to medium-grained sandstone occurs in braided channels. Thin layers of conglomerate within the braided channel complex record flood surges in the distal-fan sequences. Carbonates, including both conglomerates and interbedded laminated algal stromatolites, occur in some distal-fan environments.

Facies relationships, textural trends, succession of sedimentary structures, and dip directions of crossbeds indicate a northerly sediment-transport direction. The fan system is interpreted to have accumulated along a basin margin adjacent to a southern highland.