Coarse-grained submarine-fan deposits of magmatic arc affinity in the late Precambrian Aaron Formation, North Carolina, U.S.A.

Abstract

Coarse-grained submarine-fan deposits in the late Precambrian Aaron Formation in the Carolina slate belt are derived from a volcanic arc as indicated in the detrital grain population. Lithic volcanic clasts (L v) are the major component, followed by plagioclase (P) and subordinate monocrystalline quartz (Q m). Recrystallisation at lower greenschist facies has not been sufficient to destroy relict grains or mesoscopic sedimentary structures in these units. Seven sedimentary facies are recognizable in the Aaron Formation: (1) massive framework-supported conglomerate (2) massive to stratified pebbly arenite (3) trough crossbedded arenite (4) horizontally stratified arenite (5) siltstone (6) argillite and (7) vitric tuff. These facies are found in 4 facies associations A through D which are stacked in a sequence displaying an upward-fining and thinning of coarse beds. The overall upward-fining of the sequence is analogous to a coarse-grained retrogradational submarine-fan model. Associations A and B are equivalent to braided inner fan(?) to mid-fan channels, whereas association C may represent mid-fan or suprafan depositional lobes. Association D records the transition to basin plain sediments in which outer-fan cycles are absent. The sedimentary sequence of the Aaron Formation is analogous to a “poorly efficient” submarine fan system in which rapid erosion in the source terrane provides abundant coarse-grained material to the depositional basin. The Aaron Formation may be related to other late Precambrian volcanic-sedimentary sequences, especially those of the Pan-African orogens. The distinct similarity of constituents in the Aaron to those of younger magmatic arc terranes suggests that active plate margin sedimentation and volcanism was prevalent at this locality in the late Precambrian.