Abstract:
The stratigraphy of the Ecca Group has been
subdivided into the Prince Albert, Whitehill, Collingham,
Ripon, and Fort Brown Formations in the Eastern Cape
Province, South Africa. In this article, we present
detailed stratigraphic and facies analyses of borehole
data and road-cut exposures of the Ecca Group along
regional roads R67 (Ecca Pass), R344 (GrahamstownAdelaide), R350 (Kirkwood-Somerset East), and national roads
N2 (Grahamstown-Peddie) and N10 (Paterson-Cookhouse).
Facies analysis of the Ecca Group in the study area was
performed to deduce their depositional environments.
Based on the lithological and facies characteristics, the
stratigraphy of the Prince Albert, Whitehill, Collingham,
and Fort Brown Formations is now subdivided into two
informal members each, while the Ripon Formation is
subdivided into three members. A total of twelve lithofacies were identified in the Ecca Group and were further
grouped into seven distinct facies associations (FAs),
namely: Laminated to thin-bedded black-greyish shale
and mudstones (FA 1); Laminated black-greyish shale
and interbedded chert (FA 2); Mudstone rhythmite and
thin beds of tuff alternation (FA 3); Thin to thick-bedded
sandstone and mudstone intercalation (FA 4); Medium to
thick-bedded dark-grey shale (FA 5); Alternated thin to
medium-bedded sandstone and mudstone (FA 6); and
Varved mudstone rhythmite and sandstone intercalation
(FA 7). The FAs revealed gradually change of sea-level
from deep marine (FA 1, FA 2, FA 3 and FA 4, FA 5, and
FA 6) to prodelta environment (FA 7). This implies that
the main Karoo Basin was gradually filling up with Ecca
sediments, resulting in the gradual shallowing up of the
water depth of the depositional basin.
