Pickerill, R.K.; Donovan, S.K.; Dunn, J.T.
Author Affiliation, Ana.
Geography and Geology; Faculty of Pure and Applied Sciences
Enigmatic cobbles and boulders in the Paleogene Richmond Formation of eastern Jamaica
Caribbean Journal of Science
Date of Publication
The Roadside Member (early Eocene) of the Richmond Formation between Pagee Point and Forges Point, east of Port Maria, northeast coastal Jamaica, exposes several horizons containing outsize cobbles and boulders or, alternatively, isolated boulders within an otherwise thinly bedded deep water, turbiditic sequence. These are found: (i) as randomly dispersed and oriented clasts in massively bedded, laterally continuous or channelized, muddy siltstone or fine-grained sandstone horizons; (ii) in the uppermost horizons and projecting through laterally continuous muddy siltstone or fine-grained sandstone layers; and (iii) as isolated boulders that penetrate the thinly bedded turbidites. The conclusion is that cobbles and boulders of categories (i) and (ii) were emplaced in association with high strength debris flows, whereas boulders of category (iii) probably represent isolated outrunner slide blocks introduced seaward of contemporaneous mass flow deposits or, alternatively, represent vestiges of dilute debris flows. Lithologically the cobbles and boulders are comprised of a varied suite of sedimentary, intrusive igneous and extrusive igneous rocks, though they are numerically dominated by andesites and rhyolites. Collectively these lithologies suggest derivation mainly, or even wholly, from the Clarendon Block located to the southwest, rather than the Blue Mountain Block to the east.....