CONGLOMERATIC TRIASSIC JURASSIC ROCKS IN BOYACá COLOMBIA: FAR FROM RHETORIC, CLOSER TO REALITY

Continuing recent researches to corroborate the hypothesis about compare the Newark Supergroup in the US to the Colombian rock of the Mesozoic rocks along ancient continental margins. This paper is about the South America area during this geological Era. It is necessary to explore surrounding areas of some cities of Boyacásuch as Duitama, Nobsa, and Tibasosa. There are several outcrops of the Girón Formation (Triassic-Jurassic) in its different levels exposed by stronger tectonic activity during Late Cretaceous and/or Early Tertiary by efforts from the West to the East when the Central Cordillera rose.

Around Nobsa city, the basal part of the Girón Formation outcrops. It composed by compact conglomerate in a reddish matrix, which is discordant over Paleozoic rocks. It shows graded stratification, sometimes laminated sandstones deposited. Above a series of fine sandstones interbedded with yellowish claystone. This faulted member has tiny displacement. The basal part of Girón Formation composed by conglomeratic strata and red-violet siltstone rocks intercalated with volcanic ash with some pillow flow as sign of dry and lacustrine environments.

In addition, through a previous exploration of groundwater for the Nobsa`s Mayor Office, the author described the area around indicating presence of some different geological events such as tectonics and erosion affecting Cuche Formation (Paleozoic.) Next, unconformity of Giron and Jordan Formations deposition (Triassic up to the Later Jurassic.) These rocks suffered a new tectonic activity possibly similar to the Laramide Orogeny in the US. After this diastrophism an erosive processes came; it produced material to the basal Tertiary rocks.