SEDIMENTOLOGICAL AND PROVENANCE ANALYSIS OF THE JURASSIC LA QUINTA FORMATION IN THE WESTERN FLANK OF THE PERIJA RANGE
The most southern area (Codazzi), the uppermost 100 m of La Quinta Formation comprise calcareous mudstone and mixed lithologies with cross beds. Farther to the north (Manaure) this unit is ca 300 m thick and consists of red conglomerates and sandstones in fining-upward successions and thin interbeds of rhyolitic tuffs. The other two sections are in the northern plunge of the Perija Range, where this unit is > 2.5 km thick. A cored well drilled 144 m of the uppermost La Quinta Formation that includes breccias, red volcaniclastic sandstones, siltstones, mudstones, and toward the top conglomerates. In the northernmost segment this unit may be divided into a lower interval that comprises cross-bedded red sandstones and mudstone, a middle interval that is more conglomeratic and include levels of breccia, and an upper interval that is dominantly red fine-grained volcaniclastic succession. The lithofacies association of La Quinta Formation described above indicates more continental lacustrine deposition to the south, while to the north dominate fluvial and gravity flow deposition; volcanic rocks are almost absent on this side of the range.
U/Pb age populations of 3 samples in the northern PR indicate that the base of the unit includes Proterozoic (2150, 1890, 1444, 1018, 741, 600 Ma), Paleozoic (450 Ma) and Triassic-Jurassic (240, 174 Ma) populations, whereas for the top most of the population is middle Jurassic (160-180 Ma). For the southern segment, a sample collected to the top of the unit yielded two populations: 160-170 and 250-350 Ma.