MULTI-PROXY AGE CONSTRAINS OF LOWER CRETACEOUS MARINE EXTENSION AND OCEANIC ANOXIA IN NORTHERN COLOMBIA: PALEOGEOGRAPHIC IMPLICATIONS

Recent paleomagnetic data suggest that the northern Andes are built by contrasting middle Mesozoic para-authoctonous terranes apparently linked to pacific subduction and widespread lower to middle Jurassic magmatism¹. Those terranes (Eastern Cordillera-ECC, Central Cordillera-CC, Perijá Range-PR and Sierra Nevada de Santa Marta-SNSM) seem to share a common geological evolution since the Late Jurassic-Lower Cretaceous when the opening of the proto Caribbean began renew the segmentation of the margin. However precise constraints on the ages of yuxtaposition of the Jurassic Terranes have are still scarce.

Here we report C-isotope chemostratigraphic data and detrital zircon U-Pb ages of organic rich mixed siliciclastic-carbonate rocks cropping out along the ECC and between the PR and SNSM to better constrain the northern Andes paleogeography during the Early Cretaceous

The Cogollo Group is a mixed carbonate-siliciclastic succession, which concordantly overlay Jurassic basaltic volcanics from the Guatapuri Formation at the SNSM. This Group displays a pronounced positive C-isotope excursion, up to 7‰, suggesting a lower Aptian (ca 123 Ma) depositional age. This C-isotope positive anomaly is also displayed by La Paja Formation, which overlies lower Cretaceous marine strata of the Rosablanca Formation- RF at the western flank of the ECC. The RF overlies continental sediments from the Arcabuco Formation, which in turn overlies Jurassic volcanic continental sediments from the Giron Group. The RF is correlative to deep marine, organic rich Lutitas de Macanal Formation-LMF at the axial zone of the ECC. This unit displays U-Pb detrital zircon ages of 134 Ma, which are in agreement with planktonic foraminifera ages, suggest a volcanic origin for 134 Ma detrital zircons of the LMF.

From the reported age data we suggest the existence of contemporaneous intraplate volcanism and extension affecting the northern Andes during Early Cretaceous. This common extensional setting ultimately restricts age of juxtaposition of parautoctonous lower-middle Jurassic Terranes in the Northern Andes and the opening of the Proto Caribbean seaway to the Aptian.

1. Bayona et al. Jour. South Ame. Earth Sci. 29 (2010)