Paper No. 4
Presentation Time: 8:00 AM-5:30 PM
CHANGING DEPOSITIONAL ENVIRONMENT CONDITIONS RECORDED IN THE MID-PERMIAN SANTA ROSA GROUP, SOUTHERN RASPACULO CATCHMENT, BELIZE, C.A
The Santa Rosa Group in Belize is dominated by immature to sub-mature sandstones and organic-rich black shales. These facies are interbedded with minor conglomerate and limestone units suggesting episodes of more tectonic activity in the region, that punctuate relatively constant clastic sedimentation. In the southern Raspaculo catchment, sediments exhibit a transition from large-scale channel sands to inter-channel muddy banks with alternating fine-grained sandstones and shales which are characterized by numerous paleocurrent indicators in a northeast to southwest current direction, in the context of the present orientation of the Maya block. The channel sands and banks were deposited on a thick sequence of fine-grained, organic-rich shales and siltstones which dominate the stratigraphy further south in adjacent drainages. Stratigraphy in this area illustrates the complexity of the sedimentation and illuminates the difficulty in correlating from one region to another within the Maya Mountains let alone the western extent of the Santa Rosa in Guatemala and southern Mexico.
The Santa Rosa group exhibits localized, minor alteration from post depositional hydrothermal fluids elevating Cu, Zn and Pb concentrations to as much as four times background levels of 10, 42 and 11 g/kg respectively. Preliminary 206/204 Pb to 207/204Pb isotopes indicate the lead associated with the hydrothermal alteration in the Maya Mountains is related to the lead associated with MVT mineralization in Guatemala. Sedimentation patterns and weakly mineralized zones of hydrothermal origin both suggest episodic, wide-spread tectonic activity that existed during deposition of the Santa Rosa group and continued post deposition. Multiple reactivation along the major strike-slip faults, including the Northern and Southern Boundary faults, produced changing localized base levels and the complex stratigraphy in the southern Raspaculo catchment.