Chapter 6 Cretaceous carbonate biostratigraphy and environments in Honduras

Abstract

Abstract A carbonate platform developed on the Chortis block beginning in the Berriasian-Aptian and ending in the Albian. This platform is represented in Honduras by carbonate strata of the Yojoa Group, mainly the Atima Formation. We report new stratigraphic and paleontological data from exposures of this carbonate package and superjacent Upper Cretaceous strata in easternmost Honduras. In addition, new paleontological data from west-central Honduras are presented confirming previous interpretations there. In west-central Honduras, carbonate deposition of the Atima Formation was interrupted in the Aptian by an influx of non-marine, terrigenous sediments of the ‘Mochito shale’, and terminated at the beginning of the Cenomanian by coarse redbed strata of the lower Valle de Angeles Group. The exact nature of the Atima/Valle de Angeles contact in west-central Honduras is not known, but may be gradational. In the Montanas de Colon area in eastern Honduras, no equivalent of the 'Mochito shale' has yet been identified, and late Albian deposition of the Atima was ended by an influx of fine-grained, shallow marine, terrigenous sediments of the Cenomanian ‘Krausirpi beds’. Although the Krausirpi beds are only known locally, we include them in the Yojoa Group as an informal member. After deposition of the Krausirpi beds, local subaerial exposure and erosion occurred prior to deposition of the redbeds of the lower Valle de Angeles Group. In west-central Honduras, carbonate platform deposition was resumed during the Cenomanian represented by the Jaitique Formation and by the slightly younger and lithologically distinct Esquias Formation just east of the outcrop area of the Jaitique. These limestone units conveniently divide the Valle de Angeles Group into lower and upper redbed sections. No equivalent limestone unit has been found in the Montanas de Colon area. Instead, deposition of continental redbeds began here in the Cenomanian and continued into latest Cretaceous, as indicated by radiometrically dated volcanic flow units within the redbeds. The Jaitique Formation consists of a lower thick-bedded limestone member overlain by a thin shaly limestone member in the area south and west of Lake Yojoa. In central Honduras the Esquias Formation consists of interbedded limestone, marl and shale. The remainder of Cretaceous deposition was fluvial clastic sediments and volcanic rocks which belong to the upper Valle de Angeles Group. New paleontologic data from limestone of the Atima Formation, shale of the Krausirpi beds, limestone conglomerate in the Valle de Angeles Group, and from the Jaitique Formation confirm the ages and depositional environments. The Atima ranges from Barremian-Aptian to late Albian based on ten foraminiferal taxa, one caprinid rudist and three calcareous algae. The Krausirpi beds are Albian-Cenomanian based on nine palynomorph taxa and two planktic foraminifers. The Jaitique is middle to late Cenomanian with the benthic foraminifer Biconcava, which is reported for the first time in the Caribbean Province. A Cenomanian dasyclad, Dissocladella undulata, was recovered in a limestone clast in the Valle de Angles Group suggesting the possibility that Cenomanian as well as older limestone units were eroded during the Late Cretaceous. The Atima records at least two shoaling upward depositional cycles, and the Jaitique was deposited in an open shelf environment that became restricted near the end of deposition.