Abstract
The Tibasosa Formation is the main source of limestones in Boyacá. This unit corresponds to a Valanginian-Albian age according to the fossil content in the Eastern Cordillera Basin, recording the first incursion of the Cretaceous sea in Firavitoba. Outcrop-based facies and stratigraphic analyzes of the ~12 m-thick siliciclastic-carbonate succession of the uppermost Tibasosa Formation indicate tidal and carbonate systems. Ten facies/microfacies are grouped into two facies associations (FAs): FA1, tidal flat deposits consist of laminated sandstones/siltstones and floatstones with a single organism dominance (bivalve shells); and FA2 comprises fossiliferous rudstones, floatstones, packstones, and wackstones, representing a carbonate platform. The petrographic description determined rock textures/genesis and the diagenetic sequence with features of the eodiagenesis, mesodiagenesis, and telodiagenesis suggesting a primary origin of these carbonates. The analysis using cathodoluminescence (CL), energy disperse spectrometry (EDS), and scanning electron microscopy (SEM) allowed identify compositional differences, cementation phases, and morphological features in different processes as micritization, neomorphism, porosity, pyritization, compaction, cementation, fracturing, and weathering. The interpretation of facies and microfacies indicated a deposition mainly in a shallow platform with variation in the hydraulic conditions, warm waters, and episodic events of storms/tsunamis that fragmented the bioclasts. A shallow marine system in the Eastern Cordillera Basin during Cretaceous indicates a large transgressive event that flooded hundreds of kilometers, being a link with the Pacific Ocean before the Andes uplift. The main diagenetic events correspond to micritization, cementation of calcite, and mechanical/chemical compaction as a result of microbial activity, dissolution, precipitation in the vadose/phreatic zone, and burial diagenesis. The diagenetic sequence events reveal the incidence of marine and meteoric process that reduced porosity and attest to the microbial activity in carbonate precipitated. This new interpretation allows the understanding of carbonate platforms in the Eastern Cordillera Basin for future correlations of the Cretaceous sea in Colombia.
Highlights
Two parameters control the limestones features, the nature of the carbonate fabric associated to depositional environments, water chemistry, and biologic action; and the diagenetic processes which affect the sediments according to the type of original material, temperature, depth, fluids, and tectonics; generating changes in texture, porosity, mineralogy, and chemistry (Boggs Jr., 2006; da Silva, 2019)
The massive mudstone (Mm) facies is associated with Sl and Fb facies, it has a pale yellow color with a thickness of 20-25 cm; the composition corresponds to clay minerals, organic matter, and rare quartz grains, exhibiting graded to net contacts
The Lm microfacies has a medium gray color; it comprises of micrite (90-92%), grains of monocrystalline quartz (4%), organic matter (2%), and fragmented/entire bivalve bioclasts (2%); it is associated with Fb microfacies presenting net contacts
Summary
Two parameters control the limestones features, the nature of the carbonate fabric associated to depositional environments, water chemistry, and biologic action; and the diagenetic processes which affect the sediments according to the type of original material, temperature, depth, fluids, and tectonics; generating changes in texture, porosity, mineralogy, and chemistry (Boggs Jr., 2006; da Silva, 2019). Changes in carbonate sediments occur in three diagenetic realms: marine, meteoric and burial with high potential of diagenesis mainly due to the abundance of aragonite-calcite which could supply CaCO3 for cement in tropical calcareous deposits in the meteoric environment (i.e., diagenetic alteration; James and Coquette, 1990; Seibel and James, 2017; Li et al, 2018), as is the case of Mesozoic limestones from Colombia which correspond to the rocks of Upper Tibasosa Formation in the Eastern Cordillera Basin, in the state of Boyacá. Renzoni (1981) defined the basal unit of the Cretaceous in the region of Sogamoso Valley as Tibasosa Formation, which is composed mainly of sandstones, siltstones, marls and many beds of limestones in the Upper Member, with a systematic thinning-northward, towards to the Floresta massif. The geological charts of Sogamoso-Paz de Rio and Duitama define this calcareous member as Upper Tibasosa Formation that will use in this work (Ulloa et al, 1998a; Renzoni and Rosas, 1967)
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