Neogene

Project description 

Title: Neogene Carbonate platform depositional and diagenesis (Geology)

Time: 2015 - 2018

Project leaders:  Juan Carlos Laya and  Fiona Whitaker

Project summary: This project aimed to study the geology of Bonaire and focused on demonstrating how the stratigraphy and depositional styles on Bonaire Island serve to understand the dynamic of sedimentation and environmental changes in the Caribbean region during the Neogene. The initial work produced two research publications with graduate students (Bowling et al., 2018, and Laya et al., 2018). Later, additional research questions were proposed to continue the project further with a focus on the geological evolution of the rocks. Those questions involved a fundamental topic in geology referred to “dolomite problem” as it is known throughout the scientific community. This subject is one of the most exciting problems in carbonate geology. With our robust dataset, we significantly advanced in the understanding of the dolomite problem by challenging different models of dolomite formation and proposing alternative conceptual approaches. Fieldwork was carried out in 2015 and 2016. The outcome of this research is three peer-reviewed publications with graduate students (See below). To achieve the project objectives, we applied innovative technology, including a digital outcrop model (DOM’s), computer flow simulation, and experimental approaches in the laboratory. As further evidence of the impact in this field, the results of this project were presented at conferences and department seminars at several universities. The following is a list of publications associated with this project including Master's and PhD thesis. 

Highlights

• Isolated carbonate platforms respond to allogenic controls by changing depositional styles.

• Allogenic factors are the dominant controls on island-scale depositional events.

• Island terrace morphology has weak impact on depositional events interpretations.

• Internal architecture reflects the dynamics of sedimentation in complex islands.

Abstract

The Neogene carbonate succession on the island of Bonaire (Netherland Antilles) shows complex geometries associated with a sequence of depositional and erosional events which reflects the history of this isolated platform and the interaction between eustasy and tectonics. Three major episodes of carbonate platform deposition are defined which show contrasting depositional styles: 1) aggradational platform (Lower-Middle Miocene) with sediments showing a fining-upward trend from mixed coral rudstone to medium-grained coralgal grain/packstone, partly dolomitized and tilted by tectonic deformation; 2) prograding platform (Upper Miocene-Pliocene) which is formed of several shallowing-upward prograding units mainly composed of reworked red algal grain/packstone, with significant dolomitization, passing upward to shoreline and aeolian deposits formed of coralgal grain/packstone and large benthic foraminifera grainstone, and 3) flat-topped platform (Pleistocene) with a reefal framework composed of a rich variety of corals in a bioclastic pack/wackestone matrix. These platform episodes exhibit contrasting stacking patterns and are separated by erosional unconformities. Overprinting this depositional succession is a series of Quaternary near-horizontal shoreline erosional terraces and vertical cliffs which have been cut into the island stratigraphy and complicate the stratal field relationships. However, this terrace morphology clearly does not represent depositional episodes, as has been suggested before. The internal architecture of each of the three carbonate platform episodes reflects interaction of the dynamics of sedimentation with allogenic controls. The latter relate to major oceanographic and tectonic events in the region, including changing ocean circulation as a result of the closure of the Panama isthmus, and Caribbean plate dynamics that affected sea-floor and island topography. The Bonaire succession provides a model for understanding and predicting isolated carbonate platform development, as well as architecture, facies and potential diagenetic changes, in an active tectonic setting.

Western Atlantic species of the New World genus Pustulatirus Vermeij and Snyder, 2006 are revised. Types of previously named taxa are figured. Species recognized as valid include P. attenuata (Reeve, 1847), range uncertain; P. eppi (Melvill, 1891), Curagao; P. ogum (Petuch, 1979), northeastern Brazil; and P. virginensis (Abbott, 1958), Bahama Islands and eastern Caribbean Sea to Aruba. Latirus karinae Nowell-Usticke, 1969 is confirmed as ajunior subjective synonym of P. virginensis. Syrinx annulata Röding, 1798, treated as a Caribbean Pustulatirus by Vermeij and Snyder (2006), and Latirus annulatus Melvill, 1891 are regarded as species inquirenda. Three new species are described: P biocellatus, northeastern Brazil; P. utilaensis, Bay Islands, Honduras and northwestern Panamá; and P. watermanorum, Honduras continental shelf and offshore Colombian banks. Most western Atlantic Pustulatirus shells exhibit little intraspecific variability in morphology or color and occur within rather precise, well-defined ranges; an exception is P. virginensis, whose shells exhibit much variability in size, morphology and color.