Academic journal article Journal of Geoscience Education

# Using Numerical Models to Teach Sequence Stratigraphic Principles and the Nature of the Stratigraphic Record

Academic journal article Journal of Geoscience Education

# Using Numerical Models to Teach Sequence Stratigraphic Principles and the Nature of the Stratigraphic Record

## Article excerpt

ABSTRACT

Sequence stratigraphy has become a central topic for sedimentology and stratigraphy. While outcrop studies are an important part of introducing sequence stratigraphic concepts to students, computer models go beyond the mostly descriptive approach in that they can be used to evaluate the importance of different factors leading to stratigraphic change (e.g., changes in sea level, sedimentation rates, etc). Students can use a combination of a stratigraphic simulation package (STRATA) and an evolutionary random branching model (BIOSTRAT) to simulate stratigraphic sequences and their bounding unconformities across a basin and the stratigraphic distribution of species within these sequences. Students can explore processes responsible for forming stratigraphic sequences, assess me relative importance of global sea-level fluctuations in unconformity generation, and investigate the underlying causes for the stratigraphic distribution of different species. Furthermore, students can use the simulated data set to perform graphic correlation in order to study how stratigraphic correlation is impacted by correlations across facies changes and important sequence stratigraphic surfaces (i.e., flooding surfaces, unconformities, etc).

INTRODUCTION

Numerical models have been developed for simulating depositional sequences and the distribution of fossil within these deposits. The correct correlation is already known with models, and thus they can be used to illustrate the influence of different environmental factors (e.g., sea level changes, sedimentation rates, etc) on the spatial and temporal distribution of organisms in stratigraphie sequences. Holland (1995) developed a model for simulating the distribution of fossils that is based on the facies control of marine organisms (BIOSTRAT). In this model, every species is assigned a preferred water depth, a depth tolerance, and a peak abundance that leads to a Gaussian-type probability of collection. BIOSTRAT, coupled to tne stratigraphic modeling package STRATA (Flemings and Grotzinger, 1996; Scnlager, 2005 (his appendix B)), has been used to investigate the effects of sequence-stratigraphic architecture on the stratigraphic distribution of fossils (e.g., Holland and Patzkowsky, 1998; 1999; 2002) and to evaluate the widely used graphic correlation technique (Herrmann et al., 1999).

BIOSTRAT output is text-only and hard to interpret. Herrmann et al. (2003) described a computer program (BioModule) that combines BIOSTRAT and STRATA output files and facilitates the interpretation of model simulation results. It is the purpose of this paper to describe how this modeling approach can be used as an effective tool to teach sequence stratigraphic principles and potential biases in the stratigraphie record (e.g., along unconformities and flooding surfaces). In addition, using a numerical model exposes students to quantitative methods in the geosciences.

SEQUENCE STRATIGRAPHY

Sequence stratigraphy (Payton, 1977; Wilgus et al., 1988) is now a central topic in many stratigraphy and sedimentology classes and several textbooks are dedicated to mis topic (e.g., Coe et al., 2003; Emery and Myers, 1996). The stratigraphic modeling package STRATA (Flemings and Grotzinger, 1996) was specifically designed to model the stratigraphy of a basin in response to user-defined sea level curves, subsidence rates, sedimentation characteristics (e.g., siliciclastic and carbonate deposition rates), and tectonic setting (e.g., foreland basin, passive margin).

In sequence stratigraphy, depositional sequences are defined as relatively conformable successions of genetically related strata bounded by unconformities or their correlative conformities (Van Wagoner et al., 1988). Students can investigate the timing and spatial distributions of these surfaces and understand them in the context of depositional and erosional processes related to sea level changes. This is done by using defined sea-level curves, subsidence rates, and sedimentation rates to explore the impact on accommodation space across the basin through time. …

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