EAGE/DGS Jurassic Field Trip 2019
Advances in Jurassic Stratigraphy: New Sequence Stratigraphic Scheme for the Shaqra Group, Jabal Tuwaiq, Central Saudi Arabia
Field Trip Overview
The Jurassic outcrop (Shaqra Group, Toarcian to Kimmeridgian) is the westernmost and landward stratigraphic record of the Jurassic stratigraphy (Marrat, Dhruma, Tuwaiq, Hanifa, Jubaila and Arab-D). These outcrops are well exposed and easily accessible along the Tuwaiq Escarpments forming spectacular west-facing continuous cuestas extending 1000 km North to South near Riyadh. To date, few studies have addressed the Jurassic outcrops of Central Arabia (e.g., Bramkamp and Steineke, in Arkell, 1952; Powers et al., 1966; Powers, 1968; Manivit et al,1990). These last comprehensive studies involved lithostratigraphic and biostratigraphic approaches. However, genetically related depositional sequences, cycle hierarchy, stacking patterns, depositional environment evolution, and effects of syndepositional tectonic events were not documented in detail.
This field trip presents one of the first attempts to apply modern sequence stratigraphic techniques to outcrops to improve our understanding of the Jurassic system regionally and globally. Moreover, the field trip reveals for the first time depositional models that subdivide the Shaqra Group into genetically related sequences that are not always obvious from core, wireline logs or seismic data. These observations provide better significant understanding of the Jurassic history and tectonostratigraphic events of the Arabian Platform.
The field trip demonstrates an integration of the previous biostratigraphic data with detailed new sedimentological measured sections and subsurface gamma-ray logs, offering robust depositional models and high-resolution sequence stratigraphic frameworks. This integration provides a comprehensive reference for the most economically important formations in the Arabian Platform. This rock-based and direct assessment provides guidelines for reservoir modeling, hydrocarbon exploration, prediction of reservoir distribution and improve seismic interpretation. The continuous record of the Jurassic can contribute to a broad understanding of controlling factors and reconstruction of the paleogeography of the Arabian Platform as well as the Neo-Tethys Ocean.
Field trip objectives
a) Provide a high-resolution sequence stratigraphic column of the entire, 1 km thick Jurassic sequence based on sequential hierarchical organization, cyclic sedimentological
patterns and geometries.
b) Characterization and hierarchy of the sequence boundaries, unconformities and timelines at different scales.
c) Understand the controls on vertical facies evolution, properly interpret depositional environments and build realistic depositional model.
d) Give new ideas on the spatial and temporal reservoir/seal rock distribution in a shallowmarine mixed carbonate-siliciclastic platform.
e) Discuss subsidence, tectonics, climate and eustasy as controls on platform development and facies vertical evolution.
The useful concepts and lessons to be learned from the field trips are:
a) Reassessment of the depositional and environmental indication of sedimentary facies and biofacies.
b) Interpretation of transgressive and regressive cycles from core and gamma ray logs.
c) Assess direction of facies migration through time (critical for exploration).
d) Understanding of carbonate platform evolution from tabular to differentiated platform
(layer-cake to clinoform) in response to accommodation and carbonate production.
e) Identification of main stratigraphic marker events (e.g., tectonic tilt, climatic change, carbonate demise, eutrophication, siliciclastic influx) that guide regional correlation.
Participants should have a basic knowledge of sedimentology and sequence stratigraphy.
The field trip is designed for a wide audience of geologists, geophysicists and paleontologists
from beginners to experienced specialists.