Discussion
On the value of seismic stratigraphy and seismic geomorphology – Comments on “development patterns of an isolated oligo-mesophotic carbonate buildup, early Miocene, Yadana field, offshore Myanmar” by Teillet et al. (2020)

https://doi.org/10.1016/j.marpetgeo.2020.104689Get rights and content

Highlights

  • Teillet et al. (2020) make interpretations that are not fully supported due to incomplete integration of 3D seismic data.

  • Teillet et al. (2020) use lithostratigraphic principles to correlate their main lithofacies.

  • Data from four wells with limited penetration cannot be solely used to justify the lateral continuity of lithofacies.

  • Lateral variability is seen within the Yadana Platform using seismic facies analysis and seismic geomorphology.

  • Teillet al. (2020) have underestimated the value of seismic stratigraphy and seismic geomorphology.

Abstract

The paper by Teillet et al., 2020b constitutes a detailed sedimentological study of the upper part of the Yadana carbonate platform (offshore Myanmar). However, the limited consideration and integration of the 3D seismic data results in a study lacking critical context, with the authors concluding that the Yadana Platform developed under strict oligo-mesophotic conditions and presents a layer-cake architecture with laterally continuous lithofacies. We suggest that the interpretations of Teillet et al., 2020b are not adequately supported because: (1) lithostratigraphic principles are applied to correlate the main lithofacies from four wells using core data across a wide platform (10–20 km); (2) the core data presented are restricted spatially as well as in depth, and are not laterally and vertically representative of the entire platform, hence these core data cannot be solely used to justify the lateral continuity of lithofacies and absence of euphotic depositional environments in the Yadana Platform; (3) the study is not integrated within a comprehensive chronostratigraphic framework and sedimentological observations are not connected in a systematic way; and (4) information extracted from the analysis of seismic facies and seismic geomorphology are ignored, even though lateral variability is observable on seismic within the platform (i.e., variability in depositional features and geometries). Seismic stratigraphy and seismic geomorphology should be considered because they allow the integration of any paleogeographic study into a comprehensive chronostratigraphic framework where 3D seismic data are available. These comments aim at stimulating a discussion on the value of seismic stratigraphy and seismic geomorphology, which should not be dismissed, to better document the evolution of carbonate platforms through time and space, and accurately assess controls on platform architecture and evolution.

Introduction

The paper by Teillet et al., 2020b proposes a detailed sedimentological analysis of the upper part (i.e., last ~160 m) of the Yadana carbonate platform (Andaman Sea, offshore Myanmar) using four cores from four different wells penetrating this interval. This Teillet et al., 2020b manuscript is a welcome addition to the literature by providing new insights into the sedimentology of the last stages of development of the Yadana Platform.

The Yadana Platform developed from the late Oligocene to early Miocene in three main stages: (1) initiation and development of two platforms separated by an interplatform seaway during the late Oligocene (i.e., the isolated Yadana North Platform and the attached Yadana South Platform); (2) subaerial exposure of both platforms during the Oligocene-Miocene transition leading to extensive karstification, followed by the deposition of a thick clastic package in the interplatform seaway (i.e., Sein Clastics Formation); and (3) re-initiation of a single extensive platform (i.e., Yadana Platform) during the early Miocene, which evolves from an attached to an isolated carbonate platform through km-scale backstepping events (Paumard et al., 2017). Within the Yadana Platform, the uppermost part of the early Miocene strata corresponds to a reservoir interval that hosts the Yadana Gas Field with ~7 Tcf of gas (Paumard et al., 2017).

The main results and interpretations of Teillet et al., 2020b can be summarized in three main points as follows: (1) the isolated Yadana Platform is an incipiently drowned carbonate depositional system developed under oligo-mesophotic conditions during the entire early Miocene interval; (2) carbonate production was controlled by three fundamental parameters (i.e., nutrient availability, water energy and turbidity) across three distinct types of carbonate factories that existed during the platform development; and (3) the Yadana Platform has a flat-topped geometry and a layer-cake stratal development showing little lateral variability in lithofacies throughout the early Miocene interval.

We consider the assertion by Teillet et al., 2020b that the Yadana Platform has a layer-cake architecture characterized by minimal variation in lithofacies to be a significant pitfall in their study for the following reasons, where Teillet et al., 2020b: (1) draw these conclusions based on evidence gleaned from four cores that are restricted both in depth (i.e., uppermost ~160 m) and spatially (i.e., western part of the platform), for a platform that at this time extends across more than 20 km; (2) use a lithostratigraphic approach to correlate the principal lithofacies, despite limitations in correlation due to sparse well control, and despite presenting data that does not support continuity of facies across the entire platform; and (3) ignore key insights available from 3D seismic data (i.e., seismic stratigraphy and seismic geomorphology).

Although the results and descriptions provided are very detailed and well documented, the limited consideration and integration of the 3D seismic data eventuates in a study lacking critical context. The intent of the present manuscript is to highlight how essential it is to integrate any stratal-based paleogeographic study into a chronostratigraphic framework using available 3D seismic data. We hope that this comment will stimulate discussion on the value of the information extractable from seismic data, the value of which cannot and should not be dismissed, and the necessity of an integrated approach to better understand carbonate depositional systems.

Section snippets

Lithostratigraphy vs. seismic stratigraphy

The correlation of well data presented by Teillet et al., 2020b; their Figure 12) is based on lithostratigraphic principles with similar lithofacies correlated between different wells and inferred to represent continuous layers. This drives the interpretation of a layer-cake and laterally continuous architecture of the platform. Fig. 1 is a modified composite of two figures published by Teillet et al., 2020b illustrating a seismic line running NW-SE directly through Wells 3 and 4 (Fig. 1a;

Value of seismic facies analysis and seismic geomorphology

Teillet et al., 2020b indicate that there is “no change in seismic facies or reflector morphology” and “lack of significant lateral changes in amplitude” within the platform. Yet, even on the seismic lines presented by the authors (e.g., Fig. 1a), variability of seismic reflection continuity and amplitude is observed. Within the upper part of the Yadana Platform, a variety of seismic reflection styles can be observed: e.g., parallel, high-amplitude reflectors; semi-chaotic, low-amplitude

Importance of context

The data used in the study of Teillet et al., 2020b are restricted in depth to the uppermost part of the platform (~160 m) and in space with the wells being located in the westernmost part of the platform. However, because the well-based results and interpretations of Teillet et al. (2020b) are not integrated through seismic stratigraphic and seismic geomorphological approaches (i.e., a sensible context), it becomes challenging to evaluate how representative their interpretations are of the

Conclusion

We are appreciative of the work done by Teillet et al., 2020b and would like to acknowledge the necessary effort provided by the authors in publishing detailed descriptions and interpretations of the cores from the Yadana Platform. The purpose of this comment is to: (1) foster discussion on the value of integrating 2D and 3D seismic data in carbonate depositional environments; and (2) emphasize a few pitfalls in the study of Teillet et al., 2020b that directly result from the lack of

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We thank the Centre for Energy of Geoscience and the School of Earth Sciences (The University of Western Australia) for their support. Victorien Paumard worked on the carbonate platforms from the Yadana area during his MSc research in Total E&P. Simon Lang and Henry W. Posamentier studied the Yadana Platform while working in Chevron Pty. Ltd. We thank two anonymous journal reviewers for their feedback on this manuscript and Massimo Zecchin for handling the publication of this paper.

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