The interplay between deformation, erosion and sedimentation in the deep‐water Mexican Ridges foldbelt, western Gulf of Mexico basin

Abstract

We analyse a regional 2D seismic section of the Mexican Ridges foldbelt (MRFB), western Gulf of Mexico, and construct excess-area diagrams for each of the structures comprising the foldbelt to estimate shortening, the onset of folding and the degradation of the folded seafloor. From the chronostratigraphy, we derive rates of tectonic and superficial mass transport and illustrate how they change across the MRFB. The resulting tectonic transport in the MRFB is 11.8 km forming a train of twelve buckle folds above a detachment at a depth of ca. 6 s of two-way travel time, with an average strain of ca. 10%. The fold train grew at a mean uplift rate of ca. 0.21 mm year À1 . Cross-sectional balancing demonstrates that shortening balances the downslip motion of the Quetzalcoatl extensional system (QES), suggesting that horizontal compaction, volume loss and other penetrative deformation mechanisms are negligible. By assuming steadystate denudation, we are able to distinguish sediments derived locally from sediments transported from distant sources. The constant of mass diffusivity, a parameter controlling the degradation rate, is ca. 0.42 m 2 year À1 , which is characteristic of rapid, episodic, superficial mass movements. The combined sedimentation rate from both, local and distal sources is ca. 0.23 mm year À1 . Those values are not constant; structures proximal to the continental shelf are rising rapidly and are being degraded more intensely than those in the distal part of the MRFB, where sedimentation outweighs tectonic uplift. Our results indicate deformation initiated up to 3 Myr earlier than estimated from stacking patterns. Moreover, we find deformation started synchronously during the Late Miocene throughout the MRFB and not in two episodes as the stacking relations suggest. The discrepancy can be explained by a delay in the sedimentary response to folding. During early fold growth, nearly constant thickness strata are deposited before a progressive unconformity and other converging geometries develop. The development of growth strata is fast in the folds near the QES, which are being uplifted rapidly and degraded vigorously. Under these conditions, the stratigraphic relations give only a broad estimate of the pretectonic/syntectonic limit when compared to the excess-area method. On the other hand, the development of growth strata took twice as much time for folds near the abyssal plain, which are being uplifted at a slower rate and where degradation is less intense. Consequently, the delay takes more time, and the use of stratigraphic relations introduces an even more pronounced bias towards younger ages in the identification of the onset of folding.Correspondence: Ismael Yarbuh,

Autogenic Organization of Syn‐Tectonic Sedimentary Patterns in Deepwater Foldbelts: A Simple Dynamic Model

“…It can be appreciated in Figures a and b that enhancing the Rouse number in our numerical experiments has the effect of delaying the transition from continuous to clastic wedges bounded by sharp erosional surfaces. Yarbuh and Contreras () documented a similar transition in the MRFB and thought that it was purely controlled by the rate of uplift and degradation. Our model now suggests that grain size and mode of transport of sediments further mask the emergence of converging geometries in deepwater foldbelts.…”

“…This process created a foldbelt that is ~110‐km wide and accommodates ~11.8 km of tectonic transport along the subhorizontal detachment. The foldbelt consists of twelve buckle folds which vary from very low strain detachment anticlines ( ε ~3%) to moderate strain detachment folds ( ε ~16%; Figure ; Yarbuh & Contreras, ; Yarbuh et al, ). Moreover, these authors observed that fold shape, amplification rate, and deposition of growth strata vary in a predictable manner with the degree of distortion of the folds.…”

“…Plot of mass diffusion coefficient, K , for each of the fold of the Mexican Ridges Foldbelt as a function of their strain, ε (based on values reported in Yarbuh & Contreras, ). The dashed red line shows the overall behavior of K .…”

“…In Figure we have plotted, in addition to the synthetic stratigraphic patterns, the Pe − S d coordinates of each of the folds of the MRFB based on the values shown in the Table . In the figure, the folds are labeled 1–12 according to their location in the foldbelt, 1 being the most eastward structure adjacent to the continental shelf and 12 being the most westward detachment fold in the abyssal plain of the Gulf of Mexico (see Figure 2 in Yarbuh & Contreras, ). We excluded from our analysis the fold 5 for being markedly asymmetrical and the fold 11 because this structure is under gravitational collapse.…”

“…The geometry of growth strata, their stacking patterns, and the development of associated unconformities are widely recognized to be the product of the interplay between superficial mass transport, tectonism, and environmental changes (Contreras, ; Hardy & Poblet, ; Morley, ; Poblet et al, ; Shaw et al, ; Storti & Poblet, ; Suppe et al, ; Whipple, ; Willett & Brandon, ; Yarbuh & Contreras, ). Critically, growth strata are routinely used as proxies of tectonic activity in compressional settings.…”