https://doi.org/10.1130/G46159.1 Manuscript received 26 December 2018 Revised manuscript received 19 February 2019 Manuscript accepted 25 March 2019 © 2019 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Published online 16 April 2019 Stratigraphic aliasing and the transient nature of deep-water depositional sequences: Revisiting the Mississippi Fan Andrew S. Madof1, Ashley D. Harris1, Sarah E. Baumgardner1, Peter M. Sadler2, Fabien J. Laugier1, and Nicholas Christie-Blick3 1Chevron Energy Technology Company, Houston, Texas 77002, USA 2Department of Earth Sciences, University of California, Riverside, California 92521, USA 3Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, USA ABSTRACT and into the effect of climatic and tectonic sig- Sequence stratigraphy remains the foremost methodology used to describe the stratigraphic nals on modulating inherently nonstationary record and to interpret the controls on deposition; yet, it relies on long-standing assumptions deposition. that few studies have sought to validate. Here, we present results from testing hypotheses related to the deep-water depositional sequence model by revisiting the seismic-based type locality: MISSISSIPPI FAN, GULF OF MEXICO the Mississippi Fan, in the central Gulf of Mexico. By independently testing the relationship The Neogene–Quaternary Mississippi Fan between cycles of relative sea-level change and those of sedimentation, we demonstrate that in the central Gulf of Mexico is one of the most >98% of Neogene–Quaternary deep-water sequences do not accumulate in a manner prescribed well-studied submarine fans on Earth. Because by long-held sequence stratigraphic conventions. Instead, over the past 5.5 Myr, sequences of the abundance of subsurface data, it has been show a temporal mismatch in frequency, phase, and amplitude with cycles of relative sea-level used to understand deep-water stratigraphic change, a concept we refer to as stratigraphic aliasing. Divergences are attributed to variable archi tecture and cyclicity, as well as relative rates of sedimentation, which were responsible for creating cycle frequencies that were both sea-level change and sedimentation. higher and lower than those of relative sea-level change, and that resulted in two modes of Mississippi Fan accumulation: lower average sedimentation rates in older sediments, and an opposite trend in younger successions. The latter mode occurred ~2.2 Myr after the onset of Architecture and Cyclicity North American glaciation, a period marked by significant continental drainage reorganiza- The Mississippi Fan is a submarine accu- tion and salt-tectonic deformation. Based on our conclusions, we recommend that the future mulation >4 km in thickness situated outboard of sequence stratigraphy be rooted firmly in assessing the reproducibility of preexisting spatio- of the Sigsbee Escarpment. Based on downlap- temporal predictions and in the rigorous use of multiple working hypotheses. ping reflections (i.e., geometric evidence for se- quence boundaries), Weimer (1990) interpreted INTRODUCTION 2016; Catuneanu and Zecchin, 2016), and on 17 laterally compensatory deep-water sequences For over 40 years, depositional systems have its ability to be treated as a set of testable hy- (Fig. 2A) and inferred each to be composed of been thought to be controlled by the interac- potheses (this study). channelized (coarse-grained) deposits flanked tion of eustasy and subsidence (i.e., “relative The Mississippi Fan, in the central Gulf of by levee-overbank (fine-grained) deposits. By sea level” of Jervey, 1988), with variability in Mexico, serves as the type locality for the seis- incorporating age control, Weimer and Dixon sediment supply providing a secondary effect mic-based model of the deep-water depositional (1994) showed that sequence duration gener- (see Vail et al., 1977; Posamentier et al., 1988; sequence. In addition to Weimer (1990), other ally decreased from 0.66 Myr (5.5–4.84 Ma; Van Wagoner et al., 1990). According to this workers identified Mississippi Fan lobes from sequence number 1) to 0.023 Myr (0.23–0.0 Ma; view, relative sea-level change drives reciprocal downlapping reflections at the base of gullwing- sequence number 17) and increased in lateral sedimentation, whereby condensed sections and shaped deposits (Garrison et al., 1982) and re- extent and overall thickness through time (Figs. nearshore deposits accumulate during rises and lated accumulations to falls in relative sea level 2B and 2C). In addition to the duration of se- high stands, and erosional surfaces and deep- (Bouma et al., 1985). While these concepts have quences, Weimer and Dixon (1994) interpreted water accumulations deposit during falls and been applied globally to deep-water systems, two major hiatuses, from 3.0 to 1.9 Ma and from low stands (Figs. 1A and 1B). While active few studies have sought to validate the initial 0.45 to 0.086 Ma. While Weimer and Dixon debate regarding both controlling mechanisms findings. Here, we revisited the Mississippi Fan (1994) may have incorrectly assumed that seis- and their stratigraphic responses has been ongo- in an attempt to independently reproduce the mic reflections were laterally continuous syn- ing since the late 1980s (see Haq et al., 1987; relationship between relative sea-level change chronous surfaces, alternative interpretations Christie-Blick et al., 1988), the community re- and sedimentation, and to test whether the lat- have not yet been proposed. mains divided on the level of applicability of ter is controlled by changes in the former. By sequence stratigraphy (see Madof et al., 2016; testing long-standing conventions, we offer Sea Level and Sedimentation Burgess, 2016), on its status as a workflow as new insights into the time-varying interactions We calculated relative sea-level change and opposed to a paradigm (see Burgess and Prince, between purported drivers and accumulation, sedimentation rates independently for the last CITATION: Madof, A.S., et al., 2019, Stratigraphic aliasing and the transient nature of deep-water depositional sequences: Revisiting the Mississippi Fan: Geology, v. 47, p. 545–549, https:// doi .org /10 .1130 /G46159.1 Geological Society of America | GEOLOGY | Volume 47 | Number 6 | www.gsapubs.org 545 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/47/6/545/4707771/545.pdf by guest on 24 September 2021 Figure 1. Schematic A 5.5 Myr of growth of the Mississippi Fan (Figs. diagram of reciprocal sedi- Sea level 3A and 3B). The former was constructed by add- mentation and deep-water Shelf depositional sequence ing the eustatic record of Miller et al. (2005, Slope their fig. 3, created from the benthic forami- model. A: Two-dimen- Basin sional transect along RSL SR RSL SR niferal δ18O record) to the back-stripped sub- continental margin show- HS * sidence rate of the northern Gulf of Mexico of ing shelfal accumulations LS developing during rela- * Diegel et al. (1995, their fig. A-3). While spe- This study cific details regarding the construction of the tive sea-level high stands B and rises, and slope-to- Relative Hypothetical Sedimentation Systems sub sidence curve remain unclear, it serves as sea level well log rates tracts basinal sedimentation the most robust (if not the only) example for occurring during low Lowstand the area. Sedimentation rates for each Missis- stands and falls. B: Each ? deep-water sequence Highstand sippi Fan sequence were calculated by dividing Transgressive develops during one e maximum preserved thickness (from Fig. 2A) by cycle of relative sea-level ? duration (from Fig. 2B); rates span two orders Sawtooth change (modified from wave Lowstand Sine Sequenc of magnitude, with older sequences display- Posamentier and Kolla, wave 4 2003), during which rate of ing lower average accumulation rates (i.e., 10 sedimentation decreases. 100 68 cm/Myr), and younger ones showing an opposite 14 18 6 Sedimentation-rate curve Low High 0 50 100 0.5 1.0 0 trend (i.e., 10 cm/Myr). Based on our analysis, Magnitude Gamma ray Normalized Percentage was created by dividing the bulk of long-term relative sea-level change = Mass transport = Weakly confined channel = Channel-levee = Hemipelagites and facies thickness (from complex and sheet complex complex muddy turbidites in the Mississippi Fan was caused by subsid- hypothetical well log) by = Sequence boundary = Facies boundary = Maximum flooding surface duration (from relative sea-level curve) and normalizing to maximum rate. Abbreviations are ence related to salt withdrawal, rather than by as follows: RSL—relative sea level; SR—sedimentation rate; HS—high stand; LS—low stand. eustatic change. A C SW NE 90°W 89°W 88°W 87°W Sequence no. Sequence no. Sections used in Fig. DR2 1 2 3 4 5 5 2 8 8 0 5. 4. 3. 3. 3.4 3. 27°N Fig. 2A-B 4.84 Gulf of Mexico Fig. 2A-B Fig. 2C 26°N N m 50 km 1000 Sequence Time Channel Deformed Mass transport = = = = = 50 km boundary line complex levee deposit complex 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 = Seismic sequence no. (levee complex) Sequence no. Sequence no. 6 7 8 9 0.071 14-17 B 9 4 1 1 8 7 0 1. 1. 1. 1. 0. 0. Lacuna 0.4 13 0.5 0.5 0.6 12 0.7 11 0.8 10 9 e 8 1.0 1.1 7 1.4 1.5 Pleistocen 6 Sequence no. Sequence no. 1.9 10 11 12 13 2.0 0.7 0.6 0.5 0.5 0.4 0.45 2.5 Lacuna 3.0 Onset of North American glaciation Age (Ma) 3.0 5 3.4 3.5 4 e 3.8 Sequence no. Sequence no. 4.0 3 14 15 16 17 4.2 Pliocen 0.0 0.04 0.04 0.0710.055 0.023 4.5 2 4.84 5.0 1 5.5 5.5 Figure 2.