Significance of active growth faulting on marsh accretion processes in the lower Pearl River, Louisiana Kevin M. Yeager a, ⁎, Charlotte A. Brunner b , Mark A. Kulp c , Dane Fischer d , Rusty A. Feagin e , Kimberly J. Schindler a , Jeremiah Prouhet b , Gopal Bera b a Department of Earth and Environmental Sciences, University of Kentucky, 101 Slone Research Building, Lexington, KY 40506-0053, United States b Department of Marine Science, University of Southern Mississippi, 1020 Balch Blvd., Stennis Space Center, MS 39529, United States c Department of Earth and Environmental Sciences, University of New Orleans, 2000 Lakefront, New Orleans, LA 70148, United States d EQT Corporation, 625 Liberty Ave Ste. 1700, Pittsburgh, PA 15222-3114, United States e Department of Ecosystem Science and Management, Texas A&M University, 1500 Research Pkwy, Ste. B223, 2120 TAMU, College Station, TX 77845, United States abstract article info Article history: Received 17 September 2011 Received in revised form 18 February 2012 Accepted 22 February 2012 Available online 3 March 2012 Keywords: Growth fault Marsh Sediment Lithostratigraphy Foraminifera Radionuclides Neotectonic processes influence marsh accretion in the lower Pearl River valley. Active growth faults are sug- gested by groupings of ponded river channel sections, transverse and linear river channel sections, and down- and across-valley contrasts in channel sinuosity. Seismic profiles identified several likely, fault-induced struc- tural anomalies, two of which parallel the axes of surface distributary networks. Lithostratigraphy and biostra- tigraphy of six cores from across a suspected fault in the West Middle River, combined with 14 C-based age control, yielded evidence of vertical offsets, indicating that this river section is on the plane of a growth fault. These data were used to estimate fault slip rates over two time intervals, 1.2 mm/y over the last 1300 yr, and 0.2 mm yr -1 over the last 3700 yr, and delineated a sinusoidal pattern of deformation moving distally from the fault, which we interpret as resulting from fault-propagation folding. Higher rates of sedi- ment accumulation (of the order of cm yr -1 from 210 Pb xs and 137 Cs activity data) on the down-thrown side are consistent with sedimentary response to increased accommodation space, and mass-based sediment accu- mulation rates (g cm -2 yr -1 ) exhibit a pattern inverse of that shown by fault-driven sinusoidal deformation. We contend that near-surface growth faults are critically important to driving accretion rates and marsh response to sea-level rise. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Our research set out to test the hypothesis that active or recently active growth faulting, expressed at the surface, can fundamentally influence one or more factors that control the rate at which coastal marshes vertically accrete. To address this hypothesis, we identified the following objectives: 1. identify an active or recently active growth fault expressed at the marsh surface and examine its Holocene history of motion; 2. assess the extent and magnitude of fault-driven vertical offset and near-surface deformation by examining across-fault relationships between lithostratigraphy, biostratigraphy, 14 C ages and depth in section; and 3. measure marsh sediment accretion rates on either side of the fault using fallout radionuclides ( 137 Cs, 210 Pb) to tie into a larger-scale, short-term understanding of tectonic effects on sediment distribu- tions and marsh accretion. Southern Louisiana and Mississippi consist of a complex geomor- phic framework of coastal, fluvial, marsh, and swamp environments, produced by numerous Late Quaternary depositional systems and processes (e.g., Coleman et al., 1991; Galloway et al., 1991). Given the high water-content substrate, dynamic coastal setting and semi- tropical climate here, even active near-surface faults may not neces- sarily manifest themselves as definitive fault scarps at the surface. Fault-induced deformation may consequently be difficult to identify, either in surface expression or within the shallow stratigraphic record. This research focuses on the premise that vertical motion or distal deformation driven by recent or ongoing fault motion within active deltaic systems can be recorded in one or more ways: A) direct control over river or distributary planform, B) similar or identical subsurface lithologic units that are vertically offset across the fault, C) chrono- stratigraphically correlative subsurface units that are vertically offset across the fault, D) similar or identical fossil assemblages in the Geomorphology 153–154 (2012) 127–143 ⁎ Corresponding author. Tel.: + 1 859 257 5451; fax: + 1 859 323 1938. E-mail addresses: kevin.yeager@uky.edu (K.M. Yeager), charlotte.brunner@usm.edu (C.A. Brunner), mkulp@uno.edu (M.A. Kulp), DAFischer@eqt.com (D. Fischer), feaginr@tamu.edu (R.A. Feagin), kimberly.schindler@uky.edu (K.J. Schindler), jeremyprouhet@yahoo.com (J. Prouhet), gopal.bera@eagles.usm.edu (G. Bera). 0169-555X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2012.02.018 Contents lists available at SciVerse ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph