Active near-surface growth faulting and late Holocene history of motion: Matagorda peninsula, Texas

Abstract

The structural framework of the northern Gulf of Mexico coastal zone includes numerous growth fault systems. Neotectonic processes in coastal environments here have been shown to be important contributors to subsidence and relative sea-level rise, as well as having significant influences on sedimentary accretion processes. One active growth fault at East Matagorda Peninsula, Texas was subjected to detailed study to address the hypotheses that (1) this fault was present and active before the peak of regional hydrocarbon recovery in the mid-20th century, and that (2) slip along this fault has been episodic over the resolved period of record. To characterize the late Holocene behavior of this fault, three core transects were established normal to the surface fault trace, and stratigraphic analysis was conducted with the use of radiocarbon (14C) for chronological control. Correlation of time-equivalent stratigraphic boundaries reveals a maximum total late Holocene offset of 0.7 m. The Matagorda fault was in place long before the peak of regional oil and gas extraction, but experienced a late Holocene rejuvenation, initiated between 2500 and 1500 years BP. The kinematic behavior of the fault expressed as temporally and spatially variable measures of expanded stratigraphic thicknesses on the downthrown extent suggest that sediment loading from the transgressive Matagorda barrier complex may have contributed to this rejuvenation, and that slip along the fault persists to the present. Radiocarbon chronology also revealed clear differences in the magnitude of fault throw during the late Holocene, with maximum displacement (0.7 m) occurring at the southwestern-most transect and minimum throw at the northeastern-most transect (0.2 m).