Characterization and origins of high-amplitude reflection packets, HARPs, along the Gulf of Mexico depositional profile

Abstract

High amplitude reflection packets (HARPs) refer to sheet-like sand deposits, showing high-amplitude seismic-reflection character, which are thought to be associated with constructional channel systems. Based on observations of Quaternary deposits from the Amazon Fan, HARPs are interpreted to be related to channel avulsion events. The depositional model from the Amazon Fan suggests when levees fail, sediment gravity flows move through the break into interchannel lows, where lack of confinement results in sheet like sand deposits. Based on 2D and 3D seismic data, HARPs from the Gulf of Mexico not only form from updip channel avulsions, but from additional geological processes. In salt withdrawal minibasins, sediment gravity flows encounter an underfilled depocenter, where lack of confinement results in sheet like deposits. After initial spill into an outboard basin and the development of a graded slope equilibrium profile, slope channel complexes develop as conduits for sediment transport. These depositional processes characterize the "fill and spill" model and can result in the creation of HARP-like deposits. At the toe-of-the Sigsbee Escarpment, turbidity currents flow through nickpoints at the seaward edge of the escarpment and become unconfined, resulting in HARP-like deposition on the abyssal floor. Seismically, these deposits are laterally continuous, have low relief, pinchout downdip, and have internal channelization. Erosive, low-relief, discontinuous channels and a low-relief, flat-bottomed trough cut into the TS-HARP deposits. On the outer fan, at the seaward limit of submarine channels, sediment gravity flows will also become unconfined and deposit HARPs. These HARPs typically consist of shingled sheet-like deposits that may form larger scale mounded features. These observations indicate that HARP-like deposits can form from a variety of depositional processes and in variable depositional settings along the Gulf of Mexico depositional profile.