Abstract
Geological structure changes, including deformations and ruptures, developed in shallow marine sediments are well recognized but were not systematically reviewed in previous studies. These structures, generally developed at a depth less than 1000 m below seafloor, are considered to play a significant role in the migration, accumulation, and emission of hydrocarbon gases and fluids, and the formation of gas hydrates, and they are also taken as critical factors affecting carbon balance in the marine environment. In this review, these structures in shallow marine sediments are classified into overpressure-associated structures, diapir structures and sediment ruptures based on their geometric characteristics and formation mechanisms. Seepages, pockmarks and gas pipes are the structures associated with overpressure, which are generally induced by gas/fluid pressure changes related to gas and/or fluid accumulation, migration and emission. The mud diapir and salt diapir are diapir structures driven by gravity slides, gravity spread and differential compaction. Landslides, polygonal faults and tectonic faults are sediment ruptures, which are developed by gravity, compaction forces and tectonic forces, respectively. Their formation mechanisms can be attributed to sediment diagenesis, compaction and tectonic activities. The relationships between the different structures, between structures and gas hydrates and between structures and authigenic carbonate are also discussed.
Highlights
Shallow marine structures are sediment deformations and ruptures developed in a shallow environment less than 1000 m below the seafloor due to many kinds of driving forces such as overpressure, differential gravity, compaction forces, tectonic forces, etc
Shallow marine structures are developed in shallow sediments at depths of less than 1000 mbsf
According to their characteristics and formation mechanisms, these structures are classified into three groups: overpressure-associated structures, diapir structures and sediment ruptures
Summary
Shallow marine structures are sediment deformations and ruptures developed in a shallow environment less than 1000 m below the seafloor (mbsf) due to many kinds of driving forces such as overpressure, differential gravity, compaction forces, tectonic forces, etc. Chen et al [3] identified gas chimneys on seismic profiles and indicated that they are related to thermogenic gas migration. The accumulation and distribution of gas hydrates are closely related to the gas and fluid migration which is primarily controlled by the structures in shallow marine sediments [17,18,19,20,21]. Gasperini et al [28] studied the tectonic fault in the Sea of Marmara and suggested that gas and fluid emissions increase along the tectonic fault system after an earthquake As introduced above, these structures are closely related to each other, and the structures are closely associated with gas and fluid migration. This article aims to provide a systematic summary of the current knowledge about the shallow structures developed in shallow sediments, to classify the shallow marine structures, identify their characteristics and explore the mechanisms of the structures, and discuss their relationships with gas and fluid migration
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