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Table 2 Reliability and potential risks of the identification marks of hydrovolcanism

From: Identification of hydrovolcanism and its significance for hydrocarbon reservoir assessment: A review

Identification marks Direct marks Degree of reliability Potential risks
Eruptive products Microtextures Quenching cracks No ***** Destroyed by diagenesis
Destroyed by later thermodynamic contact metamorphism
Bread-crusted structure No ****
Stepped fractures No ****
Cracks through particles No **
Perlitic texture No **
Grain size and its parameters No ****
Roundness No **
Quenching texture No *****
Cementation type No **
Vesicularity Yes ***** Only applied to explosive eruption identification
Chilled margin No ** Also developed in margins of ultra-shallow intrusive rocks
Also developed in lava surface layer formed in subaerial eruption
Special structures Graded structures No * Also exist when volcanic materials were transported
Turbidity deposits: Also could develop small-scale graded beddings
Hydraulic jump: Also could develop antidune beddings, water and wind beddings
Large-scale cross-beddings No *****
Pillow structures No ***** Only applied to lava in effusive facies
Also formed when the subaerial magma flows into river
Note to distinguish from non-radial joints and vacant spherical weathering
Lithofacies and facies sequences Lithofacies Perlite No ** Also formed in intrusive body under water-rich environment
Peperite No *****  
Spilite No *** Origin is controversial
Facies sequences Effusive No *****  
Explosive No **** Hard to be applied alone
Oxidation index No **** Magma content can affect the oxidation index
Secondary changes of volcanic rocks such as the late weathering
Note the oxidation in the test experiment
Associated environment Overlying sedimentary environment No ***** The following two conditions need to be cautiously applied: (1) Large-scale scouring in the bottom and depositional breaks occur; (2) Being exposed after hydrovolcanism, weathering and/or erosion
Underlying sedimentary environment No ****
  1. The quantities of * means the degree of reliability; the highest degree of reliability is shown as *****, and the lowest is shown as *