**4. Occurrence, texture and composition of peperites**

In the study area peperites often occur as sheet-like bodies along basal contacts of lava flows and the underlying wet sediments (**Figure 7A, B**). Sometimes they are encountered on the top of thin lava flows burrowing into a several m thick sequence of fine-grained sediments or along terminal parts of lava flows where they form irregularly shaped or lobate bodies. Peperite domains range in volume from less than a few m3 to several 10s m3 and sometimes they can only be some cm thick. The mingling wet sediment was commonly fine-grained volcanic ash or siliciclastic and carbonaceous silt. More rarely peperites have been recognised in association with coarser-grained volcaniclastic deposits, and most often they occur at the base of lava flows.

The most widespread type is blocky peperite whilst globular peperite and peperitic hyaloclastite are rarer in occurrence. Along the pathway of a single lava

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

The section Smrekovec G34 begins in the Kramarica Sill (**Figure 6**) and comprises three thicker lava flows attaining some 35 m, 90 m and over 50 m, respectively. Based on the occurrence of yugawaralite [37, 52] and with respect to the middle bathyal water depths, the Kramarica Sill was emplaced about 600-800 m below the then surface of stratovolcano. Pyroclastic density current deposits are far less abundant than in the section Krnes and pyroclastic flow deposits are relatively abundant only in the upper half of the section. Syn-eruptive resedimented volcaniclastic deposits are dominated by volcaniclastic debris-flow deposits. Hyaloclastites and resedimented hyaloclastites are less abundant than in the section Krnes. Altogether fifteen peperites have been recognised and most of them are related to

*Lithofacies and the principal alteration minerals in the medial-zone section Krnes.*

**308**

**Figure 5.**

terminal parts of lava flows.

## *Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

flow overriding the same layer of wet sediment the volume and texture of peperite have commonly changed. On a macroscopic scale, an initiation of peperite development along the contact of lava and fine-grained wet sediment was deformation of the underlying strata and laminae, their disintegration into clasts (**Figure 7A**) and subsequent incorporation into the lava flow where the clasts have undergone further deformation (**Figure 7B**). Terminal parts of lava flows commonly consist of blocky peperite. A clear zonation of closely packed blocky peperite next to lava and dispersed blocky peperite closer the host sediment has not been identified. Most often irregularly distributed domains of the mentioned textural types have been encountered. Some juvenile clasts may be jigsaw-fit and in some peperite domains, a part of the mingling sediment may occur in the form of clasts (**Figure 8A, B**).

### **Figure 7.**

*A, disrupted stratified fine-grained tuff underlying hyaloclastite breccia and peperite. The dotted and dashed lines mark a peperite domain (P) and a separated clast composed of disrupted and convoluted stratified tuff (SC), respectively. Hammer (33 cm) is for scale; B, peperite (P) with abundant clasts of dark-grey finegrained tuff. The dotted lines mark two larger deformed clasts originating from the underlying deposit (T).*

**311**

(**Figure 11F**).

*Submarine Stratovolcano Peperite Syn-Formational Alteration - A Case Study of the Oligocene…*

On a macroscopic scale, blocky, sharply angular juvenile clasts are the most common (**Figure 9A**) although other forms of juvenile clasts have been recognised as well (**Figure 9B**-**F**). Globular juvenile clasts can be irregularly shaped or amoeboid (**Figure 9B, C**), elongated, tapered, and a single clast can have partially fluidal and sub-planar margins. Mixed morphologies of juvenile clasts, particularly sharply angular and elongate globular have been encountered in some rhyodacitic glassy lava flows (**Figure 9E**). Glassy lavas sometimes undergo ductile fragmentation into irregularly shaped elongated and convoluted globular clasts that resemble welded glass-shards (**Figure 9F**). Intergranular space is relatively limited and poorly interconnected, and can be infilled with very fine-grained, possibly suspended sediment. Further disintegration and mingling with wet sediment produced peperites

*Blocky peperite. A, larger angular juvenile clasts (jc) and fluidised sediment (S, dotted area) in matrix (m) composed of smaller juvenile clasts and fine-grained siliciclastic sediment. Coin (2.5 cm) is for scale; B, juvenile clasts (jc) and the clasts of fine-grained tuff (Sc) in matrix composed of an intimate mixture of the host sediment and juvenile clasts. The matrix is locally extensively altered (A) to laumontite. Coin (2.5 cm) is for* 

The host sediment can penetrate magma in the form of curviplanar and vermicular indentations or enter lava flow through laminar boundary layers. The indentations (**Figure 10A**) reaching deeper into the juvenile clasts are commonly disconnected (**Figure 10B, C**) and initially, irregularly shaped droplets formed (**Figure 10D**). The droplets commonly advanced deeper into juvenile clasts changing their shapes into spherical and oval (**Figure 10E, F**). They may be very abundant, and the rock can be termed microglobular peperite, similar to that described by [5]. In an advanced stage peperites of this type may evolve into intimate mixtures of extremely irregularly shaped elongated clasts and tongues of sediment and tapered juvenile clasts having tendril and wispy forms (**Figure 11A**). The host sediment that penetrates lava through laminar boundary layers at least initially follows the laminae adopting their shape (**Figure 11B**), but then the flow with the admixed sediment seems to have changed into turbulent (**Figure 11C**). Sometimes the amount of sediment that mingled with magma in that manner is very low and only isolated patches of the entrained sediment can be encountered in the predominant magma, but there are cases where peperites locally developed as intimate mixtures of nearly equal proportions of tapered juvenile

Magma can penetrate the adjacent sediments forming platy or tapered juvenile clasts (**Figure 11E**). Magma can also penetrate the host sediment along the strata boundaries or other disconformities related to syn-sedimentary tectonic activity or erosion. The emplacement of the Kramarica Sill also disrupted partially consolidated and unconsolidated sediments and made pathways for magma penetration

When the unconsolidated mingling sediment is composed of coarse-grained volcaniclastic deposit such as volcaniclastic turbidite or debris flow deposit,

*DOI: http://dx.doi.org/10.5772/intechopen.95480*

**Figure 8.**

*scale.*

developed as intimate mixtures of both components.

clasts and deformed, elongated clasts of sediment (**Figure 11D**).

*Submarine Stratovolcano Peperite Syn-Formational Alteration - A Case Study of the Oligocene… DOI: http://dx.doi.org/10.5772/intechopen.95480*

### **Figure 8.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

flow overriding the same layer of wet sediment the volume and texture of peperite have commonly changed. On a macroscopic scale, an initiation of peperite development along the contact of lava and fine-grained wet sediment was deformation of the underlying strata and laminae, their disintegration into clasts (**Figure 7A**) and subsequent incorporation into the lava flow where the clasts have undergone further deformation (**Figure 7B**). Terminal parts of lava flows commonly consist of blocky peperite. A clear zonation of closely packed blocky peperite next to lava and dispersed blocky peperite closer the host sediment has not been identified. Most often irregularly distributed domains of the mentioned textural types have been encountered. Some juvenile clasts may be jigsaw-fit and in some peperite domains, a part of the mingling sediment may occur in the form of clasts (**Figure 8A, B**).

*A, disrupted stratified fine-grained tuff underlying hyaloclastite breccia and peperite. The dotted and dashed lines mark a peperite domain (P) and a separated clast composed of disrupted and convoluted stratified tuff (SC), respectively. Hammer (33 cm) is for scale; B, peperite (P) with abundant clasts of dark-grey finegrained tuff. The dotted lines mark two larger deformed clasts originating from the underlying deposit (T).*

**310**

**Figure 7.**

*Blocky peperite. A, larger angular juvenile clasts (jc) and fluidised sediment (S, dotted area) in matrix (m) composed of smaller juvenile clasts and fine-grained siliciclastic sediment. Coin (2.5 cm) is for scale; B, juvenile clasts (jc) and the clasts of fine-grained tuff (Sc) in matrix composed of an intimate mixture of the host sediment and juvenile clasts. The matrix is locally extensively altered (A) to laumontite. Coin (2.5 cm) is for scale.*

On a macroscopic scale, blocky, sharply angular juvenile clasts are the most common (**Figure 9A**) although other forms of juvenile clasts have been recognised as well (**Figure 9B**-**F**). Globular juvenile clasts can be irregularly shaped or amoeboid (**Figure 9B, C**), elongated, tapered, and a single clast can have partially fluidal and sub-planar margins. Mixed morphologies of juvenile clasts, particularly sharply angular and elongate globular have been encountered in some rhyodacitic glassy lava flows (**Figure 9E**). Glassy lavas sometimes undergo ductile fragmentation into irregularly shaped elongated and convoluted globular clasts that resemble welded glass-shards (**Figure 9F**). Intergranular space is relatively limited and poorly interconnected, and can be infilled with very fine-grained, possibly suspended sediment. Further disintegration and mingling with wet sediment produced peperites developed as intimate mixtures of both components.

The host sediment can penetrate magma in the form of curviplanar and vermicular indentations or enter lava flow through laminar boundary layers. The indentations (**Figure 10A**) reaching deeper into the juvenile clasts are commonly disconnected (**Figure 10B, C**) and initially, irregularly shaped droplets formed (**Figure 10D**). The droplets commonly advanced deeper into juvenile clasts changing their shapes into spherical and oval (**Figure 10E, F**). They may be very abundant, and the rock can be termed microglobular peperite, similar to that described by [5]. In an advanced stage peperites of this type may evolve into intimate mixtures of extremely irregularly shaped elongated clasts and tongues of sediment and tapered juvenile clasts having tendril and wispy forms (**Figure 11A**). The host sediment that penetrates lava through laminar boundary layers at least initially follows the laminae adopting their shape (**Figure 11B**), but then the flow with the admixed sediment seems to have changed into turbulent (**Figure 11C**). Sometimes the amount of sediment that mingled with magma in that manner is very low and only isolated patches of the entrained sediment can be encountered in the predominant magma, but there are cases where peperites locally developed as intimate mixtures of nearly equal proportions of tapered juvenile clasts and deformed, elongated clasts of sediment (**Figure 11D**).

Magma can penetrate the adjacent sediments forming platy or tapered juvenile clasts (**Figure 11E**). Magma can also penetrate the host sediment along the strata boundaries or other disconformities related to syn-sedimentary tectonic activity or erosion. The emplacement of the Kramarica Sill also disrupted partially consolidated and unconsolidated sediments and made pathways for magma penetration (**Figure 11F**).

When the unconsolidated mingling sediment is composed of coarse-grained volcaniclastic deposit such as volcaniclastic turbidite or debris flow deposit,

### **Figure 9.**

*(A) angular juvenile clast with perlitic cracks in siliciclastic host sediment. Volcanic glass in perlitic domains is altered to laumontite (white) and Fe-oxides (black); (B) various shapes of juvenile clasts (jc) with indentations (i) of the host sediment (s); (C) amoeboid juvenile clasts (gc) in the host sediment (s); (D) an intimate mixture of juvenile clasts (jc) with the sediment (s) indentations (i), (E) globular(gc) and angular (h) juvenile clasts; (F) a glassy lava fragmented into globular (g), elongated (e) and convoluted (w) juvenile clasts with altered sediment (s) filling interstitial space.*

peperites can form by erosion and incorporation of sediment into the lava flow. A small-scale penetration of magma into interstitial space has been observed along the basal contacts of lava flows and the underlying sediments (**Figure 12A**). Sometimes magma penetrated deeper into the sediment while pushing aside and redistributing its constituents such as mineral grains and volcanic rock fragments (**Figure 12B**), although the advance seems very limited as the penetrating tongues soon became thinner (**Figure 12C**) or have been stopped by an impenetrable obstacle. Magma itself possibly underwent a sort of separation of its constituents during the process of penetration. Phenocrysts are often stacked close to the magma-sediment boundary while glassy groundmass could have penetrated deeper into the sediment (**Figure 12D**).

**313**

**Figure 10.**

**5. Alteration of peperites**

*their shapes evolved by splitting of larger clasts (d).*

Microfacies of peperites has been an essential tool in recognition of alteration of peperites as it encompasses the change in mineral and chemical composition of juvenile clasts and the mingling sediment, and more rarely, the formation of interstitial cement. Juvenile blocky clasts dispersed in abundant siliciclastic silt commonly underwent only devitrification, the alteration of glassy juvenile clasts with perlitic

*(A) curviplanar indentations (i) of sediment (s) into juvenile clasts (jc); (B) interpenetrating sediment (s) and magma (m). The arrows i and p indicate the penetration directions of sediment and magma, respectively; (C) sediment (s) penetrating juvenile clast (jc). The arrows show the sediment penetration directions. Sediment (brownish) is partially unaltered and partially replaced by laumontite (Lmt). Larger detached droplets of sediment have irregular shapes whilst smaller ones tend to develop more oval or spherical shapes; (D) irregularly shaped droplets of sediment (s) penetrating a juvenile clast (m). The arrows (i) show the sediment penetration directions; (E) larger clast of sediment (s) penetrating a juvenile clast (m) is still unaltered, and smaller ones have already undergone alteration into chlorite (Chl). Some droplets of sediment show the tendency of splitting into several smaller droplets (d) and some smaller droplets already attained oval shapes (o); (F) droplets of siliciclastic sediment (s) in a juvenile clast (jc). Some droplets have oval shape (o) and some droplets indicate* 

*Submarine Stratovolcano Peperite Syn-Formational Alteration - A Case Study of the Oligocene…*

*DOI: http://dx.doi.org/10.5772/intechopen.95480*

*Submarine Stratovolcano Peperite Syn-Formational Alteration - A Case Study of the Oligocene… DOI: http://dx.doi.org/10.5772/intechopen.95480*

### **Figure 10.**

*Updates in Volcanology – Transdisciplinary Nature of Volcano Science*

peperites can form by erosion and incorporation of sediment into the lava flow. A small-scale penetration of magma into interstitial space has been observed along the basal contacts of lava flows and the underlying sediments (**Figure 12A**). Sometimes magma penetrated deeper into the sediment while pushing aside and redistributing its constituents such as mineral grains and volcanic rock fragments (**Figure 12B**), although the advance seems very limited as the penetrating tongues soon became thinner (**Figure 12C**) or have been stopped by an impenetrable obstacle. Magma itself possibly underwent a sort of separation of its constituents during the process of penetration. Phenocrysts are often stacked close to the magma-sediment boundary while glassy groundmass could have penetrated deeper

*(A) angular juvenile clast with perlitic cracks in siliciclastic host sediment. Volcanic glass in perlitic domains is altered to laumontite (white) and Fe-oxides (black); (B) various shapes of juvenile clasts (jc) with indentations (i) of the host sediment (s); (C) amoeboid juvenile clasts (gc) in the host sediment (s); (D) an intimate mixture of juvenile clasts (jc) with the sediment (s) indentations (i), (E) globular(gc) and angular (h) juvenile clasts; (F) a glassy lava fragmented into globular (g), elongated (e) and convoluted (w) juvenile* 

**312**

**Figure 9.**

into the sediment (**Figure 12D**).

*clasts with altered sediment (s) filling interstitial space.*

*(A) curviplanar indentations (i) of sediment (s) into juvenile clasts (jc); (B) interpenetrating sediment (s) and magma (m). The arrows i and p indicate the penetration directions of sediment and magma, respectively; (C) sediment (s) penetrating juvenile clast (jc). The arrows show the sediment penetration directions. Sediment (brownish) is partially unaltered and partially replaced by laumontite (Lmt). Larger detached droplets of sediment have irregular shapes whilst smaller ones tend to develop more oval or spherical shapes; (D) irregularly shaped droplets of sediment (s) penetrating a juvenile clast (m). The arrows (i) show the sediment penetration directions; (E) larger clast of sediment (s) penetrating a juvenile clast (m) is still unaltered, and smaller ones have already undergone alteration into chlorite (Chl). Some droplets of sediment show the tendency of splitting into several smaller droplets (d) and some smaller droplets already attained oval shapes (o); (F) droplets of siliciclastic sediment (s) in a juvenile clast (jc). Some droplets have oval shape (o) and some droplets indicate their shapes evolved by splitting of larger clasts (d).*
