FIG 1 - uploaded by Zhiyang Li
Content may be subject to copyright.
-A) Middle Turonian paleogeographic map showing the extent of the Western Interior Seaway (Blakey 2014). Dominant southward-directed longshore currents along the western margin of the seaway are indicated by blue arrows. Paleolatitudes are from Sageman and Arthur (1994). B) Paleogeographic reconstruction of the foreland basin of middle North America that shows evolving topography (schematic), locations of active faults, general depositional environments, forebulge position during the Turonian, and location of the study area (modified from Yonkee and Weil 2015). The sediment supply of the Tununk Shale was derived from multiple sources, including clastic sediments derived from the Sevier orogenic belt and volcanic highlands to the west, primary productivity from the upper water column, wind-borne volcanic ash, and submarine erosion at the lacuna developed in northeastern Utah. The lacuna in northeastern Utah developed as a submarine unconformity from the late Cenomanian to middle Turonian due to uplift of an intra-basinal culmination (Ryer and Lovekin 1986). HM, Henry Mountains Region; KP, Kaiparowits Plateau.
Source publication
Despite recent advances in understanding the complex dynamics of mud deposition, it remains a challenging task to characterize the grain size, origin of different components, and sedimentary textures of mudstones through detailed petrographic analysis. In this study, the Tununk Shale in Utah has been examined by optical and scanning electron micros...
Contexts in source publication
Context 1
... heating initiated by subduction, led to crustal thickening in orogenic belts such as the Sevier fold-thrust belt (Livaccari 1991;DeCelles 2004). Subsidence due to flexural loading of the crust created an asymmetric foreland basin, bounded in the west by the rising Sevier orogenic belt and in the east by the stable North American craton ( Fig. 1; Kauffman 1977Kauffman , 1985Kauffman and Caldwell 1993). During the Late Cretaceous, the foreland basin experienced active thrusting, subsidence, uplift (forebulge uplift), and extensive volcanism (DeCelles 2004;DeCelles and Coogan 2006;Yonkee and Weil 2015). A magmatic arc, comprising a belt of calc-alkaline intrusive and volcanic ...
Context 2
... the Late Cretaceous, the foreland basin experienced active thrusting, subsidence, uplift (forebulge uplift), and extensive volcanism (DeCelles 2004;DeCelles and Coogan 2006;Yonkee and Weil 2015). A magmatic arc, comprising a belt of calc-alkaline intrusive and volcanic rocks, was located along the western margin of the North American continent ( Fig. 1; Yonkee and Weil ...
Context 3
... repeated flooding of the foreland basin (Kauffman 1977(Kauffman , 1985Kauffman and Caldwell 1993;Miller et al. 2005;Hay 2008;Haq 2014). In North America, the resulting epicontinental sea, termed the Western Interior Seaway (WIS), connected the Gulf of Mexico and the Northern Boreal Sea during peak eustatic highstand in middle early Turonian time (Fig. 1). This epeiric seaway never exceeded more than a few hundred meters water depth (Weimer 1984;Kauffman 1985;Sageman and Arthur 1994), but was up to 1,500 km wide (Fig. 1). In response to sediments supplied from the Sevier orogenic belt and volcanic highlands, the WIS was broadly characterized by high siliciclastic input and high ...
Context 4
... epicontinental sea, termed the Western Interior Seaway (WIS), connected the Gulf of Mexico and the Northern Boreal Sea during peak eustatic highstand in middle early Turonian time (Fig. 1). This epeiric seaway never exceeded more than a few hundred meters water depth (Weimer 1984;Kauffman 1985;Sageman and Arthur 1994), but was up to 1,500 km wide (Fig. 1). In response to sediments supplied from the Sevier orogenic belt and volcanic highlands, the WIS was broadly characterized by high siliciclastic input and high sedimentation rates along the western margin, and little clastic input on the eastern margin (Kauffman 1977(Kauffman , ...
Context 5
... Tununk Shale was derived from multiple sources, including significant amounts of clastic sediments derived from the Sevier orogenic belt and volcanic highlands, primary productivity (e.g., foraminifera tests, fecal pellets, and coccoliths), wind-borne volcanic ash, and possibly from submarine erosion at the lacuna developed in northeastern Utah (Fig. 1). The Tununk Shale consists of a stack of four lithofacies packages that include, stratigraphically: 1) carbonate-bearing, silty and sandy mudstone (CSSM), 2) silt-bearing, calcareous mudstone (SCM), 3) carbonate-bearing, silty mudstone to muddy siltstone (CMS), and 4) noncalcareous, silty and sandy mudstone (SSM) ( Fig. 3; Li and ...
Context 6
... which are also common minerals in bentonites (Table 2). In thin sections, type 1 volcanic rock fragments show greenish brown to dark brown color under PPL and overall low to greenish or yellowish interference color under CPL (Table 2, Fig. 9). The presence and outlines of volcanic rock fragments are most clearly observed with SEM imaging (Fig. 10) where they show distinct contrast in mineral composition and texture with their surrounding fine- grained matrix (Tables 1, 2). When volcanic rock fragments are present in the fine-grained matrix, varying degrees of differential compaction can be observed around them (Fig. 10C). Volcanic rock fragments occurring in silty and sandy ...
Context 7
... of volcanic rock fragments are most clearly observed with SEM imaging (Fig. 10) where they show distinct contrast in mineral composition and texture with their surrounding fine- grained matrix (Tables 1, 2). When volcanic rock fragments are present in the fine-grained matrix, varying degrees of differential compaction can be observed around them (Fig. 10C). Volcanic rock fragments occurring in silty and sandy laminae or beds show resistance to compaction, but they also show indentation by surrounding harder grains such as quartz and feldspar ( Fig. ...
Context 8
... 1, 2). When volcanic rock fragments are present in the fine-grained matrix, varying degrees of differential compaction can be observed around them (Fig. 10C). Volcanic rock fragments occurring in silty and sandy laminae or beds show resistance to compaction, but they also show indentation by surrounding harder grains such as quartz and feldspar ( Fig. ...
Context 9
... 2 volcanic rock fragments may contain feldspar (both plagioclase and potassium feldspar), quartz, and biotite and commonly show intergrowth texture (Table 2). In thin sections, they are light-colored under PPL and show low interference color under CPL, similar to quartz and feldspar (Fig. 11). Due to small crystal size and limited resolution, the intergrown texture of type 2 volcanic rock fragments is not easily to be recognized in thin sections (Fig. 11). SEM analysis is much better at revealing the intergrown texture, as well as mineral composition and texture of type 2 volcanic rock fragments (Fig. 12). Under the SEM, ...
Context 10
... biotite and commonly show intergrowth texture (Table 2). In thin sections, they are light-colored under PPL and show low interference color under CPL, similar to quartz and feldspar (Fig. 11). Due to small crystal size and limited resolution, the intergrown texture of type 2 volcanic rock fragments is not easily to be recognized in thin sections (Fig. 11). SEM analysis is much better at revealing the intergrown texture, as well as mineral composition and texture of type 2 volcanic rock fragments (Fig. 12). Under the SEM, type 2 volcanic rock fragments can be more readily identified based on distinct contrast in mineral composition and texture with their surrounding fine- grained matrix ...
Context 11
... to quartz and feldspar (Fig. 11). Due to small crystal size and limited resolution, the intergrown texture of type 2 volcanic rock fragments is not easily to be recognized in thin sections (Fig. 11). SEM analysis is much better at revealing the intergrown texture, as well as mineral composition and texture of type 2 volcanic rock fragments (Fig. 12). Under the SEM, type 2 volcanic rock fragments can be more readily identified based on distinct contrast in mineral composition and texture with their surrounding fine- grained matrix (Fig. ...
Context 12
... (Fig. 11). SEM analysis is much better at revealing the intergrown texture, as well as mineral composition and texture of type 2 volcanic rock fragments (Fig. 12). Under the SEM, type 2 volcanic rock fragments can be more readily identified based on distinct contrast in mineral composition and texture with their surrounding fine- grained matrix (Fig. ...
Context 13
... input (i.e., bentonite) will be left in the rock record. Instead, all the resuspended volcanic materials are likely to be redistributed by storm-induced bottom currents across and along the shelf. Bedload transport and deposition of type 1 volcanic rock fragments is supported by their common occurrence in the silty and sandy laminae or beds (Fig. 10D, ...
Context 14
... lithics in the Tununk Shale are clay-to silt-dominated composite particles (Table 2). A notable distinction as compared to fecal pellets and volcanic rock fragments is the common presence of fine silt (, 20 lm) grains (quartz, feldspar, etc.) (Fig. 10D). Small amounts of pyrite may also occur in some shale lithics. If clay dominates, most shale lithics show dark brown color under PPL, and have relatively high interference color under CPL due to preferred orientation of clays (Fig. 13). Shale lithics dominated by quartz silt are light colored under PPL, and show relatively low ...
Context 15
... and volcanic rock fragments is the common presence of fine silt (, 20 lm) grains (quartz, feldspar, etc.) (Fig. 10D). Small amounts of pyrite may also occur in some shale lithics. If clay dominates, most shale lithics show dark brown color under PPL, and have relatively high interference color under CPL due to preferred orientation of clays (Fig. 13). Shale lithics dominated by quartz silt are light colored under PPL, and show relatively low interference color under CPL (Fig. 13F). Under the SEM, shale lithics that have distinctly different mineral composition compared to their surround- ing matrix are readily identified (Fig. 14). Distinguishing clay-dominated shale lithics from ...
Context 16
... of pyrite may also occur in some shale lithics. If clay dominates, most shale lithics show dark brown color under PPL, and have relatively high interference color under CPL due to preferred orientation of clays (Fig. 13). Shale lithics dominated by quartz silt are light colored under PPL, and show relatively low interference color under CPL (Fig. 13F). Under the SEM, shale lithics that have distinctly different mineral composition compared to their surround- ing matrix are readily identified (Fig. 14). Distinguishing clay-dominated shale lithics from the enclosing fine-grained matrix can be challenging but is aided by textural differences such as preferred orientation of clays in ...
Context 17
... color under CPL due to preferred orientation of clays (Fig. 13). Shale lithics dominated by quartz silt are light colored under PPL, and show relatively low interference color under CPL (Fig. 13F). Under the SEM, shale lithics that have distinctly different mineral composition compared to their surround- ing matrix are readily identified (Fig. 14). Distinguishing clay-dominated shale lithics from the enclosing fine-grained matrix can be challenging but is aided by textural differences such as preferred orientation of clays in shale lithics and differential compaction around them (Fig. 14). Most shale lithics do not appear to have suffered significant vertical shortening caused ...
Context 18
... distinctly different mineral composition compared to their surround- ing matrix are readily identified (Fig. 14). Distinguishing clay-dominated shale lithics from the enclosing fine-grained matrix can be challenging but is aided by textural differences such as preferred orientation of clays in shale lithics and differential compaction around them (Fig. 14). Most shale lithics do not appear to have suffered significant vertical shortening caused by burial compaction. When present in silty and sandy laminae, shale lithics are prone to show indentation by surrounding harder grains (Fig. ...
Context 19
... differences such as preferred orientation of clays in shale lithics and differential compaction around them (Fig. 14). Most shale lithics do not appear to have suffered significant vertical shortening caused by burial compaction. When present in silty and sandy laminae, shale lithics are prone to show indentation by surrounding harder grains (Fig. ...
Context 20
... The latter can appear similar to compaction induced preferred compaction in the enclosing matrix, but lithic-internal preferred orientation not aligning with that in the matrix, as well as differential compaction around shale lithics, helps to make the distinction (note the preferred orientation of the Tununk matrix due to compaction shown in Fig. ...
Context 21
... as well as further transport in shelf seas (Schieber 2016b). Shale lithics in the Tununk Shale could be derived from unroofing of some older fully compacted mudstone/shale successions exposed by the rising Sevier orogenic belt. An additional source for the shale lithics in the Tununk Shale could be the lacuna located in northeastern Utah (Fig. 1B). The lacuna represents a submarine unconformity, from where the deposited Cenoma- nian marine shale was entirely removed by constant reworking and erosion by wave-induced currents (Ryer and Lovekin 1986). Shale lithics derived from the lacuna could then have been transported southward by storm- induced longshore currents, and finally ...
Context 22
... to the other three types of MCP, mud rip-up clasts cannot always be recognized with confidence. Nevertheless, the MCPs presented in Figures 15 and 16 can be identified as mud rip-up clasts based on several criteria. Firstly, all the images in Figure 15 were taken from areas in very fine-grained sandstone beds showing wave-ripple or combined-flow-ripple cross lamination. ...
Context 23
... the MCPs presented in Figures 15 and 16 can be identified as mud rip-up clasts based on several criteria. Firstly, all the images in Figure 15 were taken from areas in very fine-grained sandstone beds showing wave-ripple or combined-flow-ripple cross lamination. Under the conditions when rippled sandstone beds were deposited, it is more likely for muds to be transported and deposited as MCPs rather than as discrete clay and silt particles. ...
Context 24
... cross lamination. Under the conditions when rippled sandstone beds were deposited, it is more likely for muds to be transported and deposited as MCPs rather than as discrete clay and silt particles. Secondly, these MCPs show a significant degree of vertical shortening and deformation caused by burial compaction on sections cut normal to bedding (Figs. 15, 16A-C) and highly irregular shapes on sections cut parallel to bedding (Fig. 16D, E), suggesting that the original clasts had high water contents (e.g., ~ 70 vol%, Fig. 16C). Thirdly, all the MCPs show textures suggestive of bending and squeezing and act as ''supporting'' grains (Figs. 15, 16) instead of loose material that collapsed ...
Context 25
... it is more likely for muds to be transported and deposited as MCPs rather than as discrete clay and silt particles. Secondly, these MCPs show a significant degree of vertical shortening and deformation caused by burial compaction on sections cut normal to bedding (Figs. 15, 16A-C) and highly irregular shapes on sections cut parallel to bedding (Fig. 16D, E), suggesting that the original clasts had high water contents (e.g., ~ 70 vol%, Fig. 16C). Thirdly, all the MCPs show textures suggestive of bending and squeezing and act as ''supporting'' grains (Figs. 15, 16) instead of loose material that collapsed between hard sand grains (e.g., quartz and ...
Context 26
... clay and silt particles. Secondly, these MCPs show a significant degree of vertical shortening and deformation caused by burial compaction on sections cut normal to bedding (Figs. 15, 16A-C) and highly irregular shapes on sections cut parallel to bedding (Fig. 16D, E), suggesting that the original clasts had high water contents (e.g., ~ 70 vol%, Fig. 16C). Thirdly, all the MCPs show textures suggestive of bending and squeezing and act as ''supporting'' grains (Figs. 15, 16) instead of loose material that collapsed between hard sand grains (e.g., quartz and ...
Context 27
... by burial compaction on sections cut normal to bedding (Figs. 15, 16A-C) and highly irregular shapes on sections cut parallel to bedding (Fig. 16D, E), suggesting that the original clasts had high water contents (e.g., ~ 70 vol%, Fig. 16C). Thirdly, all the MCPs show textures suggestive of bending and squeezing and act as ''supporting'' grains (Figs. 15, 16) instead of loose material that collapsed between hard sand grains (e.g., quartz and ...
Context 28
... clasts consist of clays and varying amounts of fine-silt-size minerals (mostly quartz) and a small amount of pyrite. Those documented in this study range from very fine sand to fine sand in size (Table 3). In thin sections, mud rip-up clasts show dark brown color under PPL and are prone to show overall low-order interference color under CPL (Fig. 15). Due to the close compositional similarity and minimal contrast in optical properties (Tables 1, 2), it is rather challenging to recognize mud rip-up clasts when they are enclosed in a fine-grained matrix. When surrounded by translucent grains such as quartz and feldspar, mud rip-up clasts are more readily identified, even though they ...
Context 29
... minimal contrast in optical properties (Tables 1, 2), it is rather challenging to recognize mud rip-up clasts when they are enclosed in a fine-grained matrix. When surrounded by translucent grains such as quartz and feldspar, mud rip-up clasts are more readily identified, even though they may be strongly deformed between adjacent harder grains (Figs. 15, 16). Compared to optical microscopy, SEM imaging is better suited to show the outlines of mud rip- up clasts (Fig. ...
Context 30
... are enclosed in a fine-grained matrix. When surrounded by translucent grains such as quartz and feldspar, mud rip-up clasts are more readily identified, even though they may be strongly deformed between adjacent harder grains (Figs. 15, 16). Compared to optical microscopy, SEM imaging is better suited to show the outlines of mud rip- up clasts (Fig. ...
Context 31
... that muds can be deposited as floccules or mud rip-up clasts in the 15-30 cm/s flow-velocity range ( Schieber et al. 2007Schieber et al. , 2010, which is in the same range as oscillatory currents capable of generating small wave ripples in very fine and fine sands (~ 20 to 40 cm/s as suggested by Arnott and Southard 1990;Dumas et al. 2005) (Fig. ...
Context 32
... examined through both optical microscopy and SEM). In addition, the specific type of MCP can be unequivocally determined only on the basis of mineral composition and texture as revealed through SEM analysis, especially when MCPs show similarity to other ''dirty'' particles, such as phosphate particles and weathered feldspars in thin sections (Fig. 13A, C). Therefore, optical microscopy has to be integrated with SEM analysis in order to get a firm understanding of the MCP population in ...
Context 33
... the silt-bearing, calcareous mudstone facies, which was deposited at the greatest water depth in the most distal environment, the relative abundance of MCPs that can be distinctly identified (mostly fecal pellets and a minor amount of volcanic rock fragments and shale lithics) can be more than 50% (Tables 1, 4). Bedload transport in the silt-bearing, calcareous mudstone facies is reflected by the common presence of wavy laminae and wave-ripple cross lamination made dominantly of fecal pellets and foram tests. ...
Context 34
... common occurrence of storm-generated erosional surfaces and sedimentary structures (Fig. 3), as well as the shallow bathymetry associated with the lacuna located in northeastern Utah ( Fig. 1; Ryer and Lovekin 1986), all point to the likely formation of mud rip-up clasts via bottom-current-induced erosion of surficial muds ( Schieber et al. 2010;Plint 2014;Li and Schieber 2018). Because the original muds were likely deposited via bedload transport of mud floccules, derived mud rip-up clasts and floccules would have very ...
Context 35
... of the various types of MCPs and their texture in mudstones can yield important information regarding their depositional setting and provenance. The relationship between different textures of three distinct types of MCPs and different depositional environments of the Tununk Shale is summarized in Figure 17. ...
Context 36
... the outer-shelf environment, sources of sediment supply are dominantly from primary productivity with a minor amount of terrestrial input ( Li and Schieber 2018). As a result, MCPs in the resulting silt- bearing, calcareous mudstone are dominated by fecal pellets (Fig. 17, Table 4). Influenced by storm-induced bottom currents, fecal pellets tend to concentrate and form parallel to slightly wavy laminae (Figs. 6A, 17). Although locally some fecal pellets are slightly deformed and indented by foraminifera tests during compaction, the original shape and texture of fecal pellets in this setting is generally ...
Context 37
... dominantly from primary productivity with a minor amount of terrestrial input ( Li and Schieber 2018). As a result, MCPs in the resulting silt- bearing, calcareous mudstone are dominated by fecal pellets (Fig. 17, Table 4). Influenced by storm-induced bottom currents, fecal pellets tend to concentrate and form parallel to slightly wavy laminae (Figs. 6A, 17). Although locally some fecal pellets are slightly deformed and indented by foraminifera tests during compaction, the original shape and texture of fecal pellets in this setting is generally well preserved (Fig. ...
Context 38
... 4). Influenced by storm-induced bottom currents, fecal pellets tend to concentrate and form parallel to slightly wavy laminae (Figs. 6A, 17). Although locally some fecal pellets are slightly deformed and indented by foraminifera tests during compaction, the original shape and texture of fecal pellets in this setting is generally well preserved (Fig. ...
Context 39
... shallower water depth, bioturbation intensity also generally increases in the carbonate-bearing, silty and sandy mudstone and carbonate-bearing, silty mudstone to muddy siltstone facies (Li and Schieber 2018). Commonly, fecal pellets, volcanic rock fragments, and shale lithics in these facies are randomly scattered in the fine-grained Figure 11C. This volcanic rock fragment shows intergrowth of quartz (Q) and biotite (Bio). ...
Context 40
... F, weathered feldspar. E, F) A shale lithic in the fine-grained matrix in the noncalcareous, silty and sandy mudstone facies (PPL and CPL). Note that the fine-grained matrix shows relatively high interference color (due to preferred orientation resulting from compaction) relative to the shale lithic. matrix due to disruption by bioturbation (Figs. 6B, 17). Fecal pellets can also show preferential orientation and form laminae, indicating the influence of bottom currents. Silt-to sand-size volcanic rock fragments and shale lithics can be mixed with detrital grains (e.g., quartz, feldspar) and foraminifera tests of comparable grain size to form laminae. Overall, all three types of MCPs in ...
Context 41
... the inner-shelf environment, sediment supply is dominated by terrestrial input. No fecal pellets were identified in the noncalcareous, silty and sandy mudstone facies (Fig. 17). When surrounded by the fine-grained matrix, volcanic rock fragments and shale lithics commonly show indentation by harder silt and sand grains, and may show differential compaction of the surrounding matrix. When present in silty and sandy laminae, most volcanic rock fragments and shale lithics are indented or deformed by surrounding ...
Context 42
... surrounded by the fine-grained matrix, volcanic rock fragments and shale lithics commonly show indentation by harder silt and sand grains, and may show differential compaction of the surrounding matrix. When present in silty and sandy laminae, most volcanic rock fragments and shale lithics are indented or deformed by surrounding harder grains (Fig. 17). Figures 9A and 10A. This shale lithic contains common fine silt grains (mostly quartz) and clays. The preferred orientation of this shale lithic indicates that it was consolidated before deposition. Also note the distinct difference in composition between the shale lithic (noncalcareous) and its enclosing calcareous fine-grained ...
Context 43
... present in silty and sandy laminae, most volcanic rock fragments and shale lithics are indented or deformed by surrounding harder grains (Fig. 17). Figures 9A and 10A. This shale lithic contains common fine silt grains (mostly quartz) and clays. ...
Context 44
... note the distinct difference in composition between the shale lithic (noncalcareous) and its enclosing calcareous fine-grained matrix (contains a dominant amount of siliciclastic clays and fine silt and common coccolith debris). B) Closer view of the shale lithic in the red dashed box in Figure 13A. The original shape is well preserved, probably due to its relatively high content of quart silt. ...
Context 45
... original shape is well preserved, probably due to its relatively high content of quart silt. C) Closer view of the shale lithic (particle 2) in Figures 9D and 10D. D) Closer view of the shale lithic in Figure 13B. ...
Context 46
... Closer view of the shale lithic (particle 2) in Figures 9D and 10D. D) Closer view of the shale lithic in Figure 13B. E) Closer view of the shale lithic in Figure 13C. ...
Context 47
... Closer view of the shale lithic in Figure 13B. E) Closer view of the shale lithic in Figure 13C. Shale lithics in Parts C, D, and E all show indentation by harder quartz grains. ...
Context 48
... lithics in Parts C, D, and E all show indentation by harder quartz grains. F) Closer view of the shale lithic in Figure 13E. This well-rounded shale lithic has a relatively high silt content and is lighter in color than the enclosing matrix (Fig. 13E). ...
Context 49
... D) Closer view of the shale lithic in Figure 13B. E) Closer view of the shale lithic in Figure 13C. Shale lithics in Parts C, D, and E all show indentation by harder quartz grains. F) Closer view of the shale lithic in Figure 13E. This well-rounded shale lithic has a relatively high silt content and is lighter in color than the enclosing matrix (Fig. 13E). Q, quartz; Ca, calcite. All images were acquired in backscatter electron ...
Context 50
... grain size of MCPs documented in this study ranges from fine silt to medium sand size. General recognition of MCPs coarser than fine silt can be made in polished thin sections (20-25 lm Figure 15A and B. For comparison, the organic matter labeled OM in Figure 16A is the same as the one labeled in Figure 15A. The mud rip-up clasts differ slightly from each other in composition and texture. ...
Context 51
... grain size of MCPs documented in this study ranges from fine silt to medium sand size. General recognition of MCPs coarser than fine silt can be made in polished thin sections (20-25 lm Figure 15A and B. For comparison, the organic matter labeled OM in Figure 16A is the same as the one labeled in Figure 15A. The mud rip-up clasts differ slightly from each other in composition and texture. ...
Context 52
... grain size of MCPs documented in this study ranges from fine silt to medium sand size. General recognition of MCPs coarser than fine silt can be made in polished thin sections (20-25 lm Figure 15A and B. For comparison, the organic matter labeled OM in Figure 16A is the same as the one labeled in Figure 15A. The mud rip-up clasts differ slightly from each other in composition and texture. ...
Context 53
... mud rip- up clasts are ''flattened'' to some degree and are highly indented by surrounding harder grains. B) Same view of the mud rip-up clasts (outlined by blue dashed lines) and volcanic rock fragment (white arrow) shown in Figure 15C and D. The rip-up clast, as well as some biotite flakes, are deformed between harder grains. C) Closer view of the mud rip-up clasts in Part B. The boundary of this rip-up clast in the left corner is not very distinct (question mark in Part B). ...
Similar publications
A horizontal core from the Upper Cretaceous Eagle Ford Group of South Texas provides a rare opportunity to study lateral heterogeneity of lithology, total organic carbon (TOC), and pore systems in a calcareous-argillaceous mudstone from the subsurface. The core is 182 ft (55.5 m) long and spans between 2 and 4 ft (0.6 and 1.2 m) of stratigraphic se...
Clay minerals in fine‐grained marine sedimentary successions are most commonly considered to be detrital in origin and have been used extensively by geologists as indicators of palaeoclimate conditions in the hinterland. Most of these previous studies, however, were not designed to address in depth the potential effects of mixing clay minerals from...
Citations
... Numerous studies have demonstrated that dark-black reductive carbonaceous sedimentary layers are widely developed in the roof and surrounding rocks of giant or large porphyry Mo deposits, such as the Shuidigou Formation of the Proterozoic Taihua Supergroup and the Xianrenchong Formation of the Proterozoic Luzhenguan Group, which contains graphitic schist and graphite gneiss; the Baishugou, Sanchuan, Nannihu and Meiyaogou Formations of the Neoproterozoic Luanchuan Group, which contains carbonaceous slate and shale developed in the East Qinglin-Dabie Mo mineralization belt ( Figure 1) [22,[50][51][52][53][54][55]60,61]; and the Cretaceous Mancos Formation and Mesaverde Group, which contains coal and carbonaceous shale and siltstone that are widely distributed in the Climax-Henderson Mo mineralization belt in North America [25,[62][63][64][65][66][67]. Carbonaceous sedimentary layers provide reductive agents for the porphyry mineralization system and serve as an ideal natural water-resisting layer, critical factors, and conditions for forming high-grade porphyry Mo ores. ...
... Orebodies occur in the Mesoproterozoic silver plume granite pluton [3,4,78,79]. Previous studies have demonstrated the prevalence of carbonaceous shale, sandstone, mudstone, oil shale, and coal within the Wasatch Formation and the Mesaverde Group in Wyoming and Utah in Colorado [25,[62][63][64][65][66][67]. Technically, the mean recoverable gas resources have been estimated at 7 × 10 12 m 3 with primary sources being coal, carbonaceous shale and siltstone in the Mesaverde Group [80]. ...
Porphyry Mo deposits are the most important type of Mo resource. They result from a high oxygen fugacity of the parent magma, which acts as an effective indicator for evaluating the mineralization. In the ore-forming system of porphyry Mo deposits, sulfur exists mainly as sulfate in highly oxidized magma but as sulfide in ores. What triggers the reduction in the mineralization system that leads to sulfide precipitation has not yet been determined. Most of the previous studies have focused on the origin and evolution of the ore-forming parent magma, and the effects of reductive surrounding rocks on porphyry mineralization have been ignored. In this study, a comprehensive geological–geochemical investigation and review have been performed on the typical porphyry Mo deposits, the Nannihu-Sandaozhuang, Yuchiling, and Shapingou deposits in China, and the Mt. Emmons deposits in America. Black carbonaceous sedimentary layers commonly surround porphyry Mo ores, which are widely altered and discolored during mineralization. CH4 is commonly present in fluid inclusions in the main mineralization stage, and the δ13CV-PDB values of calcite and fluid inclusions from the altered surrounding rocks and ore minerals are generally low and significantly different from those of marine sedimentary carbonate rocks, indicating that the involvement of reductive components from carbonaceous surrounding rocks might be key to the redox state transformation leading to mineral precipitation. On the other hand, the CH4 produced by the thermal decomposition of organic matter or carbonaceous reaction with H2O can diffuse into the ore-forming system along the structural fractures and reduce the SO42− in the ore-forming hydrothermal fluids to form sulfide precipitation without direct contact between the intrusion and the carbonaceous surrounding rocks. Moreover, the CH4 content controls the location of the orebody formation with the high content producing orebodies mainly in the porphyry intrusion, while the low CH4 content results in the orebodies mainly occurring at the contact zone between the porphyry and carbonaceous surrounding rocks. Compared to the magmatic stage of mineralization, the involvement of reductive components in the carbonaceous surrounding rocks during the hydrothermal stage is more favorable for forming giant/large Mo deposits. The highly oxidized porphyry with reductive carbonaceous surrounding rocks or Fe-rich volcanic rocks offers a new indicator for efficiently evaluating porphyry Mo mineralization.
... Nonetheless, parsing mudstone depositional processes is challenging because mudstone: (1) is typically darkcolored and fine-grained; (2) can appear homogeneous and featureless at initial inspection (e.g., Schieber, 2003); (3) is severely affected by weathering, which severely degrades most textural attributes (Macquaker et al., 2010b); and (4) is severely affected by mechanical compaction that generates planar fabrics and obscure the recognition of primary sedimentary structures (Schieber et al., 2010;Plint et al., 2012;Schieber and Bennett, 2013). Compaction also affects primary grain arrangements, especially in mudstone enriched in water-rich aggregates (e.g., floccules, intraclasts, fecal pellets) that are generally flattened and deformed as burial proceeds (Schieber et al., 2010;Schieber, 2016b;Li and Schieber, 2018). ...
... The petrographic examination focused on the analysis of the overall composition and distinctive characteristics of the microfacies preserved in early diagenetic concretionary horizons, and on the identification of various composite particles. The term "composite particle" is hereafter used to refer to aggregate grains composed of a mixture of multiple clay-to silt-sized mineral grains (sensu Li and Schieber, 2018). Detailed petrographic examination of thin sections in both plane-polarized light and cross-polarized light was conducted using a Zeiss Photo 2 petrographic light microscope. ...
... High magnification (<5 μm) CCI in secondary electron mode under the SEM was critical for the identification of composite particles as discrete entities that were not (or barely) captured in backscattered electron images because there is little compositional contrast between such particles (they consist mostly of calcite) and the carbonate (calcite) cement that surrounds them (cf. Li and Schieber, 2018;Schieber et al., 2019;. Mudstone lithofacies were described using the nomenclature scheme broadly proposed by Macquaker and Adams (2003) and Lazar et al. (2015b). ...
Fine-grained sedimentary rocks generally undergo severe mechanical compaction during burial, which complicates the recognition of primary mudstone fabrics and associated sedimentary features. Early diagenetic concretions, however, provide a rare glimpse of primary fabrics because cement filling the pore space prevents the collapse of original grain arrangements. Hand specimens of concretions collected from the basal condensed section of the Late Jurassic-Early Cretaceous Vaca Muerta Formation (Neuquén Basin, Argentina), allow for analysis of sedimentary processes responsible for the dispersal, accumulation and burial of organic carbon-rich sediment in an epicontinental sea. Representative samples from central basin depositional localities were examined by optical, scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS). Petrographic observations were complemented with palynological and organic geochemical analyses. Close examination of uncompacted fabrics reveals a significantly more complex and dynamic depositional scenario than previously assumed (suspension settling). Although many of the component grains in the studied samples were originally delivered to the sediment–water interface by suspension settling processes (i.e., marine snow, hypopycnal plumes, pumice rafts), there is substantial evidence of episodic sedimentation controlled by punctuated events of seafloor disturbance and erosion. The common presence of muddy intraclasts indicate that the seafloor was frequently reworked by bottom currents that caused the widespread distribution of organic carbon-rich sediment across distal basin depositional environments. Bottom current circulation supplied oxygen to the sediment–water interface and created suitable conditions for benthic life, contravening the assumption of bottom water anoxia as a prerequisite for organic carbon preservation. The excellent preservation state of freshwater algae (Pediastrum complex) suggests that organic matter contained inside composite mud particles can travel long distances before being deposited in distal depositional settings. Encapsulation protects organic components from mechanical/biogenic degradation and provides an anoxic microenvironment for preventing the oxidation of the organic matter contained inside of mud composite grains. The study shows that organic carbon encapsulation may be an important mechanism for organic carbon preservation in relatively energetic and non-anoxic settings, calling for a critical reappraisal of the processes responsible for the sequestration of organic carbon from the biosphere and its long-term storage in organic-rich mudstone successions.
... Petrographic examination indicates that dolomite grains are present only in FA3 but are absent in FA1, indicating that they are of detrital origin and were derived from hinterland erosion. Dolomite has not been observed anywhere in the Tununk Shale (Li and Schieber 2018b), hence its presence in FA3 above the T-F sequence boundary indicates that the shift from the Tununk to Ferron depositional system is accompanied by distinct changes in provenance. This is yet another strong piece of evidence that the Tununk and Ferron depositional systems separated by the T-F sequence boundary are genetically different from each other. ...
In models of siliciclastic sequence stratigraphy, the sequence boundary in distal marine environments, where the strata are mudstone dominated, is usually considered a correlative conformity—the seaward extension of a subaerial unconformity. Despite its wide usage in the literature, objective recognition criteria of a correlative conformity remain lacking, largely due to the limited number of case studies directly examining the characteristics of sequence boundaries in offshore mudstone-dominated environments. This study focuses on the mudstone-dominated transitional interval between the Tununk Shale Member and the Ferron Sandstone Member of the Mancos Shale Formation exposed in south-central Utah to extend our understanding of the characteristics of a sequence boundary developed in the distal shelf environment of a ramp setting. An integrated sedimentologic, petrographic, and sequence stratigraphic analysis was conducted to characterize the sequence boundary that separates the Tununk from the Ferron depositional system (hereafter referred to as the T-F sequence boundary) and its lateral along-depositional-strike variability.
Although manifest as a mudstone-on-mudstone contact, the T-F sequence boundary in all three measured sections is a subtle unconformity, characterized by erosional truncation below and onlap above, and marks a distinct basinward shift in facies association. The T-F sequence boundary also marks the change from the Tununk offshore mud-belt system to the Ferron Notom delta system, and therefore represents a surface that divides two genetically different depositional systems. Based on two distinct marker beds that bracket the T-F sequence boundary, the T-F sequence boundary can be traced across the study area with confidence. The lateral variability in the characteristics of the T-F sequence boundary along depositional strike indicates that it was produced by an allogenic base-level fall.
Offshore shelfal mudstone strata may contain a significantly higher incidence of subtle unconformities analogous to the T-F sequence boundary than currently appreciated. Careful sedimentologic and petrographic analyses, combined with lateral correlations constrained by reliable chronostratigraphic marker beds, are essential for identifying subtle unconformities in shelf mudstone successions. The accurate recognition of subtle unconformities in mudstone strata is critical to apply the sequence stratigraphic approach appropriately to distal shelf environments, as well as to better constrain the timing and cause (allogenic vs. autogenic) of relative changes of sea level recorded in these rocks.
... Likely erosion from underlying mudstones suggests that F3 sediments once consisted of mud-dominated composite particles (MCPs) that plausibly ranged in size from coarse silt to sand (Li et al., 2021). MCPs can survive substantial amounts of reworking and transport (Schieber et al., 2010;Schieber, 2016), and are an important component of modern and ancient muddy deposystems (Nanson et al., 1986;Rust & Nanson, 1989;Wakelin-King & Webb, 2007;Li & Schieber, 2018;Schieber et al., 2019). Smoot & Lowenstein (1991) report that scour and fill structures, beds of intraclasts and stormproduced graded beds are common in saline and hypersaline terrestrial lakes. ...
... Smoot & Lowenstein (1991) report that scour and fill structures, beds of intraclasts and stormproduced graded beds are common in saline and hypersaline terrestrial lakes. Although positive identification of MCPs requires scanning electron microscopy (Schieber, 2016;Li & Schieber, 2018), the high benthic-energy levels implied by erosion and bedform buildup strongly suggest their presence. ...
Mudstone‐dominated lacustrine strata in the Pahrump Hills area of Gale Crater, Mars, have the most extensive data set of physical and geochemical observations yet collected. Although sparse by Earth standards, a source‐to‐sink portrayal of the sedimentary system that differs substantially from previous work has been extracted by integrating sedimentology, stratigraphy, mineral and elemental analyses, geochemical modelling, laboratory experiments and Earth analogues in a sequence‐stratigraphic and palaeogeographic framework. Approximately 3.5 Ga, these 15 m thick strata contain five facies that range from fine to coarse detrital mudstone with abundant sediment‐incorporative evaporite pseudomorphs. The section is dominated by first‐cycle grains of minimally weathered primary igneous minerals but with four distinct compositions. Bedding in the mudstones comprises planar‐parallel beds, current ripples and wave‐induced structures, with common and widespread truncation. The absence of primary desiccation and synaeresis cracks is probably due to minimal clay‐mineral content, as supported by lab experiments. Evaporite minerals formed on and within detrital muds shortly after accumulation by evapoconcentration and cooling. The succession contains 16 parasequences in five depositional sequences with all the sequence‐stratigraphic elements known from terrestrial strata. Two of the sequence boundaries are unconformities that record significant shifts in the behaviour and palaeogeographic configuration of the fluvio‐lacustrine system. This contrasts with the previous view that all facies are genetically related. Most of the variability in rock composition can be attributed to stratigraphic changes in provenance that integrate changing drainage basin configurations, type of exposed bedrock and changes in weathering regime. These strata are interpreted as evaporative lake deposits that accumulated in an underfilled lake basin with closed surface hydrography but through‐flowing groundwater. Lake waters were saline to hypersaline, and lake levels, shorelines and salinities fluctuated greatly at various temporal scales.
... They are the end result of the interaction between actual particles and currents of water or air. It is for that reason that, for example, carbonate classifications have an aspect that reflects depositional energy (textural maturity, Folk, 1959;amount of mud, Dunham, 1962), and why there are mudstones that by way of fluid dynamics started out as an accumulation of sand-sized particles (Rust & Nanson, 1989;Sternberg et al., 1999;Schieber et al., 2010;Schieber, 2016;Laycock et al., 2017;Li & Schieber, 2018;Schieber et al., 2019;Li et al., 2020Li et al., , 2021. If that circumstance goes unrecognized when a seemingly simple mudstone is investigated, erroneous interpretations of depositional processes and ambient energy Ó 2022 International Association of Sedimentologists., Sedimentology conditions of these rocks are likely to follow. ...
... The origin of these fecal pellets can be related to planktonic grazers (e.g. copepods) that fed on coccolithophores in a water column with high biological activity (Li and Schieber 2018). After deposition by suspension settling, fecal pellets are intermittently reworked and transported in bedload by bottom currents during high-energy events. ...
Fine-grained sedimentary deposits generally compact severely during burial, which complicates the recognition of primary mudstone fabrics and associated sedimentary features. Early diagenetic concretions, however, provide a rare glimpse of primary fabrics because cement filling the pore space prevents the co- llapse of original grain arrangements.
For this study, we analyzed cut and polished samples of mudstone event beds preserved inside early-diagenetic concretions from the Late Jurassic-Early Cretaceous Vaca Muerta Formation, Neuquén Basin, Argentina (Otharán et al. in press). Hand specimens of carbonate concretions were collected from the organic-rich basal section of the Vaca Muerta Formation at basinal settings (Arroyo Mulichinco and Río Neuquén sections). Representative samples were examined by optical (n=18) and scanning electron microscopy (SEM, n=20). Energy dispersive X-ray spectroscopy (EDS) was applied to determine the mineral composition of grains.
The examination of thin sections and SEM samples shows the presence of mud aggregates as common components of mudstone event beds (Fig. 1A). Mud aggregates are between 70 and 350 μm in size, appear dark to pale brownish in thin section, and are composed of micron size clay and silt component grains. These aggregates are not randomly distributed within mudstone event beds; but are commonly concentrated in ripple laminasets that range in thickness from 0.2 to 1.4 mm.
SEM observations show that the original fabric of mud aggregates, though uncompacted, is still dis- rupted by expansive growth of microcrystalline calcite cement. Based on high magnification SEM characte- rization (< 5 μm), two different types of mud aggregates were identified (Fig. 1B). The first type involves mud intraclasts: subangular to subrounded dark brownish aggregates that range in size from 200 to 350 μm (Fig. 1C). The interior of these intraclasts contains detrital clays (Fig. 1D) and silt-size feldspars. Calcite cement is filling the interstitial spaces between detrital clays. Diagenetic quartz is also present (Fig. 1D). In EDS (Fig. 1E), Ca has the highest peak (in response to calcite cement). Subordinate peaks are Si, Al, K and Na, which are associated with detrital clays and silt grains. The mud intraclasts likely originated through the erosion of surficial, water-saturated muds (85-90 vol.%, Schieber 2011) by swift bottom currents (rip up clasts, Schieber et al. 2010). The subsequent bedload transport of eroded intraclasts led to the formation and migration of current mud ripples, resulting post-compaction in current-laminated mudstones. Shortly after deposition, pore spaces of the original sediment, including those of mud intraclasts, were filled with microcrystalline calcite-cement as concretion growth was initiated. The second type involves fecal pellets: subrounded to rounded pale brownish aggregates of smaller size than mud intraclasts (70-230 μm, Fig. 1F). At high SEM magnification fecal pellets are seen to mainly consist of the remains of calcareous coccoliths (Fig. 1G). Diagenetic quartz and clays are common inside fecal pellets (Fig. 1G). Coccolithophore debris is not easy to identify inside fecal pellets due to intense diagenetic overprint, such as recrystallization of primary components (Birgenheier et al. 2017). In EDS fecal pellets show a main peak of Ca and subordina- ted peaks of Si and Al (Fig. 1H), with no significant difference when compared to intraclasts. The origin of these fecal pellets can be related to planktonic grazers (e.g. copepods) that fed on coccolithophores in a water column with high biological activity (Li and Schieber 2018). After deposition by suspension settling, fecal pellets are intermittently reworked and transported in bedload by bottom currents during high-energy events. The latter are indicated by the presence of scours, internal lamina truncations, mud intraclasts and current-generated mud ripples within the studied deposits.
The recognition of both types of mud aggregates within Vaca Muerta mudstone event beds suggests an interplay between suspension settling and bottom current activity in a basinal setting. The evidence of erosion and reworking of the seafloor by bottom currents has implications for understanding the deposi- tional history of the Vaca Muerta Formation. The results from this study indicate that, in basinal settings, the basal organic-rich condensed section of the Vaca Muerta Formation is related to a significantly more complex and dynamic depositional setting than previously assumed (suspension settling paradigm), with a frequent occurrence of bedload sediment transport. The depositional setting for Vaca Muerta organic-rich shales needs to be re-evaluated.
... Ancient, high-energy muddy coastlines are notoriously difficult to recognize from geological datasets. Only recently sedimentologists have begun to erect recognition criteria for bedload transport of mud and wave-and current-dominated seafloor reworking 21,[68][69][70][71][72][73] , while the competing diagenetic pathways in those successions are not yet fully understood at the scale at which they are most pronounced (the millimetre to centimetre-scale). More texture-specific, combined S and Fe isotopic studies will corroborate the here proposed relationship between (1) microscale reservoir effects, (2) methane and/or sulfide oxidation and (3) high-frequency redox cycling associated with bioturbation and surface sediment reworking. ...
Pyrite-δ³⁴S and -δ⁵⁶Fe isotopes represent highly sensitive diagnostic paleoenvironmental proxies that express high variability at the bed (< 10 mm) scale that has so far defied explanation by a single formative process. This study reveals for the first time the paleoenvironmental context of exceptionally enriched pyrite-δ³⁴S and -δ⁵⁶Fe in bioturbated, storm-reworked mudstones of an early Ordovician storm-dominated delta (Tremadocian Beach Formation, Bell Island Group, Newfoundland). Very few studies provide insight into the low-temperature sulfur and iron cycling from bioturbated muddy settings for time periods prior to the evolution of deep soil horizons on land. Secondary ion mass spectroscopy (SIMS) analyses performed on Beach Formation muddy storm event beds reveal spatially distinct δ³⁴S and δ⁵⁶Fe values in: (a) tubular biogenic structures and trails (δ³⁴S ~ +40‰; δ⁵⁶Fe ~ −0.5‰), (b) silt-filled Planolites burrows (δ³⁴S ~ +40‰; δ⁵⁶Fe ~ +0.5 to + 2.1‰), and (c) non-bioturbated mudstone (δ³⁴S ~ +35‰; δ⁵⁶Fe ~ +0.5‰). δ³⁴S values of well above + 40.0‰ indicate at least some pyrite precipitation in the presence of a ³⁴S-depleted pore water sulfide reservoir, via closed system (Raleigh-type) fractionation. The preferential enrichment of ⁵⁶Fe in Planolites burrows is best explained via microbially-driven liberation of Fe(II) from solid iron parent phases and precipitation from a depleted ⁵⁴Fe dissolved Fe(II) reservoir. Rigorous sedimentological analysis represents a gateway to critically test the paleoenvironmental models describing the formation of a wide range of mudstones and elucidates the origins of variability in the global stable S and Fe isotope record.
... Their suitability for this purpose is predicated on the assumption that their apparent homogeneity relates to relatively simple provenance (for example, products of chemical weathering) and transport history. Recent petrographic studies of some marine mudstones, however, have revealed that these rocks may consist of common coarse silt to sand-sized muddominated composite particles (MCPs) (particles consisting of multiple clay-sized or silt-sized mineral grains; sensu Li & Schieber, 2018). If the depositional grain size of mudstones can be determined to be relatively coarse due to the dominant presence of MCPs (rather than finegrained based on the apparent grain size after compaction), the transport and deposition of muds are likely subject to more complex and dynamic processes (for example, traction currents) besides passive settling from suspension (Plint, 2014;Schieber, 2016;Laycock et al., 2017;Schieber et al., 2019). ...
... Because of their original water-rich nature and minimal lithological contrast, the recognition of autochthonous MCPs in the rock record is greatly facilitated when they are surrounded by grains/particles with sufficient compositional or textural contrast (Figs 7B and 10). Outside of such fortuitous instances, outlines of original water-rich MCPs in ancient mudstones are no longer discernible and they merge into what is commonly referred to as 'fine-grained matrix' (Figs 7D, 9I, 9J, 10E and 10F;Laycock et al., 2017;Li & Schieber, 2018;Shchepetkina et al., 2018). Therefore, the apparent decrease in grain size and increase in the proportion of 'fine-grained matrix' from the proximal to distal marine environments does not necessarily reflect a decrease in the actual grain size of the transported particles, but rather a decrease in the amount of more easily recognized allochthonous MCPs, and a concomitant increase in autochthonous MCPs with low textural preservation potential (Fig. 10). ...
... Considering the close compositional and textural similarity, these water-rich MCPs, even before compaction (E), are not easy to differentiate from one anotherimagine how challenging it would be to identify individual MCPs without outlines in (E). USA; Li & Schieber, 2018). The types of allochthonous MCPs documented in the Dunvegan prodelta mudstones are likely not exhaustive because any lithic fragments with fine-grained internal texture may end up as allochthonous MCPs in marine mudstones. ...
Despite the fact that mud‐dominated composite particles have increasingly been recognized as important components of marine mudstones, the characteristics, types and origins of these composite particles remain poorly understood. This incomplete understanding of critical mudstone parameters (for example, depositional grain size, composition at the particle scale and provenance) severely limits the ability to accurately interpret the conditions (for example, depositional environment and climate) under which these rocks were deposited. Herein, detailed petrographic analysis was conducted in core samples from a transect of contemporaneous proximal to distal deposits from the Cenomanian Dunvegan Formation, a fluvial‐dominated delta system in the Western Canada Sedimentary Basin. Within the well‐developed depositional framework, mud‐dominated composite particles can be tracked along the depositional profile of the Dunvegan Formation from the fluvial to the marine realm (from incised valley to distal prodelta). By following these particles from source (hinterland erosion) to sink (offshore deposition), the origin and dispersal of various types of mud‐dominated composite particles in marine mudstones can be unequivocally determined. Mud‐dominated composite particles derived from a wide range of origins are differentiated. Allochthonous mud‐dominated composite particles, supplied by rivers draining the hinterland, comprise volcanic rock fragments (vitric or felsic in composition), chert fragments, shale lithics (clay‐mineral‐rich or quartz‐rich in composition), metamorphic rock fragments and chlorite/siderite clasts. Autochthonous mud‐dominated composite particles include rip‐up clasts (argillaceous, sideritic or siliceous in composition) formed from intra‐basinal erosion and contemporaneous floccules. The recognition of mud‐dominated composite particles shows that the Dunvegan prodelta ‘mudstones’ are much coarser grained and more heterogeneous in terms of their petrographic composition than the grain size of their component minerals would suggest. Results of this study call for a critical reappraisal of the composition and actual grain size of mudstones in general. Recognition of mud‐dominated composite particles can provide valuable insights to unravel their provenance, transport history and depositional setting, and will greatly enhance their utility as palaeoenvironmental archives.
... Por otro lado, los agregados de fango (mud-dominated composite particles (Li y Schieber, 2018b), constituyen componentes comunes de las rocas sedimentarias de grano fino. Existen diferentes tipos de agregados, los cuales se diferencian por su tamaño, composición y contenido de agua intersticial. ...
... Existen diferentes tipos de agregados, los cuales se diferencian por su tamaño, composición y contenido de agua intersticial. Entre ellos se encuentran (Li y Schieber, 2018b): 1) flóculos, agregados con elevado contenido de agua (85%) compuestos principalmente por una mezcla de arcillas, materia orgánica y limo fino unidos entre sí por enlaces tipo van der Waals ( Fig. 5.1, Schieber et al., 2007); 2) intraclastos arcillosos (mud rip-up clasts), agregados con un contenido de agua de hasta 85 % originados a partir de la erosión de sustratos fangosos (Macquaker y Gawthorpe, 1993;Schieber et al., 2010); y 3) pellets fecales, los cuales pueden estar compuestos por una mezcla de materia orgánica y placas de cocolitos (Macquaker et al., 2010b;Birgenheier et al., 2017), o bien por arcillas (Macquaker et al., 2010b). ...
... Se interpreta que los espacios ocupados por cemento carbonático y cuarzo diagenético representan los espacios porales originales existentes dentro de estos agregados, posiblemente ocupados por agua. A diferencia de intraclastos reconocidos en depósitos compactados Li y Schieber, 2018b), los intraclastos presentes en las muestras analizadas preservan la forma y tamaño original, dado que se encuentran contenidos en el interior de concreciones carbonáticas prácticamente exentas de compactación. ...
The Vaca Muerta Formation is a fine-grained marine stratigraphic unit accumulated during the Late Jurassic-Early Cretaceous in the Neuquén Basin, Argentina. This contribution presents a sedimentological and stratigraphic analysis of Vaca Muerta´s shales emerged from the integration of regional and detailed outcrop research and subsurface data gathered from the study of different well cores.
The fieldwork comprised, on the one hand, the description of 7 stratigraphic sections of the Early Tithonian-Early Valanginian interval widely distributed across the western region of the Neuquén province and southern Mendoza province. The sedimentological and sequence-stratigraphic analysis of the different stratigraphic sections allowed integrating them into a regional N-S oriented correlation panel covering an area of 340 km. Five composite depositional sequences were recognized (GS1-GS5). They represent the evolution of a complex mixed shelf/ramp depositional system comprising from basinal/slope facies (central area) to ramp (northern area) and mixed-shelf to continental deposits (southern area). Depositional sequences are represented by thin, organic-rich (up to 10 % TOC), mudstone dominated transgressive cycles, whereas regressive cycles are commonly thicker and mainly composed of organic-lean, carbonate and mixed (carbonate/siliciclastic) facies.
On the other hand, aiming at studying the transport and accumulation processes of Vaca Muerta´s organic-rich shales, hand specimen samples of early-diagenetic carbonate concretions were collected from the organic-rich basal condensed section deposited in basinal settings. Concretion samples were thoroughly examined (mm- μm scale) integrating the observation of macroscopic polished samples, thin sections and scanning-electron microscope analyses. The evidence found inside concretions suggest an origin related to muddy underflows, possibly triggered by slope failures on the western margin of the basin. The bedload and suspended-load transport of mud within these muddy underflows would have resulted in the accumulation of graded event mudstone beds exhibiting ripple lamination. Petrographic analysis demonstrates that muddy underflows would have been important mechanisms for reworking the seafloor and redistributing mud in basinal settings. Furthermore, muddy underflows would have been effective processes for organic matter concentration in organic-rich mudstone strata (up to ≈ 6 % TOC).
The subsurface studies comprised the sedimentological analysis of seven well cores of the Vaca Muerta Formation, representing a total core data of 387 m. The descriptive facies analysis at centimeter scale allowed the recognition of a distally steepened mixed ramp system. Sediment delivery to basinal settings was mainly controlled by muddy underflows triggered by different mechanisms. Deposition from muddy underflows would have interacted with fallout processes from buoyant plumes and marine snow from the water column. The stacking pattern of the studied core deposits shows ≈ 0.5 to 3 m-thick parasequences building up prograding/retrograding parasequence sets of high-order depositional cycles (10-20 m thick).
... Similarly, the sedimentary facies in this stratigraphic interval appear variable in Mastcam images, leading to an overall interpretation that the rocks consist of heterogeneously interbedded mudstones, siltstones, and sandstones (i.e., heterolithic). Beds that have the appearance of sandstones in Mastcam images could be composed of sand-sized aggregates of mud-sized grains (for examples on Earth see Schieber andSouthard, 2009 andLi andSchieber, 2018), which would produce uniform LIBS composition and thus fall within GSR1. Thus, the depositional environment is most consistent with shallow, near-shore lacustrine facies, possibly lacking a supply of sand-sized grains. ...
The lowermost exposure of the Murray formation in Gale crater, Mars, was interpreted as sediment deposited in an ancient lake based on data collected by the Curiosity rover. Constraining the stratigraphic extent and duration of this environment has important implications for the paleohydrology of Gale. Insights into early Martian environments and paleofluid flow velocity can be obtained from grain size in rocks. Visual inspection of grain size is not always available for rocks investigated at field sites on Mars due to limited image coverage. But grain sizes can also be estimated from the Gini Index Mean Score, a grain‐size proxy that uses point‐to‐point chemical variations in ChemCam Laser Induced Breakdown Spectroscopy data. New Gini Index Mean Score results indicate that the Murray formation is dominated by mudstones with grains smaller than the spatial resolution of all rover cameras. Intervals of fine to coarse sandstone also are present, some of which are verified using observations of grain size and sedimentary structures in associated images. Overall, results demonstrate that most of the Murray consists of mudstone, suggesting settling of grains from suspension in low energy depositional environments such as lakes. Some of the mudstones contain desiccation cracks indicating periods of drying with a lowering of lake water level. However, beds and lenses of cross‐bedded sandstones are common at specific intervals, suggesting episodes of fluvial and possibly eolian deposition. The persistence of lacustrine deposits interspersed with fluvial deposits suggests that liquid water was sustained on the Martian surface for tens of thousands to millions of years.
