Magnetostratigraphy of the late Neogene purisima formation, Santa Cruz County, California

Madrid, V.; Stuart, Robert M.; Verosub, Kenneth L.

doi:10.1016/0012-821x(86)90198-6

Cited by 22 publications

(26 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The diatom-bearing lower 90 meters of the Purisima Formation yielded diatom assemblages indicating a similar age, 7–5 Ma [35]. A paleomagnetic study of the Purisima Formation indicates the Santa Cruz section is 6.07 to 2.47 Ma in age, with a depositional hiatus from 4.5 to 3.5 Ma [37]; this depositional hiatus is marked by one of the bonebeds investigated by this study.…”

Section: Geologic Backgroundsupporting

confidence: 56%

Comparative Taphonomy, Taphofacies, and Bonebeds of the Mio-Pliocene Purisima Formation, Central California: Strong Physical Control on Marine Vertebrate Preservation in Shallow Marine Settings

Boessenecker

Perry²,

Schmitt

2014

PLoS ONE

View full text Add to dashboard Cite

BackgroundTaphonomic study of marine vertebrate remains has traditionally focused on single skeletons, lagerstätten, or bonebed genesis with few attempts to document environmental gradients in preservation. As such, establishment of a concrete taphonomic model for shallow marine vertebrate assemblages is lacking. The Neogene Purisima Formation of Northern California, a richly fossiliferous unit recording nearshore to offshore depositional settings, offers a unique opportunity to examine preservational trends across these settings.Methodology/Principal FindingsLithofacies analysis was conducted to place vertebrate fossils within a hydrodynamic and depositional environmental context. Taphonomic data including abrasion, fragmentation, phosphatization, articulation, polish, and biogenic bone modification were recorded for over 1000 vertebrate fossils of sharks, bony fish, birds, pinnipeds, odontocetes, mysticetes, sirenians, and land mammals. These data were used to compare both preservation of multiple taxa within a single lithofacies and preservation of individual taxa across lithofacies to document environmental gradients in preservation. Differential preservation between taxa indicates strong preservational bias within the Purisima Formation. Varying levels of abrasion, fragmentation, phosphatization, and articulation are strongly correlative with physical processes of sediment transport and sedimentation rate. Preservational characteristics were used to delineate four taphofacies corresponding to inner, middle, and outer shelf settings, and bonebeds. Application of sequence stratigraphic methods shows that bonebeds mark major stratigraphic discontinuities, while packages of rock between discontinuities consistently exhibit onshore-offshore changes in taphofacies.Conclusions/SignificanceChanges in vertebrate preservation and bonebed character between lithofacies closely correspond to onshore-offshore changes in depositional setting, indicating that the dominant control of preservation is exerted by physical processes. The strong physical control on marine vertebrate preservation and preservational bias within the Purisima Formation has implications for paleoecologic and paleobiologic studies of marine vertebrates. Evidence of preservational bias among marine vertebrates suggests that careful consideration of taphonomic overprint must be undertaken before meaningful paleoecologic interpretations of shallow marine vertebrates is attempted.

show abstract

Section: Geologic Backgroundsupporting

confidence: 56%

Comparative Taphonomy, Taphofacies, and Bonebeds of the Mio-Pliocene Purisima Formation, Central California: Strong Physical Control on Marine Vertebrate Preservation in Shallow Marine Settings

Boessenecker

Perry²,

Schmitt

2014

PLoS ONE

View full text Add to dashboard Cite

show abstract

“…Late Neogene clockwise rotations of 35°−60° occur within a kilometre of the San Gregorio Fault zone (Horns & Verosub 1995). However, magnetostratigraphic studies of 6–7 Ma rocks directly overlying the Santa Cruz Mudstone around the city of Santa Cruz indicate no significant rotation (Madrid et al . 1986).…”

Section: Palaeostress Orientations From Sandstone Intrusionsmentioning

confidence: 99%

Fluidized sandstone intrusions as an indicator of Paleostress orientation, Santa Cruz, California

Boehm

Moore

2002

Geofluids

View full text Add to dashboard Cite

The late Miocene sandstone intrusions of northern Santa Cruz County, California, are the largest subaerial exposures of clastic intrusions on earth. The intrusions are sourced from a sandstone, underlying mudstone, accumulated in an outer shelf to upper slope environment. Dikes are the most frequent intrusion type, reach the greatest thickness and tend to strike north‐east and dip steeply. One giant dike is more than 150 m wide. Sills are least frequent, locally > 8 m thick and have no clear preferred geographical distribution. Clustered intrusions are commonly < 10 cm thick and mostly composed of dikes of various attitudes. The majority of the intrusions probably were injected shallowly as some extrude onto the seafloor. The local seafloor extrusion also indicates injection during the deposition of the Santa Cruz Mudstone (7–9 Ma). The intrusions are concentrated at the basin margin. Fluid pressure at the centre of the basin and perhaps hydrocarbons were communicated to the basin margin through the then sand, causing fluid overpressures that contributed to the fluidization and intrusion into the overlying mudstone. Primarily north‐east‐striking, steeply dipping dikes and secondarily, shallowly dipping sills are most significant in terms of regional connectivity of intrusions and physical dilation of the formation. The orientation of the dikes and sills indicates a regional stress field with a horizontal NE–SW maximum and a NW–SE minimum compressive direction. The simultaneous development of dikes and sills suggests similar magnitudes of the minimum and intermediate principal stresses. Preferential weakness along bedding contributed to the development of sills. Palaeomagnetic data indicate no significant block rotation around a vertical axis. The maximum principal stress direction indicated by the intrusions is about 55° to the San Gregorio Fault and about 70° to the San Andreas Fault during the late Miocene. This stress field is similar to the modern stress field and suggests moderate fault weakness.

show abstract

“…Therefore, in California, the Miocene/Pliocene Epoch boundary falls within Barron's (1981) Subzonc b of his Aritzschia reinholdii Zone. The last common occurrence of Rowcia californica lies in the upper part of magnetic polarity Chron 6 in California (Madrid 1982) and has an estimated age of about 6.0 Ma (Barron and Keller 1983). The first occurrence of Thalassiosira oestrupii is correlated to a level within the lower reversed event of the Gilbert polarity Chron in the equatorial Pacific by Burckle (1978) and has an estimated age of 5.1 Ma (Barron et al 1985;Baldauf 1985).…”

Section: Introductionmentioning

confidence: 99%

Thalassiosira praeoestrupii: A New Diatom Species for Recognizing the Miocene/Pliocene Epoch Boundary in Coastal California

Dumont¹,

Baldauf²,

Barron³

1986

Micropaleontology

View full text Add to dashboard Cite

A new diatom species, Thalassiosira praeoestrupii Dumont, Baldauf and Barron, is described. The first occurrence of T. praeoestrupii in coastal California diatom-bearing outcrops occurs between the last occurrence of Rouxia califbrnica at 6.0 Ma, and the first occurrence of Thalassiosira oeslrupii at 5.1 Ma. The latter two species have customarily been used to identify the Miocene/Pliocene boundary. Paleomagnetic studies at Santa Cruz. California, demonstrate that the first occurrence of T. praeoestrupii coincides with the top of magnetic polarity Chron 5, which closely approximates the MiocenePliocene Epoch boundary.

show abstract

Magnetostratigraphy of the late Neogene purisima formation, Santa Cruz County, California

Cited by 22 publications

References 11 publications

Comparative Taphonomy, Taphofacies, and Bonebeds of the Mio-Pliocene Purisima Formation, Central California: Strong Physical Control on Marine Vertebrate Preservation in Shallow Marine Settings

Comparative Taphonomy, Taphofacies, and Bonebeds of the Mio-Pliocene Purisima Formation, Central California: Strong Physical Control on Marine Vertebrate Preservation in Shallow Marine Settings

Fluidized sandstone intrusions as an indicator of Paleostress orientation, Santa Cruz, California

Thalassiosira praeoestrupii: A New Diatom Species for Recognizing the Miocene/Pliocene Epoch Boundary in Coastal California

Contact Info

Product

Resources

About