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SEDIMENTOLOGY AND OF THE LOWER , , HARTFORD BASIN

A thesis presented to

the faculty of

the College of Arts and Sciences of Ohio University

In partial fulfillment

of the requirements for the degree

Master of Science

Simret Ghirmay Zerezghi

June 2007

SEDIMENTOLOGY AND STRATIGRAPHY OF THE LOWER JURASSIC PORTLAND FORMATION, NEWARK SUPERGROUP, HARTFORD BASIN

by SIMRET GHIRMAY ZEREZGHI

has been approved for the Department of Geological Sciences and the College of Arts and Sciences by

______Elizabeth H. Gierlowski-Kordesch

Associate Professor of Geological Sciences

______

Benjamin M. Ogles

Dean, College of Arts and Sciences

Abstract

ZEREZGHI, SIMRET GHIRMAY, June 2007, Geological Sciences

SEDIMENTOLOGY AND STRATIGRAPHY OF THE LOWER JURASSIC PORTLAND FORMATION, NEWARK SUPERGROUP, HARTFORD BASIN (102 pp.) Director of Thesis: Elizabeth H. Gierlowski-Kordesch

The -Jurassic system in eastern was formed by the breakup of Pangea. The sedimentary fill and lava flows of these rift basins are collectively known as the Newark Supergroup. The Hartford basin is divided into four sedimentary formations interbedded with three basaltic flows. The Portland Formation is the youngest (-Toarcian) and exposed in the eastern half of the basin. Finer- grained facies in the central portion of the basin now can be accessed with cores recovered from the city of Hartford. This study is based on 20 out of 35 drilled cores with approximately 600 m of the lowermost Portland Formation measured and correlated.

Facies include: (1) black (Fl1), (2) ripple cross-laminated black (Fr1), (3) disrupted black mudrock (Fm1), (4) stratified red mudrock (Fl2), (5) ripple cross-

laminated red mudrock (Fr2), (6) disrupted to massive red mudrock (Fm2), (7) ripple

cross-laminated to trough cross-bedded (Srt), and (8) horizontally bedded

sandstone (Sh). Three main depositional settings are interpreted: alluvial plain to sandflat

(Fr2, Fm, Sh, Srt), shallow to playa (Fl2, Fm), and offshore perennial saline

with deltaic sheets (Fl1. Fr1, Fm1, Sh). Fourteen lake cycles were recognized, controlled

by both tectonics and climate, influencing the evolution of the lake systems.

Approved: ______

Elizabeth H. Gierlowski-Kordeschof

Associate Professor of Geological Sciences

Acknowledgments

I express my sincere thanks and profound gratitude to my advisor Dr. Elizabeth

Gierlowski-Kordesch, for her generosity, patience, and support in every step of my work.

I am grateful to Dr. Randolph Steinen, Dr. Peter Drzewiecki, Margaret Thomas, Dr.

Gregory McHone, Nancy McHone, Allen Dwyer, Tim Mailloux, and other personnel

from the Department of Environmental Protection who helped move cores to

the new Connecticut State Core Repository, thus making my data collection successful.

Thank you to Paula Gural and her husband for their hospitality during field work. Many thanks to Dr. Martin Kordesch and Dr. Aurangzeb Khan for XRD analysis of Portland mudrock samples. I am deeply grateful to my committee members, Dr. David L. Kidder and Dr. Alycia L. Stigall, for their comments as well as the use of their microscopes and photo equipment. Dr. Stigall also identified the conchostracan and Dr. Daniel

Hembree analyzed the trace fossils for me.

I also wish to thank the Department of Geological Sciences, all my professors, my colleagues, friends, family members, my sister Aster, and my husband Dawit for their encouragement and support.

5

Table of Contents

Page

Abstract ………………………………………………………………………………… 3

Acknowledgments………………………………………………………………...... 4

List of Figures ……………………….…………………………………………………. 7

List of Tables ………………………………………………………………………….... 8

Chapter One ……………………………………………………………………………. 9

1.1 Introduction ………………………………………………………………………... 9

1.2 Geologic Setting ………………………………………………………………...... 11

1.3 Previous Work ………………………………………………………………… … 18

1.4 Methodology ……………………………………………………………………... 24

Chapter Two ………………………………………………………………………...… 27

2.1 Lithofacies Descriptions and Paleoenvironmental Interpretations ………………. 27

2.1.1 Black Mudrock ………………………………………………………………. 29

2.1.1.1 Black Shale (Fl1) ……………………………………………………….. 29

2.1.1.2 Ripple Cross-Laminated Black Mudrock (Fr1)…………………………. 34

2.1.1.3 Disrupted Black Mudrock (Fm1) ………………………………………. 37

2.1.2 Red Brown Mudrock ……………………………………………………….. . 40

2.1.2.1 Stratified Red Mudrock (Fl2)…………………………………………….40

2.1.2.2 Ripple Cross-Laminated Red Mudrock (Fr2)…………………………… 43

2.1.2.3 Disrupted to Massive Red Mudrock (Fm2)……………………………....47

2.1.3 Sandstone………………………………………………………………………49

2.1.3.1 Horizontal Laminated sandstone (Sh) ……………………………...……50

6

2.1.3.2 Ripple Cross-Laminated to Trough Cross-Bedded Sandstone (Srt)…..... 51

2.2 Petrography and XRD Data ……………………………………………………… 52

2.2.1 Black Mudrock……………………………………………………………….. 53

2.2.1 Red Mudrock ………………………………………………………………… 55

2.2.3 Sandstone …………………………………………………………………….. 58

Chapter Three…………………………………………………………………………. 59

3.1 Stratigraphy ……………………………………………………………………..... 59

3.2.1 Depositional Model ………………………………………………………….. 64

3.2.2 Tectonic and Climatic Controls ……………………………………………… 67

3.2.2.1 Tectonic Control…………………………………………………………69

3.2.2.2 Climatic Control …………………………………………………………73

Chapter Four ………………………………………………………………………….. 77

4.1 Discussion ………………………………………………………………………... 77

4.2 Conclusions ………………………………………………………………………..79

References ………………………………………………………………………………80

Appendix…………………………………………………………………………………92

7

List of Figures

Fig 1.1 Simplified map of the Hartford basin and location of the study area …………...10

Fig 1.2 rifting within the of Pangea on the east coast of North

America ………………………………………………………..…………………….12

Fig 1.3 Sedimentary and volcanic deposits of the Newark Supergroup and their

paleolatitude ………………………………………………………………………...15

Fig 1.4 Location map of previous study areas in the Portland Formation ………………21

Fig 1.5 Horizontal transect of Park River Tunnel project cores ………………………...25

Fig 2.1 Black mudrock facies ………………………………………………………… ..30

Fig 2.2 Ripple cross-laminated black mudrock (Fr2)………………………………….... 35

Fig 2.3 Textures of disrupted black mudrock (Fm1)…………………………………… 38

Fig 2.4 Stratified red mudrock facies ………………………………………………...... 41

Fig 2.5 Rippled cross-laminated red mudrock (Fr2) ……………………………….…... 45

Fig 2.6 Disrupted to massive red mudrock (Fm2) ………………………………...…..... 47

Fig 2.7 Sandstone subfacies ……………………………………………………….....… 50

Fig 2.8 Thin section photos of black mudrock facies………………………………...….53

Fig 2.9 XRD analysis of black mudrock samples ……………………………………… 56

Fig 2.10 Thin sections of Fr2, Fm2, Fl2, and Sh……………………………………...…. 58

Fig 3.1 Vertical profile of lower Portland Formation from River Park Tunnel Project…60

Fig 3.2 Vertical stacking of the lower Portland Formation cores showing fourteen black

mudrock units………………………………………………………………….…… 62

Fig 3.3 Lake basin model showing relationships between accommodation space and

climate versus lake type ……………………………………………….………….....65

8

List of Tables

Table 1.1 Stratigraphy of the Hartford basin ……………………………………………19

Table 1.2 Interpreted depositional environments for sedimentary rocks of the Portland

Formation………………………………………………………………..…………. 22

Table 2.1 Facies list and paleoenvironmental interpretation for the facies of the

lowermost Portland Formation ……………………………………………………...28

9

Chapter One

1.1 Introduction

Rift basins are very common in the modern and ancient record. They occur on all

continents as well as on thin oceanic crust beneath the sea (Einsele, 2000). Many rift

basins have been studied in some detail, and it is evident that rift basins have some

unique characteristic features that distinguish them from other sedimentary basins.

Generally they tend to be deep, narrow, elongated sedimentary basins with numerous

normal zones (synthetic and anthithetic or listric faults) and volcanism (Lambiase,

1990; Einsele, 2000). The Newark rift system of eastern coast of North America is an example of an ancient rift system that developed in a continental setting (Schlische, 1993;

2003).

The Hartford basin (Fig 1.1), part of the Newark rift system, contains Upper Triassic through Lower Jurassic sedimentary and volcanic rocks that are part of the Newark

Supergroup. The Newark rift system has been known for two centuries and many studies had been conducted in the Hartford basin (Lorenz, 1988; Schlische, 1993; Gierlowski-

Kordesch and Huber, 1995; Olsen, and Kent, 1996; LeTourneau and Olsen, 2003; and many others). The uppermost unit of the Hartford basin, the Portland Formation, crops out in the eastern half of the basin (Fig 1.1). Similar to most Newark rift basins, the

Hartford basin has limited exposures, and it has been difficult to determine the sedimentology and stratigraphy of the fine sedimentary rocks of the Portland Formation in the central basin. Most of our knowledge of the Portland Formation comes from the exposed strata along the eastern margin and north central part of the basin (Gilchrist,

10

1979; LeTourneau, 1985). These exposed units are mostly composed of coarse-grained sedimentary rocks, however, and have quite different sedimentologic units than those in

Fig 1.1 Simplified map of the Hartford basin and location of the study area (adapted from Gierlowski-

Kordesch and Huber, 1995).

11 the central part of the basin. This study investigates the sedimentology and stratigraphy of the Lower Jurassic (Sinemurian- Toarcian) sedimentary rocks of the Portland Formation in central part of the Hartford basin, central Connecticut.

The study area (Fig 1.1) was chosen, because that is the only place where cores of fine-grained sedimentary rocks are available from the lowermost Portland Formation.

The purpose of this study is to interpret the depositional history based on the stratigraphy and sedimentologic processes that controlled the formation of the lowermost Portland

Formation using core material from Park River Tunnel Project of Hartford, CT (U. S.

Army Corps of Engineers, 1977). The development of a comprehensive depositional model for the Portland Formation has a direct application as a predictive tool for defining the distribution of lithofacies in the Hartford basin, by providing the spatial relationships of the various depositional environments and the possible controls on .

1.2 Geologic Setting

The to was a critical time interval in Earth history. This

time period is known for the initiation of a fundamental change in the distribution of the

continents on the surface of the Earth. It also overlaps with the timing of huge and major continental flood and includes one of the five major Phanerozoic mass extinctions

(Marzoli et al., 1999). Today we understand part of Earth history at this time period from

exposed and buried rift basins that were formed during the breakup of the super-

continent Pangea. The Newark rift system is one of these rift systems (Fig 1.2) (Olsen

and Kent, 1996; Kent and Olsen, 2000).

12

Fig 1.2 Mesozoic rifting within the supercontinent of Pangea on the east coast of North America (from

Kent and Olsen, 2000).

Rift basins of the Triassic-Jurassic age contain an extraordinary record of physical,

biologic, climatic, and tectonic conditions that lead to the deposition of extensive and very thick sedimentary sequences in the largest known rift systems around the world

(LeTourneau and Olsen, 2003). They are known from the east coast of North America,

13 northwestern and southernmost part of , central and western part of Europe, Asia, western and eastern part of South America, Australia, and northwestern Antarctica

(Schlische, 1993; Le Roy and Pique, 2001; LeTourneau and Olsen, 2003; Macdonald et al., 2003; Henrique et al., 2004). Hence, these rift systems are widely used in reconstructing and understanding the geologic history of the Earth.

The rift system in eastern North America is located on the eastern flank of the

Appalachian Orogen (Lorenz, 1988). It was formed during the earliest phases of Triassic-

Jurassic continental rifting (Gore, 1988; Smoot, 1991). The sedimentary basin fill and associated tholeiitic lava flows and plutons in these eastern North American rift basins are collectively known as the Newark Supergroup (Olsen, 1978; Lorenz, 1988).

Remnants of numerous exposed and buried basins of the Newark rift system extend from

South Carolina to (Fig. 1.2) for about 2300 km (Smoot, 1991; Olsen et al.,

1989; Schlische, 1993; 2003). The Newark rift system is a series of half- basins that are bounded by reactivated Paleozoic normal-bounding faults of variable age either on the eastern or western side of the basin (Schlische, 1993; 2003). Even though earlier studies considered the Newark rift system as one large rift valley (Russell, 1879 cited in

Lorenz, 1988; Sanders, 1963), now it is clear that each basin was developed separately.

This latest idea was confirmed based on determined ages (biostratigraphy and paleomagnetism) of the fill from different basins (LeTourneau and Olsen,

2003), suggesting that the basins were isolated from one another. In addition, geochronologic study of these basins also support a time progressive formation of basins where rifting started in early Triassic in the northern (Fundy Basin) and southern (Deep

River Basin) end of the Newark rift system and progressively developed to the center

14 which makes the Hartford basin the youngest of all (Nadon and Middleton, 1984;

LeTourneau and Olsen, 2003).

The Newark rift system has a complex structure, but its tectonic history can generally fall into three major episodic tectonic categories: 1) fracturing and initiation of the rift basins due to the continental breakup, 2) deposition of Newark Supergroup strata which was followed by rotation, tilting, uplifting, and erosion that caused exposure of the entire section as northwest- or northeast-dipping homoclines, and 3) a post-depositional compression event that imprinted complex structures over the remnants of the Newark rift system (Lorenz, 1988 Schlische, 1993; 2003).

The Newark rift system shares many features with modern active rift basins. These features include linear chains of large tectonic lakes (e.g. Lake Tanganyika formed as result of the East Africa rift system) and a tripartite cyclic stratigraphic architecture.

Tripartite sedimentary basin fills are characterized by a basal fluvial unit overlain by a lacustrine unit, the deepest water facies, and a top fluvial unit (Lambiase, 1990).

The Newark rift system records more than 35 million years of Earth history and spans more than 450 of paleolatitude, preserving a spectacular sedimentary, igneous,

tectonic, climatic, and biotic record of Triassic-Jurassic events (Fig 1.3) (LeTourneau and

Olsen, 2003). The sedimentary deposits in the Newark rift system consist mainly of

lacustrine (, shale, and ); fluvial (siltstone, sandstone, and conglomerate);

eolian; and alluvial fan deposits (sandstone, conglomerate, and fanglomerate) (Olsen et

al., 1989; Smoot, 1991; Gierlowski-Kordesch and Huber, 1995).

15

Fig 1.3 Sedimentary and volcanic deposits of the Newark Supergroup and their paleolatitude (from

LeTourneau and Olsen, 2003). TS = Tectonostratigraphic sequences defined by major pulses of regional extension.

The Newark Supergroup basins exhibit the tripartite depositional pattern, where the base and top of the basin fill are fluvial in origin, while the middle is lacustrine facies.

The upper and lower fluvial systems fit a hydrologically open system (Gore, 1988; Olsen et al., 1989; Schlische and Olsen, 1990). It is characterized by a basin-wide channel

16 system; large- to small-scale lenticular bedding; conglomeratic intervals which can stretch across the basin; paleocurrent patterns which are axial or dominated by one direction over the basin, indicating through-going drainage; and a lack of evidence for large-scale lakes (Hubert et al., 1978). However, there can be local pounding and the accumulation of paludal deposits (Smoot, 1991).

The middle section of this tripartite pattern is lacustrine and generally fits hydrologically open-to-closed lake systems. According to Olsen (1990), the Newark

Supergroup contains three different lake types: (1) the Newark type (balanced-fill lake, open or closed), the Richmond type (overfilled lake or open), and the Fundy type (under- filled or closed). The lacustrine facies are generally characterized by a systematic increase in grain size towards all boundaries of a basin, paleocurrent directions pointing away from the border fault, and cyclic beds (Olsen, 1980; Smoot, 1985). Although, the cyclic central, fine-grained sedimentary rocks are lacustrine, the basin marginal areas can be dominated by lake-margin, fluvial, deltaic, and alluvial fan sequences. Within all

Newark rift basins, the lake and fluvial depositional systems have considerable persistence in time and are the largest-scale elements of the basins’ stratigraphy (Olsen,

1980; Olsen et al., 1989; Schlische and Olsen, 1990; Smoot, 1991)

The Newark rift system is known for having abundant and diversified fossils. A compilation of invertebrates from the Newark includes several genera of conchostracans (Spinicaudata), ostracodes, a notostracan, crayfish, insects, bivalves, and gastropods, all of which are nonmarine (Olsen et al., 1978; Gore, 1987; 1988). Vertebrate remains including well-preserved fish fossils, reptile footprints, and amphibians trackways (e.g. Smoot, 1985; McDonald and LeTourneau, 1988; Lucas and Huber,

17

2003). Skeletal remains of reptiles are less common; however, small reptiles are known from a number of localities in the Newark and Hartford basins. Reptile remains include procolophonids, lacertilians, rhynchocephalians, thecodonts (, aetosaurids, pseudosuchians, and rauisuchids), saurischian (theropod teeth, coelurosaurs, and prosauropods), ornithoischian dinosaurs, and therapsids (Olsen et al., 1978; Gore,

1987; Lucas and Huber, 2003). Trails and burrows like Scoyenia are also present

(Gierlowski-Kordesch, 1991).

Plant remains (more than 80 species) are identified from the Newark Supergroup.

Black mudrock commonly contain pollen and spores, which have been useful for biostratigraphy (Olsen et al., 1978; Cornet and Olsen, 1985; 1990). Extraordinary plant fossil assemblages have been recovered from several basins, especially the Richmond,

Deep River, and Taylorsville basins (LeTourneau, 2003). Rhizoliths are abundant, particularly in red , associated with pedogenic calcite stringers and nodules

(Gore, 1987; Smoot, 1991; Tanner, 2003; Rasbury et al., 2006). Lacustrine stromatolites, oolites, pisolites, and oncolites are present in several basins (Carozzi, 1964; McDonald and LeTourneau, 1988; De Wet et al., 2002). Charophytes have been found in the Fundy basin, Nova Scotia (Gore. 1987).

All Mesozoic rift basins that preserve Jurassic strata also contain up to three distinctive horizons of tholeiitic basalts that are correlatable by age, stratigraphic position, chemistry, and petrography (McHone, 1996). Ar-Ar radiometric dating of these basaltic flows, which was supplemented by palynologic studies, shows that the age of the basalts coincides with the Triassic-Jurassic boundary of early age (Cornet,

1993; McHone, 1996). Moreover, all the sedimentary units that are found in the Newark

18 rift system are classified into different formations with respect to the stratigraphic position of these basalts, i.e. they serve as a boundary between different formations

(Lorenz, 1988; McHone, 1996).

1.3 Previous Work

The Hartford basin (Fig 1.1) is a half graben with its eastern border defined by a

west-dipping normal fault system. It is approximately 140 km long, 20-30 km wide, and

is filled with 4-7 km of sedimentary rocks and associated tholeiitic and diabase

(Table 1) (Wolela and Gierlowski-Kordesch, 2007). The sedimentary fill and associated

basaltic flows within the basin generally dip 10-20º east and increase sharply to 45º or more to near the border faults (Gierlowski-Kordesch and Huber, 1995). The Hartford basin fill is basically composed of mostly red or brown and siltstones, with lesser amounts of conglomerate near the border fault and thin lacustrine black . It has numerous paleontologic sites that contain tracks, leaf impressions, and fossil fish (Hubert et al., 1978; 1982; Gierlowski-Kordesch and Huber, 1995; Farlow and

Galton, 2003).

The Hartford basin fill consists of four sedimentary formations: New Haven Arkose,

Shuttle Meadow Formation, , and Portland Formation with their interbedded three basaltic flows: Talcott Basalt, Holyoke Basalt, and Hampden Basalt

(Table 1, Fig 1.1). These four sedimentary formations have different sedimentologic units, controlled by the tectonic development of the basin and climatic conditions. Similar to other basins in the Newark rift system, the Hartford basin follows the tripartite architectural development (Schlische and Olsen, 1990).

19

Table 1.1 Stratigraphy of the Hartford basin (from Wolela and Gierlowski-Kordesch, 2007).

The Hartford basin fill is dominantly composed of fluvial redbeds accumulated in a fairly narrow basin in its initial phase, when the new Haven Arkose was deposited. This fluvial deposition is attributed to the sedimentation rate being relatively higher than the subsidence rate (Schlische and Olsen, 1990; Smoot, 1991). However, as the rate of subsidence increases, the basin becomes an asymmetric, closed basin with crustal thinning beneath manifested by intrusion and extrusion of basaltic magma. During this phase, the Shuttle Meadow, East Berlin, and lower Portland Formations accumulate as interbedded lacustrine gray to black strata, playa redbeds, fluvial redbeds, and an eastern border-fault facies of alluvial-fan conglomerate in a closed-to-open basin drainage. The

20 third phase consists of fluvial and alluvial-fan redbeds of the upper half of the Portland

Formation, forming during easing of extensional stress and reduced subsidence. During this phase, the sedimentation rate exceeded the subsidence rate (McInerney and Hubert,

2003; Bohacs et al., 2003).

The Portland Formation is exposed along the eastern half of the basin and is the youngest sedimentary formation (Sinemurian-Toarcian). The spatial distribution of the

Portland Formation throughout the basin is not the same. In the southern part of the basin, it is exposed only as small isolated wedges of conglomerate and , but occupies a progressively wider belt of finer-grained material in the central and northern basin

(Gilchrist, 1979; LeTourneau, 1985). Only a few detailed sedimentologic analyses of the

Portland Formation in the south and central part of the basin are published on the different lithofacies assemblages (Fig. 1.4) (Gilchrist, 1979; LeTourneau, 1985;

McDonald and LeTourneau, 1988; Gierlowski-Kordesch and Huber, 1995). From these studies, it is apparent that a wide variety of rock types comprise the Portland Formation, representing a complete spectrum of coarse-to fine-grained fluvial and lacustrine sedimentary rocks.

McDonald and LeTourneau (1988) described the Portland Formation from the

Stony Brook site in north-central Connecticut (Fig 1.4). According to McDonald and

LeTourneau (1988), most of the Stony Brook section is composed of thinly bedded to massive, red brown sandstone, siltstone, and shale interbedded with at least two sequences of gray black strata. McDonald and LeTourneau (1988) have interpreted the red brown sandstones, siltstones, and shales as a shallow stream channel and floodplain

21 and the gray black units as ephemeral lake deposits. In addition, they also report the presence of several fossils: plant fossils (Brachyphyllum and Equisetites), fish scales

Fig. 1.4 Location map of previous study areas in the Portland Formation (after Gilchrist, 1978;

LeTourneau, 1985; and McDonald and LeTourneau, 1988).

22

(Semionotus), ostracodes, a conchostracans (Spinicaudata) (Cyzicus sp.), a bivalve

(Unio), and different burrows. Gilchrist (1979) describes the Portland Formation near the eastern border fault from a different locality (Fig 1.4) and identifies five perennial lake sequences characterized as black and grey interfingering with red brown fluvial and alluvial fan deposits. Surprising, Gilchrist (1979) does not report any preserved fossils from his sites. LeTourneau (1985) takes a different approach from Gilchrist

(1979), but works in almost the same sites (Fig 1.4). He divides the Portland Formation

Table 1.2 Interpreted depositional environments for sedimentary rocks of the Portland Formation from

LeTourneau (1985).

Lithosome Interpretation Facies Depositional environment

Conglomerate 1 Debris flow A Alluvial fan 1 Mid to upper fan

2 Shallow braided 2

3 Braided steam (possibly 3 Mid to lower fan

perennial)

Sandstone 4 Sheet flow 4 Lower fan

5 Ephemeral braided stream B Floodplain 5 Basin margin

and floodplain

Siltstone 6 Floodplain and minor braided 6 Basin center

stream

Dark Shale 7 Shallow water above wave C Perennial lake 7 Lake margin and

base shoreline

8 Quiet water below wave base 8 Lake bottom

23 into eight lithofacies (Table 1.2) with fossils such as fish, plants, dinosaur tracks, and burrows. However, he does not specify how many cyclic sequences of lake facies are present.

Episodic syndepositional subsidence and tilting are surmised to be the primary control on the distribution of the Portland sedimentary rocks in the basin (LeTourneau,

1985; McDonald and LeTourneau 1988). Generally, the lithofacies distribution in the

Hartford basin from east to west is as follows: progradational alluvial fan deposits, comprising coarsening up-ward sequences of conglomerate and 10-30m thick sandstone, fluvial deposits consisting of coarsening-upward relatively thinner and finer sequences, and finally thin lacustrine deposits, which all become finer toward the basin center

(Gilchrist 1979; LeTourneau, 1985). The fine-grained lacustrine deposits are characterized by organic-rich, fossiliferous black shale unlike the fluvial sandstones, which are dominated by brown to red siltstone.

With limited coring and outcrop data from the northern Hartford basin and the southern Deerfield basin to the north as well as the Park River cores of this study, Olsen et al. (2005) have established the stratigraphy of the Portland Formation, though the effect of fault block geometries in stratigraphic correlation across the basin has not been addressed in their study. They have identified five members within the lower half of the

Portland Formation, based only on color and general lithology, from bottom to top: the

Smiths Ferry Member, the Park River Member, the South Hadley Falls Member, the

Mittinegue Member, and the Stony Brook Member, encompassing about 2km of thickness. The upper half of the Portland Formation, approximately 2km in thickness as well, comprises only red fluvial siliciclastics.

24

The sedimentology, stratigraphy, and paleoenvironments of the Portland

Formation are not well known in the central and western part of the Hartford basin due to their poor exposure. Sedimentologic study of cores in this part of the Hartford basin can elucidate the lithofacies changes and stratigraphy within this portion of the rift basin and perhaps lead to insight on the tectonics and climatic signatures of the sedimentary rocks.

1.4 Methodology

The Park River diversion tunnel in Hartford, CT, in the west-central part of the

basin (Fig 1.1), was drilled in the 1970s and about 35 cores with an average length of 60

m were drilled to analyze the strength and subsurface structures of the foundation rock

for the tunnel (U.S Army Corp of Engineers, 1977). These cores were drilled almost

perpendicular to the ground surface (at an angle to the general dip of the rocks) in a W-E

direction and extended for about 3 km. These cores had a recovery rate of 90-98%. In

addition, there was a vertical overlap from core to core, and they were drilled sequentially in a transect with a horizontal separation of cores of about 100m. The vertical extent of the cores includes part of the East Berlin Formation, the Hampden Basalt, and the lowermost portion of the Portland Formation. This study describes the sedimentology of the lowermost Portland Formation in the west-central part of the Hartford basin using twenty drilled holes out of the 35 drilled cores of the Park River Tunnel Project (Fig 1.5), targeting the Smiths Ferry and Park River Members of Olsen et al. (2005).

Sedimentologic parameters, which include color, texture, biologic and physical , fossil content, nature of contact, and other important information, were collected for each core for reconstruction of the sedimentology and stratigraphy of

25 . ) 1977 , ineers g s of En p Cor y U.S. Arm ( ect cores j rk River Tunnel Pro a 1.5. Horizontal transect of P g Fi

26 the lowermost Portland Formation. The section measured in each core averaged 30-70 m in thickness. With the cores stacked together vertically, based on the engineering data containing their location and the dip of the strata, the composite section represented approximately 600m of the lower Portland Formation. The general stratigraphy and lithologic description of each core were then used to recognize the vertical and lateral distribution of lithofacies to infer the depositional environments. In addition, the measured cores were used to identify repetitive lacustrine cyclic units (Pienkowski and

Steinen, 1995) to compare to the twelve climatic lacustrine cycles identified by Olsen et al. (2005) in the Smiths Ferry and Park River Members of the Portland Formation.

For further analyses, representative samples were taken to make eleven thin sections, aiding in the analysis of the chemical composition and diagenetic alteration for the establishment of different lithofacies assemblages in paleoenvironment analysis.

These detailed stratigraphic and sedimentologic analyses of the lowermost Portland

Formation will help in reconstructing paleoclimate and tectonic history during the time of

Portland sedimentation. Also, the data from these cores will be supplemented with data from analogous modern and ancient sedimentary deposits that are comparable to the interpreted paleoenvironments for the Hartford Basin.

27

Chapter Two

2.1 Lithofacies Descriptions and Paleoenvironmental

Interpretations

Lithologic descriptions of sedimentary units and their paleoenvironment interpretation have been the main tools to understand the processes that deposit them.

Twenty sections of sedimentary core logs from the Park River Tunnel Project (U.S. Army

Corps of Engineers, 1977) with a stratigraphic thickness of 600 m representing the lowermost Portland Formation, presently located at the Connecticut State core facility, located outside Harwinton, CT, were measured to describe the lithofacies assemblages and interpret their paleoenvironmental deposition. Three major , black mudrock, red brown mudrock, and sandstone were identified based on their compositional and textural differences. These lithologies were further classified into eight facies based on the primary (depositional) and/or secondary (biogenic, compactional, and diagenetic) sedimentary structures and grain size (Table 2.1). These included (1) black shale (Fl1), (2) ripple cross-laminated black mudrock (Fr1), (3) disrupted black mudrock

(Fm1), (4) stratified red mudrock (Fl2), (5) ripple cross-laminated red mudrock (Fr2), (6) disrupted to massive red mudrock (Fm2), (7) ripple cross-laminated to trough cross- bedded sandstone (Srt), and (8) horizontally bedded sandstone (Sh).

The lowermost Portland Formation of the Hartford basin represents sedimentation in three continental environments: 1) alluvial plain to sandflat, 2) shallow lake to playa, 3) and offshore perennial saline lakes (Table 2.1). The detailed descriptions and environmental interpretations of these facies follows.

28

Table 2.1 – Facies list and paleoenvironmental interpretation for the facies of the lowermost Portland Formation in the Hartford Basin of Connecticut. Lithology Facies Type Paleoenvironment

Black Black shale Fl1 (Fl1a, Fl1b, Fl1c) Perennial saline lake

Mudrock Ripple cross-laminated black Lacustrine deltaic sheet

mudrock Fr1

Disrupted black mudrock Fm1 Post-depositional alteration of

(Fm1a, Fm1b) perennial saline lake deposits

Red brown Stratified red mudrock Fl2 Playa

Mudrock (Fl2a, Fl2b)

Ripple cross-laminated red mudrock Fr2 Sandflat/ alluvial plain (sheet

floods)

Disrupted to massive red mudrock Fm2 Post-depositional alteration of

sandflat/ alluvial plain

Sandstone Horizontally laminated sandstone Sh Lacustrine deltaic sheet or

Sandflat/ alluvial plain (sheet

floods)

Ripple cross-laminated to trough cross- Sandflat/ alluvial plain (sheet

bedded sandstone Srt floods)

29

2.1.1 Black Mudrock

This lithology composes 13% of the total composite (600m) section of the lowermost

Portland Formation. It is subdivided into three facies: finely laminated black shale (Fl1), ripple cross-laminated black mudrock (Fr1), and disrupted black mudrock (Fm1). The

average thickness of this lithology is 5m and it is dominantly found interbedded between

the red mudrock lithology, mainly separated by sharp contacts with only rare gradual

contacts.

2.1.1.1 Black Shale (Fl1)

Description

This facies comprises 80% of the measured black mudrock lithology. The black

shale has color variation in distinct units from gray to black, and rarely exhibits

gradational color variation within a unit. It is characterized by ( to

sized sedimentary rocks) laminated on the sub-mm- to cm-scale. There are three distinct

laminae styles in this unit, separated into three subfacies (Fl1a, Fl1b, Fl1c). Descriptions

follow.

Subfacies Fl1a consists of discontinuous lamina of white to light gray Mg-rich

carbonate and quartzose silt alternating with continuous, slightly thicker, black claystone

lamina (Fig 2.1A). The Mg-rich carbonate and quartzose silt (marlstone) laminae are sub-

mm to mm thick (0.5mm -1mm) as elongated lenses. These lenses are on average 1 to 4

cm long. Subfacies Fl1b comprises alternating continuous laminae of white to light gray

Mg-rich carbonate and quartzose silt (marlstone) and black claystone (Fig. 2.1B), and

subfacies Fl1c contains alternating continuous laminae of black mudstone (clay and silt)

30

(Fig. 2.1C). Both Fl1a and Fl1c with continuous lamination have relatively thicker lamination (1mm to cm) than Fl1a. The black claystone to mudstone laminae have an organic matter content of around 5-10% (Gottfried and Kotra, 1988) and are associated

Fig 2.1 Black mudrock facies A) Fl1a (core FD13-T 125 ft.), B) Fl1b (core FD19-T –126 ft.), and C) Fl1c with mudcracks (core FD30-T – 186.2 ft.), and D) mudcracks (not polygonal) in plan view (core FD13-T – 121ft.). These cores are all two inches in diameter, except for C, which is four inches in diameter.

31 with . Soft sediment deformation is not common except for a few micro- convoluted layers and load structures in Fl1b. Fl1b also has magnesian carbonate (high

Mg-calcite or magnesite?) nodules (see Fig. 2.3.2 for XRD analysis of all Fll carbonates)

that vary in diameter from 0.5cm to 2cm, and well-developed framboidal crystals of brass

yellow pyrite.

Rarely, very thin (mm-scale) mudcracks are present in Fl1b, which are filled by

silty material (Fig 2.1D). No body fossils are present in the Fl1 except for a few very small bumps on bedding planes. These bumps are composed of silty material with no internal structure. Fossil fish have been found in similar black mudrock units elsewhere in the basins of the Newark Supergroup by other researchers (Hubert et al., 1978; Olsen,

1985; Smoot, 1991; Gierlowski-Kordesch and Huber, 1995).

Interpretation

The presence of sub mm- to mm-scale lamination, fine grain size, and absence of marine fossils suggests deposition in relatively quiet perennial lacustrine waters (Hubert

et al., 1978; Gore, 1988; Demicco and Gierlowski-Kordesch, 1986; Olsen; 1990; Smoot;

1991; Dam and Surlyk 1993; Gierlowski-Kordesch and Rust, 1994). Fine-grained,

organic-rich, laminated accumulate in modern lakes in areas that are protected

from bioturbation, high clastic input, strong bottom currents, and oxidation of organic

matter (Smith, 1990; Tiercelin, 1991). These conditions are found in anoxic bottom

waters in modern meromictic to oligomictic lakes such as Lake Tanganyika, East Africa

(Tiercelin, 1991). The organic–rich claystone to mudstone laminae represent organic

matter derived from planktonic algal material from the water column (Type I kerogen)

and terrestrial plant debris (Type III kerogen) (Talbot, 1988), with microcrystalline pyrite

32 concentrations (Kotra et al., 1988; Gierlowski-Kordesch, 1998; Dickneider et al., 2003).

Lamination similar to that of Facies Fl1 has been described by Olsen (1985) as that

indicate seasonal variation in climate. However, beds dominated by finely laminated,

regular alterations of two or more sediment types are more appropriately called laminites

or rhythmites because the annual time frame of the lamination has not yet been

demonstrated (Glenn and Kelts, 1991; Warren, 2006).

Fl1a and Fl1b certainly reflect alternating conditions allowing for clay and mud

suspension settle-out and marl deposition in quiet waters with no wave action and no

biotic re-working. The lamination may result from continuous change in water chemistry

due to seasonal variations, a variable input source mechanism, formation of microbial

mats, or the accumulation of organic material with clay suspension after seasonal blooms

of phyto- and zooplankton (Hardie et al., 1978; Glenn and Kelts, 1991; Last, 1993;

Renaut, 1993; Renaut and Tiercelin, 1994; Dean et al., 1999). Anoxic conditions, whether

in the water column or only in the sediments, are crucial for preservation of organic

matter and lamination (Smith, 1990; Tiercelin, 1991). Alternatively, saline conditions can

also preserve organic matter and lamination because the salinity can promote stratification as well as exclude organisms that feed upon the organics in the bottom

sediments. Muds in modern, shallow saline lakes contain 4-40% organic material (Last,

1990; Last and DeDeckker, 1990; Last, 1993; 1994; Gierlowski-Kordesch and Rust,

1994; Renaut and Tiercelin, 1994). Carbonate laminae, composed of dolomite, calcite,

and magnesite, are common in the offshore muds of modern saline lakes (Renaut and

Stead, 1991; Last, 1990; 1994; and many others).

33

Fl1c with mudstone lamina may represent areas of higher siliciclastic influx (more

proximal and near a surface water input site) than subfacies Fl1a and Fl1b. The

introduction of terrigenous silt to the lake by runoff, followed by suspension settle-out,

can mask the precipitation of carbonate or inhibit the growth of microbes that induce precipitation (e.g. Dean, 1981; Last, 1993, Dean et al., 1999; and many others).

Pyrite forms in association with organic matter decomposition through sulfate reduction by anaerobic bacteria and through production of hydrogen sulfide, but it is not necessarily a good indicator of anoxic bottom waters (Gore, 1988; Shoonen, 2004). Pyrite can form in stratified lakes with anoxic bottom waters, but it can also form below the sediment–water interface in organic rich sediments deposited in oxygenated water, or in anoxic microenvironments in otherwise oxidizing sediments (Gore, 1988; Shoonen,

2004). Pyrite can also form in the water column of meromictic lakes (Suits and Wilkin,

1998). The presence of pyrite in Fl1 is simply illustrating the presence of degrading

organic matter in the paleolake of the Portland Formation.

The presence of rare small mudcracks in Fl1b does not necessarily indicate a quick

desiccation event. Mudcracks form in mud in three ways, from (1) subaerial exposure

(desiccation cracks), (2) subaqueous processes in saline water with expandable clay

sediments (syneresis cracks), and (3) substratal processes, such as compaction from

loading or seismic shocks (compaction cracks) (Collinson and Thompson, 1989). The

Portland Formation clays generally contain illite, smectite, and chlorite (Gottfried and

Kotra, 1988). The mudcracks in Fl1b do not exhibit polygonal features indicative of

desiccation in a subaerial environment, nor is there any reddening of the sediment from

oxidation (Hubert and Reed, 1978). Therefore, compaction or syneresis may have formed

34

the mudcracks. All the features within Fl1 and the other mudrock facies described below

suggest deposition offshore in a perennial saline lake.

The Mg-rich carbonates (high Mg-calcite, magnesite) point toward more saline conditions (Smoot, 1983; Pueyo Mur and Inglés, 1987; Renaut and Stead, 1990;

Gierlowski-Kordesch and Rust, 1994; Spötl and Burns, 1994). The lack of extensive evaporitic deposition (as in e.g. Handford, 1982) may be a problem of preservation because subsurface dilution by groundwater can dissolve away evaporites (see Bowler,

1986). An example of this is Lake Tyrrell in Australia (Teller et al., 1982; Bowler and

Teller, 1986). Also, some saline lakes do not precipitate evaporitic minerals over a long

period of time (Smoot and Lowenstein, 1991).

The silt-filled bumps found on bedding planes resemble the tiny mounds of salt-

cemented sediment that form from insect and other traces on the surface of the marginal

sediments of Lake Bogoria in Kenya (Scott et al., 2007). Salts hold together the fine

features of the bioturbated sediment as an early cementation process.

2.1.1.2 Ripple Cross-Laminated Black Mudrock (Fr1)

Description

This facies comprises 5% of the measured section of the black mudrock and

ranges in thickness from 5-25cm (Fig 2.2). Ripple cross-lamination is represented by

alternating white and black inclined laminae. The white laminae are composed mostly of

quartz and silt and vary in thickness from 0.1mm to 1mm, accounting for 10-

20% of the rock by volume. The black laminae are formed of clays with a considerable

amount of fine silt. Ripple forms include climbing ripples and asymmetric current ripples

35 with gentle slopes, indicating possible unidirectional currents. This well-developed ripple cross-laminated facies dominantly alternates within Fl1 or Fl3 units. Nodules (2-5cm in

diameter) and very shallow mudcracks (mm-scale) filled with silt in the black laminae are

rare. No body or trace fossils are recognizable in this facies in the core material.

Fig 2.2 Ripple cross-laminated black mudrock (Fr1). This core is four inches in diameter. (core FD 2T – 93 ft.).

Interpretation

Fr1 is commonly found interbedded with Fl1, interpreted as perennial lacustrine

facies. Flume studies have shown that there is a predictable sequence of bedforms that

depends on velocity, grain size, and depth of flow (Prothero and Schwab, 1996). Ripple cross-lamination is principally created by bedload transport as water moves over a bed of sediment as in unidirectional currents (current ripples), as oscillatory and bi-directional

36 currents, or a combination of both (tidal and wave ripples) (Collinson and Thompson,

1989; Prothero and Schwab, 1996).

In lakes, typical wave-generated sedimentary structures form above wave base.

Below wave base, deposition occurs from direct settling of fine sediment from suspension or sediment gravity flows initiated as currents from turbidites and slumping

(Sly, 1978; Bloesch, 2004). Fr1 is dark in color, like Fl1 suggesting anoxic conditions, but

its rippled nature excludes quiet settle-out from suspension.

Ripples can form in sediment with grain sizes of sand to coarse silt. The

dominance of clay and fine silt in Fr1 with both intercalated into the ripple forms

themselves indicate that the clay most probably was transported as bedload, like the sand

and silt, as sand- to silt-sized mud aggregates or flocculates. A modern and ancient analog of sand-sized mud aggregates transported as bedload during sheet flooding events

are documented from sheet floods of Cooper Creek of the Lake Eyre basin in Australia, the New Haven Arkose, and East Berlin and Shuttle Meadow Formations of the Hartford basin, and the Lower Red Sandstone of the Anglo-Welsh basin (Rust and Nanson, 1989;

Gierlowski-Kordesch and Rust, 1994; Gierlowski-Kordesch, 1998; Gierlowski-Kordesch and Gibling, 2002; Marriott et al., 2005). Clay can also flocculate underwater and travel as bedload, producing ripple cross-lamination (Hyne et al., 1979; Schieber et al., 2007).

The deceleration of a sheetflood will typically result in deposition of a powering- down sequence of sedimentary structures as the flow decays. Sheetflood sediments, therefore, commonly contain ripple cross-lamination, deposited during waning flows

(McKee et al., 1967; Tunbridge, 1981; Sneh, 1983). When such sheetfloods enter the rising waters of a shallow lake, the bedload is deposited subaqueously at the margins of

37 the lake, analogous to the deltaic sheets or sheet deltas of Smoot (1985) and Smoot and

Lowenstein (1991). An example of a facies sequence containing Fr1 is Fl1-Frl-Fl1 (core

FD-23T) (see Appendix). The intercalation with offshore lake deposits suggests more distal deposition. Fr1 is interpreted as a distal sheet delta deposit associated with the

perennial lake deposits of Fl1 in the Jurassic Portland Formation.

2.1.1.3 Disrupted Black Mudrock (Fm1)

Description

This unit composes 15% of the composite measured section, with an average unit

thickness of 25-50 cm. This facies is associated with Fl1 and Fr1. It is characterized by

mixed or disrupted laminae on mm- to cm-scale of claystone and carbonate to quartzose

siltstone to fine- to medium-grained sandstone (Fm1a), brecciated to chaotic bedded black

mudstone (Fm1b), or a black mudstone with a massive fabric (Fm1c). This facies

dominantly appears as Fm1a, with rare thin, mudcracked layers of claystone alternating

with carbonate to quartzose siltstone. Mudcracking to a depth of 2-3cm dissects layers

and produces clasts. Mudcracks contain fills from overlying and underlying layers (Fig

2.3A). No polygonal cracking geometry is obvious on the bedding planes in these small

cores. Some units of Fm1b with brecciated texture is similar to Fl1b but with abundant

mudcracks and Fm1b with chaotic bedding contains white sub-rounded chips of marlstone

as well as dark claystone several cm in length in random orientations, floating in a darker

mudstone matrix with rare greenish small nodules (Fig. 2.3B, C). Fm1b also contains cm-

scale vertical to sub-vertical veins filled with quartz. Fm1c appears massive but has faint

laminae interspersed with the massive dolomitic areas and tiny sub-horizontal fractures

38 filled with carbonate (Fig. 2.3D). Pyrite crystals float throughout the matrix, around 10% by volume of the unit. A single kerogen-filled fissure (5mm wide) with bifurcations is present in core FD-23T at 114.9-122.7ft (See Appendix).

Fig 2.3. Textures of Fm1. A) Mudcrack network in Fm1b (core FD-24T - 113 ft.); core is four inches in diameter, B) Chaotic texture of Fm1b (core FD-24T – 118.6 ft.), core is four inches in diameter, C)

Brecciated texture of Fm1b (core FD11-T – 90 ft.), field of view is 7cm by 10.5cm, and D) Massive texture

of Fm1c (core FD20-T - 143 ft.) with pyrite and horizontal fractures, field of view is 7cm by 10.5cm.

39

Interpretation

The different subfacies of Fm1 are dark in color and probably high in organic

matter content and are interpreted as fine-grained perennial lacustrine sediments that have

undergone post-depositional physical and/or chemical alteration. Both Fm1a and Fm1b are envisioned as more proximal than the Fl1 subfacies. Fm1a has varying thicknesses of

sandstone laminae and Fm1b comprises thick lamination with more fine sandstone than

siltstone laminae alternating with claystone laminae. This points to a position closer to a

siliciclastic source input, perhaps associated with a deltaic sheet. Some mudcracks

associated with this facies are interpreted as sub-stratal (compactional or seismic) cracks

because they are filled with underlying material (e.g. Fig. 2.3C). Alternatively, some

mudcracks are filled with overlying sandy to silty material with a possible syneresis

origin. With no obvious polygonal cracking patterns, a desiccation origin for the

mudcracks is not supported.

Because Fm1c has a massive fabric with floating pyrite crystals, it is inferred to be

a product of haloturbation of lacustrine fine-grained sediments. In addition, petrographic

analysis of this facies indicates a 50% dolomite content (see petrographic section below).

It is not clear whether the dolomite is primary or secondary in origin. The massive fabric

could also indicate bioturbation, but there is yet no definitive evidence.

The chaotic texture of Fm1b exhibits a jumble of mudstone clasts while Fm1c with its kerogen-filled tube structures is found in association with either faulting or a basalt flow. These facies are interpreted as the result of hydrothermal mixing due to fluid movement through fractures producing the described quartz-filled veins and clastic textures. The kerogen-filled tubes are fractures from the movement of hydrocarbons from

40 neighboring, source rock shale. Most of the black shales that are described from the

Newark Supergroup are characterized by average to high TOC (Kotra et al., 1988).

Kerogen analyzed from the Portland Formation (Kotra et al., 1988) has enough hydrogen- rich constituents to yield fluid hydrocarbons with much field and petrographic evidence for fluid migration (Parnell, 1986; Pratt and Burruss, 1988).

In general, the depositional environment of this facies is interpreted as offshore lacustrine sediments affected by post-depositional processes.

2.1.2 Red Brown Mudrock

This is the dominant lithology of the lowermost Portland Formation, as it comprises

about 80% of the composite section. It is subdivided into three subfacies: stratified red mudrock (Fl2), ripple cross-laminated red mudrock (Fr2), and disrupted to massive red mudrock (Fm2). Descriptions follow.

2.1.2.1 Stratified Red Mudrock (Fl2)

Description

Fl2 composes 20% of the measured red mudrock. Colors vary from dark red brown to

reddish and unit contacts are non-erosive and planar. Fl2 overlies the black mudrock

facies or is interbedded with Fr2 and Fm2. This unit has thin to thick laminated packages

averaging decimeters in thickness. There are two lamination styles in this facies: (1)

alternating continuous laminae of white calcareous siltstone and red brown siltstone to claystone (Fl2a) and (2) discontinuous laminae of white calcareous siltstone alternating with red brown claystone to siltstone (Fl2b). Fl2 is dominantly found as Fl2a (Fig 2.4A),

41

with lamination varying in thickness from sub-mm to cm scale. Fl2b has thicker laminae

with less siltstone than Fl2a (Fig. 2.4B). The density of white lamina in both subfacies is

not homogenously distributed throughout a unit. Carbonate laminae content can vary

from 20-50% by volume and claystone laminae can reach 70% by volume.

Fig. 2.4 Stratified red mudrock facies. A) Fl2a from core FD23-T – 83.2 ft., and B) Fl2b from core FD13-T – 148 ft. Both cores are four inches in diameter.

42

Mudcracks, 0.5 to 10 cm deep, are filled by coarse siltstone and sandstone in both subfacies as well. These mudcracks display polygonal patterns on core bedding planes and can be complex and wavy. They can be traced to their stratigraphic top and the source of the fills. The intensity of mudcrack distribution within Fl2b is highly variable.

Parts of Fl1b appear very brecciated with high a density of mudcracks.

Interpretation

The presence of mm- to cm-scale lamination and fine grain size suggests deposition

in relatively quiet water bodies. Fl2 is similar to Fl1 except for color. The red brown color of this unit suggests formation in an oxygenated paleoenvironmental conditions

(Andrews et al., 1991). Oxygenated environments can include subaqueous conditions in

shallow water. The polygonal pattern of mudcracks indicates times of subaerial exposure

(desiccation). Fine alternations of claystone and siltstone laminae and disruption by mudcracking (desiccation) point to a playa lake environment (Hardie et al, 1978; Bauld,

1986; Renaut, 1993; Smoot and Lowenstein, 1991; Gierlowski-Kordesch and Rust, 1994;

Shaw and Thomas, 1997; and many others). During flooding events, silt is deposited as bedload while the clay portion of the laminae settles out later. Desiccation mudcracking than can disrupt the lamination on the dry playa mudflat during dry spells (e.g. Hardie et al., 1978; Smoot and Lowenstein, 1991).

Fl2 is found in different lithofacies sequence packages within the cores of the

Portland Formation: (1) Fl1- Fl2-Fr2-Fl2 (Core FD-13T), (2) Fl1-Fl2-Sh-Fm1-Fl2-Fr2 (core

FD-22T), (3) Fl1-Fl2-Fr2-Fl2-Fr2 (core FD-23T lower black mudrock), (4) Fl1-Fr2- Fl2-

Srt-Fr2 (core FD-23T upper black mudrock), and (5) Fl1-Fm2-Fr2-Fm2-Fl2-Fm2-Sh (core

FD-9T). For example sequences (3), (4) and (5) show that Fl2 is associated mostly with

43 red mudrock and sandstone facies. Exceptions include sequences (1) and (2) which show a direct sharp contact of Fl2 with the perennial lacustrine facies of Fl1. These two

sequences indicate that Fl2 was deposited during lake lowstand or drying out of a playa lake.

In sequences (2) and (5) above, Fl2 directly overlies Fl1 units and lacks mudcracks

or concretions, indicating a less shallow part of the lake. Similarly, it supports an interpretation of a gradual regression of offshore lake to playa deposition (e.g. see cores

FD13T and FD22T). In sequences (2), (3), (4) and (5), Fl2 associated with Fr and Srt

contains an abundance of mudcracks, supporting a playa to alluvial plain deposit

(Cheadle, 1985; Smoot 1991, Gierlowski-Kordesch and Rust, 1994; Plint and Browne,

1994; Shaw and Thomas, 1997; Hofmann et al., 2000), where intense desiccation destroys other sedimentary structures and subsequent exposure can enhance soil

formation though repeated wetting and drying of the muds. Thus, Fl2 formed in playa

environments that were inundated during the expansion of the playa lake in floods and

were exposed during the contraction of the playa lake during drought conditions.

2.1.2.2 Ripple Cross-Laminated Red Mudrock (Fr2)

Description

This unit composes 45% of the red mudrock lithology of the cores. It is

characterized by different types of ripple cross-lamination, including high and low angle

inclined ripples as well as climbing ripples (Fig 2.5A, B), generally unidirectional.

Ripples with gentle angles are dominant with rare high angles at 30º. Ripple forms have

an average wavelength of 2 cm and cosets are generally a few cm in thickness. The cross-

44 lamination ripple forms are defined by white fine-grained siltstone and sandstone as well as red mudstone laminae. The proportions of silt/sand to mud laminae vary from 70% to

Fig 2.5 Ripple cross-laminated red mudrock (Fr2). A) Ripple cross-lamination in core FD28-T – 159.6 ft., B) V-shaped trace fossil interpreted as escape burrow (core FD12-T - 194 ft.), field of view is 8 cm by 10 cm, and C) Concretions, stratigraphic up to the left (core FD19-T – 79 ft.), all cores are four inches in diameter.

45

30% by volume. Soft sediment deformation is rare as convolute bedding and slump structures on the cm scale. Fr2 contains carbonate nodules and concretions of different

diameters (1-6 cm) and mudcracks (Fig. 2.5D). Mudcracks are only 1-2 cm long and rare,

filled with coarser material (sandstone). Crack morphology exhibits irregular V-shapes

with polygonal patterns on core bedding planes.

Trace fossils are prominent in this facies. One coarsely back-filled cylinder (3cm

long) with a fine clay lining is present in FD12T at 165 ft. The fill of this cylinder

includes many random clumps of sand grains distributed throughout finer-grained

backfill. Fl2b also contains traces that bend the sediment in a V-shape downward (3mm

wide and max 10cm long), mostly present as pairs. One example shows a V-shape

upward (Fig 2.5C).

Interpretation

Fr2 is very similar to the ripple cross-laminated black mudrock Fr1. The major

differences are the red color and the gentle angle of ripple forms in Fr2. The ripple

forms, incorporating both mud and silt/sand laminae, must be formed from bedload containing sand, silt, as well as mud as sand-sized aggregates (Rust and Nanson, 1989;

Gierlowski-Kordesch and Rust, 1994i; Gibling et al., 1998; Gierlowski-Kordesch and

Gibling, 2002; Marriott et al., 2005). All brown red units are formed under oxygenated conditions as deduced by their color, which indicates shallower water. Mudcracks are interpreted as desiccation cracks due to their polygonal morphology.

Fr2 is also found in five facies sequences: (1) Fl1-Fr- Fl2-Srt-Fr2 (core FD23T, upper black mudrock), (2) Fl1- Fl2-Fr2-Fl2 (core FD-13T, upper black mudrock), (3) Fl1-

Fm-Fl2-Fr2-Sh (core FD-22T), (4) Fl1-Fl2-Fr2-Fl2-Fr2 (core FD23-T, lower black

46

mudrock), and (5) Fl1-Sh-Fr2-Sh-Fl2 (core FD-26T), generally associated with facies Srt

and Fl2.

Ripples are formed in shallow lakes through wave action (bi-directional) or

sheetfloods (unidirectional) entering standing water (Collinson and Thompson, 1982;

Smoot, 1985; Prothero and Schwab, 1996; Reading, 1996). Sheetflood deposits commonly contain unidirectional ripple cross-lamination (McKee et al., 1967; Tunbridge,

1981; Sneh, 1983). A powering-down sequence representing the rapid deceleration of flow in sheetflooding (Cheadle, 1986; Smoot, 1991) is present in facies sequence (1) and

(5) above with sandstone facies (Sh and Srt) grading into facies Fr2. In addition, the

association of this facies with Fl1 (e.g. facies sequences (2) and (4)) also suggests

sheetflooding onto a “muddy sandflat” associated with playa deposits (Gierlowski-

Kordesch and Demicco, 1986; Gierlowski-Kordesch and Rust, 1994, and many others).

The playa deposits (Fl2) and the “muddy sandflat” deposits (Fr2) of the

lowermost Portland Formation cores are not as dissected with mudcracks as similar facies

in the underlying East Berlin Formation (Gierlowski-Kordesch and Rust, 1994). This could indicate reduced subaerial exposure time between flooding events and perhaps even a faster depositional rate. Trace fossils support this interpretation. The coarsely back-filled cylinder is interpreted as a weakly-organized, back-filled burrow because sand grains from the surrounding unit are incorporated into the fill randomly and the back-fill is not very well defined. This is evidence for catastrophic or quick sedimentation as the burrower was clearly in a hurry. In addition, the V-shaped features may represent quick burrowing downward or upward as the animal tries to escape the high siliciclastic influx.

47

2.1.2.3 Disrupted to Massive Red Mudrock (Fm2)

Description

This unit composes about 35% percent of the measured cores of the red brown mudrock. Two subfacies are identified: (1) mixed to disrupted layers of mostly Fr

Fig 2.6. Disrupted to massive red mudrock (Fm2). A) Mudrock disrupted by sandstone-filled mudcracks

(Fm2a) (core FD20-T – 123 ft.), core is two inches in diameter, B) Massive mudrock (Fm2b) (core FD12-T

– 220 ft.), core is four inches in diameter, C) Sandstone-filled mudcracks in Fm2a (core FD19-T – 160 ft.), core is four inches in diameter, D) Siltstone-filled mudcracks (core FD30-T - 85 ft.), core is four inches in diameter, E) Cores from FD29-T – 189 ft. level at lower left corner, showing disrupted textures, cores are four inches in diameter, and F) Cyzicus and Cornia sp. on bedding plane of core FD31-T – 155.3 ft.

48

(Fm2a), showing little preserved original depositional structure (Fig 2.6A) and (2) units with massive fabrics (Fm2b) (Fig. 2.6B). Fm2b exhibits relict sedimentary structures, such

as ripple cross-lamination and horizontal lamination, within its massive blocky to

mudcracked textures that are identical to Fm2a. Numerous mudcracks with polygonal

geometry in both subfacies are filled with sandstone and mudstone and 3-5cm in length

(Fig 2.6C). In addition, there are crooked tubes over 5 cm long of a cm-scale diameter

that are filled with sandstone and have no associated polygonal geometry. Similar

features are described by Smoot (1991). This is the only facies where fossils of

conchostracans (Spinicaudata - Cyzicus and Cornia sp.) are present (Fig 2.6D).

Fm2a represents 90% of this facies and contains irregular cm-scale patches of sand

grains as well as randomly distributed sand grains in the massive blocky mudstone

matrix. Slickensides, clay linings on fracture surfaces, are characteristic of this facies.

Nodules and concretions (some septarian) of white gray to green in color and approximately 3-7 cm in diameter are very common.

Interpretation

Relict traces of lamination suggest that these rocks were originally rippled or stratified mudrock, but are now either altered to disrupted or totally massive in texture.

Destruction of lamination can come through reworking of sediment by organisms

(bioturbation), evaporite mineral or ice growth (haloturbation or cryoturbation), or soil formation (pedoturbation) (Smoot and Olsen, 1988). The association of this facies with

Fr2 and F12 and the relict sedimentary structures in some units indicate original deposition as sheetflood to playa mudflat deposits (Hardie et al., 1978; Cheadle, 1985;

Smoot 1991; Smoot and Lowenstein, 1991; Gierlowski-Kordesch and Rust, 1994;

49

Hofmann et al., 2000). The presence of disrupted layers, abundant and deep mudcracks, blocky massive texture, abundance of slickensides, and common concretions or nodules, is typical for paleosols during times of low lake stand on an alluvial plain or “muddy sandflat” and its associated soil-forming processes in an arid to semi-arid climate (Smoot and Olsen, 1988; Smoot, 1991; Smoot and Lowenstein, 1991; Gierlowski-Kordesch and

Rust, 1994).

Conchostracans (Spinicaudata) are inhabitants of temporary pools and point to an ephemeral, freshwater environment (Gore, 1988), though there are some species that are subsaline to stenohaline (Hammer, 1986). Ponding of water can occur on the alluvial plain for short periods after depositional events (Gierlowski-Kordesch, 1991). The sand- filled tubes have been interpreted by Smoot (1991) as root structures, or rhizoliths, that filled with sand after the decay of the root.

2.1.3 Sandstone

This unit composes about 5% of the entire measured lowermost Portland

Formation core material and appears as very thin sheets of sand layers interbedded mostly with the red brown mudrock units. This lithology is divided into two subfacies:

(1) horizontally bedded sandstone (Sh) and (2) ripple cross-laminated to trough cross- bedded sandstone (Srt) (Fig 2.7).

50

2.1.3.1 Horizontally Laminated Sandstone (Sh)

Description

This unit composes 60% of the measured sandstone lithology and is 50 cm to 2 m

thick with planar and non-erosive lower contacts. Sh is very well sorted, and the grains

vary in size from fine- to medium-grained. Quartz and feldspar predominate and mud clasts are also present (Fig. 2.7A) Mud laminae intercalate commonly with the sandstone laminae in lamination on the mm-scale. Facies sequences containing Sh include (1) Fl1-

Sh-Fr2-Sh-Fl2 (core FD-26T) and (2) Fl1-Fm-Fl2-Fr2-Sh (core FD-22T). Sequence (1)

shows that Sh can directly overlie or is interbedded with black mudrock facies. Also Sh is associated with ripple cross-laminated red brown mudrock (Fr2).

A B

Fig. 2.7 Sandstone subfacies. A) Horizontally-laminated sandstone (Sh) intercalated with some siltstone with ripple cross-lamination (core FD30-T – 78 ft.), field of view is 7 cm by 8 cm and B) Trough cross- bedded sandstone (Srt) with mud cross-laminae (core FD30-T – 60 ft.), field of view is 8 cm by 10 cm.

51

Interpretation

This facies is interpreted as high-energy sheetflood deposits or deltaic sheet. Its association with black mudrock suggests deltaic depositional setting while its association with Fr2 facies suggests unidirectional current flow on a sandflat or alluvial plain

(Hardie et al., 1978; Smoot and Lowenstein, 1991). Bedding planes were not accessible

in the core material because this facies is so well-cemented. It is not possible, therefore,

to determine the presence of parting lineations to confirm this interpretation. Modern

deposits of sheetfloods commonly contain horizontally laminated sandstone (McKee et

al., 1967; Tunbridge, 1981; Sneh, 1983). The mud incorporated into the horizontal

laminae is interpreted as sand-sized mud aggregates after Rust and Nanson (1989),

Gibling et al. (1998), and Gierlowski-Kordesch and Gibling (2002). The mud aggregates

must be incorporated as bedload during deposition of these sandstones.

2.1.2.2 Ripple cross-laminated to trough cross-bedded sandstone (Srt)

Description

This unit composes 40% of the measured sandstone lithology. The grain size and

mineral composition is similar to Sh. Srt varies in thickness from 50 cm to 3 m. This

facies contains dominantly low angle, trough cross-bedding (Fig. 2.7B) with rare cm-

scale interlayers and lenses of ripple cross-lamination. Generally,the cross-laminated lenses are composed of siltstone or very fine sandstone with the trough cross-bedding

comprised of fine- to medium-grained sandstone. Ripple forms are similar to those in Fr1

and Fr2. A typical facies sequences containing Srt is Fl1-Fr- Fl2-Srt-Fr (core FD-23T),

52

which indicates that Srt is associated with playa deposits (Fl2) and finer-grained

sheetflood deposits (Fr2).

Interpretation

This unit is also interpreted as a sheetflood deposit, as it is associated with other

interpreted sheetflood deposits. Trough cross-bedding and ripple cross-lamination in

sands occurs in modern sheetflood deposits (McKee et al., 1967; Tunbridge, 1981; Sneh,

1983). The change in sedimentary structure from cross-bedding to cross-lamination is interpreted to represent changes in current strength as well as depth of the floodwaters.

The thickness and volume of the sandstone units increases toward the eastern border fault, as gauged by the three km long tract of core locations (see next section). This is consistent with the deepening of the basin toward the border fault as well as proximity of the proposed source area (LeTourneau and McDonald, 1988).

2.2 Petrography and XRD Data

Eleven thin sections, comprised of four black mudrock, five red mudrock, and

two sandstone samples, were prepared for observations on the mineralogic composition,

micro-sedimentary structures, and sediment fill of sedimentary structures in the described

facies. In addition, X-ray diffraction analysis (XRD) was performed on three bulk

samples to confirm mineralogy of the carbonates only because carbonates are crucial for

paleoenvironmental interpretation (Dean, 1981). These samples included (1) a nodule

from Fl1b, (2) a sample from Fm1c, and (3) a sample from Fl1a.

53

2.3.1 Black Mudrock

Four thin sections of the black mudrock show the distributional and compositional

variation of the subfacies. Two samples from Fl1 (Fl1a and Fl1b) both contain 20-30% by

volume of organic matter, with micritic carbonate composition (30% magnesite or high-

Mg calcite) and 40% clay. This sample of Fl1a has circular blebs of micrite on the micro-

mm scale (Fig. 2.8A) surrounded by organic matter and associated with pods of pyrite

Fig 2.8 Thin sections of black mudrock facies (FOV = 2.5mm) A) Fl1a showing blebs of organic matter surrounded by high-Mg carbonate (magnesite?) with the largest ones toward the bottom of photo, (core FD-

24T – 58 ft.) B) Laminae of Fl1b showing organic laminae and large pods of framboidal pyrite (core FD24-

T – 58 ft.). C) Massive texture of Fm1c showing dolomitic matrix and floating organic matter (core FD23T

– 114.9 ft.), and D) Kerogen-filled fracture from Fm1c (core FD23-T – 114.9 ft.).

54 framboids in a claystone matrix (first described by Pienkowski and Steinen, 1995). In the claystone laminae of Fl1b, organic matter instead manifests itself as very thin laminae

(Fig. 2.8B). Fl1b contains fine alternations of claystone laminae and white

laminae dominantly composed of siliciclastic grains with a few aligned mica crystals and

clay or micritic carbonate laminae (20% by volume).

Fl1b has the least organic matter content (3% by volume), diluted by clay and silt

or sand. Sand laminae contain abundant clay masses that are circular to flattened between

the quartz grains. These are interpreted as pedogenic mud aggregates (see Rust and

Nanson, 1989). Compaction is evident from broken carbonate laminae, which appear as

lenses, surrounded by aligned clay or mica grains that bend around the laminae. Previous

work by Gottfried and Kotra (1988) indicate that the mineralogy of the clays in the

lacustrine shales and of the lowermost Portland Formation include chlorite,

illite and smectite. An expandable clay, like smectite, is crucial for the formation of

pedogenic mud aggregates (Rust and Nanson, 1989). Clay aggregates are also reported

from other formations in the Hartford basin (Gierlowski- Kordesch and Rust, 1994;

Gierlowski-Kordesch, 1998; Gierlowski-Kordesch and Gibling, 2002).

The X-ray diffraction (XRD) analysis of select carbonate/siliciclastic bulk

samples from the black mudrock facies contributes information on the paleoenvironment

of the lowermost Portland lakes. XRD was conducted on (1) a nodule from Fl1b, (2) a

sample from Fm1c (core FD23T – 114.9 ft.), and (3) a sample from Fl1a (core FD24-T- 58

ft.). Discussion will center only on carbonate identification from the bulk mudrock

samples. The carbonate in the nodule contains Mg-rich carbonate, perhaps magnesite, though the siliciclastic mineral traces may have swamped out the carbonate peak (XRD

55

graph – Fig. 2.9A). Carbonate blebs from Fl1b have the exact same mineralogy and are

composed of Mg-rich carbonate as well, perhaps dolomite or magnesite (Fig. 2.9A).

Purer carbonate samples need to be collected for a clear trace.

Fm1c has a massive texture composed of more than 50% of a dolomitic matrix

(see XRD graph in Fig 2.9B), 10% pyrite, 5% organic matter, and 35% clay (Fig 2.8C).

The dolomitic signature suggests that haloturbation is in part responsible for the massive

texture for Fm1c. The kerogen-filled fractures (Fig. 2.8 D), as discussed in section on

facies Fm1 (2.1.1.3), exhibit displacive textures indicating fluid movement of hydrocarbons after cementation of this subfacies (see Parnell, 1986).

Gierlowski- Kordesch and Rust (1994) report magnesite from one of the perennial offshore lacustrine facies of the East Berlin Formation. Mg-rich carbonates, such as dolomite and magnesite, support the interpretation of saline lake conditions.

2.3.2 Red Mudrock

Five thin sections represent three facies: Fl2, Fr2, and Fm2. All samples have similar

texture of clay to fine sand. The sand grains are composed of dominantly sub- rounded

quartz (30-70%), mica (5%-30%), and feldspar (5%- 10%) with minor pedogenic mud

aggregates preserved between mineral grains. The red clay to silt also contain some

aligned mica (10-30%). Similar to the black mudrock lithology, the clay composition of the red mudrock is chlorite, illite, and smectite (Gottfried and Kotra, 1988).

Pedogenic mud aggregates are crucial for the incorporation of mud into current ripple cross-lamination in the red mudrock facies (Fr2) (Fig. 2.10A,B, D). The mixing of

56

Fig 2.9. XRD analysis of black mudrock samples of A) a nodule from Fl1b and Fl1a (core FD24-T-

58 ft.) and B) (2) a sample from Fm1c (core FD23T – 114.9 ft.). See text for details. D= Dolomite peak, C= Calcite peak and M= Magnesite peak. Peak intensity measured in counts.

57

Fig 2.10. Thin sections of Fr2, Fm2, Fl2, and Sh facies. FOV = 2.5mm. A) Fr2 facies showing pedogenic mud aggregates defining laminae and interspersed in the fine sand laminae (core FD12-T) – 165 ft., B)

Ripple laminae of Fr2 - sand/silt intercalated with mud laminae containing pedogenic mud aggregates

(darker round masses) (core FD-26-T – 194.5 ft.), C) Massive texture of Fm2 representing paleosol development (core FD29T – 162 ft.), D) Ripple laminae of Fr2 showing different densities of pedogenic mud aggregates (darker round masses) (core FD26-T – 114 ft.), E) Contact between sand-filled mudcrack and mudstone lamina in playa sediments (Fl2) (core FD 30-T – 155 ft.), and F) Horizontally laminated sandstone (Sh) showing pedogenic mud aggregates (core FD29T – 134.2 ft.) preserved between siliciclastic mineral grains.

58

mud and sand grains in a desiccation mudcrack (Fig. 2.10E) illustrates the beginning of soil formation processes culminating, with extended exposure, in a massive paleosol fabric (Fig. 2.10C).

2.3.3 Sandstone

Two sandstone samples were taken from Sh and Srt. The Sh facies is composed of quartz (30-50%), feldspar (15-30%), mica (5- 10 %), and pedogenic mud aggregates (5-

10%). The grains of quartz and feldspar are sub-angular in shape and pedogenic mud aggregates define laminae within the horizontal lamination (Fig. 2.7A). Pedogenic mud aggregates are preserved between siliciclastic grains (Fig. 2.10F) that can withstand compaction better than the mud aggregates (see Gierlowski-Kordesch and Gibling, 2002).

The Srt facies is grain-supported with sub-angular to angular grains. The mineral composition of the grains is quartz (45-65%), feldspar (10-20%), mica (5%), and pedogenic mud aggregates (5-10%). Distribution of pedogenic mud aggregates is similar to that in Sh (Fig. 2.7B).

59

Chapter Three

3.1 Stratigraphy

The cores comprised three formations: the East Berlin Formation, the Hampden Basalt,

and the lower Portland Formation. The focus of this study was 600 m of the lowermost

Portland Formation. The vertical and lateral extent of the lowermost Portland Formation

was reconstructed using the engineering report and preliminary geologic assessment from

the core extraction for the Park River Tunnel Project (U.S. Army Corps of Engineering,

1977). The cores were drilled vertically in a horizontal profile with approximately 100 m

distance between consecutive drill holes for a total horizontal distance of three kilometers

(Figure 1.5). The engineering document shows the exact location of the 35 cores, dip of

the units at the time of drilling, sedimentary units recognized during core logging, and

structural information.

In order to establish the lateral and vertical extent of the lower Portland Formation

for stratigraphic correlation, a series of steps were followed. Step (1): Twenty of the Park

River cores were measured and described in detail, including its lithology, sedimentary

structures, fossils, and diagenetic features. See Appendix for the twenty measured cores.

The core logs were subdivided into facies for paleoenvironmental analysis. Step (2): The

twenty core logs were placed in succession horizontally, according to their actual location

in relation to each other based on the engineering report for the Park River Tunnel Project

(U.S. Army Corps of Engineering, 1977) (see Figure 3.1). Almost all of the cores contain

from one to three black mudrock units. The black mudrock units, therefore, were the best

units for lithologic correlation within the lowermost Portland Formation. Each core was

60 Fig 3.1 Reconstructed vertical profile of lowermost Portland Formation from River Park Tunnel Project. Project. Tunnel Park River from Formation Portland lowermost of profile vertical Reconstructed 3.1 Fig

61 positioned in the reconstructed profile based on the depths of the black units as measured by the engineers of the Park River Tunnel Project (Fig. 3.1). Step (3): The lowermost

Portland Formation has a dip of approximately 10-15º so correlation among core logs was based on an average dip angle of 12º. There were very few cores that could be directly matched to the lithology of the next adjacent core because many black mudrock facies mostly correlated with deeper layers not drilled (see Figure 3.1). There is also evidence of normal faulting along the core transect, so correlation in some areas was difficult. The final correlation is not a unique solution, but the faults planes do correlate with lithology in the Portland Formation that suggests tectonic disturbance.

The vertical stacking of the units (Fig 3.2) from the top of the East Berlin

Formation, including the entire Hampden Basalt and about 600 m of the lowermost

Portland Formation, aided in the visualization of the entire composite section. Step (4):

Cyclic sequences based on the repetition of the black mudrock units in the composite section were identified to organize vertical sequences of facies changes through time.

Each cycle is defined simply by a gray to black mudrock lacustrine facies unit at the base of each cycle, followed by red brown mudrock and/or sandstone until the next gray to black mudrock unit (see an example in core FD 18 T in the Appendix). This is called a

Van Houten cycle (Olsen et al., 2005) and is interpreted to represent a climatic change from more humid conditions for lake formation, followed by drier conditions for lake contraction and the establishment of fluvial conditions. The vertical stacking of facies within cycles differs from one cycle to another, as illustrated by the various kinds of facies sequences described in the previous chapter, but the Van Houten cycles are defined by color only.

62

Fig 3.2 Vertical stacking of the lowermost Portland Formation cores showing fourteen black mudrock units within the Smiths Ferry and Park River Members of the Park River cores.

63

Previously, between six to nine black lacustrine facies units were identified by

Gilchrist (1979) and Gierlowski-Kordesch and Huber (1995) in the lower portion of the

Portland Formation, but this was based on disparate outcrop localities (Fig 1.4) and an incomplete stratigraphic framework. However, here the composite section of these Park

River cores displays at least fourteen black lacustrine facies units interbedded with the red brown mudrock and sandstone units of the Smiths Ferry and Park River Members within the lowermost Portland Formation (see Fig 3.2 and Appendix). The new tentative stratigraphy of the lowermost Portland Formation of Olsen et al. (2005) only identifies twelve Van Houten or lacustrine cycles within these two lower members. This may be attributable to the effect of fault block geometries in stratigraphic correlation across the basin that was not addressed in their correlation across the northern Hartford and southern Deerfield basins.

The various stacking patterns within Van Houten cycles as well as the overall repetitive pattern of the cycles contribute significant and useful information about the development of the basin and the main controlling factors on the development of the lithofacies distribution within the lowermost Portland Formation. In this context, several key questions need to be addressed. Do these lake units represent one lake that expanded and contracted or different lakes or did new lakes appear in each cycle? What were the controlling factors: climate, tectonics, or both? In order to discuss these issues, a lacustrine depositional model explaining sedimentation patterns in lake basins must be described first.

64

3.2.1 Depositional Model

A lacustrine water body forms by both the presence of a topographic depression and

the availability of water to fill it (Kelts, 1988). Lakes are dynamic environments, and lake

sedimentation represents the interaction of many complex physical, biological, chemical,

morphologic, and environmental variables. Consequently, efforts to understand lake

depositional models necessitates defining those factors: basin tectonics, drainage area,

bedrock, topography, rate of subsidence, nutrient level, light availability, turbidity,

oxygen availability, depth, and sedimentation rates (Katz, 1990; Barron, 1990; Bohacs et

al., 2000, 2003). All these factors are controlled ultimately by two major variables,

climate and tectonics, which govern the distribution of lakes and influence lake

productivity and preservation of organic matter (Bohacs et al., 2000, 2003).

Lakes can be classified based on their origin, salinity, hydrology, depth, and

thermal or chemical stratification (Hammer, 1986; Wetzel, 2001; Cohen, 2003). This

particular study will focus on hydrology of lake basins, since this factor controls water

and sediment input.

Lakes are generally classified into three main types based on the

precipitation/evaporation ratio (or climate) and hydrology (closed to open drainage)

based on subsidence rates of the lake basin (tectonics) (Carroll and Bohacs, 1999; Bohacs

et, al., 2000; 2003). These three types are termed underfilled, balanced-fill, and overfilled

(Figure 3.3).

Closed hydrology (underfilled): These lakes occur in basins where there is no water outlet from the lake and drainage is closed. The lakes can be perennial or ephemeral, depending upon climate and groundwater patterns (see Rosen, 1994). In this lake type,

65 rates of subsidence or accommodation space consistently outstrip available water and sediment supply, resulting in a persistently closed basin hydrology. Individual lakes are short-lived with unstable shorelines. Hence, parasequences and sequences are commonly very thin (on the scale of decimeters) (Bohacs et al., 2000, 2003)

Fig 3.3 Lake basin model showing relationships between accommodation space and climate versus lake

type (After Bohacs et al., 2000; 2003 – courtesy of Alan Carroll).

Closed to open hydrology (balanced-fill): In these lakes, evaporation and outflow are

balanced by precipitation and inflow. They occur where the rates of sediment plus water

supply and potential accommodation space are roughly in balance over the time span of

sequence development. Lake hydrology is closed during deposition of basinally-restricted

66 lowstand strata and open during highstand deposition of obliquely prograding strata. In this type of lake, climatically-driven, lake level fluctuations are common and shorelines are unstable. Parasequences and sequences might be thin or thick depending on water level (Sly, 1978; Bohacs et al., 2000, 2003).

Open hydrology (overfilled): In this type of lake basin, precipitation exceeds evaporation and there is continuous recharge of meteoric water to the lake. In this case, the rate of supply of sediment plus water consistently exceeds potential accommodation space. The resulting lake hydrology is permanently open or mostly over the time span of accumulation of depositional sequences. Overfilled lakes have relatively stable shorelines and climatically driven lake-level fluctuations are minimal. Parasequences might be thin or thick depending on the sediment input. (Sly, 1978; Bohacs et al., 2000, 2003).

Olsen (1990) and Schlische and Olsen (1990) have identified these three lake types from the Newark Supergroup basins. Underfilled lacustrine basins or the Fundy basin types are characterized by vertical aggradation of units with desiccation cycles associated with evaporites. Balanced-filled lacustrine basins or the Newark basin types are characterized by the combination of progradation of siliciclastic sediments where the lake is open and aggradation of chemical sediments if it is closed. Overfilled lacustrine basins or the Richmond basin types are characterized by interbedded units of lacustrine facies with coal, fluvial, and delta deposits.

The most fundamental and common behavior of lake formation within tectonic basins is that lake types commonly evolve from one lake type to another in a predictable pattern over the life of the basin (Bohacs et al., 2000). The pattern, as documented for the

Green River Formation in the Greater Green River basin, is from overfilled (Luman

67

Tongue), to balanced-fill (Scheggs Bed) to underfilled (Wilkins Peak Member), back to balanced-fill (Lower LaClede Bed of the Laney Member) and overfilled (upper LaClede

Bed of the Laney Member) lakes (Carroll and Bohacs, 2001).

The Hartford basin is postulated to be a fluvial basin (New Haven Arkose), evolving into a overfilled lake basin (lower ), then a balanced- fill lake basin (upper Shuttle Meadow Formation to East Berlin Formation to lower portion of the lower Portland Formation), then an overfilled lake basin (the upper protion of the lower Portland Formation), and finally back to a fluvial basin (upper Portland

Formation) (Bohacs et al., 2003).

The lowermost Portland Formation in this study shows facies transitions in the form of cyclic units that are mainly characterized, from bottom to top, by lake-playa- alluvial plain. The playa facies are intermixed with the alluvial plain facies, as evidenced by sheetfloods directly overlying some lake units, so an organized regressional sequence, as normally seen in the marine, is not really present. The Van Houten cycles of lake- fluvial alternations indicate that lake level (depth) change is caused by change in precipitation and evaporation rates or change in subsidence and sedimentation rates. The unstable shorelines of the lakes in the lowermost Portland Formation exhibit a balance- filled lithologic package (open and closed hydrology) (Bohacs et al., 2003).

3.2.2 Tectonic and Climatic Controls

The Newark Supergroup basin fill is represented by cyclic units that characterize

different depositional environments. According to Olsen (1990), lake level cycles are

related to climatic precession and short and long modulated eccentricity cycles. Some

68 researchers in the Newark Supergroup predominantly agree with Olsen (1985; 1986;

1990) and Olsen et al. (2005) that the main cause for the cyclicity of the lacustrine facies

(lake level fluctuation in Van Houten cycles) is 20ky Milankovitch climate forcing (e.g.

Hubert et al., 1982; Gore, 1988; Olsen and Kent, 1996). Four orders of climate modulation are proposed to control cyclicity of the Van Houten cycles stacking pattern in the Newark Supergroup: 100k years, 405k years, 1.75 million years, and 3.5 million years

(Olsen et al. 2005).

It is unquestionable that climate has a major control in lacustrine facies distribution, however, in tectonically active rift basins, it is unreasonable to assume only climate contributed in the cyclicity of lacustrine facies. Olsen et al. (2005) further divide the basin fills of the Newark Supergroup and other Triassic-Jurassic rift lake basins of

Pangea into four tectonostratgraphic (TS) sequences (I-IV) (see Fig. 1.3) spanning the

Permian through Jurassic Periods, defining tectonic extensional pulses. The Portland

Formation is within TS IV, which defined by the three basalt flows and most of the

Hartford basin fill, except for most of the New Haven Arkose. The change of hydrology within the Hartford basin from fluvial to lacustrine to fluvial over the span of the life of the rift basin is not addressed in this framework.

Large deep lakes can originate only during a specific phase of a rift’s tectonic evolution, and climate and other factors determine whether they actually do occur during that phase (Lambiase, 1990). Subsidence controls the depression needed to make a lake and climate determines whether that depression will be filled with water. Examples of tectonic and climatic controls in rift sedimentation are addressed in order to understand the cyclicity of lacustrine facies of the lowermost Portland Formation.

69

3.2.2.1 Tectonic Control

Tectonics is the main control on re-shaping the geomorphology of basin evolution

(Ingersoll and Busby, 1995). Different tectonic histories and scenarios can develop through the evolution of a rift. This depends on several factors: the type of rifting (half graben or graben), subsidence rate, preexisting structures, volcanism, width of the basin, drainage system within the basin, and type of rocks within the source area (Lambiase and

Bosworth, 1995). Rift basins are dominated by half graben type, like the Newark rift system, and show similar lithofacies assemblages that distinctly characterize rift basins from other tectonic settings.

There have been many models to explain the depositional system and basin evolution of half-graben rift systems (e.g. Lambiase, 1990; Gawthorpe and Leeder,

2000). Clearly, the subsidence rate of a rift basin is not continuous, but rather, it is periodic. Times or pulses of tectonic activity (subsidence) are followed by times of tectonic quiescence and isostatic rebound. This is the main control on facies distribution within a rift basin. During tectonic active times, more accommodation space is created as along with a high sedimentation rate (though this aspect is also dependent on climate).

The space created during tectonic subsidence will be reduced by sediment infilling during and after this tectonic event. The rate of infilling is dependent on the subsidence rate of the basin through time as well as the effects of isostatic rebound on accommodation space. This tectonic activity through time then can affect lithologic distribution that repeats itself throughout the geologic life of the basin as the amount of accommodation space is altered through time.

70

As documented from modern rift basins, such as the East African rift valley (e.g.

Scholz et al., 1990; Soreghan and Cohen, 1996; Le Turdu et al., 1999), the distribution and geometry of sedimentary deposits within rift basins also support a tectonically- controlled distribution of sediments. The type of structural margin in a half-graben lake, whether the steep slope of a fault escarpment margin or the more gentle slope of the hinged margin, controls the spatial arrangement of facies in that lake. For example, alluvial fans composed of gravels and coarse sands are laid down near the border faults; facies grade to fine sediments away from the main border fault. Alluvial fans could not develop on a hinged margin, instead fluvial systems would develop. Each of these depositional systems would then be altered as more proximal or distal in nature with increased subsidence following a tectonic pulse. Pietras and Carroll (2006) have shown that tectonic influences on drainage patterns can control deposition in a foreland lake basin, as documented in the Wilkins Peak Member of the Green River Formation in

Wyoming.

Schlische and Olsen (1990) modeled a rift basin (mass balance model) with an assumption of constant sediment supply and uniform rift basin subsidence throughout the history of a rift basin, using the Newark Supergroup basins as models. According to

Schlische and Olsen (1990), the initial stage of a rift basin will fill with fluvial sediment and excess sediment will leave the basin if the tectonic subsidence is slow or the rate of sediment supply is high enough. As the basin continues to subside, the same sediment volume will spread over an increasingly larger surface area and lakes will start to develop with an exponential increase in maximum possible lake depth (Schlische and Olsen

(1990). However, after a brief period of exponential increase in lake depth, the basin will

71 slowly and hyperbolically decrease in size because the half-graben cannot subside indefinitely. If the subsidence rate slows sufficiently or stops and volume of the sediment remains constant, the accumulating rate and lake depth would continue to decrease until the depositional surface could reach the basin’s outlet, thereby heralding the return of fluvial sedimentation at a rate equal to the subsidence rate (Schlische and Olsen, 1990).

This generally does not match the tectonostratigraphic (TS) sequences of Olsen et al.

(2005), but instead the tripartite classification of Lambiase (1990). This mass balance model of Schlische and Olsen (1990) may be true for uniform subsidence during the whole life of a rift basin, but the subsidence rate and periodicity of rifting are variable and certainly the basin does not subside as one continuous block (see Cohen, 1990).

Volcanism is an indication of extension during rift basin formation (Leeder, 1995;

Einsele, 2000). The Newark Supergroup basins were definitely magmatically active during deposition of sediments, as evidenced by flows and intrusions of basaltic rocks and numerous normal faults (McHone and Puffer, 2003). There are three Hettangian age basalt flows in the Hartford basin, the Talcott, Holyoke, and Hampden (Gierlowski-

Kordesch and Huber, 1995). The youngest Hampden Basalt separates the East Berlin

Formation below from the Portland Formation above (see Table 1.1). Tectonic volcanic activity certainly affected sedimentation in the Hartford basin through basalt accumulation on the landscape. Evidence for syndepositional subsidence can be found in changes in the thickness of formations in the Hartford basin, which increases toward the eastern border fault (McDonald and LeTourneau, 1988). The deepening of the basin toward the border fault and tilting of the beds of Hartford basin suggests more continuous tectonic activity during sedimentation. All this evidence clarifies the influence of

72 tectonics on sedimentation within the Hartford basin, affecting the distribution and thicknesses of facies through time.

The cyclic sequences of the lowermost Portland Formation are represented by a perennial offshore lacustrine facies overlain by playa to alluvial deposits. The position of these sequences within the lake basin is determined by tectonic and/or climatic control

(Bohacs et al., 2000; 2003). The effects of climatic change on lake sedimentation are recorded more clearly in the basin fill record of underfilled and balanced-filled. During cyclic wet and dry climate, such lakes will continuously contract (low stand) and expand

(high stand) in parasequences of transgression and regression (Bohacs et al., 2000; 2003).

If there is no subsidence, then the lake facies in the cycles should progressively contain shallower and shallower facies up-sequence as the basin fills with sediment. In other words, the depths of the lakes preserved in the cycles are reduced by an equal volume of sediment fill as balanced by subsidence rates. A series of lacustrine facies in a rift basin fill should show a sequential, general shallowing trend up-section within the cyclic lake paleoenvironments if there is no subsidence during deposition. However, if there is more or less continuous subsidence, then the types of lacustrine facies in each sequential cycle should remain similar up-sequence in the progression, because each space filled with the sediment will be created by new subsidence episodes.

The Hartford basin is an asymmetric basin tilted toward the east. This indicates that the deepest part of the basin is located at the eastern border of the basin. The core material from the lowermost Portland Formation is located in the west central part of the basin, distal from both eastern and western source areas. The black mudrock lacustrine facies in each of the fourteen identified lake cycles are very similar with offshore lake

73 facies. In the entire composite section (600m) of the lowermost Portland Formation, there is no indication of any shallowing-upward trend within the lake facies. The lake cycles simply repeat themselves over and over again. Thus, this supports the idea that the basin during lowermost Portland time was more or less continuously growing in accommodation space and maintaining a balance between subsidence and sedimentation.

Of course, this does not rule out the contribution of the climate to the cyclicity of the lowermost Portland Formation, as discussed next.

3.2.2.2 Climatic Control

Climate is considered a main driving force for changing lithofacies as well as the type and nature of sediments within sedimentary basins (e.g. Cecil, 1990; Parrish, 1993).

Van Houten (1982, as cited in Parrish, 1993) explains the reddening of the fluvial and alluvial sediments of the Newark basin as a result of alternating wet and dry climates, as opposed to a diagenetic origin (Hubert and Reed, 1978; Wolela and Gierlowski-

Kordesch, 2007). Iron is leached from easily weathered iron-bearing minerals during the wet cycle. Hematite, which is relatively stable, is then precipitated during the dry cycle.

In ranging from desert sandstones through red paleosols to even to bauxites, the reddening is allegedly dependent upon seasonality of rainfall (Parrish, 1993). Thus, redbeds form along a climatic gradient, with seasonal rainfall in a mostly dry environment at one extreme and seasonal rainfall in a mostly wet environment at the other.

Climatic models for Pangea show that monsoonal climatic conditions existed throughout most of Pangea; this pattern breaks down as wind patterns change in

74 proximity to the relief of mountain belts, comparable to the Asian monsoonal climatic conditions associated with the Himalayas (Hay et al., 1982; Parrish, 1993; Olsen and

Kent, 1996). In addition, Parrish (1993) indicates that the monsoonal climatic conditions of Pangea show variation from the to Late Triassic, where cyclic wetting and drying is related to global cooling and warming patterns. The climate patterns support Van Houten’s (1982 cited in Parrish, 1993) interpretation of the origin of the redbeds of the Newark Supergroup.

Climate is also controlled by latitude (Reading, 1996). The lithologic variation of sediment fill among the Newark Supergroup basins is governed by the latitudinal position of the Newark rift system, with in the south and evaporites in the north (Gore,

1989). In addition, the entire rift system drifted slowly northward during the Triassic and

Jurassic which cause an additional paleolatitudunal affect on sedimentation in the

Newark rift system (Hay et al., 1982; Kent and Olsen, 2000). Sedimentologic and paleontologic evidence suggests increasing aridity toward the northern end of the rift system and increasing aridity from the later Triassic into the Jurassic for all basins.

Depositional models for the lowermost Portland Formation must consider this climatic variation in the filling of the Hartford basin. It is unreasonable to assume that depositional facies patterns remain constant in tectonically active basins, during a period of continental breakup at paleolatitudes transitional from subtropical to temperate. The paleolatitudinal drift of the Hartford basin was projected initially at 8º to 13º N (see

LeTourneau and Olsen, 2003), but is now interpreted as 14ºN to ~27 or 28ºN (as extrapolated in Kent and Tauxe, 2005).

75

Olsen and Kent (1996) proposed a cause for the cyclicity of lake deposits of the

Newark basin fill based on the Milankovitch theory which predicts variations in continental tropical climate produced by the cycle of precession of the equinoxes associated with insolation. Astronomically-controlled eccentricity effects on precipitation and evaporation also the modulate the small-scale cycles forming large-scale cycles on the order of hundred of thousands to millions of years (Olsen et al., 2005). All tectonic effects on basinal sedimentation in this model are regulated to large-scale tectonostratigraphic (TS) sequences, with the assumption that the basic lacustrine cycles are solely dependent on climate. The evidence for syndepositional faulting as well as the sedimentary patterns supporting more or less continuous subsidence during basin infill argues against this climate assumption.

There are many factors that control climate of a region. Regional climates are mainly controlled by interaction of topography (rain shadow effects), wind direction, and vegetation, which may influence regional climate patterns resulting from astronomical forcing on a global scale. Tectonics can affect climate patterns through the shape and width of continents through time (Reading and Levell, 1996). The climate of the Hartford basin must have been influenced by the monsoonal climate associated with the Tethys

(Hay et al., 1982; Gierlowski-Kordesch and Gibling, 2002) and by the changing topography of the basin as subsidence and rain shadow effects increased as the rift evolved (Smoot, 1991). The progression of wetter conditions and open fluvial drainage of the New Haven Arkose (Gierlowski-Kordesch and Gibling, 2002) toward drier conditions and closed to open drainage of the East Berlin and lowermost Portland Formations

(Gierlowski-Kordesch and Rust, 1994; this study) under higher subsidence combines the

76 effects of climatic and tectonic variables. Drainage patterns must have changed as the basin rifted apart and subsidence continued with climate changing as the Hartford basin drifted northward into a drier climate zone.

It is unquestionable that climate has controlled to a certain extent the pattern of the lowermost Portland lacustrine facies patterns, because the occurrence of a lake implies a positive water balance, even if only for a relatively brief geologic time.

However this does not imply that climate change was astronomically controlled and the only factor that affected the cyclicity of lake sedimentation in the lowermost Portland

Formation. The formation of repetitive perennial lacustrine facies alternating with mostly subaerial alluvial facies indicate oscillating wet and dry conditions within the Hartford basin as well as active subsidence. Both climate and tectonics contributed to the formation of the cyclicity in the sedimentary patterns of the lowermost Portland

Formation. Tectonics caused the formation of accommodation space affecting the hydrology, and thus the lakes, of the lowermost Portland Formation (Bohacs et al., 2003), while the climate influenced the hydrology by contributing water for the lakes.

77

Chapter Four

4.1 Discussion

The lowermost Portland Formation of the Hartford basin represents sedimentation in

three continental environments: 1) alluvial plain to sandflat, 2) shallow lake to playa, and

3) offshore perennial saline lake with deltaic sheets. This assemblage of facies is part of

the middle lacustrine phase of tripartite deposition in a rift basin. The fourteen cyclic lake

sequences of the lowermost Portland Formation fit a balanced-fill lake model, because

lake level changes are evidenced by layers of deeper and shallower lacustrine facies

within each cycle. The absence of evaporite layers, which is a characteristic of

underfilled lake basins, might indicate open groundwater circulation despite closed

surface drainage (Bowler, 1986; Bowler and Teller, 1986) or periodic open drainage in

balanced-fill regime. The presence of magnesite and dolomite in the lacustrine black

mudrock facies indicates that the lake was saline at times, supporting an occasional

closed hydrologic system.

The depositional model of the Newark Supergroup, as proposed by Schlische and

Olsen (1990), postulates that lacustrine facies are formed during tectonically active intervals, where there is a continuous increase in subsidence followed by a parabolic decrease, ending with the return of fluvial deposition. The origin of the lakes of the lowermost Portland Formation and their cyclic pattern are related to subsidence, not only climate. Evidence for syn-tectonic sedimentation is abundant (e.g. McDonald and

LeTourneau, 1988) and volcanic flows interbedded with sedimentary units point to active rifting. The absence of lacustrine facies above the fourteen lacustrine cycles (from core

FD-31 T eastward in the core transect, see Fig 3.1) indicates the boundary of the

78 lowermost Portland Formation with the upper part of the lower Portland Formation.

According to Olsen et al. (2005), there are three more members in the lower Portland

Formation, the South Hadley Falls, Mittinegue, and Stony Brook Members, which also contain lacustrine cycles. The upper Portland Formation, which is solely composed of fluvial deposits, indicates that the subsidence of the Hartford basin considerably decreased or stopped forming enough accommodation space for lacustrine facies to develop. This transition, between the lower and upper Portland Formation (from dominantly lacustrine to fluvial facies), is supported by different rift models based on tectonic controls (e.g. Olsen, 1990; Lambiase, 1990; Gawthorpe and Leeder, 2000;

Hinderer and Einsele, 2002; Bohacs et al., 2003)

The sedimentology of the lowermost Portland Formation is very similar to that in the East Berlin Formation, as described by Demicco and Gierlowski-Kordesch (1986) and Gierlowski-Kordesch and Rust (1994). The East Berlin Formation is about 170 m thick and is characterized by three main depositional settings: (1) the alluvial plain/ sandflat facies assemblage (St, Sh, SF, Fr,) the playa facies assemblage (Fr, SF, Fl3 and

Fm), and (3) the lacustrine facies assemblage (Fl1 and Fl2). In addition, six complete lake

cycles and four incomplete cycles (without black shales) are identified and they are

similar to those in the lowermost Portland cyclic sequences. The cycles of the East Berlin

Formation are interpreted to be controlled by climate as well as tectonics. The similarity

in depositional features between the East Berlin and lower Portland Formations suggests

that both are part of the same depositional system, even though the East Berlin Formation

is separated from the lowermost Portland Formation by a basaltic flow (Hampden) (see

also Olsen et al., 2005). The balanced-fill nature of the Hartford basin remained the same

79 despite being interrupted by a volcanic flood basalt event – subsidence balanced with sediment input.

4.2 Conclusions

The main purpose of this study was to establish the stratigraphy and

paleodepositional environment for the lowermost Portland Formation. The identified

facies include: (1) black shale (Fl1), (2) ripple cross-laminated black mudrock (Fr1), (3) disturbed black mudrock (Fm1), (4) stratified red mudrock (Fl2), (5) ripple cross-

laminated red mudrock (Fr2), (6) disrupted to massive red mudrock (Fm2), (7) ripple

cross-laminated to trough cross-bedded sandstone (Srt), and (8) horizontally bedded

sandstone (Sh). These facies were interpreted as representing three main depositional

settings, 1) alluvial plain to sandflat (Fr2, Fm, Sh, Srt), 2) shallow lake to playa (Fl2, Fm), and 3) offshore perennial saline lakes with deltaic sheets (Fl1. Fr1, Fm1, Sh).

The vertical thickness of the core composite section was 600 m and was composed of fourteen lake cycles. Each cycle contained a basal black mudrock unit followed by red brown mudrock and sandstone units, reflecting subsidence and subsequent basin fill. The cyclicity of the lowermost Portland lacustrine cycles is interpreted to be controlled by both tectonics and climate. Tectonics produced the accommodation space through subsidence rates and the climate influenced the total amount of precipitation and evaporation in the system, affected water and sediment input.

Thus, both controlled the hydrology and resultant sedimentation patterns of the rift basin.

80

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APPENDIX

This section contains all the measured sections from the twenty cores from the Park River Core Project (U.S. Army Corps of Engineers, 1977).

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